Hypoxic end-expiratory apnea significantly increased sympathetic action potential frequency (192 to 952 APs/min, P<0.01), whereas hyperoxia suppressed this response compared to normoxia.
Does varying chemoreflex stress (hypoxia vs hyperoxia) alter sympathetic neural recruitment strategies during end-expiratory apnea in healthy males?
Hypoxia potentiates and hyperoxia suppresses the increase in sympathetic action potential frequency and incidence during apnea, highlighting the role of chemoreflex stress in neural recruitment.
p-value: p=<0.01
We sought to examine the effect of varying chemoreflex stress on sympathetic neural recruitment strategies during end-expiratory apnea. We hypothesized that increases in the firing frequency and probability of low-threshold axons at the asphyxic “break point” would be exaggerated during hypoxia and attenuated during hyperoxia. Multiunit muscle sympathetic nervous system activity (MSNA) (peroneal nerve microneurography) was measured in 10 healthy male subjects (31 ± 2 yr, 25 ± 1 kg/m 2 ). Individuals completed maximal voluntary end-expiratory apnea under normoxic, hypoxic (inspired O 2 fraction: 0.17 ± 0.01), and hyperoxic (inspired O 2 fraction: 0.92 ± 0.03) conditions. Action potential (AP) patterns were examined from the filtered raw signal with wavelet-based methodology. Multiunit MSNA was increased ( P ≤ 0.05) during normoxic apnea, because of an increase in the frequency and incidence of AP spikes (243 ± 75 to 519 ± 134 APs/min, P = 0.048; 412 ± 133 to 733 ± 185 APs/100 heartbeats, P = 0.02). Multiunit MSNA increased from baseline ( P 0.05). We conclude that increases in frequency and incidence of APs during apnea are potentiated during hypoxia and suppressed when individuals are hyperoxic, highlighting the important impact of chemoreflex stress in AP discharge patterns. The results may have implications for neural control of the circulation in recreational activities and/or clinical conditions prone to apnea. NEW & NOTEWORTHY Our results demonstrate that, compared with normoxic end-expiratory apnea, hypoxic apnea increases the frequency and incidence of action potential spikes as well as the probability of multiple firing. We further show that this response is suppressed when individuals are hyperoxic. These data highlight the potentially important role of chemoreflex stress in neural firing and recruitment and may have implications for neural control of the circulation in recreational and/or clinical conditions prone to apnea.
Ott et al. (Wed,) conducted a other in Healthy (n=10). Hypoxic and hyperoxic end-expiratory apnea vs. Normoxic end-expiratory apnea was evaluated on Multiunit muscle sympathetic nervous system activity (MSNA) and action potential (AP) frequency (p=<0.01). Hypoxic end-expiratory apnea significantly increased sympathetic action potential frequency (192 to 952 APs/min, P<0.01), whereas hyperoxia suppressed this response compared to normoxia.