An alternative method to measure the diffusing capacity of the lung for carbon monoxide in infants

Background Lung diffusion assessed by the uptake of carbon monoxide (DLCO) and alveolar volume (VA) by inert gas dilution are readily assessed in cooperative older subjects; however, obtaining these measurements in infants has been much more difficult. Our laboratory has measured DLCO and VA in sleeping infants using a mass spectrometer, which continuously measures gas concentrations, and demonstrated that infants with bronchopulmonary dysplasia (BPD) have lower DLCO, but no difference in VA compared to full‐term controls. The mass spectrometer is expensive and lacks portability; therefore, we evaluated whether measurement of end‐expiratory alveolar gas concentrations using a gas chromatograph would provide an alternative approach. Methods (1) Using our previously digitized data for infants with BPD and full‐term controls, DLCO and VA were calculated at end‐expiration rather than between 60 and 80% of expired volume, as previously reported. (2) In a new group of infants, DLCO and VA were measured using gas concentrations obtained at end‐expiration with a mass spectrometer and a gas chromatograph. Results (1) Using end‐expiratory concentrations, infants with BPD (n = 49) had significantly lower DLCO, but similar VA compared to healthy controls (n = 34) (DLCO: 4.2 vs 4.6 mL/min/mmHg, P = 0.047; VA: 614 vs 608 mL, P = 0.772). (2) Among newly evaluated infants (n = 28), DLCO and VA obtained with a mass spectrometer and a gas chromatograph were highly correlated (R2 = 0.94 and 0.99, respectively), and were not significantly different for the two analyzers. Conclusion Measuring DLCO and VA at end‐expiration using a gas chromatograph can provide an effective assessment of gas exchange in sleeping infants.