Lung compliance Flashcards
(23 cards)
what is compliance?
the distensibility or stretchiness of an elastic structure. the change in pulmonary volume per unit pressure change
where are lungs most compliant?
above functional residual capacity
what happens in an overinflated lung?
the lungs are less compliant (like trying to get more air in a balloon that is already filled to capacity)
what happens to compliance below normal FRC?
lungs are less compliant and need a lot of pressure to get a change in volume (long, thin balloon)
what is lung compliance?
distensibility of the lungs
what is chest wall compliance?
distensibility of the chest wall
what is total lung compliance?
chest wall compliance + lung compliance
what is restrictive lung disease?
reduced total lung compliance, limiting/reducing inspiration
what is pulmonary surfactant?
substance secreted by type II alveolar cells to reduce surface tension
what is pulmonary oedema?
fluid in the interstitial space and alveoli
what is consolidation?
an airless area of lungs, filled with fluid of cells
what is closing volume?
the point in FRC (particularly ERV) at which dynamic compression of the airways and collapse begins
what increases closing volume?
age, smoking, lung disease, position (supine > upright)
what is closing capacity?
closing volume + residual volume
what happens to lung compliance in ageing?
increases
what happens to chest wall compliance in ageing?
decreases - joints between the head of the ribs and spine become more stiff
what factors affect chest wall compliance?
kyphosis
scoliosis
sternal deformity
circumferential thoracic burn
raised intra abdominal pressure (harder for diaphragm to contract and descend)
abdominal distension / surgery
pregnancy
obesity
supine position
what happens to lung compliance in supine?
reduced lung compliance as many lung volumes are smaller when supine - reduced tidal volume, reduced FRC, reduced vital capacity and increased pulmonary congestion
what happens to chest wall compliance in supine?
reduced - abdominal content pushed up against the diaphragm increasing intra-abdominal pressure and altering diaphragm mechanics
what happens to expiratory flow rate in supine and what does this mean?
reduces (needed for effective coughing), increasing work of breathing
why does surgery cause reduced lung volumes?
recumbency
absorption atelectasis
pain
diaphragmatic dysfunction
immobility
decreased mucociliary transport
what is absorption atelectasis?
room air is 21% O2, 78% nitrogen. the nitrogen keeps the alveoli patent and expanded when the O2 has been utilised. if a patient has been hiven high conc oxygen (above 60%) for a long period, there isnt enough nitrogen to keep the alveoli patent so they collapse
why does immobility mean reduced lung volume?
when mobilising, we naturally take a deeper breath to sustain the increased activity. this is lost with immobility, reducing tidal volume
