School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
Department of Anaesthesiology, Mayo Clinic, Rochester, Minnesota.
Acta Physiol (Oxf). 2019 Apr;225(4):e13212. doi: 10.1111/apha.13212. Epub 2018 Nov 25.
Reducing the work of breathing during exercise improves locomotor muscle blood flow and reduces diaphragm and locomotor muscle fatigue and is thought to be the result of a sympathetically mediated reflex.
The aim of this study was to assess muscle sympathetic nerve activity (MSNA) when the work of breathing is experimentally lowered during dynamic exercise.
Healthy subjects (n = 12; age = 29 ± 9 years) performed semi-recumbent cycling trials at 40%, 60%, and 80% of peak workload. Exercise trials consisted of spontaneous breathing, reduced work of breathing (proportional assist ventilator), followed by further spontaneous breathing (post-ventilator). MSNA was recorded from the median nerve.
There was no difference in work of breathing between PAV and post-PAV at 40% peak work. At 60% peak work, the ventilator significantly (P < 0.05) reduced work of breathing (103 ± 39 vs 144 ± 47 J min ), sympathetic nerve activity (35 ± 5 vs 42 ± 8 burst min ), and (2.4 ± 0.5 vs 2.6 ± 0.5 L min ) without influencing ventilation (86 ± 9 vs 82 ± 10 L min ; P > 0.05), for PAV and post-PAV respectively. During 80% peak work (n = 8), the ventilator significantly (P < 0.05) reduced work of breathing (235 ± 110 vs. 361 ± 150 J min ), MSNA (48 ± 7 vs 54 ± 11 burst min ), and (2.9 ± 0.6 vs 3.2 ± 0.7 L min ) but not ventilation (121 ± 20 vs 123 ± 20 L min ; P > 0.05), for PAV and post-PAV respectively. There was a significant relationship between MSNA and (P < 0.0001) with a significant interaction due to the ventilator (P < 0.05).
Lowering the normally occurring work of breathing during exercise results in commensurate reductions in MSNA. Our findings provide evidence of a sympathetically mediated vasoconstrictor effect emanating from respiratory muscles during exercise.
本研究旨在评估在动态运动期间，当呼吸功被实验性降低时，肌肉交感神经活动（MSNA）的情况。
健康受试者（n=12；年龄=29±9 岁）在 40%、60%和 80%的峰值工作量下进行半卧位自行车试验。运动试验包括自主呼吸、降低呼吸功（比例辅助通气），然后进行进一步的自主呼吸（通气后）。从中指神经记录 MSNA。
在 40%的峰值工作量下，PAV 和 post-PAV 之间的呼吸功没有差异。在 60%的峰值工作量下，通气机会显著（P<0.05）降低呼吸功（103±39 对 144±47 J min）、交感神经活动（35±5 对 42±8 burst min）和（2.4±0.5 对 2.6±0.5 L min），而通气量不受影响（86±9 对 82±10 L min；P>0.05），分别为 PAV 和 post-PAV。在 80%的峰值工作量下（n=8），通气机会显著（P<0.05）降低呼吸功（235±110 对 361±150 J min）、MSNA（48±7 对 54±11 burst min）和（2.9±0.6 对 3.2±0.7 L min），但通气量不受影响（121±20 对 123±20 L min；P>0.05），分别为 PAV 和 post-PAV。MSNA 与（P<0.0001）之间存在显著的关系，由于通气机的存在，这种关系存在显著的相互作用（P<0.05）。
在运动过程中降低正常发生的呼吸功会导致 MSNA 相应减少。我们的发现提供了证据，证明运动期间呼吸肌发出的交感神经介导的血管收缩效应。
