Kiyoko Yokoyama

Accuracy of assessment of cardiac vagal tone by heart rate variability in normal subjects

The correlations of 11 indexes of heart rate variability were examined with pharmacologically determined cardiac vagal tone in 15 normal subjects at supine rest. After sympathetic influences by intravenous propranolol were eliminated, RR interval variability was measured for 10 minutes under controlled respiration (0.25 Hz), and cardiac vagal tone was determined as the decrease in mean RR interval following complete vagal blockade with atropine. Time domain indexes (standard deviation, coefficient of variance and mean successive difference) correlated strongly with vagal tone (r = 0.87, 0.81 and 0.92, respectively; p less than 0.001 for all). The same was true for frequency domain indexes for the high-frequency (0.25 Hz) component calculated both by autoregressive spectrum analysis (square root of power and coefficient of component variance) and by fast Fourier transform (mean amplitude) (r = 0.91, 0.85 and 0.86, respectively; p less than 0.0001 for all). However, frequency domain indexes for the low-frequency spectral component (0.03 to 0.15 Hz) correlated less strongly (r = 0.69, 0.55 and 0.70, respectively), and the fraction of power [power/(total power greater than 0.03 Hz)] of both components showed no correlation. Principal component analysis showed that the first 6 indexes with strong correlations contained solely the first principal component closely related to vagal tone, whereas the remaining 5 indexes also contained the second component unrelated to vagal tone. These results indicate that most of the time and frequency domain analyses in use provides an accurate and common measure of cardiac vagal tone at rest.

Decreased magnitude of heart rate spectral components in coronary artery disease. Its relation to angiographic severity.

We analyzed the spectral components of RR interval variability under controlled respiration (15 breaths/min) in 56 patients (age range, 35-73 years) referred for coronary angiography; 14 patients had multivessel disease (group M), 21 had one-vessel disease (group S), and 21 had nonsignificant disease or normal coronary artery (group N). There were 43 healthy controls (age range, 36-71 years) (group C). The patients had no clinical evidence of heart failure, hypertension, diabetes mellitus, or acute stage of infarction and had taken no medication for 3 days. The autoregressive power spectral density of RR interval variability contains two major components, respiratory sinus arrhythmia (RSA) (0.25 Hz) and Mayer wave-like sinus arrhythmia (MWSA) (0.04-0.15 Hz), which have magnitudes that are quantitative markers of cardiac vagal activity and sympathetic activity with vagal modulation, respectively. We represented the magnitudes by the coefficient of component variance (CCV), which provided the amplitude relative to the mean RR interval. The age- and sex-adjusted mean of CCVRSA significantly decreased with advancing angiographic severity (1.64 +/- 0.09%, 1.66 +/- 0.12%, 1.22 +/- 0.13%, and 0.81 +/- 0.16% for groups C, N, S, and M, respectively) (p = 0.0001). The CCVRSA was unrelated to left ventricular function, previous myocardial infarction, or stenosis of any specific artery including the sinoatrial and atrioventricular node arteries. The CCVMWSA decreased only in group M (p = 0.0462). These results indicate that coronary artery disease is associated with vagal dominant impairment in autonomic cardiac function and that reduction in the vagal cardiac function correlates with the angiographic severity.

Short- and long-term effects of cigarette smoking on heart rate variability.

The short- and long-term effects of cigarette smoking on autonomic cardiac regulation were investigated by power spectral analysis of heart rate variability under controlled respiration (15/min). The short-term effects were examined in 9 smokers without evidence of cardiopulmonary disorders after an overnight abstinence from smoking. The heart rate spectral component reflecting the respiratory sinus arrhythmia (0.25 Hz), a quantitative index of vagal cardiac control, decreased 3 minutes after smoking 1 cigarette (p = 0.0061) and the component reflecting Mayer wave sinus arrhythmia (0.04 to 0.15 Hz), which includes sympathetically mediated activity, increased after 10 to 17 minutes (p = 0.0124). The long-term effects were examined in 81 normal subjects comprising 25 nonsmokers, 31 moderate (1 to 24 cigarettes/day) smokers and 25 heavy (greater than 25 cigarettes/day) smokers after an overnight abstinence. Although the magnitude of the Mayer wave component was unaffected by the smoking status, the respiratory component in the supine position was smaller in the young (less than or equal to 30 years) heavy smokers than in the young nonsmokers or moderate smokers (p = 0.0078). Also, postural changes in the components, a decrease in the respiratory component and an increase in the Mayer wave component with standing, were observed in the nonsmokers but not in the heavy smokers. These results suggest that smoking causes an acute and transient decrease in vagal cardiac control, and that heavy smoking causes long-term reduction in vagal cardiac control in young people and blunted postural responses in autonomic cardiac regulation.

Heart rate indication using musical data

Heart rate data reflects various physiological states such as biological workload, stress at work and concentration on tasks, drowsiness and the active state of the autonomic nervous system. This paper proposes a system to indicate heart rate using musical data. Music changes physiological states for the better by relaxing people, or contributing to patient treatment through music therapy. Information in the form of music is advantageous because it does not hinder work as does verbal information and it contains more information than warning noises. We introduce and evaluate a prototype heart rate indication system and describe evaluation results of biofeedback effects on the worker during mental workload. The prototype system sequentially inputs the instantaneous heart rate into the computer, converts the data into a musical instrument digital interface, the digital music format, and outputs it from the sound source. The system uses an ECG which can be measured easily.

Development of a feedback stimulation for drowsy driver using heartbeat rhythms

We investigated the physiological response of a vibratory stimulation, which has the rhythm of heartbeats, and examined whether it is useful for the feedback stimulation for drowsy driving. We evaluated the efficiency of 4 types of vibratory rhythms for stimulation by using the sleepiness level estimated by the multiple linear regression model made from the indices of ECG and respiration. As the result, the vibratory rhythm, which has the real time heartbeats of subjects themselves, had an effect of inducing their physiological condition closer to the condition when they were struggling against the drowsiness. We concluded that the stimulation might be useful to prevent a drowsy driving if we could give it to the driver before he or she gets the severe drowsiness.

Overcoming Drowsiness by Inducing Cardiorespiratory Phase Synchronization

Drowsiness is one of the major factors leading to car accidents. Many automobile companies and institutions have been studying ways to monitor drowsiness and keep drivers awake. When drowsiness is detected during driving, audible sound, vibrations, or messages on a display are generally used to warn the driver to concentrate on driving or to take a rest. These methods help to prevent drowsiness-related crashes to some extent, but for greater safety, methods need to be developed to physiologically overcome drowsiness. The key to overcoming drowsiness is to keep the body constantly supplied with oxygen. We focused on cardiorespiratory phase synchronization (CRPS) to recover from oxygen desaturation during drowsiness. This study found it possible to induce CRPS by paced breathing (PB) using pulse sound, which synchronized with heartbeats. The experiment results showed SpO2 measured from forehead increased during this PB. The increase in SpO2 was larger than that of yawns, deep breathing, or a period of drowsiness spontaneously reduced. In conclusion, inducing CRPS by PB using pulse sound synchronized with the heartbeat has the potential to reduce drowsiness physiologically.

Visualizing physiological condition of two persons during cooperative motion

The purpose of this study is to develop a visualizing system which represents human motion and physiological conditions such as muscle activities, autonomic nervous balances of multi persons simultaneously. Our system generates avatar animation representing muscle activity and heart rate variability of multi persons by color of muscles and heart. Three kinds of assistance motion were visualized to evaluate our system. In these experiments, muscle activity and heart rate variability of assisted and service persons were represented. Physiological conditions of multi persons are presented intuitively using this system. This visualizing system is useful for analysis of workload in cooperative motion.

Development of Health Monitoring System based on Three-dimensional Imaging using Bio-signals and Motion Data

The purpose of this study is to develop a health monitoring system. This system represents human health condition and human motion simultaneously. This system obtains motion data by optical motion capture system. Electromyogram and electrocardiogram are used for health condition estimation. These are measured synchronously with motion data. Two experiments were performed to evaluate our system. In these experiments, muscle activity, motion of the heart and the autonomic nervous balance were represented as health conditions. This system contributes intuitive recognitions of health condition and high accurate estimation of health conditions.

Real-time Continuous Estimation of Respiratory Frequency during Sleep based on Heart Rate Time Series

It is reported that frequency component (RSA)of approximately 0.25Hz of heart rate time series is corresponding to the respiratory frequency. In this paper, we proposed the continuous estimation method of respiratory fequency during sleep using the number of extreme points of heart rate time series in real time. Procedure for calculation of the method is very simple. Frequency of RSAwas calculated using the proposed method from the heart rate time series during supine rest and during sleep.lt is considered that the proposed method can be applied to respiratory monitoring system during sleep.

Verification of sleep-inducing effect by excitation apparatus simulating mother's embrace and rocking motion

Recently, the number of people who suffer from a high level of stress has increased. Too much stress may cause various physical and/or mental disorders. Moreover, sleep disorders are increasing in modern society. The aim of our project is to develop a relaxation machine for reducing stress and inducing sleep by using a rocking vibration simulating a mothers embrace and rocking motion of her baby. First, we analyzed a mothers embrace and rocking motion using a 3D motion capture system, and we evaluated the sleep-inducing effect on adults by using an excitation apparatus simulating the mothers motions.We found from the experimental analysis that there are two types of motions, both consisting of linear motion and rotational motion. The effectiveness of the rocking motion for inducing sleep was verified from brain signal analysis.