Relationship between pulmonary function and sleep-induced respiratory abnormalities.

The relationships between pulmonary function and sleep-induced respiratory events were studied in 34 consecutive male patients with suspected sleep apnea syndrome. In view of the effects of obstructive airway disease on pulmonary volume and airway resistance (Raw), patients were divided into two groups, those with and those without obstructive airway disease. Percent predicted functional residual capacity (FRC) correlated significantly with the apnea-plus-hypopnea index (AHI) in patients with and without obstructive airway disease (r = -0.62 and p less than 0.01; and r = -0.57 and p less than 0.01, respectively) whereas percent predicted total lung capacity had a significant relationship with AHI only in patients with obstructive airway disease (r = -0.80; p less than 0.001). In patients without such disease, a significant correlation between inspiratory airway conductance (Gaw) and AHI (r = -0.47; p less than 0.05) was also present, while percent predicted FRC and Gaw did not correlate with normalized weight. These findings suggest that decreased pulmonary volume and increased Raw contribute to the severity of sleep-induced respiratory abnormalities in patients with sleep apnea syndrome regardless of the degree of obesity.