Novel method for evaluating the upper airway resistance using the ratio of neural respiratory drive to flow in OSA.

STUDY

OBJECTIVES

Sleep is associated with a reduction in ventilation and an increase in upper airway resistance (UAR) in patients with obstructive sleep apnea (OSA). However, there is no consensus on the standard for assessment of UAR and therefore it is important to develop a method to reliably assess UAR in patients with OSA. The purpose of the present study is to determine whether the ratio of neural respiratory drive (NRD) to flow can be used to assess changes in UAR in OSA during sleep.

METHODS

A total of 24 patients (21 men) with OSA and 10 normal subjects (6 males) were studied. The UAR was assessed by the ratio of NRD to flow, which measured by esophageal pressure (Poes), diaphragm electromyography (EMGdi) and superficial diaphragm electromyography (SEMGdi) in various stages including wakefulness, N2 sleep, N2 sleep with snoring, hypopneas, the in the "preapnea" states in OSA versus wakefulness, sleeponset, N2 sleep, N3 sleep in normal subjects. All subjects underwent overnight full polysomnography using standard techniques.

RESULTS

Our study indicate that UAR was progressively higher from wakefulness to N2 sleep, N2 sleep with snoring, hypopneas, and the in the "preapnea" states in patients with OSA and had obvious difference in statistical significance (p < 0.05). We found NRD in hypopneas was lower than that in N2-snoring while the UAR in hypopneas was higher than that in N2-snoring.The UAR and NRD increased consecutively from wakefulness to N2 sleep and N3 sleep in normal subjects while the ventilation was reduced consecutively in NREM sleep.

CONCLUSIONS

It is feasible to use the ratio of neural respiratory drive to flow to assess UAR in patients with OSA during sleep.