HOW TO OPTIMIZE RESONANCE FREQUENCIES? A BRIEF HISTORY OF THE FLUTTER

Brigitte Bouzin Initiator of various exchanges and workgroups involving Belgian universities

(UCL, Von Karman, KUL and others)

Keywords: Time and Frequency Response; Acoustic Signal Processing; Wearable Sensors and Systems; Medical Signal Acquisition, Analysis and Processing

Abstract: The Flutter is a small, purely mechanical device comprised of a metal ball and a synthetic holder. This vibratory expiratory pressure device is used by COPD patients, including people affected by cystic fibrosis, in order to help them clear their lungs.

1. INTRODUCTION

Today, using the Flutter to clear one’s lungs is one of the possibilities offered by physiotherapists to patients suffering from bronchial obstruction. A brief description of the device: it is a small pipe-shaped device inside of which a ball oscillates, exerting positive pressure while inducing pressure waves in the bronchial system. These waves supposedly have the property of generating one or several resonance frequencies.

The present paper does not claim to offer a solution to the problem of searching for pulmonary resonance. Much research on this phenomenon has been done around the world, notably by the Von Karman institute in Belgium in 2005.

In addition to the work done by Von Karman, after reading a lot of literature on the subject, it must be noted that this phenomenon has never been clearly demonstrated.

The equations used do not seem to be appropriate for a convincing solution, considering the numerous unknowns and variants interfering and given the complexity of using such a device.

This paper does not offer any solutions but asks the question of the search for suitable equations to correctly look at the problem of pulmonary resonance.

Axcan, the distributor of the Flutter, seems to have asked itself the same question for more than 30 years… and leaves the answer largely up to empiricism.

In their instruction manual, they state the following: “The oscillation frequency produced by the FLUTTER® when its stem is in the horizontal position is approximately 15 Hz. This frequency can be modulated by changing the inclination of

the FLUTTER® slightly up (higher frequency) or down (lower frequency) from its original horizontal position. Adjusting the FLUTTER® to the resonance frequency is easily accomplished by the patient who selects the angle tilt that results in the best transmission of vibrations to his/or airways.”

Given the scientific progress accomplished in 30 years, that is to say since this instruction manual was written, is it possible to envisage a more optimal manner to determine the resonance frequency or frequencies?

The purpose of detecting this would be to provide the patient with some “feedback” which would tell him or her how they must work to optimize their physiotherapy. It might be necessary to look into remote detection or teledetection.

Part of the research work has already been carried out, namely detecting the frequency of the ball inside the flutter. This approach was undertaken by some teams on a voluntary basis, but the biggest part of the job remains to be done, namely fundamental research on the optimal frequency or frequencies. If this could be determined for every patient, he or she would receive feedback on the frequency or frequencies they must use to work.

A piece of software giving « feedback » on the frequency of the ball exists.

The principle is to allow the patient to work at a certain frequency and to receive feedback from this work to then be referred to a medical professional.

However the essential point is missing, namely how to determine the preferential frequencies for each patient in order to allow each patient to work at his or her optimal frequencies.

2. DESCRIPTION

The Flutter is a small, purely mechanical device comprised of a metal ball and a synthetic holder. This vibratory expiratory pressure device is used by COPD patients, including people affected by cystic fibrosis, in order to help them clear their lungs. 3. OPERATION OF THE FLUTTER

Operating the Flutter is relatively simple: the patient is asked to blow into the Flutter. The air goes through a cone on which a ball is placed, before escaping through small holes placed at the other end of the Flutter. The pressure from the breathing will increase the pressure on the metal ball until it is pushed towards the top of the cone. By clearing the way, the pressure under the ball will decrease and thus enable the ball to go back down and obstruct the passage of air again. Then a new cycle starts. The

movement of the ball creates a cyclical variation in pressure, which generates pressure waves that propagate through the patient’s respiratory system. These waves will propagate to the lungs and cause the chest cavity to vibrate, helping to clear the lungs.

A first parameter which modifies the frequencies of the flutter is its inclination. The latter can be modified by tilting the FLUTTER® slightly upward (higher frequency) or downward (lower frequency) from its initial horizontal position.

A second parameter that also allows us to vary the frequency of the pressure waves is the flow of exhaled air: the bigger the flow of exhaled air, the higher the frequency and, conversely, the smaller the flow of exhaled air, the lower the frequency.

It is probably this second parameter which is paramount. Indeed, the Flutter is an excellent flow modulator, probably the best. The flows of the Flutter must be assessed at different levels of the Vital Capacity. Those optimal flow modulations are the ones we should investigate to actually maximize deep bronchial drainage.

The Flutter therefore allows to generate pressure waves where the frequency may easily be varied in different ways. This allows the different users of the device to adapt the frequency to suit their needs. Indeed, each individual will react differently to the different wave frequencies. Finding a way to optimize the use of the Flutter based on the individuals who use it is therefore essential. 4. OPTIMIZING THE USE OF THE

FLUTTER

The effect of these pressure waves on lung clearance is still relatively unknown and complex. The most likely hypothesis is that the pressure waves might tickle the walls of the lungs, facilitating clearance. The most efficient way to use these pressure waves would be to match their frequency (or a harmonic from this frequency) to the lungs’own frequency in order to generate a resonance of the lungs and to increase their impact.

The challenge is to correlate the patient’s own lung frequency or frequencies based on the Flutter’s pressure waves. What has already been achieved is to measure the frequency of the ball inside the flutter. Fitting the flutter with a microphone which is

connected to a piece of software makes it possible to record the frequencies of the ball of the flutter.

In this way the patient is informed of the frequency of the ball. The question is to know whether, when the patient maintains the frequency of the ball at about 15 hertz, this same frequency reverberates through the bronchial system? Given the bronchial maze which this frequency wave has to go through, one may wonder. The many ricochets on the intersections of the bronchial system probably change the entire physical properties of the frequency waves.

The search for the preferential frequency or frequencies at which the patient should work depending on the area of the lungs he wishes to drain has so far been deemed too complex to be determined theoretically (variation of the geometrical shape, complex composition …).

Currently, the only way to try and empirically measure it is by putting one’s hand on the user’s chest to feel how the pressure waves impact the patient.

In the future, it would be highly worthwhile studying further the interaction and the effects of these pressure waves on the walls of the lungs. Indeed, the initial purpose is to clear the lungs and by gaining a better understanding of this phenomenon we would undoubtedly optimize the system.

If it turns out that lung clearance is indeed facilitated by the tuning brought about by the “resonance" in the lungs, it would then be essential to find a more sophisticated way to determine when this "resonance” is achieved.

From this, we can conclude that the “flutter” has not yet revealed all its secrets.

The Flutter

5. BACKGROUND AND ACTORS

1986: Discovery of the Flutter, scientifically known as “oscillator for respiratory resistance" by its inventor Claude Liardet. 1986 / 1988: Approval by the FDA (Food and Drug Administration), numerous clinical trials and protocols by renowned pneumologists and others. Axcan (Scandipharm), worldwide distributor, publishes a technical instructions leaflet. 1998: My son, Marc, is diagnosed with cystic fibrosis (date of birth 28-01-94). 2000: Around the 2000s, contact is made with the « Von Karman » institute (ULB): https://www.vki.ac.be// 2004 / 2005: Publication by Von Karman of a study on the Flutter entitled «Study of the operating mode of the Flutter and how it contributes to evacuating mucus within the frame of physiotherapeutic treatments of cystic fibrosis». (Ref : A. Bellier, Etude du fonctionnement du Flutter et de sa contribution à l’évacuation du mucus dans le cadre des traitements physiothérapiques de la mucoviscidose). Von Karman Institute for Fluid Dynamic, Environmental and Applied Fluid Dynamics Department. 2005 (November): Following my request through the internet, some acousticians based in Switzerland are made aware of the issue, and endeavour to build the «Flower» software. This IAV group is doing admirable work on a completely voluntary basis. IAV is also seeking advice from Claude Liardet, the inventor. 2006: The “Flower” software is finalized by IAV. This software stimulates the patient while making him/her work according to specific frequency and time instructions. Website address: http://www.flower-for-all.org 2006: Presentation of the « Flower » project to the French League “Vaincre la Mucoviscidose” (Overcome Cystic Fibrosis) who accept it with great enthusiasm. The project is introduced to the Belgium League (ABLM) who give an unfavourable opinion.

Summary of the unfavourable opinion: It is the ”flow” which should be measured and not the frequency. Indeed, the Flutter is an excellent “flow” modulator, perhaps the best. It is the “flow” parameter which must be developed in order to actually optimize deep bronchial drainage. 2006: Likely suppression of copyrights on the Flutter patent. As a result, some firms become interested in exploiting the product. 2007 / 2010: My son is growing up and as a teenager, the principle of a car that you move along a track using your breath no longer holds his interest, he is getting tired of the game. Hence the search for new solutions. 2007 to 2011: Contacts with the « Facultés Polytechniques de Mons ». Development of an interface. One teacher and two students, Thierry Dutoit, Marie Baudart and François Rocca receive the "Polytech Web" award in 2008 for FluXair. Website address: http://tcts.fpms.ac.be/~fluxair/. 2008 / 2009 / 2010: it is reported that the Belgian instructions leaflet for the Flutter is incomplete. A warning is issued to the AFMPS (Federal Drugs and Health Products Agency). The AFMPS confirms the instructions of use are to be modified. 2010: IAV new source code (flapi) cf http://www.flapi.org/. Talks with Belgian universities and exchanges throughout the world. Desire from Defitech (Switzerland) to go further with the IAV project based on the flapi source code, upon request by the Pediatrics Department of the Hospital of Lausanne (Quentin de Halleux). Cf http://www.defitech.ch/FlowerForAll-en 2011: Contact is made with Peter Bingham in the USA (author of a breathing game for children with cystic fibrosis). Meeting in July. 2012: Worldwide contacts. The project draws the attention of the following people: José G. Venegas Ph.D. Associate Professor in Anesthesia (Bio-engineering) at Harvard, Department of Anesthesia Thier 429B Massachusetts General Hospital, who is currently developing a project whose philosophy would be similar to that of

the « Flower-breath-flutter » software. The result of the student’s thesis is expected in 2014. Professor Nenad Filipovic, professor at the Faculty of Mechanical Engineering, University of Kragujevac, Serbia (fica@kg.ac.rs) 2013 initiatives: written summary of the Flutter situation prompted by myself with the help of Fabien Hock, a civil engineer in aeronautics, with a view to providing the clearest possible statement of the problem. Summary entitled: « Inventory of the Flutter issue ». 2014: Formation of a study group in Canada (Montreal), whose website is at the following address: http://www.fibrosekystique.net/?q=en Aim: to study various possibilities of playful pulmonary drainage, mostly using the « PEP », but also using the « FLUTTER».

6. Reference A. Bellier. Study of the operating mode of the Flutter

and how it contributes to evacuating mucus within

the frame of physiotherapeutic treatments of cystic

fibrosis (Etude du fonctionnement du Flutter et de sa

contribution à l’évacuation du mucus dans le cadre

des traitements physiothérapiques de la

mucoviscidose). Von Karman Institute for Fluid

Dynamic, Environmental and Applied Fluid

Dynamics Department. 2005.

NB: article written by Brigitte Bouzin, self-taught in the subject; email: info@the-flutter.be