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Dr. Jitendra Patel (MBBS, MD, ACME, Ph.D…)
Medical Educator & Researcher
Associate Professor, Department of Physiology
Email: [email protected] Web: www.esphys.weebly.com
Competency
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No. PY6.2 & PY6.7 (Respiratory Physiology)
CompetencyDescribe the lung volume and capacities (6.2). Describe and discuss lung function tests & their clinical significance. (6.7)
D/L/Core K/KH/Y
AM Written/Viva voce
Integration No
Imp. Concept Lung volume and capacities
Phy. Trivia OLD Vs RLD
OUTLINE
Static Lung volume and capacities:
Definition, Value, Measurement, Physiological
& Clinical Importance, Limitations
Dynamic Lung Volume & Capacities
Differences between obstructive & restrictive
diseasea
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Restrictive-
i) P. fibrosis
ii) D. of pleura (P. effusion)
iii) Polio
iv) Myasthenia gravis
v) Kypho-scoliosis
Obstructive-
i) Emphysema
ii) Chronic bronchitis
iii) Asthma
OBSTRUCTIVE & RESTRICTIVE LUNG DISEASE
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Static lung volumes (5)
1) Tidal Volume (TV)
2) Inspiratory Reserve Volume (IRV)
3) Expiratory Reserve Volume (ERV)
4) Residual Volume (RV)
5) Closing Volume (CV)
TV- is amount of air breath in or breath out of lungs
during normal quiet respiration. (500ml)
IRV- is maximum amount of air that can be inspired over
& above normal tidal inspiration. (3200ml)
ERV- is maximum amount of air that can be expired
forcefully after normal tidal expiration. (1100ml)
RV- is amount of air remains in both the lungs even after
forceful expiration. (1200ml)
Static lung capacities (6)
1) Inspiratory Capacity (IC)
2) Expiratory capacity (EC)
3) Functional Residual Capacity(FRC)
4) Vital Capacity (VC)
5) Total Lung Capacity (TLC)
6) Closing capacity (CC)
IC- is the maximum volume of air that can be inspired
after normal tidal expiration (IRV + TV).
EC- is the maximum volume of air that can be expired
after normal tidal inspiration (ERV + TV).
VC- It is the maximum amount of air that can be expired
forcefully after maximum inspiration (IRV + ERV + TV).
FRC- is the volume of air remains in both the lungs after
normal tidal expiration. (RV + ERV).
TLC- is the amount of air present in both the lungs after
deep inspiration. (TV + ERV + IRV + RV).
Static lung volumes and capacities
1) Tidal Volume (TV) (500ml)
2) Inspiratory Reserve Volume (IRV) (3200ml)
3) Expiratory Reserve Volume (ERV) (1100ml)
4) Residual Volume (RV) (1200ml)
5) Inspiratory Capacity (IC) (3500ml) = TV + IRV
6) Expiratory capacity (EC) (1600ml) = TV + ERV
7) Functional Residual Capacity(FRC) (2300ml) = ERV + RV
8) Vital Capacity (VC) (4800ml) = IRV + TV + ERV
9) Total Lung Capacity (TLC) (6100ml) = VC + RV
Closing Volume (CV)
The volume of gas in the lungs in excess of the
residual volume at the time when
small airways in the dependent portions of the lungs
close during maximal exhalation, as measured by
the single breath nitrogen washout test.
CV = > RV
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Closing Capacity (CC)
The closing capacity (CC) is the volume in
the lungs at which its smallest airways, the
respiratory bronchioles, collapse. It is defined
mathematically as the sum of the closing volume
and the residual volume.
CC = CV + RV
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Measurement
RV, FRC & TLC are measured by He-dilution method and N2
wash-out method all other by simple/ computerized spirometer.
computerized spirometry
Measurement
TV/ERV/IRV/VC-
Measured by simple spirometer.
RV, FRC, TLC-
Measured by He dilution & N2 wash-out method
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FRC (ERV + RV)
Definition-,
Normal Value-,
Measurement-
Significance
Physio., Medico-legal & Clinical Importance of
FRC & RV
1) FRC & RV provide sufficient amount of gasses for
continuous exchange between lungs & p. capillaries (even
between breaths and during expiration),
2) FRC & RV keep almost normal PO2 & PCO2 in alveolar
air and blood.
3) Provide distending pressure to keep alveoli open
ensure continuous exchange of gasses,
4) Medico-legal-
-To find death was before or after drowning (if death is due
to drowning piece of lung will not float in water) -
- death of infant before or after birth (in still birth
collapsed lung will not float in water),
5) Clinical-
N/↑ - Obstructive disease, ↓ - Restrictive
(while ↓↓ TLC used to confirm diagnosis of RLD)
Vital Capacity (VC)
VC = TV + ERV + IRV
Definition-,
Normal Value-,
Measurement-
Factors affecting
Significance
Factors affecting the VC-
1) Sex- less in females (25% less in females), ,
2) Body built- V.C. specially more in long & thin individuals,
3) Posture- V.C. highest in standing position (due to
relatively high position of diaphragm),
4) Life Style- more in active & athletes while less in
sedentary persons,
5)Occupation- Specially more in artists who play flute etc,
6) Pregnancy- less as diaphragm is pushed up
Significance of VC-
Physiological
Indicated respiratory efficiency
(Index of pulmonary function).
Clinical
V.C. is reduced in both obstructive and restrictive
diseases V.C. used to diagnose, to asses severity and
prognosis of respiratory diseases
Limitations of VC-
i) Less sensitive test to ∆ early stages of respiratory
diseases
ii) Can’t use to differentiate obstructive and restrictive
diseases.
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Dynamic lung volumes and capacities
1) Timed / Forced vital capacity (TVC, FEV)
2) FEV1/FVC ratio-
3) Peak expiratory flow rate (PEFR)- It is the maximum rate
at which air can be expired after deep inspiration.
Value:400-600 L/min. measured by Wright’s peak flow meter.
4) Maximum Mid Expiratory Flow Rate (MMEFR)
FEF 25-75% → Patency of small airways
FEF 200-1200ml → Patency of large airways
5) Respiratory Minute Volume (RMV/PV) =
TV x R. Rate = (500 x 12-14) 6L/mt.-
The amount of air breathed in or out of lungs every minute
is called RMV
6) Alveolar Ventilation =
(TV – dead space volume) x R.R = (500 – 150) x 15
= 4.2 L/mt.-
The amount of air in lungs that participate in gaseous
exchange every minute is called AV
7) Maximum Voluntary Ventilation (MVV) or
Maximum Breathing Capacity (MBC)
= 125-170 L/mt.-
The maximum amount of air that can be breathed in and
out of lungs by forceful respiration per minute is called
MBC or MVV. Douglas bag is used for collection of air.
8) Breathing Reserve = MVV – RMV
9) Dyspneic index = MVV – RMV x 100/MVV
(90% is Normal, if <60% = Dyspnea at rest)
Forced or Timed Vital Capacity (FVC)
1) Definition-
When VC is recorded in respect to time (means performed
as soon as possible). It has 3 parts-
-FEV1 (is fraction of FVC expired in 1st sec) is 83% of FVC,
-FEV2 (forced expiratory volume at the end of 2 sec.) is 93%
-FEV3 (forced expiratory volume at the end of 3 sec.) is
97% .
It is dynamic lung test.
2) Physiological Significance –
indicate the status of airway resistance and patency of
Airways (Index of air flow rate)
3) Clinical Significance-
(i) Used to ∆ early obstructive lung diseases (FEV1 ↓ed, VC
may be normal)
(ii) Differentiate between obstructive and restrictive
diseases (FEV1 ↓ in obstructive while ↑ or N in
restrictive)
(iii)To calculate FEV1/FVC ratio (specially less in
obstructive diseases)
Normal RLD OLD
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Differences b/t obstructive & restrictive D
Lung function test Obstructive Restrictive
Vital Capacity (VC)N or ↓ N or ↓
Residual Volume (RV) ↑ ↑ ↓
Functional Residual Capacity (FRC) ↑ ↓
Total Lung Capacity (∆ of RLD) ↑ ↓↓
FEV1 (severity of OLD) ↓↓ N. or ↑
FEV1 / FVC (∆ of OLD)↓↓
N. or ↑
PEFR ↓↓ N. or ↑
FEF25-75% (small airway obstruction) ↓↓ N. or ↑
FEF200-1200 (large airway obstruction)↓↓ N. or ↑
Lung function tests (PFT) can be grouped as follows:
i) To test the efficiency of ventilation or mechanical
aspects of respiration: Static & dynamic lung tests
ii) To test efficiency of gas exchange at alveolar
level : Diffusing capacity of O2/CO2
iii) To test efficiency of R.S. in relation to exercise: 1) Dyspneic index, 2) Max. O2 uptake (VO2 max).
iv) Blood analysis: 1) PaCO2, 2) PaO2, 3) Blood pH.
(Haldane’s apparatus)
v) Gas analysis of expired air (collected by Douglas
bag) & alveolar air (collected by Haldance priestly
method)
vi) V/P studies (by N2 wash-out & radio-active xenon
method)
vii) X-ray (Chest), CT, MRI, Biopsy
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Noting is permanent even problem also…..
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