EP2383179A1 - Bubble detector for early warning of the risk of a decompression accident - Google Patents

Abstract

The device has fixing units for fixing of functional coupling of a sensor to a body of a diver. A portable computer (3) with a connection unit is connected to the sensor to provide a signal if the level of detected bubble exceeds a required level. The sensor detects cardiac electric pulses with a connection unit of the sensor to the portable computer. A processing unit (11) processes measurements of another sensor, a decoupling unit (12) and an integration unit (14). The integration unit integrates measurements of the former sensor under intervals of time. Independent claims are also included for the following: (1) a method of detection of bubbles to be utilized by a device (2) a method for controlling increase in speed of a diver for implementing detection process.

Description

The invention relates to gas measuring devices in the blood of divers and the methods using these devices to control their ascent to avoid decompression sickness.

During the ascent, the decrease in hydrostatic pressure causes a phase change of the gases dissolved in the blood when the diver was deep. The bubbles that are formed, if they are too numerous, can cause a decompression sickness in the form of pulmonary embolism or coagulopathy. The danger of these serious accidents, which can be fatal or lead to very serious disabilities, is well known to divers who apply decompression stops according to tables that are calculated according to the depths reached and gas mixtures used to breathe in order to allow at the partial pressure of the dissolved gases to rebalance in the blood during the ascent.

A first problem is that the decompression tables, despite the security taken, can not be customized, depending on the situation of an individual at a given time. There is still a small number of decompression accidents although the diver has respected the levels provided by the tables.

A second problem is the difficulty of validating decompression tables in the new operational conditions encountered by professional divers, civil or military, who have to dive deeper and deeper, with new gas mixtures. Typically, there are no validated tables for autonomous scuba dives between 80m and 100m.

It is known to those skilled in the art that the detection of bubbles in the veins of the heart region, by means of Doppler systems, provides a good indication of the physiological stress associated with decompression and thus can be used to improve the procedures of decompression to reduce the risk of accidents.

Doppler means for detecting bubbles associated with measurements of velocity or pressure in blood vessels using ultrasonic transmitters and receivers installed on the skin are described in the patent application. FR 76 34550 and the American demand US 6261233 . In particular the French patent indicates how to filter the frequencies between 800Khz and 5Mhz to detect the gas bubbles in the middle of the noises related to the blood circulation. Apparatuses of this type are used for medical studies on divers after their dive.

The patent WO 2009/090529 takes a sensor of this type, linked to a computer and a hydrostatic pressure measurement to compare the level of bubbles measured at a critical threshold and thus notify the diver whether to extend a decompression stop or limit its ascent rate. The basic device set up can be sophisticated by taking into account the history of the dive and the diver's own data to help him plan his dive and customize the decompression profiles.

However, it must be taken into account that the blood pressure is not uniform, whether during a cardiac cycle or according to the location. Bubbles that do not present a serious risk of thrombosis in one place may correspond to greater production in other parts of the body.

There is always a risk of accidents even by integrating the measurement of the levels of bubbles in the blood of the diver to correct the decompression tables. This makes it necessary to take margins, and to impose periods of decompression unnecessarily long or too slow ascent rates, because the information on the possibility of appearance of bubbles in the blood comes too late compared to the phenomenon.

The objective of the invention is therefore to obtain an alert as early as possible to be sure to identify the phenomenon of appearance of bubbles in its infancy and not when installed so that it can have physiological consequences.

To this end, the invention essentially relates to an underwater diving safety device comprising a sensor capable of detecting the gas bubbles in the plunger's blood, means for fixing and functional coupling of the sensor to the body of the plunger, a computer with a means of connection to said sensor capable of providing a signal if the detected bubble level exceeds a required level, characterized in that it comprises a cardiac electrical pulse sensor with a means of connection to the laptop, said computer having means for synchronizing the sensors, a cutting means of the cardiac cycle at sub-time intervals from the pulses measured by the bubble sensor and means for integrating the sensor measurements over these sub-time intervals to provide a bubble rate per cardiac cycle.

• une première étape de fourniture d'un signal de synchronisation donnant une base de temps de référence;
• une deuxième étape de fourniture d'un signal repérant le début et la fin d'un intervalle de temps déterminé à chaque cycle cardiaque sur la base de temps de référence ;
• une troisième étape de fourniture d'un signal échantillonnant sur la base de temps de référence les signaux du capteur de bulles, cette étape étant faite en parallèle de la précédente ;
• une quatrième étape de fourniture à chaque cycle cardiaque d'un signal intégrant le signal de la troisième étape sur l'intervalle de temps repéré par la deuxième étape.

This device detects bubbles implemented according to a method comprising the following four steps:

• a first step of providing a synchronization signal giving a reference time base;
• a second step of providing a signal identifying the beginning and the end of a determined time interval at each cardiac cycle based on reference time;
• a third step of providing a signal sampling on the basis of reference time the signals of the bubble sensor, this step being made in parallel with the previous one;
• a fourth step of providing each cardiac cycle with a signal integrating the signal of the third step over the time interval identified by the second step.

A second objective of the invention is to control the ascent of a plunger by minimizing decompression stop times with maximum safety. For this purpose, the preceding device further comprises a hydrostatic pressure sensor connected to the computer, a calculation module able to supply the data of the hydrostatic pressure sensor on the basis of common time, a calculation module able to exploit this signal and the one giving the bubble rate by cardiac cycles to provide a diving history and a calculation module able to use these data to determine the diver's ascent profile

• une cinquième étape de fourniture d'un signal par un moyen (15) apte à échantillonner sur la base de temps de référence les signaux du capteur de pression hydrostatique ;
• une sixième étape de fourniture d'un signal donnant l'historique de la plongée par un module de calcul apte à exploiter le signal de l'étape précédente et le taux de bulles par cycles cardiaques;
• une septième étape de détermination du profil de remontée à suivre par un module de calcul apte à exploiter le signal de l'étape précédente et le taux de bulles par cycles cardiaques.

Steering the ascent of a diver according to this device comprises the following complementary steps:

• a fifth step of providing a signal by means (15) adapted to sample on the basis of reference times the signals of the hydrostatic pressure sensor;
• a sixth step of providing a signal giving the history of the dive by a calculation module adapted to exploit the signal of the previous step and the rate of bubbles by cardiac cycles;
• a seventh step of determining the feedback profile to be followed by a calculation module adapted to exploit the signal of the previous step and the bubble rate by cardiac cycles.

Bubble detection is already used in medical studies of divers. To characterize the gaseous state in the blood, it is convenient to classify the measurement results in 5 levels (Spencer score): no bubbles, isolated or spaced bubbles, bubbles every 2-3 heart cycles, bubbles at each cycle cardiac, continuous flow of bubbles covering the sounds of the heart. The risk of decompression sickness has been correlated to these levels by studies under different operational conditions for the diver.

These studies have also shown that the phenomenon of gas dissolution when the pressure increases, and then their release during decompression, is complex and non-uniform in the body. The gas dissolves in the blood but also in the tissues of the human body. These tissues thus restore the gas in the blood according to their texture and the local pressure. Finally, it can be seen that the levels of bubbles in the vessels passing through vital organs can be much higher than those observed at the level of the heart when the measurement that is made integrates the results over the entire cardiac cycle.

The effect of the invention is to measure the level of bubbles at a point in the body and at a time when the pressure is minimal. On the one hand, the pressure is lower on the right side of the heart, venous return but, above all, the device can measure the bubble level on a short time, during the protodiastole, when the pressure is the lowest , without integrating the result on the whole cardiac cycle. The pressure during diastole is significantly lower than during systole. This difference in pressure, which is 18 mmHg, does not seem huge but is favorable for a phase change. In particular, if we use this signal on a Spencer scale, we will reach a higher score faster, which makes the alert earlier. The precision of the observation of the phenomenon by the device makes it possible to control the decompression in a fine and adapted manner to each.

The implementation of Doppler techniques with ultrasound to detect gas bubbles in the vascular network has been described in patents FR 76 34550 and US 6,261,233 . If these documents explain the theory of obtaining reliable results, the transmitters and receivers described therein are relatively bulky and delicate positioning. More recent studies (J Johasson & J Desling of the University of Lule "a compact Ultrasonic Transducer using the active piezoceramic material as electronic carrier") prove that integrated devices and compact, can be pressed on the body of the diver without hindering its movements, are available.

Moreover, given the acoustic frequencies used, between 800Khz and 5Mhz, the use of this technique in water is not a problem because the acoustic impedance of the fabrics is close to that of water.

The document FR 76 34550 shows that the frequencies of the noise emitted by the core being at most of the order of 500KHz, the use of Doppler instruments emitting in a frequency range between 2.5 MHz and 3.5 MHz makes it possible to easily perform a filtering the physiological sounds to obtain the bubble detection signal.

• La figure 1 représente un schéma d'un dispositif selon l'invention ;
• La figure 2 représente un enregistrement cardiaque approximatif que l'on peut obtenir avec un capteur d'impulsions électromagnétiques du coeur (électrocardiogramme),
• La figure 3 montre le procédé de traitement des données par le dispositif

The operation of the invention can be better understood by the description of an exemplary embodiment of the invention and with reference to the appended figures:

• The figure 1 represents a diagram of a device according to the invention;
• The figure 2 represents an approximate cardiac recording that can be obtained with a heart electromagnetic pulse sensor (electrocardiogram),
• The figure 3 shows the process of data processing by the device

The figure 1 shows a strap (1) surrounding the thorax, clamped with a known clamping means to hold it in position once installed and which plates an ultrasonic bubble sensor (2) against the plunger's chest. Advantageously, the strap has an elastic portion to maintain its position by accompanying the movements of the rib cage. The sensor is positioned preferably between the 2 ^nd and 3 ^rd ribs just left of the sternum to perform the measurement on the venous return at the level of the atrium and the right ventricle of the heart. If the diver uses a dry dive suit, he moistens the face of the sensor that will be pressed against his body.

The Doppler sensor operates at a frequency between 2 and 8 MHz and is equipped with an electromagnetic emission means. (6) allowing him to send his results to a laptop computer (3). Such equipment exists, we can use for example a sensor supplied by the brand Sonicaid ™.

The invention also comprises a sensor (4) capable of perceiving the electromagnetic pulses of the heart. This is known manner of electrical sensors comprising at least two electrodes which must be pressed against the body at the heart. For example, UWATEC ™ polar T ₃₁ sensor can be used. It is possible to integrate this heart pulse sensor (4) and the ultrasonic bubble sensor (2) in the same belt to obtain a compact assembly, easy to install on the chest of the diver. This sensor is also equipped with an electromagnetic transmitter for sending its results (6b).

The laptop can be advantageously attached to the wrist of the diver with its information display screen. It is itself equipped with a receiver (7) for receiving the signal emitters (6) and (6b) sensors. These transmitters and the receiver of the portable computer form wireless link means (61) and 61b) between it and the sensors (2) and (4).

The computer utilizes the measurements and to continuously provide the maximum bubble level observed during heart cycles by following the four steps described below.

The first step is performed by a synchronization module (13) capable of providing a synchronization signal which enables the calculation modules processing the following steps to have the same time base.

A second step is performed by a calculation module (12) able to determine the time interval at each cardiac cycle during which the measurement of the bubble sensor will be used to define the level at which one is placed and triggers an alert by identifying this interval relative to the time base provided by the synchronization module (13). This time interval is determined to optimize the detection by integrating the signal of the sensor only in the time zone where it is maximum, that is to say when the blood pressure is minimum, as described below.

The plot of the intensity of the electromagnetic waves generated by the heart and recorded by the sensor (4) is called electrocardiogram (ECG). It is a reflection of the activity total electric heart. The figure 2 represents approximately a normal electrocardiogram which is composed of five waves. The first, the P wave, is low amplitude and lasts about 0.08s. It results from an electrical activity in the atria, about 0.1 s after the beginning of the P wave, the auricles contract

The set of three waves, Q, R and S corresponds to an electrical activity of the ventricles before the contraction. Its complex shape reflects the unequal size of the ventricles and their different electrical characteristics. This set precedes contraction of the ventricles and has an average duration of 0.08s

The T wave is caused by the activity of the ventricles before loosening (diastole). The T wave is longer and of smaller amplitude than the Q, R and S waves.

Intracardiac pressure increases during the contraction phase (systole) of the atria (PR interval) and the ventricles (QT interval). It goes down again during the diastole, between the T wave and the P wave. It is in fact during protodiastole, a short phase following the T wave during which the ventricles relax, that the intracardiac pressure is the lowest and that the genesis of bubbles is most likely. The TP interval corresponding to the protodiastole is less than the complete relaxation period, which itself corresponds to half the duration of the cardiac revolution.

Advantageously, the calculation module (12) will target this interval TP to integrate the measurements and it will select the time interval preceding P over a period of between 30% and 40% of the total time of the cardiac revolution. Assuming that the heart beats at 75 beats per minute, the duration of the cardiac revolution will be 0.8s, so the duration of the measurement before P will be about 0.3s.

A third step is performed by a processing module (11) adapted to transform the signal from the ultrasonic bubble sensor (2) into a sampled signal on the time base provided by the synchronization module (13). The fastest bubble transit time of about 0.01s imposes a minimum sample rate on the sensor to not eliminate these bubbles during measurement. Advantageously, this sampling frequency will be greater than 100 Hz.

Steps 2 and 3 are performed in parallel and the resulting signals are processed by a fourth step. This step is performed by a calculation module (14) able to integrate the signal coming from the module (11) over the time interval provided by the module (12). This integration provides a signal proportional to the number of bubbles during the period when it reaches a maximum at each cardiac cycle. Given the transit time of the bubble (10 micro seconds), this module must do an integration calculation to define the bubble level. Advantageously, a method based on the detection of harmonics, for example that named "Empirical Mode Decomposition" described by Chapell & Payne (2005) ).

Advantageously, during this fourth step, the signal thus processed to measure the bubble level will also be placed on a Spencer scale to provide a more easily interpretable result for alerting at the very beginning of the occurrence of the phenomenon in the body of the diver.

In a more complete embodiment, the device comprises a hydrostatic pressure sensor (5) which provides the laptop (4) with the depth to which the plunger is located. Such sensors are commonly used by divers and integrated into the physical medium of the computer.

The portable computer (4) then provides instructions on the ascending speed of the diver taking into account an early alarm of decompression sickness, by following three steps following the preceding method.

A first step is performed by a module (15) adapted to transform the signal of the hydrostatic pressure sensor (5) and the signal supplied by the synchronization module (13) to a depth on the common time base.

A second step is performed by a module (16) able to combine the pressure signal supplied by the module (15) and the bubble level signal supplied by the module (14) to build a diving profile consisting of a history of the depths reached with the observed bubble levels.

A third step is performed by a calculation module (17) capable of comparing at each moment the dive profile given by the module (16) with tables and prior calculations resulting from the existing studies on the decompression of the divers provided by a, memory module (18). The result of this comparison is translated into instructions at diver who may be an alarm to stop the ascent, an authorization to resume the ascent or more complex instructions on the upcoming dive profile. The calculation modules (1b) and (17) can be physically integrated.

• Fin de pallier à 6m
  • o Pas de bulle --> « Respectez le pallier à 3m »
• Fin de pallier à 6m
  • o Bulles à chaque cycle cardiaque - > « Attendez. »
  • o Bulles tous les 2 à 3 cycles cardiaques - > « Attendez.... »

The indications provided by this third step can be for example:

• End of step at 6m
  • o No bubble ->"Respect the landing at 3m"
• End of step at 6m
  • o Bubbles at each cardiac cycle ->"Wait."
  • o Bubbles every 2 to 3 heart cycles ->"Wait...."

These instructions will also take into account the amount of gas available in the dive block. This information, which can be provided by a pressure gauge connected permanently to the computer by a wireless link, is essential to weight the instructions and thus avoid a lack of gas. It will then be exploited by the module (17) which prepares the instructions.

Advantageously, the device will also comprise a flowmeter on the breathing apparatus. This device will be coupled to the computer which will also include an interface module by which the diver can indicate the type of gas mixture used and other data specific to the current dive. A sensor measuring the CO2 expired by the plunger will also be advantageously integrated into the device. These data will be used by the calculation module (17) which exploits the bubble levels to provide instructions to the plunger.

Indeed, to reach great depths, divers use specific gas mixtures. These mixtures of gases that pass into the blood have different characteristics of absorption rate and degassing in the tissues and blood that must be taken into account in the tables.

Similarly, the measurement of CO2 makes it possible to obtain the volume of saturation of inert gas by subtraction with oxygen. The CO2 level, which is a gas of catabolism, is an index of pulmonary exchange, therefore the risk of pulmonary edema.

In a more sophisticated mode, he can take into account in a known manner the history of the diver to adapt to his physiology. It can also exploit the results of the sensor of cardiac electrical pulses (4) which gives the heart rate as a corrective element integrated in the calculation of desaturation tables. This fix calculates in a known way the time interval between two ECG waves R whose evolution gives information on the level of the exertion exerted on the diver. Eventually, it will be an additional parameter to integrate at the bubble level, for more security.

Advantageously, the device will continue to operate at least one hour after leaving the water. Indeed, the bubbles are more numerous 30 minutes after the release of the water, even if they are detectable before. The device can therefore be used to prevent the occurrence of decompression sickness after diving in critical cases. This use can also make it possible to modify the rising profiles for subsequent dives in order to limit the level of bubbles in the moments that follow it.

In an additional embodiment, a module capable of exploiting data such as the name of the diver and comparing the history of the current dive with those of previous dives will provide suitable dive profiles for the diver. The calculation module can define a correlation between the appearance of the bullar phenomenon of the user and his dive profiles. He can then prevent the appearance of bubbles to define a "rise" speed of comfort minimizing the appearance of bubbles.

This result can then be stored by the memory module (18) which will supply it to the calculation module (17).

Such a device can also be used in a decompression chamber for the treatment of diving accidents or studies.

Claims (6)

Diving safety device comprising a sensor (2) capable of detecting gas bubbles in the plunger's blood, means for attaching and operating the sensor to the plunger body (1), a computer with a means link (61) to said sensor capable of providing a signal if the detected bubble level exceeds a required level, characterized in that it comprises a sensor (4) of cardiac electrical pulses with a connecting means (61b) to the portable computer (3), said computer having a means for synchronizing the sensors (13), means for cutting the cardiac cycle in sub-time intervals (12) from the pulses measured by the sensor ( 4), a processing means (11) of the sensor measurements (2) on the same time base as the means (12) and a means (14) for integrating the sensor measurements (2) on these sub-intervals of time. Device according to claim 1 comprising a hydrostatic pressure sensor (5) connected to the computer (4), a calculation module (15) able to supply the data of the sensor (5) on the time base of the module (13) , a calculation module (16) able to exploit this signal and that of the module (14) to provide a diving history and a calculation module (17) able to use these data to determine the return profile of the plunger. Bubble detection method implemented by a device according to claim 1 comprising the following four steps: a first step of providing a synchronization signal giving a reference time base by means (13); a second step of providing a signal identifying the beginning and the end of a determined time interval for each cardiac cycle by means (12) able to process the signals of the heart pulse sensor (2) on the basis of reference time; - A third step of providing a signal by means (11) adapted to sample on the basis of reference time the signals of the bubble sensor (2), this step being made in parallel with the previous one; - A fourth step of providing each cardiac cycle of a signal by means (14) adapted to integrate the signal of the third step on the time interval marked by the second step. The method of claim 3 wherein the time interval identified in step 2 immediately precedes the P wave with a value of between 30 and 40% of the cardiac cycle. A method according to claims 3 or 4 with a further step of comparing the fourth step signal over several heart cycles to set the bubble level according to predetermined criteria, especially on a Spencer scale. Method for controlling the ascent of a plunger according to claims 2, 3 or 4, comprising the following complementary steps implemented by a device according to claim 2: - a fifth step of providing a signal by means (15) adapted to sample on the basis of reference time the signals of the hydrostatic pressure sensor (5); a sixth step of providing a signal giving the history of the dive by a calculation module (16) able to exploit the signal of the preceding step and that of the module (14); a seventh step of determining the feedback profile to be followed by a calculation module (17) able to exploit the signal of the preceding step and that of the module (14.

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