Keita Ishibashi

Inter-individual difference in pupil size correlates to suppression of melatonin by exposure to light

There are large inter-individual differences in pupil size and suppression of melatonin by exposure to light. It has been reported that melatonin suppression by exposure to light increases when pupils are pharmacologically dilated. However, the correlation between normal inter-individual difference in pupil size and melatonin suppression by exposure to light is not clear. Twenty-three healthy male subjects (22.6+/-2.7 years old) were exposed to light (1000 lx) for 2 h at night. The starting time of exposure to light was set to the ascending phase of melatonin concentration of each subject. Pupil area and saliva melatonin concentration were measured before exposure to light under dim light (15 lx) and during exposure to light. There were large inter-individual differences in melatonin suppression and pupil area. The mean and standard deviation of percentage of melatonin suppression 2 h after exposure to light was 57.2+/-22.1%. The mean and standard deviation of pupil areas before and 2 h after exposure to light were 30.7+/-7.9 mm2 and 15.9+/-4.8 mm2, respectively. The percentage of melatonin suppression by light was positively correlated with pupil area during light exposure (r=0.525, p<0.02). Interestingly, it was also correlated with pupil area measured before exposure to light, under dim light (15 lx) (r=0.658, p<0.001). These results suggest that inter-individual difference in pupil area positively correlates with melatonin suppression by light and that pupil area under dim light is a predictor of inter-individual differences in melatonin suppression by light.

Essential oil of lavender inhibited the decreased attention during a long-term task in humans.

This study examined the effects of odors on sustained attention during a vigilance task. Two essential oils (lavender and eucalyptus) and two materials (l-menthol and linalyl acetate) were compared with a control. The increase in reaction time was significantly lower with lavender than with the control. The results suggest that the administration of lavender helped to maintain sustained attention during the long-term task.

Thermoregulatory effect in humans of suppressed endogenous melatonin by pre-sleep bright-light exposure in a cold environment

This study investigated the physiological function of suppressed melatonin through thermoregulation in a cold environment. Interactions between thermoregulation directly affected by exposure to a cold environment and indirectly affected by endogenous melatonin suppression by bright-light exposure were examined. Ten male subjects were exposed to two different illumination intensities (30 and 5000 lux) for 4.5 h, and two different ambient temperatures (15 and 27°C) for 2 h before sleep under dark and thermoneutral conditions. Salivary melatonin level was suppressed by bright light (p < 0.001), although the ambient temperature condition had no significant effect on melatonin. During sleep, significant effects of pre-sleep exposure to a cold ambient temperature (p < 0.001) and bright light (p < 0.01) on rectal temperature (Tre) were observed. Pre-sleep, bright-light exposure led to an attenuated fall in Tre during sleep. Moreover, Tre dropped more precipitously after cold exposure than thermoneutral conditions (cold: −0.54 ± 0.07°C/h; thermoneutral: −0.16 ± 0.03°C/h; p < 0.001). Pre-sleep, bright-light exposure delayed the nadir time of Tre under thermoneutral conditions (p < 0.05), while cold exposure masked the circadian rhythm with a precipitous decrease in Tre. A significant correlation between the Tre nadir and melatonin level (r = −0.774, p < 0.05) indicated that inter-individual differences with higher melatonin levels lead to a reduction in Tre after cold exposure. These results suggest that suppressed endogenous melatonin inhibits the downregulation of the body temperature set-point during sleep. (Author correspondence: ishibasi@design.kyushu-u.ac.jp)

Comparison of cardiovascular response to sinusoidal and constant lower body negative pressure with reference to very mild whole-body heating

BackgroundThe purpose of the present study was to compare sinusoidal versus constant lower body negative pressure (LBNP) with reference to very mild whole-body heating. Sinusoidal LBNP has a periodic load component (PLC) and a constant load component (CLC) of orthostatic stress, whereas constant LBNP has only a CLC. We tested two sinusoidal patterns (30-s and 180-s periods with 25 mmHg amplitude) of LBNP and a constant LBNP with −25 mmHg in 12 adult male subjects.ResultsAlthough the CLC of all three LBNP conditions were configured with −25 mmHg, the mean arterial pressure (MAP) results showed a significantly large decrease from baseline in the 30-s period condition (P <0.01). In contrast, the other cardiovascular indices (heart rate (HR), stroke volume (SV), cardiac output (CO), basal thoracic impedance (Z0), total peripheral resistance (TPR), the natural logarithmic of the HF component (lnHF), and LF/HF (ln(LF/HF))) of heart rate variability (HRV) showed relatively small variations from baseline in the 30-s period condition (P <0.01). The result of the gain and phase of transfer function at the sinusoidal period of LBNP showed that the very mild whole-body heating augmented the orthostatic responses.ConclusionThese results revealed that the effect of the CLC of LBNP on cardiovascular adjustability was attenuated by the addition of the PLC to LBNP. Based on the results of suppressed HRV response from baseline in the 30-s period condition, we suggest that the attenuation may be caused by the suppression of the vagal responsiveness to LBNP.

Relative Contributions of Systemic Hemodynamic Variables to Cerebral Autoregulation during Orthostatic Stress

Postural changes impair the ability of the cerebrovasculature to buffer against dynamic pressure fluctuations, but the mechanisms underlying this impairment have not been elucidated. We hypothesized that autoregulatory impairment may reflect the impact of static central volume shifts on hemodynamic factors other than arterial pressure (AP). In 14 young volunteers, we assessed the relation of fluctuations in cerebral blood flow (CBF) to those in AP, cardiac output, and CO2, during oscillatory lower body pressure (LBP) (±20 mmHg at 0.01 and 0.06 Hz) at three static levels (-20, 0, and +20 mmHg). Static and dynamic changes in AP, cardiac output, and CO2 explained over 70% of the variation in CBF fluctuations. However, their contributions were different across frequencies and levels: dynamic AP changes explained a substantial proportion of the variation in faster CBF fluctuations (partial R2 = 0.75, standardized β = 0.83, P < 0.01), whereas those in CO2 explained the largest portion of the variation in slow fluctuations (partial R2 = 0.43, β = 0.51, P < 0.01). There was, however, a major contribution of slow dynamic AP changes during negative (β = 0.43) but not neutral (β = 0.05) or positive (β = -0.07) LBP. This highlights the differences in contributions of systemic variables to dynamic and static autoregulation and has important implications for understanding orthostatic intolerance. NEW & NOTEWORTHY While fluctuations in blood pressure drive faster fluctuations in cerebral blood flow, overall level of CO2 and the magnitude of its fluctuations, along with cardiac output, determine the magnitude of slow ones. The effect of slow blood pressure fluctuations on cerebrovascular responses becomes apparent only during pronounced central volume shifts (such as when standing). This underlines distinct but interacting contributions of static and dynamic changes in systemic hemodynamic variables to the cerebrovascular regulation.

E1-3 Effects of Active and Passive Touch on Curvature Aftereffect

凸(凹)の曲面に指で一定時間触れた後、平らな 表面を触ると、その表面が凹(凸)に知覚される という順応現象(Curvature Aftereffect)が報告 されている(図1)。先行研究では、物体への 接触方法として、自発的に手を動かして物体に触 れる能動的接触と、物体が動くことで静止した手 に触れる受動的接触の条件を設定し、両者で順応 現象が生じることを報告しているが、順応現象の 大きさは能動的接触条件のほうが受動的接触条件 に比べ大きいことが報告されている。また、この ような順応現象は物体に手で直接触れた場合だけ でなく、力覚提示デバイスのような道具を用いて 物体に触れる感覚を提示した場合においてもみら れるといわれている。しかし、その報告では能 動的接触条件でのみ順応現象が確認されており、 受動的接触条件では確認されていない。 本研究では、力触覚提示デバイスを用いた能動 的・受動的接触感の提示が順応現象にどのような 影響を及ぼすかを明らかにすることを目的とした。

Additive Effects of Sinusoidal Lower Body Negative Pressure on Cardiovascular Responses

BACKGROUND Sinusoidal lower body negative pressure (SLBNP) has been used to investigate the cardiovascular response to slow periodic changes in blood shifts, but measurements of slow fluctuations take a long time if measured for each period of SLBNP separately. Our study aimed to investigate whether the cardiovascular responses to superimposed SLBNP (S-SLBNP), which is expected to reduce the measurement time, are different from responses measured individually. METHODS S-SLBNP was configured by superimposing two conventional SLBNPs (C-SLBNP) at 180-s and 30-s periods in the pressure range from 0 to -25 mmHg. As the S-SLBNP has double the static load of C-SLBNP, we also used offset SLBNP (O-SLBNP), which has the same static load level as S-SLBNP. Heart rate (HR), thoracic impedance (Z0), and mean arterial pressure (MAP) were measured from 11 male subjects. The transfer functions of gains from MAP to HR (Gain-HR/MAP) and from Z0 to HR (Gain-HR/Z0) were calculated as indexes of arterial baroreflex and cardiopulmonary baroreflex regulation of HR, respectively. RESULTS The Gain-HR/MAP in the 180-s period (2.11 ± 0.17 bpm/mmHg; mean ± SEM) was larger than that of the 30-s period (1.04 ± 0.09 bpm/mmHg); however, there was no significant difference between the SLBNP conditions. The Gain-HR/Z0 in C-SLBNP (9.37 ± 1.47 bpm/ohm) was smaller than that of the other conditions [18.46 ± 2.45 bpm/ohm (O-SLBNP); 16.09 ± 2.29 bpm/ohm (S-SLBNP)]. DISCUSSION Using S-SLBNP could reduce the measurement time needed to examine the arterial baroreflex. However, the cardiopulmonary baroreflex was modified by the static load of SLBNP.Ishibashi K, Oyama F, Yoshida H, Iwanaga K. Additive effects of sinusoidal lower body negative pressure on cardiovascular responses. Aerosp Med Hum Perform. 2017; 88(2):137-141.