EIT Offers Easy On-Site, Drug-Free Testing for Equine Asthma
A new asthma diagnostic tool for horses could be simple enough for veterinarians to use in the field without anesthetics or even an assistant.

Electrical impedance tomography (EIT) can accurately measure airflow during inhaling and exhaling, with after-exercise readings that can distinguish between asthmatic and non-asthmatic horses. This could arm veterinarians with equipment that’s easy to use at the farm before turning to more invasive diagnostic techniques such as bronchoalveolar lavage (BAL), said Nicolas Herteman, MS, formerly at the Clinic for Equine Internal Medicine Equine Hospital, part of the University of Zurich’s Vetsuisse Faculty, in Switzerland.

“EIT wouldn’t replace BAL entirely, but it’s something that can be done in the field without anyone helping you, because all you have to do is put a belt on the horse and stand beside the horse and wait for your results,” Herteman said.

Currently, pulmonary function tests in horses usually take place in referral centers because they require specialized equipment such as facemasks, high-speed treadmills, and esophageal manometers, he said. Most of the time, horses also require sedation, making it a challenge to test horses just before and after exercise—which can be important because exercise often triggers asthmatic reactions.

Herteman and his fellow researchers wondered if EIT might provide a solution to overcome these issues. EIT is a real-time imaging technique that picks up information about any opposition to electrical currents (impedance) in the airways through an electrode belt placed around the horse’s barrel. Scientists can use that data to assess shifts in gas volume in the lungs. Researchers have already used EIT in horses to monitor airway ventilation during anesthesia and to test the airway reaction to an allergen (in sedated horses).

So Herteman’s team tested airflow using EIT equipment on 23 horses, nine of which had healthy airways. Nine others had moderate equine asthma (MEA), and five others had severe equine asthma (SEA).

They ran EIT recordings on each horse at rest and immediately after a 15-minute longeing session. They measured both peak inspiratory and peak expiratory flows. For the sake of comparison, they also took blood samples and ran a BAL on each horse after the post-exercise EIT test.

The researchers found that all EIT measurements were essentially the same when the horses were resting before exercise, Herteman said. But as soon as they returned from longeing, the asthmatic horses had dramatically different readings compared to the healthy horses.

That’s because asthma is associated with narrowing of the airways, making it more difficult to push air in and out through the passages. These modified airflow forces led to higher EIT measurements, thereby providing a reliable diagnosis of asthma, he said.

In their study population, they did not find significant differences in the EIT readings between the SEA and MEA horses, however. Even so, Herteman said he suspects differences between such horses might become clearer in a larger group of study horses.

Equine EIT isn’t limited to asthma diagnoses, Herteman added. His research team is already investigating future possibilities with EIT that could help investigate other airway issues, such as pneumonia or pulmonary edema.

“I think we’re really at the very beginning of all the things we can do with EIT in horses,” he said.

The study, “Exercise-induced airflow changes in horses with asthma measured by electrical impedance tomography,” was published in the September 2021 edition of the Journal of Veterinary Internal Medicine.