Respiratory Volumes + Pulmonary Function Tests Flashcards
Vital Capacity (VC)
The total amount of air that can be moved through the airways by a maximal
inspiration which is followed by a maximal expiration is the VITAL CAPACITY (VC)
Tidal Volume (VT)
The amount of air moved through the airways during normal breathing is the TIDAL VOLUME (VT)
INSPIRATORY RESERVE CAPACITY
The extra air that can be added to the lungs after a tidal inspiration is the INSPIRATORY RESERVE CAPACITY
EXPIRATORY RESERVE CAPACITY
The extra air that can be removed from the lungs after a tidal expiration is the EXPIRATORY RESERVE CAPACITY
RESIDUAL VOLUME
The amount of air left in the lungs after a maximal expiration is the RESIDUAL VOLUME
FUNCTIONAL RESIDUAL CAPACITY (FRC)
The amount of air left in the lungs after a tidal expiration is the FUNCTIONAL RESIDUAL CAPACITY (FRC)
Two types of diseases affect the respiratory system:
- Obstructive diseases make it more difficult to get gas out of the lungs;
- Restrictive diseases make it more difficult to gas into the lungs
Pulmonary function testing is useful for:
- Screening for obstructive + restrictive disease and observing progression;
- Evaluating pre-surgery;
- Evaluating suitability for ventilator weaning
FEV1 TESTING
- Forced expiratory volume in one second - measured using spirometry
- Most useful in the evaluation of obstructive diseases
- Begins w/ a full inspiration
- The volume of gas expired during a forced max expiration is measured over one second
- It is measuring the rate at which a person can get gas out of their respiratory system
- The total volume of gas expired during the forced maximal expiration is measured. This is the FVC (forced vital capacity)
- It is measuring the volume of gas a person can get out of their respiratory system
- A normal result gives a ratio FEV1/FVC > 70%
More on FEV1:
Low FEV1 may be due to
- airways obstruction
- loss of expiratory muscle power
- FEV1 must be interpreted using, age, gender, height, race matched normals
- Due to variation, values in range 80% - 120% of predicted are considered normal
Patient positioning and comfort must be standardised.
- Subjects should sit with the head held in a neutral position.
- Uncomfortable room temperatures, tight clothing, or uncomfortable seating lead to inaccurate measurements.
- Tests are assessed using standard criteria
OTHER INFO TO READ
Forced Expiratory Flow at 25% of FVC (FEF 25%).
- flow rate at the 25% point of the total volume (FVC) exhaled
Forced Expiratory Flow at 75% of FVC (FEF 75%).
- indicates the status of small airways
- COPD shows up in the smallest airways first
PEAK EXPIRATORY FLOW RATE (PEFR) - peak flow metre + advantages
- The max flow rate that can be generated during a forced expiration
- An obstructive disease will decrease the PEFR.
- A very useful measurement to check on asthma control.
PEFR has several advantages:
- peak flow metres are cheap
- tests can be done easily at home
- it provides good info on asthma control
- it has a physiotherapy effect
