General Flashcards
What is FEV1
Forced expiratory volume in 1 second
Person takes maximum inspiration and exhales maximally as fast as possible
What % of vital capacity could a normal person expire in 1 second
80%
See graph of Volume Time plot for forced expiratory volumes and make slides?
Plateaus
Rapid at start
Draw Flow (L/s) against Volume (x axis) graph of forced expiratory volume
Flow is greatest at the start of expiration, it declines linearly with volume. FEF25 = flow at point when 25% of total volume to be exhaled has
been exhaled
What is FVC
Forced vital capacity
The total amount of air forcibly expired
How would you use FEV1 to assess lung health
Result is compared with the predicted values
If the FEV1 is 80% or greater than predicted value = NORMAL
FEV1 below what % compared to predicted would be low
Less than 80% predicted would be abnormal
How would you use FVC to assess lung health
The result is compared with the predicted values, if the FVC is 80% or greater than the predicted value = NORMAL
Thus is the FVC is less than 80% of the predicted value = LOW i.e abnormal
What is healthy FEV1/FVC ratio
Greater than or equal to 0.7
How would you diagnose an airway obstruction
FEV1/FVC ratio <0.7
How would you diagnose an airway restriction
FVC < 80% predicted
Patient has
FEV1 = 1.1
FVC = 1.2
(Predicted FEV1=3.6; FVC=4.55)
FEV1/FVC = 1.1/1.2 = 0.92
(normal)
FVC = 26% predicted
Therefore patient has airway restriction
Patient has
FEV1 = 1.8
FVC = 3.3
(Predicted FEV1=2.94; FVC=3.70)
FVC = 89% predicted
(normal)
FEV1/FVC = 1.8/3.3 = 0.55
Therefore patient has airway obstruction
Describe Type 1 respiratory failure
pO2 (partial O2 pressure) is low
pCO2 (partial CO2 pressure) is low or normal
(type 1 means 1 definite change = low pO2)
Most common cause of Type 1 respiratory failure
Pulmonary embolism
form of ventilation-perfusion mismatch
Describe Type 2 respiratory failure
pO2 is low
pCO2 is high
(2 definite changes in type 2)
Example of cause of type 2 respiratory failure
Hypoventilation
Causes of respiratory failure
Impaired ventilation Impaired perfusion (extensive) Impaired gas exchange defects (severe)
Causes of impaired ventilation and thus respiratory failure
Neural problems e.g. narcotics, encephalitis, motor neurone disease (causing neuro-muscular weakness), cerebral space-occupying lesion etc
Mechanical problems e.g. airway obstruction (obstructive sleep apnoea), trauma, muscle disease and pleural effusion
How does obstructive sleep apnoea cause airway obstruction and thus respiratory failure
Relaxation of pharynx during sleep results in occlusion causing stimulation and wakening
Causes of impaired perfusion resulting in respiratory failure
Cardiac failure
Multiple pulmonary emboli
Causes of impaired gas exchange defects resulting in respiratory failure
Emphysema
Diffuse pulmonary fibrosis
What is hypercapnoea
High CO2 (see in type 2 resp failure if also has low O2)
Signs of hypercapnoea
Bounding pulse Flapping tremor Confusion Drowsiness Reduced consciousness
Examples of airways obstruction diseases
Asthma COPD (also airways restriction) Bronchiectasis Obstructive Sleep Apnoea Pneumonia
Examples of diseases causing hypoventilation
COPD (emphysema) Neuromuscular weakness Obesity (OHS) Chest wall deformity Reduced drive (e.g. narcotics)
Examples of diseases causing diffusion problems
Idiopathic Pulmonary Fibrosis
Other Interstitial Lung Diseases
Emphysema
What type of airway issue is asthma
Reversible
Variable airflow obstruction
What type of airway issue is COPD
Relatively fixed airflow obstruction
May be mixture of restrictive and obstructive disease
Describe appearance restrictive lung disease
Lung volumes are small due to restriction
Most breath is out in first second
(low FEV1 and FVC)
Example of restrictive lung disease
Interstitial lung disease e.g:
Fibrosing Alveolitis or Sarcoid
What is transfer co-efficient
Measure of ability of oxygen to diffuse across the alveolar membrane
How do you calculate transfer co-efficient
Can calculate by inspiring a small amount of carbon monoxide then hold breath for 10 seconds at total lung capacity (TLC)
Then measure the gas transferred
When would transfer co-efficient be low?
- Severe emphysema
- Fibrosing alveolitis
- Anaemia
- Pulmonary hypertension
- Idiopathic pulmonary fibrosis
- COPD
When would transfer co-efficient be high?
Pulmonary haemorrhage - can absorb O2 very efficiently due to bleeding resulting in more red blood cells being available
Airways restriction is from scar tissue as restricted in how much can expand
True
