Lecture 12
Artificial Respiration1-Resuscitator: consists of a tank supply of oxygen or air; a mechanism for applying intermittent positive pressure by forces air through the mask or endotracheal tube into the lungs then usually allows the air to flow passively out of the lungs during the remainder of the cycle (with some machines, negative pressure as well).
2-Tank Respirator (the Iron-Lung): the tank respirator with a patients body inside the tank and the head protruding through a flexible but airtight collar. This tank has a motor-driven leather diaphragm to perform respiration.
Effect of the resuscitator and the tank respirator on venous return
The excessive use of tank respirator can reduce the cardiac output sometimes to lethal levels because of inadequate venous return to the heart.Aviation, High-Altitude
Effects of low oxygen pressure on the body●As one go up to a high-altitude from sea level there is a decrease in barometric pressure, at sea level, the barometric pressure is 760 mm Hg. This decrease in barometric pressure is the basic cause of all the hypoxia problems in high-altitude due to decrease the atmospheric oxygen partial pressure proportionately to barometric pressure decreases.
●Even at high altitudes, carbon dioxide is continually excreted from the pulmonary blood into the alveoli. Also, water vaporizes into the inspired air from the respiratory surfaces. These two gases dilute the oxygen in the alveoli, thus reducing the oxygen concentration.
●Water vapor pressure in the alveoli remains 47 mm Hg as long as the body temperature is normal, regardless of altitude.
● PCO2 decreases as well in high altitude especially more in acclimatized person, because of increased respiration.
●The alveolar PO2 is decreased in unacclimatized person than in acclimatized person, this due to that alveolar ventilation increases much more in the acclimatized person than in the unacclimatized person.
●The saturation of hemoglobin with oxygen (when breathing air) as go up to higher altitudes is slightly decrease until it is slightly less than 70 % at 20,000 feet and much less at still higher altitudes. But when breathing pure oxygen it reaches 84% at more higher at 40,000.
●When an aviator breathes pure oxygen instead of air, most of the space in the alveoli previously occupied by nitrogen becomes occupied by oxygen and an alveolar PO2 become higher than aviator breathing air.
Acclimatization to low PO2
A person remaining at high altitudes for days, weeks, or years becomes more and more acclimatized to the low PO2. The principal means by which acclimatization comes about are:(1) A great increase in pulmonary ventilation (role of arterial chemoreceptors).
(2) Increased numbers of red blood cells (increase hemoglobin concentration).
(3) Increased diffusing capacity of the lungs.
(4) Increased vascularity of the peripheral tissues (animal). In human the cardiac output often increases as much as 30 % immediately after a person ascends to high altitude but then decreases back toward normal over a period of weeks as the blood hematocrit increases, so that the amount of oxygen transported to the peripheral body tissues remains about normal.
(5) Increased ability of the tissue cells to use oxygen despite low PO2.
Effect of rapid ascend to high altitudes
A small percentage of people who ascend rapidly to high altitudes become acutely sick and can die if not given oxygen or removed to a low altitude. The sickness begins from a few hours up to about 2 days after ascent. Two events frequently occur:
Acute cerebral edema.
Acute pulmonary edema.
Chronic mountain sickness
a person who remains at high altitude too long develops chronic mountain sickness , one of its effects which related to respiratory system is the elevated pulmonary arterial pressure due to the pulmonary arterioles become vasoconstricted because of the lung hypoxia . The elevated pulmonary arterial pressure leads to the right side of the heart fails. The alveolar arteriolar spasm diverts much of the blood flow through nonalveolar pulmonary vessels, thus causing an excess of pulmonary shunt blood flow where the blood is poorly oxygenated; this further compounds the problem.Artificial Climate in the sealed spacecraft
Because there is no atmosphere in outer space, an artificial atmosphere and climate must be produced in a spacecraft. Most important, the oxygen concentration must remain high enough and the carbon dioxide concentration low enough to prevent suffocation.
Physiology of deep-sea diving and other hyperbaric conditions
Human beings as descend beneath the sea, the pressure around them increases greatly. To keep the lungs from collapsing, air must be supplied at very high pressure to keep them inflated. This exposes the blood in the lungs also to extremely high alveolar gas pressure, a condition called hyperbarism. Beyond certain limits, these high pressures can cause a great alteration in body physiology and can be lethal.Important effect of depth is compression of gases to smaller and smaller volumes.
Effect of high partial pressures of individual gases on the body
Nitrogen narcosis at high nitrogen pressures: Nitrogen narcosis has characteristics similar to those of alcohol intoxication.Oxygen toxicity at high pressures:
a- Effect of very high pO2 on blood oxygen transport: As PO2 in the blood rises above 100 mm Hg, the amount of oxygen dissolved in to water of the blood increases markedly.
b- Effect of high alveolar PO2 on tissue PO2: Once the alveolar PO2 rises above a critical level, the hemoglobin-oxygen buffer mechanism is no longer capable of keeping the tissue PO2 in the normal, safe range between 20 and 60 mm Hg.
Acute oxygen poisoning.
Excessive intracellular oxidation as a cause of nervous system oxygen toxicity.
Chronic oxygen poisoning causes pulmonary disability. After only about 12 hours of 1 atmosphere oxygen exposure, lung passageway congestion, pulmonary edema, and atelectasis caused by damage to the linings of the bronchi and alveoli begin to develop (1 atmosphere of pressure caused by the weight of the air above the water).
3- Carbon dioxide toxicity at great depths in the sea: (The depth does not increase the rate of carbon dioxide production in the body, only in certain types of diving gear and some types of rebreathing apparatuses, carbon dioxide can build up in the dead space air of the apparatus and be rebreathed by the diver. Initially there is an increase in ventilation by (PCO2. Beyond 80-mm Hg alveolar PCO2, the situation becomes intolerable, leading finally to that the respiratory center begins to be depressed, rather than excited by a higher alveolar PCO2 and the diver develops severe respiratory acidosis, and varying degrees of lethargy, narcosis, and finally even anesthesia).
4- Decompression of the diver after excess exposure to high pressure: If a diver has been beneath the sea long enough that the amount of nitrogen dissolved in the body fluids increases. When the diver then suddenly comes back to the surface of the sea, significant quantities of nitrogen bubbles can develop in the body fluids either intracellularly or extracellularly and can cause minor or serious damage in almost any area of the body, depending on the number and sizes of bubbles formed; this is called decompression sickness. This sickness can be avoided by:
1-A diver is brought to the surface slowly, enough of the dissolved nitrogen can usually be eliminated by expiration or 2- put the diver into a pressurized tank and then to lower the pressure gradually back to normal atmospheric pressure or 3- Saturation Diving and use helium-oxygen mixtures in deep dives (before diving).