Principles of Operation
The Vibralung Acoustical Percussor uses acoustics (sound waves) as its fundamental operating principle. The sound waves (quasi-musical tones and “random noise”) are generated by an electronic digitally controlled signal generator and reproduced with a high-fidelity audio loudspeaker.
The Vibralung Acoustical Percussor generates and couples sound energy to the column of gas in the patient’s airways through a simple mouthpiece assembly. In turn, the sound energy vibrates the column of gas in the airways during both the inspiratory and expiratory phases of the patient’s breathing cycle. As the patient breathes normally through the mouthpiece attached to the HHT, the acoustic sound waveforms are superimposed over the normal respiratory waveforms and travel throughout the lungs via the conducting airway system.
A useful analogy for the manner in which various waveforms superimpose themselves over each other would be the way multiple ripples form on a pond, even ripples emanating from different directions, can pass through each other and continue along their intended pathway. Consequently, application of this technique is relatively effort-independent on the part of the patient, and does not require the patient to perform specialized breathing maneuvers, because the sound waves pass through normal respiratory pressure waves during resting breathing.
The Vibralung Acoustical Percussor generates a sinusoidal waveform composed of a continuous spectrum of overlapping frequencies (quasi-musical tones) ranging from 5 to approximately 1,200 Hz. Most of these tones are within the audible range of human hearing and can be heard by the patient and people close by.
The 5 Hz tone is generated while no other tone is being generated and represents the digital “off state.” Although it is below the normal lower limit of human hearing, it is nevertheless present.
The frequencies are separated into five operating ranges that have been labeled as Low, Medium, High, R2 and R5 to provide a simplified description. The tones emitted at the L, M and H settings deliberately resemble a series of staccato musical notes, at a tempo of about 360 beats per minute, to provide a predictable sequence of frequencies. These tones “step” through their range (frequency stepping) starting at the low end of the range and progressing to the high end of the range over a treatment period of 10 minutes. The tones at the R2 and R5 (Random Noise) settings are described as similar to “white noise” and cover the full available spectrum for either 2 or 5 minutes. These two methods for promoting airway clearance with sound waves provide the patient with different options for determining the optimal therapeutic approach.
The therapeutic benefit from application of the Vibralung is through a mechanism known as “sympathetic resonance,” not unlike the experience of having your house windows vibrate and rattle if you turn your stereo system up too loud or when your car windows and rear-view mirror vibrate intensely by extremely loud music in an adjacent vehicle. See the section entitled “Vibralung Acoustics Tutorial” for a more detailed review of the fundamentals of acoustics that are applicable to the Vibralung Acoustical Percussor.
During operation on the L, M or H settings, the Vibralung Acoustical Percussor emits a sequence of repeating tones (frequency stepping) in a pattern according to an algorithm that has been programmed into the signal generator portion of the device. The frequency range spans 55 to 350, 69 to 660, or 124 to 1,182 Hz as shown in the table above. However, we describe the resulting frequency spectrum, in round numbers, ranging from 5 to 350, 5 to 660, or 5 to 1200 Hz for simplicity, and to account for the frequency being emitted during the digital off state, which is 5 Hz.
The best way to describe the pattern is to think of it as approximating 4 musical notes one-half step apart (for example, C, C#, D and D#). After repeating the 4-note sequence for 20 seconds, the pattern shifts up at least a half step (for example, C#, D, D# and E), and then repeats another 20 seconds, and so forth for a total of 7 minutes. The pattern gradually moves from low frequencies to higher frequencies so that the airways are exposed to a full and deliberately overlapping spectrum of acoustical energy.
Conversely, the R (“random noise”) settings are exactly that: random frequencies melded together to create “white noise” with no discernible pattern.
Audible Samples of Vibralung Tones
Here are three short samples of Vibralung tones, approximately 60 seconds each, of the sequential note patterns. The actual treatment sequence consists of 10 minutes of sequential note patterns that gradually increase in frequency from the low end of the selected range to the high end. If you listen carefully to each of these short samples you will hear the repeating pattern of 4 tones (1-2-3-4-1-2-3-4-1-2-3-4, etc) at a tempo of about 360 beats per minute. Also, you can hear the “step up” frequency shift that occurs roughly every 20 seconds.
The last sample is a 15 second sample of Random Noise (RN). The Vibralung Acoustical Percussor has two modes for administering Random Noise which is a “hash” of tones generated in the 5 to 1,200 Hz range. R2 and R5 allow operation in Random Noise mode for 2 and 5 minutes, respectively.
A selected treatment setting with the Vibralung Acoustical Percussor takes up to 10 minutes, depending upon the setting that has been selected, and provided the session has not been paused at any time or held (Treatment Hold) at a particular frequency.
Five settings, representing a designated sequence of frequency ranges, have been coded into the signal generator portion of the Treatment Control Unit as shown in the following table:
A typical treatment session can be 10 or 20 minutes, depending upon what the physician and/or therapist determines is needed. A single treatment is 10 minutes. Some patients may take 2 treatments back-to-back, for a total of 20 minutes. A patient might take a single treatment on Low, Medium or High, or alternately, a treatment on Low followed by Medium, or a treatment on Medium followed by High. There is no single right or wrong protocol, although Low should precede Medium, and Medium should precede High. Beyond that one rule, whatever works best, based upon patient assessment, sputum production, and even patient feedback, is appropriate.
One optimal position for taking a Vibralung treatment is sitting straight up in a chair, if possible. Such a position allows the lungs to ventilate optimally and positions the patient in an ideal position to cough and expectorate. However, other positions are not necessarily contraindicated. Patients have reported taking treatments in a recumbent position, lying on one side for 10 minutes and then switching to the other side for 10 minutes, in order to favor the uppermost lung. Patients and therapists should feel free to evaluate alternative positions based upon the patient’s perception of therapeutic benefit and ability to cough and expectorate in a given position.