Unsedated Horses Research Articles

Electrical impedance tomography to measure lung ventilation distribution in healthy horses and horses with left-sided cardiac volume overload.

BackgroundLeft‐sided cardiac volume overload (LCVO) can cause fluid accumulation in lung tissue changing the distribution of ventilation, which can be evaluated by electrical impedance tomography (EIT).ObjectivesTo describe and compare EIT variables in horses with naturally occurring compensated and decompensated LCVO and compare them to a healthy cohort.AnimalsFourteen adult horses, including university teaching horses and clinical cases (healthy: 8; LCVO: 4 compensated, 2 decompensated).MethodsIn this prospective cohort study, EIT was used in standing, unsedated horses and analyzed for conventional variables, ventilated right (VAR) and left (VAL) lung area, linear‐plane distribution variables (avg‐max VΔZLine, VΔZLine), global peak flows, inhomogeneity factor, and estimated tidal volume. Horses with decompensated LCVO were assessed before and after administration of furosemide. Variables for healthy and LCVO‐affected horses were compared using a Mann‐Whitney test or unpaired t‐test and observations from compensated and decompensated horses are reported.ResultsCompared to the healthy horses, the LCVO cohort had significantly less VAL (mean difference 3.02; 95% confidence interval .77‐5.2; P = .02), more VAR (−1.13; −2.18 to −.08; P = .04), smaller avg‐max VΔZL Line (2.54; 1.07‐4.00; P = .003) and VΔZL Line (median difference 5.40; 1.71‐9.09; P = .01). Observation of EIT alterations were reflected by clinical signs in horses with decompensated LCVO and after administration of furosemide.Conclusions and Clinical ImportanceEIT measurements of ventilation distribution showed less ventilation in the left lung of horses with LCVO and might be useful as an objective assessment of the ventilation effects of cardiogenic pulmonary disease in horses.

Inter‐user and intra‐user variation of two tonometers in horses

It is currently unknown which of the two devices most commonly used in equine ophthalmology for intraocular pressure (IOP) estimation demonstrates the lowest inter-user and intra-user variation. To assess the inter-user and intra-user variation of two tonometers in sedated and unsedated horses. Randomised masked cross-over trial. Four examiners used the rebound (ICare® TonoVet) and applanation (TonoPen® ) tonometers to measure the intraocular pressure (IOP) in triplicate in 10 normal horses before and after sedation with xylazine. For inter-user variation, coefficient of variation (CV) values were calculated from the mean of each examiner for each condition combination. For intra-user variation, CV values were calculated from the individual measurements of each examiner for each condition combination. CV values were also assessed in relation to other variables using ANOVA. The rebound tonometer was found to have lower inter-user (15.4% vs 21.7%, P=.01) and intra-user (9.1% vs 16.1%, P<.0001) variation in unsedated horses and lower intra-user (8.4% vs 14.7%, P<.0001) variation in sedated horses than the applanation tonometer. Both instruments had similar inter-user variation in sedated horses. For the rebound tonometer, sedation did not affect inter-user or intra-user variation, but for the applanation tonometer inter-user variation was lowest while horses were sedated (16.0% vs 21.7%, P=.03). No other variable assessed was found to have an effect on IOP. No animals with ocular disease were included in this study. The rebound tonometer may be the preferred instrument to minimise intra-user and inter-user variation for IOP measurement in unsedated horses. The rebound tonometer is also likely to be the preferred instrument to minimise intra-user variation in sedated horses. If the applanation tonometer is used to perform IOP measurement in horses, it is recommended that this is performed while horses are sedated to minimise inter-user variation for this instrument.

Effect of auriculopalpebral nerve block on equine intraocular pressure measured by rebound tonometry (TonoVet® ).

To assess rebound tonometry intraocular pressure (IOP) in unsedated horses without and with auriculopalpebral (AP) nerve blocks. Twenty-two client- and twenty university-owned horses (84 total eyes) with unremarkable ophthalmic examinations were evaluated. One eye of each horse was chosen randomly, an AP block performed for that eye, and IOP measured in both eyes with a TonoVet® . The process was repeated for the contralateral eye 72hours later under the same conditions as the initial measurements. Horses were unsedated for nerve blocks and tonometry. Linear mixed-effects models were used for comparisons with statistical significance threshold of 0.05. Overall, blocked eyes had an 0.8mmHg lower average IOP than unblocked eyes (P=.039). IOP for client-owned horses was on average 3.2mmHg lower than in UGA-owned horses (P=.025) and was more impacted by AP block (1.4mmHg lower average in client-owned blocked versus unblocked eyes (P=.006)). Block effectiveness was ranked on a subjective scale ("good", "poor", no block/control), and IOP was on average lower in eyes with a good block (P=.008). Although there were statistically significant differences in IOP between blocked and unblocked eyes, between client- and UGA-owned horses, and between eyes with good and poor AP blocks, these differences were not clinically significant. Thus, AP blocks remain a useful tool for evaluating equine ophthalmic health with minimal impact on IOP assessment.

Does Diagnostic Analgesia in the Distal Aspect of the Limb of Horses Performed in a Clinical Situation Less Than 12 or 36 Hours Before Magnetic Resonance Imaging Result in Artifacts?

The potential effect of diagnostic analgesia performed <24 hours before magnetic resonance imaging (MRI) has not been assessed. It is not known whether perineural or intrasynovial analgesia performed in a clinical setting in unsedated horses might result in more tissue trauma and consequently artifacts than in sedated horses in an experimental setting. The aims of this study were to assess whether diagnostic analgesia (using mepivacaine) in the distal aspect of the limb in a clinical setting in unsedated horses, performed on the day of (<12 hours) or the day before (<36 hours) high-field and low-field MRI, results in artifacts that could confound image interpretation. Cases were limbs which had undergone diagnostic analgesia in the distal aspect of the limb <36 hours before high-field (n = 17) or low-field (n = 55) MRI. Controls had MRI of the same region as cases but had not undergone diagnostic analgesia in the distal aspect of the limb <36 hours before MRI. The regions of possible injection sites were assessed for alteration in signal intensity and/or in the contour of the limb, altered tissue architecture, or a needle tract. Distension of the dorsal pouch of the distal interphalangeal joint and of the digital flexor tendon sheath was measured. There were no artifacts resulting from diagnostic analgesia performed within 12 or 36 hours preceding low-field or high-field MRI that could confound image interpretation. Results suggest that it is reasonable and safe (from an imaging point of view) to perform diagnostic analgesia in the distal aspect of the limb shortly before MRI.

42 Comparison of inflammation, nutritional status, muscle mass, pituitary function, and age in geriatric horses

s / Journal of Equine Veterinary Science 35 (2015) 400e417 402 measures ANOVA of blood and urine concentrations at allocated sampling times showed an increase in total blood Mg concentrations and urinary Mg excretion between the control group and the Mg supplemented groups. There was a trend for Mg supplementation to decrease reaction speed (P 1⁄4 0.07) when the control was compared with both the 2.5 g and 10 g added Mg groups. There was a significant difference shown between the control and 10 g added Mg treatment (P 1⁄4 0.025) using a paired Students t-test. Mean reaction speed (±SD) was Control, 5.3 ± 2.2 m/s; 2.5 g added Mg, 3.7 ± 1.8 m/s and 10 g added Mg, 3.1 ± 1.5 m/s, with no effect of day. This was comparable to the pre-study testing where unsedated horses had a mean reaction speed of 5.3 ± 1.8 m/s compared with 3.5 ± 1.5 m/sec when sedated. This is the first time an objective measurement of behavioral change due to oral magnesium supplementation has been reported in the horse.

Application of in vivo microdialysis for investigation of unbound drug concentrations of intravenously administered sulfadimidine in the paranasal sinus mucosa of horses.

To monitor concentrations of sulfadimidine in the paranasal sinus mucosa (PSM) of unsedated horses following IV administration of trimethoprim-sulfadimidine via in vivo microdialysis. 10 healthy adult horses. Concentric microdialysis probes were implanted into the subepithelial layers of the frontal sinus mucosa of standing sedated horses. Four hours after implantation, trimethoprim-sulfadimidine (30 mg/kg) was administered IV every 24 hours for 2 days; dialysate and plasma samples were collected at intervals during that 48-hour period and analyzed for concentrations of sulfadimidine. The dialysate concentration and relative loss of sulfadimidine from the perfusate were used to calculate the PSM concentration. Microdialysis probe implantation and subsequent in vivo microdialysis were successfully performed for all 10 horses. Following the first and second administration of trimethoprim-sulfadimidine, mean ± SD peak concentrations of sulfadimidine were 55.3 ± 10.3 μg/mL and 51.5 ± 8.7 μg/mL, respectively, in plasma and 9.6 ± 4.5 μg/mL and 7.0 ± 3.3 μg/mL, respectively, in the PSM. Peak sulfadimidine concentrations in the PSM were detected at 5.9 ± 2.7 hours and 5.4 ± 2.3 hours following the first and second drug administrations, respectively. For 12 hours, mean PSM sulfadimidine concentration remained greater than the minimum inhibitory concentration indicative of sulfonamide susceptibility of equine bacterial isolates (4.75 μg/mL). In vivo microdialysis for continuous monitoring of PSM sulfadimidine concentrations in unsedated horses was feasible. Intravenous administration of trimethoprim (5 mg/kg) and sulfadimidine (25 mg/kg) proved likely to be efficient for treating sinusitis caused by highly susceptible pathogens, providing that the dosing interval is 12 hours.

Doppler Ultrasonographic Estimation of Renal Resistive Index in Horse: Comparison Between Left and Right Kidneys

The renal resistive index (RI) is the ratio of the difference between maximum and minimum (end diastolic) flow velocity derived from the Doppler spectrum of intrarenal (segmental/interlobar) arteries. It is a good indicator for acute renal disease, acute tubular necrosis, and renal obstruction. To our knowledge, no reports are available about the values of renal RI in unsedated horses. The aim of this study was to establish a normal reference range (mean ± standard error) and to assess the reliability of the renal RI obtained using transabdominal ultrasonography in unsedated healthy horses. Thirteen conscious Thoroughbred horses judged healthy based on physical examination, complete blood count, biochemical profile, urinalysis, and ultrasonography were included. The peak-systolic and end-diastolic velocities of interlobar and arcuate arteries were measured. Intrarenal arteries were scanned by pulsed Doppler ultrasonography to calculate RI. The comparison of left versus right kidneys was analyzed with analysis of covariance (ANCOVA) procedure. Significant differences (P < .05) for the RI values were observed between left and right kidneys in the geldings (left 0.50 vs. right 0.56) and mares (left 0.50 vs. right 0.57) and were observed between left and right kidneys in trained (left 0.52 vs. right 0.55) and untrained horses (left 0.48 vs. right 0.58). The renal RI has not been modified by sex.

The applicability of ambulatory electroencephalography (AEEG) in healthy horses and horses with abnormal behaviour or clinical signs of epilepsy

Background: Short-duration electroencephalography (EEG) recordings in horses are helpful in diagnosing intracranial disorders. Potentially, long-duration ambulatory EEG (AEEG) recordings in horses will enhance the chance of detecting abnormal brain activity independent of the presence of an insult.Objective: The objective of this study was to test if AEEG recordings in unsedated horses can be acquired and benefit diagnosing abnormal brain activity.Animals and methods: Recordings were taken from 8 adult control horses and 10 patients suspected of intracranial abnormalities. Self-adhesive electrodes and the ‘Porti-5’ recording system were used. Filter settings were 0.5 Hz high pass and 35 Hz low pass. The records were analysed offline at a 50–200 μV/division and 10 seconds/division scale. Abnormal activity was defined as a spike or sharp wave, a period of generalised slow wave rhythmical activity or a generalised fast rhythmical discharge. The recording time ranged from 5 to 49 hours.Results: In the control group, one horse showed pathological activity. In the patient group, six out of nine horses showed abnormal activity during the recordings. Magnetic resonance imaging confirmed the presence of an intracranial mass in one patient. Long-term recordings of high quality can be obtained in unsedated horses by allowing daily activity using AEEG, resulting in a reasonable chance of recording (inter)ictal abnormal brain activity indicating epileptic or seizure-like activity in the absence of clinical signs or seizures.Conclusions: It is concluded that abnormal behaviour can be expressed intermittently, and with the availability of AEEG a useful tool is added to the diagnostic scenario for horses.

Use of Transoesophageal Ultrasound to Visualise the Aortopulmonary Region in two Normal Friesian Horses and Three Friesians with Aortic Rupture or Aortopulmonary Fistulation

AimsAortic rupture and aortopulmonary fistulation are reported with increased incidence in the Friesian breed. In contrast to Warmblood horses, the aorta in Friesian horses typically ruptures at the level of the ligamentum arteriosum (Ploeg et al. ). This remote location often creates difficulties in identifying the rupture with transthoracic ultrasound. The aim of this study was to evaluate the usefulness of transoesophageal visualisation of the aortopulmonary region with a linear probe in both standing unsedated horses and horses suffering from aortic rupture.MethodsFive Friesian horses, 2 healthy and 3 affected, were subjected to transthoracic ultrasound (2.5 MHz sectorial probe GE) followed by transoesophageal ultrasound (7.5 or 10 MHz linear probe). Correct oesophageal introduction of the probe was guided by means of endoscopy. After visualisation of the aortopulmonary region, horses were anaesthetised, and the transoesophageal ultrasound was repeated. In 4 horses, simultaneous carotid artery catheterisation was performed, to visualise the catheter at the zone of interest. After obtaining a diagnosis, all affected horses were subjected to euthanasia and autopsies were performed.ResultsThe aortopulmonary region could be visualised in all horses. In the affected horses presence or absence of a periaortic blood cuff, aortic rupture and or aortopulmonary fistulation could be clearly identified. In one horse during carotid catheterisation, the catheter could be guided into the fistulation site, which was clearly visualised by means of transoesophageal ultrasound.Conclusions and practical significanceTransoesophageal ultrasound by means of a 7.5 or 10 MHz linear probe allows for good visualisation of the aortopulmonary region and for diagnosing aortic rupture in Friesian horses. The technique will be further developed as an elegant noninvasive way to screen Friesian horses for this pathology, even in the standing nonsedated horse.Ethical animal researchOwner informed consent was obtained for all horses. Sources of funding: This study was funded by the Dutch Royal Friesian Studbook and Scil Animal Care. Competing interests: None.

Evaluation of clinical and electrocardiographic changes during the euthanasia of horses

The objective of this prospective field study was to investigate whether commonly used criteria for clinical death occurred at the same time as cardiac death, as determined by electrocardiography. Specific ECG changes during euthanasia were also studied. Twenty-nine horses were euthanized with pentobarbital at two different dose rates and 15 of the 29 horses also received detomidine hydrochloride for sedation. ECG was recorded prior to and during euthanasia. Time to collapse, cessation of reflexes, heart sounds and asystole were recorded. ECG recordings were used to calculate RR intervals, PQ duration, QRS duration, distance from QRS complex to end of T wave corrected for HR (QTc interval), duration of T-wave from peak to end (TpeakTend) and amplitudes of T wave (Tpeak) before and during euthanasia. Differences between groups and ECG changes were evaluated using analysis of variance.Clinical determination of death occurred before cardiac death (P<0.05). Sedated horses took longer to collapse than unsedated horses (P<0.0001), but asystole occurred faster in sedated horses (P<0.0001). No significant changes in QRS duration were observed, but RR, PQ, QTc, TpeakTend and Tpeak were influenced by both pentobarbital dose and sedation (P<0.05–<0.0001). In conclusion, sedation prior to euthanasia resulted in a shorter time to asystole and is therefore recommended for the euthanasia of horses. Importantly, the results show that the clinical definition of death occurred significantly earlier than cardiac death (defined as asystole), which indicates that the clinical declaration of death in horses could be premature compared to that used in humans.

Direct intra‐abdominal pressures and abdominal perfusion pressures in unsedated normal horses

AbstractObjectivesTo determine whether direct intra‐abdominal pressures (IAP) and calculated direct abdominal perfusion pressures (APP) are location dependent within the abdomen of standing horses. We hypothesize that IAP will be increased and calculated APP will be decreased at a ventral abdominal location (V) when compared to values obtained from the left (LFl) or right flank (RFl).DesignProspective experimental design.SettingUniversity‐based equine research facility.AnimalsSeven healthy adult horses, 4 geldings and 3 mares.InterventionsMeasurements of direct IAP obtained from the RFl, LFl, and V locations via abdominal cannulation and direct arterial blood pressures obtained via catheterization of the transverse facial artery were obtained in fasted, standing, unsedated horses. APP was calculated for each location by the subtraction of IAP from the mean arterial pressure. Differences between sites of measurement for IAP, APP, and their gradients were calculated and compared by ANOVA and t‐tests.Measurements and Main ResultsMean flank IAP measurements were subatmospheric and negative compared to ventral IAP values (LFl = –3 mm Hg, RFl = –5 mm Hg, V = 25 mm Hg; P &lt; 0.001 between each flank and the ventral location). Ventrum APP was lower than flank APP (V = 82 mm Hg; LFl = 106 mm Hg; RFl = 108 mm Hg; P = 0.029 between each flank and the ventral location). Gradient calculations between sites showed the IAP increased and APP decreased from dorsal to ventral (P &lt; 0.05) and from right to left (P = 0.004) within the abdomen.ConclusionsIAP and calculated APP are location dependent. These data provide new information regarding abdominal pressure profiles in standing healthy adult horses.

Oral Abstract: Understanding the physio-pathology of myocardial mechanics * Friday 9 December 2011, 14:00-15:30 * Location: Kaposvar

Purpose: To evaluate the relationship between atrial contraction, mitral valve closure (MVC) and left ventricular isovolumic contraction. The horse is an ideal model to investigate this mechanism because of the low resting heart rate (25–45 bpm) and long atrioventricular (AV) interval. Methods: Five unsedated horses instrumented with pacing leads in the right atrium and right ventricle were evaluated during sinus rhythm (SR), ventricular pacing without preceding atrial contraction (VP) and dual-chamber pacing at AV delays ranging from 150 to 350 ms, programmed in a random sequence at a constant rate of 40 bpm. Color Doppler myocardial imaging was performed at high frame rates (>100 fps). Modified right parasternal four-chamber views were recorded for simultaneous measurements of MVC by anatomical M-mode and tissue Doppler-based left ventricular pre-ejectional peak velocity spikes and their timing. Results: During SR (AV interval 330–520 ms) and long AV intervals (300 and 350 ms), MVC occurred 12±37 ms after the onset of QRS. Two positive pre-ejectional velocity peaks were present. The first peak was identified as recoil of the left ventricle during atrial relaxation. This peak (2.5±1.1 cm/s) consistently preceded MVC (linear mixed model; P=0.84) by 44±18 ms. The second peak (4.8±1.3 cm/s) was called left ventricular isovolumic contraction and occurred after MVC. This suggests MVC caused by atrial contraction, followed by a true isovolumic contraction. However, during short AV intervals (150 and 200 ms) and VP, MVC occurred significantly later (P=0.002) at 125±5 ms after the onset of QRS. Only one pre-ejectional peak was present and the end of this peak coincided with MVC (linear mixed model; P=0.76). Peak velocity (9.2±2.4 cm/s) was remarkably higher than during SR and long AV intervals (P=0.009). These findings suggest MVC caused by left ventricular myocardial motion, resulting in a high pre-ejectional velocity peak as this contraction is not isovolumic. Conclusions: This study demonstrates the important influence of the atrioventricular interaction on mitral valve closure and pre-ejectional myocardial motion. Depending on the atrioventricular delay, mitral valve closure can be atrio- or ventriculogenic, resulting in high pre-ejectional velocities if the left ventricle is not in a true isovolumic state.

Effect of topical vapocoolant spray on response to arthrocentesis and intravenous catheterization in unsedated horses

To assess the efficacy of a commercially available topical vapocoolant spray in reducing responses to arthrocentesis of the middle carpal (MC) and metacarpophalangeal (MCP) joints and jugular vein catheterization in unsedated horses. 8 healthy research horses. Arthrocentesis of both MC and MCP joints and bilateral jugular vein catheterization were performed in each horse. Immediately prior to skin penetration, 1 randomly selected MC joint, MCP joint, and jugular vein were sprayed with a vapocoolant liquid (intervention product), and the contralateral MC joint, MCP joint, and jugular vein were sprayed with water (placebo). An observer blinded to the type of spray treatment used evaluated the horses' responses to needle or catheter placement procedures by use of a 6-point categorical scale and a 100-mm visual analog scale. Responses evaluated via the visual analog scale were significantly reduced after application of the intervention product, compared with responses after application of the placebo, for the MC and MCP joints; no difference in responses to jugular vein catheterization was detected between the 2 treatments. Vapocoolant spray was safe and effective in reducing horses' responses to arthrocentesis. The use of such products prior to joint injections may reduce procedural nociception and pain anticipation in unsedated horses and may improve the safety of personnel performing such procedures.

Ultrasound Evaluation of Cardiac Function Following Administration of Sedatives in Horses

We studied using ultrasound investigation the changes of heart function parameters as a result of acepromazine and xylazine administration in 9 adult horses, mixed breed. Comparing with control group (unsedated horses) acepromazine induced RVFWs statistically increase (p<0,05). Acepromazine also determined statistically decrease of LVIDd (p<0,05) resulting a decrease of Vd (p<0.01). Xylazine induced decrease of LVFWd (p<0.01) and increase of Vd (p<0.5). Acepromazine did not induce statistically significant changes on other parameters: RVFWd, RVIDs, RVIDd, IVSs, IVSd, LVIDs, LVFWs and LVFWd. Comparing with control group, xylazine determined same results, and did not influence RVFWs, LVIDd, Vs and Vd, so, acepromazine and xylazine did not induce any statistically changes of SF% and EF %.

Left Ventricular Radial and Circumferential Wall Motion Analysis in Horses Using Strain, Strain Rate, and Displacement by 2D Speckle Tracking

Noninvasive assessment of left-ventricular (LV) function is clinically relevant, but is incompletely studied in horses. To document the feasibility, describe the techniques, and determine the reliability of 2D speckle tracking (2DST) for characterization of LV radial and circumferential wall motion in horses. Three Standardbreds, 3 Thoroughbreds; age 8-14 years; body weight 517-606 kg. Observational study. Repeated 2-dimensional echocardiographic examinations were performed in unsedated horses by 2 observers and subsequently analyzed by 2DST. Test reliability was determined for segmental and for averaged 2DST indices (including strain, strain rate, displacement, and rotation) by estimating measurement variability, within-day interobserver variability, between-day interobserver variability, and between-day intraobserver variability. Variability was expressed as coefficient of variation (percent) and the absolute value below which the difference between 2 measurements will lie with 95% probability. 2DST analyses were feasible in 16 of 18 echocardiographic studies. The automated tracking was accurate during systole but inaccurate during diastole. Reliability was higher for radial compared to circumferential measurements. For radial strain, radial systolic strain rate, and radial systolic displacement, the test-retest variabilities ranged between 2.4 and 33.1% for segmental and between 4.1 and 16.1% for averaged measurements. Systolic radial motion of the LV at the chordal level could be reliably characterized in horses by 2DST. Circumferential measurements were less reliable. Diastolic measurements were invalid because of inaccurate tracking. The clinical value of LV wall motion analysis by 2DST in horses requires further investigation.

Methods and Reliability of Tissue Doppler Imaging for Assessment of Left Ventricular Radial Wall Motion in Horses

Noninvasive assessment of left ventricular (LV) function is incompletely studied in horses. The goals of this study were to investigate the feasibility, techniques, and reliability of tissue Doppler imaging (TDI) for characterization of LV radial wall motion in healthy horses. Three Standardbreds, 3 Thoroughbreds; age 8-14 years; body weight 517-606 kg. Repeated echocardiographic examinations were performed by 2 observers in unsedated horses using TDI. Test reliability was determined by estimating measurement variability, within-day interobserver variability, and between-day interobserver and intraobserver variability of all echocardiographic variables. Variability was expressed as coefficient of variation (CV) and the absolute value below which the difference between 2 measurements will lie with 95% probability. Assessment of LV radial wall motion by TDI was feasible in all horses. Measurement variabilities were very low (CV < 5%) to low (CV 5-15%) for most variables. Within-day interobserver variability as well as between-day interobserver and intraobserver variabilities were low to moderate (CV 16-25%) for most variables. All pulsed-wave TDI variables of systolic LV function showed very low to low variability, whereas some of the variables of LV diastolic and LA function showed moderate to high (CV > 25%) variability. Pulsed-wave TDI variables appeared more reliable than color TDI variables. Measurement of TDI indices of LV function is feasible and reliable in adult Standardbred and Thoroughbred horses. The clinical relevance of LV function assessment by TDI remains to be determined.

ULTRASONOGRAPHIC ASSESSMENT OF LARYNGOHYOID POSITION AS A PREDICTOR OF DORSAL DISPLACEMENT OF THE SOFT PALATE IN HORSES

Dorsal displacement of the soft palate is an important cause of poor performance in racehorses, yet its etiology is not fully understood. Diagnosis requires treadmill videoendoscopy, which is not widely available. The relationship of the larynx, the hyoid apparatus, and the remainder of the skull may be important in predisposing horses to dorsal displacement of the soft palate. We hypothesized that this relationship could be accurately assessed in unsedated horses through ultrasonographic examination. Fifty-six racehorses presented for evaluation of poor performance were subjected to treadmill videoendoscopy and resting ultrasonography. Using ultrasound-assisted percutaneous measures of laryngo-hyoid position, the relationship between selected anatomic structures and the occurrence of dorsal displacement of the soft palate was evaluated. A significant relationship was found between the depth of the basihyoid bone at rest and the occurrence of dorsal displacement of the soft palate at exercise (P = 0.03). Other measures of laryngohyoid position were not found to be associated with dorsal displacement of the soft palate. Thus, there is an association between the occurrence of dorsal displacement of the soft palate at exercise and the resting position of the basihyoid bone, whereby on average a more ventral location of the basihyoid bone is present in horses with dorsal displacement of the soft palate. The pathophysiologic implications of this finding are not fully understood but, based on our findings, ultrasound examination is of value in assisting in the diagnosis of dorsal displacement of the soft palate.

Methods and reliability of echocardiographic assessment of left atrial size and mechanical function in horses

To assess the feasibility, describe the techniques, and determine the reliability of transthoracic echocardiography for characterization of left atrial (LA) size and LA mechanical function in horses. 6 healthy adult horses. Repeated echocardiographic examinations were performed independently by 2 observers in standing, unsedated horses by use of 2-dimensional echocardiography, pulsed-wave flow Doppler, and tissue Doppler imaging (TDI) techniques. Test reliability was determined by estimating measurement variability, within-day interobserver variability, and between-day inter- and intraobserver variability of all echocardiographic variables. Variability was expressed as the coefficient of variation (CV) and the absolute value below which the difference between 2 measurements will lie with 95% probability. Most echocardiographic variables of LA size had low overall variability (CV, < 15%). Among the 2-dimensional indices of LA mechanical function, area-based and volume-based ejection phase indices had moderate between-day variability (CV usually < 25%). Transmitral Doppler flow indices were characterized by low to high between-day variability (CV, 6% to 35%). The TDI wall motion velocities had high between-day variability (CV, > 25%), whereas most TDI-derived time intervals had low variability (CV, < 15%). LA size and mechanical function can be reliably assessed in standing, unsedated horses by use of 2-dimensional echocardiography, transmitral blood flow velocity profiles, and analyses of LA wall motion by use of TDI. These results may provide useful recommendations for echocardiographic assessment of LA size and function in horses.

Electromyographic activity of the hyoepiglotticus muscle and control of epiglottis position in horses.

To determine whether the hyoepiglotticus muscle has respiratory-related electromyographic activity and whether electrical stimulation of this muscle changes the position and conformation of the epiglottis, thereby altering dimensions of the aditus laryngis. 6 Standardbred horses. Horses were anesthetized, and a bipolar fine-wire electrode was placed in the hyoepiglotticus muscle of each horse. Endoscopic images of the nasopharynx and larynx were recorded during electrical stimulation of the hyoepiglotticus muscle in standing, unsedated horses. Dorsoventral length and area of the aditus laryngis were measured on images obtained before and during electrical stimulation. Electromyographic activity of the hyoepiglotticus muscle and nasopharyngeal pressures were measured while horses exercised on a treadmill at 50, 75, 90, and 100% of the speed that produced maximum heart rate. Electrical stimulation of the hyoepiglotticus muscle changed the shape of the epiglottis, displaced it ventrally, and significantly increased the dorsoventral length and area of the aditus laryngis. The hyoepiglotticus muscle had inspiratory activity that increased significantly with treadmill speed as a result of an increase in phasic and tonic activity. Expiratory activity of the hyoepiglotticus muscle did not change with treadmill speed in 4 of 6 horses. Findings reported here suggest that contraction of the hyoepiglotticus muscle increases dimensions of the airway in horses by depressing the epiglottis ventrally during intense breathing efforts. The hyoepiglotticus muscle may be an important muscle for dilating the airway in horses, and contraction of the hyoepiglotticus muscle may induce conformational changes in the epiglottis.

Studies on the Experimental Induction of Ptosis in Horses

The precise appearance of ptosis due to lesions at different sites was investigated in experimental ponies. The angles of the eyelashes to the head was used as an objective measurement of ptosis after local anaesthesia of the sympathetic trunk or the palpebral nerve and the administration of an ocular alpha agonist or antagonist. It was shown that ptosis is not an inevitable consequence of palpebral nerve pathology, that ocular α antagonists can induce ptosis, and that α agonist eyedrops have an inconsistent effect on the equine pupil, but are consistent at reversing ptosis induced by sympathetic denervation in unsedated horses.