Pulmonary Ventilation pdf - Respiration

intercostals.

press the abdominal contents upward against the diaphragm, and (2)

The muscles that pull the rib cage downward during expiration are mainly

which lift the first two ribs.

ribs; and (3)

which lift upward on the sternum; (2)

muscles,

nal intercostals,

of expiration. The most important muscles that raise the rib cage are the

ration, and those muscles that depress the chest cage are classified as muscles

fore, all the muscles that elevate the chest cage are classified as muscles of inspi-

20 per cent greater during maximum inspiration than during expiration. There-

away from the spine, making the anteroposterior thickness of the chest about

ribs project almost directly forward, so that the sternum also moves forward,

backward toward the vertebral column. But when the rib cage is elevated, the

ward, as shown on the left side of Figure 37–1, thus allowing the sternum to fall

expands the lungs because, in the natural resting position, the ribs slant down-

The second method for expanding the lungs is to raise the rib cage. This

upward against the bottom of the diaphragm, thereby compressing the lungs.

abdominal muscles,

the necessary rapid expiration, so that extra force is achieved mainly by con-

heavy breathing, however, the elastic forces are not powerful enough to cause

wall, and abdominal structures compresses the lungs and expels the air. During

of the lungs, chest

ration, the diaphragm simply relaxes, and the

diaphragm pulls the lower surfaces of the lungs downward. Then, during expi-

that is, by movement of the diaphragm. During inspiration, contraction of the

methods.

anteroposterior diameter of the chest cavity. Figure 37–1 shows these two

upward movement of the diaphragm to lengthen or shorten the chest cavity,

The lungs can be expanded and contracted in two ways: (1) by downward and

Muscles That Cause Lung Expansion and Contraction

Mechanics of Pulmonary Ventilation

abnormalities.

discussion of pulmonary ventilation, and the subsequent five chapters

and other facets of respiration. This chapter is a

to and from the body’s tissue cells; and

dioxide in the blood and body fluids

transport of oxygen and carbon

of oxygen and carbon dioxide between the alveoli

the atmosphere and the lung alveoli; (2)

four major functions: (1)

achieve these goals, respiration can be divided into

the tissues and to remove carbon dioxide. To

The goals of respiration are to provide oxygen to

Pulmonary Ventilation

471

pulmonary ventilation,

which means the inflow and outflow of air between

diffusion

and the blood; (3)

(4) regulation of ventilation

cover other respiratory functions plus the physiology of special respiratory

and (2) by elevation and depression of the ribs to increase and decrease the

Normal quiet breathing is accomplished almost entirely by the first method,

elastic recoil

traction of the

which pushes the abdominal contents

exter-

but others that help are the (1) sternocleidomastoid

anterior serrati, which lift many of the

scaleni,

the (1) abdominal recti, which have the powerful effect of pulling downward on
the lower ribs at the same time that they and other abdominal muscles also com-

internal

to about –1 centimeter of water. This slight negative

during normal inspiration, alveolar pressure decreases

“alveolar pressure”) of Figure 37–2 demonstrates that

pheric pressure (below 0). The second curve (labeled

air into the alveoli during inspiration, the pressure in

0 centimeters water pressure. To cause inward flow of

to be zero reference pressure in the airways—that is,

are equal to atmospheric pressure, which is considered

parts of the respiratory tree, all the way to the alveoli,

flowing into or out of the lungs, the pressures in all

lung alveoli. When the glottis is open and no air is

Alveolar Pressure

volume of 0.5 liter. Then, during expiration, the events

37–2, showing in the lower panel the increasing nega-

changing lung volume are demonstrated in Figure

These relationships between pleural pressure and

average of about –7.5 centimeters of water.

greater force and creates more negative pressure, to an

resting level. Then, during normal inspiration, expan-

is about –5 centimeters of water, which is the amount

pressure. The

suction, which means a slightly

pleura. As noted earlier, this is normally a slight

Pleural Pressure and Its Changes

freely as the chest expands and contracts.

lungs are held to the thoracic wall as if glued there,

pleural surface of the thoracic cavity. Therefore, the

cavity. Further, continual suction of excess fluid into

thoracic cavity, surrounded by a thin layer of

from the mediastinum. Instead, the lung “floats” in the

the chest cage, except where it is suspended at its hilum

ever there is no force to keep it inflated. Also, there

The lung is an elastic structure that collapses like a

That Cause the Movement

Movement of Air In and Out of the

and cause opposite leverage.

site manner, functioning as expiratory muscles because

The internal intercostals function exactly in the oppo-

ribs to raise them upward, thereby causing inspiration.

tion to the lower ribs, and this causes leverage on the

they contract, they pull the upper ribs forward in rela-

intercostals are elongated forward and downward. As

expiration are angled downward, and the external

tion and expiration. To the left, the ribs during

Figure 37–1 also shows the mechanism by which the

472

Unit VII

Respiration

external and internal intercostals act to cause inspira-

they angle between the ribs in the opposite direction

Lungs and the Pressures

balloon and expels all its air through the trachea when-

are no attachments between the lung and the walls of

pleural

fluid that lubricates movement of the lungs within the

lymphatic channels maintains a slight suction between
the visceral surface of the lung pleura and the parietal

except that they are well lubricated and can slide

During Respiration

Pleural pressure is the pressure of the fluid in the thin
space between the lung pleura and the chest wall

negative

normal pleural pressure at the beginning of inspiration

of suction required to hold the lungs open to their

sion of the chest cage pulls outward on the lungs with

tivity of the pleural pressure from –5 to –7.5 during
inspiration and in the upper panel an increase in lung

are essentially reversed.

Alveolar pressure is the pressure of the air inside the

the alveoli must fall to a value slightly below atmos-

A–P diameter

EXPIRATION

INSPIRATION

Abdominals
contracted

Elevated
rib cage

Diaphragmatic

contraction

Increased

vertical diameter

Increased

External

intercostals

contracted

Internal

intercostals

relaxed

tion of the intercostal muscles, and elevation and depression of

Figure 37–1

Contraction and expansion of the thoracic cage during expiration
and inspiration, demonstrating diaphragmatic contraction, func-

the rib cage.

olume change (liters)

Pressure (cm H

0.25

–2

–4

–6

–8

0.50

Expiration

Inspiration

Transpulmonary pressure

Lung volume

Alveolar pressure

Pleural pressure

transpulmonary pressure during normal breathing.

Changes in lung volume, alveolar pressure, pleural pressure, and

Figure 37–2

about one third of the total lung elasticity, whereas the

to cause collapse of the air-filled lung represent only

required to expand saline solution–filled lungs. Thus,

air-filled lungs are about three times as great as those

saline solution–filled lung.

interface; therefore, the surface tension effect is not

the saline solution–filled lungs, there is no air-fluid

alveolar fluid and the air in the alveoli. In the case of

are filled with air, there is an interface between the

saline solution and when filled with air. When the lungs

tension is shown in Figure 37–4, which compares the

much more complex. The significance of surface

The elastic forces caused by surface tension are

ing even more elastic force.

stretched and unkinked, thereby elongating and exert-

then, when the lungs expand, the fibers become

among the lung parenchyma. In deflated lungs, these

The elastic forces of the lung tissue are determined

and other lung air spaces.

elastic forces caused by surface

be divided into two parts: (1)

determined by the elastic forces of the lungs. These can

The characteristics of the compliance diagram are

compliance diagram of the lungs.

expiratory compliance curve,

respectively, the

between successive steps. The two curves are called,

inspiration and expiration. Each curve is recorded by

monary pressure. Note that the relation is different for

Figure 37–3 is a diagram

after 10 to 20 seconds, will expand 200 milliliters.

sure increases 1 centimeter of water, the lung volume,

pressure. That is, every time the transpulmonary pres-

The total compliance of both lungs together in

pliance.

The extent to which the lungs will expand for each unit

recoil pressure.

piration, called the

the alveoli and that on the outer surfaces of the lungs,

pressure.

pleural pressure. This is called the

Finally, note in Figure 37–2 the

Transpulmonary Pressure.

1 centimeter of water,

During expiration, opposite pressures occur: The

Pulmonary Ventilation

Chapter 37

473

pressure is enough to pull 0.5 liter of air into the lungs
in the 2 seconds required for normal quiet inspiration.

alveolar pressure rises to about

and this forces the 0.5 liter of inspired air out of the
lungs during the 2 to 3 seconds of expiration.

difference between the alveolar pressure and the

transpulmonary

It is the pressure difference between that in

and it is a measure of the elastic forces in the lungs
that tend to collapse the lungs at each instant of res-

Compliance of the Lungs

increase in transpulmonary pressure (if enough time is
allowed to reach equilibrium) is called the lung com-

the normal adult human being averages about 200 mil-
liliters of air per centimeter of water transpulmonary

Compliance Diagram of the Lungs.

relating lung volume changes to changes in transpul-

changing the transpulmonary pressure in small steps
and allowing the lung volume to come to a steady level

inspiratory compliance curve and the

and the entire diagram is

called the

elastic forces of the lung

tissue itself and (2)
tension of the fluid that lines the inside walls of the
alveoli

mainly by elastin and collagen fibers interwoven

fibers are in an elastically contracted and kinked state;

compliance diagram of the lungs when filled with

present—only tissue elastic forces are operative in the

Note that transpleural pressures required to expand

one can conclude that the tissue elastic forces tending

Lung volume change (liters)

0.50

Expiration

Inspiration

0.25

– 4

–5

–6

Pleural pressure (cm H

Figure 37–3

Compliance diagram in a healthy person. This diagram shows
compliance of the lungs alone.

Saline-filled

Air-filled

Lung volume change (liters)

0.50

0.25

–2

– 4

–6

–8

Pleural pressure (cm H

Inspiration

Expiration

O) and pleural pressure is changed.

pheric pressure (0 cm H

filled lungs when the alveolar pressure is maintained at atmos-

Comparison of the compliance diagrams of saline-filled and air-

Figure 37–4

volumes, the limitations of the chest become extreme;

the lungs alone. Furthermore, when the lungs are

the combined system, compared with 200 ml/cm for

after removal from the chest cage. Therefore, the com-

inflate this total pulmonary system, almost twice as

a time while recording lung pressures and volumes. To

person. To do this, air is forced into the lungs a little at

The compliance of the entire pulmonary system (the

Lungs Together

still be required to expand the thoracic cage.

were not present in the thorax, muscular effort would

teristics, similar to those of the lungs; even if the lungs

lungs alone, without considering the thoracic cage. The

Thus far, we have discussed the expansibility of the

Effect of the Thoracic Cage

applied continuous positive pressure breathing.

not treated with strong measures, especially properly

adult person. This causes the condition called

and their lungs have an extreme tendency to collapse,

later than that. Therefore, many premature babies have

seventh months of gestation, and in some cases, even

Further, surfactant does not normally begin to be

in small premature babies, many of whom have alveoli

noted earlier are doubled. This is especially significant

radius (50 instead of 100 micrometers), the pressures

tension. Thus, when the alveoli have half the normal

lus, which means that the smaller the alveolus, the

Tension.

to expand the lungs.

great. Thus, one sees how important surfactant is in

be about 18 centimeters of water pressure, 4.5 times as

without any surfactant, the pressure would calculate to

(3 mm Hg). If the alveoli were lined with pure water

For the average-sized alveolus with a radius of about

alveoli, attempting to push the air out. The amount of

lapse the alveoli. This creates positive pressure in the

blocked, the surface tension in the alveoli tends to col-

Pressure in Occluded Alveoli Caused by Surface Tension.

included, between 5 and 30 dynes/cm.

without surfactant, 50 dynes/cm; normal fluids lining

water, 72 dynes/cm; normal fluids lining the alveoli but

ent water fluids is approximately the following: pure

In quantitative terms, the surface tension of differ-

surface.

water in the alveoli. This surface has from one

surface. Instead, part of the molecule dissolves,

for reducing the surface tension. It does this by not

several less important phospholipids, is responsible

The dipalmitoylphosphatidylcholine, along with

ions.

phatidylcholine, surfactant apoproteins,

dipalmitoylphos-

phospholipids, proteins, and ions. The most important

These cells are granular, containing lipid inclusions

type II alveolar epithelial cells,

greatly reduces the surface tension of water. It is

surface active agent in water,

Surfactant and Its Effect on Surface Tension.

surface tension elastic force.

elastic contractile force of the entire lungs, which is

alveoli to try to collapse. The net effect is to cause an

alveoli through the bronchi and, in doing so, causes the

This results in an attempt to force the air out of the

Here, the water surface is also attempting to contract.

raindrop. Now let us reverse these principles and see

together: that is, there is a tight contractile membrane

attempting to contract. This is what holds raindrops

another. As a result, the water surface is always

with air, the water molecules on the surface of the

When water forms a surface

Principle of Surface Tension.

Surfactant, Surface Tension, and Collapse

tension forces.

present in the alveolar fluid. Let

The fluid-air surface tension elastic forces of the

about two thirds.

474

Unit VII

Respiration

fluid-air surface tension forces in the alveoli represent

lungs also increase tremendously when the substance
called surfactant is not
us now discuss surfactant and its relation to the surface

of the Alveoli

water have an especially strong attraction for one

of water molecules around the entire surface of the

what happens on the inner surfaces of the alveoli.

called the

Surfactant is a

which means that it

secreted by special surfactant-secreting epithelial cells
called

which constitute

about 10 per cent of the surface area of the alveoli.

that are secreted in the surfactant into the alveoli.

Surfactant is a complex mixture of several

components are the phospholipid

and calcium

dissolving uniformly in the fluid lining the alveolar

while the remainder spreads over the surface of the

twelfth to one half the surface tension of a pure water

the alveoli and with normal amounts of surfactant

If the

air passages leading from the alveoli of the lungs are

pressure generated in this way in an alveolus can be cal-
culated from the following formula:

100 micrometers and lined with normal surfactant, this
calculates to be about 4 centimeters of water pressure

reducing alveolar surface tension and therefore also
reducing the effort required by the respiratory muscles

Effect of Alveolar Radius on the Pressure Caused by Surface

Note from the preceding formula that the pres-

sure generated as a result of surface tension in the
alveoli is inversely affected by the radius of the alveo-

greater the alveolar pressure caused by the surface

with radii less than one quarter that of an adult person.

secreted into the alveoli until between the sixth and

little or no surfactant in the alveoli when they are born,

sometimes as great as six to eight times that in a normal

respira-

tory distress syndrome of the newborn. It is fatal if

on Lung Expansibility

thoracic cage has its own elastic and viscous charac-

Compliance of the Thorax and the

lungs and thoracic cage together) is measured while
expanding the lungs of a totally relaxed or paralyzed

much pressure is needed as to inflate the same lungs

pliance of the combined lung-thorax system is almost
exactly one half that of the lungs alone—110 milliliters
of volume per centimeter of water pressure for

expanded to high volumes or compressed to low

Pressure

Surface tension

Radius of alveolus

This is the maximum amount of

reserve volume.

3. The

This is the amount of air that remains in

volume.

2. The

breathe in, beginning at the normal expiratory

This is the

inspiratory reserve volume.

1. The

the important pulmonary capacities, which can be

To the right in Figure 37

monary capacities.

volumes together. Such combinations are called

In describing events in the pulmonary cycle, it is

Pulmonary Capacities

1200 milliliters.

expiration; this volume averages about

4. The

1100 milliliters.

tidal expiration; this normally amounts to about

3. The

3000 milliliters.

with full force; it is usually equal to about

2. The

about 500 milliliters in the adult male.

expired with each normal breath; it amounts to

1. The

The signi

lung volumes that, when added together, equal the

To the left in Figure 37

Pulmonary Volumes

capacities,

lation, the air in the lungs has been subdivided in this

For ease in describing the events of pulmonary venti-

lung volume under different conditions of breathing.

Figure 37

sheet of paper.

into and out of the chamber, the drum rises and falls,

the mouth with the gas chamber. When one breathes

breathing gas, usually air or oxygen; a tube connects

drum counterbalanced by a weight. In the drum is a

a drum inverted over a chamber of water, with the

5. It consists of

basic spirometer is shown in Figure 37

spirometry.

of the lungs, a process called

Volume—Spirometry

Pulmonary Volumes

muscle energy for the respiratory process alone.

creased pulmonary compliance. Therefore, one of the

can increase as much as 50-fold, especially if the person

during heavy exercise, the amount of energy required

by the body is required for pulmonary ventilation. But

ration, only 3 to 5 per cent of the total energy expended

airway resistance work.

airway resistance to movement of air into the lungs,

cosity of the lung and chest wall structures, called

the lung and chest elastic forces, called

fractions: (1) that required to expand the lungs against

The work of inspiration can be divided into three

chest cage. Thus, under resting conditions, the respira-

during inspiration; expiration is almost entirely a

breathing, all respiratory muscle contraction occurs

We have already pointed out that during normal quiet

“Work” of Breathing

that of the lungs alone.

when near these limits, the compliance of the com-

Pulmonary Ventilation

Chapter 37

475

bined lung-thorax system can be less than one fifth

passive process caused by elastic recoil of the lungs and

tory muscles normally perform “work” to cause inspi-
ration but not to cause expiration.

compliance work

or elastic work; (2) that required to overcome the vis-

tissue

resistance work; and (3) that required to overcome

called

Energy Required for Respiration.

During normal quiet respi-

has any degree of increased airway resistance or de-

major limitations on the intensity of exercise that can
be performed is the person’s ability to provide enough

and Capacities

Recording Changes in Pulmonary

A simple method for studying pulmonary ventilation
is to record the volume movement of air into and out

A typical

–

and an appropriate recording is made on a moving

–6 shows a spirogram indicating changes in

diagram into four volumes and four

which

are the average for a young adult man.

–6 are listed four pulmonary

maximum volume to which the lungs can be expanded.

ficance of each of these volumes is the

following:

tidal volume is the volume of air inspired or

inspiratory reserve volume is the extra volume

of air that can be inspired over and above the
normal tidal volume when the person inspires

expiratory reserve volume is the maximum

extra volume of air that can be expired by
forceful expiration after the end of a normal

residual volume is the volume of air

remaining in the lungs after the most forceful

sometimes desirable to consider two or more of the

pul-

–6 are listed

described as follows:

inspiratory capacity equals the tidal volume

plus the
amount of air (about 3500 milliliters) a person can

level and distending the lungs to the maximum
amount.

functional residual capacity equals the

expiratory reserve volume plus the residual

the lungs at the end of normal expiration (about
2300 milliliters).

vital capacity equals the inspiratory reserve

volume plus the tidal volume plus the expiratory

air a person can expel from the lungs after first
filling the lungs to their maximum extent and then

Water

Recording
drum

Mouthpiece

Counterbalancing

weight

Floating

drum

Oxygen

chamber

Spirometer.

Figure 37–5

culated from the degree of dilution of the helium, using

diluted by the functional residual capacity gases, and the

the gases of the lungs. As a result, the helium becomes

the spirometer, and the gases of the spirometer mix with

point, the subject immediately begins to breathe from

lungs is equal to the functional residual capacity. At this

the end of this expiration, the remaining volume in the

ing from the spirometer, the person expires normally. At

with helium at a known concentration. Before breath-

helium dilution method, as follows.

used in an indirect manner, usually by means of a

functional residual capacity, the spirometer must be

one half of the functional residual capacity. To measure

into the spirometer, and this volume constitutes about

to measure the functional residual capacity, because the

capacity. The spirometer cannot be used in a direct way

pulmonary disease, it is often desirable to measure this

each normal expiration, is important to lung function.

The functional residual capacity (FRC), which is the

Volume, and Total Lung Capacity—

Residual Capacity, Residual

Determination of Functional

ERV

IRV

these interrelations.

capacities; the student should think through and verify

1. Using these symbols, we present

given in Table 37

become standardized. The more important of these are

data, a number of abbreviations and symbols have

mathematical computations. To simplify these calcula-

dures that the pulmonary physician uses daily. Many of

asthenic people.

residual volume.

possible effort (about 5800 milliliters); it is equal

4. The

476

Unit VII

Respiration

expiring to the maximum extent (about
4600 milliliters).

total lung capacity is the maximum volume to

which the lungs can be expanded with the greatest

to the vital capacity plus the

All pulmonary volumes and capacities are about 20

to 25 per cent less in women than in men, and they are
greater in large and athletic people than in small and

Abbreviations and Symbols Used
in Pulmonary Function Studies

Spirometry is only one of many measurement proce-

these measurement procedures depend heavily on

tions as well as the presentation of pulmonary function

–

here a few simple algebraic exercises showing some of
the interrelations among the pulmonary volumes and

+ V

= IC +

TLC

= VC + RV

TLC

= IC + FRC

FRC

+ RV

Helium Dilution Method

volume of air that remains in the lungs at the end of

Because its value changes markedly in some types of

air in the residual volume of the lungs cannot be expired

A spirometer of known volume is filled with air mixed

volume of the functional residual capacity can be cal-

the following formula:

FRC

Ci
Cf

Spir

Lung volume (ml)

5000

6000

1000

2000

3000

4000

Time

Inspiration

Inspiratory

capacity

Inspiratory
reserve
volume

Expiratory
reserve volume

Vital
capacity

Expiration

Total lung

capacity

Tidal

volume

Functional

residual

capacity

Residual
volume

normal breathing and during maximal inspiration

Diagram showing respiratory excursions during

Figure 37–6

and maximal expiration.

the subject suddenly takes a deep breath of oxygen. This

7. In making this measurement,

the graph in Figure 37

Measurement of the Dead Space Volume.

lungs.

atmosphere. Therefore, the dead space is very disad-

rst, before any of the air from the alveoli reaches the

On expiration, the air in the dead space is expired

because it is not useful for gas exchange.

nose, pharynx, and trachea. This air is called

sages where gas exchange does not occur, such as the

on Alveolar Ventilation

and Its Effect

alveolar ducts, and respiratory bronchioles. The rate at

blood. These areas include the alveoli, alveolar sacs,

of the lungs, where air is in proximity to the pulmonary

The ultimate importance of pulmonary ventilation is

Alveolar Ventilation

thirds these values for longer than 1 minute.

greater than 200 L/min, or more than 30 times normal.

adult man. This can give a minute respiratory volume

as the vital capacity, about 4600 milliliters in a young

per minute, and the tidal volume can become as great

The respiratory rate occasionally rises to 40 to 50

only 2 to 4 breaths per minute.

volume as low as 1.5 L/min and a respiratory rate of

respiratory volume averages about 6 L/min.

is about 12 breaths per minute. Therefore, the

about 500 milliliters, and the normal respiratory rate

The normal tidal volume is

piratory rate per minute.

minute; this is equal to the

The

Times Tidal Volume

Equals Respiratory Rate

Minute Respiratory Volume

ERV

capacity (IC) to the FRC. That is,

spirometry, from the FRC. Also, the total lung capacity

tory reserve volume (ERV), as measured by normal

volume (RV) can be determined by subtracting expira-

Once the FRC has been determined, the residual

initial volume of the spirometer.

concentration of helium in the spirometer, and Vi

concentration of helium in the spirometer, Cf

where FRC is functional residual capacity, Ci

Pulmonary Ventilation

Chapter 37

477

is initial

is final

Spir

(TLC) can be determined by adding the inspiratory

= FRC –

and

TLC

= FRC + IC

minute respiratory volume is the total amount of

new air moved into the respiratory passages each

tidal volume times the res-

minute

A person

can live for a short period with a minute respiratory

Most people cannot sustain more than one half to two

to continually renew the air in the gas exchange areas

which new air reaches these areas is called alveolar
ventilation.

“Dead Space”

Some of the air a person breathes never reaches the
gas exchange areas but simply fills respiratory pas-

dead space

air

vantageous for removing the expiratory gases from the

A simple method

for measuring dead space volume is demonstrated by

–

Table 37–1

rate of carbon monoxide uptake per minute

amount of carbon dioxide eliminated per

rate of oxygen uptake per minute

alveolar ventilation per minute

inspired volume of ventilation per minute

cardiac output

volume of alveolar gas

respiratory exchange ratio

volume of dead space gas

ACO

compliance

ow of air into

Raw

resistance of the airways to

vital capacity

TLC

total lung capacity

IRV

inspiratory reserve volume

inspiratory capacity

residual volume

ERV

expiratory reserve volume

Ppl

pleural pressure

FRC

functional residual capacity

Palv

alveolar pressure

tidal volume

Abbreviations and Symbols for Pulmonary Function

atmospheric pressure

partial pressure of oxygen

CO2

partial pressure of carbon dioxide

partial pressure of nitrogen

partial pressure of oxygen in arterial blood

CO2

partial pressure of carbon dioxide in arterial blood

AO2

partial pressure of oxygen in alveolar gas

the lung

partial pressure of carbon dioxide in alveolar gas

AH2O

partial pressure of water in alveolar gas

expired volume of ventilation per minute

shunt flow

concentration of oxygen in arterial blood

¯o

concentration of oxygen in mixed venous blood

percentage saturation of hemoglobin with oxygen

minute

percentage saturation of hemoglobin with oxygen

in arterial blood

Dlo

diffusing capacity of the lungs for oxygen

diffusing capacity of the lungs for carbon

monoxide

slightly with age.

a young adult man is about 150 milliliters. This increases

The normal dead space air in

Normal Dead Space Volume.

milliliters. The dead space would be

square centimeters, and the total volume expired is 500

graph is 30 square centimeters, the pink area is 70

Let us assume, for instance, that the gray area on the

of expired air.

is dead space air and V

cation, the following equation is used:

For exact quanti

this area is a measure of the volume of dead space air.

gure. With a little thought, the student can see that the

concentration in the alveoli, as shown to the right in the

only alveolar air remains. Therefore, the recorded nitro-

dead space air has been washed from the passages, and

space air. After still more air has been expired, all the

centration rises rapidly, because alveolar air containing

begins to reach the nitrogen meter, the nitrogen con-

gen concentration is zero. Then, when alveolar air

part of the record, only oxygen appears, and the nitro-

completely replaced by oxygen. Therefore, in the early

the respiratory passageways, where the air has been

gure. The

through a rapidly recording nitrogen meter, which

completely replace this air. Then the person expires

lls the entire dead space with pure oxygen. Some

478

Unit VII

Respiration

fi
oxygen also mixes with the alveolar air but does not

makes the record shown in the fi

first portion

of the expired air comes from the dead space regions of

large amounts of nitrogen begins to mix with the dead

gen concentration reaches a plateau level equal to its

fi
gray area represents the air that has no nitrogen in it;

where V

is the total volume

, or

500

150

30 70

Pink area Gray area

Gray area V

walls of the bronchi, less extensive curved cartilage

ve sixths of the way around the trachea. In the

trachea from collapsing, multiple cartilage rings extend

passage of air to and from the alveoli. To keep the

bronchioles.

tributed to the lungs by way of the trachea, bronchi, and

ing especially the respiratory passageways. The air is dis-

8 shows the respiratory system, demonstrat-

Figure 37

Trachea, Bronchi, and Bronchioles

Functions of the Respiratory

dioxide in the alveoli. Therefore, almost all discussions

150), or 4200 ml/min.

rate of 12 breaths per minute, alveolar ventilation

normal dead space of 150 milliliters, and a respiratory

Thus, with a normal tidal volume of 500 milliliters, a

logic dead space volume.

is the tidal volume, and V

minute, V

minute, Freq is the frequency of respiration per

Freq

areas each minute. It is equal to the respiratory rate

Rate of Alveolar Ventilation

monary diseases.

space, or 1 to 2 liters. These problems are discussed

parts of the lungs, the physiologic dead space may be as

are functional in the normal lung, but in a person with

dead space. In a normal person, the anatomic and phys-

logic dead space,

measurement of dead space, this is called the

When the alveolar dead space is included in the total

view, these alveoli must also be considered dead space.

monary capillaries. Therefore, from a functional point of

On occasion, some of the alveoli themselves are

space.

exchange areas; this space is called the

The method just

Anatomic Versus Physiologic Dead Space.

described for measuring the dead space measures the
volume of all the space of the respiratory system other
than the alveoli and their other closely related gas

anatomic dead

nonfunctional or only partially functional because of
absent or poor blood flow through the adjacent pul-

physio-

in contradistinction to the anatomic

iologic dead spaces are nearly equal because all alveoli

partially functional or nonfunctional alveoli in some

much as 10 times the volume of the anatomic dead

further in Chapter 39 in relation to pulmonary gaseous
exchange and in Chapter 42 in relation to certain pul-

Alveolar ventilation per minute is the total volume of
new air entering the alveoli and adjacent gas exchange

times the amount of new air that enters these areas
with each breath.

•

– V

)

where

is the volume of alveolar ventilation per

is the physio-

equals 12

¥ (500 –

Alveolar ventilation is one of the major factors

determining the concentrations of oxygen and carbon

of gaseous exchange in the following chapters on the
respiratory system emphasize alveolar ventilation.

Passageways

–

One of the most important problems in all the respi-

ratory passageways is to keep them open and allow easy

about fi

plates also maintain a reasonable amount of rigidity yet
allow sufficient motion for the lungs to expand and

200

300

400

500

100

Per cent nitrogen

Inspiration of pure oxygen

Air expired (ml)

itr

en concen

ration

after a single previous inspiration of pure oxygen. This record can

Record of the changes in nitrogen concentration in the expired air

Figure 37–7

be used to calculate dead space, as discussed in the text.

Local Secretory Factors Often Cause Bronchiolar Constriction.

when microemboli occlude small pulmonary arteries.

tion. Also, a bronchiolar constrictor re

noxious gases, dust, cigarette smoke, or bronchial infec-

of the respiratory passageways themselves, initiated by

exes that originate in the lungs. Most of

atropine,

effects of acetylcholine, such as

When this occurs, administration of drugs that block the

bronchiolar constriction, superimposed parasympa-

to moderate constriction of the bronchioles. When a

and, when activated, cause mild

acetylcholine

nerves penetrate the lung parenchyma. These nerves

bronchial tree.

especially epinephrine, because of its greater stimula-

of the adrenal gland medullae. Both these hormones

central portions of the lung. However, the bronchial tree

Nervous and Local Control of the Bronchiolar Musculature—

lecting in the lumens of the bronchioles.

walls, (2) edema occurring in the walls, or (3) mucus col-

Yet in disease conditions, the smaller bronchioles

only a minute amount of air must pass.

parallel terminal bronchioles, through each of which

bronchi near the trachea. The reason for this high resist-

breathing. The greatest amount of resistance to air

respiratory conditions,

Resistance to Airflow in the Bronchial Tree.

itself.

of the smaller bronchi and larger bronchioles, often

bers. Many

respiratory bronchiole,

terminal bronchiole, called the

entirely smooth muscle, with the exception of the most

bronchioles

muscle. Also, the walls of the

tilage plates, the walls are composed mainly of smooth

bronchi

trachea

Muscular Wall of the Bronchi and Bronchioles and Its Control.

enlarge, the bronchioles also enlarge, but not as much.

pressures that expand the alveoli. That is, as the alveoli

collapsing by the rigidity of their walls. Instead, they are

1.5 millimeters. The bronchioles are not prevented from

the bronchioles, which usually have diameters less than

contract. These plates become progressively less exten-

Pulmonary Ventilation

Chapter 37

479

sive in the later generations of bronchi and are gone in

kept expanded mainly by the same transpulmonary

all areas of the

and

not occupied by car-

are almost

which is mainly pulmonary epithelium and underlying
fibrous tissue plus a few smooth muscle fi
obstructive diseases of the lung result from narrowing

because of excessive contraction of the smooth muscle

Under normal

air flows through the respiratory

passageways so easily that less than 1 centimeter of
water pressure gradient from the alveoli to the atmos-
phere is sufficient to cause enough airflow for quiet

flow

occurs not in the minute air passages of the terminal
bronchioles but in some of the larger bronchioles and

ance is that there are relatively few of these larger
bronchi in comparison with the approximately 65,000

often play a far greater role in determining airflow
resistance because of their small size and because they

are easily occluded by (1) muscle contraction in their

“Sympathetic” Dilation of the Bronchioles.

Direct control of

the bronchioles by sympathetic nerve fibers is relatively
weak because few of these fibers penetrate to the

is very much exposed to norepinephrine and epineph-
rine released into the blood by sympathetic stimulation

—

tion of beta-adrenergic receptors—cause dilation of the

Parasympathetic Constriction of the Bronchioles.

A few

parasympathetic nerve fibers derived from the vagus

secrete

disease process such as asthma has already caused some

thetic nervous stimulation often worsens the condition.

can sometimes

relax the respiratory passages enough to relieve the
obstruction.

Sometimes the parasympathetic nerves are also acti-

vated by refl
these begin with irritation of the epithelial membrane

flex often occurs

Several substances formed in the lungs themselves are

Trachea

Epiglottis
Pharynx

Esophagus

Pulmonary arteries

Pulmonary

capillary

Alveolus

Pulmonary veins

Conchae

Alveoli

Glottis

Larynx, vocal

cords

Respiratory passages.

Figure 37–8

uid. But many particles smaller than 0.5

because of settled dust particles. Some of the still

For instance, termi-

Of the remaining particles, many that are between 1

cells.

the nose. This size is smaller than the size of red blood

The nasal turbulence mechanism for removing particles

tinue forward, striking the surfaces of the obstructions,

of travel as rapidly as the air can. Therefore, they con-

and momentum than air, cannot change their direction

The particles suspended in the air, having far more mass

obstructions, it must change its direction of movement.

and the pharyngeal wall. Each time air hits one of these

because they cause turbulence of the air), the septum,

turbinates,

conchae

obstructing vanes: the

That is, the air

ticles. Much more important, though, is the removal

The hairs at the entrance to

trachea. When a person breathes air through a tube

narily, the temperature of the inspired air rises to within

of the upper respiratory passageways. Ordi-

These functions together are called the

beyond the nose; and (3) the air is

8); (2) the air is

square centimeters (see Figure 37

the conchae and septum, a total area of about 160

ties: (1) the air is

As air passes through the nose, three distinct normal

helping to clear the nasal passages of foreign matter.

large amounts of air pass rapidly through the nose, thus

takes place; however, the uvula is depressed, so that

ex is triggered. A

nerve to the medulla, where the re

sageways; the afferent impulses pass in the

of the lower respiratory passages. The initiating stimu-

The sneeze re

The rapidly

tracheal slits.

bronchial

invaginate inward, so that the exploding air actually

ranging from 75 to 100 miles per hour. Importantly, the

Indeed, sometimes this air is expelled at velocities

and the epiglottis suddenly open widely, so that air

much as 100 mm Hg or more. Fourth, the vocal cords

quently, the pressure in the lungs rises rapidly to as

the internal intercostals, also contract forcefully. Conse-

the diaphragm while other expiratory muscles, such as

abdominal muscles contract forcefully, pushing against

tightly to entrap the air within the lungs. Third, the

Second, the epiglottis closes, and the vocal cords shut

First, up to 2.5 liters of air are rapidly inspired.

medulla, causing the following effect.

medulla of the brain. There, an automatic sequence of

gas. Afferent nerve impulses pass from the respiratory

bronchi) are especially sensitive, and the terminal bron-

ex. The larynx

The bronchi and trachea are so sensitive to light touch

either swallowed or coughed to the exterior.

pharynx. Then the mucus and its entrapped particles are

velocity of a few millimeters per minute, toward the

ow slowly, at a

whereas those in the nose beat downward. This contin-

pharynx. That is, the cilia in the lungs beat upward,

by the mechanism explained in Chapter 2, and the direc-

with about 200 cilia on each epithelial cell. These cilia

terminal bronchioles, is lined with ciliated epithelium,

The entire surface of the respiratory passages, both in

following manner.

The mucus itself is removed from the passages in the

cosal glands. In addition to keeping the surfaces moist,

that coats the entire surface. The mucus is secreted

minal bronchioles, are kept moist by a layer of mucus

All the respiratory passages, from the nose to the ter-

Mucus Lining the Respiratory Passageways, and Action of Cilia

the airways.

act directly on the lung tissues to initiate local, non-

dioxide, and some of the acidic elements in smog

smoke, dust, sulfur

The same irritants that cause parasympathetic con-

cially true of the slow reactive substance of anaphylaxis.

obstruction that occurs in allergic asthma; this is espe-

Therefore, they play key roles in causing the airway

reactions, especially those caused by pollen in the air.

slow reactive substance of anaphylaxis.

Two of the most important of these are

480

Unit VII

Respiration

often quite active in causing bronchiolar constriction.

histamine and

Both of these are

released in the lung tissues by mast cells during allergic

strictor reflexes of the airways—

—often

nervous reactions that cause obstructive constriction of

to Clear the Passageways

partly by individual mucous goblet cells in the epithe-
lial lining of the passages and partly by small submu-

the mucus traps small particles out of the inspired air
and keeps most of these from ever reaching the alveoli.

the nose and in the lower passages down as far as the

beat continually at a rate of 10 to 20 times per second

tion of their “power stroke” is always toward the

ual beating causes the coat of mucus to fl

Cough Reflex

that very slight amounts of foreign matter or other
causes of irritation initiate the cough refl
and carina (the point where the trachea divides into the

chioles and even the alveoli are sensitive to corrosive
chemical stimuli such as sulfur dioxide gas or chlorine

passages mainly through the vagus nerves to the

events is triggered by the neuronal circuits of the

under this high pressure in the lungs explodes outward.

strong compression of the lungs collapses the bronchi
and trachea by causing their noncartilaginous parts to

passes through

and

moving air usually carries with it any foreign matter that
is present in the bronchi or trachea.

Sneeze Reflex

flex is very much like the cough reflex,

except that it applies to the nasal passageways instead

lus of the sneeze reflex is irritation in the nasal pas-

fifth cranial

series of reactions similar to those for the cough reflex

Normal Respiratory Functions
of the Nose

respiratory functions are performed by the nasal cavi-

warmed by the extensive surfaces of

–

almost completely humidified even before it passes

partially filtered.

air conditioning

function

1°F of body temperature and to within 2 to 3 per cent
of full saturation with water vapor before it reaches the

directly into the trachea (as through a tracheostomy),
the cooling and especially the drying effect in the lower
lung can lead to serious lung crusting and infection.

Filtration Function of the Nose.

the nostrils are important for filtering out large par-

of particles by turbulent precipitation.
passing through the nasal passageways hits many

(also called

and are entrapped in the mucous coating and trans-
ported by the cilia to the pharynx to be swallowed.

Size of Particles Entrapped in the Respiratory Passages.

from air is so effective that almost no particles larger
than 6 micrometers in diameter enter the lungs through

and 5 micrometers settle in the smaller bronchioles as a
result of gravitational precipitation.
nal bronchiolar disease is common in coal miners

smaller particles (smaller than 1 micrometer in diame-
ter) diffuse against the walls of the alveoli and adhere
to the alveolar fl

tory system. Physiol Rev 79:325, 1999.

Hilaire G, Duron B: Maturation of the mammalian respira-

Curr Opin Crit Care 10:18, 2004.

for acute lung injury/acute respiratory distress syndrome.

Haitsma JJ, Papadakos PJ, Lachmann B: Surfactant therapy

Pulm Pharmacol Ther 15:277, 2002.

Foster WM: Mucociliary transport and cough in humans.

evolution of air breathing. News Physiol Sci 18:151, 2003.

Daniels CB, Orgeig S: Pulmonary surfactant: the key to the

and airway diseases. Pharmacol Ther 98:59, 2003.

Coulson FR, Fryer AD: Muscarinic acetylcholine receptors

Respirology 8:291, 2003.

Carr MJ, Undem BJ: Bronchopulmonary afferent nerves.

blocks the air passages to these resonators.

qualities of these structures. For instance, the function

Again, we are all familiar with the resonating

cavity.

chest

ciated nasal sinuses,

The resonators include the

vocalizations.

They

soft palate.

lips, tongue,

The three major organs of

gurations of the vocal cords shown in Figure 37

Finally, several other sets of small laryngeal muscles

ing them for the more bass sounds.

shapes and masses of the vocal cord edges,

Also, slips of these muscles

thyroid cartilage and, therefore, loosen the vocal cords.

muscles, can pull the arytenoid cartilages toward the

cords lateral to the vocal ligaments, the thyroarytenoid

the cricoid cartilage. Muscles located within the vocal

the arytenoid cartilages, activated by muscles stretching

The vocal cords can be stretched by either forward

cricoid cartilage.

9, the

not shown in Figure 37

The thyroid cartilage and the arytenoid

tenoid cartilages.

Posteriorly, the vocal

s apple.

thyroid cartilage,

This is attached anteriorly to

folds after removal of the mucous epithelial lining.

Figure 37

and by the mass of their edges.

mainly by the degree of stretch of the cords, but also by

cause vibration. The pitch of the vibration is determined

allow easy passage of air. During phonation, the cords

During normal breathing, the cords are wide open to

when looking into the glottis with a laryngoscope.

Figure 37

itself.

toward the center of the glottis; they are stretched and

The

vocal cords.

vocal folds,

cially adapted to act as a vibrator. The vibrating element

, is espe-

The larynx, shown in Figure 37

larynx, and (2)

functions: (1)

nasal cavities. Speech is composed of two mechanical

respiratory control centers of the brain; and (3) the

cerebral cortex, which are discussed in Chapter 57; (2)

Vocalization

permanent debility.

brous tissue in the alveolar septa, leading to

the lung lymphatics. An excess of particles can cause

explained in Chapter 33, and others are carried away by

alveolar macrophages,

remaining suspended and expelled in the expired air.

the alveoli by the diffusion process, with the balance

Unfortunately, up to one third of them do precipitate in

particles of cigarette smoke are about 0.3 micrometer.

olar air and are expelled by expiration. For instance, the

Pulmonary Ventilation

Chapter 37

481

micrometer in diameter remain suspended in the alve-

Almost none of these particles are precipitated in the
respiratory passageways before they reach the alveoli.

Many of the particles that become entrapped in

the alveoli are removed by

growth of fi

Speech involves not only the respiratory system but
also (1) specific speech nervous control centers in the

articulation and resonance structures of the mouth and

phonation, which is achieved by the

articulation, which is achieved by the

structures of the mouth.

Phonation.

–9A

is the

commonly called the

vocal cords protrude from the lateral walls of the larynx

positioned by several specific muscles of the larynx

–9B shows the vocal cords as they are seen

move together so that passage of air between them will

how tightly the cords are approximated to one another

–9A shows a dissected view of the vocal

Immediately inside each cord is a strong elastic ligament
called the vocal ligament.
the large

which is the cartilage that

projects forward from the anterior surface of the neck
and is called the “Adam’

”

ligament is attached to the vocal processes of two ary-

cartilages articulate from below with another cartilage

–

rotation of the thyroid cartilage or posterior rotation of

from the thyroid cartilage and arytenoid cartilages to

within the vocal cords can

change the
sharpening them to emit high-pitched sounds and blunt-

lie between the arytenoid cartilages and the cricoid car-
tilage and can rotate these cartilages inward or outward
or pull their bases together or apart to give the various
confi

–9B.

Articulation and Resonance.

articulation are the

and

need not be discussed in detail because we are all famil-
iar with their movements during speech and other

mouth, the nose and asso-

the pharynx, and even the

of the nasal resonators is demonstrated by the change
in voice quality when a person has a severe cold that

References

Vocal

Transverse

Thyroarytenoid
muscle

Full

abduction

Gentle

abduction

Stage

whisper

Phonation

Intermediate position–

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Lateral
cricoarytenoid
muscle

Posterior
cricoarytenoid
muscle

arytenoid

muscle

Thyroid

cartilage

Arytenoid

cartilage

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Its Disorders, 4th ed. Philadel-

from Greene MC: The Voice and

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Laryngeal function in phona-

Anatomy of the larynx.

Figure 37–9

A,
B,
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types of phonation. (Modified

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’t the elephant have a pleural space?