Changes in myocardial fluid filtration are reflected in epicardial lymph pressure

The effect of increased fluid filtration on stopped-flow epicardial lymph pressure (P(lymph)), used as an indicator of myocardial interstitial volume, was investigated in the anesthetized open-chest dog. Histamine infusion resulted in an increased systolic peak in the P(lymph) signal together with an increase in diastolic P(lymph) in four of five animals. During reactive hyperemia, systolic and diastolic P(lymph) increased to 127 +/- 8 and 121 +/- 6.7% (mean +/- SE, n = 6) of control, respectively. Peak P(lymph) was approximately 15 s later than peak coronary blood flow and venous pressure (P(ven)). When P(ven) was transiently elevated to 367 +/- 72 (systolic) and 247 +/- 45% (diastolic) of control, P(lymph) increased to 132 +/- 12 and 120 +/- 5.5% of control. The time of response was similar for P(ven) and P(lymph) (t50 approximately 2 S). The increased systolic and diastolic P(lymph) can be explained by an increase in interstitial and lymph filling. It is concluded that changes in myocardial fluid filtration are reflected in epicardial P(lymph). Furthermore, it seems that cardiac contraction constitutes an important defense mechanism against the formation of myocardial edema.