Ventilatory efficiency in athletes, asthma and obesity

Abstract

During submaximal exercise, minute ventilation (V′E) increases in proportion to metabolic rate (i.e. carbon dioxide production (V′CO2)) to maintain arterial blood gas homeostasis. The ratio V′E/V′CO2, commonly termed ventilatory efficiency, is a useful tool to evaluate exercise responses in healthy individuals and patients with chronic disease. Emerging research has shown abnormal ventilatory responses to exercise (either elevated or blunted V′E/V′CO2) in some chronic respiratory and cardiovascular conditions. This review will briefly provide an overview of the physiology of ventilatory efficiency, before describing the ventilatory responses to exercise in healthy trained endurance athletes, patients with asthma, and patients with obesity. During submaximal exercise, the V′E/V′CO2 response is generally normal in endurance-trained individuals, patients with asthma and patients with obesity. However, in endurance-trained individuals, asthmatics who demonstrate exercise induced-bronchoconstriction, and morbidly obese individuals, the V′E/V′CO2 can be blunted at maximal exercise, likely because of mechanical ventilatory constraint.

Correspondence regarding “Ventilatory efficiency in athletes, asthma and obesity”: different ventilatory phenotypes during exercise in obesity?

“…[1] described how patients with obesity have higher ventilation at rest and any given work rate due to increased metabolic costs and work of breathing. Reduced chest wall compliance leads to a shallow breathing pattern, which, however, does not seem to significantly affect the ventilatory efficiency of patients, commonly measured by minute ventilation relative to carbon dioxide production (Vʹ E /Vʹ CO 2 ), at submaximal exercise intensities [1]. Nonetheless, related scientific knowledge is less clear for severe and morbid obesity patients, particularly at elevated exercise intensities.…”

“…The Vʹ E /Vʹ CO 2 at peak exercise has thus been proposed as a clinical marker to evaluate the respiratory response to exercise, since it can provide important information regarding the underlying mechanisms of exercise intolerance [1].…”

“…Nonetheless, related scientific knowledge is less clear for severe and morbid obesity patients, particularly at elevated exercise intensities. Indeed, inadequate compensatory hyperventilation at maximal physical exertion has been described due to mechanical ventilatory constraints [2].The Vʹ E /Vʹ CO 2 at peak exercise has thus been proposed as a clinical marker to evaluate the respiratory response to exercise, since it can provide important information regarding the underlying mechanisms of exercise intolerance [1].In our recently published paper, entitled "Ventilatory response at rest and during maximal exercise testing in patients with severe obesity before and after sleeve gastrectomy", 46 patients with severe obesity (mean body mass index (BMI) 43.59±5.30 kg•m −2 ) were evaluated 1 month before and 6 months after sleeve gastrectomy. Ventilatory response and efficiency were analysed by incremental, maximal cardiopulmonary exercise testing on a treadmill [3].…”

“…Currently, it is suggested by scientific evidence that patients with severe and/or morbid obesity have a blunted ventilatory response during exercise. This condition occurs particularly at vigorous intensities, which has also been associated with exercise intolerance [1,9,10]. Expiratory flow limitation and mechanical ventilatory constraint due to fat mass surrounding the chest wall and diaphragm have been discussed as major determining factors [1,2].…”

“…This condition occurs particularly at vigorous intensities, which has also been associated with exercise intolerance [1,9,10]. Expiratory flow limitation and mechanical ventilatory constraint due to fat mass surrounding the chest wall and diaphragm have been discussed as major determining factors [1,2]. However, the ventilatory response could also be affected by pathophysiological adaptations during exercise, which may depend on chemoreception and metabolic setpoints.…”