Maximum rate of pressure development and maximal relaxation rate of respiratory muscles in patients with cystic fibrosis.

BACKGROUND Respiratory muscle function in patients with cystic fibrosis (CF) has been studied by measurement of maximal inspiratory pressure (P(Imax)), maximal expiratory pressure (P(Emax)), and the pressure-time index of the respiratory muscles (PTI(mus)). The maximum rate of pressure development (MRPD) during P(Imax) (MRPD-P(Imax)), MRPD during P(Emax) (MRPD-P(Emax)), maximal relaxation rate (MRR) during P(Imax) (MRR-P(imax)), and MRR during P(Emax) (MRR-P(Emax)) have not been studied in CF. Our aim was to study MRPD and MRR and investigate their possible application as accessory indices of respiratory muscle function in patients with CF. METHODS FEVY, FVC, and maximal expiratory flow between 25% and 75% of vital capacity, body mass index (BMI), upper arm muscle area, P(imax), P(Emax), PTI(mus), MRPD-P(Imax), MRPD-P(Emax), MRR-P(imax), and MRR-P(Emax) were assessed in 123 CF patients and in a control group of 123 healthy subjects matched for age and sex. RESULTS MRR-P(Emax) was significantly increased and MRPD-P(Emax) was significantly decreased in the CF patients, compared to the healthy controls. In the CF patients MRR-P(Imax) was significantly related to PTI(mus) (P = .02), FEV1 (P = .03), FVC (P = .001), BMI (P < .001), and upper arm muscle area (P < .001). In the CF patients, MRPD-P(Imax) and MRPD- P(Emax) were significantly related to upper arm muscle area (P < .001), BMI (P < .001 and P = .01, respectively), P(Imax) (P < .001), and P(Emax) (P < .001). CONCLUSIONS The CF patients exhibited increased MRR and decreased MRPD during maximal respiratory effort, compared to controls. The differences in MRR-P(imax) and MRPD-P(Imax) between the controls and the complete group of CF patients were not significant. MRPD and MRR were significantly related to nutritional and pulmonary function impairment in CF patients. MRPD strongly correlated to maximal respiratory muscle pressures, and MRR strongly correlated to PTI(mus) in patients with CF. These findings suggest that CF patients are at increased risk of respiratory muscle fatigue. Regular determination of MRPD and MRR may be clinically useful in CF patients and help to initiate inspiratory muscle training and noninvasive ventilation.