lecture 8

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Respiratory Physiology
Maintaining Alveolar pressure for Speech
• Reduction in relaxation pressure occurs
as air is expended
– Air flow continues
– Lung volume & elastic recoil decrease
– Decrease in the need to counteract
relaxation pressure with inspiratory
muscles
– Muscular checking force for relaxation
varies from moment to moment
Maintaining Alveolar pressure for Speech
• For any given alveolar pressure
needed for speech:
–A different balance of active &
passive muscular forces will be
required to maintain pressure at each
lung-volume level
Relaxation Pressure Curve
% VC
*Recoil forces only; no muscular activity
Resting
Lung
Volume
Alveolar Pressure (cm H2O)
Relaxation
Relaxation Pressure Curve
• Below 55% VC the elasticity of the
lungs contribute little to the curve
• Lungs compress the air nicely above
resting lung volume
• Chest works very hard below resting
lung volume to pull air into system
• Below 55% you begin to use expiratory
muscles to maintain Ps
Pressure-Volume Relationship
• Right side: Expiratory Pressure: greater
your lung volume the more force you
can generate for exhalation
• Left side: Inspiratory pressure: Less air
in your lungs the greater force you can
generate for inspiration
Pressure-Volume Relationship
Pr
% VC
Pi
Pe
Residual Air
Pulmonary Pressure (mm Hg)
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