I remember learning in medical school that infants are obligate nasal breathers, but we assumed adults had options when both awake and asleep. That's not entirely clear, a tiny 9181 suggested at least some adults are obligate nose breathers during sleep ...
... Nasal obstruction is known to cause abnormal ventilation during sleep in infants, but its effects on breathing and oxygenation during sleep in adults are unknown. However, in adults, obstruction of the nose by nasal packing has been shown to cause hypoxia, and on occasion, hypercarbia and sudden death. We have investigated the pattern of ventilation and the level of oxygenation during sleep in seven patients who had nasal packs after nasal polypectomy or septoplasty. ... Nasal packing either caused or worsened sleep-disordered breathing in all patients and significantly increased the number, duration, and frequency of episodes for the group as a whole. Several patients also had a greatly increased number and severity of episodes of nocturnal oxygen desaturation....Of course patients selected for polpyectomy are not typical; particularly in 1981 many who received surgery would today be treated as having obstructive sleep apnea. The 1981 study was repeated in 1991 with essentially the same results. Once again these patients had a surprising amount of trouble switching to mouth breathing during sleep. It's almost as though obligate nasal respiration persists in some adults throughout their lifetime.
And that was most of what I could find in my quick look, other than some review articles . They probably have more references, but in the abstracts they mostly call for "additional research". Not much new knowledge in 33 years. I wonder what medical textbooks teach today.
Medical research is strange. My own suspicion is that a significant number of adults are essentially obligate nose breathers during sleep. It would be good to have some data.
- fn -
 30+ years of research ... 3 reviews with limited follow-up.
- Mechanisms of nasal obstruction in sleep. [Laryngoscope. 1984] - PubMed - NCBI. ... If airflow resistances are increased by nasal disease, complete inspiratory obstructive closure of the pharynx and apnea can result from nasal breathing in sleeping subjects. Recumbency increases resistive swelling of inflamed nasal mucosa. Furthermore in patients with normal mucosa and unilateral nasal obstruction, contralateral recumbency induces contralateral obstruction which increases resistance to nasal breathing; and in either dorsal or lateral recumbency the congestive phase of the spontaneous nasal cycle acts in a similar way. Examples of breathing disorders in sleep and impaired quality of sleep in patients with obstructive mucosal disease and both bilateral and unilateral structural abnormalities are cited.
- Nasal obstruction as a risk factor fo... [J Allergy Clin Immunol. 1997] - PubMed - NCBI. Similar to above.
- Sleep, breathing and the nose. [Sleep Med Rev. 2005] - PubMed - NCBI ... In normal subjects, the nasal part of the upper airway contributes only little to the elevation of the total resistance, which is mainly the consequence of pharyngeal narrowing. Yet, swelling of the nasal mucosa due to congestion of the submucosal capacitance vessels may significantly affect nasal airflow. In many healthy subjects an alternating pattern of congestion and decongestion of the nasal passages is observed. Some individuals demonstrate congestion of the ipsilateral half of the nasal cavity when lying down on the side. Nasal diseases, including structural anomalies and various forms of rhinitis, tend to increase nasal resistance, which typically impairs breathing via the nasal route in recumbency and during sleep. A role of nasal obstruction in the pathogenesis of sleep-disordered breathing has been implicated by many authors. While it proves difficult to show a relationship between the degree of nasal obstruction and the number of disturbed breathing events, the presence of nasal obstruction will most likely have an impact on the severity of sleep-disordered breathing. Identification of nasal obstruction is important in the diagnostic work-up of patients suffering from snoring and sleep apnea.
- a 2012 Outside magazine article is a surprisingly good evidence-based review of mouth/nose respiration during exercise, and whether one could deliberately modify that respiration ... "I have never seen a study—and I look for them—in which any adopted pattern of breathing did anything to performance, oxygen consumption, efficiency, or fatigue."
Some post-publication discoveries, I'm going to see if I can get copies of these ...
- Impact of impaired nasal breathing on sleep-dis... [Sleep Breath. 2003] - PubMed - NCBI
- The role of the nose in sleep-di... [Am J Rhinol Allergy. 2013 May-Jun] - PubMed - NCBI
I'm back from my rushed and unjust survey of the literature. My working conclusions are unsurprising:
- The experimental data is very limited, and there's not much evidence any treatment other than CPAP helps many people with "sleep apnea"
- It's not clear what "sleep apnea" really means, there are probably multiple causes that contribute to a similar clinical presentation. It's not clear that we have the best treatment for every cause.
- We know that some infants can switch from nose to mouth breathing and we know that some adults have a lot of trouble with nocturnal mouth breathing during acute nasal obstruction. We don't know if they do better over time.
- Over a 20 year period there's often confusion between sleep disturbance, nocturnal oxygen desaturation (not to mention altitude effects), and apnea. There's also confusion between acute and chronic responses.
- North American clinicians have mostly lost interest in nasal obstruction syndromes and assume they make no contribution to nocturnal oxygen desaturation or even sleep disturbance. International clinicians still suspect nasal obstruction plays a role in some oxygen desaturation. Nobody seems interested in mere sleep disturbance without desaturation or apnea.
I don't see this in the ENT literature, but given renewed interest in hypertonic saline irrigation for chronic sinusitis, I wonder about use for nasal obstruction and sleep disturbance ...
- Hypertonic saline is more effective than normal saline in seasonal allergic rhinitis in children. [Int J Immunopathol Pharmacol. 2012 Jul-Sep] - PubMed - NCBI
- Effects of buffered 2.3%, buffered... [Eur Arch Otorhinolaryngol. 2009] - PubMed - NCBI ... "On the 20th day, there was a significant difference in SCT between the hypertonic buffered seawater group and non-buffered isotonic saline (P = 0.003). Buffered hypertonic seawater improved nasal airway patency more than the buffered isotonic saline..."
- The effect of saline solutions on... [Otolaryngol Head Neck Surg. 2007] - PubMed - NCBI. In this case hypertonic saline worked, but had no special advantage.
- Effects of buffered saline soluti... [Otolaryngol Head Neck Surg. 2004] - PubMed - NCBI This study found NO effect on nasal airway patency