Pulmonary Function Tests (PFTs)

    SYNONIMS :
        Lung Function Test (LFT), Spirometry
    DEFINITION :
        Pulmonary Function Test Is A Test To Measure The Functionality Of The Lungs, Such As :
    EXAMPLES :
        Spirometry :
            The Most Common Of The Pulmonary Function Tests (PFTs) Performed Using A Device Called Spirometer To Measures The Lung Function - Amount (Volume) And / Or Speed (Flow) Of Air That Can Be Inhaled And Exhaled.
            Important Tool Used For Generating Pneumotachographs Which Are Helpful In Assessing Conditions Such As : Asthma, Pulmonary Fibrosis, Cystic Fibrosis, And COPD

            Most Spirometers Display The Following Graphs, Called Spirograms :
                A Volume-Time Curve - Showing Volume (Liters) Along The Y-Axis And Time (Seconds) Along The X-Axis
                A Flow Volume Loop - Which Graphically Depicts The Rate Of Airflow On The Y-Axis And The Total Volume Inspired Or Expired On The X-Axis
            Methods :
                Patient Is Asked To Take The Deepest Breath They Can, And Then Exhale Into The Sensor As Hard As Possible, For As Long As Possible, Preferably At Least 6 Seconds.
                It's Sometimes Directly Followed By A Rapid Inhalation (Inspiration), In Particular When Assessing Possible Upper Airway Obstruction.
                Sometimes, The Test Will Be Preceded By A Period Of Quiet Breathing In And Out From The Sensor (Tidal Volume), Or The Rapid Breath In (Forced Inspiratory Part) Will Come Before The Forced Exhalation
                During The Test, Soft Nose Clips May Be Used To Prevent Air Escaping Through The Nose
                Filter Mouthpiece May Be Used To Prevent The Spread Of Microorganisms.
                A Bronchodilator Is Also Given In Certain Circumstances And A Pre / Post Graph Comparison Is Done To Assess The Effectiveness Of The Bronchodilator
            Limitations :
                The Manuever Is Highly Dependent On Patient Cooperation And Effort, And Is Normally Repeated At Least 3 Times To Ensure Reproducibility
                Since Result Are Dependent On Patient Cooperation, FEV1 And FVC Can Be Underestimated.
                Due To The Patient Cooperation Required, Spirometry Can Only Be Used On Children Old Enough To Comprehend And Follow The Instruction (6 Years Old Or More), And Only On Patients Who Are Able To Understand And Follow Instructions
                This Test Is Not Suitable For Patients Who Are Unconscious, Heavily Sedated, Or Have Limitations That Would Interfere With Vigorous Respiratory Efforts.
                Many Intermittent Or Mild Asthmatics Have Normal Spirometry Between Acute Exacerbation, Limiting The Usefulness Of Spirometry As A Diagnostic Tools.
                More Useful As A Monitoring Tool : A Sudden Decrease In FEV1 Or Other Spirometric Measure In The Same Patient Can Signal Worsening Control, Even If The Raw Value Is Still Normal. Patients Are Encouraged To Record Their Personal Best Measures
            Parameters - LUNG VOLUME :

                Vital Capacity (VC) :
                    The Maximum Amount Of Air A Person Can Expel From The Lungs After A Maximum Inspiration In mL.
                    FORMULA : IRV + TV + ERV
                        Equal To The Inspiratory Reserve Volume Plus The Tidal Volume Plus The Expiratory Reserve Volume.
                    Normal (Adult) : Between 3 And 5 Litres.
                Forced Vital Capacity (FVC) - THE MOST BASIC MANUEVER IN SPIROMETRY TEST
                    The Volume Of Air That Can Forcibly Be Blown Out After Full Inspiration
                Forced Expiratory Volume (FEV) At Timed Interval Of 0.5, 1.0, 2.0, And 3.0 Seconds
                    FEV0.5, FEV1, FEV2, FEV3
                    Average Values For FEV1 In Healthy People Depend Mainly On Sex And Age.
                    Values Of Between 80% And 120% Of The Average Value Are Considered Normal
                Forced Expiratory Volume 1 %
                    FEV1 / FVC (FEV1%) Is The Ratio Of FEV1 To FVC.
                    Normal (Healthy Adults) - Approximately 75–80%.
                    Obstructive Diseases (Such As : Asthma, COPD, Chronic Bronchitis, Emphysema)
                        Diminished FEV1 - Because Of Increased Airway Resistance To Expiratory Flow And
                        Decreased FVC Further - Due To Premature Closure Of Airway In Expiration.
                        This Generates A Reduced Value (<80%, Often Around 45%).
                    Restrictive Diseases (Such As : Pulmonary Fibrosis)
                        Diminished FEV1 And FVC Proportionally
                        The Value May Be Normal Or Even Increased As A Result Of Decreased Lung Compliance
                Forced Expiratory Flow 25 - 75 % (FEF 25 - 75)
                    The Flow (Or Speed) Of Air Coming Out Of The Lung During The Middle Portion Of A Forced Expiration.
                    It Can Be Given At Discrete Times, Generally Defined By What Fraction Remains Of The Functional Vital Capacity (FVC).
                    Usual Intervals - 25%, 50% And 75% (FEF25, FEF50 And FEF75), Or 25% And 50% Of FVC.
                    It Can Also Be Given As A Mean Of The Flow During An Interval, Also Generally Delimited By When Specific Fractions Remain Of FVC, Usually 25–75% (FEF25–75%).
                    Normal (Healthy Population) - Depends Mainly On Sex And Age.
                        Values Ranging From 50 - 60 % And Up To 130 % Of The Average Are Considered Normal
                    This Parameter May Be A More Sensitive Parameter Than FEV1 In The Detection Of Obstructive Small Airway Disease. However, In The Absence Of Concomitant Changes In The Standard Markers, Discrepancies In Mid Range Expiratory Flow May Not Be Specific Enough To Be Useful, And Current Practice Guidelines Recommend Continuing The Use Of FEV1, VC And FEV1/VC As Indicators Of Obstructive Disease.
                    MMEF Or MEF - Maximal (Mid-) Expiratory Flow
                        The Peak Of Expiratory Flow As Taken From The Flow-Volume Curve And Measured In Liters Per Second.
                        It Should Theoretically Be Identical To Peak Expiratory Flow (PEF) - Generally Measured By A Peak Flow Meter (Liters Per Minute).
                Forced Inspiratory Flow 25 - 75 % (FIF 25 - 75)
                    Forced Inspiratory Flow 25–75% Or 25–50% (FIF 25–75% or 25–50%) Is Similar To FEF 25–75% Or 25–50% Except The Measurement Is Taken During Inspiration.
                Peak Expiratory Flow (PEF)
                    The Maximal Flow (Or Speed) Achieved During The Maximally Forced Expiration Initiated At Full Inspiration, Measured In Liters Per Minute.
                Tidal Volume (TV)
                    Volume Of Air Inspired Or Expired In Single Breath At Rest
                Total Lung Capacity (TLC)
                    Maximum Volume Of Air Present In The Lungs
                Diffusion Capacity (DLCO)
                    Carbon Monoxide Uptake From A Single Inspiration In A Standard Time (Usually 10 Seconds - Standard Time For Inhalation), Then Rapidly Blow It Out (EXHALE)
                    The Exhale Gas Is Tested To Determine How Much Of The Tracer Gas Was Absorbed During The Breath.
                    This Will Pick Up Diffusion Impairements, For Instance In Pulmonary Fibrosis
                    Disadvantage :
                        This Result Must Be Corrected For Anemia (Rapid CO Diffusion Is Dependend) On Hemoglobin In RBC's
                            A Low Hemoglobin Concentration, Anemia, Will Reduce DLCO
                        Pulmonary Hemorrhage (Excess RBC's - Interstitium Or Alveoli) Can Absorb CO And Artificially Increase The DLCO Capacity
                Maximal Voluntary Ventilation (MVV)
                    Maximum Breathing Capacity
                    A Measure Of The Maximum Amount Of Air That Can Be Inhaled And Exhaled Within One Minute - Over A 15 Second Time Period (Liters / Minute)
                    Average Values (Males And Females)
                        140-180 And 80-120 Liters Per Minute Respectively.
                Functional Residual Capacity (FRC)
                    Cannot Be Measured Via Spirometry, But Can Be Measured With Plethysmography Or Dilution Test (Such As : Helium Dilution Test)
                Static Lung Compliance (CST)
                    When Estimating Static Lung Compliance, Volume Measurements By The Spirometer Needs To Be Complemented By Pressure Transducers In Order To Simultaneously Measure The Transpulmonary Pressure
                    The Most Sensitive Parameter For The Detection Of Abnormal Pulmonary Mechanics
                    Normal : 60% To 140% Of The Average Value In The Population For Any Person Of Similiar Age, Sex And Body Composition
                    In Those With Acute Respiratory Failure On Mechanical Ventilation - The Static Compliance Of The Total Respiratory System Is Conventionally Obtained By Dividing The Tidal Volume By The Difference Between The "Plateau" Pressure Measured At The Airway Opening (PaO) During An Occlusion At End-Inspiration And Positive End-Expiratory Pressure (PEEP) Set By The Ventilator
                Forced Expiratory Time (FET)
                    Measures The Length Of The Expiration In Seconds
                Slow Vital Capacity (SVC)
                    Maximum Volume Of Air That Can Be Exhaled Slowly After Slow Maximum Inhalation
                Maximal Pressure (PMax And Pi)
                    PMax Is The Asymptomatically Maximal Pressure That Can Be Developed By The Respiratory Muscles At Any Lung Volume And Pi Is The Maximum Inspiratory Pressure That Can Be Developed At Specific Lung Volumes
                    This Measurement Also Requires Pressure Transducers In Addition
                    Normal - 60 % - 140 % Of The Average Value In The Population For Any Person Of Similiar Age, Sex And Body Composition
                    A Derived Parameter Is The Coefficient Of Retraction (CR) Which Is PMax / TLC
                Mean Transit Time (MTT)
                    Mean Transit Time Is The Area Under The Flow-Volume Curve Divided By The Forced Vital Capacity.
            Interpretation :
                Results Are Usually Given In Both Raw Data (Litres, Litres Per Second) And Percent Predicted Values For The Patients Of Similiar Characteristics (Height, Age, Sex, And Sometimes Race And Weight)
                Results Nearest To 100% Predicted Are The Most Normal
                Results Over 80 % Are Often Considered Normal
                    Review By The Physicians Is Necessary For Accurate Diagnosis
        Body Plethysmography

A Very Sensitive Lung Measurement
            Examine The Lungs Resistance To Airflow, Distinguish Between Restrictive And Obstructive Lung Diseases, Determine The Respons To Bronchodilators, And Determine Bronchial Hyperreactivity In Response To Methacholine, Histamine, Or Isocapnic Hyperventilation.
            This Test Is Used Mainly In The Pulmonary Function Testing Laboratories
            Indication :
                Used To Detect Lung Pathology That Might Be Missed With Conventional Pulmonary Function Tests.
                May Also Be Used In Situations Where Several Repeated Trials Are Required Or Where The Patient Is Unable To Perform The Multibreath Tests.
            Method :
                By Obtaining The Absolute Volume Of Air Within One's Lungs
                Indices - Thoracic Gas Volume (VTG) & Airway Resistance (RAW)
            How To Perform :
                Test Is Done By Enclosing The Subject In An Airtight Chamber Often Referred To As A BODY BOX
                A Pneumotachometer Is Used To Measure Airflow While A Mouth Pressure Transducer With A Shutter Measures The Alvelar Pressure
        Peak Expiratory Flow
            History :
                Pioneered By Dr. Martin Wright, Who Produced The First Meter Specifically Designed To Measure This Index Of Lung Function.
                Original Design Was Introduced In The Late 1950s
                The Subsequent Development Of A More Portable, Lower Cost Version, Such As : The 'Mini-Wright' Peak Flow Meter)
            Used In Addition To Spirometer
            PEAK EXPIRATORY FLOW RATE (PEFR) - A Person's Maximum Speed Of Expiration, As Measured With A Peak Flow Meter

            Measures The Airflow Through The Bronchi And Thus The Degree Of Obstruction In The Airways, To Determine The Lung Functionality, Severity Of Asthma Symptoms, And Treatment Options
            Interpretation :
                Normal Values Depends On : Sex, Age, And Height
                Reduced In Obstructive Lung Disorders, Such As : Asthma
                Due To The Wide Range Of Normal Values And High Degree Of Variability, Peak Flow Is Not The Recommended Test To Identify Asthma
                First Measure Of Precaution Would Be To Check Patient For Signs And Symptoms Of Asthmatic Hypervolemia - This Would Indicate Whether Or Not To Even Continue With The Peak Flow Meter Procedure
                When Peak Flow Is Being Monitored Regularly, The Results May Be Recorded On A PEAK FLOW CHART
                It Is Important To Use The Same Peak Flow Meter Every Time.
                Peak Flow Readings Are Often Classified Into 3 Zones Of Measurement According To The American Lung Association : Green, Yellow, And Red.

    Nitrogen Washout
        Also Known As Fowler's Method
        A Test For Measuring Dead Space In The Lung During A Respiratory Cycle, As Well As Some Unique Parameters Related To The Closure Of Airways.

Schematic Representation Of Multiple Breath Nitrogen Washout Curves - Young Healthy Nonsmoker (normal) And An Asymptomatic Smoker (Abnormal). Expired Nitrogen Concentration Is Plotted On A Logarithmic Scale Against Cumulative Expired Volume During Pure Oxygen Breathing.

        Method :
            Performed With A Single Nitrogen Breath, Or Multiple Ones
            Both Tests Use Similiar Tools, Both Can Estimate Functional Residual Capacity And The Degree Of Nonuniformity Of Gas Distribution In The Lungs, But The Multiple Breath Test More Accurately Measures Absolute Lung Volumes
            Single Breath Nitrogen Test :
                Subject Takes A Breath Of 100% Oxygen And Exhales Through A One Way Valve Measuring Nitrongen Content And Volume.
                A Plot Of The Nitrogen Concentration (As A % Of Total Gas) VS Expired Volume Is Obtained By Increasing The Nitrogen Concentration From Zero To The Percentage Of Nitrogen In The Alveoli.
                The Ntrogen Concentration Is Initially Zero Because The Subject Is Exhaling The Dead Space Oxygen They Just Breathed In (Does Not Participate In Alveolar Exchange), And Climbs As Alveolar Air Mixes With The Dead Space Air.
                The Dead Space Can Be Determined From This Curve By Drawing A Vertical Line Down The Curve Such That The Areas Below The Curve (Left Of The Line) And Above The Curve (Right Of The Line) Area Equal.
            Most People With A Normal Distribution Of Airways Resistances Will Reduce Their Expired End Tidal Nitrogen Concentrations To Less Than 2.5 % Within Seven Minutes.
            Individuals With High Resistance In Their Airways Can Take Longer Than Seven Minutes To Remove All The Nitrogen
        Parameters :
            Closing Volume (CV)
                The Amount Of Air Remaining In The Lungs When The Flow From The Lower Sections Of The Lungs Becomes Severely Reduced Or Halts Altogether During Expiration As The Small Airways Begin To Close
            Closing Capacity (CC)
                Formula : Closing Volume + (Total Lung Capacity - Vital Capacity)
                    CV + (TLC - VC)
                    VC - Taken From The Curve Acquired From The Nitrogen Washout Test
                        Normally 70 % - 130 % - Of What Is The Average Value In The Population, Vary With Geographic Location
            Mean Slope Of The Alveolar Plateau (Phase III)
                Should Be Less Than 175% Of Population Average
            CV / VC Ratio AND CC / TLC Ratio
                Both Should Be Less Than 125 % Of Population Average
    Ventilation / Perfusion Lung Scan (V / Q Lung Scan)

        Uses Scintigraphy And Medical Isotopes To Evaluate The Circulation Of Air And Blood Within A Patient's Lung In Order To Determine The Ventilation / Perfusion Ratio
            Ventilation - The Ability Of Air To Reach All Parts Of The Lungs,
            Perfusion - Evaluates How Well Blood Circulates Within The Lung

Ventilation Perfusion Scintigraphy - Showed Decrease Activity In : Apical Segment Of Right Lobe, Anterior Segment Of Right Upper Lobe, Superior Segment Of Right Lower Lobe, Posterior Basal Segment Of Right Lower Lobe, Anteromedial Basal Segment Of Left Lower Lobe, And Lateral Basal Segment Of The Left Lower Lobe.

(A) After Inhalation Of 20.1 mCi Of Xenon-133 Gas, Scintigraphic Images Were Obtained In The Posterior Projection, Showing Uniform Ventilation To Lungs. (B) After Intravenous Injection Of 4.1 mCi Of Technetium-99m-Labeled Macroaggregated Albumin, Scintigraphic Images Were Obtained, Shown Here In The Posterior Projection.

        Indication :
            To Check For The Presence Of A Blood Clot Or Abnormal Blood Flow Inside The Lungs, Such As - Pulmonary Embolism
            Performed In The Case Of Serious Lung Disorders Such As - Chronic Obstructive Pulmonary Disease (COPD) Or Pneumonia
            Lung Performance Quantification Tool Pre And Post Lung Lobectomy Surgery
        Method :
            Ventilation And Perfusion Phases Of A V / Q Lung Scan Are Performed Together And May Include A Chest X-Ray For Comparison Or To Look For Other Causes Of Lung Disease
            A Defect In The Perfusion Images Requires A Mismatched Ventilation Defect To Be Indicative Of Pulmonary Embolism
            In The Ventilation Phase Of The Test, A Gaseous Radionuclide Such As : Xenon Or Technetium DTPA In An Aerosol Form Is Inhaled By The Patient Through A Mouthpiece Or Mask That Covers The Nose And Mouth
            In The Perfusion Phase The Test Involves The Intravenous Injection Of Radioactive Technetium Macro Aggregated Albumin (Tc99m - MAA)
            A Gamma Camera Acquires The Images For Both Phases Of The Study.
        Interpretation :
            Decreased Uptake Of The Inhaled Radioisotope - Indicate An Impaired Ability To Breathe, Airway Obstruction, Or Possible Pneumonia.
            Decreased Circulation Of The Injected MAA - Indicates A Problem With Blood Flow Into Or Within The Lungs.
            Localized Area Of Decreased Circulation Uptake (Wedge Shaped / Pie Shaped Configuration) With Normal Ventilation Images (Mismatched Defect) Suggests A Pulmonary Embolus Or Blood Clot In The Lungs, Which Leads To Reduced Perfusion.
                Decrease Perfusion - Wedge Shaped ; With Normal Ventilation

        Risk :
            Although This Test Uses Radioactive Materials, The Total Amount Of Radiation Exposure Is Low. In Order To Decrease The Radiation Exposure In Pregnant Patients, The Total Radioactive Dose May Be Decreased Or The Ventilation Phase Omitted.
            Computed Tomography With Radiocontrast Can Alternatively Be Performed.
            If Breastfeeding, Patient Must Be Counselled To Refrain From This Activity For Approximately 24 Hours.