- Respiratory Physiology 2
- volumes
- measuring RV, FRC and TLC
Link:www.youtube.com/watch?v=4nQApZ8Q0XM
- gas dilution
- helium dilution
- initial conc x reservoir volume = final conc (reservoir volume + FRC)
- underestimates as excludes unventilated areas of lung
- nitrogen washout
- initial amount in lung = total amount exhaled
- need to give 100% oxygen
- also underestimates
- body plethysmography
- radiography
- FEV1/VC = 80% in normal people
- loops
- flow - volume
- normal
- restriction
- COPD
- expiration turns into a chair
- variable extrathoracic obstruction
- during inspiration, intratracheal pressure becomes less than atmospheric pressure, causing collapse
- e.g. vocal cord paralysis
- flatter inspiration
- variable intrathoracic obstruction
- during forced expiration, intrapleural pressure exceeds intratracheal pressure, causing collapse
- e.g. traceomalacia
- flatter expiration
- fixed intrathoracic obstruction
- flatter inspiration and expiration
- e.g. tracheal stenosis
- 'remember e before i and i before e can be problematic’
- pressure -volume
- physiological dead space = 2mL/kg
- anatomical
- increased by
- increasing size of airway
- standing
- neck extension
- catheter mount
- basic airway manoeuvres
- pregnancy
- old age
- reducing % of minute vol reaching alveoli (increasing resp rate, reducing Vt)
- decreased by
- measured by Fowler’s nitrogen washout
- alveolar
- measured by Bohr equation Vd/Vt = PACO2-PeCO2/PACO2
- technically should be A, but is often approximated to a
- zones
- closing capacity
- lung volume at which small airway closure begins
- =closing volume + residual volume
- RV is when small airway closure is complete
- normally between FRC and RV
- you want it to be low!!
- increased by
- age
- FRC = CC in neonates, supine 45 year olds and standing 65 year olds
- CC does NOT change on standing, but FRC increases so they are less likely to overlap
- increased intrathoracic pressure
- obesity
- smoking
- decreased by
- PEEP
- anaesthesia
- infants
- pregnancy
- ‘C-PIAP’
- measured using Fowler’s single breath nitrogen washout: where curve starts increasing again = closing VOLUME
- age
- CDRROM
- CV
- Dead space
- Residual volume
- Rise
- in Old Men
- FRC stays the same
- TLC and VC decrease
- Metabolised by the lung
- peptides
- amines
- arachidonic acid metabolites
- PGE2
- keeps ductus arteriosus open in foetus
- PGF2alpha
- leukotrienes
- ‘A B SE noraD E F Gleuk!’
- compliance
- = stretchiness, change to this on questions!!
- lung and chest
- total = 100mL/cmH20
- lung = 200mL/cmH20
- 1/Ctotal = 1/Clung + 1/Cchest wall = 1/200 + 1/200 = 1/100mL/cmH20 (think of 2 resistors in parallel)
- changes
- increased by
- decreased by
- fibrosis
- pulmonary oedema
- atelectasis
- curve
- Top of lung is higher than bottom, alveoli have a higher starting volume and require higher pressures to inflate, BOTTOM OF LUNG VENTILATES BETTER. Think of spring hanging from ceiling.
- surface tension
- Laplace’s law: P=2T/R
- van der Waal’s forces are stronger from liquids
- think of saline filled lung compliance curve
- reduced by dipalmitoylphospatidylcholine (DPPC), a mixture of phospholipids and proteins produced by type II pneumocytes from free fatty acids
- work better in smaller alveoli due to hydrophobic heads repelling each other
- pressures
- intra-pleural
- -5cmH20 before inspiration
- -8cmH20 at peak inspiration
- less negative at the base due to pressure from weight of lung
- assessed by oesophageal pressure measurement
- intra-alveolar
- zero before inspiration
- -1 to -2cmH20 at peak inspiration
- +1 at expiration
- resistance
- = the frictional opposition from the airways to flow
- = pressure difference between mouth and alveoli / flow
- = kPa / L / S