Nasal Breathing Research

This systematic review analyzed 11 studies involving 313 participants to compare the effects of nasal versus oral breathing on brain function and respiratory muscle activation. The review searched PubMed and Scopus databases from January 2000 through May 2024, applying PRISMA guidelines.

On the brain function side, nasal breathing activated 15 brain regions during working memory tasks compared to only 10 with oral breathing. Nasal breathing enhanced default mode network activity, increased gamma-range EEG frequencies, and showed greater functional connectivity in the left cerebellum and bilateral inferior parietal gyri. Slow nasal breathing produced elevated delta and theta rhythms in prefrontal and central posterior areas, while oral breathing effects were limited to posterior regions. The review suggests nasal airflow provides a direct entry point to limbic brain areas for modulating cognitive function.

For respiratory muscles, oral breathing was associated with reduced diaphragm activation, increased compensatory upper trapezius recruitment, and forward head posture that further compromises diaphragmatic effectiveness. Nasal breathers showed more efficient respiratory muscle patterns with appropriate diaphragmatic dominance.

This nonrandomized clinical trial published in JAMA Otolaryngology investigated the effects of mouth closure on airflow patterns and sleep apnea severity in patients with obstructive sleep apnea. The study used a novel approach to measure both nasal and oral airflow simultaneously during polysomnography, comparing breathing patterns with and without mouth closure achieved through lip taping.

The researchers found that responses to mouth closure were highly variable among participants. Patients who had higher baseline oral airflow (mouth breathers) tended to benefit most from mouth closure, showing reductions in oral airflow and improvements in AHI. However, patients who were already predominantly nasal breathers did not experience significant changes, confirming that the intervention specifically targets the mouth-breathing phenotype.

The study provides important objective data on the mechanism by which mouth taping may improve sleep apnea — by redirecting airflow through the nasal passages, which offer greater airway stability than the oral route. The findings suggest mouth closure could serve as a simple, low-cost adjunctive therapy for appropriately selected OSA patients, though individual assessment of breathing route is important for predicting response.

This study directly examined mouth taping as an intervention for sleep-disordered breathing. Participants who were identified as mouth breathers during sleep used porous oral patches to encourage nasal breathing overnight.

Results showed significant reductions in snoring severity scores and improvements in sleep apnea indices (AHI) for those with mild OSA. The intervention was well-tolerated with no serious adverse events.

This is one of the few clinical studies directly testing mouth taping for sleep, providing evidence beyond anecdotal reports.

This systematic review and meta-analysis evaluated the effects of respiratory muscle training on obstructive sleep apnea (OSA). The authors searched multiple databases including PubMed, Scopus, Web of Science, and Cochrane Library to identify randomized controlled trials and quasi-experimental studies examining respiratory training interventions in adults with OSA.

The analysis included studies that used various forms of respiratory muscle training, including inspiratory muscle training, expiratory muscle training, and oropharyngeal exercises. The primary outcomes assessed were the apnea-hypopnea index (AHI), oxygen saturation, and respiratory muscle strength.

Results demonstrated that respiratory training significantly reduced AHI scores and improved minimum oxygen saturation levels in OSA patients. The findings support respiratory muscle training as a complementary therapeutic approach for managing obstructive sleep apnea, particularly for patients who struggle with CPAP adherence or seek adjunctive therapies.

This review examines the role of breathing re-education as a therapeutic approach for obstructive sleep apnea (OSA), focusing on how it addresses the condition's multiple phenotypes and endotypes. The authors describe three core dimensions of breathing re-education: restoring nasal breathing, normalizing breathing volume and rate, and establishing diaphragmatic breathing patterns.

The paper outlines four key OSA phenotypes — anatomical compromise, high loop gain (unstable ventilatory control), low arousal threshold, and poor pharyngeal muscle responsiveness — and explains how breathing re-education can target each one. Nasal breathing reduces mouth breathing-related airway collapse, slower breathing rates improve ventilatory stability, and diaphragmatic breathing supports upper airway patency through improved tracheal tug mechanics.

The authors highlight that mouth breathing during sleep is a significant contributor to OSA severity and that interventions like myofunctional therapy and mouth taping can help restore nasal breathing. They also discuss the role of nitric oxide production in the nasal passages and its vasodilatory effects on the airways. The review concludes that breathing re-education represents a low-cost, non-invasive adjunct therapy that warrants further investigation through randomized controlled trials.

This study examined the relationship between mouth breathing during sleep and various sleep quality outcomes. Researchers assessed breathing patterns during sleep and correlated them with subjective and objective sleep measures.

Mouth breathers had significantly worse sleep quality scores, more frequent snoring, and reported greater daytime sleepiness compared to nasal breathers. The association persisted after controlling for other factors.

These findings support the rationale for interventions like mouth taping that promote nasal breathing during sleep.

This paper presents the "airway centric" approach to orthodontics, which prioritizes nasal breathing and tongue posture in treatment planning.

Core Principles:

Key Arguments:

• Breathing mode shapes facial development
• Extraction orthodontics may worsen airway
• Expansion often preferable to extraction
• Tongue posture fundamental to stability

Facial Development Factors:

Treatment Implications:

• Screen for mouth breathing
• Address tongue posture before/during treatment
• Consider myofunctional therapy
• Avoid treatments that reduce airway

Relevance to Mewing:

Supports the core mewing principles: - Tongue posture matters - Nasal breathing essential - Function drives form - Proper oral posture for stability

Controversy:

• Not all orthodontists agree
• Traditional vs. functional debate ongoing
• More research needed
• Represents paradigm shift in thinking

Limitations:

• Opinion/perspective piece
• Not a controlled trial
• Represents one viewpoint in ongoing debate

This study compared nasal-only breathing versus oral breathing during graded exercise testing. Despite the perceived difficulty of nasal breathing during exercise, performance outcomes were equivalent between conditions.

Notably, nasal breathing resulted in a 22% lower ventilation rate at equivalent workloads, suggesting improved breathing efficiency. This supports the concept that trained nasal breathers can maintain performance while breathing less.

The findings encourage athletes to develop nasal breathing capacity for improved efficiency during submaximal exercise.

This retrospective study compared craniofacial and dentofacial development between 55 mouth-breathing children and 61 nasal-breathing controls, all undergoing orthodontic treatment. The results clearly demonstrate that chronic mouth breathing during critical growth periods leads to measurable changes in facial structure.

Mouth breathers showed backward and downward rotation of the mandible (clockwise rotation), increased overjet, a steeper mandible plane angle, a higher palatal plane, and narrowing of both the upper and lower dental arches at the level of the canines and first molars. Posterior crossbite was nearly twice as common in mouth breathers (49% vs 26%), and abnormal lip-to-tongue anterior oral seal was significantly more prevalent (56% vs 30%).

These findings provide strong evidence that nasal breathing is essential for normal craniofacial development in children. Nasal obstruction during critical growth periods leads to unfavorable facial growth patterns that require orthodontic intervention to correct.

This randomized, single-blind crossover study directly compared upper airway resistance during sleep between nasal and oral breathing routes in 12 healthy subjects with normal nasal resistance. The study provides some of the strongest evidence for why healthy humans predominantly breathe through the nose during sleep.

During wakefulness, upper airway resistance was similar regardless of breathing route. However, during stage two sleep in the supine position, oral breathing produced dramatically higher airway resistance (median 12.4 cmH2O/L/s) compared to nasal breathing (5.2 cmH2O/L/s). Even more striking, obstructive apneas and hypopneas were profoundly more frequent during oral breathing (apnea-hypopnea index of 43) versus nasal breathing (AHI of 1.5).

These findings demonstrate that nasal breathing provides a clear mechanical advantage during sleep, keeping the upper airway more patent and dramatically reducing the frequency of obstructive breathing events. This explains the physiological basis for why mouth breathing during sleep is associated with snoring and obstructive sleep apnea.

This foundational study demonstrated that the paranasal sinuses continuously produce nitric oxide (NO) at remarkably high concentrations. When breathing through the nose, this NO is carried into the lungs where it acts as a vasodilator, improving blood flow and oxygen uptake.

Mouth breathing bypasses this NO delivery mechanism entirely. The study showed that nasal breathing can improve arterial oxygenation by 10-15% compared to mouth breathing due to this NO effect.

This research established the scientific basis for why nasal breathing is physiologically superior to mouth breathing.

This landmark study experimentally tested whether mouth breathing affects facial development by inducing obligate oral breathing in young rhesus monkeys.

Study Design:

• Young rhesus monkeys (growing animals)
• Nasal obstruction induced via silicone nose plugs
• Forced obligate mouth breathing
• Compared to control animals (nasal breathing)
• Monitored over growth period

Key Findings:

Observed Changes:

• "Long face syndrome" development
• Lowered tongue posture
• Altered muscle function
• Narrower maxilla
• Increased facial height

Mechanism:

When nasal breathing is blocked: 1. Tongue drops to allow oral breathing 2. Loss of tongue pressure on palate 3. Cheek pressure unopposed 4. Face grows downward and narrower 5. "Adenoid facies" pattern develops

Relevance to Mewing:

This study provides foundational evidence that: - Breathing mode affects facial development - Tongue position (influenced by breathing) shapes the palate - Changes occur during growth periods

Limitations:

• Animal study (primates, not humans)
• Extreme intervention (complete obstruction)
• May not directly translate to human outcomes
• Studied growing animals, not adults

Clinical Significance:

Supports the principle that oral posture and breathing mode influence craniofacial development, though the study used extreme interventions in growing animals.