Pulmonary Function Tests - PowerPoint Presentation

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Pulmonary Function Tests

Presenter: Dr. Sofia

Patial

Moderator: Dr.

Gian

Chauhan

Slide2

GOALS

To predict presence of pulmonary dysfunction

To know the functional nature of disease.

To assess the severity of disease

To assess the progression of disease

To assess the response to treatment

Medicolegal

- to assess lung impairment as a result of occupational hazard.

To identify patients at

perioperative

risk of pulmonary complications

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INDICATIONS OF PFT IN PAC

TISI GUIDELINES FOR PREOPERATIVE SPIROMETRY

Age > 70 yrs.

Morbid obesity

Thoracic surgery

Upper abdominal surgery

Smoking history and cough

Any pulmonary disease

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ACP GUIDELINES FOR PREOPERATIVE SPIROMETRY

Lung resection

H/o smoking, dyspnoea

Cardiac surgery

Upper abdominal surgery

Lower abdominal surgery

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

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Contraindications:

Hemoptysis

of unknown origin

Pneumothorax

Unstable cardiovascular status, recent MI, pulmonary embolism

Thoracic, abdominal or cerebral aneurysms

Recent eye surgery (cataract)

Nausea, vomiting

Recent surgery on thorax or abdomen

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Components of PFT’s:

Spirometry

for measuring airway mechanics (dynamic flow rates of gases)

Measuring lung volumes and capacities

Measuring diffusion capacity of lung

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Spirometry

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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.

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FVC

Forced 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

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FEV

1

Volume

of air

forcefully

expired in 1

st

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

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FEF

25-75

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% Normal

60-79% Mild obstruction

40-59% Moderate obstruction

<40% Severe obstruction

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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

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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

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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

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Flow-Volume Loop

Illustrates maximum expiratory and

inspiratory

flow-volume curves

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

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Reversibility:

Indicate effective therapy

Spirometry

before & after bronchodilator

12% or greater improvement in FEV

1

and at least 200 ml increase in FEV

1

.

post FEV

1

-pre FEV

1

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

Pre FEV

1

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Bronchial Challenge:

Detects

hyperreactive

airway

Indication- 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 FEV

1

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Methacholine

aerosol (0.03,0.06,16mg/ml)

Positive response- 20% or more decrease in FEV

1

e.g

; PD

22

FEV

1

= 4mg/ml

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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

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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

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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.

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FACTORS AFFECTING FRC

FRC INCREASES WITH

Increased height

Erect position (30% more than in supine)

Decreased lung recoil (e.g. emphysema)

FRC DECREASES WITH

Obesity

Muscle paralysis (especially in supine)

Supine position

Restrictive lung disease (e.g. fibrosis, Pregnancy)

Anaesthesia

FRC does NOT change with age.

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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)

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MEASUREMENTS OF VOLUMES

TLC, RV, FRC – MEASURED USING

Nitrogen washout method

Inert gas (helium) dilution method

Total body plethysmography

Slide31

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)

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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

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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

Slide34

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.

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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 CO

2

retainers is possible

Underestimates FRC due to

underventilation

of areas with trapped gas

Slide36

TESTS FOR GAS EXCHANGE FUNCTION

1) 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 8

th

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

Slide37

2) DYSPNEA DIFFENRENTIATION INDEX (DDI):

To differentiate

dyspnea

due to

resp

/ cardiac disease

DDI =

PEFR x PaCO2

1000

DDI- Lower in resp. pathology

Slide38

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)

Slide39

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 predicted

DL IS MEASURED BY USING CO, coz:

High affinity for

Hb

which is approx. 210 times that of O2 , so does not rapidly build up in plasma

Therefore,

pulm

capillary partial pressure of CO ≈ 0

Slide40

DLCO decreases in-

Emphysema, lung resection,

pul

. Embolism,

anaemia

Pulmonary fibrosis,

sarcoidosis

- increased thickness

DLCO increases in:

(Cond. Which increase

pulm

.

bld

flow)

Supine positionExerciseObesityL-R shunt

Slide41

TESTS FOR CARDIOPLULMONARY INTERACTIONS

Reflects gas exchange, ventilation, tissue O2.

QUALITATIVE- history, exam, ABG, stair climbing test

QUANTITATIVE- 6 minute walk test

Slide42

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

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2) 6 MINUTE WALK TEST:

Gold standard

C.P. reserve is measured by estimating max. O2 uptake during exercise

Modified 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/min

Simultaneously

oximetry

is done & if Spo2 falls >4%- high risk

Slide44

BED SIDE PFT

1).

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

Slide45

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

Slide46

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/min

FEV1 < 1.6L

Able to blow out a match

MBC > 60 L/min

FEV1 > 1.6L

MODIFIED MATCH TEST:

DISTANCE MBC

9” >150 L/MIN.

6” >60 L/MIN.

3” > 40 L/MIN.

Slide47

5)

GREENE & BEROWITZ

COUGH TEST:

deep breath f/by cough

ABILITY TO COUGH

STRENGTH

EFFECTIVENESS

INADEQUATE 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.

Slide48

6) WRIGHT PEAK FLOW METER

: Measures PEFR

N – MALES- 450-700 L/MIN.

FEMALES- 350-500 L/MIN.

<200 L/min.–inadequate cough efficiency.

Slide49

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.

Slide50

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 OXIMETRY

10) ABG.

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THANK YOU