Neural respiratory drive and breathlessness in COPD

Abstract

The aim of this study was to test the hypothesis that neural respiratory drive, measured using diaphragm electromyogram (EMGdi) activity expressed as a percentage of maximum (EMGdi%max), is closely related to breathlessness in chronic obstructive pulmonary disease. We also investigated whether neuroventilatory uncoupling contributes significantly to breathlessness intensity over an awareness of levels of neural respiratory drive alone.EMGdi and ventilation were measured continuously during incremental cycle and treadmill exercise in 12 chronic obstructive pulmonary disease patients (forced expiratory volume in 1 s±SD was 38.7±14.5 % pred). EMGdi was expressed both as EMGdi%max and relative to tidal volume expressed as a percentage of predicted vital capacity to quantify neuroventilatory uncoupling.EMGdi%max was closely related to Borg breathlessness in both cycle (r=0.98, p=0.0001) and treadmill exercise (r=0.94, p=0.005), this relationship being similar to that between neuroventilatory uncoupling and breathlessness (cycling r=0.94, p=0.005; treadmill r=0.91, p=0.01). The relationship between breathlessness and ventilation was poor when expansion of tidal volume became limited.In chronic obstructive pulmonary disease the intensity of exertional breathlessness is closely related to EMGdi%max. These data suggest that breathlessness in chronic obstructive pulmonary disease can be largely explained by an awareness of levels of neural respiratory drive, rather than the degree of neuroventilatory uncoupling. EMGdi%max could provide a useful physiological biomarker for breathlessness in chronic obstructive pulmonary disease. @ERSpublications Exertional breathlessness in patients with severe COPD is closely related to levels of neural respiratory drive

The effect of metabolic alkalosis on the ventilatory response in healthy subjects

“…Our study adds measurement of EAdi, reflecting motor output of the central nervous system to the diaphragm muscle (American Thoracic Society/European Respiratory Society, 2002), which causes contraction of the diaphragm. EAdi is thereby a more specific and sensitive reflective of neural respiratory drive than V E , which could also be influenced by mechanical properties of the respiratory system (Jolley et al, 2015). Herrera and Kazemi studied the Fig.…”

“…First, the respiratory drive, represented by the electrical activity of the diaphragm (American Thoracic Society/European Respiratory Society, 2002; Jolley et al, 2015), is decreased with increasing arterial bicarbonate levels, resulting in a decreased V E . This is different from the findings of Oren in 1991; that study showed no difference in minute ventilation related to P et CO 2 between pre and post sodium bicarbonate administration (arterial bicarbonate from 25.5 ± 0.6 to 30.6 ± 1.7 mEq/l in 3 days) (Oren et al, 1991).…”

“…Because of the limited number of subjects and several methodological issues in that study, uncertainty remains concerning the effect of bicarbonate retention on the ventilatory response (Oren et al, 1991). Electrical activity of the diaphragm (EAdi) has been used to quantify the respiratory drive (American Thoracic Society/European Respiratory Society, 2002;Jolley et al, 2015) and is therefore a useful tool to study the effect of metabolic alkalosis on respiratory drive to the diaphragm.…”

Efficiency of neural respiratory drive for the assessment of bronchodilator responsiveness in patients with chronic obstructive pulmonary disease: an exploratory study

“…In the present study, EMGdi signals were recorded using a five-pair oesophageal electrode catheter, which has been acknowledged as an ideal method to quantify NRD since it is not easily disturbed by other respiratory muscles and not affected by electrode movement and lung volume change (8)(9)(10)(11)(12)(13). However, oesophageal electrode placement is an invasive test and may hinder its clinical application.…”

“…Recent studies have demonstrated an increase in neural respiratory drive (NRD) in COPD patients (7)(8)(9)(10), which is principally due to adverse pulmonary mechanics requiring an increased drive to maintain ventilation. However, the actual ventilation tends to descend.…”