1
LECTURE NOTES ON
HUMAN RESPIRATORY SYSTEM PHYSIOLOGY
(Dr. GÜL ERDEMLI)
CONTENTS
1. MECHANICS OF BREATHING:
2. REGULATION AND CONTROL OF BREATHING:
3. VENTILATION
4. LUNG VOLUMES AND PULMONARY FUNCTION TESTS
5. DIFFUSION
6. PERFUSION
7. GAS TRANSPORT TO THE PERIPHERY
8. ACID-BASE REGULATION
9. RESPIRATORY SYSTEM UNDER STRESS
10. RECOMMENDED FURTHER READING:
11. SELF ASSESSMENT
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1. MECHANICS OF BREATHING: m m
INSPIRATION: mInspiration mis mthe mactive mpart mof mthe mbreathing mprocess, mwhich mis minitiated mby
m the mrespiratory mcontrol mcentre min mmedulla moblongata m(Brain mstem). mActivation mof mmedulla mcauses
m a mcontraction mof mthe mdiaphragm mand mintercostal mmuscles mleading mto man mexpansion mof mthoracic
m cavity mand ma mdecrease min mthe mpleural mspace mpressure. mThe mdiaphragm mis ma mdome-shaped
m structure mthat mseparates mthe mthoracic mand mabdominal mcavities mand mis mthe mmost mimportant mmuscle
m of minspiration. mWhen mit mcontracts, mit mmoves mdownward mand mbecause mit mis mattached mto mthe mlower
m ribs mit malso mrotates mthe mribs mtoward mthe mhorizontal mplane, mand mthereby mfurther mexpands mthe mchest
m cavity. mIn mnormal mquite mbreathing mthe mdiaphragm mmoves mdownward mabout m1 mcm mbut mon mforced
m inspiration/expiration mtotal mmovement mcould mbe mup mto m10 mcm. mWhen mit mis mparalysed mit mmoves
m to mthe mopposite mdirection m(upwards) mwith minspiration, mparadoxical mmovement. mThe mexternal
m intercostal mmuscles mconnect madjacent mribs. mWhen mthey mcontract mthe mribs mare mpulled mupward mand
m forward mcausing mfurther mincrease min mthe mvolume mof mthe mthoracic mcavity. mAs ma mresult mfresh mair
m flows malong mthe mbranching mairways minto mthe malveoli muntil mthe malveolar mpressure mequals mto mthe
pressure mat mthe mairway mopening.
m
EXPIRATION: mExpiration mis ma mpassive mevent mdue mto melastic mrecoil mof mthe mlungs. mHowever,
m when ma mgreat mdeal mof mair mhas mto mbe mremoved mquickly, mas min mexercise, mor mwhen mthe mairways
m narrow mexcessively mduring mexpiration, mas min masthma, mthe minternal mintercostal mmuscles mand mthe
m anterior mabdominal mmuscles mcontract mand maccelerate mexpiration mby mraising mpleural mpressure.
COUPLING mOF mTHE mLUNGS mAND mTHE mCHEST mWALL: mThe mlungs mare mnot mdirectly
m attached mto mthe mchest mwall mbut mthey mchange mtheir mvolume mand mshape maccording mto mthe mchanges
m in mshape mand mvolume m of mthe mthoracic mcavity. mPleura mcovering mthe msurfaces mof mthe mlungs
m (visceral) mor mthe mthoracic mcavity m(parietal) mtogether mwith ma mthin m(20 mµm) mlayer mof mliquid
m between mthem mcreate ma mliquid mcoupling.
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PRESSURE-VOLUME mRELATIONSHIPS: mIn mthe mpulmonary mphysiology mabsolute mpressure
m means matmospheric mpressure m(760 mmm mHg mat msea mlevels). mThe mpressures mand mthe mpressure
m differences mof mthe mrespiratory msystem mare mexpressed mas mrelative mpressures mto mthe matmospheric
m pressure. mWhen mit mis msaid mthat malveolar mpressure mis mzero, mit mmeans mthat malveolar mpressure m=
m atmospheric mpressure.
If mone mexcises manimal mlung mand mplaces mit min ma mjar, mone mcould mmeasure mthe mchanges min mvolume
m with ma mspirometer mthrough ma mcannula mattached mto mthe mtrachea. mWhen mthe mpressure minside mthe mjar
m below matmospheric mpressure, mthe mlung mexpands mand mthe mchange min mits mvolume mis mmeasured mand
m the mpressure- mvolume mcurve mis mplotted. mWhen mthere mis mno mpressure mdistending mthe mlung mthere mis
m a msmall mvolume mof mgas m in mit. mAs mthe mpressure min mthe mjar mis mgradually mreduced, mthe mvolume mof
m the mlungs mincreases. mThis mis minitially m a mrapid mevent mbut mafter ma mcertain mpressure mthe mchanges
m become mless mevident. mIt mmeans mthat mthe mlung mis mstiffer mwhen mit mis mexpanded mand mthereby, mthe
m pressure-volume mcurves mduring minflation mand mdeflation mare
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different m= mhysteresis. mAnother mimportant mpoint mis mthe mvolume mat ma mgiven mpressure mduring
m deflation mis malways mlarger mthan mduring minflation. mEven mwhen mthe mpressure moutside mthe mlung mis
m increased mabove mthe matmospheric mpressure, mvery mlittle mfurther mair mis mlost mand mthe mair mis mtrapped
m in mthe malveoli. mThe mvolume mof mthe mair mtrapped min mthe mlung mis mincreased mwith mage mand min msome
m respiratory mdiseases.
COMPLIANCE: mThe mslope mof mthe mpressure-volume mcurve, mthe mvolume mchange mper munit
m pressure mis mknown mas mcompliance. mIn mnormal mexpanding mrange m(2-10 mmm mwater) mthe mlung mis
m very mdispensable, min mother mwords mit mis mvery mcompliant. mThe mcompliance mof mthe mhuman mlung mis
m 0.15 mL/cm mH2O. m However, mit mgets mstiffer m(compliance msmaller) mas mit mis mexpanded mabove mthe
m normal mrange. mCompliance mis mreduced mwhen
(1) The mpulmonary mvenous mpressure mis mincreased mand mthe mlung mbecomes mengorged mwith mblood
(2) There mis malveolar moedema mdue mto minsufficiency mof malveolar minflation
(3) The mlung mremains munventilated mfor ma mwhile me.g. matelectasis mand
(4) Because mof mdiseases mcausing mfibrosis mof mthe mlung me.g. mchronic mrestrictive mlung mdisease.
On mthe mcontrary min mchronic mobstructive mpulmonary mdisease m(COPD, me.g. memphysema) mthe
m alveolar mwalls mprogressively mdegenerate, mwhich mincreases mthe mcompliance. mThe mlung mcompliance
m is mchanged maccording mto mthe mlung msize: mObviously mthe mcompliance mof ma mmouse mlung mis mmuch
m smaller mthan ma mhuman mlung. mAt mthe mbirth mthe mlung mcompliance mis mthe msmallest mand mincreased
m with mage m(until madulthood) mdue mto mincrease min mthe msize mof mthe mlungs. mSpecific mcompliance
m (compliance mper munit mof mlung mvolume) mcould mbe mcalculated min morder mto mcorrect mthis mvalue mfor
m lung msize. mIn masthma m(hyperactive mairway msmooth mmuscle) mthe mlung mcompliance mis musually
m normal.
LECTURE NOTES ON
HUMAN RESPIRATORY SYSTEM PHYSIOLOGY
(Dr. GÜL ERDEMLI)
CONTENTS
1. MECHANICS OF BREATHING:
2. REGULATION AND CONTROL OF BREATHING:
3. VENTILATION
4. LUNG VOLUMES AND PULMONARY FUNCTION TESTS
5. DIFFUSION
6. PERFUSION
7. GAS TRANSPORT TO THE PERIPHERY
8. ACID-BASE REGULATION
9. RESPIRATORY SYSTEM UNDER STRESS
10. RECOMMENDED FURTHER READING:
11. SELF ASSESSMENT
, 2
1. MECHANICS OF BREATHING: m m
INSPIRATION: mInspiration mis mthe mactive mpart mof mthe mbreathing mprocess, mwhich mis minitiated mby
m the mrespiratory mcontrol mcentre min mmedulla moblongata m(Brain mstem). mActivation mof mmedulla mcauses
m a mcontraction mof mthe mdiaphragm mand mintercostal mmuscles mleading mto man mexpansion mof mthoracic
m cavity mand ma mdecrease min mthe mpleural mspace mpressure. mThe mdiaphragm mis ma mdome-shaped
m structure mthat mseparates mthe mthoracic mand mabdominal mcavities mand mis mthe mmost mimportant mmuscle
m of minspiration. mWhen mit mcontracts, mit mmoves mdownward mand mbecause mit mis mattached mto mthe mlower
m ribs mit malso mrotates mthe mribs mtoward mthe mhorizontal mplane, mand mthereby mfurther mexpands mthe mchest
m cavity. mIn mnormal mquite mbreathing mthe mdiaphragm mmoves mdownward mabout m1 mcm mbut mon mforced
m inspiration/expiration mtotal mmovement mcould mbe mup mto m10 mcm. mWhen mit mis mparalysed mit mmoves
m to mthe mopposite mdirection m(upwards) mwith minspiration, mparadoxical mmovement. mThe mexternal
m intercostal mmuscles mconnect madjacent mribs. mWhen mthey mcontract mthe mribs mare mpulled mupward mand
m forward mcausing mfurther mincrease min mthe mvolume mof mthe mthoracic mcavity. mAs ma mresult mfresh mair
m flows malong mthe mbranching mairways minto mthe malveoli muntil mthe malveolar mpressure mequals mto mthe
pressure mat mthe mairway mopening.
m
EXPIRATION: mExpiration mis ma mpassive mevent mdue mto melastic mrecoil mof mthe mlungs. mHowever,
m when ma mgreat mdeal mof mair mhas mto mbe mremoved mquickly, mas min mexercise, mor mwhen mthe mairways
m narrow mexcessively mduring mexpiration, mas min masthma, mthe minternal mintercostal mmuscles mand mthe
m anterior mabdominal mmuscles mcontract mand maccelerate mexpiration mby mraising mpleural mpressure.
COUPLING mOF mTHE mLUNGS mAND mTHE mCHEST mWALL: mThe mlungs mare mnot mdirectly
m attached mto mthe mchest mwall mbut mthey mchange mtheir mvolume mand mshape maccording mto mthe mchanges
m in mshape mand mvolume m of mthe mthoracic mcavity. mPleura mcovering mthe msurfaces mof mthe mlungs
m (visceral) mor mthe mthoracic mcavity m(parietal) mtogether mwith ma mthin m(20 mµm) mlayer mof mliquid
m between mthem mcreate ma mliquid mcoupling.
, 3
PRESSURE-VOLUME mRELATIONSHIPS: mIn mthe mpulmonary mphysiology mabsolute mpressure
m means matmospheric mpressure m(760 mmm mHg mat msea mlevels). mThe mpressures mand mthe mpressure
m differences mof mthe mrespiratory msystem mare mexpressed mas mrelative mpressures mto mthe matmospheric
m pressure. mWhen mit mis msaid mthat malveolar mpressure mis mzero, mit mmeans mthat malveolar mpressure m=
m atmospheric mpressure.
If mone mexcises manimal mlung mand mplaces mit min ma mjar, mone mcould mmeasure mthe mchanges min mvolume
m with ma mspirometer mthrough ma mcannula mattached mto mthe mtrachea. mWhen mthe mpressure minside mthe mjar
m below matmospheric mpressure, mthe mlung mexpands mand mthe mchange min mits mvolume mis mmeasured mand
m the mpressure- mvolume mcurve mis mplotted. mWhen mthere mis mno mpressure mdistending mthe mlung mthere mis
m a msmall mvolume mof mgas m in mit. mAs mthe mpressure min mthe mjar mis mgradually mreduced, mthe mvolume mof
m the mlungs mincreases. mThis mis minitially m a mrapid mevent mbut mafter ma mcertain mpressure mthe mchanges
m become mless mevident. mIt mmeans mthat mthe mlung mis mstiffer mwhen mit mis mexpanded mand mthereby, mthe
m pressure-volume mcurves mduring minflation mand mdeflation mare
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different m= mhysteresis. mAnother mimportant mpoint mis mthe mvolume mat ma mgiven mpressure mduring
m deflation mis malways mlarger mthan mduring minflation. mEven mwhen mthe mpressure moutside mthe mlung mis
m increased mabove mthe matmospheric mpressure, mvery mlittle mfurther mair mis mlost mand mthe mair mis mtrapped
m in mthe malveoli. mThe mvolume mof mthe mair mtrapped min mthe mlung mis mincreased mwith mage mand min msome
m respiratory mdiseases.
COMPLIANCE: mThe mslope mof mthe mpressure-volume mcurve, mthe mvolume mchange mper munit
m pressure mis mknown mas mcompliance. mIn mnormal mexpanding mrange m(2-10 mmm mwater) mthe mlung mis
m very mdispensable, min mother mwords mit mis mvery mcompliant. mThe mcompliance mof mthe mhuman mlung mis
m 0.15 mL/cm mH2O. m However, mit mgets mstiffer m(compliance msmaller) mas mit mis mexpanded mabove mthe
m normal mrange. mCompliance mis mreduced mwhen
(1) The mpulmonary mvenous mpressure mis mincreased mand mthe mlung mbecomes mengorged mwith mblood
(2) There mis malveolar moedema mdue mto minsufficiency mof malveolar minflation
(3) The mlung mremains munventilated mfor ma mwhile me.g. matelectasis mand
(4) Because mof mdiseases mcausing mfibrosis mof mthe mlung me.g. mchronic mrestrictive mlung mdisease.
On mthe mcontrary min mchronic mobstructive mpulmonary mdisease m(COPD, me.g. memphysema) mthe
m alveolar mwalls mprogressively mdegenerate, mwhich mincreases mthe mcompliance. mThe mlung mcompliance
m is mchanged maccording mto mthe mlung msize: mObviously mthe mcompliance mof ma mmouse mlung mis mmuch
m smaller mthan ma mhuman mlung. mAt mthe mbirth mthe mlung mcompliance mis mthe msmallest mand mincreased
m with mage m(until madulthood) mdue mto mincrease min mthe msize mof mthe mlungs. mSpecific mcompliance
m (compliance mper munit mof mlung mvolume) mcould mbe mcalculated min morder mto mcorrect mthis mvalue mfor
m lung msize. mIn masthma m(hyperactive mairway msmooth mmuscle) mthe mlung mcompliance mis musually
m normal.
