The major causes of morbidity and mortality in Cystic Fibrosis (CF) are linked to the process of chronic inflammatory of the airway, leading to the progressive damage of the small bronchioles and subsequently to the proximal bronchi. A connection between weaknesses of respiratory muscles in CF and deficits of CFTR in the muscle has been established. Insufficient cough in CF patients may advance re-current respiratory infections. A voluntary cough flow volume (C-FVC) profile incorporates the characteristics of the forced expiratory flow volume curve (FE-VC). The study aims to explore the correspondence of voluntary cough-flow-volume and maximum expiratory flow-volume maneuvers in relation to disease complications in CF patients.

Cystic fibrosis (CF) is the most common lethal life shortening genetic disease caused by mutations of the trans-membrane conductance regulator (CFTR) gene. The major causes of morbidity and mortality in CF are linked to the process of chronic inflammatory of the airway, leading to the progressive damage of the small bronchioles and subsequently to the proximal bronchi. Cough is a back-up mechanism for mucus clearance which comes into effect in health during emergency situations, such as following the inhalation of a foreign body, and in lung disease where often the primary host defense clearance mechanism, namely mucociliany clearance, is compromised

Several studies have showed a connection between weaknesses of respiratory muscles in CF and deficits of CFTR in the muscle; sustain infection of pseudomonas; lower than normal tension time index and low fat free mass [3-6]. Weakness of the respiratory muscle may insinuate insufficient cough in CF patients.

Effective cough is initiated in several mechanical stages: a) inhaling a variable amount of air, b) closure of the glottis, c) contraction of respiratory muscles, and d) forced expiration to residual volume [7-13] A voluntary cough flow volume (C-FVC) profile therefore, incorporates the characteristics of the forced expiratory flow volume curve (FEVC) in that the first "spike" represents the peak cough flow, and the volume exhaled by the cough corresponds with the vital capacity. The descending portion of the C-FVC including secondary spikes decrease in a linear fashion as lung volume goes down from total lung capacity to residual volume.10 similar to the FEVC flow decay. Any disturbance in either of the cough stages may impair its efficiency.

The aim of this study is to explore the information that can be gained on cough ability in a group of CF patients, by the performance of voluntary cough-flow-volume maneuver and in relation to the characteristics of a maximum expiratory flow-volume curve.

Study plan How does this advance the field? In this study we wish to evaluate for the first time the cough ability derived from the voluntary cough flow volume curve for detection of insufficient cough in patients with CF. We hope to show that the cough flow volume curve corresponds with changes in cough ability in these patients in relation to lung function deterioration.

What are the clinical implications? An objective following-up of cough ability deterioration may allow the opportunity to introduce special respiratory therapy for strengthening cough and ease secretion flow in these patients.

Inclusion Criteria:

• Cooperation with spirometry

Exclusion Criteria:

• exacerbation, patients younger than 8 years.

Any CF patient visiting the pulmonary function laboratory, above 8 years old, who could cooperate with spirometry and who had no exacerbation, upon signing agreement consent