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Study objective – The aim was to investigate the bidirectional functional adequacy of collateral perfusion in conscious dogs.Design – Left circumflex coronary artery (LCCA) occlusions of 1 or 2 min duration were repeated to stimulate the development of collateral perfusion to the LCCA area, and the left anterior descending coronary artery (lad) was occluded once daily to evaluate the development of retrograde LCCA-LAD flow.Subjects – 7 male mongrel dogs were used, weight 25-28 kg.Measurements and main results – Coronary collateral flow from the LCCA to the LAD perfusion area was measured as the abrupt decrease in the LCCA flow (implanted Doppler transducer) upon release of a brief LAD occlusion. Measurements were repeated daily during the development of collaterals induced by repeated, brief occlusions of the LCCA. After 35(SD17) days of such occlusions, there was no sustained reduction in LCCA regional myocardial function during an LCCA occlusion, and reactive hyperaemic repayment following the occlusion was negligible. Before and after collateral development, the LCCA to LAD collateral flow increased from 1.1(0.2) to 8.6(5.1) cm·s−1. LAD systolic segment shortening during the LAD occlusion increased from 2.1(2.0)% (first occlusion) to 19.3(8.6)% (last occlusion).Conclusions – LAD to LCCA collaterals serve as functionally significant bidirectional perfusion conduits, and monitoring of collateral perfusion development is practical by measuring the step reduction in LCCA flow upon abrupt release of an LAD occlusion. [ABSTRACT FROM PUBLISHER]

The effects of glyceryl trinitrate on collateral blood flow and regional myocardial function during a 2 min coronary occlusion were evaluated in 10 conscious dogs with well developed collateral vessels. Collateral growth was promoted by brief, repeated, reversible coronary occlusions. After partial regression in collateral function a small dose of glyceryl trinitrate (5 μg·kg−1) was injected intravenously 1 min before coronary occlusion. After pretreatment with glyceryl trinitrate the collateral blood flow velocity (mean[SD]) increased from 3.0(0.9) to 4.4(1.4) cm·s−1 (p<0.05). After 2 min of occlusion the percentage systolic subendocardial segment shortening in the collateral dependent zone increased from 7.8(6.1) to 12.6(6.7)% (p<0.05). The blood flow debt repayment after release of the occlusion decreased from 122(41) to 68(34)% (p<0.05). Thus in conscious dogs with regressed newly developed collaterals a major component of the beneficial effects of glyceryl trinitrate on collateral circulation is dilatation of collateral vessels, as evidenced by a pronounced increase in collateral blood flow and myocardial function during a transient period of coronary occlusion. [ABSTRACT FROM PUBLISHER]

The development of collateral vessels was induced by repeated brief left circumflex coronary artery occlusions in 11 conscious dogs. Subendocardial segment shortening in the central ischaemic area and the ischaemic marginal area and transmural wall thickening in the centre of the ischaemic area were measured together with circumflex coronary flow. Changes in regional myocardial function and reactive hyperaemia were determined daily. The rate of recovery of myocardial function after collateralisation was almost identical in both regions. Before myocardial contractility was restored reactive hyperaemia was greatly attenuated. These data strongly suggest that collateral flow is distributed uniformly over the ischaemic bed and that substantial areas of myocardial tissue at risk are salvaged from ischaemia as a result of effective collateral circulation. [ABSTRACT FROM PUBLISHER]

The effects of severe, spontaneous exercise were studied on mesenteric and renal blood flows and resistances before and after splenectomy in six unrestrained, healthy dogs instrumented with miniature pressure gauges in the aorta and ultrasonic Doppler flow probes on the mesenteric and renal arteries. Before splenectomy, exercise increased haematocrit from 40 to 49%, heart rate from 76 to 290/min, mean arterial pressure from 93 to 134 mm Hg, mesenteric (+ 57%) and renal (+ 55%) resistances, while mesenteric and renal flows remained essentially constant. After splenectomy, exercise failed to increase haematocrit and increased vascular resistances to a far greater extent in the mesenteric (+144%) and renal (+199%) beds than in the intact dog, while reducing mesenteric flow by an average of 33% and renal flow by an average of 44%. Thus, in the dog the spleen contributes to the response to exercise by increasing haematocrit sufficiently to obviate reduction and diversion of visceral flows. [ABSTRACT FROM PUBLISHER]

The extent to which the mesenteric, renal, and iliac beds respond with vasoconstriction to the low-output state of chronic failure was studied in conscious dogs with experimental heart failure produced by tricuspid insufficiency and pulmonary stenosis. While intense vasoconstriction occurred in the mesenteric and iliac beds, the renal circulation was relatively spared. A similar pattern of response was observed in a second group of normal conscious dogs when cardiac output and arterial pressure were acutely decreased by partial occlusion of the inferior vena cava. [ABSTRACT FROM PUBLISHER]