Transmural variation in autoregulation of right ventricular blood flow.

Abstract

We examined transmurally the right coronary autoregulatory flow response to varied perfusion pressures in 11 anesthetized, open-chest dogs. Right coronary artery flow was measured electromagneticalry, and its transmural distribution was denned with 15-(im radioactive microspheres. Heart rate, mean aortic blood pressure, right ventricular systolic pressure, end-diastolic pressure, and dP/dt_ were constant. At 100 mm Hg, subepicardial flow averaged 0.48 ±0.04 ml/min/g, and subendocardial flow averaged 0.56 ± 0.05 ml/min/g. In contrast to the left coronary circulation, right coronary hypotension did not cause preferential subendocardial ischemia. As right coronary perfusion pressure was decreased from 100 to 40 mm Hg in five dogs, subepicardial and subendocardial flows were reduced similarly by 35-36%. As right coronary perfusion pressure was elevated from 100 to 150 mm Hg in six dogs, right ventricular subepicardial blood flow increased by 31%, whereas 5 a phenomenon known as autoregulation.6 When left coronary perfusion pressure is decreased below the autoregulatory pressure range, regional flow falls more precipitously in subendocardium, 7 "9 and the subendocardial-to-subepicardial flow ratio (endo/epi) reaches approximately 0.3 at complete occlusion of the left coronary artery.8 When left coronary perfusion pressure is increased above the autoregulatory pressure range, the endo/epi ratio increases, 10 indicating that left coronary autoregulation fails first in subendocardium. To date, there have been no reports of regional autoregulatory capability in the right coronary circulation, although we recently found that right coronary artery autoregulation was less potent than left coronary autoregulation." It is possible that the blunted autoregulatory capability of the right coronary circulation has a regional basis like that of the blunted capability Received June 8, 1987; accepted November 2, 1987. of the hyperperfused left coronary circulation. 10 Thus, this investigation was conducted to define transmurally right coronary autoregulatory capability over a wide range of right coronary perfusion pressures. Materials and MethodsEleven mongrel dogs of either sex, weighing 15 to 24 kg, were anesthetized with sodium pentobarbital, 30 mg/kg i.v. initially, and supplemented as needed to maintain stable anesthesia. After tracheotomy, the dogs were ventilated by a respirator (Harvard Apparatus, South Natick, Massachusetts) with room air supplemented with oxygen to maintain normal arterial oxygen tension. A vinyl catheter was positioned in the inferior vena cava through a femoral vein for administration of supplementary anesthetic, heparin, and fluids. A second vinyl catheter was advanced into the thoracic aorta through a femoral artery to monitor aortic pressure. Right ventricular pressure was measured with a catheter-tipped transducer (Millar Instruments, Houston, Texas) inserted through the right jugular vein and across the tricuspid valve. The right ventricular pressure signal was differentiated electronically, and ...

Regulation of Coronary Blood Flow

“…Definitive studies of coronary pressure-flow autoregulation were performed by Berne, who demonstrated that this phenomenon occurs rapidly (seconds) in a highly precise manner (84) and Mosher et al who demonstrated the overall level of pressure-flow autoregulation is directly dependent on the underlying MVO 2 (690). Later studies by Guyton et al established that although autoregulatory behavior exists transmurally across the left ventricle, the range is significantly lower in the endocardial versus epicardial microcirculation (423); an effect corroborated by numerous additional studies (106, 127, 144, 407, 423, 808, 1006). Autoregulation of right coronary blood flow has also been observed by a number of laboratories; however, the overall autoregulatory capacity is significantly lower in the right versus left coronary circulation (101, 200, 369, 702, 929, 1005, 1006).…”

“…Later studies by Guyton et al established that although autoregulatory behavior exists transmurally across the left ventricle, the range is significantly lower in the endocardial versus epicardial microcirculation (423); an effect corroborated by numerous additional studies (106, 127, 144, 407, 423, 808, 1006). Autoregulation of right coronary blood flow has also been observed by a number of laboratories; however, the overall autoregulatory capacity is significantly lower in the right versus left coronary circulation (101, 200, 369, 702, 929, 1005, 1006). In particular, direct comparison of pressure-flow autoregulation in conscious, non-cannulated preparations demonstrate that right coronary blood flow decreases ~35% when perfusion pressure is lowered from 80 to 40 mmHg (101) while essentially no change in left coronary blood flow was noted over this same pressure range (146).…”

“…In a typical adult heart, baseline/resting left coronary blood flow typically ranges between ~0.5 and 1.0 mL/min/g (270, 331, 918, 919). In contrast, right ventricular blood flow averages only ~0.3 to 0.6 mL/min/g (441, 697, 1006, 1026). This phenomenon is explained by underlying differences in the rate of MVO 2 (i.e., oxidative metabolism) between the left ventricle (~50–100 μL O 2 /min/g) versus right ventricle (~30–50 μL O 2 /min/g) (270,276,387,918,919) and highlights how exquisitely dependent myocardial perfusion is on myocardial metabolism.…”

Right coronary autoregulation in conscious, chronically instrumented dogs

“…End diastole and end systole were defined as the onset of positive dP/dt and 20 ms before peak negative dP/dt, respectively. (27) utilizing a RC extracorporeal perfusion system are also shown.…”

“…right coronary circulation; right ventricular function WE PREVIOUSLY COMPARED pressure-flow autoregulation in left coronary (LC) and right coronary (RC) circulations of anesthetized dogs and found that autoregulation was much less potent in the RC (26). Subsequent studies in our laboratory confirmed poor autoregulatory ability of the RC circulation (14,19,27). However, these experiments required anesthesia, extensive surgical procedures, and an extracorporeal perfusion system, any of which might have blunted the autoregulatory response of the RC.…”