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.
de Vries A, Brearley JC, Taylor PM.Volatile agent-induced hypotension may contribute to anaesthetic-related morbidity and mortality in horses. Dobutamine is commonly used to support arterial blood pressure (ABP) but little is known about its cardiovascular effects under clinical conditions. The aim of this clinical study was to elucidate the relationship between cardiovascular function and dobutamine infusion in isoflurane-anaesthetized horses. Forty-four horses anaesthetized for a variety of surgical procedures were studied. Premedication with acepromazine, methadone and detomidine was followed by induction of anaesthesia with...
Schauvliege S, van Loon G, De Clercq D, Devisscher L, Deprez P, Gasthuys F.To examine the influence of direct current shock application in anaesthetized horses with atrial fibrillation (AF) and to study the effects of cardioversion to sinus rhythm (SR). Methods: Prospective clinical study. Methods: Eight horses successfully treated for AF (transvenous electrical cardioversion after amiodarone pre-treatment). Methods: Cardioversion catheters and a pacing catheter were placed under sedation [detomidine 10 microg kg(-1) intravenously (IV)]. After additional sedation (5-10 microg kg(-1) detomidine, 0.1 mg kg(-1) methadone IV), anaesthesia was induced with ketamine, 2.2 m...
Nyman G, Marntell S, Edner A, Funkquist P, Morgan K, Hedenstierna G.Sedation with alpha2-agonists in the horse is reported to be accompanied by impairment of arterial oxygenation. The present study was undertaken to investigate pulmonary gas exchange using the Multiple Inert Gas Elimination Technique (MIGET), during sedation with the alpha2-agonist detomidine alone and in combination with the opioid butorphanol. Methods: Seven Standardbred trotter horses aged 3-7 years and weighing 380-520 kg, were studied. The protocol consisted of three consecutive measurements; in the unsedated horse, after intravenous administration of detomidine (0.02 mg/kg) and after sub...
Kerr CL, Bouré LP, Pearce SG, McDonell WN.To evaluate cardiopulmonary effects of anesthetic induction with diazepam and ketamine or xylazine and ketamine, with subsequent maintenance of anesthesia with isoflurane, in foals undergoing abdominal surgery. Methods: 17 pony foals. Methods: Foals underwent laparotomy at 7 to 15 days of age and laparoscopy 7 to 10 days later. Foals were randomly assigned to receive diazepam, ketamine, and isoflurane (D/K/Iso; n = 8) or xylazine, ketamine, and isoflurane (X/K/Iso; 9) for both procedures. Results: During anesthesia for laparotomy, cardiac index, and mean arterial blood pressure ranged from 110...
Schauvliege S, Van den Eede A, Duchateau L, Pille F, Vlaminck L, Gasthuys F.To compare cardiac output () measurements using lithium dilution (LiDCO) and pulse contour analysis (PulseCO) techniques in isoflurane-anaesthetized ponies before and during the administration of different inotropic/vasoactive drugs. Methods: Prospective randomized experimental cross-over trial. Methods: Six ponies aged 5.0 +/- 1.6 (4-6.5) years and weighing 286 +/- 53 (212-368) kg. Methods: After sedation (romifidine) and induction (midazolam + ketamine), anaesthesia was maintained with isoflurane in oxygen. After 90 minutes (= T0), one of four treatments was administered: saline 0.1 mL kg(-1...
Shih AC, Giguère S, Sanchez LC, Valverde A, Jankunas HJ, Robertson SA.To compare cardiac output (CO) measured by lithium arterial pressure waveform analysis (PULSECO) and CO measured by transpulmonary pulse contour analysis (PICCO) in anesthetized foals, with CO measured by use of lithium dilution (LIDCO) considered the criterion-referenced standard. Methods: 6 neonatal (1- to 4-day-old) foals that weighed 38 to 45 kg. Procedures-Foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. The CO was measured by use of PULSECO, PICCO, and LIDCO techniques. Measurements were converted to specific CO (sCO) va...
Schauvliege S, Van den Eede A, Duchateau L, Pille F, Vlaminck L, Gasthuys F.To investigate the influence of calcium chloride (CaCl(2)) on the cardio-respiratory effects of enoximone in isoflurane anaesthetized ponies. Methods: Prospective consecutive experimental trial. Animals Six healthy ponies, weighing 287 +/- 55 kg were included in this study. Methods: After sedation (romifidine, 80 microg kg(-1)), anaesthesia was induced with midazolam (0.06 mg kg(-1)) and ketamine (2.2 mg kg(-1)) and maintained with isoflurane in oxygen. The ponies' lungs were ventilated to maintain normocapnia. After 90 minutes, a bolus of enoximone (0.5 mg kg(-1)) was administered, followed b...
Ricco CH, Quandt JE, Novo RE, Killos M, Graham L.To evaluate the feasibility and functionality of intra-carotid wireless device implantation in ponies, and to investigate its short-term complications. Methods: Prospective preliminary study. Methods: Five mixed breed, adult, intact male ponies weighing 104 +/- 28.8 kg (mean +/- SD) underwent surgery. Arterial blood pressure data were continuously collected from four animals. Methods: General anesthesia was induced on two consecutive days. On the first day, an intra-arterial wireless device was implanted in the right carotid artery. On the next day, a transcutaneous intra-arterial catheter was...
Durando MM, Corley KT, Boston RC, Birks EK.To compare cardiac output (CO) obtained by the lithium dilution method (LiDCO) with CO calculated from the Fick principle (FickCO), in horses maximally exercising on a high-speed treadmill. Methods: 13 Thoroughbreds. Methods: In part 1 of the study, 5 horses performed a warm-up (walk, trot, and canter) and exercise test (walk, trot, canter, and gallop [90% to 100% maximum oxygen consumption [{VO(2)max}]) with measurements of LiDCO and FickCO obtained simultaneously after 60 seconds at each exercise level, for a total of 7 measurements. In part 2 of the study, 8 horses performed a warm-up (walk...
Hollis AR, Ousey JC, Palmer L, Stephen JO, Stoneham SJ, Boston RC, Corley KT.Norepinephrine increases arterial blood pressure but may have adverse effects on renal blood flow. Fenoldopam, a dopamine-1 receptor agonist, increases urine output in normotensive foals. The combination of norepinephrine and fenoldopam may lead to improved renal perfusion compared with an infusion of norepinephrine alone. The combined effects of these drugs have not been reported in the horse. Objective: Norepinephrine will alter the hemodynamic profile of foals without affecting renal function. Addition of fenoldopam will change the renal profile during the infusions without changing the hem...
Menzies-Gow NJ.Eight normal thoroughbred horses were examined by echocardiography before and 10 minutes after they had been sedated by the intravenous administration of 0.03 mg/kg acepromazine. There were significant (P<0.025) increases in the diameters of the pulmonary artery and the aorta, measured at end-systole, and in the thickness of the interventricular septum, measured at end-systole and end-diastole. In addition, there was a significant (P<0.001) decrease in the diameter of the left atrium measured at end-diastole. The remaining cardiac dimensions, all the indices of cardiac function, and the ...
Zucca E, Ferrucci F, Croci C, Di Fabio V, Zaninelli M, Ferro E.The aim of this study was to obtain echocardiographic measurements and establish reference ranges for 14 parameters in Standardbred racehorses in training. Background: Several studies have been published about cardiac measurements in Thoroughbreds, Standardbreds, National Hunt horses, Warmbloods and ponies; however, not all parameters have been published for the Standardbred trotter in training. Methods: Thirty normal Standardbred racehorses in training were assessed by two-dimensional echocardiography (2-D) and M-mode echocardiography using standardized imaging planes. Mean values, standard d...
Grubb TL, Högman M, Edner A, Frendin JH, Heinonen E, Malavasi LM, Frostell CG, Ryden A, Alving K, Nyman GC.To assess physiologic responses and plasma endothelin (ET)-1 concentrations associated with abrupt cessation of nitric oxide (NO) inhalation in isoflurane-anesthetized horses. Methods: 6 healthy adult Standardbreds. Methods: Horses were anesthetized with isoflurane in oxygen and placed in dorsal recumbency. Nitric oxide was pulsed into the respiratory tract for 2.5 hours, and then administration was abruptly discontinued. Just prior to commencement and at cessation of NO administration, and at intervals during a 30-minute period following cessation of NO inhalation, several variables including...
Ferreira JC, Gastal EL, Ginther OJ.Transrectal color and power Doppler ultrasonography was used to study uterine blood flow and perfusion in mares with and without uterine cysts. Vascular perfusion of the uterus and blood flow velocities, vascular perfusion, diameter, circumference, and area of a cross section of the mesometrial attachment were evaluated. To study the effect of internal cysts, two matched groups (cystic and control, n=21 mares/group) were used. Uterine vascular perfusion in mares with cysts was less (P<0.0001) in the cystic than the noncystic region and less (P<0.0009) than that for controls. Mares with c...
Ennezat PV, Darchis J, Lamblin N, Tricot O, Elkohen M, Aumégeat V, Equine O, Dujardin X, Saadouni H, Le Tourneau T, de Groote P, Bauters C.Although mitral regurgitation (MR) has been associated with an increased risk of death and heart failure after myocardial infarction (MI), the relationship between post-MI MR and left ventricular (LV) remodeling has not been entirely clarified. In addition, the optimal timing for assessing MR after MI remains unknown. Methods: Post-MI MR was assessed by Doppler echocardiography at hospital discharge (baseline) and after 3 months in 261 patients with an inaugural anterior MI. We studied LV remodeling during a 1-year period and clinical follow-up after 3 years, according to MR severity at baseli...
Lépiz ML, Keegan RD, Bayly WM, Greene SA, McEwen MM.The Fick and thermodilution (TD) methods are two currently popular techniques for determination of cardiac output (CO) in adult horses. To our knowledge, a comparison of these two techniques has not been reported. Six healthy, resting, fit, adult horses of either sex and weighing 516.5+/-33.2 kg (mean+/-SD) were instrumented to enable measurement of cardiac output. Resting CO was determined by the Fick method and by thermodilution while the horses stood quietly in the stocks. Fick and thermodilution CO measurements were repeated under conditions of increased cardiac output achieved with the us...
Blissitt KJ, Raisis AL, Adams VJ, Rogers KH, Henley WE, Young LE.To determine the haemodynamic effects of halothane and isoflurane with spontaneous and controlled ventilation in dorsally recumbent horses undergoing elective surgery. Methods: Prospective randomized clinical trial. Methods: Twenty-five adult horses, body mass 487 kg (range: 267-690). Methods: Horses undergoing elective surgery in dorsal recumbency were randomly assigned to one of four treatment groups, isoflurane (I) or halothane (H) anaesthesia, each with spontaneous (SB) or controlled ventilation (IPPV). Indices of cardiac function and femoral arterial blood flow (ABF) and resistance were m...
Menzies-Gow NJ, Sepulveda MF, Bailey SR, Cunningham FM, Elliott J.To evaluate the roles of 5-hydroxytryptamine (5-HT), thromboxane A2 (TxA2), and platelet-activating factor (PAF) in endotoxin-induced digital hypoperfusion in horses. Methods: 6 healthy adult Thoroughbreds. Methods: Horses were treated with IV administration of saline (0.9% NaCl) solution (control treatment) or the 5-HT 1B/D selective antagonist, GR55562 (0.3 mg/kg), prior to tryptamine infusion (1.6 microg/kg/min for 30 minutes) to establish an effective GR55562 dose. In a crossover study, horses were treated with IV administration of saline solution (control treatment), aspirin (4 mg/kg, 2 h...
Pantaleon LG, Furr MO, McKenzie HC, Donaldson L.Small-volume resuscitation (SVR) has been advocated in place of large-volume isotonic resuscitation for the treatment of endotoxemia in horses. The effects of this type of therapy during experimental endotoxemia on electrolytes and coagulation have not been evaluated in the horse. As part of a larger project, the objective of this study was to determine the effects of SVR (hypertonic saline solution [HSS] plus hetastarch [HES]) on coagulation and serum electrolytes concentration, and to compare SVR with large- and small-volume isotonic resuscitation during experimental endotoxemia in anestheti...
Gehlen H, Bubeck K, Rohn K, Stadler P.The aim of this study was to investigate the potential haemodynamic effects of valvular insufficiency and recurrent airway obstruction (RAO) in horses with atrial fibrillation (AF). Therefore in ten healthy horses (group 1) and 40 horses with AF a clinical examination, a lung examination, echocardiography and right heart catheterization for measurement of intracardic and pulmonary pressures were performed. According to the clinical findings the horses with AF were subdivided into 4 groups (group 2: AF; group 3: AF/valvular insufficiency; group 4: AF/RAO; group 5: AF/valvular insufficiency/RAO)...
Leise BS, Fugler LA, Stokes AM, Eades SC, Moore RM.To determine the magnitude and duration of effects of acepromazine administered intramuscularly (IM) on digital and systemic hemodynamic variables in clinically healthy horses. Methods: Experimental study. Methods: Healthy adult horses (n=12). Methods- An ultrasonic Doppler flow probe was surgically implanted around the medial palmar digital artery before the study. Catheters were inserted in the transverse facial artery, lateral palmar digital artery, and jugular vein. A treatment group (n=6) was administered 0.04 mg/kg body weight of acepromazine IM; control horses (n=6) were administered an...
Geor RJ.Acute renal failure (ARF) in horses is usually prerenal or renal in origin and is most often caused by hemodynamic or nephrotoxic insults. The clinical management of patients that have ARF is largely supportive, including correction of fluid deficits and electrolyte and acid-base disturbances and treatment and reversal of the underlying cause. Use of dopamine and mannitol to promote renal blood flow and urine output is no longer recommended.
Ross J, Dallap BL, Dolente BA, Sweeney RW.To determine the pharmacokinetics and pharmacodynamics of epsilon-aminocaproic acid (EACA), including the effects of EACA on coagulation and fibrinolysis in healthy horses. Methods: 6 adult horses. Methods: Each horse received 3.5 mg of EACA/kg/min for 20 minutes, i.v. Plasma EACA concentration was measured before (time 0), during, and after infusion. Coagulation variables and plasma alpha(2)-antiplasmin activity were evaluated at time 0 and 4 hours after infusion; viscoelastic properties of clot formation were assessed at time 0 and 0.5, 1, and 4 hours after infusion. Plasma concentration ver...
Catalani G, Dottavio ME, Rasia M.During acute exercise several significant cardiovascular alterations take place, along with possible physiopathological consequences, such as Exercise Inducted Pulmonary Haemorrhage (EIPH). Given the relevance of blood rheology in the determination of flow resistance and its supposed participation in the stated events, the present paper focuses on the analysis of modifications in haematocrit, blood viscosity and erythrocyte deformability in Thoroughbred horses caused by two different levels of effort (6 to 9 m/s and 13 to 16 m/s), in the same track they train in and with their own jockeys. The...
Hofmeister EH, Mackey EB, Trim CM.To determine cardiovascular responses to administration of butorphanol in isoflurane-anesthetized horses. Methods: Retrospective evaluation of anesthetic records. Methods: Seventy-six horses anesthetized for a variety of clinical surgical procedures. Methods: Anesthetic records of clinical equine patients anesthetized between January 1999 and December 2003 were searched. The records were reviewed for horses in which anesthesia was induced with ketamine and a benzodiazepine and maintained with isoflurane, and horses that received butorphanol intraoperatively. Exclusion criteria included horses ...
Hedia M, Ibrahim S, Mahmoud K, Ahmed Y, Ismail S, El-Belely M.Apparently healthy mares with conception failure or embryonic loss may have subclinical endometritis (SE). Our objective was to document evidence of systemic immune responses against SE in mares. In apparently healthy (control) mares as well as those with chronic endometritis (ChE) or subacute suppurative endometritis (SSE), both considered classes of SE, serum concentrations of cytokines (IL-1β, IL-6, IL-10 and TNF), chemokines (IL-8), acute phase protein (SAA), and plasma concentrations of prostaglandins (PGF and PGE) were measured using validated enzyme linked immunoassays (EIA). Mixed-bre...
Lindinger MI, Waller AP.The present study determined the independent contributions of temperature, strong ion difference ([SID]), total weak acid concentration ([Atot]) and PCO2 to changes in arterial and mixed venous [H+] and total carbon dioxide concentration ([TCO2]) during 37 min of moderate intensity exercise (~50% of heart rate max) and the first 60 min of recovery. Six horses were fitted with indwelling carotid and pulmonary artery (PA) catheters, had PA temperature measured, and had blood samples withdrawn for immediate analysis of plasma ion and gas concentrations. The increase in core temperature during exe...
Valverde A, Giguère S, Morey TE, Sanchez LC, Shih A.To compare cardiac output (CO) measured by use of the partial carbon dioxide rebreathing method (NICO) or lithium dilution method (LiDCO) in anesthetized foals. Methods: Data reported in 2 other studies for 18 neonatal foals that weighed 32 to 61 kg. Methods: Foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, end-tidal isoflurane and carbon dioxide concentrations, and CO. Various COs were achieved by administration of dobutamine, norepinephrine, vasopressin, phenylephrine, and isoflurane to allow comparisons between LiDCO and NICO metho...
Cuvelliez SG, Eicker SW, McLauchlan C, Brunson DB.Anesthesia of equids is associated with pulmonary dysfunction. Cardiovascular and respiratory effects of inhalation anesthetic agents and duration of anesthesia have been studied, using oxygen as the carrier gas. To our knowledge, the effects of inspired oxygen have not been determined. We studied the cardiovascular and respiratory effects of 2 inspired oxygen fractions (0.30 and greater than 0.85) in 5 laterally recumbent, halothane-anesthetized horses. Mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base e...
Manohar M.Previous studies of pulmonary vascular pressures have utilised gradual incremental step exercise protocols, but in competitive racing at the track, horses perform rapid acceleration high-intensity exercise. The rate of rise in pulmonary vascular pressures under conditions of quick onset high-intensity exercise is unknown. Catheter mounted manometers, whose in vivo signals were matched with pressure signals obtained via transducers connected to fluid-filled lumens from same cardiovascular sites, were used to compare right heart and pulmonary vascular pressures in 8 healthy Thoroughbreds perform...
Busija DW, Orr JA, Rankin JH, Liang HK, Wagerle LC.The effect of hyperoxia on cerebral blood flow (CBF) was examined in 12 unanesthetized ponies. CBF was determined using radioactive microspheres, 15 micrometer in diam, durijng inspriation of the following gases: 1) room air (control); 2) 40% I2 in N2; and 3) approximately 100% O2 with 2.2-4.5% CO2 added to maintain isocapnia. CBF did not change from control values during either level of hyperoxia. However, cerebrospinal fluid (CSF) carbon dioxide tension (PCO2) increased during 40% O2 (delta 1.0 Torr) and approximately 100% O2 (delta 2.9 Torr). This rise in CSF PCO2, not due to a change in CB...
Muir WW, Skarda RT, Sheehan WC.The cardiopulmonary effects of two xylazine-morphine sulfate drug combinations (mixtures) given IV were evaluated in horses. In horses given xylazine (0.66 mg/kg of body weight) and morphine sulfate (0.12 mg/kv) IV (experiment 1), there were significant (P less than 0.05) decreases in heart rate, cardiac output, and respiratory rate. Central venous pressure was significantly (P less than 0.05) increased. Arterial and pulmonary arterial blood pressures increased significantly (P less than 0.05) but transiently. Arterial blood gas tensions (PaCO2 and PaO2) and pH remained unchanged. In the horse...
Edner A, Nyman G, Essén-Gustavsson B.To compare the effects of spontaneous breathing and mechanical ventilation on haemodynamic variables, including muscle and skin perfusion measured with laser Doppler flowmetery, in horses anaesthetized with isoflurane. Methods: Prospective controlled study. Methods: Ten warm-blood trotter horses (five males, five females). Mean mass was 492 kg (range 420-584 kg) and mean age was 5 years (range 4-8 years). Methods: After pre-anaesthetic medication with detomidine (10 microg kg(-1)) anaesthesia was induced with intravenous (IV) guaifenesin and thiopental (4-5 mg kg(-1) IV) and maintained using i...
Peroni JF, Harrison WE, Moore JN, Graves JE, Lewis SJ, Krunkosky TM, Robertson TP.Equine laminitis purportedly involves haemodynamic dysfunction at the level of the laminar vasculature. However, to date, no studies have been performed characterising the function of laminar arteries and veins during the prodromal stages of equine laminitis. Objective: That the prodromal stages of laminitis are associated with contractile dysfunction of the equine laminar vasculature. Objective: To assess contractile function of laminar arteries and veins to phenylephrine (PE) and 5-hydroxytryptamine (5-HT). Methods: Horses were administered black walnut heartwood extract (BWHE) or water (con...
McConnell EJ, Rioja E, Bester L, Sanz MG, Fosgate GT, Saulez MN.Alterations in cerebral haemodynamics may contribute to perianaesthetic complications in horses. Near-infrared spectroscopy (NIRS) is frequently used intraoperatively in man to provide information regarding cerebral perfusion. Objective: To determine whether NIRS can identify trends in regional cerebral oxygen saturation (rSO2) in horses and whether there is a correlation between rSO2 and venous oxygen tensions. Methods: A cerebral oximeter sensor recorded rSO2 from the dorsal sagittal sinus of 6 healthy horses. Values for rSO2, arterial and venous oxygen and carbon dioxide tensions (PaO2, PvO...
Bowen IM, Marr CM, Chester AH, Wheeler-Jones CP, Elliott J.The equine aortic valve is subject to non-inflammatory degenerative changes, associated with aortic valvular regurgitation (AR). This disease shares pathological and epidemiological features with AR in humans, and may serve as a useful model to study in-vitro functional responses associated with aging and disease. The study aim was to determine the contractile properties of the normal equine aortic valve. Methods: The contractile responses of equine aortic valves to angiotensin II, the thromboxane-mimetic U44069, endothelin-1, 5-hydroxytryptamine and the alpha-adrenoceptor agonists medetomidin...
Masri M, Freestone JF, Wolfsheimer KJ, Shoemaker K.Plasma volume (PV) decreased by 13 per cent following the completion of 1,000 m of maximal exercise in the horse. This study demonstrated that the critical reduction in PV following maximal exercise occurred within 10 mins of completion of exercise, as previously reported in man. Total plasma protein (TPP) increased by 23 per cent at 2 and 5 mins, and by 21 per cent at 10 mins post exercise. Therefore, it does not appear to be an accurate measurement to assess the degree of PV contraction in the horse. Protein was apparently added to the intravascular space either during or following exercise....
Hedenstierna G, Nyman G, Kvart C, Funkquist B.The multiple inert gas elimination technique was adapted for use in the conscious standing horse. The modifications included increased infusion rate of the inert gases (30 ml/min), extended infusion time (60 mins) in order to reach steady state, and construction of a nose mask mixing box system for collection of expired gas. Eight adult horses with a mean weight of 454 kg and a mean age of 6.1 years were studied while standing under resting conditions. Ventilation was 65.2 liters/min and cardiac output measured by thermodilution 40.2 liters/min. Systemic and pulmonary artery mean pressures wer...
Bowker RM, Van Wulfen KK, Springer SE, Linder KE.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...
Erickson BK, Erickson HH, Coffman JR.Intravenous frusemide (1.0 mg/kg bwt) or phentolamine (0.33 mg/kg bwt) was given to 7 horses 1 h before exercise and their effects on pulmonary artery and aortic pressure changes during strenuous exercise were examined. Short-term near-maximal treadmill exercise (10 m/sec, 3 degrees incline) produced increases in heart rate, mean pulmonary artery pressure (PAP), mean aortic pressure (AP), and packed cell volume (PCV). Frusemide did not affect heart rate, PAP or PCV during exercise. Frusemide significantly decreased mean AP by 10 to 15 mmHg during exercise. Phentolamine produced an increase in ...
Rugh KS, Garner HE, Sprouse RF, Hatfield DG.Systemic arterial hypertension is associated with equine laminitis, a disease precipitated by gross over-ingestion of carbohydrates. We examined the hearts from nine chronically hypertensive (161 +/- 11/99 +/- 6 mmHg) laminitic ponies and nine normotensive (128 +/- 2/76 +/- 3 mmHg) ponies postmortem for signs of left ventricular hypertrophy. The hypertensive ponies had hearts which were significantly larger (7.77 +/- 0.26 g/kg bodyweight (BW) vs. 5.67 +/- 0.22 g/kg BW), as well as increased combined left ventricle and septum weight (4.99 +/- 0.21 g/kg BW vs. 3.67 +/- 0.20 g/kg BW) and left ven...
Manohar M, Goetz TE, Hassan AS.The objective of the present study was to examine the effects of preexercise NaHCO(3) administration to induce metabolic alkalosis on the arterial oxygenation in racehorses performing maximal exercise. Two sets of experiments, intravenous physiological saline and NaHCO(3) (250 mg/kg i.v.), were carried out on 13 healthy, sound Thoroughbred horses in random order, 7 days apart. Blood-gas variables were examined at rest and during incremental exercise, leading to 120 s of galloping at 14 m/s on a 3.5% uphill grade, which elicited maximal heart rate and induced pulmonary hemorrhage in all horses ...
Muir WW, McGuirk SM.Hemodynamic measurements were obtained from 17 horses with atrial fibrillation or flutter. Eight horses had atrial fibrillation of unknown duration. In 7 horses, atrial fibrillation developed during anesthesia. Atrial flutter developed during recovery from anesthesia in 2 horses. Hemodynamic measurements were considered normal in 7 of 8 conscious horses with atrial fibrillation. Cardiac output was decreased and pulmonary arterial blood pressure and right atrial pressure were increased in 1 conscious horse which had signs of congestive heart failure. Arterial blood pressure decreased in 5 of 7 ...
Steffey EP, Dunlop CI, Farver TB, Woliner MJ, Schultz LJ.Circulatory and respiratory function was monitored in nonmedicated, spontaneously breathing horses (n = 7) immediately before, during, and 1 hour after 85 +/- 4.1 (X +/- SEM) minutes of constant 1.57% isoflurane in O2 anesthesia. Comparison of values during anesthesia with those obtained while horses were awake revealed a significant (P less than 0.05) decrease in arterial blood pressure that was related to a slight, but insignificant, decrease in cardiac output and peripheral vascular resistance. Although isoflurane anesthesia and recumbency resulted in a significant (P less than 0.05) decrea...
Vernemmen I, Paulussen E, Dauvillier J, Decloedt A, van Loon G.This case report describes the 2-dimensional transthoracic (2D-TTE), 3-dimensional transthoracic (3D-TTE) and intracardiac echocardiographic (ICE) characterization of the fossa ovalis region in 2 horses. The first case was presented for poor performance and showed an anechoic zone in the interatrial septum on 2D-TTE. Based on 3D-TTE a deepened fossa ovalis could be identified and using ICE the presence of an interatrial shunt could be excluded. The second case was referred for a cardiac murmur and the presence of turbulent flow in and around the interatrial septum on 2D-TTE color flow Doppler....
Allen D, Clark ES, Moore JN, Prasse KW.A carbohydrate overload model was used in 8 horses to evaluate Starling forces and hemodynamics of the digit during the prodromal stage of acute laminitis. A pump-perfused extracorporeal digital preparation was used to evaluate blood flow, arterial pressure, venous pressure, capillary pressure, isogravimetric capillary filtration coefficient, osmotic reflection coefficient, and vascular compliance. From these data, pre- and postcapillary resistances and pre- to postcapillary resistance ratios were determined. Vascular and tissue oncotic pressures were estimated from plasma and lymph protein co...
Skarda RT, Muir WW.To determine the analgesic, hemodynamic, and respiratory effects induced by caudal epidural administration of meperidine hydrochloride in mares. Methods: 7 healthy mares. Methods: Each mare received meperidine (5%; 0.8 mg/kg of body weight) or saline (0.9% NaCl) solution via caudal epidural injection on 2 occasions. At least 2 weeks elapsed between treatments. Degree of analgesia in response to noxious electrical, thermal, and skin and muscle prick stimuli was determined before and for 5 hours after treatment. In addition, cardiovascular and respiratory variables were measured and degree of se...
Mansour C, Chaaya R, Sredensek J, Mocci R, Santangelo B, Allaouchiche B, Bonnet-Garin JM, Boselli E, Junot SA.To compare the sublingual microcirculation between healthy horses anesthetized for elective procedures and horses with colic anesthetized for abdominal surgery and to determine the effect of mean arterial blood pressure (MAP) on the microcirculation. Methods: 9 horses in the elective group and 8 horses in the colic group. Methods: Sublingual microcirculation was assessed with sidestream dark field video microscopy. Videos were captured at 3 time points during anesthesia. Recorded microvasculature parameters were De Backer score (DBS), total density of perfused vessels (PVD) and small vessels (...
Goodwin WA, Pasloske K, Keates HL, Ranasinghe MG, Woldeyohannes S, Perkins N.To determine the suitability of alfaxalone total intravenous (IV) anaesthesia in horses and concurrently evaluate infusion rates, cardiovascular effects, pharmacokinetics and the quality of the anaesthetic recovery period. Methods: Prospective, experimental study. Methods: Eight Standardbred horses. Methods: Horses were premedicated with IV acepromazine (0.03 mg kg) and xylazine (1 mg kg) and anaesthesia was induced with guaifenesin (35 mg kg) and alfaxalone (1 mg kg). Anaesthesia was maintained for 180 minutes using an IV infusion of alfaxalone at a rate determined by a horse's response to a ...
Pan LG, Forster HV, Bisgard GE, Murphy CL, Lowry TF.We investigated arterial PCO2 (PaCO2) and pH (pHa) responses in ponies during 6-min periods of high-intensity treadmill exercise. Seven normal, seven carotid body-denervated (2 wk-4 yr) (CBD), and five chronic (1-2 yr) lung (hilar nerve)-denervated (HND) ponies were studied during three levels of constant load exercise (7 mph-11%, 7 mph-16%, and 7 mph-22% grade). Mean pHa for each group of ponies became alkaline in the first 60 s (between 7.45 and 7.52) (P less than 0.05) at all work loads. At 6 min pHa was at or above rest at 7 mph-11%, moderately acidic at 7 mph-16% (7.32-7.35), and markedly...
Honnens A, Weisser S, Welter H, Einspanier R, Bollwein H.The objective of this study was to investigate the relationships between uterine perfusion and estrogen, progesterone and the uterine nitric oxide synthase (NOS) system in five trotter mares during the estrous cycle. Color Doppler sonography for measurement of uterine blood flow and collection of blood for determination of plasma estrogen and progesterone concentrations were performed on days 0 (= ovulation), 1, 5, 11 and 15 and daily during estrus (days -1 to -4) of one estrous cycle; endometrial biopsy collection for mRNA expression analysis of NOS and estrogen receptors was performed on day...
McConaghy FF, Hodgson DR, Hales JR, Rose RJ.Cardiac output (Q) and tissue blood flows (BF) were measured in four ponies at rest, after 30 min of moderate exercise (ME) (approximately 30% VO2max) and following moderately intense exercise (M-IE) (approximately 65%) until fatigue, in a mildly hot (MH) environment (dry bulb temperature = 41 degrees C, wet bulb temperature = 27.5 degrees C). Exercise at both intensities resulted in increases in Q (15.6 +/- 1.7 [rest] vs. 35.8 +/- 2.6 [ME] vs. 48.6 +/- 3.9 [M-IE] l/min) and VO2 (4.7 +/- 0.9 vs. 24.5 +/- 1.2 vs. 55.8 +/- 5.8 ml/kg/min). When compared to ME, M-IE resulted in decreases in BF to ...
Steffey EP, Hodgson DS, Dunlop CI, Miller MF, Woliner MJ, Heath RB, Grandy J.Hemodynamic and respiratory effects of 5 h of unvarying 1.57%, end-tidal (1.2 MAC) isoflurane in O2 anesthesia were characterized in ten left laterally recumbent horses. Compared to base line values at 30 min of constant dose isoflurane, cardiac output, hematocrit, total plasma solids, PaCO2, and peak inspired gas flow progressively and significantly (P less than 0.05) increased over the course of study. Arterial blood pressure increased (P less than 0.05) during the first 2 h of constant dose of isoflurane then decreased and remained near base line values. Inspiratory time progressively decre...
Brosnan RJ, Steffey EP, LeCouteur RA, Farver TB, Imai A.To test the hypothesis that isoflurane-anesthetized horses during controlled ventilation and spontaneous ventilation exhibit temporal changes in cerebral hemodynamics, as measured by intracranial pressure and cerebral perfusion pressure, that reflect temporal changes in systemic arterial pressure. Methods: 6 healthy adult horses. Methods: Horses were anesthetized in left lateral recumbency with 1.57% isoflurane in O2 for 5 hours in 2 experiments by use of either controlled ventilation (with normocapnia) or spontaneous ventilation (with hypercapnia) in a randomized crossover design. Intracrania...
Steyn PF, Ramey DW, Kirschvink J, Uhrig J.To determine the effect of a static magnetic field on relative blood flow to the metacarpus of horses. Methods: Randomized controlled clinical trial. Methods: 6 healthy adult horses. Methods: Red blood cells were radiolabeled in vivo by administration of technetium Tc 99m (pyro- and trimeta-) phosphates, and scintigraphic images were obtained 30 minutes later. A magnetic wrap that emitted a static magnetic field was applied to 1 metacarpus and a control wrap was applied to the contralateral metacarpus. Forty-eight hours later, the wraps were removed, and scintigraphy was repeated. Relative per...
