Symptom Progression

Generally speaking, cystic fibrosis has defined identifiable symptoms. Since cystic fibrosis involved thickening of respiratory mucus, many of these symptoms are respiratory-related. These include a persistent coughing that sometimes includes phlegm and wheezing or shortness of breath. This occurs as the lungs struggle to push air out of airways that are obstructed by thick mucus. Some studies indicate that the degree of tissue hypoxia is proportionate to the degree of CTFR mutation.

 Apart from respiratory symptoms, a CF individual may also notice a salty quality to their skin as a result of the increased presence of salt in the sweat. A more commonly known symptom of CF is poor growth or weight gain despite a hearty appetite, as well as experiencing frequent greasy, bulky stools, diarrhea, or difficulty with bowel movements as a result of the decreased production of insulin and digestive enzymes that make it harder for the body to process food. This is why individuals with CF tend to have a small, petite stature.

Symptoms can be further broken down into mild to moderate (stage 2), severe (stage 3), and late stage. Each stage has defining characteristics as the disease progresses. In the mild to moderate phase, cells are hypoxic, the immune system is suppressed, and problems develop with protein metabolism and the synthesis of hormones and neurotransmitters. Mucus also begins to thicken and become stickier. In the the severe stage, the clinical picture quickly deteriorates. Respiratory problems worsen to the next stage - for example, bronchitis and bronchiolitis become bronchiectasis. The downhill slide of the respiratory system often manifests as severe dyspnea, strong chest pain and difficulty breathing. The last stage is where the individual is really fighting with death. Severe alveolar hyperventilation leads to critically low CO2 levels which can often develop into cor pulmonale (high blood pressure in the pulmonary arteries and right heart overload). This is the point where individuals often die. 

References:

http://www.normalbreathing.com/cystic-fibrosis-symptoms.php