Atte Joutsen

Sleep and the menopause - do postmenopausal women experience worse sleep than premenopausal women?

Objective To examine the sleep characteristics in three cross-sectional populations: young, premenopausal and postmenopausal women, and the associations between sleep, menopause, mood and cognitive performance. Study design Twenty-one premenopausal (45–51 years), 29 postmenopausal (59–71 years) and 11 young (20–26 years, using oral contraceptives) women were recruited. Polysomnography was used to measure objective sleep quality. Subjective sleep quality, sleepiness and mood were assessed using questionnaires. Cognitive performance was investigated by means of three attentional tests. Results Total sleep time in pre- and postmenopausal women was similar (404.9 and 384.7 minutes), but shorter than in young women (448.2 minutes, P = 0.030 and <0.003, respectively). Sleep efficiency followed the same pattern, being 84.3% in premenopausal (P = 0.027), 80.2% in postmenopausal (P < 0.003) and 93.4% in young women. Pre- and postmenopausal women had less slow wave sleep (duration or activity) and more wake time after sleep onset (duration or frequency). Insomnia complaints were more frequent after the menopause (P = 0.023). Sleepiness and mood scores were similar in all groups. Reaction speeds slowed with increasing age. After the menopause, better cognitive performance was associated with more rapid eye movement sleep. Conclusion Objective sleep measures differed significantly between the young and postmenopausal groups. These differences may be more because of the physiology of ageing than the rapid changes across the menopause, since similar sleep characteristics were already present in the premenopausal women. The increase in sleep complaints after menopause was not associated with sleepiness or disturbances in objective sleep quality, mood or cognitive performance.

Anteroposterior Difference in EEG Sleep Depth Measure is Reduced in Apnea Patients

In the present work, mean frequencies of FFT amplitude spectra from six EEG derivations were used to provide a frontopolar, a central and an occipital sleep depth measure. Parameters quantifying the anteroposterior differences in these three sleep depth measures during the night were also developed. The method was applied to analysis of 30 all-night recordings from 15 healthy control subjects and 15 apnea patients. Control subjects showed larger differences in sleep depth between frontopolar and central positions than the apnea patients. The relatively reduced frontal sleep depth in apnea patients might reflect the disruption of the dynamic sleep process caused by apneas.

Noncontact Respiration Monitoring During Sleep With Microwave Doppler Radar

This paper demonstrates the measurement of respiration waveform during sleep with a noncontact radar sensor. Instead of measuring only the respiration rate, the methods that allow monitoring the absolute respiration displacement were studied. Absolute respiration displacement can in theory be measured with a quadrature microwave Doppler radar sensor and using the nonlinear demodulation as the channel combining method. However, in this paper, relative respiration displacement measures were used as a reference. This is the first time that longer data sets have been analyzed successfully with the nonlinear demodulation method. This paper consists of whole-night recordings of three patients in an uncontrolled environment. The reference respiration data were obtained from a full polysomnography recorded simultaneously. The feasibility of the nonlinear demodulation in a real-life setting has been unclear. However, this paper shows that it is successful most of the time. The coverage of successfully demodulated radar data was ~58%-78%. The use of the nonlinear demodulation is not possible in the following cases: 1) if the chest wall displacement is too small compared with the wavelength of the radar; 2) if the radar data do not form an arc-like shape in the I Q-plot; or 3) if there are large movement artifacts present in the data. Both in academic literature and in commercial radar devices, the data are processed based on the presumption that it forms either an arc or a line in the I Q-plot. Our measurements show that the presumption is not always valid.

The electrical impedance measurements of dry electrode materials for the ECG measuring after repeated washing

Purpose The purpose of this paper was to offer more reliable dry electrode materials for long-term measuring and determine how repeated machine washing affects the measured impedance and surface resistance of the sample electrodes. The aim was to manufacture electrodes that could be used for the measurement of ECG. Skin friendly, metal sheet type, electrodes could be a solution. Design/methodology/approach In addition to two conventional electrodes already used in heart rate belts, the authors prepared and tested three different sheet metal electrodes. Three 20-mm-diameter electrodes were manufactured from the following materials: silvered knit, conductive polymer, stainless steel, silver and platinum. Electrode impedance was measured at seven frequencies from 1 Hz to 1 MHz, by placing two electrodes face-to-face. Measurements were taken on unused electrodes and after multiple machine washes at 40°C. Findings Analysis of the measurements indicates that with every material tested, the impedances are elevated after repeated washes. All metallic materials have impedances in the range of 0.01 to 4.5 Ω. Metal sheet electrodes can be integrated comfortably into the textile, and they endure textile maintenance without loss of electrical properties. Practical implications Metal sheet electrodes function well in long-term vital signs monitoring, provide a reliable signal and are resistant to maintenance. For the reasons described in this research, they can be used as a long-term wearable sensor. Originality/value Novel electrode material for long-term measuring research is important in many disciplines such as health care and apparel manufacturing. These findings suggest that pure metal electrodes are better than conductive textiles in long-term measuring.

The temporal relationship between growth hormone and slow wave sleep is weaker after menopause

OBJECTIVE To study the temporal association between growth hormone (GH) and slow wave sleep (SWS) in middle-aged women. METHODS Seventeen premenopausal and 18 postmenopausal women were studied using all-night polygraphic sleep recordings and blood sampling at 20-min intervals. The postmenopausal women were re-studied after six months on hormone therapy (HT) according to a randomized, double-blind, placebo-controlled protocol. RESULTS The total sleep time (premenopausal 361.9±81.5 min, postmenopausal 358±67.7 min) and the percentages of the sleep stages did not differ between pre- and postmenopausal women. In postmenopausal women the first GH peak after sleep onset occurred later and with a more variable time interval compared to premenopausal women. The percentage of SWS was highest 40-20 min prior to the first GH peak after sleep onset in both groups with a higher SWS proportion in premenopausal women (p=0.048), although the total SWS percent for night did not differ. HT did not affect the distribution of SWS in postmenopausal women. CONCLUSIONS The temporal relationship between GH and SWS in premenopausal women is less robust after menopause and is not improved with HT.

Investigating the measurement capability of densely-distributed subdermal EEG electrodes

This paper studies the effect of bipolar subdermal EEG lead placement on measurement sensitivity distributions. The electrodes were subdermally located on the skull of a realistic human head and arranged in a 5×5 matrix of electrodes located at the apex of the cranial vault. The effects on the measurement sensitivity were studied by means of the half-sensitivity volume (HSV). The results indicate that subdermal measurements focus the accuracy and specificity of EEG measurement; however, the size of the half sensitivity volume varies due to electrode location across one or more gyri, gray matter and cerebrospinal fluid (CSF) thickness. The results of the study suggest that subdermal needle electrodes could provide specific and accurate measurements of cortical activation but warrant further studies to understand how much the measurement sensitivity is influenced by placement of the subdermal electrodes over the gyri versus sulci.

A Versatile Synchronization System for Biomedical Sensor Development

Accurate synchronization between a custom- made sensor and a commercial reference sensor is a common problem while developing novel biomedical sensors for weara- ble or smart environment applications. This paper presents a widely applicable non-galvanic synchronization system be- tween two or more sensors. The solution is a simple, low-cost infrared link, and it was demonstrated and tested in measure- ments using a commercial full-polysomnographic recording device and a custom-made radar motion sensor. The system was successfully used in a sleep measurement study for 12 full- night recordings. The synchronization accuracy of the system is 2.2 ms which is adequate for all common biosignals. The hardware and software design are available online. This provides other sensor developers possibility to easily use the system in their research projects. Although the technology used is not novel, the aim of the paper is to ease the practical synchronization problems. Keywords—Time synchronization, Sensor data fusion.

Dry electrode sizes in recording ECG and heart rate in wearable applications

The rise of wearable electronics is paving the way for textile integrated sensor applications. ECG and heart rate monitoring are common in health care and consumer applications, respectively. In short term monitoring Ag/AgCl, conductive polymer or fabric electrodes can be used. In long term monitoring the electrolyte and adhesives may cause skin irritation, therefore textile integrated skin friendly dry electrodes may be a solution. The electrodes need to be cost-effective, easy to integrate, need no special care from the user and perform well. Conductive polymer and textile used in sports applications perform poorly when used without electrolyte. Stainless steel is common, affordable, easy to process, biocompatible (selected alloys), and provides adequate ECG quality. In this paper, we study different size stainless steel dry electrodes in ECG and heart rate monitoring and compare those with commercial disposable Ag/AgCl electrodes. The results show that stainless steel dry electrodes performed well throughout the tested activities if the circular electrode diameter was 20 mm or larger.

Performance Analysis of Novel Flexible Electrodes for Wearable ECG/Heart Rate Monitoring

The development of manufacturing methods has made it possible to add metal materials as flexible electrodes into wearables. This paper presents effective methods of manufacturing custom electrodes that give reliable ECG/HR signal and maintain textile comfort. Screen-printing, micro etching and electro plating have been used to make dry electrodes that are integrated into common types of heart rate straps. Each manufacturing method of dry electrodes is related to single electrode material. The effects of different materials on signal quality are investigated. Tested materials were platinum, silver ink and stainless steel. These heart rate straps were used during rest condition, cycling, walking and running. Ten users were included (7 male and 3 female) and were measured during physical activity. Electrode performance was measured and signals were compared simultaneously with silver/silver chloride gel electrodes. In this study, platinum has the smallest signal error; therefore, it is the most appropriate of the tested materials. Followed by Ag ink, disposable Ag/AgCl and lastly stainless steel. The results obtained during exercise indicate that, all of the tested materials worked reliably with these activities and there is no statistical difference between them. The HR error % in all materials was below 20%, which was considered the limit for reliability. It can be concluded that their signal measurement reliability is adequate for sportswear and health care applications. These electrodes did not rub or the edges scratched the skin. The additional result is that they are reasonably comfortable to wear during exercising.

Global Field Power and Averaging in Measuring Somatosensory Evoked Potentials under Anesthesia

We have recorded electroencephalography during scoliosis corrective surgery from 7 channels from a patient under anesthesia. The data was used to develop a fast method to detect a response loss indicating impending neural damage. A combination global field power utilizing reference free channel derivations and averaging of the responses yields a fast responding result enabling the surgeon to make corrective procedures to the operation technique to save the patient’s nerves from permanent injury.