Obstructive Lung Disease Flashcards
What changes to respiration occur with airflow obstruction?
Increased resistive WOB Increased sensation of breathing Increased respiratory muscle effort Active exhalation Longer time to inspire and exhale Reduced maximum ventilation
How can increased resistive WOB in obstructive lung disease lead to ventilatory failure?
Recruitment of accessory muscles
Increased O2 consumption by respiratory muscles
Risk of respiratory muscle fatigue, if obstruction is severe
Respiratory muscle fatigue causes ventilatory failure and PaO2 drops to 50mmHg
How are respiratory parameters changed in obstructive lung disease?
FVC is normal
FEV1 is reduced (<70%)
Forced expiratory flow 25%-75% (FEF) is reduced
How can you determine if obstructive lung disease is reversible or irreversible?
Provide a bronchodilator and look for improvement in FEV1
What is the normal rate of expiration?
FEV1 is 80% of FVC
Whole FVC is exhaled within 2-3 secs
What is pulsus parodoxus? What does it indicate when absent?
Pulsus paradoxus is an exaggeration of the normal decline in SBP with inspiration compared with SBP on expiration, as caused by the variation in intrapleural pressure (there is increased variation with obstructive lung disease)
Disappears when respiratory muscles fail
What is the difference between limiting factors for exercise in normal individuals vs. patient with airway obstruction?
Normally exercise is limited by achieving maximum predicted HR
In airflow obstruction, maximum ventilation can be reduced and can be reached before maximum HR is reached when exercising
What is gas trapping? When does it occur and what is its effect on respiratory parameters?
Air can be trapped beyond obstructed airways with severe airflow obstruction (can be inspired but not expired)
This increases TLC, RV and RV/TLC, can causes hyperinflation of the lungs (seen on X-ray with flattening of the diaphragm and with a clinical “barrel chest” presentation)
What happens if airflow obstruction causes uneven ventilation?
There is compensatory vasoconstriction in regions of low V/Q to reduce their hypoxaemic effects by directing deoxygenated blood to other alveoli to become oxygenated
In generalised lung disease, this causes a decrease in gas exchange and PaO2
What is the difference between low V/Q and shunting?
Shunting is an extreme form of low V/Q unit in which V/Q = 0, and will not respond to supplemental O2 (unlike low V/Q)
Can occur when lungs are filled with fluid (e.g. in severe pulmonary oedema) or in pneumonia with consolidation
Give 3 examples of obstructive lung diseases
Asthma
COPD including chronic bronchitis, emphysema and small airways disease/chronic bronchiolitis
Bronchiectasis
What is the pattern of breathing in patients with obstructive lung disease?
Slow, deep breaths