Spirometry Flashcards
What is a spirometry test?
Spirometry uses a spirometer to measure lung function. It does this by measuring volume of air expired & how quickly it can be expired.
It is the most common test to test for lung diseases e.g., COPD, used in diagnosis & monitoring of disease progress
What is spirometry used for?
Respiratory diseases can cause mechanical damage to respiratory systems. Spirometry allows us to identify the effect of lung diseases on flow & volume by measuring it
What are the indications for spirometry
- Medical diagnosis: measures the effect of lung disease on lung function, can monitor physical fitness & evaluate the health of a person. It can be used to evaluate symptoms
- Surgery: done pre & post op to ensure normal lung function, completed as a risk assessment before surgery to ensure person is able to survive under anesthetic
- Disability evaluation: used for legal purposes e.g., if a person is caught drinking & driving, used for government compensation
- Research: Used in clinical trials & studies. e.g., effect of a drug on the lungs, if lung function increases or decreases when taking the drug can be measured via spirometry
What does spirometry measure?
It measures volume & flow
Volume= flow x time
What are the units for spirometry?
L/min
S/min
Define tidal volume & residual volume
Tidal volume: the volume of gas inspired and expired in one breath
Residual volume: the volume of gas left in the lungs & airways after full expansion
Define functional residual capacity
FRC- The volume of gas left in the lungs and airways after a tidal expansion
Define ERV & IRV
ERV- the maximum volume of gas that can be exhaled in position of FRC
IRV- the maximum volume of gas that can be inhaled above the tidal volume by forced inspiration
Define inspiratory capacity
Inspiratory capacity (IC): the maximum volume of gas that can be inhaled in the position of functional residual capacity
Define relaxed vital capacity
Relaxed vital capacity (RVC) also known as slow vital capacity (SVC), this is measured in 2 ways:
Expired VC: the maximum volume of gas that can be exhaled from the lungs during a relaxed expiration from a position of a full inspiration
Inspired VC: the maximum volume of gas that can be inhaled via the lungs during a relaxed inspiration from the position of a full exhalation
What are the measurements made during spirometry?
It measures FEV1, FVC, ratio of FEV1/FVC,
PEF- peak expiratory flow
RVC- relaxed vital capacity
Define FEV1
The forced expiratory volume of gas in one second
it is measured in litres
FEV1 found on spirogram at 1 second, draw a line up to reach the curve
Describe a spirogram
A graph that has volume in L/ml on y axis
Time in s/m on x axis
Graph starts from the point of maximum inspiration
Total lung capacity is 0 at cross-section of X & Y
It is plots exhaled volume against time during a forced expiratory effort
There is a rapid rise in volume of air expired initially, and the graph begins to plateau as the patient has fully expired
FVC found at in line with top of plateau
How do you calculate the FEV1/FVC ratio?
FEV1/FVC x100= %
Over 70% is seen a normal reading
Describe a flow loop
It uses information from the same test, but is displayed differently. it measures both inspiration & expiration
inspiration measured under the graph
PEF is the peak of the flow loop
Sharp rise occurs as a person exhales, and there is a steady decline in residual volume
FEV1 cannot be measured on a flow loop! AS NO TIME ON THE GRAPH
Flow is measured on the y-axis (L/sec)
Volume on the x-axis (L)
Forced vital capacity is from 0 at x-axis to PEF
Define PEF
Peak expiratory flow is the maximum flow that can be achieved during forced expiration from total lung capacity measured in L/min
It is achieved within the first 100 ms of a forced expiration
How can we standardize lung volume measurement
When a patient breathes out air cools causing a decrease in volume according to Charles’ law
Air expired drops from body temperature of 37 to temperature in spirometer, therefore gas entering spirometer will be smaller
So to standardize we correct lung function to body temperature, barometric pressure & saturated water vapour
Define Charles’ law
This law states that at constant pressure, the temperature is directly proportional to the volume
As volume increases temperature increases & vice versa
What are the 2 types of spirometer?
Volume displacing spirometer & Flow sensing spirometry
What are the pros & cons of volume displacing spirometers
Pros: accurate, precise, simple to use, provides stable measurements and a hard copy
Cons: not portable, difficult to clean, can leak, flow signal may be noisy & needs regular servicing
What are the pros & cons of flow sensing spirometry
Pros: portable, reliable & inexpensive, easy to clean
Cons: calibration is manufacturer set so cannot be changed, readings can be effected by temperature & condensation, rotary vane is very fragile
Explain the types of flow sensing spirometry
Rotary vane- measures flow as speed of rotation of vane
Ultrasonic- detects flow as changes in speed of ultrasonic speed from source to detector
Pressure difference flow sensor- detects flow as pressure drops across the screen (nylon, acetate). Flow measurement is then integrated into given volume.
Explain the types of volume-displacing spirometry
Define forced expiratory maneuver
forced expiratory maneuverer: a patient breathes out continuously until they cannot no more
Define forced vital capacity
The volume of air that is forcefully expired from your lungs after taking the deepest breath possible
Define FEF
Forced expiratory flow is the maximum flow achievable during a max forced expiratory maneuver when X% of FVC has been exhaled
e.g., FEF at 25%, where 25% of FVC has been exhaled,
when 75% at FEF, 75% of FVC has been exhaled
FEF is generated between 25-75% of the FVC during forced expiratory maneuver
