PULMONARY FUNCTION TESTS - PowerPoint Presentation

Slide1

PULMONARY FUNCTION TESTS

Made by: Meenal AggarwalModerator: Dr. Ajay SoodSlide2

Lung Volumes & CapacitiesSlide3

Respiratory minute volume (at rest): 6 L/min

Alveolar ventilation (at rest): 4.2L/minMaximum voluntary ventilation: 125-170 L/minSlide4

Pulmonary Function Tests : Introduction

Aim: to identify abnormal lung function in hope of altering patient’s outcome by reducing risk of intra/post op ventilatory impairmentsEnables us to:

Assess the presence and severity of respiratory dysfunction

Follow the progression of impairment

Document the response to therapy

2 major groups of tests:

To detect abnormalities of gas exchange

To assess mechanical

ventilatory

functions of lungs & chest wallSlide5

Clinical Spirometry

Inventor: John Hutchinson

Vital Capacity:

The largest volume measured after the subject inspires deeply and maximally to TLC and then exhales completely to RV

Normal values are lower in supine than in sitting

Abnormal: when <80% seen in restrictive

ds

:

Lung pathologies (pneumonia,

atelectasis

,

pulmn

fibrosis)

Loss of lung tissue (Following surgical resection)

Diminished effort (muscle paralysis, abdominal swelling, )Slide6
Slide7

Time Expired Spirogram

After a maximal inspiratory effort subject exhales as forcefully and rapidly as possible

Forced Vital Capacity:

Exhaled volume if recorded with respect to time

Reflects

flow

resistive

properties of the airways

Practice attempts given, 3 acceptable tracings required

Normal: Exhalation takes at least 4 sec, should not be interrupted by coughing,

glottic

closure or any mechanical obstruction

FEV1 (Forced Expiratory volume in 1sec):

Either in Lt or FEV1/FVC percentage

Normal: 75-80 %Slide8

Abnormal: Mild obst

<70% Moderate obst <60% Severe obst <50%Restrictive diseases: dec

TLC,

dec

FVC, so

dec

FEV1 but ratio FEV1/FVC either normal or increased

Disease

state

FVC

(L)

FEV1 (L)

FEV 1/

FVC (%)

Airway

obstruction (asthma, chronic bronchitis)

N

Dec

Dec

Stiff lung (pneumonia, pulmonary edema, pulmonary

fibrosis

)

Dec

Dec

N

Resp

muscle weakness (MG,

myopathies

)

Dec

Dec

NSlide9
Slide10

PEFR: (Peak Expiratory Flow Rate)

Maximum flow rate obtainable at any time during FVC maneuverL/sec or L/minUsually measured as the average flow of gas expired after initial 200ml (k/a FEF 200-1200 or MEFR)Can be measured with a handheld flow meter (serves as a bed side test) or a

pneumotachygraph

Markedly affected by obstruction of large airways

Responsive to bronchodilator therapy so used to monitor therapeutic response in acute asthma

N value: 500Lts/min or more

If < 200Lts/min, suggests impaired cough efficiency and likelihood of post op complicationsSlide11

Also affected in muscle weakness Variable as highly dependent on patient effort

FEF25-75%: (a/k/a Forced Mid-Expiratory Flow)Middle half of FVC doesn’t require high degree of efforts

k/a Effort independent (not truly as marked reductions in effort will reduce it)

Negative effort dependence: flow rates can actually decrease with truly maximum efforts compared from a slightly

submaximal

effort (d/t dynamic airway compression)

N value: 4.5 – 5 L/sec

Sensitive indicator of early obstruction in small distal airways

Reduced even in restrictive

ds

, but FEV1/FVC is NormalSlide12

Maximum

B

reathing

Capacity:

a/k/a MVV (Maximum Voluntary Ventilation)

Largest volume that can be breathed per minute by voluntary effort

Instructed to breathe as hard and fast as possible for 12 sec, and then extrapolated to 1min

Reduced in obstructive diseases

Other factors: elasticity of lungs,

resp

muscle strength, patient co-operation

Correlates well with FEV1 (MVV= FEV1 X 35)

Normal: 150-175L/min

< 80% indicates gross impairment in

resp

functionSlide13

Respiratory Muscle

Strength:

All Above parameters are affected by muscle strength

Evaluated by maximum static respiratory pressures (pressures generated against an occluded airway during a maximal forced

inspiratory

or expiratory effort)

Measured with Aneroid gauges (at FRC, to nullify effect of elastic recoil)

PImax

(near RV) : -125cm H2O

If < -25 cm H2O, severe inability to take a deep breath

PEmax

(near TLC) : +200 cm H2O

If < +40 cm H2O, severely impaired coughing ability

Useful in evaluating patients with Neuromuscular disordersSlide14
Slide15

GaugeSlide16

Methods for Measuring Residual Volume

Body

plethysmography

Helium dilution methodSlide17

Physiological Determinant of Maximum Flow Rates

3 factors:Degree of effort (PEmax: at TLC, PImax: at RV)

Elastic recoil pressure of lungs (PL):

Max at TLC: 25-30cm H2O

Min at RV: 2-3 cm H2O

Is opposed by elastic recoil of chest wall (

Pcw

)

Net recoil

Prs

: PL +

Pcw

(zero at FRC)

Resistance to flow provided by airways (Raw): determined by size of airway, so min at TLC, max at RV

Gaw

(conductance, 1/ Raw, is related to lung volume linearly)Slide18

Flow – Volume

Relationships:

Useful as all determinants of flow are dependant on volume

During FVC, flow rises to a max at a volume close to TLC

Gradually:

In Obstructive

ds

, flows are decreased over full rangeSlide19
Slide20

Airway Compression & Flow Limitation:

Value in coughingSlide21

Sites &

Mechanisms of Decreased Airflow in Diseases:

D/t alterations in any 3 of the parameters (

PEmax

, PL, Raw)

Disease

PEmax

Raw

PL

Neuromuscular weakness

Dec

N

N

Emphysema

N

N

Dec

Asthma, Bronchitis

N

Inc

N

Peripheral Airway Disease

N

N

NSlide22

Airway Resistance: (Raw)

Technique: patient pants once or twice per second through a mouth piece with a nose clip in place (to bypass max resistive areas-nose,

nasopharynx

)

Also panting maneuver keeps larynx dilated

Subject sits in a constant volume body

plethysmograph

(body box)

Lung volume & Raw can be measured using changes in the box pressure and volume (using Boyle’s law)

Normal Raw: 2cm H2O L/sec

Head flexion causes increased Raw (measured) as it reduces the caliber of

hypopharynx

, so be as

errect

as possible during maneuver

Measurement

of Airway ObstructionSlide23

Forced Expiratory Maneuvers (FVC, FEV1, PEFR):

Tells whether obstruction is present

Flow-Volume

loops:

Allows to discriminate b/w upper airway obstructive lesions

Subject inhales fully to TLC and then performs FVC maneuver, followed immediately by a max inspiration as quickly as possible to TLC

Whole inspiration and expiration near TLC are effort dependent (Normal = 1.0)

Mid VC ratio: ratio of expiratory flow to

inspiratory

flow at 50% VC Slide24
Slide25

Help to localize site & nature of obstruction

Upper airway obstruction: inspiratory

flow reduced more than expiratory, so mid VC ratio >1

Fixed airway

obst

: both inspiration and expiration reduced to same extent so plateaus of constant flow, so ratio = 1

Variable obstruction: Lesion whose influence varies with the phase of respiration

Extrathoracic

: l/t increased

obst

during forced inspiration, mid VC ratio >2

Intrathoracic

: Increased obstruction during forced inspiration, mid VC ratio is lowSlide26
Slide27
Slide28
Slide29
Slide30

Small airway disease, minimal airway dysfunction, early obstructive lung disease

It is a fore runner of chronic bronchitis & emphysema

Alveolar –Arterial Oxygen Tension Difference:

Detects regional V/Q mismatch

PaO2 =measured easily

PAO2 = PiO2 – PaCO2 / R

Difference : PAO2- PaO2

Normal value at room air: 8 mm Hg

Increases with age (occurs d/t

dec

PaO2)

Tests of Early Lung DysfunctionSlide31

Frequency Dependence of Compliance:

In normal lung: compliance not dependent on respiratory frequency

In small airway obstruction, d/t asynchronous

behaviour

of lung units where some areas of lung are moving out of phase with others, the compliance decreases with a high respiratory rate

If it falls to <80% : k/a compliance to be frequency dependentSlide32

Multiple- Breath Nitrogen Washout:

Mild obstructive airway disease leads to uneven distribution of ventilation, measured by SBNW

Normal : lung behaves as a single compartment and produces a fast single exponential curve for N2 wash out

Abnormal : Lung appears to have more than one

ventilatory

compartment (d/t uneven dist of ventilation)

So different units have their N2 diluted at different rates, and so producing a tail on the washout curve

Very sensitive test, but requires computerization for analysis of curveSlide33

Single Breath N2 Washout:

Described by Fowler in 1949

Expired N2

conc

was measured after inspiration of 1 L of O2 from FRC

The change in N2 concentration b/w 750-1250 ml of expired volume in seen

Modified method: Instead of just 1 L, patient makes a full

inspiratory

effort in 100% O2. the alveolar nitrogen slope with this method is less steep (as now whole lung is filled with O2, c/f 1L in which only lung bases are filled leading to an inc Apex base difference, so steeper slope)

The slope of alveolar nitrogen plateau is larger in old subjects (reflecting uneven

evntilation

)

<2% normal, Even

Upto

10% in smokersSlide34
Slide35

Closing Volume:

Lung volume at which the airways in the dependent areas in the lungs begin to close

Occurs because lower portions of lungs are subject to

Ppl

pressure in excess of airway pressure, l/t closure of airways

Technique: tagging of these lung areas by giving them a different concentration of a tracer gas c.f. apex.

2 methods: Bolus gas (uses He)

Resident gas (uses N2)

First a gradient is created, and then expiratory levels of gas are plotted. The volume at which phase 3 begins is known as closing volume

Closing capacity = closing volume + RV

Increases with age, in smokersSlide36

Bed-Side PFT’s

1. Snider’s Match Blowing Test:

Mouth wide open

Match held at 15 cm distance

Chin supported

No head tilting

Match stick & mouth at same level

Cannot blow out a match:

MBC < 60 L/min

FEV1 <1.6 L

* Modified Snider’s test:

3 inches: MBC >40 L/min

6 inches: MBC >60L/min

9 inches: MBC >150 L/minSlide37

2.

Forced Expiratory Time:

FET < 3 sec (restrictive disease)

FET > 6 sec (obstructive

disease

)

3.

Seberese’s

Single Breath Count:

Patient is asked to take a deep breath followed by counting, till the time he cannot hold breath

Shows trends of deteriorating/ improving lung functions

4.

Seberese’s

Breath Holding Time:

Subject is asked to N tidal inspiration & hold breath

Normal >= 40 sec

< 15 sec C/I for surgerySlide38

5. Cough test:

Observe for ability to cough (strength & effectiveness)

Wet productive cough = prone for

pulm

complications

Inadequate cough= FVC < 20 ml/kg, FEV1 < 15ml/kg

6. De

Bono’s

Whistle Test:

Wide bore tube with a whistle at end and an adjustable leak hole at the side, whistle blows only when air flow exceeds a certain value

7. Wright’s Peak Flow Meter:

Normal males: 450- 700 l/min

Females: 300-500 l/min

Values< 200 l/min suggests impaired cough efficiencySlide39

Peak flow meterSlide40

Indications for PFT in Surgical Patients:

Patient

factors:

Known Chronic pulmonary disease

Heavy smoker (>1 pack/day)

Chronic productive cough

Recent

respiratory infections

Advanced age (>70

yrs

)

Obesity

(>30% over ideal wt)

Thoracic cage deformity (

kyphoscoliosis

)

Neuromuscular disease (MG)

Procedure:

Thoracic or upper abdominal surgery

Pulmonary resection

Prolonged anesthesiaSlide41

Pre-op Measures to Improve Lung Function:

Goal: to reduce intra/post op pulmonary complications

4 basic modalities:

Smoking cessation: after 2-4 wk (reduced secretions, airway reactivity & improved

mucociliary

clearance)

Treatment of

bronchospasm

(Beta 2 agonists,

antichol

,

theophylline

)

Removal of secretions (AB therapy, adequate hydration,

mucolytics

, postural drainage, chest percussions)

Motivation & Stamina (incentive

spirometry

)Slide42

Thank You