Pushing and pulling with no end in sight! The role of cross-talk between different forms of respiratory plasticity in modifying sleep apnoea

A randomized controlled crossover trial of acute intermittent and continuous hypoxia exposure in mild-moderate obstructive sleep apnea: A feasibility study

In a prospective, randomized, controlled crossover study, we explored the effects of acute intermittent hypoxia and acute continuous hypoxia on patients with mild-moderate obstructive sleep apnea. Over three single-night sessions, subjects were alternately exposed to normoxia, acute continuous hypoxia and acute intermittent hypoxia before sleep. The apnea-hypopnea index and oxygen desaturation index were used to diagnose obstructive sleep apnea and evaluate efficacy. A responder was defined as a participant with a ≥ 50% reduction in apnea-hypopnea index between normoxia and hypoxia exposure. Sixteen participants with mild-moderate obstructive sleep apnea completed the study. Compared with normoxia, the mean apnea-hypopnea index decreased by 8.9 events per hr (95% confidence interval, 4.2-13.6, p = 0.001) with acute intermittent hypoxia and by 4.1 events per hr (95% confidence interval, 0.5-8.8, p = 0.082) with acute continuous hypoxia, equating to a mean decrease in apnea-hypopnea index of 4.8 events per hr (95% confidence interval, 0.1-9.5, p = 0.046) with acute intermittent hypoxia compared with acute continuous hypoxia. Compared with normoxia, the mean oxygen desaturation index decreased by 9.8 events per hr (95% confidence interval, 4.4-15.1, p = 0.001) with acute intermittent hypoxia but did not significantly decrease with acute continuous hypoxia; the mean oxygen desaturation index decreased by 7.2 events per hr (95% confidence interval, 1.8-12.6, p = 0.010) with acute intermittent hypoxia compared with acute continuous hypoxia. Of the 16 participants, 11 responded to acute intermittent hypoxia and four responded to acute continuous hypoxia (p = 0.032), of whom eight of 11 cases and all four cases had oxygen desaturation indexes <5 events per hr, respectively (p = 0.273). All participants tolerated acute intermittent hypoxia and there were no obvious adverse events during acute intermittent hypoxia exposure. In conclusion, acute intermittent hypoxia exposure improved apnea-hypopnea index and oxygen desaturation index in patients with mild-moderate obstructive sleep apnea, suggesting that further prospective validation of intermittent hypoxia exposure in patients with obstructive sleep apnea is needed to establish its clinical feasibility as a therapeutic modality.

Randomised, controlled crossover trial of intermittent and continuous transcutaneous electrical stimulation of the genioglossus muscle for obstructive sleep apnoea

PURPOSE

Continuous transcutaneous electrical stimulation (CTES) of the genioglossus muscle may benefit patients with obstructive sleep apnoea (OSA). However, the therapeutic value of intermittent transcutaneous electrical stimulation (ITES) for OSA is unclear.

METHODS

This was a randomised, controlled, crossover study to compare the effects of ITES and CTES of the genioglossus muscle. Over three single-night sessions, participants were alternately subjected to three genioglossus stimulation modalities during sleep (sham, CTES and ITES). The apnoea-hypopnoea index (AHI) and oxygen desaturation index (ODI) were used for OSA diagnosis and to evaluate efficacy. A responder was defined as an individual with a ≥50% reduction in AHI together with <10 AHI events per hour and/or an ODI reduction of ≥25% between sham stimulation and electrical stimulation nights.

RESULTS

Fifteen men with OSA completed the study. Compared with sham, the median AHI with ITES decreased by 13.3 events/hour (95% CI 3.1 to 23.5, p=0.030) and by 7.3 events/hour (95% CI -3.9 to 18.5, p=0.825) with CTES. The median ODI was reduced by 9.25 events/hour (95% CI 0.5 to 18.0) with ITES and 3.3 events/hour (95% CI -5.6 to 12.2) with CTES; however, there was no significant difference between groups. Furthermore, ITES outperformed CTES with respect to longest apnoea duration (median (95% CI), 9.5 (0.0 to 19.0), p=0.011)) and the highest sleep efficiency (12.2 (2.7 to 21.7), p=0.009). Of the 15 participants, 8 responded to ITES and 3 responded to CTES (p=0.058), of whom all eight cases and two out of three cases had ODIs <5 events/hour, respectively. All participants tolerated ITES well.

CONCLUSIONS

ITES improved upper airway obstruction in patients with OSA, suggesting that further prospective validation of the intermittent approach is warranted.

TRIAL REGISTRATION NUMBER

ChiCTR2100050138.

Retinoic acid receptor alpha activation is necessary and sufficient for plasticity induced by recurrent central apnea

Reductions in respiratory-related synaptic inputs to inspiratory motor neurons initiate a form of plasticity that proportionally enhances inspiratory motor output, even in the absence of changing blood gases. This form of plasticity is known as inactivity-induced inspiratory motor facilitation (iMF). iMF triggered by brief, recurrent reductions in respiratory neural activity requires local retinoic acid (RA) synthesis, but receptor subtypes activated by RA are unknown. To test the hypothesis that retinoic acid receptor alpha (RARα) is necessary for iMF, RAR subtype-specific inhibitors were delivered intrathecally above the phrenic motor pool in urethane-anesthetized, ventilated rats before 5, ∼1 min central apneas (without hypoxia; separated by 5 min) while monitoring phrenic inspiratory output. Pretreatment with a spinal RARα inhibitor impaired the capacity for recurrent central apnea to trigger long-lasting increases in phrenic inspiratory output, but plasticity was expressed in rats pretreated with an RARβ/γ inhibitor. Intrathecal RA application in the absence of reduced respiratory neural activity elicited an increase in phrenic inspiratory output, which was prevented by pretreatment with an RARα inhibitor. These data indicate that spinal RARα activation is necessary for iMF triggered by recurrent reductions in respiratory neural activity, and that RARα activation in/near the phrenic motor pool in the absence of respiratory neural activity deprivation is sufficient to elicit phrenic inspiratory motor facilitation. Understanding cellular cascades underlying plasticity induced by reductions in respiratory neural activity may define avenues for pharmacological intervention in disorders in which endogenous compensatory mechanisms that defend ongoing inspiratory motor output are impaired.NEW & NOTEWORTHY Local mechanisms near phrenic motor neurons respond to reductions in respiratory-related synaptic inputs by triggering a chemoreflex-independent, proportional enhancement in inspiratory output, a form of plasticity called inactivity-induced inspiratory motor facilitation (iMF). Here, we show that activation of spinal retinoic acid receptor alpha (RARα) is necessary to trigger phrenic iMF, and that spinal RARα activation in the absence of respiratory neural activity deprivation is sufficient to elicit phrenic inspiratory facilitation.