Intrapulmonary Acoustical Airway Clearance (IAAC)
The IAAC concept consists of a number of individual operational assumptions that must be considered together, but sequentially, as they apply to the task of promoting airway clearance acoustically.
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Intrapulmonary
The Vibralung Acoustical Percussor delivers an internal pulmonary treatment.
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The patient breathes normally through the mouthpiece attached to the Vibralung Acoustical Percussor. The sound waves generated by the Vibralung Acoustical Percussor's transducer and delivered via the mouthpiece, are directly coupled to the patient's airways. The Vibralung is the only device that has powered sound waves or frequencies applied in this manner.
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Acoustical
The battery powered Vibralung Acoustical Percussor generates sound waves or acoustics via a transducer (loudspeaker).
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Airway Clearance
The Vibralung Acoustical Percussor has been shown to be highly-effective for airway clearance.
By applying the physics principle of resonance, at or near sympathetic or resonant frequency, the oscillatory sound waves result in the mucus, mucus plaque, and/or the airway surfaces themselves vibrating, that is resonating, creating a shearing effect, then promoting the breaking down, and mobilization of, mucus secretions.
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The sound waves are continuous, that is they are effective during both inhalation and exhalation. As a powered device generating acoustic sound waves, the treatment is independent of a patient's ability to breathe or perform for efficacy.
This therapy make it easier for the respiratory system to expel the secretions.
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Another principle of sound is that the smaller the structure the higher the frequency. In the case of the lung bronchial branches both diameter and length determine the frequency of that part of the lung. This principle is seen in a pipe organ which has smaller and shorter pipes for the higher notes, and larger and longer pipes for the lower notes.
The largest airways, or the mucus/mucus plague it them, will vibrate at the lowest frequencies so the first step is to clear them. This will help create a clear path for mucus cleared further down in the lungs in the smaller airways to be expelled when the patient uses the higher frequency fanges.
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At one time, the lungs were thought to have a Resonant Frequency (RF) of between 5 and 40 Hz. Consequently, it is widely believed that vibrating the lungs and airways at or near their resonant frequency will generate the greatest shear stress at the interface between mucus and the airway surface, and will therefore be most effective.
This old idea is incorrect. The lung has multiple resonant frequencies because it has multiple airways of many different lengths and diameters. Treating the lung with a single frequency or a low range frequencies is not going to effectively create resonance in all the airways.
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For effective airway clearance the lung must be exposed to a wide range of frequencies, starting with very low frequencies and progressing gradually to higher frequencies. The Vibralung Acoustical Percussor is the only airway clearance therapy that produces random noise, which appears to reduce constriction of the airways.
This is the basis of Intrapulmonary Acoustical Airway Clearance and the reason why the Vibralung Acoustical Percussor applies such a wide range of frequencies (5 to 1,200 Hz) in two different kinds of acoustic patterns (random noise and sequential tone pulses).
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To make the case for requiring a wide range of frequencies, according to well-accepted physiological treatises that describe the lungs in terms of their corresponding electrical circuitry, the airways of the lungs are essentially a series of impedances (multiple impedances in series). We know that there are 23 divisions in the normal adult human tracheobronchial tract, so there are 23 different “stages,” and countless hundreds of actual bifurcations, at which flow dynamics can change, as gas passes from one division to another.
This anatomical and physiological fact has been summed up nicely in this classic diagram:
Essentially, this chart describes a series of airways that are becoming ever-smaller over 23 generations. Representative values are assigned for generational airway length and diameter, as well as quantity and the resulting cross-sectional area they would cover. From this data, the resistance (R) and compliance or conductance (C), as well as the impedance (L) of each bronchopulmonary division level can be approximated.
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In electrical nomenclature, an airway segment is similar to an LCR circuit, where L=impedance, C=conductance (or compliance), and R=resistance. Those familiar with electronics will recognize that the simple LCR circuit shown here is fundamentally an oscillator, or tone generator. An LCR circuit has the following schematic representation (with V being voltage, or pressure change):
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The complete tracheobronchial tract, from trachea to alveolus, can be modeled as a series of LCR circuits.
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Because LCR circuits can resonate under certain conditions, their RF can be predicted when other parameters are known. When the RFs are measured from such LCR circuit modeling, a progressively higher frequency is rendered as shown on the oscilloscope screen shot below.
Frequency is on the horizontal axis, ranging from 100 Hz to 100 KHz.
And so, the final assumption is that treating the lung with a single vibratory frequency is probably insufficient. Therefore, the Vibralung Acoustical Percussor is designed to treat the lung with a multitude of frequencies that incrementally advance over one of three ranges, from low to high, in a span of 10 minutes per treatment.
The use of “random noise” spanning the frequency range of 5 to 1,200 Hz is recommended for at least two minutes, the R2 setting, at end after a L - Low, M - Medium, or H - High. It may also be used before those treatments, particularly if there is wheezing or tightness in the lungs. It may also be used on its own for conditions such as dry asthma for up to fifteen minutes such as three of the R5 setting. R2 and R5 are both random noise for two minutes and five minutes respectively.
Reference
McPeck M. Vibralung Acoustical Percussor: A New Paradigm in Airway Clearance Therapy. Respir Ther 2014; 9(Oct-Nov): 45-47. Scroll to beginning of article on page 45 of the journal.