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Electromyographic activity of respiratory muscles: The possibility of considering diaphragmatic EMG as an isolated signal
Respiratory Physiology & Neurobiology 158 (2007) 3–4
Reply to the Letter to the Editor
Electromyographic activity of respiratory muscles: The possibility of considering diaphragmatic EMG as an isolated signal We would like to thank our colleagues from Amsterdam, G.J. Hutter, L.A. van Eykern, J.M. Crobben and W.M.C. van Aalderen, for their insightful comments on our recent publication (Nobre et al., 2007). We are grateful to encounter such keen interest in our study and for their additional evidence concerning the electromyographic activity of respiratory muscles. Respiratory muscle electromyography (EMG) is a reliable method of assessing the ventilatory muscle function (ATS/ERS, 2002). Although superficial EMG has proven an important tool in assessing ventilatory patterns and the muscles involved in this process, this method remains controversial. The electromyographic signal can easily be contaminated by non-physiological signals, the electrical activity of the heart and adjacent muscles signals in a phenomenon known as cross-talk (Sinderby et al., 1996). Dr. Hutter et al. correctly emphasized this phenomenon. The scalene muscle and diaphragm muscles are more affected by the cross-talk phenomenon. Due to its anatomic position, EMG measurements of the diaphragm muscle may be contaminated by the intercostal and abdominal muscles, thereby hampering the evaluation of isolated diaphragm action. However, some studies have demonstrated a possible distinction between muscles. This broadens future expectations regarding surface EMG application (Maarsingh et al., 2006). Our hypothesis regarding interference from intercostal muscle action was based on previous published studies, which demonstrated that inspiratory intercostal action is located in the dorsal and superior regions of the costal ribcage, whereas expiratory action is placed in the ventral and inferior regions, which are common to the placement of electrodes used to obtain diaphragm action. However, this action is not coincident to the inspiratory phasic action, suggesting minimal interference from the intercostal muscles (De Troyer et al., 2005). Tonic activation of abdominal action throughout the respiratory cycle should be attenuated by the postures adopted, preferably when using non-orthostatic positions. Another important factor in reducing interference from abdominal muscles during diaphragm activation stems from the normalization process of the electromyographic signal in relation to the basal
DOI of original article:10.1016/j.resp.2007.03.014. 1569-9048/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2007.03.017
signal, which analyses only relative increases in the pre-existing signals (basal activity, external noise, ECG) (Burden et al., 2003; Sinderby et al., 1998). Expiratory phasic activity from abdominal muscles, such as the intercostal muscles described above, seems to interfere somewhat in EMG reading, because muscle actions occur in different phases of the respiratory cycle. In other words, the action of intercostal and abdominal muscles adjacent to the electrodes is predominantly expiratory. As the diaphragm is an inspiratory muscle, this interference should be minimal. We therefore agree with our colleagues concerning the possibility of considering diaphragmatic EMG as an isolated signal. Recently, we had an opportunity to evaluate inspiratory muscular activation during application of load in both patients with chronic obstructive pulmonary disease and healthy elderly individuals (Dornelas de Andrade et al., 2005). We evaluated the participation of the diaphragm and the sternocleidomastoid muscle in overcoming a load using superficial EMG. It was important to show the EMG readings of each muscle separately, as shown in Fig. 1 on the sternocleidomastoid muscle EMG and Fig. 2 on diaphragmatic EMG. Despite the justifications presented above, which facilitate analyses of the diaphragm as an isolated muscle, we would like to clarify that the aim of the study in question was to analyze the ventilatory pattern adopted in reply to the loads by comparing the muscle activity of the superior costal ribcage to the
Fig. 1. EMG recordings of sternocleidomastoid muscle in COPD patient during: (a) pre-loading and (b) loading periods (load 30% maximal inspiratory pressure) (Dornelas de Andrade et al., 2005).
4
Reply to the Letter to the Editor / Respiratory Physiology & Neurobiology 158 (2007) 3–4
Fig. 2. EMG recordings of diaphragm muscle in healthy elderly during: (a) pre-loading and (b) loading periods (load 30% maximal inspiratory pressure) (Dornelas de Andrade et al., 2005).
De Troyer, A., Kirkwood, P.A., Wilson, T.A., 2005. Respiratory action of the intercostal muscles. Physiol. Rev. 85, 717–756. Dornelas de Andrade, A., Silva, T.N., Vasconcelos, H., Marcelino, M., Rodrigues-Machado, M.G., Galindo Filho, V.C., Moraes, N.H., Marinho, P.E.M., Amorim, C.F., 2005. Inspiratory muscular activation during threshold therapy in elderly healthy and patients with COPD. J. Electromyogr. Kinesiol. 15 (6), 631–639. Maarsingh, E.J., Oud, M., van Eykern, L.A., Hoekstra, M.O., van Aalderen, W.M., 2006. Electromyographic monitoring of respiratory muscle activity in dyspneic infants and toddlers. Respir. Physiol. Neurobiol. 150, 191–199. Nobre, M.E., Lopes, F., Cordeiro, L., Marinho, P.E., Silva, T.N., Amorim, C., Cahalin, L.P., Dornelas deAndrade, A., 2007. Inspiratory muscle endurance testing: pulmonary ventilation and electromyographic analysis. Respir. Physiol. Neurobiol. 155 (1), 41–48. Sinderby, C., Beck, J., Spahija, J., Weinberg, J., Grassino, A., 1998. Voluntary activation of the human diaphragm in health and disease. J. Appl. Physiol. 85 (6), 2146–2158. Sinderby, C., Friberg, S., Comtois, N., Grassino, A., 1996. Chest wall muscle cross talk in canine costal diaphragm electromyogram. J. Appl. Physiol. 81 (5), 2312–2327.
Arm`ele Dornelas de Andrade ∗ Thayse Santos Silva Elizabeth Nobre Department of Physical Therapy, Federal University of Pernambuco, Recife, Pernambuco, Brazil
inferior activity through superficial EMG correlated with pulmonary scintilography. We believe that as our study was with healthy volunteers, for whom the diaphragm is the most important inspiratory muscle, we can also consider muscle activity of the lower ribcage as diaphragm activity. References American Thoracic Society/European Respiratory Society (ATS/ERS), 2002. Statement on respiratory muscle testing. Am. J. Respir. Crit. Care Med. 166 (4), 518–624. Burden, A.M., Trew, M., Baltzopoulos, V., 2003. Normalisation of gait EMGs: a re-examination. J. Electromyogr. Kinesiol. 13, 519–532.
∗ Corresponding
author at: Department of Physical Therapy, Cidade Universit´aria, 50670-901 Recife, Pernambuco, Brazil. Tel.: +55 81 21268496; fax: +55 81 21268496. E-mail address: [email protected] (A. Dornelas de Andrade)
Reply to the Letter to the Editor
Electromyographic activity of respiratory muscles: The possibility of considering diaphragmatic EMG as an isolated signal We would like to thank our colleagues from Amsterdam, G.J. Hutter, L.A. van Eykern, J.M. Crobben and W.M.C. van Aalderen, for their insightful comments on our recent publication (Nobre et al., 2007). We are grateful to encounter such keen interest in our study and for their additional evidence concerning the electromyographic activity of respiratory muscles. Respiratory muscle electromyography (EMG) is a reliable method of assessing the ventilatory muscle function (ATS/ERS, 2002). Although superficial EMG has proven an important tool in assessing ventilatory patterns and the muscles involved in this process, this method remains controversial. The electromyographic signal can easily be contaminated by non-physiological signals, the electrical activity of the heart and adjacent muscles signals in a phenomenon known as cross-talk (Sinderby et al., 1996). Dr. Hutter et al. correctly emphasized this phenomenon. The scalene muscle and diaphragm muscles are more affected by the cross-talk phenomenon. Due to its anatomic position, EMG measurements of the diaphragm muscle may be contaminated by the intercostal and abdominal muscles, thereby hampering the evaluation of isolated diaphragm action. However, some studies have demonstrated a possible distinction between muscles. This broadens future expectations regarding surface EMG application (Maarsingh et al., 2006). Our hypothesis regarding interference from intercostal muscle action was based on previous published studies, which demonstrated that inspiratory intercostal action is located in the dorsal and superior regions of the costal ribcage, whereas expiratory action is placed in the ventral and inferior regions, which are common to the placement of electrodes used to obtain diaphragm action. However, this action is not coincident to the inspiratory phasic action, suggesting minimal interference from the intercostal muscles (De Troyer et al., 2005). Tonic activation of abdominal action throughout the respiratory cycle should be attenuated by the postures adopted, preferably when using non-orthostatic positions. Another important factor in reducing interference from abdominal muscles during diaphragm activation stems from the normalization process of the electromyographic signal in relation to the basal
DOI of original article:10.1016/j.resp.2007.03.014. 1569-9048/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2007.03.017
signal, which analyses only relative increases in the pre-existing signals (basal activity, external noise, ECG) (Burden et al., 2003; Sinderby et al., 1998). Expiratory phasic activity from abdominal muscles, such as the intercostal muscles described above, seems to interfere somewhat in EMG reading, because muscle actions occur in different phases of the respiratory cycle. In other words, the action of intercostal and abdominal muscles adjacent to the electrodes is predominantly expiratory. As the diaphragm is an inspiratory muscle, this interference should be minimal. We therefore agree with our colleagues concerning the possibility of considering diaphragmatic EMG as an isolated signal. Recently, we had an opportunity to evaluate inspiratory muscular activation during application of load in both patients with chronic obstructive pulmonary disease and healthy elderly individuals (Dornelas de Andrade et al., 2005). We evaluated the participation of the diaphragm and the sternocleidomastoid muscle in overcoming a load using superficial EMG. It was important to show the EMG readings of each muscle separately, as shown in Fig. 1 on the sternocleidomastoid muscle EMG and Fig. 2 on diaphragmatic EMG. Despite the justifications presented above, which facilitate analyses of the diaphragm as an isolated muscle, we would like to clarify that the aim of the study in question was to analyze the ventilatory pattern adopted in reply to the loads by comparing the muscle activity of the superior costal ribcage to the
Fig. 1. EMG recordings of sternocleidomastoid muscle in COPD patient during: (a) pre-loading and (b) loading periods (load 30% maximal inspiratory pressure) (Dornelas de Andrade et al., 2005).
4
Reply to the Letter to the Editor / Respiratory Physiology & Neurobiology 158 (2007) 3–4
Fig. 2. EMG recordings of diaphragm muscle in healthy elderly during: (a) pre-loading and (b) loading periods (load 30% maximal inspiratory pressure) (Dornelas de Andrade et al., 2005).
De Troyer, A., Kirkwood, P.A., Wilson, T.A., 2005. Respiratory action of the intercostal muscles. Physiol. Rev. 85, 717–756. Dornelas de Andrade, A., Silva, T.N., Vasconcelos, H., Marcelino, M., Rodrigues-Machado, M.G., Galindo Filho, V.C., Moraes, N.H., Marinho, P.E.M., Amorim, C.F., 2005. Inspiratory muscular activation during threshold therapy in elderly healthy and patients with COPD. J. Electromyogr. Kinesiol. 15 (6), 631–639. Maarsingh, E.J., Oud, M., van Eykern, L.A., Hoekstra, M.O., van Aalderen, W.M., 2006. Electromyographic monitoring of respiratory muscle activity in dyspneic infants and toddlers. Respir. Physiol. Neurobiol. 150, 191–199. Nobre, M.E., Lopes, F., Cordeiro, L., Marinho, P.E., Silva, T.N., Amorim, C., Cahalin, L.P., Dornelas deAndrade, A., 2007. Inspiratory muscle endurance testing: pulmonary ventilation and electromyographic analysis. Respir. Physiol. Neurobiol. 155 (1), 41–48. Sinderby, C., Beck, J., Spahija, J., Weinberg, J., Grassino, A., 1998. Voluntary activation of the human diaphragm in health and disease. J. Appl. Physiol. 85 (6), 2146–2158. Sinderby, C., Friberg, S., Comtois, N., Grassino, A., 1996. Chest wall muscle cross talk in canine costal diaphragm electromyogram. J. Appl. Physiol. 81 (5), 2312–2327.
Arm`ele Dornelas de Andrade ∗ Thayse Santos Silva Elizabeth Nobre Department of Physical Therapy, Federal University of Pernambuco, Recife, Pernambuco, Brazil
inferior activity through superficial EMG correlated with pulmonary scintilography. We believe that as our study was with healthy volunteers, for whom the diaphragm is the most important inspiratory muscle, we can also consider muscle activity of the lower ribcage as diaphragm activity. References American Thoracic Society/European Respiratory Society (ATS/ERS), 2002. Statement on respiratory muscle testing. Am. J. Respir. Crit. Care Med. 166 (4), 518–624. Burden, A.M., Trew, M., Baltzopoulos, V., 2003. Normalisation of gait EMGs: a re-examination. J. Electromyogr. Kinesiol. 13, 519–532.
∗ Corresponding
author at: Department of Physical Therapy, Cidade Universit´aria, 50670-901 Recife, Pernambuco, Brazil. Tel.: +55 81 21268496; fax: +55 81 21268496. E-mail address: [email protected] (A. Dornelas de Andrade)