Effects of transcutaneous auricular vagus nerve stimulation at left cymba concha on experimental pain as assessed with the nociceptive withdrawal reflex, and correlation with parasympathetic activity.

The aim of this study was to clarify the effects of transcutaneous auricular vagus nerve stimulation (taVNS) to the left cymba concha on the pain perception using nociceptive withdrawal reflex (NWR), which is known to be associated with chronic pain, and to investigate whether there is a relationship between taVNS-induced suppression of the NWR and parasympathetic activation. We applied either 3.0 mA, 100 Hz taVNS for 120 s on the left cymba concha (taVNS condition) or the left earlobe (Sham condition) for 20 healthy adults. NWR threshold was measured before (Baseline), immediately after (Post 0), 10 min (Post 10) and 30 min after (Post 30) stimulation. The NWR threshold was obtained from biceps femoris muscle by applying electrical stimulation to the sural nerve. During taVNS, electrocardiogram was recorded, and changes in autonomic nervous activity measured by heart rate variability (HRV) were analyzed. We found that the NWR thresholds at Post 10 and Post 30 increased compared with baseline in the taVNS group (10 min after: p = .008, 30 min after: p = .008). In addition, increased parasympathetic activity by taVNS correlated with a greater increase in NWR threshold at Post 10 and Post 30 (Post 10: p = .003; Post 30: p = .001). The present results of this single-blinded study demonstrate the pain-suppressing effect of taVNS on NWR threshold and suggest that the degree of parasympathetic activation during taVNS may predict the pain-suppressing effect of taVNS after its application.

Discrimination of the moving direction is improved depending on the pattern of the mechanical tactile stimulation intervention.

BACKGROUND: The mechanical tactile stimulation, such as plastic pins and airflow-driven membrane, induces cortical activity. The cortical activity depends on the mechanical tactile stimulation pattern. Therefore, the stimulation pattern of mechanical tactile stimuli intervention may influence its effect on the somatosensory function. However, the effect of the mechanical tactile stimulation input pattern on the somatosensory function has not yet been investigated at the behavioral level. The present study aimed to clarify the effects of mechanical tactile stimuli intervention with different stimulation patterns on the ability to discriminate moving directions. RESULTS: Twenty healthy adults participated in the experiment. Three conditions were used for mechanical tactile stimuli intervention: (1) the whole stimulus surface was stimulated, (2) the stimulus moved within the stimulus surface, and (3) a no-stimulus condition. The effects of mechanical tactile stimuli intervention on tactile discrimination were evaluated using a simple reaction task and a choice reaction task to discriminate the movement direction. Reaction time, correct rate, and rate correct score were calculated to measure task performance. We examined the effects of mechanical tactile stimuli intervention on the ability to discriminate the moving direction for a certain period under three intervention conditions. The results showed that the mean reaction time during the simple reaction task did not differ significantly before and after the intervention under all intervention conditions. Similarly, we compared the data obtained before and after the intervention during the choice reaction task. Our results revealed that the mean reaction time and correct rate did not differ significantly under vertical and horizontal conditions. However, the rate correct score showed a significant improvement after the horizontal moving tactile stimulation intervention under both vertical and horizontal conditions. CONCLUSIONS: Our results showed that the effect of mechanical tactile stimuli intervention on mechanical tactile stimulation moving direction discrimination function depended on the input pattern of mechanical tactile stimuli intervention. Our results suggest the potential therapeutic benefits of sustained tactile stimulation intervention. This study revealed that it is possible to change behavioral levels via mechanical tactile stimuli intervention as well as the potential of mechanical tactile stimuli intervention in the field of rehabilitation.

Intramuscular and abdominal fat measured by computed tomography and mortality of hemodialysis patients.

BACKGROUND: In hemodialysis patients, high body mass index is associated with low mortality while abdominal obesity relates to increased mortality. We aimed to investigate the association between muscle mass, intramuscular fat and abdominal fat measured by abdominal computed tomography (CT), and mortality in this patients population. METHODS: This two-center retrospective cohort study included hemodialysis patients who underwent abdominal CT between January 2013 and December 2018. Skeletal muscle mass index (SMI), muscle radiation attenuation (MRA) as an index of intramuscular fat, and visceral fat to subcutaneous fat ratio (VSR) were calculated using CT images at the third lumbar vertebral level. Multivariate Cox proportional hazards model was used to determine the independent predictors of all-cause, cardiovascular and non-cardiovascular mortalities. RESULTS: The study included 344 patients (median age 71.0 years; female 33.7%), among whom 145 died during a median follow-up of 4.9 years-46 and 99 from cardiovascular and non-cardiovascular causes, respectively. Lower MRA [hazard ratio (HR) 0.71, 95% confidence interval (CI) 0.58-0.87, P = .001] and higher VSR (HR 1.17, 95% CI 1.01-1.37, P = .04) were independently associated with higher all-cause mortality but not with lower SMI (HR 0.87, 95% CI 0.68-1.11, P = .26). Lower MRA (HR 0.51, 95% CI 0.35-0.73, P < .001) and higher VSR (HR 1.29, 95% CI 1.09-1.54, P = .003) were also associated with cardiovascular and non-cardiovascular mortality, respectively. CONCLUSIONS: Intramuscular fat and abdominal fat as measured using abdominal CT in hemodialysis patients are stronger independent predictors of mortality than muscle mass.

Beta resting-state functional connectivity predicts tactile spatial acuity.

Tactile perception is a complex phenomenon that is processed by multiple cortical regions via the primary somatosensory cortex (S1). Although somatosensory gating in the S1 using paired-pulse stimulation can predict tactile performance, the functional relevance of cortico-cortical connections to tactile perception remains unclear. We investigated the mechanisms by which corticocortical and local networks predict tactile spatial acuity in 42 adults using magnetoencephalography (MEG). Resting-state MEG was recorded with the eyes open, whereas evoked responses were assessed using single- and paired-pulse electrical stimulation. Source data were used to estimate the S1-seed resting-state functional connectivity (rs-FC) in the whole brain and the evoked response in the S1. Two-point discrimination threshold was assessed using a custom-made device. The beta rs-FC revealed a negative correlation between the discrimination threshold and S1-superior parietal lobule, S1-inferior parietal lobule, and S1-superior temporal gyrus connection (all P < 0.049); strong connectivity was associated with better performance. Somatosensory gating of N20m was also negatively correlated with the discrimination threshold (P = 0.015), with weak gating associated with better performance. This is the first study to demonstrate that specific beta corticocortical networks functionally support tactile spatial acuity as well as the local inhibitory network.

Association between somatosensory sensitivity and regional gray matter volume in healthy young volunteers: a voxel-based morphometry study.

Two-point discrimination (2PD) test reflects somatosensory spatial discrimination ability, but evidence on the relationship between 2PD and cortical gray matter (GM) volume is limited. This study aimed to analyze the relationship between cortical GM volume and 2PD threshold in young healthy individuals and to clarify the characteristics of brain structure reflecting the individual differences in somatosensory function. 2PD was measured in 42 healthy (20 females) volunteers aged 20-32 years using a custom-made test system that can be controlled by a personal computer. The 2PD of the right index finger measured with this device has been confirmed to show good reproducibility. T1-weighted images were acquired using a 3-T magnetic resonance imaging scanner for voxel-based morphometry analysis. The mean 2PD threshold was 2.58 ± 0.54 mm. Whole-brain multiple regression analysis of the relationship between 2PD and GM volume showed that a lower 2PD threshold (i.e. better somatosensory function) significantly correlated with decreased GM volume from the middle temporal gyrus to the inferior parietal lobule (IPL) in the contralateral hemisphere. In conclusion, a lower GM volume in the middle temporal gyrus and IPL correlates with better somatosensory function. Thus, cortical GM volume may be a biomarker of somatosensory function.

Associations between bioelectrical impedance analysis-derived phase angle, protein-energy wasting and all-cause mortality in older patients undergoing haemodialysis.

AIM: Protein-energy wasting (PEW) is a common syndrome in patients undergoing haemodialysis (HD) and is associated with poor prognosis. Bioelectrical impedance analysis (BIA)-derived phase angle (PA) is useful for predicting PEW, but sex and age need to be considered. We aimed to reveal sex-specific cut-off values of PA predicting PEW in HD patients aged ≥65. METHODS: This two-centre retrospective cohort study included patients on HD who underwent BIA. PEW was detected using the International Society of Renal Nutrition and Metabolism (ISRNM) criteria as a reference. The PA was measured using a multifrequency bioimpedance device. Sex-specific cut-off values of PA predicting PEW were detected by receiver-operator characteristic analysis. We investigated the association between PEW determined using sex-specific cut-off values for PA and all-cause mortality. RESULTS: This study included 274 patients undergoing HD, with a median age of 75 (70-80) years, mean PA of 3.8 ± 1.1° and PEW of 43%. Over a median follow-up duration of 1095 (400-1095) days, 111 patients died. Cut-off values of PA predicting PEW were as follows: female, 3.00° (sensitivity, 87.3%; specificity, 77.5%), and male, 3.84° (sensitivity, 77.6%; specificity, 71.4%). The kappa coefficient between sex-specific cut-off values of the PA and ISRNM criteria had a moderate coincidence level of 0.55. PEW detected by PA was independently associated with all-cause mortality (hazard ratio: 2.40; 95% confidence interval: 1.51-3.85; p < .001). CONCLUSIONS: Sex-specific cut-off values for PA in older HD patients may be useful as a screening tool for predicting PEW and mortality.

Comparison of intradialytic continuous and interval training on hemodynamics and dialysis adequacy: A crossover randomized controlled trial.

AIM: Circulating blood volume (BV) during exercise changes depending on the intensity and duration, and post-exercise hypotension is observed after continuous exercise. We investigated the safety and efficacy of both interval and continuous IDE at anaerobic threshold (AT) levels with respect to hemodynamic stability and dialysis efficiency. METHODS: In this crossover randomized controlled trial, 16 patients on haemodialysis were subjected to three trial arms, including non-IDE, interval-IDE, and continuous-IDE arms. Systolic blood pressure (SBP), BV, and ultraviolet absorbance - an indicator of dialysis efficiency - were continuously measured, and each change was compared between the three arms by two-way analysis of variance. RESULTS: Continuous IDE decreased SBP from post-exercise to the end of dialysis compared with baseline (pre 142.8 ± 19.0 vs. post 127.5 ± 24.5 mmHg, p = .02), whereas interval IDE maintained better SBP levels post-exercise (pre 139.9 ± 17.1 vs. post 140.1 ± 15.8 mmHg, p = 1.0) than continuous IDE (non-IDE 133.2 ± 19.9 vs. interval 140.1 ± 15.8 vs. continuous 127.5 ± 24.5 mmHg, p = .04). Moreover, interval IDE caused less tiredness and few symptoms (p < .05), despite reaching higher intensity than continuous IDE (p = .001). The BV of each IDE arm decreased during exercise and recovered post-exercise to the same level as non-IDE. Ultraviolet absorbance was not different between each arm (p = .16). CONCLUSION: AT-level interval IDE maintains better hemodynamic stability from post-exercise to the end of dialysis and may represent a novel approach that can be effectively performed with fewer symptoms.

Gray Matter Volume Variability in Young Healthy Adults: Influence of Gender Difference and Brain-Derived Neurotrophic Factor Genotype.

Although brain gray matter (GM) plastically changes during short-term training, it is still unclear whether brain structures are stable for short periods (several months). Therefore, this study aimed to re-test the short-term variability of GM volumes and to clarify the effect of factors (gender and BDNF-genotype) expected to contribute to such variability. The subjects comprised 41 young healthy adults. T1-weighted images were acquired twice with an interval of approximately 4 months using a 3 T-MRI scanner. Voxel-based morphometry (VBM) was used to calculate GM volumes in 47 regions. The intraclass correlation coefficient (ICC) and Test-retest variability (%TRV) were used as indices of variability. As a result, the ICCs in 43 regions were excellent (ICC > 0.90) and those in 3 regions were good (ICC > 0.80), whereas the ICC in the thalamus was moderate (ICC = 0.694). Women had a higher %TRV than men in 5 regions, and %TRV of the Val66Val group was higher than that of the Met carrier group in 2 regions. Moreover, the Female-Val66Val group had a higher %TRV than the Male-Met carrier group in 3 regions. These results indicate that although the short-term variability of GM volumes is small, it is affected by within-subject factors.

Association of Postexercise Vagal Dysfunction With Protein-Energy Wasting and Noncardiovascular Outcomes in Patients Receiving Hemodialysis: A Retrospective Cohort Study.

OBJECTIVE: Postexercise vagal dysfunction is linked to noncardiovascular mortality in hemodialysis patients, but the mechanism is unknown. This study aimed to determine the association of cardiovagal neuropathy with systemic inflammation, protein-energy wasting, and noncardiovascular hospitalization. METHODS: This 2-center retrospective cohort study analyzed data from 280 hemodialysis patients who underwent exercise test. Patients were assessed for heart rate (HR) recovery (bpm) for 1 minute after exercise, a marker of vagal function, and were divided into 3 categories (Low: ≤ 6, Mid: 7-11, High: ≥ 12 bpm). We followed 1-year changes in the systemic inflammation-based prognostic score (Glasgow Prognostic Score [GPS]), body weight, and creatinine generation rate (CGR), an indicator of muscle mass, as well as 2-year hospitalization. RESULTS: The HR recovery category was associated with serum C-reactive protein and albumin levels and GPS. After 1 year, the low HR recovery category was associated with worsening in GPS (low, 0 [0-0.5]; mid, 0 [0-1]; high, 0 [0-0]), weight (low, 100.0 [96.1-102.5]; mid, 101.3 [98.9-105.0]; high, 100.5 [98.2-102.9]%), and CGR (low, 97.0 [88.5-111.4]; mid, 110.2 [90.9-124.8]; high, 106.2 [95.5-115.5]%), and the correlations with GPS and CGR remained consistent after adjusting for confounders such as exercise capacity and hospitalization during the follow-up period. There were 117 patients hospitalized. Compared to the high HR recovery category, the mid (hazard ratio: 1.8, 95% confidence interval [CI]: 1.1-3.1, P = .02) and low (hazard ratio: 2.4, 95% CI: 1.5-4.0, P = .001) categories were independently associated with an increased risk of all-cause hospitalization. For noncardiovascular disease hospitalization, the low HR recovery category was independently associated with increased risk of hospitalization (hazard ratio: 2.1, 95% CI: 1.2-3.7, P = .007). CONCLUSIONS: Vagal neuropathy in this population can contribute to adverse outcomes associated with systemic inflammation and protein-energy wasting.

Association of cardiac autonomic neuropathy assessed by heart rate response during exercise with intradialytic hypotension and mortality in hemodialysis patients.

The heart rate (HR) reflects the dynamic behavior of the autonomic nervous system, and HR profiles during the exercise test provide prognostic information. However, there are no reports of these factors in hemodialysis patients. Data from 256 patients (mean 68.8 years old) who underwent an exercise test were statistically analyzed. Patients were evaluated for the percent HR reserve from HR at peak exercise, HR recovery for one minute after peak exercise, and exercise capacity, as well as intradialytic hypotension (IDH). The prevalence of chronotropic incompetence (96.1%), defined as under 80% HR reserve, and abnormal HR recovery (60.5%), defined as under 12 beats, were very common. Eighty-four deaths occurred during the follow-up period (median, 3.8 years). A slow HR recovery under 7 beats was associated with IDH after adjustment (odds ratio 2.7, 95% confidence interval 1.1-6.4). HR recovery under 12 beats (hazard ratio over study period 5.1, 95% confidence interval 2.5-10.5), HR reserve under 26.2% (3.4, 1.7-6.8), and IDH (1.7, 1.1-2.8) were associated with all-cause mortality after adjustment. Considering the confounding of all three variables, only HR recovery under 12 beats remained associated with the all-cause and cause-specific mortality ("cardiovascular" and "non-cardiovascular"). This association was consistent even in subgroup analyses based on the presence of diabetes and cardiovascular disease. Thus, HR profiles during the exercise can reflect potential health conditions related to cardiac autonomic neuropathy in hemodialysis patients that affect IDH and their survival.

An equation to predict peak heart rate for prescribing exercise intensity in middle-aged to older patients requiring hemodialysis.

PURPOSE: Exercise prescription based on a population-specific physiological response can help ensure safe and effective physical interventions. However, as a facile approach for exercise prescription in hemodialysis population that is based on their exercise capacity has not yet been established, the aim of our study was to develop a unique prediction formula for peak heart rate (HR) that can be used in this population. METHODS: This cross-sectional study measured physical function and HR at peak exercise and anaerobic threshold (AT) during cardiopulmonary exercise tests in 126 individuals. Participants were randomly assigned to the development group (n = 78), whose data were used to calculate the prediction equation, or the validation group (n = 48). RESULTS: The HR reserve in this population was significantly lower (0.44 ± 0.20%) and there was a large discrepancy between conventional age-predicted maximal HR and measured peak-HR values (R = 0.36). The average of the ratio between HR at AT point and peak HR was 85% (95% CI, 83.5%-86.4%). The peak-HR prediction equation was based on resting HR, presence of diabetes, physical dysfunction (gait speed < 1.0 m/s), and hypoalbuminemia (< 3.5 g/dL). It showed high prediction accuracy (R2 [95%CI] = 0.71 [0.70-0.71]) with similar correlation coefficients between the development and validation groups (R = 0.82). CONCLUSION: Aerobic exercise based on estimated peak HR < 85% obtained from the equation in this study may enable safe and effective physical intervention in this population.

Perceived Exertion Correlates with Multiple Physiological Parameters During Cardiopulmonary Exercise Testing.

The purpose of this study was to investigate the relationship of the Borg scale score with leg-muscle oxygenated haemoglobin (O2Hb) and deoxygenated haemoglobin (HHb) levels on near infrared spectroscopy (NIRS) and the work rate, heart rate (HR), oxygen uptake (VO2) and minute ventilation (VE) during supine cardiopulmonary exercise testing (CPET) in healthy adult men. We also investigated the relationships between the leg-muscle O2Hb and HHb levels and the work rate during supine CPET. Fifteen healthy male volunteers (mean age, 20.7 ± 0.6 years; mean height, 172.1 ± 5.7 cm; mean body weight, 61.7 ± 6.6 kg) participated in this study. The cardiopulmonary and NIRS parameters were assessed during each minute of supine CPET and at the end of the test. The Borg scale score significantly correlated with the work rate, HR, VO2, and VE during supine CPET (Rs = 0.86-0.94, p < 0.05). Furthermore, the Borg scale score significantly correlated with the leg-muscle O2Hb and HHb levels during supine CPET (Rs = -0.6, and 0.8, respectively; p < 0.05). The leg-muscle O2Hb and HHb levels had significant correlations with the work rate (R = -0.62 and 0.8, respectively; p < 0.05). The Borg scale score may be used to determine the rating of perceived exertion, whole-body fatigue and local-muscle fatigue during supine exercise. Moreover, leg-muscle oxygenation is associated with the work rate in supine exercise, similar to that observed in upright exercise.

The intervention of mechanical tactile stimulation modulates somatosensory evoked magnetic fields and cortical oscillations.

The different cortical activity evoked by a mechanical tactile stimulus depends on tactile stimulus patterns, which demonstrates that simple stimuli (i.e., global synchronous stimulation the stimulus area) activate the primary somatosensory cortex alone, whereas complex stimuli (i.e., stimulation while moving in the stimulus area) activate not only the primary somatosensory cortex but also the primary motor area. Here, we investigated whether the effects of a repetitive mechanical tactile stimulation (MS) on somatosensory evoked magnetic fields (SEFs) and cortical oscillations depend on MS patterns. This single-blinded study included 15 healthy participants. Two types interventions of MS lasting 20 min were used: a repetitive global tactile stimulation (RGS) was used to stimulate the finger by using 24 pins installed on a finger pad, whereas a sequential stepwise displacement tactile stimulation (SSDS) was used to stimulate the finger by moving a row of six pins between the left and right sides on the finger pad. Each parameter was measured pre- and post-intervention. The P50m amplitude of the SEF was increased by RGS and decreased by SSDS. The modulation of P50m was correlated with its amplitude before RGS and with the modulation of beta band oscillation at the resting state after SSDS. This study showed that the effects of a 20-min MS on SEFs and cortical oscillations depend on mechanical tactile stimulus patterns. Moreover, our results offer potential for the modulation of tactile functions and selection of stimulation patterns according to cortical states.

Corticospinal excitability of untrained side depends on the type of motor task and degree of improvement in motor function.

Unimanual motor tasks change the corticospinal excitability of the trained and untrained side. However, whether the motor task type influences the modulation of the corticospinal excitability of the untrained side remains unclear. This study aimed to clarify the effects of motor tasks on the corticospinal excitability of the untrained side and the relationship between the excitability and motor function. In Experiment I, we measured the corticospinal excitability of the untrained side and motor function after 10 min of motor training in two conditions (gripping task and ball rotation task). The gripping task decreased the excitability. In contrast, excitability remained unchanged after the ball rotation task; further, the modulation of excitability and motor function showed a correlation. In Experiment II, we measured the corticospinal excitability of the untrained side and motor function after two sessions of the ball rotation task. The excitability increased, but motor function remained unchanged after the first session, whereas the excitability decreased to the level observed before training, and motor function improved after the second session. We suggest that the training condition modulates the corticospinal excitability of the untrained side and that this is related to the modulation of motor function.

Relationship Between the Borg Scale Rating of Perceived Exertion and Leg-Muscle Deoxygenation During Incremental Exercise in Healthy Adults.

INTRODUCTION: The Borg scale rating of perceived exertion is a reliable indicator and widely used to monitor and guide exercise intensity. We aimed to evaluate the relationships between the Borg scale score and oxygenated hemoglobin (O2Hb) and deoxygenated hemoglobin (HHb) concentrations in the leg muscle as measured by near-infrared spectroscopy (NIRS) during cardiopulmonary exercise testing (CPET) in healthy adult men. We also investigated the relationships between the Borg scale score and the work rate (WR), heart rate (HR), oxygen uptake (VO2), and minute ventilation (VE). METHODS: Participants comprised 12 healthy men. Cardiopulmonary and NIRS parameters were assessed during each minute of CPET and at the end of the test. RESULTS: The Borg scale score was significantly correlated with cardiopulmonary parameters including WR, HR, VO2, and VE during CPET (Rs = 0.87-0.95; p < 0.05). Furthermore, the Borg scale score was significantly correlated with NIRS parameters including O2Hb and HHb levels during CPET (Rs = -0.48 and 0.45, respectively; p < 0.05). DISCUSSION: The Borg scale score is significantly correlated with cardiopulmonary parameters (WR, HR, VO2, and VE), as well as with leg-muscle oxygenation parameters as assessed by NIRS, during CPET in healthy adults. The correlation coefficients obtained from NIRS parameters were lower than those of cardiopulmonary parameters. CONCLUSIONS: The Borg scale score might better reflect cardiopulmonary responses than muscle deoxygenation during exercise. These results can aid in the planning of rehabilitation programs for healthy adults.

Changes in the Laterality of Oxygenation in the Prefrontal Cortex and Premotor Area During a 20-Min Moderate-Intensity Cycling Exercise.

A recent study based on near-infrared spectrometry (NIRS) showed that a single session of moderate-intensity exercise increases the cortical oxyhemoglobin (O2Hb) level. However, changes in the laterality of O2Hb throughout such exercises remain unknown. In the present study, we evaluated changes in the laterality of O2Hb in the prefrontal cortex (PFC) and premotor area (PMA) during moderate-intensity cycling for 20 min. Twelve healthy volunteers performed the exercise at 50% of the maximal oxygen consumption after a 3-min rest period. O2Hb levels in the right (R-) and left (L-) PFC and PMA were measured using multichannel NIRS and averaged every 5 min during the exercise period, and the laterality index (LI) for each 5-min period was calculated. LI for PFC showed significant changes in each period (first, second, third, and fourth periods: -0.40 ± 0.21, -0.03 ± 0.12, 0.14 ± 0.15, and 0.16 ± 0.10, respectively; p < 0.05), whereas that for PMA showed no significant changes (-0.07 ± 0.09, 0.23 ± 0.08, 0.17 ± 0.12, and 0.19 ± 0.09, respectively; p = 0.12). These findings suggest that the laterality of cortical oxygenation in PFC of healthy, young individuals changes during moderate-intensity exercise for 20 min, thus providing an insight into the mechanisms underlying exercise-induced improvements in brain function.

Relationship Between Decrease of Oxygenation During Incremental Exercise and Partial Pressure End-Tidal Carbon Dioxide: Near-Infrared Spectroscopy Vector Analysis.

A previous study considered that a decrease in cerebral oxyhemoglobin (O2Hb) immediately before maximal exercise during incremental exercise is related to cerebral blood flow (CBF) and partial pressure end-tidal carbon dioxide (PETCO2). This study aimed to investigate the relationship between O2Hb, PETCO2, and the estimated value of cerebral blood volume (CBV) with cerebral oxygen exchange (COE) by using vector analysis. Twenty-four healthy young men participated in this study. They performed the incremental exercise (20 W/min) after a 4-min rest and warm-up. The O2Hb and deoxyhemoglobin (HHb) in the prefrontal cortex (PFC) were measured using near-infrared spectroscopy (NIRS). The PETCO2 was measured using a gas analyzer. The O2Hb, HHb, and PETCO2 were calculated as the amount of change (ΔO2Hb, ΔHHb, and ΔPETCO2) from an average 4-min rest. Changes in the CBV (ΔCBV) and COE (ΔCOE) were estimated using NIRS vector analysis. Moreover, the respiratory compensation point (RCP), which relates to the O2Hb decline, was detected. The Pearson correlation coefficient was used to establish the relationships among ΔO2Hb, ΔPETCO2, ΔCBV, and ΔCOE from the RCP to maximal exercise. The ΔPETCO2 did not significantly correlate with the ΔO2Hb (r = 0.03, p = 0.88), ΔCOE (r = -0.19, p = 0.36), and ΔCBV (r = -0.21, p = 0.31). These results showed that changes in the ΔPETCO2 from the RCP to maximal exercise were not related to changes in the ΔO2Hb, ΔCOE, and ΔCBV. Therefore, we suggested that the decrease of O2Hb immediately before maximal exercise during incremental exercise may be related to cerebral oxygen metabolism by neural activity increase, not decrease of CBF by the PETCO2.

Enhancement of spinal reciprocal inhibition depends on the movement speed and range of repetitive passive movement.

Repetitive passive movement (RPM) is a rehabilitation technique that increases spinal reciprocal inhibition (RI) as movement speed increases. However, characterization of the RPM number, frequency and range relative to the afferent impulses of muscle spindles and RI modulation has not been performed. In this study, we attempted to clarify these factors and evaluate their relationship to RI. We used 20 healthy adults for our first experiment (Experiment 1) and 16 healthy adults for our second experiment (Experiment 2). In Experiment 1, the RPM task was performed in the 80°-120° range for the ankle joint for 618 times at 80°/s (80°/s_618 times), 309 times at 160°/s (160°/s_309 times) and 618 times at 160°/s (160°/s_618 times). In Experiment 2, the RPM task focused on two ranges for the ankle joint (80°-100° and 100°-120°) and was performed at 160°/s with a movement time of 10 min. To measure RI, electrical stimulation was used to evoke a conditioning stimulus in the common peroneal nerve and the test stimulus in the tibial nerve. Conditions included the test stimulus only and conditioning stimulation-test stimulation intervals (CTI) of 2 and 20 ms. RI was measured before (Pre); immediately after; and 5, 10, 15 and 20 min after the task. Our findings suggest that the faster the movement speed of the RPM and the wider the movement range, the greater the increase in Ia firing. This may have enhanced RI by activating the inhibitory interneurons of RI.

Cerebral Oxygenation Dynamics of the Prefrontal Cortex and Motor-Related Area During Cardiopulmonary Exercise Test: A Near-Infrared Spectroscopy Study.

Near-infrared spectroscopy (NIRS) during cardiopulmonary exercise test (CPX) has shown a correlation between prefrontal cortex (PFC) oxygenated hemoglobin (O2Hb) level and negative affective responses. We hypothesized that O2Hb changes differ between the PFC and motor-related areas. This study investigated changes in hemoglobin levels in the PFC and motor-related areas during CPX. Twelve young healthy adults participated in this study. They performed a CPX after 4 min of rest and 4 min of warming up. Cortical O2Hb, deoxygenated hemoglobin (HHb), and total hemoglobin (THb) levels were measured with NIRS during CPX. Regions of interest (ROI) were the PFC, premotor area (PMA), supplementary motor area (SMA), and primary motor cortex (M1). The anaerobic threshold (AT), respiratory compensation (RC), and peak oxygen uptake (Peak) points were determined. The rest, AT, RC and Peak points of O2Hb, HHb, and THb were averaged over 5 s; hemoglobin slopes, from RC to the Peak points, were calculated to compare functional changes in cortical oxygenation. Average values of O2Hb, HHb, and THb in each ROI were compared among the rest, AT, RC, and Peak points. Average values of hemoglobin slopes, from RC to Peak points, were compared among ROIs using Bonferroni multiple comparisons. The HHb of all ROIs significantly increased at Peak point, compared with at the AT point. THb of the PFC, PMA, and SMA significantly increased at the RC or Peak points, compared with at the rest point. Hemoglobin slopes, from RC to Peak, showed no significant differences among ROIs. Each ROI exhibited similar changes, regardless of cortical function.

Effect of Exercise Duration on Post-Exercise Persistence of Oxyhemoglobin Changes in the Premotor Cortex: A Near-Infrared Spectroscopy Study in Moderate-Intensity Cycling Exercise.

Measurement of oxyhemoglobin (O2Hb) changes in the cerebral cortex using near-infrared spectroscopy (NIRS) shows that its levels increase during moderate-intensity exercise and persists after exercise. However, the effects of exercise duration on O2Hb persistence in the premotor cortex (PMC) are unknown. We aimed to determine the effects of exercise duration on the persistence of O2Hb changes after moderate-intensity cycling as exercise. Healthy young volunteers were recruited to participate in this study. After a 3-min rest period, the exercise was initiated at a workload corresponding to 50% VO2peak. The exercise continued for 10 min and 20 min, followed by 15 min of rest. The O2Hb levels in the right (R-PMC) and left premotor cortices (L-PMC) were measured using an NIRS system. The O2Hb values during the 15-min post-exercise rest period in the R-PMC were 0.010 ± 0.011 mM·cm after the 10-min exercise and 0.035 ± 0.010 mM·cm after the 20-min exercise, without significant differences (p = 0.104). The O2Hb value in the L-PMC during post-exercise rest (0.055 ± 0.010 mM·cm) after the 20-min exercise was significantly higher than that after the 10-min exercise (0.023 ± 0.007 mM·cm; p = 0.014). Thus, the effects of exercise duration on O2Hb persistence have laterality in the PMC.