PHGY 210 Lecture Notes - Lecture 31: Vagus Nerve, Pressure Measurement, Heart

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21 Jul 2016
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respiratory%frequency%if%it%happens%for%a%long%timeN%not%impt%and%doesn’t%really%happen%unless%
you’re%breathing%in%large%tidal%volumes.%If%you%inflate%the%lungs%to%such%a%high%volume,%the%reflex%is%to%
take%time%to%breathe%out%instead%of%taking%a%new%breathN%this%is%the%first%feedback%loop%that%ever%
occurred%in%phygy.%The%stretch%receptors%tell%then%the%size%of%the%lung%volume%at%which%you%are%at.%
The%irritant=%stimulated%by%noxious%gasses%ex.%Histamine%leads%to%bronchi%contrictionN%stimulation%
of%irritant%receptors%and%leads%to%hypernea.%Juxta%capillary%receptorsN%located%in%alveolar%walls%and%
are%innervated%by%nonmyelinated%fibersN%stimulated%by%edema%etc%and%the%reflex%causes%rapid%and%
shallow%respiration,%but%if%intense,%causes%apnea!%Left%heart%failure%and%edema%triggers%these%
receptors!%
!You%need%at%least%the%medulla%to%get%the%signal%to%breathe,%if%you%cut%above%it,%you%still%get%rhythms%
but%there%is%no%control%over%tidal%volume.%The%upper%pons%turn%off%inspiration.%If%you%have%the%upper%
pons,%you%will%have%a%normal%tidal%volume.%You%get%the%rhythm%with%or%without%the%vagus%nerves.%%
!Mechanics%of%breathingN%the%lungs%as%a%balloonN%how%easy%it%is%to%inflate%or%deflate%it.%The%pleural%
space%is%the%space%between%the%ribcage%and%the%lungs,%and%there%is%two%of%them.%It%couples%the%lungs%
to%the%chest%so%that%the%brain%can%control%the%rib%cage%and%therefore%the%inflation%and%deflation%of%the%
lungs.%PneumothoraxN%the%pressure%in%the%pleural%space%is%negative%at%rest%as%you%breathe%in%and%it%
gets%more%and%more%negative.%The%lungs%want%to%collapse.%If%you%remove%the%coupling,%the%ribs%will%
spring%out,%the%lungs%will%want%to%get%smaller.%That%means%that%normally%at%rest,%the%chests%are%
actually%at%compressed,%because%if%you%release%the%coupling,%it%expands.%This%is%why%the%pleural%
space%pressure%is%negative,%because%the%chest%wants%to%expand%and%the%lungs%want%to%collapse.%%
!The%elastic%properties%of%the%lungs%and%chest%wallsN%you%can%apply%a%lot%of%pressure,%but%the%resulting%
volume%is%also%due%to%elasticity%ie%how%much%the%balloon%an%actually%expand.%The%manometer%
measures%the%applied%pressure%needed%to%inflate%the%lungs%in%cm%water.%If%we’re%going%to%measure%
the%pressure,%the%pressure%outside%the%lungs%is%not%atmospheric!!%It’s%pleural%pressure!!%So%how%do%
we%measure%pleural%pressure??%The%esophagus%is%close%to%the%pleural%space,%so%measure%the%
esophagus=%measure%the%pressure%of%the%pleural%space.%The%goal%is%characterize%the%elastic%
properties%of%the%lungs%with%knowledge%of%the%pressure%surrounding%it.%You%can%measure%the%volume%
using%a%spirometer.%You%can%measure%the%elastic%properties%by%building%a%pressure%volume%curve.%
The%alveolar%pressure%is%the%pressure%when%the%subject%is%holding%his%or%her%breath.%Atm%pressure%or%
body%surface%pressure%is%the%same%as%alveolar%pressure%when%the%mouth%and%nose%is%open!%If%closed,%
the%pressure%is%the%alveolar%pressure%and%this%is%different%from%outside.%ComplianceN%the%change%in%
volume%for%a%given%change%in%pressure.%If%you%were%to%imaging%the%lungs%outside%the%subject%so%that%
the%pressure%surrounding%is%the%atm%pressure%rather%than%the%pleural%space,%you%could%make%the%
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