Studies on ventilatory function in chronic neuromuscular disorders

Abstract

Ventilatory dysfunction is common in neuromuscular disorders (NMD). The present studies aimed at evaluating and developing methods for diagnosis of ventilatory function in NMD.

Methods included were diaphragmatic EMG (EMGdi), blood gas monitoring assessed at rest and during exercise and nocturnal respiratory and sleep parameters. Diaphragmatic EMG frequently used to study patterns of respiratory muscle activation, was evaluated with regard to its reliability. When quality indices for the EMGdi spectral analysis were introduced, it was concluded that signals obtained by two electrodes mounted on an esophageal catheter at levels below 15-20% of relative force and inspiratory volumes below 30% of total lung volume were subject to significant artifactual influence. However, using a multi-array electrode mounted on an esophageal catheter, an optimal electrode pair with respect to electrode-muscle distance could be identified. No significant and consistent changes in signal characteristics could be seen at different chest wall configurations and lung volumes due to improved signal quality when signals for analysis were obtained from the optimal electrode pair.

The most reproducible maneuver to assess the relative EMGdi was inspiration-to total lung capacity. The relative electrical activation of the diaphragm was five times higher in severe chronic obstructive pulmonary disease patients and post polio patients when compared to healthy subjects although there was no difference in force. In post polio patients it was shown that physical exercise provoked blood gas impairment that was not evident at rest. Blood gas abnormalities occurred despite non-fatiguing diaphragm force levels. In a group of patients with slowly progressive NMD, those patients with respiratory induced sleep abnormalities were identified by non invasive blood gas monitoring. Sleep parameters did not add any clinical useful information to nocturnal blood gas monitoring. Abnormal accessory respiratory muscle activity was seen in 70% of the patients during deep and REM sleep stages.