Blood pressure is dependent on cardiac output, systemic vascular resistance, and blood volume. In this activity you will examine the effect of exercise on cardiac output and systemic vascular resistance and their role in determining blood pressure.
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Blood pressure is the driving force that causes blood to flow through arteries into capillaries, then veins and back to the heart. Blood pressure in large arteries occurs in pulses. It is highest during ventricular systole (systolic blood pressure) and lowest during ventricular diastole (diastolic pressure). As blood flows into smaller arteries and arterioles, the pressure becomes relatively constant over the course of the cardiac cycle. Mean arterial pressure (MAP) is the average blood pressure in the arteries.
Rapid adjustments in blood pressure, such as those that occur during changes in posture and exercise, occur because of changing cardiac output (CO) and blood vessel diameter. Increasing CO, either by increasing stroke volume or heart rate, increases blood pressure while decreasing CO decreases blood pressure. Blood vessel diameter, especially the diameter of arterioles, results in changes in systemic vascular resistance (SVR). A decrease in blood vessel diameter (vasoconstriction) increases SVR and therefore blood pressure while an increase in blood vessel diameter (vasodilation) decreases SVR and blood pressure. Viscosity and blood vessel length also affect SVR, but because these factors do not change quickly, they do not play a role in rapid changes in SVR.
Changes in the diameter of arteries, along with blood pressure, also affects blood flow. Dilation of arteries to an organ and increased blood pressure increases blood flow to that organ. Exercise increases blood flow to the skin, heart, and skeletal muscles but reduces flow to other organs (urinary, reproductive, and digestive organs).
Systolic and diastolic blood pressures are measured using a sphygmomanometer or blood pressure cuff. Sounds of blood flow are monitored with a microphone or stethoscope (Korotkoff Sounds) to determine what blood pressure is during systole and diastole. Magnetic Resonance Imaging (MRI) is used to measure stroke volume. Electrocardiography (ECG) is used to measure heart rate.
