Canine myocardial capillary blood flow during systole and diastole: The effects of regional collagenase

Measurement of phasic capillary blood flow during the cardiac cycle within the myocardium has been an enigma The role of extravascular systolic compression in regulating capillary flow has been called in question by the observation that the myocyte and capillary are tethered by collagen struts. Using a laser Doppler velocimeter which measured unidirectional red cell flux, a 250(4 lensed fiberoptic probe was placed in the interstitial space either deep (n=3) or superficial (n=2) in the anterior wall of the left ventricle adjacent to the left anterior descending artery (LAD) in an open chest canine preparation. Reference measurements were made of LAD flow, left ventricular and aortic pressures. Following control measurements a needle was placed in the interstitial space in proximity to the laser probe. One ml of saline was infused in the region as a vehicle control. Following return to control 0.5 or 1 mg (n=4) of collagenase was infused and observations continued for 40 minutes. Sections for scanning EM were obtained from control and study regions at the end of the study. Observations: Capillary red cell flux peaked during isovolumic systole, isovolumic diastole and diastole with no periods of zero flow. Collagenase had only transient effects on arterial flow. Capillary flux had lower peaks than during control and decreased at some sites. Preliminary SEM studies demonstrate that following collagenase some rupture of myocyte to capillary collagen struts struts was observed. These preliminary observations demonstrate that collagen struts play a minor but significant role in capillary blood flow regulation during the cardiac cycle.