Lung Pressure and Power:
A Potpourri of Topics
Air and Breath Control
is crucial to voice production. It is the flow of air through
the various constrictions
in the vocal tract that generates sound, and air is
also the medium which transmits that sound to our ears.
The ability to skillfully control the pressure and
flow of air is a large part of successful voice use;
new singing students often spend several lessons on
proper breath control before doing any serious work
on the voice itself. There are several rather specialized
breath-related skills that serious singers must develop.
With extended training, vocalists can improve their
lung capacity, learn to take a larger breath while
taking less time to do it, learn to take a 'silent'
breath, and keep a steady airflow going to their vocal
folds without generating any excess tension in the
upper body or neck area.
Each of these skills is essential to good singing,
and those who use their voices for speaking - actors,
lawyers, sales personnel, etc. - can also benefit
from improved breath control. Speech-language pathologists
who work with voice patients may find it helpful
to learn more about the training of singers and actors.
The breath control skills used for performers' voices
may also be used with persons with voice disorders
to facilitate healing of tissue or overcoming a disorder.
Flow and Pressure
The airflow necessary for singing or speaking is generated by pressure exerted
on our lungs by the diaphragm and abdominal muscles. This flow is measured
in cubic meters of air passing a given point per second (m3/s).
Pressure is measured in Pascals (Pa); a Pascal is defined as a pressure of
one Newton per square meter (N/m2). Since one Pascal
is a rather small amount of pressure, the kilopascal (1000 Pascals; the symbol
is kPa) tends to be used for pressures relevant to voice use. A kilopascal
is approximately equal to the weight of an apple distributed over a 10 cm2 surface
(around half the size of a credit card).
The Pascal is named for the French scientist and philosopher Blaise Pascal,
who discovered a principle now known as Pascal's Law: pressure is transmitted
rapidly and uniformly throughout an enclosed fluid at rest. So, for instance,
if we contract our lower abdominal muscles with our glottis closed, the pressure
in the lower part of our lungs is increased, and this change is quickly transmitted
to the rest of our lungs. If the glottis is then opened, air will then rush
out until the lung pressure is equal to the pressure of the surrounding air.
Our lungs are composed of millions of tiny alveoli, or air sacs. These
sacs are connected by a network of ducts, beginning with the trachea, then
separating into smaller and smaller tubes in each lung, called bronchioli.
Pascal's law dictates that the pressure in each of these millions of tiny sacs
is the same, and it is called the alveolar pressure.
An instrument called a U-tube manometer can be
used for measuring the maximum lung pressures a person
can generate; the instrument consists of a U-shaped
tube partially filled with liquid. The test subject
blows into one end of the tube, and the amount of
liquid displaced is measured to determine the pressure.
This is not a particularly useful test for voice
research, however, since the U-tube manometer closes
off the airway during the test. During singing and
speech, the airway remains open, and directly measuring
lung pressure accurately while keeping the airway
open can be difficult.
Lung pressure can be indirectly measured, however,
by placing a pressure transducer between a subject's
lips and having the subject say a word that begins
with /p/. A measurement would be taken while the
lips are closed and just before they burst open with
the /p/. Pascal's Law tells us that the pressure
in the mouth must be the same as that of the alveoli.
The total volume of air that an average adult can hold in his/her lungs is
around 6-7 liters. However, only part of this air can actually be used; around
2 liters of that is always present in the lungs, and is called residual
volume. This air can't be expelled unless the lungs collapse.
The remaining volume of 4-5 liters, the tidal
volume, is usable for respiration or voice
use. However, we rarely use all of this capacity;
at rest, we may only breathe in and out around
10-15% of the tidal volume. The rest is held in
reserve for more demanding physical activities,
such as exercise or singing, which can demand our
entire tidal volume.
This law, named for the British scientist Robert Boyle, states that - in a
soft-walled enclosure at constant temperature - pressure and volume are
inversely related. Increasing volume causes a proportional decrease in
pressure, and vice versa. Boyle's Law explains why our lung pressure decreases
when we increase the volume of our lungs by expanding the rib cage and contracting
the diaphragm to inhale. Conversely, when we exhale, the rib cage contracts
and the diaphragm relaxes into its more curved position, thus decreasing
the lung volume and causing pressure to rise. This pressure then causes air
to rush out of the lungs.
Muscle Use in
The cycle of breathing can be divided into four discrete phases of muscular
- Inspiration: the abdominal muscles and internal
intercostals (rib muscles) must relax, and the
external intercostals contract to fully expand
the rib cage; the diaphragm contracts and descends,
which also enlarges the lung space.
- Expiration, first phase: since the rib cage has
been expanded more than it is at rest, it will
tend to 'relax' back to its rest position if no
muscular effort is keeping it expanded; this is
called elastic recoil. The pressure from
recoil is all that is needed to start the airflow;
in fact, if an especially deep breath was taken,
the pressure from the recoil will be greater than
desired, and the air pressure will need to be restrained
somewhat by continued contraction of the diaphragm.
- Expiration, second phase: The last of the elastic
recoil is used up in this phase, aided by contraction
of the internal intercostals. These pressures shrink
the rib cage, adding to the lung pressure.
- Expiration, third phase: The abdominal muscles
are used to provide the last bit of lung pressure
||Diaphragm and/or external
||Elastic recoil, diaphragm
used to prevent excess pressure from recoil
||Elastic recoil, internal
intercostals, continuing until no more recoil
||Internal intercostals, abdominals