Masahiro Horiuchi

Skin blood flow influences cerebral oxygenation measured by near-infrared spectroscopy during dynamic exercise

AbstractPurposeNear-infrared spectroscopy (NIRS) is widely usedn to investigate cerebral oxygenation and/or neural activation during physiological conditions such as exercise. However, NIRS-determined cerebral oxygenated hemoglobin (O2Hb) may not necessarily correspond to intracranial blood flow during dynamic exercise. To determine the selectivity of NIRS to assess cerebral oxygenation and neural activation during exercise, we examined the influence of changes in forehead skin blood flow (SkBFhead) on NIRS signals during dynamic exercise.MethodsIn ten healthy men (age: 20xa0±xa01xa0years), middle cerebral artery blood flow velocity (MCA Vmean, via transcranial Doppler ultrasonography), SkBFhead (via laser Doppler flowmetry), and cerebral O2Hb (via NIRS) were continuously measured. Each subject performed 60xa0% maximum heart rate moderate-intensity steady-state cycling exercise. To manipulate SkBFhead, facial cooling using a mist of cold water (~4xa0°C) was applied for 3xa0min during steady-state cycling.ResultsMCA Vmean significantly increased during exercise and remained unchanged with facial cooling. O2Hb and SkBFhead were also significantly increased during exercise; however, both of these signals were lowered with facial cooling and returned to pre-cooling values with the removal of facial cooling. The changes in O2Hb correlated significantly with the relative percent changes in SkBFhead in each individual (rxa0=xa00.71–0.99).ConclusionsThese findings suggest that during dynamic exercise NIRS-derived O2Hb signal can be influenced by thermoregulatory changes in SkBFhead and therefore, may not be completely reflective of cerebral oxygenation or neural activation.

Impact of ischemic preconditioning on functional sympatholysis during handgrip exercise in humans

Repeated bouts of ischemia followed by reperfusion, known as ischemic preconditioning (IPC), is found to improve exercise performance. As redistribution of blood from the inactive areas to active skeletal muscles during exercise (i.e., functional sympatholysis) is important for exercise performance, we examined the hypothesis that IPC improves functional sympatholysis in healthy, young humans. In a randomized study, 15 healthy young men performed a 10‐min resting period, dynamic handgrip exercise at 10% maximal voluntary contraction (MVC), and 25% MVC. This protocol was preceded by IPC (IPC; 4 × 5‐min 220‐mmHg unilateral occlusion) or a sham intervention (CON; 4 × 5‐min 20‐mmHg unilateral occlusion). Near‐infrared spectroscopy was used to assess changes in oxygenated hemoglobin and myoglobin in skeletal muscle (HbO2 + MbO2) in response to sympathetic activation (via cold pressor test (CPT)) at baseline and during handgrip exercise (at 10% and 25%). In resting conditions, HbO2 + MbO2 significantly decreased during CPT (−11.0 ± 1.0%), which was significantly larger during the IPC‐trial (−13.8 ± 1.2%, P = 0.006). During handgrip exercise at 10% MVC, changes in HbO2 + MbO2 in response to the CPT were blunted after IPC (−8.8 ± 1.5%) and CON (−8.3 ± 0.4%, P = 0.593). During handgrip exercise at 25% MVC, HbO2 + MbO2 in response to the CPT increased (2.0 ± 0.4%), whereas this response was significantly larger when preceded by IPC (4.2 ± 0.6%, P = 0.027). Collectively, these results indicate that IPC‐induced different vascular changes at rest and during moderate exercise in response to sympathetic activation. This suggests that, in healthy volunteers, exposure to IPC may alter tissue oxygenation during sympathetic stimulation at rest and during exercise.

Impact of viewing vs. not viewing a real forest on physiological and psychological responses in the same setting.

We investigated the impact of viewing versus not viewing a real forest on human subjects’ physiological and psychological responses in the same setting. Fifteen healthy volunteers (11 males, four females, mean age 36 years) participated. Each participant was asked to view a forest while seated in a comfortable chair for 15 min (Forest condition) vs. sitting the same length of time with a curtain obscuring the forest view (Enclosed condition). Both conditions significantly decreased blood pressure (BP) variables, i.e., systolic BP, diastolic BP, and mean arterial pressure between pre and post experimental stimuli, but these reductions showed no difference between conditions. Interestingly, the Forest viewing reduced cerebral oxygenated hemoglobin (HbO2) assessed by near-infrared spectroscopy (NIRS) and improved the subjects’ Profile of Mood States (POMS) scores, whereas the Enclosed condition increased the HbO2 and did not affect the POMS scores. There were no significant differences in saliva amylase or heart rate variability (HRV) between the two conditions. Collectively, these results suggest that viewing a real forest may have a positive effect on cerebral activity and psychological responses. However, both viewing and not viewing the forest had similar effects on cardiovascular responses such as BP variables and HRV.

Face cooling with mist water increases cerebral blood flow during exercise: effect of changes in facial skin blood flow

Facial cooling (FC) increases cerebral blood flow (CBF) at rest and during exercise; however, the mechanism of this response remains unclear. The purpose of the present study was to test our hypothesis that FC causes facial vasoconstriction that diverts skin blood flow (SkBFface) toward the middle cerebral artery (MCA Vmean) at rest and to a greater extent during exercise. Nine healthy young subjects (20 ± 2 years) underwent 3 min of FC by fanning and spraying the face with a mist of cold water (~4°C) at rest and during steady-state exercise [heart rate (HR) of 120 bpm]. We focused on the difference between the averaged data acquired from 1 min immediately before FC and last 1 min of FC. SkBFface, MCA Vmean, and mean arterial blood pressure (MAP) were higher during exercise than at rest. As hypothesized, FC decreased SkBFface at rest (−32 ± 4%) and to a greater extent during exercise (−64 ± 10%, P = 0.012). Although MCA Vmean was increased by FC (Rest, +1.4 ± 0.5 cm/s; Exercise, +1.4 ± 0.6 cm/s), the amount of the FC-evoked changes in MCA Vmean at rest and during exercise differed among subjects. In addition, changes in MCA Vmean with FC did not correlate with concomitant changes in SkBFface (r = 0.095, P = 0.709). MAP was also increased by FC (Rest, +6.2 ± 1.4 mmHg; Exercise, +4.2 ± 1.2 mmHg). These findings suggest that the FC-induced increase in CBF during exercise could not be explained only by change in SkBFface.

Kinetics of exercise‐induced neural activation; interpretive dilemma of altered cerebral perfusion

Neural activation decreases cerebral deoxyhaemoglobin (HHbC) and increases oxyhaemoglobin concentration (O2HbC). In contrast, patients who present with restricted cerebral blood flow, such as those suffering from cerebral ischaemia or Alzheimers disease, and during the course of ageing the converse occurs, in that HHbC increases and O2HbC decreases during neural activation. In the present study, we examined the interpretive implications of altered exercise‐induced cerebral blood flow for cortical oxygenation in healthy subjects. Both O2HbC and HHbC (prefrontal cortex) were determined in 11 healthy men using near‐infrared spectroscopy (NIRS). Middle cerebral artery mean blood velocity (MCA Vmean) was determined via transcranial Doppler ultrasonography. Measurements were performed during contralateral hand‐grip exercise during suprasystolic bilateral thigh‐cuff occlusion (Cuff+) and within 2 s of cuff release (Cuff–) for the acute manipulation of cerebral perfusion. During Cuff+, both MCA Vmean and O2HbC increased during exercise, whereas HHbC decreased. In contrast, the opposite occurred during the Cuff– manipulation. These findings highlight the inverse relationship between cerebral blood flow and cerebral oxygenation as determined by NIRS, which has interpretive implications for the kinetics underlying exercise‐induced neural activation.

Economical Speed and Energetically Optimal Transition Speed Evaluated by Gross and Net Oxygen Cost of Transport at Different Gradients

The oxygen cost of transport per unit distance (CoT; mL·kg-1·km-1) shows a U-shaped curve as a function of walking speed (v), which includes a particular walking speed minimizing the CoT, so called economical speed (ES). The CoT-v relationship in running is approximately linear. These distinctive walking and running CoT-v relationships give an intersection between U-shaped and linear CoT relationships, termed the energetically optimal transition speed (EOTS). This study investigated the effects of subtracting the standing oxygen cost for calculating the CoT and its relevant effects on the ES and EOTS at the level and gradient slopes (±5%) in eleven male trained athletes. The percent effects of subtracting the standing oxygen cost (4.8 ± 0.4 mL·kg-1·min-1) on the CoT were significantly greater as the walking speed was slower, but it was not significant at faster running speeds over 9.4 km·h-1. The percent effect was significantly dependent on the gradient (downhill > level > uphill, P < 0.001). The net ES (level 4.09 ± 0.31, uphill 4.22 ± 0.37, and downhill 4.16 ± 0.44 km·h-1) was approximately 20% slower than the gross ES (level 5.15 ± 0.18, uphill 5.27 ± 0.20, and downhill 5.37 ± 0.22 km·h-1, P < 0.001). Both net and gross ES were not significantly dependent on the gradient. In contrast, the gross EOTS was slower than the net EOTS at the level (7.49 ± 0.32 vs. 7.63 ± 0.36 km·h-1, P = 0.003) and downhill gradients (7.78 ± 0.33 vs. 8.01 ± 0.41 km·h-1, P < 0.001), but not at the uphill gradient (7.55 ± 0.37 vs. 7.63 ± 0.51 km·h-1, P = 0.080). Note that those percent differences were less than 2.9%. Given these results, a subtraction of the standing oxygen cost should be carefully considered depending on the purpose of each study.

Differential effect of sympathetic activation on tissue oxygenation in gastrocnemius and soleus muscles during exercise in humans

What is the central question of this study? The normal ability of sympathetic nerves to cause vasoconstriction is blunted in exercising skeletal muscle, a phenomenon termed ‘functional sympatholysis’. Animal studies suggest that functional sympatholysis appears to occur preferentially in fast‐twitch type II glycolytic compared with slow‐twitch type I oxidative skeletal muscle. We asked whether these findings can be extended to humans. What is the main finding and its importance? We show that skeletal muscles composed largely of fast‐twitch type II fibres may also be more sensitive to functional sympatholysis in humans, particularly at lower exercise intensities. Additionally, independent of muscle fibre type composition, the magnitude of sympatholysis is strongly related to exercise‐induced increases in metabolic demand.

Comparisons of energy cost and economical walking speed at various gradients in healthy, active younger and older adults

Background/ObjectivenOxygen consumption during walking per unit distance (Cw ; mL/kg/m) is known to be greater for older adults than younger adults, although its underlying process is controversial.nnnMethodsnWe measured the Cw values at six gait speeds from 30xa0m/min to 105xa0m/min on level ground and gradient slopes (±5%) in healthy younger and older male adults. A quadratic approximation was applied for a relationship between Cw and gait speeds (v; m/min). It gives a U-shaped Cw -v relationship, which includes a particular gait speed minimizing the Cw , the so-called economical speed (ES). The age-related difference of the Cw -v relationship was assessed by comparisons of ES and/or Cw .nnnResultsnA significantly greater Cw at 30xa0m/min and slower ES were found for older adults at the downhill gradient, suggesting that a combination of leftward and upward shifts of the Cw -v relationship was found at that gradient. Only a slower ES was found for older adults at the uphill gradient, suggesting that a leftward shift was found for older adults at that gradient. Neither a significant leftward nor an upward shift was found at the level gradient. Leg length significantly correlated to the ES for younger adults at the level and downhill gradients, while such a significant relationship was observed only at the level gradient for older adults. The maximal quadriceps muscle strength significantly correlated to the ES for older adults at all gradients, but not for younger adults.nnnConclusionnThe age-related alteration of the Cw -v relationship depends on the gradient, and its related factors were different between age groups.

Walking economy at simulated high altitude in human healthy young male lowlanders

ABSTRACT We measured oxygen consumption during walking per unit distance (Cw) values for 12 human healthy young males at six speeds from 0.667 to 1.639u2005mu2005s−1 (four min per stage) on a level gradient under normobaric normoxia, moderate hypoxia (15% O2), and severe hypoxia (11% O2). Muscle deoxygenation (HHb) was measured at the vastus lateralis muscle using near-infrared spectroscopy. Economical speed which can minimize the Cw in each individual was calculated from a U-shaped relationship. We found a significantly slower economical speed (ES) under severe hypoxia [1.237 (0.056) m s−1; mean (s.d.)] compared to normoxia [1.334 (0.070) m s−1] and moderate hypoxia [1.314 (0.070) m s−1, P<0.05 respectively] with no differences between normoxia and moderate hypoxia (P>0.05). HHb gradually increased with increasing speed under severe hypoxia, while it did not increase under normoxia and moderate hypoxia. Changes in HHb between standing baseline and the final minute at faster gait speeds were significantly related to individual ES (r=0.393 at 1.250u2005mu2005s−1, r=0.376 at 1.444u2005mu2005s−1, and r=0.409 at 1.639u2005mu2005s−1, P<0.05, respectively). These results suggested that acute severe hypoxia slowed ES by ∼8%, but moderate hypoxia left ES unchanged. Summary: Acute severe hypoxia slowed the economical speed (ES) which can minimize energy cost of walking. Muscle O2 extraction may be one of the determining factors of an individuals ES.

Relationship between aerobic endurance training and dynamic cerebral blood flow regulation in humans.

The incidence of orthostatic intolerance is elevated in endurance‐trained individuals. We sought to test the hypothesis that aerobic endurance training is associated with an attenuated control of the cerebral vasculature. Endurance trained (ET, nu2009=u200913) and age‐matched untrained (UT, nu2009=u200911) individuals (peak O2 consumption, meanu2009±u2009SEM; 63u2009±u20091 vs 42u2009±u20091u2009mL/min/kg, Pu2009<u20090.05) were examined while supine and seated upright. Dynamic cerebral autoregulation (CA) was assessed by calculation of the rate of regulation (RoR) from the arterial blood pressure (ABP) and middle cerebral artery (MCA) mean blood velocity (Vmean) responses to a bilateral thigh cuff release, which evoked a transient hypotension. Cerebral oxygenation (oxyhemoglobin; HbO2) was determined with near‐infrared spectroscopy. When seated upright, cuff release evoked a greater decrease in ABP (Pu2009<u20090.001), MCA Vmean (Pu2009=u20090.096) and HbO2 (Pu2009<u20090.001) in ET compared with UT. However, RoR was similar in ET and UT individuals while seated upright (to 0.193u2009±u20090.039 vs 0.129u2009±u20090.029/s, Pu2009>u20090.05), and there was no significant difference in the relative change in RoR from the supine to upright positions (ΔRoR: −65u2009±u20097 and −69u2009±u20097%, for ET and UT, respectively). These findings suggest that aerobic endurance training is not associated with an attenuation in dynamic CA.