Resp conditions Flashcards
What is the pathophysiology of cystic fibrosis
- mutation in the cystic fibrosis transmembrane receptopor
- results in impaired chloride secretion
- causes sodium and water to move into cells leaving viscous secretions behind
- this predisposes to infection
What type of inheritance pattern is cystic fibrosis
autosomal recessive
Why is sweat high in sodium in patient with cystic fibrosis
Primary secretion of sweat duct is normal but CFTR does not absorb chloride ions, which remain in the lumen and prevent sodium absorption.
Why is pancreatic insufficiency a feature in patients with cystic fibrosis
Production of pancreatic enzymes is normal but defects in ion transport produce relative dehydration of pancreatic secretions, causing their stagnation in the pancreatic ducts.
Why is cystic fibrosis associated with gastrointestinal disease
Low-volume secretions of increased viscosity, changes in fluid movement across both the small and large intestine and dehydrated biliary and pancreatic secretions cause intraluminal water deficiency.
Why is biliary disease associated with cystic fibrosis
Defective ion transfer across the bile duct causes reduced movement of water in the lumen so that bile becomes concentrated, causing plugging and local damage.
How does cystic fibrosis effects the resp system
- Dehydration of the airway surfaces reduces mucociliary clearance
- This favours bacterial colonisation
- local bacterial defences are impaired by local salt concentrations and bacterial adherence is increased by changes in cell surface glycoproteins.
- Increased bacterial colonisation and reduced clearance produce inflammatory lung
Which mediators are involved in the neutrophilic response in CF that causes inflammatory lung damage
IL8
Neutrophil elastase
What screening is available to detect CF
- immunoreactive trypsinogen (IRT) on blood spot Day 6
- abnormally raised IRT levels will undergo CFTR mutation screening
What are the key signs in CF
Finger clubbing. Cough with purulent sputum. Crackles. Wheezes (mainly in the upper lobes). Forced expiratory volume in one second (FEV1) showing obstruction.
What presentation of CF may be picked up perinatally
- Screening.
- Bowel obstruction with meconium ileus (bowel atresia).
- Haemorrhagic disease of the newborn.
- Prolonged jaundice.
What presentation of CF may be picked up in infancy and childhood
- FH
- Recurrent respiratory infections.
- Diarrhoea.
- Failure to thrive
- Nasal polyps
- Acute pancreatitis.
- Portal hypertension and variceal haemorrhage.
- Pseudo-Bartter’s syndrome, electrolyte abnormality.
- Hypoproteinaemia and oedema.
How may adolescence present with CF
Family history. Recurrent respiratory infections. Atypical asthma. Bronchiectasis. Chronic pulmonary disease. Chronic sinus disease. Male infertility with congenital bilateral absence of the vas deferens. Heat exhaustion/electrolyte disturbance. Portal hypertension and variceal haemorrhage.
What investigations should be done is suspecting CF
- sweat test
- molecular genetic testing
- CT chest/CXR
- lung functions test (>6yrs)
- Sputum microbiology
What findings on sweat test would be indicative of CF
- Chloride concentration >60 mmol/L with sodium concentration lower than that of chloride on two separate occasion
- > 98% sensitive
