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

RestingLungVolume

Relaxation

% V

C

Alveolar Pressure (cm H2O)

*Recoil forces only; no muscular activity

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%

VC

Pi Pr

Pe

Residual Air

Pulmonary Pressure (mm Hg)

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