A patient has atherosclerosis which produces a stenosis of h

A patient has atherosclerosis which produces a stenosis of his aorta of 25% diameter reduction. a. What is the resultant reduction in flow rate? b. Assuming laminar flow, how much pressure increase is necessary to compensate for this reduction? Under normal conditions, the mean systemic arterial pressure at the aortic root is 95 mm Hg and the corresponding central venous pressure is 0 mm Hg. The corresponding pressures in the pulmonary artery and the left atrium are 13 mm Hg and 4 mm Hg, respectively. If the cardiac output is 5.2 l/min, compute the peripheral resistance in the systemic and pulmonary circulation. Express your answers in SI units. In the case of moderate exercise, the mean aortic pressure rose to 150 mm Hg and the cardiac output increased by three times the normal value. Compute the percentage change in the systemic peripheral resistance. (I mm Hg = 133.3 Pa.)

Solution

Q.No 6

a. Speed of blood flow decreases dramatically being the blood moves from arteries to arterioles to capillaries. This slow flow rate allows more for exchange processes to occur. As blood flows through the veins, the rate of velocity increases, as blood is returned in to the heart.

b. During exhalation, when air pressure increases for the thoracic cavity, pressure in the thoracic veins increases, speeding blood flow into the heart while valves in the veins prevent blood from flowing backward from your thoracic and abdominal veins. Vasoconstriction increases pressure within a vein as it does within artery, but in veins, the increased pressure increases flow. The pressure in the atria, into which the venous blood will flow, could be very low, approaching zero not part of the relaxation phase on the cardiac cycle.   In the arterial system, as resistance increases, blood pressure increases and flow decreases. Inside the venous system, constriction increases blood pressure as it does in arteries; the increasing pressure helps to come back blood in to the heart. Plus, constriction causes the vessel lumen that they are more rounded, decreasing resistance and increasing blood flow.

Q.No 7

Total peripheral resistance = 80* (MAP-CVP)/cardiac output

Total Pulmonary Resistance = 80* (13-4)/5.2

                                              = 138.5 PRU or mmHg/min/ml