Arterial occlusion versus isofiltration pulmonary capillary pressures during very high flow.

Pressure in the compliant middle segment of the pulmonary vascular bed (PM), as determined by arterial occlusion, was compared with pressure at the filtration site (effective filtration pressure, EFP), determined by the isofiltration technique, at very high (7-10 times normal) pulmonary flow in six in situ perfused canine left upper lobes. At these flow rates inflow and left atrial pressures averaged 41.9 +/- 1.3 and 2.5 +/- 0.5 (SE) mmHg, respectively. PM was 30.9 +/- 1.6 mmHg, and EFP was 32.3 +/- 1.9 mmHg with no significant difference between the two measurements by paired t test. The results indicate that the arterial occlusion technique yields a pressure that is equivalent to EFP even during very high pulmonary blood flow where the longitudinal distribution of resistance is quite different from that obtained during normal flow.