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Coronary pressure-flow autoregulation protects myocardium from pressure-induced changes in oxygen consumption
X J Bai1, T Iwamoto, A G Williams
1Department of Physiology, University of North Texas Health Science Center at Fort Worth 76107-2699.
Insights
Pressure-flow autoregulation protects the heart by minimizing changes in coronary vascular volume and oxygen consumption when coronary perfusion pressure fluctuates. Effective autoregulation is key to this protective mechanism.
Area of Science:
- Cardiovascular Physiology
- Myocardial Metabolism
Background:
- Coronary blood flow (CBF) is regulated to maintain stable myocardial oxygen supply despite changes in coronary perfusion pressure (CPP).
- The role of pressure-flow autoregulation in controlling coronary vascular volume (CVV) and its impact on myocardial oxygen consumption (MVO2) remains less understood.
Purpose of the Study:
- To investigate whether pressure-flow autoregulation mitigates CPP-induced alterations in CVV.
- To determine if CVV-dependent changes in MVO2 are minimized by effective autoregulation.
Main Methods:
- Anesthetized dogs (n=11) underwent controlled alterations in CPP across a wide range (60-180 mmHg).
- Cannulation of the left anterior descending coronary artery allowed for precise measurements.
- Systemic hemodynamics and cardiac mechanics were monitored to ensure stable conditions.
Main Results:
- Hearts with effective autoregulation (closed-loop gain > 0.4) showed minimal increases in CVV (0.06%/mmHg) and MVO2 (0.04%/mmHg) with CPP changes.
- Hearts with ineffective autoregulation (closed-loop gain < 0.4) exhibited significant increases in CVV (0.97%/mmHg) and MVO2 (0.41%/mmHg) with CPP changes.
- MVO2 and CVV were directly correlated (r=0.69), with CPP significantly impacting MVO2 only when autoregulation was impaired.
Conclusions:
- Pressure-flow autoregulation effectively protects the myocardium from detrimental changes in CVV.
- By stabilizing CVV, autoregulation prevents significant CPP-induced variations in myocardial oxygen consumption.
Abstract:
Pressure-flow autoregulation minimizes changes in coronary blood flow (CBF) when coronary perfusion pressure (CPP) is altered. This investigation determined if autoregulation also minimizes CPP-induced changes in coronary vascular volume (CVV) and CVV-dependent changes in myocardial oxygen consumption (MVO2). In 11 anesthetized dogs, the left anterior descending coronary artery was cannulated, and responses to 20-mmHg changes in CPP were examined over a range of CPP from 60 to 180 mmHg. Changes in CPP had no significant effect on systemic hemodynamics or on left ventricular end-diastolic segment length, end-systolic segment length, or percent segment shortening. In hearts with effective pressure-flow autoregulation [closed-loop gain (GC) > 0.4], CVV increased 0.06%/mmHg change in CPP. For the same hearts, MVO2 increased 0.04%/mmHg change in CPP. In hearts with ineffective autoregulation (GC < 0.4), CVV increased 0.97%/mmHg (P < 0.001 vs. autoregulating hearts), and MVO2 increased 0.41%/mmHg (P < 0.001 vs. autoregulating hearts). MVO2 and CVV were correlated (r = 0.69, P < 0.0001) independently of autoregulatory capability, but only when autoregulation was poor and capacitance was elevated did CPP significantly affect MVO2. We conclude that pressure-flow autoregulation protects myocardium from CPP-induced changes in CVV, which in turn produces changes in oxygen consumption.