Evolution of upper airway resistance syndrome

The question of whether upper airway resistance syndrome (UARS) is a distinct disease or an initial feature of obstructive sleep apnoea syndrome is still a matter of debate. We evaluated a retrospective group of UARS patients to determine the evolution of UARS over time and the relationship between clinical evolution and subjects' phenotype. Investigations were performed in 30 patients, in whom UARS was diagnosed between 1995 and 2000 by the use of full polysomnography (PSG) without oesophageal pressure (Pes) measurement. The time between initial and follow-up investigations was 6.6 +/- 2.6 years. All subjects had full PSG with Pes measurement and completed a sleep questionnaire, including the Epworth Sleepiness Scale. In 19 subjects, PSG results were compatible with UARS. In nine subjects, obstructive sleep apnoea-hypopnoea syndrome (OSAHS) was diagnosed. In two subjects, PSG did not demonstrate breathing abnormalities. The mean +/- SD apnoea-hypopnoea index in the UARS group was 1.5 +/- 1.7 h(-1) and 25.2 +/- 19 h(-1) in the OSAHS group (P < 0.01). The increase in body mass index (BMI) between initial and follow-up investigations in the UARS group was from 29.4 +/- 4 to 31 +/- 5.7 kg m(-2) (P = 0.014) and in the OSAHS group from 30 +/- 4.1 to 32.4 +/- 4.7 kg m(-2)(P = 0.004). Amplitude of Pes swings during respiratory events was significantly higher in OSAHS than that in UARS (P = 0.014). Our results suggest that UARS is part of a clinical continuum from habitual snoring to OSAHS. Progression from UARS to OSAHS seems to be related to an increase in the BMI.