Determination of the Pulmonary Capillary Blood Flow in Man

Abstract

A method is described for the measurement of the pulmonary capillary blood flow in human subjects with normal lungs. The method depends on the performance of a vital capacity maneuver using nitrous oxide as the test gas. It attempts to circumvent the deficiencies of previous respiratory methods by using an infrared analyzer for the continuous measurement of the concentration of N 2 O in expired air, by ensuring that the respiratory maneuver is completed before recirculation occurs, and by determining simultaneously the values involved in the formula used for the calculation of the flow. As a basis for the method, the pulmonary recirculation time and the rate of N 2 O absorption by the lungs were measured separately. The values for the pul monary capillary blood flow obtained by the N 2 O method correlate well with those obtained by the direct Fick method: in 12 subjects, the average value by the N 2 O method was 5.65 L./min. in comparison with 5.55 L./min. by the direct Pick method; the mean Percentile deviation between the values obtained by the two methods in each subject was 11 per cent. The results obtained by the N 2 O method were also shown to be reproducible : In 14 subjects, successive measurements on the same occasion showed a mean percentile deviation of 6 per cent.

Determination of Pulmonary Blood Flow by Rebreathing of Soluble Inert Gases

“…The recirculation times in our experiments are in agreement with those reported in the literature for inert gases [8,10,12,28,30,34] and are longer than those found with the use of tracers that do not leave the vascular system. Sutton et al [33], with tagged erythrocytes found a recirculation time of 8.5 sec in man and Starr and Collins [32], with dye injection, reported that in dogs 21 % of the cardiac output had recirculated in 10 sec.…”

Pulmonary Capillary Blood Flow in Man Measured by a New N2o Analyzer

“…Cardiac outputs (pulmonary blood flow per minute) measured by this method correspond well to those obtained by direct FICK (LINDERHOLM et al, 1962). Since this report, many investigators have tried to measure the cardiac outputs by a N2O method (DUBOIS and MARSHAL, 1957 ;CANDER and FORSTER, 1959 ;RIGATTO et al, 1961;WASSER-MAN and COMROE, 1962 ;SALVADEO et al, 1963 andBOSMAN et al, 1964).…”

Measurement of Cardiac Output by Alveolar Gas Exchange

“…This difference can be attributed to I ) absorption of NzO by blood perfusing the pulmonary capillaries and 2) absorption of NzO by the lung tissues. Rigatto et al (74) reported that the lung tissues did not absorb "a significant amount of NzO during a single breath of this gas." Therefore they believed that the difference between the volume of NzO inspired and the volume expired during the vital capacity maneuver measured the volume of NzO taken up by pulmonary blood flow.…”

“…Ideally the change in amount and concentration of the inspired soluble gas should be measured prior to the recirculation of the venous blood that might contain the gas. This time is -13 s at rest and 8 s at heavy exercise (74,93). Finally, neither the respiratory-maneuvers nor the soluble gas utilized should alter Qc.…”