Biomedical subjects

Tracey L Weissgerber

Publications and source records attributed to Tracey L Weissgerber.

6 recordsLinked to original sources

PubMed2006

Physiological adaptation in early human pregnancy: adaptation to balance maternal-fetal demands.

After conception, the corpus luteum, placenta, and developing embryo release hormones, growth factors, and other substances into the maternal circulation. These substances trigger a cascade of events that transform the functioning of the maternal cardiovascular, respiratory, and renal systems, which in turn alter the physicochemical determinants of [H(+)]. Following implantation, maternal adaptations fulfill 4 important functions that support fetal growth. Increased availability of substrates and precursors for fetal-placental metabolism and hormone production is mediated by increases in dietary intake, as well as endocrine changes that increase the availability of glucose and low-density lipoprotein (LDL) cholesterol. Transport capacity is enhanced by increases in cardiac output, facilitating the transport of substrates and precursors to the placenta, and fetal waste products to maternal organs for disposal. Maternal-fetal exchange is regulated by the placenta after 10-12 weeks gestation, but it may occur through histiotrophic mechanisms before this time. Disposal of additional waste products (heat, carbon dioxide, and metabolic byproducts) occurs through peripheral vasodilation and increases in skin blood flow, ventilation, and renal filtration. The maternal physiological adaptations described above must meet the combined demands of maternal exercise and fetal growth. More research is needed to formulate evidence-based guidelines for healthy physical activity in early pregnancy.

Adaptation, Physiological↗

PubMed2006

Cold pressor test protocol to evaluate cardiac autonomic function.

The primary objective of this study was to develop a cold pressor test (CPT) protocol to evaluate cardiac autonomic function. Secondary objectives were to assess CPT protocol reliability and to examine gender differences in response to orthostatic stress and the CPT. Healthy, normotensive men and women (n = 12 per group) completed 2 trials on different days in the left lateral decubitus and standing postures and during a 6 min CPT (hand immersion while seated). Measurements included R-R interval, blood pressure, ventilatory responses, spontaneous baroreflex sensitivity, and heart rate variability indices. During the CPT, blood pressure and the sympathetic nervous system (SNS) indicator increased significantly and low-frequency power, high-frequency power (normalized for tidal volume), and the parasympathetic nervous system (PNS) indicator decreased significantly. Standing caused significant increases in the SNS indicator and decreases in the R-R interval in both genders. The PNS indicator was higher in women than in men in the left lateral decubitus posture. The 6 min hand-immersion CPT provoked cardiac sympathetic activation and parasympathetic withdrawal; however, it is best suited to studies with a repeated measures design, as analysis of reliability suggests that responses are highly variable between individuals. Performing the CPT in the left lateral decubitus position may prevent vasovagal responses.

Adult↗

PubMed2006

Exercise in the prevention and treatment of maternal-fetal disease: a review of the literature.

Evidence-based guidelines indicate that regular prenatal exercise is an important component of a healthy pregnancy. In addition to maintaining physical fitness, exercise may be beneficial in preventing or treating maternal-fetal diseases. Women who are the most physically active have the lowest prevalence of gestational diabetes (GDM), and prevention of GDM may decrease the incidence of obesity and type 2 diabetes in both mother and offspring. However, few studies have investigated the effectiveness of exercise in delaying or preventing GDM in at-risk women, and exercise prescriptions that optimize outcomes for women with GDM are lacking. Physically active women are also less likely to develop pre-eclampsia, and we have proposed the following 4 mechanisms that may explain this protective effect: enhanced placental growth and vascularity, reduced oxidative stress, reduced inflammation, and correction of disease-related endothelial dysfunction. Exercise may also prevent reproductive complications associated with maternal obesity. Obesity increases the risk of infertility and miscarriage, and weight loss programs that incorporate diet and exercise are a cost-effective fertility treatment that may also reduce the probability of obesity-related complications during pregnancy. Regular exercise following conception may prevent excessive gestational weight gain and reduce post-partum weight retention.

Algorithms↗

PubMed2005

Serial respiratory adaptations and an alternate hypothesis of respiratory control in human pregnancy.

This study determined the time course of changes in resting and exercising respiratory responses during the first half of human pregnancy, and examined the potential roles of plasma osmolality and the strong ion difference ([SID]) as mediators of pregnancy-induced increases in ventilation. Healthy active women (n = 11) were studied serially from 7 to 22 weeks gestation. Responses were compared with preconception data from 14 subjects (six of whom were tested in early pregnancy), and with late-gestation resting data from 10 additional women. Resting and exercising measurements included ventilation, PaCO2, progesterone, osmolality and [SID]. Results were analyzed using mixed-model linear regression. By 7 weeks gestation, increased ventilation resulted in a very large decrease in PaCO2 at rest and during moderate-intensity exercise. Large correlations (r > 0.5) between resting progesterone and PaCO2 support the traditional theory that circulating progesterone stimulates ventilation during pregnancy. The similar time course of changes and large correlations between raw and delta values of PaCO2 and each of plasma osmolality and [SID] also suggest that both variables may influence respiratory control at rest and during exercise in the first half of pregnancy. Future experiments should continue to explore the hypothesis that osmolality and [SID] contribute to pregnancy-induced respiratory changes.

Acclimatization↗

PubMed2004

The role of regular physical activity in preeclampsia prevention.

Preeclampsia affects 2-7% of pregnancies and is a leading cause of maternal and fetal morbidity and mortality. Despite extensive study, the etiology of preeclampsia is poorly understood. Abnormal placental development, predisposing maternal constitutional factors, oxidative stress, immune maladaptation, and genetic susceptibility have all been hypothesized to contribute to the development of preeclampsia. Physical conditioning and preeclampsia have opposite effects on critical physiological functions. This suggests that regular prenatal exercise may prevent or oppose the progression of the disease. Epidemiologic studies show that occupational and leisure-time physical activity is associated with a reduced incidence of preeclampsia. We hypothesize that this protective effect results from one of more of the following mechanisms: 1) stimulation of placental growth and vascularity, 2) reduction of oxidative stress, and 3) exercise-induced reversal of maternal endothelial dysfunction. Future research should include prospective epidemiological case-control studies that accurately measure occupational and leisure-time physical activity. Controlled randomized clinical trials examining the effects of prenatal exercise on biochemical markers for endothelial dysfunction, placental dysfunction, and oxidative stress are also needed. If future research supports the idea that exercise effectively protects against preeclampsia, this would provide a low-cost intervention that could dramatically improve prenatal care for women at risk of this disease.

Epidemiologic Studies↗

PubMed2003

Clinical physiology of exercise in pregnancy: a literature review.

OBJECTIVES: To review the existing literature on the physiology of exercise in pregnancy as a basis for clinical practice guidelines for prenatal exercise prescription. METHODS: MEDLINE search for English language abstracts and articles published between 1966 and 2003 related to physiological adaptations to pregnancy, effects of pregnancy on responses to acute exercise and aerobic conditioning, effects of acute maternal exercise on indexes of fetal well-being, impact of physical conditioning on birth weight and other pregnancy outcomes, and use of exercise to prevent or treat gestational diabetes mellitus and preeclampsia. RESULTS: Maximal aerobic power (VO(2)max, L/min) is well-preserved in pregnant women who remain physically active, but anaerobic working capacity may be reduced in late gestation. The increase in resting heart rate, reduction in maximal heart rate, and resulting smaller heart rate reserve render heart rate a less precise way of estimating exercise intensity. As rating of perceived exertion (RPE) is not altered by pregnancy, the use of revised pulse rate target zones along with Borg's RPE scale is recommended to prescribe exercise intensity during pregnancy. Responses to prolonged submaximal exercise (>30 min) in late gestation include a moderate reduction in maternal blood glucose concentration, which may transiently reduce fetal glucose availability. The normal response to sustained submaximal exercise is an increase in fetal heart rate (FHR) baseline. Transient reductions in FHR reactivity, fetal breathing movements, and FHR variability may also occur in association with more strenuous exercise. Controlled prospective studies have demonstrated that moderate prenatal exercise during the second and third trimesters is useful to improve aerobic fitness and maternal-fetal physiological reserve without affecting fetal growth. CONCLUSIONS: The Physical Activity Readiness Medical Examination for Pregnancy is recommended for use by physicians and midwives to provide medical clearance for prenatal exercise. Evidence-based prenatal exercise guidelines are needed to counsel healthy and fit pregnant women on the safety of involvement in more strenuous physical conditioning. Future study is also recommended to determine the usefulness of prenatal exercise in the prevention and treatment of gestational diabetes mellitus and preeclampsia.

Adult↗