Respiratory muscle function in patients with cystic fibrosis

Abstract

Respiratory muscle function in patients with cystic fibrosis (CF) can be assessed by measurement of maximal inspiratory pressure (Pimax ), maximal expiratory pressure (Pemax ), and pressure-time index of the respiratory muscles (PTImus ). We investigated the differences in maximal respiratory pressures and PTImus between CF patients with no gross hyperinflation and healthy controls and described the effects of pulmonary function and nutrition impairment on respiratory muscle function in this group of CF patients. Forced expiratory volume in 1 sec (FEV1 ), forced vital capacity (FVC) and maximal expiratory flow between 25% and 75% of VC (MEF25-75 ), body mass index (BMI), upper arm muscle area (UAMA), Pimax , Pemax , and PTImus were assessed in 140 CF patients and in a control group of 140 healthy subjects matched for age and gender. Median Pimax and Pemax were significantly lower in CF patients compared to the controls [Pimax = 74 (57-94) in CF vs. 84 (66-102) in controls, P = 0.009], [Pemax = 71 (50-95) in CF vs. 84 (66-102) in controls, P < 0.001]. Median PTImus in CF patients compared to controls was significantly increased [PTImus = 0.110 (0.076-0.160) in CF vs. 0.094 (0.070-0.137) in controls, P = 0.049] and it was significantly higher in CF patients with impaired pulmonary function. In CF patients, PTImus was significantly negatively related to upper arm muscle area (r = 0.184, P = 0.031). These findings suggest that CF patients with no severe lung disease compared to healthy subjects exhibit impaired respiratory muscle function, while CF patients with impaired pulmonary function and nutrition indices exhibit higher PTImus values.

Time constant of inspiratory muscle relaxation in cystic fibrosis

“…Differences between the two study groups or between younger (7-11-y old) and older participants (12-34-y old) were tested for significance using the Mann-Witney rank sum test or χ 2 test, as appropriate. Since younger children have significantly different respiratory muscle function than older children and young adults (9), a general linear model was applied to evaluate the possible effect of: (i) health status (CF diagnosis vs. non-CF); (ii) age group (7-11 y of age vs. 12-34 y of age); and (iii) the interaction of health status with age, on τ. Kendall-tau rank correlation coefficient was used to examine the relationship of τ with BMI z-score, UAMA, RR, and TV in both patients with CF and control participants. For CF patients only, the correlations of τ with FVC z-score, FEV 1 z-score, and FEF z-score were also assessed.…”

“…surface diaphragmatic electromyography can be affected appreciably by electrical "noise" from neighboring or underlying muscle groups or by levels of subcutaneous fat. Moreover, the noninvasive tension-time index of the respiratory muscles has been explored in CF patients in a number of studies and high values of TT mus have been reported, also indicating an increased risk of inspiratory muscle fatigue and respiratory failure (2,3,9). Unfortunately, measurement of the tensiontime index requires the utilization of pneumotachograph and differential-pressure transducers, i.e., a technical setup which is only found in specialized research laboratories.…”

“…Determinants of respiratory muscle compromise in CF have been reported in detail (1)(2)(3)9,19,20). Airway obstruction impacts on inspiratory muscle function by increasing the load against which the respiratory muscles are forced to operate (1) and hyperinflation places the respiratory muscles in mechanical disadvantage (2).…”

“…Airway obstruction impacts on inspiratory muscle function by increasing the load against which the respiratory muscles are forced to operate (1) and hyperinflation places the respiratory muscles in mechanical disadvantage (2). Moreover, malnutrition affects the diaphragmatic pressure-generating capacity (20), given that decreased somatic muscle mass indices have been consistently associated with decreased maximal respiratory pressures in CF patients (3,9). Furthermore, chronic respiratory infection (5) and nutritional deficiencies (19) might also be implicated in the pathophysiology of respiratory muscle dysfunction in CF.…”

“…Inspiratory muscle impairment in patients with CF has been studied in the literature using maximal respiratory pressures (8), diaphragmatic electromyography (10), the tension-time index of the respiratory muscles (2,3,9), and endurance testing by breathing against increased external loads (11,21,22). Although maximal respiratory pressures describe the pressure-generating capacity of the respiratory muscles at a given point of time, they would not be appropriate for the assessment or prediction of respiratory muscle function over time (14).…”