respiratory mechanics Flashcards
resistance: explain the concept of airway resistance in the lung, and explain it effects, and is affected by, changes in pulmonary function
pattern of resistance through respiratory tree generations
increases as airway narrows, peaking at generation 4, then decreases
relationship of conductance (volume of air reaching alveoli) and resistance
as lung volume increases, airways get larger linearly; resistance decreases exponentially as airways dilate
calculate transmural pressure
pressure inside - pressure outside
effect on transmural pressure during inspiration and reason
increases (+5 to +8) to prevent airway collapse
pre-inspiration: pressures in lungs, atmosphere and intrapleural space
at functional residual capacty, pressure in lungs and atmosphere is 0 so no airflow; intraplueral space at -5 due to recoil
mid-inspiration: intrapleural tension and outcome
increases to -8 cmH2O, creating pressure gradient for air to move in
end-inspiration: intrapleural tension, lung pressure and atmospheric pressure
intrapleural tension remains at -8 cmH2O, but lung and atmospheric pressure are at 0 cmH2O
hard expiration: pressures in intra-pleural space and effect on transmural pressure
creates bigger positive pressure in intra-pleural space, so transmural pressure now surpassed collapsing pressure and airway should collapse
hard expiration: why don’t airways collapse
cannot maintain pressure, and cartilage splinting prevents airway collapse
compliance, elastance and resistance in obstructive lung disease
high compliance (loss of elastic fibres, so alveoli can keep inflating), low elastance, high resistance (small airways damaged)
compliance, elastance and resistance in restrictive lung disease
low compliance (fibrosed so can’t inflate), high elastance (scar tissue can stretch), no change to airway resistance as not altered
define obstructive lung disease
reduced ability to exhale air completely from lungs
define restrictive lung disease
reduced ability to inhale air completely into lungs
