CLINICAL-ASSESSMENT OF GAS-EXCHANGE IN MATURE HORSES

There are limited methods of assessing pulmonary function in horses at rest. We developed clinical techniques to measure gas exchange effici ency in horses and evaluated 3 groups of horses that were 1) asymptoma tic based on auscultation with rebreathing, transtracheal aspirate cyt ology, and thoracic radiographs (n = 6), 2) asymptomatic at rest but s ymptomatic with rebreathing (n = 11) and 3) symptomatic at rest (n = 9 ). Blood samples were obtained from the transverse facial artery and j ugular vein. Maximal end-tidal CO2 tension (PETCO2) was measured by an infrared capnograph through a facemask, Alveolar O-2 tension, dead sp ace fraction (V-D/V-T), and physiological shunt fraction (Q(S)/Q(T)) w ere calculated using standard formulae. Arterial O-2 tension in Group 1 horses (mean +/- s.d. 103 +/- 3 mmHg) was significantly higher than in Group 2 or Group 3 horses, Q(S)/Q(T) in Group I horses (0.37 rt 0.9 8%) was significantly lower than in Group 2 and Group 3 horses. Mean /- s.d. V-D/N-T in Group 1 horses (-18.2 +/- 3.1) was significantly lo wer than Group 3 horses but not Group 2 horses.