Obligate nasal breathing

Human infants are commonly described as obligate nasal breathers as they breathe through their nose rather than the mouth.[11] Most infants, however, are able to breathe through their mouth if their nose is blocked.[11] There are however certain infants with conditions such as choanal atresia in which deaths have resulted from nasal obstruction.[11] In these cases there are cyclical periods of cyanosis. The infant initially attempts to breathe through the nose, and is unable to; hypercapnia occurs, and many babies instinctively begin to cry. While crying, oral ventilation occurs and cyanosis subsides. There is variation in the length of time until a baby begins oral breathing, and some will never cease attempts at nasal breathing. It has also been suggested that infants may not be able to sustain oral breathing for significant lengths of time, because of the weakness of the muscles required to seal the nasal airway and open the oral airway.[11]

While mouth breathing may occur during exercise, a 2018 study published in the International Journal of Kinesiology and Sports Science, indicates that nasal breathing offers a greater advantage over mouth breathing during exercise. This is due to the fact that "breathing through the nose releases nitric oxide, which is necessary to increase carbon dioxide (CO2) in the blood, which, in turn, is what releases oxygen. Mouth breathing does not effectively release nitric oxide, which means the cells are not getting as much oxygen as through nasal breathing, which could lead to fatigue and stress."[12] Professor Michael Flanell makes a similar argument in the 2019 article "The Athlete's Secret Ingredient: The Power of Nasal Breathing." He refers to nasal breathing as "the secret to improved health and athletic performance and recovery" since "for the athlete the ability to consume more O2 into their muscles while keeping carbon dioxide levels low is the difference between mediocracy and greatness in athletes."[13]

Yogis such as B. K. S. Iyengar advocate both inhaling and exhaling through the nose in the practice of yoga, rather than inhaling through the nose and exhaling through the mouth.[14][15][16] They tell their students that the "nose is for breathing, the mouth is for eating."[15][17][18][14]

Studies and trials are currently underway that examine the possible benefits of nitric oxide in the treatment of Covid-19.[19][5] This research is based on the fact that nitric oxide was investigated as an experimental therapy for SARS.[20]

Just as Nitric Oxide (NO) is developed and increased in the human body through nasal breathing, it is likewise decimated by mouth breathing. A May 2020 study notes that in the same way that “mouth breathing has been associated with many health issues, including abnormal facial and dental development, cardiovascular disease, fatigue, halitosis, headaches, hypertension, inflammation, sleep apnea, snoring, stress, and tooth decay,” mouth breathers also were found to have “lower levels of NO within the respiratory tract compared to nasal breathers.”[5] The researchers thus conclude that replacing mouth breathing with nasal breathing is a “lifestyle change” that “may also help to reduce SARS-CoV-2 viral load and symptoms of COVID-19 pneumonia by promoting more efficient antiviral defense mechanisms in the respiratory tract.”[5] In addition, Brian Strickland, MD, a fellow in Wilderness Medicine at Massachusetts General Hospital who studies “acute respiratory distress” in high altitudes, is applying this research towards Covid-19.[21][22] He is currently involved in clinical trials which apply the use of inhaled nitric oxide as a treatment for Covid-19.[23] This approach was inspired by the work of Associate Professor of Emergency Medicine at the Harvard Medical School N. Stuart Harris, who has been studying the effects of altitude sickness on mountain climbers, such as those who climb Mount Everest. Harris noticed that the consequences of high level altitude sickness on the human body mirrored Covid -19’s dysfunctional impact on the lungs. His focus on nitric oxide comes from its role in being able to breathe in high altitudes.[21]

The Johns Hopkins School of Medicine’s handbook, Bouncing Back From Covid-19: Your Guide to Restoring Movement, offers a series of breathing exercises that require the inhalation and exhalation of breath through the nose only, with closed lips and with the tongue on the roof of the mouth.[24][25]