Bluetooth network for medical data transfer in an outpatient environment

Mihai Chetan SC. MED.CO SRL

mihai.chetan@medco.ro

Alexandru Morega “Politehnica” University of Bucharest

amm@iem.pub.ro

Abstract

The latest developments and demands in the

healthcare domain overwhelm the outpatients sector, while providing the security of patient monitorising against out of hospital risks becomes increasingly important. The paper presents a distributed data acquisition system for biomedical data that complies with the specific standards to continuous vital parameters monitorization at home. The system is conceived by using an ad hoc Bluetooth network composed of off the shelf accessible medical devices such as blood pressure monitor, blood glucose meter, body composition monitor, ECG monitor and a computer (desktop, laptop, PDA, etc) with regular internet connection. 1. Introduction

The last improvement made in the medical system focused the ambulatory sector. The most frequent question put nowadays is how we may guarantee the security of patients during the treatment out of hospital.

Heart-related diseases and disorders dominate the European population. Over 500.000 sudden cardiac deaths, over 3 million patients with atrial fibrillation and about 600.000 heart attacks every year have a significant influence in the cost structure of the European system of health assurance [1].

The effective therapy in this area is usually no longer a problem. The medical devices and the wide range of medication have had a remarkable success in saving the lives of patients with heart disorders. Much more crucial is the lack of diagnosis. The statistics show now, that a high-risk patient, visit his physician every three to six months for a check up. If the health situation becomes worse in between visits, it is recognized only if the symptoms become acute. Due the unreasonable fear of hospitals, many patients wait until their health condition develops into an unbearable situation, in most of the cases, impossible of treated. It

is the point that they call the emergency services and they are brought to the hospital. In most of the cases they have to remain in the hospital for days or even weeks, until their health condition is well enough to return home, costing a great the healthcare system [2].

An obvious solution for today and for the future, which may satisfy the needs of medical system is the ambulatory healthcare system. It may offer the security of cardiac patient and his relatives, without the permanent threat of an unknown event. This system, which may be combined with others vital sensors, may be an ideal platform for hospitals, programs of managing illness, tele monitoring centre, and others societies offering health services.

Next, are presented such a system, able to fulfill the requirements of healthcare monitoring at home. 2. Types of devices used in vitals parameters monitoring 2.1. Blood pressure monitors

Hypertension is the main heart disease and a major problem of public heath, increasing by age. Over 50% of populations having over 60 years suffer of hyper-tension, it being the main factor of heart attack and stroke risk. The sooner diagnosis and treatment of it, substantial reduces the risk of cardio-vascular events.

Figure 1 – WHO classification for blood pressure

WHO recommends the measurement of blood pressure at home, twice/day, in the morning and in the evening, approximate at the same hours and in the same conditions [3]. This may be done with the automatic blood pressure monitors using the oscillometric method. The memory of those devices, allow to stock the data and with the Bluetooth adapter, is possible to transfer important patient data (systolic and diastolic blood pressure and pulse) to a computer. In figure 1, are shown the classification al blood pressure made by World Health Organization (WHO).

2.2. Blood glucose monitors

All the recent data offered by World Health Organization and International Diabetes Federation (IDF), indicate that the number of patients with diabetes in the world is in a spiralling out of control, diabetes becoming the illness of XXI century [4]. Glycemia measured at home represents a rapid and very easy method to control the diabetes and has a favourable effect for the quality of patients’ life.

Monitoring glycemia is useful for: - measurement the variation during a day for a

better treatment - detecting hypoglycemia - evaluation of the glycemic balance in some

specific situation (fever, too much food, hard physical activity).

2.3. Electrocardiograph

The heart rate has a constant value, between some close limits. For measure it, we use the interval R-R of the heart beat, during sleep, for avoid the external influences.

Figure.2 – The interval R-R

The analysis of the instantaneous heart rate using the interval R-R (fig.2) is known like ‘the analysis of the heart rate variability – HRV“, giving the possibility to evaluate some cardiovascular diseases; for ex. a small rate of R-R interval, indicate a high risk of stoke while a small variability in case of the patients with cardiovascular illness increase the risk of ventricular tachycardia.

The measurement may be done with portable an electrocardiograph with one channel, which is used very easy by the patient, the results being memorized first on the device memory card and then, download on the doctor’s computer.

The study published [5], H. Holzgreve, shows that using such a device (for ex HG801 from OMRON) we may obtain the some precise results like using a standard ECG device.

3. Data transfer technologies for biomedical signals

The biomedical signals sensed by the sensors of data acquisition devices are often sent via serial ports, in real time, to a PC for further processing and transmission. The analog to digital conversion of the signals can be performed on 8, 10, 12, or 16 bytes, depending on desired level of accuracy. Following Shannon’s sampling theorem, the signal sampling frequency, fsamp, has to be twice the highest frequency in the signal, fmax,sign, [6-9]

signsamp ff max,⋅= 2 (1)

For instance, for an analog to digital conversion of a sample on 8 bytes the requested minimum transmission frequency

sampbit ff ⋅= 8 (2)

But, when a serial port is utilized, the specific protocol requests the existence of beginning (Start) byte, parity byte and end (Stop) byte, available for any data transmission [10] – Figure 3.

Figure.3 - The structure of the transfer protocol through a serial port.

Thus, for the transmission of each data sample 8+3

bytes are to be transmitted. So, actually ( ) sampbit ff ⋅+= 38 (3)

In general, considering the resolution of the analog to digital conversion, the necessary minimal frequency for transmission in real time for a sample is:

sampbit fknf ⋅⋅⎟⎠⎞

⎜⎝⎛= 11 , (4)

where n is the resolution (number of bytes) of the analog to digital conversion, k (= 8) is the resolution (number of bytes) of the transmission by the serial port.

Table 1 summarizes the transmission speeds for different types of biomedical signals, acquired by analog to digital conversion on 8/10/12/16 bytes, considering the frequency domains of the signals and Shannon theorem [9].

Table 1. Types of biomedical signals.

Type of signal

Freq. range [Hz]

Transmission speed for A/D conversion 8/10/12/16 bit/s

Blood flow 0-20 440/550/660/880 Blood

pressure 0-50 1100/1375/1650/2200

Blood Ph 0-2 44/55/66/88 EKG 0.01-250 5500/6875/8250/11000 EEG 0-150 3300/4125/4950/6600 EMG 0-10000 220000/275000/330000/

440000 Phono-

cardiogram 5-2000 44000/55000/66000/

88000 Neuronal voltage

0-10000 220000/275000/330000/ 440000

For better evidencing what port is more appropriate

for transmitting a specific signal, the rate of transfer has to be evaluated (Table 2).

Table 2. Transfer rates for different ports.

Port type Transfer rate Serial RS 232 115 kB/s

IrDA 2400 B/s – 115 kB/s FireWire 400 MB/s

USB (high speed version) 480 MB/s

Table 3. Communication ports recommended for streaming medical signals in real time [11], [12].

Type of biomedical signal

Transfer rate

Blood flow RS232, IrDA, FireWire, USB Blood pressure RS232, IrDA, FireWire, USB

Blood Ph RS232, IrDA, FireWire, USB EKG RS232, IrDA, FireWire, USB EEG RS232, IrDA, FireWire, USB EMG FireWire, USB

Phonocardiogram RS232, IrDA, FireWire, USB Neuronal voltage FireWire, USB

Table 3 sums up the type of data that can be sent in

real time through different ports. It is noticeable that for signals with fbit lower than 115 kB/s all regular PC ports may be used, and only when exceeding a certain threshold value FireWire and USB ports are to be used.

Depending on the analog to digital resolution, the

frequencies, fmax,sign, beyond which only FireWire, USB and Bluetooth are utilized for medical conversion are:

• 8 bytes – 5227.25 Hz; • 10 bytes – 4181.8 Hz; • 12 bytes – 3484.8 Hz; • 16 bytes – 2613,6 Hz.

4. Communication channels

The information exchange between two devices,

transmitter-receiver, is performed through the existing technologies, as the serial port, parallel port, FireWire interface, USB, wireless and Bluetooth technologies [9], [11-14]. Of all these technologies, the Bluetooth is most suitable for biomedical applications because it complies with the performances of all biomedical signals, it is very flexible, and it necessitates a relatively simple infra-structure. Consequently, our approach to biomedical data transfer will utilize the Bluetooth conveyor.

4.1 Bluetooth characteristics

Bluetooth is a short-range communications

technology intended to replace the cables connecting portable and, or fixed devices while maintaining high levels of security [15-16]. The key features of the Bluetooth technology are robustness, low power, and low cost. The Bluetooth specification defines a uniform structure for a wide range of devices to connect and communicate with each other.

Designed as a replacement for the cable connections between several devices, the Bluetooth technology operates through radio bands. In fact, it is a WiFi version with a smaller speed than the IEEE 802.x standards. It operates within the 2.4 GHz Industrial Scientific Medicine (ISM) range, and transmitted data rate is 1 Mbps.

4.2 Bluetooth specification

In most countries the frequency domain allocated

to Bluetooth communications is within the range 2400-2483.5 MHz. For the United States, Europe and most of the countries the channels frequencies may be found by [13]

f = 2402 + k MHz[ ], (5)

where k = 0-78, and the interval between channels is 1 MHz.

Bluetooth uses the Gaussian Frequency Shift Keying (GFSK) [17]. In this approach, the logical states 1” and “0” are related to frequency shifting

about a reference value. Thus, the binary “1“ is represented by a positive shift in frequency and the binary “0“ is represented by a negative shift.

4.3. PicoNet

Bluetooth technology provides the effectiveness of

full duplex transmission through the use of a Time-Division Duplex (TDD) scheme. In this approach, data is transmitted between Bluetooth enabled devices in packets, each of them on a different hopping frequency. Normally, each packet covers a single slot, but it can be extended to cover several slots, however not more than 5. TDD scheme (Figure 4) allows both master and slave equipments to transmit data alternatively.

Figure. 4 - Data transmission using the duplex schema with time division.

A Bluetooth system is composed of a radio unit, a relational control unit, a relational management, and the host terminal interface unit (figure 5)[13].

Figure 5 - The block schema of a Bluetooth system.

When two units are involved then Bluetooth technology realizes point-to-point connections, and point-to-multipoint otherwise. In a point-to-multipoint connection, the channel is divided in several Bluetooth units [18], [13]. Two or more units sharing the same channel form a PicoNet. In this type of net, one Bluetooth unit acts as a master and the other units (not more than 7) act as slaves.

Several slave units can remain “parked” to a master unit. These parked slave units cannot be activated within the channel, but remain synchronized with the master unit. The master unit controls the slave units,

and also the parked units. Every PicoNet has one single master unit.

Figure. 6 - PicoNets operation: with one slave, multi-slave, and disperse operation.

4.4. Secure Bluetooth connection

In order to provide for data protection and

confidentiality, the system is designed with secure data at the application level, as well as at the connection level. In every Bluetooth unit, the authentication and cryptic routes are implemented in the same way. To keep the security of the relational level, four different units are implemented

1. A public address, which is unique for every user; 2-3. Two secret keys; 4. A unique number, for every transaction. The Bluetooth device address is unique, 48 bytes

long. The secret keys result after the initialization process. In Bluetooth pairing, two devices (phones, PCs etc.) can communicate under the name of “trusted pair“ [19].

The security within the Bluetooth communication depends on the secret PIN. In order to simplify the management of PINs within a PicoNet, a “smart manager” equipment is used, which is responsible with the keeping secret the connections by assigning a secret PIN for every PicoNet device.

Data encryption can be used to further enhance the degree of Bluetooth security. The transmission scheme (FHSS) provides another level of security in itself. Instead of transmitting over one frequency within the 2.4GHz band. Bluetooth radios use a fast frequency-hopping spread spectrum (FHSS) technique, allowing only synchronized receivers to access the transmitted data.

5. Modular system for tele medical needs using an ad hoc bluetooth network

The automatic module for healthcare surveillance

(AMHS) is a holistic system designed for diagnosis, which allow active people to monitor their health.

The system involves personal devices for measuring blood pressure, weight and body fat, glycemia and the variation of heart rate.

The personal devices transmit the measured values by a rapid wireless connection to a laptop, which, via internet, sends the data to a medical centre. Here a specialized program analyses these data and makes an user health profile, giving also, some preventing common suggestions, underlining the eventually cardiovascular risk factors.

AMHS has to be designed for active people who care for their health and who want to minimise these risks from the very beginning.

This system wishes to be an open and extensible platform which might include in the future much more testing parameters, allowing the user to assume his health problems from an incipient stage, saving in this way, long term resources by avoiding medical treatments.

This may be an important contribution to reducing the burden of healthcare system. Also, it should be interesting for GP’s, like an instrument for improving the relationship between the doctor and the patient.

AMHS should carry out the following requests: - to be robust and safe when it records the health

parameters (blood pressure, weight and body fat, glycemia and the variation of heart rate)

- wireless connectivity (BT) for a PDA, PC or laptop

- special functions for recording and evaluation the personal health parameters

- personal data base containing details about the life style of patient (smoker or not, for ex.) and also, others data measured in the laboratory (hemoglobin….)

- simple operation phase 1. measurement 2. cardiovascular risk analyze using special

medical algorism 3. identification of parameters which increase

these risks 4. setting the specific objectives

Figure 7 shows a networking concept for cardio-vascular data assistance, where personal devices convey acquired, related physiological data by a rapid wireless connection, e.g., Bluetooth, to a laptop that may implement data reduction analysis. The laptop may then forward the data via either regular Public Switched Telephone Network (PSTN), or mobile telephony, or Public Data Switched Network (PSDN) [9] to a specialized, decisional centre. Here, a patient personal health profile is drawn and completed, and useful suggestions of preventing actions with special references to the potential cardiovascular risk are added to it.

Figure. 7 - The diagram of a modular system using an ad adhoc bluetooth network .

5.1 Internet connection

PicoNet showed above has many possibilities to achieve an internet connection [20], [21]:

a) Access point and print server AP&PS – Access point with delivery priorities and security for critical data transactions. Thin AP architectures allow information technology staff to manage the entire wireless network from a single point.

b) SW&R + laptop - connection to internet through wireless local area network (WLANs ,802.11)

c) Phone + laptop – voice over internet protocol (VoIP) telephones to improve clinician communications

d) Cellular + laptop – improve communications by e-mail with clinicians 6. Conclusions

Developing a Bluetooth network for collection and

analysis of biological parameters, and conveying the results to a decisional centre is both feasible and resourceful to higher quality medical assistance. Several key activities may benefit of this enabling technology: A. Monitoring patients and medical data transfer

• Improving medical services from prevention and monitoring to diagnostic, treatment and rehabilitation is supported lately by the rapid development of interdisciplinary sciences, of biomedical engineering and of medical informatics.

• By combing biomedical engineering with the latest telemetric methods, the monitoring devices are able to measure, analyze and transfer the clinical data of one patient to persons or institutions that would stock it in personal files, strictly confidential, and accessible to authorized medical personnel only.

• Remote monitoring of patients requires the creative usage not only of measured values or equipments, but also communication technologies and organizing services.

• Lately, monitoring patient vital signals in other places than hospitals becomes a necessity, because certain relevant parameters (blood pressure, pulse, cholesterol and blood glucose, EKG signals), may be measured and conveniently sent, from time to time, to medical institutions. Bluetooth technology can optimize this process and facilitate the transmission.

B. The benefits of using Bluetooth technology • Flexibility –wires and connectors are

suppressed. • Mobility – reduced installation and

maintenance time. • Accessibility –programming, actualization and

control with the help of one device (e.g., controller, laptop) with wireless option.

Future work will address several practical issues met in developing a PicoNet system: PicoNet connectivity at device level, signal processing, and data analysis.

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