Questions for physics of cardiovascular system
Q1.Estimate the volume of blood your heart pumps to your systemic circulation each day.Volume of blood =80 cm3/beat
(80 cm3 /beat)(72 beats/min)(1440 min/day)=8.3x10 cm3/day
Q2. If white blood cells have an average diameter of 12μ m ,what percentage of the blood volume is white blood cells?
Number of cell/mm3=8000/mm3
(No. of cells/mm3)(vol. of a cell in mm3)=fraction of cell
(8000/mm3) {(4/3)π (6x 10 -6)3mm3} =7x 10-3 = 0.7%
Q3.If a platelet has a diameter of about 2μ m ,what percentage of the blood volume is platelets?
Number of platelet cells/mm3 = (3x 103/mm3)
(3x 103/mm3){(4/3)π (10-3)3 mm3 } =10-3 = 0.1%
Q4. If the average power consumed by the heart is 10 W, what percentage of a 2500 kilocalorie daily diet is used to operate the heart?(4.2J =1 calorie).
(2500kcal)(4.2x 10 3 J/kcal)=107 J/day
10 W=10J/sec
(10J/sec)(3600sec/hr)(24hr/day)=8.6 x 105J/day
= 8.6 x105 = 8.6 x 10-2
107 or 8.6%Q.5 An artery with a 3 mm radius is partially blocked with plaque ;
in the constricted region the effective radius is 2mm and the
average blood velocity is 50 cm /sec.
(a) What is the average velocity of the blood in the un constricted region .
(b) Would there be turbulent flow in either region ?
(c) For the blood in the constricted region , find the equivalent
pressure due to the kinetic energy of the blood.
R1= 3 mm,
R2 =2mm,
A = π R²
A1/A2=[π (3mm )² /π (2 mm )² ]
A1 V1= A2 V2
V1 = (4/9) 50 cm/sec
V1 =22 cm /sec
(b) No
( c ) ρ(density ) of blood =1.04 gm /cm³
½ ρ v2² = ½ (1.04 )( 50 )²
= 1300 ergs / cm³
= 1 mm Hg
Q .6 If the radius of an arteriole changed from 50 μm to 40 μm ,
how much would the flow rate through it decrease ?Flow rate Q = (Pa – Pb ) π R⁴
8 η L
New Flow rate Q = (Pa – Pb )π(40μm)⁴
8 η L