Pulse rate variability estimation method based on imaging-photoplethysmography and application to telepsychiatry

The worldwide adoption of telehealth services may benefit people who otherwise would not be able to access mental health support. In this paper, we present a novel algorithm to obtain reliable pulse and respiration signals from non-contact facial image sequence analysis. The proposed algorithm involved a skin pixel extraction method in the image processing part and signal reconstruction using the spectral information of RGB signal in the signal processing part. The algorithm was tested on 15 healthy subjects in a laboratory setting. The results show that the proposed algorithm can accurately monitor respiration rate (RR), pulse rate (PR), and pulse rate variability (PRV) in rest conditions.Clinical Relevance- The main achievement of this study is enabling non-contact PR and RR signal extraction from facial image sequences, which has potential for future use and support for psychiatrists in telepsychiatry.

Remote sensing of vital signs by medical radar time-series signal using cardiac peak extraction and adaptive peak detection algorithm: Performance validation on healthy adults and application to neonatal monitoring at an NICU

BACKGROUND AND OBJECTIVE

Continuous monitoring of vital signs plays a pivotal role in neonatal intensive care units (NICUs). In this paper, we present a system for monitoring fully non-contact medical radar-based vital signs to measure the respiratory rate (RR), heart rate (HR), I:E ratio, and heart rate variability (HRV). In addition, we evaluated its performance in a physiological laboratory and examined its adaptability in an NICU.

METHODS

A non-contact medical radar-based vital sign monitoring system that includes 24 GHz radar installed in an incubator was developed. To enable reliable monitoring, an advanced signal processing algorithm (i.e., a nonlinear filter to separate respiration and heartbeat signals from the output of radar), template matching to extract cardiac peaks, and an adaptive peak detection algorithm to estimate cardiac peaks in time-series were proposed and implemented in the system. Nine healthy subjects comprising five males and four females (24 ± 5 years) participated in the laboratory test. To evaluate the adaptability of the system in an NICU setting, we tested it with three hospitalized infants, including two neonates.

RESULTS

The results indicate strong agreement in healthy subjects between the non-contact system and reference contact devices for RR, HR, and inter-beat interval (IBI) measurement, with correlation coefficients of 0.83, 0.96, and 0.94, respectively. As anticipated, the template matching and adaptive peak detection algorithms outperformed the conventional approach. These showed a more accurate IBI close to the reference Bland-Altman analysis (proposed: bias of -3 ms, and 95% limits of agreement ranging from -73 to 67 ms; conventional: bias of -11 ms, and 95% limits of agreement ranging from -229 to 207 ms). Moreover, in the NICU clinical setting, the IBI correlation coefficient and 95% limit of agreement in the conventional method are 0.31 and 91 ms. The corresponding values obtained using the proposed method are 0.93 and 21 ms.

CONCLUSION

The proposed system introduces a novel approach for NICU monitoring using a non-contact medical radar sensor. The signal processing method combining cardiac peak extraction algorithm with the adaptive peak detection algorithm shows high adaptability in detecting IBI the time series in various application settings.

An mHealth App for the Non-contact Measurement of Pulmonary Function Using the Smartphone's Built-in Depth Sensor

The use of smartphones in clinical practice is referred to as mobile health (mHealth). This has attracted great interest in both academia and industry because of its potential to augment healthcare. In this study, we developed an mHealth app for the non-contact measurement of chest-wall movements using the iPhone ' s built-in depth sensor, thereby enabling a pulmonary self-monitoring function for personal use. The depth sensor provides depth values for each pixel and 2D mapping of the chest-wall movements. To extract respiratory signals from the right and left thoracic regions and abdomen, a 2D-depth image-segmentation method was implemented. The method was based on the anatomy and physiology of chest-wall movements, assuming differences in the anterior displacement in the thoracic and abdominal regions. It was observed that the differences were significant in the segmented regions of interest (ROIs) of the right and left thoracic region and abdomen. Respiratory signals extracted from each ROI were compared with the contact bio-impedance signals, which were highly correlated (r=0.94).

Design and Evaluation of Digital Filters for Non-Contact Measuring of HRV using Medical Radar and Its Application in Bedside Patient Monitoring System

A non-contact bedside monitoring system using medical radar is expected to be applied to clinical fields. Our previous studies have developed a monitoring system based on medical radar for measuring respiratory rate (RR) and heart rate (HR). Heart rate variability (HRV), which is essentially implemented in advanced monitoring system, such as prognosis prediction, is a more challenging biological information than the RR and HR. In this study, we designed a HRV measurement filter and proposed a method to evaluate the optimal cardiac signal extraction filter for HRV measurement. Because the cardiac component in the radar signal is much smaller than the respiratory component, it is necessary to extract the cardiac element from the radar output signal using digital filters. It depends on the characteristics of the filter whether the HRV information is kept in the extracted cardiac signal or not. A cardiac signal extraction filter that is not distorted in the time domain and does not miss the cardiac component must be adopted. Therefore, we focused on evaluating the interval between the R-peak of the electrocardiogram (ECG) and the radar-cardio peak of the cardiac signal measured by radar (R-radar interval). This is based on the fact that the time between heart depolarization and ventricular contraction is measured as the R-radar interval. A band-pass filter (BPF) with several bandwidths and a nonlinear filter, locally projective adaptive signal separation (LoPASS), were analyzed and compared. The optimal filter was quantitatively evaluated by analyzing the distribution and standard deviation of the R-radar intervals. The performance of this monitoring system was evaluated in elderly patient at the Yokohama Hospital, Japan.

Proof-of-principle Experiment on 24 GHz Medical Radar for Non-contact Vital Signs Measurement

Medical radar for non-contact vital signs measurement exhibits great potential in both clinical and home healthcare settings. Especially during the corona virus spreading time, non-contact sensing more clearly shows the advantages. Many previous studies have concentrated on medical radar-based healthcare applications, but pay less attention to the working principles. A clear understanding of medical radars at both the mathematical and physical levels is critically important for developing application-specific signal processing algorithms. Therefore, this study aims to re-define the operating principle of radar, and a proof-of-principle experiment was performed on both actuator and human subjects using 24 GHz Doppler radar system. Experimental results indicate that there is a difference in the radar output signals between the two cases, where the displacement is greater than and less than half of the wavelength. For the former situation, the displacement x = n.λ/2 (n ≥ 1), one peak of radar signals corresponds to n peaks of baseband signals. By contrast, for the latter situation, the displacement x < λ/2, one peak of radar signals corresponds to one peak of baseband signals. Strikingly, with human measurement on the dorsal side, the the number of respiration peaks are seen from the radar raw signals.

Non-contact Measurement of Pulse Rate Variability Using a Webcam and Application to Mental Illness Screening System

The COVID-19 pandemic is a global health crisis. Mental health is critical in such uncertain situations, particularly when people are required to significantly restrict their movements and change their lifestyles. Under these conditions, many countries have turned to telemedicine to strengthen and expand mental health services. Our research group previously developed a mental illness screening system based on heart rate variability (HRV) analysis, enabling an objective and easy mental health self-check. This screening system cannot be used for telemedicine because it uses electrocardiography (ECG) and contact photoplethysmography (PPG), that are not widely available outside of a clinical setting. The purpose of this study is to enable the extension of the aforementioned system to telemedicine by the application of non-contact PPG using an RGB webcam, also called imaging- photoplethysmography (iPPG). The iPPG measurement errors occur due to changes in the relative position between the camera and the target, and due to changes in light. Conventionally, in image processing, the pixel value of the entire face region is used. We propose skin pixel extraction to eliminate blinks, eye movements, and changes in light and shadow. In signal processing, the green channel signal is conventionally used as a pulse wave owing to the absorption characteristics of blood flow. Taking advantage of the fact that the red and blue channels contain noise, we propose a signal reconstruction method for removing noise and strengthening the signal in the pulse rate variability (PRV) frequency band by weighting the three signals of the RGB camera. We conducted an experiment with 13 healthy subjects, and showed that the PRV index and pulse rate (PR) errors estimated by the proposed method were smaller than those of the conventional method. The correlation coefficients between estimated values by the proposed method and reference values of LF, HF, and PR were 0.86, 0.69, and 0.96, respectively.

A Non-contact Spirometer with Time-of-Flight Sensor for Assessment of Pulmonary Function

Assessment of pulmonary function is vital for early detection of chronic diseases such as chronic obstructive pulmonary disease (COPD) in home healthcare. However, monitoring of pulmonary function is often omitted owing to the heavy burden that the use of specific medical devices places on the patients. In this study, we developed a non-contact spirometer using a time-of-flight sensor that measures very small displacements caused by chest wall motion during breathing. However, this sensor occasionally failed when estimating the values from breathing waveforms because their shape depends on the subject test experience. As a result, further measurements were required to address motion artifacts. To accomplish high accuracy estimation in the face of these factors, we developed methods to estimate parameters from a part of the waveform and remove outliers from multiple-region measurements. According to laboratory experiments, the proposed system achieved an absolute error of 5.26 % and a correlation coefficient of 0.88. This study also addressed the limitations of depth sensor measurements, thereby contributing to the implementation of high-accuracy COPD screening.

Infection Screening System Using Thermography and CCD Camera with Good Stability and Swiftness for Non-contact Vital-Signs Measurement by Feature Matching and MUSIC Algorithm

Screening systems for infectious diseases based on fever have been implemented at international airports to prevent the spread of infection for over a decade. Currently, only Infrared Thermography (IRT) is used for screening and measuring facial skin temperature, which is one of clinical indicators of potential infection. Aiming at higher accuracy in screening, our group adopted heart rate (HR) and respiration rate (RR) for the first time as the new screening parameters. In our previous study, we proposed a screening system based on dual image sensors, which include IRT and a charged-coupled devices (CCD) camera. The sensors can measure three vital signs simultaneously, namely HR, RR, and facial skin temperature. For the measurement of RR in this system, stability and swiftness must be applied for application in airports. In this study, we introduce feature matching and multiple signal classification (MUSIC) algorithm in this system. Feature matching between thermal images and RGB images captured by a CCD camera and IRT, respectively, is used to detect the nose and mouth in IRT, which helps extract respiration signals corresponding to airflow from breathing. In addition, the MUSIC algorithm improves the accuracy of RR frequency estimations in limited time respiration signal and achieves swiftness. The proposed method improves stability by simultaneously detecting the nose and mouth in thermal images, and enhances the accuracy of estimated RR using the MUSIC algorithm. By using this system, we evaluate the accuracy of the estimated vital signs. The performance of this screening system was evaluated using data obtained from 12 influenza patients and 13 healthy subjects at a clinical facility in Fukushima, Japan.

Non-contact monitoring of heart rate variability using medical radar for the evaluation of dynamic changes in autonomic nervous activity during a head-up tilt test

Electrocardiography (ECG) is a mandatory standard for monitoring electrical activity of the heart in many clinical settings such as intensive care and emergency units. However, in situations wherein the skin is damaged, such as acute burn injuries, it is impossible to efficiently attach electrodes to the skin. In this study, we developed a non-contact cardiac monitoring system using a 24-GHz medical radar for directly measuring the beat-to-beat heart mechanical activity at a distance from a subject. The heart rate variability (HRV) was analysed using an autoregressive model (AR) from the measured beat-to-beat intervals during a head-up tilt test. To investigate the feasibility of the proposed system, we compared medical radar and ECG recording by using Lin's correlation coefficient and Bland-Altman analysis, which showed a negligible mean difference from the substantial agreement of Lin's correlation coefficient of 0.9 between the radar and ECG. The non-contact radar clearly monitored dynamic changes in HRV indices induced by the head-up tilt test. This type of non-contact HRV-sensing technique as an alternative approach has significant potential for advancing personal healthcare in both clinical and out-of-hospital settings.

Stable Contactless Sensing of Vital Signs Using RGB-Thermal Image Fusion System with Facial Tracking for Infection Screening

Infrared thermography (IRT) has been used to screen febrile passengers in international airports for over a decade. However, fever-based infection screening using IRT suffered from low sensitivity because measurements can be affected by ambient temperature, humidity, etc. In our previous study, we proposed an RGB-thermal image fusion system to measure vital signs i.e., the RGB camera detects tiny changes in color from facial skin, associated with blood flow, to estimate heart rate, and IRT senses temperature changes around the nasal area, caused by respiration, to measure respiratory rate). The inclusion of heart and respiratory rates lead to increased screening accuracy. In the present study, to promote the widespread use of our system in real-world settings, a face detection and tracking method was developed and implemented into the system, thereby enabling the accurate and stable measurement of vital signs. We assessed heart and respiratory rate estimation via an RGB-thermal image fusion system using Bland-Altman plots and statistical analysis.

Extracting Cardiac Information From Medical Radar Using Locally Projective Adaptive Signal Separation

Electrocardiography is the gold standard for electrical heartbeat activity, but offers no direct measurement of mechanical activity. Mechanical cardiac activity can be assessed non-invasively using, e.g., ballistocardiography and recently, medical radar has emerged as a contactless alternative modality. However, all modalities for measuring the mechanical cardiac activity are affected by respiratory movements, requiring a signal separation step before higher-level analysis can be performed. This paper adapts a non-linear filter for separating the respiratory and cardiac signal components of radar recordings. In addition, we present an adaptive algorithm for estimating the parameters for the non-linear filter. The novelty of our method lies in the combination of the non-linear signal separation method with a novel, adaptive parameter estimation method specifically designed for the non-linear signal separation method, eliminating the need for manual intervention and resulting in a fully adaptive algorithm. Using the two benchmark applications of (i) cardiac template extraction from radar and (ii) peak timing analysis, we demonstrate that the non-linear filter combined with adaptive parameter estimation delivers superior results compared to linear filtering. The results show that using locally projective adaptive signal separation (LoPASS), we are able to reduce the mean standard deviation of the cardiac template by at least a factor of 2 across all subjects. In addition, using LoPASS, 9 out of 10 subjects show significant (at a confidence level of 2.5%) correlation between the R-T-interval and the R-radar-interval, while using linear filters this ratio drops to 6 out of 10. Our analysis suggests that the improvement is due to better preservation of the cardiac signal morphology by the non-linear signal separation method. Hence, we expect that the non-linear signal separation method introduced in this paper will mostly benefit analysis methods investigating the cardiac radar signal morphology on a beat-to-beat basis.

Twenty-four-hour continuous and remote monitoring of respiratory rate using a medical radar system for the early detection of pneumonia in symptomatic elderly bedridden hospitalized patients

Respiratory rate is often measured manually and discontinuously by counting of chest wall movements in routine clinical practice. We introduce a novel approach to investigate respiration dynamics using a noncontact medical radar system for identifying patient at risk of infection. The system enables early detection of pneumonia in bedridden hospitalized patients.

Simple and objective screening of major depressive disorder by heart rate variability analysis during paced respiration and mental task conditions

Since objective biomarkers for major depressive disorder (MDD) are not readily available, clinical psychiatrists diagnose patients with MDD subjectively based on clinical interviews and diagnostic criteria. It often raises various concerns, including false responses by patients, subjective factors, and inexperience of the attendants leading to incorrect diagnosis. Here, we developed a self-monitoring system for simple and objective screening of MDD using a photoplethysmography (PPG) sensor and a 24-GHz microwave radar, which was based on the analysis of heart rate variability (HRV) during paced respiration and mental task conditions. In our previous study, we assessed the reactivity of HRV measurements during a mental task (random number generation) condition in patients with MDD and healthy control subjects. The HRV indices are less reactive in patients with MDD compared to healthy subjects during the mental task, which enabled us to identify the patients at risk for depression. In this study, the reactivity of HRV was measured not only in the mental task but also during paced respiration (i.e., 5-s inhalation and 5-s exhalation) conditions, thereby assessing more detailed autonomic nervous system (ANS) activity via HRV indices. To investigate the effect of paced respiration on MDD screening, we compared the ANS activity via HRV indices in with/without paced respiration conditions in 28 drug-naïve patients with MDD and 27 healthy control subjects. The result showed that ANS significantly activated during the paced respiration condition (p<;0.05). The sensitivity in detecting patients with MDD was 86% under paced respiration and mental task conditions, which was higher than the sensitivity (68%) under mental task condition alone.

Applications of Infrared Thermography for Noncontact and Noninvasive Mass Screening of Febrile International Travelers at Airport Quarantine Stations

Infrared thermography (IRT), one of the most valuable tools, is used for noncontact, noninvasive, and rapid monitoring of body temperature; this has been used for mass screening of febrile travelers at places such as airport quarantine stations for over 10 years after the 2003 severe acute respiratory syndrome (SARS) outbreak. The usefulness of thermography for mass screening has been evaluated in many recent studies; its sensitivity varies from 40 to 89.4% under various circumstances. In this chapter, we perform IRT evaluations for detecting febrile international travelers entering Japan at Nagoya Airport, immediately after the SARS epidemic, from June 2003 to February 2004, and at Naha International Airport from April 2005 to March 2009. The correlation of body surface temperature measured via thermography with the axillary temperature was significant. Through IRT, febrile individuals were detected with good accuracy and the detection accuracy was improved by corroborating surveillance with self-reporting questionnaires. However, there are several limitations associated with the use of IRT for fever screening. For instance, taking antifebrile medications results in rapid modification of the body temperature and directly affects the efficiency of IRT. To solve this unreliability and obtain higher accuracy in mass screening, we have developed a novel infection screening system using multisensor data, i.e., heart and respiration rates are determined by microwave radar in noncontact manner and facial skin temperature is monitored through IRT. The detection accuracy of the system improved, which is notably higher compared to the conventional screening method using only IRT.

Remote sensing of multiple vital signs using a CMOS camera-equipped infrared thermography system and its clinical application in rapidly screening patients with suspected infectious diseases

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Remotely monitoring multiple vital signs is proposed for rapid infection screening.

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Vital-sign-based infrared thermography is more sensitive than conventional systems.

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The proposed method will provide an alternative to conventional screening.

Background

Infrared thermography (IRT) is used to screen febrile passengers at international airports, but it suffers from low sensitivity. This study explored the application of a combined visible and thermal image processing approach that uses a CMOS camera equipped with IRT to remotely sense multiple vital signs and screen patients with suspected infectious diseases.

Methods

An IRT system that produced visible and thermal images was used for image acquisition. The subjects’ respiration rates were measured by monitoring temperature changes around the nasal areas on thermal images; facial skin temperatures were measured simultaneously. Facial blood circulation causes tiny color changes in visible facial images that enable the determination of the heart rate. A logistic regression discriminant function predicted the likelihood of infection within 10 s, based on the measured vital signs. Sixteen patients with an influenza-like illness and 22 control subjects participated in a clinical test at a clinic in Fukushima, Japan.

Results

The vital-sign-based IRT screening system had a sensitivity of 87.5% and a negative predictive value of 91.7%; these values are higher than those of conventional fever-based screening approaches.

Conclusions

Multiple vital-sign-based screening efficiently detected patients with suspected infectious diseases. It offers a promising alternative to conventional fever-based screening.

An Objective Screening Method for Major Depressive Disorder Using Logistic Regression Analysis of Heart Rate Variability Data Obtained in a Mental Task Paradigm

BACKGROUND AND OBJECTIVES

Heart rate variability (HRV) has been intensively studied as a promising biological marker of major depressive disorder (MDD). Our previous study confirmed that autonomic activity and reactivity in depression revealed by HRV during rest and mental task (MT) conditions can be used as diagnostic measures and in clinical evaluation. In this study, logistic regression analysis (LRA) was utilized for the classification and prediction of MDD based on HRV data obtained in an MT paradigm.

METHODS

Power spectral analysis of HRV on R-R intervals before, during, and after an MT (random number generation) was performed in 44 drug-naïve patients with MDD and 47 healthy control subjects at Department of Psychiatry in Shizuoka Saiseikai General Hospital. Logit scores of LRA determined by HRV indices and heart rates discriminated patients with MDD from healthy subjects. The high frequency (HF) component of HRV and the ratio of the low frequency (LF) component to the HF component (LF/HF) correspond to parasympathetic and sympathovagal balance, respectively.

RESULTS

The LRA achieved a sensitivity and specificity of 80.0 and 79.0%, respectively, at an optimum cutoff logit score (0.28). Misclassifications occurred only when the logit score was close to the cutoff score. Logit scores also correlated significantly with subjective self-rating depression scale scores (p < 0.05).

CONCLUSION

HRV indices recorded during a MT may be an objective tool for screening patients with MDD in psychiatric practice. The proposed method appears promising for not only objective and rapid MDD screening but also evaluation of its severity.

Effects of antimuscarinic drugs on both urinary frequency and cognitive impairment in conscious, nonrestrained rats

Recent studies indicate a risk of learning and memory impairments when patients with senile dementia are treated with antimuscarinic drugs. In this study, we compared the effectiveness of propiverine hydrochloride (propiverine) and oxybutynin chloride (oxybutynin) on the increased urinary frequency and cognitive impairment induced by nucleus basalis magnocellularis (nBM) lesioning in conscious and nonrestrained rats. For examination of bladder function, nBM-lesioned rats were given total parenteral nutrition regimens for 8 days. Propiverine administered orally at 0.3, 3 and 30 mg/kg on the postoperative day 7 significantly lessened the increase in the frequency of voiding caused by the nBM lesion, whereas oxybutynin administration did not show any improvement at 0.1 or 1 mg/kg but did so at 10 mg/kg. To examine the memory impairment, we trained nBM-lesioned rats in an 8-arm radial maze task for 20 days and then evaluated the effectiveness of oral drug administration on 19th and 20th radial maze performance. The higher rate of errors caused by nBM lesioning was significantly aggravated by oxybutynin at 30 and 100 mg/kg. Propiverine showed slight aggravation of errors, but with no statistical significance at any dose, 30, 100 or 300 mg/kg. These results suggest that propiverine has comparatively less effect on the cognitive impairment than oxybutynin.

Cardioprotective effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor, on cardiac dysfunction induced by ischemia/reperfusion in isolated rat hearts

Inhibition of fatty acid metabolite accumulation may be beneficial for treatment of cardiac dysfunction induced by ischemia. MET-88, 3-(2,2,2-trimethylhydrazinium)propionate dihydrate, inhibits gamma-butyrobetaine hydroxylase which catalyzes conversion of gamma-butyrobetaine to carnitine. In this study, we investigated whether MET-88 has cardioprotective effects against cardiac dysfunction induced by ischemia/reperfusion. Rats were divided into four groups: (1) control; (2) MET-88 at 50 mg/kg; (3) MET-88 at 100 mg/kg; (4) nifedipine at 30 mg/kg. MET-88 was administered orally once a day for 10 days, and nifedipine was administered orally 30 min before the experiments. Cardiac functions (heart rate, left ventricular systolic pressure and coronary flow) were measured in rat working heart preparations for 30 min under ischemia followed by 20 min under reperfusion. Myocardial carnitine levels were measured at the end of the experiments. Before ischemia, MET-88 did not affect cardiac functions, but nifedipine significantly increased only coronary flow. Under the ischemic condition, cardiac functions were markedly decreased in all groups. During reperfusion, MET-88 and nifedipine promoted recovery of cardiac functions and decreased the incidence of ventricular fibrillation. MET-88 also prevented the accumulation of long-chain acylcarnitine induced by ischemia. These results indicated that MET-88 protected against cardiac dysfunction in ischemia/reperfusion, and preventing the accumulation of long-chain acylcarnitine may be responsible for the cardioprotective effects.

Inhibition of carnitine synthesis modulates protein contents of the cardiac sarcoplasmic reticulum Ca2+-ATPase and hexokinase type I in rat hearts with myocardial infarction

It was previously reported that inhibition of carnitine synthesis by 3-(2,2,2-trimethyl-hydrazinium) propionate (MET-88) restores left ventricular (LV) systolic and diastolic function in rats with myocardial infarction (MI). Preservation of the calcium uptake function of sarcoplasmic reticulum Ca2+-ATPase (SERCA2) is one of the possible mechanisms by which MET-88 alleviates hemodynamic dysfunction. To test this hypothesis, the effects of MET-88 on protein content of SERCA2 were evaluated using the same rat model of heart failure. Myocardial protein content of hexokinase, which is one of the key enzymes of glucose utilization, was also measured. Either MET-88 (MET-88 group) or a placebo (MI group) was administered for 20 days to rats with MI induced by coronary artery ligation. The control group underwent sham surgery (no ligation) and received placebo. In LV myocardial homogenates, the myocardial SERCA2 protein content was 32% lower (p<0.05) in the MI group than in the control group. However, in the MET-88 group myocardial SERCA2 content was the same as in the control group. Hexokinase I protein content was 29 % lower (p<0.05) in the MI group compared with the control. In contrast, hexokinase II protein content did not differ significantly among the three groups. Consequently, inhibition of carnitine synthesis ameliorates depression of SERCA2 and hexokinase I protein content which may reduce tissue damage caused by MI.

Effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor, on tissue carnitine and lipid levels in rats

MET-88, 3-(2,2,2-trimethylhydrazinium) propionate, suppresses carnitine synthesis by inhibiting (gamma-butyrobetaine hydroxylase. The purpose of this study was to clarify the effects of suppression of carnitine synthesis on carnitine and lipid contents in tissues. MET-88 (50, 100, 200 or 400 mg/kg/d) was administered orally to male SD rats for 10, 30 or 60 d. Total carnitine and lipid (triglycerides, non-esterified fatty acids) contents were measured in heart and liver. In both tissues, treatment with MET-88 dose-dependently decreased total carnitine levels, and the reduction reached the plateau state after 30 d at each dose. MET-88 had no effect on lipid content in the heart, but increased the lipid content in the liver at the highest doses. Treatment with MET-88 at 400 mg/kg for 60 d resulted in no pathologic findings in the histological study, and also had no effect on parameters of liver function such as glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase as judged from the results of blood biochemical analysis. We concluded that long-term treatment with MET-88 decreased the carnitine content to a constant level in both heart and liver, but had no effect on lipid contents in the heart, although it affected lipid metabolism in the liver.

MET-88, a gamma-butyrobetaine hydroxylase inhibitor, improves cardiac SR Ca2+ uptake activity in rats with congestive heart failure following myocardial infarction

We previously reported that MET-88, 3-(2,2,2-trimethylhydrazinium) propionate, improved left ventricular diastolic dysfunction induced by congestive heart failure (CHF) in rats. The present study was designed to investigate the mechanism by which MET-88 improved the cardiac relaxation impaired in CHF rats. The left coronary artery of the animals was ligated, and the rats were then orally administered vehicle (control), MET-88 at 50 or 100 mg/kg or captopril at 20 mg/kg for 20 days. Myocytes were isolated from the non-infarcted region in the left ventricle, and cell shortening and [Ca2+]i transients were measured with a video-edge detector and by fluorescence analysis, respectively. In CHF control rats, the diastolic phase of cell shortening was prolonged compared with that of the sham-operated (sham) rats. This prolongation was prevented by treatment with MET-88 at 100 mg/kg or captopril at 20 mg/kg. CHF control rats also showed an increase in the decay time of [Ca2+]i transients compared with sham rats. MET-88 at 100 mg/kg and captopril at 20 mg/kg attenuated the increase in decay time of [Ca2+]i transients. Ca2+ uptake activity of the sarcoplasmic reticulum (SR) isolated from the non-infarcted region in the left ventricle was measured, and Lineweaver-Burk plot analysis of the activity was performed. CHF control rats revealed a decrease in the Vmax for SR Ca2+ uptake activity without alteration in Kd. MET-88 at 100 mg/kg significantly prevented the decrease in Vmax, but had no effect on Kd. Also, treatment with MET-88 at 100 mg/kg improved myocardial high-energy phosphate levels impaired in CHF rats. These results suggest that one of the mechanisms by which MET-88 improved cardiac relaxation in CHF rats is based on the amelioration of [Ca2+]i transients through increase of SR Ca2+ uptake activity.

Beneficial effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor in rats with heart failure following myocardial infarction

Myocardial ischemia can cause myocardial infarction and as a consequence, heart failure. 3-(2,2,2-trimethylhydrazinium) propionate (MET-88) inhibits gamma-butyrobetaine hydroxylase and has cardioprotective effects on the ischemic heart. We now examined the effects of MET-88 in rats with congestive heart failure following myocardial infarction. Congestive heart failure was produced by left coronary artery ligation in rats. MET-88 at 100 mg/kg/day was orally administered from the 2nd day after surgery. We performed a survival study for 181 days, and measured ventricular remodeling, cardiac function, and myocardial high-energy phosphate levels after treatment for 20 days. MET-88 prolonged survival with a median 50% survival of 103 days compared to 79 days for the heart-failure control rats. The expansion of the left ventricular cavity (ventricular remodeling) in heart-failure rats was prevented by treatment with MET-88, and the effect of MET-88 was similar to that of captopril at 20 mg/kg. MET-88 attenuated the rise in right atrial pressure in heart-failure rats and augmented cardiac functional adaptability against an increased load. Also, MET-88 improved the myocardial energy state in heart-failure rats. The present results indicate that MET-88 improves the pathosis in rats with heart failure induced by myocardial infarction.

Beneficial effects of MET-88 on left ventricular dysfunction and hypertrophy with volume overload in rats

We examined the effects of MET-88 on haemodynamics and cardiac hypertrophy in rats with an aortocaval shunt (A-V shunt). On the day of surgery, an A-V shunt was produced by using an 18-gauge needle in Wistar rats as described by Garcia and Diebold. MET-88 and captopril were orally administered to rats 1 week after surgery, and the administration was continued for 3 weeks. Four weeks after the surgery, A-V shunt-operated rats had biventricular hypertrophy and higher right atrial pressure (RAP) and left ventricular end-diastolic pressure (LVEDP) than sham-operated rats. Compared with untreated A-V shunt rats, those treated with MET-88 showed significant attenuation of the development of left ventricular (LV) hypertrophy and of the increased LVEDP. Captopril-treated A-V shunt rats also failed to show increases in LV weight and LVEDP. In in vitro studies, MET-88 had no effect on renin and angiotensin-converting enzyme (ACE) activities in the plasma of normal rats. These results suggest that MET-88 improved LV hypertrophy and LV dysfunction in rats with an A-V shunt. Furthermore, the data indicate that the beneficial effects of MET-88 may be attributed to some pathway, not involving the renin-angiotensin system, such as myocardial energy metabolism, venous return, etc. We conclude that MET-88 may be a novel agent for the therapy of chronic heart failure.

Cardioprotective profile of MET-88, an inhibitor of carnitine synthesis, and insulin during hypoxia in isolated perfused rat hearts

3-(2,2,2-trimethylhydrazinium) propionate (MET-88) is an inhibitor of carnitine synthesis. This study was carried out to investigate whether or not reduction of carnitine content could attenuate hypoxic damage in isolated perfused rat hearts. Rats were divided into four groups: 1) vehicle control; 2) pretreatment with MET-88 (MET-88); 3) application of insulin (500 muU/mL) in the perfusate (insulin); and 4) pretreatment with MET-88 and application of insulin (MET-88 + insulin). MET-88 (100 mg/kg) was orally administered once a day for 10 days until the day before the experiments. Hearts were initially perfused for a 10 min period under normoxia, followed by a 30 min period under hypoxia. Hearts were frozen at the end of hypoxia for the measurement of high-energy phosphates, carnitine derivatives, and glycolysis intermediates. In a separate series of untreated and MET-88 treated hearts, exogenous glucose and palmitate oxidation was measured. MET-88 decreased the extent of the depression of cardiac contractility (+dP/dt), and aortic flow during the hypoxic state. Insulin also improved cardiac function, and co-treatment of MET-88 and insulin additionally improved cardiac function during hypoxia. MET-88 prevented the decrease of high-energy phosphate and the increase of long-chain acylcarnitine after 30 min of hypoxic perfusion. In addition, MET-88 increased the steady state of glucose oxidation in hypoxic perfused rat hearts. These results indicate that MET-88 has cardioprotective effects on contractile function and energy metabolism of isolated perfused rat hearts in a hypoxic condition. Preventing the accumulation of long-chain acylcarnitine may serve to protect hypoxic hearts.

Inhibition of carnitine synthesis protects against left ventricular dysfunction in rats with myocardial ischemia

During myocardial ischemia, inhibition of the carnitine-mediated transportation of fatty acid may be beneficial because it facilitates glucose utilization and prevents an accumulation of fatty acid metabolites. We orally administered 3-(2,2,2-trimethyl hydrazinium) propionate (MET), an inhibitor of carnitine synthesis, for 20 days to rats. Then we evaluated left ventricular (LV) function during brief ischemia by using a buffer-perfused isovolumic heart model. After 15 min of reoxygenation after the transient ischemia, LV peak systolic pressure (PSP) almost completely returned to the baseline level in rats given MET (96 +/- 4%), whereas it was only partially (77 +/- 16%) recovered in the placebo-treated rats. We induced myocardial infarction in other rats by ligating the left anterior descending coronary artery. Then the animals were given MET for 20 days, and LV function was compared. In the placebo-treated rats (with myocardial infarction, but without drug treatment), LVPSP was lower than that in the sham group [108 +/- 19 (n = 10) vs. 136 +/- 15 mm Hg (n = 13); p < 0.05], and the time constant (T) of LV pressure decay was elongated (36 +/- 4 vs. 30 +/- 7 ms; p < 0.05). In MET-treated groups, however, neither PSP nor T differed from those in the sham group. In conclusion, inhibition of the carnitine-mediated transportation of fatty acid by MET protected against left ventricular dysfunction in acute and chronic myocardial ischemia.

Beneficial effect of MET-88, a gamma-butyrobetaine hydroxylase inhibitor, on energy metabolism in ischemic dog hearts

The effect of MET-88 [3-(2, 2, 2-trimethylhydrazinium) propionate], a gamma-butyrobetaine hydroxylase inhibitor, on the ischemic changes of energy metabolism was studied in the anesthetized dog. In the dog pretreated orally with MET-88 (50, 100 or 200 mg/kg/day) or placebo for 10 days, the left anterior descending coronary artery was occluded for 60 min, and the myocardium was taken from the left anterior descending coronary area (ischemic area) and left circumflex area (nonischemic area) for metabolic analysis. In the ischemic area, occlusion of the left anterior descending coronary artery decreased the tissue levels of adenosine triphosphate, adenosine diphosphate and creatine phosphate, increased the tissue levels of adenosine monophosphate and lactate, and decreased the value of the energy charge potential. These metabolic alterations, induced by occlusion of the left anterior descending coronary artery, were dose-dependently attenuated by MET-88. In the nonischemic area, MET-88 did not markedly change either the tissue levels of energy metabolites or the value of the energy charge potential. These results indicate that MET-88 attenuates the derangement of the energy metabolism in the ischemic myocardium, without affecting the energy metabolism in the nonischemic myocardium.

[Effects of levocarnitine chloride (LC-80) on the cardiovascular system]

The cardiovascular effects of levocarnitine chloride (LC-80) were investigated in in vitro and in vivo experiments, and the following results were obtained: (1) In isolated rabbit cardiac muscle preparations, LC-80 at the high concentration of 10(-2) M had little influence on the atrial rate of spontaneously beating right atria, while it caused a gradual increase in the contractile tension of both spontaneously beating right atria and electrically driven papillary muscle that reached a maximum level after 10 min of administration and lasted for 20-30 min. However, the LC-80-induced positive inotropic effect may be negligible in whole animal experiments or clinical trials, since it was elicited only after the administration of LC-80 in an extremely large dose. Furthermore, LC-80 in a high concentration (10(-2) M) had no influence on the isoproterenol-induced positive inotropic effect in electrically driven papillary muscles. (2) LC-80 in high concentrations of 10(-3)-10(-2) M did not affect the high K+-induced contraction in isolated canine left circumflex coronary artery and saphenous vein. (3) In anesthetized dogs, intraarterial injection of LC-80 in high doses of up to 10 mg did not change the blood flow of coronary, femoral, renal, mesenteric or vertebral arteries and on the adenosine-induced vasodilator action. (4) In anesthetized dogs, intravenous injection of LC-80 in doses of 100-300 mg/kg did not modify the blood pressure responses induced by norepinephrine, acetylcholine, carotid occlusion and vagal stimulation. These results suggest that the cardiovascular effects of LC-80 are extremely mild or negligible. Therefore, LC-80 may be a drug having a new pharmacological feature in its mechanism which enables it to exert a beneficial effect in the treatment of ischemic heart disease, being different from the commonly used antianginal drugs.

[Effects of levocarnitine chloride (LC-80) on hemodynamics and myocardial metabolism in anesthetized open-chest dogs under normoxic or hypoxic conditions]

The effects of LC-80, infused intravenously at a rate of 10 mg/kg/min for 30 min, on hemodynamics and myocardial metabolism were investigated in anesthetized open-chest dog preparations under a normal oxygen tension of arterial blood (PaO2) ranging from 100 to 120 mmHg or low PaO2 ranging from 40 to 50 mmHg. (1) Normal PaO2 + High free fatty acidemia (HFFA): HFFA was produced by the intravenous infusion of Intralipid at a rate of 0.1 ml/kg/min after the rapid intravenous injection of 500 U/kg of heparin. Under this experimental condition, no significant changes in hemodynamics and myocardial metabolism were observed in both the LC-80 treated group and control group. (2) Low PaO2 + HFFA: Under this condition, there was no significant difference in hemodynamics between the LC-80 treated group and the control group, and the myocardial function in both groups tended to decrease. However, the increase in the coronary flow of the LC-80 treated group tended to be slight as compared with that of the control group. On the other hand, the decrease in the arterio-coronary venous difference of lactate was significantly less in the LC-80 treated group as compared to that in the control group. Furthermore, the reduction in myocardial redox potential (delta Eh) of the LC-80 treated group tended to be slight as compared with that of the control group. (3) Low PaO2 + HFFA + stress load: The hemodynamic responses (heart rate, left ventricular pressure, max dP/dt and cardiac work) to isoproterenol-induced stress were slightly but not significantly better in the LC-80 treated group than in the control group. While myocardial lactate production and the reduction of delta Eh in both groups became more prominent under this experimental condition, their degrees were apparently less in the LC-80 treated group as compared to those in the control group. These results suggest that LC-80 may have an improving effect on the anaerobic myocardial metabolism under anaerobic conditions such as hypoxia or stress load.