Work of breathing (physio) Flashcards
What is compliance?
Stretchability of chest wall and lungs
What is airway resistance?
Resistance to flow of air
How does compliance affect air flow?
Increased compliance -> air flows in more easily
What can cause compliance of chest wall to decrease?
Skeletal deformities of ribs and spine
Measure of lung stretchability
Change in lung vol/unit change in airway pressure
How does compliance affect work of breathing?
Decreased compliance -> decreased stretchability -> increased work of breathing
What is elastic recoil?
Due to elastic fibres in lung tissue
Ability to recoil after stretching force is released
What is a major determinant for compliance of the lungs?
Surface tension of alveoli
How is surface tension (T) generated in alveoli?
Attractive forces btw adjacent molecules pull alveolar surface tgt
How is pressure (P) generated within alveoli?
Surface tension causes alveoli to contract -> air within alveoli contract -> pressure generated
Describe pressure in a smaller alveoli
Smaller alveoli has higher pressure -> empty into bigger alveoli
R/s btw pressure (P), tension (T) and radius (r)
P directly proportional to T/r
- P directly proportional to T
- P inversely proportional to r
Why do smaller alveoli have tendency to collapse?
Surface tension forces create pressure that is higher in smaller alveoli
- more subatmospheric (distending) pressures needed to keep small alveoli distended (stretched)
How to improve compliance?
Reduce T -> reduce P -> increases compliance
NOTE: r cannot be changed
How to reduce alveolar surface tension?
Surfactant -> disperse themselves btw liquid molecules -> decrease attractive forces btw them -> reduce surface tension of alveoli -> prevent collapse
How does narrowing of the airways change resistance?
Increases resistance
Ways that airways can be narrowed
Contraction of smooth muscle of bronchioles
Mucus accumulation
Decreased lung vol -> decreased size of bronchioles
How does increased resistance affect work of breathing?
Increases work of breathing (to draw air into lungs)
What mediates bronchoconstriction?
Parasympathetic nerves
What mediates bronchodilation?
Sympathetic mediators
What does FEV1 refer to?
Forced expiratory vol of air exhaled in 1 sec after full inspiration
What is FVC?
Forced vital capacity -> total vol expired forcefully after full inspiration
Why do we measure forced expiratory volumes?
Picks up changes in resistance to airflow and compliance of lungs
What happens to FEV1 and FVC when lung compliance decreases?
Both values decrease
- high recoil -> can’t expand properly -> lung vol small -> total exhaled air decrease
What happens to FEV1 and FVC when airway resistance increases?
Narrow airways -> slow exhalation -> FEV1 decrease
Narrow airways -> can’t exhale completely -> FVC decrease
Effects of cigarette smoke on the respiratory sys
Cumulative irritation of airways and lungs
Chronic inflammation of airways and lungs
Increased mucus secretion
Depressed ciliary fn
Lung diseases -> COPD and lung cancer
What is barrel chest and which grp of pts is it seen in?
Hyperinflation of lungs and chest
Pts w/ COPD
How do COPD pts get barrel chest?
Airways narrowed in COPD -> air trapping during expiration
