DIRECT VISUALIZATION OF THE CORONARY 
MICROCIRCULATION OF THE LEFT ATRIUM 
OF THE CAT 
R. J. Bing* and K. D. Hellberg' 
High-speed cinematography and transillumination 
were used to investigate red cell velocity of the coronary 
microcirculation of the left atrial appendage of the cat. 
The potassium-chloride-arrested, as well as the normally 
beating heart in vivo, were used. Under both circum- 
stances, countercurrents and asymmetric capillary 
arrangements were found. This has far-reaching im- 
portance for the oxygenation of the heart muscle and 
makes doubtful previous calculations for the oxygen 
transport' from the capillary to the surrounding tissue. 
Recruitment, denoting an increase in the number of 
perfused capillaries, was observed with a rise in per- 
fusion pressure in the arrested heart and following 
the administration of nitroglycerin and nicotine in the 
beating heart. Capillary autoregulation was also noticed, 
since red cell velocity appeared to be independent of 
perfusion pressure. Definite patterns of red cell velocity 
in the capillaries of the left atrium of the cat emerged. 
Nicotine and nitroglycerin had little effect on red cell 
velocity. However, following hemorrhage alone and 
after the administration of nitroglycerin following 
hemorrhage, marked changes in the red cell velocity 
were seen. Two major peaks in red cell velocity in atrial 
muscle were observed, the first large one immediately 
preceding or at the onset of ventricular systole, the sec- 
ond smaller one immediately following ventricular sys- 
tole. The results illustrate that, using transillumination, 
it is possible to measure quantitatively red cell velocity 
in the coronary circulation of the cat under a variety of 
experimental conditions. 
INTRODUCTION*** 
In the past, studies on the microcirculation 
have been carried out on a variety of animals 
and organ systems, such as the frog lung, the 
tail of the eel, and the stickleback.^-^ Steven 
Hales first used the mesentery of the dog, a 
preparation still frequently employed in the 
•Huntington Institute of Applied Medical Research, Pasadena, 
California. 
♦•University of Southern California, Los Angeles, California. 
•••Supported by grants from the Margaret W. & Herbert Hoover, 
Jr. Foundation and the American Medical Association Education and 
Research Foundation. 
study of the microcirculation.* We have chosen 
the cat's heart from the beginning of our 
studies. 
There are several publications in the litera- 
ture dealing with the coronary microcirculation, 
most of them using epiillumination.^'^ Epiillumi- 
nation would certainly be the ideal way of vis- 
ualizing the coronary microcirculation, since it 
would permit a wide field of observation and 
would not restrict observations to any particular 
portion of the heart muscle. From the onset, 
we were well aware of the advantages of this 
technique and have attempted for the last year 
to adapt epiillumination to the heart in order to 
make it more useful for the study of coronary 
microcirculation. In the course of these experi- 
ments, we have attempted holography, a method 
of three-dimensional presentation, using laser 
beams. This method was found to be unsatis- 
factory because of the appearance of "speckles" 
peculiar to the coherence light of the laser. We 
also have tried epiillumination by means of sur- 
face illumination with one or several quartz 
rods or quartz rings. This also was only partially 
successful because of reflection of light, which 
made visualization in depth and sufficient resolu- 
tion and contrast difficult. 
Quite recently we have achieved more promis- 
ing results with another approach to epiillumi- 
nation, namely the use of light from fiber-optic 
bundles which conduct light from a xenon arc 
into a surface layer of a cat's heart with a micro 
needle. It is too early to predict whether this 
technique will give adequate resolution and 
permit enough light for high-speed cinema- 
tography. 
Why was this particular preparation se- 
lected? In the first place, the left atrium is the 
right size and the muscle is of sufficient tensile 
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