We reviewed 656 consecutive nocturnal PSGs performed at the Mount Sinai Sleep Center between 2002 and 2006, 272 of them in former WTC rescue and recovery workers and volunteers. Age, height, weight, and WTC worker/volunteer status were determined before, or on the date of the PSG. The latter group was required to have met eligibility criteria to receive medical services at the WTC Health Effects Treatment Program (WTC HETP) at Mount Sinai Medical Center. The exposure duration criterion consisted of a minimum of 24 hours of rescue, recovery, and service restoration work (or volunteering) during the period from September 11 to September 30, 2001, or of 80 hours from September 11 to November 30, 2001. The worksite location criterion included sites south of Canal Street in Manhattan, the Staten Island landfill, the barge loading piers, and the Office of the Chief Medical Examiner. Virtually every occupational group present during the rescue and recovery of the WTC site is represented in the WTC HETP population.

Nocturnal PSGs were conducted using Embla recording systems (Embla, Broomfield, CO), consisting of nocturnal recordings of the following physiologic channels: O1–A2, O2–A1, C3–A2, and C4–A1 electroencephalograms (sampled at 256 Hz), right and left electrooculograms, a single bipolar electrocardiogram, chin electromyogram, oxyhemoglobin saturation by pulse oximetry, chest and abdominal excursion by inductance plethysmography, airflow by nasal cannula, and body position by a mercury gauge. If the PSG was performed with a split-night protocol (ie, continuous positive airway pressure (CPAP) was applied and titrated for the second half of the study), only the data from the diagnostic part of the test were reviewed. Forty-seven PSGs were excluded because their protocol and montage differ from what was described above, or the original data were unavailable for this review.

Polysomnographic diagnoses were categorized as: no sleep disordered breathing (SDB), simple snoring, REM-related obstructive sleep apnea (OSA), upper airway resistance syndrome (UARS), and mild, moderate, and severe OSA. These categories were mutually exclusive, and hierarchically assigned when coexistent. The apnea-hypopnea index (AHI) served to define and categorize the severity of OSA. AHI ranges of 5 to 14.9, 15 to 29.9, and at least 30 events/hour defined the mild, moderate, and severe OSA categories, respectively.⁸ Simple snoring, UARS, and REM-related OSA all required a normal overall AHI (fewer than 5 events/hour), but the latter required a REM AHI at least twice the non-REM AHI, with at least 30 minutes of REM sleep present during the recording. UARS was diagnosed indirectly by the presence of flattened inspiratory nasal cannula pressure tracing in association with an arousal—a respiratory effort–related arousal (RERA). A subset of subjects without any PSG diagnosis of SDB as described above were diagnosed with simple snoring if snoring was evident during the study.

Univariate (t test and chi-square test), logistic regression, and nominal regression analyses (using age, gender, and body mass index [BMI] as predictors) were used as appropriate, to examine differences in predictor and outcome variables between the WTC and non-WTC groups. The first outcome variable examined was AHI. The second outcome variable was OSA, defined categorically by an AHI of 5 events/hour or more. A post hoc analysis defining OSA with an AHI of 15 or more was conducted as well. The third outcome variable was polysomnographic diagnosis, with the 7 categories defined above. The discrimination of the logistic regression model for OSA diagnosis was evaluated by means of the c statistic, and 95% confidence intervals were calculated for the estimates.

Two-tailed statistical significance required a p value of less than .05. Statistical analyses were conducted using the SPSS statistical package (version 17.0; SPSS, Chicago, IL) for all analyses, except for logistic regression models, for which the SAS statistical package (version 9.1; SAS Institute, Cary, NC) was used.

This study was approved by the Institutional Review Board at Mount Sinai School of Medicine.