Work of breathing influences muscle sympathetic nerve activity during semi‐recumbent cycle exercise. (25th November 2018)

• Record Type: Journal Article
• Authors: Dominelli, Paolo B.; Katayama, Keisho; Vermeulen, Tyler D.; Stuckless, Troy J.R.; Brown, Courtney V.; Foster, Glen E.; Sheel, Andrew William
• Is Part Of: Acta physiologica. Volume 225:Number 4(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-11-25
• Subjects: blood flow distribution -- exercise physiology -- proportional assist ventilation -- respiratory metaboreflex; Physiology -- Periodicals; Physiology -- Research -- Periodicals; 612
• DOI: 10.1111/apha.13212
• Languages: English
• ISSNs: 1748-1708

Abstract

Abstract: 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. Aim: The aim of this study was to assess muscle sympathetic nerve activity (MSNA) when the work of breathing is experimentally lowered during dynamic exercise. Methods: 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. Results: 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 −1 ), sympathetic nerve activity (35 ± 5 vs 42 ± 8 burst min −1 ), and V ˙ O 2 (2.4 ± 0.5 vs 2.6 ± 0.5 L min −1 ) without influencing ventilation (86 ± 9 vs 82 ± 10 L min −1 ; 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 −1 ), MSNA (48 ± 7 vs 54 ± 11 burst min −1 ), and V ˙ O 2 (2.9 ± 0.6 vs 3.2 ± 0.7 L min −1 ) but not ventilation (121 ± 20 vs 123 ± 20 L min −1 ; P > 0.05), for PAV and post‐PAV respectively. There was a significant relationship between MSNA and V ˙ O 2 ( P < 0.0001) with a significant interaction due to the ventilator ( P < 0.05). Conclusion: 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.