A 24-year-old woman participates in a study of changes in blood pressure during aerobic exercise. She is healthy and takes no medications. During the study she is asked to run on a treadmill at incrementally increasing speed until her heart rate reaches 90% of her expected maximum heart rate. Compared to at rest, which of the following changes in blood pressure are expected during this time?

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11ec160b_3ca1_552e_9249_791f5be3f488_MD0001_00 Diastolic blood pressure (DBP) is the baseline hydrostatic pressure in the arterial system and is directly related to systemic vascular resistance (SVR) and arterial blood volume. Pulse pressure (PP) is the amount that arterial pressure increases above DBP during left ventricular contraction; it is directly related to stroke volume and inversely related to aortic compliance (which is generally constant but decreases with advancing age). Systolic blood pressure (SBP) is the summation of DBP and PP. During aerobic exercise, there is vasoconstriction of splanchnic arterioles and a larger degree of vasodilation of skeletal muscle arterioles, which shunts blood to exercising muscle and leads to overall reduced SVR. In addition, venoconstriction of capacitance veins mobilizes stored blood to increase venous return (ie, increased preload), and myocardial contractility is also increased. Both the increased preload and increased myocardial contractility increase stroke volume, which in combination with increased heart rate, markedly increases cardiac output. The reduced SVR during aerobic exercise facilitates decreased DBP but it is somewhat offset by mobilization of a higher percentage of blood volume from the venous to the arterial circulation (due to venoconstriction and increased heart rate), resulting in slightly decreased or unchanged DBP. The increased stroke volume leads to increased PP, and consequently increased SBP. (Choice A) Decreased DBP and unchanged PP results in decreased SBP. Such changes are expected with reduced SVR and no change in stroke volume. (Choice B) Increased DBP and decreased PP can result in unchanged SBP. Such changes are expected with increased SVR and decreased stroke volume. (Choice D) Increased DBP and unchanged PP results in increased SBP. Such changes are expected with increased SVR and no change in stroke volume. (Choice E) Increased DBP and increased PP results in greatly increased SBP. Such changes occur with resistance exercise (eg, heavy weightlifting) as SVR is increased due to arteriolar compression by vigorously contracting muscles, and stroke volume is increased due to increased venous return and myocardial contractility. Educational objective: Diastolic blood pressure (DBP) is largely determined by systemic vascular resistance (SVR), and pulse pressure is largely determined by stroke volume. During aerobic exercise, reduced SVR leads to slightly decreased or unchanged DBP, and increased stroke volume leads to increased pulse pressure and systolic blood pressure. __________ References: Physiology, pulse pressure. (http://www.ncbi.nlm.nih.gov/pubmed/29494015)

A 24-Year-Old Woman Participates in a Study of Changes in Blood