Tracking supercritical geothermal fluid distribution from continuous seismic monitoring.

Continuous seismic monitoring could play a pivotal role in deep geothermal energy exploration. We monitored seismicity near geothermal production areas of the Kuju volcanic complex with a dense seismic network and automated event detection. Most events were shallow (less than 3 km below sea level) and distributed along a boundary between regions of high and low resistivity and S-wave velocity, interpreted as a lithological boundary or related fracture zone. Deeper events located on top of subvertical conductors may reflect fracturing associated with magmatic fluid intrusion. A correlation may exist between seismicity and heavy rainfall three days prior to increased pore pressure in pre-existing fractures. Our findings support the presence of supercritical geothermal fluids and demonstrate the importance of continuous seismic monitoring in supercritical geothermal energy exploration.

Temporal changes in anthropogenic seismic noise levels associated with economic and leisure activities during the COVID-19 pandemic.

Seismic ambient noise with frequencies > 1 Hz includes noise related to human activities. A reduction in seismic noise during the COVID-19 pandemic has been observed worldwide, as restrictions were imposed to control outbreaks of the SARS-CoV-2 virus. In this context, we studied the effect of changes in anthropogenic activities during COVID-19 on the seismic noise levels in the Tokyo metropolitan area, Japan, considering time of day, day of the week, and seasonal changes. The results showed the largest reduction in noise levels during the first state of emergency under most conditions. After the first state of emergency was lifted, the daytime noise reverted to previous levels immediately on weekdays and gradually on Sundays. This was likely because economic activities instantly resumed, while non-essential outings on Sundays were still mostly avoided. Furthermore, the daytime noise level on Sundays was strongly reduced regardless of changes on weekdays after the second state of emergency, which restricted activities mainly at night. Sunday noise levels gradually increased from the middle of the second state of emergency, suggesting a gradual reduction in public concern about COVID-19 following a decrease in the number of infections. Our findings demonstrate that seismic noise can be used to monitor social activities.

Continuous monitoring system for safe managements of CO2 storage and geothermal reservoirs.

We have developed a new continuous monitoring system based on small seismic sources and distributed acoustic sensing (DAS). The source system generates continuous waveforms with a wide frequency range. Because the signal timing is accurately controlled, stacking the continuous waveforms enhances the signal-to-noise ratio, allowing the use of a small seismic source to monitor extensive areas (multi-reservoir). Our field experiments demonstrated that the monitoring signal was detected at a distance of ~ 80 km, and temporal variations of the monitoring signal (i.e., seismic velocity) were identified with an error of < 0.01%. Through the monitoring, we identified pore pressure variations due to geothermal operations and rains. When we used seafloor cable for DAS measurements, we identified the monitoring signals at > 10 km far from the source in high-spatial resolution. This study demonstrates that multi-reservoir in an extensive area can be continuously monitored at a relatively low cost by combining our seismic source and DAS.

Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake.

Monitoring of earthquake faults and volcanoes contributes to our understanding of their dynamic mechanisms and to our ability to predict future earthquakes and volcanic activity. We report here on spatial and temporal variations of seismic velocity around the seismogenic fault of the 2016 Kumamoto earthquake [moment magnitude (Mw) 7.0] based on ambient seismic noise. Seismic velocity near the rupture faults and Aso volcano decreased during the earthquake. The velocity reduction near the faults may have been due to formation damage, a change in stress state, and an increase in pore pressure. Further, we mapped the post-earthquake fault-healing process. The largest seismic velocity reduction observed at Aso volcano during the earthquake was likely caused by pressurized volcanic fluids, and the large increase in seismic velocity at the volcano's magma body observed ~3 months after the earthquake may have been a response to depressurization caused by the eruption. This study demonstrates the usefulness of continuous monitoring of faults and volcanoes.

Differential effects of azelnidipine and amlodipine on sympathetic nerve activity in patients with primary hypertension.

OBJECTIVE: Calcium channel blockers (CCBs) are used as antihypertensive agents and have a strong vasodilatory effect; however, the sympathetic activation mediated by baroreflex might cause adverse effects. A recently developed CCB, azelnidipine, decreases the heart rate (HR) while lowering blood pressure (BP), possibly by inhibiting sympathetic nerve activity in animal models. In this study, we evaluated whether azelnidipine inhibited sympathetic nerve activity, compared to amlodipine, in primary hypertensive patients. DESIGN AND METHODS: We conducted a prospective, randomized, open-label, and crossover study of 14 patients. We measured the patients' BP, HR and baroreflex sensitivity, and directly recorded muscle sympathetic nerve activity (MSNA), via microneurography, after treatment with either CCB for 8 weeks. RESULTS: Although systolic and diastolic BPs did not differ between the azelnidipine and amlodipine groups, the HR in the azelnidipine group significantly decreased compared with that in the amlodipine group. MSNA was significantly reduced in the azelnidipine compared with the amlodipine group (47.7 ±â€Š14.9 vs. 61.5 ±â€Š10.7  bursts per 100 beats, P < 0.05). However, no significant difference was observed in terms of the baroreflex control of HR, or MSNA, between the two groups. CONCLUSION: Our data show, first, that azelnidipine, compared with amlodipine, exerted a favorable effect on sympathetic nerve activity, without affecting baroreflex sensitivity, in hypertensive patients. These results indicate that azelnidipine might be useful for treating hypertensive patients, in whom hypertension is complicated by heart failure and ischemic heart disease.

Augmented single-unit muscle sympathetic nerve activity in heart failure with chronic atrial fibrillation.

Atrial fibrillation (AF) is a common complication in heart failure (HF) patients. However, it remains unclear whether irregular ventricular response patterns induced by AF increase sympathetic nerve activity. We measured resting multi- and single-unit muscle sympathetic nerve activity (MSNA) in 21 age-matched HF patients with chronic AF (n = 11) rhythm or sinus rhythm (SR, n = 10). The multi-unit MSNA, which was expressed as total activity, was similar between HF + AF patients and HF + SR patients. However, the single-unit MSNA in HF + AF patients was significantly greater than that in HF + SR patients (62 ± 9 spikes min(-1) vs. 42 ± 4 spikes min(-1), P < 0.05). Moreover, the incidence of multiple firing of single-unit MSNA within a given burst was augmented in HF + AF patients as compared with HF + SR patients (48 ± 8% vs. 26 ± 3%, P < 0.01). A significant negative relationship was observed between the reduced diastolic pressure induced by a prolonged cardiac interval in AF subjects and single-unit MSNA frequency within one cardiac interval in each HF + AF subject. The firing characteristics of single-unit MSNA were different between HF patients with AF and HF patients with SR; particularly, those with a prolonged long RR interval showed multiple firings of single-unit MSNA. These findings suggest that AF per se leads to the instantaneous augmentation of single-unit MSNA induced by decreased diastolic pressure, which might partially contribute to disease progression in HF patients.

Effect of pioglitazone on muscle sympathetic nerve activity in type 2 diabetes mellitus with α-glucosidase inhibitor.

Activation of the sympathetic nervous system is augmented in patients with type 2 diabetes mellitus (DM). Pioglitazone, an anti-diabetic drug, improves insulin resistance, but its influence on sympathetic nerve activity is not clear. To identify the relationship between insulin resistance and sympathetic activity, we examined muscle sympathetic nerve activity (MSNA) in controlled type 2 DM patients with alpha-glucosidase inhibitor (GI). We measured MSNA and calculated homeostasis model assessment of insulin resistance index (HOMA-IR) in twelve DM patients treated with alpha-GI and thirteen age-matched healthy subjects. In DM patients with alpha-GI, all parameters were reexamined after three months of treatment with pioglitazone. MSNA and HOMA-IR were significantly greater in DM patients with alpha-GI compared to healthy subjects. Hemoglobin A1c did not differ in DM patients before and after pioglitazone. However, pioglitazone significantly decreased MSNA in DM patients compared with alpha-GI (21.7±5.2 vs. 32.0±6.8 burst/min, p<0.01). Furthermore, MSNA level in pioglitazone was similar to that in healthy subjects. HOMA-IR significantly decreased after pioglitazone, and a significant relationship was found between the absolute change in MSNA and HOMA-IR (r=0.65, p<0.05). These results suggest that improved insulin resistance with pioglitazone provides an additional effect on inhibition of sympathetic nerve activity.

Altered firing pattern of single-unit muscle sympathetic nerve activity during handgrip exercise in chronic heart failure.

Sympathetic activation in chronic heart failure (CHF) is greatly augmented at rest but the response to exercise remains controversial. We previously demonstrated that single-unit muscle sympathetic nerve activity (MSNA) provides a more detailed description of the sympathetic response to physiological stress than multi-unit nerve recordings. The purpose of this study was to determine whether the reflex response and discharge properties of single-unit MSNA are altered during handgrip exercise (HG, 30% of maximum voluntary contraction for 3 min) in CHF patients (New York Heart Association functional class II or III, n = 16) compared with age-matched healthy control subjects (n = 13). At rest, both single-unit and multi-unit indices of sympathetic outflow were augmented in CHF compared with controls (P < 0.05). However, the percentage of cardiac intervals that contained one, two, three or four single-unit spikes were not different between the groups. Compared to the control group, HG elicited a larger increase in multi-unit total MSNA (Delta1002 +/- 50 compared with Delta636 +/- 76 units min(-1), P < 0.05) and single-unit MSNA spike incidence (Delta27 +/- 5 compared with Delta8 +/- 2 spikes (100 heart beats)(-1)), P < 0.01) in the CHF patients. More importantly, the percentage of cardiac intervals that contained two or three single-unit spikes was increased (P < 0.05) during exercise in the CHF group only (Delta8 +/- 2% and Delta5 +/- 1% for two and three spikes, respectively). These results suggest that the larger multi-unit total MSNA response observed during HG in CHF is brought about in part by an increase in the probability of multiple firing of single-unit sympathetic neurones.

Altered interaction between plasminogen activator inhibitor type 1 activity and sympathetic nerve activity with aging.

BACKGROUND: It has been reported that sympathetic nerve activity (SNA) is associated with fibrinolysis, but the interaction between SNA and the fibrinolytic system with aging has not been elucidated in humans. The purpose of this study was to examine the effect of age-related SNA on the activity of plasminogen activator inhibitor type 1 (PAI-1) and tissue plasminogen activator (tPA) using muscle SNA (MSNA). METHODS AND RESULTS: This study included 16 young subjects (mean age 26.1 years) and 10 aged subjects (mean age 56.9 years). Lower body negative pressure (LBNP) was performed at -40 mmHg for 30 min. LBNP significantly increased both tPA and PAI-1 activity (from 5.2+/-0.5 to 7.3+/-1.2 IU/ml and from 2.85+/-0.68 to 4.06+/-0.73 U/ml, p<0.01, respectively) in the aged group. In the young group, tPA activity tended to increase, whereas PAI-1 activity was unchanged. There was a correlation between MSNA and PAI-1 activity in the aged group (r=0.47, p<0.01). CONCLUSIONS: SNA in an aging subject leads to an increase in the activity of PAI-1, which indicates that an altered interaction between SNA and PAI-1 activity contributes to increased cardiovascular events in the elderly population.

Detecting mental disorders in dental patients with occlusion-related problems.

Dentists often treat patients who may be suffering from comorbid mental disorders without paying attention to their symptoms. This leads to a delay in starting the treatment of mental disorders and to inappropriate dental treatments for physical symptoms originating from mental disorders. In the present study, the ways in which dentists can easily detect mental disorders in dental patients with occlusion-related problems were examined. Fifty-three patients who visited the Occlusion Clinic of Kanagawa Dental College were interviewed by a psychiatrist and a dentist specialized in psychosomatic medicine. Thirty-five patients (66.0%) were diagnosed as having DSM-IV Axis I disorders. The demographic and psychological factors that correlate with the presence of mental disorders are duration of chief complaint, number of clinics and hospitals visited for the current symptom, total score of the General Health Questionnaire (GHQ), the scores of the anxiety and insomnia and social dysfunction subscales in the GHQ and the scores of the confusion-bewilderment and fatigue-inertia subscales in the Profile of Mood States (POMS). A logistic regression analysis indicated that number of clinics and hospitals visited markedly correlated with cormobidity of a mental disorder. This information may be useful for screening mental disorder patients. Dental patients having comorbid mental disorders should be treated both odontologically and psychologically.