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Biomedical subjects

Ilkka Korhonen

Publications and source records attributed to Ilkka Korhonen.

13 recordsLinked to original sources
PubMed2006

Activity classification using realistic data from wearable sensors.

Automatic classification of everyday activities can be used for promotion of health-enhancing physical activities and a healthier lifestyle. In this paper, methods used for classification of everyday activities like walking, running, and cycling are described. The aim of the study was to find out how to recognize activities, which sensors are useful and what kind of signal processing and classification is required. A large and realistic data library of sensor data was collected. Sixteen test persons took part in the data collection, resulting in approximately 31 h of annotated, 35-channel data recorded in an everyday environment. The test persons carried a set of wearable sensors while performing several activities during the 2-h measurement session. Classification results of three classifiers are shown: custom decision tree, automatically generated decision tree, and artificial neural network. The classification accuracies using leave-one-subject-out cross validation range from 58 to 97% for custom decision tree classifier, from 56 to 97% for automatically generated decision tree, and from 22 to 96% for artificial neural network. Total classification accuracy is 82 % for custom decision tree classifier, 86% for automatically generated decision tree, and 82% for artificial neural network.

Activities of Daily Living↗
PubMed2006

The effects of dexmedetomidine/remifentanil and midazolam/remifentanil on auditory-evoked potentials and electroencephalogram at light-to-moderate sedation levels in healthy subjects.

Avoidance of excessively deep sedation levels is problematic in intensive care patients. Electrophysiologic monitoring may offer an approach to solving this problem. Since electroencephalogram (EEG) responses to different sedation regimens vary, we assessed electrophysiologic responses to two sedative drug regimens in 10 healthy volunteers. Dexmedetomidine/remifentanil (dex/remi group) and midazolam/remifentanil (mida/remi group) were infused 7 days apart. Each combination of medications was given at stepwise intervals to reach Ramsay scores (RS) 2, 3, and 4. Resting EEG, bispectral index (BIS), and the N100 amplitudes of long-latency auditory-evoked potentials (ERP) were recorded at each level of sedation. During dex/remi, resting EEG was characterized by a recurrent high-power low-frequency pattern which became more pronounced at deeper levels of sedation. BIS Index decreased uniformly in only the dex/remi group (from 94 +/- 3 at baseline to 58 +/- 14 at RS 4) compared to the mida/remi group (from 94 +/- 2 to 76 +/- 10; P = 0.029 between groups). The ERP amplitudes decreased from 5.3 +/- 1.3 at baseline to 0.4 +/- 1.1 at RS 4 (P = 0.003) in only the mida/remi group. We conclude that ERPs in volunteers sedated with dex/remi, in contrast to mida/remi, indicate a cortical response to acoustic stimuli, even when sedation reaches deeper levels. Consequently, ERP can monitor sedation with midazolam but not with dexmedetomidine. The reverse is true for BIS.

Acoustic Stimulation↗
PubMed2006

Blood pressure and heart rate responses in men exposed to arm and leg cold pressor tests and whole-body cold exposure.

OBJECTIVES: Comparison of the effects of different types of cold exposure on blood pressure and heart rate. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty healthy men were exposed to three different types of cold exposure: cold pressor tests for hands and feet, and a 2-h cold air exposure at an ambient temperature of +10 degrees C. RESULTS: All types of cold exposure caused a rise in systolic and diastolic blood pressures. Heart rate increased in the foot cold pressor test. In the cold chamber test, heart rate fell, causing a decrease in the rate:pressure product. No statistically significant correlations were found between the blood pressure responses to cold pressor and cold chamber tests. The increased rate:pressure product observed in the cold pressor tests is indicative of an increased oxygen consumption in the heart muscle. CONCLUSIONS: The measured cardiovascular responses indicate that a sudden local exposure to severe cold would be more stressful than a long lasting, milder exposure to cold, even when the latter is applied to the whole body

Adult↗
PubMed2005

Long-term self-monitoring of weight: a case study.

The aim of this study was to examine the self-monitoring of weight on a daily basis over a long period of time in order to understand the process of weight regain. An obese female client measured her weight every morning over a period of 10 years. The subject made a total of 2081 weight measurements. Thus, her weight was measured on 67% of all possible days. After the initial weight loss a pattern of gradual weight gain was observed. The subject gained weight during August and September, and at the end of December, in particular. Furthermore, her weight increased slightly at the weekends. This case study highlights the advantage of self-monitoring of weight on a daily basis. Individual patterns of weight change possibly associated with season and weekly variation may be crucial when obese subjects try to maintain their weight after weight loss. However, it may take several months or even years to detect the weekly and yearly rhythms or other patterns in the data. Thus, self-control of weight is problematic, since patterns in the weight regain process are difficult to detect. This may be one reason why self-control of weight is so difficult.

Female↗
PubMed2005

Circadian activity rhythm in demented and non-demented nursing-home residents measured by telemetric actigraphy.

There is a need to develop unobtrusive methods for long-term monitoring of sleep/wake and circadian activity patterns in the elderly both in nursing homes and at home settings as sleep is important for health and well-being. The IST Vivago WristCare is an active social alarm system, which provides continuous telemetric monitoring of the user's activity. We examined how the activity signal measured by IST Vivago differed between demented and non-demented subjects living in a nursing home, and how it correlated with the subjective assessment of sleep quality and daytime alertness. The activity signal data together with subjective assessments of sleep quality and daytime vigilance were collected from 42 volunteers (aged 56-97 years; 23 demented and 19 non-demented) for at least 10 days. The demented subjects had lower daytime activity and higher nocturnal activity than the non-demented subjects. Correlations between the activity parameters and self-assessments were weak but statistically significant. We also found correlation between functional ability and diurnal activity. The results are in line with previous studies with demented and non-demented elderly subjects and suggest that the IST Vivago system provides a valid instrument for unobtrusive continuous long-term monitoring of the circadian rhythm and sleep/wake patterns in the elderly.

Aged↗
PubMed2004

The effect of interruption to propofol sedation on auditory event-related potentials and electroencephalogram in intensive care patients.

INTRODUCTION: In this observational pilot study we evaluated the electroencephalogram (EEG) and auditory event-related potentials (ERPs) before and after discontinuation of propofol sedation in neurologically intact intensive care patients. METHODS: Nineteen intensive care unit patients received a propofol infusion in accordance with a sedation protocol. The EEG signal and the ERPs were measured at the frontal region (Fz) and central region (Cz), both during propofol sedation and after cessation of infusion when the sedative effects had subsided. The EEG signal was subjected to power spectral estimation, and the total root mean squared power and spectral edge frequency 95% were computed. For ERPs, we used an oddball paradigm to obtain the N100 and the mismatch negativity components. RESULTS: Despite considerable individual variability, the root mean squared power at Cz and Fz (P = 0.004 and P = 0.005, respectively) and the amplitude of the N100 component in response to the standard stimulus at Fz (P = 0.022) increased significantly after interruption to sedation. The amplitude of the N100 component (at Cz and Fz) was the only parameter that differed between sedation levels during propofol sedation (deep versus moderate versus light sedation: P = 0.016 and P = 0.008 for Cz and Fz, respectively). None of the computed parameters correlated with duration of propofol infusion. CONCLUSION: Our findings suggest that use of ERPs, especially the N100 potential, may help to differentiate between levels of sedation. Thus, they may represent a useful complement to clinical sedation scales in the monitoring of sedation status over time in a heterogeneous group of neurologically intact intensive care patients.

Aged↗
PubMed2004

Measuring depth of sedation with auditory evoked potentials during controlled infusion of propofol and remifentanil in healthy volunteers.

Avoiding excessively deep levels of sedation is a major problem in intensive care patients. We studied whether clinically relevant levels of sedation can be objectively assessed using long latency auditory evoked potentials. We measured the auditory evoked potentials at 100 ms after the stimulus (N100) in 10 healthy volunteers during stepwise increasing, clinically relevant levels of sedation (Ramsay score [RS] 2-4). The volunteers were studied on three separate occasions and received an infusion of either propofol or a combination of propofol and remifentanil. Effects of remifentanil infusion alone were tested during target controlled infusion (target plasma concentrations: 1, 2, and 3 ng/mL). Remifentanil did not affect evoked potential amplitudes and latencies. During both propofol-induced and propofol/remifentanil-induced sedation, the N100 amplitude decreased similarly without an effect on the latencies as the level of sedation increased from Ramsay score 2 to Ramsay score 4 (P < 0.01). At the same clinical level of sedation, propofol plasma concentrations were larger when sedation was achieved by propofol alone (propofol versus propofol/remifentanil, RS 3: 2.12 mug/mL +/- 0.51 versus 1.32 +/- 0.43, P < 0.01; RS 4: 3.37 +/- 0.47 versus 1.86 +/- 0.34, P < 0.01). Our results suggest that long latency auditory evoked potentials provide an objective electrophysiological analog to the clinical assessment of sedation independent of the sedation regime used.

Adult↗
PubMed2003

Automatic sleep-wake and nap analysis with a new wrist worn online activity monitoring device vivago WristCare.

STUDY OBJECTIVE: Vivago WristCare is a new activity monitoring device, which allows long-term online monitoring of the activity of the user. This study evaluates the ability of the device to discriminate sleep/wake patterns during nighttime and during napping. DESIGN: Participants spent one night in the sleep laboratory where signals from polysomnography, actigraphy and WristCare were acquired. In addition, actigraphy and WristCare were used for 3-6 days for nap-analysis. SETTING: NA. PATIENTS OR PARTICIPANTS: Participants were 32 adults aged 26-89 years. The participants were studied in three study groups: all subjects, senior subjects (age > 65 years) and middle-aged subjects (age < 65 years). INTERVENTIONS: NA. RESULTS: Sleep/wake patterns were extracted from polysomnography, actigraphy and WristCare for the night slept in sleep laboratory. The agreement percents between the scorings of polysomnography and actigraphy, and between polysomnography and WristCare were about 80 % for all study groups. As total sleep time was estimated and the algorithm was optimized for this measure, the performance of the WristCare and actigraphy were similar. Both actigraphy and WristCare overestimated appreciably total sleep time (TST). Also in nap-analysis, actigraphy and WristCare performed similarly as the number of naps and the length of the naps were compared. CONCLUSIONS: The performance of the WristCare can be assumed to be well comparable to actigraphy in sleep/wake studies. The study suggests that the device may be used in long-term monitoring of sleep/wake patterns with similar performance to actigraphy.

Adult↗
PubMed2002

Assessment of postoperative sedation level with spectral EEG parameters.

OBJECTIVES: Several sedation scores have been developed, but still a need exists for an objective method to monitor sedation level during intensive care. Our study presents a procedure for finding a combination of electroencephalogram (EEG) characteristics, which could be used in estimating sedation level. METHODS: We measured EEG in 29 cardiac surgical patients prior to and after the cardiac bypass grafting operation at different sedation levels. The clinical assessment of sedation levels was evaluated with the Ramsay Score. Spectral EEG parameters were computed and a linear model to predict postoperative sedation level was constructed by using principal component analysis and regression analysis. RESULTS: Sedation levels modified all computed spectral EEG parameters. The model based on optimal combination of EEG parameters predicted the observed Ramsay Score value with a prediction probability of 88%. CONCLUSIONS: This study suggests that a combination of spectral EEG parameters may discriminate between 3 sedation levels: awake, moderate sedation and deep sedation.

Adult↗
PubMed2002

Methods for assessing adequacy of anesthesia.

Assessing adequacy of anesthesia requires evaluation of its components: hypnosis, analgesia, and neuromuscular transmission. In order to do this, many methods have been developed that process signals representing different modalities. Assessment of hypnosis requires cortical measures of the central nervous system (CNS); methods that assess analgesia concentrate on subcortical and spinal levels of the CNS; and neuromuscular transmission is a peripheral phenomenon. This article presents an overview of the current state of methods available for measuring each of these components. We conclude that, whereas important gains have been made in the area of assessment of hypnosis, mainly owing to the advancement of methods using EEG and auditory evoked potentials, and whereas neuromuscular transmission can be objectively monitored using motor nerve stimulation, assessment of analgesia still contains many challenges.

Anesthesia↗
PubMed1997

Postural sway and stepping response among working population: reproducibility, long-term stability, and associations with symptoms of the low back.

OBJECTIVE: To investigate the day-to-day reproducibility and long-term (9 months) stability of variables of postural control, and the associations of these variables with low-back and lower-extremity pain in a working population. DESIGN: Test-retest measurements of 18 healthy subjects. Cross-sectional study of 165 working women and 343 men. BACKGROUND: Sudden loss of postural balance may result in microtraumas of back structures. Therefore workers with decreased postural control may run an increased risk of low-back pain. There are few reports describing the reproducibility of force-plate-based posturography. METHODS: Amplitude and velocity of postural sway were measured with a force-plate in a two-feet stance with eyes open and closed, and in a one-foot stance with eyes open. A stepping response test was developed to measure the dynamic components of balance. RESULTS: The mean differences between the repeated measurements were generally 5-10% and the standard deviations of these differences were up to a quarter or one third of the mean measurement values. Sway velocity showed the best overall reproducibility. Men had a larger sway than women independent of age and anthropometry. The group of non-symptomatic subjects showed wide variation and a slightly lower sway than the groups with low-back or lower-extremity pain. CONCLUSIONS: Postural sway has moderate stability, wide variation, and slight associations with low-back symptoms in a working population.

Journal Article↗