EQUINE VETERINARY EDUCATION / AE / OCTOBER 2014
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Highlights of recent clinically relevant papers
Magnetic blanket use in horses Magnetic products are often used in horses with the claim that they improve muscle blood flow and reduce muscular tension, hence they are promoted for the treatment of muscular back injuries. In this blinded, placebo controlled crossover study by A. Edner and colleagues in Sweden, the blood flow, skin temperature, nociceptive threshold and behaviour in 10 horses with both magnetic blankets and a placebo blanket were analysed. Intramuscular blood flow was measured using a photoplethysmographic technique which uses light-emitting diodes and photo detectors which are placed on the skin. Changes in muscle tenderness were measured using a pressure algometry technique, which is less subjective than muscular palpation. Skin temperature was measured using skin thermistors and thermography; each horse was videoed throughout the study to allow subjective analysis of behavioural changes. The blanket was placed for 60 min, with the order of treatment or placebo blanket being assigned randomly and the alternative blanket assessed on the following day. Blood flow and skin temperature were recorded for 5 min intervals from 30 min before blanket placement to 30 min after removal. Mechanical nociceptive thresholds, measured using the pressure algometry technique, were recorded 35 min before blanket placement, and at 5 min and 30 min following removal. There was no statistically significant difference in any of the measured parameters between treatment and placebo groups, although some data was not presented for blood flow, thermography and pressure algometry due to technical problems. The researchers did not find any evidence to support the
hypothesis that magnetic blankets improve muscular blood flow or reduce nociceptive threshold in horses.
Assessment of recurrent airway obstruction
In this study, H. Rettmer and colleagues in Switzerland and the USA compared the subjective assessment of clinical progression by owners of horses suffering from recurrent airway obstruction (RAO) with clinical and clinicopathological findings. Of the 62 horses enrolled in the study, approximately half
were affected with RAO while the other half were healthy. Owners were asked to describe the horses’ clinical history, frequency of coughing and presence of nasal discharge. Clinical examination was then undertaken which included assessment of breathing pattern, severity of coughing and lung auscultation, blood was also collected from the common carotid artery to determine the partial pressure of oxygen. Further assessment was performed by tracheal endoscopy and bronchoalveolar lavage (BAL) with samples collected for differential cell counts. Finally plethysmography and bronchoprovocation with nebulised histamine was used to characterise the breathing pattern. There was a clear differentiation in bronchoprovocation findings, auscultation findings and PaO2 in horses that coughed frequently, compared to controls. There was overlap between affected and control groups in terms of endoscopically derived mucus grades and BAL fluid differential cell counts. The sign which most consistently differentiated healthy horses
from asymptomatic RAO horses was airway hyper- responsiveness identified with plethysmography with histamine bronchoprovocation. The authors concluded that significant airway inflammation may be present in the absence of coughing and nasal discharge. Respiratory cytology can overlap between normal and RAO cases and histamine bronchoprovocation can help differentiate these.
Heart rate and pain in horses with laminitis
In this study, Claudia Halmer and colleagues at the University of Vienna and the University of Edinburgh have examined the correlation of heart rate and heart rate variability with Obel grading of pain in horses with laminitis. Heart rate variability (HRV) is often used to evaluate pain
and/or stress in animals, with lower HRV indicating a higher level of pain. In this study, HRV was used to obtain more information about the pain state of laminitis than is available from the heart rate (HR) alone. Heart rates and HRV of 12 horses clinically affected by laminitis were collected and compared to HR and HRV of 5 healthy control horses. Mean HR was found to be significantly higher in the laminitic group at the first measurement after clinic admission than in the control group. HRV batches of 100 and 500 consecutive heart beats were selected, and root mean square successive differences (RMSSD) were calculated from these data. The RMSSD of the 100 beat batches (RMSSD100) was significantly lower in the laminitic group at the first measurement after clinic admission than in the control group. No significant difference was found between the control group and the laminitic group at the second measurement after clinic admission for either HR or RMSSD100, while RMSSD500 was not different between the groups at any of the time points. At the first evaluation after admission to the clinic there was a highly significant positive correlation between Obel grade and heart rate, as well as a highly significant negative correlation between Obel grade and RMSSD100. This study suggests that HRV is of only limited additional benefit for the evaluation of even severe laminitic pain in the horse compared to HR. Therefore the additional effort to obtain HRV may not be justified, as HR is routinely obtained as part of the clinical examination.
Ventricular arrhythmias in horses with colic
In this recent study, Olga Seco Díaz and colleagues in the USA examined 111 horses with colic to determine the prevalence of myocardial injury on the basis of high concentrations of cardiac troponin I (cTnI). Blood was first drawn at admission then 12 and 24 h later for
medically treated cases, and 12 and 24 h following surgery for those horses treated surgically. Arrhythmias were evaluated from a 24-h ambulatory ECG beginning the morning after admission in medically treated cases or following surgery. Associations between cTnI concentrations and other variables were determined from the clinical and clinicopathological data.
The authors found that an abnormal cTnI concentration
(≥0.10 ng/ml) at admission was significantly associated with ventricular arrhythmias, outcome and surgical treatment. This
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