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Common Congenital Heart Lesions - page 61 / 126

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61 / 126

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Things that affect resistance

  • External compression

    • o

      Greatest during systole, when the myocardium contracts and compresses the coronary vessels

      • o

        SUBENDOTHELIUM is most susceptible to damage, because it is closest to the highest pressures

  • Intrinsic control of coronary tone

      • o

        The heart gets the max amount of O2 out of the blood with each cycle— there is not the reserve available as there is in other tissues.

      • o

        Any additional O2 requirements must be met by an increase in blood flow!

      • o

        It does this by changing the resistance.

Autoregulation of Coronary Vascular Resistance

  • Metabolic factors

    • o

      Local metabolites accumulate during times of HYPOXIA, when aerobic metabolism is inhibited

      • o

        ADP and AMP accumulate because they can’t be made into ATP.

      • o

        They are degraded into ADENOSINE, a potent VASODILATOR

      • o

        Adenosine binds to vasc. smooth muscle and prevents Ca entry, leading to relaxation, vasodilation and increased blood flow = O2 = adenosine = dilation

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