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The second major factor that influences gas flow is...
- The resistance to airflow
- The caliber of the conducting airway plays the major role
Airflow is determined by the...
Driving pressure (Pel) and the resistance of the airways upstream (Rus) of the EPP
Volume displacement spirometers
- Collect exhaled air
- Older ans bulker
- Gold standard
- Very accurate for measuring exhaled volume
- Easy to use
- Can develope leaks
Examples of volume displacement spirometers!
- Water seal – “gold standard”
- Rolling seal
Flow sensing spirometers
- Measure flow, then calculate volume (integration)
- Require computerization
- Smaller and portable
- Currently these are the most common types of spirometers found in laboratories
- Frequent and careful calibration checks required
- Moisture and secretions concerns for some devices
Examples of Flow sensing spirometers!
- Heated-wire anemometer
- Every day of use
- Use 3-liter calibration syringe
- Inject at different speeds
- Very slow to very fast to assess linearity
- Leak testing of volume-displacement spirometers
- Calibration check limit = ± 3.5%
- Documentation of calibration checks
If not leaks are present...
- The volume on the computer should equal the syringe volume within +- 3.5%
- 2.90 to 3.11 liters
If the spirometer measures FVC, it should be able to accumulate...
- Volume for at least 15 seconds and measure volumes of at least 8 liters
- Should be able to measure flow rates between 0 and 14 liters/sec
Patient preparation for PFT
- Scheduling: inform patient about medications, smoking, etc
- Determining age, height, weight
- Age on day of test
- Height with accurate device and no shoes
- Explain the test
- Determine if contraindications exist
- Postponement is sometimes necessary
Contraindications for spirometry!
- Recent use of a bronchodilator
- A current or recent viral infection within 2 to 3 weeks
- A serious illness
- Smoking or a heavy meal within a hour of testing
The three main parts to evaluate when a patient performs the FVC maneuver!
- Rapid and maximal inspiration
- Blast out hard and fast
- Continued and complete exhalation
There are four main within maneuver acceptability criteria!
- Good start of test
- No cought during the first second
- No variable flow
- No early termination of exhalation
- Obtain at least 3 acceptable maneuvers
An unsatisfactory start is characterized by...
- Excessive hesitation
- The extrapolated volume may be greater than 5% of the FVC or 0.150 liter, whichever is greater
How to determine if the patient exhaled long enough!
- The patient should not or canot continue further exhalation
- The volume time spirogram shows a plateau or no change in volume for at least 1 second
- The patient has tried to exhale for at least 6 seconds
Between maneuver repeatability for spirometry
- Assess repeatability after at least 3 acceptable maneuvers have been obtained
- Two largest FVC and FEV1 values from acceptable maneuvers should agree within 0.150 L
Hazards of spirometry
- Decreasing flows can occur with repeated efforts – can induce bronchospasm
- Syncope, dizziness, numbness in extremeties
- Decreased cerebral blood flow
- Decrease cardiac output
Comparision of the FEF50%/FIF50% on flow volume loop
- May help determine the site of obstruction
- Normal lungs FEF50%/FIF50% = 1.0 or slightly less
Fixed large airway obstruction
- Equally reduced flows at 50% of inspiratory & expiratory VC
- Appears rectangular
Variable extrathoracic obstruction on flow volume loop
- Decreased inspiratory flow rates
- FEF50%/FIF50% >1- increased
- Flattened inspiratory loop
- Example: VCD
Variable intrathoracic obstruction on flow volume loop
- Decreased FEV
- Scooped out apperance
- expiratory flow remains constant until small airways→ “squared-off” expiratory limb
- FEF50%/FIF50% <1- decreased
F-V loop seen with OSA
“Sawtooth” pattern on inspiratory & expiratory limbs of – “redundant tissue of the upper airway”
Reporting results of flow-volume loop
- Largest FVC and the largest FEV1 should be reported, even if the two values come from different maneuvers
- Other measurements (e.g., FEF25–75% or instantaneous flows) should be obtained from the single best test curve (largest sum of FVC + FEV1)
- Include comments about quality of testing and patient cooperation, effort, and technique
Airflow limitation or obstruction
- Reduced FVC and FEV1, and FEV1/FVC ratio
- GOLD standard FEV1/FVC < 70% = obstruction
Reduced FVC and FEV1, but FEV1/FVC ratio is normal or elevated
- 12% and 0.200 L increase in FEV1 or FVC is considered meaningful
- FEV1/FVC ratio should not be used to measure response to a bronchodilator
- Wait at least 10 to 15 minutes before repeating pulmonary test
Testing technique recommended for Maximun voluntary ventilation!
- Tidal volume should approximate 50% of the VC
- Breathing frequency of approximately 90 breaths/min
- Obtain at least two MVV maneuvers, with a repeatability goal of ± 10%.
- •If variability is > than 20%, obtain additional maneuvers
- •Report highest acceptable MVV and MVV rate
A calculation or approximation of MVV can be made using the following formula:
MVV = FEV1 x 40
- Three test should be permormed
- Two highest SVC values should agree within 0.150 L
- Largest SVC from acceptable maneuvers should be reported
SVC vs FVC
- In healthy individuals their is little difference between SVC and FVC
- Patients with airflow obstruction, the FVC causes gas trapping, and thus is smaller than SVC
- Restrictive disease will decrease SVC
Three methods to measure FRC
- Body plethysmograph or body box
- Helium dilution
- Nitrogen washout
- In healthy subjects and individuals with pure restrictive lung disease, these 3 methods show good agreement
Body plethysmograph or body box
- includes measurement of those air spaces not measured by gas dilution-washout methods, and thus is the method of choice in patients with airflow obstruction.
- Considered the most accurate of the three methods for measuring FRC because it measures the total gas volume in the thoracic cage or thoracic gas volume
Testing technique for body box
- Obtain at least 3 to 5 acceptable panting maneuvers
- FRCpleth values should agree with 5%
- Highest minus lowest divided by mean < 5%
- Mean FRCpleth value from acceptable and repeatable maneuvers should be reported
In healthy individuals the FRC is approximately...
40% to 50% of the TLC
In healthy individuals RV is approximately...
25% to 30% of the TLC
The measurement of DL,CO can be performed using three general techniques
- Steady state- most common
- Single breath
CO is more suitable to measure diffusing capacity than other gases because
- It has a great affinity for Hb (210 times that of O2)
- It is soluble in blood
- Its concentration in venous blood is insignificant
Conditions that can lower DL,CO value
- Respiratory muscle weakness or deformity preventing maximal inflation
- Reduced Hb
- Pulmonary emboli
- Increased CO or inspired O2 concentration
- Lung resection
- Interstitial lung disease
Conditions that can increase DL,CO value
- Increased Hb (polycythemia)
- Decreased intrathoracic pressure (resistance breathing)
- Supine position
- Left-to-right intracardiac shunts
- Left heart failure
Test Gas for DL,CO
- One of three tracer gases is used
- Helium (He)
- Neon (Ne)
- Methane (CH4)
- CO concentration is 0.3%
- Balance air (O2 and N2)
Washout volume for DL, CO
- The washout volume should be 0.75 to 1.00 liter.
- Washout volume is volume of gas that must be expired and discarded to clear anatomic and mechanical dead space before the alveolar sample is collected
- If the alveolar sample is contaminated with dead space gas, the resulting DL,CO will likely be underestimated.
Number of maneuvers and repeatability for DL, CO!
- Perform at least two acceptable maneuvers that agree within ± 10% or 3 mL/min/mmHg, whichever is larger
- More than five maneuvers is not recommended
The greater the elastic recoil...
The lower the Raw
Raw is increased, when there is...
A loss of elastic recoil
Raw depends on several factors
- Size of airways
- Number of airways
- Elastic recoil
In healthy individuals, the decreasing size of airways distal to the trachea is more than compensated for...
by the increased number of airways
During quiet breathing the majority of Raw is in...
the trachea and large airways
The length of time short acting beta agonist should be withheld before PFT!
4 to 6 hours
The length of time long acting beta agonist should be witheld before PFT!
12 to 24 hours
Provides information about the strength of the diaphragm, intercostals, and inspiratory accessory muscles
This test provides information about the strength of the abdominal muscles, intercostals, and other expiratory accessory muscles
Determine the degree of respiratory muscle weakness in patients with:
- Neuromuscular disease (e.g., myasthenia gravis, Guillain-Barré syndrome, amyotrophic lateral sclerosis, stroke)
- Obstructive lung disease causing hyperinflation, and unexplained dyspnea
Predicted MIP value in healthy men aged 20 to 54 years
-120 +- 40
Predicted MIP value in healthy women aged 20 to 54 years
Predicted MEP value in healthy men aged 20 to 54 years
Predicted MEP value in healthy women aged 20 to 54 years
To convert volumes measured at ATPS to volumes at BTPS, a factor must be applied!
VBTPS= VATPS X factor
How to determine patient effort in a spirometry and FVC test!
- PEFR or FEF max
- Has a sharp point or peak with good effort
- Rounded pattern with poor effort
TV + IRV
Total lung capacity
IRV + TV + ERV + RV
TV + IRV + ERV
The He dilution and N2 washout methods underestimate...
the true FRC in patients with airflow obstruction.
If there is a segnafiance difference in the FRC inthe body box and the gas dilution method then...
airflow obstructing (air trapping)
Helium dilution method
- The patient should continue to breathe on mouthpiece until equilibration is reached
- Equilibration is by a plateau in the He concentration (i.e., the change in He concentration is less than 0.02% over 30 seconds)
The technique for helium dilution!
- Method involves diluting He, an inert gas, in the lungs by rebreathing the gas in a closed system over a short time (usually 2 to 10 minutes).
- Measures only the lung volume in communication with the mouth.
The ATS technique recommendations for DL, CO
- 85% of the inspired volume should be inspired within 4 deconds
- The breath hold must last 8 to 12 seconds
- The expiratory time should be less than 4 seconds
Testing technique for MIP!
- Have patient attach to mouthpiece and apply nose clip properly
- Instruct the patient to blow out slowly to RV, and then inhale against the occluded valve with as much force as possible while keeping the lips sealed tightly around the mouthpiece.
- Vigorously coach the patient to suck in hard Maximum pressure should be maintained for at least 1 second
Testing technique for MEP
- Have patient attach to mouthpiece and apply nose clip properly
- Instruct the patient to take a big, deep breath and then exhale against the occluded valve with as much force as possible while keeping the lips sealed tightly around the mouthpiece.
- Vigorously coach the patient to blow out hard.
- Watch the patient carefully to assure there are no leaks
Repeatibility of MIP and MEP!
Obtain at least 3 maneuvers, and the 2 highest values should agree within 10%
What is filtered from the gas sample that we analyze?
How is alveolar pressured measured in the body box?
- Measured at the mouth when panting against a closed shutter
- gas volume can then be measured by applying Boyle's law
A very low defusion usually below 50% of predicted is usually associated with what?