Volitional apnea maneuvers increased muscle sympathetic activity compared to baseline (P<0.01), demonstrating an obligatory role of the peripheral chemoreflex in producing peak sympathetic responses.
What are the specific contributions of lung-stretch and chemoreflex drive to the peak sympathetic response during volitional apnea?
The peripheral chemoreflex plays an obligatory role in producing peak sympathetic responses during apnea, while dynamic ventilation blunts this activity at similar chemoreflex stresses.
p-value: p=<0.01
Volitional Apnea produces a robust peak sympathetic response through several interacting mechanisms. However, the specific contribution of each mechanism has not been elucidated. Muscle sympathetic activity was collected in participants (n = 10; 24 ± 3 years) that performed four maximal volitional apneas aimed at isolating lung-stretch (mechanical) and chemoreflex drive: (Ainslie and Duffin ) end-expiratory breath-hold, (Ainslie et al. ) end-inspiratory breath-hold, (Alpher et al. ) prehyperventilation breath-hold, and (Andersson and Schagatay ) prehyperoxia breath-hold. A final repeated rebreathe breath-hold protocol was performed to measure the peak sympathetic response during successive breath-holds at increasing chemoreflex stress. Finally, the influence of dynamic ventilation was assessed through asphyxic rebreathe. Muscle sympathetic activity was calculated as the change in burst frequency (burst/min), burst incidence (burst/100 heart-beats), and amplitude (au) between baseline and prevolitional breakpoint. Rebreathe was analyzed at similar chemoreflex stress as inspiratory breath-hold. All maneuvers increased muscle sympathetic activity compared to baseline (P < 0.01). However, prehyperoxia exhibited a smaller increase (+22.18 ± 9.13 burst/min; +25.52 ± 11.7 burst/100 heart-beats) compared to inspiratory, expiratory, and prehyperventilation breath-holds. At similar chemoreflex strain, rebreathe sympathetic activity was blunted compared to inspiratory breath-hold (P < 0.01). Finally, muscle sympathetic activity was not different between the repeated rebreathe trials, despite elevated chemoreflex stress and lower breath-hold duration with each subsequent breath-hold. We have demonstrated an obligatory role of the peripheral, but not central, chemoreflex (prehyperventilation vs. prehyperoxia) in producing peak sympathetic responses. At similar chemoreflex stresses the act of dynamic ventilation, but not static lung stretch per se, blunts muscle sympathetic activity. Finally, similar peak sympathetic responses during successive repeated breath-holds suggest a sympathetic ceiling may exist.
Busch et al. (Tue,) reported a other. Volitional apnea protocols vs. Baseline was evaluated on Muscle sympathetic activity (change in burst frequency, incidence, and amplitude) (p=<0.01). Volitional apnea maneuvers increased muscle sympathetic activity compared to baseline (P<0.01), demonstrating an obligatory role of the peripheral chemoreflex in producing peak sympathetic responses.
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