Chapter 2 Ventilation 1

8/2/2019 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 (

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Chapter 2 Ventilation 1