Dehydration hastens the decline in cerebral blood flow (CBF) during incremental exercise, whereas the cerebral metabolic rate for O2 (CMRO2 ) is preserved. It remains unknown whether CMRO2 is also ...maintained during prolonged exercise in the heat and whether an eventual decline in CBF is coupled to fatigue. Two studies were undertaken. In study 1, 10 male cyclists cycled in the heat for ∼2 h with (control) and without fluid replacement (dehydration) while internal and external carotid artery blood flow and core and blood temperature were obtained. Arterial and internal jugular venous blood samples were assessed with dehydration to evaluate CMRO2 . In study 2, in 8 male subjects, middle cerebral artery blood velocity was measured during prolonged exercise to exhaustion in both dehydrated and euhydrated states. After a rise at the onset of exercise, internal carotid artery flow declined to baseline with progressive dehydration (P < 0.05). However, cerebral metabolism remained stable through enhanced O2 and glucose extraction (P < 0.05). External carotid artery flow increased for 1 h but declined before exhaustion. Fluid ingestion maintained cerebral and extracranial perfusion throughout nonfatiguing exercise. During exhaustive exercise, however, euhydration delayed but did not prevent the decline in cerebral perfusion. In conclusion, during prolonged exercise in the heat, dehydration accelerates the decline in CBF without affecting CMRO2 and also restricts extracranial perfusion. Thus, fatigue is related to a reduction in CBF and extracranial perfusion rather than CMRO2 .
The β2-receptor mediates the metabolic response to epinephrine. This study investigates the impact of the β2-receptor gene (ADRB2) polymorphism Gly16Arg on the metabolic response to epinephrine ...before and after repetitive hypoglycemia. Twenty-five healthy men selected according to ADRB2 genotype being homozygous for either Gly16 (GG) (n = 12) or Arg16 (AA) (n = 13) participated in 4 trial days (D1-4): D1pre and D4post with epinephrine 0.06 μg kg-1 ⋅ min-1 infusion and D2hypo1-2 and D3hypo3 with three periods of hypoglycemia by an insulin-glucose clamp. At D1pre, the insulin (mean ± SEM of area under the curve 44 ± 8 vs. 93 ± 13 pmol ⋅ L-1 h; P = 0.0051), glycerol (79 ± 12 vs. 115 ± 14 μmol ⋅ L-1 h; P = 0.041), and free fatty acid (724 ± 96 vs. 1,113 ± 140 μmol ⋅ L-1 h; P = 0.033) responses to epinephrine were decreased in AA participants compared with GG participants but without a difference in glucose response. There were no differences in response to epinephrine between genotype groups after repetitive hypoglycemia at D4post. The metabolic substrate response to epinephrine was decreased in AA participants compared with GG participants but without a difference between genotype groups after repetitive hypoglycemia.
This study investigates the impact of the β2-receptor gene (ADRB2) polymorphism Gly16Arg on the metabolic response to epinephrine before and after repetitive hypoglycemia. Healthy men homozygous for either Gly16 (n = 12) or Arg16 (n = 13) participated in the study. Healthy people with the Gly16 genotype have increased metabolic response to epinephrine compared with the Arg16 genotype but without a difference between genotypes after repetitive hypoglycemia.
Abstract
Context
The Arg16 variant in the β2-receptor gene is associated with increased risk of severe hypoglycemia in subjects with type 1 diabetes mellitus.
Objective
We hypothesized that the Arg16 ...variant is associated with decreased metabolic and symptomatic responses to recurrent hypoglycemia.
Methods
Twenty-five healthy male subjects selected according to ADRB2 genotype and being homozygous for either Arg16 (AA; n = 13) or Gly16 (GG; n = 12) participated in 2 consecutive trial days with 3 periods of hypoglycemia (H1-H3) induced by a hyperinsulinemic hypoglycemic clamp. The main outcome measure was mean glucose infusion rate (GIR) during H1-H3.
Results
During H1-H3, there was no difference between AA or GG subjects in GIR, counter-regulatory hormones (glucagon, epinephrine, cortisol, growth hormone), or substrate levels of lactate, glycerol, and free fatty acids (FFAs), and no differences in symptom response score or cognitive performance (trail making test, Stroop test). At H3, lactate response was reduced in both genotype groups, but AA subjects had decreased response (mean ± standard error of the mean of area under the curve) of glycerol (–13.1 ± 3.8 μmol L–1 hours; P = .0052), FFA (–30.2 ± 11.1 μmol L–1 hours; P = .021), and β-hydroxybutyrate (–0.008 ± 0.003 mmol L–1 hour; P = .027), while in GG subjects alanine response was increased (negative response values) (–53.9 ± 20.6 μmol L–1 hour; P = .024).
Conclusion
There was no difference in GIR between genotype groups, but secondary outcomes suggest a downregulation of the lipolytic and β-hydroxybutyrate responses to recurrent hypoglycemia in AA subjects, in contrast to the responses in GG subjects.
Brain temperature appears to be an important factor affecting motor activity, but it is not known to what extent brain temperature
increases during prolonged exercise in humans. Cerebral heat ...exchange was therefore evaluated in seven males during exercise
with and without hyperthermia. Middle cerebral artery mean blood velocity (MCA V mean ) was continuously monitored while global cerebral blood flow (CBF) and cerebral energy turnover were determined at the end
of the two exercise trials in three subjects. The arterial to venous temperature difference across the brain (v-a D temp ) was determined via thermocouples placed in the internal jugular vein and in the aorta. The jugular venous blood temperature
was always higher than that of the arterial blood, demonstrating that heat was released via the CBF during the normothermic
as well as the hyperthermic exercise condition. However, heat removal via the jugular venous blood was 30 ± 6 % lower during
hyperthermia compared to the control trial. The reduced heat removal from the brain was mainly a result of a 20 ± 6 % lower
CBF (22 ± 9 % reduction in MCA V mean ), because the v-a D temp was not significantly different in the hyperthermic (0.20 ± 0.05 °C) compared to the control trial (0.22 ± 0.05 °C). During
hyperthermia, the impaired heat removal via the blood was combined with a 7 ± 2 % higher heat production in the brain and
heat was consequently stored in the brain at a rate of 0.20 ± 0.06 J g â1 min â1 . The present results indicate that the average brain temperature is at least 0.2 °C higher than that of the body core during
exercise with or without hyperthermia.
This study examined to what extent the human cerebral and femoral circulation contribute to free radical formation during basal and exercise-induced responses to hypoxia. Healthy participants (5♂, ...5♀) were randomly assigned single-blinded to normoxic (21% O2) and hypoxic (10% O2) trials with measurements taken at rest and 30 min after cycling at 70% of maximal power output in hypoxia and equivalent relative and absolute intensities in normoxia. Blood was sampled from the brachial artery (a), internal jugular and femoral veins (v) for non-enzymatic antioxidants (HPLC), ascorbate radical (A•-, electron paramagnetic resonance spectroscopy), lipid hydroperoxides (LOOH) and low density lipoprotein (LDL) oxidation (spectrophotometry). Cerebral and femoral venous blood flow was evaluated by transcranial Doppler ultrasound (CBF) and constant infusion thermodilution (FBF). With 3 participants lost to follow up (final n = 4♂, 3♀), hypoxia increased CBF and FBF (P = 0.041 vs. normoxia) with further elevations in FBF during exercise (P = 0.002 vs. rest). Cerebral and femoral ascorbate and α-tocopherol consumption (v < a) was accompanied by A•-/LOOH formation (v > a) and increased LDL oxidation during hypoxia (P < 0.043–0.049 vs. normoxia) implying free radical-mediated lipid peroxidation subsequent to inadequate antioxidant defense. This was pronounced during exercise across the femoral circulation in proportion to the increase in local O2 uptake (r = −0.397 to −0.459, P = 0.037–0.045) but unrelated to any reduction in PO2. These findings highlight considerable regional heterogeneity in the oxidative stress response to hypoxia that may be more attributable to local differences in O2 flux than to O2 tension.
Display omitted
•Hypoxia, and to a greater extent exercise, overwhelm human antioxidant defenses.•Hypoxia and exercise result in cerebral and femoral formation of free radicals.•Radical formation is most pronounced during the combined stress of hypoxic exercise.•Radical formation exceeds that predicted by the sum of the individual stressors.•Radical formation linked to increased oxygen flux and not reduced oxygen tension.
Fluctuations in cardiac stroke volume during rowing Sejersen, Casper; Fischer, Mads; Mattos, João D. ...
Scandinavian journal of medicine & science in sports,
April 2021, Letnik:
31, Številka:
4
Journal Article
Recenzirano
Preload to the heart may be limited during rowing because both blood pressure and central venous pressure increase when force is applied to the oar. Considering that only the recovery phase of the ...rowing stroke allows for unhindered venous return, rowing may induce large fluctuations in stroke volume (SV). Thus, the purpose of this study was to evaluate SV continuously during the rowing stroke. Eight nationally competitive oarsmen (mean ± standard deviation: age 21 ± 2 years, height 190 ± 9 cm, and weight 90 ± 10 kg) rowed on an ergometer at a targeted heart rate of 130 and 160 beats per minute. SV was derived from arterial pressure waveform by pulse contour analysis, while ventilation and force on the handle were measured. Mean arterial pressure was elevated during the stroke at both work rates (to 133 ± 10 P < .001 and 145 ± 11 mm Hg P = .024, respectively). Also, SV fluctuated markedly during the stroke with deviations being largest at the higher work rate. Thus, SV decreased by 27 ± 10% (31 ± 11 mL) at the beginning of the stroke and increased by 25 ± 9% (28 ± 10 mL) in the recovery (P = .013), while breathing was entrained with one breath during the drive of the stroke and one prior to the next stroke. These observations indicate that during rowing cardiac output depends critically on SV surges during the recovery phase of the stroke.
We hypothesised that in acute high-risk surgical patients, a lower intraoperative peripheral perfusion index (PPI) would indicate a higher risk of postoperative complications and mortality.
This ...retrospective observational study included 1338 acute high-risk surgical patients from November 2017 until October 2018 at two University Hospitals in Denmark. Intraoperative PPI was the primary exposure variable and the primary outcome was severe postoperative complications defined as a Clavien–Dindo Class ≥III or death, within 30 days.
intraoperative PPI was associated with severe postoperative complications or death: odds ratio (OR) 1.12 (95% confidence interval CI 1.05–1.19; P<0.001), with an association of intraoperative mean PPI ≤0.5 and PPI ≤1.5 with the primary outcome: OR 1.79 (95% CI 1.09–2.91; P=0.02) and OR 1.65 (95% CI 1.20–2.27; P=0.002), respectively. Each 15-min increase in intraoperative time spend with low PPI was associated with the primary outcome (per 15 min with PPI ≤0.5: OR 1.11 (95% CI 1.05–1.17; P<0.001) and with PPI ≤1.5: OR 1.06 (95% CI 1.02–1.09; P=0.002)). Thirty-day mortality in patients with PPI ≤0.5 was 19% vs 10% for PPI >0.5, P=0.003. If PPI was ≤1.5, 30-day mortality was 16% vs 8% in patients with a PPI >1.5 (P<0.001). In contrast, intraoperative mean MAP ≤65 mm Hg was not significantly associated with severe postoperative complications or death (OR 1.21 95% CI 0.92–1.58; P=0.2).
Low intraoperative PPI was associated with severe postoperative complications or death in acute high-risk surgical patients. To guide intraoperative haemodynamic management, the PPI should be further investigated.
Results in rowing have improved and here we estimate results for Olympic and World rowing championships based on the winning results from 1893 to 2019 obtained in the current seven Olympic events for ...men (n = 556) and women (n = 239). Data were collected from the official World Rowing Federation online records and from published results and the development analysed by linear regression analysis for the year of competition. Results improved by about 0.7 s per year (15 ± 9.4%) (mean ± SD). Depending on the event, 2020 predicted mean time for the winning boat for men is 363 s (range 326-397) vs. 404 s (362-439) for women (10.3 ± 1.1% slower). The ten-year coefficient of variance for the original boats in Olympic and World Rowing Federation regatta remaining within the Olympic programme, single scull and eight, decreased from 9 ± 2% (1893-1903) to 2 ± 0.4% (2009-2019). Reduced variability in winning times illustrates the standardization of the rowing course and boats, and the improvement in performance point to that body size becomes ever more important for success in competitive rowing.
Volume responsiveness can be evaluated by tilting maneuvers such as head‐down tilt (HDT) and passive leg raising (PLR), but the two procedures use different references (HDT the supine position; PLR ...the semi‐recumbent position). We tested whether the two procedures identify “normovolemia” by evaluating the stroke volume (SV) and cardiac output (CO) responses and whether the peripheral perfusion index (PPI) derived from pulse oximetry provides similar information. In randomized order, 10 healthy men were exposed to both HDT and PLR, and evaluations were made also when the subjects fasted. Central cardiovascular variables were derived by pulse contour analysis and changes in central blood volume assessed by thoracic electrical admittance (TEA). During HDT, SV remained stable (fasted 110 ± 16 vs. 109 ± 16 ml; control 113 ± 16 vs. 111 ± 16 ml, p > 0.05) with no change in CO, TEA, PPI, or SV variation (SVV). In contrast during PLR, SV increased (fasted 108 ± 17 vs. 117 ± 17 ml; control 108 ± 18 vs. 117 ± 18 ml, p < 0.05) followed by an increase in TEA (p < 0.05) and CO increased when subjects fasted (6.7 ± 1.5 vs. 7.1 ± 1.5, p = 0.007) with no change in PPI or SVV. In conclusion, SV has a maximal value for rest in supine men, while PLR restores SV as CBV is reduced in a semi‐recumbent position and the procedure thereby makes healthy volunteers seem fluid responsive.
Volume responsiveness can be evaluated by tilting manoeuvres such as head‐down tilt (HDT) and passive leg raising (PLR), but the two procedures use different references (HDT the supine position; PLR the semi‐recumbent position). Stroke volume has a maximal value for rest in supine men, while PLR restores SV as central blood volume is reduced in a semi‐recumbent position and the procedure thereby makes healthy volunteers seem fluid responsive.
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