Measurement of pulmonary diffusing capacity for carbon monoxide and functional residual capacity during rebreathing in conscious Thoroughbreds

Abstract

Summary A rebreathing method for measurement of pulmonary diffusing capacity for carbon monoxide (DlCO) and functional residual capacity (frc) was evaluated in conscious horses. Horses were manually ventilated through an endotracheal tube, using a custom-made syringe filled with a gas mixture containing 18-carbon monoxide (18CO) and helium (He). The 18CO and He concentrations were continuously monitored by use of a mass spectrometer connected to the rebreathing circuit. Values for DlCO and frc were calculated from changes in the concentration of these 2 gases. In 11 Thoroughbreds, mean (± sd) DlCO was 330.3 ± 56.9 ml•min−1•mm of Hg−1, and frc was 20.21 ± 3 35 L. Body weight normalization yielded mean (± sd) values of 0.652 ± 0.114 ml•min−1•mm of Hg−1•kg−1 for DlCO, and 39.9 ± 6.4 ml•kg−1 for frc.