Clinical Investigations Respiration 2004;71:385–390 DOI: 10.1159/000079644 Comparison of Nasal Prong Pressure and Thermistor Measurements for Detecting Respiratory Events during Sleep Ahmed BaHammam Sleep Disorders Center, Respiratory Unit, Department of Medicine, College of Medicine, King Saud University, Riyadh, Saudi Arabia Received: August 25, 2003 Accepted after revision: March 16, 2004 Dr. Ahmed BaHammam, Associate Professor Director, Sleep Disorders Center Respiratory Unit, College of Medicine, Department of Medicine 38 King Saud University, Box 2925, Riyadh 11461 (Saudi Arabia) Tel. +966 1 467 1521, Fax +966 1 467 2558 E-Mail ashammam2@yahoo.com or ashammam@ksu.edu.sa ABC Fax + 41 61 306 12 34 E-Mail karger@karger.ch www.karger.com © 2004 S. Karger AG, Basel 0025–7931/04/0714–0385$21.00/0 Accessible online at: www.karger.com/res Key Words Airflow W Nasal prong W Thermistor W Respiratory effort-related arousals W Apnea W Cannula Abstract Introduction and Objectives: Thermistor (TH) measure- ments have been traditionally used to determine airflow during polysomnographic studies (PSG). However, low accuracy in detecting hypopneas is a major drawback. Nasal prong pressure (NPP) measurements are becom- ing increasingly popular for quantifying respiratory events during sleep. We prospectively compared NPP and TH measurements with respect to their ability to detect respiratory events during routine PSG. Methods: Forty consecutive patients (26 male, 14 female) with clin- ically suspected sleep-disordered breathing (SDB) un- derwent routine diagnostic PSG. Airflow was measured using NPP and TH devices simultaneously. PSG was scored manually according to R and K criteria. Respirato- ry events were scored in two passes. During the first pass, the TH signal was disabled and the NPP signal was scored. During the second pass, the NPP signal was dis- abled and the TH signal was scored. Scorers for one method were blinded from the results of the other meth- od. To assess respiratory events, we used the respiratory arousal index (RAI), which was defined as the number of apneas and/or hypopneas followed by an arousal per hour of sleep, as detected by TH (RAI-TH) or NPP (RAI- NPP). Agreement analysis of the results obtained using the two different techniques was performed using the methodology of Bland-Altman. Results: Twenty-six pa- tients had obstructive sleep apnea, 10 had respiratory effort-related arousals and 4 had habitual snoring. The failure time of the flow signal on the raw data was not different between the two methods (NPP: 6 B 13 min, TH: 4 B 7 min). The Bland-Altman analysis of RAIs dem- onstrated that more events were nearly always detected using NPP compared to TH devices (44.4 B 37 vs. 35.4 B 31, p ! 0.001). No difference in the index of central apneas between the two methods could be detected. Sleep position had no effect on either measurement method. Conclusions: NPP measurements are superior to TH measurements for detecting obstructive respirato- ry events during sleep. Measurement of NPP is a simple, practical, sensitive and reliable method for detecting the whole spectrum of SDB. We recommend incorporating nasal prongs in routine polysomnographic monitoring. Copyright © 2004 S. Karger AG, Basel Introduction Obstructive sleep-disordered breathing (SDB) ranges from obstructive apneas and obstructive hypopneas to respiratory effort-related arousals (RERAs). Obstructive sleep apnea hypopnea syndrome (OSAHS) is character- ized by a repetitive reduction or cessation of airflow dur-