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Respiratory System
Mechanics of Ventilation Part II
10
Physiology
Undergraduate 4
02/20/2012

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Term
Lung Volume During a Respiratory Cycle:
-Static Lung Volume
-Dynamic Lung Volume
Definition
Static Lung Volume- 3.2 Liters
Dynamic Lung Volume- 3.7 Liters

Static Lung fully filled until expiration, and the dynamic lung volume decreases to 3.2 liters
Term
Lung Pressure
-Intrapleural Pressure (Static --> Dynamic --> Static)
-Transpulmonary Pressure (Static --> Dynamic --> Static)
Definition
Intrapleural Pressure:
-At around -5 cmH2O at empty static lung
-Decreases to -7.5 and stays there until the second static state
*Decreases at inspiration, increases at expiration

Transpulmonary Pressure:
-Same as Pip, but more gradual and linear so that 1/2 full lung is 1/2 down the curve, not all the way down the curve.
Term
Alveolar Pressure During Respiratory Cycle
Definition
-0 unders static conditions
-During inspiration, rapidly becomes negative, then back to 0 by the end of inspiration
-During expiration, rapidly becomes positive, then back to 0 by the end of expiration
Term
Airflow (V with dot) During Respiratory Cycle
Definition
-0 under static conditions
-during inspiration, rapidly becomes negative then back to 0 by the end of inspiration
-during expiration, rapidly becomes positive then 0 by the end of expiration
Term
2 Effects of Negative Transpulmonary Pressure during inspiration
Definition
1) Body invests energy into making P(a) more negative, resulting in air flowing into the lungs, making lung volume greater.
2) Body invests a greater fraction of energy into making Transpulmonary Pressure more positive, thereby maintaining a higher lung volume.
*Body has now used all energy from the change in Pip (transpulmonary pressure) and no longer expands
Term
Effect of Airway Resistance on the Rate of Lung Inflation
Definition
-time constant is a measure of how long it takes to fill the lungs to 63% capacity
-healthy lungs- .2 seconds
-diseased lungs- 1 second
-So, obviously, increased resistance (whether it be by restriction or obstruction) slows airflow
Term
Effect of Airway Resistance on Tidal Volume
Definition
-Healthy lungs- lung volume remains relatively steady at increasing frequencies (respiratory cycles/second)
-Diseased Lung- Lung volume decreases at a low respiratory frequency and continues to decrease with increasing respiratory frequencies
Term
Effect of Respiratory Frequency on Tidal Volume
Definition
-Change in lung volume decreases as respiratory frequency increases
*makes sense-short frequent breaths leads to a decrease in the change of lung volume over each respiratory cycle
Term
Equation for Airflow
Definition
V (with dot) = P(b) - (P(a)/R(aw))
Term
Equation for Airway Resistance (R(aw))
Definition
R(aw)= P(a) - (P(b)/V(with dot))
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