I know that, vasoconstriction results in increased total peripheral resistance which is responsible for the rise in diastolic blood pressure. Also, cardiac output is responsible for the systolic blood pressure. But there are conditions, as in administering nor adrenaline, where there is severe vasoconstriction and a fall in cardiac output but a rise in both systolic and diastolic blood pressure. In this case, I understand that the rise in diastolic blood pressure is due to vasoconstriction produced by nor adrenaline. I am not able to account for the rise in systolic blood pressure in the setting of falling cardiac output. Can severe vasoconstriction also influence the systolic blood pressure?


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    $\begingroup$ Yes. Imagine you're blowing into a balloon. Your airflow into the balloon represents 'cardiac output'. As the balloon gets larger and larger, the pressure inside the balloon (the 'peripheral resistance') rises, and the amount of air you can blow in ('cardiac output') falls. Your systolic and diastolic BP both rise. Does that make sense? $\endgroup$ Aug 4 '20 at 5:44
  • $\begingroup$ Yes I understand, I had come to a similar conclusion. Thank you for confirming it. $\endgroup$ Aug 4 '20 at 9:12
  • $\begingroup$ 'Total peripheral resistance determines diastolic pressure, cardiac output determines systolic pressure'—what is the source of this statement? In what context was it made? $\endgroup$
    – Adhish
    Aug 4 '20 at 9:25
  • $\begingroup$ Highest pressure measured in an arterial pulse pressure trace, systolic blood pressure, is during the systole of the heart, so it is the cardiac output responsible for this whereas the lowest pressure in an arterial pulse pressure trace, diastolic blood pressure, is maintained by the tone of the blood vessel (total peripheral resistance). This is my understanding. $\endgroup$ Aug 4 '20 at 9:59
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    $\begingroup$ I think the heuristic 'total peripheral resistance determines diastolic pressure, cardiac output determines systolic pressure' is not a good one after all. E.g., it does not explain the effects of norepinephrine. Nor does it explain the phenomenon of age-related change in blood pressure: see ahajournals.org/doi/full/10.1161/01.cir.96.1.308. Part of the reason is, it does not take into account vascular compliance, which has a major role in determining pulse pressure. $\endgroup$
    – Adhish
    Aug 4 '20 at 13:36

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