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Neural respiratory drive and breathlessness during incremental cycle and treadmill exercise in chronic obstructive pulmonary disease
Poster Abstracts
Neural respiratory drive and breathlessness during incremental cycle and treadmill exercise in chronic obstructive pulmonary disease Caroline Jolley, Yuan-Ming Luo, Joerg Steier, Gerrard Rafferty, Michael Polkey, John Moxham
Abstract Background Breathlessness is an important cause of exercise limitation and reduced quality of life for patients with chronic obstructive pulmonary disease (COPD). One of the challenges of breathlessness management in COPD is the lack of physiological markers that reliably correlate with patients' symptoms. The aim of this study was to test the hypothesis that neural respiratory drive (NRD), measured with diaphragm electromyogram (EMGdi) activity, is closely related to breathlessness in COPD. We also investigated whether neuroventilatory uncoupling, which is the dissociation of ventilation from NRD as a consequence of abnormal pulmonary mechanics, contributes to breathlessness intensity over an awareness of levels of NRD alone. Methods EMGdi and ventilation were measured continuously during exhaustive incremental cycle and treadmill exercise in 12 patients with COPD (mean FEV1 38·7% predicted [SD 14·5]). EMGdi was expressed as a percentage of maximum (EMGdi%max), and relative to tidal volume expressed as a percentage of predicted vital capacity (EMGdi%max/VT%VCpred) to measure neuroventilatory uncoupling. Breathlessness (modified Borg scale) was recorded at baseline, at the end of each minute of exercise, and at completion of exercise. Linear regression analysis was used to determine the associations between breathlessness, EMGdi%max, neuroventilatory uncoupling, and ventilation. Findings EMGdi%max was closely related to breathlessness in both cycle (r=0·98, p=0·0001) and treadmill exercise (r=0·94, p=0·005), this association being at least as strong as that between neuroventilatory uncoupling and breathlessness (cycle r=0·94, p=0·005; treadmill r=0·91, p=0·01). The association between breathlessness and ventilation was poor when expansion of tidal volume became restricted, whereas the association between EMGdi%max and breathlessness remained close. Interpretation EMGdi%max is closely related to the intensity of exertional breathlessness in COPD. These data suggest that breathlessness in COPD can be largely explained by an awareness of levels of NRD, rather than the association between NRD and achieved ventilation. EMGdi%max could provide a useful physiological biomarker for breathlessness, with advantages over mechanical and ventilatory indices in COPD and the many other diseases in which neuroventilatory uncoupling occurs. Funding UK Medical Research Council, British Council. Contributors CJ, Y-ML, JS, GR, MP, and JM conceptualised and designed the study. CJ, JS, and Y-ML did the study. CJ analysed the data. All authors contributed to the interpretation of the data and approved the final abstract.
Published Online February 26, 2014 Poster 10 Division of Asthma, Allergy and Lung Biology, King's College London, King's Health Partners, London, UK (C Jolley PhD, J Steier PhD, G Rafferty PhD, Prof J Moxham MD); State Key Laboratory of Respiratory Disease, Guangzhou Medical College, Guangzhou, China (Prof Y-M Luo PhD); Lane Fox Respiratory Unit, Sleep Disorders Centre, Guy's and St Thomas' NHS Foundation Trust, London, UK (J Steier); NIHR Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust, London, UK (Prof M Polkey PhD); National Heart and Lung Institute, Imperial College London, London, UK (Prof M Polkey); and Royal Brompton Hospital, London, UK (Prof M Polkey) Correspondence to: Dr Caroline Jolley, Division of Asthma, Allergy and Lung Biology, King's College London (King's College Hospital Denmark Hill Campus), Bessemer Road, London SE5 9RS, UK [email protected]
Conflicts of interest We declare that we have no conflicts of interest.
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Neural respiratory drive and breathlessness during incremental cycle and treadmill exercise in chronic obstructive pulmonary disease Caroline Jolley, Yuan-Ming Luo, Joerg Steier, Gerrard Rafferty, Michael Polkey, John Moxham
Abstract Background Breathlessness is an important cause of exercise limitation and reduced quality of life for patients with chronic obstructive pulmonary disease (COPD). One of the challenges of breathlessness management in COPD is the lack of physiological markers that reliably correlate with patients' symptoms. The aim of this study was to test the hypothesis that neural respiratory drive (NRD), measured with diaphragm electromyogram (EMGdi) activity, is closely related to breathlessness in COPD. We also investigated whether neuroventilatory uncoupling, which is the dissociation of ventilation from NRD as a consequence of abnormal pulmonary mechanics, contributes to breathlessness intensity over an awareness of levels of NRD alone. Methods EMGdi and ventilation were measured continuously during exhaustive incremental cycle and treadmill exercise in 12 patients with COPD (mean FEV1 38·7% predicted [SD 14·5]). EMGdi was expressed as a percentage of maximum (EMGdi%max), and relative to tidal volume expressed as a percentage of predicted vital capacity (EMGdi%max/VT%VCpred) to measure neuroventilatory uncoupling. Breathlessness (modified Borg scale) was recorded at baseline, at the end of each minute of exercise, and at completion of exercise. Linear regression analysis was used to determine the associations between breathlessness, EMGdi%max, neuroventilatory uncoupling, and ventilation. Findings EMGdi%max was closely related to breathlessness in both cycle (r=0·98, p=0·0001) and treadmill exercise (r=0·94, p=0·005), this association being at least as strong as that between neuroventilatory uncoupling and breathlessness (cycle r=0·94, p=0·005; treadmill r=0·91, p=0·01). The association between breathlessness and ventilation was poor when expansion of tidal volume became restricted, whereas the association between EMGdi%max and breathlessness remained close. Interpretation EMGdi%max is closely related to the intensity of exertional breathlessness in COPD. These data suggest that breathlessness in COPD can be largely explained by an awareness of levels of NRD, rather than the association between NRD and achieved ventilation. EMGdi%max could provide a useful physiological biomarker for breathlessness, with advantages over mechanical and ventilatory indices in COPD and the many other diseases in which neuroventilatory uncoupling occurs. Funding UK Medical Research Council, British Council. Contributors CJ, Y-ML, JS, GR, MP, and JM conceptualised and designed the study. CJ, JS, and Y-ML did the study. CJ analysed the data. All authors contributed to the interpretation of the data and approved the final abstract.
Published Online February 26, 2014 Poster 10 Division of Asthma, Allergy and Lung Biology, King's College London, King's Health Partners, London, UK (C Jolley PhD, J Steier PhD, G Rafferty PhD, Prof J Moxham MD); State Key Laboratory of Respiratory Disease, Guangzhou Medical College, Guangzhou, China (Prof Y-M Luo PhD); Lane Fox Respiratory Unit, Sleep Disorders Centre, Guy's and St Thomas' NHS Foundation Trust, London, UK (J Steier); NIHR Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust, London, UK (Prof M Polkey PhD); National Heart and Lung Institute, Imperial College London, London, UK (Prof M Polkey); and Royal Brompton Hospital, London, UK (Prof M Polkey) Correspondence to: Dr Caroline Jolley, Division of Asthma, Allergy and Lung Biology, King's College London (King's College Hospital Denmark Hill Campus), Bessemer Road, London SE5 9RS, UK [email protected]
Conflicts of interest We declare that we have no conflicts of interest.
www.thelancet.com
63