Pulmonary Function Tests Spirometer A device that measures the volume of gas entering or leaving the...

Pulmonary Function

Tests

Spirometer

• A device that measures the volume of gas entering or leaving the mouth

• A spirometer measures changes in lung volume

• A spirometer measures subdivisions of vital capacity

• A spirometer does NOT measure RV

Vt Tidal volume

VC Vital Capacity

ERV/IRV Expiratory/Inspiratory reserve volumeThese are all measured easily with spirometers

FRC Functional residual capacity

RV residual volume

TLC Total lung capacity (RV + VC)

Measuring these requires more specialized equipment

RESPIRATORY MANOEUVRE

Maximal breath in

Maximal breath out

Tidal Volume

VtTotal Lung Capacity

Vital Capacity

VC

TLCVt

Residual Volume

RV

VC

TLCVt

Residual Volume

Functional Residual Capacity

RV

VtTLC

FRC

IC

TLC=VC + RV

RV

VC

TLCVt

Residual Volume

Subdivisions of Lung Volume

RV

ERV

IRV

VtVC

TLC

FRC

IC

TLC

Tidal volume

Dead space

? Totallungcapacity

Vital capacityTidal volume

Inspiratory reservevolume

Expiratory reservevolume

LUNG VOLUMES

? ResidualVolume

Capacities

• Total Lung Capacity– TLC = IC + FRC– TLC = RV + ERV + VT + IRV

• Functional Residual Capacity– FRC = RV + IRV

• Vital Capacity– VC = ERV + VT + IRV– VC= ERV + IC

FEV1 & FVC

• Forced expiratory volume in 1 second

– young trained athletes: 4.0 L

• Forced vital capacity– young trained athletes:

5.0 L

• FEV1/FVC = 80%

FEV1

FVC

By calculation: RV = TLC - VC

by spirometry

by body plethysmography or helium dilutionTLC

FRC = TLC - IC

VCFRC

RV

TLC

Vt

Normal

RV

ERV

IC

RV

VC

TLC

RV

VC

RV

VC

RV

VC

NormalObstructive Restrictive

Vital capacity is reduced in both obstructive and restrictive diseases

By definition means a reduced total lung capacity

Reduced vital capacity can suggest restriction

Restrictive lung disease

Vt

VCFRC

RV

TLC

Why measure residual volume?Look at two people with identical vital capacity

VCFRC

RV

TLC

Vt

Vt

VC

FRC RV

TLC

Be careful before citing “restrictive deficits” in people with obstructive lung disease

VCFRC

RV

TLC

Vt

Vt

VC

FRC RV

TLC

Emphysema Normal

in respiratory patients

FLOW-VOLUME CURVE

FVC + FEV1

FEV1/FVC

FEV1 + FVC cst FEV1/FVC

• Obstructive disease– resistance to

airflow – e.g., COPD,

asthma

FVC + FEV1

FEV1/FVC= cst

• Restrictive disease – expansion of the

lung – e.g., interstitial

fibrosis

Indication for lung volume test :• Low FVC : -? Restrictive -? Obstructive with hyperinflation and air trapping -? Mixed pattern -? Equivocal spirometry findings (FEV1&FVC at lower limit of normal)

Measuring TLC

• To measure TLC or FRC, which include RV, spirometry is insufficient

• Techniques:

–Gas dilution–Plethysmography (body box)

Gas dilution tests: Lung volume can be measured when a person breathes

nitrogen or helium gas through a tube for a specified period of time.

The final dilution of the gas used to calculate the volume of air in the thorax.

It is sensitive to errors Leakage of gas Failure to measure the volume of gas in lung

bullae.because helium may not mix with all parts of the lung . Helium doesn’t readily diffuse across the alveolar capillary membrane .

C1=N/Vbox

C2=N/(Vbox+FRC)

Gas Dilution

C1V1 C2

C2 C2

V2=V1 + FRC

C1V1 = C2V2

• Body Plethysmography (BP)

– Measurement of FRC by body plethysmograph is based on an application of Boyle’s law

P1V1 = P2V2

or

V1 = P2V2

P1

Lung Volumes / Gas Distribution

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• Boyle’s Law: for fixed mass of gas at constant temperature: P1V1 = P2V2

• Brief occlusion at airway opening to seal a fixed mass of gas in the lungs (V1) - i.e the FRC to be measured

• Pressure within lungs at end expiration (P1) ~ atmospheric pressure.

• P2 and V2 represent the pressure and volume in the lungs after a respiratory effort against the occlusion.

Plethysmography (Body Box)

• Boyle’s Law :• P1V1= k• Closed container whose volume can be

adjusted so that the pressure in the container increases in proportion to the fractional decrease in container volume.

Plethysmograph

Pm

Pbox

• No flow at the mouth so that DPm = Dpalv

• Pbox• Vbox is the volume of the

box (known)• Vth is the volume of the

thorax (unknown) Vth

Vbox

Plungx Vlung=P’lungx V’lung

V’lung = Vlung +∆VP’lung =Plung+∆P

Pbox x Vbox= P’box x V’box V’box =Vbox+∆VP’box =Pbox+∆P

Plung

Pbox x Vbox

Vlung

Plethysmography- measures total thoracic gas volume, but is more cumbersome. Uses Boyle’s law to calculate RV.

Plethysmography: Situation at end expiration, prior to any

respiratory efforts against an occlusion valve

During inspiratory efforts against the occlusion

As lung volume increases,box volume decreases and box pressure increasesAs lung volume

increases,alveolar pressure decreases and hence pressure at mouth decreases

P1 -ΔP

Changes in box pressure calibrated in terms of volume using a calibrated syringe


– Unlike gas dilution tests, BP includes both air in communication with open airways as well as air trapped within noncommunicating thoracic compartments

– In patients with air trapping, plethysmography lung volumes are usually larger those measured with gas dilution methods

– Volume measured is referred to as thoracic gas volume (TGV or VTG)

– ATS is recommending term be dropped and changed to “plethysmographic lung volume” (VL, pleth), and “FRC by body plethysmography” or TGV at FRC (FRCpleth)


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Body plethysmography

The patient sits inside a fully enclosed rigid box and breath through mouthpiece connected through a shutter to the internal volume of the box

The subject makes respiratory efforts against the closed shutter (like panting), causing their chest volume to expand and decompressing the air in their lungs.

while breathing in and out again into a mouthpiece. The volume of all gas within the thorax can be measured by Changes in pressure inside the box and allow determination of the lung volume.



Procedure

•Patient is required to support cheeks with both hands and pant with an open glottis at a rate of 0.5 - 1 Hz (30 – 60 breaths/min)

•BP shutter is suddenly closed at end-expiration prior to inspiration

•Panting is continued for several breaths against closed shutter (no air flow)

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Procedure

•The thoracic-pulmonary volume changes during panting , produce air volume changes within the BP cabinet

•Decreases in cabinet volume are an equal inverse response to thoracic volume increase (As thoracic volumes increase with panting inspiration, BP cabinet volume decreases and visa versa)

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Criteria of Acceptability

•Panting maneuver shows a closed loop without drift

•Tracing does not go off the screen

•Panting is 0.5 – 1 Hz

•Tangents should be within 10%

•At least 3 FRCpleth values should agree within 5% and the mean reported

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The history of clinical whole body plethysmography

• 1923 - 1959 Verzar, Du Bois, Mead etc

• 1972, 2005 Matthys „Historische Entwicklung der klinischen Ganzkörperplethysmographie“

Atemw.u.Lungenkrkh. 31/4, 204-211

1790 Menzies „Dissertation on Respiration“ 1881/2 Gad und Pflüger, „Residualvolumen“


• Body Plethysmograph– Two types

• Constant-volume, variable-pressure • “Pressure Plethysmograph”

• Flow or variable-volume• “Flow Plethysmograph”

• Both measure thoracic gas volumes and airway resistance and it derivatives

• Both use a pneumotachometer to measure flow and a mouth transducer with a shutter to measure alveolar pressure

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• Body Box– Calibration– Mouth pressure is verified with

a mercury or water barometer– Flows are verified with a

rotometer (flow-metering device) or a 3-liter syringe

– Box pressure is calibrated by using a sine-wave rotary pump

• simulates inspiratory/expiratory volumes

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INTERPRETATION of RESULTS

• In patients with obstructive diseases– airway closure occurs at an abnormally high lung volume

FRC (functional residual capacity) RV (residual volume)

• Patients with reduced lung compliance (e.g., diffuse interstitial fibrosis)

– stiffness of the lungs + recoil of the lungs to a smaller resting volume

FRC RV

Clinical Applications and Interpretations

FRC

• gas trapping due to intrathoracic airway obstruction

• cystic lung disease

FRC

• abnormal alveolar development

• reduced recoil of chest-wall

• decreased lung compliance

• atelectasis47

What do the results mean: Algorhithim for PFT's

Assessing severity of restrictive defects

• Without TLC measurement, base severity on the FVC– ≥80% is considered “normal”– 70-80% is considered mild– 60-70%% is considered moderate– 60% is considered severe

• When TLC is measured– Gold standard to define restrictive ventilatory

defect– Only order “Full PFTs” if you suspect

restrictive or interstitial lung disease (expensive!)

yes n o

yes n o

yes n o

What do the results mean: Algorhithim for PFT'sIs the FEM adequate?

Is the FEV1/FVC lower than predicted?

Interpretation may be limited by falsely low FVC

This is the definition of obstructionMild FEV1 >70%Moderate FEV1 60-70%Mod severe FEV1 50-60%Severe FEV1 <50%Very severe FEV1 <40%

Is FVC reduced?

Restriction may be present; Need TLC to definitively diagnose restriction

Lung volumes:Severity determined bythe reduction in TLCMild 65-80%Moderate 50-65%Severe <50%

Spirometry:Severity is determined by the reduction in VCMild 70-80%Moderate 60-70%Severe <60%

Normal pulmonary mechanics

Restriction

What can PFTs tell you about the patient

• Normal or abnormal• What diseases can you diagnose?

– Only asthma is defined by its PFTs

• Estimation of impairment, or severity of disease

• Response to therapy• Occupational surveillance

What PFTs cannot tell you

• Does the degree of abnormality explain the patients symptoms?

• “Normality” does not exclude the presence of disease

• Abnormal test may not reflect loss of lung function

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By this technique we will be able to know

Residual volume (RV) Tidal volume (TV) Total Lung Capacity (TLC) Expiratory reserve volume (ERV) Inspiratory Reserve Volume (IRV) Inspiratory capacity (IC) Functional residual capacity (FRC) Vital Capacity (VC)

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Residual volume (RV) It is the volume of air remaining in the lungs at the end of maximal expiration. Normally it accounts for about 25% of TLC. - RV increased in airway narrowing with air trapping (Asthma) or in loss of elastic recoil (emphysema).- RV decreased in Increased elastic recoil (pulmonary fibrosis)

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Tidal volume (TV) It is the volume of air inspired or expired with each breath during normal breathing ( 7ml/kg) 400-700mlTV decreased in severe RLD

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Total Lung Capacity (TLC)It is the total volume of air within the lung after maximum inspiration. (the maximum volume of air that the lung can contain). TLC = FVC + RV OR TLC = RV + ERV + TV + IRVTLC Increased in airway narrowing with air trapping (Asthma) or in loss of elastic recoil (emphysema). TLC Decreased in RLD , increased recoil (Pulmonary fibrosis), muscle weakness, Obesity…

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Expiratory reserve volume (ERV):

It is the maximal volume of air exhaled from the resting end-expiratory level. ( volume expired by active expiration after passive expiration.ERV: From TV to RV ERV decreased in RLD

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Inspiratory Reserve Volume (IRV):

It is the maximal volume of air inspired with effort in excess of tidal volume IRV: From TV to TLC

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Inspiratory capacity (IC):

It is the maximal volume of air inspired from resting expiratory level

IC= IRV+TV.

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Functional Residual Capacity (FRC) It is the volume of air remaining in the lungs at the end of resting

(normal) expiration. FRC = RV + ERV.-FRC Increased (>120% of predicted) in Emphysema (decreased elastic recoil), Asthma, bronchiolar obstruction (air trapping)-FRC decreased in intrinsic ILD or by upward movement of diaphragm (obesity,painful thoracic or abdominal wound)

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Vital Capacity: volume of gas measured on complete expiration after complete inspiration without effort

VC= TLC – RV or VC= IRV+TV+ERVdecreased in OLD and RLD( VC < 15 ml/kg (and VT < 5ml/kg) indicates likely need for mechanical ventilation

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Lung volumes & capacities

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Lung Volume in Obstructive Lung Disease

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Obstructive Lung Disease

Narrowing and closure of airways during expiration tends to lead to gas trapping within the lungs and hyperinflation of the chest.

Air trapping → increase in RV Hyperinflation → increases TLC

RV tends to have a greater percentage increase than TLC

RV/TLC ratio is therefore increased (nl 20-35%)

Gas trapping may occur without hyperinflation (increase in RV & normal TLC)

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Gas trapping and airway closure at low lung volume cause the patient to breath at high lung volume so FRC (RV+ERV) increased

This will prevent airway closure and improve ventilation-perfusion relationship

It will reduce mechanical advantage of respiratory muscles and increases the work of breathing

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Obstructive Lung Disease cont.

RV increasedTLC Nl/increasedRV/TLC increasesFRC increasedVC decreased*Air trapping :Normal TLC with

increase RV/TLC

*Hyperinflation: Increase in both

TLC and RV/TLCl/

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Lung Volume in Restrictive Lung Disease

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Reduction in TLC is a cardinal feature

1. In Intrinsic RLD (Interstitial Lung Disease)

TLC will decrease

RV will decrease because of increased elastic recoil (stiffness) of the lung and loss of the alveoli.

Breathing take place at low FRC because of the increased effort needed to expand the lung .

RV/TLC normal

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2. In extrinsic RLD (chest wall disease :kyphoscoliosis or neuromuscular disease:ALS,MG)

TLC is reduced either because of mechanical limitation to chest wall expantion or because of respiratory muscle weakness

RV is Normal because Lung tissue and elastic recoil is normal

So RV/TLC ratio will be high

Breathing take place at low FRC because of the increased effort needed to expand the lung .

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Restrictive Lung Disease:

RLD Intrinsic & severe chest wall dis (pleural and skeletal) TLC decreasedRV decreasedRV/TLC normalFRC decreasedVC decreased

Extrinsic RLD TLC decreasedRV normalRV/TLC HighVC decreasedFRC decreased

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3. In combined obstructive and restrictive disease (e,g.sarcoidosis ,COPD+IPF)

Obstructive pattern on spirometry and Reduced lung volume

4. In equivocal spirometry result :e,g.when FEV1,FVC at lower limit of normal If TLC or RV raised the diagnosis is obstructivelung disease

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RLD Extrinsic

RLD Interinsic

Obstructive Lung dis.

FEV1

FVC

FEV1/FVC

RV

TLC

RV/TLC

VC

FRC

Interpretation: no significant differences of the measured data from the normal reference values

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Interpretation: Cough with light obstructive ventilatory defect and relative overinflation

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Interpretation: severe effort dependant intrathoracic airway obstruction with overinflation and trapped air

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Interpretation: Severe intrathoracic airway obstruction,slightly reversible overinflation after ß2-agonist

inhalation

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Interpretation: Mixed restrictive and obstruciveventilatory defect with relative overinflation

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Interpretation: Carbacholtest positive, overinflation with good reversibility after ß2-agonist inhalation

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The infant plethysmograph

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Infant plethysmography

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Plethysmography: Closed system: changes in thoracic volume are inversely proportional to changes in ‘box’ volume.

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Pulmonary Function Tests Spirometer A device that measures the volume of gas entering or leaving the...

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Transcript of Pulmonary Function Tests Spirometer A device that measures the volume of gas entering or leaving the...