Pulmonary Function Testing

Frank Sciurba, M.D.

Indications for Pulmonary Function Testing

1. Categorization of the type and severity of physiologic perturbation

• Restrictive vs. obstructive categorization– Asthma vs. emphysema

2. The objective assessment of pulmonary symptoms.– Documentation of abnormality– Disability assessment

3. Documentation of progression of disease. – COPD– Neuromuscular disease such as ALS

Indications for Pulmonary Function Testing

4.Documentation of the patient’s response to therapy.• Asthma control• Lung volume reduction surgery

5.Preoperative assessment• Lung cancer resection• Timing of lung transplantation

6.Screening for sub clinical disease• Emphysema in a tobacco smoker.• Occupational risk.

Component of respiration

Pulmonary function test

Ventilation a. Spirometry (FVC, FEV1 etc.)

b. Lung volume (RV, FRC, TLC)– Plethysmography

– Helium dilution

c. Inspiratory and expiratory pressure (MIP, MEP)

d. Lung compliance (rarely actually measured clinically)

e. Maximal voluntary ventilation (MVV)

f. Exercise ventilation (Ve-max, Vd/Vt)

Diffusion Diffusing capacity

Exercise Oxygen Saturation

Circulation Diffusing capacity (DlCO)

Cardiopulmonary exercise testing (VO2-

max)

Control (see Sanders lecture)

Spirometry

• Measures how much and how fast

• Most common and simple test

(can be performed in primary care office)

Spirometry

• Only measures what comes out

• How much and how fast?

• How much: Vital Capacity– A strong prognostic indicator in Framingham

study for all cause mortality

• Slow vital capacity (SVC) vs Forced Vital Capacity (FVC)

Measurement of Forced Vital Capacity (FVC)

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Liters(BTPS

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FVC = 5.8 L

Spirometry: How Fast?

• Forced expiratory volume in one second (FEV1)– Reduced with both small lungs (restriction) and with

diseases causing resistance to airflow (obstruction)

• FEV1/FVC ratio– Value < 0.70 defines obstruction

• FEF 25-75– Only important when FVC and FEV1 are normal

– Sensitive to earlier disease “minimal obstruction”

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Seconds

Liters(BTPS

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FEV1 = 4 L

Measurement of Forced Expiratory Volume (FEV1 )

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Seconds

Liters(BTPS

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Spirometric Changes with Increasing Degrees of

Obstruction

Hyperinflation in Emphysema

Spirometry-Quality Control

• Technician dependent• Acceptable effort

– sharp peak

– gradual return to 0 flow

– At least 4 seconds

• 3 acceptable maneuvers within 5% of each other

• Often more easily seen on Flow-volume tracings

Normal/Predicted Values

• Height

• Age

• Gender

• Race– 10% lower in Asian and African than European

descent

Predicted Normal Examples

• 21yo 6’6” male- FVC predicted- 6.9 L– Therefore a measured value of 2.1 L would be

only 30% predicted.

• 80yo 4’10” female- FVC predicted- 1.9 L– Therefore a measured value of 2.1 L would be

111% predicted

Which individual would be most likely to tolerate lung resection?

Spirometry and Detection of DiseaseNormal Values

• FVC 80% of predicted

• FEV1 80% predicted

• FEV1/FVC ratio 0.70

• FEF 25-75 65% predicted– Greater variance in the measurement

Obstruction vs.

Restriction

Obstructive Lung Disease

• FEV1/FVC < 0.70 defines obstruction

• FEV1 usually decreased

• FVC may be decreased – e.g. if expiration incomplete due to air trapping

• If FEF 25-75 decreased and all of the above are normal – “Minimal airways obstruction”

Restrictive Lung Disease

• FVC Decreased

• FEV1 often decreased proportionate to FVC

• FEV1/FVC Normal or Increased

• Can have simultaneous obstruction and restriction

• May need lung volume measurements (RV, FRC, TLC) to confirm.

• Patient retested before and after administration of a beta agonist bronchodilator

• Determines reversibility (asthma)

• 15% and 200ml improvement indicates a positive bronchodilator response

Bronchodilator Response

Bronchial Challenge Testing

• Pulmonary function in the laboratory may not represent the function at the time of symptoms.

• Attempt to mimic condition of symptoms– Work place chemicals– Cold air– Exercise

• Methacholine (histamine derivative) induces bronchospasm in occult asthmatics

• 20% decrease indicates a positive challenge test

Peak Expiratory Flow (PEF)

• Can be obtained during spirometry

• Portable devices can be used to make meaurements at home or in work place

Flow-Volume loops

•same data as volume-time plots but separate graphical representations allow the human eye to recognize patterns.

Normal Obstructed

F-V loops

• The assessment of patient effort on repetitive testing

• The presence of specific patterns for upper airway obstruction

• Specific patterns in other disease processes confirm but add little to spirometry numbers

F-V loops in Upper Airway Obstruction

• Intra vs. Extra-thoracic

• Variable vs. Fixed

Variable Extrathoracic Upper Airway Obstruction

•“inspiratory plateau”

•e.g. glottic tumor

Variable Extrathoracic Upper Airway Obstruction

Intrathoracic Variable Upper Airway Obstruction

•“expiratory plateau”

•e.g. tracheal tumor

Intrathoracic Variable Upper Airway Obstruction

Fixed Upper Airway Obstruction

Measurement of lung volume

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Seconds

Liters(BTPS

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Spirometric Changes with Increasing Degrees of

Obstruction

Hyperinflation in Emphysema

Severe Emphysema (decreased FVC but increased FRC & RV)

Measurement of lung volume

• Helium dilution

• Body plethysmography

Helium Dilution Lung Volume Measurement

Body Plethysmography

Box Pressure

Mouth Pressure

Plethysmographic Determination of FRCPlethysmographic Determination of FRC

Body Plethysmography- Technique

Plethysmography vs. Helium technique

• Plethysmography equipment more expensive and requires more technical expertise

• Helium falsely low in bullous emphysema– Plethysmography measures all air in the chest

including non-communicating bullae; Helium only measures alveoli communicating with the mouth

Measurement of Diffusing Capacity

Diffusing Capacity

• Gas exchange (not ventilation)• Clinically assesses pulmonary capillary bed

in contact with ventilated alveoli• Influenced by

– Capillary volume– Capillary surface area

• Single breath Carbon Monoxide (CO) technique now most common.

Single breath Carbon Monoxide Diffusing Capacity (DlCO)

• Simple/automated

• Standardized normal values available

• 10 second breath hold

• Inspire mixture of CO, He and O2

• Measure change in volume of CO between inspiration and expiration adjusted for dilution effect with He

Single breath Carbon Monoxide Diffusing Capacity (DlCO) Technique

Conditions Lowering Diffusing Capacity

1. Loss of alveolarcapillary membrane• emphysema• pulmonary fibrosis• pulmonary vascular disease

2. alveolar filling diseases• congestive heart failure• pulmonary alveolar proteinosis

3. decreased total lung volume• neuromuscular disease• chest wall deformities• patient post pneumonectomy

Conditions Increasing Diffusing Capacity

• Polycythemia

• Mild congestive heart failure

• Asthma

• Pulmonary hemorrhage.

Thank You