Pulmonary Function Test Flashcards
What is Pulmonary Function Test
-Pulmonary Function test are a group of tests that measure inspiratory and expiratory airflow rates and lung volumes
-Three areas of PFTs
-Pulmonary function test
-Testing: Method and procedures -Evaluations: Interpretation and assessment
Indications for PFT
-PFT testing is indicated any time that an assessment of the respiratory system is required or desired
-Specifically, PFTs will evaluate -Evaluate the cause of pulmonary symptoms such as dyspnea cough, wheezing, sputum, exercise intolerance, and chest pain -Presence of lung disease -Extent of abnormal lung function -Amount of disability due to dysfunction -Progression of the disease -Nature of the dysfunction or type of disease -Course of therapy for the dysfunction -Response to therapy
Pulmonary Function Equipment • Spirometers
- Several types of spirometers are used to measure volumes and flow rates
• Dry-rolling seal (horizontal piston)
measures volume and time
• Water-seal (Collins, Stead-Wells)
- measures volume and time
- Water-sealed spirometers (Collins) still remain the most accurate and are the best machine to use to check the accuracy of other PFT equipment
Pulmonary Function Equipment
- Recording Devices
• Kymograph
- Rotating drum on which movement is recorded on graph paper
- Plots volume (y-axis) against time (x-axis)
- Inspiration will cause an upward deflection of the pen and expiration will cause a downward deflection of the pen
Pulmonary Function Equipment
- Recording Devices
• X-Y Recorder
- Plots volume (x-axis) against flow (y-axis)
- Advantage over kymograph - allows for recording of flow-volume loops
Pulmonary Function Equipment
• Pneumotachometers (Flow)
- Turbine device (Wright respirometer) - measures flow ***
• Rotating vane with gears • Flow causes vanes to move and then registers a volume on the faceplate • Measures flows 3-300 L/min. ********* - Flowrates above 300 L/min may break the vanes - Flowrates less than 3 L/min will give inaccurate readings - Pressure Differential (Fleisch)
• Measures flow • Commonly found in the body box
- Minute Ventilation (Ve) ****
• Volume of gas inhaled and exhaled during 1 minute
- Have the patient sit comfortably and breathe (resting) through the mouthpiece with nose clips in place
- Count number of exhalations for 1 minute
- Measured in LPM
- Vital Capacity (VC) ***
• Maximum volume of air that can be exhaled after a maximal inspiration
- Have the patient breathe evenly through mouthpiece with nose clips on - Instruct patient to take maximal inspiration - Instruct patient to breathe out slowly but completely - Repeat maneuver to get 3 consistent results
- Tidal Volume (Vt) **
• Amount of air moved into or out of a resting patient’s lungs with each normal breath
• To achieve Vt, have the patient perform the minute ventilation maneuver, noting the patient’s respiratory rate
- Divide minute volume by number of respirations to calculate tidal volume to
• Peak Flow Meters ***
- Device that measures how well air moves out of the lungs
- Patient exhales forcefully through a device, which incorporates a resistor and a moveable indicator
- Accuracy is affected by patient effort
- Moisture and debris can affect accuracy
- Maneuver should be repeated 3 times for consistent results
- Zone System
• Green Zone ****
≥ 80% of personal best
- Good control
- No symptoms present
- Take medicine as usual
- Zone System
• Yellow Zone ***
(50 - 79% of personal best)
- Caution
- Take an inhaled short-acting beta agonist
- If still in yellow, talk to physician about changing daily meds
- Zone System
• Red Zone ***
<50% of personal best
- Medical alert
- Take short-acting beta agonist immediately
- Call physician or go straight to the ER
• Maximal Inspiratory Pressure (MIP)/Negative
Inspiratory Force (NIF ***)
- The amount of negative pressure a patient is able to generate when trying to inhale
- Indicator of muscle strength
- Used to monitor and assess the readiness to wean in ventilator patients
• Also used to monitor and assess the degree of respiratory muscle impairment in neuromuscular disease
- The patient exhales then takes a breath in as quickly and hard as possible
- Repeat maneuver 3 times
- Measurement of < -20 m20 indicates inspiratory muscle weakness
• Maximum Expiratory Pressure (MEP) ***
- Helpful in evaluating a patient’s ability to maintain an airway and clear secretions (their ability to cough effectively)
- Patient inhales to total lung capacity then blasts out air as quickly and hard as possible
- Repeat maneuver 3 times
- Measurements of <+40 cmH2o indicates poor ability to clear airway secretions
• Calibration ***
- All equipment must meet standards
- Volume calibration and leak tests are done by using a large volume syringe (“3.0 Liter Super
Syringe”)
- Flow calibration is done using a rotometer
Method and Procedures
- Height
• Height is the most important factor influencing lung *******
size and predicted values
- Generally, a taller person will have larger predicted lung volumes and flow rates
- For patients with spinal deformities (kyphoscoliosis) arm span is measured to derive the height…measure from fingertip to fingertip
Testing: Method and Procedures
Weight
• Weight is relatively unimportant in determining lung volumes and flow rates **
- As a person gains weight, lung volumes and flow rates do not change until the person become very obese
Testing: Method and Procedures
- Gender *****
• When individuals are matched for height and weight, males normally have larger lung volume than females
Testing: Method and Procedures
- Age ***
• Most people reach their maximum lung function in their 20s and 30s
• Even healthy nonsmokers without exposure to air pollution gradually lose lung function starting in late 30s to early 40s
Testing: Method and Procedures
- Race **
• African-Americans, Asians, and East Indians generally have approximately 12% smaller lung volumes than Caucasians of the same age, gender, and height
• Hispanics and American Indians have intermediate lung volumes that generally do not need correction
Testing: Method and Procedures
- Other Considerations
• Most of pulmonary functions maneuvers are patient effort dependent
• Another consideration is the ability of the respiratory therapist to teach/coach the patient and assess the patient’s effort
- Patient Preparation
• Completing necessary paperwork
• Explaining purpose of the test
• Determine any contraindications
• Obtaining patient’s age, height, weight
• Positioning patient
• Positioning patient
- Patient should have on loose fitting clothes
- Dentures left in place unless they are loose
- Patient should be sitting straight up with feet flat on the floor
• Vital Capacity (VC, SVC)
- Patient is instructed to take a maximal inspiration followed by a maximal exhalation without force
- Typical value = 4800 ml or 4.8 liters **
- The Slow Vital Capacity (SVC) will provide the important Volumes used to measure Restrictive Disease
- The following Volumes and Capacities will be measured
• Vt
normal breathing
- The following Volumes and Capacities will be measured
• IRV
inspiratory reserve volume - largest volume of gas that can be inspired above a normal tidal volume
- IRV = IC - Vt or IRV = VC - ERV - Vt
- The following Volumes and Capacities will be measured
• ERV
- expiratory reserve volume - largest volume of gas that can be expired from a resting end-expiratory level
- ERV = VC - IC or ERV = FRC - RV
- The following Volumes and Capacities will be measured
• VC
- vital capacity (IRV + Vt + ERV)
- Decreased volumes indicate Restrictive Disease
- Decreased Vital Capacity is the BEST indicator of Restrictive lung disease
• Forced Vital Capacity (FVC)
- The volume that can be expired as forcefully and as rapidly as possible after a maximum inspiration
- The patient is instructed to take a maximal inspiration followed by a maximal expiration as forcefully and rapidly as possible
- The FVC maneuver/procedure will provide the important Flow Rates used to measure Obstructive Disease ***
- The following values can be measured
• FEV, - Forced Expiratory Volume in 1 second ***
• FEF 200-1200 - Forced Expiratory Flow 200-1200 ***
• FEF 25-75 - Forced Expiratory Flow 25-75 ***
• PEFR - Peak Expiratory Flow Rate **
• FVC - Forced Vital Capacity ***
- Forced Expiratory Volumes (FEV 0.5, 1.0, 2.0, 3.0) ***
• Volume of gas expired over a given time interval (0.5 seconds, 1.0 second, 2.0 seconds, or 3.0 seconds)
• Most individuals can exhale all of their air in about 2 seconds
• The FEV, is generally the best flowrate to monitor for obstructive disease
- The following Volumes and Capacities will be measured
• IC
- inspiratory capacity - largest volume that can be inspired from resting end-expiration
- IC = IRV + Vt or IC = VC - ERV or IC = TLC - FRC
- FEV/ FVC ratio
• FEV for a given interval expressed as a % of FVC
• Values of FEV/FVC x 100 = FEV/FVC ratio
Measurement Minimum Acceptable
FEV 0.5 / FVC
60%
FEV 1.0 / FVC
70%
FEV 2.0 / FVC
94%
FEV 3.0 / FVC
97%
Decreased FEV1/FVC is the BEST indicator of
OBSTRUCTIVE DISEASE
• Decreased values = obstructive disease
• Normal values = not obstructive disease but may still be restrictive
• If the FEV1 is decreased but the FEV1/FVC ratio is normal, then the patient is restrictive only
- Forced Expiratory Flow 200 - 1200 (FEF 200-1200)
• Average flow during the first 1000 mL after 200 mL expired
• Decreased values are associated with large airway obstruction
• Measures airflow within the large airways
- Forced Expiratory Flow 25% - 75% (FEF 25-75)
• Average flow rate during the mid portion of the FVC
• Decreased in the early stages of obstructive disease
• Measures airflow within the small airways
- Peak Expiratory Flow Rate
• Effort dependent
• May appear normal in abnormal patients
• Sometimes used to evaluate asthmatic patients, pre & post bronchodilation
- FVC - this is NOT a FLOW, it is a Volume and should be equal to the SVC
• May be used as a substitute for the SVC
• If the FVC is smaller than the SVC, indicates obstructive disease (air trapping)
• If the FVC cannot be completed in 3 seconds, indicates obstruction
• 80% or less indicates RESTRICTEVE disorder
• Maximum Voluntary Ventilation
- The largest volume and rate that can be breathed per minute by voluntary effort
- The patient is told to breathe in and out as fast as possible until told to stop
- Performed for 12 - 15 seconds
- Measures the muscular mechanics of breathing
- Decreased = obstructive disease, increased airway resistance, muscle weakness, decreased compliance, and poor patient effort
• Pre and Post Bronchodilator PFT Testing
- Used to measure the reversibility of an obstructive pattern
- Minimum increase of 12% in the FEV1 is considered to be a reversible condition
- All bronchodilator therapy should be held 8 hours prior to testing
- Wait 15 - 20 minutes before performing the post-bronchodilator test results after administering most bronchodilators
• Flow-Volume Loops
- Displays the volumes and flow rates of the FVC
- The flow rates are measured directly on the vertical axis
- Expiratory flows are above the base line… inspiration is below the line
- Volume is measured directly on the horizontal axis
- The shape of the flow-volume loop is diagnostic
• Restrictive = skinny and tall loop
• Obstructive = short and wide loop
Evaluation of Pulmonary Function
• Predicted Normal Values
- All measured values are compared with the predicted normal values for that individual
- The relationship is expressed as a percent
• Actual value / predicted value = % of predicted
- Predicted values are primarily based on
• Age, height, sex/gender
• Classification of Interpretation
- 80 - 100% of predicted = normal PFT
- 60 - 79% of predicted = mild disorder
- 40 - 59% of predicted = moderate disorder
- < 40% of predicted = severe disorder
• Remember: Patients can be any of the following
- Restrictive only…decreased volumes (VC or FVC)
- Obstructive only…decreased flows (FEV1, FEV1/FVC)
- Both Obstructive and Restrictive (decreased flow and decreased volumes)
- Neither Obstructive or Restrictive (normal volumes and flows)
• Obstructive and Restrictive Disease
- Decreased Flows indicate obstructive disease
• (CBABE)…Cystic Fibrosis, Bronchitis, Asthma, Bronchiectasis, Emphysema
- Decreased volumes indicate restrictive disease
• Inflammatory diseases, cardiac disease,
neurological/neuromuscular diseases, pleural disease, thoracic, deformities, post-surgical patients, fibrotic diseases, obesity, and anything you can think of!!
• The following results are obtained from a 58 year old woman
Predicted Observed % Predicted
FVC (L)
5.10 3.30 64.7%
FEV1 (L)
3.83 3.18 83.0%
FEV1/FVC (%)
75% 96%
• Interpretation: The volume measurement (FVC) is decreased (65%) so there is a mild restrictive problem. The flows (FEV1) are normal (83% of predicted) so there is no obstructive problem.
Plethysmograph (Body Box)
• Equipment:
• Based on Boyle’s Law that pressure and volume vary inversely if temperature is constant.
- Measures TGV (thoracic gas volume) which is the same as FRC (functional residual capacity) …FRC is directly measured…RV and TLC is also measured
- Measures airway resistance (Raw) which is the difference in pressure between the mouth (atmospheric) and the alveoli
Plethysmograph (Body Box)
• Technique:
- Patient breathes normally for several breaths
- At end-expiration, the shutter closes and the patient “Pants” …at this point, no airflow is present
- A pressure transducer measures the pressure at the mouth, which is equal to alveolar pressure when there is no airflow…so, P mouth = P alveolar
- A second pressure transducer measures the pressure in the box, which is equal to the volume of gas in the thorax..so, P box = TGV
- Significance…measures gases that are trapped and otherwise excluded from the FRC measured by other procedures
Plethysmograph (Body Box)
• Testing and Procedures:
• Measuring Airway Resistance (Raw)
- Raw is the ratio of alveolar pressure (P) to Airflow (V)
- Patient pants with the shutter open and the flow is plotted against box pressure that produces an S-shaped curve on the oscilloscope
- At the end of a normal expiration, the shutter momentarily closes and a second curve is produced that plots mouth pressure against box pressure
- Raw is then calculated from these two curves
Plethysmograph (Body Box)
• FRC Measurement (RV, TLC)
- He dilution - (Closed Method) a known % of He is diluted by the patient’s FRC. The change in the He is used to determine the FRC
- N2 wash out - (Open Method) the FRC is washed out of the lung by having the patient inspire 100% 02 to replace the N2 from the FRC. The amount of Na removed is used to calculate the FRC
Plethysmograph (Body Box)
• Gas Diffusion (DLCO)
- DLCO - Carbon monoxide diffusion capacity
• Measures all the factors that affect the diffusion of a gas across the A-C membrane
- DLCO - Single breath
• Patient inhales a vital capacity of gas containing a known amount of CO, He, and air
- They hold their breath 10 seconds, then exhales the gas forcefully into the machine where the gas concentrations are analyzed
• The amount of CO that diffuses across the A-C membrane is equal to the total amount of CO used, minus the amount returned plus the amount remaining in the residual volume
- Normal DLCO
25 mL CO/min/mmHg
- Factors that affect the DLCO
• Hb, Hct, PCO2, body position, breath holding time, blood volume
- Decreased DLCO (decreased diffusion) occurs in:
• Pulmonary fibrosis
• Sarcoidosis
• ARDS
• Edema
• Emphysema (the only obstructive disease)
• The advantage of the body box is that it will more accurately measure FRC in patients with obstructive lung disease
• Disadvantages of the body box include:
- Patient may be unable to enter box due to physical limitations
- Claustrophobia prohibits patient from entering box
- Patient may be unable to pant acceptably
- The following values can be measured
• FEV, - Forced Expiratory Volume in 1 second
• FEF 200-1200 - Forced Expiratory Flow 200-1200
• FEF 25-75 - Forced Expiratory Flow 25-75
• PEFR - Peak Expiratory Flow Rate
• FVC - Forced Vital Capacity
• Determine any contraindications
- Recent use of bronchodilator (hold for a minimum of 4 hours…preferably 8 hours) ***
- Current or recurrent illness
- Smoking (recording patients pack years)
» NOTE: important to note whether patient still smokes
» NOTE: avoid smoking for a minimum of 1 hour
- Heavy meal (2 hours prior to testing)
- Forced Expiratory Volumes (FEV 0.5, 1.0, 2.0, 3.0)
• Volume of gas expired over a given time interval (0.5 seconds, 1.0 second, 2.0 seconds, or 3.0 seconds)
• Most individuals can exhale all of their air in about 2 seconds
• The FEV, is generally the best flowrate to monitor for obstructive disease
