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SummaryBackground 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 (VO2max) under field conditions. Objectives Design and validate a facemask with the potential to accurately measure VO2max in the field. Study design Experiment with 6 x 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. VO2 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. VO2max 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

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 (V̇ODesign and validate a facemask with the potential to measure V̇OExperiment with 6 × 6 Latin square design.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. V̇OBlood gases and V̇OSome rebreathing of expired air from mask dead space.Masks capable of measuring V̇O

Summary Reasons for performing study: The ability to obtain breath-by-breath measures of ventilatory mechanics for the entirety of an exercise test, regardless of speed(s) or duration enables evaluations of equine ventilation during exercise that are necessary for assessments of performance. Objective: Evaluation of a new ergospirometer (Quadflow; QF) system's accuracy and repeatability for measuring pulmonary variables in contrast to the established pneumotachometer-based system (control) and assessment of its effects, if any, on exercise capacity at high speeds. Materials and methods: Five Thoroughbred horses each performed 10 incremental exercise tests to fatigue, 5 with the QF system and 5 with an open-circuit flow system. Measures of pulmonary variables were evaluated to determine repeatability. Heart rate, pulmonary variables, arterial blood gases, distance run and time to fatigue measured with each system were compared to assess similarity of results and effect on performance. Results: Results from both systems had high repeatability with low coefficients of variation. The QF was associated with greater resistance to airflow, higher breathing rate at submaximal speeds, lower minute ventilation and peak inspiratory and expiratory airflows, greater acidaemia, hypoxaemia and hypercapnoea, and decreased total run time and total distance run when compared to control system results. Conclusion: The greater resistance of the QF was responsible for altered blood gases, respiratory parameters and performance when compared to the control mask. The QF system reliably measured equine pulmonary airflows and volumes and is suitable for research and clinical use provided optimal gas exchange and best possible physical performance are not required.

Summary Reasons for performing study: The antifibrinolytic, 6-aminohexanoic acid, also named aminocaproic acid (ACA), has been used empirically as a treatment for exercise-induced pulmonary haemorrhage (EIPH) on the unsubstantiated basis that transient coagulation dysfunction may contribute to its development. Objective: To assess the effect of ACA on bronchoalveolar lavage fluid (BALF) erythrocyte counts in horses performing treadmill exercise at an intensity greater than that needed to reach maximal oxygen consumption. Methods: Eight Thoroughbreds were exercised to fatigue 3 times on a 10% inclined treadmill at a speed for which the calculated oxygen requirement was 1.15 times. Horses were treated with a saline placebo, 2 and 7 g ACA i.v. 4 h before exercise, with a crossover design being used to determine the order of the injections. Exercise-induced pulmonary haemorrhage severity was quantified via the erythrocyte count in BALF. Bronchoalveolar lavage fluid was collected 4 h before and 30–60 min post exercise. Results were expressed as mean ± s.e.m. and analysed by one way repeated measures ANOVA (P

Summary Reasons for performing study: Prolonged equine exercise can cause hypochloraemic alkalosis and hypokalaemia secondary to the loss of hypertonic sweat. Movement of ions in and out of erythrocytes during exercise may help regulate acid-base balance and changes in plasma ion concentrations. The extent to which this happens during prolonged equine exercise has not been reported. Objectives: To measure changes in blood gases and major plasma and intraerythrocytic (iRBC) ion concentrations of horses undergoing prolonged submaximal exercise. Methods: Six horses were trotted at ∼30% VO2max on a treadmill for 105 min. Arterial (a) and mixed venous (v) blood samples were collected every 15 min, and pre- and post exercise. Blood gases and plasma (pl) concentrations of sodium, potassium, chloride and protein were measured and their iRBC concentrations calculated and compared (P

It has been postulated that the hypoxaemia and hypercapnoea that characterize strenuous equine exercise are partly due to flow limitations imposed by high breathing frequencies (fb), and that gas exchange would be improved if fb could be lowered. To evaluate this possibility, 6 Thoroughbred horses underwent 4 incremental treadmill exercise tests at inclines of 0, 5, 10 and 25%, respectively. In the test, horses were given a warm-up for 2 min, then ran sequentially for 1 min each at 60, 100 and 115% VO2max. Oxygen consumption (VO2), blood gas tensions (PaO2, PaCO2), fb, tidal volume (VT), minute ventilation (Ve), transpulmonary pressure (Ptp), peak inspiratory and expiratory airflows (VI, VE) and work of breathing (Wrm) were determined during the last 15 s of exercise at each intensity. The only effect of fb on PaO2 was seen at 60% VO2max. Also, maximal transpulmonary pressure difference (delta Ptpmax), and peak VI, and VE on a 25% slope were lower than those recorded at the other 3 inclines at 60% VO2max. At 100 and 115% VO2max, the effect of fb was less clear. While fb still differed, the only effects of fb at 100% VO2max were on delta Ptpmax. At 115% VO2max, fb on a 25% incline was lower than that for 0 and 5% slopes. The only other difference noted at this intensity was in VT on 10% slope. However, there was no difference between VTS recorded at inclines of 0, 5 or 25% at 115% VO2max. There was no effect of fb or exercise intensity on Ve at 100 or 115% VO2max. There was no change in PaO2, fb, VT, delta Ptpmax or VI and VE as exercise intensity increased from 60-115% VO2max on slopes of 0, 5 or 10%. However, for exercise on the 25% incline (i.e. with lower fb), each of these parameters increased (or decreased for PaO2) from 60-100%, but not from 100-115% VO2max. Failure of peak airflow and VT to increase when intensity increased was associated with the development of hypoxaemia and hypercapnoea, regardless of slope or fb. It is concluded that while a low fb may have some beneficial effect on gas exchange during submaximal exercise at approximately 60% VO2max, this effect disappears as exercise intensity increases. There appear to be limits to the peak airflows that can be generated by horses during strenuous exercise, and these limits may be reached regardless of fb. Flow limitation per se may play a greater role in the development of exercise-induced hypoxaemia and hypercapnoea in horses than dose fb.

Summary Reasons for performing study: Horses experience major perturbations in acid-base balance during supramaximal exercise. Ion movement in and out of erythrocytes (RBCs) is believed to be important in maintaining acid-base balance but it is unclear as to the extent to which this happens, nor how it affects single measurements of ion concentrations in arterial and venous blood. Objectives: To clarify the role RBCs play in mitigating perturbations in acid-base balance during high speed exercise in horses, and to describe associated differences in arterial (a) and mixed venous (v) concentrations of key ions. Methods: Six exercise-trained Thoroughbreds galloped to fatigue at speeds calculated to have an oxygen demand that was 115% of the VO2max. Blood samples (a and v) were collected pre-exercise, during warm-up, at fatigue, and immediately post exercise. Packed cell volume (PCV), pH, PCO2, and plasma concentrations of bicarbonate (HCO3−), chloride (Cl−), sodium (Na+), potassium (K+), and lactate (Lac−) and strong ion difference (SID) were determined, and RBC concentrations of Lac− and electrolytes calculated for each sample. Data were analysed using a 2-way ANOVA for repeated measures testing for effects of sampling time and site (P

Introduction Healthy and poorly performing horses can display arrhythmias during exercise and immediately afterwards. The relationship of arrhythmias to exercise intensity or type, and their frequency of recurrence, are poorly understood. Clarification of these issues was the objective of this investigation. Methods Electrocardiograms were recorded on 9 Thoroughbreds during maximal and submaximal exercise on a racetrack (RA) and treadmill (TM). The frequency of atrial and ventricular arrhythmias for RA and TM were compared using Fisher's Exact Test. Results 65 workouts (TM = 46, RA = 19; median[range]: 4/horse[2–14]) were performed. Exercising arrhythmias were detected in 4/9 horses (12/65 workouts) and there were post-exercise arrhythmias in 7/9 horses (20/65 workouts). A single exercising electrocardiogram per horse often did not display all arrhythmias detected over several workouts. 3/9 horses exhibited arrhythmias during the first and second runs while the other 6 had none. 4/9 had 1 post-exercise arrhythmia. Of 6 horses with >3 runs, 1 displayed arrhythmias each time, 3 never had arrhythmias and 2 sometimes showed arrhythmias during exercise (1/9 and 4/8 workouts, respectively). All 6 intermittently had post-exercise arrhythmias (median[range]: 50% [9–75%] of workouts). Presence of arrhythmias was positively related to intensity and all occurred at ≥94%HRmax. The frequency of arrhythmias following RA (29%) and TM (12.5%) was not statistically different. Conclusions Gallops on TM or RA were equally effective for detecting arrhythmias. The presence/absence of exercising arrhythmias was more repeatable than post-exercise arrhythmias. Arrhythmias are more likely to be detected at maximal or near-maximal intensities. A larger population needs to be studied before firm conclusions are drawn. Ethical Animal Research The study was approved by an Institutional Animal Care and Use Committee protocol. Sources of funding: Department of VCS, Washington State University. Competing interests: none.

Introduction Big respiratory cycles (BRCs) are a sporadic but normal occurrence during galloping exercise. Their relationship to performance capacity as reflected by maximal oxygen consumption (VO2max) is unclear. Methods 7 Thoroughbreds completed multiple incremental exercise tests up to 13 m/s on a treadmill to determine their VO2max while wearing a mask that measured inspired and expired volumes (VI, VE) and VO2 on a breath-by-breath basis. Frequency and duration of BRCs were related to speed and VO2max using regression analysis. Numbers of BRCs for each test were counted and the duration, VI, VE and VO2 of each BRC determined and compared to the corresponding average values of the 5 breaths following the BRCs, and VO2max for the exercise bout. Significance was set at P

Introduction The ability to accurately assess equine oxygen consumption (VO2) under field conditions has been limited by the need for unrestricted gas exchange. Methods Two variations of a mask and an associated electronics control module (ECM) were designed to enable breath-by-breath measurement of airflows with two 8.0 cm diameter pneumotachometers located 7.5 cm in front of each narus and connected to differential pressure transducers mounted on the outside of the mask. The ECM was comprised of electronics for signal filtering to the flow transducers, an oxygen sensing cell, and an analog-to-digital converter all powered by a lithium-ion battery. The battery also 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. VO2 was determined from these recordings by an operator using a customized software analysis program. One mask encased the lower head (E). The other left the jaw free so horse could wear a bit and be ridden (R). Multiple treadmill exercise tests were undertaken by 6 horses to measure VO2max and blood gases. Each mask was worn twice and results compared to those from an open flow-through system (O) by 2-way RMANOVA (P

Introduction Measurement of maximal oxygen consumption (VO2max) is the gold standard for assessing aerobic capacity, but in horses requires use of stationary equipment and a high-speed treadmill. Study objectives were to evaluate a portable system designed to measure VO2 in a field setting and to describe these measurements in a cohort of untrained Thoroughbreds. Methods Ventilatory parameters and VO2 were measured in 41 untrained Thoroughbreds (16 colts, 25 fillies, 19.8 ± 1.4 months) using an ergospirometry and oximetry mask with customized software validated for horses galloping on a treadmill with an open-circuit flow-through gas collection system. Horses were instrumented with a GPS-HR monitor, light-weight mask and data-capture equipment. Data was collected as horses travelled riderless up a 2% inclined woodchip track. Pre- and 5 minute post-exercise plasma lactate ([La5]), HRpeak, maximal velocity (Vmax) and exercise distance were recorded and analysed by unpaired t-test and Pearson's correlation (P ≤ 0.05). Results All horses tolerated the mask and saddle pad. Exercise distance was 1700.5 ± 33.4 m, Vmax 15.0 ± 1.4 m/s, HRpeak 221.2 ± 9.6 bpm and [La5] 22.7 ± 5.5 mmol/l. Average VO2peak, based on 6 breaths, was 117.7 ± 24.1 ml/kg/min, breathing frequency 125.8 ± 7.1 bpm, inspiratory volume 13.2 ± 1.7 L, expiratory volume 13.4 ± 1.9 L and minute ventilation 1669.3 ± 193.3 L/min. VO2peak was not significantly different between colts (112.2 ± 27.7 ml/kg/min) and fillies (121.4 ± 21.3 ml/kg/min). There were no correlations between VO2peak and other measured parameters. There was a positive linear correlation between VO2peak and HRpeak (P = 0.046, R2 = 0.16). Conclusions VO2peak values were similar to published reports for yearling Thoroughbreds. The high exercise intensity and linear relationship between VO2peak and HRpeak provides confidence in the system for field studies of aerobic capacity in untrained, unridden horses. Ethical Animal Research Institutional Animal Research Ethics Committee approval was obtained. Sources of funding: Science Foundation Ireland (11-P1- 1166). Competing interests: None.

The possibility that pre-exercise inhalation of a bronchodilator by healthy horses could improve their mechanics of breathing and enhance performance was investigated. Ipratropium bromide (0.35 microg/kg bwt; n = 7) was administered by nebulisation 30 min before exercise and frusemide (1 mg/kg bwt; n = 6) was given in the same manner 2 h before exercise. Albuterol sulphate (360 and 720 microg; n = 7) were administered with a metered dose inhaler 2 h before exercise. Each drug was investigated independently of the others using cross-over protocols. Horses completed incremental exercise tests and oxygen consumption, carbon dioxide production, arterial blood gases, heart rate and measures of breathing mechanics including total pulmonary resistance (RL) and nasopharyngeal resistance (RU) were determined for each exercise intensity. The resistance of the lower airways was calculated subsequently from the difference between RL and RU. None of the drugs tested had an effect on any of the variables measured, possibly because maximal bronchodilation is stimulated in healthy horses by the normal sympathoadrenergic response to exercise. Therefore, the pre-exercise inhalation of a bronchodilator by a healthy horse is unlikely to improve performance capacity.