Pulmonary Function Testing

SPECIALIZED TEST REGIMENS

The diagnosis of specific pulm. disorders requires

certain testing

 The subject must go through a thorough Hx RegimensClinic or MDs office– VC, FVC, FEVT, FEVT%, FEF 25-75, 200-1200, MVV,

VT, f, VE

Hospital lab & CP lab– lung volumes and diffusing capacity

PULMONARY FUNCTION TESTING IN CHILDREN

Uses many of the same basic tests as for adults

Differences exists in dimensions and two main areas of concern– newborns, infants, and very young children cannot

strictly perform tests that require and depend on pt. cooperation ( VC, FVC, MVV and DLCO)

– young children may perform with variability those tests that are effort dependent and require cooperation

A cooperative patient and good PFT technologist

Children may not meet ATS criteria but careful evaluation of partial parameters can provide important information.

Techniques for infants and young children

Partial Exp. Flow-Volume Curves ( PEFV) -

record of the maximal flow developed over a portion of the VC

The forced exhalation is obtained by applying either a positive pressure to the thorax and abdomen or a negative pressure to the airway

RAPID THORACOABDOMINAL

COMPRESSION ( RTC) the “squeeze” or “hug”

Non-intubated infantsuses an inflatable jacket that surrounds the thorax and abdomen– the PEFV is obtained by rapidly applying pressure

to the thorax and abdomen at the end of insp.– performed after the infant has fallen asleep or

slightly sedated ( chloral hydrate)– flow is measured using an infant mask sealed with

a lubricant and attached to a low Ds pneumotach

Flow @ FRC or Vmax FRC

By Rapid Thoraco-Abd. Compression(Squeeze) expiratory flow

limitations can now also be measured in babies. The baby wears an inflatable cuff with the help of which a forced expiration is produced.From Viasys (Jaeger)

WOW!

testing

RAISED VOLUME RAPID THORACOABDOMINAL

COMPRESSION - RVRTC

 Standardization of spirometry is dependent on TLC

during insp., flow is augmented by a pump to increase pressure and volume

the airway is occluded at the exh. port using a cuff with variable pressure - rapid chest compression is then performed - higher flows are generated– uses a pump to increase volume before the squeeze

is performed

METHODS 

FORCED DEFLATION TECHNIQUE - The infant needs to intubated, sedated & paralyzed– the lungs are manually inflated to TLC using approx. +40

cmH20 - performed 4 times with a 2-3 sec breath hold– the airway is then connected to a source of negative

pressure ( -40 cmH20)– air is evacuated for a max. of 3 secs or until airflow

ceases– exp. flow is plotted on a flow - volume graph– lungs are reinflated with 100 % O2 – reserved for the critically ill

BRONCHODILATOR BENEFIT TEST

Is the dz is reversible? Let’s find out.

Indication– a pt. with an FEV1% of less than 70%

Technique– follow guidelines on withholding certain meds prior

to test– do PFT - give tx with bronchodilator via neb or

MDI - wait 15-20 mins before doing post tests– monitor pt. for adverse effects

Significance

Calculate “ percent change of each parameter”

%change = postdrug - predrug predrug

FEV 1 or FVC are evaluated - an increase of > 12 % and > 200 ml is significant

asthma shows the best improvement

SGaw should increase 30-40 % to be significant

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

FVC FEV1 SGAW

% Pred

% Pred Postdrug

% Change

BRONCHOPROVOCATION  (METHACHOLINE CHALLENGE)

Methacholine

Used to determine whether or not a patient has a disorder of airway hypersensitivityAnd to what extentIs a parasympathomimetic – May trigger bronchospasm

Methacholine challenge

the test is positive when there is a 20 % decrease in the FEV 1 - the concentration at which the decrease occurs is called the provocative concentration or PC20% Healthy subjects do not display a decrease in FEV1 greater than 20 %

SGaw can be used with FEV1 to demonstrate a reactionUse a 16 mg/ml stock methacholine solution

Technique

Subjects should be tested when asymptomatic, baseline FEV 1 > 70 % of the pt. normWithhold meds according to chart2 methods accepted by ATS,1st baseline spiro– 5-breath dosimeter method– 2-minute tidal breathing

method

5-Breath Dosimeter Method

Dosimeter- deliveres a consistent volume of drug– Uses 5 doses each 4 x larger than the previous– pt. inhales 5 nebulized NS breaths 1st – perform spirometry– if no positive response, start dosimeter

inhalations of 5 breaths for 2 minutes– Repeat spirometry

• Use largest FEV1 and the average of 2 RAW

• Look for > 20% drop in FEV1 and > 35% drop in SGAW

2-Minute Tidal Breathing Method

Use nebulizer, nose clips and relaxed breathingPerform diluent inhalation first, then spirometry10 double concentrated doses are used, each dose is breathed for exactly 2 minutesSpirometry is performed 30 & 90 seconds after the dose– Look for > 20% in FEV1 and >35% drop in SGAW

– Give a bronchodilator & repeat spirometry in 10”

To caluculate the percent of decrease

%Decrease =Con. FEV1 – Current FEV1

Control FEV1

Preoperative PF Testing- to…

Estimate postop lung functionPlan periop careEstimate morbidity & mortalityLook at– Spirometry/obstruction– Bronchodilation studies– ABG’s, Ex. Testing &

DLCO

PULMONARY FUNCTION TESTING FOR DISABILITY

Respiratory impairment - the failure of one or more functions of the lungs as determined by PFTDisability - the inability to perform tasks required for employment and includes medically determinable physical or mental impairment - the impairment must be expected to result in death or last for at least 12 months

To determine impairment

should characterize the type, extent and cause of impairmentother factors need to be known - age, educational background and the subjects motivation and energy requirementsfor pulm. dz impairment, you also need a hx, physical, CXR, other appropriate imaging techniques and PFT’s - (should be specific to disorder being investigated)

FVC and FEV1

spirometry is the most useful for determination of impairment caused by airway obstruction– the subject should be stable- use largest of the 3 tests– the 2 largest FVC and FEV1 should be within 5% or 100 cc– should be cont. for 6 secs or no volume change detected for 2 secs– - must have a volume-time tracing so hand calculations can be performed– before and after bronchodilator - all parameters reported in BTPS and ht.

obtained without shoes or arm span method– must use disability limits– Calibration of equipment is specific and must be documented

DLCO & ABG’s

useful in determining disability for restrictive disorders– should not be corrected for Hgb or COHb abnormalities but…

the values at the time of the test should be noted– if the DLCO is > 40% predicted but < 60% , get resting ABG

ABGs – may be nonspecific due to various factors – look at other parameters along with ABGs

Exercise Testing

subjects considered should have resting ABGsa Steady State protocol using the treadmill is preferredspecific protocols should be followedLimits for determining disability on the bases of pulm. impairment have been set for the US by the SS administration