scholarly journals Cerebral Hemodynamic and Ventilatory Responses to Hypoxia, Hypercapnia, and Hypocapnia during 5 Days at 4,350 m

2013 ◽  
Vol 34 (1) ◽  
pp. 52-60 ◽  
Author(s):  
Thomas Rupp ◽  
François Esteve ◽  
Pierre Bouzat ◽  
Carsten Lundby ◽  
Stéphane Perrey ◽  
...  
Keyword(s):  
Near Infrared ◽  
Cerebral Oxygenation ◽  
Acute Mountain Sickness ◽  
Oxygenation Index ◽  
Short Term ◽  
Ventilatory Responses ◽  
Altitude Exposure ◽  
Total Hemoglobin ◽  
Tissue Oxygenation Index ◽  
Mountain Sickness

This study investigated the changes in cerebral near-infrared spectroscopy (NIRS) signals, cerebrovascular and ventilatory responses to hypoxia and CO2 during altitude exposure. At sea level (SL), after 24 hours and 5 days at 4,350 m, 11 healthy subjects were exposed to normoxia, isocapnic hypoxia, hypercapnia, and hypocapnia. The following parameters were measured: prefrontal tissue oxygenation index (TOI), oxy- (HbO2), deoxy- and total hemoglobin (HbTot) concentrations with NIRS, blood velocity in the middle cerebral artery (MCAv) with transcranial Doppler and ventilation. Smaller prefrontal deoxygenation and larger ΔHbTot in response to hypoxia were observed at altitude compared with SL (day 5: ΔHbO2−0.6±1.1 versus −1.8±1.3  μmol/cmper mm Hg and ΔHbTot 1.4±1.3 versus 0.7±1.1  μmol/cm per mm Hg). The hypoxic MCAv and ventilatory responses were enhanced at altitude. Prefrontal oxygenation increased less in response to hypercapnia at altitude compared with SL (day 5: ΔTOI 0.3±0.2 versus 0.5±0.3% mm Hg). The hypercapnic MCAv and ventilatory responses were decreased and increased, respectively, at altitude. Hemodynamic responses to hypocapnia did not change at altitude. Short-term altitude exposure improves cerebral oxygenation in response to hypoxia but decreases it during hypercapnia. Although these changes may be relevant for conditions such as exercise or sleep at altitude, they were not associated with symptoms of acute mountain sickness.

Enhanced muscular oxygen extraction in athletes exaggerates hypoxemia during exercise in hypoxia

2016 ◽  
Vol 120 (3) ◽  
pp. 351-361 ◽  
Author(s):  
Ruud Van Thienen ◽  
Peter Hespel
Keyword(s):  
Oxygen Consumption ◽  
Near Infrared ◽  
Vastus Lateralis ◽  
Acute Mountain Sickness ◽  
Maximal Oxygen Consumption ◽  
Arterial Occlusion ◽  
Oxygenation Index ◽  
High Rate ◽  
Oxygen Extraction ◽  
Mountain Sickness

High rate of muscular oxygen utilization facilitates the development of hypoxemia during exercise at altitude. Because endurance training stimulates oxygen extraction capacity, we investigated whether endurance athletes are at higher risk to developing hypoxemia and thereby acute mountain sickness symptoms during exercise at simulated high altitude. Elite athletes (ATL; n = 8) and fit controls (CON; n = 7) cycled for 20 min at 100 W (EX100W), as well as performed an incremental maximal oxygen consumption test (EXMAX) in normobaric hypoxia (0.107 inspired O2 fraction) or normoxia (0.209 inspired O2 fraction). Cardiorespiratory responses, arterial Po2 (PaO2), and oxygenation status in m. vastus lateralis [tissue oxygenation index (TOIM)] and frontal cortex (TOIC) by near-infrared spectroscopy, were measured. Muscle O2 uptake rate was estimated from change in oxyhemoglobin concentration during a 10-min arterial occlusion in m. gastrocnemius. Maximal oxygen consumption in normoxia was 70 ± 2 ml·min−1·kg−1 in ATL vs. 43 ± 2 ml·min−1·kg−1 in CON, and in hypoxia decreased more in ATL (−41%) than in CON (−25%, P < 0.05). Both in normoxia at PaO2 of ∼95 Torr, and in hypoxia at PaO2 of ∼35 Torr, muscle O2 uptake was twofold higher in ATL than in CON (0.12 vs. 0.06 ml·min−1·100 g−1; P < 0.05). During EX100W in hypoxia, PaO2 dropped to lower ( P < 0.05) values in ATL (27.6 ± 0.7 Torr) than in CON (33.5 ± 1.0 Torr). During EXMAX, but not during EX100W, TOIM was ∼15% lower in ATL than in CON ( P < 0.05). TOIC was similar between the groups at any time. This study shows that maintenance of high muscular oxygen extraction rate at very low circulating PaO2 stimulates the development of hypoxemia during submaximal exercise in hypoxia in endurance-trained individuals. This effect may predispose to premature development of acute mountain sickness symptoms during exercise at altitude.

scholarly journals Dynamics of cortical oxygenation during immediate adaptation to extrauterine life

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Léa Leroy ◽  
Mahdi Mahmoudzadeh ◽  
Jean Gondry ◽  
Arthur Foulon ◽  
Fabrice Wallois
Keyword(s):  
Near Infrared ◽  
Cerebral Oxygenation ◽  
Oxygenation Index ◽  
Perinatal Period ◽  
Multiple Strategies ◽  
The Status ◽  
Tissue Oxygenation Index ◽  
Term Newborns ◽  
Lactate Levels ◽  
Index Value

AbstractThe neonatal transition involves physiological modifications as a consequence of the complexity of the perinatal period. Various strategies can be used to attain the same level of postnatal cerebral oxygenation, depending on the status of the infant at birth. We evaluated such strategies by recording 20 full-term newborns by near-infrared spectroscopy during the first 10 min of life. The acid–base status at birth revealed two clustered profiles of cerebral oxygenation dynamics. Lower pH and base excess and higher lactate levels were associated with more rapid attainment of the 95% maximal tissue oxygenation index value. These results suggest that metabolic mechanisms drive initial cerebral oxygenation dynamics during this critical period. These results confirm the capacity of newborns to develop multiple strategies to protect the brain.

Dietary nitrate improves muscle but not cerebral oxygenation status during exercise in hypoxia

2012 ◽  
Vol 113 (5) ◽  
pp. 736-745 ◽  
Author(s):  
Evi Masschelein ◽  
Ruud Van Thienen ◽  
Xu Wang ◽  
Ann Van Schepdael ◽  
Martine Thomis ◽  
...  
Keyword(s):  
Exercise Tolerance ◽  
Near Infrared ◽  
Cerebral Oxygenation ◽  
Acute Mountain Sickness ◽  
Oxygenation Index ◽  
Whole Body ◽  
Time To Exhaustion ◽  
Dietary Nitrate ◽  
Nitrate Supplementation ◽  
Oxygenation Status

Exercise tolerance is impaired in hypoxia, and it has recently been shown that dietary nitrate supplementation can reduce the oxygen (O2) cost of muscle contractions. Therefore, we investigated the effect of dietary nitrate supplementation on arterial, muscle, and cerebral oxygenation status, symptoms of acute mountain sickness (AMS), and exercise tolerance at simulated 5,000 m altitude. Fifteen young, healthy volunteers participated in three experimental sessions according to a crossover study design. From 6 days prior to each session, subjects received either beetroot (BR) juice delivering 0.07 mmol nitrate/kg body wt/day or a control drink (CON). One session was in normoxia with CON (NORCON); the two other sessions were in hypoxia (11% O2), with either CON (HYPCON) or BR (HYPBR). Subjects first cycled for 20 min at 45% of peak O2 consumption (VO2peak; EX45%) and thereafter, performed a maximal incremental exercise test (EXmax). Whole-body VO2, arterial O2 saturation (%SpO2) via pulsoximetry, and tissue oxygenation index of both muscle (TOIM) and cerebral (TOIC) tissue by near-infrared spectroscopy were measured. Hypoxia per se substantially reduced VO2peak, %SpO2, TOIM, and TOIC (NORCON vs. HYPCON, P < 0.05). Compared with HYPCON, VO2 at rest and during EX45% was lower in HYPBR ( P < 0.05), whereas %SpO2 was higher ( P < 0.05). TOIM was ∼4-5% higher in HYPBR than in HYPCON both at rest and during EX45% and EXmax ( P < 0.05). TOIC as well as the incidence of AMS symptoms were similar between HYPCON and HYPBR at any time. Hypoxia reduced time to exhaustion in EXmax by 36% ( P < 0.05), but this ergolytic effect was partly negated by BR (+5%, P < 0.05). Short-term dietary nitrate supplementation improves arterial and muscle oxygenation status but not cerebral oxygenation status during exercise in severe hypoxia. This is associated with improved exercise tolerance against the background of a similar incidence of AMS.

Which common NIRS variable reflects muscle estimated lactate threshold most closely?

2006 ◽  
Vol 31 (5) ◽  
pp. 612-620 ◽  
Author(s):  
Lixin Wang ◽  
Takahiro Yoshikawa ◽  
Taketaka Hara ◽  
Hayato Nakao ◽  
Takashi Suzuki ◽  
...  
Keyword(s):  
Lactate Threshold ◽  
Near Infrared ◽  
Ventilatory Threshold ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
Oxygenation Index ◽  
Muscle Lactate ◽  
Tissue Oxygenation Index ◽  
The Mean ◽  
Tissue Hemoglobin

Various near-infrared spectroscopy (NIRS) variables have been used to estimate muscle lactate threshold (LT), but no study has determined which common NIRS variable best reflects muscle estimated LT. Establishing the inflection point of 2 regression lines for deoxyhaemoglobin (ΔHHbi.p.), oxyhaemoglobin (ΔO2Hbi.p.), and tissue oxygenation index (TOIi.p.), as well as for blood lactate concentration, we then investigated the relationships between NIRS variables and ventilatory threshold (VT), LT, or maximal tissue hemoglobin index (nTHImax) during incremental cycling exercise. ΔHHbi.p. and TOIi.p. could be determined for all 15 subjects, but ΔO2Hbi.p. was determined for only 11 subjects. The mean absolute values for the 2 measurable slopes of the 2 continuous linear regression lines exhibited increased changes in 3 NIRS variables. The workload and VO2 at ΔO2Hbi.p. and nTHImax were greater than those at VT, LT, ΔHHbi.p., and TOIi.p.. For workload and VO2, ΔHHbi.p. was correlated with VT and LT, whereas ΔO2Hbi.p. was correlated with nTHImax, and TOIi.p. with VT and nTHImax. These findings indicate that ΔO2Hb strongly corresponds with local perfusion, and TOI corresponds with both local perfusion and deoxygenation, but that ΔHHb can exactly determine deoxygenation changes and reflect O2 metabolic dynamics. The finding of strongest correlations between ΔHHb and VT or LT indicates that ΔHHb is the best variable for muscle LT estimation.

scholarly journals Acetazolamide reduces exercise capacity and increases leg fatigue under hypoxic conditions

2003 ◽  
Vol 94 (3) ◽  
pp. 991-996 ◽  
Author(s):  
Luke A. Garske ◽  
Michael G. Brown ◽  
Stephen C. Morrison
Keyword(s):  
Exercise Capacity ◽  
Ventilatory Response ◽  
Acute Mountain Sickness ◽  
Peak Exercise ◽  
Double Blind ◽  
Ventilatory Responses ◽  
Hypoxic Conditions ◽  
Mountain Sickness ◽  
Randomized Crossover Study ◽  
Hypoxic Exercise

Acetazolamide (Acz) is used at altitude to prevent acute mountain sickness, but its effect on exercise capacity under hypoxic conditions is uncertain. Nine healthy men completed this double-blind, randomized, crossover study. All subjects underwent incremental exercise to exhaustion with an inspired O2 fraction of 0.13, hypoxic ventilatory responses, and hypercapnic ventilatory responses after Acz (500 mg twice daily for 5 doses) and placebo. Maximum power of 203 ± 38 (SD) W on Acz was less than the placebo value of 225 ± 40 W ( P < 0.01). At peak exercise, arterialized capillary pH was lower and Po 2 higher on Acz ( P < 0.01). Ventilation was 118.6 ± 20.0 l/min at the maximal power on Acz and 102.4 ± 20.7 l/min at the same power on placebo ( P < 0.02), and Borg score for leg fatigue was increased on Acz ( P < 0.02), with no difference in Borg score for dyspnea. Hypercapnic ventilatory response on Acz was greater ( P < 0.02), whereas hypoxic ventilatory response was unchanged. During hypoxic exercise, Acz reduced exercise capacity associated with increased perception of leg fatigue. Despite increased ventilation, dyspnea was not increased.

Intermittent altitude exposures reduce acute mountain sickness at 4300 m

2004 ◽  
Vol 106 (3) ◽  
pp. 321-328 ◽  
Author(s):  
Beth A. BEIDLEMAN ◽  
Stephen R. MUZA ◽  
Charles S. FULCO ◽  
Allen CYMERMAN ◽  
Dan DITZLER ◽  
...  
Keyword(s):  
Acute Mountain Sickness ◽  
Urine Volume ◽  
Barometric Pressure ◽  
Self Report ◽  
Altitude Exposure ◽  
Cerebral Symptom ◽  
Cycle Training ◽  
Mountain Sickness ◽  
End Tidal ◽  
Rest And Exercise

Acute mountain sickness (AMS) commonly occurs at altitudes exceeding 2000–2500 m and usually resolves after acclimatization induced by a few days of chronic residence at the same altitude. Increased ventilation and diuresis may contribute to the reduction in AMS with altitude acclimatization. The aim of the present study was to examine the effects of intermittent altitude exposures (IAE), in combination with rest and exercise training, on the incidence and severity of AMS, resting ventilation and 24-h urine volume at 4300 m. Six lowlanders (age, 23±2 years; body weight, 77±6 kg; values are means±S.E.M.) completed an Environmental Symptoms Questionnaire (ESQ) and Lake Louise AMS Scoring System (LLS), a resting end-tidal partial pressure of CO2 (PETCO2) test and a 24-h urine volume collection at sea level (SL) and during a 30 h exposure to 4300 m altitude-equivalent (barometric pressure=446 mmHg) once before (PreIAE) and once after (PostIAE) a 3-week period of IAE (4 h·day-1, 5 days·week-1, 4300 m). The previously validated factor score, AMS cerebral score, was calculated from the ESQ and the self-report score was calculated from the LLS at 24 h of altitude exposure to assess the incidence and severity of AMS. During each IAE, three subjects cycled for 45–60 min·day-1 at 60–70% of maximal O2 uptake (VO2 max) and three subjects rested. Cycle training during each IAE did not affect any of the measured variables, so data from all six subjects were combined. The results showed that the incidence of AMS (%), determined from both the ESQ and LLS, increased (P<0.05) from SL (0±0) to PreIAE (50±22) at 24 h of altitude exposure and decreased (P<0.05) from PreIAE to PostIAE (0±0). The severity of AMS (i.e. AMS cerebral symptom and LLS self-report scores) increased (P<0.05) from SL (0.02±0.02 and 0.17±0.17 respectively) to PreIAE (0.49±0.18 and 4.17±0.94 respectively) at 24 h of altitude exposure, and decreased (P<0.05) from PreIAE to PostIAE (0.03±0.02 and 0.83±0.31 respectively). Resting PETCO2 (mmHg) decreased (i.e. increase in ventilation; P<0.05) from SL (38±1) to PreIAE (32±1) at 24 h of altitude exposure and decreased further (P<0.05) from PreIAE to PostIAE (28±1). In addition, 24-h urine volumes were similar at SL, PreIAE and PostIAE. In conclusion, our findings suggest that 3 weeks of IAE provide an effective alternative to chronic altitude residence for increasing resting ventilation and reducing the incidence and severity of AMS.

The repeated-bout effect: influence on biceps brachii oxygenation and myoelectrical activity

2011 ◽  
Vol 110 (5) ◽  
pp. 1390-1399 ◽  
Author(s):  
Makii Muthalib ◽  
Hoseong Lee ◽  
Guillaume Y. Millet ◽  
Marco Ferrari ◽  
Kazunori Nosaka
Keyword(s):  
Eccentric Exercise ◽  
Isometric Contraction ◽  
Muscle Activation ◽  
Near Infrared ◽  
Biceps Brachii ◽  
Oxygenation Index ◽  
Repeated Bout Effect ◽  
Myoelectrical Activity ◽  
Total Hemoglobin ◽  
Repeated Bout

This study investigated biceps brachii oxygenation and myoelectrical activity during and following maximal eccentric exercise to better understand the repeated-bout effect. Ten men performed two bouts of eccentric exercise (ECC1, ECC2), consisting of 10 sets of 6 maximal lengthening contractions of the elbow flexors separated by 4 wk. Tissue oxygenation index minimum amplitude (TOImin), mean and maximum total hemoglobin volume by near-infrared spectroscopy, torque, and surface electromyography root mean square (EMGRMS) during exercise were compared between ECC1 and ECC2. Changes in maximal voluntary isometric contraction (MVC) torque, range of motion, plasma creatine kinase activity, muscle soreness, TOImin, and EMGRMS during sustained (10-s) and 30-repeated isometric contraction tasks at 30% (same absolute force) and 100% MVC (same relative force) for 4 days postexercise were compared between ECC1 and ECC2. No significant differences between ECC1 and ECC2 were evident for changes in torque, TOImin, mean total hemoglobin volume, maximum total hemoglobin volume, and EMGRMS during exercise. Smaller ( P < 0.05) changes and faster recovery of muscle damage markers were evident following ECC2 than ECC1. During 30% MVC tasks, TOImin did not change, but EMGRMS increased 1–4 days following ECC1 and ECC2. During 100% MVC tasks, EMGRMS did not change, but torque and TOImin decreased 1–4 days following ECC1 and ECC2. TOImin during 100% MVC tasks and EMGRMS during 30% MVC tasks recovered faster ( P < 0.05) following ECC2 than ECC1. We conclude that the repeated-bout effect cannot be explained by altered muscle activation or metabolic/hemodynamic changes, and the faster recovery in muscle oxygenation and activation was mainly due to faster recovery of force.

Comparison between maximal lengthening and shortening contractions for biceps brachii muscle oxygenation and hemodynamics

2010 ◽  
Vol 109 (3) ◽  
pp. 710-720 ◽  
Author(s):  
Makii Muthalib ◽  
Hoseong Lee ◽  
Guillaume Y. Millet ◽  
Marco Ferrari ◽  
Kazunori Nosaka
Keyword(s):  
Muscle Damage ◽  
Near Infrared ◽  
Biceps Brachii ◽  
Oxygenation Index ◽  
Creatine Kinase Activity ◽  
Muscle Oxygenation ◽  
Biceps Brachii Muscle ◽  
Before And After ◽  
Tissue Oxygenation Index ◽  
Systemic Oxygen

Eccentric contractions (ECC) require lower systemic oxygen (O2) and induce greater symptoms of muscle damage than concentric contractions (CON); however, it is not known if local muscle oxygenation is lower in ECC than CON during and following exercise. This study compared between ECC and CON for changes in biceps brachii muscle oxygenation [tissue oxygenation index (TOI)] and hemodynamics [total hemoglobin volume (tHb) = oxygenated-Hb + deoxygenated-Hb], determined by near-infrared spectroscopy over 10 sets of 6 maximal contractions of the elbow flexors of 10 healthy subjects. This study also compared between ECC and CON for changes in TOI and tHb during a 10-s sustained and 30-repeated maximal isometric contraction (MVC) task measured immediately before and after and 1–3 days following exercise. The torque integral during ECC was greater ( P < 0.05) than that during CON by ∼30%, and the decrease in TOI was smaller ( P < 0.05) by ∼50% during ECC than CON. Increases in tHb during the relaxation phases were smaller ( P < 0.05) by ∼100% for ECC than CON; however, the decreases in tHb during the contraction phases were not significantly different between sessions. These results suggest that ECC utilizes a lower muscle O2 relative to O2 supply compared with CON. Following exercise, greater ( P < 0.05) decreases in MVC strength and increases in plasma creatine kinase activity and muscle soreness were evident 1–3 days after ECC than CON. Torque integral, TOI, and tHb during the sustained and repeated MVC tasks decreased ( P < 0.01) only after ECC, suggesting that muscle O2 demand relative to O2 supply during the isometric tasks was decreased after ECC. This could mainly be due to a lower maximal muscle mass activated as a consequence of muscle damage; however, an increase in O2 supply due to microcirculation dysfunction and/or inflammatory vasodilatory responses after ECC is recognized.

Frontal cortical oxygenation changes during gravity-induced loss of consciousness in humans: a near-infrared spatially resolved spectroscopic study

2007 ◽  
Vol 103 (4) ◽  
pp. 1326-1331 ◽  
Author(s):  
Koichi Kurihara ◽  
Azusa Kikukawa ◽  
Asao Kobayashi ◽  
Toshio Nakadate
Keyword(s):  
High Performance ◽  
Near Infrared ◽  
Cerebral Oxygenation ◽  
Oxygenation Index ◽  
Loss Of Consciousness ◽  
Spatially Resolved ◽  
Hemoglobin Saturation ◽  
Significant Difference ◽  
Concentration Changes ◽  
Spatially Resolved Spectroscopy

Gravity (G)-induced loss of consciousness (G-LOC), which is presumably caused by a reduction of cerebral blood flow resulting in a decreased oxygen supply to the brain, is a major threat to pilots of high-performance fighter aircraft. The application of cerebral near-infrared spectroscopy (NIRS) to monitor gravity-induced cerebral oxygenation debt has generated concern over potential sources of extracranial contamination. The recently developed NIR spatially resolved spectroscopy (SRS-NIRS) has been confirmed to provide frontal cortical tissue hemoglobin saturation [tissue oxygenation index (TOI)]. In this study, we monitored the TOI and the standard NIRS measured chromophore concentration changes of oxygenated hemoglobin and deoxygenated hemoglobin in 141 healthy male pilots during various levels of +Gz (head-to-foot inertial forces) exposure to identify the differences between subjects who lose consciousness and those who do not during high +Gz exposure. Subjects were exposed to seven centrifuge profiles, with +Gz levels from 4 to 8 Gz and an onset rate from 0.1 to 6.0 Gz/s. The SRS-NIRS revealed an ∼15% decrease in the TOI in G-LOC. The present study also demonstrated the TOI to be a useful variable to evaluate the effect of the anti-G protection system. However, there was no significant difference found between conditions with and without G-LOC in subjects with terminated G exposure. Further studies that elucidate the mechanism(s) behind the wide variety of individual differences may be needed for a method of G-LOC prediction to be effectively realized.

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