Abnormalities in the flow-volume loop in obstructive sleep apnoea sitting and supine

Area of Science:

• Respiratory Medicine
• Sleep Medicine
• Pulmonary Function Testing

Background:

• Obstructive sleep apnea (OSA) is a common sleep disorder.
• Flow-volume loops are used to assess airflow limitations.
• The influence of patient posture on flow-volume loop interpretation for OSA diagnosis requires clarification.

Purpose of the Study:

• To evaluate the effect of posture (sitting vs. supine) on the sensitivity and specificity of flow-volume loop abnormalities for diagnosing obstructive sleep apnea (OSA).

Main Methods:

• Thirty patients with suspected OSA underwent flow-volume loop recordings in both sitting and supine positions.
• Abnormalities were defined by FEF50/FIF50 ratio > 1 or presence of the sawtooth sign.
• Nocturnal polysomnography was used to confirm OSA diagnosis.

Main Results:

• Both sensitivity and specificity of flow-volume loop criteria for OSA were higher in the supine position compared to the sitting position.
• Even in the supine posture, sensitivities for sawtoothing (41%) and FEF50/FIF50 ratio > 1 (47%) were low.
• The sawtooth sign demonstrated high specificity (92%) for OSA diagnosis.
• Patients with OSA and sawtoothing showed a greater fall in oxygen saturation.

Conclusions:

• While flow-volume loops alone are not sensitive enough for routine OSA screening, the sawtooth sign is a specific indicator.
• The presence of the sawtooth sign warrants further investigation for OSA.
• Posture influences upper airway configuration, affecting flow-volume loop abnormalities in OSA patients.