Positive pleural pressure decreases coronary perfusion

Pressure surrounding the heart (P(SH)) rises with maneuvers that increase pleural pressure. This may decrease left ventricular (LV) oxygen demand by reducing LV afterload. However, positive P(SH) may also directly impede coronary flow. To study the effects of positive P(SH) on coronary perfusion, P(SH) was increased in 10-mmHg increments from 0 to 60 mmHg in an isolated canine heart-lung preparation with constant venous return, arterial pressure, and lung volume. Increased P(SH) caused a rapid significant (P < 0.001) fall in left atrial transmural pressure (P(LATM)) of up to 1.28 ± 0.31 mmHg. With constant venous return and lung volume, this was interpreted to reflect decreased LV afterload. However, at levels of P(SH) > 30 mmHg, initial decreases in P(LATM) were followed by sustained increases, suggesting that there was a deterioration in cardiac function despite the lower level of afterload. Increased P(SH) was also associated with decreases in circumflex coronary artery flow [flow (ml/min) = 52.4 - 0.4P(SH), P < 0.01]. Moreover, when the circumflex coronary artery was maximally dilated with adenosine, the effects of P(SH) were amplified [flow (ml/min) = 137.9 + 1.78P(SH), P < 0.001], indicating that positive P(SH) mechanically impeded coronary flow. When P(SH) was raised to 60 mmHg for 90 ls, the aortic-coronary sinus lactate concentration difference fell from 0.71 ± 0.09 to 0.10 ± 0.21 mM (mean ± SE, P < 0.001, n = 8), suggesting myocardial ischemia. We conclude that positive P(SH) directly decreases myocardial perfusion. This may lead to ischemic cardiac dysfunction, especially in patients with low arterial pressure or coronary artery disease.