Airway Mechanics

Formula for Raw
( Pressure - Pressure) /

Airway resistance:
Difference in pressure between the and the , related to gas at the mouth.
Typical value - cmH2O / L/sec
Measured by body pleth: Pt pants gently with open shutter at a rate of - breaths per second. This creates an 2 shaped curve on screen that plots flow against box pressure. Shutter closes and second curve is produced that plots mouth pressure against box pressure. Raw is calculated from these 2 graphs.

Normal Raw Values
Nose, mouth, upper airway: %
Trachea, Bronchi: %
Small Airways: %

Airway Conductance ()
Flow per unit of change in L/sec/cmH2O
Reciprical of Raw: 1/
conductance is the same but is measured by liter of volume: (1/Raw)/ or
Normal Value: . - L/sec/cmH20
More appropriate than Raw for small airway disease

Compliance
Volume Change per unit of Pressure change
CLT = Lungs and = L/cmH2O
CL = Only = L/cmH2O
CT = only = L/cmH2O

In vented patients record plateau pressure at different lung volumes.

Compliance:
Balloon Technique
Catheter with inflatable is marked cm from the tip.
Balloon is inserted through the nose and swallowed into .
In the stomach pressure swings on inspiration and on expiration after 1 ml of air is injected.
Balloon is retracted into and the pressure swings .
Catheter is - cm from the nose.
Air is evacuated from the balloon, then ml is injected.
Pt inspires to before taking any measurements to standardize.
Have pt inspire again - pressure and volume measurements are taking at zero flow.
Lung compliance is taken from slope of P-V over segment from FRC to +.5L
At FRC balloon pressure should equal cmhO
Max elastic pressure is the most pressure at TLC
Static lung compliance is the difference of pressure and mouth .

Static Lung Compliance
Change in lung per unit change in transpulmonary measured over the straight portion of P-V curve between FRC and FRC +
Δ / Δ

Normal Value = L/cmH2O

Abnormal Compliance
CL is in disease like pneumonia, atelectasis, pulm fibrosis
CL is in emphysema because of loss of
CT is with chest wall deformities and obesity.

Maximum Static Recoil Pressure
Most pressure obtained at TLC
Normal value is - cmH2O

CoEffecient of Retraction
COR is used to express the maximal static recoil of the lung relative to the lung (TLC)
COR = (Pst at ) /
Normal Value = - cmH2O/L