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.
Trim CM, Eaton SA, Parks AH.An 8-year-old Thoroughbred gelding with colic was anesthetized for surgical correction of right dorsal displacement of the ascending colon. Removal of the nasogastric tube at the end of surgery resulted in hemorrhage from the nares and loss of 24 L of blood. Treatment included administration of acetated Ringer's solution, hypertonic saline solution, and dobutamine. A blood transfusion was started after hemorrhage was controlled, and arterial pressure was restored to the prehemorrhage value, but was stopped after infusion of 2.7 L of blood because of a suspected adverse reaction. This case indi...
Young LE, Blissitt KJ, Clutton RE, Molony V.To evaluate the hemodynamic effects of a 60-minute infusion of dopexamine in horses anesthetized with halothane. Methods: 7 adult Thoroughbreds. Methods: Measurements of left ventricular function obtained by transesophageal Doppler echocardiography and cardiac catheterization. Results: Infusion of dopexamine (4 micrograms/kg of body weight/min) significantly increased heart rate, cardiac output, maximal rates of increase and decrease of left ventricular pressure, and maximal acceleration and maximal velocity of aortic blood flow. Left ventricular ejection time significantly increased, and pre-...
Jones PA, Tomasic M, Gentry PA.To evaluate the oncotic, hemodilutional, and hemostatic effects of IV infusions of a large volume of isotonic saline solution and 2 doses of 6% hydroxyethyl starch (HES) in clinically normal ponies. Methods: 12 adult ponies. Methods: Ponies were assigned to 3 treatment groups and received the following IV infusions: 80 ml of 0.9% sodium chloride/kg; 10 ml of 6% HES (in 0.9% sodium chloride)/kg; or 20 ml of 6% HES (in 0.9% sodium chloride)/kg. Blood samples were collected for determination of colloid oncotic pressure (COP), PCV, plasma total protein concentration, platelet count, von Willebrand...
Birks EK, Mathieu-Costello O, Fu Z, Tyler WS, West JB.Thoroughbred horses develop extremely high pulmonary vascular pressures during galloping, all horses in training develop exercise-induced pulmonary hemorrhage, and we have shown that this is caused by stress failure of pulmonary capillaries. It is known that the capillary transmural pressure (Ptm) necessary for stress failure is higher in dogs than in rabbits. The present study was designed to determine this value in horses. The lungs from 15 Thoroughbred horses were perfused with autologous blood at Ptm values (midlung) of 25, 50, 75, 100 and 150 mmHg, and then perfusion fixed, and samples (d...
Cipone M, Pietra M, Gandini G, Boari A, Guglielmini C, Venturoli M.A pulsed wave-Doppler ultrasonographic evaluation of common carotid arterial blood flow was carried out on 63 healthy Italian Saddlebred horses. Vessel diameter and tracing morphology were evaluated and blood flow parameters (systolic, diastolic and mean velocity, acceleration and deceleration of the systolic wave, carotid pulse volume) were calculated and correlated with class variables (sex, age and body weight). On the basis of the presence of an incisure in the ascending branch of the systolic curve, subjects were divided in two groups: one with a bifid systolic curve and the other with a ...
McConaghy FF, Hales JR, Hodgson DR.Heat-induced increases in skin blood flow (BF) are well known to be reduced if exercise is superimposed.' However, whether exercise-induced increases in muscle BF are compromised by superimposed heat stress remains a controversial issuc. The horse has now been studied because of its human-like thermoregulatory mechanisms and good exercise capacity.
Flaherty D, Reid J, Welsh E, Monteiro AM, Lerche P, Nolan A.The pharmacodynamics of infusions of propofol alone (group 1) were compared with the pharmacodynamics of infusions of propofol and ketamine together (group 2) in eight ponies undergoing castration. Anaesthesia was induced with detomidine, 20 micrograms kg-1, followed by ketamine, 2.2 mg kg-1. Subsequently, a bolus dose of propofol, 0.5 mg kg-1, was administered intravenously to both groups, and an infusion of propofol was given for an average of 74 minutes to group 1, and an infusion of propofol and ketamine was given for 60 minutes to group 2. The mean (SD) infusion rates of propofol were 0.3...
Wood SC, Fedde MR.Splenic contraction in racing horses increases the hematocrit (hct), thereby increasing blood viscosity. We tested as to whether racing also affects the elastic properties of blood. Mares and geldings were studied for thus purpose. After racing, there was: (i) an increased erythrocyte count independent of gender and race distance (0.32 to 1.7 km): (ii) an increased mean erythrocyte volume in both sexes; (iii) an increased heterogeneity of RBC size in both sexes; (iv) an increased plasma fibrinogen concentration and erythrocyte sedimentation rate in both sexes; and (v) an increased elastic yiel...
Christley RM, Hodgson DR, Evans DL, Rose RJ.The relationship between different grades of laryngeal function, as assessed by endoscopy at rest, and the measurements of indices of gas exchange and exercise capacity was assessed during a standardised treadmill exercise test in 149 horses. Horses with abnormalities other than idiopathic laryngeal hemiplegia (ILH) were excluded from the study and laryngeal function was graded according to an established system. There were no significant differences in age, weight, maximum oxygen uptake, maximum carbon dioxide production, maximum respiratory exchange ratio, maximum oxygen pulse and run time b...
Blissitt KJ, Young LE, Jones RS, Darke PG, Utting J.Measurement of cardiac output by Doppler echocardiography were compared to simultaneous measurements by thermodilution in 9 conscious horses. In the Doppler technique, mean blood flow velocities for estimation of cardiac output were recorded from the aorta and pulmonary artery. The flow area of each vessel was calculated from the vessel diameter, measured from a 2-dimensional ultrasound image. Differences in the site and method of measuring the vessel diameter altered the estimation of cardiac output by the Doppler method. Cardiac output was modified by the i.v. infusion of 4 micrograms/kg bwt...
Young LE, Blissitt KJ, Bartram DH, Clutton RE, Molony V, Jones RS.In order to determine if transoesophageal Doppler echocardiography could be used to estimate cardiac output in anaesthetized horses, we have compared the technique with estimations of cardiac output by thermodilution in eight healthy adult thoroughbreds. Measurements of aortic blood flow velocity were made by high pulse repetition frequency (HPRF) and continuous wave (CW) Doppler echocardiography from a 3.5-MHz transoesophageal probe. Cardiac output was increased during the study by administration of dobutamine, providing a range of cardiac output measurements by thermodilution from 15.0 to 64...
Still J, Serteyn D, van der Merwe CA.Anaesthesia was induced in horses (n = 6) with a mixture of thiopentone and guaiphenesin and maintained by mechanical ventilation with a mixture of oxygen, air and isoflurane. Inspiratory and end-expiratory concentrations of oxygen, carbon dioxide and isoflurane were measured. Electrocardiography was used to evaluate heart rate and rhythm. Mean systemic arterial pressure (SAPm), pulmonary artery pressure (PAPm), right atrial pressure (RAPm) and pulmonary capillary wedge pressure (PCWP) were measured directly. Cardiac output was determined using the thermodilution method. Microcirculation in th...
Grubb TL, Foreman JH, Benson GJ, Thurmon JC, Tranquilli WJ, Constable PD, Olson WO, Davis LE.Calcium gluconate was administered to conscious horses at 3 different rates (0.1, 0.2, and 0.4 mg/kg/min for 15 minutes each). Serum calcium concentrations and parameters of cardiovascular function were evaluated. All 3 calcium administration rates caused marked increases in both ionized and total calcium concentrations, cardiac index, stroke index, and cardiac contractility (dP/dtmax). Mean arterial pressure and right atrial pressure were unchanged; heart rate decreased markedly during calcium administration. Ionized calcium concentration remained between 54% and 57% of total calcium concentr...
Manohar M, Goetz TE.Exercise-induced pulmonary hemorrhage (EIPH) is a common occurrence in racehorses. The objective of this study was to compare pulmonary vascular pressures of healthy Thoroughbred horses with and without postexertion endoscopically detectable fresh blood in the trachea. The nasopharynx, larynx, and trachea (down to the carina) of horses were examined weekly with an endoscope 55-60 min postexertion, and the diagnosis of EIPH was confirmed by the presence of fresh blood in the trachea. Measurements of heart rate and right atrial, pulmonary arterial, and pulmonary arterial wedge pressures were mad...
Manohar M, Goetz TE, Griffin R, Sullivan E.To determine the effects of phenylbutazone administration on heart rate and right atrial and pulmonary vascular pressures in Thoroughbreds during rest and during exercise performed at maximal heart rate. Methods: 7 healthy, exercise-conditioned Thoroughbreds. Methods: Horses were studied on 3 occasions: without medication [control], after i.v. administration of phenylbutazone (4.4 mg/kg of body weight) at 12-hour intervals for 2 days and a final dose given 1 hour before exercise, and after i.v. administration of phenylbutazone for 2 days in the same manner, but with the final dose given 24 hou...
Weiss DJ, Geor RJ, Burger K.To determine whether pentoxifylline treatment altered hematologic, rheologic, electrolyte, or blood gas test results of Thoroughbreds during submaximal treadmill exercise. Methods: 5 healthy Thoroughbreds that had raced within the past year and had no history of exercise-induced pulmonary hemorrhage. Methods: Mixed venous blood samples were obtained before exercise, at treadmill speeds of 9 and 13 m/s, and 20 minutes after exercise; hematologic, rheologic, electrolyte, and blood gas test results were determined. Results: Pentoxifylline treatment resulted in a 45% reduction in RBC filtration pr...
Skarda RT, Muir WW.To examine and compare effects of 2 alpha 2-adrenergic receptor agonists, xylazine and detomidine, administered into the sacrococcygeal epidural space to induce safe and effective perineal analgesia on cardiovascular and respiratory functions, head ptosis, and position of pelvic limbs in healthy mares. Methods: 8 healthy mares. Methods: Blood samples were drawn and systemic hemodynamics were determined, including cardiac output and pulmonary arterial, systemic arterial, and right atrial pressures. Two-way ANOVA with repeated measures was used to detect significant (P < 0.05) differences bet...
Bernard SL, Glenny RW, Erickson HH, Fedde MR, Polissar N, Basaraba RJ, Hlastala MP.We determined the spatial distribution of pulmonary blood flow at rest and during increasing levels of exercise (34, 59, and 90% of maximal oxygen consumption) in Thoroughbred racehorses (n = 4) using 15-microns fluorescent microspheres. After the horses were killed, the lungs were flushed free of blood, removed, air-dried at total lung capacity, and sliced into isogravitational planes, which were sampled in a systematic fashion for three-dimensional reconstruction. The fluorescence was measured for quantification of blood flow. Mean pulmonary blood flow heterogeneity (expressed as a coefficie...
Clarke KW, Song DY, Alibhai HI, Lee YH.Cardiopulmonary parameters were measured in 12 ponies (small horses) before anaesthesia and, following induction with xylazine and ketamine, during maintenance of anaesthesia with desflurane. In six of the ponies (group A) anaesthesia was maintained for three hours with desflurane at an end-tidal concentration of 7.4 per cent. In the other six ponies (group B), anaesthesia was maintained in the same way for one hour and then the effects of end-tidal desflurane concentrations of 7.4 per cent and 9.6 per cent with and without artificial ventilation were investigated. In group A ponies the arteri...
Moore RM, Charalambous AC, Masty J.To measure colonic arterial (CA) and colonic venous (CV) plasma neuropeptide concentrations during low-flow ischemia and reperfusion of the large colon in horses. Methods: 10 adult horses. Methods: CA and CV plasma samples collected from anesthetized horses during experimentally induced low-flow colonic ischemia and reperfusion were assayed for vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and substance P (SP), using radioimmunoassays. In 6 anesthetized horses, colonic ischemia (20% of baseline (BL]) was maintained for 3 hours, then blood flow was restored an...
Mitten LA, Hinchcliff KW, Pate JL.The effect of inhibition of cyclooxygenase activity on the hemodynamic response to exertion was examined in 6 horses. Rates of O2 consumption and CO2 production and carotid, pulmonary arterial, and right atrial pressures were measured while the horses performed a standardized exercise test on a treadmill after treatment with phenylbutazone or a placebo. Phenylbutazone (8.8 mg/kg p.o. for 2 days and 4.4 mg/kg i.v. 60 min before exertion) abolished the exertion-induced increases in plasma 6-ketoprostaglandin F1 alpha and thromboxane B2 concentrations, confirming inhibition of cyclooxygenase acti...
Moore RM, Bertone AL, Muir WW.To evaluate the effect of high-molecular weight (MW) dextran macromolecules on low-flow ischemia and reperfusion of the large colon in horses. Methods: Horses subjected to low-flow ischemia and reperfusion of the large colon were treated with either 0.9 NaCl (group 1, n = 6) or high-MW dextran (group 2, n = 6) solutions. Methods: 12 adults horses. Methods: Horses were subjected to 3 hours' low-flow ischemia followed by 3 hours' reperfusion. A dose of either 0.9% NaCl or a 6% solution of high-MW (250,000) dextran (10 ml/kg of body weight) was administered i.v., 30 minutes prior to reperfusion. ...
McConaghy FF, Hodgson DR, Rose RJ, Hales JR.Radioactive microspheres were used to measure cardiac output and blood flow to most major tissues in 4 ponies at rest in thermoneutral (16 degrees C/60% RH) and mildly hot (41 degrees C/34% RH) environments. In response to heat stress there were increases in cardiac output (2-fold), respiratory frequency (5-fold), blood flow to the skin of the body (3-fold), and limbs (50%), respiratory muscles (2-fold) and the upper respiratory tract (3-fold). Ponies were able to maintain body temperature in the hot environment by increasing blood flow to the tissues involved in heat dissipation, while blood ...
Williams DO, Boatwright RB, Rugh KS, Ross CR, Sarazan RD, Garner HE, Griggs DM.Adult-grade ponies were surgically instrumented with a Doppler flow probe and pneumatic cuff occluder on the left anterior descending coronary artery (LAD), sonomicrometry crystals and intraventricular micromanometer in the left ventricle, and catheters in the left atrium, anterior interventricular vein, and, in some animals, the LAD. Conscious-animal studies were begun 2 wk after surgery. Measured variables included regional left ventricular systolic function, end-diastolic wall thickness, oxygen extraction, lactate extraction, and hydrogen ion release. Changes in collateral perfusion were de...
Weiss DJ, Geor RJ, Burger K.To determine whether furosemide treatment altered the blood flow properties and serum and RBC electrolyte concentrations of Thoroughbreds during submaximal treadmill exercise. Methods: Thoroughbreds were subjected to submaximal treadmill exercise with and without treatment with furosemide (1 mg/kg of body weight, IV). Methods: 5 healthy Throughbreds that had raced within the past year and had no history of exercise-induced pulmonary hemorrhage. Methods: Venous blood samples were obtained before exercise, at treadmill speeds of 9 and 13 m/s, and 10 minutes after exercise, and hemorheologic and ...
Sinha AK, Gleed RD, Hakim TS, Dobson A, Shannon KJ.The object of this study was to relate pulmonary capillary pressure to arterial and wedge pressures during exercise. Pulmonary vascular pressures were measured in six standardbred horses exercising at speeds equivalent to 75, 90, and 100% of maximal heart rate. Vascular pressures were measured with transducer-tip catheters and expressed relative to esophageal pressure. Pulmonary capillary pressure was estimated by the arterial-occlusion technique modified for exercise. Mean pulmonary arterial, capillary and wedge pressures increased from 30.5 +/- 6.3, 17.8 +/- 4.3, and 13.4 +/- 1.6 mmHg, respe...
Bryant CE, Clarke KW, Thompson J.Medetomidine was administered intravenously to six sheep at 5, 10 and 20 micrograms kg-1 and to one horse and four ponies at 5 and 10 micrograms kg-1. In both species medetomidine resulted in significant decreases in heart rate and cardiac output and, initially, in an increase in arterial blood pressure. In the ponies this increase in blood pressure was followed by a significant and prolonged decrease, but in the sheep the secondary decrease in blood pressure was not statistically significant. In the sheep, the three doses of medetomidine resulted in profound and significant decreases in arter...
Mama KR, Steffey EP, Pascoe PJ.To evaluate selected hemodynamic, respiratory, and behavioral responses to propofol in horses premedicated with xylazine or detomidine. Methods: Xylazine (0.5 and 1.0 mg/kg of body weight) was administered IV on different days to each of 6 horses prior to IV administration of propofol (2 mg/kg). In a second group of 6 horses, detomidine (15 and 30 micrograms/kg) was similarly studied. Methods: 2 groups of 6 mature healthy horses. Methods: Rectal temperature, heart and respiratory rates, arterial blood gas tensions, and direct arterial blood pressures were recorded before and at fixed intervals...
Kindig CA, Ramsel C, McDonough P, Poole DC, Erickson HH.Capillary stress failure-induced (exercise-induced) pulmonary haemorrhage (EIPH) during intense running in horses is thought to involve both intravascular (i.e. mean pulmonary arterial pressure [Ppa] > 100 mmHg) and extravascular (e.g. negative inspiratory pressure swings) mechanisms. Objective: That inclined running would reduce breathing frequency (coupled to stride frequency) and increase tidal volume thus increasing lung volume changes and intrapleural pressure swings resulting in more pronounced EIPH. Methods: Six Thoroughbred horses were run to volitional fatigue (incremental step tes...
Flaherty D, Reid J, Welsh E, Monteiro AM, Lerche P, Nolan A.The pharmacodynamics of infusions of propofol alone (group 1) were compared with the pharmacodynamics of infusions of propofol and ketamine together (group 2) in eight ponies undergoing castration. Anaesthesia was induced with detomidine, 20 micrograms kg-1, followed by ketamine, 2.2 mg kg-1. Subsequently, a bolus dose of propofol, 0.5 mg kg-1, was administered intravenously to both groups, and an infusion of propofol was given for an average of 74 minutes to group 1, and an infusion of propofol and ketamine was given for 60 minutes to group 2. The mean (SD) infusion rates of propofol were 0.3...
Wilson KAT, Raisis AL, Drynan EA, Lester GD, Hosgood GL.To determine agreement between invasive blood pressures measured in three peripheral arteries in anaesthetized horses undergoing elective surgery. Methods: Prospective balanced incomplete block design. Methods: A total of 18 client-owned horses. Methods: Invasive blood pressure (IBP) was measured simultaneously in one of the following three combinations: 1) transverse facial and facial artery; 2) transverse facial and metatarsal artery; and 3) facial and metatarsal artery. The agreement in blood pressure measured for each combination was performed in six horses. At each sample time, systolic (...
Hardy J, Bertone AL, Muir WW.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...
Garner HE, Hahn AW, Salem C, Coffman JR, Hutcheson DP, Johnson JH.Acute laminitis-hypertension was produced experimentally by carbohydrate overloading of the gastrointestinal tract in 8 horses, and the resulting hemodynamic changes were measured. Statistically significant (P less than 0.01) increases in cardiac output, left ventricular ejection rate, heart rate, and arterial pressure were related to statistically nonsignificant changes in peripheral resistance and a delayed (Obel grade 3 plus 24 hours) decrease in plasma volume. When compared with control values, the doubling of cardiac output and left ventricular ejection rate simultaneous with little or no...
Wilsterman S, Hackett ES, Rao S, Hackett TB.To investigate a technique of central venous pressure (CVP) measurement using a newly developed catheter in healthy adult horses. Methods: Prospective experimental study. Methods: University research facility. Methods: Twenty healthy adult horses. Methods: An equine central venous catheter was inserted into the jugular vein to a length of approximately 80 cm from the mid-cervical region in an attempt to catheterize the pulmonary artery. Pulmonary arterial catheterization was confirmed by echocardiography. Insertion distance and pressure were measured at this location with a disposable manomete...
Hoffmann KL, Wood AK, Kirby AC.To obtain Doppler ultrasonographic images of renal arteries in horses and to establish reference range values for systolic and diastolic renal arterial blood flow and resistive indices. Also to determine whether Doppler ultrasonography could be used in horses to detect changes in renal blood flow after IV administration of furosemide. Methods: 11 clinically normal adult horses. Methods: Pulsed-wave Doppler examinations were performed on arcuate arteries of 5 sedated horses. Continuous-wave Doppler examinations were performed on pyelorenal arteries in 7 nonsedated horses and were repeated in 6 ...
Moore JN, Garner HE, Shapland JE, Hatfield DG.Effects of a sublethal IV dose (10 micrograms/kg of body weight) of Escherichia coli endotoxin were studied in 7 conscious ponies. Arterial blood gases and plasma lactic acid were determined periodically throughout the 180 minutes of the study. Arterial hypoxemia occurred within 5 minutes despite intense hyperventilation. Colic and diarrhea occurred in all ponies within 30 minutes after endotoxin administration. Metabolic acidosis developed within 30 minutes and persisted throughout the study, indicating widespread reduced tissue perfusion.
Andrade FSRM, Ambrósio AM, Rodrigues RR, Faccó LL, Gonçalves LA, Garcia Filho SG, Dos Santos RT, Rossetto TC, Pereira MAA, Fantoni DT.Electrical impedance tomography (EIT) has been an essential tool for assessing pulmonary ventilation in several situations, such as the alveolar recruitment maneuver (ARM) in PEEP titration to maintain the lungs open after atelectasis reversion. In the same way as in humans and dogs, in horses, this tool has been widely used to assess pulmonary aeration undergoing anesthesia, mechanical ventilation, recruitment maneuver, standing horses, or specific procedures. Unassigned: The present study aimed to evaluate the distribution of regional ventilation during ARM based on lung monitoring assessmen...
Jarvis KA, Steffey EP, Tyler WS, Willits N, Woliner M.Results of recent investigations in humans and dogs indicate that gravity-independent factors may be important in determining the distribution of pulmonary blood flow. To further evaluate the role of gravity-independent factors, pulmonary blood flow distribution was examined using 15-microns radionuclide-labeled microspheres in five prone ponies over 5 h of pentobarbital sodium anesthesia. The ponies were killed, and the lungs were excised and dried by air inflation (pressure 45 cmH2O). The dry lungs were cut into transverse slices 1-2 cm thick along the dorsal-ventral axis, parallel to gravit...
Boegli J, Schwarzwald CC, Mitchell KJ.Noninvasive blood pressures (NIBP) and pulse pressures (PP) have not been published in horses with aortic and mitral regurgitation (AR or MR). Objective: To investigate NIBP and PP in healthy Warmblood horses and horses with AR and MR and propose PP cutoffs to identify and stage AR severity. Methods: Seventy-three Warmblood horses (healthy, 10; AR, 31; MR, 32). Methods: Retrospective study. All horses had NIBP and an echocardiogram recorded. Cases were categorized based on severity of regurgitation. Pulse pressures were compared among healthy, MR, and AR groups and among AR severity groups. Cu...
Hallowell GD, Corley KT.Hypertonic saline and hydroxyethyl starches have been proposed as alternatives to isotonic crystalloids for reversal of hypovolemia in horses with colic. However, no direct comparison of these fluids has been performed in a clinical setting. Objective: Preoperative administration of hypertonic saline or pentastarch would produce similar effects on intra operative hemodynamics in horses with colic. Methods: Thirty horses requiring colic surgery were enrolled in this prospective, randomized, open-label clinical trial. Inclusion criteria were owner consent, and at least 2 of 3 clinicopathologic a...
Hatazoe T, Kubota C, Fujiki M, Misumi K.To evaluate the influence of mating behavior on cardiac function, changes in heart rate (HR), electrocardiogram (ECG), hematocrit (Hct) and serum concentration of alpha-atrial natriuretic peptide (alpha-ANP) were evaluated in 10 clinically sound Thoroughbred stallions before and after mating behavior. The stallions were submitted twice to experimental pseudomating in the same month in 2009 and 2010. Measurements and blood samples were collected at a stable before mating (baseline) and at a covering yard before and after mating. ECG was recorded by a Holter-ECG system. Arrhythmias were detected...
Bucca S, De Oliveira IRS, Cunanan JC, Vinardell T, Troedsson MHT.Assessment of pregnancy viability in the equine patient is currently based on gestational profiles of limited prognostic value. In recent years Doppler technology has been applied to uterine and umbilical arteries of pregnant mares to monitor fetal responsive haemodynamics, suggestive of compromise. To date, uterine artery Doppler indices failed to provide sufficient evidence of pregnancy viability and the umbilical cord of the equine fetus is inconsistently visualized past 250 days gestation. The objectives of this study were to: i) evaluate intracranial blood flow impedance by Doppler examin...
DeRossi R, Sampaio BF, Varela JV, Junqueira AL.Epidural administration of bupivacaine and meperidine produces analgesia in several animal species and in humans. A prospective randomized study was conducted in 18 healthy horses to compare the effect of these 2 drugs administered by the epidural route. Animals were divided into 3 treatment groups of 6 animals each. All drugs were injected by the epidural route in all animals between the 1st and 2nd coccygeal vertebrae. Treatment 1 (BUP)--0.06 mg/kg of body weight of 0.5% hyperbaric bupivacaine; treatment 2 (MEP)--0.6 mg/kg of body weight of 5% meperidine; treatment 3 (SS)--0.9% saline soluti...
Dixon PM.Horses clinically affected with chronic obstructive pulmonary disease (COPD) were found to have pulmonary artery hypertension which was associated with systemic arterial hypoxia. The pulmonary hypertension in symptomatic COPD-affected horses was partially reversible upon remission of clinical signs or by oxygen administration. The induction of acute hypoxaemia caused an increase in pulmonary artery pressure in both normal and COPD-affected horses.
Manohar M.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...
De Lange L, Vernemmen I, van Loon G, Decloedt A.The ductus arteriosus (DA) and foramen ovale (FO), including the septum primum (SP) and septum secundum (SS), are important structures in fetal circulation and are unexplored in neonatal equids. The objective of this study is to describe echocardiographic characteristics in a hospital-based population of neonatal foals. On days 2, 5 and 10 after parturition, cardiac ultrasound was performed, and clinical data were collected in healthy and diseased Warmblood foals. Fifty healthy ( = 15) and diseased ( = 35) Warmblood foals were examined. A left-sided and right-sided holosystolic murmur was audi...
Eaton SA, Allen D, Eades SC, Schneider DA.Starling forces and hemodynamics in the digits of 5 horses were studied during early laminitis induced by oral administration of an aqueous extract of black walnut (Juglans nigra). The black walnut extract was prepared from heartwood shavings and was administered by nasogastric tube. Heart and respiratory rates, rectal temperature, central venous and arterial pressures, digital pulses, and signs of lameness were monitored. Blood samples were collected for determination of WBC count, hemoglobin concentration, and PCV and for endotoxin and tumor necrosis factor assays. Total WBC count and centra...
Luna SP, Taylor PM, Bloomfield M.To investigate the effects of inhalation and total IV anesthesia on pituitary-adrenal activity in ponies. Methods: 9 healthy ponies: 5 geldings and 4 mares. Methods: Catheters were placed in the cavernous sinus below the pituitary gland and in the subarachnoid space via the lumbosacral space. After 72 hours, administration of acepromazine was followed by induction of anesthesia with thiopentone and maintenance with halothane (halothane protocol), or for the IV protocol, anesthesia induction with detomidine and ketamine was followed by maintenance with IV infusion of a detomidine-ketamine-guaif...
McKeever KH, Hinchcliff KW, Reed SM, Hamlin RL.Six intact (IN) and five splenectomized (SP) mares were subjected to an incremental exercise test to examine the effects of splenectomy on blood pressure responses during exercise. During the test the horses ran up a 6 degree grade on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s every 1 min until heart rate (HR) reached a plateau. Hemodynamic data were collected continuously and analyzed for the last 18 s of the 4, 5, 6, and 7 m/s steps of the exercise test. There were no differences (P > 0.05) between the groups for resting means for any parameter measured in the...
Manohar M.It has been reported in exercising ponies that O2 supply to all regions of the brain increased primarily due to a large increment in CaO2 and it was implied that this may reflect a generalized increase in brain metabolism during strenuous exercise. Splenectomy ameliorates the rise in CaO2 observed with exercise in ponies. Thus, the objective of the present study was to examine changes in regional brain blood flow and O2 supply of splenectomized ponies with sub-maximal and maximal exercise and to compare these data with previous observations in normal ponies. It was reasoned that in the absence...
Schnuelle ML, Hopster K, Toribio RE, Hurcombe SD.To compare the effects of 7.2% hypertonic and 0.9% isotonic saline (sodium chloride) solutions on cardiovascular parameters and plasma arginine vasopressin (AVP) concentrations in healthy, isoflurane-anesthetized horses. Methods: 8 healthy horses. Methods: In a prospective, randomized, crossover study, horses were anesthetized with isoflurane twice with a 14-day washout period between anesthetic episodes. While anesthetized, horses received a bolus (4 mL/kg) of 7.2% hypertonic saline solution (HS) or 0.9% isotonic saline solution (IS). Heart rate; systolic, mean, and diastolic arterial blood p...
Wagner AE, Dunlop CI, Wertz EM, Chapman PL.To determine whether hemodynamic responses of halothane-anesthetized horses undergoing surgical procedures depended on anesthetic induction protocols used, and to determine whether hemodynamic responses to surgical manipulation could be detected. Methods: Prospective experimental study without controls. Methods: 36 clinically normal horses. Methods: Horses were allotted to 5 groups according to anesthetic induction protocol: acepromazine/guaifenesin/thiamylal, acepromazine/guaifenesin/ketamine, xylazine/guaifenesin/thiamylal, xylazine/guaifenesin/ketamine, and xylazine/diazepam/ketamine. Anest...
Vera L, Campos Arias D, Muylle S, Stergiopulos N, Segers P, van Loon G.Arterial rupture in horses has been observed during exercise, after phenylephrine administration or during parturition (uterine artery). In human pathophysiological research, the use of computer models for studying arterial hemodynamics and understanding normal and abnormal characteristics of arterial pressure and flow waveforms is very common. The objective of this research was to develop a computer model of the equine arterial circulation, in order to study local intra-arterial pressures and flow dynamics in horses. Morphologically, large differences exist between human and equine aortic arc...
Littlejohn A, Howell W, Killeen V.In ten Thoroughbred racehorses which suffered epistaxis during a race, the mean pulmonary arterial diastolic pressure (PADP) was significantly higher, and the mean pulmonary arterial oxygen tension (PaO2) was significantly lower, than the corresponding mean values of a sample of fourteen clinically normal Thoroughbreds in training. The authors conclude that in horses with epistaxis during a race, pulmonary dysfunction may persist for up to two months after the episode, and that the results indicate a need for pulmonary function studies before and after racing, in order to resolve problems conc...
Hall LW, Nigam JM.Central venous pressure measurements were made in 74 horses and ponies free from clinical evidence of cardiopulmonary disease. Using the sternal manubrium as the zero reference point, the mean value obtained was 12 cm H2O (S.D. +/- 6). There was a significant correlation with body weight (r=0.6, p less than 0.001) but there was none with age, sex, breed or type. During halothane anaesthesia, using the same reference point, the mean value was 24.5 cm H2O (S.D. +/- 6) in 28 animals in right lateral recumbency, 29 cm H2O (S.D. +/- 8) in 17 animals in left lateral recumbency and -6 cm H20 (S.D. +/...
Muir WW, Milne DW, Skarda RT.Intravenous administration of furosemide in the horse resulted in an immediate and significant decrease in right atrial pressure, pulmonary arterial pressure, pulmonary arterial wedge pressure, cardiac output, and stroke volume (P less than 0.05). There was a significant increase in total systemic vascular resistance and heart rate (P less than 0.05). There were no significant alterations in mean arterial pressure. Coincidental with these hemodynamic changes were increased urine production and associated increase in packed cell volume and total serum protein. All variables except cardiac outpu...
Bennett RC, Taylor PM, Brearley JC, Johnson CB, Luna SP.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...
Muir WW, Sams RA, Hubbell JA, Hinchcliff KW, Gadawski J.To determine the effects of IV administration of enalaprilat on cardiorespiratory and hematologic variables as well as inhibition of angiotensin converting enzyme (ACE) activity in exercising horses. Methods: 6 adult horses. Methods: Horses were trained by running on a treadmill for 5 weeks. Training was continued throughout the study period, and each horse also ran 2 simulated races at 120% of maximum oxygen consumption. Three horses were randomly selected to receive treatment 1 (saline [0.9% NaCl] solution), and the remaining 3 horses received treatment 2 (enalaprilat; 0.5 mg/kg of body weig...
