erythropoietin: regulator of erythropoiesis · 2020. 1. 9. · types of dead space 1. anatomical...
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Competency
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No. PY6.X (Respiratory Physiology)
CompetencyDescribe the dead space and alveolar ventilation & their clinical significance.
D/L/Core K/KH/Y
AM Written/Viva voce
Integration No
Imp. ConceptRapid shallow breathing Vs Slow deep breathing
Phy. Trivia Radford’s Formula (DS)
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Definition
Normal Value
Types
Measurement
Factors affecting:
Physiological, Pathological
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Definition
The part of the respiratory tract where there is no
gaseous exchange is called dead space.
The air present in the dead space is called dead space
air.
Value: 150 ml (approximately equal to the body weight
in pounds). It is 30 % of Tidal volume.
Only the first 350 mL of the 500 mL inspired with each
breath at rest mixes with the air in the alveoli.6
Types of Dead space
1. Anatomical dead space:
It is the space from nose up to Terminal
bronchioles (up to generation 16 conducting zone).
2. Physiological (total) dead space:
It is the anatomical dead space + Alveoli with
wasted ventilation, wasted ventilation occur due to
Underperfusion / overinflation of alveoli
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Total Dead space (Physiological Dead space) =
Anatomical Dead space + Alveolar Dead space
In normal person, Alveolar Dead space is zero
∴ Physiological Dead space = Anatomical Dead space
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Measurement of Dead space
1. Bohr’s equation:
for physiological dead space
2. Fowler’s method:
by single breath N2 wash out method for
anatomical dead space (pure O2 is inhaled then
expired into N2 meter)
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Measurement of Dead space
3. The Radford’s Formula:
By this one can predict anatomical dead space
By this formula……
Weight in pounds = Dead space in ml.
However, this prediction is fairly reliable for
healthy individuals, but not in patient with
respiratory problems.
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Factors affecting
Physiological factors:
• More in males ,
• ↑es with age (as lung inflate)
• Body height
Pathological factors:
• ↑Es in emphysema (as lung inflate),
• Bronchiectasis ( as bronchi dilates),
• Pulmonary embolism (as pulmonary blood flow ↓es) 12
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Alveolar Ventilation
The amount of air in lungs that participate
in gaseous exchange every minute is called
Alveolar Ventilation.
Alveolar Ventilation = (TV – DS) x RR
= (500 – 150) x 12 = 4.2 L/min
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Effect of variations in respiratory rate and depth on alveolar ventilation.
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Alveolar Ventilation…
The alveolar ventilation - the amount of air
reaching the alveoli per minute, is less than the
RMV.
Note that because of the dead space, rapid
shallow breathing produces much less
alveolar ventilation than slow deep breathing
at the same RMV
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Effect of variations in respiratory rate and depth on alveolar ventilation.
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Rapid shallow breathing Slow deep breathing
Measurement of Rs parameters
R parameter Method or Technique
1) TV, IRV, VC, IC simple / computerized spirometer,
respirometer,
2) RV, FRC & TLC He – dilution (close circuit) & N2
wash-out method
3) PEFR Wright’s peak flow meter
4) Sample of air (for
partial pressure)
alveolar (by Haldane-Priestly tube)
expired (by Douglas bag) & blood
(by Haldane’s appara.)
5) Diffusion capacity By DC of CO (x 1.23 for O2)
6) Dead space Indirect - by single breath oxygen / CO2 /
nitrogen,
direct- Bohr equation
7) Work done Pressure-volume (relaxation) curve by P
X V
8) Static
compliance
Slope of P-V curve by P / V
9) Intra pleural
pressure
Indirectly by intra-esophageal balloon
10) Partial
pressure of air
in alveoli
By alveolar gas equation
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