ABSTRACT
This chapter focuses on regional vascular adjustments to dynamic exercise with large muscle groups—a condition during which total vascular conductance and cardiac output must be matched by reflexes to maintain arterial blood pressure. Blood flow to inactive muscle in the forearm decreases during exercise. Elimination of nervous control of splanchnic blood vessels and of the adrenal medulla by thoracic sympathectomy prevented the dogs and the patient from maintaining cardiac output during exercise. During mild exercise, renal and splanchnic blood flows comprise a significant fraction of total blood flow so that their vasoconstriction can significantly affect blood pressure. Possibly the most important difference in cardiovascular function among different species during exercise is that the pumping capacity of the heart differs so greatly. An early idea was that muscle vascular conductance rose more rapidly than cardiac output at the onset of exercise, causing blood pressure to fall and trigger an arterial baroreflex.
