Download Lung Function Tests (LFT)

Lung Function Tests (LFT)
By
Dr.M.B.Bhat.
Pulmonary Volumes & Capacities
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Volumes –Simple volume obtained only by
recording from the instrument
Capacities – Consists of more than one
volume; Obtained either directly by
recording or by addition of different
volumes
Method of study by – Spirometry
Apparatus used – Spirometer (Spirograph)
Record obtained -- Spirogram
Lung Volumes
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2.
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Tidal volume (TV) –500ml
Inspiratory reserve volume (IRV) –3100ml
Expiratory reserve volume (ERV) –1200ml
Residual volume (RV) –1200ml
Significance of RV –
Prevent collapse of alveoli
Ensuring continuous Blood-Gas exchange
Buffering of alveoli gas – Keep the composition
of alveolar gases constant
Pulmonary Capacities
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2.
3.
4.
Inspiratory capacity (IC) –IRV + TV =3600ml
Functional residual capacity (FRC) or
Functional residual volume (FRV) –RV + ERV =
2400ml
Vital capacity (VC) or Forced Vital capacity
(FVC) –IRV + TV (IC) + ERV = 4800ml
Total lung capacity (TLC) -- IRV + TV (IC) +
ERV + RV = 6000ml (6 liters)
Variations
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All lung volumes & Capacities can –
Vary depending upon sex, size & body
build of the individual
It increases proportionate to size
About 20 to 25% less in female than male
More in athletic & large persons
Limitation of spirometry
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With spirometry – the volumes &
capacities that can be expired out only
canbe measured
Hence, the volume which cannot be
measured by spirometry are–
Residual volume
So, also, FRC & TLC
Measurement of RV
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3.
Open circuit method (Nitrogen washed
out method)
Closed circuit method (Helium method)
By Body Plethysmograph method
N2 Washed out method
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Start experiment after forceful expiration –
By inspiring pure O2 & expire the gas into
Douglas bag –for 10 minutes
(In normal person, all N2 present in the
alveoli is washed out within 2 minutes.
Even in disease person (asthma Or
emphysema) all N2 present in the alveoli is
washed out within 7 minutes)
Calculation
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Volume of air collected in Douglas bag at
the end of experiment– (say 60 liters)
Concentration of N2 in collected air –(2%)
Total volume of N2 in collected air = Total
volume of air X conc. Of N2 (60 X 2%)
Residual volume = Total volume of N2/
concentration of N2 in atmospheric air
(80%)
= (60 X 2%)100/80
Helium method
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Keep the known concentration of Helium
gas mixture (of known volume) in the
chamber & during experiment period, the
subject rebreath in & out with the
chamber (for 10 minutes)
Calculation –RV = {(Ci He/C2 He) –1} V1
Ci He = Initial conc. Of He in the chamber
C2 He = Final conc. Of He in the chamber
V1 = Volume of gases in the chamber
Body Plethysmograph
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Based on Boyle’s law -- PV = P1V1
P = Alveolar pressure;
V= Volume of gas in alveoli –to be found
out
First measure P ; start experiment by
inspiring known volume (∆V) gas &
measure new P (P1)
Calculation =
PV = P1 (V + ∆V) ; PV = P1 V + P1 ∆V
PV –P1 V = P1 ∆V ; V (P –P1) = P1 ∆V
V = P1 ∆V / (P –P1)
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All three methods, depending upon the
starting condition of the experiment, the
following volume can be obtained –
After normal expiration – FRC
After forceful expiration –RV
After maximal inspiration – TLC
Thoracic gas volume – the volume of gas in
thorax, including gas in the noncommunicable alveoli.
In normal person it is equal to FRC
It canbe measured only by body
plethysmograph
Dead Space Volume (DSV)
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Definition
Function – Purification, Humidification & Airconditioning
Types –2
Anatomical dead space volume– volume of gas
in respiratory tract ( up to terminal bronchiole).
Normal value – 150ml
Physiological dead space volume (Total dead
space volume) –
Anatomical DSV + Volume of gas in unperfused
alveoli in Normal person – same as Anatomical
DSV
Normal healthy person –
Physiological DSV = Anatomical DSV
Determination of Anatomical DSV
(Fowler’s method –Single breathe pure O2 –
Nitrogen measurement)
Physiological dead space volume
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Measurement by using –
Bohr’s formula (Bohr’s equation)–
Dynamic Lung volume & Capacities (or)
Lung Function tests
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1. Respiratory minute volume (RMV) or
Pulmonary ventilation = TV X RR
(Range of TV –Up to ½ of VC; Normal
range of RR –12 to 18; varies from 4 to
40/min)
2. Alveolar ventilation = (TV – DSV) X RR
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3. Maximum Voluntary Ventilation (MVV) or
Maximum Breathing capacity (MBC) = 80 to
120L/min
Determination –With maximum voluntary
effort breath as deep & as quick as possible
for 15 sec (reason?), the volume obtained
is multiplied by 4 & expressdper minute.
Varies with age, sex & body size
Also depend on – muscular force available,
compliance of thoracic wall & lungs, air way
resistance.
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4. Pulmonary reserve or Breathing reserve
= MVV – RMV
5. dyspnoeicIndex (DI) – Pulmonary
reserve expressed as % of MVV
(MVV – RMV)/MVV X 100
When DI is < 60 to 70% dyspnoea
present
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6. PEFR (Peak expiratory flow rate)->400L/min (respiratory Muscle endurance)
7. MMEFR (Maximal mid-expiratory flow rate
-- > 300L/min (sensitive indicator of small air
way diseases; so in obstructive diseases it is
decreased)
(Both are measured by Wright’s flow meters)
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8. Timed Vital Capacity (TVC) or Forced Vital
Capacity (FVC) –VC measured at each unit time
(second). Accordingly, volume expired each unit and
expressed as % of TVC; as -FEV1 –80 to 85%
FEV2 – 90 to 95%
FEV3 -- >97%
Helps to differentiate Restrictive with Obstructive
type of respiratory diseases.
In both types of diseases -- Flow rates & MVV
Restrictive disorders -- VC; FEV1 normal
(Pulmonary fibrosis; Kyphoscoliosis; Ankyosis
spondylitis)
Obstructive diseases –VC normal & FEV1 (Bronchial
asthma; Emphysema)
Some Respiratory terms
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Eupnoea – Normal Breathing
Dyspnea – difficult or labored breathing in which the
subject is conscious of shortness of breathing
Hyperpnoea – increase in rate & depth of breathing
regardless of subject’s subjective sensation
Normal individual is not conscious of respiration until
ventilation is doubled.
Ventilation is not uncomfortable until it is > tripled or
quadrupled
Tachypnea –is rapid shallow breathing
Hypercapnia -- CO2…..
Hypoxia –O2 
Alveolar air sampling
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By Haldane & Priestly method
Tube of 120cm long & 2.5cm wide with
evacuated gas sampling side tube
Last 10ml of expired air collected as
sample of alveolar gas
Gas analysis
Lloyd's modification of Haldane’s volumetric
apparatus --procedure
Gas sample (known volume) – pass through KOH
solution (CO2 absorbed) –pass through alkaline
pyrogallol solution (O2 absorbed)
Oxymeter –Para-magnetic properties of O2
CO & CO2 analyzer –Infra-red absorption
(spectroscopic method)
Nitrogen meter –N2 emits light in electric field in
vacuum
Caltharmometry –using thermal properties of
gases
Gas-chromatography & mass spectrometry
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Blood-Gas analysis
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Van Slyke’s apparatus –
Blood + acidified, air-free ferric cyanide solution
is subjected to vacuum.
Acid –drive off CO2
Ferric cyanide – drive off O2
Vacuum –drive off N2
Haldane Blood-gas apparatus –
Oxalated blood is treated with sapoin (for
hemolysis), then Potassium ferric cyanide is
added to liberated O2.
End of LFT