Evaluation of a mask for breath-by-breath respirometry during exercise in horses

Comparison of ventilatory and oxygen consumption measurements of yearling Thoroughbred colts and fillies exercising unridden on an all-weather track

Sex effects on ventilatory and oxygen consumption (V̇O2) measurements during exercise have been identified in humans. This study's aim was to evaluate the hypothesis that there are sex effects on ventilatory and V̇O2 measurements in exercising, untrained yearling Thoroughbreds (Tb). Forty-one Tbs (16 colts, 25 fillies; 19.8 ± 1.4 months old) were recruited. Physiological, ventilatory and exercise data were gathered from horses exercising unridden at high intensity on an all-weather track from a global positioning-heart rate unit and a portable ergospirometry system. Data were analysed with an unpaired Student's t-test and the Benjamini-Hochberg correction for multiple testing (P ≤ 0.05 significant). Mean bodyweight (BW, P = 0.002) and wither height (P = 0.04) were greater for colts than fillies. There were no differences in physiological and exercise data and absolute peak V̇O2 between groups. However, fillies had a higher mass specific peak V̇O2 (P = 0.03) than colts (121.5 ± 21.6 mL/kg.min vs. 111.9 ± 27.4 mL/kg.min). The peak breathing frequency was greater for fillies (P < 0.001) while the peak inspiratory (P < 0.001) and expiratory air flow (P < 0.001), peak expiratory tidal volume (VTE; P < 0.001) and peak minute ventilation (V̇E; P = 0.01) were greater for colts; there were no differences for peak VTE and V̇E when adjusted for BW. Differences in BW explain the differences in mass specific peak V̇O2 between groups. Given their morphological differences, it is likely that lung volumes and airway diameters are smaller for fillies, resulting in greater resistance and lower air flows and volumes. Further research is required to investigate the ventilatory differences and how they may change with maturation and impact performance.

Workload of horses on a water treadmill: effect of speed and water height on oxygen consumption and cardiorespiratory parameters

Background

Despite the use of water treadmills (WT) in conditioning horses, the intensity of WT exercise has not been well documented. The workload on a WT is a function of water height and treadmill speed. Therefore, the purpose of this study was to determine the effects of these factors on workload during WT exercise.

Fifteen client-owned Quarter Horses were used in a randomized, controlled study. Three belt speeds and three water heights (mid cannon, carpus and stifle), along with the control condition (dry treadmill, all three speeds), were tested. Measured outcomes were oxygen consumption (V̇O₂), ventilation (respiratory frequency, tidal volume (V_T)), heart rate (HR), and blood lactate. An ergospirometry system was used to measure V̇O₂ and ventilation. Linear mixed effects models were used to examine the effects of presence or absence of water, water height and speed (as fixed effects) on measured outcomes.

Results

Water height and its interaction with speed had a significant effect on V̇O₂, V_T and HR, all peaking at the highest water level and speed (stifle at 1.39 m/s, median V̇O₂ = 16.70 ml/(kg.min), V_T = 6 L, HR = 69 bpm). Respiratory frequency peaked with water at the carpus at 1.39 m/s (median 49 breaths/min). For a given water height, the small increments in speed did not affect the measured outcomes. Post-exercise blood lactate concentration did not change.

Conclusions

Varying water height and speed affects the workload associated with WT exercise. The conditions utilized in this study were associated with low intensity exercise. Water height had a greater impact on exercise intensity than speed.

Validation of masks for determination of V̇O2 max in horses exercising at high intensity

BACKGROUND

The need for a horse to be ridden while wearing a measurement device that allows unrestricted ventilation and gas exchange has hampered accurate measurement of its maximal oxygen consumption (V̇O₂ max) under field conditions.

OBJECTIVES

Design and validate a facemask with the potential to measure V̇O₂ max accurately in the field.

STUDY DESIGN

Experiment with 6 × 6 Latin square design.

METHODS

Two variations of a mask and associated electronic control module (ECM) were designed to enable breath-by-breath measurement of airflows through two 7.8 cm diameter pneumotachometers located 7.5 cm in front of each narus. The ECM was comprised of an analogue-to-digital converter and a lithium-ion battery that provided power and signal filtering to the pneumotachometers and an oxygen sensing cell, and powered a pump connected to gas sampling ports between the nares and pneumotachometers. Airflow and oxygen content of inspired and expired gases were recorded through the ECM and electronically transferred to a notebook. V̇O₂ was determined from these recordings using a customised software program. Mask B encased the lower jaw. Mask R left the jaw free so the horse could wear a bit if ridden. V̇O₂ max and arterial blood gases were measured in 6 horses during multiple treadmill tests. Each mask was worn twice and results compared to those from an established open flow-through system (O) by ANOVA-RM (P<0.05). System utility was evaluated using the intraclass correlation coefficient of 4 independent raters.

RESULTS

Blood gases and V̇O₂ max (151.9±7.0 [mean±s.d.; O], 151.5±9.6 [B], 149.5±7.5 [R] ml/[kg.min]) were not different between masks. V̇O₂ max measures were reproducible for each mask. Intraclass correlation coefficient between raters = 0.99.

MAIN LIMITATIONS

Some rebreathing of expired air from mask dead space.

CONCLUSION

Masks capable of measuring V̇O₂ max during treadmill exercise were developed, tested and found to be accurate. Mask R has potential application to measurement of V̇O₂ max under field conditions.