W. M. Bayly

Effects of a polymerized ultrapurified bovine hemoglobin blood substitute administered to ponies with normovolemic anemia.

The development of ultrapurified hemoglobin-based oxygen carriers has eliminated many problems associated with whole-blood transfusions in other species. We hypothesized that the administration of polymerized ultrapurified bovine hemoglobin (PUBH) would result in improved hemodynamic parameters in ponies with normovolemic anemia without adverse effects on renal function or coagulation times. Normovolemic anemia was induced in 6 healthy adult ponies. Over a 3-day period, at least 45 mL/kg of whole blood was withdrawn from each pony until a target PCV of <12% was attained. Plasma was separated from the red blood cells via centrifugation and readministered to the ponies on each day. After the final plasma transfusion, 15 mL/kg of hetastarch (control, n = 6) or 15 mL/kg of PUBH (treatment, n = 6) was administered at 10 mL/kg/h IV. Administration of PUBH at a rate of 10 mL/kg/h was not associated with any adverse effects in 5 of the 6 ponies. One pony experienced an anaphylactoid reaction during infusion of PUBH. The reaction, characterized by intense pruritus, tachycardia, and tachypnea resolved shortly after stopping the infusion. Ponies receiving PUBH had significantly lower cardiac indices (P = .03) and heart rates (P = .002) than control animals. A significantly greater increase in central venous pressure was observed in the PUBH group compared to the hetastarch group (P = .02). No adverse renal or coagulation effects were observed with PUBH infusion. These results suggest that PUBH improves hemodynamics and oxygen transport parameters in horses experiencing normovolemic anemia. Patients should be monitored closely during infusion for any adverse reactions.

Effects of intravenous aminocaproic acid on exercise‐induced pulmonary haemorrhage (EIPH)

REASONS FOR PERFORMING STUDY The antifibrinolytic, 6-aminohexanoic acid, also named aminocaproic acid (ACA), has been used empirically as a treatment for exercise-induced pulmonary haemorrhage (EIPH) on the unsubstantiated basis that transient coagulation dysfunction may contribute to its development. OBJECTIVE To assess the effect of ACA on bronchoalveolar lavage fluid (BALF) erythrocyte counts in horses performing treadmill exercise at an intensity greater than that needed to reach maximal oxygen consumption. METHODS Eight Thoroughbreds were exercised to fatigue 3 times on a 10% inclined treadmill at a speed for which the calculated oxygen requirement was 1.15 times VO2max. Horses were treated with a saline placebo, 2 and 7 g ACA i.v. 4 h before exercise, with a crossover design being used to determine the order of the injections. Exercise-induced pulmonary haemorrhage severity was quantified via the erythrocyte count in BALF. Bronchoalveolar lavage fluid was collected 4 h before and 30-60 min post exercise. Results were expressed as mean ± s.e.m. and analysed by one way repeated measures ANOVA (P < 0.05). RESULTS Aminocaproic acid administration had no effect on any measured variables (VO2max = 48 ± 3.0 [C]; 148 ± 3.0 [2 g ACA]; 145 ± 3.0 [7 g ACA] ml/kg bwt/min, respectively; run time = 77 ± 3 [C]; 75 ± 2 [2 g ACA]; 79 ± 3 [7 g ACA] seconds, respectively). All horses developed EIPH: 1691 ± 690 vs. 9637 ± 3923 (C); 2149 ± 935 vs. 3378 ± 893 (2 g ACA); 1058 ± 340 vs. 4533 ± 791 (7 g ACA) erythrocytes/µl pre- vs. post exercise recovered in BALF, respectively. CONCLUSION Aminocaproic acid was not effective in preventing or reducing the severity of EIPH or improving performance under the exercise conditions of this study.

Responses of horses to a water deprivation test

Summary An investigation was made to determine the effects of water deprivation induced dehydration on changes in urine specific gravity (Usg) and urine osmolality (Uosm) in 6 horses with normal renal function. In addition, the effects of dehydration on serum and urine urea nitrogen, creatinine and various electrolytes as well as the effects of dehydration on acid-base status were studied. Following water deprivation sufficient to produce 12–15% decrease in body weight, 95% of the normal horses should have a Usg of at least 1.042, a Uosm of 1310 mOsmg/kg and a urine osmolality/serum osmolality ratio of 4.14. After 72 hours of water deprivation, the mean weight loss was 13.5% of previous body weight. Serum and urine urea nitrogen concentrations increased by 68% and 130%, respectively, while plasma sodium and chloride concentrations increased by 10% and 14%, respectively. In contrast, urine chloride and calcium concentrations decreased by 90.8% and 52.5%, respectively. There was little change in plasma potassium, phosphorus or calcium concentrations. Urine sodium and potassium concentrations increased initially but were near normal after 72 hours of water deprivation. Azotemia developed and was considered to be of extrarenal origin on the basis of normal routine urinalysis and renal clearance ratio of sodium.

Airflow mechanics in models of equine obstructive airway disease under conditions simulating exercise

Effects of respiratory tract obstructions on ventilatory mechanics in horses exercising at high speeds were tested with a fibreglass replica of the airways (nares to mainstem bronchi) of an adult horse. Segmental pressures were recorded at six sites along the model at four different unidirectional flows (1300-4100 litre min-1), and the respective resistances (R) to airflow were calculated. The external nares and the larynx made the greatest contributions to the total resistance (RTOT) when no obstruction was present. Modifying the model to simulate severe pharyngeal lymphoid hyperplasia (PLH) had no effect on R at the larynx or at any point in the trachea under these flow conditions. Two 16 litre anaesthetic rebreathing bags were attached to the bronchial end of the model, and tidal ventilation generated by a piston pump. Upper (nares to pharynx) and lower tract R (RU and RL) and RTOT, and dynamic compliance were determined for pump volumes (Vp) of six and 12 litres, at pumping frequencies (fp) of 20-100 min-1 while the airway was clear, and after modifying it to simulate either PLH or partial bronchial obstruction. Model condition had no effect on RU. However, RL and RTOT were higher in the PLH simulated condition when fp > or = 90 and Vp = 12 litres (P < 0.05). This suggested that severe PLH may significantly interfere with airflow distal to the site of the lesions during high frequency high volume ventilation of the type seen in galloping horses. With partial bronchial obstruction RL and RTOT were increased when fp > 34 with each Vp. The applicability of the model was verified by comparing results from the unobstructed state with those from normal horses exercising on a treadmill.

Parathyroid hormone evaluation in normal horses and horses with renal failure

Summary Immunoreactive parathyroid hormone (iPTH), calcium, and inorganic phosphorus levels were measured in the serum of 13 apparently normal horses and in six horses with renal insufficiency. Serum iPTH levels were measured by radioimmunoassay using an antisera produced by immunization of guinea pigs with bovine parathyroid hormone. The antisera reacts primarily with the carboxy-terminal hormone fragment. Serum iPTH level in the normal horses was 504.5 ± 191.4 pg/ml and varied from 246 to 750 pg/ml. Serum iPTH levels in three horses with chronic renal failure, hypercalcemia and hypophosphatemia were below the limits of detection for the assay (

Effects of inhalation of albuterol sulphate, ipratroprium bromide and frusemide on breathing mechanics and gas exchange in healthy exercising horses

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

Respiratory responses to exercise in the horse

Horses are elite athletes when compared with other mammalian species. In the latter, performance is limited by cardiovascular or musculoskeletal performance whereas in athletic horses it is the respiratory system that appears to be rate limiting and virtually all horses exercising at high intensities become hypoxaemic and hypercapnoeic. This is due to both diffusion limitation and a level of ventilation inadequate for the metabolic level that enables horses to exercise at these intensities. In conjunction with these blood gas changes, total pulmonary resistance increases and the work of breathing rises exponentially and airflow eventually plateaus despite increases in inspiratory and expiratory intrapleural pressures. Horses breathe at comparatively high frequencies when galloping due to the tight 1:1 coupling of strides to breathing. Whether this effects gas exchange and, if so, to what extent, has not been fully elucidated.

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.

Evaluation of a mask for breath‐by‐breath respirometry during exercise in horses

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

Changes in arterial, mixed venous and intraerythrocytic ion concentrations during prolonged exercise

REASONS FOR PERFORMING STUDY Prolonged equine exercise can cause hypochloraemic alkalosis and hypokalaemia secondary to the loss of hypertonic sweat. Movement of ions in and out of erythrocytes during exercise may help regulate acid-base balance and changes in plasma ion concentrations. The extent to which this happens during prolonged equine exercise has not been reported. OBJECTIVES To measure changes in blood gases and major plasma and intraerythrocytic (iRBC) ion concentrations of horses undergoing prolonged submaximal exercise. METHODS Six horses were trotted at ∼ 30% VO2max on a treadmill for 105 min. Arterial ((a)) and mixed venous ((v)) blood samples were collected every 15 min, and pre- and post exercise. Blood gases and plasma (pl) concentrations of sodium, potassium, chloride and protein were measured and their iRBC concentrations calculated and compared (P < 0.05). RESULTS P(a)CO(2) decreased in all horses. pl[Cl(-)]v decreased and [HCO(3)(-)]v increased. Due to the exhalation of CO(2) and chloride shifting, [HCO(3)(-)]a<[HCO(3)(-)]v, pl[Cl(-)]a>pl[Cl(-)]v)and iRBC[Cl(-)]a<iRBC[Cl(-)]v. pl[K(+)]a and pl[K(+)](v) both initially increased then decreased and horses were hypokalaemic post exercise. Both iRBC[Cl(-)](a) and iRBC[Cl(-)](v) decreased over the course of exercise but there was no change in the arteriovenous difference between them. There was no arteriovenous difference in pl[K(+)]. iRBC[K (+)]a>iRBC[K(+)]v. Conversely, iRBC[Na(+)]a<iRBC[Na(+)]v). pl[Na(+)]a<pl[Na(+)]v and [TP]a<[TP]v. CONCLUSIONS Significant arteriovenous differences in iRBC and plasma concentrations of chloride, potassium and sodium reflect the role that movement of ions across erythrocyte cell membranes play in regulating acid-base balance and plasma concentrations of these ions. Exhalation of CO(2) has a major influence on this ion flux.