An overview of Exercise Induced Inspiratory Symptoms (EIIS) in humans, and a comparative approach to future understanding of upper respiratory tract collapse.

EIIS are a relatively newly described set of pathologies causing breathing difficulties at exercise in otherwise healthy individuals. The majority of these pathologies are associated with transient, reversible laryngeal narrowing. Consequently these conditions are collectively labelled Exercise Induced Laryngeal Obstruction (EILO) (1). Human and equine patients present in a similar way: reduced athletic performance with dyspnea, frequently with stridor. In humans panic reactions can occur. Symptoms improve as soon as exercise is ceased (1). Prevalence in the general population is 5-7 % (2). Gold standard for diagnosis is treadmill endoscopy (1). The exact setup and monitoring varies between clinics, but most include real-time endoscopy and ECG. In humans respiratory flow loops, respiratory gas analysis, sound and video recordings are also used as well as alternative forms of exercise such as swimming, rowing or riding a bike (1, 3). As with equines, some forms of EILO appear to be positional or associated with a particular activity, hence the importance of recreating the situation that predisposes to collapse, as veterinarians do with tack and poll flexion in the treadmill test.

EILO is classified as supraglottic; involving the corniculate, cuneiform cartilages and aryepiglottic folds collapsing over the laryngeal vestibule, and glottic pertaining to inappropriate adduction of the vocal folds (4). There is no such anatomical division in equines but the same anatomical structures are involved. The underlying pathophysiology is considered multifactorial; most likely a predisposed phenotype being unable to support the soft tissue structures of an otherwise normal airway during the increased pressure gradients of exercise. With the most severe symptoms occurring at maximal exertion (1). In equines dynamic respiratory tract collapse is a well-documented group of pathologies, in humans, however they are relatively newly described and the significance of the collapse of certain structures has not been established. EILO has until recently been misdiagnosed as Exercise Induced Asthma, hysteria and a stress reaction (1, 4). A failure to establish precise nomenclature, diagnostic criteria and outcome measures has hampered current understanding of EILO (4). It is therefore hoped that by working collaboratively a better understanding of pathogenesis and treatment can be achieved for both equine and human. Current research in humans is focused on determining an outcome measure and more robust information about the severity of collapse. From experience in the equine world tracheal pressure measurements are now being introduced into EILO investigation. It is hoped that they will give an objective measure of collapse and an objective outcome measure. Other areas of research interest are in development of computer models and automated visual analysis techniques to improve diagnostics.

Treatment of EILO is dependent on the structures involved with supraglottic collapse being treated both conservatively and surgically, while glottic collapse is treated conservatively (1). Conservative treatments include both systemic and local medication, respiratory muscle training, breathing techniques, biofeedback and psychotherapy. Surgical techniques include laser supraglottoplasty and epiglottic augmentation (1).