lung volumes and capacities hala salah2012
TRANSCRIPT
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Lung volumes and
capacities
BY
Dr/HALA SALAHPhysiologyofProf.
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Determination of lung volumes is
used to :
1-assess the efficiency of the respiratory system.
2-diagnose respiratory diseases.Most of these volumes can be measured
using a simplespirometer
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THE SPIROMETER Old version
spirometer bell
kymograph pen
New version
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LUNG
VOLUMES
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It is the volume of air inspired or
expired each breath during normalquiet breathing. It is about 500 ml.
Tidal volume (VT)
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Tidal volume
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Inspiratory reserve volume (IRV)
It is maximal
volume of air
which can beinspired after a
normal
inspiration. It is
about 3000 ml.
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Expiratory reserve volume (ERV)
It is the maximal
volume of air
which can be
expired after a
normalexpiration. It is
about 1100 ml.
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Residual volume (RV)
It is the volume ofair remaining in
the lungs after
maximal
expiration.
It is about 1200ml.
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Tidal volume
Dead space
Tidal volume
Inspiratory reserve
volume
Expiratory reserve
volume
LUNG VOLUMES
Residual
Volume
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LUNGCAPACITIES
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PULMONARY CAPACITIES
A capacity is two volumes or more added
together.
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Inspiratory capacity (IC)
It is the maximalvolume of air that
can be inspired
from the resting
expiratory
volume.IC3500 mL
IC500+ 3000
ICTV + IRV
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Functional residual capacity (FRC)
It is the volume of air which remains in the lung
at the resting expiratory level (after normal
expiration).
FRC = RV + ERV
= 1200 + 1100
2300 ml
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Vital capacity (VC)
It is the maximum volumeof air that can beexpelled from lung bya maximal expiration
after a maximalinspiration.
VC = IRV + TV + ERV
3000 +500 +1100 =4600It is a good index for
pulmonary efficiency.
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Total lung capacity (TLC)
It the volume of air contained in the lung at
the end of maximal inspiration.TLC = IRV + TV + ERV + RV
= 3000 + 500+ 1100 + 1200 =
5800 ml.
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Lung volumes and capacities are
Decreased in
The recumbent position than in standing.
Women than in men by about 20-25% .Small and athenic persons.
Old age.
Increased in :Larger and athletic persons.
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All lung volume and capacities are measured
except:spirometerdirectly by
Functional Residual capacity FRC.
Total lung capacity TLC.
Residual volume RV.
Because the air in the residual volume of the lung cannot be
expired into the spirometer and this volume constitutes
part of FRC, TLC.
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Lung volumes measured by spirometer
For the others parameters additional measurements needed
Values obtained by simple spirometry
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Race Weight Height Sex Age
Factors affecting lung volumes and
capacities
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% Predicted Value
Observed value/predicted value x100%
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Determination of RV and FRC
They are measured indirectly using
helium dilution method
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Helium dilution
Spirometer of known volume (Vs)and HeConc .(C1) connected to the patient.
At end of normal expiration.
-Closed circuit
-After several minutes of breathing.
-C1XV1=C2X(Vs+VL)
-C2= final He conc,VL=FRC.
At beginning After several minutes
Unknown lung volume can be calculated
[He] initial Vs = [He] final (Vs + VL)
Determination of RV and FRC
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Clinical significance of FRCFRC maintains gas exchange with blood in between
breaths.
The large volume of FRC prevents marked rise in
alveolar pressure of oxygen i.e. it provides stability of
oxygen pressure in the arterial blood.
Normally the residual volume should be less than30%
of the total lung capacity. It exceeds that level insome pathological conditions e.g. Bronchial asthma
(RV/TLC>30 % ).
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Factors affecting the vital capacity
Posture .
Movement of diaphragm.
Strength of Respiratory Muscles.Thoracic wall expansibility.
Resistance to air flow.
Lung elasticity.Restrictive lung disease.
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Timed vital capacity
It is the volume of expired air at the end of the
first, second or third second, when measuring
vital capacity.
also called forced expiratory volume (FEV).
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TIMED VITAL CAPACITY (FVC)
Importance of the timed VC
The timed vital capacity is a useful test to
differentiate between obstructive lungdiseases (COPD) as emphysema and
chronic bronchitis and restrictive lung
diseases as interstitial lung fibrosis.
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How to measure FVC ?
The patient is asked to
inspire as deep as
possible and expires as
deep and as rapid as hecan into the spirometer
that measures not only
the volume expired but
also the time taken in
expiration. Normally
the FVC takes place in
4 seconds.
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Spirometry
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FEV1 & FVC
Forced expiratory volume
in 1 second (FEV1) in
young trained athletes: 4 L
FVC in young trainedathletes: 5 L
FEV1/FVC %=
80%-83%
FEV1
FVC
FVC
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In obstructive lung diseases, the air way
resistance is greatly increased, the vital
capacity is reduced and FEV1 is markedly
reduced FEV1/FVC is less than 80%. While inrestrictive lung disease FEV1/FVC is normal or
even increased 90% due to proportionate
decrease in both FEV1 and FVC.
S i t I t t ti Ob t ti R t i ti
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Spirometry Interpretation: Obstructive vs. Restrictive
diseases
Obstructive Disorders
FEV1/FVC
Restrictive Disorders
FEV1/FVC normal or
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Restrictive lung diseases
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Minute Respiratory Volume
Minute Ventilation=
VT X breathing frequency
= 500 ml X12 b/min
= 6000 ml/min
= 6 L/min
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Maximal voluntary ventilation
M i l V l t V til ti
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Maximal Voluntary Ventilation
(MVV)
It is the maximal volume of air that can be breathed per minuteusing the fastest rate and the deepest respiratory effortpossible.
The subject breathes as fast and as deep as possible for 15
seconds only-To avoid fatigue of the respiratory muscles.
-To avoid wash out of CO2 .
Normal MVV = 80-160 L/min for male,
= 60-120 L /min for females,average 100 L/minute .
It is a better index for:
1- respiratory efficiency.
2- physical fitness .
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Breathing reserve (BR)
It is the difference between MVV and minute
Respiratory volume
BR = MVVMRV
1006 = 94 L/min.
It is a good test for the functional reserve of the respiratory
system and the higher is the BR, the better the state of
physical fitness.
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THANK
YOU
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Al l d d
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Alveolar dead space
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Dead space
It is the volume of air which does notundergo gas exchange with pulmonarycapillaries .
Types of dead space:
Anatomical dead space.
Alveolar dead space.
Physiological dead space.
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Dead Space Ventilation [VDS]
Includes ventilation of both:
1. the anatomic dead space: the portion of the
breath that enters and leaves the conductingzones of the airways (nose terminalbronchioles)
2. the alveolar dead space: air that reaches the
alveoli but does not participate in gas exchangeAlveolar DS + Anatomic DS= Physiologic DS
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Measurement of dead space
By using Bohr's equation (physiological DS):
DS =TVXPCO2 in alveolar airPCO2 in expired air
PCO2 in alveolar air
PCO2 in arterial blood 40mmHgPCO2 in expired air 28mmHgT.V 500ml
= 500 X
40
2840
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Nitrogen-meter method
Fowlers Method
(Anatomic DS)
M t f A t i D d S
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Measurement of Anatomic Dead Space.[ Fowlers Method ]
The Fowlers method is based of the
principle that the last bit of air you breath
in, you breath out first & it represents gasin the anatomic dead space (conductingairways).
The remaining expired gas represents amixture of gas in the alveoli and anatomicdead space.
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Nitrogen-meter method
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Procedure
maximal expiration to RV maximal inspiration to TLC of100% O2 maximal expiration to RV performed slowly
measure the [N2] during expiration.Phase Ifirst bit of gas expired from TLC, 0% N2:pure anatomic dead spacegasPhase IItransition phase, mixture of 100% O2 in anatomic DS & alveolargasPhase IIIalveolar plateau, gas from alveoli(40 %N2)
VDS measured as the volume expired between beginning ofexpiration & mid point determined geometrically
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Functions of the dead space:-
Conduction of air to and from the alveoli.
Conditioning of inspired air.
Filtration of inspired air.Initiation of sneezing and cough reflexes.
Secretion of immunoglobulin (antibodies).
Perception of smell sensation.
Production of sound (phonation
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Alveolar Ventilation
Alveolar ventilation
the portion of breathing
that reaches the alveoli
& participates ingas exchange
Ventilation: Minute(MRV)
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Ventilation: Minute(MRV),Alveolar(VA )& Dead Space(VDS)
MRV=VT X breathing frequency =
500ml X12= 6.0 L/min.
VA=VA X breathing frequency =
(VT-VDS)XR.R=
(500-350)X12=350ml X12= 4.2 L/min
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Dyspneic index
It is the ratio between BR and MVV and it isusually about 90%. If it is decreased below 60%
dyspnea (difficulty in breathing) occurs onslightest effect and the person is consideredphysically unfit.
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