What do we mean by low lung volumes?
- reduced tidal volume (shallow breathing)
- reduced vital capacity (inability to take a deep
breath) - reduced FRC (generalised loss of volume)
- reduced TLC (generalised loss of volume)
Reduced Tidal Volume (VT) results in
- less gas moving in & out of the alveoli
- less fresh gas in the alveoli
- less O2 to move into the blood
- O2 movement problem
Reduced VT (shallow breathing) without Sighs results in
less gas moving in & out of the alveoli
reduced stretch of the alveoli
reduced surfactant production
increased surface tension/more inwards recoil
Smaller alveoli (some may even close)
General loss of volume (FRC) & Changed distribution of ventilation
Reduced VC results in
reduced Inspiratory volume/deep breath in
reduced volume to exhale
reduced expiratory flow rate
reduced cough effectiveness
Secretion movement problem
FRC is
- The amount of air left in your lungs after a normal breath out
- The inward recoil of your lungs equals the outward recoil of the chest wall
- Allows gas exchange to occur continuously in the clungs
FRC is reduced in
Chest wall and /or lungs less compliant
* Supine position
* Obesity
* Anaesthesia
* Thoracic & abdominal surgery
Chest wall more compliant/floppy so lung recoil pulls chest wall in
* Neonates
* Acute cervical spinal cord injury (SCI)
what is Closing Capacity
The point at which dependent small airways close during inspiration & expiration
Most common causes of increased CC (closing capacity)
when airways lose rigidity (become more floppy), as in
– Increased age
– Smoking
what happens when CC > FRC
small airways close during normal
breathing
what happens when FRC > CC
gas exchange to continuously occur
common causes of Localised Volume Loss
- Lobar or segmental lung collapse
- Pleural effusion
- Rib #
Consequences of a Pleural Effusion
- Disassociates the chest wall from lung (reduces intrapleural pressure)
- Underlying lung tissue is not expanded
- Eventuates in closure of underlying alveoli ->
localised O2 movement problem
Consequences of Fractured Ribs
- Pain causes a decrease in tidal volume
- Chest wall may be unstable due to # -> reduced local chest wall movement
- Chest wall may be stiff due to soft tissue injury
- Eventuates in secondary atelectasis or collapse
PLUS - Any bruising of underlying lung tissue alters the surfactant production and directly stiffens the lung
- Consequently impairments can include
– General O2 movement
– Localised O2 movement problem
Effect of Reduced Lung Volumes on
Secretion Clearance
increased risk of infection
Signs & Symptoms of Reduced Volumes
- May complain of shortness of breath
- Observation/Palpation:
– reduced expansion of chest wall
– increased RR
– +/- use of accessory muscles - Cyanosis (if PaO2 reduced significantly)
- Auscultation:
– reduced or absent breath sounds
– fine end inspiratory crackles
Relaxed Breathing aim
encourage relaxation of the upper chest and
shoulders
Techniques to Increase Lung Volumes
- increase inspired volume
– Deep breathing exercises including breath holds - increase FRC
– Upright positioning - Re-expand localised area of loss of volume
– Specific positioning
Aims of Deep Breathing Exercises
- Increase gas movement (O2) by increasing tidal volume and FRC
- Prevent possible secondary effects on secretion clearance
- Prevent possible secondary effects on respiratory load
Factors that affect distribution of ventilation during deep breathing exercises
– Volume of inspiration
– Muscle recruitment
– Inspiratory flow rate
– Addition of inspiratory hold (end inspiratory
pause)
– Alveolar interdependence
- Intercostal / accessory muscle recruitment: leads to gas going
to non-dependant regions
Diaphragm recruitment: leads to gas going
to dependant regions
what is the impact of a slow inspiratory flow rate
reduces the effect of airway resistance on where gas goes
Inspiratory Hold
- Adding a 2-3 second pause at the end of a deep breath
- Allows gas to travel through collateral channels, opening up adjacent closed alveoli
Alveolar Interdependence
- Alveoli are connected to each other and therefore a change in volume in one exerts a stretch on those around it
