Medical Physiology 2005

Problem Set 7:  Vascular Physiology

 

Chapter 1: Estimating Fluid Compartment Volumes

 

1. A large man was injected with a solution containing 10,000 counts/min of radioactive RBC's and 500 mg of inulin.  After equilibration, a 10 ml blood sample was drawn.  The entire blood sample contained 12 counts/min of radioactive RBC's and an inulin concentration of 18 mg/liter.  The man had voided 200 ml of urine which had an inulin concentration of 400 mg/liter but no RBC's.  The hematocrit was 0.4. Calculate the following:

            a. total blood volume

            b. extracellular fluid volume

            c. plasma volume

            d. interstitial fluid volume

 

2.  Suppose we inject 2.0 grams of inulin and 5 milligrams of Evan's blue into a small person.  Following equilibration, we take an arterial blood sample and find that the inulin concentration is 0.1mg/mL; the Evan's blue concentration is 2.0 mg/ml; and the hematocrit is 40%.  During the equilibration period, the individual voided 200mL of urine containing 4mg/mL of inulin and no Evan's blue.  From these data, calculate the person's:

            a. extracellular fluid volume.

            b. plasma volume.

            c. interstitial fluid volume.

            d. total blood volume.

 

3. Suppose we now inject 45mL of D2O and 1.5 grams of inulin into a different person.  Following equilibration, we take an arterial blood sample and find that the D2O concentration is 0.001mL/mL, the inulin concentration is 70mg/L, and the hematocrit is 45%.  During the equilibration period, the person voided 150mL of urine containing 1.2mg/mL inulin, but negligible amounts of D2O.  Using these data, calculate the volume of the intracellular fluid compartment.

 

 

 

Chapter 2: Hemodynamic Principles

 

4.  For a patient with a resting cardiac output of 5.5 L/min, what is the velocity of blood flowing through the aorta assuming that the diameter of the aorta is 20 mm?  Would you expect the velocity of blood flow in systemic capillaries to be higher, lower, or the same as the velocity of blood flow in the aorta?  Explain.

 

5.  For a patient with a systolic arterial pressure of 135mmHg, a diastolic arterial pressure of 90mmHg, and a cardiac output of 5L/min, what is their total peripheral resistance?

 

6.  In comparing the pulmonary and systemic circulations, we note that the pressures within the pulmonary artery are only a fraction of those found in the aorta.  Since the major factor driving blood flow is the pressure gradient, explain how the right ventricle is able to pump an equivalent amount of blood through the pulmonary circuit when pressures in the pulmonary artery are usually on the order of 25/10mmHg compared to 120/80mmHg in the aorta.

 

7.  For a patient with a pulmonary arterial pressure of 25/10 mmHg, a pulmonary venous pressure of 0 mmHg, and a pulmonary vascular resistance of 4 mmHg · min / L, what is their cardiac output?

 

8.  Consider the following data from a resting skeletal muscle.  The mean arterial pressure is 100mmHg, the mean venous pressure is 0mmHg, and the blood flow to the muscle is 5mL/min.

            a.  What is the vascular resistance of this muscle at rest?

            b.  If we assume that during exercise, blood pressure does not change and that the resistance vessels to this muscle dilate so that their internal radius doubles, what is the blood flow to this muscle during exercise?

            c. What is the vascular resistance of this exercising muscle?

 

9.   Explain why capillaries offer less relative resistance (as determined by the pressure drop) to flow than arterioles, considering that their dimensions are smaller.

 

10.  Concerning total peripheral resistance (TPR):

a.       Is TPR greater or lesser than the resistance to flow through any given systemic organ?

b.      All other factors being equal, a decrease in renal vascular resistance will do what to TPR?

 

 

Chapter 3:  Control of the Peripheral Vasculature

 

11.  Many vascular smooth muscle cells possess stretch-activated Cl- channels.  Explain why these the Cl- flux is directed out of the cell upon opening of these channels given that extracellular chloride concentrations are higher than intracellular concentrations.

 

 

Chapter 4:  Microcirculation

 

12.  An investigator wishes to quantify the rate of glucose uptake by a certain skeletal muscle.  Accordingly she obtains samples from the blood supply of this muscle, recording the following data:

            arterial [glucose] = 50 mg/100 mL

            venous [glucose] = 30 mg/100 mL

            blood flow through this muscle = 60 mL/min

 

a.       Is there sufficient information ot calculate the rate of glucose uptake, Jglucose, and if so what is it?

b.      Is there sufficient information to calculate capillary permeability, and if so, what is it?

 

13.  Explain why vertical immersion to the neck in tepid water produces a diuresis in many people.

 

Chapter 5:  Special Circulations:

 

14.  There are a number of circumstances in which a normal, healthy adult may experience dizziness or possibly even faint.  Explain the physiological basis of why these events might occur when a person:

            a. hyperventilates.

            b. suddenly stands up from a prone position.

            c. undertakes strenuous exercise in a hot environment.

 

15.  Explain how coronary blood flow can increase when all the sympathetic nerves to the heart are excited, including those vasoconstrictor fibers supplying coronary vessels.  Under these circumstances, what would be the effect of an increase in circulating epinephrine levels?

 

 

16.  A patient complains of severe leg pains after walking a short distance, but the pains disappear after rest.  Explain.

 

17.  With regard to exercising skeletal muscles:

a.       Explain why a given skeletal muscle might be more prone to fatique with an isometric as opposed to an isotonic contraction.

b.      Why do muscles swell during exercise?

 

 

Chapter 6:  Cardiovascular Reflexes

 

18.  Describe what will happen to heart rate following:

a.       Massage of the neck region over the carotid sinus.

b.      Encasing the carotid sinus in plaster and then increasing blood pressure.

c.       Compressing the common carotid artery.

 

19.  Compare and contrast the effects of infusing norepinephrine and epinephrine on heart rate, cardiac output, total peripheral resistance, and blood pressure.

 

 

 

 

 

Chapter 7:  Coordinated Cardiovascular Responses

 

20.  A patient experiencing hypovolemic shock exhibits a number of symptoms.  Explain why such a patient would demonstrate:

a.       Skin is pale and cold

b.      Rapid but weak pulse

c.       Muscle weakness

d.      Mental disorientation

 

21. During World War I, it was observed that wounded men who were rescued quickly and warmed in blankets survived severe hemorrhage less successfully than men who were could not be reached for some time.  Explain.