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Biomedical subjects

D J Marlin

Publications and source records attributed to D J Marlin.

At least 19 recordsLinked to original sources
PubMed2000

Comparison of the performance of linear resistance and ultrasonic pneumotachometers at rest and during lobeline-induced hyperpnoea.

The performance of a Fleisch No. 5 pneumotachometer (F), and two commercial ultrasonic pneumotachometers, the BRDL (B) and the Spiroson (S) systems were compared in respect to their use for determination of ventilatory parameters at rest and during lobeline-induced hyperpnoea. Five clinically healthy Thoroughbred horses were tested with the three pneumotachometers in random order. Respiratory airflow, respired gas concentrations, oesophageal pressures, pressures within the mask systems and arterial blood gases were determined before and during lobeline-induced hyperpnoea. Because measured peak expiratory airflow rates exceeded the stated linear range of the Fleisch pneumotachometer ( approximately +/- 25 l s(-1)) differential pressure-flow curves were determined in vitro over the range of flows recorded in vivo. Expired flows greater than the linear range were corrected according to the derived regression equation. No differences in any of the measured variables among the three systems were present at rest. At peak ventilation of lobeline-induced hyperpnoea mask pressures [Delta P(mask)(mean (SEM)): F: 9.6 (2.8) cm H(2)O, B: 0.8 (0.4) cm H(2)O, S: 1.4 (0.8) cm H(2)O] and end tidal carbon dioxide [ ET CO(2)(mean (SEM)): F: 2. 6 (0.1)%, B: 2.1 (0.2)%, S: 2.1 (0.1)%] were significantly higher in system F. Despite a tendency for respiratory frequency and peak inspired and expired flows, to be lower with system F, no significant differences in the measurements of ventilatory mechanics were detected. In conclusion, the ultrasonic flowmeters pose significantly lower resistive loads onto the respiratory system during ventilation above resting levels than Fleisch No 5 pneumotachometers. However, at the flowrates achieved during lobeline-induced hyperpnoea an in vitro calibration of the differential pressure-flow relationship allows correction for expiratory alinearity in system F. In addition, the performance of the Spiroson flowmeter is accurate in determining ventilatory mechanics at rest and during lobeline-induced hyperpnoea.

Animals↗
PubMed2000

Cardiac output measured by lithium dilution, thermodilution, and transesophageal Doppler echocardiography in anesthetized horses.

OBJECTIVE: To assess the suitability of lithium dilution as a method for measuring cardiac output in anesthetized horses, compared with thermodilution and transesophageal Doppler echocardiography. ANIMALS: 6 horses (3 Thoroughbreds, 3 crossbreeds). PROCEDURE: Cardiac output was measured in 6 anesthetized horses as lithium dilution cardiac output (LiDCO), thermodilution cardiac output (TDCO), and transesophageal Doppler echocardiographic cardiac output (DopplerCO). For the LiDCO measurements, lithium chloride was administered i.v., and cardiac output was derived from the arterial lithium dilution curve. Sodium nitroprusside, phenylephrine hydrochloride, and dobutamine hydrochloride were used to alter cardiac output. Experiments were divided into 4 periods. During each period, 3 LiDCO measurements, 3 DopplerCO measurements, and 3 sets of 3 TDCO measurements were obtained. RESULTS: 70 comparisons were made between LiDCO, DopplerCO, and triplicate TDCO measurements over a range of 10 to 43 L/min. The mean (+/- SD) of the differences of LiDCO - TDCO was -0.86 +/- 2.80 L/min; LiDCO = -1.90 + 1.05 TDCO (r = 0.94). The mean of the differences of DopplerCO - TDCO was 1.82 +/- 2.67 L/min; DopplerCO = 2.36 + 0.98 TDCO (r = 0.94). The mean of the differences of LiDCO - DopplerCO was -2.68 +/- 3.01 L/min; LiDCO = -2.53 + 0.99 DopplerCO (r = 0.93). CONCLUSIONS AND CLINICAL RELEVANCE: These results indicate that lithium dilution is a suitable method for measuring cardiac output in horses. As well as being accurate, it avoids the need for pulmonary artery catheterization and is quick and safe to use. Monitoring cardiac output during anesthesia in horses may help reduce the high anesthetic mortality in this species.

Animals↗
PubMed2000

Frequency domain analysis of heart rate variability in horses at rest and during exercise.

The pattern of variation in heart rate on a beat-to-beat basis contains information concerning sympathetic (SNS) and parasympathetic (PNS) contributions to autonomic nervous system (ANS) modulation of heart rate (HR). In the present study, heart period (RR interval) time series data were collected at rest and during 3 different treadmill exercise protocols from 6 Thoroughbred horses. Frequency and spectral power were determined in 3 frequency bands: very low (VLF) 0-< or = 0.01, low (LO) >0.01-< or = 0.07 and high (HI) >0.07-< or = 0.5 cycles/beat. Indicators of sympathetic (SNSI = LO/HI) and parasympathetic (PNSI = HI/TOTAL) activity were calculated. Power in all bands fell progressively with increasing exercise intensity from rest to trot. At the gallop VLF and LO power continued to fall but HI power rose. SNSI rose from rest to walk, then fell with increasing effort and was lowest at the gallop. PNSI fell from rest to walk, then rose and was highest at the gallop. Normalised HI power exceeded combined VLF and LO power at all gaits, with the ratio HI to LO power being lowest at the walk and highest at the gallop. ANS indicators showed considerable inter-horse variation, and varied less consistently than raw power with increasing physical effort. In the horses studied, the relationship between power and HR changed at exercise intensities associated with heart rates above approximately 120-130 beats/min. At this level, humoral and other non-neural mechanisms may become more important than autonomic modulation in influencing heart rate and heart rate variability (HRV). HRV at intense effort may be influenced by respiratory-gait entrainment, energetics of locomotion and work of breathing. HRV analysis in the frequency domain would appear to be of potential value as a noninvasive means of assessing autonomic modulation of heart rate at low exercise intensities, only. The technique may be a sensitive method for assessing exercise response to experimental manipulations and disease states.

Algorithms↗
PubMed2000

Respiratory responses of mature horses to intravenous lobeline bolus.

The respiratory stimulant lobeline has been used in equine clinical practice to increase inspiratory and expiratory airflow rates at rest in order to facilitate investigation of both lower and upper airway function. Some of the responses to lobeline in the pony have been reported, but the detailed time course, effect of dose, possible side effects and reproducibility associated with lobeline administration have not been described in the horse. Respiratory airflow rates and oesophageal pressure were measured with a Fleisch No. 5 pneumotachometer and lightweight facemask and a microtip pressure transducer catheter, respectively. The output of the Fleisch pneumotachometer was calibrated for flow rates up to +/- 70 l/s. Seven mature horses with no clinical signs of respiratory disease were studied. Investigations were conducted to determine: (1) the responses to different doses of lobeline (0.15, 0.20, 0.25 and 0.30 mg/kg bwt) as a rapid i.v. bolus (6 horses); (2) arterial blood gases during and after lobeline administration (0.20 mg/kg bwt; 3 horses); and (3) the reproducibility of lobeline-stimulated hyperpnoea (5 horses; 2 doses of 0.20 mg/kg bwt lobeline, 15 min apart). All horses tolerated the lobeline-stimulated hyperpnoea well, although one always coughed or snorted at the onset. Mild tremor was noted following the highest dose in several horses. Apnoea of approximately 40 s was common after the hyperpnoea. Both tidal volume (VT) and frequency (fR) increased with lobeline dose. During peak hyperpnoea at a dose of 0.30 mg/kg bwt, peak inspired flow rate (PIF), peak expired flow rate (PEF) and minute ventilation (VE) were mean +/- s.e. 41+/-5 l/s, 61+/-10 l/s and 920+/-99 l/min, respectively. The hyperpnoea also caused marked changes in arterial PaO2, PaCO2 and pHa at 90 s after lobeline (0.20 mg/kg bwt) administration (mean +/- s.e. 146.0+/-6.9 mmHg, 20.6+/-0.8 mmHg and 7.707+/-0.020, respectively) compared to at rest (mean +/- s.e. 104.0+/-4.0 mmHg, 50.6+/-2.8 mmHg and 7.432+/-0.012). Dynamic lung compliance (Cdyn) was unaltered by lobeline administration. The lobeline-induced hyperpnoea was highly reproducible, with no significant difference in any of the parameters during 2 stimulations 15 min apart. Lobeline induced highly reproducible responses without any apparent adverse effects and may be useful in the investigation of pulmonary function in healthy horses and those with airway disease.

Animals↗
PubMed1999

Metabolic effects of nitric oxide synthase inhibition during exercise in the horse.

The effect of nitric oxide synthase (NOS) inhibition during exercise on lactate production was investigated in five Thoroughbred horses. A standard exercise test (SET), consisting of three canters (approximately 55 per cent VO2max), with walking and trotting between each canter, was performed twice (control and test, in random order) by each horse. Nphi-nitro-L-arginine methyl ester (L-NAME; 20 mg kg-1), a competitive inhibitor of NOS, induced a significant increase (P < 0.05) in plasma lactate [5.7 (2.9) vs 11.8 (3.8) mmol L-1], which continued to increase despite administration of L-arginine, the substrate for NOS. There were no differences in cardiac output (Q) or the total body oxygen consumption (VO) between each SET. The results show that non-specific inhibition of NOS isoforms during exercise in the horse increases plasma lactate concentration, although the mechanism/s remain uncertain.

Animals↗
PubMed1999

Effects of inhaled nitric oxide 10 ppm in spontaneously breathing horses anaesthetized with halothane.

Inhaled nitric oxide, a selective pulmonary vasodilator, is known to improve arterial oxygenation after cardiopulmonary bypass and during acute respiratory distress syndrome in humans. During general anaesthesia with spontaneous ventilation, healthy adult horses develop large alveolar-arterial oxygen tension differences. In this study, we have determined the effects of inhaled nitric oxide (10 parts per million (ppm)) on venous admixture and pulmonary haemodynamics in horses anaesthetized with halothane. Seven adult horses were studied twice in random sequence. After premedication with romifidine 100 micrograms kg-1, anaesthesia was induced with ketamine 2.2 mg kg-1 and maintained with 1.1 MAC (0.95%) of halothane in oxygen. Horses breathed spontaneously. After 65 min, each horse had nitric oxide 10 ppm added to the inspired gas for 20 min (procedure HA + NO) or anaesthesia was continued with halothane in oxygen (procedure HA). Cardiac output, minute ventilation, arterial and mixed venous oxygen and carbon dioxide tensions, and mean pulmonary and carotid arterial pressures were measured for 100 min. Shunt fraction and pulmonary and systemic vascular resistances were calculated. Shunt fraction (SF) and mean pulmonary artery pressure (PPA mean) were not different between the two groups after 65 min of general anaesthesia (HA: SF 0.20 (SD 0.06), PPA mean 45 (8) mm Hg; HA + NO: SF 0.21 (0.04), PPA mean 44 (7) mm Hg) or after 85 min (HA: SF 0.22 (0.07), PPA mean 45 (8) mm Hg; HA + NO: SF 0.20 (0.03), PPA mean 43 (7) mm Hg). There were no significant effects of time or nitric oxide inhalation on any other variable. There was a significant correlation (r = 0.80, P < 0.05) between calculated shunt fraction 65 min after induction of anaesthesia and body weight.

Administration, Inhalation↗
PubMed1999

Physiological responses of horses to a treadmill simulated speed and endurance test in high heat and humidity before and after humid heat acclimation.

To investigate whether horses were able to acclimate to conditions of high temperature and humidity, 5 horses of different breeds were trained for 80 min on 15 consecutive days on a treadmill at 30 degrees C and 80%RH. Training consisted of a combination of long duration low-intensity exercise, medium duration medium intensity exercise and short duration high intensity exercise. Between training sessions the horses were maintained at 11+/-3 degrees C and 74+/-2%RH. Before (PRE-ACC) and after acclimation (POST-ACC) the horses undertook a simulated Competition Exercise Test (CET), designed to represent the Speed and Endurance Test of a 3-day event, at 30 degrees C/80%RH. Maximal oxygen uptake (VO2PEAK) was not changed following acclimation (PRE-ACC 141+/-8 ml/min/kg bwt vs. POST-ACC 145+/-9 ml/min/kg bwt [STPD], P>0.05). Following acclimation, 4 of the 5 horses were able to complete a significantly greater amount of Phase D in the CET (PRE-ACC 6.3+/-0.3 min vs. POST-ACC 7.3+/-0.3 min, P<0.05; target time = 8 min). Resting body temperatures (pulmonary artery [TPA], rectal [TREC] and tail-skin [TTSK] temperatures) were all significantly lower following acclimation. During exercise, metabolic heat production (M) and heat dissipation (HD), for the same exercise duration, were both significantly lower following acclimation (P<0.05), although heat storage (HS) was significantly higher (P<0.05). The higher heat storage following acclimation was associated with a lower TTSK for a given TPA and a decreased total fluid loss (% bodyweight, P<0.05). Plasma volume was not changed following acclimation. The relationship of sweating rate (SR) to TPA or TTSK on either the neck or the gluteal region was not significantly altered by acclimation, although the onset of sweating occurred at a lower TPA or TTSK following acclimation (P<0.05). The horses in the present study showed a number of physiological adaptations to a period of 15 days of exposure to high heat and humidity consistent with a humid heat acclimation response. These changes were mostly similar to those reported to occur in man and other species and were consistent with thermal acclimation and an increased thermotolerance, leading to an improved exercise tolerance. It is concluded that a 15 day period of acclimation is beneficial for horses from cooler and or drier climates, that have to compete in hot humid conditions and that this may redress, to some extent, the decrement in exercise tolerance seen in nonacclimated horses and reduce the risk of heat related disorders, such as heat exhaustion.

Acid-Base Equilibrium↗
PubMed1999

Cardiovascular demands of competition on low-goal (non-elite) polo ponies.

Knowledge of the competitive demands of different sports or activities is important for designing appropriate training programmes to ensure that animals reach a sufficient level of fitness to reduce the risk of overexertion and injury or illness and to achieve the best possible performance in relation to an individual's genetic potential. Whilst the physiological demands of many equestrian sports have been described, to the best of our knowledge the cardiovascular demands of polo have not. The aims of the present study were therefore to record heart rate during and after competitive polo games in a group of low-goal (non-elite) polo ponies in order to describe the absolute heart rates during play, the relationship of these heart rates to maximal heart rate and the characteristics of a typical chukka in terms of effort. Six low-goal polo ponies were studied during a total of 59 chukkas. Heart rate was monitored continuously before, during and after competition using a commercial heart rate monitor. Maximal heart rate was determined with field and treadmill incremental exercise tests and used to express work intensity in terms of time during play that each ponies heart rate was less than 75% HRmax, between 75 and 90% HRmax and greater than 90% HRmax. Mean maximum heart rate was not different during play or during field and treadmill exercise tests; 215+/-7 (mean +/- s.d.), 211+/-7 and 213+/-2 beats/min, respectively (P>0.05). Mean heart rate for all ponies over all chukkas was 166+/-6 beats/min with a mean chukka duration of 611+/-18 s. Of this time, 44+/-7% of the time was spent below 75% HRmax, 39+/-8% between 75 and 90% HRmax and 17+/-8% of time above 90% HRmax. When only one chukka had been played, there was a good correlation between mean heart rate during play and 3 min recovery heart rate (r = 0.63, P<0.001). Based on these observations, it is proposed that low-goal polo places moderate to high stress on the cardiovascular system.

Animals↗
PubMed1999

Modelling impact-initiated wave transmission through lung parenchyma in relation to the aetiology of exercise-induced pulmonary haemorrhage.

Recently we proposed that exercise-induced pulmonary haemorrhage (EIPH) results from locomotory-impact-induced trauma by impact of the scapula on the chest wall during footfall and the consequent transmission of waves through the lung. A computational model has been developed to demonstrate that wave amplification and focusing occur in the dorsocaudal tip of the lung for waves originating on the anterior subscapular surface. The propagation of an acoustic wave was investigated in a simplified 2-dimensional representation of a vertical anterio-dorsal section of horse lung. It was demonstrated that a complicated pattern of waves is transmitted from the scapula to the dorsal region. Wave motion was characterised using the instantaneous rate of change of pressure with time (dp/dt) which is associated with lung injury. Due to wave reflection and focusing, dp/dt is transiently very high on the spinal and diaphragmatic lung walls, particularly in the vicinity of the dorsal tip. The model therefore predicts that lung injury may occur in the region in which EIPH is reported to originate.

Animals↗
PubMed1999

The effects of training on ventilation and blood gases in exercising thoroughbreds.

The effects of training on ventilation and blood gases during exercise were investigated in 6 clinically normal, detrained Thoroughbred horses. They underwent a 16 week training programme similar to the type frequently used for Thoroughbred racehorses in Great Britain. Standardized treadmill exercise tests (2 min canter at 8 and 10 m/s C8 and C10[ and 2 min gallop at 12 m/s [G12], on a level surface) were performed prior to and after 16 weeks of training. Respiratory flow rates were measured using ultrasound flow transducers. Blood samples were drawn from a transverse facial artery and the right atrium. Minute ventilation, respiratory frequency and tidal volume were not significantly altered by training. Peak inspiratory flow rate was lower following training at 8 and 10 m/s, but not at 12 m/s. Arterial oxygen tension was decreased during trot and canter following training. Blood lactate concentration post G12 decreased following training (10.5 +/- 2.2 mmol/l vs. 7.7 +/- 2.2 mmol/l; P < 0.05). The increase in the degree of exercise-induced arterial hypoxaemia following training may reflect a lack of pulmonary adaptation to training in the face of improved cardiovascular and muscular function.

Animals↗
PubMed1999

Effect of exercise on concentrations of immunoreactive endothelin in bronchoalveolar lavage fluid of normal horses and horses with chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) represents a major cause of loss of performance in the horse. The role of endothelin (ET), a potent bronchoconstrictive and vasoactive peptide, is currently being investigated in asthma and other obstructive respiratory diseases in man. We have previously found elevated systemic and pulmonary endothelin levels in horses during exacerbation of COPD. In the present study, our aim was to examine possible variations in ET concentrations occurring during exercise in COPD horses. We compared the effects of intense treadmill exercise on the recovery of endothelin (ET) in the bronchoalveolar lavage fluid (BALF) as well as in arterial and venous blood, in a group of 5 healthy horses and a group of 5 COPD horses studied alternately in remission and while symptomatic. We also investigated the possible correlations between ET levels and pulmonary function tests during the study. While exercise did not affect the ET levels recovered in BALF among controls, it caused a significant increase (P = 0.02) among symptomatic COPD horses. During remission, wide variations of ET levels among horses, at rest and during exercise, made any significant interpretation difficult. No correlation could be found between exercise-induced changes in ET concentrations and pulmonary function tests or changes in arterial oxygen tension with exercise. We conclude that exercise appears to affect the release of ET by the airways in COPD horses, in contrast to healthy horses. It is still unclear, however, whether these differences relate to adjustments of lung function during exercise.

Animals↗
PubMed1999

Pre- and post exercise echocardiography in horses performing treadmill exercise in cool and hot/humid conditions.

We hypothesised that exercise in a hot and humid environment would affect echocardiographic indices of cardiac dimensions and function more than exercise in a cool environment. M-mode echocardiograms were obtained in 5 clinically normal horses before, and at 0, 10, 30 and 60 min after a treadmill exercise test. The test was performed in a controlled environment at 20 degrees C/40% relative humidity (RH) and again at 30 degrees C/80% RH. All the horses completed the exercise test in cool conditions, but only one horse completed the exercise test in the hot/humid environment. The relaxation time index (RTI) correlated significantly and inversely with heart rate (HR). Heart rate was increased and RTI was decreased immediately after exercise in cool conditions. HR recovery appeared to be prolonged following exercise in hot/humid conditions. Post exercise RTI was significantly decreased in hot/humid environment. In hot/humid conditions, the left ventricular internal dimensions measured in diastole and systole (LVIDd, LVIDs) were reduced following exercise and continued to fall throughout the 60 min after exercise. The left ventricular fractional shortening (FS%) was lower than resting levels immediately after exercise in hot/humid conditions. Significant decreases were found in LVIDs and LVIDd, which may reflect a reduction in preload arising from dehydration or re-distribution of blood throughout the recovery period following exercise in the hot/humid environment. It was concluded that echocardiography was a useful tool in assessing cardiac responses to exercise in different climates.

Aerobiosis↗
PubMed1999

Feasibility of scintigraphy in exercise-induced pulmonary haemorrhage detection and quantification: preliminary studies.

We hypothesised that scintigraphic imaging of the lungs following injection of 99mTc labelled red blood cells (99mTc-RBC) in the exercising horse might enable exercise-induced pulmonary haemorrhage (EIPH) quantification. Ideally, to favour detection of bleeding, circulating 99mTc-RBC not involved in the haemorrhage should be removed from the circulation quickly. Altering RBC during labelling to stimulate splenic uptake of 99mTc-RBC may encourage this. In order to investigate this hypothesis, 99mTc-RBC distribution was followed for 1 h in 2 groups of horses. Group 1 was injected i.v., at rest, with radioactive nondenatured RBC (99mTc-NDRBC); Group 2 received labelled RBC partly denatured by heating (99mTc-HDRBC). In Group 2, splenic uptake was higher at all times and radioactivity in the lung was proportionally higher and decreased less quickly than in Group 1. Hence, the time-consuming 99mTc-HDRBC labelling technique did not demonstrate any advantage over the easier 99mTc-NDRBC labelling procedure. Additionally, the feasibility of scintigraphic visualisation of a small amount of pulmonary bleeding was confirmed with the following trial: using an endoscope, a radioactive solution mimicking 50 ml of bleeding was deposited at the usual site of EIPH in a live horse. The radioactivity recorded in that area was compared to the one obtained in the same region in Group 1 and 2. The activity measured 20 min post endoscopy corresponded to 33% of the activity obtained in Group 1 vs. 8% in Group 2 at that timing. Once again, there was no advantage of using 99mTc-HDRBC vs. 99mTc-NDRBC. These results demonstrated that small amounts of bleeding might potentially be detected with scintigraphy; they also suggest that the limiting factor for detecting small amounts of bleeding may be the level of lung background radioactivity.

Animals↗
PubMed1999

Thermoregulatory strategies during short-term exercise at different intensities.

Previously we have observed a decline in sweating rate (SR) during high intensity exercise in an incremental test protocol. In man, the sweating sensitivity (SR/degree C) has been shown to vary with exercise intensity. The aim of the present study was to determine if thermoregulatory responses in the horse, a prolific sweater with a high rate of metabolic heat production, were modified by exercise intensity. The effect of 3 separate exercise intensities (50 (S), 70 (M) and 90% (F) VO2peak on neck (SRN) and gluteal sweating rate (SRG), pulmonary artery (TPA), rectal (TREC) and skin temperatures on the neck (TSK-N) and gluteal region (TSK-G) were investigated. Horses were exercised for approximately 2 min at each exercise intensity in a randomised order. The rate of increase in TPA increased with exercise intensity (P < 0.05) (0.27 +/- 0.05, 0.43 +/- 0.04 and 0.77 +/- 0.05 degree C/min during S, M and F, respectively. The TPA and TSK temperatures at the onset of sweating were not different between exercise intensities (P > 0.05). Despite the increased rate of heat production with increasing exercise intensity, sweating sensitivity decreased on both the neck (P < 0.05) (18.2 +/- 3.4 (S), 12.0 +/- 3.5 (M) and 2.9 +/- 0.7 (g/m2/min)/degree C (F)[ and gluteal region (P < 0.05) (8.9 +/- 2.0 (S), 5.1 +/- 1.7 (M) and 0.8 +/- 0.3 (g/m2/min)/degree C (F)[. During exercise at 90% VO2peak sweating sensitivity and the rate of increase in skin temperature were markedly reduced compared to at 70% VO2peak. The present investigation demonstrates that the drive to thermoregulate is overridden during short-term, high-intensity exercise, resulting in greater heat storage (TPA) as a result of a lower SR sensitivity.

Animals↗
PubMed1999

Sweating and skin temperature responses of normal and anhidrotic horses to intravenous adrenaline.

Anhidrosis has been recognised for over half a century, but despite some excellent epidemiological studies, there has been little progress in understanding the aetiology of the condition. Using a modified ventilated capsule, we obtained dynamic, quantitative data on sweating responses in anhidrotic horses and normal sweating controls from the same environment. Ten horses with current seasonal anhidrosis and 10 matched normal sweating controls were selected. Each horse was given two 10 min infusions of 1 and 2 micrograms/kg/min adrenaline, separated by at least 6 h. Sweating responses and skin temperatures on the neck and gluteal region were measured. Plasma and sweat for analysis of total protein and electrolytes and plasma for analysis of adrenaline were collected. Anhidrotic horses produced significantly less sweat, had lower initial and peak sweat rates and a greater neck:gluteal ratio for sweat production. Plasma adrenaline at rest or at the time of peak sweating rate was not different between groups. In nearly three-quarters of the anhidrotic horses, the shape of the sweat rate against time curve was different compared to controls. Volume of sweat produced was significantly correlated with skin temperature on the neck of controls and anhidrotic horses and on the gluteal region of controls, but not anhidrotic horses. Plasma total protein and electrolyte concentrations were not different between groups. There were significant differences in sweat electrolyte concentrations between controls and anhidrotic horses. These differences were reduced when sweat electrolytes were expressed per g of total protein, and no differences existed when expressed as g/m2. This study has provided insight into the response of anhidrotic horses to beta 2 adrenergic stimulation and may be a useful technique to investigate this condition.

Animals↗
PubMed1998

Plasma aspartate aminotransferase and creatine kinase activities in thoroughbred racehorses in relation to age, sex, exercise and training.

In order to investigate the effect of age, sex and month on the response of plasma aspartate aminotransferase (AST) and creatine kinase (CK) to exercise, blood samples were collected once a month between March and September from a group of 40 2- and 3-year-old (2yo and 3yo) thoroughbred racehorses (kept under the same managemental regimen) at rest before exercise (PRE) and at 2 (2H) and 24 h (24H) post-exercise. The absolute change in activities between the 2H and PRE samples (2H delta) and the 24H and PRE samples (24H delta) was also calculated. Age had a significant effect on all measured and calculated parameters for colts (C), apart from 24H delta CK but showed no effect in the fillies (F). Sex only had a significant effect in the 3yo in the 2H delta CK. In the 2yo, significant effects of sex were found for both CK and AST in the PRE, 2H and 24H samples. The effect of month varied according to the classification group with only the 2yoC not showing any significant effect on any parameter. Fillies were, in general, more likely than colts to show greater than a twofold increase in CK activity at 2H post-exercise and the number of animals showing such an increase decreased as the season progressed. Very little change in AST activities occurred with exercise.

Age Factors↗
PubMed1998

Effects of administration of water versus an isotonic oral rehydration solution (ORS) at rest and changes during exercise and recovery.

The administration of 41 of an isotonic, plasma-like oral rehydration solution (ORS) with an osmotic skeleton and 41 of water (water; no osmotic skeleton), were evaluated in five thoroughbred horses. Solutions were administered by nasogastric tube 4 h after feeding. Uptake of deuterium, concentrations of plasma sodium, potassium, chloride, glucose, total protein and packed cell volume, pH, PCO2, HCO3-, total CO2, actual base excess, standard base excess, plasma volume and weight loss were assessed both at rest, and during and after exercise on a treadmill. Each horse underwent four experimental sessions (water-resting; ORS-resting; water-exercise; ORS-exercise). There was an indication of uptake of both water and ORS by 10 min post-administration. Based on the appearance of deuterium in plasma, there was no significant difference in the rate of uptake of water or ORS at rest, although there was a trend for the uptake of ORS to be slower than water during the exercise session. The mean decrease in total protein (TP, 3.0 g l-1) and the increase in plasma volume (PV, 4.6 ml kg-1) after administration of ORS at rest was greater (P < 0.05) than that of water (TP, 1.3 g l-1 and PV, -1.2 ml kg-1). There was no significant difference in TP or PV following administration of water or ORS during the exercise treatment. Exercise had little effect on plasma sodium concentration. The results confirmed that administration of 41 of isotonic, plasma-like ORS provided a much more distinct and durable contribution to the maintenance of plasma volume and circulation than administration of an equal amount of water at rest. Subsequent exercise may, however, mask some of the effects observed at rest.

Acid-Base Equilibrium↗