Kiyokazu Sekikawa

Do the kinetics of peripheral muscle oxygenation reflect systemic oxygen intake

Abstract To examine whether the kinetics of local muscle oxygenation reflect systemic oxygen intake, we measured the kinetics of local muscle oxygenation and systemic oxygen consumption (V˙O2). This study included 16 healthy males who performed an exercise tolerance test on a bicycle ergometer. During the exercise test, expiratory gas analysis was performed with an expiratory gas analyzer, and the kinetics of vastus lateralis muscle oxygenation were determined by near-infrared spectroscopy (NIRS). Oxygenated hemoglobin (OxyHb) and tissue blood oxygen saturation (StO2) gradually decreased during the exercise test, while deoxygenated hemoglobin (DeoxyHb) gradually increased. We examined correlations between the mean values of these parameters, which were calculated by time-integrating the values obtained using NIRS and dividing them by the integral time, and V˙O2. There was a marked positive correlation between DeoxyHb and V˙O2 (r=0.893 − 0.986), and a marked negative correlation between StO2 and V˙O2 (r=0.859 − 0.995). There was a negative correlation between V˙O2 and OxyHb (r=0.726 − 0.978), and no correlation between TotalHb and V˙O2. These results suggest that the kinetics of peripheral muscle oxygenation reflect systemic V˙O2.

Characteristics of patients with severe heart failure exhibiting exercise oscillatory ventilation.

This study aims to elucidate the characteristics of patients with severe nonischemic heart failure exhibiting exercise oscillatory ventilation (EOV) and the association of these characteristics with the subjective dyspnea. Forty-six patients with nonischemic heart failure who were classified into the New York Heart Association (NYHA) functional class III underwent cardiopulmonary exercise testing (CPX) and were divided into two groups according to the presence or absence of EOV. We evaluated the patients by using the Specific Activity Scale (SAS), biochemical examination, echocardiographic evaluation, results of CPX and symptoms during CPX (Borg scale), and reasons for exercise termination. EOV was observed in 20 of 46 patients. The following characteristics were observed in patients with EOV as compared with those without EOV with statistically significant differences: more patients complaining dyspnea as the reason for exercise termination, lower SAS score, higher N-terminal pro-brain natriuretic peptide level, larger left atrial dimension and volume, left ventricular end-diastolic volume, higher Borg scale score at rest and at the anerobic threshold, higher respiratory rate at rest and at peak exercise, and higher slope of the minute ventilation-to-CO2 output ratio, and lower end-tidal CO2 pressure at peak exercise. Among the subjects with NYHA III nonischemic heart failure, more patients with EOV had a stronger feeling of dyspnea during exercise as compared with those without EOV, and the subjective dyspnea was an exercise-limiting factor in many cases.

Determinants of the daily rhythm of blood fluidity

Background Numerous processes in the living body exhibit daily rhythmicity. In this study, we characterized a daily rhythm of blood fluidity and identified its determinants. Methods The subjects were nine young males. We measured the physiological parameters and performed hematological and biochemical analyses. We repeated the measurements six times during the day at 7:30 (just after getting up and before breakfast), 10:00, 13:30 (after lunch), 16:30, 19:30 (after dinner), and 21:30. The subjects performed sedentary work all day, and the contents and time of the meals were uniform. Investigation of blood rheology was based on Kikuchis microchannel method. Results Blood passage time varied significantly with time of day. Stepwise regression analysis was used to determine the significant factors affecting blood passage time. Body temperature, heartbeat, hematocrit, white blood cell and total cholesterol were significant determinants of blood passage time. Conclusion We confirmed that blood fluidity has a daily rhythm. In addition, we found that the determinants of blood fluidity included physiological parameters such as body temperature and heartbeat, hematological parameters such as hematocrit, and white blood cell and total cholesterol.

Pulmonary Oxidative Stress Is Induced by Maximal Exercise in Young Cigarette Smokers

INTRODUCTION Oxidative stress is induced by both cigarette smoking and acute exercise. It has also been reported that exercise can induce plasma oxidative stress in young cigarette smokers. However, no previous report has demonstrated that exercise induces pulmonary oxidative stress in cigarette smokers. The aim of this study was to determine whether pulmonary oxidative stress is induced by maximal exercise in cigarette smokers as measured by reactive oxygen species generation and total antioxidant content. METHODS Fifteen male smokers (mean age: 25.9 ± 2.9 years) and 18 male nonsmokers (mean age: 24.2 ± 4.3 years) participated in this study. Hydrogen peroxide (H(2)O(2)) concentration and biological antioxidant potential (BAP) in exhaled breath condensate (EBC) were measured at baseline and after maximal exercise in the Wingate anaerobic test. RESULTS A significant interaction of group by time was observed for EBC H2O2 concentration (p = .015). After exercise, EBC H(2)O(2) concentrations were significantly increased in the smoking group (p = .030) but not in the nonsmoking group. There were no significant changes in EBC BAP in either group. CONCLUSIONS These findings indicate that in cigarette smokers, maximal exercise induces pulmonary oxidative stress, which may lead to oxidative damage in the lungs.

Cigarette Smoking does not Induce Plasma or Pulmonary Oxidative Stress after Moderate-intensity Exercise.

[Purpose] Cigarette smoking increases oxidative stress, which is a risk factor for several diseases. Moreover, strenuous exercise has been shown to induce plasma and pulmonary oxidative stress in young cigarette smokers. However, no previous reports have demonstrated whether plasma and pulmonary oxidative stress occur after moderate-intensity exercise. Therefore, the aim of this study was to clarify whether moderate-intensity exercise induces pulmonary and plasma oxidative stress in smokers. [Subjects] Ten young male smokers and 10 young male nonsmokers participated in this study. [Methods] Plasma hydroperoxide concentrations were measured at baseline and then immediately and 15 min after moderate-intensity exercise. Hydrogen peroxide concentrations in exhaled breath condensate were measured at baseline and after exercise. [Results] No significant interactions were found between smokers and nonsmokers in terms of hydroperoxide or hydrogen peroxide concentrations following moderate-intensity exercise at any time point. [Conclusion] These findings suggested that moderate-intensity exercise did not induce plasma or pulmonary oxidative stress in young cigarette smokers.

The neural influence on the occurrence of locomotor–respiratory coordination

This study focused on the neurogenic mechanisms of coordination between locomotor and respiratory rhythms. The aim of the present study was to investigate the influence of peripheral neurogenic drive from moving limbs, and the level of consciousness, on locomotor-respiratory coordination. Subjects performed movement for 20 min in a supine position using a bicycle ergometer. The movement comprised three types of leg movements: active (loadless) movement, passive movement while awake and passive movement during sleep. We found no difference between active and passive movement in the degree of coordination. However, the degree of coordination during sleep was significantly lower than that while awake (p<0.05). We conclude that peripheral neurogenic drive from moving limbs is able to generate locomotor-respiratory coordination, and that the level of consciousness may influence the degree of coordination.

Plasma oxidative stress is induced by single‐sprint anaerobic exercise in young cigarette smokers

Cigarette smoking increases oxidative stress, which is a risk factor for several diseases. Smoking has also been reported to enhance plasma oxidative stress during strenuous exercise. However, no prior study has examined the changes in plasma oxidative stress after single‐sprint anaerobic exercise in cigarette smokers. The purpose of this study was to investigate these changes in young cigarette smokers by measuring reactive oxygen species generation and total antioxidant content. Participants were 15 male smokers (mean age: 25·9 ± 2·9 years) and 18 male non‐smokers (mean age: 24·2 ± 4·3 years). Hydroperoxide concentration and biological antioxidant potential (BAP) in plasma were measured at baseline and after the Wingate anaerobic test. A significant interaction between group and time was observed for plasma hydroperoxide concentration (P = 0·037). Plasma hydroperoxide concentration was significantly increased after exercise in both smokers and non‐smokers (P = 0·001 and <0·001, respectively). However, no significant interaction was observed between groups by time on plasma BAP (P = 0·574), and a main effect of time was observed (P<0·001). Plasma BAP was significantly increased after exercise in both groups (both, P<0·001). These findings indicate that plasma oxidative stress is higher in cigarette smokers than in non‐smokers after single‐sprint anaerobic exercise, which may increase the risk of oxidative damage.

The effect of exercise on blood fluidity: Use of the capillary model to assess the clogginess of blood.

AIM The goal was to evaluate the effects of exercise on the clogginess of blood as well as the effect of increased blood cell count and hematocrit levels after exercise. We also investigated the mechanisms underlying the clogginess of blood. METHODS The time required for blood to pass through microchannels was measured. We focused on assessing the consecutive passage times for serial 20 μL volumes. We used heparinized peripheral blood obtained from subjects after exercise conducted at three intensity levels. Blood samples were also adjusted to achieve specific hematocrit levels or supplemented by addition of adenosine diphosphate (ADP). RESULTS The sequential blood passage times of consecutive 20 μL volumes increased with platelet aggregation and adhesion of white blood cells (WBC). We also observed an increase with blood cell counts and hematocrit levels. These changes occurred after high intensity exercise but not after low or medium intensity exercise. Furthermore, the sequential blood passage times of 20 μL volumes increased with platelet aggregation and adhesion of WBC at an ADP concentration at the threshold of aggregation but not at higher levels of hematocrit. CONCLUSIONS These findings suggested that high intensity exercise might induce the clogginess of blood by enhanced platelet aggregation and adhesion of WBC.

Phase-dependent modulation of corticospinal excitability during the observation of the initial phase of gait

Abstract This study was undertaken to identify the temporal characteristics of corticospinal excitability of tibialis anterior muscle during the observation of the initial phase of gait. For this purpose, using transcranial magnetic stimulation, we recorded motor evoked potentials (MEPs) during the observation of the second step of an actor’s first three steps of gait initiation with (complex gait) or without (normal gait) an obstacle and unstable surface. The results demonstrate that (1) MEPs during the observation of the initial phase of normal gait were significantly increased only at early swing phase, but not other phases (mid-swing, heel contact, mid-stance, and heel off) and (2) MEPs during the observation of the initial phase of complex gait were significantly increased at early swing and also at mid-swing and heel contact phases. These findings provide the first evidence that corticospinal excitability during the observation of gait, especially the initial phase, is modulated in phase- and motor-demanded-dependent manners.

Effect of body weight support on predicted locomotive physical activity

[Purpose] This study aimed to evaluate the effect of body weight support with an assistive device on predicted locomotive physical activity measured using triaxial accelerometers in healthy young subjects. [Subjects and Methods] Sixteen healthy subjects aged 21.9 ± 1.1 years walked on a treadmill at speeds of 45 and 55 meters/min under 0%, 10%, 20%, and 30% body weight support conditions. Predicted metabolic equivalents and number of steps were evaluated using triaxial accelerometers. Measured metabolic equivalents and number of steps were evaluated using a metabolic system and observers, respectively. Raw data of synthetic accelerations were also obtained. [Results] Predicted metabolic equivalents and number of steps and raw data of synthetic accelerations decreased with increasing amounts of body weight support. [Conclusion] These findings suggest that accelerometers may underestimate locomotive physical activity with increasing amounts of body weight support using assistive devices. Thus, it is important to consider the amount of body weight support when assessing physical activities in subjects using assistive devices for mobility.