POSITIONAL VS NONPOSITIONAL OBSTRUCTIVE SLEEP-APNEA PATIENTS - ANTHROPOMORPHIC, NOCTURNAL POLYSOMNOGRAPHIC, AND MULTIPLE SLEEP LATENCY TESTDATA

Study objectives: To compare anthropomorphic, nocturnal polysomnograph ic (PSG), and multiple sleep latency test (MSLT) data between position al (PP) and nonpositional (NPP) obstructive sleep apnea (OSA) patients . Design: This is a retrospective analysis of anthropomorphic, PSG, an d MSLT data of a large group of OSA patients who underwent a complete PSG evaluation in our sleep disorders unit. The patients were divided in two groups: the PP group, those patients who had a supine respirato ry disturbance index (RDI) that was at least two times higher than the lateral RDI, and the NPP group, those patients in whom the RDI in the supine position was less than twice that in the lateral position. Sub jects: From a group of 666 consecutive OSA patients whose conditions w ere diagnosed in our unit from September 1990 to February 1995, 574 pa tients met the following criteria and were included in the study: RDI> 10; age>20 years, and body mass index: (BMI)>20. Results: Of all 574 p atients, 55.9% were found to be positional. No differences in height w ere observed but weight and BMI were significantly higher in the NPP g roup, these patients being on the average 6.5 kg heavier than those in the PP group. The PP group was, on average, 2 years younger than the NPP group. Nocturnal sleep quality was better preserved in the PP grou p. In this group, sleep efficiency and the percentages of deep sleep ( stages 3 and 4) were significantly higher while the percentages of lig ht sleep (stages 1 and 2) were significantly lower than in the NPP gro up. No differences for rapid eye movement (REM) sleep were found. In a ddition, wakefulness after sleep onset and the number of short arousal s (<15 s) were significantly lower in the PP group. Apnea index and to tal RDI were significantly higher and the minimal arterial oxygen satu ration in REM and non-REM sleep was significantly lower in the NPP. No differences in periodic limb movements data were found between the tw o groups. The average MSLT was significantly shorter in the NPP group. Univariate and multivariate stepwise logistic regression analysis sho wed that the most dominant variable that correlates with positional de pendency in OSA patients is RDI, followed by BMI which also adds a sig nificant contribution to the prediction of positional dependency. Age, although significant, adds only a minor improvement to the prediction of this positional dependency phenomenon. A severe, obese, and older OSA patient is significantly less likely to be positional than a mild- moderate, thin, and young OSA patient. In four obese OSA patients who lost weight, a much more pronounced reduction was seen in the lateral RDI than in the supine RDI, and three of these cases who were previous ly NPP became PP. Conclusions: In a large population of OSA patients, most were found to have at least twice as many apneas/hypopneas in the supine than in the lateral position. These so-called ''positional pat ients'' are on the average thinner and younger than ''nonpositional pa tients.'' They had fewer and less severe breathing abnormalities than the NPP group. Consequently their nocturnal sleep quality was better p reserved and, according to MSLT data, they were less sleepy during day -time hours. RDI was the most dominant factor that could predict the p ositional dependency followed by-BMI and age. RDI showed a threshold e ffect, the prevalence of PP in those with severe RDI (RDI greater than or equal to 40) was significantly lower than in those OSA patients wi th mild-moderate RDI. BMI showed a major significant inverse relations hip with positional dependency, while age had only a minor although si gnificant inverse relationship with it. Body position during sleep has a profound effect on the frequency and severity of breathing abnormal ities in OSA. patients.