Mck. Khoo et al., VENTILATORY DYNAMICS OF TRANSIENT AROUSAL IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA, Respiration physiology, 112(3), 1998, pp. 291-303
The hyperpnea that accompanies arousal at the end of obstructive apnea
is believed to be due to the progressive build-up in chemical drive d
uring the apnea and a state-related decrease in upper airway resistanc
e. We postulated the existence of a third component: a state-related t
ransient increase in neural drive to the ventilatory pump muscles. To
quantify this contribution, we measured the ventilatory response to ar
ousal (VRA) in eight patients with obstructive sleep apnea (OSA) durin
g continuous positive airway pressure (CPAP) therapy, applied at indiv
idually titrated levels. CPAP application reduced total pulmonary resi
stance (RL) to approximately normal levels, stabilizing ventilation an
d sleep state. Transient arousal from stage 2 sleep was induced using
5-sec tones (60-90 dB). Mean inspiratory flow increased above control
on the second and third post-arousal breaths (P < 0.05), with a peak i
ncrease of 7.8 +/- 2.9 L/min while the accompanying changes in RL were
significant. The time-course of VRA measured in three normal subjects
under CPAP was similar to that observed in the OSA patients. However,
elimination of CPAP prolonged the VRA time-course. Taken together, th
ese findings demonstrate that: (1) during arousal, the increase in sta
te-related neural respiratory drive is short-lived but not substantial
; and (2) the resulting VRA time-course is shaped by the dynamics of t
he upper airway response to arousal. (C) 1998 Elsevier Science B.V. Al
l rights reserved.