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Thursday, August 7, 2008

Warwick's Vest Letter from 2007

I post this in the spirit of information sharing to my fellow CFers. Warwick is so dedicated to CF care that it is my assumption that he would be ok with me posting this to help and prolong the lives of my fellow CFers.

Everything that follows are his words:


Warren J. Warwick,
March 27, 2007


The four High Frequency Chest Compression (HFCC) systems in use today are the asymmetric sine waveform machines (the ElectroMed SmartVest and the Hill/Rom Model 104tm and Model 105tm, the symmetrical sine waveform Hill/Rom Model 103tm and the triangle waveform Respirtech InCourage Systemtm. All but the Hill/Rom Model 103tm, the most widely used HFCC system, are commercially available. The symmetrical sine waveform Hill/Rom Model 103tm is, in my opinion, better than the asymmetric sine waveform machines I expect it to be in use for many years,

The positive aspects of using HFCC therapy include; the simplicity of the HFCC technology, the ease of its use, and that it always works with 100% of the settings on the dials over the whole time of therapy. I believe that HFCC will always provide better treatment than other effective techniques including manual chest clearance, Autogenic Breathing and Active Cycle Breathing as well as the Flutter and Acapella.


HFCC works most effectively when patients breathe with their normal pattern of short inspiration and longer passive expiration. When the patient breaths at the prescribed highest pressures that are tolerated for each frequency the chest compressions, push micro-coughs of air flow through the airways and at the same time oscillating the air in the airway passages. There is a separate simultaneously beneficial effect, for patients with cystic fibrosis, for whom the triangle waveform pressure pulsations will increase the amount of water secreted by the respiratory mucous secreting cells and glands.

I recommend two HFCC therapy sessions of 30 minutes every day for routine preventive therapy (with a pause to cough about every five minutes of HFCC therapy). When the patient has a worsening lung problem, I recommend doing three HFCC therapy sessions a day with up to 60 minutes for therapy each session.


The sine waveform vests must be inflated before HFCC can start. That inflating compression pressure on the chest reduces the patient's lung volume making breathing difficult. Before HFCC therapy starts, every patient must use extra energy and more muscles to breathe. In addition, the Hill-Rom machines must have a tube disconnected from the vest or the machine after each 5 minutes so that the patient will be able to take the deep breath require for coughing.

With the InCourage Systemtm and The SmartVesttm the vest pressure drops to atmospheric pressure when compression pulses stop so a tube does not need to be detached.

Our prescription for HFCC frequencies was developed over 16 years ago measuring the airflow and velocity on 100 patients with CF who used the same vest with each machine. We found a wide scatter of 'best' velocities and volumes; sometimes with several frequencies having almost identical 'best' values. Milla CE, Hansen LG, Warwick WJ. Different Frequencies Should Be Prescribed For Different High Frequency Chest Compression Machines. Biomed Instrum Technol. 2006 Jul-Aug;40(4):319-24. Every frequency was a best frequency for at least one patient. For the sine waveform machine 103tm machine, and by analogy interpreting that data for all triangle waveform machines the best frequencies for large volumes are 6, 8 and 9 Hz and the best frequencies for highest velocities are 18, 19 and 20 Hz. The least effective frequencies are 10 to 17 Hz. Each of these frequencies is used for five minutes in any order followed with a pause for the patient to cough to clear the moved sputum.

With the original square waveform (101TM and 102tm) machines and the triangle waveform inCourage machine both the best flows and volumes are 6, 7, 8, 10, 11 and 14 Hz. The "triangle waveform" frequencies are the same as the square waveform machines.
For the inCourage System I recommend frequencies 6, 7, 8, 10, 11 and 14 for individual frequencies but I prefer the "Quick Start" that continuously, pulse by pulse, increases from 6 to 14 and then from 14 to 6 Hz over a five minute cycle followed with a pause for the patient to cough to clear the moved sputum.


The sine waveform interaction between frequencies and pressures was recognized immediately after the Model 103TM became available for which we developed a clinical adjustment and a teaching table that has now been improved by laboratory research. The guideline for the use of the table remained unchanged. The pressure change is in the 18, 19, and 20 table line for two "4's" for the 103TM and for two "5's" for the 1004TM.

For the "sine waveform" machines, the pressure column is determined by starting with frequency 6 and pressure 3. Then after a few breaths increasing the pressure to 4. If the patient notices no difference to increase the pressure 5 dial setting...and so forth... until the parent notices that the new pressure changes the breathing pattern or the patient complains that the new pressure makes breathing harder. That frequency is TOO high.

The previous lower pressure column is then selected to use to reduce the vest pressure at higher frequencies. For example if the patient notices a difference in breathing with pressure 7 then the patient should use pressure column 6 for all the frequencies. This will need to be checked each year for a growing child in good health and more frequently if changes in height or growth or health are significant.

Patients using Model 103tm or any "symmetric sine waveform" system should adjust frequencies and pressures using the Table for the Model 103tm with frequencies 6, 8, 9, 18, 19 and 20 in sequence, for 5 minutes each frequency followed by a cough. The frequencies 10 to 17 have been shown in our Minnesota Research to be the least likely to be a useful for airway clearance.

Table for the Model 103tm

Frequencies to be used in sequence Pressure Columns
6 3 4 5 6 7 8 9 10
8 and 9 2 3 4 5 6 7 8 9
18, 19 and 20 1 2 3 4 4 5 6 7

Patients using the Model 104tm should use the Model 104tm table with frequencies 6, 8, 9, 18, 19 and 20 in sequence, for 5 minutes each frequency followed by a cough.

Table for the Model 104tm

Frequencies to be used in sequence Pressure Columns
6 5 6 7 8 9 10
8 and 9 4 5 6 7 8 9
18, 19 and 20 3 4 5 5 6 7

*This graphic is simply to help understand the information posted above. I realize that the numbers aren't the same as what Warwick says, so please follow Warwick's instruction rather than what appears on the table. The graphic is simply to help you better visualize what Warwick is talking about

Neither the SmartVest nor the ICS can have dial frequency and dial pressures settings with too great a variation for the preparation of a table for adjusting dial pressure with the dial frequency. The SmartVest System has such a high increase in vest pressure as frequencies are raised that the pressure to use for each frequency will have to be individually determined for each patient.

The ICS system jacket pressure has a large drop in vest pressure as frequencies are increased so the RespirTech Inc's guidance should be used. Using the QuickStart ramp with frequencies going up and down, 6 to 14 Hz and back to 6 Hz, wit the highest pressure that can be tolerated over the five-minute cycle is proving to be very effective. The goal is to have the patient use 100% of power.

When the patient first starts HFCC therapy I recommend rechecking the pressure columns after several weeks because strengthening of the chest muscle may make a higher pressure column a better choice. I will be very pleased to hear from patients about their experience.


The InCourage Systemtm and the Model102TM use valve systems rather than a piston equivalent pressure system to generate the HFCC compressions. Therefore we used the Model 102TM best frequencies we compared this triangle waveform versus the Model 103tm symmetric sine waveform ( Milla CE, Hansen LG, Weber A, Warwick WJ. High-frequency Chest Compression: Effect of the Third Generation Compression Waveform. Biomed Instrum Technol. 2004 Jul-Aug; 38(4):322-8). With the triangle waveform was used with frequencies 6, 7, 8, 10, 11 and 14 Hz frequencies with the highest tolerated pressure. With the symmetric sine waveform using the Model 103tm these patients used the 103 table to adjust the pressures with the frequencies 6, 8, 9, 18, 19 and 20. [U]The patients using the triangle waveform system produced an average of 22% more sputum than with the sine waveform. [/U]

I recommend that the InCourage Systemtm Quick Start program start at frequency 6 Hz and go up to 14 Hz and then back to 6 Hz over five minutes:... then to stop the pulsations for a brief time to cough. After coughing, the patient will repeat these steps five more times. Each ramp provides a virtual 3000+ frequency, in sequence, pulses from low to high and high to low during each 5-minute cycle. All the airways, regardless of dimensions, will have optimum frequencies plus harmonics and hypo-harmonics many times throughout each cycle.

The InCourage Systemtm has a unique range of pressures. Pressures 10% to 50% have been designed for babies and very small children. The use of these pressures should be considered experimental because we have not yet studied this use. At this time, I recommend that these low pressures should be used only under close medical supervision since accidental use of these pressures by toddlers and older patients show that, for users after infancy, these pressures are too low for effective airway clearance of sputum.

So far we have found that with every constant pressure setting the InCourage Systemtm jacket pressures decrease as the frequencies are increased. Each patient should test a pressure setting over a "Quick Start" ramp cycle to determine the highest pressure that the patient can tolerate over the cycle. The cycle is hardest to breath at the start and end of the cycle and easier during the middle of the cycle. My goal is to have all patients using 100% of the machine pressure. I recommend that patients 4 years and older start at 80%. For younger patients I recommend starting at 70%. No patient should use pressure below 70% for therapy although 60% may be used to accommodate small children to the feel of HFCC. I recommend working with the patient to adapting the 100% pressure..

The InCourage Systemtm and Models 103tm and 104tm and the SmartVest have collectively and successfully been used by over sixty thousands of patients for over 28 years with success, mostly without my guidelines. Never the less when one of these patients tries these recommendations I frequently hear that their system works better. These guidelines are the best guidelines I have developed.


At this time, only RespirTech has specific directions for the measurement of the patient and the adjustment of their jackets to fit with the vest circumference/chest circumference ratio is about 110%. Regardless of the HFCC system every patient's vest/jacket should fix the 110% circumference ratio by means of safety-pins or re-adjust the circumference ratio fitting to about 110% with every use. The safety pin fixation should be checked when the patient has grown, gained weight or changes the clothes that are worn during HFCC therapy. For all machines, the vest/jacket should cover all of the rib cage, from the collar bones down to the lowest ribs, with the un-inflated circumference of the vest/ chest circumference being about 110%.

If an increase of pressure alters breathing or breathing becomes uncomfortable, assume that that pressure is, at least for a while, too high for daily use. This may require daily testing of pressure, see above. Keep in mind that, as the airways become cleaner, higher-pressure pulses the patient's breathing may become less comfortable and effective.

Our basic science research has developed much of the information discussed above and confirmed earlier work. We are studying the Minnesota HFCC technology that has built or inspired the development of the Models 101tm, 102tm, 103tm, 104tm, 104tm, the SmartVest and the ICS systems. Graduate students working in the Minnesota Defense of The Lungs Project have earned three MS degrees and one PhD degree with two more PhD's expected later in 2007.

Our laboratory research ranking of estimated effectiveness, which will need to be confirmed by CF patient studies by other researchers and, is that the ICS > Model 103tm > Models 104tm and 105tmand the SmartVestTM which we assume to be equal because all three have almost identical asymmetric sine waveform output.

Your observations and questions will help us define tasks to solve and will help us improve all forms of HFCC.

My expiration date for these recommendations is March 27, 2008.


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