Effects of pressure gradients between branches of the left coronary artery on the pressure axis intercept and the shape of steady state circumflex pressure-flow relations in dogs.

Abstract

SUMMARY. When steady state pressure-flow relations are studied in the circumflex coronary artery, pressure gradients develop between it and other branches of the left coronary artery. To assess the effects of these pressure gradients, we compared the pressure axis intercept and shape of steady state circumflex pressure-flow relations in the presence and absence of gradients after autoregulation was abolished, both in the beating heart and during long diastoles in dogs. We used peripheral coronary pressures and radionuclide-labeled microspheres to assess arterial collateral flow. In the beating heart, interarterial pressure gradients reduced the curvature at low circumflex pressures, and overestimated the mean pressure axis intercept by 7.8 mm Hg (P < 0.05). The results were similar for the pressure-flow relations derived during long diastoles. This overesrimation exaggerates the difference between the pressure axis intercept and coronary sinus pressure. The peripheral coronary pressure and microsphere results indicate that these effects are mediated largely by arterial collateral flow. {Circ Res 56: 11-19, 1985) CORONARY arterial pressure-flow relations have been used to investigate the physical forces that regulate coronary blood flow (Cross et al., 1961;Downey and Kirk, 1975;Bellamy, 1978). The pressure axis intercept of these relations has been interpreted as the downstream pressure opposing forward flow in the coronary circulation; however, this pressure has greatly exceeded the coronary sinus pressure, which traditionally has been assumed to be the downstream pressure. The shape of these relations, found to be linear by some (Dole and Bishop, 1982;Eng et al., 1982) but curvilinear by others (L'Abbate et al., 1980;Klocke et al., 1981), is thought to convey information about the conductance of the coronary circulation. Because of this variability of the pressure axis intercept and the shape of coronary arterial pressure-flow relations, the physiological significance of both remains uncertain.One factor that might account for this variability is the specific coronary artery in which the pressureflow relation is obtained. In our laboratory, we have consistently found that the pressure axis intercept of a steady state circumflex pressure-flow relation (Verrier et al., 1980;Vlahakes et al., 1982) is much higher than that in a steady state left main coronary arterial pressure-flow relation (Rouleau et al., 1979;Uhlig et al., 1984). A possible explanation for the higher pressure axis intercept of the circumflex pressure-flow relation may be that when circumflex pressure is selectively lowered below that in the other branches of the left coronary artery, interarterial pressure gradients occur and are accompanied by collateral flow that is not measured by the upstream flow transducer. This error in measurement could underestimate total circumflex flow and thus overestimate the pressure axis intercept. Whether these pressure gradients also affect the shape of a circumflex pressure-flow relation is unknown.To assess...

Minimal effect of collateral flow on coronary microvascular resistance in the presence of intermediate and noncritical coronary stenoses

“…These mechanical determinants of coronary resistance yield a pressure-flow relation that is straight in the physiological range of arterial pressures, but is curvilinear for pressures below 40 mmHg. This has been clearly demonstrated by observations on pressure-flow relations obtained under experimental conditions where collateral effects were absent because of lack of a pressure gradient between the epicardial arteries (7,13,19). Moreover, the coronary pressure-flow relation is also shifted rightward in ventricles with elevated wall stress, e.g., because of hypertrophy, again without any contribution of collateral flow (12).…”

Role of K+ ATP channels and adenosine in the regulation of coronary blood flow during exercise with normal and restricted coronary blood flow.

“…In the present study, we did not measure myocardial tissue blood flow. However, Messina et al (36) reported that collateral blood flow begins to contribute significantly to myocardial tissue blood flow when intercoronary pressure gradients exceed 70 mmHg. In the present study, during exercise mean aortic pressure was in the range of 100-110 mmHg while the pressure at zero flow was in the range of 30-40 mmHg, which would suggest that the collateral driving pressure was probably not sufficient to result in a considerable contribution of collateral blood flow to total myocardial tissue flow.…”

Influence of Acute Renal Failure on Coronary Vasoregulation in Dogs

“…Intrinsic autoregulatory mechanisms adjust tone within the microvasculature to maintain distribution of myocardial blood flow over a range of oxygen supply and demand requirements (9). Factors that are involved include intra-and extravascular compressive forces (12,13), left ventricular (LV) preload and afterload (14), LV volume, coronary collateral blood flow (15), neuronal status (16,17), arterial structure (18), and endothelial function (19); these factors can be modulated significantly under physiologic or pathologic conditions. Although it is established that underlying cardiac disease compromises kidney function in humans, it is not clear how impaired renal function affects coronary blood flow regulation, myocardial blood flow distribution, and cardiovascular reserve.…”