Why is nasal breathing more difficult when in a supine position?

Why Nasal Breathing Is More Difficult When Supine

Breathing through the nose is more difficult in the supine position primarily due to anatomical changes that occur when lying flat, including reduced airway patency and increased airflow resistance.

Physiological Mechanisms

When a person lies on their back (supine position), several physiological changes occur that affect nasal breathing:

1. Airway Geometry Changes

   • In the supine position, gravity causes soft tissues in the upper airway to shift posteriorly
   • The tongue and soft palate may fall backward, partially obstructing the airway 1
   • The retropalatal space (behind the soft palate) becomes more vulnerable to narrowing 2

2. Vascular Effects

   • Blood pools in the nasal mucosa and turbinates due to gravitational effects
   • This causes increased nasal congestion and swelling of nasal tissues
   • Results in narrowed nasal passages and increased resistance to airflow

3. Reduced Lung Volume

   • Supine positioning decreases functional residual capacity (FRC) 3
   • This reduction in lung volume has been shown to negatively affect upper airway patency
   • Studies show that FRC is significantly lower in the supine position compared to lateral or upright positions 3, 4

Evidence from Imaging Studies

CT imaging analysis has demonstrated measurable differences in airway dimensions based on body position:

• When changing from supine to lateral position, the retroglossal space (area behind the tongue) increases significantly 2
• The minimal cross-sectional area of the airway is smaller in the supine position compared to lateral positioning 2
• These anatomical changes are more pronounced in individuals with obstructive sleep apnea but occur in all people to some degree

Clinical Implications

The positional effect on nasal breathing has important clinical implications:

• Sleep-Related Breathing Disorders: More than half of all obstructive sleep apnea patients have position-dependent symptoms that worsen in the supine position 5, 1
• Heart Failure Patients: Those with chronic left ventricular failure show a dramatic 80.5% increase in respiratory airflow resistance when changing from sitting to supine position 4
• Recovery Position: For individuals with decreased consciousness, the recovery position (lateral recumbent) is often recommended over supine to maintain airway patency 6

Recommendations for Specific Populations

1. General Population:

   • If experiencing difficulty with nasal breathing while sleeping, consider lateral (side) sleeping position
   • Elevating the head slightly may help, but complete elevation of the head of the bed is not always effective 6

2. Patients with Sleep Apnea:

   • Positional therapy (avoiding the supine posture during sleep) can be beneficial for mild to moderate OSA 5, 1
   • The lateral position significantly improves passive airway anatomy and collapsibility 3

3. Patients with Heart Failure:

   • May experience more significant breathing difficulties in the supine position
   • Studies show airflow resistance increases dramatically when lying flat 4

Pitfalls and Caveats

• Infants: Despite nasal breathing being more difficult in the supine position, infants should always be placed on their backs to sleep to reduce SIDS risk 6, 7
• Mistaking Normal Physiology for Pathology: Some degree of increased nasal resistance in the supine position is normal and not necessarily indicative of a medical condition
• Overreliance on Positional Changes: While changing position can help with nasal breathing, it should not replace appropriate medical evaluation for persistent breathing difficulties

Understanding these physiological changes can help explain why many people find it more comfortable to sleep in a lateral position and why certain medical conditions worsen when lying flat.