Ante Šantić

Measurement of gait parameters from free moving subjects

In this paper a telemetry system for real-time force measurement in the legs and crutches or cane is presented. The system provides a quantitative gait analysis of orthopaedic patients with details, which are often hidden to a visual observation. Three vertical force components in each leg are measured. For this purpose flat and pliable capacitive sensors, which are placed on the sole of the shoes, were developed. The infrared telemetry is applied to enable free and unconstrained movements of the patient inside a wide indoor environment. Measured forces, after transmission and processing on the receiver side, are presented on the computer monitor as eight channel time diagrams. An original software package (GAS) for on-line monitoring and processing of vertical force data was developed. The processing enables calculation of many diagnostically important parameters (e.g. temporal parameters, average force, force-time integral, sum of forces, etc.), spectral and time-frequency analysis and many other. As an example of clinical application, temporal parameters during ten strides for 20 normal subjects and 20 patients with lower extremities degenerative joint diseases were calculated and compared.

Two methods for determination of diastolic and systolic pressures in fingers

Two methods of blood pressure measurement in fingers are presented. One method is based on blood pulse delay-time between proximal cuff and distal pulse sensor. On the time-delay curve the first minimum which occurs during deflation determinate the diastolic pressure. The another method is based on pulse amplitude differences which occur between proximal cuff signals and distal pulse sensor signals during deflation time of proximal cuff. The amplitude difference is lowest after diastolic pressure. The pressure in the cuff corresponding to the 45% of the difference between highest and lowest amplitude difference taken from lowest value is considered to be diastolic pressure by this method. This two methods and their combination are proved to be quite accurate. The accuracy of this measurements is given as well. Blood pressure measurement on the fingers is more comfortable for blood pressure measurement than on the upper arm.

Micropower Electronic Switches for Implanted Instrumentation

Low-power miniature switching circuits for controlling the power supply to an implanted electronic circuit are described. These circuits can be used as power supply switches for conserving battery power on implanted systems. Monostable and bistable switches that can be triggered either by radio-frequency energy or light are presented. Circuits, having standby currents as low as 25 nA and operated at voltages of 1.35 V, are described. A hybrid microelectronics realization of a radio-frequency triggered bistable switch is described. Radio-frequency triggering by induction can be carried out over distances ranging from 2 to 10 cm, depending on the circuit used. Light triggering using either electronic photoflash lamps or low-power incandescent lights can be achieved over distances as great as 250 cm.

Simultaneous application of multiple oscillometric methods for blood pressure measurement in finger

A noninvasive system for measurement of systolic and diastolic arterial blood pressure is realized. The measurement is based on the application of two oscillometric methods for systolic and three for diastolic pressure. The relevant signals for systolic and diastolic pressure calculation are acquired during cuff deflation. Before determined pressure is shown on a display a weight is given to each measured value which depends on the accuracy of the particular method.

Plethysmography measurements using short current pulses with low-duty cycle

Pulse plethysmography with very low-duty cycle offers much lower current load of examined bio-tissue in comparison to sine-wave impedance plethysmography. This enables application of strong current pulses with the same bio-tissue loading effect as for impedance plethysmography, resulting in larger signal and better signal to noise ratio. Determination of an equivalent electrical circuit of electrodes connected with bio-tissue is possible by fitting the measured waveshape with a resistor and capacitor connected in series, or better with three or four elements. A simplified block diagram of the pulse plethysmograph is given as well. Blood pressure wave-shape obtained on arteries and volume changes during respiration are measured and shown.

A system for measuring forces in the legs and crutches from ambulatory patients

A system for measuring force in both legs and crutches or cane during patient walking is developed. The force in each leg is divided into three components. Following measured data during therapy, rehabilitation progress can be established. Pathological gait patterns depending on disease can be estimated. For vertical force measurement in the leg three capacitive sensors are developed. A special sensor based on infrared radiation changes is realized for force measurement in the crutches or cane. To extend a patients free mobility, an infrared telemetry system is applied. This specially designed telemetry system with multiple receivers and an intelligent summing unit makes possible free walking to the patient in a large room or in more rooms and staircases as well. All eight channels of measured data are presented in real time on the PC-monitor, where each force component can be displayed separately or in the sum. Afterwards an average of repeated gait cycles or their spectra can be calculated and shown on the monitor.

A computer based vertical force monitoring and analysis system for gait evaluation

Measurement of vertical force in gait assessment of injured persons is a method for objective control of the recovery rate during the rehabilitation process. We describe our computer based system for continuous monitoring and analysis of vertical forces. The system uses the original multisegmented capacitive transducers for force measurement and originally developed software CAS for real-time monitoring and post-processing. The software performance and some methods of vertical force signal processing in time and frequency domain are discussed. The feasibility of the system for further clinical use is proved.

Features of pulse plethysmography and a comparison with impedance plethysmography

The features of current pulse plethysmography are given. The skin capacitance and resistance are depending upon pulse duration but not the internal resistance. The internal resistance changes depend of arteries volume changes. A comparison between pulsed plethysmography and sine-wave plethysmography is discussed. The advantages of pulsed plethysmography like much lower current load through the tissue, higher sensitivity and less noise in the recorded signal versus impedance sine-wave plethysmography is pointed out.

Optimization of infrared biotelemetry systems

An infrared telemetry system is analysed, particularly on the receiver side. How an array of photodiodes and choice of optimal load resistance can improve the photoreceiver sensitivity in current and photovoltaic mode is shown. In photovoltaic mode also a parallel load resistor to each diode is necessary to obtain highest photo voltage. Pulse modulation with low duty-cycle is optimal in case when transmitter has to save energy because is carried by the patient. The limit in number of channels and channel bandwidth related to pulse width is discussed. Also an advantage of simple relay unit is described.