lung volumes and lung function testing Flashcards
lung compliance
= stretchiness.
at high pressure, lung is stiffer, hence compliance is lover and vice versa.
lung bases are more compliant than the apex- better ventilation. compliance is followed by elastic recoil.
decreased compliance e.g. pulmonary fibrosis, alveolar oedema.
increased compliance- normal ageing lung
total lung compliance is dependent on:
thoracic cage and elasticity
what do healthy people tend to have for efficient ventilation
- high lung compliance
- low alveolar surface tension due to surfactant.
surface tension
a thin film of liquid lines the alveoli and possess surface tension which is always trying to reduce the alveoli to the smallest possible size. alveoli tend to favour a low surface tension. high surface tension -> collapse of the alveoli, affecting gas diffusion
surfactants
reduce surface tension- disrupt interactions between surface molecules.
secreted by type II alveolar epithelial.
comprises of a mixture of phospholipids, proteins and ions.
reducing surface tension by surfactants increase stability of the alveoli; prevents lungs from collapsing
infant respiratory destress syndrome IRDS/ NRDS
insufficient surfactant production -> air sacs collapse -> lungs are difficult to inflate.
surfactant is secreted into the alveoli between the 6th/7th month of gestation. fatal if not treated.
management:
- pre-birth- corticosteroids to speed up lung development.
- surfactant replacement therapy immediately after birth.
- high levels of oxygen
lung function tests need to assess:
- mechanical condition of the lungs e.g. compliance.
- resistance of the airways- narrowing e.g. asthma
- diffusion across the alveolar membrane- pulmonary fibrosis
lung volumes- spirometer
dependent on the lung’s elastic properties and the properties of the muscles of the chest wall. provides information on lung volume and capacity.
volumes using spirometry: TV IRV ERV VC
TV- tidal volume- volume of air entering and leaving the lung with each normal breath.
IRV- inspiratory reserve volume- extra volume of air inspired above the normal tidal volume with full force.
ERV- expiratory reserve volume- extra volume of air expired by forceful expiration at the end of normal tidal expiration.
VC- vital capacity- maximum amount of air expelled from the lungs after filling the lungs after first filling the lungs to a maximum then expiring to a maximum: TV+IRV+ERV
volumes not measured using spirometry:
RV
FRC
TLC
RV- residual volume- volume of air remaining is the lungs after the most forceful expiration.
FRC- functional residual capacity- amount of air that remains in the lungs at the end of normal expiration (ERV+RV)
total lung capacity (TLC)- the maximum volume of air the lungs can hold
lung volumes: FVC and FEV
FVC- forced vital capacity- total volume exhaled.
FEV- forced expiratory volume (FEV)1.0= volume expired in the first second. typically >70% FVC.
FVC and FEV1.0 are defined as a ratio
-FRV1.0/FVC
lung function test- functional residual capacity
residual air cannot be directly expired into the spirometer. FRC are measures using helium dilution or nitrogen washout
nitrogen washout
- patient inspires 100% oxygen
- expires into the spirometer system
- procedure repeated until N2 in lungs is replaces with O2.
- FRC calculated by exhaled N2 and estimated alveolar N2
restrictive deficit
lung expansion is compromised- alterations in lung parenchyma, disease of the pleura of chest wall. lungs do not fill to capacity hence they are less full before expiration. FVC is reduced, but the FEV1.0 is relatively normal. the FEV1/FVC also remains relatively normal/ increased.
obstructive deficits
characterised by airway obstruction. if airways are narrowed, lungs can still fill to capacity. resistance is however increased on expiration. e.g. asthma, COPD. FEV1.0 will be reduced, but FVC will be relatively normal. a low FEV1.0/FVC will be recorded
