According to recent studies and statistics, cardiovascular diseases (CVD) are among the most frequent cause of death. The total cost and the indirect mortality cost estimated for CVD are higher than for any other major diagnostic group
In this paper we investigate a possibility of using virtual instrumentation in the development of two physiological parameters monitoring system, in order to assess a cardiovascular parameter, the Pulse Wave Velocity (PWV). We choose to monitor this parameter due to major incidence and impact of cardiovascular diseases (CVD).
Early diagnosis of CVD could prevent further complications, leading to improvement of patient’s quality of life and, for long term, can decrease the costs of the medical system. One step further to this goal is the long term monitoring of the patients, in their usual habitat and during daily activities, without restricting their freedom of movement.
The studies in the health area have shown the major influence that arterial stiffness has on appearance and evolving of atherosclerosis, rheumatoid arthritis, complications due to high blood pressure, development of myocardium and coronary diseases, affection of vascular bed of several organs, such as brain or kidney. One of the non- invasive techniques of assessing the arterial stiffness is the measurement of Pulse Transit Time (PTT) / Pulse Wave Velocity (PWV).
PTT is a technique that measures the time needed for a blood pressure pulse wave to cross a known section of the arterial tree, and the PWV represents the ratio between the length of the measured arterial segment and the elapsed time from the ventricular ejection until the pulse pressure reaches the distal measurement site.
In this paper we investigate a possibility of using virtual instrumentation in the development of two physiological parameters monitoring system, in order to assess a cardiovascular parameter, the Pulse Wave Velocity (PWV).
Our system for measuring the PWV is based on recording the ECG and photoplethysmographic (PPG) signals. This technique uses the R-wave extracted from the ECG signal as the beginning of the ventricular contraction, which is the start moment of the pulse wave, which travels from the heart to distal regions. The arrival moment of the pulse wave to the index of the left hand is determined from the PPG signal.
The system was made using two ez430-RF2500 boards from Texas Instruments . The ez430-RF2500 is an ultra- low power wireless development system that has an MSP430F2274 microcontroller with a 10 bits A/D converter, for gathering and converting the data from the analog modules, and a wireless transceiver CC2500 at 2.4GHz, working in ISM (industrial, scientific and medical) radio band, for data transmission.
The ez430-RF2500 boards use the SimpliciTI protocol developed by Texas Instruments for small RF ultra-low-power wireless sensor networks. The programming of the two ez430-RF2500 modules was done using the IAR Embedded Workbench for MSP430. One of the ez430-RF2500 modules was programmed to scan in the same cycle, both the ECG and PPG channels, at a frequency of 200 times per second, converting the signals from analog to digital.
The ECG module, made in our laboratory, is a low-power device, supplied from two AAA 1.5V batteries and detects one lead ECG signal by measuring the skin potentials using 3 electrodes placed on the skin surface.
Information collected is transmitted to a mobile device, in this case, a HTC X7500 smartphone, which has an USB interface, for connecting to the receiver module, and uses Windows Mobile 5 as operating system
The software that runs on the mobile device was developed by using LabVIEW 2010 from National Instruments, a graphical system design which offers the tools needed to create and deploy measurement and control systems.
In terms of medical applications and patient’s welfare, we implemented the virtual instrumentation software on a mobile device, creating a tool for long term monitoring of patients at home, in their daily living and usual activities, improving their quality of life. Use of mobile devices in this way offer the possibility of transmitting data through GSM/GPRS or WiFi to the remote units, for the storage and further analysis.
Virtual instrumentation is a concept that permits customizable modular software measurement and the development of the user-defined tools for control, process and visualization of data, creating versatile systems, using modular programming, intuitive and easy to use.
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