Please wait while the transcript is being prepared...
0:00
Hello. I am Henry Fessler,
Professor of Medicine at
Johns Hopkins University
School of Medicine.
I'm the Director of Education in
the division of Pulmonary
and Critical Care Medicine.
This lecture will cover the
basic classical physiology of
lung volumes and
the factors that
determine them in any
given individual.
The companion lecture will
discuss how we measure
these volumes in
the pulmonary function
laboratory and
how we interpret and
apply the findings.
0:28
In this talk, we'll review
some basic vocabulary so that
we can all communicate
with the same language.
I'll show you the
compliances of the lung,
chest wall, and
their combination,
the respiratory system, including
the concept of hysteresis.
I'll briefly describe
the function of
the inspiratory
muscles in so far
as they are relevant
to lung volumes.
Finally, I'll show you how
these mechanical factors
determine the
standard lung volumes
to which we have ascribed names.
0:56
The field of study
of the determinants
of lung volumes is
termed statics.
It includes a
relationship between
inflating pressure and
the volume of the lung,
the chest wall, and the
two structures together.
This is term statics
because it deals
strictly with the conditions
in which there's no air flow.
The mechanics of airflow Is
term dynamics, a topic
for another day.
1:19
Let's start with
some vocabulary.
The relationship between volume
and pressure of any
elastic structure
is more specifically
the relationship
between its volume and
its transmural pressure.
The pressure across the
wall of the structure.
This is always defined
as the pressure on
the inside minus the
pressure on the outside.
A few of these pressures in
the respiratory system have
their own particular names.
The transmural pressure
of the lung is called
the transpulmonary
pressure inside to equal
to the alveolar pressure
minus the plural pressure.
This is also known as the
elastic recoil pressure,
recognizing that the
outward pressure
distending the lungs is exactly
equal to the inward
pressure that the lungs
are exerting through
their elastic properties.
The transmeral pressure across
the diaphragm is termed
the transdiaphragmatic
pressure because
the diaphragm is concave down,
the inside pressure is
abdominal pressure.
When the diaphragm is
relaxed, TDI is zero.
When, it contracts, TDI
is a positive value,
the positive abdominal pressure
minus the negative
pleural pressure.
