Studies of Cardiopulmonary Blood Volume

The volume of blood in the heart and lungs can be measured, by the Stewart-Hamilton principle, as the product of cardiac output and the mean transit time from right atrium to the aortic root. Although previous investigators have estimated a variety of central blood volumes, measurements of the true cardiopulmonary blood volume in man have not previously been reported. Eighty-one measurements of the total cardiopulmonary blood volume were obtained in 15 normal human subjects. At rest, total cardiopulmonary blood volume ranged from 301 to 546 ml/m 2 , with a mean of 422 ml/m 2 , and it represented 15% of estimated total blood volume. Cardiopulmonary blood volume was significantly larger in the male subjects than in the female. Reproducibility of measurements was good: the mean discrepancy between successive replications was 25 ml/m 2 and the mean coefficient of variation 3.7%. There was no correlation between cardiac output and cardiopulmonary blood volume but a significant correlation (r=0.79, P <0.0001) was evident between cardiopulmonary blood volume and stroke volume. With elevation of the legs to the pedals of a bicycle ergometer, a small but statistically significant increase occurred in cardiopulmonary blood volume, but no significant changes occurred in cardiac output, heart rate, or stroke volume. With exercise, no further significant change in cardiopulmonary blood volume occurred, despite significant increases in output, rate, and stroke volume. Analysis of cardiac output measurements, both at rest and during exercise, indicates that aortic root sampling is characterized by an appreciably higher reproducibility than that reported for peripheral arterial sampling.