Blood Pressure during Supine Exercise in Idiopathic Orthostatic Hypotension

Abstract

The arterial blood pressure was measured during exercise in six patients with idiopathic orthostatic hypotension. In five there was a pronounced fall of arterial pressure while the subjects exercised in the supine position on a horizontal table. The systolic and diastolic pressures fell by an average of 50 and 32 mm. of mercury, respectively. During comparable exercise with the table tilted 15 degrees head downward, the pressures fell to a similar degree. Thus, an abnormal response of blood pressure occurred under conditions in which venous pooling was unlikely to be present. It is suggested that the fall in blood pressure during exercise in the supine position was the result of failure of compensatory constriction of other vascular beds and not of failure of the cardiac output to increase. Thus, the net peripheral resistance in such patients is less than that in normal persons performing comparable exercise.

Regulation of Increased Blood Flow (Hyperemia) to Muscles During Exercise: A Hierarchy of Competing Physiological Needs

“…At that time and for a few decades before the advent of effective drug therapy for hypertension, various forms of surgical sympathectomy were used to treat severe hypertension. These procedures were frequently effective in lowering blood pressure, but orthostatic hypotension was a common side effect (301,508). Even when this subject shown in FIGURE 9 exercised in the head-down position to maximize venous return and stroke volume, blood pressure still fell during exercise.…”

“…However, there were hints that this was an issue as early as the 1960s (301). In this review we consider the many factors that contribute to the homeostatic and regulatory mechanisms operating to meet the two main physiological needs emphasized above.…”

“…The idea that these two important physiological needs "compete" arises when the mass and vasodilator capacity of skeletal muscle are considered in the context of the maximum values for cardiac output seen during exercise. This raises the possibility that vasodilation in the contracting muscles might outstrip cardiac output and threaten blood pressure regulation (68,301,392,393).…”

“…The points about small and large muscle mass exercise are critical for our later discussion about how skeletal muscle vasodilation is "managed" during heavy exercise to regulate mean arterial pressure. This is important because mean arterial pressure is "the" regulated variable in the cardiovascular system (301), and the brain is above heart level in upright humans.…”

“…An early key observation with bearing on the concept that the sympathetic nervous system restrains blood flow to maintain arterial pressure is that arterial pressure falls during exercise in humans with autonomic nervous system failure (301). FIGURE 9 shows the blood pressure responses in a patient studied in the early 1960s who had undergone thoracolumbar sympathectomy to treat malignant hypertension.…”