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.
van Aarde MN, Littlejohn A, Van der Walt JJ.A method was developed for determining the ratio of cardiopulmonary blood volume to stroke volume, in horses. The radioisotope 99 Tc (technetium 99m pertechnetate) was injected into the jugular vein as a bolus, which was then detected in the right and left ventricles consecutively by a scanning device consisting of a Na I crystal, a collimator, an amplifier and a discriminator. The radiocardiogram (RCG) and the ECG were recorded simultaneously by a two-channel writing device. The ratio of cardiopulmonary blood volume to stroke volume (cardiopulmonary flow index = CPFI) was then determined from...
Pan LG, Forster HV, Bisgard GE, Dorsey SM, Busch MA.We assessed the relationship of ventilation (VE) to cardiodynamic variables and CO2 transport in seven normal ponies during treadmill exercise. At 1.8, 3, and 6 mph, respectively, VE increased from 15 l/min at rest to 43, 51, and 86 l/min by 1 min and 48, 68, and 125 l/min by 8 min. In three ponies at the same work loads, cardiac output (Qc) increased from approximately 12 l/min at rest to 19.7, 28.1, and 40.3 l/min between 30-60 s (P less than 0.05) and then decreased by about 20% to a steady state by 3-4 min. Heart rate (HR) shows a similar biphasic response during exercise. Mean right ventr...
Forster HV, Pan LG, Bisgard GE, Dorsey SM, Britton MS.We characterized the temporal patterns of pulmonary O2 consumption (VO2) and CO2 excretion (VCO2) in exercising ponies. We also assessed the cardiac, ventilatory, and hematologic contributions to the VO2-VCO2 changes during exercise. At five moderate treadmill work loads in normal ponies, VO2 and VCO2 generally increased progressively throughout the 1st min reaching, respectively, approximately 95 and 80% of steady state by 45-60 s. Between 1 and 1.5 min, Vo2 and Vco2 were either stable or they decreased 300-500 ml, but then each increased slightly, reaching steady-state levels between 3 and 5...
Pan LG, Forster HV, Bisgard GE, Dorsey SM, Busch MA.We assessed cardiovascular variables and blood O2 contents in order to characterize O2 transport in ponies during treadmill exercise. In normal ponies at 1.8, 3, and 6 mph, respectively, cardiac output (Qc) increased from 12 l/min at rest to maximum levels of 19.7, 28.7, and 39.9 l/min between 30 and 60 s. Qc then decreased to steady-state levels of 18.2, 24.6, and 32.7 l/min by 4 min. Heart rate (HR) showed a similar biphasic response in the 1st min of exercise. Systolic and diastolic arterial blood pressure (BP) decreased at the onset of exercise by 20-25 Torr (P less than 0.05) and then inc...
Stewart JH, Rose RJ, Barko AM.Simultaneous echocardiograms, phonocardiograms and electrocardiograms were performed on 16 foals at the following times after birth: 15 mins, 60 mins, 2, 4, 12, 24, 48 h, four, seven, 14 days and four, eight and 12 weeks. Positive correlations were found between both age and body weight and the following measurements: left ventricular end-diastolic dimension, right ventricular end-diastolic dimension, left atrial dimension and aortic root dimension, posterior left ventricular wall thickness and interventricular septal thickness. Heart rate was negatively correlated with left ventricular electr...
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...
Miller PJ, Holmes JR.Systolic time intervals (STIs), isovolumic contraction time (ICT) and left ventricular ejection time (LVET) were recorded from seven horses with supraventricular arrhythmia. The STIs were measured over a number of beats (33 to 100) directly from the left ventricular (LV) and aortic (Ao) pressure contours which were recorded simultaneously using two catheter-mounted transducers. ICT was significantly (P less than 0.01) and directly related to beat-by-beat heart rate (HR = 60/pulse interval) and LVET was significantly (P less than 0.01) and inversely related to heart rate in each of five horses....
Miller PJ, Holmes JR.A method is described of processing transaortic valve pressures in the horse using the first derivative of the left ventricular pressure to define the beginning and end of each systolic complex. To determine the beginning of each systole three definitions of left ventricular end diastolic pressure (LVEDP), based on a 100, 150 or 200 mmHg/sec rate of left ventricular diastolic pressure rise, were evaluated. These definitions were also evaluated for their ability to determine isovolumic contraction time (ICT) and pulse interval. The best of these, LVEDP 150, was defined as the last point in dias...
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 ...
Hall LW.Respiratory dead-space, tidal volume, respiratory rate, blood gases, cardiac output, heart rate and arterial and pulmonary arterial blood pressures were measured in two conscious, trained ponies in the standing position and in left lateral recumbency. The ponies were reluctant to remain lying down for more than about 20 mins but the reason for this did not become apparent. Tidal volume was reduced during recumbency but the respiratory rate increased, tending to maintain the minute volume at about that of the standing animal. Arterial carbon dioxide tension did not change significantly from sta...
Bayly WM, Grant BD, Modransky PD.Arterial blood samples were collected during maximal exercise over 1.6 km in a thoroughbred horse with left laryngeal hemiplegia. Acid-base and blood gas measurements were performed on each sample and compared to the results from samples which were similarly collected 48 hours after laryngoplasty surgery was performed. Before surgery, the PaO2 was 53.2 mm Hg and the PaCO2 was 58.1 mm Hg after 1.6 km. After surgery, the corresponding results were 83.6 mm Hg (PaO2) and 39.0 mm Hg (PaCO2). There was no significant difference in the times taken for each gallop. The exercise intolerance associated ...
Holmes JR, Miller PJ.The paper describes clinical observations in three horses with ruptured mitral valve chordae. Horses with ruptured mitral valve chordae may have a history of sudden onset of acute distress with predominantly respiratory symptoms. On auscultation there will be a widespread pansystolic murmur with an extension of the area of cardiac auscultation. The third heart sound may be very pronounced and unduly prolonged, associated with high volume flow during early ventricular filling in diastole. However, these sounds are not specific for chordal rupture--they are typical of severe mitral regurgitation...
Kalpravidh M, Lumb WV, Wright M, Heath RB.The analgesic and behavioral effects of butorphanol (0.22 mg/kg), flunixin (2.2 mg/kg), levorphanol (0.033 mg/kg), morphine (0.66 mg/kg), and xylazine (2.2 mg/kg), given IM were observed in 8 ponies. These ponies were instrumented to measure response objectively to painful superficial and visceral stimuli. Effects on the cardiopulmonary system and rectal temperature also were evaluated in 6 of these ponies. Observations were conducted before drug injection (base-line values) and after injection at 30, 60, 120, 180, and 240 minutes. Xylazine provided the highest pain threshold for the first 60 ...
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...
Parry BW, McCarthy MA, Anderson GA.Resting coccygeal blood pressure values were measured, indirectly, on 296 horses (97 Thoroughbreds, 97 Standardbreds and 102 hacks). Blood pressure was found to vary with the class of horse examined; on average Thoroughbreds had significantly higher values than Standardbreds and hacks, whereas blood pressures of the last two groups were not significantly different. There was no demonstrable effect of sex, height or heart rate on blood pressure, but temperature and age did influence the value recorded. Mean (+/- sd) (n = 296) coccygeal uncorrected values (systolic pressure/diastolic pressure) w...
Wagerle LC, Orr JA, Shirer HW, Kiorpes AL, Fraser DB, DeSoignie RC.The purpose of these studies was to examine the time course of the cerebrovascular response to acute hypoxia in unanesthetized ponies. An electromagnetic flow transducer chronically placed on the internal carotid artery of the pony allowed continuous recording of internal carotid artery blood flow (ICBF) which has been shown to be representative of cerebral blood flow (CBF). The ponies were subjected to three levels of acute isocapnic hypoxia (PaO2 = 62, 44, and 39 mm Hg for hypoxia level I, II, and III, respectively), and the temporal and steady-state cerebrovascular response was examined. IC...
Parks CM, Manohar M.Blood flow to the brain, heart, kidneys, diaphragm, and skeletal muscles was studied at rest and during graded treadmill exercise, using radionuclide-labeled microspheres (15 microns diameter), in 11 healthy adult ponies. Hemodynamic changes brought about by exercise included marked increases in cardiac output, mean aortic pressure, left ventricular end-diastolic pressure, and right ventricular systolic and end-diastolic pressures. Blood flow to the brain stem and cerebral hemispheres was unchanged during both moderate exercise (heart rate = 154 +/- 3 beats/min) and severe exercise (heart rate...
Robertson JT, Muir WW.A xylazine and butorphanol drug combination produced minimal and transient hemodynamic effects and no significant respiratory depression when administered to 6 healthy horses. Combining xylazine and butorphanol produced a synergistic analgesic effect and provided good chemical restraint for a standing surgical procedure.
Miller PJ, Holmes JR.Transaortic blood pressures were recorded in seven horses using catheter mounted transducers during various types of supraventricular arrhythmia. Changes in left ventricular (LV) and aortic (Ao) pulse contours were associated with variation in pulse interval (PI). When PI lengthened there was a rise in LV end diastolic pressure (LVEDP) associated with a prolonged filling time. In contrast, a long PI resulted in a reduced end diastolic Ao pressure (AoEDP) due to a prolonged arterial 'run off'. LVdP/dt max representing the peak rate of rise of pressure during the isovolumic contraction period wa...
Parks C, Manohar M, Lundeen G.To examine the effects of tachycardia on coronary circulation, transmural distribution of myocardial blood flow (MBF, 15-micron diameter radionuclide-labeled microspheres) was studied in six healthy adult ponies at rest (heart rate = 60 +/- 7 beats . min-1), during ventricular pacing at 150 and 200 beats . min-1, as well as with ventricular pacing at 250 beats . min-1 before and during maximal coronary vasodilatation (iv adenosine infusion; 4 mumole . kg-1 . min-1). Mean aortic pressure and cardiac output were unchanged from control values with ventricular pacing. Whereas ventricular pacing at...
Muir WW, Wade A, Grospitch B.Systolic, diastolic, and mean arterial blood pressures and heart rate were determined in 73 horses, using an indirect automatic oscillometric technique. Blood pressure and heart rate data obtained by sphygmomanometry were compared with similar data obtained from cannulation of the horses' facial or dorsal metatarsal arteries. Good correlation between direct (actual) and indirect (oscillometric) blood pressures and heart rate measurements were obtained when the heart rate was low, using high sensitivity setting. Cardiac arrhythmias or hypotension prevented oscillometric measurements from being ...
Parks CM, Manohar M.Transmural distribution of myocardial blood flow and coronary vasodilator reserve (15-microns-diam radionuclide-labeled microspheres) was studied in 11 adult, healthy ponies at rest and during moderate and severe exercise performed on a treadmill (heart rate 56 +/- 4, 154 +/- 3, and 225 +/- 7 beats . min-1, respectively.). Exercise resulted in a marked increase in cardiac output, mean aortic pressure, right ventricular (RV) systolic and end-diastolic pressure, left ventricular (LV) end-diastolic pressure, and the maximum rate of rise of LV pressure LV (dP/dtmax). Accompanying these changes was...
Bayly WM, Gabel AA, Barr SA.Seven healthy, unexercised, previously trained, adult Standardbred horses were allotted to 2 groups and trained 78 days on a treadmill set at a 7 degree 30' angle. The groups were trained on different schedules, and the effects of training on heart rate, cardiac output, stroke volume, arteriovenous oxygen difference, systemic blood pressure, and venous lactic acid were determined. Measurements were made at rest, during exercise on the treadmill at rates of 55 m/min, 75 m/min, 100 m/min, and 154 m/min, and at 5 minutes after exercise (standardized exercise test). Heart rate and cardiac output d...
Moore AB, Roesel OF, Fessler JF, Bottoms GD.The value of naloxone (1 mg/kg of body weight/hr for 4 hrs), a beta-endorphin antagonist, was assessed in the management of endotoxin-induced shock in ponies. Three groups of 5 ponies each were used: controls, ponies given Escherichia coli endotoxin put untreated, and ponies given endotoxin and then treated with naloxone. Endotoxin-induced changes in hemodynamics, blood chemical values, regional blood flow, plasma enzymes, and energy supplies were measured at selected times during the first 6 hours after endotoxin was given. There was no evidence that beta-endorphins released during shock were...
Dintenfass L, Fu-lung L.Nineteen racehorses have been studied for haemorheologic factors as earlier studies showed a definite correlation between physical fitness and these factors in humans. Results included individual values for all viscosity factors, and the arithmetic means, the latter showing 4.70 +/- 0.49 cP for blood viscosity measured at a shear rate of 180 s-1; 1.100 +/- 0.048 cP for plasma viscosity; 1.045 +/- 0.063 for the rigidity of red cells defined by term 'Tk'; 42.2 +/- 4.1% haematocrit; 290 +/- 39 mg per 100 ml for fibrinogen level; and 278 +/- 75 mm h-1 for aggregation of red cells at 37 degrees C (...
Holmes JR.This paper discusses certain aspects of circulatory physiology, including foetal circulation and the role of the thorax, and gives parameters for total blood volume, cardiac output, stroke volume and the distribution of blood between the pulmonary and peripheral circulation within the horse. The reader is taken on a journey around the circulatory system, beginning in the left atrium, into which richly oxygenated blood runs from the pulmonary veins. From here the blood is squeezed via the mitral valve into the left ventricular pump, where it is forced under high pressure through the peripheral ...
Moore JN, Garner HE, Shapland JE, Roberts MC.The infusion (IV) of prostacyclin (PGI2) into conscious ponies resulted in systemic arterial hypotension and tachycardia. Mean systemic arterial pressure decreased from 103.3 mm of Hg to 88.5 mm of Hg when 125 ng of PGI2/kg/minute was infused, and heart rate increased from 55.0 to 102.0 beats/minute. When 208 ng of PGI2/kg/minute was infused, mean systemic arterial pressure decreased from 103.3 to 78.0 mm of Hg and heart rate increased from 55.0 to 109.3 beats/minute. There were no significant alterations in pulmonary arterial pressure, lactate, PCV, total WBC count, platelet count, serum lact...
Bottoms GD, Templeton CB, Fessler JF, Johnson MA, Roesel OF, Ewert KM, Adams SB.This study had 2 objectives: (i) to correlate plasma thromboxane and prostaglandin I2 (epoprostenol) concentrations with hemodynamic changes occurring in equine endotoxin shock, and (ii) to determine the effects of flunixin meglumine on plasma concentrations of these prostaglandins relative to hemodynamic changes. Shock was induced in 2 groups, each of 4 anesthetized ponies, and in a 3rd group of 2 ponies. Group A ponies were given endotoxin only (and were not treated), and group B ponies were given endotoxin and then treated with flunixin meglumine. Group C ponies were treated with flunixin m...
Olson NC.Effects of endotoxemia on lung water, hemodynamics, and gas exchange were determined in ponies breathing a mixture of halothane and 100% O2. Escherichia coli endotoxin was infused IV at 20 micrograms/kg of body weight for 1 hour followed by 10 micrograms/kg/hr the subsequent 4 hours. By 0.25 hour, endotoxin increased mean pulmonary artery pressure and pulmonary vascular resistance; this was followed by a return to base-line values by 0.5 and 1 hour, respectively. A 2nd increase in pulmonary vascular resistance occurred by 5 hours of endotoxemia. During the last 2 hours of endotoxin infusion, c...
Van Hoogmoed LM, Snyder JR, Nieto J, Harmon FA.To determine whether a customized solution could attenuate the effects of low-flow ischemia and reperfusion injury of the equine jejunum. Methods: A segment of jejunum obtained from 21 healthy adult horses. Methods: A segment of jejunum was maintained in an isolated extracorporeal circuit, and arterial flow was reduced to 20% of baseline for 40 minutes (ischemia) followed by 60 minutes of reperfusion. In 1 group, a customized solution was infused at a rate of 1 ml/min during low-flow ischemia and 3 ml/min during reperfusion. In a second group, the solution was infused at the same rate during l...
Foreman JH, Waldsmith JK, Lalum RB.Three-day event horses are subject to various external environmental stresses including changes in ambient temperature, humidity, altitude, and test severity. Considerable research on the adverse effects of increased heat and humidity preceded the 1996 Olympic Summer Games in Atlanta, Georgia USA, but no research has been done previously on the effects of altitude on 3-day eventing. Physical and venous blood gas data were collected on horses (n = 24) competing in the High Prairie Preliminary (CCN*) and Intermediate (CCN**) 3-day events and Preliminary Horse Trials in Parker, Colorado (1900 m a...
Hunt RJ, Moore JN, Allen D.In 6 adult horses anesthetized with pentobarbital, the hemodynamic responses of the equine digit to infusion of dopamine were evaluated by use of an isolated extra corporeal pump perfused digital preparation. Digital blood flow was maintained at a constant rate that was independent of systemic hemodynamic changes. Three sequential experiments were performed on each horse. In the first experiment (n = 6), dopamine was infused IV at rates of 1.0, 2.5, and 5.0 micrograms/kg/min. For the second experiment (n = 5), dopamine (400 micrograms/ml) was infused into the digital artery at the rates of 0.0...
Foth PW, Gardner A, Pereira CR, Cooper E, Schroeder E, Mudge MC.To assess oral buccal microcirculation by hand-held videomicroscopy in horses during colic surgery, comparing microcirculation values with macrocirculatory parameters and with those of healthy elective surgical horses. Methods: Clinical prospective study. Methods: Client-owned horses (nine in the colic group; 11 in the elective group). Methods: In the colic group, buccal mucosal side stream dark-field microscopy (DFM) videos, cardiac output (CO), mean arterial pressure (MAP), and lactate were obtained at three timepoints under general anesthesia (30, 90, and 150 min after induction). Video a...
Veenman JN, Dujardint CL, Hoek A, Grootendorst A, Klein WR, Rutten VP.Equine acute abdominal disease is often associated with shock. Important aspects in the onset of this complication include hypovolaemia, the translocation of endotoxins from the gut and the subsequent activation of the cytokine network. The clinical efficacy of high volume continuous venovenous haemofiltration (HV-CVVH) and the clearance of cytokines were therefore investigated in an equine endotoxaemic model. Ten male Shetland ponies received a slow infusion of LPS (2 microg/kg bwt) under general anaesthesia. The treatment group (n = 5) received HV-CVVH (2 ml/kg bwt/min) using a 75 kD polymet...
Gasthuys F, de Moor A, Parmentier D.Haemodynamic and respiratory responses to halothane were investigated in dorsally recumbent, ventilated ponies during 2 hours. Normocapnia was maintained using intermittent positive pressure ventilation. Compared to the base line values at 30 minutes of constant dose halothane, no significant changes in heart rate, systemic blood pressure, cardiac output, cardiac index, stroke volume and left ventricle work were observed during a 2 hours anaesthesia. Arterial oxygenation increased initially (greater than 300 mm Hg) but tended to decrease non-significantly during the rest of the anaesthesia. Bl...
Amin TM, Sirs JA, Allen BV, Colles CM.A preliminary investigation has been undertaken of blood rheology in horses and ponies, its variation in navicular disease and the changes following treatment with warfarin. Erythrocyte flexibility, measured by a centrifuge packing technique, is higher in horses (30 per cent min-1) than in ponies (23.8 per cent min-1). There are corresponding differences in blood viscosity. The high erythrocyte flexibility in horses is caused by an unknown factor present in plasma. The erythrocyte flexibility in horses with navicular disease is even higher, at 38.5 per cent min-1. Treatment with warfarin reduc...
Lester GD, DeMarco VG, Norman WM.To evaluate the efficacy of inhaled nitric oxide (NO) in anesthetized healthy newborn foals with experimentally induced pulmonary hypertension. Methods: Five 1- to 3-day-old foals. Methods: Anesthesia was induced and maintained with propofol, and foals were intubated and mechanically ventilated. Systemic pressure and pulmonary arterial pressure (P(PA)) were recorded every 30 seconds. Hypertension was induced via a hypoxic gas mixture or chemical vasoconstriction, using the thromboxane mimetic U46619. Nitric oxide was added at a concentration of 80 parts per million (ppm) for 6 minutes under ba...
Witherington DH.The post-race heart rates have been recorded in 1,000 Thoroughbreds following Flat, Hurdle and Steeplechase races in varying climatic conditions and on 54 different British racecourses. The post-race deceleration of the heart rate, under racecourse conditions, was marked by an apparent three-phase recovery period. Reference is made to the normal heart sounds and to the relationship between the heart and respiratory rates.
Bayly WM, Grant BD, Modransky PD.Arterial blood samples were collected during maximal exercise over 1.6 km in a thoroughbred horse with left laryngeal hemiplegia. Acid-base and blood gas measurements were performed on each sample and compared to the results from samples which were similarly collected 48 hours after laryngoplasty surgery was performed. Before surgery, the PaO2 was 53.2 mm Hg and the PaCO2 was 58.1 mm Hg after 1.6 km. After surgery, the corresponding results were 83.6 mm Hg (PaO2) and 39.0 mm Hg (PaCO2). There was no significant difference in the times taken for each gallop. The exercise intolerance associated ...
Matthews NS, Lindsay SL.Minimum alveolar concentration (MAC) for halothane was measured before and after administration of intravenous butorphanol (0.022 and 0.044 mg/kg in bodyweight in nine yearling Shetland ponies. Arterial blood pressure, heart rate, respiratory rate, expired CO2 and rectal temperature was also measured. Even though mean MAC values decreased 10 and 9 per cent after the low and high doses respectively, they were not statistically different from those measured prior to butorphanol. Halothane MAC values increased after butorphanol in two ponies, both animals increasing locomotor activity and demonst...
Boatwright RB, Williams DO, Rugh KS, Sarazan RD, Ross CR, Garner HE, Griggs DM.Coronary collateral growth was stimulated in chronically instrumented conscious ponies by a previously validated intermittent coronary occlusion method. Changes in regional myocardial function (sonomicrometry) and reactive hyperemia (Doppler method) were used to monitor collateral growth and to program measurements of regional myocardial blood flow (microsphere method). A serial analysis of the transmural and lateral distributions of collateral blood flow was performed at the native and three superimposed levels of collateral growth. Results in nine animals undergoing an average of 553 +/- 188...
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...
Raisbeck MF, Garner HE, Osweiler GD.Gram negative endotoxins play a contributory role in the syndrome which results from over consumption of carbohydrates by horses and ponies. Since the antibiotic polymyxin B exerts a direct anti-endotoxin effect by chemically modifying the active lipid A moiety of endotoxin, it might be expected to protect horses after carbohydrate overload and provide a new therapeutic and experimental tool for this condition. The present study was undertaken to evaluate the effect of polymyxin B on hemostatic, hemodynamic, acid-base, and clinical aspects of the syndrome resulting from carbohydrate overload. ...
Moore AB, Roesel OF, Fessler JF, Bottoms GD.The value of naloxone (1 mg/kg of body weight/hr for 4 hrs), a beta-endorphin antagonist, was assessed in the management of endotoxin-induced shock in ponies. Three groups of 5 ponies each were used: controls, ponies given Escherichia coli endotoxin put untreated, and ponies given endotoxin and then treated with naloxone. Endotoxin-induced changes in hemodynamics, blood chemical values, regional blood flow, plasma enzymes, and energy supplies were measured at selected times during the first 6 hours after endotoxin was given. There was no evidence that beta-endorphins released during shock were...
Steffey EP, Dunlop CI, Cullen LK, Hodgson DS, Giri SN, Willits N, Woliner MJ, Jarvis KA, Smith CM, Elliott AR.Cardiovascular and respiratory changes that accompany markedly long periods (12 hours) of halothane anesthesia were characterized. Eight spontaneously breathing horses were studied while they were positioned in left lateral recumbency and anesthetized only with halothane in oxygen maintained at a constant end-tidal concentration of 1.06% (equivalent to 1.2 times the minimal alveolar concentration for horses). Results of circulatory and respiratory measurements during the first 5 hours of constant conditions were similar to those previously reported from this laboratory (ie, a time-related sign...
Clark ES, Moore JN.Lateral cecal arterial blood flow, carotid arterial pressure, heart rate, and mechanical activity of the circular and longitudinal muscle layers of the cecal body were measured in 7 conscious healthy horses during IV infusion of physiologic saline solution for 60 minutes (control), during a 60-minute IV infusion of dopamine (at dosages of 1, 2.5, and 5 micrograms/kg/min), and for 60 minutes after IV infusion of dopamine. The mean values for lateral cecal arterial blood flow during IV infusion of dopamine at a dosage of either 1 or 2.5 micrograms/kg/min were not significantly different from the...
Raisis AL, Young LE, Meire H, Walsh K, Taylor PM, Lekeux P.The purpose of this study was to determine the repeatability of femoral blood flow recorded using Doppler ultrasound in anaesthetised horses. Doppler ultrasound of the femoral artery and vein was performed in 6 horses anaesthetised with halothane and positioned in left lateral recumbency. Velocity spectra, recorded using low pulse repetition frequency, were used to calculate time-averaged mean velocity (TAV), velocity of component a (TaVa), velocity of component b (TaVb), volumetric flow, early diastolic deceleration slope (EDDS) and pulsatility index (PI). Within-patient variability was deter...
Powers SK, Beadle RE, Thompson D, Lawler J.The purpose of these experiments was to examine the temporal pattern of arterial carbon dioxide tension (PaCO2) to assess the relationship between alveolar ventilation (VA) and CO2 return to the lung at the onset and offset of submaximal treadmill exercise. Five healthy ponies exercised for 8 min at two work rates: 50 m/min 6% grade and 70 m/min 12% grade. PaCO2 decreased (P less than 0.05) below resting values within 1 min after commencement of exercise at both work rates and reached a nadir at 90 s. PaCO2 decreased maximally by 2.5 and 3.5 Torr at the low and moderate rate, respectively. Aft...
Wagerle LC, Orr JA, Shirer HW, Kiorpes AL, Fraser DB, DeSoignie RC.The purpose of these studies was to examine the time course of the cerebrovascular response to acute hypoxia in unanesthetized ponies. An electromagnetic flow transducer chronically placed on the internal carotid artery of the pony allowed continuous recording of internal carotid artery blood flow (ICBF) which has been shown to be representative of cerebral blood flow (CBF). The ponies were subjected to three levels of acute isocapnic hypoxia (PaO2 = 62, 44, and 39 mm Hg for hypoxia level I, II, and III, respectively), and the temporal and steady-state cerebrovascular response was examined. IC...
Amend JF, Ross JN, Garner HE, Rosborough JP, Hoff HE.This report describes the measurement of systolic time intervals in a nine year old female domestic pony which was found at necropsy to show coarctation of the aorta and bilateral ventricular hypertrophy. Electrocardiogram, phonocardiogram and direct arterial blood pressure were recorded from the pony in a standing unmedicated state and systolic time intervals were measured from the resulting tracings. A prolongation of left ventricular ejection time and shortening of the pre-ejection period were observed in comparison to a group of normal ponies similarly examined. Such changes are consistent...
Parks AH, Stick JA, Arden WA, Chou CC, Hengemuhle SM.The influence of distention (high baseline intraluminal pressure) and neostigmine methylsulfate on intestinal vascular resistance, oxygen uptake, and intraluminal pressure changes (rhythmic contractions) was studied in terminal jejunal segments, which were perfused at a constant rate, in 16 anesthetized ponies. When baseline intraluminal pressure was increased to 10 mm of Hg, the intestinal vascular resistance and amplitude of rhythmic contractions were increased. Neostigmine induced cyclic increases in amplitude of rhythmic contractions whether intraluminal pressure was 0 or 10 mm of Hg. Neos...
Marlin DJ, Young LE, McMurphy R, Walsh K, Dixon P.There is evidence that halothane inhibits nitric oxide synthase in vitro, but the effect of intravenous anaesthetic agents is less clear. This study was undertaken to compare the rate of exhaled nitric oxide production (VNO) in spontaneously breathing horses anaesthetized with halothane or an intravenous regimen. Seven adult horses were studied twice in random order. After premedication with romifidine 100 microg kg(-1), anaesthesia was induced with ketamine 2.2 mg kg(-1) and maintained with halothane in oxygen (HA) or by an intravenous infusion of ketamine, guaiphenesin and romifidine (IV). I...
Lee YH, Clarke KW, Alibhai HI.The effects on intramuscular blood flow and cardiopulmonary parameters of changing from anaesthesia with halothane to isoflurane and vice versa were investigated in six ponies (small horses). Anaesthesia was induced with xylazine, ketamine and diazepam, maintained for one hour with halothane at an end tidal concentration of 1 per cent and then with isoflurane at 1.5 per cent for a further hour (halo/iso). On another occasion the order in which the volatile agents were administered was reversed (iso/halo). After one hour of anaesthesia the mean (sd) arterial blood pressure (MAP) and cardiac out...
Ambrisko TD, Coppens P, Kabes R, Moens Y.This study compares cardiac output (CO) measurements obtained by lithium dilution (LiDCO), pulse power analysis (PulseCO), and continuous thermodilution (CTD) with bolus thermodilution (BTD) in ponies. Methods: Eight isoflurane-anaesthetized Shetland ponies received xylazine, ketamine, and midazolam infusions (0.3, 1.2, and 0.018 mg kg(-1) h(-1), respectively). CO was measured with BTD, CTD, LiDCO, and PulseCO. Lithium was injected into the jugular vein and blood was sampled from the facial artery for lithium detection and this artery was also used for PulseCO. Measurements were obtained durin...
Nollet H, Van Loon G, Deprez P, Sustronck B, Muylle E.To establish reference values for right ventricular maximal rate of increase in pressure (dP/dt(max)) in horses and determine the usefulness of this variable to evaluate cardiac contractility. Methods: 15 crossbred horses, 3 to 20 years old. Methods: Cardiac catheterization was performed, using a high-fidelity catheter tip micromanometer, to determine right ventricular dP/dt(max). The following mathematic corrections were made: for preload, (dP/dt(max))/instantaneous total pressure, (dP/dt(max))/instantaneous developed pressure, and (dP/dt(max))/end diastolic pressure; for afterload, (dP/dtCPI...
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...
Manohar M, Duren SE, Sikkes B, Day J, Baker JP.Distribution of blood flow among various respiratory muscles was examined in 8 healthy ponies during submaximal exercise lasting 30 minutes, using radionuclide labeled 15-microns diameter microspheres injected into the left ventricle. From the resting values (40 +/- 2 beats/min; 37.3 +/- 0.2 C), heart rate and pulmonary arterial blood temperature increased significantly at 5 (152 +/- 8 beats/min; 38.6 +/- 0.2 C), 15 (169 +/- 6 beats/min; 39.8 +/- 0.2 C), and 26 (186 +/- 8 beats/min; 40.8 +/- 0.2 C) minutes of exertion, and the ponies sweated profusely. Mean aortic pressure also increased progr...
