Accelerometer-based body-position sensing for ambulatory electrocardiographic monitoring

Our objective is to validate the ability of 3 appropriately placed accelerometers to determine body position during ambulatory electrocardiographic (ECG) monitoring and to demonstrate the clinical applicability of this method. During ambulatory (Holter) monitoring, the ability to know a patient's position (lying down, sitting, standing, or changing from one position to another) is important in the evaluation of common symptoms such as dizziness, palpitations, and syncope. Changes in body position are also known to alter the electrical axis of the heart, resulting in artifactual changes in QRS amplitude and ST-segment morphology. We have developed an ambulatory patient-monitoring instrument that, through the use of microfabricated accelerometers, can simultaneously record body-position information and 2 channels of ECG data. The accelerometers measure the effects of gravity and dynamic acceleration, allowing determination of a patient's orientation and movements. The accelerometer and ECG signals are input to a portable recorder and are filtered and digitized. Algorithms were developed to automatically determine body position. Ten healthy volunteers wore the device for 1 hour and followed a protocol of standing, sitting, walking, lying supine, and lying in the left and right lateral decubitus positions. An observer manually recorded times of position changes. Data were recorded and analyzed using software designed with MATLAB. The ability of the accelerometers and computer algorithms to determine body position was analyzed in terms of the sensitivity and specificity for each body position. The sensitivities for sitting, standing, walking, lying supine, lying right, and lying left were 98.8%, 99.2%, 95.5%, 99.1%, 98.9%, and 94.8%, respectively. The specificities were 99.7%, 99.4%, 99.6%, 99.0%, 99.8%, and 99.9%, respectively. The use of microfabricated accelerometers is a clinically feasible method to determine body position and can be applied to future studies correlating body position with ECG or other physiologic data.     

Numerical study to evaluate the effect of a surface-based sensor on arterial tonometry

Abstract

Arterial tonometry is a widely used non-invasive blood pressure measurement method. In contrast to the cuff-based method, it is possible to obtain a continuous pressure profile with respect to systolic and diastolic pressures using this method. However, due to a requirement of arterial tonometry—that a sensor needs to be placed directly above a blood vessel—placement error is inevitable if the measurement device is only capable of measuring local regions. This study assumed that the plate sensor is flexible, thus reducing the placement error. We investigated the pressure distribution along the wrist surface rather than the local region through the contact simulation between the flexible plate sensor and the wrist. As a result, we concluded that there is a unique pressure distribution for any specific wrist, regardless of the length and position of the plate, and that it is possible to measure the blood pressure using the response at the wrist surface to the pressure inside the radial artery.     

A Measurement of Electrocardiography and Photoplethesmography in Obese Children

The purpose of this study was to establish heart rate variability normative data on obese children and to comparing the accuracy of two medical technologies photoplethesmography (PPG) with electrocardiography (ECG) while measuring heart rate variability (HRV). PPG is a relatively new technique that holds promise for health care practitioners as an evaluative tool and biofeedback instrument due to its cost and easy administration. This study involved ten children who were recruited for an after-school program designed to reduce obesity. Three-five-minute recordings of HRV were collected while the children were lying in the supine position on a therapy bed. PPG was measured from a thumb sensor and ECG from sensors placed under wristbands on both wrists. The results indicate that PPG is as effective as ECG in measuring the eleven parameters of heart rate variability.     

The sit-up position in breast surgery

Breast shape is best evaluated while the patient is in an upright position. However, many surgeons are reluctant to have a patient sit upright during surgery because of concerns over the patient's hemodynamic instability. Therefore, the purpose of this study was to prospectively measure cardiovascular parameters, including heart rate and mean arterial pressure, in a series of 30 patients who were placed upright during various aesthetic and reconstructive breast procedures. Data regarding the number of times the patient was placed upright and the amount of time spent in the upright position were also recorded. Measurements were obtained immediately before and after elevating the head of the bed to 80 to 90 degrees during the procedure. The average supine mean arterial pressure was 73 +/- 3 mmHg and that for an upright position was 70 +/- 3 mmHg. The average supine heart rate was 73 +/- 4 beats per minute and that for an upright position was 76 +/- 4 beats per minute. Although the difference between these results is statistically significant (p < 0.05), there was no clinical significance to placing patients in an upright seated position in this study, and no patient had to be laid back down because of hemodynamic instability. Therefore, the upright seated position is strongly advocated for intraoperative evaluation of breast shape, and a safe and effective method to accomplish this is described.     

Automatic sleep/wake scoring from body motion in bed: validation of a newly developed sensor placed under a mattress

The purpose of this study was to formulate a "sleep/wake" scoring algorithm for processing activity measurements obtained using a newly developed nonwear actigraphy (NWA) device, and to test its validity. The NWA device has a highly sensitive pressure sensor and is placed under a mattress. It can continuously record the activity of a person lying on the mattress and identify an "in-bed/out-of-bed" state from the vibrations of the mattress. We formulated the sleep/wake scoring algorithm by using data obtained simultaneously by wrist actigraphy (Act) and the NWA device in 33 healthy participants. Agreement rate, sensitivity, and specificity with Act were 95.7%, 97.6%, and 75.8% (33 healthy people); the corresponding values were 85.9%, 89.1%, and 79.8% for 12 nursing home residents and 93.7%, 97.2%, and 60.8% for 60 nights for 6 healthy persons who slept 10 nights on their futons. Agreement rate, sensitivity, and specificity with polysomnography were in almost perfect agreement with Act (12 nights; 6 healthy persons who slept 2 nights). All our validation results indicate that the NWA device, placed under a mattress or a futon, can produce almost identical sleep/wake scores to Act. It is expected that the NWA device, a nonwear device for scoring sleep/wake and in-bed/out-of-bed, enables convenient long-term sleep-related evaluation in various fields, including hospital settings, home-care settings, and care facility settings such as nursing homes.     

The computer-vibromyography as a biometric progress in studying muscle function

Muscular vibrations were recorded from different relaxed and contracted skeletal muscles in human subjects, with the use of a piezo-electric device. Simultaneous wire-EMG recordings were performed. Spectral analysis of the acceleration curves (vibromyograms) disclosed muscle and function dependent compound frequency patterns. We suggest that the activity of motor units including the action of central reflex loops and oscillatory driving is mainly responsible for the muscular vibrations. Other sources are discussed. Computer-Vibromyography as a mechanical ensemble measurement supplements bioelectric EMG techniques and classical tremor analysis and provides further insights into the function of muscle and motor-system.     

Measuring very negative water potentials with polymer tensiometers: principles,performance and applications

In recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research questions are now open to experimental exploration. Furthermore, the instrument may well allow the development of more water-efficient irrigation strategies by recording water potential rather than soil water content. The principle of the sensor is to fill it with a polymer solution instead of water, thereby building up osmotic pressure inside the sensor. A high-quality ceramic allows the exchange of water with the soil while retaining the polymer. The ceramic has pores sufficiently small to remain saturated even under very negative matric potentials. Installing the sensor in an unsaturated soil causes the high pressure of the polymer solution to drop as the water potentials in the soil and in the POT equilibrate. As long as the pressure inside the polymer chamber remains sufficiently large to prevent cavitation, the sensor will function properly. If the osmotic potential in the polymer chamber can produce a pressure of approximately 2.0 MPa when the sensor is placed in water, proper readings down to wilting point are secured. Various tests in disturbed soil, including an experiment with root water uptake, demonstrate the operation and performance of the new polymer tensiometer and illustrate how processes such as root water uptake can be studied in more detail than before. The paper discusses the available data and explores the long term perspectives offered by the instrument.     

Influence of age on the immediate heart rate response to the active orthostatic test.

Dynamics of the heart rate changes following standing up from the supine position was investigated in 41 healthy men aged 20 to 59 years, classified according to the age into three groups: (22 to 26 yrs, n = 14), (33 to 49, yrs, n = 13) and (51 to 59 yrs, n = 14). The protocol consisted of twice repeated sequence: lying down-standing up-lying down. The subjects remained in each position for 8 minutes. The average and beat-to-beat heart rate (HR) were continuously calculated using the specialized computer program analysing ECG. The initial response was analysed using both the indices known from literature and newly introduced by the authors. The high reproducibility of the response was observed and the correlations between the indices were analysed. The relationship between the indices characterising the pattern of the response and age were analysed using the linear regression model. Most of these indices showed a tendency towards attenuation of the HR response with age. The closest correlation with age was found for the index characterising the initial increase of HR after standing up (r = -0.610, p < 0.001). There were no correlations between the indices of HR response to standing up and the height or body mass of the healthy subjects.     

A Novel Wearable Real-Time Sleep Apnea Detection System Based on the Acceleration Sensor

Background and objectiveThe apnea syndrome is characterized by an abnormal breath pause or reduction in the airflow during sleep. It is reported in the literature that, it affects 2% of middle-aged women and 4% of middle-aged men, approximately. This study has vital importance, especially for the elderly, the disabled, and pediatric sleep apnea patients.MethodsIn this study, a device is developed to detect apnea events to alert the patient. The device records continuously accelerations on the diaphragm by using an acceleration sensor, which is placed on the patient's diaphragm. When the apnea is detected by the accelerometer-based system, a signal is sent to the wristband, and then the vibration motor on the wristband vibrates until the patient starts breathing again. The force of the vibration motor can be adjusted according to the patients' sleep debt, especially for elderly, disabled, or pediatric patients. There is no need for a sleeping room to see the patients' breathing properties since those parameters can be stored by using the developed device on a secure digital memory card (SD) at patients' homes during sleeping.ResultsA study group were formed of 10 patients (4 males (40%) and 6 females (60%)) with different characteristics ([mean] age, 36.3; height, 169.6 cm; and body weight, 81.4 kg). The patients in the study group have sleep apnea (SA). All the apnea events were detected, and all the patients were successfully alerted. Also, the lying position, which is a significant issue, is performed in this study.ConclusionsThis work proposed using an acceleration sensor as a reliable method of sleep apnea screening, detection of an apnea event, sending alert to the patient, and detection of the patient lying position. The developed device is more economical, comfortable, and convenient than existing systems for not only the patients but also the doctors. The patients can easily use this device in their home environment.     

The effects of the distribution of training on learning feedback-assisted cardiac acceleration

In order to test a hypothesis derived from a motor skills learning model of cardiac acceleration control, groups of subjects were given biofeedback training for four sessions to learn cardiac acceleration under four different training schedules: (1) all sessions in one day, (2) daily sessions, (3) sessions every other day, and (4) weekly sessions. Ability to accelerate heart rate both with and without feedback was determined at each session. Also ability to accelerate heart rate without feedback was determined 1 week after the last training session as a measure of retention. Although there was highly significant (p less than.0001) evidence of heart rate control both with and without feedback, there were no differences in degree of control attributable to distribution of training sessions. There was, however, a trend (p less than .10) for subjects trained under the most distributed training schedule (weekly) to show more retention than subjects trained under a less distributed schedule (daily).     

中频电刺激腹股沟血管丛对下肢近端血液循环变化的初步探讨

目的:探讨中频电刺激股沟血管丛对下肢血液循环的影响.方法:32名健康男性随机分为2组,将LDF探头、热敏探头以双面胶固定在受试者右膝关节内侧上方5cm处,电流强度为感觉阈上.一组接受调制中频电刺激,另一组是对照组.刺激时间为20分钟,休息15分钟后,连续监测时间为30分钟,每5分钟为一个时间段,生理信号记录的是第一个5分钟、第三个5分钟、第五个5分钟、第六个5分钟共四次.记录指标为皮肤表面血流量、表面温度和心率变异性(HRV).结果:研究表明,皮肤表面温度、血流量、HRV的LF值随时间间隔出现明显变化,HF与LF/HF并没有显著变化;调制中频电组的部分指标与对照组有显著性差异.结论:调制中频电组效果优于空白对照组,阈上强度的中频电刺激腹股沟血管丛能够明显改善下肢血液循环,防止下肢出现水肿或麻木的情况.     

Behaviour and leg injuries in dairy cows kept in cubicle systems with straw bedding or soft lying mats

In order to reduce straw input, soft lying mats are used increasingly instead of straw bedding in cubicle systems for dairy cows. This study aimed at comparing different types of soft lying mats with straw bedding regarding cow behaviour and leg injuries. Data were collected on five farms with straw bedding and on 13 farms using four types of soft lying mats consisting of different materials. On each farm, lying behaviour of 10 cows was recorded automatically during 3 days by means of a pneumatically operated resting sensor fitted in a belt. In addition, standing up and lying down behaviour of cows was quantified by direct observations, and all cows on a given farm were checked once for leg injuries.There were no significant differences between cows kept in cubicle systems with soft lying mats and straw bedding regarding the total time spent lying per day and the number of lying bouts per day. Standing up and lying down behaviour also did not differ between cows with access to soft lying mats and straw bedding. Leg injuries were most frequent in the tarsal and carpal joints. Cows kept in cubicle systems with soft lying mats had a significantly higher incidence of both hairless patches more than 2 cm in diameter (P<0.001) and scabs or wounds less than 2 cm in diameter (P<0.001) located in the tarsal joints than cows in cubicle systems with straw bedding. With the carpal joints, on the other hand, the incidence of leg injuries did not differ significantly between these two housing conditions. In conclusion, the results of this study indicate that soft lying mats are equivalent to straw bedding in terms of cow behaviour but less favourable with respect to leg injuries located in the tarsal joints.     

Investigation of subclinical signs of autonomic neuropathy in the early stage of childhood diabetes

It has been suggested that subclinical signs of neuropathy appear earlier than microvascular complications of diabetes. To evaluate the occurrence of autonomic nervous system dysfunction in the early stage of childhood diabetes, subclinical signs of autonomic neuropathy (resting heart rate, hyperventilatory arrhythmia, standing/lying heart rate ratio, orthostatic decrease in blood pressure, and increase in blood pressure during sustained handgrip) were investigated in 54 children with type 1 diabetes divided into three groups: 14 recent-onset diabetics (3 weeks after the diagnosis), 20 diabetics in the remission phase, and 20 patients after the remission phase. 30 healthy age-matched children were used as control group. The mean resting heart rates of the diabetic groups in the remission phase and after the remission phase were significantly higher than those in the healthy control group (81.7 +/- 5/min and 88.5 +/- 6/min vs. 72.2 +/- 8/min; p less than 0.01). The hyperventilatory arrhythmia in the group of diabetic children after the remission phase in comparison with the control group was significantly decreased (29.1 +/- 4/min vs. 22.7 +/- 3/min; p less than 0.01). In a few cases of the recent-onset diabetic group, the increase in resting heart rate, the decrease in hyperventilatory arrhythmia, and the standing/lying heart rate ratio proved to be significant. In the remission phase, the same parameters showed abnormal values in one third to one fifth of the children.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of acetylcholinesterase inhibition with pyridostigmine on cardiac parasympathetic function in sedentary adults and trained athletes

Heart rate variability and postexercise heart rate recovery are used to assess cardiac parasympathetic tone in human studies, but in some cases these indexes appear to yield discordant information. We utilized pyridostigmine, an acetylcholinesterase inhibitor that selectively augments the parasympathetic efferent signal, to further characterize parasympathetic regulation of rest and postexercise heart rate. We measured time- and frequency-domain indexes of resting heart rate variability and postexercise heart rate recovery in 10 sedentary adults and 10 aerobically trained athletes after a single oral dose of pyridostigmine (30 mg) and matching placebo in randomized, double-blind, crossover trial. In sedentary adults, pyridostigmine decreased resting heart rate [from 66.7 (SD 12.6) to 58.1 beats/min (SD 7.6), P = 0.005 vs. placebo] and increased postexercise heart rate recovery at 1 min [from 40.7 (SD 10.9) to 45.1 beats/min (SD 8.8), P = 0.02 vs. placebo]. In trained athletes, pyridostigmine did not change resting heart rate or postexercise heart rate recovery when compared with placebo. Time- and frequency-domain indexes of resting heart rate variability did not differ after pyridostigmine versus placebo in either cohort and were not significantly associated with postexercise heart rate recovery in either cohort. The divergent effects of pyridostigmine on resting and postexercise measures of cardiac parasympathetic function in sedentary subjects confirm that these measures characterize distinct aspects of cardiac parasympathetic regulation. The lesser effect of pyridostigmine on either measure of cardiac parasympathetic tone in the trained athletes indicates that the enhanced parasympathetic tone associated with exercise training is at least partially attributable to adaptations in the efferent parasympathetic pathway.     

Practical do-it-yourself device for accurate volume measurement of breast

A simple and accurate method of measuring differences in breast volume based on Archimedes' principle is described. In this method, a plastic container is placed on the breast of the patient who is lying in supine position. While the breast occupies part of the container, the remaining part is filled with water and the volume is measured. This method allows the measurement of the volume differences of asymmetric breasts and also helps the surgeon to estimate the size of the prosthesis to be used in augmentation mammaplasty.     

A note on overdispersion as an index of behavioural synchrony: a pilot study in dairy cows

We developed a method for studying the synchrony of behaviour based on calculations of overdispersion of a binomial process. The lying behaviour of cows was investigated under two different housing units inside the same barn. The first unit housed 30 cows undergoing conventional milking and the second unit housed 27 cows undergoing automatic milking. The lying behaviour of the cows was observed over 3 weeks in 12 periods of 6 h each. Every 5 min, we counted the number of cows lying down in the cubicles. As external cues, like feeding and conventional milking, can promote synchrony in dairy cows, we expected that cows conventionally milked would show more behavioural synchrony than automatically milked cows. Cows lied down synchronously in both units (overdispersion 1.67, P < 0.01). Lying synchrony tended to be slightly bigger in automatically than in conventionally milked cows (overdispersion 1.76 v. 1.58, P = 0.09), although the proportion of cows lying down was on average greater in conventionally than in automatically milked cows (60.7% v. 45.6%). This suggests that synchronized lying behaviour in cows is a constant phenomenon that depends on social facilitation rather than on external cues. The overdispersion index appears to be a useful tool for studying the synchrony of animal behaviour when observations are made at the group level.     

Calibration of remotely collected acceleration data with behavioral observations of roe deer (<Emphasis Type="Italic">Capreolus capreolus</Emphasis> L.)

Long-term, remote monitoring of animals under natural conditions is essential for obtaining information on animal activity. Advances in biotelemetry have led to the construction of low-power accelerometers placed on Global Positioning System (GPS) collars. Such acceleration data from roe deer have not yet been classified to the various behavioral categories. Here, we determined the threshold values of such data for different behavioral categories. We equipped captive roe deer with Global Positioning System–Global System for Mobile Communications/dual-axis acceleration sensor neck collars and simultaneously measured their movement and observed their behavior. The difference between feeding and slow locomotion was significant on the x- but not the y-axis, and both of these two behavioral categories differed significantly from resting and fast locomotion. Specific thresholds for the behavioral categories—resting, feeding, and slow and fast locomotion—were established by recursive partitioning. We compared the behavior determined by these threshold values with observed behavior and found that 92% of the behavioral categories were correctly assigned. A comparison of our results with those of earlier studies showed that thresholds derived for one species cannot be directly applied to another species. We provide recommendations for the further development of acceleration sensors based on the results obtained in this study.     

Design and demonstration of a new instrumented spatial linkage for use in a dynamic environment: application to measurement of ankle rotations during snowboarding

Joint injuries during sporting activities might be reduced by understanding the extent of the dynamic motion of joints prone to injury during maneuvers performed in the field. Because instrumented spatial linkages (ISLs) have been widely used to measure joint motion, it would be useful to extend the functionality of an ISL to measure joint motion in a dynamic environment. The objectives of the work reported by this paper were to (i) design and construct an ISL that will measure dynamic joint motion in a field environment, (ii) calibrate the ISL and quantify its static measurement error, (iii) quantify dynamic measurement error due to external acceleration, and (iv) measure ankle joint complex rotation during snowboarding maneuvers performed on a snow slope. An "elbow-type" ISL was designed to measure ankle joint complex rotation throughout its range (+/-30 deg for flexion/extension, +/-15 deg for internal/external rotation, and +/-15 deg for inversion/eversion). The ISL was calibrated with a custom six degree-of-freedom calibration device generally useful for calibrating ISLs, and static measurement errors of the ISL also were evaluated. Root-mean-squared errors (RMSEs) were 0.59 deg for orientation (1.7% full scale) and 1.00 mm for position (1.7% full scale). A custom dynamic fixture allowed external accelerations (5 g, 0-50 Hz) to be applied to the ISL in each of three linear directions. Maximum measurement deviations due to external acceleration were 0.05 deg in orientation and 0.10 mm in position, which were negligible in comparison to the static errors. The full functionality of the ISL for measuring joint motion in a field environment was demonstrated by measuring rotations of the ankle joint complex during snowboarding maneuvers performed on a snow slope.     

Reduction in extracellular muscle volume increases heart rate and blood pressure response to isometric exercise

To investigate the effect of local dehydration on heart rate and blood pressure during static exercise, six healthy male subjects performed exercise of the calf muscles with different extracellular volumes of the working muscles. Exercise consisted of 5 min of static calf muscle contractions at about 10% of maximal voluntary contraction. The body position during exercise was identical in all tests, i.e. supine with the knee joint 90 degrees flexed. During a 25-min pre-exercise period three different protocols were employed to manipulate the calf volume. In test A the subjects rested in the exercise position; in test B the body position was the same as in A but calf volumes were increased by venous congestion [cuffs inflated to 10.67 kPa (80 mmHg)]; in test C the calf volumes were decreased by lifting the calves about 40 cm above heart level with the subjects supine. To clamp the changed calf volumes in tests B and C, cuffs were inflated to 300 mmHg 5 min before the onset of exercise. This occlusion was maintained for 1 min after the termination of exercise. Compared to tests A and B, the reduced volume of test C led to significant increases in heart rate and blood pressure during exercise. Oxygen uptake did not exceed resting levels in tests B and C until the cuffs were deflated, indicating that only calf muscles contributed to the neurogenic peripheral drive. It is concluded that extracellular muscle volume plays a significant role in adjusting heart rate and blood pressure during static exercise.     

Behavior, episodic secretion of cortisol, and adrenocortical reactivity in bulls subjected to tethering

To study the effect of individual housing on behavior and adrenocortical activity, eight bulls were moved to a novel housing environment and subjected to 5 weeks of tethering in individual stanchions with a concrete and partially slatted floor. During the first and fourth week, resting behavior and episodic cortisol secretion were analyzed over two 24-hr periods and compared to those of eight control bulls kept free on deep straw. In addition, in the fifth week adrenocortical reactivity after ACTH(1-24) stimulation was analyzed in all subjects. Resting behavior was markedly influenced by type of housing. Although duration of lying down over 24 hr was similar in tethered and control bulls, the number of periods of lying down was significantly reduced and the frequency of investigating the lying area prior to lying down was significantly increased in tethered bulls. In the first week of study, the cortisol secretory patterns of experimental and control bulls differed. The frequency of secretory episodes was significantly reduced, and the mean amplitude of the episodes increased, though not significantly in experimental compared with control bulls. After 4 weeks of tethering, however, the secretory pattern had returned to levels similar to those of control bulls. Despite this return of the basic cortisol secretion, adrenocortical reactivity after a high dosage of ACTH(1-24) was significantly reduced in tethered bulls. The results suggest that an adaptation to tethering at the brain-pituitary level does not occur, but that the return of the basal cortisol secretion could be due to changes at the adrenocortical level.