No abstract

Relative decay rate of inspiratory muscle electrical activity (RDRI) in patients with chronic airway obstruction increased with decreasing expiratory time (TE), being faster than in normal subjects for a given TE. Time course of decay was similar in shape to that of normal subjects, whereas persistence time of activity during expiration was about half. Hence, braking action of inspiratory muscles in patients was smaller than in normal subjects. No tonic activity of inspiratory muscles was found in patients, even when frequency was increased and hyperinflation enhanced. Hence tonic activity of inspiratory muscles found by others in asymptomatic asthmatic or normal subjects after histamine inhalation seems elicited by histamine. In normal subjects breathing under resistive load, RDRI became similar to that of patients for a given TE: tonic activity of extradiaphragmatic inspiratory muscles occurred only if frequency was voluntarily increased at least three times, an unphysiological condition with resistive load. Under discontinuous inspiratory elastic load, RDRI of patients decreased or did not change, whereas previously that of normal subjects was found to increase.

No abstract

Thirteen patients with chronic obstructive pulmonary disease (COPD) performed forced vital capacity (FVC) maneuvers either immediately after a rapid inspiration (maneuver 1) or after a slow inspiration with a 4- to 6-s end-inspiratory pause (maneuver 2). Seated in a body plethysmograph, they breathed through a pneumotachograph. Inspirations were initiated from resting end-expiratory lung volume. Abdominal muscle activity was recorded by means of surface electrodes. With maneuver 1: (1) expiratory flows were 20 to 40% larger in the volume range 10 to 95% FVC; (2) peak expiratory flow was on average 30% higher; and (3) FEV1, expressed as percent of FVC, increased by about 8%. No substantial differences in the pattern of abdominal muscle activity occurred between maneuvers. The dependence of maximal flow-volume curves on the time course of the preceding inspiration is probably related in part to the viscoelastic elements present within the respiratory system, which, stretched during rapid inspirations, increase the effective elastic recoil during the FVC maneuver 1. This cannot occur with maneuver 2, because of stress relaxation of the viscoelastic elements during the 4- to 6-s breathhold preceding the FVC maneuver. Other factors (e.g., time constant inequality) might also be involved. In any case, the results imply that the inspiratory maneuver prior to FVC must be standardized.

No abstract