Post on 12-Jan-2017
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Lung function Tests
Dr. PARTHA PRATIM DEKA
Pulmonary function tests (PFTs)• Pulmonary function testing is a valuable
tool for evaluating the respiratory system• comparing the measured values for
pulmonary function tests obtained on a patient at any particular point with normal values derived from population studies.
• The percentage of predicted normal is used to grade the severity of the abnormality.
Pulmonary Function Tests•Evaluates 1 or more major aspects of the respiratory system
PFTs• Four lung components include : The airways (large and small),
Lung parenchyma (alveoli, interstitium),
Pulmonary vasculature, and The bellows-pump mechanism
PFTs• PFTs can include: simple screening spirometry, Flow Volume Loop Formal lung volume measurement,
Bronchoprovocation testing Diffusing capacity for carbon monoxide, and
Arterial blood gases. Measurement of maximal respiratory pressures
• These studies may collectively be referred to as a complete pulmonary function survey.
Spirometry
• Measurement of the pattern of air movement into and out of the lungs during controlled ventilatory maneuvers.
• Often done as a maximal expiratory maneuver
Importance
• Patients and physicians have inaccurate perceptions of severity of airflow obstruction and/or severity of lung disease by physical exam
• Provides objective evidence in identifying patterns of disease
Spirometry
Simple, office-based
Measures flow, volumes
Volume vs. Time
Can determine:- Forced expiratory volume in one second (FEV1)- Forced vital capacity (FVC)- FEV1/FVC- Forced expiratory flow 25%-75% (FEF25-75)
Spirometry
The most readily available most useful pulmonary function test
It takes ten to 15 minutes carries no risk
Spirometry• Spirometry is the most commonly used lung function
screening study.• should be the clinician's first option• other studies being reserved for specific indications• easily performed• in the ambulatory setting, physician's office, emergency
department, or inpatient setting.
Patient care/preparations• Two choices are available with respect to bronchodilator and
medication use prior to testing. Patients may withhold oral and inhaled bronchodilators to establish baseline lung function and evaluate maximum bronchodilator response, or they may continue taking medication as prescribed. If medications are withheld, a risk of exacerbation of bronchial spasm exists.
Spirometry• The slow vital capacity (SVC) can also be measured with
spirometers collect data for at least 30 seconds when airways obstruction is present, the forced vital capacity
(FVC) is reduced and slow vital capacity (SVC) may be normal
Spirometry• When the slow or forced vital capacity is within the normal
range: No significant restrictive disorder .
No need to measure static lung volumes (residual volume and total lung capacity).
Indications — Diagnosis
Evaluation of signs and symptoms- SOB, exertional dyspnea, chronic cough
Screening at-risk populations
Monitoring pulmonary drug toxicity
Abnormal study- CXR, EKG, ABG, hemoglobin
Preoperative assessment
Indications — Diagnosis
Evaluation of signs and symptoms- SOB, exertional dyspnea, chronic cough
Screening at-risk populations
Monitoring pulmonary drug toxicity
Abnormal study- CXR, EKG, ABG, hemoglobin
Preoperative assessment
Smokers > 45yo(former & current)
Indications — Diagnosis
Evaluation of signs and symptoms- SOB, exertional dyspnea, chronic cough
Screening at-risk populations
Evaluation of occupational symptoms
Monitoring pulmonary drug toxicity Abnormal study
- CXR, EKG, ABG, hemoglobin
Preoperative assessment
Indications — Prognostic
■ Assess severity
■ Follow response to therapy
■ Determine further treatment goals
■ Referral for surgery
■ Disability
Contraindications for spirometry• Relative contraindications for spirometry include hemoptysis
of unknown origin, pneumothorax, unstable angina pectoris, recent myocardial infarction, thoracic aneurysms, abdominal aneurysms, cerebral aneurysms, recent eye surgery (increased intraocular pressure during forced expiration), recent abdominal or thoracic surgical procedures, and patients with a history of syncope associated with forced exhalation
Spirometry• Spirometry requires a voluntary maneuver in which a seated
patient inhales maximally from tidal respiration to total lung capacity and then rapidly exhales to the fullest extent until no further volume is exhaled at residual volume
Spirometry• The maneuver may be performed in a forceful manner to
generate a forced vital capacity (FVC) or in a more relaxed manner to generate a slow vital capacity (SVC).
• In normal persons, the inspiratory vital capacity, the
expiratory SVC, and expiratory FVC are essentially equal. However, in patients with obstructive airways disease, the expiratory SVC is generally higher than the FVC.
Interpretation of spirometry results(1)
•should begin with an assessment of test quality.
to inspect the graphic data (the volume-time curve and the flow-volume loop)
Interpretation of spirometry results(2)•to ascertain whether the study meets certain well-defined acceptability and reproducibility standards
acceptable spirometry (ATS)• 1) minimal hesitation at the start of the forced expiration
(extrapolated volume (EV) <5% of the FVC or 0.15 L, whichever is larger
• Time to PEF is <120 ms (optional until further information is available)
(2) no cough in the first second of forced exhalation,• 3) meets 1 of 3 criteria that define a valid end-of-test
Valid end-of-test• (a) smooth curvilinear rise of the volume-time tracing to a
plateau of at least 1-second duration; (b) if a test fails to exhibit an expiratory plateau, a forced expiratory time (FET) of 15 seconds; or (c) when the patient cannot or should not continue forced exhalation for valid medical reasons.
• If both of these criteria are not met, continue testing until:
Both of the criteria are met with analysis of additional acceptable spirograms or
• A total of eight tests have been performed or • Save a minimum of three best maneuvers
Acceptability Criteria• Good start of test• No coughing• No variable flow• No early termination• Reproducibility
The volume-time tracing • The volume-time tracing is most useful in assessing whether
the end-of-test criteria have been met
Spirometry
Flow-volume loop•the flow-volume loop is most valuable in evaluating the start-of-test criteria.
Flow-Volume Loop
•
Ruppel GL. Manual of Pulmonary Function Testing, 8th ed., Mosby 2003
Repeatability Criteria• After three acceptable spirograms have been obtained, apply
the following tests. Are the two largest FVCs within 0.2 L of each other?
• Are the two largest FEV1s within 0.2 L of each other?• If both of these criteria are met, the test session may be
concluded
Lung Volumes
Lung Volumes
• 4 Volumes• 4 Capacities
• Sum of 2 or more lung volumes
IRV
TV
ERV
RV
IC
FRC
VCTLC
RV
Spirometry
Lung Factors Affecting Spirometry• Mechanical properties • Resistive elements
Mechanical Properties• Compliance
• Describes the stiffness of the lungs• Change in volume over the change in pressure
• Elastic recoil• The tendency of the lung to return to it’s resting state• A lung that is fully stretched has more elastic recoil and thus
larger maximal flows
Resistive Properties• Determined by airway caliber• Affected by
• Lung volume• Bronchial smooth muscles• Airway collapsibility
Factors That Affect Lung Volumes
• Age• Sex• Height• Weight• Race• Disease
Technique• Have patient seated comfortably• Closed-circuit technique
• Place nose clip on• Have patient breathe on mouthpiece• Have patient take a deep breath as fast as possible• Blow out as hard as they can until you tell them to stop
Terminology
• Forced vital capacity (FVC):• Total volume of air that can be
exhaled forcefully from TLC• The majority of FVC can be
exhaled in <3 seconds in normal people, but often is much more prolonged in obstructive diseases
• Measured in liters (L)
FVC
• Interpretation of % predicted:• 80-120% Normal• 70-79% Mild reduction• 50%-69% Moderate reduction• <50% Severe reduction
FVC
Terminology
• Forced expiratory volume in 1 second: (FEV1)• Volume of air forcefully
expired from full inflation (TLC) in the first second
• Measured in liters (L)• Normal people can exhale
more than 75-80% of their FVC in the first second; thus the FEV1/FVC can be utilized to characterize lung disease
FEV1
• Interpretation of % predicted:• >75% Normal• 60%-75% Mild obstruction• 50-59% Moderate obstruction• <49% Severe obstruction
FEV1
FVC
Terminology
• Forced expiratory flow 25-75% (FEF25-75)• Mean forced expiratory flow
during middle half of FVC • Measured in L/sec• May reflect effort independent
expiration and the status of the small airways
• Highly variable• Depends heavily on FVC
FEF25-75
• Interpretation of % predicted:• >60% Normal• 40-60% Mild obstruction• 20-40% Moderate obstruction• <10% Severe obstruction
Flow-Volume Loop
• Illustrates maximum expiratory and inspiratory flow-volume curves
• Useful to help characterize disease states (e.g. obstructive vs. restrictive)
Ruppel GL. Manual of Pulmonary Function Testing, 8th ed., Mosby 2003
Categories of Disease• Obstructive• Restrictive• Mixed
Obstructive Disorders
• Characterized by a limitation of expiratory airflow• Examples: asthma, COPD
• Decreased: FEV1, FEF25-
75, FEV1/FVC ratio (<0.8)• Increased or Normal:
TLC
Spirometry in Obstructive Disease
• Slow rise in upstroke• May not reach plateau
Restrictive Lung Disease
• Characterized by diminished lung volume due to:• change in alteration in lung
parenchyma (interstitial lung disease)
• disease of pleura, chest wall (e.g. scoliosis), or neuromuscular apparatus (e.g. muscular dystrophy)
• Decreased TLC, FVC• Normal or increased: FEV1/FVC ratio
Restrictive Disease
• Rapid upstroke as in normal spirometry
• Plateau volume is low
Large Airway Obstruction
• Characterized by a truncated inspiratory or expiratory loop
Normal Spirometry
Obstructive Pattern ■ Decreased FEV1
■ Decreased FVC
■ Decreased FEV1/FVC
- <70% predicted
■ FEV1 used to follow severity in COPD
Obstructive Lung Disease — Differential Diagnosis
Asthma
COPD - chronic bronchitis
- emphysema
Bronchiectasis
Bronchiolitis
Upper airway obstruction
Restrictive Pattern
Decreased FEV1
Decreased FVC
FEV1/FVC normal or increased
Restrictive Lung Disease —Differential Diagnosis
Pleural
Parenchymal
Chest wall
Neuromuscular
Spirometry Patterns
Bronchodilator Response
Degree to which FEV1 improves with inhaled bronchodilator
Documents reversible airflow obstruction
Significant response if:- FEV1 increases by 12% and >200ml
Request if obstructive pattern on spirometry
Flow Volume Loop
“Spirogram”
Measures forced inspiratory and expiratory flow rate
Augments spirometry results
Indications: evaluation of upper airway obstruction (stridor, unexplained dyspnea)
Flow Volume Loop
Upper Airway Obstruction
Variable intrathoracic obstruction
Variable extrathoracic obstruction
Fixed obstruction
Upper Airway Obstruction
Lung Volumes
Measurement:- helium- nitrogen washout- body plethsmography
Indications: - Diagnose restrictive component
- Differentiate chronic bronchitis from emphysema
Pulmonary Function Testing
The Basics of Interpretation
Lung Volumes – Patterns
Obstructive
- TLC > 120% predicted- RV > 120% predicted
Restrictive
- TLC < 80% predicted- RV < 80% predicted
Diffusing Capacity
Diffusing capacity of lungs for CO
Measures ability of lungs to transport inhaled gas from alveoli to pulmonary capillaries
Depends on:- alveolar—capillary membrane- hemoglobin concentration- cardiac output
Diffusing Capacity
Decreased DLCO (<80% predicted)
Obstructive lung disease
Parenchymal disease
Pulmonary vascular disease
Anemia
Increased DLCO (>120-140% predicted)
Asthma (or normal)
Pulmonary hemorrhage
Polycythemia
Left to right shunt
DLCO — Indications
Differentiate asthma from emphysema
Evaluation and severity of restrictive lung disease
Early stages of pulmonary hypertension
Expensive!
Bronchoprovocation
Useful for diagnosis of asthma in the setting of normal pulmonary function tests
Common agents:
- Methacholine, Histamine, others
Diagnostic if: ≥20% decrease in FEV1
Continued…
↓SYMPTOMS
PFTs
OBSTRUCTION?
YES NO
TREATBRONCHOPROVOCATION
Obstruction?TREAT
No Obstruction? Other Diagnosis
↓
↓
↓ ↓
↓
↓ ↓
PFT Interpretation Strategy
What is the clinical question?
What is “normal”?
Did the test meet American Thoracic Society (ATS) criteria?
Don’t forget (or ignore) the flow volume loop!
Obstructive Pattern — Evaluation
Spirometry FEV1, FVC: decreased FEV1/FVC: decreased (<70% predicted)
FV Loop “scooped”
Lung Volumes TLC, RV: increased
Bronchodilator responsiveness
Restrictive Pattern – Evaluation
Spirometry FVC, FEV1: decreased FEV1/FVC: normal or increased
FV Loop “witch’s hat”
DLCO decreased
Lung Volumes TLC, RV: decreased
Muscle pressures may be important
PFT Patterns
Emphysema
FEV1/FVC <70%
“Scooped” FV curve
TLC increased
Increased compliance
DLCO decreased
Chronic Bronchitis
FEV1/FVC <70%
“Scooped” FV curve
TLC normal
Normal compliance
DLCO usually normal
PFT Patterns
Asthma
FEV1/FVC normal or decreased
DLCO normal or increased
But PFTs may be normal bronchoprovocation
Thank you