lung function tests

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