Aims and objectives: Obstructive sleep apnea (OSA) is a common disorder manifested with snoring, daytime sleepiness, fatigue, metabolic, and cardiovascular symptoms. Manual continuous positive airway pressure (CPAP) titration is the gold standard to determine the amount of positive pressure required to abolish the airflow limitations. The current American Academy of Sleep Medicine (AASM) criteria for manual titration are very stringent, elegant but difficult. The AASM protocol does not favor the use of automatic positive airway pressure (APAP) in a split-night study. This study was done to look into changes in sleep and respiratory parameters following diagnostic polysomnography (PSG) and subsequent APAP titration, as a split-night protocol. Materials and method: Records of 80 patients were scrutinized who had done level 1 PSG in a sleep laboratory in Kolkata, India. The laboratory used APAP titration for all kinds of titrations. This is a descriptive study, where data were compared between diagnostic and therapeutic nights of the same patients, done as a split-night study. Results: The diagnostic night was denoted by visit 1 and therapeutic night as visit 2; the study was done as a split-night study. The rapid eye movement (REM) sleep time was found to be significantly increased from 15.08 minutes in V1 (SD 16.26) to 29.69 minutes (24.45) in V2 with a p <0.001. The total respiratory events were found to be significantly reduced from baseline median value of 206–14 in the follow-up visit posttreatment, p <0.001 as computed by Wilcoxon's signed-rank test. The REM SpO₂ was found to be significantly increased from baseline value of 90.87 ± 7.105 to 93.29 ± 6.312 in the follow-up visit posttreatment, p <0.001 as computed by paired sample t-test. Discussion and conclusion: The wake stages, N1 and N2 sleep, were reduced significantly in the therapeutic night than diagnostic night, but N3 sleep was increased in therapeutic night, though statistically not significant. The total arousals and arousal index were also decreased significantly, although there were wide interindividual variations. So overall, patients had an improved sleep architecture during therapeutic night and often with REM rebound. Overall respiratory parameters showed very significant improvement in terms of apnea and hypopnea index (AHI). Oximetry data showed very significant improvements in terms of oxygen saturation, nadir oxygen saturation, and REM time oxygen level. So we can formulate the hypothesis that even a 2 hours split-night APAP titration can perform a good titration and significant improvements in sleep and respiratory parameters.