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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.
Vasodilator reserve in respiratory muscles during maximal exertion in ponies. Eight healthy adult grade ponies were studied at rest as well as during maximal exertion carried out with and without adenosine infusion (3 microM X kg-1 X min-1 into the pulmonary artery) on a treadmill to compare levels of blood flow in respiratory muscles with those in other vigorously working muscles and to ascertain whether there remained any unutilized vasodilator reserve in respiratory muscles of maximally exercising ponies. Radionuclide-labeled 15-micron-diam microspheres, injected into the left ventricle, were used to study tissue blood flows. During maximal exertion, there were incre...
Effects of acetylpromazine on the hemodynamics of the equine metatarsal artery, as determined by two-dimensional real-time and pulsed Doppler ultrasonography. Heart rate, blood velocity, volumetric blood flow, and arterial diameter for 10 horses given acetylpromazine were determined from measurements of the dorsal metatarsal artery 3 (the great metatarsal artery), using 2-dimensional real-time and gated pulsed Doppler ultrasonography. Acetylpromazine induced significant increases in arterial diameter (P less than 0.01) and volumetric flow rate (P less than 0.05)--all compatible with adrenergic blockade. There was a trend indicating that there was increased blood velocity. Heart rate was unchanged.
Effects of spontaneous, assisted, and controlled ventilatory modes in halothane-anesthetized geldings. Cardiopulmonary effects of spontaneous, assisted, and controlled ventilatory modes were determined with 6 young, healthy geldings anesthetized with halothane at a constant dose (1.3 minimum alveolar concentration). All horses were in lateral recumbency, and all modes of ventilation were studied at least once during each anesthetic exposure. Cardiac output did not differ between spontaneous and assisted ventilation modes, but both modes were associated with significantly (P less than 0.05) higher cardiac output than that with controlled ventilation. The PaCO2 differed significantly (P less than...
Neuromuscular and cardiovascular effects of atracurium in ponies anesthetized with halothane. Atracurium besylate, a recently developed, intermediate-duration acting, neuromuscular-blocking agent, was given to 15 halothane-anesthetized ponies to produce surgical relaxation (95% to 99% reduction of hoof twitch). All 15 ponies were given 3 injections; 8 of the 15 ponies were given 2 additional injections. Initial dosage of 0.11 +/- 0.01 mg/kg (mean +/- SD) and all subsequent injections of 0.052 mg/kg produced desired relaxation. Paralysis phase (maximum twitch reduction to 10% twitch recovery) lasted 24 +/- 5 minutes for the initial injection. Paralysis from subsequent injections lasted ...
Heart rate and ECG response to twitching in Thoroughbred foals and mares. Changes of the heart rate and ECG to twitching were examined using 5 Thoroughbred foals at various ages and their mares. The effect of the heart rate decrease to twitching was significantly greater in the foals than in the mares. The decreased heart rate in the foals continued during and after the twitching. Changes of the T wave in the A-B lead ECG shown as enhancement of the negative ingredient of the T wave were observed both in the foals and in the mares, accompanied by a decrease in the heart rate during and/or after the twitching. Two out of the five foals showed second-degree A-V block ...
J.B. Wolffe memorial lecture. Is the lung built for exercise? In summary, we have shown that the design of the pulmonary system from the architectural capacities of the lung parenchyma and respiratory muscles to the remarkable, multi-level neural integration of breathing pattern and respiratory muscle recruitment is clearly intended for the exercising state. Furthermore, the system shows remarkable capability for true adaptation, both phylogenetically and even within only a few generations within a species, when preservation of the organism's ability to survive and function is at stake. At the same time there are limits to the system's homeostatic capabi...
Diseases of the heart. Diagnostic ultrasound has allowed significant findings to be made in the investigation of cardiac disease in the horse. Because of the limited value of thoracic radiography in the adult horse with cardiac disease, ultrasound is the method of choice to document chamber enlargement, pericardial effusion, valvular abnormalities, and decreased contractility of the myocardium. The apparent changes in the flow characteristics and suspicion of abnormality in the right heart of racehorses need further investigation to fully document the etiopathogenesis of spontaneous contrast.
Pulmonary function in the horse during anaesthesia: a review. The effect of abnormal body position on cardiovascular and pulmonary function in the awake and anaesthetised horse is reviewed. Parameters such as pulmonary shunt, lung volumes, blood gases and alveolar-arterial oxygen partial pressure differences are discussed. Withholding food for 24 hours and mechanical ventilation may be used to improve blood gas values associated with abnormal recumbency during anaesthesia. During prolonged recovery, horses should be encouraged to adopt sternal recumbency.
Independence of exercise hyperpnea and acidosis during high-intensity exercise in ponies. We investigated arterial PCO2 (PaCO2) and pH (pHa) responses in ponies during 6-min periods of high-intensity treadmill exercise. Seven normal, seven carotid body-denervated (2 wk-4 yr) (CBD), and five chronic (1-2 yr) lung (hilar nerve)-denervated (HND) ponies were studied during three levels of constant load exercise (7 mph-11%, 7 mph-16%, and 7 mph-22% grade). Mean pHa for each group of ponies became alkaline in the first 60 s (between 7.45 and 7.52) (P less than 0.05) at all work loads. At 6 min pHa was at or above rest at 7 mph-11%, moderately acidic at 7 mph-16% (7.32-7.35), and markedly...
Pressures in the right side of the heart and esophagus (pleura) in ponies during exercise before and after furosemide administration. Pressures in the right side of the heart and esophagus (pleural) have not been determined in the exercising equine subjects. In the present study, 8 healthy ponies were examined to determine the changes in these variables caused by 2 degrees of exercise done on a treadmill (heart rate:183 +/- 5 beats/min [trot] and 220 +/- 6 beats/min [canter]). Measurements were also made during both degrees of exertion 10 minutes and 120 minutes after furosemide (1.0 mg/kg) administration. It was observed that both gaits resulted in significant increases in pulmonary artery, right ventricular, and right atri...
[Electrocardiography in the horse. (3)]. The use of the ECG to separate the different phases of the heart cycle registering other physiological signals, to evaluate the fitness and state of training of a horse and to detect a pregnancy of a mare is reported and illustrated in this text.
Cervicothoracic (stellate) ganglion block in conscious horses. Seven adult horses were used to compare the cardiovascular and respiratory effects of unilateral (right side) and bilateral cervicothoracic ganglion (CTG) blockade. An 18-gauge, 25-cm needle was placed midventrally between articulations of the 1st and 2nd ribs from a cranial and paratracheal site. One gram of lidocaine HCl in aqueous solution (100 ml) was used to infiltrate the CTG. Cervicothoracic sympathetic blockade was characterized by Horner's syndrome, increased skin temperature and profuse sweating over the face, neck, and thoracic limb. Comparison of base-line data with data obtained d...
The use of atropine to control heart rate responses during detomidine sedation in horses. Detomidine is a sedative-analgesic which has a pharmacological profile similar to xylazine. There is evidence that the sedative effects are mediated through alpha-2 adrenoceptors. Cardiopulmonary responses were determined using detomidine as the principal agent and as a preanesthetic prior to the induction of general anesthesia. Compatibility with guaifenesin, sodium thia-mylal and halothane were determined. As in the case of xylazine, detomidine produces a slowing of heart rates. This was found to be either sinus bradycardia or heart block. There may be a corresponding increase in systolic bl...
Dose-related effects of ethylketazocine on nociception, behaviour and autonomic responses in the horse. Sensitive methods for measuring the analgesic, physiological and behavioural effects of opioids in the horse have recently been developed. Fentanyl, a prototypic mu-opiate receptor agonist, has been previously shown to produce a syndrome characterized by marked analgesia and locomotor stimulation as well as tachycardia, tachypnoea and behavioural arousal. To determine whether other opiate receptors mediate some of the actions of the narcotic analgesics in the horse, an agent with activity at kappa- and to lesser extent mu-receptors was studied using a vigorous experimental protocol. Like fenta...
Paroxysmal atrial fibrillation in racehorses. The paper describes five cases of atrial fibrillation detected after racing. In four of them, the arrhythmia disappeared spontaneously within 24 h and they were regarded as paroxysmal in type. In the fifth case, which won its race, the arrhythmia persisted for at least 45 h after racing. It was therefore regarded as an example of persistent atrial fibrillation. It was then treated with quinidine sulphate which restored sinus rhythm. It would seem that paroxysmal atrial fibrillation may be a cause of sudden decrease in racing performance.
Use of dopamine hydrochloride during general anesthesia in the treatment of advanced atrioventricular heart block in four foals. Heart block is a relatively common arrhythmia in the adult horse. It may be a normal physiologic phenomenon or it may have pathologic implication. Four foals in which advanced heart block developed during anesthesia were unresponsive to atropine sulfate and supportive treatment alone. Resolution of the heart blocks was achieved after the addition of dopamine hydrochloride to the therapeutic regimen.
Sudden death in training and racing Thoroughbred horses. We reviewed case records, necropsy reports, and histologic sections from 25 Thoroughbred racehorses that died suddenly at 3 Chicago racetracks. These were young horses ranging in age from 2 to 5 years. There were more females (n = 16) than males (n = 9), and the incidence of death increased slightly in the spring and summer. Twenty-one of the 25 horses died while racing or training. Only 8 of the 25 horses (32%) had lesions sufficient to account for the death. In 6 of those 8 cases, death was caused by massive thoracic or abdominal hemorrhage. The site or nature of the vascular defect in these...
Cardiovascular adaptations to exercise and training. The cardiovascular system provides the link between pulmonary ventilation and oxygen usage at the cellular level. During exercise, efficient delivery of oxygen to working skeletal and cardiac muscles is vital for maintenance of ATP production by aerobic mechanisms. The equine cardiovascular response to increased demand for oxygen delivery during exercise contributes largely to the over 35-fold increases in oxygen uptake that occur during submaximal exercise. Cardiac output during exercise increases greatly owing to the relatively high heart rates that are achieved during exercise. Heart rate i...
Effects of flunixin meglumine on cardiopulmonary responses to endotoxin in ponies. The effects of endotoxemia on cardiopulmonary parameters, before and after cyclooxygenase blockade, were determined in anesthetized ponies spontaneously breathing a mixture of halothane and 100% O2. Escherichia coli endotoxin was infused intravenously at 20 micrograms/kg for 1 h followed by 10 micrograms X kg-1 X h-1 the subsequent 4 h. By 15 min endotoxin increased mean pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR), and alveolar dead space ventilation (VDA/VT), and these were followed by a return to base-line values by 30 min. A second increase in PVR occurred by 5 h ...
Echocardiographic detection of ventricular septal defects in large animals. Ventricular septal defects in a foal, a 2-year-old filly, and 2 calves were demonstrated with M-mode and two-dimensional real-time echocardiography. The studies were performed with the animals unsedated, either standing or in lateral recumbency. Cardiac windows were located between the 4th and 7th intercostal spaces, approximately at the level of the olecranon. In each case, the septal defect was visualized high in the membranous portion of the interventricular septum. Defects were visualized by use of sector scanning or linear-array ultrasonic equipment, with transducer frequencies of 2.25 to...
Atrial septal defect of the persistent ostium primum type with hypoplastic right ventricle in a Welsh pony foal. Valvular competency of the foramen ovale (patent foramen ovale) is regarded as a common finding in the neonatal foal and usually occurs in isolation. True atrial septal defects appear to be uncommon and are usually associated with other congenital cardiac lesions. The present report describes a case of atrial septal defect type 1 (persistent ostium primum) complicated by hypoplastic right ventricle, and tricuspid dysplasia, in a Welsh Mountain pony foal, and discusses the embryogenesis of the abnormality. A critical review of the literature suggests that atrial septal defects may occur more fr...
Traumatic gastropericarditis in a horse. An ingested metallic foreign body migrated from the stomach and induced restrictive pericarditis in a horse. Necropsy revealed chronic abdominal and acute thoracic lesions. Although rare, ingested foreign body migration should be considered in the differential diagnosis of body cavity disease in horses.
Visceral analgesia: effects of xylazine, butorphanol, meperidine, and pentazocine in horses. The visceral analgesic, cardiorespiratory, and behavioral effects induced by xylazine, butorphanol, meperidine, and pentazocine were determined in 9 adult horses with colic. Colic was produced by inflating a balloon in the horses' cecum. Heart rate, respiratory rate, mean arterial blood pressure, and cardiac output increased after cecal balloon inflation. Xylazine and butorphanol decreased the hemodynamic response to cecal balloon inflation. Meperidine and pentazocine had minimal effects on the cardiorespiratory changes induced by cecal balloon inflation. Xylazine produced the most pronounced ...
Effects of strenuous exercise on myocardial blood flow. Myocardial blood flow is the major determinant of oxygen delivery to the myocardium, since oxygen extraction by the myocardium is near maximum in the resting state. Regulation of flow during exercise depends on local metabolic factors and, to a small extent, on autonomic tone. Maximum flow of 5-6 times resting has been measured in reactive hyperemia experiments. In strenuous exercise, myocardial oxygen delivery appears to be adequate and flow reserve seems capable of handling the increased oxygen demand. No evidence of myocardial failure in normal hearts due to excess exercise has been present...
Total intravenous anaesthesia in the horse with propofol. The use of propofol, solubilised in a non-ionic emulsifying agent, for the induction and maintenance of anaesthesia in experimental ponies was assessed. Pilot studies revealed that premedication with xylazine (0.5 mg/kg bodyweight [bwt]) intravenously (iv) followed by propofol (2.0 mg/kg bwt) iv provided a satisfactory smooth induction. Two infusion rates (0.15 mg/kg bwt/min and 0.2 mg/kg bwt/min) were compared for maintenance of anaesthesia. An infusion rate of 0.2 mg/kg/min produced adequate anaesthesia in these ponies. Cardiovascular changes included a decrease in arterial pressure and card...
