Utility of Oxygen Saturation and Heart Rate Spectral Analysis Obtained From Pulse Oximetric Recordings in the Diagnosis of Sleep Apnea Syndrome* Carlos Zamarro ´ n, MD; Francisco Gude, MD; Javier Barcala, MD; Jose R. Rodriguez, MD; and Pablo V. Romero, MD Objectives: We prospectively evaluate the spectral characteristics of nocturnal arterial oxygen saturation (SaO 2 ) and heart rate variability obtained from pulse oximetric recording as a diagnostic test for obstructive sleep apnea (OSA). Subjects and measurements: Three hundred referred outpatients with symptoms compatible with the diagnosis of OSA were studied using nocturnal pulse oximetric recording performed simultaneously with polysomnography. Power spectral analysis of SaO 2 and heart rate data were analyzed using fast Fourier transformation of a Hamming-windowed signal. Design and results: Recording test results were classified as abnormal (suspicion of OSA) if the periodogram showed a peak in the period 30 to 70 s in either of the signals. A normal test result was defined as the absence of this peak in the periodogram in both signals. Two independent observers performed a single-blind evaluation. The total area of the periodogram (STOT), the ratio of the area enclosed in the periodogram within the period 30 to 70 s (S 30 –70 ), the ratio of the area enclosed in the periodogram within the period 30 to 70 s with respect to the total area of the periodogram (S), and the peak amplitude of the periodogram in the period 30 to 70 s (PA) were measured in both signals. The presence of a peak in the periodogram in either of the signals has a sensitivity of 94%, a specificity of 82%, a positive predictive value of 87%, and a negative predictive value of 92% with respect to the OSA diagnosis. The patients in the OSA group had higher values for STOT,S 30 –70 , S, and PA than the group without OSA. Conclusions: SaO 2 and heart rate spectral analysis obtained by nocturnal pulse oximetry as well as the identification of a peak within 30 to 70 s in either signal could be useful as a diagnostic technique for patient with OSA. (CHEST 2003; 123:1567–1576) Key words: heart rate; obstructive sleep apnea; oximetry; polysomnography; spectral analysis Abbreviations: AHI = apnea-hypopnea index; BMI = body mass index; CI = confidence interval; FFT = fast Fourier transform; OSA = obstructive sleep apnea; PA = peak amplitude of the periodogram in the period 30 to 70 s; Sao 2 = arterial oxygen saturation; REM = rapid eye movement; S = ratio of the area enclosed in the periodogram within the period 30 to 70 s with respect to the total area of the periodogram; S 30 –70 = area enclosed in periodogram within the period 30 to 70 s; Stot = total area of the periodogram O bstructive sleep apnea (OSA) is a respiratory disorder characterized by recurrent airflow ob- struction caused by total or partial collapse of the upper airway. 1 The “gold standard” for a definitive diagnosis of OSA is polysomnography, 2 which is an expensive tool and not widely available. Given the high prevalence of OSA, 3,4 its potential importance as a contributing factor to cardiovascular morbidi- ty, 5–8 and the availability of an effective treatment for this disease, 9,10 numerous efforts have been undertaken to preselect subjects to undergo further clinical investigation. *From the Sleep Unit, Division of Respiratory Medicine (Drs. Zamarro ´ n, Barcala, and Rodriguez), and Clinical Epidemiology Unit (Dr. Gude), Hospital Clı´nico Universitario, Santiago; and Lung Function Test Laboratory (Dr. Romero), Division of Respiratory Medicine, Ciutat Sanitaria y Universitaria de Bell- vitge, Barcelona. Spain. This study was supported by Fondo Investigacio ´ n Sanitaria grant (96/0811) and Secretaria Xeral de Investigacion e Desenvolve- mento grant (PGIDT99PXI90201A). Manuscript received October 2, 2001; revision accepted Decem- ber 17, 2002. Reproduction of this article is prohibited without written permis- sion from the American College of Chest Physicians (e-mail: permissions@chestnet.org). Correspondence to: Carlos Zamarro ´n, MD, Servicio de Neumo- logı ´a, Hospital Clı ´nico Universitario de Santiago, C/Choupana s/n 15706, Santiago de Compostela, Spain; e-mail: carlos.zamarron. sanz@sergas.es. www.chestjournal.org CHEST / 123 / 5 / MAY, 2003 1567