PULMONARY FUNCTION TESTS - PowerPoint Presentation

Slide1

PULMONARY FUNCTION TESTS

PRESENTED BY: RASHMI BHATT

MODERATOR: Dr GIRISH SHARMASlide2

Assessment of pulmonary functions

MEASUREMENT OF VENTILATORY FUNCTION

Bedside tests

Measurement of lung volumes

Measurement of expiratory flow rates

Measurement of airway

hyperresponsiveness

Respiratory muscle testing

Distribution of ventilation

Gas transfer and exchange

EXERCISE TESTINGSlide3

BEDSIDE TESTS

SEBARESE’S BREATH HOLDING TEST

:

>30 sec

: normal value

20-30 sec : decreased respiratory reserve

<20 sec : severe pulmonary disease

SNIDERS MATCH BLOWING TEST

:

It tests the subject’s ability to blow out a lit up matchstick at a distance of 15 cm from the mouth, after a deep inspiration followed by forced expiration without pursing the lips. The ability to do so suggests an FEV1 more than 1.5

litres

.

WRIGHT’S PEAK FLOWMETER & DE BONO’S WHISTLE

: After a deep inspiration, air is blown out through peak flow meter with force. Adults : 500L/min or more ;

males:450-700L/min ; females

: 300-500 L/min

children : 200-250L/min

<200L/min: impaired cough efficiency and a higher risk of post operative pulmonary complications Slide4

BEDSIDE TESTS (contd.)

WATCH AND STETHOSCOPE TEST

:

Breath sounds over the trachea are heard and the expiration time is noted.

≤ 4sec : normal

↑

ed

: Obstructive airway disease

GREENE & BEROWITZ COUGH TEST

:

vigorous coughing is induced in the pre op period and the following noted:

•ability to cough •strength

•effectiveness •nature of mucus

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 impairmentSlide5
Slide6

Spirometry

The subject is first asked to breathe with a normal, resting tidal pattern followed by maximal inspiration and exhalation. Several lung volumes can be determined through

spirometry

, except residual volume.

VITAL CAPACITY

: most common measurement of lung function.

Largest volume measured after the subject inspires deeply and maximally to TLC and then exhales completely to residual volume, without concern for rapidity of effort

TIDAL VOLUME: amount of air moving in and out of lungs during normal, quiet breathing. 10 ml/kgSlide7

INSPIRATORY RESERVE VOLUME: amount of air inspired with max effort in excess of TV

EXPIRATORY RESERVE VOLUME: volume of air expelled by active expiratory effort after passive expiration

RESIDUAL VOLUME: amount of air left in the lungs after maximal expiratory effort

RESP MINUTE VOLUME: volume of air inspired per minute (500ml*12 = 6000ml/min)

INSPIRATORY CAPACITY: TV + IRV

ALVEOLAR VENTILATION( at rest) 4.2 L/minSlide8
Slide9

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 Slide10

GAS DILUTION METHODS

HELIUM DILUTION METHOD

:

The subject is asked to

rebreathe

a known volume of gas in a closed circuit

spirometer

which has helium as a trace. Once equilibrium is attained, total system volume(

lungs+spirometer

) is known. Deducting the

spirometer

volume gives the FRC and further deducting the ERV gives the RV.MULTIBREATH NITROGEN WASHOUT TECHNIQUE

:

Tracer gas used is nitrogen which is normally present in the lungs. It is washed out by breathing 100% O2. by measuring the exp N2 quantity, FRC can be derived, having known the initial

conc

of N2 in the alveoli.

Slide11

PLETHYSMOGRAPHIC VOLUME DETERMINATION

:

Used for measuring FRC & RV. Uses the

boyle’s

law, whereby the subject and the box behave as a closed system. volume changes in the subject are reflected as pressure changes in the gas tight box i.e. P1V1=P2V2

It is also used to evaluate airway obstruction by measuring the airway resistance. Normally it is <2cmH2O L/sec.

The reciprocal of Raw known as airway conductance

Gaw

can be calculated, which when divided by the FRC gives the specific conductance which is a highly reproducible measurement.Slide12

Measurement of expiratory flow rates

These parameters are recorded with respect to time i.e. the rapidity of the effort is significant. The maneuvers are to be completed either as rapidly as possible or within a specified time range.

1) FORCED VITAL CAPACITY

:

The subject is asked to inhale

upto

TLC and then exhale as forcefully as possible for not less than 4 seconds. It is reduced in lung pathologies like pneumonia

atelectasis

, fibrosis, surgical excision and muscle weakness,

abd

pain or swelling. Normally, it is almost equal to VC. A discrepancy suggests the presence of airway obstruction and air trapping.

2) FEV1

:

It measures the

vol

of air exhaled forcefully in 1 sec during an FVC maneuver. Normally it varies from 3.0 to 4.5 L. value of 1.5 to 2.5 L signifies mild to mod obstruction while less than this is suggestive of a severe impairment. FEV1: 75-80% FVC , FEV2: 83-90% FVC, FEV3:97% FVC.Slide13

3) FEV1/FVC RATIO

:

This parameter is a better indicator of airway obstruction, wherein FEV1 while FVC remains normal or only slightly reduced, leading to a decrease in the ratio. In case of

restr

lung disease, both decrease proportionately and the ratio is more or less the same, while TLC is

dec

.

<70%: mild

obst

,

<60% mod

obst,

<50%: severe

obst

.

4) PEAK FLOW RATE

:

The max flow rate during a forced exp from TLC( initial 0.1 sec) in L/min or L/sec. in normal individuals, it is ≥500L/min. it can be used to monitor response to bronchodilator therapy.Slide14

5) FORCED MIDEXPIRATORY FLOW/ FEF25-75%:

It measures the air flow during the middle half of FVC, which is the effort independent portion. It varies with the value of FVC, normally4.5-5.0 L/sec. sensitive indicator of small airway obstruction.

6) MAX BREATHING CAPACITY/ MAX VOLUNTARY VENTILATION

:

Largest

vol

that can be breathed per min by voluntary effort. Measured over 12 sec and extrapolated to 1 min. in healthy adults: 150-175L/min. it is approx 35 times the value of FEV1. ABOUT 80% of MVV can be sustained by healthy individuals for 15 min or so.Slide15

Flow volume loopsSlide16
Slide17

Graphic analysis of air flows at various lung volumes to differentiate various cause of airway disease. The loop is plotted while the patient performs an FVC maneuver.

MID VC RATIO: the ratio of expiratory flow to

inspiratory

flow at 50% of VC. Normally it is 1

The entire

inspiratory

portion of the loop and the expiratory curve near the TLC are effort dependent

Fixed

obstr

: ratio remains 1. the airway diameter does not change and both

insp

and exp flows show a plateau.

Variable

extrathoracic

obstr

: airway collapses during

insp

while exp flow is N so ratio>2.0.

Variable

intrathoracic

obstr

: ratio<1.0 due to reduction in exp flow only

Diffuse

obstr

: mid VC ratio is lowSlide18

Closing volume

Its measurement is associated with the concept of small airway obstruction

It is the lung volume at which airways in dependent areas of the lungs cease to contribute to exhalation

Due to gravity dependent gradients in pleural pressure

Techniques used: bolus technique ( using

xenon,argon

or helium) and the residual gas technique (using N2)

Normally CV is 15-20% of vital capacitySlide19

Measurement of airway hyper-responsiveness

Useful in the patients with clinical suspicion but normal

spirometry

.

Airway hyper-responsiveness is precipitated by the use of agents like histamine,

methacholine

, cold air, exercise etc.

After measuring the baseline FEV1, %change in lung function is recorded

The test is considered positive if ≤8.0µmol of the agent produced a 20% fall in FEV1.

It is useful to exclude asthma in patients with similar symptoms. Slide20

respiratory muscle testing

Respiratory muscle strength alters the measurement of

pulm

function which require patient effort.

The parameters used to measure it are

PImax

and

PEmax

. These are recorded while the airway is occluded, during max

insp

and exp effort, using

anaeroid gauges.PImax is recorded near RV, it is -125cmH2O

PEmax

is recorded near TLC, it is +200cmH20

These are static pressures measured at FRC and measure the pressure due to the

resp

muscles alone, by eliminating that due to elastic recoil of the

resp

system.

Low

PImax

suggests an inability to take a deep

insp

while a low

PEmax

suggests an impaired coughing ability Slide21

Distribution of ventilation and gas exchange function

ALVEOLAR-ARTERIAL O2 TENSION DIFFERENCE (PAO2-Pao2): sensitive indicator of V/Q abnormalities. Normally it is >8mmHg and increase with age(d/t

dec

in PaO2)

Dyspnoea

differentiation index: to distinguish cardiac cause from pulmonary cause of

dyspnoea

.

DDI = PEFR*PaO2/1000

Multiple breath N2 washout: the curve of N2 washout is single exponential in case of uniform ventilation,

Diffusing capacity of lung using CO(DLCO): measure of the ability of gases to diffuse from the alveoli into the capillaries. It depends upon the gradient and the thickness of

alveolo-capillary membrane. Also suggests the no of functioning capillaries being ventilated.

technique is single breath CO test

normal value is 20-30ml/min/mmHg

it is

dec

in emphysema, lung resection,

pulm

emboli,

anaemia

, fibrosis,

sarcoidosis

etc.

it is inc in assoc with increased

pulm

blood volume (supine position exercise, left to right

cardiac shunts).Slide22

EXERCISE TESTING

Stair climbing

: the ability to climb three flights of stairs at the patient’s own pace, without stopping. Quantitative assessment is 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

6 minute walk test

: distance walked in 6 min, at patient’s own pace. The ability to walk 180 feet in 1 min (6 min-walk distance of 1080 feet) corresponds to a VO2max of 12ml/kg/min.Slide23

Degree of impairment

NORMAL

: FVC>= 80% of predicted ; FEV1>=80% of

pred

FEV1/FVC>=0.75 ; DLCO>=80% of

pred

MILD IMPAIRMENT :

FVC: 60-79% ; DLCO : 60-79%

FEV1 : 60-79% ; FEV1/FVC ratio : 0.60-0.74

MODERATE IMPAIRMENT :

FVC : 51-59% ;

DLCO : 41-59% ; FEV1 : 41-59%; FEV1/FVC : 0.41-0.59

SEVERE IMPAIRMENT:

FVC≤50% ; DLCO≤ 40%

FEV1≤40% ; FEV1/FVC≤0.40Slide24

THANK YOUSlide25
Slide26
Slide27