Synchronization of locomotion and respiration in trotting ponies

Use of external nasal strip influences alveolar cell population of horses after exercise

ABSTRACT The nasal strip is widely used in horses during exercise, but effects of using a nasal strip are controversial and little is known about its effect on horses undergoing endurance events. The aim of this study was to determine whether the use of nasal strips influences alveolar cell population assessed by bronchoalveolar lavage (BAL), tidal volume, and nasal airflow rate. Six Arabian horses were subjected to two low intensity tests on a treadmill, with and without application of a commercial external nasal strip. Tidal volumes and airflow rates were measured during the test; two hours after the test, BAL was performed to assess cytology of pulmonary secretions. The lavage fluid showed increased neutrophil count after exercise in animals with the nasal strip (P<0.05). This suggests that turbulence of airflow through the nasal cavity may have diminished with nasal strip use, thus allowing larger particles to be deposited more distally in the respiratory system, inducing a more intense neutrophilic response. No differences in tidal volumes or airflow rates were observed between groups (with or without nasal strips) during the test (P>0.05). The use of nasal strips seems to influence alveolar cell population during and after exercise in horses after low intensity exercise tests. Further studies are needed to verify whether alveolar cell population is related to poor exercise performance in horses.

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.

Oxygen consumption and gait variables of Arabian endurance horses measured during a field exercise test

REASONS FOR PERFORMING STUDY

Arabian horses have morphological, muscular and metabolic features designed for endurance races. Their gas exchange and gait variables were therefore measured during a field exercise test. This study presents original respiratory and locomotor data recorded in endurance horses under field conditions.

HYPOTHESIS AND OBJECTIVES

Respiratory gas exchange ratio (RER) of Arabian horses at the speed required to win endurance races (18 km/h for 120-160 km) are <1 and running economy (RE) is also low in order to maintain exercise intensity using aerobic metabolism for long intervals. The purpose of this study was to measure oxygen consumption and gait variables in Arabian endurance horses running in the field in order to estimate RER and RE.

MATERIALS AND METHODS

Five Arabian horses trained for endurance racing were test ridden at increasing speeds on the field. Their speed was recorded and controlled by the rider using a GPS logger. Each horse was equipped with a portable respiratory gas analyser, which measured breath-by-breath respiratory variables and heart rate. The gait variables were recorded using tri-axial accelerometer data loggers and software for gait analysis. Descriptive statistics and linear regressions were used to analyse the speed related changes in each variable with P < 0.05 taken as significant.

RESULTS

At a canter speed corresponding to endurance race winning speed (18 km/h), horses presented a VO(2) = 42 ± 9 ml/min/kg bwt, RER = 0.96 ± 0.10 and RE (= VO(2) /speed) = 134 ± 27 l/km/kg bwt. Linear relationships were observed between speed and VO(2,) HR and gait variables. Significant correlations were observed between VO(2) and gait variables.

CONCLUSIONS AND POTENTIAL RELEVANCE

The RER of 0.96 at winning endurance speed indicates that Arabian horses mainly use aerobic metabolism based on lipid oxidation and that RER may also be related to a good coordination between running speed, respiratory and gait parameters.

Effect of repeated exercise and recovery on heart rate variability in elite trotting horses during high intensity interval training

REASONS FOR PERFORMING STUDY

Interval training is a commonly used training method for trotting horses. In addition, trainers are provided with efficient and inexpensive heart rate monitor devices for the management of training.

HYPOTHESIS

Since the high frequency (HF) frequency peak (fHF) of heart rate variability (HRV) corresponds to the breathing frequency in combination with stride frequency during trotting, it is hypothesised that modifications of breathing and stride frequencies induced by repeated exercise could be detected from fHF.

METHODS

RR interval time series of 7 trotting horses were recorded during an interval training session. Interval training was made up of 5 successive 800 m high-velocity trotting runs (H1, H2...H5) separated by 1 min recovery bouts at low speed (R1, R2...R5). Fast Fourier transform (FFT) and Poincaré plot analysis techniques were applied to RR series.

RESULTS

Repeated exercise had significant effects on HRV components during interval training. Despite constant trotting velocities during high-speed and recovery, repetition induced a decrease in mean RR interval (H1: 295 +/- 19 vs. H5: 283 +/- 15 msec, P<0.05) and in the root mean square of successive differences in RR series (RMSSD; H1: 6.31 +/- 1.28 vs. H5: 5.31 +/- 1.31 msec, P<0.05). Furthermore, high-speed and recovery repetitions induced an increase in fHF (H1: 1.37 +/- 0.35 vs. H5: 1.62 +/- 0.40 Hz and R1: 0.22 +/- 0.02 vs. R4: 0.64 +/- 0.38 Hz, P<0.05). Hence, recovery induced a decrease in the s.d. of the successive RR series (SDRR; R3: 10.5 +/- 3.96 vs. R5: 6.17 +/- 2.65 msecs, P>0.05) and in the long term index of Poincaré plot (SD2; R1: 43.29 +/- 28.90 vs. R5: 18.19 +/- 9.35 msecs, P<0.05).

CONCLUSIONS

The observed increase in fHF during the interval training could be induced by alterations of the coupling between breathing and stride frequency linked to the emergence of fatigue. The decrease in SD2 and SDRR during successive recovery bouts could be linked with a deterioration of the recovery pattern.

POTENTIAL RELEVANCE

HRV can provide breathing frequency data of Standardbreds during training without any respiratory device. Furthermore, HRV could provide useful makers of the emergence of fatigue states during training.

Factors influencing variation in locomotor-respiratory coupling in Standardbred Trotters in the field

REASONS FOR PERFORMING STUDY

A close relationship between limb and respiratory rhythms has been shown in clinically healthy galloping horses due to mechanical constraints in the thoracic region. This synchronisation leads to a 1/1 ratio between stride frequency (SF) and respiratory frequency (RF) during galloping. Very little is known about locomotor-respiratory coupling (LRC) during fast trot.

OBJECTIVES

To investigate stride and respiratory rates during a standardised exercise test on the track in Standardbred Trotters.

METHODS

Forty-four French trotters age 2-10 years performed a standardised exercise test consisting of three 3 min steps at constant speeds. Speed (V) of exercise varied between 500 and 750 m/min. Variables measured during exercise: SF, heart rate, RF using a microphone between the nostrils, blood lactate concentration. Physiological variables V4 and V200 were calculated and race performance index recorded.

RESULTS

There was no age-related difference in RF or in LRC. Two LRC strategies were found: around 1/1 ratio and 3/2 ratio between SF and RF, respectively. A relationship between SF/RF ratio and physiological parameters showed a higher LRC in good performers because of a lower RF during submaximal and maximal exercise.

CONCLUSION

RF is significantly lower and LRC significantly higher in good compared to poor performers.

POTENTIAL RELEVANCE

Investigation is required to ensure that the breathing techniques of trotters may be used in the selection process of racehorses.

The physiological responses to simulated race tests on a track and on a treadmill in Standardbred trotters

REASON FOR PERFORMING STUDY

It is unclear to what extent the physiological response to a standardised treadmill exercise test simulating racing conditions resembles the circulatory and metabolic response observed after a simulated race on a track.

OBJECTIVES

To compare the physiological responses of a standardised treadmill exercise test used to simulate racing conditions and a simulated race performed on a track on the same Standardbred trotting horses, all in racing condition.

METHODS

Six Standardbred trotters in racing condition performed a standardised inclined treadmill exercise test protocol simulating racing conditions (ST) and a simulated race on a field track (FT). Heart and respiratory rates, haemoglobin, packed cell volume (PCV), glucose, pH, total carbon dioxide and potassium in venous blood and plasma lactate and total plasma protein were measured before and immediately after exercise and during recovery.

RESULTS

No differences were observed in heart rate, haemoglobin, PCV, total plasma protein, glucose concentrations after exercise and during recovery between the tests. Plasma lactate was higher and total carbon dioxide concentrations and pH were lower in blood at the end of exercise in the FT compared to the ST. Plasma lactate concentrations were still higher 30 min post exercise in the FT compared to the ST. Blood pH returned to resting values at 15 min of recovery for the ST and at 60 min of recovery for the FT. At 60 min of recovery total carbon dioxide concentrations had still not returned to resting values in any of the tests. Respiratory rate at the end of exercise and body temperature at 15 min of recovery was higher after the ST than the FT. Exercise caused an increase in blood potassium concentrations at the end of exercise in both tests, but concentrations were lower after the FT compared to the ST.

CONCLUSIONS

The haemodynamic response to the ST test at the end of exercise and during recovery, assessed from heart rate, Hb, and PCV, was similar to the response observed in the FT test. The differences observed in plasma lactate, blood pH and TCO2 concentrations between the ST and FT show that anaerobic metabolism was greater in the FT as this test included a finish at maximal speeds.

POTENTIAL RELEVANCE

The treadmill test used in this study to simulate a race resembles the haemodynamic response but not the anaerobic metabolic response observed after a simulated race on a track.

Effects of inhaled ipratropium bromide on breathing mechanics and gas exchange in exercising horses with chronic obstructive pulmonary disease

Six Warmblood horses suffering an acute exacerbation of COPD were tested to investigate whether inhalation of ipratropium bromide (IB) dry powder (2,400 microg) 30 min preexercise would improve their exercise capacity. A cross-over protocol with an inert powder placebo (P) was used. Mechanics of breathing and arterial blood gases were determined before treatment, after treatment but pre-exercise, and during an incremental exercise test. Oxygen consumption (VO2) was also measured before and during exercise, and the time to fatigue recorded. Inhalation of IB reduced total pulmonary resistance (RL) and maximum intrapleural pressure changes (deltaPpl(max)) and increased dynamic compliance before exercise. The onset of exercise was associated with a marked decrease in RL in P-treated horses but not those receiving IB, so that RL during exercise was not affected by treatment. Although deltaPpl(max) was lower at 8,9 and 10 m/s with IB, there were no treatment-related changes in VO2, blood gases, time to fatigue or any other measurement of breathing mechanics. Therefore, although inhalation of IB prior to exercise may have improved deltaPpl(max), it had no apparent impact on the horses' capacity for exercise.

Gas exchange during exercise in standardbred trotters with mild bronchiolitis

To investigate the gas exchange response during exercise in horses with mild bronchiolitis (MB), we studied 7 Standardbred trotters. In order to determine pulmonary gas exchange and red cell volume in relation to bodyweight (CV/BW), submaximal graded exercise tests were performed. VO2 was monitored from an open bias flow system without valves. Heart rate, respiratory rate and mean pulmonary and systemic artery pressures were measured. Cardiac output and alveolar ventilation were calculated. Arterial and mixed venous blood were drawn for blood gas analysis and pH measurements. Pulmonary gas exchange was assessed by conventional blood gas variables, and the ventilation-perfusion distribution was estimated using the multiple inert gas elimination technique. The dispersion of perfusion and ventilation distribution and the difference between measured arterial oxygen tension and that predicted on the basis of the amount of ventilation-perfusion mismatching and shunt were determined in order to reflect diffusion limitation. The results were compared, using analysis of variance, with data from an earlier study on healthy Standardbred trotters (LH) during a similar exercise test. No differences in pulmonary gas exchange were obtained between LH and MB. However, CV/BW, pulmonary artery mean pressure (PAP) and systemic arterial mean pressure (SAP) were significantly higher in MB than in LH. Lactate concentration, arteriovenous oxygen content differences C(av)O2[ and pH were significantly lower in MB horses than in LH. We conclude that Standardbred trotters with mild subclinical bronchiolitis can achieve an adequate gas exchange compared to healthy Standardbred trotters, during a graded exercise test; however, the significantly increased CV/BW in MB horses may be a compensatory mechanism for hypoxaemia during maximal work.

Pulmonary eosinophilia associated with increased airway responsiveness in young racing horses

Horses are known to acquire small airway disease (SAD), an allergen-induced naturally occurring syndrome of reversible obstructive lung disease accompanied by airway hyperresponsiveness and increased inflammatory cell numbers on bronchoalveolar lavage (BAL). This disorder has received scant attention in young racehorses. The purpose of the present report was to examine the effect of BAL eosinophilia in young racehorses on clinical examination, BAL, hematology, airway responsiveness, and on pulmonary function at rest and after a standardized exercise challenge. Five (3 males, 2 females; age 2.6 +/- 0.9 years) with a history of respiratory compromise and BAL eosinophil differential count > 5% and 6 controls (4 males, 2 females; age 3.5 +/- 1.0 years) training and performing to expectation with normal BAL cell differential (eosinophils < 1%) were studied. Respiratory system clinical examination was performed and expressed as a clinical score. Arterial blood gas measurements, CBC, and pulmonary function testing were performed at rest. Pulmonary mechanics measurements were repeated 1 hour and 20 hours after a standardized treadmill exercise challenge. Incremental histamine inhalation challenge was performed and the concentration of histamine effecting a 35% decrease in dynamic compliance (PC35CDyn) was determined. Significant differences were noted between and controls with regard to clinical score (P = .01), blood eosinophils (P = .04), BAL cell count (P = .04), BAL macrophage differential (P = .04), PC35CDyn (P = .008), and tidal volume and respiratory rate at 20 hours following exercise challenge (P = .05). We conclude that pulmonary eosinophilia and airway hyperresponsiveness are manifest in some young horses without overt airway obstruction at rest. We speculate that these may be early events in the natural progression of heaves.

Pulmonary-locomotory interactions in exercising dogs and horses

In exercising quadrupeds, limb movement is often coupled with breathing frequency. This finding has lead some investigators to conclude that locomotory forces, associated with foot plant, abdominal visceral displacements or lumbo-sacral flexion, are the primary determinants of airflow generation. Analysis of respiratory muscle electrical activation (EMG) and contraction profiles in chronically instrumented dogs and horses, along with measurements of esophageal pressure (Pes) changes and limb movements, provide evidence that each breath during the exercise hyperpnea is determined by respiratory neuromuscular events. Specifically: (1) Phasic diaphragmatic EMG and tidal shortening are always synchronous with decreases in Pes; (2) decrements in Pes are always associated with inspiratory flow generation; and (3) strict phase coupling between breathing and stride frequency is not obligatory. Thus, although locomotory-associated forces may minimally assist with flow generation, they are not the primary determinants of breathing during exercise.

The effects of locomotor-respiratory coupling on the pattern of breathing in horses

1. To investigate the effect of locomotor activity on the pattern of breathing in quadrupeds, ventilatory response was studied in four healthy horses during horizontal and inclined (7%) treadmill exercise at different velocities (1.4-6.9 m s(-1)) and during chemical stimulation with a rebreathing method. Stride frequency (f(s)) and locomotor-respiratory coupling (LRC) were also simultaneously determined by means of video recordings synchronized with respiratory events. 2. Tidal volume (V(T)) was positively correlated with pulmonary ventilation (V(E)) but significantly different linear regression equations were found between the experimental conditions (P < 0.0001), since the chemical hyperventilation was mainly due to increases in V(T), whereas the major contribution to exercise hyperpnoea came from changes in respiratory frequency (f(R)). 3. The average f(R) at each exercise level was not significantly different from f(S), although there was not always a tight 1:1 LRC. At constant speeds, f(S) was independent of the treadmill slope and hence the greater V(E) during inclined exercise was due to increased V(T). 4. At any ventilatory level, the differences in breathing patterns between locomotion and rebreathing or locomotion at different slopes derived from different set points of the inspiratory off-switch mechanism. 5. The percentage of single breaths entrained with locomotor rhythm rose progressively and significantly with treadmill speed (P < 0.0001) up to a 1:1 LRC and was significantly affected by treadmill slope (P < 0.001). 6. A LRC of 1:1 was systematically observed at canter (10 out of 10 trials) and sometimes at trot (5 out of 14) and it entailed (i) a 4- to 5-fold reduction in both V(T) and f(R) variability, and (ii) a gait-specific phase locking of inspiratory onset during the locomotor cycle. 7. It is concluded that different patterns of breathing are employed during locomotion and rebreathing due to the interference between locomotor and respiratory functions, which may play a role in the optimization and control of exercise ventilation in horses.

Oxygen cost of ventilation in the resting horse

The purpose of this study was to develop a technique to measure the oxygen cost of ventilation and the values of ventilatory parameters in seven normal horses rebreathing carbon dioxide (CO2). All the horses responded to increased inspiratory levels of CO2 by increasing their tidal volume (VT) and frequency of breathing (Vf). The mean (SE) oxygen cost litre-1 of ventilation, measured at rates of ventilation greater than 200 litres min-1 was 1.7 (0.04) ml litre-1, similar to that of normal human subjects ventilating submaximally. It was concluded that the CO2 rebreathing test is a practical, non-invasive means of measuring the oxygen cost of breathing and the ventilatory response to CO2 in horses.

Gait and respiration in standardbred horses when pacing and galloping

The relationship between gait and the respiratory response to exercise was examined in five standardbred racehorses which exercised on a treadmill at a pace and a gallop. After an initial warm-up, respiratory rate and stride frequency were measured after one and two minutes of treadmill exercise at 80 per cent of maximal oxygen consumption (VO2max), after one minute at 100 per cent VO2max and after two minutes at 100 per cent VO2max (galloping horses only). Exercise at 100 per cent VO2max continued until the horses showed signs of fatigue. Arterial blood was collected during exercise and when they were fatigued for the measurement of oxygen and carbon dioxide tensions, haemoglobin saturation and pH. Venous blood temperature was also recorded. The mean (SE) time to signs of fatigue was significantly (P < 0.05) less in the pacing horses (7.2 [0.4] minutes) than in the galloping horses (8.0 [0.4] minutes). The mean (SE) resting PCO2 was 47.7 (1.9) torr. During the pacing and galloping exercises at 80 per cent and 100 per cent VO2max the PCO2 remained in the range of 41.1 to 66.8 torr, despite concurrent hyperthermia and acidosis. The PCO2 during exercise was not significantly dependent on gait or exercise intensity. The PO2 was significantly higher in pacing horses during exercise at 80 per cent VO2max (111 [7] vs 96 [6] torr). The mean (SE) arterial blood pH decreased from 7.428 (0.025) during pacing at 5 m sec-1 to 7.250 (0.042) when the horses were fatigued.(ABSTRACT TRUNCATED AT 250 WORDS)