Engineering June 2004 Vol 10/2 []

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of theEstonian Academy of Sciences.

Engineering



Volume 10 No. 2 June2004

Special issue on biomedical engineering



Model-based interpretation of intramyocardialelectrograms for cardiac risk assessment and surveillance; 69–81

Helmut Hutten

Abstract. Intramyocardialelectrograms (IEGMs), which are acquired by using implanted devices withtelemetric capability, offer a challenging potential for long-term cardiac riskassessment and surveillance. However, new approaches to the interpretation ofthese signals are required. There­fore, a model has been developed for thesimulation of excitation spreading across the myocardium and of the subsequentcontraction. It allows to analyse systematically the influence of all relevantparameters including the position of the electrode for stimulation andrecording. The model can be matched to individual heart geometries, forexample, taken from ultrafast CT images. This approach helps to utilize theinformation represented in the morphology of IEGMs for permanent cardiac riskmonitoring.



Interaction of low-level microwave radiation withnervous system – a quasi-thermal effect?; 82–94

Hiie Hinrikus,Jaanus Lass, and Viiu Tuulik

Abstract. This analytical review is focused on the discussion of apossible interaction mechanism of microwave radiation with the nervous system.Energy level of the non-thermal electromagnetic field effects has a lowerboundary, limited by the principal physical noise, and an upper boundary,limited by the thermal effects. The thermal energy that introduces disturbancesin energy distribution of ions and movement in neurones is about 10–5 eV.The electrical field of 10–10 V/cm can introduce an equivalentdisturbance of the thermal equilibrium inside a cell of 10 mmradius. If caused by the low-level microwave exposure, this phenomenon may notbe associated with an increase in temperature. Fluctuations, initiated by thehigh-frequency field in the movement of ions and membranes, affect the gatingvariables and nerve cell properties like the increase in temperature does. The hypothesis that microwave radiation can affectpermeability of the membranes of nerve fibres or myelin sheaths was examinedexperimentally. A 450 MHz microwave field, with and without modulation,polarized perpendicular or parallel to the nerve axon, was applied. Themeasured field power density at the skin was 0.87 mW/cm2. Theleft and right nervus medianus motornerve fibres of two young female subjects were under the study. The results of20 cycles of measurements show that the low-level microwave field causedstatistically significant increase in the nerve pulse propagation velocity inhuman motor nerve fibre. The increase was detected only for polarization,perpendicular to the nerve fibre. The 100% amplitude modulation decreased thiseffect. The effect may be related rather to the threshold voltage of the nerveaxon than to the myelin sheath.



EEG signal in monitoring brain function inanesthesia and intensive care: a review; 95–109

Tarmo Lipping andVille Jäntti

Abstract. Duringrecent years EEG has become the “golden standard” by estimating depth ofanesthesia of individual patients in clinical work. Several monitors, based onprocessing EEG and showing graphically indices of “depth of anesthesia”, havebeen developed and millions of patients have been monitored with these. In thispaper we first shortly discuss the terminology, particularly the meaning of“depth of anesthesia”. Next, a review of different methods and algorithms usedin anesthesia monitoring is presented. Finally, we summarize the methods andoutline the future development of anesthesia monitoring.



Using photoplethysmographic signal for increasingthe accuracy of indirect blood pressure measurement; 110–122

ÁkosJobbágy

Abstract. Automatic andsemi-automatic blood pressure meters are widespread in home health monitoring.However, their results are not accurate and reproducible enough, thereliability of self-assessment is not satisfactory and medical doctors havereservations about their results. The aim of this study was to increase theaccuracy and reproducibility of the indirect, cuff-based blood pressuremeasurement with the help of the photoplethysmographic (PPG) signal. Theadditional information gained from the PPG signal during slow inflation providesmore accurate results than conventional indirect methods and assures that thecuff pressure only slightly (by less than 10 mm Hg) exceeds the systolicpressure. Measuring the pulse wave transit time and its variation during slowinflation and deflation makes it possible to characterize the sympatheticcontrol of the cardiovascular system and the rigidity of the brachial arteries.The PPG signal also indicates if the cuff is placed or inflated improperly. Themethod has been validated making 420 measurements on 51 subjects.



Optical and electrical methods for pulse wavetransit time measurement and its correlation with arterial blood pressure; 123–136

Jaanus Lass, KaljuMeigas, Rain Kattai, Deniss Karai, Jüri Kaik, and Mart Rossmann

Abstract. This paper gives an overview of aresearch, which is focused on the development of a convenient method forcontinuous non-invasive monitoring of the arterial blood pressure (BP).The method is based on the presumption that there is a single relationshipbetween the pulse wave propagation time in arterial system and BP. The pulsewave transit time (PWTT) measurement involves the registration of two timemarkers, one of which is usually based on ECG registration and another on thedetection of the pulse wave in peripheral arteries. This study makes acomparative evaluation of four different methods for pulse wave detection:1) self-mixing in a diode laser, which can detect the skin surfacevibrations near the artery, 2) photoplethysmography (PPG) that reflectsvolumetric changes in peripheral vasculature, 3) cardiosynchronizedcomponent of bioimpedance associated with blood displacement in the vascularsystem, and 4) direct pressure pulsations of finger arteries, detectednoninvasively by the piezoelectric transducer. Linear correlation of PWTT,obtained with different methods, with arterial blood pressure is calculated. Asa result of the current study it is shown that time intervals, which arecalculated from PPG waveforms, are in good correlation with systolic BP duringthe exercise (linear correlation coefficient r = – 0.7). At restslightly better results are obtained by diode-laser pulse profile (LPP) sensor(r = – 0.9)as compared to PPG (r = – 0.87). The correlations of pulsatilebioimpedance (BI) sensor (r = – 0.57) and piezoelectric pulse wave (PW)transducer (r = – 0.47) based PWTT calculations with arterial non-invative BP(NIBP) were not as good as for optical parameters (PPG, LPP). The diastolic BPdid not correlate well with any of the parameters representing PWTT (| r | < 0.35).It is concluded that the PPG signal is the best for PWTT measurement. It isalso most easily detectable and less sensitive to motion artefacts compared toother pulse signals.



Estimation of the finger arterial pressure–volumerelationship and blood pressure waveform from photoplethysmographic signals; 137–147

Jaak Talts

Abstract. A method for deriving the finger arterialpressure–volume (P–V) relationship and blood pressure waveform from twophotoplethysmographic (volumetric) signals is presented. The new approach makesit possible to estimate also the beat-to-beat as well as instantaneous valuesof the dynamic arterial compliance of small arteries. The identification of theP–V relationship was per­formed applying an asymmetric tangentapproximation and non-linear fitting. The results of modelling demonstrate thattwo finger photoplethysmographic waveforms, recorded at different cuff pressurelevels, can be used for the estimation of the finger arterial pressure–volumerelation­ship, dynamic compliance and arterial blood pressure waveform.