Validation of measurements of ventilation-to-perfusion ratio inequality in the lung from expired gas.
The analysis of the gas in a single expirate has long been used to estimate the degree of ventilation-perfusion (Va/Q) inequality in the lung. To further validate this estimate, we examined three measures of Va/Q inhomogeneity calculated from a single full exhalation in nine anesthetized mongrel dogs under control conditions and after exposure to aerosolized methacholine. These measurements were then compared with arterial blood gases and with measurements of Va/Q inhomogeneity obtained using the multiple inert gas elimination technique. The slope of the instantaneous respiratory exchange ratio (R slope) vs. expired volume was poorly correlated with independent measures, probably because of the curvilinear nature of the relationship due to continuing gas exchange. When R was converted to the intrabreath Va/Q (iV/Q), the best index was the slope of iV/Q vs. volume over phase III (iV/Q slope). This was strongly correlated with independent measures, especially those relating to inhomogeneity of perfusion. The correlations for iV/Q slope and R slope considerably improved when only the first half of phase III was considered. We conclude that a useful noninvasive measurement of Va/Q inhomogeneity can be derived from the intrabreath respiratory exchange ratio.
Prisk
G Kim
GK
Department of Medicine 0931, University of California, San Diego, La Jolla, California 92093, USA. kprisk@ucsd.edu
Guy
Harold J B
HJ
West
John B
JB
Reed
James W
JW
D000465:Algorithms; D000758:Anesthesia; D000818:Animals; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000032:analysis; D004285:Dogs; D005740:Gases / Q000032:analysis* / Q000378:metabolism*; D008168:Lung / Q000502:physiology*; D013058:Mass Spectrometry; D016210:Methacholine Chloride; D018721:Muscarinic Agonists; D005741:Noble Gases; D010100:Oxygen / Q000032:analysis; D011659:Pulmonary Gas Exchange / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
D005740:Gases; D018721:Muscarinic Agonists; D005741:Noble Gases; D016210:Methacholine Chloride; D002245:Carbon Dioxide; D010100:Oxygen