262 
PULMONARY MODELS 
Figure 1. — Photograph of metallurgic microscope in 
position for viewing from the superior aspect of the 
lung. The microscope is mounted on a movable sup- 
port for horizontal and vertical movement. The 
quartz-iodide lamp is shown behind the microscope 
and the xenon burner to the right. The still camera is 
to the left. The objective of the microscope fits 
against a cover slip mounted in the suction foot on 
the lung. 
observations can be made from either the supe- 
rior or inferior surface of the exposed lung. The 
view of the inferior, dependent surface of the 
lung v\^hich is subject to the higher hydrostatic 
force of gravity of some 10 to 15 cm of v^^ater 
has shown vastly different circulatory changes 
than those seen at the upper surface of the lung. 
Healthy mongrel dogs of both sexes weighing 
12-15 kilos were anesthetized lightly with pen- 
tobarbital and given three mgm heparin per kil- 
ogram. An endotracheal tube was inserted and 
the animals ventilated with room air with a 
Harvard mechanical respirator throughout the 
experimental period utilizing a positive end ex- 
piratory pressure of 5 cm H2O. Tidal volume 
and rate were adjusted to maintain normal pH 
and blood gases. A femoral artery cannula was 
inserted for monitoring arterial pressure and 
another catheter placed in the femoral vein for 
infusions. The lung was exposed through the 
fifth intercostal space and the animal positioned 
so that the lung could be viewed through the 
open chest from above, or by turning the animal 
over, this portion of the lung became dependent 
and could be viewed from underneath. The ani- 
mals were bled into an airless heparinized plas- 
tic bag to a mean arterial pressure of 40 mm 
mercury from the opposite femoral artery dur- 
ing a 10 minute period. At the end of two hours 
of observation all shed blood was reinf used over 
a 20 minute period. The pulmonary microcircu- 
lation was observed before and during the pe- 
riod of shock and for two hours after reinfu- 
sion. 
OBSERVATIONS UNDER THE MICROSCOPE 
Pre-shock 
Arterioles. The arterioles are seen to have a 
pulsatile flow and to repeatedly divide in a 3-di- 
mensional manner almost enveloping the alveoli 
and giving off branches at right angles which 
enter the capillary circulation. The amplitude of 
pulsation and rate of flow decreases markedly 
with distance from large arteriolar supply 
points. 
Capillaries. The capillary structure allows 
red blood cells to pass in single file across the al- 
veolus, each of which has from one or two to 
many identifiable and sometimes intermerged 
capillaries. The red blood cells are observed as a 
rapid continuous stream but the individual cap- 
illaries open and close over periods of one to five 
Figure 2. — View of microscope reversed to view the 
lung from underneath. The movie camera is on the 
right and the quartz-iodide lamp is behind the scope. 
The animal has simply been turned over so that the 
thoracotomy is dependent. 
