Search PubMed⌕ Search

Biomedical subjects

W M Bayly

Publications and source records attributed to W M Bayly.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effect of exercise on acid-base status of horses.

Exercise in horses is associated with a wide variety of physiological changes in fluid, electrolyte and acid base balance. The integration of physiologic and physiochemical mechanisms acts to minimize alterations in pH and enhance removal of carbon dioxide produced by exercising muscles. This article provides a description of the changes that take place during exercise and how these changes affect acid-base balance in the horse.

Acid-Base Equilibrium↗
PubMed1998

Does an acute COPD crisis modify the cardiorespiratory and ventilatory adjustments to exercise in horses?

The present study was conducted to understand better the mechanisms leading to the decrease in exercise capacity observed in horses suffering from chronic obstructive pulmonary disease (COPD). Five COPD horses were submitted to a standardized submaximal treadmill exercise test while they were in clinical remission or in acute crisis. Respiratory airflow, O2 and CO2 fractions in the respired gas, pleural pressure changes and heart rate were recorded, and arterial and mixed venous blood were analyzed for gas tensions, hemoglobin, and plasma lactate concentrations. O2 consumption, CO2 production, expired minute ventilation, tidal volume, alveolar ventilation, cardiac output, total pulmonary resistance, and mechanical work of breathing were calculated. The results showed that, when submaximally exercised, COPD horses in crisis were significantly more hypoxemic and hypercapnic and that their total pulmonary resistance and mechanical work of breathing were significantly higher and their expired minute ventilation significantly lower than when they were in remission. However, their O2 consumption remained unchanged, which was probably due to the occurrence of compensatory mechanisms, i.e., higher heart rate, cardiac output, and hemoglobin concentration. Last, their net anaerobic metabolism seemed to be more important.

Animals↗
PubMed1998

Effect of prolonged heavy exercise on pulmonary gas exchange in horses.

During short-term maximal exercise, horses have impaired pulmonary gas exchange, manifested by diffusion limitation and arterial hypoxemia, without marked ventilation-perfusion (VA/Q) inequality. Whether gas exchange deteriorates progressively during prolonged submaximal exercise has not been investigated. Six thoroughbred horses performed treadmill exercise at approximately 60% of maximal oxygen uptake until exhaustion (28-39 min). Multiple inert gas, blood-gas, hemodynamic, metabolic rate, and ventilatory data were obtained at rest and 5-min intervals during exercise. Oxygen uptake, cardiac output, and alveolar-arterial PO2 gradient were unchanged after the first 5 min of exercise. Alveolar ventilation increased progressively during exercise, from increased tidal volume and respiratory frequency, resulting in an increase in arterial PO2 and decrease in arterial PCO2. At rest there was minimal VA/Q inequality, log SD of the perfusion distribution (log SDQ) = 0.20. This doubled by 5 min of exercise (log SDQ = 0.40) but did not increase further. There was no evidence of alveolar-end-capillary diffusion limitation during exercise. However, there was evidence for gas-phase diffusion limitation at all time points, and enflurane was preferentially overretained. Horses maintain excellent pulmonary gas exchange during exhaustive, submaximal exercise. Although VA/Q inequality is greater than at rest, it is less than observed in most mammals and the effect on gas exchange is minimal.

Animals↗
PubMed1997

Plasma von Willebrand factor in thoroughbreds in response to high-intensity treadmill exercise.

OBJECTIVE: To determine whether plasma von Willebrand factor (vWf) concentration changes in horses during and after treadmill exercise. ANIMALS: 5 mature, fit Thoroughbreds. PROCEDURE: A blood sampling catheter was placed in the right jugular vein. A warm-up period was followed by a 3-minute rest period. Horses were galloped at racing pace until fatigued (about 2 minutes). Blood samples were collected prior to warm-up, during the postwarm-up rest period, 1 minute into the run, at cessation of the run, and 5 to 120 minutes after cessation of the run. vWf activity was measured by ELISA and corrected for plasma volume changes (measured by changes in plasma albumin concentration). Platelet-poor plasma from 10 clinically normal, resting horses was pooled, assigned a value of 100 U/dl, and served as a control for all assays. RESULTS: vWf activity began increasing 1 minute after horses reached full speed. At 5 minutes after cessation of exercise, vWf values had increased by mean of 92% (P < 0.05) from baseline. vWf activity returned baseline by 15 minutes after exercise, and remained there until 90 minutes after exercise, when it began to increase. CONCLUSION AND CLINICAL RELEVANCE: The spontaneous decrease in vWf values after completion of exercise was unexpected because vWf has a long half-life in circulation. This unexpected finding is compatible with increased vWf consumption and suggests that microvascular trauma may occur in horses during strenuous exercise.

Animals↗
PubMed1995

Haematuria, pigmenturia and proteinuria in exercising horses.

The effects of exercise on urinary excretion of red blood cells, pigments (haemoglobin and myoglobin) and protein were studied in 8 mares performing treadmill exercise at speeds eliciting 40, 60 and 95% of the maximal oxygen consumption (VO2max). Gross haematuria and pigmenturia were observed in all horses during exercise at the 2 higher intensities, while these findings were detected in only one of 8 mares during exercise at 40% of the VO2max. For the remaining 7 mares exercised at 40% of the VO2max, increased urinary excretion of red blood cells (RBCs) and pigments was evident after centrifugation of urine samples and reagent strip analysis of the supernatant fractions. An increase in urine flow (UF) during exercise at 40% of the VO2max may have contributed to the infrequent observation of gross haematuria and pigmenturia during exercise at this intensity. A transient increase in UF following exercise at 60 and 95% of the VO2max resulted in rapid resolution of gross haematuria and pigmenturia, but increased urinary excretion of RBCs and pigments remained evident by reagent strip analysis for up to 60 min following exercise. Mean +/- s.e. urinary protein excretion increased from a resting value of 2.2 +/- 0.2 mg/min to 5.6 +/- 0.9, 14.5 +/- 4.7 and 78.4 +/- 18.6 mg/min after exercise at 40, 60 and 95% of the VO2max, respectively. These results demonstrate that exercise induced haematuria and pigmenturia and post exercise proteinuria are common in horses. Their occurrence is transient and does not appear to be associated with any lasting changes in renal function.

Analysis of Variance↗
PubMed1994

Influence of air movement, facemask design and exercise on upper airway, transpulmonary, and transdiaphragmatic pressures in thoroughbred horses.

The influences of facial airflow, exercise and wearing a facemask on gas exchange and upper airway (Pu), transpulmonary (PTP) and transdiaphragmatic (PTD) pressures were investigated in 6 horses performing an incremental exercise test on an inclined (10%) treadmill. The test consisted of a 2 min walk followed by two 2 min exercise bouts at intensities which produced 40% and 80% of maximal oxygen consumption. Horses performed the test 4 times, once for each of 4 protocols, which involved not wearing a facemask (A), wearing a mask with either no biased flow through it (B), with an expiratory bias of 6300 L/min through it (C), or with an inspiratory bias of the same magnitude (D). Although no statistically significant differences in arterial blood gases, Pu, PTP, or PTD could be attributed to the various protocols, trends that may have been physiologically important were detected. Hypoxemia and hypercapnia associated with exercise were most marked with protocol B and least severe with protocols A or D. PTP was lowest for all tests with protocol D. Of the 3 conditions that required the wearing of a mask, protocol D was associated with the lowest Pu. While impelling air into the respiratory tract, as presumedly occurs with horses exercising over ground, may enhance respiratory function during exercise, this preliminary study does not clearly demonstrate this. Because this is an important consideration when conducting studies involving horses on treadmills, further investigations at higher exercise intensities and with additional methodologies are needed to clarify the issue.

Acid-Base Equilibrium↗
PubMed1993

Dissipation of metabolic heat in the horse during exercise.

Horses were exercised at 40, 65, and 90% of their maximum O2 uptake (VO2max) until moderately fatigued (approximately 38, 15, and 9 min, respectively) to assess heat loss through different routes. Approximately 4,232, 3,195, and 2,333 kcal of heat were generated in response to exercise at these intensities. Of this, approximately 7, 16, and 20% remained as stored heat 30 min postexercise. Respiratory heat loss, estimated from the temperature difference between blood in the pulmonary and carotid arteries and the cardiac output, was estimated to be 30, 19, and 23% of the heat produced during exercise at the three intensities. The kinetics of the increases in muscle and blood temperature were similar, with the greatest change in temperature occurring in muscle (+3.8, 5.2, and 6.1 degrees C after exercise at 40, 65, and 90% of VO2max, respectively). The temperature of blood in the superficial thoracic vein was approximately 2 degrees C below that of arterial blood at rest. This difference had increased to approximately 3 degrees C during the last minute of exercise. The rate of sweating at sites on the back and neck increased with exercise intensity to a common peak of approximately 40 ml.m-2.min-1. If complete evaporation had occurred, water loss in response to exercise (estimated to be 12, 10, and 7.7 liters for the different intensities of exercise) greatly surpassed that required for dissipation of the metabolic heat load.

Animals↗
PubMed1993

Equine plasma and blood volumes decrease with dehydration but subsequently increase with exercise.

The effects of dehydration and 40 min of exercise at approximately 40% of maximal O2 consumption on plasma volume (PV) and blood volume (BV) were studied in six horses. Horses were exercised while euhydrated (C); 4 h after administration of furosemide (1.0 mg/kg i.v.; FDH), which induced isotonic dehydration; and after 30 h without water (DDH), which caused hypertonic dehydration. Dehydration resulted in decreases of 6.3 and 9.9% for PV and BV, respectively, with FDH and 10.7 and 8.5%, respectively, with DDH. During exercise in C, PV and BV increased by 12.7 and 20.0%, respectively; during exercise with FDH, they increased by 11.7 and 26.1%, respectively; and during exercise with DDH, PV decreased by 1.3% from predehydration values, while BV increased by 18.7%. Hematocrit and total plasma protein concentration rose to higher values throughout exercise in FDH and DDH than in C; plasma [Na+] was higher in DDH than in FDH and C, [Cl-] was higher in DDH and lower in FDH than in C, and [K+] was lower in FDH and DDH than in C through exercise and recovery. From these results, we conclude that increases in PV and BV are normal features of low-intensity exercise in the horse. The increases in BV not only augment O2 carriage but also help maintain circulating volume. These increases can be modified by preexercise dehydration, the nature of which affects the extent of modification.

Animals↗
PubMed1993

Effects of dehydration on thermoregulatory responses of horses during low-intensity exercise.

Effects of dehydration on thermoregulatory and metabolic responses were studied in six horses during 40 min of exercise eliciting approximately 40% of maximal O2 consumption and for 30 min after exercise. Horses were exercised while euhydrated (C), 4 h after administration of furosemide (FDH; 1.0 mg/kg i.v.) to induce isotonic dehydration, and after 30 h without water (DDH) to induce hypertonic dehydration. Cardiac output was significantly lower in FDH (144.1 +/- 8.0 l/min) and in DDH (156.6 +/- 6.9 l/min) than in C (173.1 +/- 6.2 l/min) after 30 min of exercise. When DDH, FDH, and C values were compared, dehydration resulted in higher temperatures in the middle gluteal muscle (41.9 +/- 0.3, 41.1 +/- 0.2, and 40.6 +/- 0.2 degrees C, respectively) and pulmonary artery (40.8 +/- 0.3, 40.1 +/- 0.2, and 39.7 +/- 0.2 degrees C, respectively). Temperatures in the superficial thoracic vein and subcutaneous sites on the neck and back and peak sweating rates on the neck and back were not significantly different in DDH and C. In view of higher core temperatures during exercise after dehydration and decrease in cardiac output without concomitant increases in peripheral temperatures or reduced sweating rates, we conclude that the impairment of thermoregulation was primarily due to decreased transfer of heat from core to periphery.

Animals↗
PubMed1992

Respiratory mechanics of horses during stepwise treadmill exercise tests, and the effect of clenbuterol pretreatment on them.

Normal Standardbred horses were given an incremental exercise test on a horizontal treadmill to evaluate the influence of exercise on gas exchange, resistance, dynamic compliance and inertance of the respiratory system. The exercise test consisted of 2 min exercise steps at each of the following speeds: 2.4 m/sec (walk), 4.5 m/sec (slow trot), 7.0 m/sec (fast trot) and 10 m/sec (gallop). At rest and after 1 min of exercise at each step, airflow, tidal volume, respiratory frequency, pharyngeal, mid-oesophageal and transdiaphragmatic pressures and arterial blood gas tensions were measured. The same horses were subsequently treated intravenously with clenbuterol (0.8 microgram/kg) and an identical exercise test and measurement performed 10 min after clenbuterol injection. In response to exercise, there were large increases in tidal volume, respiratory frequency, airflow and pressures. Exercise was associated with a decrease in upper airway resistance but total pulmonary resistance was unchanged. Exercise did not alter inertance or dynamic compliance, horses became hypoxaemic, and at 10 m/sec (galloping) also developed hypercarbia. Treatment with clenbuterol did not alter any of these measurements in response to exercise. These data suggest that dilation of upper airways occurs during exercise, and that inertial forces are important in strenuously exercising horses and may influence the accuracy of dynamic compliance determinations at high exercise intensities.

Airway Resistance↗
PubMed1992

Effects of transport on constituents of bronchoalveolar lavage fluid from horses.

To determine whether road transport affected pulmonary phagocyte activity, 7 healthy Thoroughbred horses were shipped 1,160 kilometers over 36 hours. Fluid collected by bronchoalveolar lavage (BAL) 12 hours, and 7 and 14 days after transport was analyzed. Results were compared to those from the same horses pre-transport, and 7 non-transported control horses that had BAL performed at the same times as the transported horses. Of cells recovered with BAL the percentage of viable pulmonary alveolar macrophages (PAMs) declined from 90.0 +/- 0.9% pre-transport to 80.0 +/- 3.7% by 2 weeks post transport. Although the ability of PAMs to inhibit the growth of Staphylococcus epidermidis had decreased by 2 weeks post-transport (19.2 +/- 3.7% vs. 8.8 +/- 2.3% inhibition) this could not be attributed to transport as a similar effect occurred in the control group. In contrast, the ability of PAMs to phagocytose sheep erythrocytes labelled with rabbit anti-erythrocyte antibodies increased from 74.0 +/- 8.1% to 92.3 +/- 1.5% by 12 hours post-transport. As all variables were unchanged or only mildly altered following transport, we conclude that this form of transport did not alter the PAM functions we assessed.

Albumins↗
PubMed1991

Acute hemolytic anemia after oral administration of L-tryptophan in ponies.

The hematologic and pathologic effects of orally administered L-tryptophan and indoleactic acid and of L-tryptophan administered IV were studied in ponies. Sixteen adult Shetland ponies were allotted into 4 experimental groups. Group 1 consisted of 5 ponies (1-5) given 0.6 g of tryptophan/kg of body weight in a water slurry via stomach tube. Group 2 included 4 ponies (6-9) given 0.35 g of tryptophan/kg orally. Group-3 ponies (10-13) were given 0.35 g of indoleacetic acid/kg orally. Group 4 consisted of 3 ponies (14-16) given a single 4-hour IV infusion of 0.1 g of tryptophan/kg. Restlessness, increased respiratory rate, hemolysis, and hemoglobinuria were detected in 4 of the 5 group-1 ponies. Only pony 7 in group 2 developed hemolysis, hemoglobinuria, and a significant increase in respiratory rate. Renal pathologic lesions, consistent with hemoglobinuric nephrosis, were seen in ponies 2, 4, 5, and 7. Bronchiolar degeneration was evident in 4 of 9 ponies given tryptophan orally. The importance of these respiratory lesions was unknown. Clinical or pathologic abnormalities were not noticed in the ponies of groups 3 and 4. Mean plasma tryptophan values increased significantly in groups 1 and 2 at 6 hours after dosing. A second peak of tryptophan was detected in both groups at 12 hours. Values returned to predose values by 48 hours. Plasma indole and 3-methylindole concentrations were detectable in only 2 ponies (4 and 7). In vitro incubations of cecal fluid from ponies 6, 8, and 9 yielded a percentage conversion of tryptophan to indole of 16.75%, 5.84%, and 7.96%, respectively. 3-Methylindole was not produced. These results suggested that indole was the major metabolite of orally administered tryptophan in these ponies.

Acute Disease↗
PubMed1991

Acute hemolytic anemia induced by oral administration of indole in ponies.

Eight ponies were allotted to 2 groups of 4. Group-1 ponies (1-4) were given 0.2 g of indole/kg of body weight orally and group-2 ponies (5 to 8) were given 0.1 g of indole/kg. Various physical, hematologic, and physiologic measurements were obtained after administration of indole. Intravascular hemolysis and hemoglobinuria were detected in both groups within 24 hours of dosing. Hemolysis was reflected by decreases in PCV, hemoglobin concentration, and RBC count, and an increase in indirect bilirubin. Erythrocyte fragility appeared to increase in both groups at 8 hours after dosing and peaked at 16 hours after dosing. At 72 hours after dosing, the RBC fragility value was less than predose measurements. Heinz body formation was noticed in group-2 ponies, but not in group 1. Plasma indole concentrations increased in both groups from the nondetectable predose concentrations. Group-1 values were 203% of group-2 values. In group 2, plasma indole was nondetectable by 12 hours, whereas low concentrations could still be measured in the group-1 ponies at 24 hours. Ponies in group 1 died or were euthanatized between 24 and 72 hours after dosing, whereas group-2 ponies were euthanatized between 48 and 120 hours. At necropsy, all body fat, mucous membranes, and elastic tissue were stained yellow. Hemoglobinuric nephrosis was the most prominent microscopic lesion. Results of this study indicated that indole, a metabolite of the amino acid tryptophan, causes acute intravascular hemolysis in ponies.

Acute Disease↗
PubMed1990

Melanoma as a cause of spinal cord compression in two horses.

Spinal cord compression by melanomas at C7-T1 is described in 2 horses. Despite similar location of the lesions, the onset of neurologic signs and clinical progression varied. Both horses were gray, but few cutaneous melanomas were found. Internal dissemination, however, was extensive in both horses. Antemortem diagnosis was made in one horse, and surgical decompression of the spinal cord was performed. Neoplasms of the vertebral canal and spinal cord are uncommon in horses. Melanoma in the spinal canal should be included in the differential diagnosis of neurologic disease, especially in mature gray horses.

Animals↗
PubMed1990

Respiratory and metabolic responses in the horse during moderate and heavy exercise.

Thoroughbred horses were exercised to fatigue on a treadmill at 62% and 100% of their VO2max. Hypoxemia occurred at the onset of exercise under both exercise conditions. This hypoxemia persisted to fatigue during the heavy exercise but progressively diminished as the exercise continued and had disappeared by the end of exercise at the lighter load. As a result of the hypoxemia the oxygen content of arterial blood during exercise at VO2max was 17% below its carrying capacity. However, under both experimental conditions the CaO2 still exceeded that of rest owing to an elevation in hemoglobin concentration. The temperature of blood at the point of fatigue was similar, 41.0 +/- 0.2 degrees C and 41.1 +/- 0.2 degrees C, for exercise at 62% and 100% VO2max, respectively. Muscle samples collected at rest and at the termination of exercise did not demonstrate major differences between the exercise conditions except for a higher [lactate] and lower pH following the heavy exercise. From these results it can be suggested that the combined effects of an elevated body temperature, changes in muscle pH, and oxygen delivery may all be factors contributing to limit exercise capacity in the horse.

Adenosine Triphosphate↗
PubMed1990

Kinetics of VO2 and VCO2 in the horse and comparison of five methods for determination of maximum oxygen uptake.

To determine whether maximum oxygen uptake (VO2max) in the horse in influenced by type of exercise test, five different protocols were evaluated in eight untrained Thoroughbreds exercised on a treadmill. With all protocols, horses were given a 5 min warm-up on a 10 per cent treadmill slope. Three protocols were at a 10 per cent slope and included: 1) increasing the running speed by 1 to 2 m/sec every 60 secs from 4 m/sec to a maximum of 12 m/sec; 2) running at 12 m/sec until fatigue; and 3) running for 3 to 4 mins at speeds ranging from 6 to 12 m/sec with rest pauses between exercise bouts. The fourth protocol employed a 24 per cent slope where animals exercised for 5 mins at 2 m/sec followed by 3 mins at 5 m/sec, and 2 mins at 6 m/sec. The fifth test involved running at 11 m/sec while the slope of the surface was increased every 2 mins until the horses could not maintain the pace. A plateau in VO2 occurred in all protocols except when exercise was performed on a 24 per cent slope. Slow speed exercise at a steep grade (24 per cent) produced the highest VO2 (P < 0.05) even though there was no plateau in the VO2. A steady state for VO2 and VCO2 existed 90 secs after the onset of exercise with all protocols which involved 2 mins or more at each speed. The VO2 and VCO2 values at all speeds of the rapid incremental exercise test were not different to those found at steady state in the third exercise protocol.

Animals↗