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Topic:Hemodynamics
Hemodynamics in horses refers to the study of blood flow and the forces involved in circulation within the equine cardiovascular system. It encompasses the examination of heart function, blood pressure, and the distribution of blood to various tissues and organs. Key parameters in equine hemodynamics include cardiac output, vascular resistance, and blood volume. These factors are integral to understanding how horses respond to exercise, stress, and various health conditions. This page aggregates peer-reviewed research studies and scholarly articles that explore the mechanisms, measurement techniques, and clinical implications of hemodynamic processes in equine physiology and veterinary medicine.
Hemodynamic effects of thyroidectomy in sedentary horses. To investigate hemodynamic effects of thyroidectomy in horses at rest. Methods: 6 healthy aged Quarter Horse mares. Methods: Horses were monitored for 5 months before and 4 weeks after thyroidectomy and for an additional 4 weeks after administration of thyroid hormone supplement (2.5 microg of thyroxine/kg of body weight, PO, q 12 h, and 0.6 microg of triiodothyronine/kg, PO, q 12 h). Responses to thyroid-stimulating hormone (TSH) were measured before and 4 weeks after thyroidectomy. Other variables monitored daily were resting rectal temperature (T), heart rate (HR), respiratory rate (RR), an...
The cardiopulmonary effects of clenbuterol when administered to dorsally recumbent halothane-anaesthetised ponies–failure to increase arterial oxygenation. Clenbuterol (0.8 microg kg(-1) intravenously) was investigated in ponies (small horses) anaesthetised with acepromazine, detomidine and thiopentone, then halothane in oxygen alone (hyperoxic group) or with nitrous oxide (hypoxic group). Following instrumentation, ponies were placed in dorsal recumbency for 60 minutes, clenbuterol (both groups) or a saline control (hyperoxic group) given, and cardiopulmonary parameters monitored for a further 60 minutes. In the hyperoxic group, clenbuterol administration resulted in a transitory (<five minutes) 15 per cent fall in arterial blood pressure and...
Endocrine and metabolic responses to plasma volume expansion during halothane anesthesia in ponies. The study was designed to contribute to identification of the stimulus to adrenocortical activity during halothane anaesthesia in equidae. Two groups of six ponies were premedicated with acepromazine before induction of anaesthesia with thiopentone and maintenance for 120 min with halothane in oxygen. In group H Haemaccel modified gelatine plasma replacer was infused (48+/-13 mL/kg) to maintain mean arterial blood pressure (MABP) close to preanaesthetic values. In group DH, blood pressure was maintained close to preanaesthetic levels with a lower dose of Haemaccel (10 mL/kg) combined with an i...
Effects on the intramuscular blood flow and cardiopulmonary function of anaesthetised ponies of changing from halothane to isoflurane maintenance and vice versa. The effects on intramuscular blood flow and cardiopulmonary parameters of changing from anaesthesia with halothane to isoflurane and vice versa were investigated in six ponies (small horses). Anaesthesia was induced with xylazine, ketamine and diazepam, maintained for one hour with halothane at an end tidal concentration of 1 per cent and then with isoflurane at 1.5 per cent for a further hour (halo/iso). On another occasion the order in which the volatile agents were administered was reversed (iso/halo). After one hour of anaesthesia the mean (sd) arterial blood pressure (MAP) and cardiac out...
Pituitary-adrenocortical effects of methoxamine infusion on halothane anaesthetised ponies. This study investigated whether maintenance of normotension using a methoxamine infusion would prevent activation of the stress response during halothane anaesthesia in ponies. After acepromazine premedication, anaesthesia was induced with thiopentone in six ponies, and maintained for 120 minutes with halothane in oxygen and ventilation to normocapnia. Methoxamine (M, 0.013+/-0.005 mg kg(-1) min(-1)) or saline (C) was infused throughout anaesthesia. Sequential blood samples were taken for cortisol and ACTH assay. During anaesthesia normotension (mean arterial blood pressure 101-124 mm Hg) was ...
Effects of dopamine, dobutamine, dopexamine, phenylephrine, and saline solution on intramuscular blood flow and other cardiopulmonary variables in halothane-anesthetized ponies. To evaluate the effect on intramuscular blood flow (IMBF) and hemodynamic variables of 4 antihypotensive agents given during anesthesia. Methods: 8 ponies. Methods: Halothane-anesthetized ponies (n = 6) positioned in lateral recumbency received, on separate occasions, infusions of each of the following 4 agents in serially increasing dosages or saline solution: phenylephrine hydrochloride (0.25, 0.5, 1, and 2 microg/kg of body weight), dopamine (2.5, 5, 10, and 20 microg/kg), dobutamine (1, 2.5, 5, and 10 microg/kg), and dopexamine (0.5, 1, 5, and 10 microg/kg). Changes in IMBF (by laser-Doppl...
Hepatic blood flow in horses during the recuperative period from maximal exercise. To determine effects of walking or standing on hepatic blood flow of horses after brief, intense exercise. Methods: 6 adult Thoroughbreds (4 mares, 2 geldings). Methods: Horses were preconditioned on a treadmill to establish uniform level of fitness. Once fit, treadmill speed causing each horse to exercise at 120% of maximal oxygen consumption was determined and used in simulated races at 14-day intervals. In a three-way crossover study, horses were exercised at a speed inducing 120% of maximal oxygen consumption until fatigued or for a maximum of 2 minutes. Three interventions were studied: r...
Comparison of two techniques for total intravenous anesthesia in horses. To characterize responses associated with two 1-hour total intravenous anesthesia techniques in horses. Methods: 6 mature, healthy mares. Methods: Each horse was anesthetized 3 times. Treatment order was determined by a series of Latin squares. After baseline measurements and instrumentation, horses were given xylazine (XYL) i.v.; anesthesia was induced 5 minutes later with 10% guaifenesin given i.v., then either ketamine (KET) or propofol (PRO) was given i.v. After anesthesia induction, each horse received an infusion of XYL and either KET or a low or high dose of PRO. Cardiopulmonary variabl...
Local hemodynamics, permeability, and oxygen metabolism during acute inflammation of innervated or denervated isolated equine joints. To determine oxygen metabolism, permeability, and blood flow in isolated joints in response to interleukin 1beta (IL-1beta) and contribution of innervation. Methods: One metacarpophalangeal (MCP) joint of 24 adult horses. Methods: The MCP joint was isolated for 6 hours in a pump-perfused, auto-oxygenated, innervated or denervated preparation. Isolated joints were assigned to the following 4 groups: control, control-denervated, inflamed, and inflamed-denervated, and inflammation was induced by intra-articular injection of IL-1beta. Circuit arterial and venous pressures, flows, and blood gas ten...
Functional anatomy of the cartilage of the distal phalanx and digital cushion in the equine foot and a hemodynamic flow hypothesis of energy dissipation. To examine macro- and microscopic characteristics of cartilage of the distal phalanx (ungual cartilage [UC]) and digital cushion in the equine foot and to relate them to the foot's function of energy dissipation. Methods: 85 horses and 5 foals of various breeds and ages. Methods: Feet, obtained at necropsy, were perfused with India ink (n = 30), latex (5), or polymer plastic (10). Select feet were examined histologically for tissue architecture and to identify elastic fibers. Immunochemistry to identify substance P peptides in nerves (feet from foals) and gold chloride impregnation of axons (n...
Temporal effects of an infusion of dobutamine hydrochloride in horses anesthetized with halothane. To evaluate temporal hemodynamic effects of dobutamine in horses anesthetized with halothane. Methods: 8 adult Thoroughbreds. Methods: Anesthesia was induced by i.v. administration of romifidine and ketamine and maintained using halothane in oxygen. After 60 minutes, dobutamine was administered i.v. for 60 minutes at 4 micrograms/kg of body weight/min. Measurements of left ventricular function were obtained by transesophageal echocardiography and cardiac catheterization. Results: Mean, systolic, diastolic, aortic, pulmonary arterial, and left and right ventricular end-diastolic and systolic pr...
Effect of intravenous lidocaine on halothane minimum alveolar concentration in ponies. This study investigated the effect of lidocaine i.v. on halothane minimum alveolar concentration (MAC) in ponies. Six ponies were anaesthetised with thiopentone and succinylcholine, intubated and anaesthesia maintained with halothane. Ventilation was controlled and blood pressure maintained within clinically acceptable limits. Following a 2 h equilibration period, baseline halothane MAC was determined. The ponies were then given a loading dose of lidocaine (2.5 or 5 mg/kg bwt) or saline over 5 min, followed by a constant infusion of lidocaine (50 or 100 microg/kg/min, or saline, respectively)....
Haemodynamic effects of a sixty minute infusion of dopamine hydrochloride in horses anaesthetised with halothane. To describe the haemodynamic effects of a 60 min infusion of dopamine 4 microg/kg bwt/min during halothane anaesthesia, 7 mature Thoroughbred horses were studied. The infusion began 1 h after induction of anaesthesia by romifidine (100 microg/kg) and ketamine (2.2 mg/kg bwt). Throughout the period of dopamine infusion and for 30 min after its discontinuation, the horses were ventilated by intermittent positive pressure to maintain PaCO2 between 4.6-5.4 KPa. Inspired halothane concentration was adjusted to maintain an end tidal halothane concentration of 0.9%. Haemodynamic variables were measur...
Increase in blood viscosity in the sprinting horse: can it account for the high pulmonary arterial pressure? Blood was taken from 49 Thoroughbred horses before and after racing at the track to determine if frusemide modified the apparent viscosity of the blood and to determine the effects of changes in shear rate and packed cell volume (PCV), associated with strenuous exercise, on apparent and relative viscosities. Small increases in apparent viscosity of the blood (at a specified PCV and shear rate) occurred in horses given frusemide compared to those receiving no frusemide; however, no differences were seen in relative viscosity. Although 2 groups of horses, those receiving frusemide before racing ...
Characteristics of respiratory function during swimming exercise in thoroughbreds. Equine respiratory patterns during swimming were examined in five normal horses. The experiment included a preliminary warming-up stage and 6 circuits of swimming around an annular pool of a 50-meter-circumference. The horses were examined for respiratory rates, intratracheal pressures, inspiratory time (TI), expiratory time (TE), respiratory cycle (T; TI + TE), heart rates, blood lactate concentrations, hematocrit and blood gases. The respiratory rates were maintained around 25/min. Blood gas values changed significantly during swimming. The intratracheal pressures during expiration and inspi...
Effects of a sudden flow reduction on red blood cell rouleau formation and orientation using RF backscattered power. In most studies that were aimed at evaluating the kinetics of red blood cell (RBC) aggregation, human blood was initially circulated at a high shear rate to disrupt the aggregates, and measurements were performed following a complete flow stoppage, during the process of rouleau formation. However, it is known that a very low shear rate can enhance the formation of aggregates, as demonstrated by the modal relationship of the shear-rate dependence of RBC aggregation. The objective of the present study was, thus, to evaluate the influence of sudden flow reductions compared to a complete flow stop...
Comparison of detomidine/ketamine and guaiphenesin/thiopentone for induction of anaesthesia in horses maintained with halothane. This prospective clinical study compared the physiological effects of two commonly used anaesthetic induction techniques in horses maintained with halothane. One hundred horses admitted for elective surgery were randomly allocated to receive either guaiphenesin (to effect) and thiopentone (5 mg/kg), or detomidine (20 microg/kg) and ketamine (2 mg/kg) for the induction of anaesthesia after acepromazine premedication. Anaesthesia was maintained with halothane in oxygen. There were no significant differences in breed, age, sex, weight, type of surgery and duration of anaesthesia between the group...
L-NAME does not affect exercise-induced pulmonary hypertension in thoroughbred horses. The present study was carried out to examine the effects of nitric oxide synthase inhibition with Nomega-nitro-L-arginine methyl ester (L-NAME) on the right atrial as well as on the pulmonary arterial, capillary, and venous blood pressures of horses during rest and exercise performed at maximal heart rate (HRmax). Experiments were carried out on seven healthy, sound, exercise-trained Thoroughbred horses. Using catheter-tip manometers, with signals referenced at the point of the shoulder, we determined phasic and mean right atrial and pulmonary vascular pressures in two sets of experiments [con...
Fluid administration attenuates the haemodynamic effect of frusemide in running horses. The effect of blood volume repletion after frusemide administration on the right atrial and pulmonary artery pressure responses of horses to exercise has not been reported. We examined right atrial and pulmonary artery pressure and plasma atrial natriuretic peptide concentration (ANP) responses to an incremental exercise test in 6 Standardbred mares. Horses were treated, in a 3 way cross over design, with isotonic saline, frusemide (1 mg/kg bwt, i.v.), and frusemide followed 3 h later by lactated Ringer's solution (12 ml/kg bwt, i.v.). Three and a half hours after saline or frusemide administr...
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 ...
Vascular and transsynovial forces of the isolated stationary equine joint. To provide quantitative assessment of forces affecting filtration of synovial fluid in response to incremental changes in arterial and venous hemodynamics. Methods: 7 clinically normal adult horses. Methods: Using a stationary, isolated metacarpophalangeal joint preparation, blood flow (Qa[cir]), tissue perfusion, arterial pressure (Pa[cir]), venous pressure (Pv[cir]), transsynovial fluid flow, total vascular resistance, vascular compliance, and tissue compliance were evaluated before and after arterial and venous pressure manipulations. At isogravimetric conditions, pre- and postcapillary res...
Pulmonary vascular pressures of strenuously exercising Thoroughbred horses after administration of phenylbutazone and frusemide. The present study was carried out to examine the effects of phenylbutazone treatment on the pulmonary haemodynamic effects of frusemide in strenuously exercising horses. Using catheter mounted manometers, whose in vivo signals were referenced at the point of the shoulder, heart rate, right atrial, right ventricular and pulmonary vascular pressures were measured in 3 different sets of experiments. Seven Thoroughbreds were subjected to 1) control (no medications), 2) frusemide control and 3) phenylbutazone + frusemide. The experiments were carried out in random order and were separated by 7 days...
Evaluation of digital and laminar blood flow in horses given a low dose of endotoxin. To measure blood flow in the palmar digital artery and laminae corium, using ultrasonic and laser Doppler flowmetry, respectively. Methods: 6 healthy horses. Methods: Digital blood flow and laminar perfusion, respectively, were measured by placing a flow probe around the palmar digital artery and a laser Doppler flow probe in a hole in the dorsal aspect of the hoof wall. All horses were given saline (0.9% NaCl) solution (1 L, IV, during a 30-minute period). Seven days later, each horse was given endotoxin (0.1 microgram/kg of body weight, IV, in 1 L of saline solution, during a 30-minute perio...
Aorto-cardiac fistulas in seven horses. This report describes the history, clinical, electrocardiographic and echocardiographic findings, treatment, outcome and post-mortem findings in seven horses with aorto-cardiac fistula. Affected horses included 5 stallions, one gelding and one mare; 2 each of the Thoroughbred, Arabian and Standardbred breeds and one Thoroughbred-cross with a mean +/- s.d. age of 12 +/- 4 years, range 6-18 years. The presenting signs were acute distress (four horses), exercise intolerance (two horses) and the lesion was detected during a routine examination in one horse. Five horses had monomorphic ventricular ...
[Intramural blood vessels of the large intestine of the horse (Equus przewalskii f. caballus)]. The vascular system of the large intestine of 12 horses was examined by means of vascular corrosion casts, histology and transmission electron microscopy providing the following results. The Aa. et Vv. breves et longae leave the mesenteric vessels, respectively the subserously on the teniae lying cecal vessels to reach the tela subserosa at the mesenteric margin. The short vessels enter the deeper layers of the wall instantly, whereas the Aa. et Vv. longae move towards the submucosa by penetrating the muscular layers after a variable subserous course. The tela submucosa contains an arterial an...
Effect of platelet-activating factor antagonist L-691,880 on low-flow ischemia-reperfusion injury of the large colon in horses. To determine the effect of platelet-activating factor (PAF) antagonist L-691,880 on low-flow ischemia and reperfusion (I-R) of the large colon in horses. Methods: 12 adult horses. Methods: Horses were anesthetized, and the large colon was exteriorized through a ventral median celiotomy and instrumented. Colonic arterial blood flow was reduced to 20% of baseline (BL) and maintained for 3 hours; flow was then restored, and the colon was reperfused for 3 hours. One of two solutions was administered intravenously 30 minutes before reperfusion: group 1, 10 mL/kg 0.9% NaCl; and group 2, 5 mg/kg PAF ...
