Cardiopulmonary function testing Flashcards
Airway function: Expiratory function
Most common methods:
- Spirometry (FEV1 and FVC): Forced Expiratory Volume in 1” and Forced Vital Capacity.
- Flow-Volume curves
- Peak Expiratory Flow (PEF)
Airway fx: Spirometry (Graph page 62)
In the normal spirogram the major part of FVC is expelled in 1” (FEV1)
Reduction in FEV1 with relative preservation of FVC or VC is known as an “obstructive” pattern. Most of air takes way more than 1” to be expelled.
Reduction in both FEV1 and FVC with an increase in the FEV1/FVC ratio is called “restrictive” pattern. Most of air is expelled in less than 1”.
Airway fx: Flow-Volume curves (Graph page 63)
Can provide information about the nature of airway obstruction.
In the test, the gas flow from full volume expiration is plotted against the expired volume as the lung empties.
The flow of gas from the lung reaches a Peak Expiratory Flow (PEF) after about 100 ms and then declines linearly.
Air obstruction from asthma or chronic bronchitis appears as a concave expiratory limb and reduced inspiratory flows.
In emphysema, the exp flows are suddenly attenuated but the inspiratory flows are relatively well preserved.
A rigid obstruction to a major airway can produce an oval loop.
Inspiratory flows are reduced in diaphragm weakness or extrathoracic tracheal obstruction.
Airway fx: Peak Expiratory Flow (PEF)
The real value of the PEF lies in its repeatability and its portability.
PEF provides an objective measurement for pt to use to monitor their asthma as part of a self-managed plan and it can be used during hospital admissions to record the progress and predict the discharge of pt with airway disease.
Physical properties of the lungs
When supine, the vital capacity normally falls by 8-10% but when diaphragm weakness is present it may fall by >30%.
Respiratory failure
Defined as inadequate O2 delivery.
The critical PaO2 level is ~8kPa (60 mmHg), since a lower pressure than this will prejudice O2 saturation and delivery.
Respiratory failure is defined by convention as PaO2<7.3kPa (55 mmHg)
If the PaCO2 is elevated above 6.5kPa (50 mmHg), this is termed ventilatory failure and is associated with chronic airflow limitation or other forms of hypoventilation.
Oxygen prescription
An indication for long-term O2 therapy (LTOT) is a PaO2 <7.3 kPa, when breathing room air during a period of clinical stability.
Pt without chronic hypoxaemia and LTOT should be considered for ambulatory O2 if they have demonstrable desaturation on exercise. Level of desaturation should be at least 4%, to a saturation <90%, on a standard exercise test while breathing room air. An improvement of at least 10% in distance and/or breathlessness score on repeat testing with supp O2 warrants its prescription.
Field exercise tests
> 12’ walk test and 6’ walk test (6MWT)
> 20 m shuttle (or 10 m shuttle for pt with lung disease)
