Reduced Lung Volumes Flashcards
what does a ‘low lung volume’ refer to? (5)
reduced:
- VT: shallow breathing
- vital capacity: inability to take deep breath in
- FRC: generalised loss of volume
- TLC: generalised loss of volume
- localised loss of volume: eg atelectasis
explain the general mechanism of reduced VT
- less gas moves in and out of alveoli 2. less fresh gas in alveoli
- less O2 moving into blood
= O2 mvt problem
explain the effect of reduced VT (shallow breathing) without sighs
- less gas moves in and out of alveoli 2. less stretch of alveoli
- less surfactant production
- increased surface tension + more inward recoil
- smaller or collapsed alveoli
4 + 5 = reduced lung compliance
=
a. changed distribution of ventilation
b. general loss of volume (FRC)
explain the mechanism of reduced VC
- decreased inspiratory volume/deep breath in
- less volume to exhale
- decreased expiratory flow rate
- decreased cough effectiveness
= secretion movement problem
explain what FRC is and how it contributes to effective breathing
amount of air left in your lungs after a normal breath out
the inward recoil of lungs = outward recoil of chest wall
this allows gas exchange to occur continuously
explain the effect of regional differences in IPP on ventilation distribution in normal lungs
in the upright position with normal FRC:
- top of lungs more stretched open than bottom
- during a breath it is easier to stretch parts which are less stretched already
- ie for any given pressure change, there is a bigger volume change at the bottom
explain the effect of regional differences in IPP on ventilation distribution in low volume lungs (RV)
compliance of different parts of lung changes with
- bottom alveoli collapsed
- top of lungs stretch more easily than bottom
- ie for any given pressure change there is bigger volume change at the top
list the 2 reasons FRC may be reduced and examples of situations where this may occur
- chest wall/lungs less compliant
- supine
- obese
- anaesthesia
- thoracic/abdominal surgery
- fibrosing lung conditions
- thoracic spine deformities - chest wall more compliant/floppy so lung recoil pulls chest wall in
- neonates
- cervical spinal cord injury
what are the most common causes of increased CC?
when airways lose rigidity (become floppy)
- increased age
- smoking - copd
describe what happens when CC > FRC
- when CC > FRC, small airways close during normal breathing which reduces ventilation
- normally, FRC > CC for continuous gas exchange
- CC > FRC can happen due to CC increasing, FRC decreasing or combination
what are 3 common causes for localised volume loss and what is the impairment as a result?
- lobar or segmental lung collapse
- pleural effusion
- rib #
impairment = localised O2 movement problem
what would you see on CXR for a lobar collapse?
- increased opacity in the lobe
- shift of trachea/mediastinum to side of collapse
- elevated horizontal fissure
- elevated hemidiaphragm on the collapsed side
what would you see on CXR for a pleural effusion?
- increased opacity affected side
- loss of diaphragm border and angles affected side
- meniscus line
how does pleural effusion contribute to a localised O2 movement problem?
- fluid dissociates chest wall from lung = reduced IPP
- harder to stretch lung open = underlying tissue not expanded
- closure of alveoli in the area
how does rib # contribute to a general and/or localised O2 movement problem?
- localised pain at site = reduced tidal volume and deep breaths (general O2 mvt)
- chest wall unstable + chest wall stiff due to soft tissue injury = reduced local movement = secondary atelectasis/collapse
(local) - bruising/contusion of lung tissue alters surfactant production = stiffening and decreased compliance
