Compliance is
Volume change per unit of pressure change
essentially how hard it is to breathe in
Total compliance of the respiratory system consists of
elastic forces of the lung (CL ) and chest wall (CCW)
CL + CCW = CRS
low compliance
harder to breathe in
high compliance
easy to breathe in
lung compliance (Cl) reduced in
– Low lung volume
– Loss of surfactant
– Fibrosing disorders
– Pneumonia
– Pulmonary congestion
– Alveolar or interstitial oedema
Lung compliance (CL) is increased in
– Older age
– Emphysema
Reduced chest wall compliance(CCW) (stiffer)
– Kyphoscoliosis
– Chest wall hyperinflation
– Restrictive pleural disease eg asbestosis
– Pleural effusion/pneumothorax
– Obesity
increased chest wall (CCW) (floppier)
– Neonates
– Acute cervical/high thoracic SCI
Airway Resistance
For air to be moved into or out of the lungs, a pressure difference between the atmosphere and the alveoli must be established
- Clinically there are 2 factors that influence which tubes (airways) gas flows through for any given pressure gradient
– Type of gas flow
– Size of the airway lumen
laminar is what type of gas flow
slow
turbulent is what type of gas flow
faster
factors affecting Raw (airway resistance)
* Without lung disease
– Airway generation
– Phase of breathing cycle
* Expiration > resistance than inspiration
– Lung volume
* As lung volume , resistance since airways become more narrow
Factors affecting RAW (airway resistance)
* With lung disease
– Smooth muscle contraction (bronchospasm)
* Asthma
– Secretions
* Cystic fibrosis
– Oedema/inflammation
* Asthma, infection
– Loss of structural support
* Emphysema
– Tumour
Dynamic Hyperinflation also known as
“Reversible” hyperinflation
Dynamic Hyperinflation can occur during
– Acute exacerbation: when there is increase airflow resistance (from swelling,
secretions, spasm)
– Exercise: when there is increase ventilatory demand
Signs & symptom of working harder to breathe
- Change in pattern of breathing
- Bracing/lean forward position
- Pursed lips breathing (PLB)
- Nasal flaring
- Dyspnoea
Pursed Lips Breathing
– Increases airway pressure (back pressure)
– Prevents dynamic airway collapse
– Decreases end expiratory lung volume
Management of Increased WOB
- Reduce load
- If load cannot be reversed
- Physiotherapy implications: manage breathlessness
Definition of Dyspnoea
- Perception of uncomfortable/unpleasant respiratory sensations
Mechanism of Dyspnoea
- Multifactorial in origin
- Mismatch between motor output and incoming afferent signals
Measurement of dyspnoea
- Modified Borg scale (intensity)
- VAS or NRS (intensity)
- New York Classification of breathlessness (task)
- Modified Medical Research Council (mMRC) dyspnoea
scale (task) - QOL questionnaires – St George’s, Guyatt
Modified Borg Scale of Breathlessness
0 No breathlessness at all
0.5 Very, very slight
1 Very Slight
2 Slight breathlessness
3 Moderate
4 Some what severe
5 Severe breathlessness
6
7 Very, severe
8
9 Very, very severe
breathlessness
10 Maximum breathlessness
Dysponea and Upper limb activity
- When active, accessory muscles help reduce the work of the diaphragm by assisting in ventilation
- During upper limb activity/exercise these muscles cannot function as respiratory muscles
