The peripheral vascular response to severe exercise in untethered dogs before and after complete heart block

Abstract

A B S T R A C T The peripheral vascular response to severe exercise was studied in 11 healthy conscious dogs instrumented with Doppler ultrasonic flow probes on the mesenteric, renal, and iliac arteries, and miniature pressure gauges in the aorta. The response to severe exercise was restudied in six of these dogs after recovery from a second operation producing complete heart block by the injection of formalin into the atrioventricular (AV) node. Three of these dogs also exercised while their ventricles were paced at rates of 100/min and 200/min. The untethered normal dogs ran at speeds of 15-25 miles/hr behind a mobile recording unit for a distance averaging 1.5 miles, while continuous measurements of arterial blood pressure and blood flow were telemetered and recorded on magnetic tape. Severe exercise in normal dogs increased heart rate from 84 to 259/min, arterial pressure from 89 to 140 mm Hg, flow resistance in the mesenteric and renal beds by 59 and 52% respectively, and iliac blood flow 479% above control, while mesenteric and renal blood flows remained constant and iliac resistance decreased by 73%.In dogs with complete AV block, severe exercise at speeds of 10-18 miles/hr increased heart rate from 47 to 78/min, mean arterial pressure from 81 to 89 mm Hg, iliac flow 224%, resistance in the renal bed by 273%, and mesenteric bed by 222% while it decreased blood flow in mesenteric and renal beds by 61 and 65% respectively, and iliac resistance by 62%. A similar response occurred during exercise with pacing at 100/min,

Mechanism of postarrhythmic renal vasoconstriction in the anesthetized dog.

“…Comparison of changes in femoral arterial catecholamine levels in these six dogs in response to atrial fibrillation revealed no significanit difference from those seen in the nine animals reported in Table II. The changes from preintervention control hemodvnamics to control hemodynamiiics during an intervention (SQ 20881, phentolamine, propranolol, vagal cooling, atropine renal denervation, bretylium, and hexamethonium) were the same as have been previously reported in the pentobarbital-anesthetized dog and will not be discussed further unless appropriate to the focus of this study (10)(11)(12)(13)(14). tribution of blood flow have been observed in response his study caused a dis-to exercise in the conscious dog with complete heart ion of renal blood flow block (15). Because the response of the renal vascular could be accounted for bed during an arrhythmia was not affected by vagal put.…”

Abnormal coronary vascular response to exercise in dogs with severe right ventricular hypertrophy.

“…At this time all the animals appeared healthy and vigorous. During the exercise period, instrumentation necessary for the continuous transmission of aortic pressure, RV pressure, and right main coronary artery blood flow signals by radiotelemetry (described in detail previously) were carried by each dog in a backpack (6,7). The exercise regimen consisted of each dog running freely behind a mobile recording van over a hilly, 0.3-mile course.…”

Regional myocardial blood flow during graded treadmill exercise in the dog.

“…Heavy exercise was the level of exercise necessary to achieve heart rates greater than 220 beats/min. Mean (1)(2)(3)(4). Heart rate, mean arterial pressure, and mean left atrial pressure were measured directly from the recording during rest and each level of exercise.…”

“…Received for publication 12 June 1974 and in revised form 29 August 1974. ercise (1)(2)(3)(4), regional myocardial blood flow has not been measured previously during exercise. Since perfusion of the subendocardial myocardium occurs principally during diastole, uniform transmural myocardial perfusion requires a gradient of coronary vascular resistance during diastole with resistance lower in the subendocardium than the subepicardium.…”