Stroke Volume Heart Rate and Systemic Vascular Resistance Interact in Affecting Mean Arterial and Pulse Pressures

When cardiac changes in the face of a constant SVR, mean arterial pressure is influenced according to the formula Pa = CO X SVR. The influence of a change in cardiac output on mean arterial pressure is independent of the cause of the change— heart rate or stroke volume (remember that CO = SV X HR). In contrast, the effect of a change in cardiac output on pulse pressure greatly depends on whether stroke volume or heart rate changes. Below we consider the effects of changes in heart rate, stroke volume, cardiac output, SVR, and arterial compliance on pulse pressure and mean arterial pressure.

Effect of Changes in Heart Rate and Stroke Volume With No Change in Cardiac Output. If an increase in heart rate is balanced by a proportional and opposite change in stroke volume, mean arterial pressure does not change because cardiac output remains constant. However, the decrease in stroke volume that occurs in this situation results in a diminished pulse pressure,- the diastolic pressure increases, while the systolic pressure decreases around an unchanged mean arterial pressure. An increase in stroke volume with no change in cardiac output likewise causes no change in mean arterial pressure. The increased stroke volume, however, produces a rise in pulse pressure, systolic pressure increases and diastolic pressure decreases.

Another way to think about these events is depicted in Figure 15.3A. The first two pressure waves have a diastolic pressure of 80 mm Hg, systolic pressure of 120 mm Hg, and mean arterial pressure of 93 mm Hg. Heart rate is 72 beats/min. After the second beat, the heart rate is slowed to 60 beats/min, but stroke volume is increased sufficiently to maintain the same cardiac output. The longer time interval between beats allows the diastolic pressure to fall to a new (lower) value of 70 mm Hg. The next systole, however, produces an increase in pulse pressure because of the ejection of a greater stroke volume, so systolic pressure rises to 130 mm Hg. The pressure then falls to the new (lower) di-astolic pressure, and the cycle is repeated. Mean arterial pressure does not change because cardiac output and SVR are constant. The increased pulse pressure is distributed evenly around the same mean arterial pressure.

If an increase in heart rate is balanced by a decrease in stroke volume so that there is no change in cardiac output, the result is no change in mean arterial pressure but a decrease in pulse pressure. Systolic pressure decreases and di-astolic pressure increases.

Effect of Changes in Cardiac Output Balanced by Changes in Systemic Vascular Resistance. Mean arterial pressure may remain constant despite a change in cardiac output because of an alteration in SVR. A good exam-

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Responses

  • tamara
    How does change in co and svr affect mean arterial pressure?
    8 years ago
  • bartosz wilson
    How mean arterial pressure decreases stroke volume?
    8 years ago
  • Dirk
    What does the mean arterial pressure remain constant?
    8 years ago
  • eliseo
    Why stroke volume and heart rate are in opposite direction?
    8 years ago
  • tom
    Which of the following increases systemic vascular resistance, stroked volume, and heart rate?
    8 years ago
  • adelia
    How does stroke volume affect vascular resistance?
    5 years ago
  • helen
    How influence ofstroke volume on systemic vascular resistance?
    3 years ago
  • Armando
    What happens to the heart rate with increased svr?
    3 years ago
  • santeri
    What increases systemic vascular resistance stroke volume and heart rate?
    3 years ago
  • Jaxon
    Does increase in mean arterial pressure increases or decreases the stroke volume?
    2 years ago
  • Giada
    How stroke volume affect arterial pressure?
    2 years ago
  • tom underhill
    What resistance does the heart muscle face?
    2 years ago
  • mikko
    Is HR, SV, SVR, CO decreased or increase for all sock types?
    2 years ago
  • Celendine
    How does volume affect svri?
    1 year ago
  • Mario
    DOES INCREASING SVR LOWER HEART RATE?
    10 months ago
  • amaranth
    Does increasing heart rate increase resistance?
    8 months ago
  • Janina
    What happens if the stroke volume is increased and heart rate remains constant?
    8 months ago
  • Burtuka
    How does peripheral vascular resistance effect heart rate?
    8 months ago
  • Marco
    Does heart rate affect mean arterial pressure?
    7 months ago
  • maddalena
    Why mean arterial pressure depends on HR, stroke volume?
    4 months ago

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