Cough characteristics and FVC maneuver in cystic fibrosis

Cough is part of life in patients with cystic fibrosis (CF). Weak coughing may add to increased respiratory disease that affects the mechanical properties of cough in these patients. In this study, we investigated cough characteristics in relation to forced expiratory flow/volume indices in CF.

This prospective study included 54 subjects (26 ± 10 y old) with CF. Similar indices of the maneuvers were compared. Additionally, other cough characteristics revealed by the maneuvers were investigated. Cough was considered efficient with 6 or more secondary spikes at a flow of > 2.67 L/s.

Cough peak flows similar to peak expiratory flows (regardless of FEV1 severity level) were found in 98% of subjects. The secondary spike flows deteriorated alongside the percent-of-predicted FEV1 (r(2) = 0.17, P = .002), yet inefficient secondary spike flows could also be found when FEV1 was within normal range. Mean efficient spike number was low (2.5 ± 1.2 spikes/maneuver). Most cough spike flows were very small (< 0.9 L/s), resembling vibration that may contribute to the propulsion of mucus toward the central airways. Cough maneuver duration ended faster than forced expiration duration (3.7 ± 1.7 s vs 6.8 ± 2.5 s, P < .001), resulting in a smaller cough vital capacity compared with expiratory vital capacity (2.1 ± 0.9 l vs 3.1 ± 0.7 l, P < .001). Inspiratory volume below 2.23 ± 0.07 L reduced efficient secondary spike number.

The cough flow/volume maneuver reveals abnormalities in cough velocities and volume. A low secondary spike correlates with FEV1 severity level. The method may lead to earlier intervention to assist cough in CF.