Oxygen consumption, locomotory-respiratory coupling and exercise-induced pulmonary hemorrhage in horses during the Paso Fino gait

Background

Workload associated with the high frequency Colombian Paso Fino gait has not been evaluated.

Objectives

To determine the oxygen consumption (V̇O₂), heart rate (HR), stride frequency: breathing ratio, and hematology associated with the Paso Fino gait, including whether exercise-induced pulmonary hemorrhage (EIPH) occurs.

Animals

Eleven Paso Fino horses.

Methods

Prospective cohort study. Horses performed a standardized Paso Fino gait test across a wooden sounding board, simulating competition. V̇O₂ and ventilatory parameters (tidal volume [V_T]; peak inspiratory and expiratory airflows [PkV̇_I, PkV̇_E]; respiratory rate [RR], minute ventilation [V̇E]) were measured using a portable ergospirometry facemask. Heart rate was measured using electrocardiograms. Post-exercise lactate, hematocrit, bicarbonate, pH, electrolytes, and biochemistry concentrations were measured. EIPH was assessed via tracheobronchoscopy. Four horses completed a secondary high-intensity gallop to elicit peak V̇O₂ for comparative purposes.

Results

Median [IQR] mean individual HR during the Paso Fino gait was 190 [178, 201] bpm. Relative V̇O₂ measured 49.8 [48.4, 59.5] mL/(kg min; V_T = 8.6 [8.0, 10.7] L; RR = 87.1 [75.4, 99.5] bpm; V̇E = 869 [740, 902] L/min; PkV̇_I = 33.4 [32.7, 37.2] L/s; PkV̇_E = 44.2 [40.3, 46.0] L/s). Horses took 2.8 [2.7, 2.9] strides/second and had a stride frequency: breathing ratio of 2.0 [1.8, 2.3]. Post-exercise blood lactate concentration and hematocrit measured 2.7 mmol/L and 50% respectively. Three horses showed endoscopic evidence of Grade-1 EIPH. The Paso Fino gait V̇O₂ and HR equaled 79% V̇O₂pk and 91% maximal HR, respectively, based on the high-intensity gallop.

Conclusions and Clinical Importance

The Paso Fino gait represents submaximal exercise based on V̇O₂ < V̇O₂pk and blood lactate.