Acute effects of combined exercise and oscillatory positive expiratory pressure therapy on sputum properties and lung diffusing capacity in cystic fibrosis: a randomized, controlled, crossover trial

Abstract

Background: Regular airway clearance by chest physiotherapy and/or exercise is critical to lung health in cystic fibrosis (CF). Combination of cycling exercise and chest physiotherapy using the Flutter® device on sputum properties has not yet been investigated.

Methods: This prospective, randomized crossover study compared a single bout of continuous cycling exercise at moderate intensity (experiment A, control condition) vs a combination of interval cycling exercise plus Flutter® (experiment B). Sputum properties (viscoelasticity, yield stress, solids content, spinnability, and ease of sputum expectoration), pulmonary diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) were assessed at rest, directly and 45 min post-exercise (recovery) at 2 consecutive visits. Primary outcome was change in sputum viscoelasticity (G', storage modulus; G", loss modulus) over a broad frequency range (0.1-100 rad.s^{- 1}).

Results: 15 adults with CF (FEV₁range 24-94% predicted) completed all experiments. No consistent differences between experiments were observed for G' and G" and other sputum properties, except for ease of sputum expectoration during recovery favoring experiment A. DLNO, DLCO, alveolar volume (V_A) and pulmonary capillary blood volume (V_cap) increased during experiment A, while DLCO and V_cap increased during experiment B (all P < 0.05). We found no differences in absolute changes in pulmonary diffusing capacity and its components between experiments, except a higher V_A immediately post-exercise favoring experiment A (P = 0.032).

Conclusions: The additional use of the Flutter® to moderate intensity interval cycling exercise has no measurable effect on the viscoelastic properties of sputum compared to moderate intensity continuous cycling alone. Elevations in diffusing capacity represent an acute exercise-induced effect not sustained post-exercise.

Trial registration: ClinicalTrials.gov; No.: NCT02750722 ; URL: clinical.trials.gov; Registration date: April 25th, 2016.

Keywords: Airway clearance; Diffusing capacity for nitric oxide; Exercise; Lung disease; Mucus; Sputum viscoelasticity.

Fig. 1

Experimental study design. f_R, respiratory frequency; HR, heart rate; SpO₂, oxygen saturation; V’CO₂, carbon dioxide production; V’E, minute ventilation; V’O₂, oxygen consumption; VT, tidal volume. The grey shaded area represents the periods when the participants breathed through the mouthpiece for metabolic cart measurements

Fig. 2

Rheology and spinnability of cystic fibrosis sputum. (a) Spinnability of sputum was assessed at the end of rheological measurements by lifting up the upper plate at a constant velocity of 3.6 mm s^− 1. (b) Amplitude sweep (at 1 rad s^− 1) showing a linear viscoelastic (LVE) regime up to about 1% deformation. The dashed violet lines show the graphical determination of the dynamic yield point / stress. (c, d) Frequency sweeps depicting G’ (storage modulus), G” (loss modulus) and η^* (complex viscosity). The grey dashed lines represent the vertically shifted fitting curves (fitting between 0.1–10 rad s^− 1). The blue dashed lines in (b, c) indicate the calculated instrument inertia limit