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Kai K. Lee, MD; Katie Ward, PhD; Gerrard F. Rafferty, PhD; John Moxham, MD; Surinder S. Birring, MD
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: None declared.

FUNDING/SUPPORT: Dr Lee was supported by an unrestricted investigator grant from the King's College Hospital NHS Foundation Trust.

CORRESPONDENCE TO: Surinder S. Birring, MD, Division of Asthma, Allergy and Lung Biology, Denmark Hill Campus, King’s College London, Denmark Hill, London SE5 9RS, UK


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2016;149(1):286-287. doi:10.1016/j.chest.2015.09.035
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Dr Turner asks whether the stronger cough observed in patients with chronic cough compared with control subjects could be due to an increase in respiratory muscle activation in our article published in CHEST. Respiratory muscle activation can be assessed by means of electromyography (EMG) by using fine wire electrodes inserted directly into the muscle or by using surface electrodes on the skin. We measured surface EMG because it has the advantage of being noninvasive, but this technique has limitations because the signal quality and total activity level can vary among individuals because of differences in body habitus. We measured abdominal muscle EMG from the rectus abdominis muscle. Peak abdominal EMG activity (EMGabdo) was measured as the peak of the root-mean-square EMG trace (50-millisecond windows) for any given cough., Because of the limitation of comparison of raw EMG values between subjects, we expressed our cough EMGabdo data for all group analyses as a fraction of the largest EMGabdo observed for each subject’s maximum voluntary cough and following nonvolitional thoracic nerve root magnetic stimulation at 100% stimulator output. There was no statistical difference in EMGabdo during maximum voluntary cough between patients with chronic cough and control subjects (Table 1). This finding suggests that the differences in maximum voluntary cough flow and pressure were not due to an increase in muscle activation. EMGabdo during spontaneous cough was similar to that during induced (capsaicin) cough (0.07 ± 0.04 vs 0.06 ± 0.04; P = .64) but less than that observed during maximum voluntary cough (0.07 ± 0.04 vs 0.11 ± 0.11; P = .01), findings similar to those for cough esophageal and gastric pressures and flow.

Table Graphic Jump Location
Table 1 EMG During Maximum Voluntary Cough in Patients With Chronic Cough and Healthy Subjects

Data are presented as mean ± standard deviation. Maximum voluntary cough from 10 attempts. EMG = electromyography; EMGabdo = peak abdominal EMG activity; EMGabdo:Tw = abdominal electromyographic activity normalized to EMG during twitch magnetic stimulation.

Dr Turner also asks whether we assessed the relationship between physiologic measures of intensity of spontaneous cough and cough-related quality of life. We did not find a relationship between baseline Leicester Cough Questionnaire score and physiologic measures of spontaneous cough intensity. In our opinion, the lack of association is not surprising because the Leicester Cough Questionnaire is a measure of cough-specific quality of life during a 2-week period, whereas our physiologic assessment of spontaneous cough was performed during a single recording in a laboratory setting. Furthermore, quality of life is influenced by numerous other factors such as frequency of cough and its adverse effects. We did not assess subjective ratings of cough intensity in the patient’s own environment to enable a comparison with quality of life. As Dr Turner points out, our sample size of subjects who underwent study of spontaneous cough was underpowered for comparisons with quality-of-life measures, which also may be relevant. A more suitable comparison may be possible once ambulatory measures of cough intensity are developed. Combining longitudinal assessments of cough intensity with already available measures of cough frequency may allow a comprehensive objective assessment of cough and help establish their relationship with patients' perception of cough severity and effect on quality of life.

References

Lee KK, Ward K, Rafferty GF, Moxham J, Birring SS. The intensity of voluntary, induced and spontaneous cough [published online ahead of print July 2, 2015].Chest.http://dx.doi.org/10.1378/chest.15-0138.
 
Lavorini F. .Fontana G.A. .Chellini E. .Magni C. .Pistolesi M. .Widdicombe J. . Respiratory expulsive efforts evoked by maximal lung emptying. Chest. 2011;140:690-696 [PubMed]journal. [CrossRef] [PubMed]
 
Lasserson D. .Mills K. .Arunachalam R. .Polkey M. .Moxham J. .Kalra L. . Differences in motor activation of voluntary and reflex cough in humans. Thorax. 2006;61:699-705 [PubMed]journal. [CrossRef] [PubMed]
 
Fontana G.A. .Pantaleo T. .Lavorini F. .Boddi V. .Panuccio P. . A noninvasive electromyographic study on threshold and intensity of cough in humans. Eur Respir J. 1997;10:983-989 [PubMed]journal. [CrossRef] [PubMed]
 
Cox I.D. .Wallis P.J. .Apps M.C. .et al An electromyographic method of objectively assessing cough intensity and use of the method to assess effects of codeine on the dose-response curve to citric acid. Br J Clin Pharmacol. 1984;18:377-382 [PubMed]journal. [CrossRef] [PubMed]
 

Figures

Tables

Table Graphic Jump Location
Table 1 EMG During Maximum Voluntary Cough in Patients With Chronic Cough and Healthy Subjects

Data are presented as mean ± standard deviation. Maximum voluntary cough from 10 attempts. EMG = electromyography; EMGabdo = peak abdominal EMG activity; EMGabdo:Tw = abdominal electromyographic activity normalized to EMG during twitch magnetic stimulation.

References

Lee KK, Ward K, Rafferty GF, Moxham J, Birring SS. The intensity of voluntary, induced and spontaneous cough [published online ahead of print July 2, 2015].Chest.http://dx.doi.org/10.1378/chest.15-0138.
 
Lavorini F. .Fontana G.A. .Chellini E. .Magni C. .Pistolesi M. .Widdicombe J. . Respiratory expulsive efforts evoked by maximal lung emptying. Chest. 2011;140:690-696 [PubMed]journal. [CrossRef] [PubMed]
 
Lasserson D. .Mills K. .Arunachalam R. .Polkey M. .Moxham J. .Kalra L. . Differences in motor activation of voluntary and reflex cough in humans. Thorax. 2006;61:699-705 [PubMed]journal. [CrossRef] [PubMed]
 
Fontana G.A. .Pantaleo T. .Lavorini F. .Boddi V. .Panuccio P. . A noninvasive electromyographic study on threshold and intensity of cough in humans. Eur Respir J. 1997;10:983-989 [PubMed]journal. [CrossRef] [PubMed]
 
Cox I.D. .Wallis P.J. .Apps M.C. .et al An electromyographic method of objectively assessing cough intensity and use of the method to assess effects of codeine on the dose-response curve to citric acid. Br J Clin Pharmacol. 1984;18:377-382 [PubMed]journal. [CrossRef] [PubMed]
 
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