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

Abstract

Background: Conventional lung function parameters, such as forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) and inspiratory capacity (IC) are often used to assess the therapeutic outcomes of bronchodilators, but they lack sensitivity. A novel indicator, namely efficiency of neural respiratory drive (NRD), may objectively evaluate the physiological changes in patients with chronic obstructive pulmonary disease (COPD). We investigated whether this indicator could be used to more accurately assess the responsiveness to inhaled bronchodilators.

Methods: Thirty-six subjects with moderate-to-severe COPD were randomized into group A (n=18) and group B (n=18). Participants in group A inhaled 400 µg placebo, 400 µg salbutamol and 80 µg ipratropium in sequence whereas those in group B had the salbutamol and ipratropium reversed. At different time points after administration of placebo or bronchodilators, evaluated indices included FEV1, FVC, IC, root mean square (RMS) of diaphragm electromyogram (EMGdi), and efficiency of NRD [herein defined as the ratio of minute ventilation (VE) to RMS, or VE/RMS].

Results: FEV1, FVC, IC, RMS, and VE/RMS significantly improved after inhaled bronchodilators and VE/RMS had the largest improvement among five indices. The detection efficiency of VE/RMS was greater than FEV1, FVC, IC (all P<0.05), but not different from RMS. The accuracy and sensitivity of VE/RMS were significantly higher than FEV1, FVC, IC, and RMS (all P<0.05).

Conclusions: Efficiency of NRD may be a sensitive tool to evaluate the efficacy of inhaled bronchodilators in COPD.

Keywords: Chronic obstructive pulmonary disease (COPD); bronchodilator; neural respiratory drive (NRD); respiratory function tests.

Conflict of interest statement

Conflicts of Interest: The authors have no conflicts of interest to declare.

Figures

Figure 1

Subjects inhaled placebo, salbutamol and ipratropium in sequence and related indices were measured at different time points. T0 was baseline, TP was identified as 30 min after inhalation of placebo, T1 was identified as 15 min after salbutamol or 30 min after ipratropium alone, and T2 was identified as after inhalation of both drugs.

Figure 2

The improvement of the five indices after inhaled bronchodilators is shown. *, in comparison with FEV1, IC, FVC, P<0.05; #, in comparison with RMS, P<0.05. FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; IC, inspiratory capacity; RMS, root mean square; VE, minute ventilation.