Browsing by Subject "coronary"
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Item Interplay between metabolic and myogenic mechanisms in coronary pressure-flow autoregulation(2022-05) Warne, Cooper M.; Tune, Johnathan D.; Dick, Gregory M.; Mallet, Robert T.The local metabolic hypothesis proposes that myocardial oxygen tension, indexed by coronary venous PO2 (CvPO2), determines the degree of coronary pressure-flow autoregulation. Conversely, the myogenic hypothesis proposes that pressure-induced vascular tone, indexed by the pressure at which coronary flow is zero (Pzf), determines autoregulation. My working hypothesis posits that if metabolism predominates, then autoregulation will be directly related to CvPO2, irrespective of reductions in coronary vasomotor tone. Conversely, if a myogenic mechanism predominates, then autoregulation will be directly related to Pzf, regardless of underlying CvPO2. I tested these hypotheses by examining the extent to which exaggeration of the metabolic error signal and attenuation of myogenic tone influences coronary autoregulation. Experiments were performed in anesthetized, open-chest swine in which a coronary artery was cannulated and connected to a servo-controlled roller pump system. This allowed coronary perfusion pressure (CPP) to be incrementally reduced from 140 to 40 mmHg before and during hypoxemia (SO2 ~50%). CvPO2 decreased 13 mmHg and coronary blood flow fell 57% as CPP was reduced. Hypoxemia augmented myocardial oxygen consumption (P < 0.01), increased coronary blood flow (P < 0.0001), and reduced CvPO2 (P < 0.0001) over the same CPP range. Coronary blood flow during hypoxemia maintained myocardial oxygen delivery (P = 0.20). Hypoxemia increased closed-loop autoregulatory gain (Gc) over a CPP range of 120 to 60 mmHg (P = 0.02). Gc was inversely correlated to CvPO2 and Pzf, but the correlation was stronger for CvPO2. These findings support that coronary pressure-flow autoregulation is augmented by hypoxemia-induced increases in the local metabolic error signal, regardless of the myogenic tone.Item Renal Hypertension Impairs Coronary Hyperemia During Exercise(2003-08-01) Williams, Maurice A.; Patricia GwirtzWilliams, Maurice A., Renal Hypertension Impairs Coronary Hyperemia During Exercise. Doctor of Philosophy (Biomedical Sciences), August, 2003, 103 pp., 2 tables, 10 illustrations, bibliography, 180 titles. High blood pressure (hypotension) is a common disease that greatly impacts cardiovascular disease and quality of life making it a high priority for early detection and treatment. Hypertension is a major risk factor for coronary artery disease, heart failure, stroke and sudden death. The incidence of hypertension is increasing as the population ages. Exercise intolerance or exertional fatigue is a common complaint of patients with hypertension. We tested the hypothesis that the acute onset of renovascular hypertension results in a sustained, elevated sympathetic adrenergic stimulation of the heart which blunts the coronary hyperemic response and reduces the cardiac contractile response to exercise. Studies were conducted in chronically instrumented dogs before and after the acute onset of renosvascular hypertension of only 2 weeks. This degree of hypertension would normally go undetected or untreated by physicians. Short-term hypertension blunted coronary blood flow at rest and during each level of submaximal exercise. Hypertensive dogs showed a significant reduction in cardiac pump function during submaximal exercise compared to the responses in the normotensive dogs. These changes were very dramatic for such a short term of a mild hypertension. These studies were designed to examine mechanisms mediating the blunted coronary hyperemic response during exercise which imposes a limit on cardiac function. The results of these experiments addressed fundamental questions regarding alterations in neurohumoral control of cardiac contractile function and the mechanisms by which neurohumoral control of the heart is altered by hypertension. These studies should also clarify the mechanistic rationale for medical therapies to treat patients with hypertension.