Maternal cardioautonomic responses during and following exercise throughout pregnancy

Heat production during exercise in pregnancy: discerning the contribution of total body weight

Studies have reported enhanced thermoregulatory function as pregnancy progresses; however, it is unclear if differences in thermoregulation are attributed to weight gain or other physiological changes. This study aimed to determine if total body weight will influence thermoregulation (heat production (Hprod)), heart rate, and perceptual measurements in response to weight-bearing exercise during early to late pregnancy. A cross-sectional design of healthy pregnant women at different pregnancy time points (early, T1; middle, T2; late, T3) performed a 7-stage weight-bearing incremental exercise protocol. Measurements of Hprod, HR, and RPE were examined. Two experimental groups were studied: (1) weight matched and (2) non-weight matched, in T1, T2, and T3. During exercise, equivalent Hprod at T1 (326 ± 88 kJ), T2 (330 ± 43 kJ), and T3 (352 ± 52 kJ) (p = 0.504); HR (p = 0.830); and RPE (p = 0.195) were observed in the WM group at each time point. In the NWM group, Hprod (from stages 1-6 of the exercise) increased across pregnancy time points, T1 (291 ± 76 kJ) to T2 (347 ± 41 kJ) and T3 (385 ± 47 kJ) (p < 0.001). HR increased from T1 to T3 in the warm-up to stage 6 (p = 0.009). RPE did not change as pregnancy time point progressed (p = 0.309). Total body weight, irrespective of pregnancy time point, modulates Hprod and HR during exercise. Therefore, accounting for total body weight is crucial when comparing thermoregulatory function during exercise across pregnancy.

A narrative review of exercise dose during pregnancy

The current recommendations for prenatal exercise dose align with those from the American College of Sports Medicine; 150 min of moderate intensity every week of pregnancy. However, recent works suggest there may be a dose-dependent beneficial effect for mother and offspring; maternal and offspring health outcomes respond differently to low, medium, and high doses of prenatal exercise. It is, therefore, our aim to summarize the published evidence (years 1950-2023) for five metrics of prenatal exercise training commonly reported, that is, "FITT-V": Frequency (number of sessions), Intensity (metabolic equivalents "METs"), Time (duration of sessions), Type (exercise mode), Volume (exercise MET*mins). The target audience includes clinicians and health care professionals, as well as exercise professionals and physiologists. Data suggest that moderate exercise frequency (3-4 times weekly) appears safe and efficacious for mother and offspring, while there is contradictory evidence for the safety and further benefit of increased frequency beyond 5 sessions per week. Moderate (3-6 METs) and vigorous (>6 METs) intensity prenatal exercise have been shown to promote maternal and offspring health, while little research has been performed on low-intensity (<3 METs) exercise. Exercise sessions lasting less than 1 hr are safe for mother and fetus, while longer-duration exercise should be carefully considered and monitored. Taken together, aerobic, resistance, or a combination of exercise types is well tolerated at medium-to-high volumes and offers a variety of type-specific benefits. Still, research is needed to define (1) the "minimum" effective dose of exercise for mother and offspring health, as well as (2) the maximum tolerable dose from which more benefits may be seen. Additionally, there is a lack of randomized controlled trials addressing exercise doses during the three trimesters of pregnancy. Further, the protocols adopted in research studies should be more standardized and tested for efficacy in different populations of gravid women.

Assessment of physical fitness during pregnancy: validity and reliability of fitness tests, and relationship with maternal and neonatal health - a systematic review

Objectives

To systematically review studies evaluating one or more components of physical fitness (PF) in pregnant women, to answer two research questions: (1) What tests have been employed to assess PF in pregnant women? and (2) What is the validity and reliability of these tests and their relationship with maternal and neonatal health?

Design

A systematic review.

Data sources

PubMed and Web of Science.

Eligibility criteria

Original English or Spanish full-text articles in a group of healthy pregnant women which at least one component of PF was assessed (field based or laboratory tests).

Results

A total of 149 articles containing a sum of 191 fitness tests were included. Among the 191 fitness tests, 99 (ie, 52%) assessed cardiorespiratory fitness through 75 different protocols, 28 (15%) assessed muscular fitness through 16 different protocols, 14 (7%) assessed flexibility through 13 different protocols, 45 (24%) assessed balance through 40 different protocols, 2 assessed speed with the same protocol and 3 were multidimensional tests using one protocol. A total of 19 articles with 23 tests (13%) assessed either validity (n=4), reliability (n=6) or the relationship of PF with maternal and neonatal health (n=16).

Conclusion

Physical fitness has been assessed through a wide variety of protocols, mostly lacking validity and reliability data, and no consensus exists on the most suitable fitness tests to be performed during pregnancy.

PROSPERO registration number

CRD42018117554.

The research of correlation between blood pressure and nailfold capillary parameters in exercising and non-exercising pregnant women

Background/Aim: With an increase in cardiac output, blood pressure values in pregnancy increase. The aim of the study was to examine the effect of prenatal exercises on the circulatory parameters and the correlation between blood pressure and nailfold capillary parameters in healthy pregnant women. Methods: The blood pressure shape and length of nailfold capillary were assessed in 35 non-exercising pregnant women and 35 pregnant women who exercised, at the beginning of the study (between 20 and 32 gestational week) and the end of the study (28 - 40 gestational week). Results: The elevation in blood pressure was significantly lower in pregnant women who exercised in relation to non-exercising pregnant women. After eight weeks, the length of the capillary loops was increased by 30 µm and the number of pregnant women with pronounced shape changes of capillary loops increased, with no difference between the groups. Non-exercisers had a correlation between the change in diastolic pressure and the increase in capillary length (r = 0.53, p = 0.001). In the experimental group, the correlation between the change in blood pressure and the increase in the length of capillary loops was not determined. Conclusion: Prenatal physical activity had a beneficial impact on the circulation of pregnant women. In pregnant women in the third trimester, after eight weeks of follow-up, the length of the nailfold capillary loops and the presence of pronounced shape changes of capillary loops were increased, without difference between exercisers and non-exercisers. In non-exercising pregnant women, the capillary length was increased with the elevation of diastolic blood pressure, while the correlation was not found in pregnant women who exercised.

Cardiovascular function during triplet pregnancy

Pregnancy is recognized as a natural physiological stressor to the maternal cardiovascular system. Cardiovascular adaptation is markedly greater in twin pregnancy compared with singleton pregnancy; however, these changes are sparsely documented in triplet pregnancy. The aim of this case series was to compare maternal cardiac function, cardioautonomic regulation, and blood pressure reactivity in healthy singleton, twin, and triplet pregnancies. Resting cardiac structure and function (echocardiography), beat-by-beat blood pressure variability (BPV; photoplethysmography), and heart rate variability (HRV; electrocardiogram) were measured in two triplet, three twin, and three singleton pregnancies (matched for maternal age, prepregnancy body mass index, and gestational age). Hemodynamic responses to a 3-min cold pressor test were also recorded to assess blood pressure reactivity. Due to the small sample size of this case series, statistical comparisons were not made between groups. Compared with singleton and twin pregnancies, individuals pregnant with triplets had greater resting cardiac output but lower cardiac deformation (longitudinal strain, basal circumferential strain, and torsion), sympathetic dominance in cardioautonomic regulation (lower HRV and higher BPV), and elevated blood pressure reactivity in response to the cold pressor test. Taken together, these observations suggest that females with triplet pregnancies may have reduced cardiovascular function, which may contribute to the heightened risk of complications in multifetal pregnancies.NEW & NOTEWORTHY Individuals with healthy triplet pregnancies had greater resting cardiac output but lower left ventricular mechanics when compared with singleton and twin pregnancies matched for gestational age. In addition, triplet pregnancies had greater blood pressure variability and lower overall heart rate variability compared with singleton pregnancies, as well as greater blood pressure reactivity to the cold pressor test. Healthy triplet pregnancies may have reduced cardiovascular function as well as a greater sympathetic contribution to cardiac control.

Cardioautonomic control in healthy singleton and twin pregnancies

In conjunction with significant cardiovascular adaptation, changes in cardioautonomic balance, specifically greater sympathetic activation and vagal withdrawal, are considered normal adaptations to healthy singleton pregnancy. Cardiovascular adaptation to twin pregnancy is more profound than that of singleton pregnancies; however, the changes in cardioautonomic control during multifetal gestation are unknown. To address this gap, beat-by-beat blood pressure (photoplethysmography) and heart rate (lead II electrocardiogram) were measured continuously in 25 twin pregnancies and 25 singleton pregnancies (matched for age, prepregnancy body mass index, and gestational age) during 10 min of rest. Data extracted from a 3- to 5-min period were used to analyze heart rate variability (HRV), blood pressure variability (BPV), cardiovagal baroreflex gain, and cardiac intervals as indicators of cardioautonomic control. Independent t tests were used to determine statistical differences between groups (α = 0.05), and the false rate discovery was determined to adjust for multiple comparisons. Resting heart rate was greater in twin compared with singleton pregnancies (91 ± 10 vs. 81 ± 10 beats/min; P = 0.001), but blood pressure was not different. Individuals with twin pregnancies had lower HRV, evidenced by lower standard deviation of R-R intervals (32 ± 11 vs. 47 ± 18 ms; P = 0.001), total power (1,035 ± 810 vs. 1,945 ± 1,570 ms²; P = 0.004), and high frequency power (224 ± 262 vs. 810 ± 806 ms²; P < 0.001) compared with singleton pregnancies. There were no differences in cardiac intervals, BPV, and cardiovagal baroreflex gain between groups. Our findings suggest that individuals with twin pregnancies have greater sympathetic and lower parasympathetic contributions to heart rate and that cardiac, but not vascular, autonomic control is impacted during twin compared with singleton pregnancy.NEW & NOTEWORTHY Individuals with healthy twin pregnancies had lower overall heart rate variability compared with those with singleton pregnancies at similar gestational ages. These results suggest a greater sympathetic and reduced parasympathetic contribution to cardiac control in twin pregnancies. Baseline heart rate was elevated, while arterial pressure and spontaneous cardiovagal baroreflex gain were not different between groups. This was result of the upward resetting of the cardiovagal baroreflex during healthy twin pregnancy, thus maintaining arterial pressure.

The sympathetic muscle metaboreflex is not different in the third trimester in normotensive pregnant women

Isometric handgrip (IHG) is used to assess sympathetic nervous system responses to exercise and may be useful at predicting hypertension in both pregnant and nonpregnant populations. We previously observed altered sympathetic nervous system control of blood pressure in late pregnancy. Therefore, we measured muscle sympathetic nerve activity (MSNA) and blood pressure during muscle metaboreflex activation (IHG) in normotensive pregnant women in the third trimester compared with in healthy nonpregnant women. Further, 19 pregnant (32 ± 3 wk gestation) and 14 nonpregnant women were matched for age, non/prepregnant body mass index (BMI), and parity. MSNA (microneurography), heart rate (ECG), and arterial blood pressure (Finometer) were continuously recorded during 10 min of rest, and then during 2 min of IHG at 30% of maximal voluntary contraction, and 2 min of postexercise circulatory occlusion (PECO). Baseline sympathetic nerve activity (SNA) was elevated in pregnant (41 ± 11 bursts/min) compared with nonpregnant women (27 ± 9 bursts/min; P = 0.005); however, the sympathetic baroreflex gain and neurovascular transduction were not different between groups (P = 0.62 and P = 0.32, respectively). During IHG and PECO, there were no significant differences in the pressor responses (ΔMAP) between groups, (P = 0.25, main effect of group) nor was the sympathetic response different between groups (interaction effect: P = 0.16, 0.25, and 0.27 for burst frequency, burst incidence, and total SNA, respectively). These data suggest that pregnant women who have maintained sympathetic baroreflex and neurovascular transduction also have similar sympathetic and pressor responses during exercise.NEW & NOTEWORTHY We compared sympathetic nervous system activation by muscle metaboreflex between pregnant women in the third trimester and nonpregnant women. We show that the sympathetic nerve activity and associated pressor responses to isometric handgrip and post-exercise circulatory occlusion are not different between third-trimester pregnant and nonpregnant women. These data suggest that unlike other reflexes (e.g., cold pressor test or head-up tilt), metaboreflex control is maintained in pregnant women.

Preeclampsia is not associated with elevated muscle sympathetic reactivity

To determine whether increased chemoreflex tonic activity is associated with augmented muscle sympathetic nervous system activity (MSNA) in women diagnosed with preeclampsia. Women with preeclampsia (n = 19; 32 ± 5 yr old, 31 ± 3 wk of gestation) were matched by age and gestational age with pregnant women (controls, n = 38, 32 ± 4 yr old, 31 ± 4 wk gestation; 2:1 ratio). MSNA (n = 9 preeclampsia) was assessed during baseline, peripheral chemoreflex deactivation (hyperoxia), and a cold pressor test (CPT). Baroreflex gain and diastolic blood pressure at which there is a 50% likelihood of MSNA occurring (T50) and plasma noradrenaline concentrations were measured. Baseline mean arterial pressure (MAP: 106 ± 11 vs. 87 ± 10 mmHg, P < 0.0001), noradrenaline concentrations (498 ± 152 pg/mL vs. 326 ± 147, P = 0.001), and T50 (79 ± 7 vs. 71 ± 9 mmHg, P = 0.02) were greater in women with preeclampsia than in controls. However, baseline MSNA (burst incidence [BI]: 41 ± 16 vs. 45 ± 13 bursts/100 hb, P = 0.4) was not different between groups. Responses to hyperoxia (ΔBI -5 ± 7 vs. -1 ± 8 bursts/100 hb, P = 0.1; ΔMAP -1 ± 3 vs. -2 ± 3 mmHg, P = 0.7) and CPT (ΔBI 15 ± 7 vs. 12 ± 11 bursts/100 hb, P = 0.6; ΔMAP 10 ± 4 vs. 12 ± 11 mmHg, P = 0.6) were not different between groups. Our findings question the assumption that increased MSNA contributes to hypertension in women with preeclampsia. The chemoreflex does not appear to contribute to an increase in MSNA in women with preeclampsia.NEW & NOTEWORTHY We wanted to determine whether increased chemoreflex tonic activity is associated with augmented muscle sympathetic nervous system activity (MSNA) in women diagnosed with preeclampsia. The chemoreflex does not contribute to increased MSNA in women with preeclampsia. Our data also challenge the belief that preeclampsia is associated with sympathetic neural hyperactivity. Thus, targeting sympathetic neural hyperactivity as therapeutic strategy is unlikely to be the most efficacious approach to treatment and management.

Cardiopulmonary exercise testing during pregnancy

The goal of this review is to examine practical considerations when conducting cardiopulmonary exercise testing during pregnancy. In a clinical and research setting, cardiopulmonary exercise testing during pregnancy is valuable in identifying underlying cardiopulmonary conditions, stratifying the risk of adverse pregnancy outcomes, as well as establishing exercise tolerance/limitations. This review encompasses information regarding the unique physiological adaptations that occur throughout gestation (e.g., changes in resting heart rate, blood pressure, glucose, etc.) and how these adaptations impact the interpretation of physiological measurements. There are also key concerns that are unique to pregnant populations that should be considered when participating in exercise (i.e., fetus, ventilation, thermoregulation, urinary incontinence, low back pain, and pelvic girdle pain). This step-by-step review of cardiopulmonary exercise testing outlines pregnancy related adjustments to standardized methods (i.e., screening/documentation, pre- and post-test measurements, protocol specifics, modality selection, and fetal monitoring) which should be considered for the safety of both the participant and fetus. Currently, pregnancy specific exercise testing guidelines are lacking. Therefore, we will be discussing the limitations of current recommendations such as a safe cut off for resting heart rate and pregnancy specific test termination criteria.

Effects of High-Fat Diet and Exercise Intervention on the Metabolism Regulation of Infant Mice

Maternal exercise is crucial for promoting the health of the offspring. Previous studies showed that long-term maternal exercise improves energy metabolism during pregnancy. Whether swimming exercise can reverse the metabolic disorders caused by high-fat exposure in the early life of the offspring is yet to be elucidated. Three-week-old C57BL/6 female mice were randomly assigned to the standard chow diet group (SC), standard chow diet and exercise group (SC-Ex), high-fat diet group (HFD), and high-fat diet and exercise group (HFD-Ex). After swimming intervention for 13 weeks, male and female mice were caged, and the exercise intervention lasted until delivery. Then, the mothers were fed standard chow diet. A total of 8 offsprings/group were randomly selected after 4 weeks of lactation for GTT and ITT. After body composition analysis, the mice were sacrificed to obtain specimens. The levels of metabolism factors and IL-6 were measured by suspension microarray. Subsequently, 15 min after starting the GTT and ITT, the curve detected significant difference between the HFD and other groups. The body fat percentage of the HFD-Ex offspring was significantly lower than that of HFD offspring (p < 0.05) irrespective of the gender. The levels of IL-6 and TG in the male offspring in the HFD-Ex group were improved significantly (p < 0.05). Compared to the HFD offspring, serum glucose and GIP in the female offspring in the HFD-Ex group was significantly reduced (p < 0.05). Long-term exercise of the mother effectively improved the metabolic disorder caused by high-fat exposure in the infant offspring. Thus, the metabolic inheritance of the offspring is gender-dependent; the maternal metabolism can make male offspring genetically susceptible.

Determination of minimal recording period to assess resting heart rate variability during pregnancy

Traditionally, resting heart rate variability (rHRV) is measured for 10 min using the last 5 min for analyses (e.g., criterion period). It is unknown whether the measurement period can be shortened in pregnant women as there are currently no established standards. We aimed to compare shorter time segments (e.g., from the 1st to 10th minutes) of the parasympathetic index natural logarithm transformation of root mean square of successive R–R differences (Ln rMSSD) with the criterion period in pregnant and nonpregnant women. Twelve pregnant (age: 30.8 ± 3.4 years; gestational age: 20.1 ± 5.0 weeks) and 15 nonpregnant women (age: 29.8 ± 4.0 years) were included. rHRV was measured using a portable heart rate monitor for 10 min while sitting. Ln rMSSD difference/agreement between shorter time segments and criterion period was analyzed. The result observed between the 4th–5th minutes was the shortest time segment not different from/highly agreed with the criterion period in pregnant women (difference [95% confidence interval (CI)]: −0.10 [−0.22 to 0.02]/bias ± 1.96 × SD: −0.06 [−0.38 to 0.25]). In nonpregnant women, the 2nd–3rd-minute segment was the shortest with similar results (difference [95% CI]: −0.04 [−0.15 to 0.07]/bias ± 1.96 × SD: −0.03 [−0.39 to 0.32]). The Ln rMSSD was found to be stable from the 5th–10th minutes and the 3rd–10th minutes in pregnant and nonpregnant women, respectively. A shortened rHRV assessment can increase its applicability in clinical/exercise-training settings.

Novelty Ln rMSSD can be measured for 5 min in pregnant women, with the last 1-min segment analyzed. The last 1-min segment from 3 min can be used for rHRV measurement in nonpregnant women. The shortened rHRV assessment can facilitate its applicability in clinical/exercise-training settings.

Heart rate variability is reduced in normal pregnancy irrespective of trimester: A cross-sectional study from Gujarat, India

Background:

Pregnancy is associated with profound cardiovascular adaptation with altered cardiac autonomic balance. It can be studied by heart rate variability (HRV) which indicates beat to beat RR interval variation on ECG.

Objective:

We studied 5 min HRV in normal pregnant females divided by trimesters, compared to matched control.

Methodology:

We recruited 89 normal pregnant females and 30 age matched controls. Five minutes resting HRV was measured by Variowin HR, software-based instrument, by standard protocols to yield time-domain, frequency domain, and Poincare plot parameters. They were further compared between groups for difference.

Results:

Case groups (three based on trimesters) and control group were comparable. There was reduced HRV in case than control group, with statistical significance for all, more for frequency domain than time-domain or Poincare plot parameters. There was no pattern of HRV trend across three trimesters, but mostly second trimester was associated with major decline. Primipara revealed significantly reduced HRV than multipara, but anemia or working status was not significantly associated with HRV in case group.

Conclusion:

There is global HRV reduction in normal pregnancy across all trimesters, associated with primiparity. This indicates pregnancy as a significant risk with reference to altered cardiac balance and use of HRV as a good tool to assess the same.