Topic:Cardiovascular Health
Cardiovascular health in horses encompasses the study of the heart and blood vessels, focusing on their structure, function, and associated disorders. The equine cardiovascular system is responsible for the circulation of blood, delivering oxygen and nutrients to tissues, and removing waste products. Research in this area includes the examination of cardiac anatomy, the electrophysiology of the heart, and common cardiovascular conditions such as arrhythmias, valvular diseases, and heart murmurs. Diagnostic tools such as echocardiography, electrocardiography, and cardiac biomarkers are utilized to assess cardiovascular function and detect abnormalities. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological mechanisms, diagnostic approaches, and therapeutic strategies related to cardiovascular health in horses.
Combined use of detomidine with opiates in the horse. The effects of administration of one of four opiates (pethidine 1 mg/kg bodyweight (bwt), morphine 0.1 mg/kg bwt, methadone 0.1 mg/kg bwt, and butorphanol 0.05 mg/kg bwt) given intravenously to horses and ponies already sedated with detomidine (10 micrograms/kg bwt) were investigated. Behavioural, cardiovascular and respiratory effects of the combinations were compared with those occurring with detomidine alone. Addition of the opiate increased the apparent sedation and decreased the response of the animal to external stimuli. At doses used, butorphanol produced the most reliable response. Sid...
Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone in the horse. Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone were studied in the horse. Acepromazine and xylazine produced cardiovascular effects whereas methadone mainly affected respiratory rate. Decreases in heart rate, arterial blood pressure and respiratory rate were seen. Sedation was superior to that of acepromazine, xylazine or a combination of these. No serious side effects were seen.
Cardiorespiratory responses to HCl vs. lactic acid infusion. Previous reports indicate that intravenous infusion of HCl can alter breathing and blood pressure even if reductions in systemic arterial pH are prevented. To extend these findings, as well as to determine whether other acids elicit comparable results, this report compares the cardiopulmonary response between right atrial infusion of lactic acid and HCl in awake ponies. Lactic acid, infused at a dose of 1.5 mmol/kg over 18 min, lowered systemic and pulmonary arterial pH 0.062 and 0.092 U, respectively, and increased pulmonary arterial pressure (delta Ppa, 4 mmHg), heart rate (HR, 4/min), and t...
Effects of frequency and airway pressure on gas exchange during interrupted high-frequency, positive-pressure ventilation in ponies. Cardiovascular effects and pulmonary gas exchange were compared during conventional mechanical ventilation (CMV) and interrupted high-frequency, positive-pressure ventilation (IHFPPV) in 6 anesthetized ponies in dorsal recumbency. When the peak airway pressure (Paw) was held constant at control values attained during CMV (18 to 20 cm of H2O), and the ventilator frequency of IHFPPV was varied over the range, 2.5 to 12.5 Hz, significant (P less than 0.05) changes from control values were observed only in the ratio of dead-space volume to tidal volume (VD/VT) and in the respiratory minute volume ...
Neuromuscular and cardiovascular effects of atracurium administered to healthy horses anesthetized with halothane. Neuromuscular and cardiovascular effects of atracurium, a nondepolarizing neuromuscular blocking agent, were evaluated in 10 halothane-anesthetized adult horses. Hind limb digital extensor tension (hoof twitch) was measured with a strain gauge to quantitate the muscle relaxant effects of atracurium. Response of facial muscles was compared with hoof twitch. Five injections of atracurium were given. Initial mean (+/- SEM) dosage of 0.07 +/- 0.01 mg of atracurium/kg of body weight caused 98.6 +/- 0.8% reduction of the preinjection hoof twitch. Subsequent dosages of 0.04 +/- 0.003 mg/kg induced a ...
The foramen ovale of the foetal and neonatal foal. Hearts from 24 foals were studied; 10 were from foetuses ranging in gestational age from 230 to 322 days and 14 were from newborn and young foals aged between birth and 17 days. The foramen ovale and associated vena caval and atrial structures were examined by scanning electron microscopy. Additional observations were made by light and transmission electron microscopy. A tube-like flap of tissue was observed, extending from the aperture in the caudal vena cava to the lumen of the left atrium. In the younger foetuses, the distal end of this tube was covered with a thread-like network of tissue....
Effects of flunixin meglumine on jejunal blood flow, motility, and oxygen consumption in ponies. Using isolated autoperfused intestinal segments, the effects of flunixin meglumine administration on systemic arterial blood pressure, jejunal blood flow, vascular resistance, motility, arteriovenous oxygen difference, and oxygen consumption were determined in 10 anesthetized ponies ventilated with a mixture of halothane and oxygen. Saline solution or flunixin meglumine (1.1 mg/kg of body weight) was infused as a single bolus into the left jugular vein. By 10 minutes, flunixin meglumine increased systemic arterial blood pressure and increased intestinal vascular resistance. The jejunal blood f...
A morphological study on the obliteration processes of the ductus arteriosus in the horse. The obliteration processes of the ductus arteriosus of equine foetuses and newborn foals were studied morphometrically and histologically. The length, internal and external diameters and circumference of the ductus in equine foetuses increased progressively and linearly up to 310 days with advancing foetal age, but the values, especially the internal diameter, decreased from 320 to 330 days. After birth, the ductal measurements decreased gradually and ductal closure was found in three of 14 foals examined on the first day post partum, in two of six on the second day and in nine of nine on the ...
Effect of splenectomy on exercise-induced pulmonary and systemic hypertension in ponies. Large increases in systemic and pulmonary arterial pressures of exercising healthy ponies have been observed. Because exercise causes a considerable increase in PCV of ponies, we examined the effect of splenectomy on exercise-induced changes in systemic and pulmonary pressures. These pressures (taken with catheter-tip micromanometers) and indicator dilution cardiac output were determined on 9 healthy ponies that had undergone splenectomy 4 to 9 weeks before the study. Data obtained at rest and during submaximal (10.5 to 11.0 mph) and maximal (14 to 15 mph) exercise from these ponies were compa...
A morphometric study of foetal and newborn cardiac growth in the horse. A morphometric study of hearts in 81 equine foetuses, ranging in age from 190 to 330 days of foetal age, and in 26 newborn foals is reported. The mean weight, external dimensions, ventricular wall thickness and circumference of the atrio-ventricular orifice were measured. Features of the main associated vessels of the heart were also recorded. All cardiac measurements of foetuses increased linearly throughout the latter half of pregnancy and were highly correlated with foetal age. This linear growth pattern was also found in the parameters of the associated arterial trunks. The ratio of the ri...
Cardiovascular effects of hydralazine HCl administration in horses. Six standing awake adult horses were instrumented for measurement of mean arterial, central venous, and pulmonary arterial blood pressures (mm of Hg), thermodilution cardiac output (ml/kg/min), and pulmonary arterial blood temperature (C). Total peripheral resistance was calculated from these values. Base-line data were accumulated, and a single dose of hydralazine HCl (0.5 mg/kg) was administered IV. Horses were monitored for 420 minutes after hydralazine administration. Mean arterial and central venous blood pressures did not change from the base-line values. Cardiac output and heart rate we...
Effects of xylazine on cecal mechanical activity and cecal blood flow in healthy horses. Mechanical activity of the cecal body, lateral cecal arterial blood flow, carotid arterial pressure, and heart rate were measured in 6 conscious healthy horses 30 minutes before and for 120 minutes after IV administration of xylazine at dosages of 1.1 mg/kg of body weight, 0.55 mg/kg, and 0.275 mg/kg. Xylazine at a dosage of 1.1 mg/kg reduced the mean motility index (the product of the mean amplitude of contractions and the total duration of contractile activity divided by the recording time) of the circular and longitudinal muscle layers for the first, second, third, and fourth 30-minute peri...
Hemodynamic and respiratory responses in halothane-anesthetized horses exposed to positive end-expiratory pressure alone and with dobutamine. The influence of positive end-expiratory pressure (PEEP) on the alveolar-arterial O2 tension difference [P(A-a)O2], physiologic right-to-left shunt fraction, physiologic dead space-to-tidal volume ratio, and hemodynamic variables was studied in halothane-anesthetized horses maintained in dorsal recumbency during controlled ventilation. Dobutamine was used to minimize the adverse cardiovascular consequences of PEEP. Six adult horses were anesthetized, using xylazine (2.2 mg/kg of body weight, IM), guaifenesin (50 mg/kg, IV), thiamylal Na (4.4 mg/kg, IV), and halothane (1.5 to 2% inspired) in 10...
Determination and repeatability of maximum oxygen uptake and other cardiorespiratory measurements in the exercising horse. A rapid incremental treadmill exercise test was used to determine the repeatability of the following measurements in exercising horses: maximal oxygen consumption (VO2max), maximal heart rate (HRmax), velocity at a heart rate of 200 beats/min (V-200), oxygen consumption at a heart rate of 200 beats/min (VO2-200), oxygen consumption at HRmax (VO2-HRmax), work rate at a heart rate of 200 beats/min (W-200), work rate at HRmax (W-HRmax) and treadmill velocity at HRmax (V-HRmax). Six Standardbred geldings were exercised on three separate occasions on a treadmill set at an inclination of 6 degrees. ...
Sudden and unexpected death in horses and ponies: an analysis of 200 cases. An analysis was made of the causes of death in horses and ponies over one year of age which died suddenly (Group 1) or were found dead but were considered normal when last seen (Group 2). There were 49 animals in Group 1. Thoroughbreds were overrepresented, but there were no ponies in this group. No cause of death was found in 30.6 per cent of cases and 16.3 per cent died from each of the following causes: haemorrhage in the respiratory system, central nervous system, and adverse drug reactions. Cardiovascular lesions were the cause of death in 14.4 per cent and the remaining 3.1 per cent had ...
Cardiovascular and respiratory responses to submaximal exercise training in the thoroughbred horse. Cardiovascular and respiratory responses to submaximal exercise training were investigated in 6 thoroughbred racehorses. Oxygen uptake, heart rate (HR) and arteriovenous oxygen content difference were measured during incremental treadmill exercise tests, before and after 7 weeks of treadmill training. Cardiac output during exercise was calculated by the direct Fick technique. Maximal oxygen uptake (VO2max) was increased by 23% after training, from 129.7 ml/kg/min to 160.0 ml/kg/min. The treadmill speed at which VO2max was attained increased by 19%. The increased aerobic power after training wa...
Effect of a respiratory gas collection mask on some measurements of cardiovascular and respiratory function in horses exercising on a treadmill. The effects of a respiratory gas collection mask on arterial blood gases, acid base values, oxygen content, respiratory frequency and heart rate, were investigated in standardbred horses during treadmill exercise at speeds up to 10 m sec-1 and a treadmill slope of 10 per cent. The mask had no significant effect on heart rates during exercise, but respiratory frequency was lower when the mask was used. The increase in respiratory frequency as treadmill velocity increased was also significantly slower with the mask operative. Arterial carbon dioxide tensions were significantly higher during exer...
Diaphragmatic O2 and lactate extraction during submaximal and maximal exertion in ponies. Diaphragmatic O2 and lactate extraction were studied in 10 healthy ponies at rest and during treadmill exercise. The phrenic vein was aseptically catheterized via a lateral thoracotomy 8-35 days before the study. Arterial and phrenic venous blood samples were obtained simultaneously at rest and at 30-s intervals during 4 min of exertion. Three levels of exertion were studied (moderate, 10 mi/h; heavy, 15 mi/h; maximal, 20 mi/h), and a rest period of at least 90 min was allowed between them. Each pony was studied twice at least 2-3 days apart. At rest the diaphragmatic venous PO2, O2 saturation...
Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise. Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake (VO2 max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% VO2 max, the oxygen consumption (VO2) increased to mean values of approximately 130 ml/kg.min, which ...
O2 transport in the horse during rest and exercise. We studied mechanisms of O2 transport in 6 adult (2-5 year old) horses at rest and during steady-state exercise on a treadmill (0% slope) at 12 m/s (a submaximal gallop). Oxygen consumption was measured using an open-flow system. Arterial and mixed venous blood samples were simultaneously obtained for measurement of O2 content and hemoglobin concentration. VO2 increased from 1.5 +/- 0.2 L/min at rest to 46.2 +/- 4.8 L/min during exercise. HR increased from a resting value of 36.9 +/- 2.5 bpm to 196.5 +/- 10.9 bpm and the arterio-venous O2 content difference (a-v O2) increased from 4.2 +/- 0.8 ...
Pulmonary mechanics during treadmill exercise in race ponies. Exercise-induced variations in their ventilatory mechanics were studied in 8 healthy ponies 4.2 +/- 1.4 years old and weighing 282 +/- 11 kg. Airflow (V), tidal volume (VT), esophageal pressure, mask pressure and electrocardiogram were simultaneously recorded before, during and after a treadmill (incline 8.3 degrees) exercise which consisted of 2 min walking (1.5 m.sec-1), 3 min slow trotting (3.0 m.sec-1) and 3 min fast trotting (3.5 m.sec-1). The results of three consecutive daily measurements were averaged for each pony. Heart rate, minute volume (Ve), respiratory frequency (f) and peak ins...
Circulatory, respiratory and metabolic responses in Thoroughbred horses during the first 400 meters of exercise. These studies investigated circulatory, respiratory and metabolic responses in four Thoroughbred geldings during the first 400 metres of galloping (mean speed 14.4 +/- 0.38 m.s-1), cantering (mean speed 10.0 +/- 0.61 m.s-1) and walking (mean speed 1.58 +/- 0.05 m.s-1) from a standing start. A radio-controlled device which collected blood samples anaerobically during each 100 m section of the exercise track allowed analyses of changes in and functional relationships of the variables measured. During the 400 m gallop, the mean heart rate (HR) increased from 125 to 201 beats.min-1 and the haemato...
Cardiovascular and respiratory responses in Thoroughbred horses during treadmill exercise. Six detrained Thoroughbred horses performed incremental treadmill tests. Maximal oxygen uptake (VO2max) was measured during exercise by analysis of expired gas. The relationships between oxygen consumption (VO2) and work rate, heart rate (HR), cardiac output (Q), stroke volume (SV) and arteriovenous oxygen content difference [C(a-v)O2] were examined during submaximal and maximal exercise. The relative contributions of blood flow and extraction of oxygen from muscle capillaries were assessed during exercise at VO2max. Mean VO2max was 129.7 +/- 2.9 (mean +/- S.E.M.) ml kg-1 min-1, which occurred...
Factors affecting prognosis and conversion in equine atrial fibrillation. Sixty-seven horses presented with atrial fibrillation (AF) from January 1, 1980 to August 1, 1986. All horses were evaluated for the type and severity of the underlying cardiac disease and the probable duration of the arrhythmia. Fifty-two (78%) of the horses were treated with quinidine sulfate and/or digoxin. The response to treatment was assessed in each horse. Horses were followed for periods extending from 8 months to 7 years. Standardbreds, young horses, and males predominated in the study group. There were more male horses (stallions and geldings) than mares. Most horses with AF had no e...