Browsing by Author "Takala, Panu"

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  • Cardiac exercise studies with bioelectromagnetic mapping
    (2001-11-17) Takala, Panu
     Doctoral dissertation (article-based)
    Bioelectric currents in the heart give rise to differences in electric potential in the body and on its surface. The currents also induce a magnetic field within and outside the thorax. Recording of the electric potential on the surface of the body, electrocardiography (ECG), is a well established clinical tool for detecting insufficient perfusion of blood, i.e., ischemia during exercise testing. In a more recent technique, magnetocardiography (MCG), the cardiac magnetic field is recorded in the vicinity of the chest. Despite the clinical significance of the exercise ECG recordings in patients with suspected coronary artery disease (CAD), little is known about the effect of stress in the MCG of healthy subjects and patients with CAD. Methods for analysing multichannel MCG signals, recorded during physical exercise testing, were developed in this thesis. They were applied to data recorded in healthy subjects to clarify the normal response to exercise in the MCG, and to data of patients with CAD to detect exercise-induced myocardial ischemia. Together with the MCG, spatially extensive ECG, i.e., body surface potential mapping (BSPM) was studied and the exercise-induced alterations in the two mappings were compared. In healthy volunteers, exercise was found to induce more extensive alterations in the MCG than in the BSPM during the ventricular repolarisation. In patients with CAD, when optimal recording locations were found and evaluated, alterations of the ST segment in the MCG could be used as indicators of ischemia. Also, ischemia was found to induce a rotation of magnetic field maps (MFMs) which illustrate the spatial MCG signal distribution. The MFM orientation could successfully be used as a parameter for ischemia detection. In the BSPM, regions sensitive to ischemia-induced ST segment depression, ST segment elevation, and ST segment slope decrease were identified. An analysis method was also developed for monitoring the development of the MCG and the BSPM distributions. It enables examination of different features of the MCG and the BSPM signals as a function of time or the heart rate. In this thesis, the method was used for quantifying exercise-induced change in the orientation of MFMs. Adjustment of the orientation change with the corresponding alteration of the heart rate was found to improve ischemia detection by the exercise MCG. When data recorded during the recovery period of exercise testing were evaluated with similar type of analysis methods, the MCG showed better performance in ischemia detection than the simultanously recorded 12-lead ECG.
  • Comparison between patient spirometry and ventilator spirometry
    (2011) Jenu, Saana
     School of Science | Master's thesis
  • Kaasujenvaihdon mittausten verifikaatiolaitteiston suunnittelu
    (2011) Tommila, Rurik
     School of Science | Master's thesis
    GE Healthcare Finland site in Vallila produces different kinds of gas modules, one of which is E-COVX designed to measure patient's gas exchange. The module provides information which may be vital to the patient, and therefore they must be tested before sending to customer. This testing has traditionally been taken care of with a hardware based on Deltatrac II metabolic monitor, heralded as a golden standard when measuring gas exchange. However, the service of the monitor will be shut down, and therefore new solutions for testing the modules must be sought. This thesis presents a solution to replace the old hardware. The goal was to achieve at least the same accuracy as the old hardware and improve its usability. Based on these goals, the chance to acquire a commercial solution is studied. When no such solution is found, we design and execute a whole new system for testing the modules. Based on the preliminary verification measurements concluded on the new solution, it can be said to achieve almost the same accuracy as the Deltatrac and clearly better accuracy than the modules tested. There is still room for improvement: The measurement can be fully automatized and more accurate components can be acquired in order to improve overall accuracy.
  • Rasitusergometri kardiomagneettisissa mittauksissa
    (1997) Takala, Panu
     Helsinki University of Technology | Master's thesis
    Sydänlihaksen solujen yhdenaikaisen aktivaation seurauksena sydämessä esiintyy biosähköisiä virtoja, jotka synnyttävät heikon magneettikentän kehoon ja sen ulkopuolelle. Magnetokardiografialla (MKG) tarkoitetaan tämän magneettikentän mittaamista kehon ulkopuolelta ja kentän muutosta ajan kuluessa kutsutaan magnetokardiogrammiksi. Rasituksen aikana tehtyjä MKG-mittauksia käsitteleviä tutkimuksia on julkaistu vain vähän. Tehdyt tutkimukset ovat kohdistuneet terveisiin koehenkilöihin eikä yhtään potilasmittausta ole raportoitu. Yksi syy tähän on kaupallisesti saatavan, tarkoitukseen soveltuvan rasitusergometrin puuttuminen. Tavanomaisissa ergometreissä olevien magneettisten osien aiheuttamat häiriöt tekevät sydämen tuottaman heikon magneettikentän rekisteröinnin mahdottomaksi rasituksen aikana. Tässä työssä rakennettiin rasitusergometri, jolla suoritettavan rasituskokeen yhteydessä voidaan rekisteröidä tutkittavan henkilön magnetokardiogrammi. Laitteen keskeisin piirre on, ettei se sisällä magneettisia osia. Ergometri kalibroitiin ja sillä tehtiin rasituskokeita yhteensä kymmenellä potilaalla ja terveellä koehenkilöllä. Mittauksissa rekisteröitiin tutkittavien magnetokardiogrammi, 12-kytkentäinen elektrokardiogrammi (EKG) sekä sähköiset pintapotentiaalit rasituksen aikana. Työssä tehtiin myös MKG-mittausten alustava analysointi. Tehdyt rasituskokeet osoittivat, että myös liikuntaan tottumattomat ja huonokuntoiset potilaat pystyvät suorittamaan rasituskokeen ergometrillä. Kokeissa ergometri toimi ongelmitta eikä yhtään koetta jouduttu keskeyttämään tai peruuttamaan ergometristä johtuvista syistä. Mitatussa MKG-signaalissa ei havaittu ergometrin aiheuttamia häiriöitä. Mittausdatan alustavan analyysin perusteella voidaan todeta sydänlihaksen iskemian olevan havaittavissa rasituksen aikaisella MKG-mittauksella. Vasemman sepelvaltimon ahtaumasta (LAD) kärsivistä potilaista puolella nähtiin välittömästi rasituksen jälkeen mitatun MKG:n ST-väliltä muodostetussa keskiarvokartassa yli 3 pT:n ero suurimman ja pienimmän arvon välillä. Terveillä koehenkilöillä tämä ero oli keskimäärin 1.7 pT. MKG:n QRS-kompleksin ajalta muodostetun keskiarvokartan maksimiarvo oli kaikilla terveillä koehenkilöillä sekä LAD-potilailla levossa suurempi kuin välittömästi rasituksen päätyttyä. Oikean sepelvaltimon ahtaumasta (RCA) kärsivillä potilailla tilanne oli keskimäärin päinvastainen ja rasituksen jälkeen mitatusta MKG:sta QRS-kompleksin ajalta muodostetun keskiarvokartan maksimin suhde lepovaiheen vastaavan kartan maksimiin oli kaikilla RCA-potilailla suurempi kuin yhdelläkään muihin ryhmiin kuuluvista.
  • Improving respiratory rate estimation by combining information from impedance pneumography and electrocardiography
    (2016-10-31) Mäntykangas, Mika
     Sähkötekniikan korkeakoulu | Master's thesis
    Variations in respiratory rate (RR) are found to commonly precede acute patient deterioration. However, its importance is often neglected in hospital environments, and the current monitoring technologies possess high false alarm rates especially in ambulatory patient context. Thus, non-invasive and minimally obstructive RR monitoring systems suitable for moving patients are constantly being sought. Impedance pneumography is a well-adopted technology for bedside breathing rate monitoring. It can be utilised with the same measurement electrodes as electrocardiography that is used for the heart's electrical activity monitoring in intensive care but also in sub-acute care settings. Respiration modulates the electrocardiogram in several ways. Therefore, it is possible to calculate the breathing rate also from ECG without additional measurement equipment. This thesis focused on creating advanced RR estimation algorithms that could convey breathing rates during activities typically found in hospital general ward environments. Algorithm development targeted to create accurate RR estimates from impedance pneumography as well as two ECG-derived methods, based on heart rate variation and amplitude modulation. RR estimates were also fused together for more robust and accurate results. Both individual and fusion methods used novel signal quality indices (SQIs). Performance of all methods was evaluated against capnography reference measurement using statistical analysis. The main results were that using signal quality as a part of the estimation process has a substantial effect on impedance pneumography results, while its effect on ECG-derived methods are subtle. Another main finding was that fusing RR estimates from multiple signal sources improves the overall estimate. The key to motion artefact -resistant algorithms was found to be signal quality estimation. Further work with SQIs is recommended to make them more adaptive and individualised.
  • Magnetocardiography in ecercise studies in detection of left ventricular hypertrophy
    (1999) Takala, Panu
     Helsinki University of Technology | Licentiate thesis
  • Photoplethysmographic Waveform as an Indicator of Hypovolemia
    (2010) Keskinen, Juhani
     School of Science | Master's thesis
    Ensuring adequate cardiac output is crucial in patient care in intensive care units. Currently there is no generally accepted direct method for monitoring patient blood volume status, and the care personnel makes the decision about fluid administration based on indirect methods. Respiratory variation indices, derived from invasive arterial blood pressure waveform, have been found to correlate with blood volume deficiency, or hypovolemia. Also photoplethysmographic indices have been studied, to lesser extent. In this thesis the hypovolemia correlation of two photoplethysmographic respiratory variation indices, pulse peak variation (PPV) and stroke volume variation (SVV), are compared with three invasive arterial blood pressure -derived indices, systolic pressure variation (SPV), PPV and SVV. Commonly monitored parameters mean arteral blood pressure (MABP) and central venous pressure (CVP) are used as reference parameters. The photoplethysmographic and arterial blood pressure data used in the evalution was recorded from twelve ventilated pig test subjects. The subjects were drained 450 ml of blood to induce a hypovolemic state, and then administered fluid infusion to bring the blood volume status back to normal. Of the evaluated hypovolemia indices, the best correlation was found in arterial blood pressure PPV and SVV, with Pearson correlation coefficients (rP) over 0.50 and p-values under 0.01. The photoplethysmographic indices showed less correlation with hypovolemia, but were not substantially worse than blood pressure-derived ones, with of rP 0.47 (PPV) and 0.39 (SVV), and p-values of 0.03 (PPV) and 0.09 (SVV). SPV had the least correlation with hypovolemia of the evaluated indices. MABP had the best correlation values as the reference parameter (rP = -0.71, p < 0.001). The study also showed, that the ventilator frequency has effect on the hypovolemia indices. Further, in severe anemic, but non-hypovolemic state, the respiratory variation of the photoplethysmographic and arterial blood pressure waveforms increase. The value of photoplethysmographic hypovolemia indices in fluid therapy guidance is evident, and the noninvasive nature of the measurement encourages to research photoplethysmography -based hypovolemia detection further.
  • Sidestream gas exchange measurements and signal synchronization during bias flow ventilation
    (2010) Salonen, Juuso
     School of Electrical Engineering | Master's thesis