258 
PULMONARY MODELS 
CO 
H 
D 
O 
u 
< 
< 
U 
350 
300 
250 
200 
150 
100 
50 
• •• • 
10 20 30 40 50 60 70 80 
INCREASE IN PA PRESSURE 
Figure 4. — Hypoxia produced capillary recruitment 
does not correlate with the magnitude of the rise in 
pulmonary artery pressure. Data shown in this figure 
are from top of lung. 
poxia. The recruitment response probably 
serves to increase the surface area of the air- 
blood interface and therefore would seem to be 
advantageous during airway hypoxia. 
As outlined in the Introduction, there are 3 
problems that must be solved to make useful mi- 
croscopic observations of the pulmonary circu- 
lation. The problem of movement of the surface 
of the lung has been solved by a combination of 
suction manifolds surrounding the window and 
by placing the window over an area of lung 
where respiratory movement is minimal. The 
motion arresting suction manifolds cause only 
minimal changes in the alveoli. The pulmonary 
microcirculation in these studies has flow pat- 
terns that we have come to accept as normal: 
there is no evidence of blood sludging, or hypo- 
perfusion from emboli or other causes. The 
highly filtered light source does not cause de- 
tectable heat damage. 
As indicated in Table I, the animals are in a 
reasonable physiological condition. The exten- 
sive surgical procedures do not cause shock as 
indicated by normal systemic arterial pressures. 
Both the animal as a whole and the observation 
field appear to be normal during these experi- 
ments. 
ACKNOWLEDGMENTS 
This work was supported in part by a grant 
from the National Institute of Health HE 13961 
and contract No. DAD417-68-C-8071 from the 
U.S. Army Medical R and D command. The au- 
thors are indebted to Drs. J. V. Weil, R. F. 
Grover, G. F. Filley, and M. Kay for encourage- 
ment and advice about this work. 
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