Patients with interstitial lung disease (ILD) have a rapid shallow breathing pattern while awake that is thought to be due to activation of lung reflexes. We wondered whether sleep would result in changes in respiratory control and thus cause hypoxemia and poor sleep quality. Eleven patients with ILD (5 men and 6 women) and 11 age- and sex-matched control subjects were studied during sleep. Sleep quality was worse in patients with ILD, with more time in Stage 1 (33.7% of total sleep time (TST) versus 13.5%) and less time in REM sleep (11.8 versus 19.9% TST) than found in control subjects, and more fragmentation of sleep (13.7 +/- 3.1 arousals/h and 24.3 +/- 6.0 sleep stage changes/h versus 6.9 +/- 1.0 and 12.7 +/- 1.4, respectively). Patients with ILD with awake SaO2 less than 90% had greater abnormalities in sleep structure than did those with SaO2 greater than 90%. The incidence of apneas and hypopnea periods in patients with ILD was low (apnea plus hypoventilation index of 1.3 +/- 0.45 versus 2.9 +/- 0.82 in control subjects, p = NS). Oxygen saturation dropped during REM sleep in patients, especially in those with more severe awake hypoxemia. Expiratory time (Te), inspiratory time (Ti), and their sum (Ttot) were shorter in the patients, whereas Ti/Ttot was the same as in control subjects. No systematic changes during sleep were seen in these variables. The variability of inspiratory volume index, Ti, Te, and Ti/Ttot was similar to that in control subjects, and was lowest during NREM sleep. The incidence of snoring was comparable in patients and control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)