Pulmonary Function Testing

The Basics of Interpretation

Anatomy

• Lungs comprised of – Airways– Alveoli

http://www.aduk.org.uk/gfx/lungs.jpg

Weibel ER: Morphometry of the Human Lung. Berlin and New York: Springer-Verlag, 1963

The Airways

• Conducting zone: no gas exchange occurs

– Anatomic dead space

• Transitional zone: alveoli appear, but are not great in number

• Respiratory zone: contain the alveolar sacs

The Alveoli

• Approximately 300 million alveoli

• 1/3 mm diameter• Total surface area if

they were complete spheres 85 sq. meters (size of a tennis court)

Murray & Nadel: Textbook of Respiratory Medicine, 3rd ed., Copyright © 2000 W. B. Saunders Company

Pulmonary function test :Group of procedures that measure the function of the

lungs

1. Spirometry

2. Lung volumes

3. Gas transfer

4. Bronchial chalenge

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

Spirometry

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)

What is a spirometry ??Spirometry is a measure of airflow and

lung volumes during a forced expiratory

maneuver from full inspiration

1. Volume Time Graph 2. Flow-volume loops

Lung Volumes

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

Spirometry

Volume Time Graph The volume is plotted against the time, it displays

the expiration.

1. FVC

2. FEV1

3. FEV1/FVC

4. FEF25%

5. FEF75%

Forced Vital Capacity (FVC)

The total amount of air expired as quickly as possible after taking the deepest possible breath.

FEV1 :

Volume of air which can be forcibly exhaled from the lungs in the first second of a forced expiratory maneuver.

FEV1/FVC

Ratio of FEV1 to FVC :

It indicates what percentage of the total FVC was expelled from the lungs during the first second of forced exhalation

This value is critically important in the diagnosis of obstructive and restrictive diseases

FEF25%

Amount of air that was forcibly expelled in the first

25% of the total forced vital capacity test.

FEF75%

The amount of air expelled from the lungs during the

first (75%) of the forced vital capacity test.

FEF25%-75%

The amount of air expelled from the lungs during the

middle half of the forced vital capacity test.

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 loops

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

• 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

Flow Volume Loop

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

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

Upper Airway Obstruction

Variable intrathoracic obstruction

Variable extrathoracic obstruction

Fixed obstruction

Fixed obstruction1. Post intubation stenosis

2. Goiter

3. Endotracheal neoplasms

4. Bronchial stenosis

Maximum airflow is limited to a similar extent in both inspiration and expiration

Variable extrathoracic

Obstruction1. Bilateral and unilateral vocal cord

paralysis

2. Vocal cord constriction

3. Reduced pharyngeal cross-sectional area

4. Airway burns

The obstruction worsens in inspiration because the negative pressure narrows the trachea and inspiratory flow is reduced to a greater extent than expiratory flow

In variable intrathoracic

obstruction

1. Tracheomalacia

2. Polychondritis

3. Tumors of the lower trachea or main bronchus.

The narrowing is maximal in expiration because of increased intrathoracic pressure compressing the airway.

The flow volume loop shows a

greater reduction in the expiratory phase

Upper Airway Obstruction

Lung Volumes

Measurement:- helium- nitrogen washout- body plethsmography

Indications: - Diagnose restrictive component

- Differentiate chronic bronchitis from emphysema

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

Case 1

CC/HPI: A 36yo WM, nonsmoker, presents to your clinic with c/o episodic cough for 6mo. Also reports occasional wheezing and dyspnea with exertion during softball practice.

Exam: Heart RRR, no murmurs; Lungs CTAB, no labored breathing

Based on your exam and a thorough review of systems, you suspect asthma and decide to order spirometry for further evaluation.

Continued…

PFTs: FEV1 86% predicted

FEV1/FVC 82% predicted

Flow Volume Loop: normal inspiratory and expiratory pattern

You still suspect asthma. What is your next step in the workup of this patient?

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

↓

↓

↓ ↓

↓

↓ ↓

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

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

Pulmonary Function Testing

Which of the following is used to follow disease severity in COPD patients?

a. Total lung capacity (TLC)

b. Degree of responsiveness to bronchodilators

c. Forced vital capacity (FVC)

d. Forced expiratory volume in 1 second

e. Diffusing capacity (DLCO)

Pulmonary Function Testing

Which of the following is used to follow disease severity in COPD patients?

a. Total lung capacity (TLC)

b. Degree of responsiveness to bronchodilators

c. Forced vital capacity (FVC)

d. Forced expiratory volume in 1 second

e. Diffusing capacity (DLCO)

Pulmonary Function Testing

A 36yo WF, non-smoker, presents to your office for follow-up of ‘recurrent bronchitis.’ You suspect asthma and decide to order spirometry. Which of the following would you include in your prescription for testing?

a. Diffusing Capacity (DLCO)b. If no obstruction present, add trial of bronchodilatorc. If no obstruction present, perform methacholine challenged. Flow volume loope. b and c

Pulmonary Function Testing

A 36yo WF, non-smoker, presents to your office for follow-up of ‘recurrent bronchitis.’ You suspect asthma and decide to order spirometry. Which of the following would you include in your prescription for testing?

a. Diffusing Capacity (DLCO)b. If no obstruction present, add trial of bronchodilatorc. If no obstruction present, perform methacholine challenged. Flow volume loope. b and c

Pulmonary Function Testing

A 68yo HM is admitted to the ICU with acute respiratory distress. A CXR obtained in the ED demonstrates bilateral pulmonary infiltrates, and his DLCO is elevated. What is the most likely diagnosis?

a. Pulmonary edemab. Aspiration pneumonitisc. Pulmonary embolid. Alveolar hemorrhagee. Interstitial lung disease

Pulmonary Function Testing

A 68yo HM is admitted to the ICU with acute respiratory distress. A CXR obtained in the ED demonstrates bilateral pulmonary infiltrates, and his DLCO is elevated. What is the most likely diagnosis?

a. Pulmonary edemab. Aspiration pneumonitisc. Pulmonary embolid. Alveolar hemorrhagee. Interstitial lung disease

Contraindications

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 History of syncope associated with forced exhalation

Obstructive V/S restrictive lung disease ???

Obstructive Lung Diseases

Common Obstructive Lung Diseases

• Asthma

• COPD (chronic bronchitis, emphysema and the overlap between them).

• Cystic fibrosis.

-Airflow is reduced because the airways narrow and the FEV1 is reduced -Spirogram may continue to rise for more than 6 seconds because lung take longer to empty -FVC may also be reduced because gas is trapped behind obstructed bronchi due to increase in intrathoracic pressure during maneuver compresses airways causing early airway closure and gas trapping but this reduction to a lesser extent than FEV1

FEV1 ≥ 80% of predicted Normal

FEV1 60-80% of predicted mild obst.

FEV1 40-60% of predicted moderate

FEV1 ≤ 40% of predicted severe

The cardinal feature is FEV1/FVC ratio If

the ratio less than 70 consider obstructed

disease .*Predictors: Sex, Age, Ht

Flow volume loop in

Obstructive lung disease

Asthma Peak expiratory flow reduced

so maximum height of the loop is reduced

Airflow reduces rapidly with the reduction in the lung volumes because the airways narrow and the loop become concave

Concavity may be the indicator of airflow obstruction and may present before the change in FEV1 or FEV1/FVC

Emphysema

Airways may collapse during forced expiration because of destruction of the supporting lung tissue causing very reduced flow at low lung volume and a characteristic (dog-leg) appearance to the flow volume curve

Reversibility • Improvement in FEV1 by 12-15%

or 200 ml in repeating spirometry after treatment with Sulbutamol 2.5mg or ipratrobium promide by nebuliser after 15-30 minutes

• Reversibility is a characterestic feature of B.Asthma

• In chronic asthma there may be only partial reversibility of the airflow obstruction

• While in COPD the airflow is irriversible although some cases showed significant improvement.

Interpretation of PFTs

Step 1. Look at the Flow-Volume loop to determine acceptability of the test, and look for upper airway obstruction pattern.

Step 2. Look at the FEV1 to determine if it is normal (≥ 80% predicted).

Step 3. Look at FVC to determine if it is within normal limits (≥ 80%).

Step 4. Look at the FEV1/FVC ratio to determine if it is within normal limits (≥ 70%).

Step 5. Look at FEF25-75% (Normal (≥ 60%)

• If FEV1, FEV1/FVC ratio, and FEF25-75% all are normal, the patient has a normal PFT.

• If both FEV1 and FEV1/FVC are normal, but FEF25-75% is ≤ 60% ,then think about early obstruction or small airways obstruction.

• If FEV1 ≤ 80% and FEV1/FVC ≤ 70%, there is obstructive defect, if FVC is normal, it is pure obstruction. If FVC ≤ 80% , possibility of additional restriction is there.

• If FEV1 ≤ 80% , FVC ≤ 80% and FEV1/FVC ≥ 70% , there is restrictive defect, get lung volumes to confirm.

Small Airways obstruction

• Diseases affecting primarily the small (peripheral) airways can be extensive yet not affect the FEV1(e.g. early COPD, interstitial granulomatous disorders).

• Small airways status is reflected by the FEF25-75% (mid-range flow), best determined from the flow-volume loop.

• Some patients have normal spirometry with the exception of a reduced FEF25-75%, this is suggestive of possible small airways dysfunction and potentially early obstruction.

Effect of Smoking:• Smoking in patients with COPD is associated

with decline in FEV1 of 90-150 mL/year

• Smoking cessation is (associated with

increase in FEV1 for first year) followed with a decline of only 30 mL/year

Restrictive Lung Diseases

A. Intrinsic Restrictive Lung Disorders

1. Sarcoidosis

2. Idiopathic pulmonary fibrosis

3. Interstitial pneumonitis

4. Tuberculosis

5. Pnuemonectomy (loss of lung)

6. Pneumonia

B. Extrinsic Restrictive Lung Disorders

1. Scoliosis, Kyphosis

2. Ankylosing Spondylitis

3. Pleural Effusion

4. Pregnancy

5. Gross Obesity

6. Tumors

7. Ascites

8. Pain on inspiration - pleurisy, rib fractures

C. Neuromuscular Restrictive Lung Disorders

1. Generalized Weakness – malnutrition

2. Paralysis of the diaphragm

3. Myasthenia Gravis

4. Muscular Dystrophy

5. Poliomyelitis

6. Amyotrophic Lateral Sclerosis

• Full expantion of the lung is limited and therefore the FVC is reduced

• FEV1 may be reduced because the stiffness of fibrotic lungs increases the expiratory pressure

• FEV1/FVC will be Normal or Increased

*if you suspect restrictive pattern you must check TLC

Flow volume loop in

Restrictive lung disease

Flow volume loop in Restrictive lung disease :

Full lung expantion is prevented by fibrotic tissue in the lung parenchyma and the FVC is reduced .

Elastic recoil may increased by fibrotic tissue lead to increase the airflow

Both FEV1 and FVC may be reduced because the lungs are small and stiff ,but the peak expiratory flow may be preserved or even higher than predicted leads to tall,narrow and steep flow volume loop in expiratory phase.

Obstructive & restrictive defects

Parameter Obstruction Restriction

FEV1 Reduced Reduced

FVC Normal Reduced

FEV1/FVC Reduced Normal

 

A breathless 23-year-old woman has the following lung function tests: FEV1 1.1L (60%)/ FVC 1.3 L (55%)/ FEV1/FVC ratio = 84%/ TLC = 66% predicted/ RV = 57% predicted/ TLCO = 55% predicted/ KCO = 110% predicted What is the most likely diagnosis?

A : Acute sickle crisis

B : systemic lupus erythematosus (SLE) pneumonitis

C : Scoliosis

D : Asthma

E : Cystic fibrosis.

 

 

 

 

C : Scoliosis

The lung function tests show a significant restrictive defect. Only kyphoscoliosis or a pneumonitis may fit this picture but given the normal/high KCO (i.e. after correcting for alveolar volumes), the most likely answer is kyphoscoliosis as the gas exchange after correcting for the alveolar volume would in fact be high. 

A 35 year old lady with systemic sclerosis has breathlesness on exertion. She has bilateral basal crepitations in the chests and corresponding interstitial shadowing on the CXR. Which is likely to be found on her lung function tests?  

A. P02 of 11 desaturating to 10 on exertion

B. FEV1 to FVC ratio of 65%

C. Diffusion capacity (DLCO) of 17 (predicted 23)

D. Increased residual volume

E. FEV1 of 5 L

c) diffusion capacity (DLCO) of 17 (predicted 23). A decrease in diffusion capacity (DLCO) indicates interstitial lung disease, which is likely in a patient with basal crepitations and a predisposing connective tissue disease

A 30 year old man has kyphoscoliosis affecting his respiratory function. Which one of the following is associated?

A. Inclusion body myositis

B. Genital ulceration  

C. Klebsiella pneumonia

D. Pectus excavatum

E. Osteogenesis imperfecta

 

Answer: e) osteogenesis imperfecta.

Kyphoscoliosis occurs in :Connective tissue disorders -osteogenesis imperfecta, neurofibromatosis, MarfansNeuromuscular disorders – poliomyelitis, Duchenne’s , Friedrich’s ataxia, syringomyeliaPulmonary disorders – Unilateral fibrosis, empyema, pneumonectomy.

A restrictive defect occurs due to a reduction in FVC. Hypoxia is the first consequence, later hypercapnia and cor pulmonale may occur. Pectus excavatum is an inward chest wall deformity which may be due to the pull of diaphragmatic fibres during development. It is seldom symptomatic as is pectus carinatum, which is a protrusion deformity due to skeletal overgrowth.