Voluntary activation of the diaphragm after inspiratory pressure threshold loading

Abstract

Abstract After a bout of isolated inspiratory work, such as inspiratory pressure threshold loading (IPTL), the human diaphragm can exhibit a reversible loss in contractile function, as evidenced by a decrease in transdiaphragmatic twitch pressure (PDI,TW). Whether or not diaphragm fatigability after IPTL is affected by neural mechanisms, measured through voluntary activation of the diaphragm (D‐VA) in addition to contractile mechanisms, is unknown. It is also unknown if changes in D‐VA are similar between sexes given observed differences in diaphragm fatigability between males and females. We sought to determine whether D‐VA decreases after IPTL and whether this was different between sexes. Healthy females (n = 11) and males (n = 10) completed an IPTL task with an inspired duty cycle of 0.7 and targeting an intensity of 60% maximal transdiaphragmatic pressure until task failure. PDI,TW and D‐VA were measured using cervical magnetic stimulation of the phrenic nerves in combination with maximal inspiratory pressure maneuvers. At task failure, PDI,TW decreased to a lesser degree in females vs. males (87 ± 15 vs. 73 ± 12% baseline, respectively, p = 0.016). D‐VA decreased after IPTL but was not different between females and males (91 ± 8 vs. 88 ± 10% baseline, respectively, p = 0.432). When all participants were pooled together, the decrease in PDI,TW correlated with both the total cumulative diaphragm pressure generation (R2 = 0.43; p = 0.021) and the time to task failure (TTF, R2 = 0.40; p = 0.30) whereas the decrease in D‐VA correlated only with TTF (R2 = 0.24; p = 0.041). Our results suggest that neural mechanisms can contribute to diaphragm fatigability, and this contribution is similar between females and males following IPTL.

Keywords

• inspiratory pressure threshold loading
• respiratory muscle fatigability
• respiratory physiology
• voluntary activation