Effect of gas collection system on respiratory and stride frequency and stride length

Abstract

The objective of this study was to determine the effects of 2 different gas collection systems on locomotor and ventilatory responses to exercise in a group of 8 Standardbred pacers. Each horse completed the same incremental treadmill exercise test (8, 9, 10 and 11 m/s on a 3° incline) using an open (flow‐through) system (OS) and a closed system (CS) incorporating one way valves. Only 2 horses completed the final (11 m/s) step using the CS. Peak values for V̇O2, O2 pulse, plasma lactate and respiratory exchange ratio (RER) were significantly higher for the OS compared with the CS. There was no change in breathing frequency (Vf) or stride frequency (Sf) (mean ± s.e. 128 ± 2 strides/min) throughout either exercise test, however Vf was significantly lower when horses exercised in the CS (68 ± 6 breaths/min) when compared to the OS (100 ± 3 breaths/min). There was a linear increase in stride length (SL) with speed (3.8 ± 0.1 m/stride at 8 m/s to 5.0 ± 0.2 m at 11 m/s) but no difference in SL between systems. There was also a linear increase in VT measured in the CS. Incremental exercise did not alter the Sf:Vf ratio, however Sf:Vf was significantly lower in the OS (1.3:1) when compared to the CS (2.1:1). There was a significant difference between systems for PaO2 and PaCO2 values at all increments of exercise. The lower Vf measured in the CS was associated with marked hypercapnia (59 ± 7 mmHg at 10 m/s) and hypoxaemia (45 ± 3 mmHg at 10 m/s). The higher Vf measured in the OS was associated with hypocapnia (35 ± 2 mmHg) at 8 m/s. It was concluded that although Vf varied between OS and CS, Vf and Sf did not change during incremental exercise with either system. Therefore the increase in speed was achieved solely by an increase in SL. Although the CS did not alter locomotor parameters or V̇O2 at lower increments of exercise, the altered Vf appeared to limit work capacity. © 1995 EVJ Ltd