Factors influencing coronary vascular resistance during hypothermia

Factors influencing total coronary vascular resistance (CVR) during hypothermia were studied in 30 mongrel dogs. Complete isolation of the heart in situ was achieved by transection of all cardiac neural and vascular connections in 15 dogs (denervated, Group I). Cardiac innervation was maintained in the other 15 dogs using systemic normothermic cardiopulmonary bypass (innervated, Group II). The aortic root was perfused with heparinized oxygenated blood at a constant flow rate at variable myocardial temperatures. Electromechanical arrest was achieved using potassium chloride (KCl) (25 meq/liter) added to the coronary perfusate. In each group, 5 dogs were maintained at a flow rate of 10 cc/kg/min without KCl and allowed to beat spontaneously, another 5 at a flow rate of 10 cc/kg/min and arrested with KCl, and the remaining 5 at a flow rate of 5 cc/kg/min with KCl. Total coronary vascular resistance was calculated from aortic root pressure, right atrial pressure, and flow rate and expressed in units per 100 grams of cardiac tissue. At 37 degrees C, resistance was lower in the denervated arrested (1.3 +/- 0.2) than in the innervated arrested hearts (2.1 +/- 0.2) (P less than 0.001). Preservation of spontaneous electromechanical activity in the innervated hearts resulted in a lower resistance (0.4 +/- 0.1) (P less than 0.001). A progressive decrease in myocardial temperature to 15 degrees C resulted in a corresponding decrease in coronary vascular resistance to a plateau value (0.5 to 0.7 U) in all arrested groups. The data suggest that at normothermia, innervation increases vascular tone in the coronary vascular bed, while electromechanical activity decreases it.(ABSTRACT TRUNCATED AT 250 WORDS)