Pulmonary Function Tests

Presenter: Dr. Sofia PatialModerator: Dr. Gian Chauhan

GOALS To predict presence of pulmonary

dysfunctionTo know the functional nature of disease.To assess the severity of diseaseTo assess the progression of diseaseTo assess the response to treatmentMedicolegal- to assess lung impairment

as a result of occupational hazard.To identify patients at perioperative risk

of pulmonary complications

INDICATIONS OF PFT IN PAC

TISI GUIDELINES FOR PREOPERATIVE SPIROMETRY

Age > 70 yrs.Morbid obesity Thoracic surgeryUpper abdominal surgerySmoking history and coughAny pulmonary disease

ACP GUIDELINES FOR PREOPERATIVE SPIROMETRY

Lung resectionH/o smoking, dyspnoeaCardiac surgeryUpper abdominal surgeryLower abdominal surgeryUncharacterized pulmonary

disease (defined as history of pulmonary Disease or symptoms and no PFT in last 60 days)

Contraindications:Hemoptysis of unknown originPneumothoraxUnstable cardiovascular status, recent

MI, pulmonary embolismThoracic, abdominal or cerebral

aneurysmsRecent eye surgery (cataract)Nausea, vomitingRecent surgery on thorax or abdomen

Components of PFT’s:

Spirometry for measuring airway mechanics (dynamic flow rates of gases)

Measuring lung volumes and capacities

Measuring diffusion capacity of lung

Spirometry

PREREQUISITIES Prior explanation to the patient Not to smoke /inhale short acting

bronchodilators 4 hrs prior or oral aminophylline and long acting bronchodilator 12hrs prior.

Remove any tight clothings/ waist belt/ dentures

Pt. Seated comfortably If obese, child < 12 yrs- standing Nose clip to close nostrils. 3 acceptable tracings taken & largest value is

used.

FVCForced vital capacity (FVC): Total volume of air that can be

exhaled forcefully from TLC Exhalation time at least 6sec for

adults & children> 10 yrs 3 sec for children< 10 years Interpretation of % predicted:

◦ 80-120% Normal◦ 70-79% Mild reduction◦ 50%-69% Moderate

reduction◦ <50% Severe reduction

FEV1

Volume of air forcefully expired in 1st second of FVC

N- FEV1 (1 SEC)- 75-85% OF FVC FEV2 (2 SEC)- 94% OF FVC FEV3 (3 SEC)- 97% OF FVC

FEV1/FVC ratio Reduced in obstructive lung

diseases <70%: mild obst, <60% mod obst, <50%: severe obst

FEF25-75

Mean forced expiratory flow in middle half of FVC

Reflect status of small airways Effort independent expiration N value – 4.5-5 l/sec Or 300 l/min. Upto 2l/sec- acceptable. CLINICAL SIGNIFICANCE:

SENSITIVE & 1st INDICATOR of obstruction of small distal airways

Interpretation of % predicted:>79% Normal60-79% Mild obstruction40-59% Moderate obstruction<40% Severe obstruction

PEFR max. Flow rate during initial

0.1 sec of FVC . DETERMINED BY : Function of caliber of

airways Expiratory muscle strength Pt’s coordination & effort Normal value in young

adults (<40 yrs) > 500L/min Clinical significance - values

of <200 L/m- impaired coughing & hence likelihood of post-op complication

MAXIMUM BREATHING CAPACITY: (MBC/MVV)

Largest volume that can be breathed per minute by voluntary effort , as hard & as fast as possible.

N – 150-175 l/min. Estimate of max. ventilation available to meet

increased physiological demand. Measured for 12 secs – extrapolated for 1 min. MVV = FEV1 X 35 MVV altered by- airway resistance - Elastic property -Muscle strength - Learning, Coordination, Motivation

RESPIRATORY MUSCLE STRENGTH

MAX STATIC INSP. PRESSURE: (PIMAX)- Measured when inspiratory muscles are at their optimal

length i.e. at RV PI MAX = -125 CM H2O CLINICAL SIGNIFICANCE: IF PI MAX< 25 CM H2O – Inability to take deep breath. MAX. STATIC EXPIRATORY PRESSURE (PEMAX): Measured after full inspiration to TLC N VALUE OF PEMAX IS =200 CM H20 PEMAX < +40 CM H20 – Impaired cough ability Particularly useful in pts with NM Disorders during

weaning

Flow-Volume Loop

Illustrates maximum expiratory and inspiratory flow-volume curves

Useful to help characterize disease states (e.g. obstructive vs. restrictive)

Reversibility: Indicate effective therapySpirometry before & after

bronchodilator12% or greater improvement in

FEV1 and at least 200 ml increase in FEV1 .

post FEV1-pre FEV1

% improvement= ------------------------- x100

Pre FEV1

Bronchial Challenge:Detects hyperreactive airwayIndication- patients of seasonal or

exercise induced wheezing with normal spirometry results

use of agents like histamine, methacholine, cold air, exercise etc.

Start with NS aerosol- positive response: 10% or more decrease in FEV1

Methacholine aerosol (0.03,0.06,16mg/ml)Positive response- 20% or more decrease in FEV1

e.g; PD22FEV1 = 4mg/ml

NORMAL VALUES

MALES IRV 3.3 L TV 0.5 L ERV 1.0 L RV 1-2 L

TLC 6.0 L

FEMALES 1.9 L

0.5 L

0.7 L

1.1 L

4.2 L

FACTORS INFLUENCING VC PHYSIOLOGICAL : physical dimensions- directly proportional to ht. SEX – more in males : large chest size, more muscle power,

more BSA. AGE – decreases with increasing age Strength of respiratory muscles POSTURE – decreases in supine position PREGNANCY- unchanged or increases by 10% ( increase in

AP diameter In pregnancy) PATHOLOGICAL: disease of respiratory muscles Abdominal condition : pain, dis. and splinting

DIFFERENT POSTURES AFFECTING VC

POSITION

TRENDELENBERG

LITHOTOMY PRONE RT. LATERAL LT. LATERAL

DECREASE IN VC

14.5% 18% 10% 12% 10%

in post operative period if VC falls below 3 times VC– artificial respiration is needed to maintain airway clear of secretions.

FACTORS AFFECTING FRCFRC INCREASES WITHIncreased height Erect position (30% more than in supine) Decreased lung recoil (e.g. emphysema)FRC DECREASES WITHObesity Muscle paralysis (especially in supine) Supine position Restrictive lung disease (e.g. fibrosis,

Pregnancy) AnaesthesiaFRC does NOT change with age.

FUNCTIONS OF FRC Oxygen store Buffer for maintaining a steady arterial

po2 Partial inflation helps prevent atelectasis Minimise the work of breathing Minimise pulmonary vascular resistance Minimised V/Q mismatch

- only if closing capacity is less than FRC Keep airway resistance low (but not

minimal)

MEASUREMENTS OF VOLUMESTLC, RV, FRC – MEASURED USING Nitrogen washout methodInert gas (helium) dilution

methodTotal body plethysmography

1) HELIUM DILUTION METHOD:

Patient breathes in and out of a spirometer filled with 10% helium and 90% o2, till conc. In spirometer and lung becomes same

As no helium is lost; (as He is insoluble in blood) C1 X V1 = C2 ( V1 +V2)

2) TOTAL BODY PLETHYSMOGRAPHY: Subject sits in an air tight box. At the end of normal exhalation – shuttle of mouthpiece

closed and pt. is asked to make resp. efforts. As subject inhales – expands gas volume in the lung so lung

vol. increases and box pressure rises and box vol. decreases.BOYLE’S LAW: PV = CONSTANT (at constant temp.)For Box – p1v1 = p2 (v1- ∆v)For Subject – p3 x v2 =p4 (v2 - ∆v)P1- initial box pr. P2- final box pr.V1- initial box vol. ∆ v- change in box vol.P3- initial mouth pr., p4- final mouth pr.V2- FRC

DIFFERENCE BETWEEN THE TWO METHODS: In healthy people there is very little difference. Gas dilution technique measures only

communicating gas volume. Thus, Gas trapped behind closed airways Gas in pneumothorax => are not measured by gas dilution technique, but

measured by body plethysmograph

3) N2 WASH OUT METHOD: Following a normal expiration (FRC), Pt. inspires 100% O2 and

then expires it into spirometer ( free of N2) over next few minutes (usually 6-7 min.), till all the N2 is

washed out of the lungs. N2 conc. of spirometer is calculated followed by total vol.of AIR

exhaled. As air has 80% N2 →so actual FRC calculated.

PROBLEMS WITH N2 WASH OUT METHOD

Atelectasis may result from washout of nitrogen from poorly ventilated lung zones (obstructed areas)

Elimination of hypoxic drive in CO2 retainers is possible

Underestimates FRC due to underventilation of areas with trapped gas

TESTS FOR GAS EXCHANGE FUNCTION1) ALVEOLAR-ARTERIAL O2 TENSION

GRADIENT: Sensitive indicator of detecting regional V/Q

inequality N value in young adult at room air = 8 mmHg to

upto 25 mmhg in 8th decade (d/t decrease in PaO2) AbN high values at room air is seen in

asymptomatic smokers & chr. Bronchitis (min. symptoms)

PAO2 = PIO2 – PaCo2 R

2) DYSPNEA DIFFENRENTIATION INDEX (DDI):

- To differentiate dyspnea due to resp/ cardiac disease

DDI = PEFR x PaCO2 1000- DDI- Lower in resp. pathology

3) DIFFUSING CAPACITY OF LUNG:

depends upon gradient and thickness of alveolo-capillary membrane.

defined as the rate at which gas enters into blood divided by its driving pressure.

DRIVING PRESSURE: gradient b/w alveoli & end capillary tensions.

DL CO = Vco /(P A CO–P c CO)

SINGLE BREATH TEST USING CO

Pt inspires a dilute mixture of CO and hold the breath for 10 secs.

CO taken up is determined by infrared analysis

N range 20- 30 ml/min./mmhg.NORMAL- 75-120% of predictedDL IS MEASURED BY USING CO, coz:A) High affinity for Hb which is approx. 210

times that of O2 , so does not rapidly build up in plasma

B) Therefore, pulm capillary partial pressure of CO ≈ 0

DLCO decreases in-Emphysema, lung resection, pul.

Embolism, anaemia Pulmonary fibrosis, sarcoidosis- increased

thicknessDLCO increases in:(Cond. Which increase pulm. bld flow)Supine positionExerciseObesityL-R shunt

TESTS FOR CARDIOPLULMONARY INTERACTIONS

Reflects gas exchange, ventilation, tissue O2.

QUALITATIVE- history, exam, ABG, stair climbing test

QUANTITATIVE- 6 minute walk test

1) STAIR CLIMBING TEST: If able to climb 3 flights of stairs without stopping/

dypnoea at his/her own pace-↓ed morbidity & mortality

If not able to climb 2 flights – high risk Quantitative assessment by measuring the max O2

uptake during exercise(VO2max). A 2-flight stair climb (20 steps/min) without dyspnea is

approx VO2max of 16ml/kg/min. VO2max≥20ml/kg/min: minimal risk VO2max≤15ml/kg/min: inc cardiopulmonary risk VO2max≤10ml/kg/min: high risk with 30% mortality

2) 6 MINUTE WALK TEST:Gold standardC.P. reserve is measured by estimating max.

O2 uptake during exerciseModified if pt. can’t walk – bicycle/ arm

exercises If pt. is able to walk for >2000 feet during 6

min, VO2 max > 15 ml/kg/min If 1080 feet in 6min( 180 feet in 1 min): VO2

of 12ml/kg/minSimultaneously oximetry is done & if Spo2

falls >4%- high risk

BED SIDE PFT1).Sabrasez breath holding test:

>25 sec.-normal

15-25 sec- limited CPR <15 sec- very poor CPR (Contraindication for elective

surgery) 25- 30 SEC - 3500 ml VC 20 – 25 SEC - 3000 ml VC 15 - 20 SEC - 2500 ml VC 10 - 15 SEC - 2000 ml VC 5 - 10 SEC - 1500 ml VC

2). SINGLE BREATH COUNT: It is a measure of the FRC. >15 : normal <15 : dec reserve 11-15 : mild impairment 5-10 : mod impaired <5 : severe impairment

3). FET (WATCH AND STETHOSCOPE TEST ): After deep breath, exhale maximally and forcefully & keep

stethoscope over trachea & listen. N. – 3-5 SECS. OBS.LUNG DIS. - > 6 SEC RES. LUNG DIS.- < 3 SEC

4) SCHNEIDER’S MATCH BLOWING TEST: Measures MBC

Ask to blow a match stick from a distance of 6” (15 cms) with- Mouth wide open, Chin rested, No purse lipping No head movement, No air movement in the room Mouth and match at the same level Can not blow out a match

MBC < 60 L/minFEV1 < 1.6L

Able to blow out a matchMBC > 60 L/minFEV1 > 1.6L

MODIFIED MATCH TEST: DISTANCE MBC 9” >150 L/MIN. 6” >60 L/MIN. 3” > 40 L/MIN.

5) GREENE & BEROWITZ COUGH TEST:deep breath f/by cough ABILITY TO COUGH STRENGTH EFFECTIVENESSINADEQUATE COUGH IF: FVC<20 ML/KG FEV1 < 15 ML/KG PEFR < 200 L/MIN. VC ~ 3 times TV for effective cough. wet productive cough / self propagated

paraoxysms of coughing – patient susceptible for pulmonary Complication.

6) WRIGHT PEAK FLOW METER: Measures PEFR

N – MALES- 450-700 L/MIN. FEMALES- 350-500 L/MIN. <200 L/min.–inadequate cough

efficiency.

7) DEBONO WHISTLE BLOWING TEST: Measures PEFR.Patient blows down a wide bore tube at the end of which is a whistle, on the side is a hole with adjustable knob. As subject blows → whistle blows leak hole is gradually increased till intensity of whistle disappears. At the last position at which the whistle can be blown , the PEFR can be read off the scale.

8)Wright respirometer : measures TV, MV (15 secs times 4) Instrument- compact, light and portable. Disadvantage: It under- reads at low flow rates and over- reads

at high flow rates. Can be connected to endotracheal tube or face mask Prior explanation to patients needed. Ideally done in sitting position. MV- instrument record for 1 min. And read directly TV-calculated and dividing MV by counting Respiratory Rate. Accurate measurement in the range of 3.7-20l/min.(±10%) USES: 1)bed side PFT 2) ICU – weanig pts. from ventilation.9) BED SIDE PULSE OXIMETRY10) ABG.

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