Melbourne School of Psychological Sciences - Research Publications

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    Inspiratory-resistive loading increases the ventilatory response to arousal but does not reduce genioglossus muscle activity on the return to sleep
    Cori, JM ; Nicholas, CL ; Baptista, S ; Huynh, I ; Rochford, PD ; O'Donoghue, FJ ; Trinder, JA ; Jordan, AS (AMER PHYSIOLOGICAL SOC, 2012-09)
    Arousals from sleep are thought to predispose to obstructive sleep apnea by causing hyperventilation and hypocapnia, which reduce airway dilator muscle activity on the return to sleep. However, prior studies of auditory arousals have not resulted in reduced genioglossus muscle activity [GG-electromyogram (EMG)], potentially because airway resistance prior to arousal was low, leading to a small ventilatory response to arousal and minimal hypocapnia. Thus we aimed to increase the ventilatory response to arousal by resistive loading prior to auditory arousal and determine whether reduced GG-EMG occurred on the return to sleep. Eighteen healthy young men and women were recruited. Subjects were instrumented with a nasal mask with a pneumotachograph, an epiglottic pressure catheter, and intramuscular GG-EMG electrodes. Mask CO(2) levels were monitored. Three- to 15-s arousals from sleep were induced with auditory tones after resting breathing (No-Load) or inspiratory-resistive loading (Load; average 8.4 cmH(2)O·l(-1)·s(-1)). Peak minute ventilation following arousal was greater after Load than No-Load (mean ± SE; 8.0 ± 0.6 vs. 7.4 ± 0.6 l/min, respectively). However, the nadir end tidal partial pressure of CO(2) did not differ between Load conditions (43.1 ± 0.6 and 42.8 ± 0.5 mmHg, respectively), and no period of reduced GG activity occurred following the return to sleep (GG-EMG baseline, minimum after Load and No-Load = 2.9 ± 1.2%, 3.1 ± 1.3%, and 3.0 ± 1.3% max, respectively). These findings indicate that the hyperventilation, which occurs following tone-induced arousal, is appropriate for the prevailing level of respiratory drive, because loading did not induce marked hypocapnia or lower GG muscle activity on the return to sleep. Whether similar findings occur following obstructive events in patients remains to be determined.
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    Acetazolamide Attenuates the Ventilatory Response to Arousal in Patients with Obstructive Sleep Apnea
    Edwards, BA ; Connolly, JG ; Campana, LM ; Sands, SA ; Trinder, JA ; White, DP ; Wellman, A ; Malhotra, A (OXFORD UNIV PRESS INC, 2013-02-01)
    STUDY OBJECTIVES: The magnitude of the post-apnea/hypopnea ventilatory overshoot following arousal may perpetuate subsequent respiratory events in obstructive sleep apnea (OSA) patients, potentially contributing to the disorder's severity. As acetazolamide can reduce apnea severity in some patients, we examined the effect of acetazolamide on the ventilatory response to spontaneous arousals in CPAP-treated OSA patients. DESIGN: We assessed the ventilatory response to arousal in OSA patients on therapeutic CPAP before and after administration of acetazolamide for 7 days. SETTING: Sleep research laboratory. PARTICIPANTS: 12 (7M/5F) CPAP-treated OSA patients. INTERVENTIONS: Sustained-release acetazolamide 500 mg by mouth twice daily for one week. MEASUREMENTS AND RESULTS: A blinded investigator identified spontaneous arousals (3-15 s) during NREM sleep. Breath-by-breath measurements of minute ventilation, end-tidal CO(2), tidal volume, expiratory/inspiratory-time, and total breath duration were determined (4-s intervals) 32 s prior and 60 s following each arousal. Acetazolamide significantly increased resting ventilation (7.3 ± 0.2 L/min versus 8.2 ± 0.4 L/min; P < 0.05) and attenuated the percent increase in ventilation following arousal by ~2.5 fold (122.0% ± 4.4% versus 108.7% ± 3.5% pre-arousal level; P < 0.05). There was a positive correlation between the mean increase in ventilatory response to arousal and mean AHI (r(2) = 0.44, P = 0.01). However, absolute peak levels of ventilation following arousal remained unchanged between conditions (8.8 ± 0.4 L/min versus 8.9 ± 0.1 L/min). CONCLUSIONS: Acetazolamide substantially attenuates the increase in ventilation following spontaneous arousal from sleep in OSA patients. This study suggests an additional mechanism by which acetazolamide may contribute to the improvement in ventilatory instability and OSA severity. The data also provide support for reinforcing the importance of ventilatory control in OSA pathogenesis.