Tidal breath flow-volume curves in obstructive sleep apnea

Area of Science:

• Respiratory Medicine
• Sleep Medicine
• Pulmonary Physiology

Background:

• Obstructive sleep apnea (OSA) is a common disorder characterized by repeated upper airway collapse during sleep.
• The supine position during sleep is a known risk factor for OSA due to gravitational effects and muscle relaxation.
• Assessing upper airway function in the supine position may offer insights into OSA pathophysiology.

Purpose of the Study:

• To investigate whether passive expiration in the supine position can identify upper airway pathophysiology in obstructive sleep apnea (OSA).
• To determine if positional changes in tidal breath flow-volume curves (TBFVC) are associated with OSA.
• To explore the relationship between TBFVC changes, OSA, and standard pulmonary function tests.

Main Methods:

• Prospective enrollment of 92 subjects with varying clinical conditions.
• Measurement of reproducible tidal breath flow-volume curves (TBFVC) during passive expiration in both sitting and supine positions using a ventilator.
• Standard pulmonary function tests (spirometry, lung volumes) were also performed in both positions.

Main Results:

• A positional change in the terminal portion of TBFVC was observed in 60% of subjects with documented OSA (n=20).
• This positional change was significantly more frequent in OSA patients compared to those with snoring history (32%) or no OSA (9%).
• The observed positional TBFVC change was not attributable to measurable pulmonary function abnormalities or body mass index.

Conclusions:

• Positional changes in TBFVC during passive expiration in the supine position may serve as an indicator of upper airway functional narrowing in OSA.
• This finding suggests that passive expiratory maneuvers could potentially reflect upper airway pathophysiology relevant to OSA.
• Further research is warranted to validate TBFVC as a diagnostic or monitoring tool for OSA.