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.
[Training-induced changes of reference vectors in the QRS complex of the EKG of young trotting horses]. After the onset of training ("breaking") in young standardbred horses within continuing investigations changes of vectors in the QRS-complex were considered. These changes accomplished in two stages. Mainly within the first three months of training the vector R (VR) in limb leads changed to the left and to caudal and dorsal. In a second interval between five and seven months after breaking the vector S (VS) changed to cranial. As main cause the different character of training in both phases is discussed. Additional indicators of age- or development-related causes were not found.
Diaphragm does not produce ammonia or lactate during high-intensity short-term exercise. To ascertain whether costal diaphragm engages in ammonia and lactate production (like limb muscles) during high-intensity short-term exercise, experiments were carried out on six healthy trained ponies in which phrenic venous catheters had been implanted 5-9 days earlier. Simultaneous anaerobically obtained blood samples from abdominal aorta and the phrenic vein at rest and during 4 min of exertion at 32 km/h and at a 7% grade were analyzed for blood-gas variables as well as lactate and ammonia concentrations using standard procedures. At rest, heart rate was 47 +/- 4 beats/min and the diaphra...
Clinical exercise testing in the normal thoroughbred racehorse. To evaluate normal cardiorespiratory and metabolic responses of Thoroughbred horses to a standardised treadmill exercise test, we examined 28 horses ranging in age from 1 to 4 years. The group consisted of eight yearlings, eight 2-year-olds and twelve 3 and 4-year-olds. All horses except the yearlings were in training, and either racing or ready to race, at the time of examination. None of the horses had histories of performance problems. On the first day the horses received a full physical examination, resting electrocardiogram, upper respiratory tract endoscopy and either one or two acclimat...
Echocardiographic detection of an intact aneurysm in a horse. Two-dimensional real-time echocardiographic examination of a 3-year-old Thoroughbred gelding with pleuropneumonia revealed an intact aneurysm of the right sinus of Valsalva, which was confirmed at postmortem examination. The horse had no clinical signs associated with the aneurysm.
Changes in coagulation and fibrinolysis in horses during exercise. Changes in clotting time (CT) and fibrinolytic activity (FA) were evaluated in 6 mature, female horses during exercise. Two trials were performed on consecutive days, using a randomized crossover design. Each mare was assigned to either an exercise trial or a control trial on the first day, and to the alternate trial 24 hours later. Mares exercised for 20 minutes on a treadmill at an elevation of 2 degrees and a velocity of 5 m/s. Venous blood samples were collected immediately before exercise, at 4, 8, 12, 16 and 20 minutes during exercise, and 15 minutes after cessation of exercise. Blood wa...
[The effect of respiratory activity on the QRS complex in the ECG in clinically healthy horses and horses with chronic lung diseases]. Interrelations between respiration and changes in amplitudes of the QRS-complex of the ECG of horses were investigated. The value of the R-vector and both its components Rx and Ry decrease during inspiration and increase in the expiration phase. It means, that the R-waves in leads from cranial to caudal (y, II, aVF) and from right to left (I) become smaller with inspiration and larger with expiration. The difference of the amplitudes may be important, especially in horses with respiratory problems, so that it has to be noted when evaluating electrocardiograms. For that purpose it is not necess...
Effect of low-dose butorphanol on halothane minimum alveolar concentration in ponies. Minimum alveolar concentration (MAC) for halothane was measured before and after administration of intravenous butorphanol (0.022 and 0.044 mg/kg in bodyweight in nine yearling Shetland ponies. Arterial blood pressure, heart rate, respiratory rate, expired CO2 and rectal temperature was also measured. Even though mean MAC values decreased 10 and 9 per cent after the low and high doses respectively, they were not statistically different from those measured prior to butorphanol. Halothane MAC values increased after butorphanol in two ponies, both animals increasing locomotor activity and demonst...
Doxapram infusion during halothane anaesthesia in ponies. Doxapram, 0.05 mg/kg bodyweight/min, was infused during the second hour of 2 h halothane anaesthesia in six ponies. Two of the ponies were anaesthetised on a second occasion as controls and given 5 per cent dextrose in place of the doxapram. Respiratory depression typical of halothane anaesthesia in ponies developed in the first hour of anaesthesia and continued during the second hour in the control animals. During doxapram infusion arterial carbon dioxide tension decreased and pH increased. Arterial blood pressure increased but there was no change in pulse rate, the electrocardiogram or arter...
Time-related responses to a constant-dose halothane anaesthesia in dorsally recumbent ventilated ponies. Haemodynamic and respiratory responses to halothane were investigated in dorsally recumbent, ventilated ponies during 2 hours. Normocapnia was maintained using intermittent positive pressure ventilation. Compared to the base line values at 30 minutes of constant dose halothane, no significant changes in heart rate, systemic blood pressure, cardiac output, cardiac index, stroke volume and left ventricle work were observed during a 2 hours anaesthesia. Arterial oxygenation increased initially (greater than 300 mm Hg) but tended to decrease non-significantly during the rest of the anaesthesia. Bl...
Cardiovascular and respiratory effects of inspired oxygen fraction in halothane-anesthetized horses. Anesthesia of equids is associated with pulmonary dysfunction. Cardiovascular and respiratory effects of inhalation anesthetic agents and duration of anesthesia have been studied, using oxygen as the carrier gas. To our knowledge, the effects of inspired oxygen have not been determined. We studied the cardiovascular and respiratory effects of 2 inspired oxygen fractions (0.30 and greater than 0.85) in 5 laterally recumbent, halothane-anesthetized horses. Mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base e...
Effect of age on isoproterenol-induced maximal heart rate in horses. The effect of age on maximal heart rate induced by IV infusion of isoproterenol was studied in 19 healthy, sedentary, normothermic horses ranging in age from 0.25 to 9.90 years. Isoproterenol was administered IV (1.0 micrograms/kg of body weight/min) for 3 minutes, and the heart rate attained during the last 30 seconds of the infusion was determined. Linear regression of the maximal heart rate on age suggested that the rate decreased with age in a trend described by the equation: maximal heart rate (beats/min) = 209.63 - 3.28 x age (years). The regression coefficient (r) for this relation was ...
Effect of hypertonic vs isotonic saline solution on responses to sublethal Escherichia coli endotoxemia in horses. Cardiovascular responses to sublethal endotoxin infusion (Escherichia coli, 50 micrograms/ml in lactated Ringer solution at 100 ml/h until pulmonary arterial pressure increased by 10 mm of Hg) were measured 2 times in 5 standing horses. In a 2-period crossover experimental design, horses were either administered hypertonic (2,400 mosm/kg of body weight, IV) or isotonic (300 mosm/kg, IV) NaCl solution after endotoxin challenges. Each solution was administered at a dose of 5 ml/kg (infusion rate, 80 ml/min). Complete data sets (mean arterial, central venous, and pulmonary arterial pressures, pul...
Halothane-sparing effect of benzodiazepines in ponies. The halothane-sparing effect of 2 benzodiazepines, diazepam and temazepam, were investigated in ponies by measuring the minimum alveolar concentration (MAC) for halothane before and after drug administration. The MAC value for halothane decreased 29% and 16% when either 0.044 mg/kg of diazepam or 0.044 mg/kg of temazepam, respectively, was administered intravenously. Heart rate, respiratory rate, systolic and mean arterial blood pressure, and expired CO2 were also measured. No differences were present in these variables before and after drug administration nor were differences noted between th...
Haemodynamic effects of small volume hypertonic saline in experimentally induced haemorrhagic shock. A comparison of the haemodynamic benefits of small volume hypertonic saline (2,400 mOsm/litre) versus isotonic saline (300 mOsm/litre) was conducted in 12 adult horses using a haemorrhagic shock model. The horses were anaesthetised and intravascular catheters placed for the measurement of haemodynamic data. Mean systemic arterial pressure was then reduced to 50 to 60 mmHg by controlled haemorrhage and maintained at that level for 40 mins. Cardiac output, stroke volume, mean systemic arterial pressure, plasma volume and urine production decreased significantly following blood loss. Hypertonic o...
A comparative study of interval and conventional training in thoroughbred racehorses. Eight horses with previous racing experience were used in a comparative study of training methods for Thoroughbred racehorses. They were randomly assigned to two groups of four horses each. One group was trained using an interval training method (IT) and the other using conventional training (CT) methods. Peak heart rates, heart rate recovery curves, peak plasma lactate levels, plasma lactate clearance rates and run times were used to evaluate differences in the training methods. Peak heart rates, heart rate recovery curves, and run times were not significantly different between the groups. Ho...
Alterations in plasma volume, plasma constituents, renin activity and aldosterone induced by maximal exercise in the horse. Plasma volume (PV) decreased by 13 per cent following the completion of 1,000 m of maximal exercise in the horse. This study demonstrated that the critical reduction in PV following maximal exercise occurred within 10 mins of completion of exercise, as previously reported in man. Total plasma protein (TPP) increased by 23 per cent at 2 and 5 mins, and by 21 per cent at 10 mins post exercise. Therefore, it does not appear to be an accurate measurement to assess the degree of PV contraction in the horse. Protein was apparently added to the intravascular space either during or following exercise....
Cardiorespiratory drift during exercise in the horse. The purpose of the present study was to measure the time-course and degree of cardiovascular and respiratory 'drift' during constant submaximal exercise in the horse. One Thoroughbred and four Morgan mares were instrumented for simultaneous measurement of respiratory and blood gases which also enabled cardiac output (Q) to be calculated. Data were collected at rest, and at 10, 20 and 30 mins during a constant workload which elicited an initial exercising heart rate (HR) of 150 beats/min, and an approximate 15-fold increase in oxygen consumption (VO2). Significant cardiac and respiratory drift ...
Effects of treadmill elevation on heart rate, blood lactate concentration and packed cell volume during graded submaximal exercise in ponies. Six ponies performed a standardised exercise test on a motorised treadmill at each of three randomly assigned treadmill elevations (1, 4, or 7 degrees). The exercise test consisted of four, 4 min increments of increasing treadmill speed from 1.0 to 3.4 m/sec. Heart rate, blood lactate concentration, and packed cell volume (PCV) were determined, during the last min of each exercise level, and at 4 and 12 mins post exercise. Regardless of treadmill elevation, no differences were observed in pre-exercise heart rate (49 +/- 2) beats/min), lactate (1.2 +/- 0.1 mM), and PCV (0.32 +/- 0.01 litres. Du...
Accuracy of formulae for calculating left ventricular volumes of the equine heart. Echocardiography may be an accurate method of measuring left ventricular (LV) volumes and mass of the horse's heart. If so, studies of the heart size and hypertrophy would be possible. This study evaluated geometric models of the external and internal LV shapes, to determine which could be applied to echocardiographic measurements. We preserved 30 horses' hearts and measured their dimensions and cross sectional areas. These measurements were entered into seven formulae representing different geometric models of the ventricle and its chamber. We derived a correction factor to estimate the long ...
Standardized exercise test and daily heart rate responses of thoroughbreds undergoing conventional race training and detraining. Ten healthy sedentary male Thoroughbreds with previous race training experience were studied for 14 weeks. Horses were trained for 9 weeks, using a program designed after those used commonly in the United States. Horses were trained conventionally by slow trotting (250 m/min) for 2 weeks and galloping (390 to 450 m/min) for 4 weeks, followed by 3 weeks of galloping (440 to 480 m/min) and intermittent sprinting exercises (breezes) at distances between 600 and 1,000 m (900 to 950 m/min). The horses were then pasture rested for 5 weeks. A standardized exercise test (SET) involving an 800-m gallop...
Pulmonary artery, aortic and oesophageal pressure changes during high intensity treadmill exercise in the horse: a possible relation to exercise-induced pulmonary haemorrhage. This study investigated changes in packed cell volume (PCV), pulmonary artery and aortic pressures, and the interaction between oesophageal pressure and pulmonary artery and aortic pressures during strenuous exercise in the horse. It was hypothesised that oesophageal pressure changes summate with pulmonary artery and aortic pressures during exercise and contribute to exercise-induced pulmonary haemorrhage (EIPH). Acute treadmill exercise (10 m/sec, 3 degrees incline) produced increases in heart rate (HR) from 50 to 202 beats/min; mean pulmonary artery pressure (PAP) from 28 to 80 mmHg; mean ao...
Isoproterenol-induced maximal heart rate in normothermic and hyperthermic horses. The heart rate (HR) induced by maximal beta-adrenergic activation, which was elicited by infusion of isoproterenol, was studied in 8 healthy horses before (control) and after hyperthermia was induced by IV administration of 2,4-dinitrophenol (DNP). Isoproterenol was administered IV at 1.0 micrograms.kg-1.min-1 for 3 minutes, and the HR was determined during the final 30 seconds of the infusion. As the rectal temperature increased (P less than 0.001) from 38.2 +/- 0.1 C (mean +/- SEM; normothermic control) to 40.1 +/- 0.1 C at 60 minutes after DNP administration, the isoproterenol-induced HR al...
Cardiopulmonary effects of positive end-expiratory pressure in anesthetized, mechanically ventilated ponies. To investigate the cardiopulmonary effects of positive end-expiratory pressure (PEEP), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After IV induction of general anesthesia, PEEP was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of PEEP in these ponies caused a linear increase in the mean (+/- SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 +/- 0.24 L to 2.2 +/- 0.31, 2.9 +/- 0.32 and 3.4 +/- 0.3 L...
Renal and systemic hemodynamic responses to sustained submaximal exertion in horses. We investigated the effects of 1 h of sustained submaximal exertion on the renal and systemic hemodynamics of six horses. The horses ran on a treadmill at a speed that produced heart rates of 55-60% of each horse's maximum heart rate. Exertion produced heart rates of 121 +/- 6.6 and 126 +/- 6.1 (SE) beats/min after 15 and 60 min, respectively. Cardiac output increased significantly (P less than 0.05) from 70.1 +/- 3.1 to 246.2 +/- 4.7 ml.min-1.kg body wt-1 after 15 min of exertion and thereafter did not change. There was no significant change from rest in p-aminohippuric acid and creatinine cl...
Tracheobronchial perfusion during exercise in ponies. Tracheobronchial circulation during exercise has previously not been examined. Therefore blood flow to the trachea and bronchi (up to 7th generation of branching) was studied in seven healthy adult ponies at rest and during the 3rd and 10th min of exercise performed at a treadmill speed setting of 25 km/h. The ambient air temperature varied from 19 to 20 degrees C and humidity from 35 to 45%. To determine blood flow radionuclide-labeled 15-microns-diameter microspheres were injected into the left ventricle via a catheter advanced from the left carotid artery (exposed using local anesthesia), a...
Relationship between plasmatic concentrations of K, Na and Ca, and ECG from foals during postnatal phase. The correlations between different electrocardiographic variables and plasma concentrations of K, Na and Ca ions were studied in foals of 1 to 14 days of age. The results obtained are only significant in neonate individuals of 1 day of age. Whilst the PQ segment and R wave duration showed a positive linear correlation (p less than or equal to 0.05) with plasma concentrations of Na and Ca ions respectively, the amplitude of the T wave showed a negative linear correlation (p less than or equal to 0.05) with the K ion. Moreover, the variability in duration of the QT and ST intervals can be explai...
Propafenone kinetics in the horse. Comparative analysis of compartmental and noncompartmental models. The propafenone kinetics after intravenous (i.v.) administration have been studied in the horse by a comparative analysis of compartmental and noncompartmental models. The pharmacokinetic parameters showed a large distribution (Vdss = 1021 +/- 211 L) and a high clearance (CI = 7019 +/- 1746 mL/min) of the drug. The plasma concentrations were very low, under 1 microgram/mL, in most cases; after 30 min these concentrations can be considered as nonefficient for the treatment of arrhythmia. There were no significant differences between pharmacokinetic parameters found with the use of compartmental...