Filtration profile in isolated zone 1 and zone 3 dog lungs at constant high alveolar pressure.
We measured the rate of liquid filtration in isolated dog lung lobes inflated to a constant alveolar pressure of 25 cmH2O and with all open vessels filled with plasma. We measured lung weight gain at vascular pressures ranging from 5 to 40 cmH2O relative to pleural pressure. We confirmed that under zone 1 conditions the "arterial" and "venous" extra-alveolar segments have essentially the same filtration characteristics. Using the combined extra-alveolar vascular system, we determined when recruitment of filtration surface area occurred as we increased vascular pressure from 0 to 40 cmH2O. Based on an abrupt increase in filtration rate as vascular pressure approached the zone 1/3 boundary, we infer that a sudden recruitment of exchange surface area occurred at that point. Based on the slopes of the zone 1 and zone 3 filtration profiles, we conclude that extra-alveolar vascular segments contribute approximately 25% of total to filtration in the lung under zone 3 conditions, although the exact vessels filtering under zone 1 conditions have yet to be determined. Our analysis of the data supports the concept that there is a difference in the perimicrovascular pressure around alveolar and extra-alveolar vessels, which in part may account for the apparent high filtration fraction apportioned to extra-alveolar vessels.
Gropper
M A
MA
Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
Bhattacharya
J
J
Staub
N C
NC
D000818:Animals; D004285:Dogs; D005260:Female; D005374:Filtration; D008297:Male; D008833:Microcirculation; D009929:Organ Size; D011312:Pressure; D011650:Pulmonary Alveoli / Q000502:physiology*; D011652:Pulmonary Circulation