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Biomedical subjects

I Korhonen

Publications and source records attributed to I Korhonen.

At least 19 recordsLinked to original sources
PubMed2006

Diurnal and weekly rhythms of health-related variables in home recordings for two months.

Several telecare systems for long-term monitoring of the well-being of patients at home have been developed as an aid in healthcare and to reduce hospitalization costs. Most of the systems have been designed to measure only one or two variables. Because well-being is a combination of both psychological and physiological wellness, there is a need to monitor several psychophysiological variables simultaneously in out-of-hospital conditions for a long period. To understand better the variability of patients' wellness-related variables in long-term recordings, the knowledge of the normal variation in health-related variables in healthy people is necessary. In our study, 14 healthy working middle-aged men were studied daily for 24 h and periods of 50 to 79 days. The variables measured were beat-to-beat heart rate, motor activity, blood pressure, body weight, and temperature. At night respiratory frequency, time of movements, amount of quiet sleep, and ballistocardiographic respiratory variation were also measured. Heart rate variability in the waking period was calculated later (standard deviation of the 5 min average of the successive normal to normal beat to beat intervals). Daily self-reported well-being, activities, and consumption of alcohol were monitored by keeping a behavioral diary. After normalizing the physiological data, the diurnal and weekly variability was calculated for each variable. In several variables the most notable diurnal and weekly variability was found between working time and free time. In conclusion, diurnal and weekly rhythms in several wellness-related physiological and psychological variables were identified, depending on working and free-time in healthy middle-aged men.

Adult↗
PubMed2006

Novel multiparameter approach for measurement of nociception at skin incision during general anaesthesia.

BACKGROUND: Direct indicators for the evaluation of the nociceptive-anti-nociceptive balance during general anaesthesia do not exist. The aim of this study was to combine physiological parameters to obtain such an indicator. METHODS: Fifty-five females scheduled for surgery under general anaesthesia combining target-controlled infusions of propofol and remifentanil were studied. Propofol was given to maintain state entropy (SE) at 50 and remifentanil was targeted at 1, 3 or 5 ng ml(-1). The patients' reactions and clinical signs of nociception, remifentanil levels and estimation of noxious intensity of incision were combined into a clinical score [Clinical Signs-Stimulus-Antinociception (CSSA)] to evaluate the nociceptive-anti-nociceptive balance. ECG, photoplethysmography (PPG), response entropy (RE) and SE were recorded from 60 s before to 120 s after skin incision. Differences between post- and pre-incision values of heart rate variability (HRV), PPG and pulse transition time related parameters were analysed off-line to evidence the best predictors of CSSA. Those best predictors of CSSA served to develop a response index of nociception (RN), scaled from 0 to 100. This index was further tested in 10 additional patients. RESULTS: HRV, RE, RE-SE and PPG variability were the best predictors of CSSA. The prediction probability of RN at predicting CSSA was 0.78. RN response was higher after larger incision, in movers and with lower remifentanil concentrations. CONCLUSIONS: The empirically developed algorithm of RN leads to an index that seems to adequately estimate the nociceptive-anti-nociceptive balance at skin incision during general anaesthesia. In the future, CSSA may serve as a reference for studies investigating methods aimed at evaluating this pharmacodynamic component of anaesthesia.

Adult↗
PubMed2006

Stimulation induced variability of pulse plethysmography does not discriminate responsiveness to intubation.

BACKGROUND: Hypnotic depth but not haemodynamic response to painful stimulation can be measured with various EEG-based anaesthesia monitors. We evaluated the variation of pulse plethysmography amplitude induced by an electrical tetanic stimulus (PPG variation) as a potential measure for analgesia and predictor of haemodynamic responsiveness during general anaesthesia. METHODS: Ninety-five patients, ASA I or II, were randomly assigned to five groups [Group 1: bispectral index (BIS) (range) 40-50, effect site remifentanil concentration 1 ng ml(-1);Group 2: BIS 40-50, remifentanil 2 ng ml(-1); Group 3: BIS 40-50, remifentanil 4 ng ml(-1); Group 4: BIS 25-35, remifentanil 2 ng ml(-1); Group 5: BIS 55-65, remifentanil 2 ng ml(-1)]. A 60 mA tetanic stimulus was applied for 5 s on the ulnar nerve. From the digitized pulse oximeter wave recorded on a laptop computer, linear and non-linear parameters of PPG variation during the 60 s period after stimulation were computed. The haemodynamic response to subsequent orotracheal intubation was recorded. The PPG variation was compared between groups and between responders and non-responders to intubation (anova). Variables independently predicting the response were determined by logistic regression. RESULTS: The probability of a response to tracheal intubation was 0.77, 0.47, 0.05, 0.18 and 0.52 in Groups 1-5, respectively (P<0.03). The PPG variability was significantly higher in responders than in non-responders but it did not improve the prediction of the response to tracheal intubation based on BIS level and effect site remifentanil concentration. CONCLUSION: Tetanic stimulation induced PPG variation does not reflect the analgesic state in a wide clinical range of surgical anaesthesia.

Adult↗
PubMed2005

Recovery of N100 component of auditory event-related potentials and EEG after cardiac arrest during propofol sedation.

We report on the EEG monitoring of a patient who suffered an episode of postoperative ventricular fibrillation (VF) following coronary artery bypass grafting (CABG). VF initially caused a considerable suppression and slowing of the EEG. The recovery of cerebral function was evaluated by recording both EEG and auditory event related potentials (ERPs). Six hours after the episode of VF, when the patient was asleep but arousable to voice command, the N100 component of the auditory ERPs had recovered to the level measured before the operation, whereas the EEG was still very slow for that level of sedation. This may have been due to VF having less effect on the N100 component than on the background EEG. Our findings suggest that measuring evoked potentials may improve the evaluation of brain function after cardiac arrest.

Aged↗
PubMed2005

Pituitary and autonomic responses to cold exposures in man.

This review presents hormonal responses to various cold exposures and their calorigenic effects in man and some animals. Previous studies in rats have shown that cold exposures activate the hypothalamic-pituitary-thyroid axis. Increased thyroid hormone concentrations lead to heat production via general stimulation of metabolism (obligatory thermogenesis) and possibly via activation of thyroid hormone receptors and uncoupling protein 1 (UCP 1) and deiodinase enzyme genes in the brown adipose tissue (BAT). In human subjects long-term cold exposures do not seem to activate the pituitary-thyroid axis, but rather accelerate the elimination of triiodothyronine (T3), leading to low serum concentrations of free T3 hormone. In corollary to this a hypothyreotic condition with increased serum thyroid-stimulating hormone and impaired mood and cognitive performance can be observed after long-term cold exposures such as wintering. During cold exposures the sympathetic nerve system is activated and noradrenaline is released to blood circulation and to BAT, where it leads to production of cAMP, lipolysis and free fatty acids. Free fatty acids open the mitochondrial proton channel protein in BAT. Protons enter the mitochondria and inhibit ATP synthesis (uncoupling). By this way energy is transformed into heat (facultatory or adaptive thermogenesis). In adult human subjects the amount of BAT is small and adaptive thermogenesis (non-shivering thermogenesis) has a smaller role. UCP 1 with other uncoupling proteins may have other functions in the control of body weight, sugar balance and formation of reactive oxygen species.

Adipose Tissue, Brown↗
PubMed2004

Comparison of closed-loop and open-loop models in the assessment of cardiopulmonary and baroreflex gains.

OBJECTIVES: Both open- and closed-loop models of beat-to-beat cardiovascular control have been suggested. We tested whether the modelling yields different results with real data while assessing cardiopulmonary and baroreflex gains. METHODS: Two autoregressive models are described to resolve causal relationships between systolic blood pressure (SBP), RR-interval (RRI) and instantaneous lung volume (ILV): a closed-loop model which takes into account both the RRI changes induced by changes in SBP and the SBP changes mediated by changes in RRI, and an open-loop model which does not have a link from RRI to SBP. The performance of the models was compared in 14 healthy men in supine and standing positions under control conditions and under conditions of beta -sympathetic and parasympathetic pharmacological blockades. Transfer function gains were computed from ILV to RRI (cardiopulmonary gain) and from SBP to RRI (baroreflex gain). The measurements were done under controlled random-interval breathing. RESULTS: The gains identified by the open-loop model tended to be higher than those from the closed-loop model, but the differences did not reach statistical significance. Importantly, the two models discriminated the changes in transfer gains between different interventions equally well. CONCLUSIONS: Because the interactions between SBP and RRI occur physiologically in a closed-loop condition, the closed-loop model provides a theoretical advantage over the open-loop model. However, in practise, it seems to be little reason to select one over the other due to methodological errors when estimating cardiopulmonary or baroreflex transfer gains.

Adrenergic beta-Antagonists↗
PubMed2001

Estimation of frequency shift in cardiovascular variability signals.

Spectral analysis of heart rate (HR) and blood pressure (BP) oscillations has traditionally concentrated on spectral power, although a shift in spectral frequency characterises the variability better than power in some cases. Experimental data were obtained from 14 healthy males in control and pharmacological blockade conditions. When parasympathetic control was reduced, LF oscillations of HR and BP tend to shift towards lower frequencies. Three parameters were compared to estimate the spectral shift within the low frequency (LF, 0.04-0.15 Hz) band in HR and BP variability: mean (fmean), median (fmed), and central frequency (fc). Parameter variance (pSTD) and sensitivity to noise were also estimated using realistic HR, systolic BP (SBP) and diastolic BP (DBP) data. fmean showed the lowest parameter variance both for an autoregressive (AR) method (SBP pSTD 3.1 vs 4.8 vs 4.7 mHz for fmean, fmed and fc, respectively; p<0.001) and an FFT method (SBP pSTD 4.7 vs 7.7 mHz for fmean and fmed, respectively; p<0.001). Furthermore, fmean was least sensitive to noise. fc showed the poorest performance being especially sensitive to noise. To analyse the spectral shift, fmean is preferred, since it performs better than fc, which has been used in most previous studies. To quantify the frequency of oscillations in cardiovascular signals, the mean frequency is recommended, with analyses across different spectral bands.

Adrenergic beta-Antagonists↗
PubMed2001

TERVA: system for long-term monitoring of wellness at home.

Long-term monitoring of physiological and psychosocial variables in out-hospital conditions would be beneficial for investigating changes in wellness status of an individual or to understand interaction between physiological and behavioral processes. We aimed to design a personal wellness monitoring system (TERVA), which would allow monitoring of wellness-related variables at home for several weeks or even months. The designed TERVA system runs on a laptop computer and interfaces with different measurement devices through a serial interface. Measured variables include beat-to-beat heart rate, motor activity, blood pressure, weight, body temperature, respiration, ballistocardiography, movements, and sleep stages. In addition, self-assessments of daily well-being and activities are stored by keeping a behavioral diary. To test the system, one healthy man used the system for 10 weeks. The system was successfully applied in out-hospital conditions. The success rate of the measurements was 70-91%, depending on the variable under consideration. The pilot study indicated that the recorded data accurately reflected the health status of the subject. The TERVA system provides a method to record and investigate wellness-related data over several weeks, or even months, outside the hospital among subjects capable of using a personal computer. Several applications of the system are discussed.

Diagnosis, Computer-Assisted↗
PubMed2001

Habituation of thermal sensations, skin temperatures, and norepinephrine in men exposed to cold air.

We studied habituation processes by exposing six healthy men to cold air (2 h in a 10 degrees C room) daily for 11 days. During the repeated cold exposures, the general cold sensations and those of hand and foot became habituated so that they were already significantly less intense after the first exposure and remained habituated to the end of the experiment. The decreases in skin temperatures and increases in systolic blood pressure became habituated after four to six exposures, but their habituations occurred only at a few time points during the 120-min cold exposure and vanished by the end of the exposures. Serum thyroid-stimulating hormone, total thyroxine and triiodothyronine, norepinephrine, epinephrine, cortisol, and total proteins were measured before and after the 120-min cold exposure on days 0, 5, and 10. The increase in norepinephrine response became reduced on days 5 and 10 and that of proteins on day 10, suggesting that the sympathetic nervous system became habituated and hemoconcentration became attenuated. Thus repeated cold-air exposures lead to habituations of cold sensation and norepinephrine response and to attenuation of hemoconcentration, which provide certain benefits to those humans who have to stay and work in cold environments.

Adult↗
PubMed2001

Serum concentrations of thyroid and adrenal hormones and TSH in men after repeated 1 h-stays in a cold room.

We exposed six healthy men to 1-h cold air (10 degrees C) daily for 11 days and measured adrenal and thyroid hormones and TSH in serum before and after the cold air exposure on days 0, 5 and 10. We observed that on days 0, 5 and 10 the resting levels and the levels after the cold exposure in serum adrenaline, thyroid hormones and TSH did not significantly change, whereas the serum noradrenaline levels showed a significant 2.2-2.5-fold increase in response to the cold air exposures. The increases were similar indicating that the subjects did not show signs of habituation in their noradrenaline responses. Therefore the 1-h cold air exposure is not sufficiently intensive to reduce the cold-induced sympathetic response.

Adaptation, Physiological↗
PubMed2000

Technical description of the IBIS data library. Improved Monitoring for Brain Dysfunction in Intensive Care and Surgery.

The IBIS Data Library (DL) is an annotated data library that contains practically all the monitored data and other clinical information from critically ill patients during surgery and in intensive care. The data have been collected at three sites: the intensive care unit of the Kuopio University Hospital, Finland; Royal Brompton Hospital, London, UK; and St. Bartholomew's Hospital, London, UK. The purpose of the DL is to form the basis for development of biosignal interpretation methods in the Improved Monitoring for Brain Dysfunction in Intensive Care and Surgery project in the European Union (EU) BIOMED2 programme (BMH4-97-2570). The DL contains continuous electroencephalography signals, multimodal evoked potential recordings and diagnostic electrocardiography recorded during intensive care and surgery. In addition, signal types similar to those recorded during an earlier project, the EU-BIOMED1 project IMPROVE, are stored in the DL. In addition, trend data from patient monitors, laboratory data, annotations, nursing actions, and medications recorded and stored by a Patient Data Management System (PDMS) during routine care are included. The data obtained routinely are complemented by special annotations made by a physician who observes the patient during the data collection session. Annotations include, for example, assessment of the awareness of the patient and specific events during surgery not recorded routinely by the PDMS. Inclusion of information about the care plan and the aims of the care make the contents of the DL complete. The present paper describes the technical set-up used for recording of the DL and the contents of the DL. The paper also includes an appendix defining a new data format, the extended evoked potentials format, used for storage of sweep data in the DL.

Brain↗
PubMed2000

Detection of artifacts in monitored trends in intensive care.

In intensive care, decision-making is often based on trend analysis of physiological parameters. Artifact detection is a pre-requisite for interpretation of trends both for clinical and research purposes. In this study, we developed and tested three methods of artifact detection in physiological data (systolic, mean and diastolic artery and pulmonary artery pressures, central venous pressure, and peripheral temperature) using pre-filtered physiological signals (2-min median filtering) from 41 patients after cardiac surgery. These methods were: (1) the Rosner statistic; (2) slope detection with rules; and (3) comparison with a running median (median detection). After tuning the methods using data from 20 randomly chosen patients, the methods were tested using the data from the remaining patients. The results were compared with those obtained by manual identification of artifacts by three senior intensive care unit physicians. Out of an average of 22,480 data points for each variable, the three observers labelled 0.98% (220 data points) as artifacts. The inter-observer agreement was good. The average (range) sensitivity for artifact detection in all variables in the test database was 66% (33-92%) for the Rosner statistic, 64% (24-98%) for slope detection and 72% (41-98%) for median detection. All methods had a high specificity (> or = 94%). Slope detection had the highest mean positive prediction rate (53%; 21-85%). When the performance was measured by the cost function, slope detection and running median performed equally well and were superior to Rosner statistics for systemic arterial and central venous pressure and peripheral temperature. None of the methods produced acceptable results for pulmonary artery pressures. We conclude that median filtering of physiological variables is effective in removing artifacts. In post-operative cardiac surgery patients, the remaining artifacts are difficult to detect among physiological and pathophysiological changes. This makes large databases for tuning artifact algorithms mandatory. Despite these limitations, the performance of running median and slope detection were good in selected physiological variables.

Algorithms↗
PubMed2000

Quantification of haemodynamic response to auditory stimulus in intensive care.

Measuring effects of sensory stimuli on haemodynamics could provide information about the interplay between central and autonomous nervous system (ANS). However, ANS response to sensory stimulus has received little attention. In this paper we present a signal processing scheme to extract the responses of heart rate and systemic arterial pressure on auditory stimulus in intensive care patients (N=5). In short, the effect of mechanical ventilation is rejected by optimal linear modelling. Other disturbances are attenuated by filtering and efficient rejection of outlying sweeps of data. The results show identifiable responses on three out of five cases. The response characteristics may be explained by synchronisation of spontaneous variability in systemic arterial pressure to auditory stimulus.

Acoustic Stimulation↗
PubMed2000

Single sweep analysis of event related auditory potentials for the monitoring of sedation in cardiac surgery patients.

Event-related potentials (ERPs) from the auditory system were investigated in 28 post-operative cardiac patients in order to assess their relevance in the monitoring of patient sedation level. Midazolam (17 patients) and propofol (11 patients) were the sedative agents used. The auditory ERP components of N100 (HAB100) and mismatch negativity (MMN) were considered. A single sweep method based on the AutoRegressive with eXogenous input (ARX) model, which is able to enhance the evoked responses to each single stimulus, was used to process each sweep and to compute traditional parameters on a sweep-by-sweep basis. Differences in the measured parameters were related to variations in the patient sedation levels classified through Ramsay score. Significant differences (P<0.05) in both MMN and HAB100 parameters were found between light sedation (LS) and deep sedation (DS) levels.

Aged↗
PubMed1999

Circadian profile of low-frequency oscillations in blood pressure and heart rate in hypertension.

Electrocardiogram and intraarterial blood pressure (BP) were recorded in 35 normotensive (NT), 29 borderline hypertensive (BHT), and 30 mildly hypertensive (HT) men (aged 35 to 45 years) by the Oxford method over a 24-h period. Consecutive data segments of 5 min were extracted from the recordings for frequency domain analysis. Heart rate (HR) and BP variability was calculated for oscillations between 0.05 and 0.12 Hz, usually referred to as Mayer waves. Power and median frequency of the oscillations were determined. Some 10% of the segments were excluded from the analysis because of artifacts and transients. The results were averaged for 5-h periods in the evening, at night, and during the day. In the BHT subjects, the median frequency of the Mayer waves was shifted to lower frequencies as compared with the NT subjects. This was seen at night and during the day. The phenomenon presumably reflects an increased latency in the sympathetic vasomotor control of the baroreceptor reflex. No between-group differences were found in the normalized spectral power values. Five years later, 24 NT, 22 BHT, and 19 HT subjects were reassessed using casual BP and noninvasive ambulatory 24-h monitoring. In the initial phase, the median frequencies for the 5-h periods showed no evident linear relationship with the corresponding BP levels. However, the median frequencies showed high inverse correlations with the follow-up ambulatory BP levels. In the evening and during the day, the median frequency showed a significant inverse correlation also with the increment in BP. No clear relationship was found between power estimates and BP levels or future increments in BP. In conclusion, the frequency shift of Mayer waves to lower frequencies is associated with an increased risk of developing established hypertension.

Adult↗
PubMed1999

Warming of insufflation gas during laparoscopic hysterectomy: effect on body temperature and the autonomic nervous system.

BACKGROUND: Hypothermia is a known side effect of laparoscopic operations. It may increase the sympathetic activity of the autonomic nervous system (ANS), which can be evaluated noninvasively by heart rate variability (HRV). We tested the hypothesis that warming of the delivered CO2 insufflation gas helps to maintain the normal body temperature. METHODS: Thirty-seven healthy women undergoing laparoscopic hysterectomy were randomized into heated (37 degrees C, n=18) or unheated (24 degrees C, n = 19) gas insufflation groups. Anesthesia was induced with propofol and maintained with sevoflurane in O2-air. Tympanic (ttymp) temperature was recorded before, during and after the operation. Nasopharyngeal (tnaso) temperature was recorded only during operation. Electrocardiograms were recorded and stored to evaluate changes in HRV. The individual changes in HRV were compared after decibel (dB) transformation. RESULTS: A median decrease in tympanic temperatures during the operation was 0.7 degrees C in the heated and 0.3 degrees C in the unheated group (P = 0.01 between groups), and in nasopharyngeal 0.3 degrees C and 0.1 degrees C (P = 0.03), respectively. Preanesthetic tympanic values were reached within 90 min after anesthesia. After dB transformation, HRV high frequency power differed between the groups. It was better preserved in the patients receiving unheated gas. CONCLUSION: The heating of insufflation gas does not prevent a decrease in body temperature and is thus unnecessary during laparoscopic hysterectomy.

Adult↗
PubMed1999

The effects of two rewarming strategies on heat balance and metabolism after coronary artery bypass surgery with moderate hypothermia.

BACKGROUND: Postoperative hypothermia is common in cardiac surgery with hypothermic cardiopulmonary bypass (CPB). This trial was designed to evaluate whether rewarming over the normal bladder temperature (over 37 degrees C) at the end of hypothermic CPB combined with passive heating methods after CPB might result in a better heat balance, lower energy expenditure (EE) and decrease of disturbances in oxygen balance compared to only rewarming the patients to a bladder temperature of 35-37 degrees C. METHODS: A prospective, randomized controlled clinical study was performed in 38 patients scheduled for elective coronary artery bypass surgery. Twenty patients (group C) were rewarmed to a bladder temperature of 35-37 degrees C at the end of hypothermic (28 degrees C) CPB. Eighteen patients (group W) were rewarmed to a bladder temperature of 37-38.5 degrees C. RESULTS: At the end of CPB, the bladder temperature was 36.2+/-0.7 degrees C (mean+/-SD) in group C and 37.9+/-0.5 degrees C in group W. After half an hour's stay in the ICU, the mean body temperature (MBT) was 35.1+/-0.6 degrees C in group C and 36.6+/-0.7 degrees C in group W. During the following five hours, MBT increased to 37.4+/-0.8 degrees C in group C and to 38.0+/-0.6 degrees C in the other group. The peak value of EE in the ICU was 1.73+/-0.44 (group C) vs 1.35+/-0.29 (W/kg) (group W) (P=0.003). EE was significantly (P=0.044) higher in group C than in the other group between 1.5 and 5.5 h in the ICU. The increased energy expenditure due to heat production was associated with an increase in O2 consumption (VO2) 61.6+/-30.4% vs 25.2+/-24.1%, (peak values) compared to the basal values of the two groups measured before anesthesia (between groups P<0.001). Between 1.5 and 5.5 h in the ICU, group C had significantly higher VO2 (P=0.026), CO2 production (P=0.017), venous pCO2 (P<0.001) and minute ventilation (p=0.014) than group W. Venous pH was lower (P<0.001) in group C. The peak value of oxygen extraction was also higher (P=0.045) in group C. On the other hand, the lowest value of venous oxygen saturation was higher (P=0.04) in group W. CONCLUSION: With rewarming the patients at the end of CPB to a bladder temperature of over 37 degrees C combined with passive heating methods after CPB, it was possible to decrease EE and VO2 compared to the control group (rewarmed to bladder temperature of 35-37 degrees C) after coronary artery bypass surgery with moderate hypothermia.

Body Temperature↗