Researchers conduct an experiment to determine hemodynamic changes during exercise. Invasive monitoring of various parameters is performed to obtain a left ventricular pressure-volume loop. Compared to at rest, which of the following changes is most likely to be observed during moderate to heavy exercise?(solid line: at rest; dashed line: during exercise)

Question

Researchers conduct an experiment to determine hemodynamic changes during exercise.  Invasive monitoring of various parameters is performed to obtain a left ventricular pressure-volume loop.  Compared to at rest, which of the following changes is most likely to be observed during moderate to heavy exercise?(solid line: at rest; dashed line: during exercise)

Quizplus · Accepted Answer

11ec160b_3c9f_ce89_9249_bb1a270fe785_MD0001_00 During moderate to heavy exercise, several cardiovascular changes occur to facilitate adequate oxygen delivery to skeletal muscle. These changes and their effects on the left ventricular (LV) pressure-volume loop are as follows: Vasoconstriction of capacitance veins mobilizes blood from the legs and increases venous return (ie, increased preload), which shifts LV end-diastolic volume to the right. There is also vasoconstriction of the splanchnic circulation and a higher degree of vasodilation in skeletal muscle, which shunts blood away from the gastrointestinal tract toward skeletal muscle and causes overall reduced systemic vascular resistance (SVR). The reduced SVR also contributes to increased preload by allowing cardiac output to return to the right atrium more quickly and easily. Myocardial contractility is markedly increased, shifting point 3 up and to the left. Both the increased contractility and the increased preload contribute to increased stroke volume (ie, the horizontal distance between points 1 and 3 is increased). Although reduced SVR typically leads to a slight decrease in diastolic pressure during exercise, the increase in myocardial contractility and stroke volume causes systolic pressure to rise. This results in an overall increase in afterload due to increased peak LV and aortic pressure during LV contraction. The increase in stroke volume, combined with an increase in heart rate, increases cardiac output to meet the metabolic demands of exercise. (Choice B) This graph shows an increase in contractility that leads to increased stroke volume and a slight increase in afterload. Such changes are expected with a positive inotropic agent such as digoxin. (Choice C) This graph shows an increase in afterload with a consequent reduction in stroke volume (end-systolic volume is increased). Such changes are expected with the obstruction to LV outflow that occurs with aortic stenosis. (Choice D) This graph shows an increase in preload (end-diastolic volume) with a consequent increase in stroke volume and slight increase in afterload. Such changes are expected with the increase in intravascular volume that occurs with the infusion of normal saline. (Choice E) This graph shows decreased preload with a consequent decrease in stroke volume and slight reduction in afterload. Such changes are expected with the selective venous vasodilation that occurs with nitroglycerin. Educational objective: With moderate to heavy exercise, the changes to the left ventricular pressure-volume loop include increased preload and increased contractility that both contribute to increased stroke volume. Although reduced systemic vascular resistance decreases afterload, the increase in systolic pressure caused by increased preload and contractility override the decrease, resulting in overall increased afterload.

Researchers Conduct an Experiment to Determine Hemodynamic Changes During Exercise