PULMONARY FUNCTION TESTS

03/22/15 Dr. Nilesh Kate ESIC MEDICAL COLLEGE GULBARGA

A Review of Pulmonary function testsDr Nilesh N Kate.Associate Professor,ESIC MEDICAL COLLEGEGULBARGA.

Objectives At the end of the lecture you should know:

Definition & normal values of TV, IRV, ERV, RV, IC, FRC, VC, TLC, TVC, FEF25-75%, MV, PEFR, MVV, Breathing Reserve & Dyspnoeic Index.

Clinical significance: obstructive & restrictive lung diseases.

Factors affecting VC. Normal functioning of spirometer & normal spirogram. Measurement of FRC by nitrogen washout and helium

dilution method. Dead space: definition, normal value, types, measurement

and significance.

Introduction Lung volumes and capacities are

quantitative measurements of pulmonary ventilation.

Ventilation is the process whereby the lungs replenish the gas in the alveoli.

Measures gas volume contained in the lungs under certain circumstances and the rate at which gas can be expelled from the lungs.

History Borelli –(1679) Earliest physiologist

(Hutchinson) Humphrey Davy (1800) by mercurial air

holding machine & H2 dilution technique measured own RV

Hutchinson-Capacity of lung & respiratory function

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Indication

Diagnostic—1st grade and 2nd grade Evaluation and control of treatment In surgery Occupational hazards--Bysinosis

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Lung volumes & capacities It can be of two types:

Static lung volumes & capacities: Time factor not involved. Measured in ml or liters. TV, IRV, ERV, RV, IC, FRC, VC, TLC

Dynamic lung volumes & capacities: Time dependent. Measured in ml/min or l/min. TVC, FEF25-75%, MV, PEFR, MVV

Most of these can be measured by spirometry

Tidal Volume (TV)

IRV

TV

ERV

RV

IC

FRC

VCTLC

RV

Volume of air inspired or expired during normal quiet breathing.

Males = 500 ml

Females = 500 ml

Inspiratory Reserve Volume (IRV)

IRV

TV

ERV

The maximum amount of air that can be inhaled after a normal tidal inspiration.

Males =3300 ml Females = 1900 mlRV

IC

FRC

VCTLC

RV

Expiratory Reserve Volume (ERV)

IRV

TV

ERV

Maximum volume of air that can be expired after a normal tidal expiration.

Males =1000 ml Females = 700ml

RV

IC

FRC

VCTLC

RV

Residual Volume (RV)

IRV

TV

ERV

Volume of air remaining in the lungs after maximal expiration.

Males =1200 ml Females = 1100 ml

RV

IC

FRC

VCTLC

RV

Inspiratory Capacity (IC)

IRV

TV

ERV

Maximum amount of air which can be inspired after completing tidal expiration.

IC = IRV + TV Males =3800 ml Females = 2400

mlRV

IC

FRC

VCTLC

RV

Functional Residual Capacity (FRC)

IRV

TV

ERV

Volume of air remaining in the lungs at the end of tidal expiration.

FRC = ERV + RV

Males =2200 ml Females = 1800 mlRV

IC

FRC

VCTLC

RV

Vital Capacity (VC)

IRV

TV

ERV

Maximal volume of air that can be exhaled from the lungs after a maximum inspiration.

VC = IRV + TV +ERV

Males =4800 ml Females = 3100 ml

RV

IC

FRC

VCTLC

RV

Factors affecting VC Physiological:

Physical dimensions – size & physical dev. (M>F) Age – dec. in old age Strength of respiratory muscles – inc. in swimmers & divers Posture- standing > sitting > lying Pregnancy- dec. VC

Pathological: Diseases of respiratory system- obstructive & restrictive Diseases of the heart- CHF Diseases of the pleura- pleural effusion Diseases of the abdominal cavity- ascitis

Total Lung Capacity (TLC)

IRV

TV

ERV

Volume of air in the lungs after a maximal inspiration

TLC = IRV + TV + ERV + RV

Males =6000 ml Females = 4200mlRV

IC

FRC

VCTLC

RV

Important

Spirometer

Instrument used to measure lung volumes & capacities.

It records the amount of air and the rate of air that is breathed in and out over a specified time.

SpirometerSpirometer

Spirometer Can not measure RV, FRC &

TLC.

FRC is measured by: Nitrogen washout method Helium dilution method

RV = FRC – ERV

Nitrogen washout method

Helium-Dilution method method

DEAD SPACE

Introduction Total 23 generations of

airways b/w trachea & alveolar sac.

First 16 generations: Conducting zone No gaseous exchange Up to terminal bronchiole

Last 7 generations Transitional & respiratory zone Gaseous exchange Include respiratory bronchiole,

alveolar ducts & alveoli

Dead Space Part of the tidal volume that does not take part

in gaseous exchange with pulmonary capillary blood.

This can be: Anatomical dead space Alveolar dead space Total (Physiological) dead space

Anatomical dead space Gas in the conducting areas of the

respiratory passage, where no gaseous exchange occurs.

Volume of air from nose to terminal bronchiole.

Approximately equal to the body weight in pounds.

So, in a 68 kg (150 lb) manSo, in a 68 kg (150 lb) manAnatomical dead space = 150 mlAnatomical dead space = 150 ml

i.e. out of 500 ml inspired air, only 350 ml i.e. out of 500 ml inspired air, only 350 ml reaches the alveoli for gaseous exchange.reaches the alveoli for gaseous exchange.

rest 150 ml just fills the anatomical dead spacerest 150 ml just fills the anatomical dead space

During expiration,During expiration,First 150 ml – dead space airFirst 150 ml – dead space airLast 350 ml – alveolar air Last 350 ml – alveolar air

Anatomical dead space

Alveolar ventilation (amount of air reaching the alveoli per min) is less than the respiratory minute volume.

If, tidal volume = 500 ml & RR = 12/minIf, tidal volume = 500 ml & RR = 12/minDead space volume = 150 mlDead space volume = 150 mlThen, air reaching the alveoli = 500-150 mlThen, air reaching the alveoli = 500-150 ml = 350 ml= 350 ml

Minute volume = 500 x 12 = 6 l/minMinute volume = 500 x 12 = 6 l/min

Alveolar ventilation = (500-150) x 12Alveolar ventilation = (500-150) x 12 = 350 x 12= 350 x 12 = 4200 ml= 4200 ml

Anatomical dead space

Rapid shallow breathing produces much less alveolar ventilation than slow deep breathing at the same respiratory minute volume.

Respiratory rate Respiratory rate 30/min 30/min 10/min 10/minTidal volume Tidal volume 200 mL 200 mL 600 mL 600 mLMinute volume Minute volume 6 L 6 L 6 L 6 LAlveolar ventilation (200 – 150) x 30 (600 – 150) x 10Alveolar ventilation (200 – 150) x 30 (600 – 150) x 10

= 1500 mL = 4500 mL= 1500 mL = 4500 mL

Alveolar dead space

Gas present in under-perfused or non-perfused alveoli and excess gas present in over-ventilated alveoli.

Alveolar air that is not equilibrating with the pulmonar capillary blood.

If, Tidal volume = 500 mlIf, Tidal volume = 500 mlAnatomical dead space = 150 mlAnatomical dead space = 150 mlAlveolar dead space = 100 mlAlveolar dead space = 100 ml

Effective alveolar ventilation = 500 – 150 – 100Effective alveolar ventilation = 500 – 150 – 100 = 250 ml= 250 ml

Total (Physiological) dead space Total volume of inspired air that

does not equilibrate with the pulmonary capillary blood.

Total DS = Anatomical DS + Alveolar DS

In a healthy individual, Total DS and Anatomical DS are equal.

Measurement of dead space Anatomic dead space – Single breath N2 curve

Total dead space – Bohr’s equation PECO2 x VT = PaCO2 x (VT – VD) + PICO2 x VD

PCO 2 of the expired gas (PECO 2)Arterial PCO 2 (PaCO 2)PCO 2 of inspired air (PICO 2)Tidal volume (VT)Dead space volume (VD)

Single breath N2 curve

Subject is asked to take a deep breath of Oxygen.

This fills the entire dead space with pure Oxygen.

Some Oxygen also mixes with the alveolar air but does not completely replace their air.

Then the person expires through a rapidly recording Nitrogen meter

end exp

VT

VD

VA

Results obtained First portion- from the dead

space regions-Nitrogen concentration is zero.

After some time- Nitrogen concentration rises rapidly because alveolar air containing Nitrogen + dead space air.

At end- only air from alveoli- high steady concentration of nitrogen.

CALCULATION :

VE = total volume of expired air.

VD = dead space air

Suppose gray area = 30 cm ² Suppose gray area = 30 cm ² Pink area Pink area = 70 cm ² = 70 cm ² Total volume expired is 500 mlTotal volume expired is 500 ml

Then dead space would be : Then dead space would be : 30 x 50030 x 500 30+7030+70 = 150 ml= 150 ml

Timed Vital Capacity (FEV1)(Forced Expiratory Volume in 1 sec. )

Measures the fraction of FVC expired in 1 sec.

The majority of FVC can be exhaled in <3 seconds in normal people.

FEV1 = 80%

FEV2 = 93%

FEV3 = 98% Helps to differentiate b/w

obstructive & restrictive patterns of lung diseases.

If FVC = 5 liter &If FVC = 5 liter &Volume of air expired in first second = 4 literVolume of air expired in first second = 4 liter

FEVFEV11 = 4/5 x 100 = 4/5 x 100 = 80 %= 80 %

Forced Expiratory Flow 25-75% (FEF25-75%)(Maximum Mid-Expiratory Flow Rate, MMEFR)

Mean forced expiratory flow during middle half of FVC.

Measured in L/min Normal = 300 L/min

May reflect effort independent expiration and the status of the small airways.

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Minute ventilation (MV)Pulmonary Ventilation (PV)

Volume of air inspired or expired by lungs in one minute.

MV=TV x RR= 500 x 12

= 6 liter/min

Maximum Breathing Capacity (MBC)Maximum Voluntary Ventilation (MVV)

Largest volume of air that can be moved into and out of lungs in one minute by maximum voluntary effort.

Normally 90-170 l/min

Pulmonary Reserve (PR)Breathing Reserve (BR)

Maximum volume of air above the pulmonary ventilation, which can be breathed in and out of lungs in one min.

BR = MVV – PV

If, MVV = 100 l/min &PV = 6 l/min

BR = 100 – 6 l/min = 94 l/min

Dyspnoeic Index (DI)(Percentage Pulmonary Reserve)

PR expressed as % of MVV

DI = (MVV-PV) x 100MVV

DI = (100-6) x 100 = 94% 100

Normal DI > 60-70% (~90%)If <60%, dyspnoea is usually present.

Peak Expiratory Flow Rate (PEFR) Maximum velocity with

which air is forced out of the lungs in a single forced expiratory effort.

Normal – 350-400 l/min

Usually indicate large central airway obstruction.

Measured by Wright’s peak flow meter.

Obstructive vs Restrictive d/s Obstructive

Asthma Chronic obstructive lung

disease (chronic bronchitis, emphysema)

Bronchiectasis Cystic fibrosis Bronchiolitis

Restrictive—Parenchymal Sarcoidosis Idiopathic pulmonary fibrosis Pneumoconiosis Drug- or radiation-induced

interstitial lung disease

Restrictive—Extraparenchymal

Neuromuscular Diaphragmatic

weakness/paralysis Myasthenia gravis Cervical spine injury

Chest wall Kyphoscoliosis Obesity Ankylosing spondylitisa

Obstructive vs Restrictive d/s

03/22/15 Dr. Nilesh Kate GMC A'BAD

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Flow chart for rapid interpretation of pulmonary function tests.

Short & systematic way of interpretation

See FVC normal / Abnormal See FEV1 normal / Abnormal

If both normal-- PFT Normal If both decreased – Diseased

(Obstructive/restrictive) If FEV1% -- 69% or <69%--Obstructive If FEV1% -- 80-90% or > 80%--Restrictive

03/22/15 Dr. Nilesh Kate GMC A'BAD