Study objectives: To assess whether the measurement of breathing reduction during obstructive sleep events depends on using the flow or the volume signals recorded with a pneumotachograph.
Design: Prospective observational study.
Setting: Sleep laboratory in a University Hospital.
Patients or participants: Data from 10 male patients with sleep apnea (54 +/- 11 years, apnea-hypopnea index: 43 +/- 21 events/hour, body mass index: 30 +/- 2 kg/m2).
Interventions: Slow modification of continuous positive airway pressure was performed during full-polysomnography continuous positive airway pressure titration.
Measurements and results: Air flow was measured by a pneumotachograph, and volume was computed by numerical integration. Obstructive events of different magnitude were selected. In 500 breathing cycles analyzed, the reduction in tidal volume was greater than the reduction in the flow amplitude: mean difference of 0.091 (i.e., 9.1% amplitude) and limits of agreement of 0.095 and -0.277 (i.e., 9.5% and -27.7% amplitude). In 14% of the cycles, the reduction in flow was < 50%, whereas the reduction in volume was > 50%, resulting in discordant event classification.
Conclusions: The quantification of breathing reduction depends on whether the flow or the volume signal is used to assess breathing during sleep.