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WEEK 16:
Lung volumes and lung function testing:
| Question | Answer |
|---|---|
| lung compliance meaning | stretchiness |
| lung compliance at high pressure | low |
| lung compliance at low pressure | high |
| what is compliance followed by | elastic recoil |
| compare compliance between lung bases and apex | base is more compliant as it can hold more volume, which is better for ventilation because that is where alveoli is found |
| elastic recoil in lungs | lung deflates after inhalation |
| condition with decreased compliance | pulmonary fibrosis and alveolar oedema |
| healthy lungs have what (2) | increased compliance and low alveolar surface tension due to surfactant |
| lung compliance depends on what (2) | thoracic cage and elasticity |
| explain surface tension in alveoli | water molecules in liquid lining the alveoli are attracted to each other which causes surface tension and this reduces alveoli size |
| high surface tension in alveoli | decreases alveoli size and collapses alveoli affecting gas exchange |
| surface tension | water molecules attracted to each other making a force (surface tension) |
| surfactant role | disrupt interaction between surface molecules |
| what are surfactants secreted by | type II alveolar epithelial |
| what are surfactants made of | phospholipids, proteins and ions |
| infant respiratory distress syndrome (IRDS)/ neonatal respiratory distress syndrome | premature infants born before 6/7th month of gestation produce little or no surfactant causing alveoli to collapse |
| when is surfactant secreted into the alveoli of infants | 6/7th month of gestation |
| management for IRDS (3) | 1- corticosteroids (betamethasone) can be given before birth to speed up lung development. 2- surfactant replacement therapy immediately after birth. 3- give high levels of O2 |
| what do lung tests assess (3) | 1- mechanical condition of lungs eg compliance. 2- resistance of airways eg narrowing. 3- diffusion across alveolar membrane |
| what is used to measure long volumes | spirometer |
| what does a spirometer measure (4) | tidal volume (TV), vital capacity (VC), inspiratory reserved volume (IRV), expiratory reserved volume (ERV) |
| tidal volume (TV) | air moved in and out lungs at rest |
| vital capacity (VC) | maximum amount of air moved in and out during forced inhalation/ exhalation (eg deep breath in deep breath out) |
| inspiratory reserved volume (IRV) | extra volume of air you can breathe in after normal inhalation with force |
| expiratory reserved volume (ERV) | extra volume of air you can breathe out after normal exhalation with force |
| total lung capacity (TLC) | all air you can fit in lungs |
| residual volume (RV) | air left in lungs after forced exhalation |
| functional residual volume (FRC) | air left in lungs after normal exhalation |
| how do you calculate vital capacity (VC) | TV + IRV + ERV |
| what does spirometry NOT measure | RV, FRC, TLC |
| vitalograph measures what (2) | forced vital capacity (FVC) and forced expiratory volume (FEV)1.0 |
| FVC in vitalograph | measures total volume exhaled forcefully (5L) |
| FEV1.0 in vitalograph | volume expired in first second (>70% FVC) |
| link between FVC and FEV1.0 in vitalograph | you exhale 70% of FVC (total volume exhaled) in the first second |
| how are FVC and FEV1.0 defined as a ratio | FEV1.0/ FVC |
| how can you diagnose lung conditions with FEV1.0/ FVC | anything below 70% can be diagnosed as a lung condition |
| explain FVC in pulmonary fibrosis | lower because scarring makes lungs less compliant reducing the amount of air that can be exhaled forcefully |
| explain FEV1.0 in asthma | decreased because narrow airways mean less air can be exhaled in the first second than normal |
| explain race and pulmonary function tests | race is put into spirometer (often assumed by operators) to adjust results based on race (race correction) |
| how can FRC, TLC and RV be measured (2) | using helium dilution or nitrogen washout |
| why is helium dilution used to calculate FRC, TLC and RV | is not metabolised in the body so the amount of volume can be measured without some volume disappearing |
| how does helium dilution (closed system) measure FRC | a known concentration and volume of helium is used first, then patient breathes in which changes the concentration |
| before equilibration expression of helium dilution (closed system) | C1 x V1 |
| after equilibiration expression of helium dilution (closed system) | C2 x (V1 +V2) |
| how do before and after equilibration expressions link | C1 X V1 = C2 X (V1+ V2) |
| how do you calculate V2 (FRC) **formula provided yay | V1 X (C1 -C2)/C2) |
| what is V2 in helium dilution | volume left in lungs of patient (FRC) |
| how does nitrogen washout work to calculate FRC | inhale 100% O2 and expires into spirometer until all N2 in lungs replaced with O2. FRC calculated from exhaled N2 and estimated alveolar N2 |
| explain restrictive deficits | lung expansion compromised due to alteration in lung parenchyma or disease so lungs do not fill enough before expiration. FVC decreases but FEV1.0 remains the same so the FEV1.0: FVC ratio is normal. |
| explain obstructive deficits | airway obstruction eg narrowed airways. Lung can fill to capacity but there is increased resistance during expiration. FEV1.0 decreases but FVC is normal giving a low FEV1.0: FVC ratio |
| example of disease with restrictive deficits | pulmonary fibrosis |
| example of disease with obstructive deficits | asthma |
| how does a peak expiratory flow (PEF) rate work | deep breath in (TLC) and breathe out as fast as you can (RV) |
| how is TLC- PEF effort dependent | more effort increases PEF rate as more is inhaled |
| how is PEF- RV effort independent | more effort breathing out fast does not increase PEF rate |
| flow volume loops | forcefully breathe in (TLC) and forcefully breathe out (RV) and breathes back in (loop) |
| nomogram | shows normal values for PEF rate considering height, age and sex |
| function of diffusion conductance | measures how easily carbon monoxide crosses from alveolar air to blood |
| why is CO used in diffusion conductance | has a higher affinity to haemoglobin than O2 so easier to measure movement across membrane |
| how does diffusion conductance work | patient takes a single breath of dilute CO and hold it for 10 seconds |
| how do you calculate diffusion capacity from diffusion conductance | calculated from lung volume and the percentage of CO in alveoli at the beginning and end of 10 second breath-hold |
| diffusion conductance clinical relevance | shows conditions eg fibrosis where gas diffusion is compromised |
Created by:
kablooey
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