Chemoreflex Mediated Arrhythmia during Apnea at 5050m 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 &lt; 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 &lt; 0.001). Sherpa exhibited a reduced bradycardia response during apnea compared with Lowlanders ( P &lt; 0.001) and did not develop arrhythmias. Hyperoxia blunted bradycardia (nadir −10 ± 14 beats/min; P &lt; 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 &lt; 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 &amp; 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. </jats:p

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

Lowland-dwelling populations exhibit persistent sympathetic hyperactivity at altitude that may alter vascular function. High altitude populations, such as Sherpa, exhibit greater peripheral blood flow in response to acute stress, suggesting Sherpas may exhibit lower sympathetic activity and reactivity to stress than Lowlanders. Muscle sympathetic activity (MSNA; microneurography) including frequency (bursts/min), incidence (bursts/100HB), amplitude (% of max burst), was measured at rest in Lowlanders (n=14; age=27±6yrs) at 344m and following a 8- 9 days of graded ascent to 5050m. Sherpa (age=32±11yrs) were tested at 5050m (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 minutes) and post exercise circulatory occlusion (PECO; 3 minutes). Total normalized SNA (au/min) was calculated over 10 cardiac cycles during baseline and pre-volitional apnea breakpoint. Lowlander burst frequency (11±5 bursts/min to 30±7 bursts/min; Mean±SD; p<0.001) and burst incidence (25±13 bursts/100HB to 53±15 bursts/100HB; p<0.001) increased at 5050m. In contrast, Sherpas had lower burst frequency (23±11 bursts/min; p<0.05) and incidence (30±13 bursts/100HB; p<0.05) at 5050m. MSNA increases in Lowlanders and Sherpa during apnea at 5050m were significantly lower than Lowlanders at 344m (both P<0.05), with a possible sympathetic ceiling reached in Lowlanders at 5050m. MSNA increased similarly during the IHG/PECO in Lowlanders at 334m and 5050m altitude and Sherpa at 5050m. Sherpa demonstrate overall lower sympathetic activity and reactivity during severe stress. This may be a result of improved systemic hemodynamic function associated with evolutionary adaptations to permanent residency at altitude

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 \u27very low\u27 quality evidence suggesting no increased odds of miscarriage (23 studies, n=7125 women; OR 0.88, 95% CI 0.63 to 1.21, I-2=0%) or perinatal mortality (13 studies, n=6837 women, OR 0.86, 95% CI 0.49 to 1.52, I-2=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 \u27very low\u27 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 \u27safe\u27 with respect to miscarriage and perinatal mortality

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=15982 women) were included. Low\u27 to moderate\u27 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, I-2=60%) and in the postpartum period (10 RCTs, n=1682 women; OR 0.63, 95%CI 0.51, 0.79, I-2=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\u27 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, I-2=64%) and following pregnancy (three RCTs, moderate\u27 quality evidence; SMD -0.54, 95% CI -0.87 to -0.22, I-2=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

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 \u27very low\u27 quality evidence from 14 studies (n=78 735) reporting on prenatal exercise and the odds of congenital anomalies, and \u27very low\u27 to \u27low\u27 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, I-2=0%). A small but significant increase in maternal temperature was observed from pre-exercise to both during and immediately after exercise (during: 0.26 degrees C, 95% CI 0.12 to 0.40, I-2=70%; following: 0.24 degrees C, 95% CI 0.17 to 0.31, I-2=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\u27 gestation when the risk of de novo congenital anomalies is negligible

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=131406) were included. Moderate\u27 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, I-2=10%) and the odds of prenatal depression by 67% (5 RCTs, n=683; OR: 0.33, 95%CI 0.21 to 0.53, I-2=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, 150min 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

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). \u27Very low\u27 to \u27moderate\u27 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, \u27very low\u27 to \u27moderate\u27 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 \u27very low\u27 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

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. \u27Moderate\u27 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