Preserved ratio impaired spirometry and restrictive spirometric pattern in obese populations: Clinical relevance with daytime hypercapnia.

OBJECTIVE

Obesity hypoventilation syndrome is defined as daytime hypercapnia in obese individuals without other underlying causes, associated with reduced lung volume. Preserved ratio impaired spirometry (PRISm) and restrictive spirometric pattern (RSP) are different spirometry patterns. In this pilot study, we investigated the association between PRISm (with or without RSP) and daytime hypercapnia in obese patients.

METHODS

We conducted a cross-sectional study in 106 obese patients (body mass index ≥ 30 kg/m2). Daytime hypercapnia was defined as an arterial carbon dioxide partial pressure (PaCO2) > 45 mmHg based on arterial blood gas analysis. PRISm was defined as FEV1/FVC ≥ 0.70 and FEV1 < 80 % predicted, and RSP was defined as FEV1/FVC ≥ 0.70 and FVC < 80 % predicted. We categorized PRISm and RSP into mutually exclusive groups (normal, PRISm alone, RSP alone, and PRISm + RSP).

RESULTS

Among the 106 obese patients (mean age 47.5 ± 14.0 years, 65.1 % male), 30 (28.3 %) had daytime hypercapnia. The prevalence of daytime hypercapnia was 23.5 % (16/68) in the normal spirometry group, 63.6 % (7/11) in the PRISm alone group, and 23.1 % (6/26) in the PRISm + RSP group. In multivariable logistic regression analyses, after adjusting for age, sex, body mass index, ever smoking, apnea-hypopnea index, mean oxygen saturation by pulse oximetry, and FEV1, PRISm alone was independently associated with daytime hypercapnia (P = 0.043).

CONCLUSIONS

Our study observed an association between non-restrictive PRISm and daytime hypercapnia in obese patients. Further research is needed to elucidate the underlying mechanisms and clinical significance of this association.