The pressure-resistance relationships of regional resistances within the coronary circulation and the steal phenomenon

Abstract

On narcotized dogs the descending branch of the left coronary artery was ligated and the peripheral vascular bed embolized with microspheres. A maximal phar. macological dilatation was induced with carbochromen and dipyridamol and the pressure flow relation of the regional resistances within the coronary circulation investigated. An increase in the aortic pressure from 100 to 120 mmI-Ig decreased the total resistance of the circumflex branch by 6%. The precollateral resistance, however, which represents chiefly the resistance of large coronary vessels, at the same time increased by 8%.A decrease with increasing pressure was also shown by the nutritive resistance (chiefly resistance of small vessels and arteriols) and the collateral resistance (resistance of spontaneous collaterals). An increase in perfusion pressure from 70 to 90 mmHg diminished the nutritive resistance by 13% and the collateral resistance by 17%.In the course of an increase in aortic pressure, collateral flow decreased if the relationship precollateral resistance/postcollateral resistance (RJR~) on one hand and collateral resistance/nutritive resistance 1~/1~ on the other hand increased. Collateral flow, however, increased when the quotients RI/R 4 and R3/R 2 remained either unchanged or decreased, when aortic pressure was enhanced.From these results it can be concluded that not every increase in aortic pressure necessarily leads to an increase in collateral flow. A decrease in collateral flow, which can produce the steal phenomenon, can also develop in the follow of an increase in aortic pressure in as much as the regional resistances which influence collateral flow are changed correspondingly.The importance of the perfusion pressure for the blood flow in spontaneous collaterals has been repeatedly described (2,6,7, 11,13,17,18). In an earlier investigation on narcotized dogs with an acute infarct we *) The paper was supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 30, Dfisseldorf.

Influence of the ischemic coronary bed on collateral blood flow

“…The following procedure, used to abolish flow through the ischemic vascular bed, had previously been described in detail (4,6,21,24,25). A 25 % suspension of latex microspheres (25_ 5 ~ in diameter) in gum arabic (7 %) was vigorously agitated and slowly flushed into the LAD via the coronary cannula and tubing system, and the peripheral vascular bed of the LAD was embolized.…”

“…Microsphere embolization was terminated when inflow from the carotid artery had subsided to 0.5 ml/min. This method is based on several assumptions which have been extensively discussed in previous publications (4,6,21,24,25). The detail drawing in figure 1 and the resistance model in figure 2 show mierocirculalion including one collateral.…”

“…Downey and Kirk demonstrated a vascular waterfall mechanism in the coronary circulation of the beating heart (5), suggesting that if the pressure to a given coronary vessel drops below a certain critical level, blood flow *) This study was supported in part by DFG grant Er 100/3-1 ceases. Thus retrograde flow represented total collateral flow and outflow pressure of retrograde flow (PRF) could be varied without draining blood into the ischemic bed (4,6,21,24,25). However, it has not been shown if a critical pressure also exists for collateral vessels.…”

“…At this critical pressure, the resistance of the vascular bed would become very large. When retrograde flow is interrupted, pressure in the occluded coronary artery represents the pressure in the ischemic borderzone, i.e., the collateral perfusion pressure (CPP) (4,6,21,24,25). Since collaterals are vessels with a minireal density of smooth muscle, they could be considered "collapsible tubes", and a waterfall phenomenon could also apply to the collateral vasculature.…”

“…However, it has not been shown if a critical pressure also exists for collateral vessels. Collateral resistance can thus be determined from the pressure across the collateral bed and retrograde flow (4,6,21,24,25). Thus collateral blood flow would not depend on PPC in the ischemic bed, since: Collateral Blood Flow = (CPP-Surrounding Tissue Pressure)/Collateral Resistance (17).…”