A 48-year-old man with diet-controlled type 2 diabetes mellitus is being evaluated for occasional retrosternal chest pain. He has no history of hypertension, and his blood pressure measurements during office visits were always within normal limits. There is no family history of cardiovascular disease. The patient undergoes exercise treadmill stress testing. He walks for 7 minutes on the treadmill and stops due to fatigue but does not experience chest pain. His ECG does not show any abnormal changes. Heart rate ranges from 70/min at rest to 132/min at peak and mean blood pressure ranges from 95 mm Hg at rest to 112 mm Hg at peak. Which of the following parameters was most likely decreased during peak stress compared to the resting state in this patient?

Question

A 48-year-old man with diet-controlled type 2 diabetes mellitus is being evaluated for occasional retrosternal chest pain.  He has no history of hypertension, and his blood pressure measurements during office visits were always within normal limits.  There is no family history of cardiovascular disease.  The patient undergoes exercise treadmill stress testing.  He walks for 7 minutes on the treadmill and stops due to fatigue but does not experience chest pain.  His ECG does not show any abnormal changes.  Heart rate ranges from 70/min at rest to 132/min at peak and mean blood pressure ranges from 95 mm Hg at rest to 112 mm Hg at peak.  Which of the following parameters was most likely decreased during peak stress compared to the resting state in this patient?

Quizplus · Accepted Answer

11ec160b_3c9f_3243_9249_271273448986_MD0001_00 Exercise is associated with several hemodynamic and vasoregulatory adjustments to provide maximal blood flow to the active muscles. Stimulation of mechano- and chemoreceptors in the exercising muscle causes sympathetic activation and withdrawal of vagal tone, resulting in increased heart rate (HR), stroke volume, and overall cardiac output (Choice A). At higher levels of exercise, HR is predominantly responsible for most of the increase in CO. Sympathetic discharge causes contraction of the arterioles in all tissues except the actively working muscles, effectively shunting blood toward the exercising muscle. This also results in an increase in systolic blood pressure, which helps improve perfusion of actively contracting skeletal muscle (Choice D). However, the rise in the mean arterial pressure is much lower due to an overall decrease in systemic vascular resistance. This occurs due to the substantial arteriolar vasodilation in active skeletal muscles, which is mediated by local release of adenosine, potassium ions, ATP, CO₂, and lactate. (Choice B) Left ventricular (LV) end-diastolic volume and pressure both rise during exercise due to an increase in LV filling (increased venous return) by peripheral vasoconstriction and the pumping actions of actively contracting muscles. (Choice C) Pulmonary artery systolic pressure typically rises during exercise; however, similar to systemic circulation, the rise in pulmonary pressure is much smaller than the increase in blood flow across the pulmonary circulation due to a fall in pulmonary vascular resistance. Educational objective: Exercising muscles can receive up to 85% of the total cardiac output during periods of strenuous activity. Although sympathetic discharge during exercise causes increased cardiac output and splanchnic vasoconstriction, there is only a modest increase in mean blood pressure as vasodilation within active skeletal muscles significantly decreases the total systemic vascular resistance. __________ References: Reflex control of the circulation during exercise: chemoreflexes and mechanoreflexes. (http://www.ncbi.nlm.nih.gov/pubmed/2228848) Hemodynamic and neurohumoral responses to dynamic exercise: normal subjects versus patients with heart disease. (http://www.ncbi.nlm.nih.gov/pubmed/2890448)

A 48-Year-Old Man with Diet-Controlled Type 2 Diabetes Mellitus Is