To evaluate sleep-related obstructive breathing events in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), we developed a technique for digital recording and analysis of esophageal pressure (Pes) and elucidated the Pes parameters. Pes was recorded overnight with a microtip-type pressure transducer in 74 patients with OSAHS. Simultaneously, in all patients digital polysomnography was recorded. The mean nadir end-apneic Pes swing (Pes Nadir) ranged from -20.2 to -147.4 cmH(2)O, with a mean of -53.6+/-2.9 cmH(2)O. Correlation of the mean Pes Nadir indicated a linear relationship with the mean ratio of maximal Pes swing to apnea duration (r(2)=0.70) and the mean area of the Pes (Pes Area) (r(2)=0.82). Significant correlations were noted between the mean Pes Nadir and apnea-hypopnea index (AHI, ranging from 7.9 to 109.5 per hour; r(2)=0.66), minimum SpO(2) (r(2)=0.60), oxygen desaturation index (ODI) of more than 3 (r(2)=0.65), arousal index (r(2)=0.54), and between the mean Pes Area and AHI (r(2)=0.63), minimum percutaneous arterial oxygen saturation (SpO(2); r(2)=0.57), ODI (r(2)=0.69), and arousal index (r(2)=0.41). Pes parameters were found to be significant in the evaluation of the severity of the respiratory effort during the sleep-related obstructive breathing events for patients with OSAHS.