Chest wall restriction causes diaphragm fatigue in low intensity exercise
Creators: name: Tomczak, Simone E.
Publisher: name: University of British Columbia
Year: 2009

description: Artificially induced chest wall restriction (CWR) has been used in numerous studies as a model of restrictive lung disease, as CWR has been shown to mimic the breathing mechanics of such conditions. Fast, shallow breathing, reduced resting and operational lung volumes and a greater work of breathing than unrestricted controls characterizes CWR. Diaphragm fatigue has been shown to occur in healthy humans exercising at very high intensities until volitional fatigue. A high work of breathing is associated with diaphragm fatigue, however, to date there have been no investigations examining the relationship between CWR and diaphragm fatigue. Accordingly the purpose of this study was to examine the relationship between diaphragm fatigue in CWR subjects exercising at low intensities. It was hypothesized that exercise at 45% of VO₂MAX with chest wall restriction would result in a higher work of breathing and significant diaphragm fatigue compared to unrestricted exercise. The work of breathing was determined by averaging the area under the transpulmonary pressure-volume curve for 8-10 breaths during exercise. Diaphragm fatigue was assessed by performing a series of non potentiated and potentiated twitches, before exercise, 10 and 30 minutes after control exercise and at 10, 30 and 60 minutes after CWR exercise. The average amplitude of the transdiaphragmatic pressure (Pdi) from the different groups of twitches was compared using a repeated measures one-way ANOVA. Post-hoc analysis was done using multiple t-tests with a Bonferonni correction. A total of 7 men gave informed consent and participated in this study. All subjects showed a significantly higher work of breathing in the CWR exercise compared to the control exercise at the 8th and 10th minute (At the 8th minute CWR = 720 ± 159cmH₂O/min vs. control = 536 ± 151cmH₂O/min and at the 10th minute CWR = 796 ± 216cmH₂O/min vs. control = 566 ± 136cmH₂O/min, p &lt; 0.05). Five of the 7 subjects showed a greater than 15% drop in twitch Pdi 10 minutes post exercise, indicating diaphragm fatigue. The twitch Pdi post CWR exercise was significantly less than baseline for the potentiated twitches (36.5 ± 15.3 cmH₂O vs. 47.4 ± 16.6 cmH₂O, p &lt; 0.01) and for the non potentiated twitches (24.6 ± 8.5 cmH₂O vs. 30.7 ± 8.6 cmH₂O, p &lt; 0.05). Furthermore, the percent drop in twitch Pdi after CWR exercise was correlated to the elastic work of breathing on inspiration (R² = 0.73992, p &lt; 0.05). The resting and operational lung volumes were significantly reduced in all subjects in the CWR condition compared to the control condition and all subjects showed a tachypneic breathing pattern throughout the CWR exercise. Expiratory flow limitation towards the end of the CWR exercise was present in all subjects and 3 of the 7 subjects showed dynamic hyperinflation. This data suggests that CWR reduces lung volumes and alters the breathing mechanics, to the degree of causing diaphragm fatigue after low intensity exercise. The diaphragm fatigue is likely attributed to the high work of breathing and reduced lung volumes.