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Fujii N, McGarr GW, Amano T, Nishiyasu T, Sigal RJ, Kenny GP. Type 2 diabetes impairs vascular responsiveness to nitric oxide, but not the venoarteriolar reflex or post-occlusive reactive hyperaemia in forearm skin. Exp Dermatol 2021; 30:1807-1813. [PMID: 34114706 DOI: 10.1111/exd.14408] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 04/21/2021] [Accepted: 06/01/2021] [Indexed: 11/28/2022]
Abstract
The venoarteriolar reflex (VAR) is a local mechanism by which vasoconstriction is mediated in response to venous congestion. This response may minimize tissue overperfusion, preventing capillary damage and oedema. Post-occlusive reactive hyperaemia (PORH) is used to assess microvascular function by performing a brief local arterial occlusion resulting in a subsequent rapid transient vasodilation. In the current study, we hypothesized that type 2 diabetes (T2D) attenuates VAR and PORH responses in forearm skin in vivo. In 11 healthy older adults (Control, 58 ± 8 years) and 13 older adults with controlled T2D (62 ± 10 years), cutaneous blood flow measured by laser-Doppler flowmetry was monitored following a 3-min venous occlusion of 45 mm Hg that elicited the VAR, followed by a 3-min recovery period and then a 5-min arterial occlusion of 240 mm Hg that induced PORH. Finally, sodium nitroprusside, a nitric oxide donor, was administered to induce maximum vasodilation. VAR and PORH variables were similar between groups. By contrast, maximal cutaneous blood flow induced by sodium nitroprusside was lower in the T2D group. Taken together, our observations indicate that T2D impairs vascular smooth muscle responsiveness to nitric oxide, but not VAR and PORH in forearm skin.
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Affiliation(s)
- Naoto Fujii
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Japan
| | - Gregory W McGarr
- Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Canada
| | - Tatsuro Amano
- Laboratory for Exercise and Environmental Physiology, Faculty of Education, Niigata University, Niigata, Japan
| | - Takeshi Nishiyasu
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Japan
| | - Ronald J Sigal
- Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Canada.,Departments of Medicine, Cardiac Sciences and Community Health Sciences, Faculties of Medicine and Kinesiology, University of Calgary, Canada
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Canada
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2
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Tsuji B, Filingeri D, Honda Y, Eguchi T, Fujii N, Kondo N, Nishiyasu T. Effect of hypocapnia on the sensitivity of hyperthermic hyperventilation and the cerebrovascular response in resting heated humans. J Appl Physiol (1985) 2018; 124:225-233. [DOI: 10.1152/japplphysiol.00232.2017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Elevating core temperature at rest causes increases in minute ventilation (V̇e), which lead to reductions in both arterial CO2 partial pressure (hypocapnia) and cerebral blood flow. We tested the hypothesis that in resting heated humans this hypocapnia diminishes the ventilatory sensitivity to rising core temperature but does not explain a large portion of the decrease in cerebral blood flow. Fourteen healthy men were passively heated using hot-water immersion (41°C) combined with a water-perfused suit, which caused esophageal temperature (Tes) to reach 39°C. During heating in two separate trials, end-tidal CO2 partial pressure decreased from the level before heating (39.4 ± 2.0 mmHg) to the end of heating (30.5 ± 6.3 mmHg) ( P = 0.005) in the Control trial. This decrease was prevented by breathing CO2-enriched air throughout the heating such that end-tidal CO2 partial pressure did not differ between the beginning (39.8 ± 1.5 mmHg) and end (40.9 ± 2.7 mmHg) of heating ( P = 1.00). The sensitivity to rising Tes (i.e., slope of the Tes − V̇E relation) did not differ between the Control and CO2-breathing trials (37.1 ± 43.1 vs. 16.5 ± 11.1 l·min−1·°C−1, P = 0.31). In both trials, middle cerebral artery blood velocity (MCAV) decreased early during heating (all P < 0.01), despite the absence of hyperventilation-induced hypocapnia. CO2 breathing increased MCAV relative to Control at the end of heating ( P = 0.005) and explained 36.6% of the heat-induced reduction in MCAV. These results indicate that during passive heating at rest ventilatory sensitivity to rising core temperature is not suppressed by hypocapnia and that most of the decrease in cerebral blood flow occurs independently of hypocapnia. NEW & NOTEWORTHY Hyperthermia causes hyperventilation and concomitant hypocapnia and cerebral hypoperfusion. The last may underlie central fatigue. We are the first to demonstrate that hyperthermia-induced hyperventilation is not suppressed by the resultant hypocapnia and that hypocapnia explains only 36% of cerebral hypoperfusion elicited by hyperthermia. These new findings advance our understanding of the mechanisms controlling ventilation and cerebral blood flow during heat stress, which may be useful for developing interventions aimed at preventing central fatigue during hyperthermia.
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Affiliation(s)
- Bun Tsuji
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan
- Department of Health Sciences, Prefectural University of Hiroshima, Hiroshima, Japan
| | - Davide Filingeri
- Environmental Ergonomics Research Centre, Loughborough Design School, Loughborough University, Loughborough, United Kingdom
| | - Yasushi Honda
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan
| | - Tsubasa Eguchi
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan
| | - Naoto Fujii
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan
| | - Narihiko Kondo
- Faculty of Human Development, Kobe University, Kobe, Japan
| | - Takeshi Nishiyasu
- Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan
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Effects of Changes in Arterial Carbon Dioxide and Oxygen Partial Pressures on Cerebral Oximeter Performance. Anesthesiology 2017; 128:97-108. [PMID: 29084012 DOI: 10.1097/aln.0000000000001898] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Cerebral oximetry (cerebral oxygen saturation; ScO2) is used to noninvasively monitor cerebral oxygenation. ScO2 readings are based on the fraction of reduced and oxidized hemoglobin as an indirect estimate of brain tissue oxygenation and assume a static ratio of arterial to venous intracranial blood. Conditions that alter cerebral blood flow, such as acute changes in PaCO2, may decrease accuracy. We assessed the performance of two commercial cerebral oximeters across a range of oxygen concentrations during normocapnia and hypocapnia. METHODS Casmed FORE-SIGHT Elite (CAS Medical Systems, Inc., USA) and Covidien INVOS 5100C (Covidien, USA) oximeter sensors were placed on 12 healthy volunteers. The fractional inspired oxygen tension was varied to achieve seven steady-state levels including hypoxic and hyperoxic PaO2 values. ScO2 and simultaneous arterial and jugular venous blood gas measurements were obtained with both normocapnia and hypocapnia. Oximeter bias was calculated as the difference between the ScO2 and reference saturation using manufacturer-specified weighting ratios from the arterial and venous samples. RESULTS FORE-SIGHT Elite bias was greater during hypocapnia as compared with normocapnia (4 ± 9% vs. 0 ± 6%; P < 0.001). The INVOS 5100C bias was also lower during normocapnia (5 ± 15% vs. 3 ± 12%; P = 0.01). Hypocapnia resulted in a significant decrease in mixed venous oxygen saturation and mixed venous oxygen tension, as well as increased oxygen extraction across fractional inspired oxygen tension levels (P < 0.0001). Bias increased significantly with increasing oxygen extraction (P < 0.0001). CONCLUSIONS Changes in PaCO2 affect cerebral oximeter accuracy, and increased bias occurs with hypocapnia. Decreased accuracy may represent an incorrect assumption of a static arterial-venous blood fraction. Understanding cerebral oximetry limitations is especially important in patients at risk for hypoxia-induced brain injury, where PaCO2 may be purposefully altered.
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Fujii N, Nikawa T, Tsuji B, Kenny GP, Kondo N, Nishiyasu T. Wearing graduated compression stockings augments cutaneous vasodilation but not sweating during exercise in the heat. Physiol Rep 2017; 5:5/9/e13252. [PMID: 28483859 PMCID: PMC5430121 DOI: 10.14814/phy2.13252] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Accepted: 03/20/2017] [Indexed: 11/24/2022] Open
Abstract
The activation of cutaneous vasodilation and sweating are essential to the regulation of core temperature during exercise in the heat. We assessed the effect of graduated compression induced by wearing stockings on cutaneous vasodilation and sweating during exercise in the heat (30°C). On two separate occasions, nine young males exercised for 45 min or until core temperature reached ~1.5°C above baseline resting while wearing either (1) stockings causing graduated compression (graduate compression stockings, GCS), or (2) loose‐fitting stockings without compression (Control). Forearm vascular conductance was evaluated by forearm blood flow (venous occlusion plethysmography) divided by mean arterial pressure to estimate cutaneous vasodilation. Sweat rate was estimated using the ventilated capsule technique. Core and skin temperatures were measured continuously. Exercise duration was similar between conditions (Control: 42.2 ± 3.6 min vs. GCS: 42.2 ± 3.6 min, P = 1.00). Relative to Control, GCS increased forearm vascular conductance during the late stages (≥30 min) of exercise (e.g., at 40 min, 15.6 ± 5.6 vs. 18.0 ± 6.0 units, P = 0.01). This was paralleled by a greater sensitivity (23.1 ± 9.1 vs. 32.1 ± 15.0 units°C−1, P = 0.043) and peak level (14.1 ± 5.1 vs. 16.3 ± 5.7 units, P = 0.048) of cutaneous vasodilation as evaluated from the relationship between forearm vascular conductance with core temperature. However, the core temperature threshold at which an increase in forearm vascular conductance occurred did not differ between conditions (Control: 36.9 ± 0.2 vs. GCS: 37.0 ± 0.3°C, P = 0.13). In contrast, no effect of GCS on sweating was measured (all P > 0.05). We show that the use of GCS during exercise in the heat enhances cutaneous vasodilation and not sweating.
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Affiliation(s)
- Naoto Fujii
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Japan.,Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Canada
| | - Toshiya Nikawa
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Japan
| | - Bun Tsuji
- Faculty of Human Culture and Science, Prefectural University of Hiroshima, Hiroshima, Japan
| | - Glen P Kenny
- Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Canada
| | - Narihiko Kondo
- Faculty of Human Development, Kobe University, Kobe, Japan
| | - Takeshi Nishiyasu
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Japan
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5
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Low DA, Bailey TG, Timothy Cable N, Jones H. Thermoregulatory responses to combined moderate heat stress and hypoxia. Microcirculation 2016; 23:487-494. [PMID: 27418172 DOI: 10.1111/micc.12297] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Accepted: 07/11/2016] [Indexed: 11/29/2022]
Abstract
OBJECTIVE The aim of this study was to examine the cutaneous vascular and sudomotor responses to combined moderate passive heat stress and normobaric hypoxia. METHOD Thirteen healthy young males, dressed in a water-perfused suit, underwent passive heating (Δcore temperature ~0.7°C) twice (Normoxia; 20.9% O2 and Hypoxia; 13% O2 ). Chest and forearm skin blood flow (SkBF; laser-Doppler flux) and sweat rate (SR; capacitance hygrometry), core (intestinal pill), and skin temperatures, were recorded. RESULTS Hypoxia reduced baseline oxygen saturation (98±1 vs 89±6%, P<.001) and elevated chest (P=.03) and forearm SkBF (P=.03), and HR (64±9 vs 69±8 beats.min-1 , P<.01). During heating, mean body temperature (T¯BODY) thresholds for SkBF (P=.41) and SR (P=.28) elevations were not different between trials. The SkBF: T¯BODY linear sensitivity during the initial phase of heating was lower at the chest (P=.035) but not different at the forearm (P=.17) during hypoxia. With increasing levels of heating chest SkBF was not different (P=.55) but forearm SkBF was lower (P<.01) during hypoxia. Chest (P=.85) and forearm (P=.79) SR: T¯BODY linear sensitivities were not different between trials. CONCLUSION While sudomotor responses and the initiation of cutaneous blood flow elevations are unaffected, hypoxia differentially effects regional SkBF responses during moderate passive heating.
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Affiliation(s)
- David A Low
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK.
| | - Tom G Bailey
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK
| | - Nigel Timothy Cable
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK.,Aspire Academy for Sports Excellence, Doha, Qatar
| | - Helen Jones
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK
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Tsuji B, Hayashi K, Kondo N, Nishiyasu T. Characteristics of hyperthermia-induced hyperventilation in humans. Temperature (Austin) 2016; 3:146-60. [PMID: 27227102 PMCID: PMC4879782 DOI: 10.1080/23328940.2016.1143760] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 01/14/2016] [Accepted: 01/14/2016] [Indexed: 11/11/2022] Open
Abstract
In humans, hyperthermia leads to activation of a set of thermoregulatory responses that includes cutaneous vasodilation and sweating. Hyperthermia also increases ventilation in humans, as is observed in panting dogs, but the physiological significance and characteristics of the hyperventilatory response in humans remain unclear. The relative contribution of respiratory heat loss to total heat loss in a hot environment in humans is small, and this hyperventilation causes a concomitant reduction in arterial CO2 pressure (hypocapnia), which can cause cerebral hypoperfusion. Consequently, hyperventilation in humans may not contribute to the maintenance of physiological homeostasis (i.e., thermoregulation). To gain some insight into the physiological significance of hyperthermia-induced hyperventilation in humans, in this review, we discuss 1) the mechanisms underlying hyperthermia-induced hyperventilation, 2) the factors modulating this response, and 3) the physiological consequences of the response.
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Affiliation(s)
- Bun Tsuji
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Japan; Department of Health Sciences, Prefectural University of Hiroshima, Hiroshima, Japan
| | - Keiji Hayashi
- Junior College, University of Shizuoka , Shizuoka, Japan
| | - Narihiko Kondo
- Faculty of Human Development, Kobe University , Kobe, Japan
| | - Takeshi Nishiyasu
- Institute of Health and Sport Sciences, University of Tsukuba , Tsukuba City, Japan
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7
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Lund A, Secher NH, Hirasawa A, Ogoh S, Hashimoto T, Schytz HW, Ashina M, Sørensen H. Ultrasound tagged near infrared spectroscopy does not detect hyperventilation-induced reduction in cerebral blood flow. Scandinavian Journal of Clinical and Laboratory Investigation 2015; 76:82-7. [DOI: 10.3109/00365513.2015.1101485] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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8
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Tsuji B, Honda Y, Ikebe Y, Fujii N, Kondo N, Nishiyasu T. Voluntary suppression of hyperthermia-induced hyperventilation mitigates the reduction in cerebral blood flow velocity during exercise in the heat. Am J Physiol Regul Integr Comp Physiol 2015; 308:R669-79. [PMID: 25632021 DOI: 10.1152/ajpregu.00419.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Accepted: 01/27/2015] [Indexed: 11/22/2022]
Abstract
Hyperthermia during prolonged exercise leads to hyperventilation, which can reduce arterial CO2 pressure (PaCO2 ) and, in turn, cerebral blood flow (CBF) and thermoregulatory response. We investigated 1) whether humans can voluntarily suppress hyperthermic hyperventilation during prolonged exercise and 2) the effects of voluntary breathing control on PaCO2 , CBF, sweating, and skin blood flow. Twelve male subjects performed two exercise trials at 50% of peak oxygen uptake in the heat (37°C, 50% relative humidity) for up to 60 min. Throughout the exercise, subjects breathed normally (normal-breathing trial) or they tried to control their minute ventilation (respiratory frequency was timed with a metronome, and target tidal volumes were displayed on a monitor) to the level reached after 5 min of exercise (controlled-breathing trial). Plotting ventilatory and cerebrovascular responses against esophageal temperature (Tes) showed that minute ventilation increased linearly with rising Tes during normal breathing, whereas controlled breathing attenuated the increased ventilation (increase in minute ventilation from the onset of controlled breathing: 7.4 vs. 1.6 l/min at +1.1°C Tes; P < 0.001). Normal breathing led to decreases in estimated PaCO2 and middle cerebral artery blood flow velocity (MCAV) with rising Tes, but controlled breathing attenuated those reductions (estimated PaCO2 -3.4 vs. -0.8 mmHg; MCAV -10.4 vs. -3.9 cm/s at +1.1°C Tes; P = 0.002 and 0.011, respectively). Controlled breathing had no significant effect on chest sweating or forearm vascular conductance (P = 0.67 and 0.91, respectively). Our results indicate that humans can voluntarily suppress hyperthermic hyperventilation during prolonged exercise, and this suppression mitigates changes in PaCO2 and CBF.
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Affiliation(s)
- Bun Tsuji
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan; and
| | - Yasushi Honda
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan; and
| | - Yusuke Ikebe
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan; and
| | - Naoto Fujii
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan; and
| | - Narihiko Kondo
- Faculty of Human Development, Kobe University, Kobe, Japan
| | - Takeshi Nishiyasu
- Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, Japan; and
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9
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Fujii N, Honda Y, Komura K, Tsuji B, Sugihara A, Watanabe K, Kondo N, Nishiyasu T. Effect of voluntary hypocapnic hyperventilation on the relationship between core temperature and heat loss responses in exercising humans. J Appl Physiol (1985) 2014; 117:1317-24. [PMID: 25257867 DOI: 10.1152/japplphysiol.00334.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Two thermolytic thermoregulatory responses, cutaneous vasodilation and sweating, begin when core temperature reaches a critical threshold, after which response magnitudes increase linearly with increasing core temperature; thus the slope indicates response sensitivity. We evaluated the influence of hypocapnia induced by voluntary hyperventilation on the core temperature threshold and sensitivity of thermoregulatory responses. Ten healthy males performed 15 min of cycling at 117 W (29.5°C, 50% RH) under three breathing conditions: 1) spontaneous ventilation, 2) voluntary normocapnic hyperventilation, and 3) voluntary hypocapnic hyperventilation. In the hypocapnic hyperventilation trial, end-tidal CO2 pressure was reduced throughout the exercise, whereas it was maintained around the normocapnic level in the other two trials. Cutaneous vascular conductances at the forearm and forehead were evaluated as laser-Doppler signal/mean arterial blood pressure, and the forearm sweat rate was measured using the ventilated capsule method. Esophageal temperature threshold was higher for the increase in cutaneous vascular conductance in the hypocapnic than normocapnic hyperventilation trial at the forearm (36.88 ± 0.36 vs. 36.68 ± 0.34°C, P < 0.05) and forehead (36.89 ± 0.31 vs. 36.75 ± 0.31°C, P < 0.05). The slope relating esophageal temperature to cutaneous vascular conductance was decreased in the hypocapnic than normocapnic hyperventilation trial at the forearm (302 ± 177 vs. 420 ± 178% baseline/°C, P < 0.05) and forehead (236 ± 164 vs. 358 ± 221% baseline/°C, P < 0.05). Neither the threshold nor the slope for the forearm sweat rate differed significantly between the hypocapnic or normocapnic hyperventilation trials. These findings indicate that in exercising humans, hypocapnia induced by voluntary hyperventilation does not influence sweating, but it attenuates the cutaneous vasodilatory response by increasing its threshold and reducing its sensitivity.
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Affiliation(s)
- Naoto Fujii
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
| | - Yasushi Honda
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
| | - Ken Komura
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
| | - Bun Tsuji
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
| | - Akira Sugihara
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
| | - Kazuhito Watanabe
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
| | - Narihiko Kondo
- Faculty of Human Development, Kobe University, Kobe, Japan
| | - Takeshi Nishiyasu
- Institute of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan; and
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10
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Gagnon D, Matthew Brothers R, Ganio MS, Hastings JL, Crandall CG. Forehead versus forearm skin vascular responses at presyncope in humans. Am J Physiol Regul Integr Comp Physiol 2014; 307:R908-13. [PMID: 25100073 DOI: 10.1152/ajpregu.00204.2014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Facial pallor is commonly observed at presyncope in humans, suggestive of reductions in facial skin blood flow (SkBF). Yet, cutaneous vasoconstriction is usually minimal at presyncope when measured at the forearm. We tested the hypothesis that reductions in forehead SkBF at presyncope are greater than in the forearm. Forehead and forearm SkBF (laser-Doppler) and blood pressure (Finometer or radial artery catheterization) were measured during lower body negative pressure (LBNP) to presyncope in 11 normothermic and 13 heat-stressed subjects (intestinal temperature increased ∼1.4°C). LBNP reduced mean arterial pressure from 91 ± 5 to 57 ± 7 mmHg during normothermia (P ≤ 0.001) and from 82 ± 5 to 57 ± 7 mmHg during heat stress (P ≤ 0.001). During normothermia, LBNP decreased forehead SkBF 55 ± 14% compared with 24 ± 11% at the forearm (P = 0.002), while during heat stress LBNP decreased forehead SkBF 39 ± 11% compared with 28 ± 8% in the forearm (P = 0.007). In both conditions, most (≥68%) of the decreases in SkBF were due to decreases in blood pressure. However, a greater contribution of actively mediated reductions in SkBF was observed at the forehead, relative to the forearm during normothermia (32 ± 13% vs. 11 ± 11%, P = 0.031) and heat stress (30 ± 13% vs. 10 ± 13%, P = 0.004). These data suggest that facial pallor at presyncope is due to a combination of passive decreases in forehead SkBF secondary to reductions in blood pressure and to active decreases in SkBF, the latter of which are relatively greater than in the forearm.
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Affiliation(s)
- Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - R Matthew Brothers
- Environmental and Autonomic Physiology Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas
| | - Matthew S Ganio
- Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, Arkansas; and
| | - Jeffrey L Hastings
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas; Veterans Affairs North Texas Health Care System, Dallas, Texas
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas;
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11
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Kolyva C, Ghosh A, Tachtsidis I, Highton D, Cooper CE, Smith M, Elwell CE. Cytochrome c oxidase response to changes in cerebral oxygen delivery in the adult brain shows higher brain-specificity than haemoglobin. Neuroimage 2013; 85 Pt 1:234-44. [PMID: 23707584 PMCID: PMC3898943 DOI: 10.1016/j.neuroimage.2013.05.070] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 05/05/2013] [Accepted: 05/13/2013] [Indexed: 11/19/2022] Open
Abstract
The redox state of cerebral mitochondrial cytochrome c oxidase monitored with near-infrared spectroscopy (Δ[oxCCO]) is a signal with strong potential as a non-invasive, bedside biomarker of cerebral metabolic status. We hypothesised that the higher mitochondrial density of brain compared to skin and skull would lead to evidence of brain-specificity of the Δ[oxCCO] signal when measured with a multi-distance near-infrared spectroscopy (NIRS) system. Measurements of Δ[oxCCO] as well as of concentration changes in oxygenated (Δ[HbO2]) and deoxygenated haemoglobin (Δ[HHb]) were taken at multiple source-detector distances during systemic hypoxia and hypocapnia (decrease in cerebral oxygen delivery), and hyperoxia and hypercapnia (increase in cerebral oxygen delivery) from 15 adult healthy volunteers. Increasing source-detector spacing is associated with increasing light penetration depth and thus higher sensitivity to cerebral changes. An increase in Δ[oxCCO] was observed during the challenges that increased cerebral oxygen delivery and the opposite was observed when cerebral oxygen delivery decreased. A consistent pattern of statistically significant increasing amplitude of the Δ[oxCCO] response with increasing light penetration depth was observed in all four challenges, a behaviour that was distinctly different from that of the haemoglobin chromophores, which did not show this statistically significant depth gradient. This depth-dependence of the Δ[oxCCO] signal corroborates the notion of higher concentrations of CCO being present in cerebral tissue compared to extracranial components and highlights the value of NIRS-derived Δ[oxCCO] as a brain-specific signal of cerebral metabolism, superior in this aspect to haemoglobin. NIRS was used to measure oxidised cytochrome c oxidase (Δ[oxCCO]) in healthy brain. Δ[oxCCO] changed in the same direction as changes in cerebral oxygen delivery. Magnitude of Δ[oxCCO] response increased with increasing light penetration depth. Corresponding haemoglobin changes showed no dependence on light penetration depth. NIRS-measured Δ[oxCCO] has higher brain specificity than haemoglobin.
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Affiliation(s)
- Christina Kolyva
- Dept. of Medical Physics and Bioengineering, University College London, London, UK.
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12
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Mutch WAC, Patel SR, Shahidi AM, Kulasekara SI, Fisher JA, Duffin J, Hudson C. Cerebral oxygen saturation: graded response to carbon dioxide with isoxia and graded response to oxygen with isocapnia. PLoS One 2013; 8:e57881. [PMID: 23469096 PMCID: PMC3585256 DOI: 10.1371/journal.pone.0057881] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 01/27/2013] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Monitoring cerebral saturation is increasingly seen as an aid to management of patients in the operating room and in neurocritical care. How best to manipulate cerebral saturation is not fully known. We examined cerebral saturation with graded changes in carbon dioxide tension while isoxic and with graded changes in oxygen tension while isocapnic. METHODOLOGY/PRINCIPAL FINDINGS The study was approved by the Research Ethics Board of the University Health Network at the University of Toronto. Thirteen studies were undertaken in healthy adults with cerebral oximetry by near infrared spectroscopy. End-tidal gas concentrations were manipulated using a model-based prospective end-tidal targeting device. End-tidal carbon dioxide was altered ±15 mmHg from baseline in 5 mmHg increments with isoxia (clamped at 110±4 mmHg). End-tidal oxygen was changed to 300, 400, 500, 80, 60 and 50 mmHg under isocapnia (37±2 mmHg). Twelve studies were completed. The end-tidal carbon dioxide versus cerebral saturation fit a linear relationship (R(2) = 0.92±0.06). The end-tidal oxygen versus cerebral saturation followed log-linear behaviour and best fit a hyperbolic relationship (R(2) = 0.85±0.10). Cerebral saturation was maximized in isoxia at end-tidal carbon dioxide of baseline +15 mmHg (77±3 percent). Cerebral saturation was minimal in isocapnia at an end-tidal oxygen tension of 50 mmHg (61±3 percent). The cerebral saturation during normoxic hypocapnia was equivalent to normocapnic hypoxia of 60 mmHg. CONCLUSIONS/SIGNIFICANCE Hypocapnia reduces cerebral saturation to an extent equivalent to moderate hypoxia.
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Affiliation(s)
- W Alan C Mutch
- Department of Anesthesia and Perioperative Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
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