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Biomedical subjects

I Korhonen

Publications and source records attributed to I Korhonen.

At least 19 recordsLinked to original sources
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↗
PubMed1999

Wide-band spectral analysis of blood pressure and RR interval variability in borderline and mild hypertension.

The aim of this study was firstly to investigate whether indices of wide-band spectral analysis in borderline hypertensive (BHT) or mildly hypertensive (HT) subjects differ from those in normotensive (NT) subjects, and secondly to assess the predictive value of these indices for future hypertension. Electrocardiogram and intra-arterial 24 h ambulatory blood pressure (BP) were recorded in 32 NT, 29 BHT and 30 HT middle-aged men. From the recordings, a 16 h period was extracted for wide-band spectral analysis. A single spectrum of BP and RR interval (RRI) variability was computed for each period by the fast Fourier transform method. The slopes of the spectra were assessed on a log-log scale by linear fitting of the spectral values. Power spectral densities were calculated over regions of 0-0.003, 0.003-0.04, 0.04-0.15, 0.15-0.40 and 0-0.4 Hz. No between-group differences were found in the slopes of BP and RRI spectra. The between-group differences in spectral powers for BP variability were almost invariably significant. The spectral powers for RRI variability did not show between-group differences. Five years later, 22 NT, 22 BHT and 18 HT subjects were re-assessed using casual BP measurements. In a logistic regression model for the combined group of NT and BHT subjects who became HT (22 of 44) during the five-year period, none of the parameters of wide-band spectrum predicted the development of hypertension. In conclusion, parameters of wide-band spectral analysis may not be useful in predicting future hypertension in NT and BHT subjects. Because the BP level is a major factor influencing BP variability, the between-group differences in wide-band spectral powers in BP may be due to differences in BP level rather than differences in cardiovascular regulatory mechanisms.

Adult↗
PubMed1998

Heart rate and blood pressure responses to isometric exercise in young and older men.

The aim of this study was to examine the isometric endurance response and the heart rate and blood pressure responses to isometric exercise in two muscle groups in ten young (age 23-29 years) and seven older (age 54-59 years) physically active men with similar estimated forearm and thigh muscle masses. Isometric contractions were held until fatigue using the finger flexor muscles (handgrip) and with the quadriceps muscle (one-legged knee extension) at 20%, 40%, and 60% of the maximal voluntary contraction (MVC). Heart rate and arterial pressure were related to the the individual's contraction times. The isometric endurance response was longer with handgrip than with one-legged knee extension, but no significant difference was observed between the age groups. The isometric endurance response averaged 542 (SEM 57), 153 (SEM 14), and 59 (SEM 5) s for the handgrip, and 276 (SEM 35), 94 (SEM 10) and 48 (SEM 5) s for the knee extension at the three MVC levels, respectively. Heart rate and blood pressure became higher during one-legged knee extension than during handgrip, and with increasing level of contraction. The older subjects had a lower heart rate and a higher blood pressure response than their younger counterparts, and the differences were more apparent at a higher force level. The results would indicate that increasing age is associated with an altered heart rate and blood pressure response to isometric exercise although it does not affect isometric endurance.

Adult↗
PubMed1997

Frequency shift in baroregulatory oscillation in borderline hypertensive subjects.

The aim of this study was to quantify the frequency shift in vasomotor oscillations in blood pressure we observed in borderline hypertensive individuals in our previous study. Electrocardiogram and intraarterial blood pressure were recorded in 33 normotensive, 29 borderline hypertensive, and 33 mildly hypertensive men (aged 35 to 45 years). Five-minute stationary periods in supine, sitting, and standing positions, and during sleep were extracted from the recordings for autoregressive frequency domain analysis. In borderline hypertensive subjects vasomotor oscillations in the range of 0.05 to 0.12 Hz in blood pressure and heart rate, assumed to be associated with baroreceptor activity, were shifted to lower values as compared with the other two groups. The frequency shift was assessed by median frequency of the oscillations. Significant between-group differences were observed in the supine and sitting positions. No significant between-group differences were seen in normalized spectral power estimates. Further studies are required to determine whether the frequency shift provides prognostic information on cardiovascular morbidity.

Adult↗
PubMed1997

Multivariate closed-loop model for analysis of cardiovascular dynamics.

This paper introduces a closed-loop model for the analysis of interactions between heart rate and blood pressure variability, and respiration. The respiratory influence is modeled with an anti-causal structure to control the possible phase lead of heart rate to instantaneous lung volume. The closed-loop structure between heart rate and blood pressure allows the analysis of inter-relationships between the signals. Simulations and results on experimental data show the identifiability of the model and the robustness of the noise source contribution analysis over a wide range of model orders.

Blood Pressure↗
PubMed1997

Framework for biosignal interpretation in intensive care and anesthesia.

Improved monitoring improves outcomes of care. As critical care is "critical", everything that can be done to detect and prevent complications as early as possible benefits the patients. In spite of major efforts by the research community to develop and apply sophisticated biosignal interpretation methods (BSI), the uptake of the results by industry has been poor. Consequently, the BSI methods used in clinical routine are fairly simple. This paper postulates that the main reason for the poor uptake is the insufficient bridging between the actors (i.e., clinicians, industry and research). This makes it difficult for the BSI developers to understand what can be implemented into commercial systems and what will be accepted by clinicians as routine tools. A framework is suggested that enables improved interaction and cooperation between the actors. This framework is based on the emerging commercial patient monitoring and data management platforms which can be shared and utilized by all concerned, from research to development and finally to clinical evaluation.

Anesthesia↗
PubMed1996

Multivariate autoregressive model with immediate transfer paths for assessment of interactions between cardiopulmonary variability signals.

Multivariate autoregressive modelling provides a method to analyse the dynamic interactions between heart rate (HR), blood pressure (BP) and respiration (RESP) by means of noise source contributions (NSCs). The conventional approach presumes the modelled noise sources are mutually independent. This presumption is, in general, not satisfied and causes an error in the results. In the present study, the effect of this error is analysed. A method is presented to remove the error by making the noise sources independent. The method is based on the inclusion of immediate transfer paths in the model. To quantify the strength of the interactions, a measure called NSC ratio (NSCR); is calculated; this states the amount of variability of the signal arising from other signals. The method is demonstrated by studying the inter-relationships between HR, BP and RESP in a healthy male subject in supine and standing positions. It is found that the error is marked and that the presented method provides corrected estimates for spectral decomposition and NSC analysis. The results show it is necessary to include the immediate transfer mechanisms in the model, while analysing the cardiopulmonary dynamics by means of HR and BP variability.

Blood Pressure↗