Abstract
Myogenic responses (pressure-dependent contractions) of coronary arterioles play a role in autoregulation (relatively constant flow vs. pressure). Publications on myogenic reactivity in swine coronaries vary in caliber, analysis, and degree of responsiveness. Further, data on myogenic responses and autoregulation in swine have not been completely compiled, compared, and modeled. Thus, it has been difficult to understand these physiological phenomena. Our purpose was to: (a) analyze myogenic data with standard criteria; (b) assign results to diameter categories defined by morphometry; and (c) use our novel multiscale flow model to determine the extent to which ex vivo myogenic reactivity can explain autoregulation in vivo. When myogenic responses from the literature are an input for our model, the predicted coronary autoregulation approaches in vivo observations. More complete and appropriate data are now available to investigate the regulation of coronary blood flow in swine, a highly relevant model for human physiology and disease.
Highlights
Myogenic reactivity can be described as the mechanism underlying the Bayliss effect (Bayliss, 1902)
left anterior descending (LAD) and left circumflex (LCx) LAD and LCx aWeight estimated from growth charts using age provided. bApproximate age estimated from weight using growth chart
Muller et al demonstrated that endurance exercise training increased the myogenic reactivity of coronary arterioles from swine (Muller et al, 1993), while Sellke and colleagues documented the deleterious effects of coronary bypass and cardioplegia on the myogenic reactivity of swine coronary arterioles (Wang et al, 1995)
Summary
Myogenic reactivity can be described as the mechanism underlying the Bayliss effect (Bayliss, 1902). Autoregulation is the phenomenon where coronary blood flow remains relatively constant over a wide range of perfusion pressures (Mosher et al, 1964). The Hagen-Poiseuille relationship predicts that—in the absence of other changes—when the pressure gradient increases, flow should increase. This is because flow is directly related to the pressure gradient and to the 4th power of the vessel radius, while inversely related to blood viscosity and vessel length. The mechanism by which coronary resistance vessels alter their diameter in response to pressure changes is the myogenic response. We aim to synthesize the relevant existing data for coronary myogenic responses and autoregulation in a single species: swine. Myogenic Reactivity and Coronary Autoregulation experimental models because of similarities with humans in coronary anatomy, physiology, and disease (Suzuki et al, 2011; Lelovas et al, 2014)
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