To examine the impact of using a nasal pressure sensor only vs the American Academy of Sleep Medicine (AASM) recommended combination of thermal and nasal pressure sensors on (1) the apnea index (AI), (2) the apnea-hypopnea index (AHI), where the AHI is calculated using both AASM definitions of hypopnea, and (3) the accuracy of a diagnosis of obstructive sleep apnea (OSA).
Retrospective review of previously scored in-laboratory polysomnography.
A tertiary-hospital clinical sleep laboratory.
Patients or Participants:
One hundred sixty-four consecutive adult patients with a potential diagnosis of OSA, who were examined during a 3-month period.
Measurements and Results:
Studies were scored with and without the use of the oronasal thermal sensor. AIs and AHIs, using the nasal pressure sensor alone (AInp and AHInp), were compared with those using both a thermal sensor for the detection of apnea and a nasal pressure transducer for the detection of hypopnea (AIth and AHIth). Comparisons were repeated using the AASM recommended (AASMrec) and alternative (AASMalt) hypopnea definitions. AI was significantly different when measured from the different sensors, with AInp being 51% higher on average. Using the AASMrec hypopnea definition, the mean AHInp was 15% larger than the AHIth; with large interindividual differences and an estimated 9.8% of patients having a false-positive OSA diagnosis at a cutpoint of 15 events and 4.3% at 30 events per hour. Using AASMalt hypopnea definition, the mean AHInp was 3% larger than the AHIth, with estimated false-positive rates of 4.6% and 2.4%, respectively. The false-negative rate was negligible at 0.1% for both hypopnea definitions.
This study demonstrates that using only a nasal pressure sensor for the detection of apnea resulted in higher values of AI and AHI than when the AASM recommended thermal sensor was added to detect apnea. When the AASMalt hypopnea definition was used, the differences in AHI and subsequent OSA diagnosis were small and less than when the AASMrec hypopnea definition was used. In situations in which a thermal sensor cannot be used, for example, in limited-channel diagnostic devices, the AHI obtained with a nasal pressure sensor alone differs less from the AHI obtained from a polysomnogram that includes a thermal sensor when the AASMalt definition rather than the AASMrec definition of hypopnea is used. Thus, diagnostic accuracy is impacted both by the absence of the thermal sensor and by the rules used to analyze the polysomnography. Furthermore, where the thermal sensor is unreliable for sections of a study, it is likely that use of the nasal pressure signal to detect apnea will have modest impact.
Thornton AT; Singh P; Ruehland WR; Rochford PD. AASM criteria for scoring respiratory events: interaction between apnea sensor and hypopnea definition. SLEEP 2012;35(3):425-432.