WO2005060826A1

WO2005060826A1 - Heart rate meter

Info

Publication number: WO2005060826A1
Application number: PCT/IB2004/052848
Authority: WO
Inventors: Pierre Rigaux
Original assignee: Compex Medical S.A.
Priority date: 2003-12-19
Filing date: 2004-12-17
Publication date: 2005-07-07

Abstract

The invention relates to a heart rate meter including means for measuring and indicating the derivative of a patient's heart rate. In one embodiment of the invention, the heart rate meter further includes means for determining and indicating the derivative of the derivative of the patient's heart rate.

Description

Heart Rate Meter

Field of the invention

The present invention relates to the field of heart rate measuring devices commonly known as heart rate meters.

State of the art

Various models of cardio-frequency meter are known which can be used in the medical or sports field.

US Patent 3978849 (ITT) presents a heartbeat indicator which can be in the form of a wristwatch which indicates the heartbeat and the variations of the heartbeat. The user is warned of a variation of the pulsation by a change of color of the indicator.

The international patent application WO 96/20640 (POLAR), filed in 1995, describes a device which measures variations in the heart rate. The subject of this request relates more precisely to how to measure variations in heart rate.

The following patent documents also describe devices making it possible to measure variations in the heart rate and or in the shape of the ECG profile: - US 4022192 (BRUKER-PHYSIK AG) - US 3835837 (PEEK) - EP 0 172 747 (NIPPON KOKAN) - US 3473526 (LIFEGUARD WATCH) - US 3742938 (STERN) - EP 1 059 102 (OMRON)

The aforementioned devices of the prior art certainly make it possible to determine the variations in the heart rate over time, but always discontinuously. The information they deliver is limited to a succession of absolute values of the heart rate (named HR in the remainder of this text).

Summary of the invention.

One of the objectives of the invention is to obtain new information relating to the heart rate that the devices of the prior art cannot offer.

This objective is achieved by means of the cardio-frequency meter according to the invention which comprises means for continuously determining the variations in the heart rate over time. More specifically, the cardio-frequency meter according to the invention comprises means for determining the derivative of the

FC.

According to an advantageous embodiment of the invention, the heart rate monitor further comprises means for determining the derivative of the derivative of the HR.

The advantages offered by the cardio-frequency meter according to the invention are described in more detail below.

The knowledge of the derivative of the HR, named VC (for Cardiac Velocity) thereafter, offers different information usable for the analysis and the control of the physical effort or the sports training.

applications

Two main types of applications can be considered, either during an increase in HR or when the effort decreases or stops and the HR decreases. Increase in CV and HR:

• Demonstration of central or nervous fatigue during explosive strength training

The control of the heart rate (HR) between the rest frequency (FR) and 100 pulses per minute is essentially under the control of the central command, i.e. the central nervous system via a withdrawal or inhibition of the parasympathetic nervous system . Thus during a physical effort, the VC between FR and 100 pulsations per minute depends on the freshness of the central control. When central or nervous fatigue develops during physical activity, the nervous system decreases its ability to quickly produce a frequency variation between FR and 100 pulses per minute. During force-speed type trainings characterized by alternating long periods of rest and abrupt, intense and brief effort, monitoring the CV between FR and 100 pulses per minute makes it possible to observe a decrease in CV of all the more marked as the central fatigue increases. Thus this monitoring of the CV between FR and 100 pulsations per minute makes it possible to control the force-speed trainings to note on the one hand the insufficiency or not of the effort 'and on the other hand the development of central fatigue which indicates that the training must be suspended because it is no longer effective.

• Maximum oxygen consumption and maximum aerobic speed or power test

The practice of a sports activity of endurance type (great beginner as confirmed sportsman) requires knowing basic performance data: V02max (maximum oxygen consumption) and maximum aerobic speed or power (VMA). This data compared with the FC allows to train with more safety and more efficiency. There is a linear relationship between HR and VO2, and it is therefore possible to know according to HR at what level of oxygen consumption we are located in relation to its maximum. This allows the effort to be effectively measured according to the aim pursued. Usually to find out the VO2max and the VMA you have to resort to heavy and complicated laboratory tests. The cardio-frequency meter according to the invention offers here a method particularly simple, safe, fast and comfortable to determine the V02max and the VMA.

The test consists in indicating a very soft VC which the user must respect so as to bring it by a very progressive effort up to a HR of 100 pulsations per minute. Once this stable HR of 100 pulses per minute is reached and the CV is then zero, it is enough for the subject to time the time it takes to make a standardized effort (lap of athletics track on foot or 1 km by bike on a flat terrain). The device thus has the time that the individual has taken to make a determined distance when he keeps his effort stable at 100 pulses per minute. This effort at a stable HR of 100 corresponds in all individuals to 40% of the VO2max. By calculation, knowing the weight of the individual, the time it takes to make the standard effort at an effort intensity corresponding to 40% of his V02max we easily obtain the V02max and the VMA. We can then display instead of HR the effort as a% of VO2max or VMA or convert the VO2 to calorie since it corresponds very precisely to an expenditure of Kcla for each ml of oxygen consumed.

• Cardiac safety during exercise for seniors so as to avoid acute cardiovascular stress with too rapid increase in HR and blood pressure During physical effort, cardiovascular adaptation is made with a certain delay compared to the intensity of effort. That is to say that there is a change in the sensitivity of the carotid sinuses asking the cardiovascular system to respond with an increase in blood pressure. However, this increase in pressure is not instantaneous. There is a delay, and this causes a pressure error. The greater this pressure error, that is to say the faster the progression in the intensity of the effort, the more the cardiovascular system is subjected to stress. It follows that the cardiovascular system will respond all the more intensely, by an acceleration of the heart and a vasoconstriction, as the pressure error is significant. This is responsible for this feeling of racing heart and violent pulsations that we sometimes feel when we suddenly make an intense effort. The method consists, to limit this cardiovascular stress and therefore the inherent risk in older subjects during physical activity, to indicate a range of CV during each variation of effort which minimizes the error of pressure and therefore cardiovascular stress. • Progressiveness of effort adapted to aerobic endurance training

The pressure error reported in the previous chapter also corresponds to a transition from aerobic metabolism to anaerobic metabolism. During pure endurance training, the effort related to aerobic metabolism must be favored at the expense of anaerobic metabolism. Thanks to an appropriate range of CV, in which the sportsman must maintain himself during the variation of effort, one limits the error of pressure and thus the parasitic incursions in the anaerobic metabolism.

• Progressiveness of effort adapted to anaerobic resistance training Unlike the previous situation, resistance training must favor anaerobic metabolism. The pressure error corresponds to the muscular level to a perfusion deficit and therefore of oxygen compared to the intensity of the effort; oxygen deficit which "stimulates" anaerobic metabolism. Thus, during resistance training, we can give a range of CV that the sportsman must respect during each increase in effort so as to maximize anaerobic metabolism.

The cardio-frequency meter according to the invention can be used in other applications related to the increase in HR and CV, in particular: • Determination of the maximum individual HR • Determination of the anaerobic threshold (Conconi test) Negative CV slope and decreased HR

The following applications are cited without limitation. • Control of the decrease in effort after a workout

When after training the subject abruptly stops his effort there is a rapid decrease in HR which results in an equivalent decrease in cardiac output. This results in a deficit in the supply of blood and therefore of oxygen to muscles which for a certain time retain increased metabolic needs despite the suspension of the effort. This situation produces an increase in blood lactate and an increase in muscle oxygen debt. It is for this reason that athletes are advised to perform a gradual "cool-down" after exercise in order to avoid too rapid a reduction in HR and therefore in cardiac output. The problem for the subject is obviously to know what exactly means "return to calm". How to manage the slowing of the effort according to the intensity and the amount of effort provided during training?

VC provides the solution. The intensity and the amount of effort are evaluated by recording the HR during training and based on this a suitable CV is proposed to the subject in order to have a progressive and perfectly adequate decrease in HR. the effort previously provided.

• Control of interval training type training Interval training type training consists of reproducing intense efforts (the duration of which is of the order of a few tens of seconds to a few minutes) interspersed with relatively short recovery periods also . During the recovery phases the HR decreases but the slope, that is to say the CV, becomes all the weaker as a marked cardiovascular fatigue sets in. Once the CV slope becomes too low, that is to say that the cardiovascular fatigue is too intense and the recovery capacities are blunted, the training should be suspended. So a Negative CV which becomes too weak during the recovery phases will indicate to the subject that he has finished his training.

• Assessment of cardiovascular fatigue A training interval test (brief and standardized) repeated regularly (once a week or per month) makes it possible to compare the negative CVs of the recovery phases. Thus the subject can assess his state of cardiovascular fatigue according to whether the negative slope of the CV is more or less marked from one test to another. • Relaxation capacity

The ability to relax and therefore to control stress is all the more marked when an individual is able to quickly lower his HR from a starting value to a value close to that of rest. The resting HR must be introduced into the device with a few measurements in the morning upon waking. Then the evaluation can be done at any time as follows: the subject in the seated position performs some isometric contractions of his forearm muscles to bring the HR to the value of 100 pulses per minute. Then, he relaxes as best he can until the HR is stabilized at a value close to the rest value. The more marked the negative slope of the CV, the better the relaxation capacities and vice versa in the other case.

Determination of VC

By way of non-limiting example, a method of determining VC will be described below. It goes without saying that other methods for obtaining VC can also be used in the context of the present invention. With this method, we assume that VC is determined in real time, which means that the only information accessible at a given time applies to what happened before and until that time. It goes without saying that this method can be extended to the general case where the determination of VC would be carried out after all of the information is known.

HR is defined as the inverse of the period between two heart beats. A beat is defined as a QRS signal, which is a picture of the electrical activity of the heart muscle (combination of action potentials). The letters Q, R and S, known to those skilled in the art, relate to peaks / valleys of a graphical representation of the ECG. Between each beat, the period is considered to be equal to the last period measured.

In the present case, it is considered that the means of obtaining the position of HR over time is available (eg by means of an ECG and signal processing). This allows us to consider that each beat n is recorded at a defined time t „(corresponding for example to the peak of the QRS complex).

The period between two beats is defined as follows:

The FC between t _n and t _n + ι is defined by HR _π = -. The HR is reassessed after each

heartbeat.

In conclusion, we have the instantaneous HR, updated at each instant t _n . This HR is constant between two successive heart beats.

Since we have a measurement of each heartbeat, it is possible to know the derivative of the HR.

Several methods can be used to calculate this derivative. We present here one of them, but several other numerical methods allowing to obtain this instantaneous derivative are presented in particular in: - JP Nougier, Numerical calculation methods, Masson, Paris, 1987, ISBN 2-225- 81086-9 - K. Arbenz and A. Wohlhauser, Numerical analysis, PPR, Lausanne, 1983, ISBN 2- 88074-016-9

By definition, the derivative of a function is f '(x) = - = lim _{Δ (→ 0} J- -ï - - - dx Δt

In our case, we do not have an analytical function but a discrete function. So we have to use discrete methods.

The simplest way to get a discrete expression of the HR derivative is to reassess that derivative after each heartbeat, using the last two heartbeats. In this case, the derivative of the FC is given at each instant t _n by:

This value of the VC is reassessed at each instant t _n and is considered to be constant between two heartbeats.

It is possible to calculate the mean as a function of time from the formula developed in the previous equation. Different averaging methods can be used. Two are shown below.

Simple average

AvCV _n = - (CV _n _ _k + CV _{n +]} _ _k + ... + CV _n ) where k is an integer describing the order of the mean. Average with "absence of memory filter":

AvCV _n = a • Ai + b • CV _n where a + b = 1 and a <b (for example a = 0.2 and b = 0.8)

Many other methods of obtaining CV can be implemented. Some are presented in the aforementioned bibliographical references and can be easily used in the context of the present invention.

It goes without saying that the cardio-frequency meter according to the invention can be used in fields not explicitly described in the present text. Likewise, it is not limited to the VC measurement method or its derivative which is described in the preceding paragraph. Any other method of measuring and displaying VC and / or its derivative is part of the field of the invention. Finally, it should be noted that the present invention covers all the ways of providing the user with the data relating to VC and / or its derivative (visual, encrypted or graphic indications, sound, etc.).

Claims

claims

1. Cardio-frequency meter comprising means for measuring and indicating the heart rate of a subject, characterized in which further comprises means for determining and indicating the derivative of the heart rate of said subject.

2. Heart rate meter according to claim 1 further comprising means for measuring and indicating the derivative of the derivative of the heart rate of said subject.

3. Use of a cardio-frequency meter according to claim 1 for the demonstration of central or nervous fatigue during explosive force training.

4. Use of a heart rate monitor according to claim 1 as a test of maximum oxygen consumption and maximum aerobic speed or power

5. Use of a cardio-frequency meter according to claim 1 as a means of cardiac exercise security for the elderly so as to avoid acute cardiovascular stress with too rapid increase in HR and blood pressure.

6. Use of a cardio-frequency meter according to claim 1 for the measurement of the progressiveness of effort adapted to aerobic endurance training.

7. Use of a cardio-frequency meter according to claim 1 for the measurement of the progressiveness of effort adapted to anaerobic resistance training.

8. Use of a heart rate monitor according to claim 1 for the determination of the maximum individual HR.

9. Use of a cardio-frequency meter according to claim 1 for the determination of the anaerobic threshold (Conconi test)

10. Use of a cardio-frequency meter according to claim 1 for the evaluation and control of recovery after exercise.

11. Use of a cardio-frequency meter according to claim 1 for the evaluation of the stress control capacity.

12. Use of a cardio-frequency meter according to claim 1 for monitoring relaxation exercises.