In patients with asthma, chemical, and mechanical afferents, via central processing, are involved in increasing neural discharge to the respiratory muscle (RM) and modifying breathing pattern. In asthmatics with mild airway obstruction we assessed neural respiratory drive (NRD) during either hypercapnic rebreathing (HR) or inhalation of progressively doubling histamine concentrations (HBPT). During HR patients exhibited a normal or increased response of diaphragmatic electromyography to carbon dioxide tension ΔEMGd/ΔPCO2 compared to the average response slope of a normal control group; for a given ΔEMGd/ΔPCO2, the response of mouth occlusion pressure measured after 0.1 sec to carbon dioxide tension ΔP0.1/ΔPCO2 appeared to be significantly reduced in patients. HPBT resulted in a significant decrease in forced expiratory volume in one second (FEV1), paralleled by a significant increase in P0.1, EMGd, electromyographic activity of the parasternal intercostal muscles (EMGint) and of the sternomastoid muscles (EMGst). P0.1/EMGd ratio was directly related to FEV1 changes (% control). These data confirm previous observations and extend them in that P0.1 does not seem accurately to reflect the amount of NRD. Respiratory frequency (Rf) may increase in spontaneous bronchospasm. If Rf increase is linked to some extent to bronchial mucosa inflammation, steroids by inhibiting every stage of inflammatory response might be able to modulate such a pattern of breathing. In asthmatics with severe to moderate level of bronchial hyperresponsiveness HBPT resulted in rapid and shallow breathing. Treatment for one month with beclomethasone dipropionate (BDP) (2 mg · day-1) resulted in a marked decrease in the provocative concentration of histamine producing a 20% fall in FEV1 (PC20FEV1) and modulation of the histamine-induced change in breathing pattern. In acute severe asthma mean inspiratory flow (VT/TI) may increase with the increasing severity of airway obstruction. Nonetheless, even an unchanged VT/TI faced with increase in airflow resistance indicates increased NRD. We conclude that the analysis of the respiratory control system at central (EMG), muscular (P0.1) and ventilatory (VE, VT, Rf, VT/TI) levels seems to be a potential tool in clinical assessment of patients with asthma.
|Number of pages||5|
|Journal||European Respiratory Review|
|Publication status||Published - 1993|
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine