Validation of forehead venous pressure as a measure of respiratory effort for the diagnosis of sleep apnea.

ABSTRACT

OBJECTIVES: The aim of the study was to validate the measurement of Forehead Venous Pressure derived from a single site on the forehead as an alternative to esophageal manometry and respiratory effort bands in the differential diagnosis of sleep apnea. METHODS: Fourteen subjects underwent a laboratory polysomnography concurrently with ARES Unicorder at Walter Reed Army Medical Center. Two-hundred respiratory events were selected by a scorer boarded in sleep medicine and classified into six event categories used in the differential diagnosis of sleep disordered breathing. Four sets of events were prepared, each containing airflow and one of four measures of respiratory effort (i.e., esophageal manometer, chest and abdomen bands, and forehead venous pressure). A second board-certified scorer scored each set of events twice while blinded to the type of the effort signal. RESULTS: The inter-rater Kappa scores across all event types indicated all four effort signals provided moderate agreement (kappa = 0.43-0.47). When comparing the intra-rater Kappa scores, the chest belt was superior (kappa = 0.88) to the esophageal manometry, FVP and abdomen belt (kappa = 0.78-0.82). The Kappa scores for the intra-rater comparison with the esophageal serving as the gold standard, FVP abdomen and chest all showed near perfect agreement (kappa = 0.81-0.86). The esophageal manometer and FVP provided slightly better inter-rater agreement in the detection of both obstructive hypopneas and apneas as compared to the chest and abdomen belts. There was a 20-30% drop in inter-rater reliability in the detection of flow-limitation and ventilation-change events compared to obstructive events, and all effort signals showed poor inter-rater agreement for central and mixed events. CONCLUSIONS: The results of the study suggest that the FVP can serve as an alternative to respiratory bands in the differential diagnosis of sleep disordered breathing, and in the recognition of patients appropriate for bilevel continuous positive airway pressure devices.