Pulmonary Function Testing

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Pulmonary Function Testing
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PFTs Defined

• PFT is a general term describing a broad area of
  testing to assess a patients ability to
  effectively ventilate their lungs
• Involves having patients perform certain insp.
  and exp. maneuvers to measure lung volumes and
  capacities, flowrates, diffusion capacities, and
  distribution of ventilation

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Indications for PFTs

• Screen for pulmonary disease - can detect
  functional or mechanical lung change caused by
  disease in general population and high-risk
  groups
• Evaluation of surgical risk - ID those at
  increased risk of pulm. complications after
  surgery
• Assessment of disease progression - can also
  tell if disease is reversible

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Indications (contd)

• Assist in the determination of pulmonary
  disability - determine degree of disability
  caused by occupational lung diseases
• To modify the therapeutic approach to patient care

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Contraindications of PFTs

• Patient with poor coordination or lack of ability
• Patient with sever dyspnea
• Very old or very young patient
• Those who cannot follow specific instructions
• Patients with contagious diseases, i.e., Tb
• Patients with aneurysms, hernias, pulm. emboli,
  or arrhythmias

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Lung Volumes

• Vt vol. of gas inspired or expired during
  normal resp.
• RV (residual volume) vol. of gas remaining in
  the lung after a max. expir.
• IRV (inspir. reserve vol.) the max. vol. that
  can be inspired after a normal insp.
• ERV (exp. reserve vol.) the max. vol. exhaled
  after a normal expiration

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Lung Capacities

• FRC (functional residual capacity) the total
  amt. of vol. in lungs after a normal expiration
  (ERV RV)
• IC (insp. capacity) max. amt. of gas that can
  be inspired after a normal expiration (Vt IRV)
• VC (vital capacity) max. amt. of gas exhaled
  after max. insp. (VtIRVERV)
• TLC (total lung cap.) VtIRVERVRV

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PFT Abbreviations

• FVC (forced vital capacity)
• FIVC (forced insp. vital capacity)
• FEVt (forced exp. vol., timed) i.e. FEV1
• FEV1/FVC
• FEFx (forced exp. flow related to some part of
  the FVC curve) i.e. FEF200-1200
• FEF75 forced exp. flow at the point when 75 of
  FVC is exhaled

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PFT abbrev, (contd)

• FEF 25-75 mean forced exp. flow during the
  middle half of FVC
• PEFR
• MVV - equals FEV1 x 35
• DLCO
• N2WO

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Spirometry and Pulmonary Mechanics Tests

• FVC - vol. measured must be corrected to
  BTPS - test validity depends on subjects
  effort and cooperation - a decreased FVC
  can be caused by obstruction or
  restriction - in patients without obstruction,
  FVC and SVC should be within 5 of each other

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Spirometry (contd)

• FEVt - FEV1 is most widely used - must
  be corrected to BTPS - usually expressed as a
  ratio, i.e., FEVt/ FVC or FEVt - normal
  FEV1 75-85 - see decreased FEVt in
  obstruction and normal or supranormal in
  restriction

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Criteria for accepting FVC, FEV

• Tracing should show at least 6 seconds of forced
  effort and an obvious plateau with no volume
  change for at least 2 seconds
• If maneuver shows a slow start, must
  back-extrapolate. If back-extrapol. is gt 5 of
  FVC or 100 ml (whichever is greater), must
  repeat test
• Must do 3 maneuvers and 2 largest should be
  within 5 or 100 ml of each other

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FEF 200 - 1200

• The average flowrate for the liter of gas expired
  after the first 200 ml during an FVC maneuver
• The 1st 200 ml is disregarded because it is
  expired at a slower rate due to inertia of the
  lung-thorax system and due to some types of
  metering systems
• Decreased values indicate a mechanical problem
  see greater decrease in obstruct.

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FEF 200 - 1200 (contd)

• A good index of airflow characteristics of the
  larger airways
• See decrease with age is lower in females
• Normally see 6 -7 l/sec. for healthy young male,
  in obstruction can be as lowas 1 l/sec

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FEF 25 - 75

• Is the avg. flowrate during middle half of an
  FEV, see 4.7 l/sec in healthy young male
• Normally slower than FEF 200-1200
• Is indicative of the status of small - medium
  sized airways
• Decreased flowrates are common in the early
  stages of obstr. disease
• Test depends on voluntary effort, but is more
  reproducible than FEF 200-1200

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Peak Flow (PEFR)

• Max. flow rate attainable at any time during an
  FEV
• Normal value in healthy young male 10 l/sec
• PEFR are of limited value because patients with
  obstructive disease may develop an initially high
  flowrate before airway closing occurs

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Flow - Volume Curves

• Is the graphic analysis of the flow generated
  during an FEV maneuver followed by an FIV
  maneuver, versus the volume change
• The flow at 50 of the VC is commonly reported as
  the Vmax 50 - in a normal pt. flow decreases
  linearly with volume over most of the VC range
  giving a straight line appearance, in obstruction
  flow is decreased at lower lung volumes giving a
  scooped-out appearance

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Flow - volume curves (contd)

• Decreases in Vmax50 correlate well with FEF
  25-75 in obstructive lung disease
• Obstruction of the upper airway, trachea, and
  mainstem bronchi show characteristic limitations
  to exp. flow and insp. flow and the F-V loop is
  useful in dx. these lesions
• See shift to the left with obstruction and
  shift to the right with restriction

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MVV

• Is the largest volume that can be breathed per
  min. by voluntary effort
• Must correct to BTPS
• Measures the status of the resp. muscles, the
  compliance of the lung-thorax system, and the
  resistance offered by the airways and tissues
• FEV1 x 35 will indicate good pt. effort
• Decreased in obstruct., normal in restrict.

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MVV (contd)

• The volume-time tracing should show a continuous,
  rhythmic effort for at least 12 seconds
• At least two acceptable maneuvers should be
  performed and not differ by more than 10

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PFT Equipment

• Water-sealed Spirometer - consists of a
  thin-walled lightweight cylindrical bell
  suspended in a container of H2O - used to
  measure lung vol. capacities, diffusion cap.,
  and flow measurements
• Dry rolling-seal spirometer - flexible seal
  attached to a piston which is displaced by pts.
  inspir. and expir. - same tests as water-seal

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Wedge Spirometer

• Uses an expandable bellows to collect exhaled
  vol. and a graph to display vol. vs. time
• Measure VC, flowrates, and MVV

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Pneumotachometers

• A flow sensing device that integrates flow
  signals to obtain a volume measurement
• Types include pressure-drop pneumotach (Fleish),
  temperature-drop pneumotach, and ultrasonic flow
  pneumotach

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Body Box (plethysmograph)

• Large airtight box in which patient sits
• Airway pressure changes and box pressure and
  volume changes are measured
• Uses Boyles law to derive lung volumes
• Used to measure FRC, Raw, Gaw