Could Nasal Breathing During Exercise Inhibit the Development of Cardiac Fibrosis and Arrhythmia Associated with Endurance Training? a Brief Literature Review with Theoretical Analysis

The increased incidence of myocardial scarring and atrial fibrillation in lifelong endurance athletes has been attributed to a dose-response relationship resulting from high-volume, high-intensity training carried out over the long term. However, this outcome is contradictory to and inconsistent with the well-established benefits of cardiovascular endurance training. In this short literature review along with theoretical analysis from previously published data, we propose that an athlete's breathing technique may play a role in this process. Based on current evidence, it is plausible that adapting to nasal-only breathing during exercise may be a viable strategy for endurance athletes to mitigate the relative hyperventilation created by breathing orally during exercise, and counter the conditions conducive to myocardial ischemia. Breathing nasally could increase myocardial blood flow at a given exercise intensity compared to breathing orally, with the most significant effects likely to occur at the highest intensities of exercise, and thereby prevent pathogenic myocardial changes. In particular, the higher pulmonary end-tidal carbon dioxide values seen while using nasal breathing during exercise suggest that arterial carbon dioxide may be relatively higher in the nasal breathing condition, thereby acting as a vasodilator to increase myocardial perfusion. Consequently, a nasal breathing approach during exercise might attenuate the effects of exercise-induced myocardial vasoconstriction and ischemia produced by breathing orally which is a probable mechanism for the increased myocardial fibrosis and arrhythmia seen in endurance athletes without concurrent cardiovascular disease, making it a topic worthy of increased research focus.