Conscious Horses Research Articles

Pharmacodynamic effects and pharmacokinetic profile of a long‐term continuous rate infusion of racemic ketamine in healthy conscious horses

Ketamine (KET) possesses analgesic and anti-inflammatory activity at sub-anesthetic doses, suggesting a benefit of long-term KET treatment in horses suffering from pain, inflammatory tissue injury and/or endotoxemia. However, data describing the pharmacodynamic effects and safety of constant rate infusion (CRI) of KET and its pharmacokinetic profile in nonpremedicated horses are missing. Therefore, we administered to six healthy horses a CRI of 1.5 mg/kg/h KET over 320 min following initial drug loading. Cardiopulmonary parameters, arterial blood gases, glucose, lactate, cortisol, insulin, nonesterified fatty acids, and muscle enzyme levels were measured, as were plasma concentrations of KET and its metabolites using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Levels of sedation and muscle tension were scored. Respiration and heart rate significantly increased during the early infusion phase. Glucose and cortisol significantly varied both during and after infusion. During CRI all horses scored 0 on sedation. All but one horse scored 0 on muscle tension, with one mare scoring 1. All other parameters remained within or close to physiological limits without significant changes from pre-CRI values. The mean plasma concentration of KET during the 1.5 mg/kg/h KET CRI was 235 ng/mL. The decline of its plasma concentration-time curve of both KET and norketamine (NKET) following the CRI was described by a two-compartmental model. The metabolic cascade of KET was NKET, hydroxynorketamine (HNK), and 5,6-dehydronorketamine (DHNK). The KET median elimination half-lives (t1/2alpha and t1/2beta) were 2.3 and 67.4 min, respectively. The area under the KET plasma concentration-time curve (AUC), elimination was 76.0 microg.min/mL. Volumes of C1 and C2 were 0.24 and 0.79 L/kg, respectively. It was concluded that a KET CRI of 1.5 mg/kg/h can safely be administered to healthy conscious horses for at least 6 h, although a slight modification of the initial infusion rate regimen may be indicated. Furthermore, in the horse KET undergoes very rapid biotransformation to NKET and HNK and DHNK were the major terminal metabolites.

Subarachnoidally administered hyperbaric morphine, buprenorphine, methadone, and 10% dextrose on cardiopulmonary function and behavior in horses

The study was done to compare the heart rate, arterial blood pressure, arterial blood gases, respiratory rate, body temperature, and behavior after subarachnoid administration of hyperbaric morphine (MorphineD10), buprenorphine (BuprenorphineD10), methadone (Methadone D10), and 10% dextrose (D10) in conscious horses. Six adult horses were studied. Treatments were administered into the lombo-sacral subarachnoid space through an epidural catheter, MorphineD10 at 0.01mg kg-1, BuprenorphineD10 at 0.001mg kg-1, MethadoneD10 at 0.01mg kg-1, and 10% dextrose as a control group. The results showed that there are minimum changes in heart and respiratory rate, blood gases, blood pressure, and body temperature after subarachnoid administration of hyperbaric opioids in horses. No sedation and nor motor impairment or behavioral changes occur.

A technique for the collection and the study of biochemical and microbial characteristics of postprandial gastric contents from conscious horses

The objective of this study was to collect gastric contents from conscious horses via naso-gastric (NG) intubation to facilitate the study of the microbial ecosystem of the equine stomach. Six healthy Arabian horses (from 3 to 5 years old) were used according the following procedure. Two hours after the morning feeding, horses were sedated and restrained for NG intubation. A video-endoscope passed through a NG tube was used to position the NG tube in contact with the digesta. The video-endoscope was removed, the digesta were aspirated through the NG tube and collected. Each horse was sampled two times on 2 days according to the protocol. Volume, pH, temperature, dry matter (DM), total anaerobes and lactobacilli microbial populations, volatile fatty acids (VFA), ammonia (NH 3), d-glucose and d-/ l-lactate concentrations were measured on each sample. Repeatability and reproducibility were calculated for each variable. The technique allowed collection of 190 ± 68 ml of gastric contents during each sampling time, which provided the necessary quantities for the various analyses performed. Repeatability of the variables studied ranged from 0.39 for DM up to 0.90 for lactobacilli counts, whereas reproducibility ranged from 0.19 for volume to 0.89 for d-glucose concentration. Paired with classical endoscopic exam for equine gastric ulcer syndrome (EGUS) diagnosis, this collection technique can be easily used by scientists and veterinarians to study the relationship between some major chyme characteristics such as pH, microbial populations and lactate, and the occurrence of diseases such as EGUS.

Effect of romifidine on the nociceptive withdrawal reflex and temporal summation in conscious horses

To investigate the action of a single IV administration of romifidine on the thresholds of the nociceptive withdrawal reflex (NWR) and temporal summation in conscious horses. 10 adult horses. Single electrical stimulations were applied on the digital nerves to evoke NWR from the left forelimb and hind limb. Repeated electrical stimulations (10 stimuli, 5 Hz) were given to obtain temporal summation. Surface electromyographic reflex activity was recorded from the common digital extensor and cranial tibial muscles. After baseline assessment of NWR and temporal summation thresholds, romifidine (80 microg x kg(-1), IV) was administered. Successive determinations of NWR and temporal summation thresholds were performed 5, 25, and 55 minutes after administration. Romifidine significantly increased the current intensities necessary to evoke NWR and temporal summation in forelimbs and hind limbs of horses. Values were significantly higher than baseline values 55 minutes after romifidine administration. After administration of romifidine, a facilitation of reflex components of tactile origin was observed when repeated stimulations were applied. Results confirm antinociceptive activity of romifidine and may represent an objective demonstration of the well-known hypersensitivity to tactile stimuli observed in horses receiving alpha2-adrenoreceptor agonists in clinical practice. Romifidine can be included in analgesic and anesthetic protocols to provide additional analgesia in horses.

Subtotal Ostectomy of Dorsal Spinous Processes Performed in Nine Standing Horses

To describe and evaluate subtotal ostectomy of dorsal spinous processes (DSP) performed in standing horses. Retrospective study. Nine adult horses. The diseased portions of the DSP were removed with the horses standing and sedated after infiltrating a local anesthetic agent around the affected DSP. Medical records of affected horses were reviewed to determine history, findings of physical and radiographic examination, surgical technique, postoperative complications, and outcome. Five horses had subtotal ostectomy of DSP because of osteomyelitis, and 4 because of impingement and/or fracture of DSP. Affected portions of DSP were removed safely and effectively, with no apparent discomfort to the horses; hemorrhage was minimal. Subtotal ostectomy of DSP can be performed safely in standing, conscious horses and the risks associated with general anesthesia are eliminated. Hemorrhage is minimal compared to that which occurs when the procedure is performed with horses anesthetized and in lateral recumbency. Access and visibility are better when subtotal ostectomy of the DSP is performed with the horse standing rather than anesthetized and in lateral recumbency. Performing subtotal ostectomy of diseased DSP with the horse standing avoids the expense and risks of general anesthesia.

High inspired oxygen concentrations increase intrapulmonary shunt in anaesthetized horses

ObjectivesTo compare pulmonary function and gas exchange in anaesthetized horses during and after breathing either O2-rich gas mixtures or air. AnimalsSix healthy standard bred trotters (age range 3–12 years; mass range 423–520 kg), four geldings and two mares. Study designRandomized, cross-over experimental study. MethodsHorses were anaesthetized on two occasions with tiletamine-zolazepam after pre-anaesthetic medication with acepromazine, romifidine and butorphanol. After endotracheal intubation and positioning in left lateral recumbency, animals were allowed to breathe spontaneously. One of two, randomly allocated inspired gas treatments was provided: either i) room air (fractional concentration of inspired O2 [FiO2] = 0.21) provided throughout anaesthesia; or ii) an O2-rich gas mixture (FiO2 = >0.95) for 15 minutes, followed by room air. The alternative treatment was delivered at the second anaesthetic. Respiratory and haemodynamic variables and the distribution of ventilation-perfusion (VA/Q) ratios (using the multiple inert gas elimination technique) were determined in the standing conscious horse (baseline) after sedation and during anaesthesia. ResultsBreathing O2-rich gas was associated with a decreased respiratory rate (p = 0.015) increased PaCO2 (p < 0.001) and increased PaO2 (p = 0.004) compared with breathing air. All horses developed intrapulmonary shunt during anaesthesia, but shunt was significantly greater (13 ± 5%) when O2-rich gas was delivered compared with air breathing (5 ± 2%; p = 0.013). Ten minutes after O2-rich gas was replaced by air, shunt remained larger in horses that had initially received oxygen compared with those breathing air (p = 0.042). Mixed venous oxygen tensions were significantly lower during sedation than at baseline (p < 0.001) and during anaesthesia (p < 0.001). ConclusionsDuring dissociative anaesthesia, arterial oxygenation was greater when horses breathed gas containing more than 95% oxygen, compared with when they breathed air. However, breathing O2-rich gas increased intrapulmonary shunt and caused hypoventilation. The intrapulmonary shunt created during anaesthesia by high inspired O2 concentrations remained larger when FiO2 was reduced to 0.21, indicating that absorption atelectasis produced during O2-rich gas breathing persisted throughout anaesthesia. Clinical relevanceIn healthy horses undergoing short-term dissociative anaesthesia, air breathing ensures a level of oxygen delivery that meets tissue demand. There is no benefit to horses in breathing O2-rich gas after the gas supply is discontinued. On the contrary, the degree of shunt induced by breathing O2-rich gas persists. The clinical relevance of this during recovery requires investigation.

Effects of Topical Nitroglycerine Patches and Ointment on Digital Venous Plasma Nitric Oxide Concentrations and Digital Blood Flow in Healthy Conscious Horses

To measure and compare palmar digital venous plasma nitric oxide (NO) concentrations and digital arterial blood flow after application of topical nitroglycerine (NTG). Experimental study. Healthy adult horses (n=8). Digital blood flow was measured by an ultrasonic Doppler flow probe surgically implanted around the medial palmar digital artery. Blood was collected from a catheter placed in the medial palmar digital vein for quantification of NO. NTG patches, NTG ointment or control patches were placed over the palmar digital vessels at the level of the fetlock. Two horses had an intra-arterial infusion of an NTG solution into the medial palmar digital artery in a pilot study. Digital arterial blood flow did not change significantly with application of the NTG patches, NTG ointment, or control patches. There were no statistically significant or biologically important changes in digital venous NO concentrations across time or between treated and control horses. In the pilot study, digital arterial blood flow and palmar digital venous NO concentrations increased with intra-arterial infusion of NTG. In clinically healthy horses, digital arterial blood flow and digital venous plasma NO concentrations did not change significantly with application of the NTG patches/ointment. These treatments are unlikely to have an effect on the digital vasculature of laminitic horses, however, further investigation is warranted. Although NTG patches have been used as a method of decreasing vasomotor tone and improving digital blood flow in horses with laminitis, this study provides evidence in healthy conscious horses that this treatment is not effective in altering digital blood flow.

Effect of systemic lidocaine on visceral and somatic nociception in conscious horses

Commonly used analgesics (nonsteroidal anti-inflammatory agents, opioids and alpha2-agonists) have unwanted side effects. An effective alternative with minimal adverse effects would benefit clinical equine pain management. To compare the effect of lidocaine or saline on duodenal and rectal distension threshold pressure and somatic thermal threshold in conscious mature horses. Systemically administered lidocaine would increase somatic and visceral nociceptive thresholds. Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min for 2 h) or saline was administered to 6 horses each carrying a permanently implanted gastric cannula, in a randomised, blinded cross-over design. Thermal threshold was measured using a probe containing a heater element placed over the withers which supplied heat until the horse responded. A barostatically controlled intraduodenal balloon was distended until a discomfort response was obtained. A rectal balloon was inflated until extruded or signs of discomfort noted. Thermal threshold was increased significantly 30 and 90 mins after the start of lidocaine infusion. There was no change in duodenal distension pressure and a small but clinically insignificant change in colorectal distension pressure in the lidocaine group. At the dose used, systemically administered lidocaine produced thermal antinociception but minimal changes in visceral nociception. At these doses, lidocaine may play a role in somatic analgesia in horses.

Effects of acepromazine on pulmonary gas exchange and circulation during sedation and dissociative anaesthesia in horses

ObjectiveTo study pulmonary gas exchange and cardiovascular responses to sedation achieved with romifidine and butorphanol (RB) alone, or combined with acepromazine, and during subsequent tiletamine–zolazepam anaesthesia in horses. AnimalsSix (four males and two females) healthy Standardbred trotters aged 3–12 years; mass 423–520 kg. Study designRandomized, cross-over, experimental study. Materials and methodsHorses were anaesthetized on two occasions (with a minimum interval of 1 week) with intravenous (IV) tiletamine–zolazepam (Z; 1.4 mg kg−1) after pre-anaesthetic medication with IV romifidine (R; 0.1 mg kg−1) and butorphanol (B; 25 μg kg−1 IV). At the first trial, horses were randomly allocated to receive (protocol ARBZ) or not to receive (protocol RBZ) acepromazine (A; 35 μg kg−1) intramuscularly (IM) 35 minutes before induction of anaesthesia. Each horse was placed in left lateral recumbency and, after tracheal intubation, allowed to breathe room air spontaneously. Respiratory and haemodynamic variables and ventilation–perfusion ( V˙A/Q˙; multiple inert gas elimination technique) ratios were determined in the conscious horse, after sedation and during anaesthesia. One- and two-way repeated-measures anova were used to identify within- and between-technique differences, respectively. ResultsDuring sedation with RB, arterial oxygen tension (PaO2) decreased compared to baseline and increased V˙A/Q˙ mismatch was evident; there was no O2 diffusion limitation or increase in intrapulmonary shunt fraction identified. With ARB, PaO2 and V˙A/Q˙ remained unaffected. During anaesthesia, intrapulmonary shunt occurred to the same extent in both protocols, and V˙A/Q˙ mismatching increased. This was less in the ARBZ group. Arterial O2 tension decreased in both protocols, but was lower at 25 and 35 minutes of anaesthesia in RBZ than in ARBZ. During sedation, heart rate (HR) and cardiac output ( Q˙t) were lower while arterial-mixed venous oxygen content differences and haemoglobin concentrations were higher in RBZ compared with ARBZ. Total systemic vascular resistance, mean systemic, and mean pulmonary arterial pressures were higher during anaesthesia with RBZ compared to ARBZ. Conclusions and clinical relevanceAcepromazine added to RB generally improved haemodynamic variables and arterial oxygenation during sedation and anaesthesia. Arterial oxygenation was impaired as a result of increased shunt and V˙A/Q˙ mismatch during anaesthesia, although acepromazine treatment reduced V˙A/Q˙ disturbances and falls in PaO2 to some extent. Haemodynamic variables were closer to baseline during sedation and anaesthesia when horses received acepromazine. Acepromazine may confer advantages in healthy normovolaemic horses.

Colorectal distention in the horse: visceral sensitivity, rectal compliance and effect of i.v. xylazine or intrarectal lidocaine

Most current models of visceral sensitivity testing in the horse have required visceral cannulation. Colorectal distention (CRD) is a widely used, noninvasive method for testing in other species and could be adapted for use in horses. To develop a protocol of controlled CRD in the conscious horse and to evaluate the effect of i.v. xylazine or intrarectal lidocaine on CRD threshold and rectal compliance. Eight horses were used for baseline studies (3 trials each) and 6 horses to evaluate treatments (4 trials, 2 per treatment). A 45 cm diameter polyvinyl balloon attached to plastic tubing was used for rectal distention following a stepwise barostat-controlled inflation pattern. The procedure was well tolerated by all horses. Mean baseline threshold pressure was 14.17 mmHg. Xylazine i.v. resulted in significantly (P < 0.05) higher mean threshold pressures compared to baseline or rectal lidocaine. Rectal compliance increased following lidocaine treatment relative to baseline or xylazine. CRD offers a noninvasive method for visceral sensitivity testing in the horse. Xylazine raises CRD threshold, while lidocaine increases rectal compliance. The increased rectal compliance following intrarectal lidocaine administration may explain the benefit of its use to facilitate rectal examination.

Reconstruction of in vivo time-evolving neuroendocrine dose-response properties unveils admixed deterministic and stochastic elements.

Homeostasis in the intact organism is achieved implicitly by repeated incremental feedback (inhibitory) and feedforward (stimulatory) adjustments enforced via intermittent signal exchange. In separated systems, neurohormone signals act deterministically on target cells via quantifiable effector-response functions. On the other hand, in vivo interglandular signaling dynamics have not been estimable to date. Indeed, experimentally isolating components of an interactive network definitionally disrupts time-sensitive linkages. We implement and validate analytical reconstruction of endogenous effector-response properties via a composite model comprising (i) a deterministic basic feedback and feedforward ensemble structure; (ii) judicious statistical allowance for possible stochastic variability in individual biologically interpretable dose-response properties; and (iii) the sole data requirement of serially observed concentrations of a paired signal (input) and response (output). Application of this analytical strategy to a prototypical neuroendocrine axis in the conscious uninjected horse, sheep, and human (i) illustrates probabilistic estimation of endogenous effector dose-response properties; and (ii) unmasks statistically vivid (2- to 5-fold) random fluctuations in inferred target-gland responsivity within any given pulse train. In conclusion, balanced mathematical formalism allows one to (i) reconstruct deterministic properties of interglandular signaling in the intact mammal and (ii) quantify apparent signal-response variability over short time scales in vivo. The present proof-of-principle experiments introduce a previously undescribed means to estimate time-evolving signal-response relationships without isotope infusion or pathway disruption.

Quantitative Electromyographic Examination in Myogenic Disorders of 6 Horses

Electromyographic needle examination (EMG), including the semiautomatic quantitative analysis of motor unit action potential (MUAP), is an important diagnostic tool for myopathy in humans. The diagnostic possibilities of this technique have not been fully explored in horses; however, recent studies have shown that MUAP analysis can be performed in conscious horses. To determine the diagnostic possibilities of EMG in horses, we compared the EMG results of the subclavian muscle, the triceps, and the lateral vastus muscle in 6 equine patients thought to have myogenic disorders with those in 7 normal control horses. The EMG results were compared with the results of the histopathologic examination of the lateral vastus muscle in patients and controls. Histopathologic examination showed muscle disease in 3 patients. In the patient group, several types of abnormal spontaneous activities were observed (mainly fibrillation potentials and positive sharp waves), and the MUAPs of the patient group had a markedly shorter duration and lower amplitude than those of the control group. In the subclavian muscle, triceps, and lateral vastus muscle of affected horses, the MUAP duration was 5.0 +/- 0.4 (mean +/- SD), 3.9 +/- 0.3, and 4.7 +/- 1.1 milliseconds, respectively. The MUAP amplitude was 217 +/- 55, 150 +/- 74, and 180 +/- 54 microV; the number of phases was 2.4 +/- 0.2, 2.5 +/- 0.3, and 2.3 +/- 0.1; and the number of turns was 2.6 +/- 0.2, 2.4 +/- 0.2, and 2.8 +/- 0.5, respectively. In conclusion, it appears that the EMG may be a more sensitive method than other techniques for examining muscle biopsies for diagnosis of early-stage myopathy in horses.

Quantitative analysis of motor unit action potentials in the subclavian muscle of healthy horses.

To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses. 10 healthy adult Dutch Warmblood horses. Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses. Mean +/- SD duration of insertional activity was 471.7 +/- 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 RV (95% confidence interval [CI], 349 to 410 microV). Mean MUAP duration of the subclavian muscle was 727 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP defined as MUAP with > 4 phases, was 77%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP CONCLUSIONS AND CLINICAL RELEVANCE: This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses.

Pharmacokinetics and toxic effects of lithium chloride after intravenous adminstration in conscious horses.

To determine the pharmacokinetics and toxic effects associated with IV administration of lithium chloride (LiCl) to conscious healthy horses. 6 healthy Standardbred horses. Twenty 3-mmol boluses of LiCl (0.15 mmol/L) were injected IV at 3-minute intervals (total dose, 60 mmol) during a 1-hour period. Blood samples for measurement of serum lithium concentrations were collected before injection and up to 24 hours after injection. Behavioral and systemic toxic effects of LiCl were also assessed. Lithium elimination could best be described by a 3-compartment model for 5 of the 6 horses. Mean peak serum concentration was 0.561 mmol/L (range, 0.529 to 0.613 mmol/L), with actual measured mean serum value of 0.575 mmol/L (range, 0.52 to 0.67 mmol/L) at 2.5 minutes after administration of the last bolus. Half-life was 43.5 hours (range, 32 to 84 hours), and after 24 hours, mean serum lithium concentration was 0.13+/-0.05 mmol/L (range, 0.07 to 0.21 mmol/L). The 60-mmol dose of LiCl did not produce significant differences in any measured hematologic or biochemical variables, gastrointestinal motility, or ECG variables evaluated during the study period. Distribution of lithium best fit a 3-compartment model, and clearance of the electrolyte was slow. Healthy horses remained unaffected by LiCl at doses that exceeded those required for determination of cardiac output. Peak serum concentrations were less than steady-state serum concentrations that reportedly cause toxic effects in other species.

Electromyography under caudal epidural anaesthesia as an aid to the diagnosis of equine motor neuron disease

Electromyography was used as an aid to the diagnosis of equine motor neuron disease in a conscious horse while it was under caudal epidural anaesthesia. A muscle biopsy was taken...

Variability of Doppler ultrasound measurements of hindlimb blood flow in conscious horses.

Ultrasonography of the left and right femoral artery and vein was performed in 5 conscious horses. Velocity waveforms, 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) and volumetric flow. Waveform analysis included calculation of early diastolic deceleration slope (EDDS) and pulsatility index (PI) and subjective description of the waveform. Measurements were recorded at monthly intervals for 6 months. The repeated measurements were used to determine the within-horse variation. Horses were then anaesthetised with halothane and the same measurements recorded 60 min after induction. Differences between measurements recorded in conscious and anaesthetised horses were determined. Within-horse variability for diameters of femoral arteries and veins was small (CV<10%). Within variability for all other measurements was marked (CV>11%), with within-horse variability being the largest for femoral venous flow (CV>35%). Source of variability was measurement error and biological variation. Despite variability in conscious horses it was possible to detect changes in blood flow during anaesthesia. In the femoral arteries, volumetric flow was lower and EDDS and PI was higher in anaesthetised horses. In the femoral veins, volumetric flow was also lower in anaesthetised horses. Therefore Doppler ultrasound appears to be a useful technique for studying blood flow in conscious and anaesthetised horses.

Difference in the Motile Reactivity of Jejunum, Cecum, and Right Ventral Colon to Xylazine and Medetomidine in Conscious Horses.

We investigated effects of xylazine and medetomidine on contractive motility in different regions of the intestine in conscious horses, to provide some insight into elucidation of the regional difference in the painrelieving effect of α2-adrenergic agonists. We used 6 healthy adult male thoroughbread horses. Horses were intravenously given one of two calmatine-anodines, xylazine (1.0 mg/kg) and medetomidine (0.0075 mg/kg). The jejunum, cecum, and right ventral colon were examined for contractive motility. Both xylazine and medetomidine inhibited contractive motility for relatively similar durations, the effect of medetomidine was more potent than that of xylazine. After the horses were treated with both drugs, the contractive motility of the cecum and colon was inhibited for a longer duration and the inhibition was more intense than the corresponding duration and intensity of inhibition of the jejunum. These results suggest that the cecum and colon of the horse is more sensitive than the jejunum to α2-adrenergic agonists.

The effect of orally administered cisapride on intestinal motility in conscious horses.

Seven Thoroughbred horses were laparotomized and Force Transducers were fixed on the proximal jejunal and cecal serosa. After observation of the digestive tract motility in consciousness, cisapride (0, 0.5, 0.75 or 1 mg/kg) was orally administered. In horses treated with 0.75 mg/kg or 1.0 mg/kg cisapride, the migrating contraction (MC) of the jejunum was significantly increased in frequency.

Sonographic observations of the peripheral vasculature of the equine thoracic limb.

Investigations of the equine peripheral vascular system have been constrained by the lack of a non-invasive method of examining the arteries and veins of the limbs of the conscious horse. Precise correlations were established between the gross anatomical features of the peripheral vessels and their B-mode sonographic appearance in each thoracic limb of 35 horses. A sonographic imaging protocol was established. Additional Doppler sonographic recordings defined the arterial waveforms and demonstrated that blood flow to the foot could be evaluated in the lateral proper digital artery, distal to the level of the coronary band. Valves (with 2-4 cusps) were identified in the lumina of the medial and lateral palmar common digital veins and those of the medial and lateral palmar proper digital veins. Spontaneous echo contrast, a smoke-like haze of echoic blood, was seen in the lateral and medial palmar common digital veins, the distal deep palmar venous arch and communicating branches, and the palmar proper digital veins, and occasionally seen in the distal deep palmar arterial arch and distal proper palmar digital arteries. The value of duplex sonography (B-mode and Doppler) for anatomical and physiological studies of the peripheral vasculature of the horse was clearly established. Such data could be applied to the investigation of diseases affecting the peripheral circulation.

Hemodynamic and metabolic alterations associated with intravenous infusion of a combination of adenosine triphosphate and magnesium chloride in conscious horses

Abstract Objective To determine hemodynamic and metabolic effects of IV infusion of ATP-MgCl2 combination and maximal safe IV infusion rate in conscious horses. Animals 6 adult female horses. Procedure All horses received an IV infusion of ATP-MgCl2 combination, beginning at a rate of 0.05 mg of ATP/kg of body weight/min, which was increased by 0.05 mg/kg/min increments at 10-minute intervals until a rate of 1.0 mg/kg/min was achieved. Data were collected prior to the start of the infusion, at the end of each infusion rate, and at 15-minute intervals for the next hour after discontinuation of the infusion. Measured or calculated hemodynamic variables included cardiac output, cardiac index, heart rate, stroke volume, systemic and pulmonary arterial pressures, and systemic and pulmonary vascular resistances. Arterial blood gas tensions, CBC, plasma biochemical profiles, urine volume and specific gravity, and selected clinical signs of disease also were evaluated. Results Intravenous infusion of ATP-MgCl2 significantly increased cardiac output, decreased systemic vascular resistance, and caused mild pulmonary hypertension. Magnitude of the hemodynamic alterations was dependent on rate of infusion. Maximal safe infusion rate for these horses was 0.3 mg/kg/min. All horses became lethargic, and their appetites diminished during the infusion; 5 horses had mild signs of abdominal discomfort. Flank sweating was observed in all horses as infusion rate increased. Urine volume and specific gravity and hematologic, biochemical, and arterial blood gas alterations were detected during and after infusion. Conclusions and Clinical Relevance Intravenous administration of ATP-MgCl2 in healthy, conscious, adult horses caused various metabolic and hemodynamic alterations that were without appreciable detrimental effects. (Am J Vet Res 1999;60:1140–1147)