Submitted on December 14, 2007
Accepted on August 18, 2008
Predicting diffusive alveolar oxygen transfer from carbon monoxide diffusing capacity in exercising foxhounds
Connie C.W. Hsia1*, Peter D. Wagner2, D. Merrill Dane3, Harrieth E. Wagner4, and Robert L. Johnson, Jr.1
1 Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, United States
2 Departments of Medicine and Bioengineering, University of California-San Diego, La Jolla, California, United States
3 Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, United States
4 Medicine, UCSD, LA Jolla, California, United States
* To whom correspondence should be addressed. E-mail: connie.hsia{at}utsouthwestern.edu.
Although lung diffusing capacity for carbon monoxide (DLCO) is a widely used test of diffusive O2 transfer, few studies have directly related DLCO to O2 diffusing capacity (DLO2); none has used the components of DLCO, i.e., conductance of alveolar membrane (DMCO) and capillary blood, to predict DLO2 from rest to exercise. To understand the relationship between DLCO and DLO2 at matched levels of cardiac output, we analyzed cumulative data from rest to heavy exercise in 43 adult dogs, with normal lungs or reduced lung capacity following lung resection, that were studied by two techniques: a) A rebreathing technique (RB) was used to measure DLCO and pulmonary blood flow at two O2 tensions independent of O2 exchange. DLCO was partitioned into DMCO and Vc using the Roughton-Forster equation, and converted into an equivalent DLO2, [DLO2(RB)]. b) A multiple inert gas elimination technique (MIGET) was used to measure ventilation-perfusion distributions, O2 and CO2 exchange under hypoxia, to derive DLO2 [DLO2(MIGET)] by the Lilienthal-Riley technique and Bohr integration. For direct comparisons, DLO2(RB) was extrapolated to the cardiac output measured by the Fick principle corresponding to DLO2(MIGET). The DLO2/DLCO ratio averaged 1.61. Correlation between DLO2(RB) and DLO2(MIGET) was similar in normal and post-resection groups. Overall DLO2(MIGET)=0.975.DLO2(RB); mean difference between the two techniques were under 5% for both animal groups. We conclude that despite various uncertainties inherent in these two disparate methods, the RF equation adequately predicts diffusive O2 transfer from rest to heavy exercise in canines with normal as well as reduced lung capacities.
