Obstructive Sleep Apnea Syndrome: Disease Severity Based on Multivariate Analysis of Patient Polysomnographic Records
Robert H.I. Blanks Ph.D. and Victor V. Strelzow, M.D., FACA, FRCS-C
Journal of Vertebral Subluxation Research ~ Volume 3 ~ Number 1 ~ Pages 1-7
Attempts to understand and treat obstructive sleep apnea syndrome (OSAS), characterized by recurrent episodes of upper airway obstruction during sleep, have been complicated by the lack of generally accepted clinical scoring methods describing the severity of the disease. In this study, 178 unselected OSAS patients (164 males; 14 females) ranging in age from 19 years to 79 years (mean ± s.d. = 51 ± 11 years) were studied. The clinical diagnosis of OSAS was made on the basis of OSAS-related symptoms such as excessive daytime sleepiness, loud snoring, the patient’s sleep history and polysomnographic (PSG) evaluation. The PSG results were subjected to multivariate (factor and principal component analyses) and correlation analysis; 21 standard variables describing the severity of sleep disruption, oxygen saturation, respiratory, and cardiovascular function were included in the calculations. Results indicate that the severity of OSAS is predicted by seven variables in the PSG records. These are: 1) the respiratory disturbance index (RDI), i.e., number of hypopneas and apneas per hour of sleep, 2) the minimum percent oxygen desaturation during sleep (SaO2), 3) the percent of sleep in stage 1 (STAGE1), and 4-7) the average respiratory and heart rates while awake and during sleep. Given the similarity of sleep and awake values, only the sleep respiratory (SRR) and heart (SHR) were considered further. These five remaining variables were statistically weighted using factor analysis and expressed as the OSAS “Sleep Baseline Score” (SBS) value: [SBS = .310(RDI) – .320(SaO2) + .291(STAGE1) + .216(SHR) + .246(SRR) + 15]. SBS values for OSAS patients range from 5-89 (mean ± s.d. = 29.2 ± 17.0) compared to normative values which predict a mean score of 8. We propose, that quantitative polysomnographic measurements combined into a statistically weighted severity score (SBS) should be considered for longitudinally monitoring the severity of OSAS to deter-mine the effectiveness of clinical therapy.
Key Words: Obstructive Sleep Apnea Syndrome, Polysomnographic Testing, Human Patients, Disease Severity.