How are wheezes produced?
Not like the tone of an organ pipe (i.e., by vibration of air within the pipe, so that the pipe’s length and
diameter correlate with the tone’s pitch [with larger and longer pipes producing the lower pitch]). If wheezes
were generated this way:
Airways would have to be 4–8 feet long, which is the necessary length for producing some of the lowest-pitched wheezes of asthma. Instead, the bronchial tree is <1 foot long.
The frequency of a wheeze generated by a particular airway would stay constant throughout respiration
(while instead it differs by as much as 1 octave between inspiration and expiration).
The pitch of a wheeze would change when breathing a mixture of helium and oxygen (just as the pitch of
an organ pipe would rise when blown with helium).
Instead, the pitch is constant. Hence, wheezes are not generated like tones of organ pipe, but rather like notes of a toy trumpet’s reed —or, even better, like sounds of a harmonica’s reeds.
In this model (first suggested by Forgacs in the 1960s), airflow sets each individual reed into oscillation between opening and closure, thus generating a note of constant frequency. Air flowing at high velocity through a narrow bronchus has a similar sucking effect on the airway wall, by pulling it inward and thus
initiating a flutter (i.e., a wheeze) of closing and opening, resembling very much the vibration of a toy
trumpet’s reed. This fluttering typically delivers a note of constant frequency that depends on the mass and
elasticity of the bronchial walls, the tightness of the narrowing, and the rate of gas flow through it.
Not like the tone of an organ pipe (i.e., by vibration of air within the pipe, so that the pipe’s length and
diameter correlate with the tone’s pitch [with larger and longer pipes producing the lower pitch]). If wheezes
were generated this way:
Airways would have to be 4–8 feet long, which is the necessary length for producing some of the lowest-pitched wheezes of asthma. Instead, the bronchial tree is <1 foot long.
The frequency of a wheeze generated by a particular airway would stay constant throughout respiration
(while instead it differs by as much as 1 octave between inspiration and expiration).
The pitch of a wheeze would change when breathing a mixture of helium and oxygen (just as the pitch of
an organ pipe would rise when blown with helium).
Instead, the pitch is constant. Hence, wheezes are not generated like tones of organ pipe, but rather like notes of a toy trumpet’s reed —or, even better, like sounds of a harmonica’s reeds.
In this model (first suggested by Forgacs in the 1960s), airflow sets each individual reed into oscillation between opening and closure, thus generating a note of constant frequency. Air flowing at high velocity through a narrow bronchus has a similar sucking effect on the airway wall, by pulling it inward and thus
initiating a flutter (i.e., a wheeze) of closing and opening, resembling very much the vibration of a toy
trumpet’s reed. This fluttering typically delivers a note of constant frequency that depends on the mass and
elasticity of the bronchial walls, the tightness of the narrowing, and the rate of gas flow through it.