Physiology II
Cardiovascular Case F

essential hypertension 

the patient: a 55-year-old man

history and clinical examination: This patient had been examined by his family physician and found to have a blood pressure of 196/124 mm Hg. The patient admitted that he had been told that he was hypertensive a number of years earlier, but he had refused treatment because he felt that he was in excellent health. He denied any significant headaches, disturbances in vision, or dizzy spells. His older brother had recently suffered a severe stroke, which had made the patient understandably apprehensive about his own condition and which was the motivating factor for making an appointment with his physician for a physical examination. A diagnostic workup failed to reveal any disease with which the hypertension might have been associated as a secondary manifestation. The diagnosis of essential hypertension was made and the patient placed on antihypertensive therapy, including diuretic and sympatholytic vasodilator agents.

For the following three months, the patient complained of dizzy spells that persisted in spite of attempts to adjust his therapy. He was therefore instructed to discontinue his therapy for two weeks and was admitted to Brighton Medical Center for more thorough study. His blood pressure on admission was 184/120 mm Hg, and a neurological examination performed on admission was negative. He was started on a carefully graded increase in dosage of a vasodilator agent over a period of three days, at which time his blood pressure was reduced to 152/96 mm Hg. On the fourth day his blood pressure was 142/88 mm Hg and the patient experienced a number of dizzy spells while strolling around the ward.

His drug therapy was discontinued once again, and two days later the patient was brought to a laboratory equipped with a tilt-table. Lying horizontally, the patient's brachial artery pressure was 175/118 mm Hg. The table was then tilled to a 60-degree angle (feet down) and his blood pressure was carefully followed. After 20 sec in this position, he complained of feeling dizzy; at this point his brachial artery pressure was 116/90 mm Hg.

STUDY QUESTIONS

1. What would be the effect of a DECREASE IN VASCULAR WALL COMPLIANCE in the area of the carotid sinus on the baroreceptor reflex?  There would be less stretch of the vascular wall.  This would create less of an activation of the baroreceptors.  As the BP rises, the baroreceptors would normally be activated to reduce the BP.  With less wall compliance, the baroreceptors would not be stretched as normal.

2. What is the physiological rationale for the use of a DIURETIC AGENT in a patient with hypertension? for SYMPATHOLYTIC AGENTS?  You would use a diuretic to reduce the "volume" of blood within the vessels...thus reducing BP.  The sympatholytic agents help prevent sympathetic responses...thus reducing BP again.

3. What is the normal response of the cardiovascular system to moving from a SUPINE to a STANDING position? Include in your answer a discussion of cardiac output, vascular resistance, mean arterial pressure, and central venous pressure.   When you are supine, the walls of the veins are more compliant.  When you stand the blood falls into your legs that means that there is less blood returning to your heart.  With less blood returning to your heart, there is less stretch of the ventricles so they don't contract as forcibly so your C.O. drops.  The drop in C.O. causes a drop in pulse pressure (less stroke volume) and a drop in mean arterial pressure.  Also with the venous blood pooling, there is a drop in CVP (notice a decrease in the arterial / venous pressure gradient).  Because of the drop in pressure there is a sympathetic response for the heart to increase its contractility.  Also the vascular smooth muscle decreases the compliance of the veins helping to move the blood up to the heart from the feet.  So within a few heart beats, the body has already compensated and brought the mean BP up.

4. Why is a TILT-TABLE useful in challenging the cardiovascular system of a human subject, and why is a 60-degree feet-down position on a tilt-table more stressful than simply standing up?  (Just guessing here)  Because you are not using any muscles to help push the blood up out of the legs.  

5. What is the apparent MINIMUM MEAN SYSTEMIC ARTERIAL PRESSURE required for adequate cerebral perfusion in this patient?  According to the chart below, it is somewhere between 106 (where he was dizzy) and 115 (where he was not dizzy).

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