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

Workload and spirometry associated with untethered swimming in horses

BACKGROUND

Swimming has been used empirically for rehabilitation and conditioning of horses. However, due to challenges imposed by recording physiological parameters in water, the intensity of free swimming effort is unknown.

OBJECTIVES

Measure the physiological workload associated with untethered swimming in horses. Five fit Arabian endurance horses were assessed while swimming in a 100 m-long indoor pool. Horses were equipped with a modified ergospirometry facemask to measure oxygen consumption (V̇O2) and ventilatory parameters (inspired/expired volumes, VI, VE; peak inspiratory/expiratory flows, PkVI, PkVE; respiratory frequency, Rf; minute ventilation, VE; inspiratory/expiratory durations and ratios, tI, tE, tI/ttot, tE/ttot); and an underwater electrocardiogram that recorded heart rate (HR). Postexercise venous blood lactate and ammonia concentrations were measured. Data are reported as median (interquartile ranges).

RESULTS

Horses showed bradypnea (12 breaths/min (10-16)) for the first 30 s of swimming. V̇O2 during swimming was 43.2 ml/(kg.min) (36.0-56.6). Ventilatory parameters were: VI = 16.7 L (15.3-21.8), VE = 14.7 L (12.4-18.9), PkVI = 47.8 L/s (45.8-56.5), PkVE = 55.8 L/s (38.3-72.5), Rf = 31.4 breaths/min (20.0-33.8), VE = 522.9 L/min (414.7-580.0), tI = 0.5 s (0.5-0.6), tE = 1.2 s (1.1-1.6), tI/ttot = 0.3 (0.2-0.4), tE/ttot = 0.7 (0.6-0.8). Expiratory flow tracings showed marked oscillations that coincided with a vibrating expiratory sound. HR was 178.0 bpm (148.5-182.0), lactate = 1.5 mmol/L (1.0-1.9) and ammonia = 41.0 µmol/L (36.5-43.5).

CONCLUSIONS

Free (untethered) swimming represents a submaximal, primarily aerobic exercise in horses. The breathing pattern during swimming is unique, with a relatively longer apneic period at the beginning of the exercise and an inspiratory time less than half that of expiration.

Field-training in young two-year-old thoroughbreds: investigating cardiorespiratory adaptations and the presence of exercise induced pulmonary hemorrhage

BACKGROUND

Comparatively little is known regarding the initial cardiorespiratory response of young racehorses to training. The objectives were to compare physiological parameters before and after introductory training and determine whether young Thoroughbreds show endoscopic signs of exercise-induced pulmonary hemorrhage (EIPH). Ten Thoroughbreds (20-23 months) underwent 12-weeks of introductory training, including weekly speed sessions. Two 600 m high-speed exercise tests (HSET) were performed following weeks 4 and 12 while wearing a validated ergospirometry facemask. Peak oxygen consumption (V̇O2pk) and ventilatory parameters (tidal volume, VT; peak inspiratory and expiratory flow, PkV̇I, PkV̇E; respiratory frequency, Rf; minute ventilation, V̇E) were measured. The ventilatory equivalent of oxygen (V̇E/V̇O2) and the aerobic and anaerobic contributions to energy production were calculated. Maximal heart rate (HRmax) and HR at maximal speed (HRVmax) were determined. Post-exercise hematocrit, plasma ammonia and blood lactate were measured. Evidence of EIPH was investigated via tracheobronchoscopy post-exercise. Results were compared (paired t-test, P < 0.05).

RESULTS

Horses were faster following training (P < 0.001) and V̇O2pk increased 28 ml/(kg total mass.min) (28 ± 16%; P < 0.001). Ventilatory (V̇E, P = 0.0015; Rf, P < 0.001; PkV̇I, P < 0.001; PkV̇E, P < 0.001) and cardiovascular parameters (HRmax, P = 0.03; HRVmax, P = 0.04) increased. The increase in V̇E was due to greater Rf, but not VT. V̇E/V̇O2 was lower (26 ± 3.6 vs 23 ± 3.7; P = 0.02), indicating improved ventilatory efficiency. Anaerobic contribution to total energy production increased from 15.6 ± 6.1% to 18.5 ± 6.3% (P = 0.02). Post-exercise hematocrit (P < 0.001), plasma ammonia (P = 0.03) and blood lactate (P = 0.001) increased following training. Horses showed no signs of EIPH.

CONCLUSIONS

Young two-year-old Thoroughbreds responded well to introductory training without developing tracheobronchoscopic evidence of EIPH.

Effects of hyperthermia and acidosis on mitochondrial production of reactive oxygen species

Exercise is associated with the development of oxidative stress, but the specific source and mechanism of production of pro-oxidant chemicals during exercise has not been confirmed. We used equine skeletal muscle mitochondria to test the hypothesis that hyperthermia and acidosis affect mitochondrial oxygen consumption and production of reactive oxygen species (ROS). Skeletal muscle biopsies were obtained at rest, after an acute episode of fatiguing exercise, and after a 9-wk conditioning program to increase aerobic fitness. Mitochondrial oxygen consumption and ROS production were measured simultaneously using high-resolution respirometry. Both hyperthermia and acidosis increased nonphosphorylating (LEAK) respiration (5.8× and 3.0×, respectively, P < 0.001) and decreased efficiency of oxidative phosphorylation. The combined effects of hyperthermia and acidosis resulted in large decreases in phosphorylating respiration, further decreasing oxidative phosphorylation efficiency from 97% to 86% (P < 0.01). Increased aerobic fitness reduced the effects of acidosis on LEAK respiration. Hyperthermia increased and acidosis decreased ROS production (2× and 0.23×, respectively, P < 0.001). There was no effect of acute exercise, but an aerobic conditioning program was associated with increased ROS production during both nonphosphorylating and phosphorylating respiration. Hyperthermia increased the ratio of ROS production to O2 consumption during phosphorylating respiration, suggesting that high-temperature impaired transfer of energy through the electron transfer system despite relatively low mitochondrial membrane potential. These data support the role of skeletal muscle mitochondria in the development of exercise-induced oxidative stress, particularly during forms of exercise that result in prolonged hyperthermia without acidosis.NEW & NOTEWORTHY The results of this study provide evidence for the role of mitochondria-derived ROS in the development of systemic oxidative stress during exercise as well as skeletal muscle diseases such as exertional rhabdomyolysis.

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.

Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500 mL, in 5-7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2 minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT:spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [-15% (-46-32)] and expiratory [10% (-32-20)] flows and inspiratory [-6% (-25-18)] and expiratory [5% (-9-20)] times. Agreement for nadir flows was poor [-22% (-87-369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horses.

A Preliminary Investigation into Ridden Water Submersion Training as an Adjunct to Current Condition Training Protocols in Performance Horses

Simple Summary

Superficial Digital Flexor Tendon (SDFT) injuries are the most common musculoskeletal injury reported in equestrian jumping disciplines. In an attempt to reduce incidences of injuries in elite event horses, Ridden Water Submersion Training (RWST) is a form of condition training that involves submerging the horse up to sternum height in water and trotting for set intervals. It is used by a small number of trainers to increase cardiovascular fitness whilst potentially minimising tendon temperature increase, which is typically reported during traditional condition training sessions. The results of this study suggest that RWST acted as a moderate sub-maximal intensity level of exercise in a group of elite international event horses whilst preventing the accompanying increase of distal limb temperature commonly associated with condition training on land. RWST could thus be a useful adjunct to current condition training protocols, particularly for horses that compete in disciplines that have high incidence rates of tendon injury. However, further research is required to provide a more comprehensive understanding of the workload imposed during RWST training.

Abstract

This observational study aimed to elucidate the effects of RWST on the cardiovascular and musculoskeletal systems of horses and concurrently determine whether RWST limits distal limb temperature increases previously reported during gallop training on land. A group of 15 clinically sound international event horses were recruited, and heart rate (HR), speed (km/h) and thermal images of the distal limb were analysed at set intervals during RWST training. Intervals of RWST produced a total mean HR_max value of 65.18 ± 3.76%, which is within the parameters for increased aerobic stamina. Mean HR increased significantly (p < 0.01) while mean distal limb temperature decreased significantly (p < 0.01) between warm-up and RWST, which contrasts with positive correlations previously reported during gallop training on land. These preliminary results suggest that RWST can be classed as a moderate submaximal intensity exercise in elite international event horses whilst restricting an increase in temperature of the distal limb that is commonly associated with tendon rupture. Horses competing at very elite levels of eventing only represent a small percentage of the total performance population; therefore, further research is needed to ascertain the physiological effects of RWST in non-elite performance horses, as well as horses competing across various equestrian disciplines.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

Conditioning equine athletes on water treadmills significantly improves peak oxygen consumption

Equine water treadmills (WT) were initially designed for rehabilitation of musculoskeletal injuries, but are also commonly used for conditioning sport horses, however the effects are not well documented. The purpose of this study was to test the effect of an 18-day WT conditioning programme on peak oxygen consumption (V̇O2peak). Nine unfit Thoroughbreds were used in a randomised controlled trial. Six horses worked daily for 18 days in stifle-height water (WT group), while 3 control horses worked without water (dry treadmill group (DT)). Preconditioning and postconditioning maximal exercise racetrack tests (800 m) were performed using a portable ergospirometry system. Measured outcomes were V̇O2, tidal volume, minute ventilation, breathing frequency, heart rate, blood lactate and instantaneous and average speed. The workload as assessed by V̇O2 was 21.7 per cent of preconditioning V̇O2peak values for WT horses. V̇O2peak on the racetrack increased by 16.1 per cent from preconditioning to postconditioning in the WT horses (P=0.03), but did not change in the DT horses. Therefore, exercising horses in high water heights may improve conditioning.

Efficacy of dexamethasone, salbutamol, and reduced respirable particulate concentration on aerobic capacity in horses with smoke-induced mild asthma

Background

Mild asthma in horses decreases racing performance and impairs gas exchange. The efficacy of treatment on performance is unknown.

Hypothesis

Treatment targeting lung inflammation improves V˙O₂peak in horses with mild asthma.

Animals

Thoroughbred polo horses (n = 12) with smoke‐induced mild asthma. Horses were exposed to increased ambient particulate matter (35.51 μg/m³ [PM_2.5]; day mean, centrally measured) from day −33 to 0, from bushfire smoke (natural model).

Methods

Prospective, randomized, placebo‐controlled, double‐blinded clinical trial. All horses completed 3 V˙O₂peak tests, measuring aerobic and anaerobic variables: day 0 ‐baseline; day 16 ‐after dexamethasone (20 mg IM q24h; DEX, n = 6) or saline treatment (SALINE, n = 6), under improved ambient PM_2.5 concentrations (7.04 μg/m³); day 17‐15‐30mins after inhaled salbutamol (1500 μg). Bronchoalveolar lavage and mucus scoring were performed on day −8 and day 20. Linear mixed effects models were used to examine the effects of timepoint and treatment group on BAL differential cell counts, mucus scores, aerobic and anaerobic variables.

Results

Horses’ mucus scores improved significantly from day −8 to 20 by 1.27 ± .38 (P = .01). There was a significant increase in V˙O₂peak of 15.5 ± 4.0 mL(min.kg)⁻¹ from day 0 to 17 (P = .002), representing an average (mean) increase in V˙O₂peak of 13.2%. There was no difference in V˙O₂peak between treatment groups (SALINE versus DEX) at any timepoint.

Conclusions and Clinical Importance

This study highlighted the key role of improved air quality on functionally important airway inflammation. Evidence provided is central to increasing owner compliance regarding improved air quality for the treatment and prevention of mild asthma.

Relative aerobic and anaerobic energy contribution in race fit endurance and Thoroughbred racehorses during strenuous exercise

The objective was to compare fit Arabian endurance and Thoroughbred racehorses’ responses to a maximal intensity standardised incremental treadmill test (MaxSIT) with respect to: (1) their relative aerobic contributions during maximal exercise; and (2) selected physiological parameters related to performance. Six high-level endurance Arabians and six race-ready Thoroughbreds performed a MaxSIT starting at 8 m/s and increasing by 1 m/s increments 60 s until maximum oxygen consumption (V̇O2max) was reached. Heart rate (HR), blood lactate concentration (BLac), haematocrit (Hct), minute ventilation (V̇E) and oxygen consumption (V̇O2) were measured. V̇O2max, the speeds at which the HR were 200 and 160 bpm, respectively (V200, V160), the speed at which the BLac reached 4 mmol/l (VLa4) and lactate at HR200 (BLa200) were calculated. The relative aerobic energy input was determined using ΔBLacPeak-Resting increase as previously described. Data were expressed as median with interquartile range and analysed with a Wilcoxon rank sum test (P<0.05). Endurance horses had greater V̇O2max (202.5 ml/(kg.min) (190.3-211) vs 152.7 ml/(kg.min) (140.5-158.3); P<0.001) and had a greater aerobic energy contribution to total exercise effort (89.9% (87.0-96) vs 82.8% (81.1-84.1); P=0.009) than Thoroughbreds. Endurance horses reached HR>200 bpm on the treadmill, but had a lower HRmax (210 bpm (205-217) vs 226 bpm (219-228); P=0.008), BLa200 (3.8 mmol/l (2.7-5.5) vs 4.8 mmol/l (3.6-5.2); P<0.001) and Hctmax (56.4% (54.9-57.5) vs 61.5% (59-64); P=0.002). Endurance horses median VLa4 was 11.6 m/s (11.0-13.0); V200=11.9 m/s (10.9-12.3) and V160=8.5 m/s (7.2-8.6). Because of the HR and speed characteristics of modern endurance races, we proposed BLa200 as a new calculated parameter with which to assess endurance horses. Trained endurance horses accumulate less lactate, have a greater V̇O2max and relative aerobic contribution to their energy requirements at maximal intensity exercise despite a lower blood haematocrit.

Effect of different protocols on the mitigation of exercise-induced pulmonary hemorrhage in horses when administered 24 hours before strenuous exercise

BACKGROUND

Public pressure exists in the United States to eliminate race-day furosemide administration despite its efficacy in decreasing the severity of equine exercise pulmonary hemorrhage (EIPH). No effective alternative prophylaxis strategies have been identified.

OBJECTIVE

To investigate alternative protocols to race-day furosemide that might mitigate EIPH.

ANIMALS

Seven fit Thoroughbreds with recent EIPH.

METHODS

Double-blinded placebo-controlled Latin square crossover using a treadmill followed by a blinded placebo-controlled crossover study at a racetrack. First, horses exercised supramaximally to fatigue 24 hours after initiating 5 EIPH prophylaxis protocols: 0.5 and 1.0 mg/kg furosemide IV 24 hours pre-exercise with and without controlled access to water, and 24 hour controlled access to water. Effects were compared to those measured after giving a placebo 24 hours pre-exercise, and 0.5 mg/kg furosemide IV 4 hours pre-exercise. Bronchoalveolar lavage (BAL) erythrocyte count was determined 45-60 minutes postexercise after endoscopy to assign an EIPH score. Data were analyzed using linear mixed effects models. The most promising protocol from the treadmill study was further evaluated in 6 horses using endoscopy and BAL after 1100 m simulated races.

RESULTS

Intravenous furosemide (0.5 mg/kg) administered 24 hours pre-exercise combined with controlled access to water decreased the severity of EIPH on the treadmill and at the racetrack.

CONCLUSION AND CLINICAL IMPORTANCE

Administering 0.5 mg/kg furosemide 24 hours pre-racing combined with controlling water intake may be a strategy to replace race-day furosemide administration for the management of EIPH. A larger study is indicated to further evaluate whether this protocol significantly mitigates EIPH severity.

Assessment of high-intensity over-ground conditioning and simulated racing on aerobic and anaerobic capacities in racehorses

A prospective, randomised study assessed the impact of high-intensity racetrack conditioning on aerobic and anaerobic capacities in seasoned Thoroughbred racehorses. The effect of 10 weeks race conditioning and two simulated races on V̇O2maxand maximum accumulated oxygen deficit (MAOD) were evaluated. An incremental treadmill test to determine V̇O2max, followed by three supramaximal runs to fatigue (at speeds (V105%, V115%, V125%) corresponding to oxygen requirements 105%, 115% and 125% of V̇O2max, in randomised order) were performed at each timepoint (T1 [pre-conditioning] and T2 [post-conditioning]). Prior to T1, racehorses were briefly de-trained for four-six weeks and given low-level treadmill conditioning to prepare them for the more strenuous race conditioning after T1. Paired variables between T1 and T2 were analysed using a paired t-test. A 2-way RM ANOVA compared variables with >1 measurement. Speed at V̇O2max(P=0.04) and V̇O2max(P=0.01) increased with conditioning. Calculated speeds for the supramaximal runs increased for V105% (P=0.02) and V115% (P=0.03) but not for V125% (P=0.08). There was no conditioning effect on time to fatigue (P=0.34), although it was different between all intensities (2.8, 2.2 and 1.4 mins at V105%, V115% and V125% respectively at T2). O2demand increased with conditioning (P=0.02) for each supramaximal intensity. On average, horses’ aerobic capacity improved 4.43% after conditioning. MAOD was unchanged with conditioning (P=0.25) and unaffected by exercise intensity. Fit racehorses that have undergone repeated intensive training programs, experience smaller, incremental improvement than completely unfit horses. The anaerobic capacity of previously trained racehorses is relatively stable, despite brief periods of de-training.

Cardiovascular Response to Exercise and Training, Exercise Testing in Horses

The physiology of exercise and training is fascinating, and hundreds of interesting studies have given insight into its mechanisms. Exercise testing is a useful clinical tool that can help veterinarians assess poor performance, fitness, and performance potential and prevent injuries. The clinically applicable aspects of cardiovascular adaptions to training and exercise testing are highlighted in this review. Different exercise tests should be used to evaluate horses performing in different disciplines and levels. Exercise tests that simultaneously assess several body systems can be beneficial when assessing poor performance, because this is often a multifactorial problem with signs not detectable at rest.