How does the supine position worsen Central Sleep Apnea (CSA)?

How Supine Position Worsens Central Sleep Apnea

The supine position worsens central sleep apnea primarily by altering ventilatory drive and upper airway mechanics, leading to increased frequency and severity of apneic events. 1, 2

Physiological Mechanisms

• The cross-section and closing pressures of the pharynx differ according to body position, with the supine position creating less favorable airway geometry 1, 2
• Ventilatory drive is dependent on body position, with altered respiratory control in the supine position 1
• The supine position leads to reduced lung volume compared to lateral positions, which negatively impacts respiratory mechanics 2
• In the supine position, there is decreased ability of airway dilator muscles to adequately compensate as the airway collapses 2

Impact on Apneic Events

• Apnea events are significantly longer in the supine position compared to non-supine positions across all OSA severity categories:

  • 6.3% longer in mild OSA
  • 12.5% longer in moderate OSA
  • 11.1% longer in severe OSA 3

• Desaturation areas are larger in the supine position:

  • 5.7% larger in moderate OSA
  • 25.5% larger in severe OSA 3

• The individual severity of apneic events is elevated in the supine position, not just their frequency 3, 4

Clinical Evidence

• Using the definition of positional OSA as a supine AHI (Apnea-Hypopnea Index) at least twice as high as the lateral position AHI, approximately 50% of OSA patients can be classified as having positional OSA 1, 5

• Even in patients with severe non-positional OSA (those who have apneas in all positions), apneic events occurring in the supine position are more severe than those occurring in the lateral position, with:

  • Longer apnea duration
  • Greater oxygen desaturation
  • Longer arousal duration
  • Higher maximum snoring loudness
  • Greater heart rate changes 4

Therapeutic Implications

• Positional therapy (avoiding the supine position during sleep) can yield moderate reductions in AHI but is clearly inferior to CPAP for treating OSA 1

• Positional therapy may be most effective for:

  • Younger patients
  • Those with lower AHI
  • Less obese patients 1

• Different devices such as tennis balls, vests, positional alarms, and pillows can be used to avoid the supine position, though long-term compliance with positional therapy is generally poor 1

Clinical Pitfalls and Caveats

• The effectiveness of positional therapy is limited even in patients with clear positional sleep apnea 1

• Long-term compliance with positional therapy is poor, with only 29% of patients still using positional devices after 2 years in one study 1

• If positional therapy is used, sleep studies should be performed to document individual success, and long-term compliance should be monitored through follow-up studies 1

• While CPAP is slightly more effective at reducing AHI, positional therapy typically shows better compliance in terms of hours used per night 1