The isolated rat lung preparation is ventilated, using a respirator,
with a normoxic or hypoxic gas mixture containing 5% CO2 (to maintain normal perfusate pH). The perfusate (either blood
or Krebs-albumin solution) is pumped into the pulmonary artery
from a reservoir, and the outflow returns to the reservoir passively
through a large cannula in the left atrium. Most often, the flow
rate is kept constant (0.04 ml/min/g of body weight as a rule),
so that the changes in measured perfusion pressure reflect changes
in vascular resistance. However, quite often we also measure the
pressure-flow relationship by varying the flow rate and plotting
it against the resulting changes in pressure.
PEEP = positive end-expiratory pressure (typically we use 2.5
cm H2O). |
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