Pressure-volume behavior of perivascular interstitium measured in isolated dog lung

Abstract

Pulmonary perivascular interstitial fluid pressure (Px) was measured as a function of extravascular water accumulation (W). Px was measured directly by wick catheters and open-ended needles inserted in the interstitium near the hilus of isolated perfused dog lobes. Lobes were studied at constant transpulmonary pressure (Ptp) and vascular pressure (Pv, arterial equal to venous pressure). Px-W behavior had two distinct phases: an initial low compliance phase interpreted as perivascular filling, followed sometimes by an abrupt transition to a high compliance phase interpreted as alveolar flooding. W at transition was between 20 and 50% of the initial lung weight. Perivascular compliance during filling at a Ptp of 6 cmH2O was 0.1 g.g wet lobe wt-1.cmH2O-1, which was one-sixth that during alveolar flooding and 2.5 times that at a Ptp of 25 cmH2O. At the start of alveolar flooding, estimated alveolar interstitial fluid pressure was slightly (2 cmH2O) below alveolar pressure (PAlv) at a Ptp of 6 cmH2O but considerably belov PAlv at high lung volumes. These findings support the concept that alveolar surface tension reduces the interstitial fluid pressure below PAlv.

Pulmonary Circulation and Regulation of Fluid Balance

“…The compliance of the lung interstitial tissue is a nonlinear function 195 and has two phases: a low compliance at low interstitial fluid volumes and high compliance during the interstitial edema or alveolar flooding phase. At low levels of tissue hydration, tissue pressure changes markedly in response to a small change in tissue volume, indicative of low tissue compliance.…”

“…176 Alveolar wall fluid is propelled by the prevailing pressure gradient away from the alveolus and toward the extra-alveolar space. [194][195][196] Increases in interstitial fluid volume are handled by increases in pulmonary lymph flow. 197,198 However, the relationship between interstitial fluid volume and lymph flow is not linear because, beyond a critical fluid volume, pulmonary lymph flow no longer increases in proportion to the increase in fluid volume.…”

“…Interstitial liquid pressure gradients have been measured from the alveolar wall to the lung hilum [194][195][196] (Fig. 6-11), and these pressure gradients from the alveoli to hilar interstitial space form the basis for interstitial drainage of the liquid filtered across the microvessels.…”

Distribution of Alveolar Edema in Ventilated and Unventilated Canine Lung Lobes

“…Interstitial extravascuJar Jung water (QwlldQI) can generaJly increase up to 35% prier to alveolar flooding (31)(32)(33)(34)(35). Therefore, it is an important safety factor that protects against alveolar flooding.…”

“…Thcre is a consensus that mechanical ventilation with PEEP is beneficial in treating the hypoxemia and hypercarbia in clinical and experimental pulmonary edema (32,53,54).…”