By Melissa Sykes
Researchers at Oklahoma State University recently completed a study on airway cooling and mucosal injury during cold weather exercise. Using the Thoroughbred racehorse as a model, scientists found that even cantering in subfreezing temperatures can induce airway obstruction (bronchoconstriction, or airway contraction). The research appeared in the February issue of the Journal of Applied Physiology
Human subjects that routinely perform strenuous exercise in cold conditions have a higher prevalence of chronic airway inflammation and hyperactivity (often referred to as "ski asthma" because its effects are often found in cross-country skiers). The scientists set out to determine whether exercise while breathing cold air could cause chronic airway disease in the equine athlete.
Previous studies in both humans and horses have confirmed that when exercising in subfreezing temperatures with low humidity, the upper airways fail to fully warm the inhaled air, leading to considerable loss of heat and water from the lower airways. These studies also confirmed that this stimulus is associated with airway mucosal damage.
"Our data show that exercising in cold air can provoke airway changes in otherwise healthy horses and may in fact be a part of the cause of the eventual development of chronic airway disease in equine athletes," explained lead researcher Dr. Michael S. Davis.
The effects were seen in horses exposed to exercise/cold air during a single challenge (five minutes of easy cantering).
"We intentionally ran the horses at a slow canter to avoid airway bleeding and, as a result, had to reduce the temperature of the inhaled air to compensate," said Davis. "We published an earlier study (in a supplement to the Equine Veterinary Journal
in 2002) in which we demonstrated that a similar challenge will be delivered at a fast canter or gallop with air temperatures above freezing. Thus, this is not just an issue for horses running way up north or in the dead of winter. Part of our previous study was done on horses training at Pimlico (in Baltimore, Md.) in late March and early April."
Once the challenge was over, the airways returned to normal, but, "We don't know how long it took as we allowed them a minimum of two weeks before we tried anything else."
Davis added, "The reality is that horses that experience one challenge are likely to experience repeated challenges three to four times a week while training. The time it takes these cumulative challenges to resolve is probably quite a bit longer.
"We've done similar studies in sled dogs and found that it takes more than four months to resolve," he said. "We are considering studies in both horses and sled dogs to see if they perform better if and when we make the airway inflammation go away."
Researchers feel the effects of cold weather exercise might inhibit the immune response.
But, Davis stressed, these studies do not demonstrate conclusively that the horse's immune system is suppressed, "Only that they have trouble responding to certain types of infection."
"We're currently developing those studies (on the immune response)," added Davis.
"Obviously, the results would potentially apply to humans since the cold and flu season seems to be in the winter."