ON THE EXISTENCE OF STRETCHABLE PORES IN THE EXCHANGE VESSELS OF THE ISOLATED RABBIT LUNG PREPARATION

Abstract

In the present work our aim has been to seek evidence
for or againat the existence of stretchable
porea in the exchange vessel of the lungs. In isolated
rabbit lungs ventilated by positive pressure and perfused
with homologous blood we performed repeated
tests with fluid filtration from the exchange
vessels. In these tests the outflow pressure was elevated
to specific values for periods of 6 min. The
rate of weight gain of the preparation during the
last 2 min of each test period was taken as the rate
or fluid filtration from the exchange vessels. We
found a linear relationship between rate of filtration
and outflow pressure in the range from 5 to 20
mm Hg. Thi indicates that the hydraulic conductilfty
of the exchange vessels did not change with
outflow pressure and thus that no pore stretching
occurred within this pressure range. An abrupt increase
in filtration rate took place when the outflow
pressure was set at 25 or 30 mm Hg. The
hydraulic conductivity of the exchange vessels was
therefore probably increased at these high pressures.
Since in 3 lungs this increase in filtration rate was
fully reversible we suggest that a stretching of pores
in the exchange vessels of the lungs contributed to
the increase in hydraulic conductivity. This stretching
of pores occurred only when vascular pressures
were at or above the upper level of the physiological
pressure range for the lungs.