Left ventricular pressure transmission to myocardial lymph vessels is different during systole and diastole

In six open-thorax-anaesthetized dogs with paced hearts and a retrogradely cannulated epicardial lymph vessel, the sensitivity of myocardial lymph pressure to left ventricular pressure during systole and during diastole was determined. The lymph vessels were cannulated using PE-90 tubing, and lymph pressure was measured by connecting the cannula to a microtip pressure transducer. To obtain the systolic sensitivity, left ventricular pressure was changed by clamping the descending aorta, which caused left ventricular pressure to increase. The diastolic sensitivity was obtained from natural variation to left ventricular pressure caused by atrial contractions during induced long diastoles. The mean ratio of the pulse in lymph pressure to the pulse in left ventricular pressure was determined: systole: 0.069 +/- 0.013, n = 213, diastole: 0.76 +/- 0.16, n = 249 and, if possible, linear regression analysis between lymph and left ventricular pressure was performed. The systolic regression coefficients could be determined in six dogs and the diastolic coefficients in three dogs. During long diastoles lymph pressure variations are on average 76 per cent of those in the left ventricle. However, during systole, the sensitivity of lymph pressure to left ventricular pressure is more than ten times lower. It is not unlikely that the structural embedment of lymph vessels within the myocardium is such that volume variations by cardiac contraction are limited.