PSIO 532 Study Guide - Midterm Guide: Alveolar Pressure, Phrenic Nerve, Transpulmonary Pressure
PSL – Respiratory Physiology
Types of Pressures
Changing the pressure, will ultimately result in a change of volume
The relationship between volume and pressure in the alveoli is demonstrated in
the simple model shown on left
Note that when the volume in a fixed space increases, the pressure decreases; in
contrast, when volume decreases, the pressure increases
Since the chest wall is trying to expand and lungs want to recoil, this creates the
small intrapleural space
Transmural pressure is the pressure across a given structure → this is measured via the
pressure inside subtract the pressure outside, which will give you the
sum pressure acting on the structure.
At resting position, you don’t hae any airflo occurring (no airflo
entering the lungs); no pressure differences. At FRC, the pressure
difference between pressure at alveoli and pressure at atmosphere is
ZERO → No pressure gradient → No airflow. At this point, the
intrapleural pressure is -4 mmHg, hence the pressure across the lungs
is 4 mmHg (0 – (-4)) = +4 mmHg across the lungs; [intrapulmonary
pressure – intrapleural pressure] → +4mmHg means that at FRC, we
still have a pressure that is tending to expand the lungs (keeping the lungs open)
The recoil pressure of the chest wall (Pcw) is the difference between intrapleural pressure (Ppl)
and atmospheric pressure (Patm).
Pcw = Ppl – Patm
The recoil pressure of the lungs, transpulmonary pressure (PL – pressure across the lung), is
the difference between the alveolar pressure (Palv) (note that Palv is referred to as the
intrapulmonary pressure in the above diagram) and Ppl. When there is no air flow (closed nose
and mouth) Palv and the pressure measured at the mouth are the same.
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Document Summary
Changing the pressure, will ultimately result in a change of volume. The relationship between volume and pressure in the alveoli is demonstrated in the simple model shown on left. Note that when the volume in a fixed space increases, the pressure decreases; in contrast, when volume decreases, the pressure increases. Since the chest wall is trying to expand and lungs want to recoil, this creates the small intrapleural space. Transmural pressure is the pressure across a given structure this is measured via the pressure inside subtract the pressure outside, which will give you the sum pressure acting on the structure. At resting position, you don"t ha(cid:448)e any airflo(cid:449) occurring (no airflo(cid:449) entering the lungs); no pressure differences. At frc, the pressure difference between pressure at alveoli and pressure at atmosphere is. Zero no pressure gradient no airflow. The recoil pressure of the chest wall (pcw) is the difference between intrapleural pressure (ppl) and atmospheric pressure (patm).
