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PULMONARY FUNCTION TESTS

Speaker : Maj SR JaiswalDNB Resident Medicine

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Indications

• Differential diagnosis of dyspnea• Provides objective assessment of symptoms

versus severity• Determine fitness for surgery• To guide therapy • To follow the course of a disease

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Physiologic classification of disease

• Obstructive Impairment- Airway limitation due to the resistive properties of the respiratory system

• Restrictive Impairment- Loss of volume capacity of the lung due to loss of air space units or inability to expand the respiratory system

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Obstructive Processes

• L ocal obstruction• A sthma• C hronic bronchitis (COPD)• E mphysema

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Restrictive Processes

• P leural disease• A lveolar filling processes• I nterstial lung disease• N euromuscular diseases• T horacic cage abnormailites

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Spirometry

• Most widely performed study and is important in initial screening of patients

• Easily and quickly performed in many settings

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Prior to testing

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Performing the maneuver• It is a forced expiratory maneuver and the

patient must be sitting upright in a chair with lips around a mouthpiece

• After a maximal inspiration, a forced and rapid expiration is made

• Quality of the maneuver needs to be assessed noting that the patient started at zero, had a maximal initial efffort and lasted 6 seconds.

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Normal spirometry

• FVC - The maximum volume of air that is forcefully exhaled after a maximum inspiration

• FVC >80% of predicted (normal)

• FEV1 - The volume of air exhaled during the first second of the FVC maneuver

• FEV1 >80% of predicted (normal)

• Lung volume = 80 - 120% of predicted (normal)

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Normal Flow - Volume curve

PEF - peak expiratory flow; RV - residual volume; TLC - total lung capacity

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Measurements

• FVC• FEV1• FEV1/FVC

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FVC Measurement

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FEV1 Measurement

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Effort

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Poor effort

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Acceptability

• Test acceptability is best determined by studying the flow-volume loops

• Criteria– Freedom from artifacts– Good starts– Satisfactory expiratory time

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Reproducibility of data

• Criteria

– The two largest forced vital capacity (FVC) – 0.2 L or 5% of each other

– The two largest FEV1 – 0.2 L or 5% of each other

Up to eight efforts may be performed

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Obstructive Ventilatory Defects FEV1: FVC <70% (OVD)

• Once the diagnosis of an OVD has been made the defect needs to be fully characterized by

– Quantifying the severity of the OVD– Assessing the reversibility of the obstruction– Determining whether there is hyperinflation– Determining whether there is air trapping

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Quantifying the severity of the OVD

• Normal: FEV1 >80% of predicted

• Mild: FEV1 = 65 - 80% of predicted

• Moderate: FEV1 = 50 - 64% of predicted

• Severe: FEV1 <50% of predicted

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Assessing the reversibility

• Postbronchodilator FEV1 improves by both 12% and 200 mL,

OR

• Postbronchodilator FVC improves by both 12% and 200 mL

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Hyperinflation

• TLC >120% of predicted,

OR

• RV >120% of predicted

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Air trapping

• SVC > FVC by both 12% and 200 mL

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The methacholine challenge test

• Asthma - reversible obstructive airway disease

• Multiple pfts may only demonstrate normal spirometry

• Bronchial provocation testing

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• The administration of a sterile saline aerosol

• FEV1 after 3 - 5 mins

• Increasing concentrations of methacholine at 5-min intervals (0.003 mg/mL to 16 mg/mL)

• FEV1 is measured 3 - 5 mins

• Decrease in FEV1 >20% is a positive response

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Upper Airway Obstruction

Variable extrathoracic obstruction

Variable intrathoracic obstruction

Fixed upper airway obstruction

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Restrictive Ventilatory Defects

• TLC <80% of predicted (RVD)• Normal or increased FEV1: FVC ratio

• The defect needs to be quantified

– Normal: TLC >80% of predicted– Mild: TLC = 65 - 80% of predicted– Moderate: TLC = 50 - 64% of predicted– Severe: TLC <50% of predicted

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Bronchodilator Response

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Bronchodilator testing

• No short acting agents for 4 hrs• No long acting beta agonists for 12 hrs• No theo for 12 hrs• No smoking for 1 hr • Beta agonist given recommended 4 puffs and

wait 10-15 minutes later

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Lung Volumes• May be measured by multiple methods

• Is important to understand what volumes the lung is composed of

• The total volume of the lung is TLC

• The subdivisions include ERV, IRV, TV,and RV

• Capacities are composed of 2 or more volumes.

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Volumes : (1) tidal volume (VT), (2) inspiratory reserve volume (IRV), (3) expiratory reserve volume (ERV), (4) residual volume (RV)

Capacities: (1) total lung capacity (TLC), (2) vital capacity (VC), (3) inspiratory capacity (IC), (4) functional residual capacity (FRC)

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Methods

• Body Plethysmography – Pressure (Closed-Type) Plethysmograph– Volume (Open-Type) Plethysmograph– Pressure-Volume Plethysmograph

• Gas Dilution Methods– The opencircuit nitrogen (N2) method – The closed-circuit helium (He) method

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The Opencircuit Nitrogen (N2) method

Involves having nitrogen in patients lung being washed out by inhaling 100% O2 for several minutes.Widely used, easy to perform but may underestimate bullous lung diseasePerformed by having the patient breath comfortably for several minutes and then turn in to 100% O2 at FRC.Monitor N2 concentrations and test ends when falls below 1%Easy to see leaks

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Nitrogen Washout

• Concept is C1V1= C2V2– C1 = Nitrogen concentration at the start of the test– V1 = FRC volume– C2 =N2 concentration in exhaled volume– V2 = Total exhaled volume during O2 breathing

period– Nitrogen is measured by photoelectric principle

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The closed-circuit helium (He) method

• Uses an inert gas, helium and by a closed circuit technique, allow it to come to equilibrium and FRC is measured

• May underestimate lung volumes in bullous lung disease

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• 10% He

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Body Plethsymography

• Is a sealed box with a fixed volume

• Uses Boyle’s Law that changes in pressure are brought about by changes in volume and pressure for the person seated in the box

• P1V1= P2V2

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Pressure (Closed-Type) Plethysmograph

The subject breathes through a shutter / pneumotachygraph

When the shutter is closed, mouth pressure is measured by a pressure transducer (1). The pneumotachygraph measures airflow with another transducer (2). Plethysmograph pressure is measured by a third transducer (3).

The signals from the three transducers are processed by a computer.

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Volume (Open-Type) Plethysmograph

This constant-pressure, variable-volume type of Plethysmograph

The subject breathes through a shutter / pneumotachygraph. In the closed-shutter mode mouth pressure is measured by a transducer (1) The pneumotachygraph measures flow via another transducer (2)

Flow is integrated electronically to obtain volume, Changes in volume of theplethysmograph, reflecting movement of the chest wall, are measured with a spirometer and a linear volumedisplacementtransducer (LVDT)

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Pressure-Volume Plethysmograph

This type of plethysmograph combines features of the closed and open types

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Lung volume measurements

• FRC is directly measured as well as SVC

• Other volumes and capacities can be calculated

• Lung volume measurements are important to confirm RLD

• TLC and RV the usual volumes assessed

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Interpretation

• RLD

– TLC is reduced in all

– Predicted values and interpret same as FVC and FEV1

• OLD

– TLC can be increased and is then called hyperinflation (120%)

– RV can be increased in asthma and COPD indicating air trapping

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Lung Elastic Recoil

• Lung elastic recoil pressure, or transpulmonary pressure (PL)• PL = Palv – PPl

– Palv - the alveolar pressure,– Ppl - the pleural pressure

• The muscles of inspiration must maintain a pleural pressure of about 12 cm H2O below atmospheric pressure (pPl = -12 cm H2O).

• Under conditions of no flow, pressure at the mouth, alveoli, and atmosphere are equal: pL = 0 - (-12 cm h2o)

• PPl rises from -12 to 0 cm H2O and palv from 0 to +12 cm H2O at the instant before flow begins

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All that is needed to measure lung elastic recoil pressure and lung compliance is a measurement of PPl in relation to lung volume.

Because the esophagus passes through the pleural space

Pressure within the esophagus approximates pPl

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Diffusing Capacity

• Provides information about the transfer of gas between the alveoli and the pulmonary capillary bed

• It is the only noninvasive test of gas exchange

• Performed by a single breath technique and uses CO as the inert gas

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Diffusing Capacity

• Diffusion of a gas is dependent of the area, the concentrations, the thickness of the membrane and the diffusing properties of the gas

• Diffusion is the rate at which a gas is transferred across the alveolar capillary membrane, the plasma, the RBC and ultimately combined with Hgb

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Diffusing Capacity

• CO is typically used because it is freely diffusable

• It usually is not present in significant amounts in the blood except in some heavy smokers

• Helium or methane is also used to measure volume

• A single maximal inspiration is taken and held for 10 sec

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Diffusing Capacity

• Normal result is >80%

• Can be reduced in interstitial diseases such as sarcoid or asbestosis

• Can be reduced also in emphysema or pulmonary vascular diseases

• False low measurements in anemia or lung resection and elevated in alveolar hemm

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Bedside evaluation of Pulmonary Function

• Snider’s match blowing test• Modified Snider’s test• Seberese’s single breath count• Seberese’s breath holding test• Cough test• De Bono’s Whistle test• Wright’s peak flow meter test• Bed side pulse oximetry• Blow against the hand

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Snider’s match blowing test

• Mouth wide open• Match held at 15 cm distance• Chin is supported• No head tilting• Match stick and mouth at the

same level

• Cannot blow out a match– MBC < 60 L / min– FEV1 < 1.6 L

• Able to blow out a match– MBC > 60 L / min– FEV1 > 1.6 L

Modified Snider’s test

• When the Match is placed at a distance of– 3 inches – MBC > 40 L / min– 6 inches – MBC > 60 L / min– 9 inches – MBC > 150 L min

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• Deep breath followed by cunting 1,2,3,…….. Till the time the subject cannot hold the breath

• Shows treands of deterioration / improving pulmonary function in pre and post op patients

Seberese’s breath holding test

• Subject is asked to take a normal tidal inspiration and hold the breath

– Normal ->= 40 sec– < 15 sec is a C/I for elective

surgery

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• Observe for ability to cough,strength and effectiveness

• Wet productive cough candidate for pulmonary complications

• Inadequate cough FVC < 20 ml / kg

De Bono’s whistle test

• Ability to blow into the whistle is tested

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• Volume < 200 L / min in surgical candidate suggest impaired cough efficiency

• Normal males 450 – 700 L / min• Normal females 300 –500 L/min

Blow against the closed hand

• Check I : E ratio

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Summary

• Spirometry- Most commonly performed and useful screening test.

• Lung volumes- Can be measured several different ways. Are used to evaluate for restrictive disease and will also show air trapping

• Diffusing Capacity - Transfer of gas across the alveolar membrane

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References

• Murray & Nadel's Textbook of Respiratory Medicine, 4th ed

• Washington Manual(R) Pulmonary Medicine Subspecialty Consult

• Oxford Handbook of Respiratory Medicine• Current recommendation is NHANES III