The single-breath diffusing capacity for carbon monoxide in obstructive sleep apnea and obesity

Area of Science:

• Pulmonary physiology
• Sleep medicine
• Respiratory diagnostics

Background:

• Elevated single-breath diffusing capacity for carbon monoxide (Dco) has been observed in patients with obstructive sleep apnea (OSA).
• This study aimed to confirm these findings and identify factors influencing diffusion indices in OSA patients.

Purpose of the Study:

• To confirm elevated Dco in OSA patients.
• To determine factors influencing diffusion indices, particularly in relation to weight excess.
• To evaluate the adequacy of existing prediction equations for obese subjects.

Main Methods:

• Retrospective data collection at a university hospital.
• Measurement of Dco in patients with OSA and nonapneic control subjects.
• Comparison of results against established reference values and prediction equations.

Main Results:

• In moderate/severe OSA (apnea/hypopnea index [AHI] ≥ 30), both Dco and transfer coefficient (KCO) were increased.
• KCO positively correlated with AHI and body mass index (BMI).
• Diffusion indices were similar between OSA patients and BMI-matched controls; KCO correlated with BMI in controls. Obese patients showed Dco ~10% and KCO 20-25% higher than predicted.

Conclusions:

• Increased Dco and KCO are observed in moderate/severe OSA, primarily attributed to excess weight rather than OSA itself.
• Body mass index (BMI) is a key determinant of diffusion indices in obese individuals, irrespective of OSA status.
• Standard prediction equations for diffusion indices may underestimate values in obese subjects.