Muscle sympathetic reactivity to apneic and exercise stress in high-altitude Sherpa.

Lowland-dwelling populations exhibit persistent sympathetic hyperactivity at altitude that alters vascular function. High-altitude populations, such as Sherpa, have previously exhibited greater peripheral blood flow in response to acute stress than Lowlanders, which may be explained through lower sympathetic activity. Our purpose was to determine whether Sherpa exhibit lower sympathetic reactivity to stress than Lowlanders. Muscle sympathetic nerve activity (MSNA; microneurography) was measured at rest in Lowlanders (n = 14; age = 27 ± 6 yr) at 344 m and between 1 and 10 days at 5,050 m. Sherpa (age = 32 ± 11 yr) were tested at 5,050 m (n = 8). Neurovascular reactivity (i.e., change in MSNA patterns) was measured during maximal end-expiratory apnea, isometric hand grip (IHG; 30% maximal voluntary contraction for 2-min), and postexercise circulatory occlusion (PECO; 3 min). Burst frequency (bursts/min) and incidence (bursts/100 heartbeats) and total normalized SNA (arbitrary units/min) were analyzed at rest, immediately before apnea breakpoint, and during the last minute of IHG and PECO. Vascular responses to apnea, IHG, and PECO were also measured. MSNA reactivity to apnea was smaller in Sherpa than Lowlanders at 5,050 m, although blood pressure responses were similar between groups. MSNA increases in Lowlanders during apnea at 5,050 m were significantly lower than at 344 m (P < 0.05), indicating that a possible sympathetic ceiling was reached in Lowlanders at 5,050 m. MSNA increased similarly during IHG and PECO in Lowlanders at both 334 m and 5,050 m and in Sherpa at 5,050 m, while vascular changes (mean brachial arterial pressure, contralateral brachial flow and resistance) were similar between groups. Sherpa demonstrate overall lower sympathetic reactivity that may be a result of heightened vascular responsiveness to potential apneic stress at altitude.

Exercise for the prevention and treatment of low back, pelvic girdle and lumbopelvic pain during pregnancy: a systematic review and meta-analysis.

OBJECTIVE: The purpose of this review was to investigate the relationship between prenatal exercise, and low back (LBP), pelvic girdle (PGP) and lumbopelvic (LBPP) pain. DESIGN: Systematic review with random effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were eligible (except case studies and reviews) if they were published in English, Spanish or French, and contained information on the population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [eg, dietary; "exercise + co-intervention"]), comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and outcome (prevalence and symptom severity of LBP, PGP and LBPP). RESULTS: The analyses included data from 32 studies (n=52 297 pregnant women). 'Very low' to 'moderate' quality evidence from 13 randomised controlled trials (RCTs) showed prenatal exercise did not reduce the odds of suffering from LBP, PGP and LBPP either in pregnancy or the postpartum period. However, 'very low' to 'moderate' quality evidence from 15 RCTs identified lower pain severity during pregnancy and the early postpartum period in women who exercised during pregnancy (standardised mean difference -1.03, 95% CI -1.58, -0.48) compared with those who did not exercise. These findings were supported by 'very low' quality evidence from other study designs. CONCLUSION: Compared with not exercising, prenatal exercise decreased the severity of LBP, PGP or LBPP during and following pregnancy but did not decrease the odds of any of these conditions at any time point.

Prenatal exercise is not associated with fetal mortality: a systematic review and meta-analysis.

OBJECTIVE: To perform a systematic review of the relationship between prenatal exercise and fetal or newborn death. DESIGN: Systematic review with random-effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were included (except case studies) if they were published in English, Spanish or French and contained information on the population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [eg, dietary; "exercise + co-intervention"]), comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and outcome (miscarriage or perinatal mortality). RESULTS: Forty-six studies (n=2 66 778) were included. There was 'very low' quality evidence suggesting no increased odds of miscarriage (23 studies, n=7125 women; OR 0.88, 95% CI 0.63 to 1.21, I2=0%) or perinatal mortality (13 studies, n=6837 women, OR 0.86, 95% CI 0.49 to 1.52, I2=0%) in pregnant women who exercised compared with those who did not. Stratification by subgroups did not affect odds of miscarriage or perinatal mortality. The meta-regressions identified no associations between volume, intensity or frequency of exercise and fetal or newborn death. As the majority of included studies examined the impact of moderate intensity exercise to a maximum duration of 60 min, we cannot comment on the effect of longer periods of exercise. SUMMARY/CONCLUSIONS: Although the evidence in this field is of 'very low' quality, it suggests that prenatal exercise is not associated with increased odds of miscarriage or perinatal mortality. In plain terms, this suggests that generally speaking exercise is 'safe' with respect to miscarriage and perinatal mortality.

Effects of prenatal exercise on incidence of congenital anomalies and hyperthermia: a systematic review and meta-analysis.

OBJECTIVE: To investigate the relationships between exercise and incidence of congenital anomalies and hyperthermia. DESIGN: Systematic review with random-effects meta-analysis . DATA SOURCES: Online databases were searched from inception up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were eligible (except case studies and reviews) if they were published in English, Spanish or French, and contained information on population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [e.g., dietary; "exercise + co-intervention"]), comparator (no exercise or different frequency, intensity, duration, volume or type of exercise) and outcome (maternal temperature and fetal anomalies). RESULTS: This systematic review and meta-analysis included 'very low' quality evidence from 14 studies (n=78 735) reporting on prenatal exercise and the odds of congenital anomalies, and 'very low' to 'low' quality evidence from 15 studies (n=447) reporting on maternal temperature response to prenatal exercise. Prenatal exercise did not increase the odds of congenital anomalies (OR 1.23, 95% CI 0.77 to 1.95, I2=0%). A small but significant increase in maternal temperature was observed from pre-exercise to both during and immediately after exercise (during: 0.26°C, 95% CI 0.12 to 0.40, I2=70%; following: 0.24°C, 95% CI 0.17 to 0.31, I2=47%). SUMMARY/CONCLUSIONS: These data suggest that moderate-to-vigorous prenatal exercise does not induce hyperthermia or increase the odds of congenital anomalies. However, exercise responses were investigated in most studies after 12 weeks' gestation when the risk of de novo congenital anomalies is negligible.

Impact of prenatal exercise on maternal harms, labour and delivery outcomes: a systematic review and meta-analysis.

OBJECTIVE: To perform a systematic review of the relationships between prenatal exercise and maternal harms including labour/delivery outcomes. DESIGN: Systematic review with random effects meta-analysis and meta-regression. DATASOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were included (except case studies) if they were published in English, Spanish or French and contained information on the population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise), comparator (no exercise or different frequency, intensity, duration, volume and type of exercise, alone ["exercise-only"] or in combination with other intervention components [e.g., dietary; "exercise + co-intervention"]) and outcome (preterm/prelabour rupture of membranes, caesarean section, instrumental delivery, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms (author defined) and diastasis recti). RESULTS: 113 studies (n=52 858 women) were included. 'Moderate' quality evidence from exercise-only randomised controlled trials (RCTs) indicated a 24% reduction in the odds of instrumental delivery in women who exercised compared with women who did not (20 RCTs, n=3819; OR 0.76, 95% CI 0.63 to 0.92, I 2= 0 %). The remaining outcomes were not associated with exercise. Results from meta-regression did not identify a dose-response relationship between frequency, intensity, duration or volume of exercise and labour and delivery outcomes. SUMMARY/CONCLUSIONS: Prenatal exercise reduced the odds of instrumental delivery in the general obstetrical population. There was no relationship between prenatal exercise and preterm/prelabour rupture of membranes, caesarean section, induction of labour, length of labour, vaginal tears, fatigue, injury, musculoskeletal trauma, maternal harms and diastasis recti.

Effectiveness of exercise interventions in the prevention of excessive gestational weight gain and postpartum weight retention: a systematic review and meta-analysis.

OBJECTIVE: Gestational weight gain (GWG) has been identified as a critical modifier of maternal and fetal health. This systematic review and meta-analysis aimed to examine the relationship between prenatal exercise, GWG and postpartum weight retention (PPWR). DESIGN: Systematic review with random effects meta-analysis and meta-regression. Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs in English, Spanish or French were eligible (except case studies and reviews) if they contained information on the population (pregnant women without contraindication to exercise), intervention (frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [eg, dietary; "exercise + co-intervention"]), comparator (no exercise or different frequency, intensity, duration, volume or type of exercise) and outcomes (GWG, excessive GWG (EGWG), inadequate GWG (IGWG) or PPWR). RESULTS: Eighty-four unique studies (n=21 530) were included. 'Low' to 'moderate' quality evidence from randomised controlled trials (RCTs) showed that exercise-only interventions decreased total GWG (n=5819; -0.9 kg, 95% CI -1.23 to -0.57 kg, I2=52%) and PPWR (n=420; -0.92 kg, 95% CI -1.84 to 0.00 kg, I2=0%) and reduced the odds of EGWG (n=3519; OR 0.68, 95% CI 0.57 to 0.80, I2=12%) compared with no exercise. 'High' quality evidence indicated higher odds of IGWG with prenatal exercise-only (n=1628; OR 1.32, 95% CI 1.04 to 1.67, I2=0%) compared with no exercise. CONCLUSIONS: Prenatal exercise reduced the odds of EGWG and PPWR but increased the risk of IGWG. However, the latter result should be interpreted with caution because it was based on a limited number of studies (five RCTs).

Prenatal exercise for the prevention of gestational diabetes mellitus and hypertensive disorders of pregnancy: a systematic review and meta-analysis.

OBJECTIVE: Gestational diabetes mellitus (GDM), gestational hypertension (GH) and pre-eclampsia (PE) are associated with short and long-term health issues for mother and child; prevention of these complications is critically important. This study aimed to perform a systematic review and meta-analysis of the relationships between prenatal exercise and GDM, GH and PE. DESIGN: Systematic review with random effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were included (except case studies) if published in English, Spanish or French, and contained information on the Population (pregnant women without contraindication to exercise), Intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [e.g., dietary; "exercise + co-intervention"]), Comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and Outcomes (GDM, GH, PE). RESULTS: A total of 106 studies (n=273 182) were included. 'Moderate' to 'high'-quality evidence from randomised controlled trials revealed that exercise-only interventions, but not exercise+cointerventions, reduced odds of GDM (n=6934; OR 0.62, 95% CI 0.52 to 0.75), GH (n=5316; OR 0.61, 95% CI 0.43 to 0.85) and PE (n=3322; OR 0.59, 95% CI 0.37 to 0.9) compared with no exercise. To achieve at least a 25% reduction in the odds of developing GDM, PE and GH, pregnant women need to accumulate at least 600 MET-min/week of moderate-intensity exercise (eg, 140 min of brisk walking, water aerobics, stationary cycling or resistance training). SUMMARY/CONCLUSIONS: In conclusion, exercise-only interventions were effective at lowering the odds of developing GDM, GH and PE.

Glucose responses to acute and chronic exercise during pregnancy: a systematic review and meta-analysis.

OBJECTIVE: To perform a systematic review and meta-analysis to explore the relationship between prenatal exercise and glycaemic control. DESIGN: Systematic review with random-effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were included (except case studies and reviews) if they were published in English, Spanish or French, and contained information on the population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of acute or chronic exercise, alone ('exercise-only') or in combination with other intervention components (eg, dietary; 'exercise+cointervention') at any stage of pregnancy), comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and outcome (glycaemic control). RESULTS: A total of 58 studies (n=8699) were included. There was 'very low' quality evidence showing that an acute bout of exercise was associated with a decrease in maternal blood glucose from before to during exercise (6 studies, n=123; mean difference (MD) -0.94 mmol/L, 95% CI -1.18 to -0.70, I2=41%) and following exercise (n=333; MD -0.57 mmol/L, 95% CI -0.72 to -0.41, I2=72%). Subgroup analysis showed that there were larger decreases in blood glucose following acute exercise in women with diabetes (n=26; MD -1.42, 95% CI -1.69 to -1.16, I2=8%) compared with those without diabetes (n=285; MD -0.46, 95% CI -0.60 to -0.32, I2=62%). Finally, chronic exercise-only interventions reduced fasting blood glucose compared with no exercise postintervention in women with diabetes (2 studies, n=70; MD -2.76, 95% CI -3.18 to -2.34, I2=52%; 'low' quality of evidence), but not in those without diabetes (9 studies, n=2174; MD -0.05, 95% CI -0.16 to 0.05, I2=79%). CONCLUSION: Acute and chronic prenatal exercise reduced maternal circulating blood glucose concentrations, with a larger effect in women with diabetes.

Impact of prenatal exercise on both prenatal and postnatal anxiety and depressive symptoms: a systematic review and meta-analysis.

OBJECTIVE: To examine the influence of prenatal exercise on depression and anxiety during pregnancy and the postpartum period. DESIGN: Systematic review with random effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were included (except case studies) if they were published in English, Spanish or French and contained information on the Population (pregnant women without contraindication to exercise), Intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise), Comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and Outcome (prenatal or postnatal depression or anxiety). RESULTS: A total of 52 studies (n=131 406) were included. 'Moderate' quality evidence from randomised controlled trials (RCTs) revealed that exercise-only interventions, but not exercise+cointerventions, reduced the severity of prenatal depressive symptoms (13 RCTs, n=1076; standardised mean difference: -0.38, 95% CI -0.51 to -0.25, I2=10%) and the odds of prenatal depression by 67% (5 RCTs, n=683; OR: 0.33, 95% CI 0.21 to 0.53, I2=0%) compared with no exercise. Prenatal exercise did not alter the odds of postpartum depression or the severity of depressive symptoms, nor anxiety or anxiety symptoms during or following pregnancy. To achieve at least a moderate effect size in the reduction of the severity of prenatal depressive symptoms, pregnant women needed to accumulate at least 644 MET-min/week of exercise (eg, 150 min of moderate intensity exercise, such as brisk walking, water aerobics, stationary cycling, resistance training). SUMMARY/CONCLUSIONS: Prenatal exercise reduced the odds and severity of prenatal depression.

Impact of prenatal exercise on neonatal and childhood outcomes: a systematic review and meta-analysis.

OBJECTIVE: We aimed to identify the relationship between maternal prenatal exercise and birth complications, and neonatal and childhood morphometric, metabolic and developmental outcomes. DESIGN: Systematic review with random-effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were eligible (except case studies and reviews) if published in English, Spanish or French, and contained information on the relevant population (pregnant women without contraindication to exercise), intervention (subjective/objective measures of frequency, intensity, duration, volume or type of exercise, alone ('exercise-only') or in combination with other intervention components (eg, dietary; 'exercise+cointervention')), comparator (no exercise or different frequency, intensity, duration, volume, type or trimester of exercise) and outcomes (preterm birth, gestational age at delivery, birth weight, low birth weight (<2500 g), high birth weight (>4000 g), small for gestational age, large for gestational age, intrauterine growth restriction, neonatal hypoglycaemia, metabolic acidosis (cord blood pH, base excess), hyperbilirubinaemia, Apgar scores, neonatal intensive care unit admittance, shoulder dystocia, brachial plexus injury, neonatal body composition (per cent body fat, body weight, body mass index (BMI), ponderal index), childhood obesity (per cent body fat, body weight, BMI) and developmental milestones (including cognitive, psychosocial, motor skills)). RESULTS: A total of 135 studies (n=166 094) were included. There was 'high' quality evidence from exercise-only randomised controlled trials (RCTs) showing a 39% reduction in the odds of having a baby >4000 g (macrosomia: 15 RCTs, n=3670; OR 0.61, 95% CI 0.41 to 0.92) in women who exercised compared with women who did not exercise, without affecting the odds of growth-restricted, preterm or low birth weight babies. Prenatal exercise was not associated with the other neonatal or infant outcomes that were examined. CONCLUSIONS: Prenatal exercise is safe and beneficial for the fetus. Maternal exercise was associated with reduced odds of macrosomia (abnormally large babies) and was not associated with neonatal complications or adverse childhood outcomes.

Prenatal exercise (including but not limited to pelvic floor muscle training) and urinary incontinence during and following pregnancy: a systematic review and meta-analysis.

OBJECTIVE: To examine the relationships between prenatal physical activity and prenatal and postnatal urinary incontinence (UI). DESIGN: Systematic review with random effects meta-analysis and meta-regression. DATA SOURCES: Online databases were searched up to 6 January 2017. STUDY ELIGIBILITY CRITERIA: Studies of all designs were included (except case studies) if they were published in English, Spanish or French and contained information on the Population (pregnant women without contraindication to exercise), Intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [e.g., dietary; "exercise + co-intervention"]), Comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and Outcome (prenatal or postnatal UI). RESULTS: 24 studies (n=15 982 women) were included. 'Low' to 'moderate' quality evidence revealed prenatal pelvic floor muscle training (PFMT) with or without aerobic exercise decreased the odds of UI in pregnancy (15 randomised controlled trials (RCTs), n=2764 women; OR 0.50, 95% CI 0.37 to 0.68, I2=60%) and in the postpartum period (10 RCTs, n=1682 women; OR 0.63, 95% CI 0.51, 0.79, I2=0%). When we analysed the data by whether women were continent or incontinent prior to the intervention, exercise was beneficial at preventing the development of UI in women with continence, but not effective in treating UI in women with incontinence. There was 'low' quality evidence that prenatal exercise had a moderate effect in the reduction of UI symptom severity during (five RCTs, standard mean difference (SMD) -0.54, 95% CI -0.88 to -0.20, I2=64%) and following pregnancy (three RCTs, 'moderate' quality evidence; SMD -0.54, 95% CI -0.87 to -0.22, I2=24%). CONCLUSION: Prenatal exercise including PFMT reduced the odds and symptom severity of prenatal and postnatal UI. This was the case for women who were continent before the intervention. Among women who were incontinent during pregnancy, exercise training was not therapeutic.

TV time, physical activity, sedentary behaviour and cardiometabolic biomarkers in pregnancy-NHANES 2003-2006.

OBJECTIVES: This study examined the impacts of individual and combined associations between moderate-to-vigorous physical activity (MVPA) and sedentary time (ST) (accelerometer-derived), as well as MVPA and television (TV) time (self-reported) on cardiometabolic biomarkers during pregnancy. METHODS: Participants were 332 pregnant women from the 2003-2006 cycles of the National Health and Nutrition Examination Survey (NHANES). Multiple linear regression models were conducted to examine the relationships between individual and combinations of high/low MVPA, ST, and TV time with cardiometabolic biomarkers: body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), high-density lipoprotein cholesterol (HDL), and C-reactive protein (CRP). RESULTS: Women with high MVPA (≥ 17 min/day) compared to those with low MVPA (< 17 min/day) had significantly lower BMI. Women with low ST (< 503 min/day) compared to those with high ST (≥ 503 min/day) had significantly lower SBP and DBP. Women with low TV (< 3 h/day) compared to those with high TV (≥ 3 h/day) had significantly lower BMI and log-transformed CRP. Women with a combination of low ST/high MVPA had lower SBP and DBP (ptrend < 0.03). Women with a combination of low TV/high MVPA had lower BMI and log-transformed CRP (ptrend < 0.00). CONCLUSION: We need to consider both physical activity and sedentary time for improved cardiometabolic health during pregnancy.

RéSUMé: OBJECTIFS: Notre étude porte sur les effets des associations individuelles et combinées entre l'activité physique modérée à vigoureuse (APMV) et le temps de sédentarité (TS) (mesuré par accéléromètre), ainsi qu'entre l'APMV et le temps de télévision (TT) (autodéclaré) et les biomarqueurs cardiométaboliques durant la grossesse. MéTHODE: Les participantes étaient 332 femmes enceintes ayant participé aux cycles 2003­2006 de la National Health and Nutrition Examination Survey (NHANES). Des modèles de régression linéaire multiple ont été appliqués aux liens individuels et combinés entre l'APMV, le TS et le TT élevés/faibles et les biomarqueurs cardiométaboliques suivants : indice de masse corporelle (IMC), pression systolique (PS), pression diastolique (PD), cholestérol à lipoprotéines de haute densité (HDL) et protéine C réactive (CRP). RéSULTATS: L'IMC était significativement plus faible chez les femmes dont l'APMV était élevée (≥ 17 min/j) que chez celles dont l'APMV était faible (< 17 min/j). La PS et la PD étaient significativement plus faibles chez les femmes dont le TS était faible (< 503 min/j) que chez celles dont le TS était élevé (≥ 503 min/j). L'IMC et la protéine CRP log-transformée étaient significativement plus faibles chez les femmes dont le TT était faible (< 3 h/j) que chez celles dont le TT était élevé (≥ 3 h/j). La PS et la PD étaient plus faibles (ptendance < 0,03) chez les femmes qui présentaient une combinaison de TS faible et d'APMV élevée. Et l'IMC et la protéine CRP log-transformée étaient plus faibles (ptendance < 0,00) chez les femmes qui présentaient une combinaison de TT faible et d'APMV élevée. CONCLUSION: Il faut tenir compte à la fois de l'activité physique et du temps de sédentarité pour améliorer la santé cardiométabolique durant la grossesse.

Peripheral chemoreceptor deactivation attenuates the sympathetic response to glucose ingestion.

Acute increases in blood glucose are associated with heightened muscle sympathetic nerve activity (MSNA). Animal studies have implicated a role for peripheral chemoreceptors in this response, but this has not been examined in humans. Heart rate, cardiac output (CO), mean arterial pressure, total peripheral conductance, and blood glucose concentrations were collected in 11 participants. MSNA was recorded in a subset of 5 participants via microneurography. Participants came to the lab on 2 separate days (i.e., 1 control and 1 experimental day). On both days, participants ingested 75 g of glucose following baseline measurements. On the experimental day, participants breathed 100% oxygen for 3 min at baseline and again at 20, 40, and 60 min after glucose ingestion to deactivate peripheral chemoreceptors. Supplemental oxygen was not given to participants on the control day. There was a main effect of time on blood glucose (P < 0.001), heart rate (P < 0.001), CO (P < 0.001), sympathetic burst frequency (P < 0.001), burst incidence (P = 0.01), and total MSNA (P = 0.001) for both days. Blood glucose concentrations and burst frequency were positively correlated on the control day (r = 0.42; P = 0.03) and experimental day (r = 0.62; P = 0.003). There was a time × condition interaction (i.e., normoxia vs. hyperoxia) on burst frequency, in which hyperoxia significantly blunted burst frequency at 20 and 60 min after glucose ingestion only. Given that hyperoxia blunted burst frequency only during hyperglycemia, our results suggest that the peripheral chemoreceptors are involved in activating MSNA after glucose ingestion.

Chemoreflex mediated arrhythmia during apnea at 5,050 m in low- but not high-altitude natives.

Peripheral chemoreflex mediated increases in both parasympathetic and sympathetic drive under chronic hypoxia may evoke bradyarrhythmias during apneic periods. We determined whether 1) voluntary apnea unmasks arrhythmia at low (344 m) and high (5,050 m) altitude, 2) high-altitude natives (Nepalese Sherpa) exhibit similar cardiovagal responses at altitude, and 3) bradyarrhythmias at altitude are partially chemoreflex mediated. Participants were grouped as Lowlanders ( n = 14; age = 27 ± 6 yr) and Nepalese Sherpa ( n = 8; age = 32 ± 11 yr). Lowlanders were assessed at 344 and 5,050 m, whereas Sherpa were assessed at 5,050 m. Heart rate (HR) and rhythm (lead II ECG) were recorded during rest and voluntary end-expiratory apnea. Peripheral chemoreflex contributions were assessed in Lowlanders ( n = 7) at altitude after 100% oxygen. Lowlanders had higher resting HR at altitude (70 ± 15 vs. 61 ± 15 beats/min; P < 0.01) that was similar to Sherpa (71 ± 5 beats/min; P = 0.94). High-altitude apnea caused arrhythmias in 11 of 14 Lowlanders [junctional rhythm ( n = 4), 3° atrioventricular block ( n = 3), sinus pause ( n = 4)] not present at low altitude and larger marked bradycardia (nadir -39 ± 18 beats/min; P < 0.001). Sherpa exhibited a reduced bradycardia response during apnea compared with Lowlanders ( P < 0.001) and did not develop arrhythmias. Hyperoxia blunted bradycardia (nadir -10 ± 14 beats/min; P < 0.001 compared with hypoxic state) and reduced arrhythmia incidence (3 of 7 Lowlanders). Degree of bradycardia was significantly related to hypoxic ventilatory response (HVR) at altitude and predictive of arrhythmias ( P < 0.05). Our data demonstrate apnea-induced bradyarrhythmias in Lowlanders at altitude but not in Sherpa (potentially through cardioprotective phenotypes). The chemoreflex is an important mechanism in genesis of bradyarrhythmias, and the HVR may be predictive for identifying individual susceptibility to events at altitude. NEW & NOTEWORTHY The peripheral chemoreflex increases both parasympathetic and sympathetic drive under chronic hypoxia. We found that this evoked bradyarrhythmias when combined with apneic periods in Lowlanders at altitude, which become relieved through supplemental oxygen. In contrast, high-altitude residents (Nepalese Sherpa) do not exhibit bradyarrhythmias during apnea at altitude through potential cardioprotective adaptations. The degree of bradycardia and bradyarrhythmias was related to the hypoxic ventilatory response, demonstrating that the chemoreflex plays an important role in these findings.

Lactate in the brain: an update on its relevance to brain energy, neurons, glia and panic disorder.

Lactate is considered an important metabolite in the human body, but there has been considerable debate about its roles in brain function. Research in recent years has suggested that lactate from astrocytes may be crucial for supporting axonal function, especially during times of high metabolic demands or hypoglycemia. The astrocyte-neuron lactate transfer shuttle system serves a protective function to ensure a supply of substrates for brain metabolism, and oligodendrocytes appear to also influence availability of lactate. There is increasing evidence for lactate acting as a signaling molecule in the brain to link metabolism, substrate availability, blood flow and neuronal activity. This review will attempt to connect evidence to the relationship lactate has to panic disorder (PD), which suggests that its transporters, receptors or metabolism warrant investigation as potential therapeutic targets in PD.