Clinical assessment of gas exchange in mature horses.

Abstract

There are limited methods of assessing pulmonary function in horses at rest. We developed clinical techniques to measure gas exchange efficiency in horses and evaluated 3 groups of horses that were 1) asymptomatic based on auscultation with rebreathing, transtracheal aspirate cytology, and thoracic radiographs (n = 6), 2) asymptomatic at rest but symptomatic with rebreathing (n = 11) and 3) symptomatic at rest (n = 9). Blood samples were obtained from the transverse facial artery and jugular vein. Maximal end-tidal CO2 tension (PETCO2) was measured by an infrared capnograph through a facemask. Alveolar O2 tension, dead space fraction (V(D)/V(T)), and physiological shunt fraction (Q(S)/Q(T)) were calculated using standard formulae. Arterial O2 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 1 horses (0.37+/-0.98%) was significantly lower than in Group 2 and Group 3 horses. Mean +/-s.d.V(D)/V(T) in Group 1 horses (-18.2+/-3.1) was significantly lower than Group 3 horses but not Group 2 horses.