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.
Harfoush K, Guintard C, Desfontis JC, Thorin C, Douart C, Mallem MY, Betti E.Dysfunction of venous valves can lead to hemodynamic disorders causing venous stasis, which would favour the occurrence of equine laminitis. However, very few studies have investigated venous valves in the horse digit. The purpose of this study was to compare valvular density between thoracic and pelvic limbs and to study the relationship between valvular density of veins and their location, diameter and wall thickness. After dissection, valvular density was calculated based on the number of valves counted in the principal veins of 7 thoracic and 7 pelvic limbs from 7 horses. Our results showe...
Drynan EA, Schier M, Raisis AL.To determine the bias and precision of noninvasive versus invasive blood pressure measurements obtained using the Surgivet V9203 in anaesthetized horses; to compare these with the current American College of Veterinary Internal Medicine Hypertension Consensus Panel (AHCP) and Veterinary Blood Pressure Society (VBPS) recommendations; and to investigate whether noninvasive blood pressure monitoring could be a clinically useful alternative to invasive blood pressure monitoring in anaesthetized horses. Methods: Prospective clinical study in a university teaching hospital. Methods: Forty-three hors...
Ferreira JC, Ignácio FS, Rocha NS, Thompson DL, Pinto CR, Meira C.The present experiment was divided into two studies to investigate the effect of age and endometrial degeneration on uterine blood flow of mares throughout the immediate post-breeding period. In study 1, uterine blood flow was characterized in mares (n = 7 mares/group) with minimal, moderate or severe endometrial degenerative changes (GI, GII and GIII, respectively). In study 2, the effect of age was investigated using young (≤ 6 years) and old (≥ 15 years) mares (n = 7 mares/group). Uterine vascular perfusion and mesometrial pulsatility index (PI) were evaluated every hour from H0 (moment...
Brünisholz HP, Schwarzwald CC, Bettschart-Wolfensberger R, Ringer SK.The aim of the present study was to investigate the effect of pentastarch on colloid osmotic pressure (COP) and cardiopulmonary function during and up to 24 h after anaesthesia in horses. Twenty-five systemically healthy horses were anaesthetised using isoflurane-medetomidine balanced anaesthesia. Twelve were assigned to treatment with hydroxyethyl starch (HES) (H group) and 13 to no HES (NH group). In the H group, 6 mL/kg of pentastarch 10% HES (200/0.5) was infused over 1 h starting 30 min after induction of anaesthesia. Horses of the NH group received an equal amount of lactated Ringer's so...
Van Der Vekens N, van Dievoet MA, De Puydt H, Decloedt A, Ven S, De Clercq D, Deprez P, van Loon G.Although cardiac troponin T (cTnT) assays have been used to detect myocardial damage in horses, a cTnT assay has not been analytically validated, to our knowledge. The aims of this study were to estimate the precision of a high-sensitivity cTnT assay in horses and determine the effect of hemolysis on the measured cTnT concentration. Serum samples from horses were mixed in 3 different pools. Pool 1 consisted of samples from 3 healthy horses, pool 2 from 6 horses with heart failure or atypical myopathy, and pool 3 from 10 horses with atypical myopathy. The within- and between-run coefficients of...
Kutter AP, Bettschart-Wolfensberger R, Schwarzwald CC, Portier KG, Ringer SK.To evaluate the non-calibrated, minimally invasive cardiac output (CO) monitor FloTrac/Vigileo (FloTrac) against thermodilution (TD) CO in standing horses. Methods: Prospective, experimental trial. Methods: Nine adult horses weighing a median (range) of 535 (470-602) kg. Methods: Catheters were placed in the right atrium, pulmonary artery and carotid artery under local anaesthesia. CO was measured 147 times by TD and FloTrac and indexed to body weight. Changes in CO were achieved with romifidine or xylazine and dobutamine constant rate infusions. Bland-Altman analysis, concordance and polar pl...
Tearney CC, Guedes AG, Brosnan RJ.Accurate blood pressure measurement is essential for effective clinical assessment and appropriate interventions in anaesthetised horses. Information on the accuracy of oscillometry for blood pressure measurement on the appendages of mature horses is limited. Objective: To assess equivalence between invasive and oscillometric blood pressures at different anatomic locations in horses. Methods: Prospective experimental study using 6 healthy mature horses. Methods: Blood pressure was measured invasively in the right transverse facial artery and noninvasively by oscillometry in nondependent limbs ...
McKenzie EC, Di Concetto S, Payton ME, Mandsager RE, Arko M.To determine the effect of dantrolene premedication on various cardiovascular and biochemical variables and recovery in isoflurane-anesthetized horses. Methods: 6 healthy horses. Methods: Each horse was anesthetized twice with a 21- to 28-day washout period between anesthetic sessions. Food was not withheld from horses before either session. During each session, dantrolene (6 mg/kg in 2 L of water) or water (2 L) was administered via a nasogastric tube 1 hour before anesthesia was induced. Anesthesia was maintained with isoflurane for 90 minutes, during which blood gas analyses and lithium-dil...
Braganti G.In 1916 Louis Desliens, veterinary practitioner; submitted to the Academy of Sciences a description of a new way of exploring the cardiovascular system: percutaneous catheteri- zation. In 1935 he published the results of thirty years of explorations in hemodynamics mainly in horses: physiology, pathophysiology and pharmacodynamics. The text considers the very pioneering nature of these studies.
Umar MA, Fukui S, Kawase K, Itami T, Yamashita K.Cardiovascular effects of total intravenous anesthesia using ketamine-medetomidine-propofol drug combination (KMP-TIVA) were determined in 5 Thoroughbred horses undergoing surgery. The horses were anesthetized with intravenous administration (IV) of ketamine (2.5 mg/kg) and midazolam (0.04 mg/kg) following premedication with medetomidne (5 µg/kg, IV) and artificially ventilated. Surgical anesthesia was maintained by controlling propofol infusion rate (initially 0.20 mg/kg/min following an IV loading dose of 0.5 mg/kg) and constant rate infusions of ketamine (1 mg/kg/hr) and medetomidine (1.25...
Ishizuka T, Tamura J, Nagaro T, Sudo K, Itami T, Umar MA, Miyoshi K, Sano T, Yamashita K.Effects of intermittent positive pressure ventilation (IPPV) on cardiopulmonary function were evaluated in horses anesthetized with total intravenous anesthesia using constant rate infusions of medetomidine (3.5 µg/kg/hr), lidocaine (3 mg/kg/hr), butorphanol (24 µg/kg/hr) and propofol (0.1 mg/kg/min) (MLBP-TIVA). Five horses were anesthetized twice using MLBP-TIVA with or without IPPV at 4-week interval (crossover study). In each occasion, the horses breathed 100% oxygen with spontaneous ventilation (SB-group, n=5) or with IPPV (CV-group, n=5), and changes in cardiopulmonary parameters were ...
Villalba M, Santiago I, Gómez de Segura IA.The aim of this investigation was to determine the isoflurane-sparing effect and impact on arterial blood pressure and anaesthetic recovery of a constant rate infusion of medetomidine-propofol in horses. In a prospective, crossover, randomised study, six healthy horses (mean ± SD age, 13.7 ± 7.7 years; weight, 433 ± 51 kg) were anaesthetised twice with isoflurane and were randomly assigned to receive one of two treatments on each occasion, at least 2 weeks apart. The first treatment was saline (CTL group) and the second a medetomidine-propofol infusion (MP group; 1.25 µg/kg...
Balakrishnan A, Abbadi R, Oakland K, Jamdar S, Harper SJ, Jamieson NV, Huguet EL, Jah A, Praseedom RK.Equestrian sports are common outdoor activities that may carry a risk of liver injury. Due to the relative infrequency of equestrian accidents the injury patterns and outcomes associated with liver trauma in these patients have not been well characterized. Methods: We examined our experience of the management of equestrian liver trauma in our regional hepatopancreaticobiliary unit at a tertiary referral center. The medical records of patients who sustained liver trauma secondary to equestrian activities were analysed for parameters such as demographic data, liver function tests, patterns of in...
Rezende ML, Grimsrud KN, Stanley SD, Steffey EP, Mama KR.The aim of the study was to describe the pharmacokinetics and selected pharmacodynamics of intravenous dexmedetomidine in horses. Eight adult horses received 5 μg/kg dexmedetomidine IV. Blood samples were collected before and for 10 h after drug administration to determine dexmedetomidine plasma concentrations. Pharmacokinetic parameters were calculated using noncompartmental analysis. Data from one outlier were excluded from the statistical summary. Behavioral and physiological responses were recorded before and for 6 h after dexmedetomidine administration. Dexmedetomidine concentrations dec...
Tünsmeyer J, Hopster K, Feige K, Kästner SB.To determine the agreement of high definition oscillometry (HDO) with direct arterial blood pressure measurements in normotensive, hypotensive and hypertensive horses during general anaesthesia. Methods: Experimental study. Methods: Seven healthy warmblood horses, aged 3-11 years, weighing 470-565 kg. Methods: Measurements from a HDO device with the cuff placed around the base of the tail were compared with pressures measured invasively from the facial artery. High blood pressures were induced by intravenous (IV) administration of dobutamine (5 μg kg(-1) minute(-1)) over ten minutes followed ...
Palmer J.Despite advances in neonatal intensive care sepsis, severe sepsis and septic shock remain the biggest killers of neonatal foals. Management of this severe syndrome remains difficult, requiring intensive intervention. Key aspects of management include infection control, hemodynamic support, immunomodulatory interventions, and metabolic/endocrine support. Infection control largely consists of early antimicrobial therapy, plasma transfusions, and local therapy for the infected focus. In cases with severe sepsis or septic shock, hemodynamic support with fluids, vasoactive agents, and respiratory s...
Shih AC, Queiroz P, Vigani A, Da Cunha A, Pariaut R, Ricco C, Bornkamp J, Garcia-Pereira F, Bandt C.To assess the accuracy of an ultrasound velocity dilution cardiac output (UDCO) method, compared with that of the lithium dilution cardiac output (LiDCO) method, for determination of cardiac output (CO) in juvenile horses with experimentally induced hypovolemia. Methods: 12 anesthetized 2- to 6-month-old horses. Methods: For each anesthetized horse, CO was determined by the LiDCO and UDCO methods prior to any intervention (baseline state), after withdrawal of approximately 40% of the horse's blood volume (low CO state), after maintenance of hypovolemia and infusion of norepinephrine until mean...
Hopster K, Ambrisko TD, Stahl J, Schramel JP, Kästner SB.Previous studies showed an influence of xylazine on the LiDCO sensor in vitro and in standing horses, but did not prove that this interaction caused error in LiDCO measurements. Therefore, agreement of cardiac output (CO) measurements by LiDCO and bolus-thermodilution (BTD) was determined in horses receiving xylazine infusions. Methods: Prospective, experimental study. Methods: Eight Warmblood horses. Methods: All horses were premedicated with xylazine. Anaesthesia was induced with midazolam and ketamine and was maintained with isoflurane in oxygen. During six hours of anaesthesia CO measureme...
Benmansour P, Husulak ML, Bracamonte JL, Beazley SG, Withnall E, Duke-Novakovski T.To examine the cardiopulmonary effects of infusions of remifentanil or morphine, and their influence on recovery of horses anesthetized with isoflurane and dexmedetomidine. Methods: Randomized crossover study with 7-day rest periods. Methods: Six adult horses (507 ± 61 kg). Methods: After the horses were sedated with xylazine, anaesthesia was induced with ketamine and diazepam, and maintained with isoflurane. After approximately 60 minutes, a dexmedetomidine infusion was started (0.25 μg kg(-1) then 1.0 μg(-1) kg(-1) hour(-1) ) in combination with either saline (group S), morphine (0.15 mg ...
Scott VH, Williams JM, Mudge MC, Hurcombe SD.To assess effects of body position on direct measurements of intra-abdominal pressure (IAP) and abdominal perfusion pressure (APP) in horses anesthetized with total intravenous anesthesia (TIVA). Methods: 9 healthy adult horses. Methods: Instrumentation in unsedated standing horses involved insertion of an arterial catheter for blood pressure measurements and 3 intraperitoneal cannulas (left flank, right flank, and ventral abdomen) for IAP measurements. Baseline values were measured for heart rate, respiratory rate, systolic arterial blood pressure, mean arterial blood pressure (MAP), diastoli...
Hopster K, Ohnesorge B, von Borstel M, Rohn K, Kästner S.In most ocular procedures, a central position of the eye is necessary. This can be achieved using a deep plane of anaesthesia, locoregional blocks or with neuromuscular blocking agents. The aim of this study was to evaluate the influence of atracurium on cardiovascular parameters, and on recovery quality and duration in horses. Methods: Thirty-four warmblood horses undergoing in total 50 vitrectomies were divided into two groups. Premedication, induction and maintenance were identical in all patients. After 20 minutes, horses of group A received atracurium (0.1 mg/kg) while in the control grou...
Epstein KL, Bergren A, Giguère S, Brainard BM.Lower molecular weight and molar substitution formulations of hydroxyethyl starch (HES) solutions might maximize cardiovascular function and colloid osmotic pressure (COP) and minimize adverse effects on coagulation. Objective: To compare effects of 1 low and 1 high molecular weight and molar substitution HES solution on cardiovascular variables, COP, and hemostasis in normal horses. Methods: Eight healthy adult horses. Methods: Randomized, crossover designed study: 10 mL/kg bolus of 6% HES (600/0.75) (hetastarch) (HS), 6% HES (130/0.4) tetrastarch (TS), and 0.9% NaCl (NS). Variables recorded ...
Ambrisko TD, Moens Y.In a previous in vitro study using saline medium, the authors showed that certain drugs changed the voltages of lithium dilution cardiac output (LiDCO) sensors and also influenced their accuracy in measuring lithium concentrations. These two parameters correlated and so we examined whether such drug-sensor interaction exists when LiDCO sensor was exposed to xylazine in blood. Methods: Five healthy adult warm-blood horses were injected with 0.5 mg kg(-1) xylazine i.v. Physiological saline solution and venous blood were consecutively sampled through the same LiDCO sensor at 60, 45, 30, 15, and 0...
Pequito M, Amory H, de Moffarts B, Busoni V, Serteyn D, Sandersen C.The effects of norepinephrine (NOR) infusion on hemodynamic alterations induced with sedative doses of acepromazine (ACP) were evaluated. Infusion of NOR at 1 μg/kg body weight (BW)/minute for 15 min was administered to 5 standing horses 45 min (T45) after intravenous injection of ACP at 0.1 mg/kg BW. Systolic arterial blood pressure (SAP) and hemodynamic parameters were evaluated on the median artery. Parameters were evaluated every 5 min from 45 to 65 min (T65) at 75 (T75), 90 (T90), and 105 (T105) minutes after ACP administration, and the vessel's surface (SURF), diameter (DIAM), circumfer...
Ambrósio AM, Ida KK, Souto MT, Oshiro AH, Fantoni DT.To assess if positive end-expiratory pressure (PEEP) titration improves gas exchange and respiratory mechanics, without hemodynamic impairment in horses during anesthesia. Methods: Prospective, randomized study. Methods: Thirteen isoflurane-anesthetized healthy horses. Methods: After 60 minutes of anesthesia with spontaneous breathing, mechanical ventilation was initiated with an inspiratory-expiratory ratio of 1:2, PEEP of 5 cmH2O, tidal volume of 10-20 mL kg(-1) and respiratory rate adjusted to maintain normocapnia. Constant PEEP of 5 cmH2O was continued (control group; n = 6) or titrated (P...
The Journal of physiologyJuly 1, 2013
Volume 591, Issue 18 4499-4513 doi: 10.1113/jphysiol.2013.257956
Vengust M, Staempfli H, Viel L, Swenson ER, Heigenhauser G. During intense exercise in horses the transvascular fluid flux in the pulmonary circulation (Jv-a) represents 4% of cardiac output (Q). This fluid flux has been attributed to an increase in pulmonary transmural hydrostatic forces, increases in perfused microvascular surface area, and reversible alterations in capillary permeability under conditions of high flow and pressure. Erythrocyte fluid efflux, however, accounts for a significant fraction of Jv-a. In the lung the Jacobs-Stewart cycle occurs with diffusion of CO2 into alveolar space with possible accompanying chloride (Cl-) and water ...
La Gerche A, Daffy JR, Mooney DJ, Forbes G, Davie AJ.It has been observed that microbubbles may pass through the pulmonary circulation of dogs and humans during exercise. In humans, this phenomenon has been associated with lower pulmonary artery pressures, enhanced right ventricular function and greater exercise capacity. In the exercising Thoroughbred horse, extraordinarily high cardiac outputs exert significant pulmonary vascular stresses. The aim of this study was to determine, using contrast echocardiography, whether Thoroughbred horses performing strenuous exercise developed pulmonary transit of agitated contrast microbubbles (PTAC). At res...
Whelchel DD, Tennent-Brown BS, Giguère S, Epstein KL.To compare the pharmacodynamics of once daily and twice daily administration of low molecular weight heparin (LMWH) administration in horses. Methods: Randomized cross over study. Methods: Adult mixed breed healthy mares (n = 6). Methods: LMWH (dalteparin) was administered (50 U/kg subcutaneously) either every 12 or 24 hours for 3 consecutive days. Anti-factor Xa activity was measured before and at select time points after LMWH administration. Packed cell volume (PCV), platelet count, partial thromboplastin time (PTT), and anti-thrombin (AT) activity were monitored throughout the study. Result...
Wong DM, Witty D, Alcott CJ, Sponseller BA, Wang C, Hepworth K.Renal replacement therapy (RRT) has been implemented extensively in people to facilitate recovery from acute renal failure (ARF). RRT has not been explored in horses, but might provide a further treatment option in horses with ARF. Objective: To investigate efficacy and safety of RRT in horses. Methods: Five healthy adult horses. Methods: A prospective study was performed on horses restrained in stocks and intravenously connected to a commercial RRT machine to allow continuous venovenous hemodiafiltration to be performed for 6 hours. The RRT machine was set at the following flow rates: blood ...
Ohta M, Kurimoto S, Tokushige H, Kuroda T, Ishikawa Y.To determine hemodynamic effects of hydroxyethyl starch (HES) infusion during anesthesia in horses, incremental doses of 6% HES were administered to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and administered 3 intravenous dose of 6% HES (5 ml/kg) over 15 min with 15-min intervals in addition to constant infusion of lactated Ringer's solution at 10 ml/kg/hr. Hemodynamic parameters were measured before and e...
Hobo S, Yoshida K, Yoshihara T.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...
Fielding CL, Magdesian KG.Sepsis and septic shock represent a major cause of morbidity and mortality in equine neonates and in all species. Early recognition of the condition is important, but definitive examination and laboratory variables to predict equine neonatal sepsis are lacking. Early and aggressive treatment should include broad-spectrum antimicrobial coverage, source control, and hemodynamic support. Field practitioners and intensive care clinicians work together in the management of this condition because the recognition and initial treatment should begin as early as possible.
Hinchcliff KW, McKeever KH, Muir WW.The effect of furosemide administration (1 mg/kg body weight, i.v.) on plasma and blood volumes in 6 intact and 4 splenectomized horses was measured using Evans blue dye dilution, hematocrit, and hemoglobin and plasma total solids concentrations. Body weight decreased by 33.6 +/- 3.3 and 33.7 +/- 0.8 g/kg 4 h after furosemide administration to intact and splenectomized mares, respectively. Plasma volume, estimated by Evans blue dye dilution, was reduced by 8.3 +/- 3.3% (mean +/- SE) 4 h after furosemide administration. The reduction in plasma volume was first detectable 5-10 min after furosemi...
Geor RJ, Weiss DJ, Burris SM, Smith CM.The effects of furosemide and pentoxifylline on blood flow properties in horses were investigated. Hematologic and rheologic changes were examined in 4 horses before and 3 minutes after administration of epinephrine (1 mg, IV). The next day, hemorheologic changes were determined before and 3 hours after administration of furosemide (1 mg/kg of body weight, IM), and after administration of epinephrine at the sampling at 3 hours. Hematologic and rheologic changes were evaluated weekly in 3 horses given pentoxifylline (8.5 mg/kg, q 12 h, PO) for 28 days. In addition, hemorheologic responses to ep...
Brosnan RJ, Steffey EP, LeCouteur RA, Imai A, Farver TB, Kortz GD.To measure the effects of isoflurane end-tidal concentration and mode of ventilation (spontaneous vs controlled) on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in horses. Methods: adult horses of various breeds. Methods: Anesthesia was induced and maintained with isoflurane in O2 in 6 healthy, unmedicated, adult horses. Using a subarachnoid strain gauge transducer, ICP was measured. Blood gas tensions and carotid artery pressures also were measured. Four isoflurane doses were studied, corresponding to the following multiples of the minimum alveolar concentration (MAC): 1....
Villalba M, Santiago I, Gomez de Segura IA.Lidocaine and ketamine are administered to horses as a constant rate infusion (CRI) during inhalation anaesthesia to reduce anaesthetic requirements. Morphine decreases the minimum alveolar concentration (MAC) in some domestic animals; when administered as a CRI in horses, morphine does not promote haemodynamic and ventilatory changes and exerts a positive effect on recovery. Isoflurane-sparing effect of lidocaine, ketamine and morphine coadministration has been evaluated in small animals but not in horses. Objective: To determine the reduction in isoflurane MAC produced by a CRI of lidocaine ...
Kieffer PJ, Williams JM, Shepard MK, Giguère S, Epstein KL.The objectives of the study were to: i) determine baseline microvascular perfusion indices (MPI) and assess their repeatability in healthy horses under general anesthesia, and ii) compare the MPIs of 3 microvascular beds (oral mucosa, colonic serosa, and rectal mucosa). Healthy adult horses were anesthetized and sidestream dark field microscopy was used to collect video loops of the oral mucosa, rectal mucosa, and colonic serosa under normotensive conditions without cardiovascular support drugs; videos were later analyzed to produce MPIs. Baseline MPI values were determined for each site, whic...
Sarazan RD, Starke WA, Krause GF, Garner HE.The cardiovascular effects of detomidine and xylazine were compared in six chronically instrumented, conscious ponies. Ponies were instrumented with a micromanometer in the left ventricular chamber, a Doppler flow probe on a coronary artery and sonomicrometer crystals in the left ventricular free wall. Heart rate, ventricular systolic pressure, stroke work, dP/dtmax, minute work and coronary blood flow were measured for 4 h following intravenous injection of detomidine at several doses or xylazine at 1.1 mg/kg. Both drugs caused a profound hypertensive response at 15 s post-injection. The magn...
Boscan P, Watson Z, Steffey EP.To investigate the changes in colloid osmotic pressure (COP) and total protein concentrations during routine general anesthesia in horses. Methods: Prospective, clinical study. Methods: Twelve adult healthy horses aged 9.1 +/- 4.7 years and weighing 474 +/- 79 kg presented for elective surgery and 14 adult horses aged 8.7 +/- 7.3 years and weighing 510 +/- 85 kg. Methods: All horses were premedicated with xylazine and anesthesia induced with ketamine, diazepam and guaifenesin, and maintained with isoflurane for 2.5 hours. Lactate Ringer's solution was administered at 11 mL kg(-1) hour(-1). Osm...
Swanson CR, Muir WW, Bednarski RM, Skarda RT, Hubbell JA.The hemodynamic changes induced by constant infusions of dopamine or dobutamine (each 3, 5, and 10 micrograms/kg/min) were observed in halothane-anesthetized horses. Left ventricular dp/dt and cardiac output were increased in horses given dobutamine at dosage of 3 micrograms/kg/min and in those given either of the drugs at dosages of 5 and 10 micrograms/kg/min. Concomitant increases in systemic arterial blood pressure occurred at lower infusion dosage rates of dobutamine than those of dopamine and were modulated by dosage-related changes in peripheral vascular resistance that were different be...
Raisis AL, Young LE, Blissitt KJ, Brearley JC, Meire HB, Taylor PM, Lekeux P.The purpose of this study was to compare the haemodynamic effects of equipotent isoflurane and halothane anaesthesia. Six adult horses were investigated on two separate occasions at least 4 weeks apart. On both occasions anaesthesia was induced by ketamine 2.2 mg/kg bwt given 5 min after i.v. administration 100 microg/kg bwt romifidine. Anaesthesia was maintained either by halothane or isoflurane (end-tidal concentrations 0.9-1.0% and 1.3-1.4%, respectively). Horses were ventilated by intermittent positive pressure to maintain PaCO2 between 40-50 mmHg. Haemodynamic variables were measured usin...
Weber JM, Dobson GP, Parkhouse WS, Wheeldon D, Harman JC, Snow DH, Hochachka PW.This study characterizes the effects of exercise on the cardiac output (Q) and the metabolic rate (VO2) of trained Thoroughbred racehorses. Heart rate, Q, and arteriovenous (a-v)O2 difference were measured at rest and at three levels of submaximal treadmill exercise (1.6 m/s walk and 3-4 m/s trot at 6% incline, and 6.5 m/s horizontal canter). Heart rate and (a-v)O2 difference were also measured during maximal exercise (12.5 m/s gallop, 5% incline) to obtain an estimate of maximum O2 uptake (VO2max). The walk, trot, and canter represented 25, 45, and 55% VO2max. Mean heart rate went from 48.9 (...
Khanna AK, McDonell WN, Dyson DH, Taylor PM.The cardiopulmonary effects of eucapnia (arterial CO2 tension [PaCO2] 40.4 +/- 2.9 mm Hg, mean +/- SD), mild hypercapnia (PaCO2, 59.1 +/- 3.5 mm Hg), moderate hypercapnia (PaCO2, 82.6 +/- 4.9 mm Hg), and severe hypercapnia (PaCO2, 110.3 +/- 12.2 mm Hg) were studied in 8 horses during isoflurane anesthesia with volume controlled intermittent positive pressure ventilation (IPPV) and neuromuscular blockade. The sequence of changes in PaCO2 was randomized. Mild hypercapnia produced bradycardia resulting in a significant (P < 0.05) decrease in cardiac index (CI) and oxygen delivery (DO2), while ...
Manohar M, Goetz TE.The present study examined whether Thoroughbred horses performing strenuous exercise exhibit intrapulmonary arteriovenous shunting that may contribute to the observed arterial hypoxemia. Experiments were carried out on seven healthy, exercise-trained Thoroughbreds at rest, maximal exercise (galloping at 14 m/s on a 3.5% uphill grade for 120 s), and submaximal exertion (8 m/s on a 3.5% uphill grade for 150 s). Along with blood gas/hemodynamic parameters, intrapulmonary arteriovenous shunting was studied by injecting 15-microm-diameter microspheres, labeled with different stable isotopes, into t...
Lombard CW, Evans M, Martin L, Tehrani J.Twelve newborn pony foals underwent cardiovascular examinations (auscultation, arterial blood pressure measurements, electrocardiograms and M-mode echocardiograms) on their first day of life and then on Days 7, 14, 21, 30, 60 and 90. An age dependent, statistically significant, rapid increase of the arterial blood pressure in the first month was documented together with a slower decrease of the resting heart rate after two and three months of life. Innocent soft systolic murmurs were audible over the left heart base in a large number of the foals. The electrocardiograms showed age dependent in...
Umar MA, Yamashita K, Kushiro T, Muir WW.To evaluate the cardiovascular effects of total IV anesthesia with propofol (P-TIVA) or ketamine-medetomidine-propofol (KMP-TIVA) in horses. Methods: 5 Thoroughbreds. Methods: Horses were anesthetized twice for 4 hours, once with P-TIVA and once with KMP-TIVA. Horses were medicated with medetomidine (0.005 mg/kg, IV) and anesthetized with ketamine (2.5 mg/kg, IV) and midazolam (0.04 mg/kg, IV). After receiving a loading dose of propofol (0.5 mg/kg, IV), anesthesia was maintained with a constant rate infusion of propofol (0.22 mg/kg/min) for P-TIVA or with a constant rate infusion of propofol (...
Pantaleon LG, Furr MO, McKenzie HC, Donaldson L.Small volume resuscitation has been advocated as a beneficial therapy for endotoxemia in horses but this therapy has not been investigated in a prospective manner. The objective of this study was to determine the cardiopulmonary effects of small-volume resuscitation using hypertonic saline solution (HSS) plus Hetastarch (HES) during experimental endotoxemia in anesthetized horses. Objective: Treatment of horses with induced endotoxemia using HES-HSS does not alter the response of various cardiopulmonary indices when compared to treatment with either small- or large-volume isotonic crystalloid ...
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...
Reef VB, Spencer P.Echocardiographic evaluation of 23 horses with aortic insufficiency was performed, using M-mode (n = 23) and 2-dimensional real-time echocardiography (n = 14 of 23). Echocardiograms were evaluated for abnormalities of aortic and mitral valves and alterations in motion of these valves. Changes in left ventricular chamber size and function, as well as aortic root size, were evaluated. The presence of other cardiac disease was also evaluated. Horses with aortic insufficiency had significant increases (P less than 0.01) in mean values of left ventricular chamber size, aortic root diameter, and sho...
Qin Z, Durand LG, Allard L, Cloutier G.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...
Hinchcliff KW, Muir WW.Furosemide, a diuretic, is frequently administered to horses for the prophylaxis of exercise-induced pulmonary hemorrhage and the treatment of a number of clinical conditions, including acute renal failure and congestive heart failure. Furosemide increases the rate of urinary sodium, chloride, and hydrogen ion excretion. Plasma potassium concentration decreases after furosemide administration but urinary potassium excretion in horses is minimally affected. Renal blood flow increases after furosemide administration. Systemically, furosemide increases venous compliance and decreases right atrial...
Valverde A, Rickey E, Sinclair M, Rioja E, Pedernera J, Hathway A, Cruz A.The effects of lidocaine combined with medetomidine or lidocaine alone on cardiovascular function during anaesthesia and their effects on recovery have not been thoroughly investigated in isoflurane-anaesthetised horses. Objective: To determine the effects of an intraoperative i.v. constant rate infusion of lidocaine combined with medetomidine (Group 1) or lidocaine (Group 2) alone on cardiovascular function and on the quality of recovery in 12 isoflurane-anaesthetised horses undergoing arthroscopy. Objective: The combination would depress cardiovascular function but improve the quality of rec...
Oku K, Ohta M, Katoh T, Moriyama H, Kusano K, Fujinaga T.We examined the influence of propofol infusion on cardiovascular system at the rate of 0.14, 0.20 and 0.30 mg/kg/min in six adult Thoroughbred horses. The cardiovascular parameters were heart rate (HR), mean arterial pressure (MAP), mean right atrial pressure (MRAP), stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR), pre-ejection period (PEP) and ejection time (ET). In order to keep the ventilation conditions constantly, intermittent positive pressure ventilation was performed, and the partial arterial CO(2) pressure was maintained at 45 to 55 mmHg during maintenance ...
Divers TJ.Nephrotoxic and hemodynamically mediated disorders are the most common causes of acute renal failure (ARF) in horses and foals. Leptospira spp. is the most common infectious cause of ARF. Initial treatments for ARF include elimination of nephrotoxic drugs, correction of predisposing disorders, and fluid therapy to promote diuresis. Horses and foals with polyuric ARF often have a good prognosis, while those with oliguric or anuric ARF have a guarded to poor prognosis. When fluid therapy is unsuccessful in improving urine production, various drugs treatments have been used in an attempt to incre...
Muir WW, Sams R.Eight adult horses were used in a study to determine ketamine's ability to reduce halothane requirement. To obtain steady-state plasma concentrations of 0.5, 1.0, 2.0, 4.0, and 8.0 micrograms/ml, loading doses and constant infusions for ketamine were calculated for each horse on the basis of data from other studies in which the pharmacokinetic properties of ketamine were investigated. Blood samples for determination of plasma ketamine concentrations were collected periodically during each experiment. Plasma ketamine concentrations were determined by capillary gas chromatography/mass spectromet...
Hubbell JA, Muir WW, Robertson JT, Sams RA.Sodium penicillin, sodium cefazolin, and sodium citrate were administered to six adult horses on separate occasions, when awake and during anesthesia. The order of administration was randomized and studies were separated by a minimum of 7 days. Arterial blood pressure decreased significantly (less than 0.05) from control 5 minutes after intravenous (IV) sodium penicillin in awake and anesthetized horses. Systolic arterial blood pressure remained significantly (less than 0.05) decreased 10 minutes after IV sodium penicillin in anesthetized horses. Sodium cefazolin and sodium citrate did not sig...
Cullen LK, Steffey EP, Bailey CS, Kortz G, da Silva Curiel J, Bellhorn RW, Woliner MJ, Elliott AR, Jarvis KA.The effects of different arterial carbon dioxide tensions (PaCO2) on cerebrospinal fluid pressure (CSFP) and intraocular pressure (IOP) were studied in 6 male halothane-anesthetized horses positioned in left lateral recumbency. Steady-state anesthetic conditions (1.06% end-tidal halothane concentration) commenced 60 minutes following anesthetic induction with only halothane in oxygen. During atracurium neuromuscular blockade, horses were ventilated, and respiratory rate and peak inspiratory airway pressure were maintained within narrow limits. The CSFP and IOP were measured at 3 different leve...
Caillaud C, Connes P, Bouix D, Mercier J.Exercise-induced arterial hypoxemia (EIAH), i.e., a significant drop of O2 arterial partial pressure during sea level exercise, has been shown in both aerobically trained athletes and athletic animal species. The mechanisms potentially involved include ventilation/perfusion inequality and/or pulmonary diffusing capacity limitation. In thoroughbred horses, EIAH is going with pulmonary haemorrhage (EIPH). Stress failure of pulmonary capillaries leading to diffusion limitation has been proposed. Indeed, during intense exercise, the increased cardiac output and blood viscosity combine to rise capi...
Yamanaka T, Oku K, Koyama H, Mizuno Y.To clarify time-related changes in equine cardiovascular system during maintenance anesthesia (180 min, 1.2 minimum alveolar concentration) with sevoflurane (Sev-group) compared to isoflurane (Iso-group) as the basis for clinical use of Sev, horses were examined for the heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), systemic vascular resistance (SVR) and pre-ejection period (PEP)/ejection time (ET) that is an index of the cardiac contractility. The HR was almost 30 beats/min in both groups without significant temporal change. MAP was significantly elevated with time but the...
