Chapter 2 Ventilation 1
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Transcript of Chapter 2 Ventilation 1
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Ventilation
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SymmetryAlveolar unitConsists of thin blood/gasbarrierSimple diffusion of gasgasesVentilation brings O 2 Blood flow brings CO
2Ventilation consists of bringing O 2 & eliminationof CO 2 from lungs
FIGURE 2.1
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Airway StructureAlveolar unit or Lung as aunitLarge airways formconducting zoneNo gas exchange hereAnatomic dead spaceResp. zone. MoleculardiffusionAlveolar membraneStroke volume in capillary
FIGURE 2.1
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Ventilation: Volumes & Flows
Left side volumes:Tidalvolume, dead space volume,alveolar gas, capillaryvolume
Right side flows: minutevolume (total ventilation);frequency (respiratory rate),pulmonary blood flow
Total or minute ventilationAlveolar ventilationBlood flow Vs Alveol. venti
FIGURE 2.1
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Hutchinsons Expts Noninvasive experimentIn 1846Exhale into the machine
Measure expired air volumeIn large variety of peopleTitle: Giants & dwarfs
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Spirometer
Upturned bell with watersealPen moves up when inhaleIt moves down when exhaleTidal breathing (500 ml)Forced expiration after deepinspiration: VCCan not determine RV and
any measurement with RVFRC = RV + ERVTLC = VC + RV
FIGURE 2.2
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C1 = known concentrationV1 = known volumeUnknown is V 2After a period of breathingHe concentration is steadyMeasure the concentrationC2Calculation based on the
formula
Helium dilution method
FIGURE 2.3
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Nitrogen washout method
Subject breathes pure O 2Expired gas collectedSeven minutes of breathingV
1= lung volume(unknown)
C1 = N 2 concentration- 80%C2 = N 2 concentration afterequilibrationV2 = Total volume of gasexhaledC1 x V 2 = C 2 x V 2V1 = C 2 x V 2 /80%
FIGURE 2.6A
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Body Plethysmograph method
Large tight boxMake respiratory effortsExhale effort compresses
gas in lung (lung volume ) Gas in box expandsBox pressure Changes volume in box( V)
Apply Boyles law tolungP1 x P 2 =P2 x (V1- V)
FIGURE 2.4
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Advantages & Disadvantages
Poorly ventilated areas are notcounted in He and N 2 washoutmethods
FRC could be underestimatedPlethysmograph measures gaswhich is trapped behind closed
airwaysIn old and sick subjects theerror could very large
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Total ventilation or Minuteventilation
Subject breathes througha valve box
Inspired air comes fromoutsideExpired air goes to a bagAir in bag is measuredError in untrainedsubjects
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Ventilation: high altitude exercise
Exercise: more reliableBicycle Ergometer used
Hyperventilate at highaltitude19,000 ft Himalayas
Ventilation is increasedPIO 2 is halved becauseof decrease inbarometric pressure
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Ventilation: high altitude exercise
Exercise: at 24,000 ft inHimalayas
Ventilation is increasedOxygen uptake is only1/3 rd
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Exercise, Ventilation andCardiac output
Total ventilation atvarious work levels atsea levelTotal ventilation at restis about 7 liters/minDuring exercise (O 2 uptake) both ventilationand CO increased
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Alveolar Ventilation
Measure dead spacevolumeSubtract from tidalvolumeMultiply with rateDead space volume has tobe measuredAlveolar ventilation =total ventilation deadspace ventilation
FIGURE 2.5
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Alveolar Ventilation
Measured from expiredCO 2 concentration No CO 2 in anatomic
dead spaceCO 2 is from alveolarareaArterial PCO 2 is
inversely related to thealveolar ventilation
FIGURE 2.5
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Alveolar PCO 2
Single expiration usingCO2 analyzerFirst exhaled gas has no
CO2Then concentration of CO2 increasesFinally pure alveolar gas
comes alveolar plateau
FIGURE 2.6
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Fowlers method Anatomic dead space
Subject breathes pure O 2 N2 meter shows 0 During expiration firstgas has no N 2Gradually N 2 shows upN2 is from alveolar areaMeasure the volumeAdd half of transitionalvolume (A or B)
FIGURE 2.6
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Bohrs method Physiologic dead space
Measure CO 2 volumeCO 2 comes fromalveolar area
Not from anatomic deadspaceCO 2 is a physiologicalmeasurement
Therefore, Physiologicaldead space
FIGURE 2.5
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Regional distribution of ventilation
Single breath of radioactive Xenon 133Hold the breathMeasure radiation overthe chestIt is more at the bottom
On a unit basisventilation is more at thebottom, less at the top
FIGURE 2.7
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Regional inequality of ventilation
Intrapleural pressure isnegative (