Pulmonary Function Testing. INTRODUCTION btCs btCs .

Pulmonary Function Testing

INTRODUCTION

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Introduction

• Pulmonary function testing has come into widespread use since the 1970s.

• This has been facilitated by several developments.

Because of miniaturization and advances in computer technology, microprocessor devices have become portable and automated with fewer moving parts. Testing equipment, patient maneuvers, and testing techniques have become widely standardized throughout the world through the efforts of professional societies.

• Widely accepted normative parameters have been established.

Introduction• Pulmonary function testing is a valuable tool for evaluating the

respiratory system, representing an important adjunct to the patient history, various lung imaging studies, and invasive testing such as bronchoscopy and open-lung biopsy.

• Insight into underlying pathophysiology can often be gained by comparing the measured values for pulmonary function tests obtained on a patient at any particular point with normative values derived from population studies.

• The percentage of predicted normal is used to grade the severity of the abnormality.

• Practicing clinicians must become familiar with pulmonary function testing because it is often used in clinical medicine for evaluating respiratory symptoms such as dyspnea and cough, for stratifying preoperative risk, and for diagnosing common diseases such as asthma and chronic obstructive pulmonary disease.

Introduction

• Pulmonary function tests (PFTs) is a generic term used to indicate a battery of studies or maneuvers that may be performed using standardized equipment to measure lung function. PFTs can include simple screening spirometry, formal lung volume measurement, diffusing capacity for carbon monoxide, and arterial blood gases. These studies may collectively be referred to as a complete pulmonary function survey.

Introduction• Before a spirogram can be meaningfully interpreted, one needs to inspect

the graphic data (the volume-time curve and the flow-volume loop) to ascertain whether the study meets certain well-defined acceptability and reproducibility standards.

• Tests that fail to meet these standards can provide useful information about minimum levels of lung function, but, in general, they should be interpreted cautiously. The interpretive strategy usually involves establishing a pattern of abnormality (obstructive, restrictive, or mixed), grading the severity of the abnormality, and assessing trends over time.

• Various algorithms are available. Automated spirometry systems usually have built-in software that can generate a preliminary interpretation, especially for spirometry; however, algorithms for other pulmonary function studies are not as well established and necessitate appropriate clinical correlation and physician oversight.

Flow Volume Loops

Categories of Pulmonary Function Tests

• Pulmonary function studies use a variety of

maneuvers to measure and record the properties of

four lung components. These include the airways

(large and small), lung parenchyma (alveoli,

interstitium), pulmonary vasculature, and the

bellows-pump mechanism. Various diseases can

affect each of these components.

Categories of Pulmonary Function Tests

• Measurement of dynamic flow rates of gases

through the airways

• Measurement of lung volumes and capacities

• Measurement of the lung’s ability to diffuse gases

Indications for Pulmonary Function Testing

• Evaluation of the cause of pulmonary symptoms

such as dyspnea, coughing, wheezing, and exercise

intolerance

• Evaluation of abnormalities noted on chest X-ray

• Determination of the course of a disease and the

response to treatment of the disease


• Evaluation of risk for perioperative pulmonary

complications

• Performance of epidemiological surveillance for

pulmonary disease


• Rule out significant pulmonary pathology in people

with high risk for pulmonary dysfunction, such as

smokers, firefighters, and those exposed to asbestos

• Evaluation of degree of disability

Monitoring

•To assess therapeutic interventions Bronchodilator therapy•Steroid treatment for asthma, interstitial lung disease, etc.•Management of congestive heart failure•Other (antibiotics in cystic fibrosis, etc.)•To describe the course of diseases affecting lung function Pulmonary diseases•Obstructive small airway diseases•Interstitial lung diseases•Cardiac diseases•Congestive heart failure•Neuromuscular diseases•Guillain-Barré syndrome

Evaluation of Disability or Impairment

To assess patients as part of a rehabilitation program Medical•Industrial•VocationalTo assess risks as part of an insurance evaluation•To assess persons for legal reasons Social Security or other government compensation programs•Personal injury lawsuits•Other

Contraindications for Pulmonary Function Testing

• Performing lung function tests can be physically demanding for a minority of patients. It is recommended that patients should not be tested within 1 month of a myocardial infarction.

• Chest or abdominal pain of any cause• Oral or facial pain exacerbated by a mouthpiece• Stress incontinence• Dementia or confusional state• Patients with any of the conditions are unlikely to achieve

optimal or repeatable results• Age of patient, ages of 8 and less render less accurate results

Patient Position for Pulmonary Function Testing

• Testing may be performed either in the sitting or standing position, and the position should be recorded on the report

• Sitting is preferable for safety reasons in order to avoid falling due to syncope. The chair should have arms and be without wheels. If a wheelchair is used, the wheels should be

• locked. If the standing position is used, a chair can be placed behind the patient/subject, so that they can be quickly and easily moved into a sitting position if they become lightheaded during the maneuver.

Patient Position for Pulmonary Function Testing

• Obese subjects, or those with excessive weight at the mid-section, will frequently obtain a deeper inspiration when tested in the standing position. Consequently, forced expiratory volumes and flows may improve with the standing position in these individuals.

• Normal-weight subjects typically have equivalent values when tested sitting or standing, but, for longitudinal studies, the same test position should be used each time.

PATIENT DETAILS for Pulmonary Function Testing

• Age, height and weight• The patient’s age, height and weight (wearing indoor clothes

without shoes) are recorded for use in the calculation of reference values. The age should be expressed in years. Height and weight should be expressed with the units in use in the country, corresponding to the ones of the selected reference equation.

• Body mass index should be calculated as kg. The height should be measured without shoes, with the feet together, standing as tall as possible with the eyes level and looking straight ahead, and using an accurate measuring device.


• Age, height and weight• For patients with a deformity of the thoracic cage,

such as kyphoscoliosis, the arm span from fingertip to fingertip can be used as an estimate of height. Arm span should be measured with the subject standing against a wall with the arms stretched to attain the maximal distance between the tips of the middle fingers. A regression equation using arm span, race, sex and age has been found to account for 87% of the variance in standing height with the standard error of the estimate for height ranging from 3.0 to 3.7 cm.


• Therapy• The operator should record the type and dosage of

any (inhaled or oral) medication that may alter lung function and when the drugs were last administered.

• Typically SVN therapy is withheld to render a more reflective exam.


• Subject preparation• Subjects should avoid the activities listed below and

these requirements should be given to the patient at the time of making the appointment. On arrival, all of these points should be checked, and any deviations from them recorded

• Smoking within at least 1 h of testing• Consuming alcohol within 4 h of testing• Performing vigorous exercise within 30 min of testing• Wearing clothing that substantially restricts full chest and

abdominal expansion• Eating a large meal within 2 h of testing


• Subject preparation• Subjects should be as relaxed as possible before and

during the tests. The decision to avoid long- and short-acting bronchodilators is a clinical one, dependent on the question being asked. If the study is performed to diagnose an underlying lung condition, then avoiding bronchodilators is useful. If the study is carried out to determine a response to an existing therapeutic regimen, then one may choose not to withhold bronchodilator medications.


• Subject preparation• Patients should be asked to loosen tight-fitting

clothing.• Dentures should normally be left in place; if they are

loose, they may interfere with performance and are, therefore, best removed.


• LABORATORY DETAILS• Ambient temperature, barometric pressure and time of day

must be recorded. Temperature is an important variable in most pulmonary function tests and is often measured directly by the instrument.

• The way in which it is measured and used may vary from instrument to instrument. For example, it may be measured with a simple thermometer or an internal thermistor.

• Ideally, when patients return for repeat testing (e.g. at a clinic), the equipment and the operator should be the same, and the time of day should be within 2 h of previous test times


• LABORATORY DETAILS• The order for performing lung function tests should take into

account the optimum work flow in the laboratory, potential influences of one test on another and the ability of the subject to undertake the test.

• Possible order for undertaking lung function tests in a laboratory

• Dynamic studies: spirometry, flow–volume loops, PEF• Static lung volumes• Inhalation of bronchodilator agent (if used)• Diffusing capacity• Repeat dynamic studies (if a bronchodilator was given)


• LABORATORY DETAILS• The choice of order of testing should consider the potential

effect of one test on the subsequent test. For example, the measurement of carbon monoxide diffusing capacity of the lung (DL,CO) immediately after a nitrogen washout measurement of the total lung capacity (TLC) will be affected by the increased oxygen content in the lungs, unless enough time has passed to allow the oxygen concentration to return to normal.


• LABORATORY DETAILS• Also, tidal breathing maneuvers may be disturbed by a

recently performed maximal forced expiratory maneuver.• Bronchodilator administration may affect static lung volumes,

reducing hyperinflation by up to 0.5 L .• While bronchodilators do not seem to affect diffusing capacity

when measured, they may allow 10% of patients to obtain a measurement of diffusing capacity that was not possible pre-bronchodilator


• Quality Control• Quality control is important to ensure that the laboratory is

consistently meeting appropriate standards. In any quality control program, an important element is a manual of procedures that contains the following: calibration procedures, test-performance procedures, calculations, criteria, reference values source, and action to be taken when ‘‘panic’’ values are observed.

• Calibration of the equipment should always be done prior to any pulmonary function test

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American Thoracic Society Standards

• Developed in conjunction with the European

Respiratory Society and published in 2005

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monary-function-testing.php

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• Sets standards for equipment used in testing

– Able to measure volumes between 0.5 and 8 L

– Able to measure flow from 0 to 14 L/sec

– Capable of accumulating volume for 15 seconds


• Sets standards for equipment used in testing

– Maximum allowable error of ± 3% or ± 0.05 L, whichever

is greater

– Resistance and back pressure < 1.5 cm H2O/L/sec


• Details considerations of patients being tested

– Lists determination of patient height and weight

– Suggests patient activities that should be avoided and

interval between activity and test


• Sets standards for infection control of pulmonary

function equipment

• Lists qualifications for personnel administering

pulmonary function testing

List of abbreviations and meanings• ATPD Ambient temperature,

ambient pressure, and dry• ATPS Ambient temperature

and pressure saturated with water vapor

• BTPS Body temperature (i.e. 37°C), ambient pressure, saturated with water vapor

• COHb Carboxyhemoglobin• DLCO Diffusing capacity for

the lungs measured using carbon monoxide, also known as transfer factor

• DLCO/VA Diffusing capacity for carbon monoxide per unit of alveolar volume, also known as KCO

• DM Membrane-diffusing capacity

• DT Dwell time of flow .90% of PEF

• EFL Expiratory flow limitation

• ERV Expiratory reserve volume

• EV Back extrapolated volume

List of abbreviations and meanings• EVC Expiratory vital capacity• FEF25-75% Mean forced

expiratory flow between 25% and 75% of FVC

• FEV1 Forced expiratory volume in one second

• FEVt Forced expiratory volume in t seconds

• FRC Functional residual capacity

• FVC Forced vital capacity• IC Inspiratory capacity

• MVV Maximum voluntary ventilation

• PEF Peak expiratory flow• RV Residual volume• STPD Standard temperature TGV

(or VTG) Thoracic gas volume• TLC Total lung capacity• Tr Tracer gas• VA Alveolar volume• VC Vital capacity• VD Dead space volume• VI Inspired volume• VS Volume of the expired sample

gas

Differentiation of Obstructive and Restrictive Disease

Characteristic Obstructive Disease Restrictive Disease

Anatomy affected Airways Lung parenchyma, thoracic pump

Breathing phase difficulty

Expiration Inspiration

Pathophysiology Increased airway resistance

Decreased lung and/or thoracic compliance

Useful measurements Flow rates Volumes and/or capacities

Lung Volumes

• Residual volume (RV)

– Volume of gas remaining in the lung after a maximal

exhalation

– Normal value – 1.2 L, approximately 20 % of total lung

capacity

Lung Volumes

• Expiratory reserve volume (ERV)

– Volume of gas that can be exhaled after a normal

exhalation

– Normal value – 1.2 L, approximately 20% of total lung

capacity

Lung Volumes

• Tidal volume (VT)

– Volume of gas inspired during a normal inhalation

– Normal value – 0.5 L, approximately 10% of total lung

capacity

Lung Volumes

• Inspiratory reserve volume (IRV)

– Volume of gas that can be inspired after a normal

inspiration

– Normal value – 3.1 L, approximately 50% to 55% of total

lung capacity

Lung Capacities

• Total lung capacity (TLC)

– Volume of gas contained in the lung at maximum

inspiration

– TLC = RV + ERV + VT + IRV

– Normal – 6.0 L

Lung Capacities

• Inspiratory capacity (IC)

– Maximum volume of gas that can be inhaled after a

normal exhalation

– IC = VT + IRV

– Normal – 3.6 L, approximately 60% of TLC

Lung Capacities

• Vital capacity (VC)

– Maximum volume of gas that can be exhaled following

a maximal inhalation

– VC = IRV + VT + ERV


Lung Capacities

• Functional residual capacity (FRC)

– Volume of gas that remains in the lung following a

normal exhalation

– FRC = RV + ERV


Spirogram

Lung Volumes & Capacities

Physiology• Ventilation is the process of generating the forces necessary to

move the appropriate volumes of air from the atmosphere to the alveoli to meet the metabolic needs of the body under a variety of conditions.

• Simply, the contraction of the diaphragm and other inspiratory muscles expands the thorax, generating negative pressure in the pleural space.

• One component of pleural pressure, known as transpulmonary pressure, causes a flow of air into the airways and lungs (inspiration). When the transpulmonary and alveolar pressures equilibrate, airflow stops, the inspiratory muscles relax, and the lungs and chest wall elastic recoil raise pleural pressure, forcing air out of the lungs (expiration)

Physiology

• With a forced exhalation, the early portion of the spirometry maneuver is characterized by high flows, mostly from large airways, and the latter portion is characterized by low flows with a larger contribution from the smaller airways.

• Forced inspiration is generally not flow limited and is a function of overall muscular effort. In contrast, a variety of factors affect expiratory flow, including the overall driving pressure, airway diameter, overall distensibility of the lungs and chest wall, dynamic airway collapse (from a flow-limiting segment), and muscular effort. The overall driving pressure is the pressure head at the alveolus, or PALV, which is the difference between pleural pressure (PPL) and negative transpulmonary pressure (PTP).

Physiology

• PALV = PPL + PTP

• The mechanism for the maximal expiratory airflow limitation seen in normal airways results from the gradual drop in pressure inside the conducting airways from the alveoli to the mouth, creating a transmural pressure gradient with the pleural pressure. This can cause dynamic airway compression and narrowing or closure of airways that have lost elastic recoil support from the lung parenchyma.

Spirometry

• Tests basic pulmonary mechanics

• Measures forced vital capacity (FVC), forced expiratory

volumes (FEV), forced expiratory flows (FEF), forced

inspiratory flows (FIF), and maximum voluntary ventilation

(MVV)

• Can be done at bedside or in a lab via handheld spirometer

Spirometry

• Vital capacity

– Technique – subject breaths normally for several

breaths, followed by a maximal inspiration and a

maximal exhalation

– Resting expiratory level must be stable to obtain valid

results

Spirometry

• Forced vital capacity (FVC)

– Technique – subject breaths normally for several

breaths, then inspires maximally and exhales as

forcefully and fully as possible

– Should be within 200 mL of VC

Spirometry

• Forced expiratory volume (most commonly FEV1)

– Volume which can be exhaled in one second using

maximum patient effort

– Determined from the FVC

– Decrease in value indicates obstructive changes in small

airways

Spirometry

• Forced Expiratory Volume (Most Commonly FEV1)

– FEV1% - Percentage of FVC That can be Expired in one

Second (can Measure any Time Interval by Changing

Subscript)

– FEV1% = x 100

Spirometry


– Normal values

• FEV0.5% − 50% to 60% of FVC

• FEV1% − 75% to 85% of FVC

• FEV3% − 95% to 100% of FVC

Spirometry – FEV

Spirometry


– FEV1% tends to decrease with age as lung elasticity

decreases

– Decrease in value is the most important indicator of

obstructive lung disease

– May be increased or normal in restrictive lung disease

Spirometry

• FEF25%-75%

– Average expiratory flow rate of the middle 50% of the

FVC

– Measured in liters per second

– Indicates flow from medium and small airways

– Changes from smoking occur in medium airways prior to

changes in small airways

Spirometry – FEF25%-75%

Spirometry

• FEF200-1200

– Average expiratory flow rate between the first 200 mL

and 1200mL of exhaled volume of the FVC

– Measured in large airways

– Reflects flow from large airways

Spirometry – FEF200-1200

Spirometry

• Maximum voluntary ventilation (MVV)

– Calculates the maximum volume of gas that a patient can

ventilate in one minute

– Technique – subject is directed to breathe rapidly and

deeply for 12 to 15 seconds; the total volume inspired or

expired is measured; the volume is extrapolated to one

minute

Spirometry

• Maximum voluntary ventilation (MVV)

– Normal value – 150 to 200 L/min

– Decrease indicates increase in airway resistance or

obstruction, decrease in lung or thoracic compliance, or

ventilatory muscle weakness

Spirometry – MVV

Spirometry

• Peak expiratory flow (PEF)

– Highest expiratory flow rate

– Generally occurs during early part of exhalation

– Normal value – males: 400 to 600 L/min; females: 300

to 500 L/min

Flow Volume Loop

Graphic depiction of flow rate plotted against volume change during an FVC maneuver

Flow-Volume Loop

• Technique – subject maximally inspires, followed

by a single forced exhaled vital capacity (FEVC)

and forced inspired vital capacity (FIVC)

Examples of Flow-Volume Loops in Disease States

Review

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Measurement of Total Lung Capacity Helium Dilution

• Helium is a metabolically inert gas; based on

assumption that, with a known concentration of

helium in the air of a closed system and no helium

in the patient’s lungs, equilibration will occur

between the spirometer and the lungs


• Spirometer is filled with a known volume of air

and helium is added until approximately a 10%

concentration is achieved

• The concentration and volume are then measured

precisely


• The patient breathes through a valve-mouthpiece

connected to a rebreathing system with a carbon

dioxide absorber

• Oxygen is added at the rate of the patient’s

oxygen consumption in order to maintain a

concentration of approximately 21%


• The valve is opened at the end of expiration and

the patient breathes on the closed circuit until the

concentration of helium stabilizes; for healthy

patients, this is usually from 2 to 5 minutes; for

patients with obstructive disease, equilibration

may take as long as 20 minutes


• At stabilization, the concentration of helium in the

system is measured

• A correction factor of 30 mL of helium is

subtracted from the volume for each minute of

helium breathing, up to a total of 200 mLs


• Functional Residual Capacity is Calculated

– FRC =[ ] x [ ]

Measurement of Total Lung Capacity Nitrogen Washout

• Nitrogen composes approximately 80% of the air

in the lung, including 80% of the FRC; therefore

the volume of nitrogen in the total exhaled gas

will equal approximately 80% of the FRC


• Patient breathes 100% oxygen through a valve-

mouthpiece system for seven minutes or until the

alveolar concentration of nitrogen decreases to

approximately 1%

• A valve is opened at the end of a normal exhalation,

allowing the patient to breathe into the closed circuit


• A rapid response nitrogen analyzer and a spirometer

measure breath-by-breath nitrogen concentration

and exhaled volume

• Values are summed to provide the total volume of

nitrogen washed out


• Functional residual capacity is calculated

– FRC = (VE x FEN2) / (0.78 – FAN2)

where VE is the total volume of gas exhaled during the

test, FEN2 is the fractional concentration of exhaled

nitrogen in the total gas volume, and FAN2 is the

fractional concentration of nitrogen in the alveoli at

the end of the test


• Also used to determine closing volume (CV) and

closing capacity (CC)

– Closing volume - volume of gas remaining in the

patient’s vital capacity when the small airways

start to close


• Also used to determine closing volume (CV) and

closing capacity (CC)

– Closing capacity – volume of gas remaining in the

patient’s lungs when the small airways start to

close (CV + RV)

– Used to determine small airway disease

Measurement of Total Lung Capacity Plethysmography

• Test calculates the total thoracic gas volume,

including gas trapped distal to completely

obstructed airways or located in the abdomen or

intestines

• The patient is placed in the plethysmography or

body box and breathes through a mouthpiece


• The mouthpiece contains a shutter valve that,

when closed, obstructs the airway

• Airway pressure at the mouth is measured using a

pressure transducer attached to the mouthpiece


• During testing, patient breathes gas while within

the box

• Patient pants at 1 to 2 breaths per second while

pressures within the box and at the mouth are

measured simultaneously


• At FRC, the shutter valve is closed briefly to

obstruct the airway and pressures are again

measured

• Changes in lung volume are reflected by changes

in box pressure


• Mouth pressure theoretically equals alveolar

pressure when the shutter valve occludes the

airway as flow drops to zero

• The total volume of the plethysmograph is known

and the volume displaced by the patient is

calculated


• The volume of the thoracic gas is calculated using

Boyle’s law

– VTG1 x Palv1 = VTG2 x Palv2

where VTG is the thoracic gas volume before and after

occlusion and Palv is the alveolar pressure before and after

occlusion

Diffusion Capacity (DL) – Purpose

• Assess ability of the lungs to exchange gas

across the alveolar-capillary membrane

Diffusion Capacity (DL)

• Also known as the transfer factor

• Expressed as mL/min/mm Hg

Diffusion Capacity (DL) – Rationale

• By measuring the difference between an inhaled

volume of carbon monoxide (single breath) and

the exhaled volume, the amount of carbon

monoxide that diffused across the alveolar-

capillary membrane can be calculated

Diffusion Capacity (DL) – Rationale

– Carbon monoxide (CO) used because of its strong

affinity for hemoglobin

– Only limiting factor is the surface area of the

alveoli

– Normally, the partial pressure of CO in the

alveolus is 0 mmHg

Factors Affecting Diffusion

• Diffusion coefficient of the gas

• Surface area of the membrane

• Thickness of the membrane

Factors Affecting Diffusion

• Hemoglobin and blood flow in the pulmonary

capillaries

• Distribution of the inspired gas

(ventilation/perfusion ratio)


• The patient maximally inhales from a mixture of

gases containing 0.3% CO with 10% He and the

balance room air

• Patient holds breath for 10 seconds


• Patient exhales; following exhalation of a volume

approximating the anatomic dead space, the

remaining gas is collected

• Sample is analyzed to determine concentrations of

CO and He in the exhaled alveolar gas


• The change in He concentration reflects

dilution and is used to calculate the initial

mean capillary partial pressure of CO prior to

diffusion


• DLCO is Calculated Using the Following Equation:

– DLCO =

Where CO is the Pulmonary Capillary Uptake of CO in

mL/min, PACO is the Mean Alveolar Partial Pressure of CO,

and PCCO is the Mean Capillary Partial Pressure of CO,

Usually Zero

Diffusion Capacity (DL) – Normal Values

• Males – 25 mL/min/mm Hg CO

• Females – slightly lower due to smaller lung

volumes

• May increase 2 to 3 times during exercise

Bronchial Provocation Tests – Purpose

• Assess patients with normal PFT results and

symptoms of bronchospasm

• Quantify severity of asthma and assess changes in

airway reactivity

• Screen those at risk from or to document the effects

of environmental or occupational exposure to toxins

Bronchial Provocation Tests

• Before the test

– Patients must be asymptomatic

– Bronchodilators and antihistamines must be withheld prior

to the test (duration of time determined by the individual

bronchodilator)

– No smoking or caffeine on the day of the test

– No exercise prior to the test

Bronchial Provocation Tests – Procedure

• Obtain baseline spirometry

• Administer SVN treatment with normal saline

– Perform spirometry

– If FEV1 decreases by less than 20%, proceed with protocol


• Administer 3 mL of 0.031 mg/mL Methacholine

– Use noseclip to ensure mouth breathing

– Administer treatment over 2 minutes


• Perform spirometry

– If FEV1 has decreased < 20%, administer next larger

dose

– If FEV1 has decreased ≥ 20%, test is concluded


• Repeat sequence of administering methacholine

and performing spirometry, doubling dose of

methacholine each administration until either the

FEV1 has decreased ≥ 20% or the dosage of

methacholine is 16 mg/mL, whichever occurs first

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Interpreting the DLCO

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Interpreting the PFT Report

• The FEV1/FVC ratio is a good place to start; reduced (<70%) with obstructive lung disease

• If TLC less than 80% of predicted normal and FEV1/FVC is normal, restrictive disease is present.

• If DLCO is <80% of normal, a diffusion defect is present.– Reduced surface area = emphysema– Thickened AC membrane = pulmonary fibrosis

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Interpretation

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