CARDIAC CONTRACTION AND INTRAMYOCARDIAL VENOUS-PRESSURE GENERATION INTHE ANESTHETIZED DOG

1. Two hypotheses relating to the influence of contraction of the hear t on coronary venous pressure (P-v) were tested. The first assumes a d irect transmission of left ventricular pressure (P-LV). According to t he alternative hypothesis the P-v is caused by cyclical changes in the elastance of the surrounding tissue. 2. A small epicardial vein was c annulated retrogradely in eight open-chest dogs deeply anaesthetized w ith fentanyl. The duration of diastoles was varied after induction of a heart block with formaldehyde. Coronary arterial inflow and perfusio n pressure mere controlled by a perfusion system connected to the left main coronary artery by a Gregg cannula. Stopped-flow P-v was studied with intrinsic coronary tone (IT) and after maximal dilatation with a denosine. 3. The P-v pulse in the first contraction after a long diast ole was not significantly correlated to the P-LV pulse, with a slope o f 0.5, in any dog, either with IT or during adenosine treatment. Compa ring the first contraction after the long diastole with the last beat before, systolic P-v pulse decreased significantly in seven out of eig ht dogs, but systolic P-LV pulse increased in five dogs and was unalte red in three dogs in both conditions. In contrast, end-diastolic P-v w as significantly correlated to the systolic P-v in each individual ani mal under either condition. 4. The results indicate that pressure gene ration in the small coronary veins can be explained on the basis of th e time-varying elastance hypothesis and that a direct transmission of P-LV to P-v is absent.