PSIO 532 Study Guide - Midterm Guide: Pulmonary Compliance, Elastin, Intrapleural Pressure
PSL – Respiratory Physiology
Lung Compliance
Ultimately the volume of air we take into the lungs is going to be dependent upon its
relationship to the change in pressure. If your lungs are more
compliant, then you will be able to take in greater volume for
a given change in pressure.
To begin our discussion of respiratory mechanical behaviour,
we will consider the lung itself without the chest wall and
without gas flow. The compliance of the lung is defined as a
change in volume per unit pressure.
A water spherometer is attached to the isolated lung cut from a sheep; the lung is
suspended in a flask, which is considered to be the chest wall → the space that exists
between the lung and the flask is the intrapleural space
A pump is also attached to this (on the right) → it alters the pressure that exists within
the space between the lung and flask (altering the intrapleural pressure); by altering
this pressure, the lung will either expand or contract, and as this expansion or
contraction happens, it will move the bell up and down → this can be traced to detect
changes in lung volume that occur with the changes in pressure
The X-axis is the change in intrapleural pressure; Y-axis indicate the changes in volume
The figure shows the change in lung volume that occurs when intrapleural pressure
changes. The upward and downward arrows indicate the inflation and deflation curves,
respectively. The difference between the inspiratory and expiratory curves is referred
to as hysteresis
As the intrapleural pressure becomes more negative, the volume increases (linearly);
but then it flattens at the ends (-40 and 0 cmH2O)
The difference in inspiration and expiration is that for inspiration, the little bit of
pressure becoming negative (up to -cH), we do’t see uch change in volume
→ this relatioship does’t exist for expiratio
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Document Summary
Ultimately the volume of air we take into the lungs is going to be dependent upon its relationship to the change in pressure. If your lungs are more compliant, then you will be able to take in greater volume for a given change in pressure. To begin our discussion of respiratory mechanical behaviour, we will consider the lung itself without the chest wall and without gas flow. The compliance of the lung is defined as a change in volume per unit pressure. The x-axis is the change in intrapleural pressure; y-axis indicate the changes in volume. The figure shows the change in lung volume that occurs when intrapleural pressure changes. The upward and downward arrows indicate the inflation and deflation curves, respectively. The difference between the inspiratory and expiratory curves is referred to as hysteresis. As the intrapleural pressure becomes more negative, the volume increases (linearly); but then it flattens at the ends (-40 and 0 cmh2o)
