April 18, 2019
Craig Steinback.1, Graeme Purdy 1, Brittany Matenchuk 2, Margie Davenport1
1Neuromuscular Health Lab, Program for Pregnancy and Post Partum Health, Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton AB
2 Department of Pediatrics, University of Alberta, Edmonton AB
The nine short months of pregnancy are associated with profound physiological adaptations to the cardiovascular and nervous systems. This includes a 50% increase in blood volume, 30% increase in cardiac output and 20% increase in heart rate at rest. The autonomic nervous system is responsible for alterations in heart rate, and simple, non-invasive techniques to measure the health of the autonomic nervous system have been developed. Baroreflex gain is the strength of the relationship between fluctuations in blood pressure and the time interval between heart beats. This reflex acts to ensure blood pressure is maintained during normal activities. Heart rate variability is another measure of the natural variation in the time interval between heart beats and indicates how active the autonomic nervous system is in monitoring and adjusting heart-rate. Both measures are associated with health outcomes and the functioning of the cardiovascular system. We know pregnancy influences autonomic control of the heart and exercise in non-pregnant populations is a significant stressor influencing baroreflex gain and heart rate variability.
The recent Society for Obstetricians and Gynecologists of Canada/Canadian Society for Exercise Physiology 2019 Canadian Guideline for Physical Activity throughout Pregnancy encourages all pregnant women without contraindication engage in at least 150 minutes of moderate intensity physical activity spread over at least three days of the week.
These evidence-based guidelines demonstrate prenatal exercise has a 40% reduction in the risk of developing gestational diabetes, gestational hypertension and preeclampsia without increasing the risk of having a miscarriage, small baby, or preterm baby. Although prenatal exercise is established to be both safe and beneficial for both mother and baby, it has been suggested that pregnant women may have an increased risk of having low blood pressure and feeling faint at the end of exercise. Although, the physiology behind this phenomenon has not been established. We hypothesized this may be due to differences in autonomic control of the heart and how it responds to changes in blood pressure. Therefore, our study examined the impact of a single bout of exercise to volitional exhaustion in the first, second and third trimesters of pregnancy on autonomic function, compared to non-pregnant women.
We demonstrated that pregnant women had significantly reduced responsiveness to fluctuations in blood pressure (blunted baroreflex gain) and a lower heart rate variability at rest, this is in part due to their higher resting heart rate. However, pregnant women had comparable cardio-autonomic control during and following exercise compared to non-pregnant women. This suggests that although autonomic control of the heart is altered at rest during pregnancy, pregnant women are still able to respond to, and recover from, exercise in a manner similar to non-pregnant women. This has important implications for the promotion and implementation of exercise in pregnant populations – they are at no apparent greater risk of post-exercise hypotension than their non-pregnant peers.
Graeme M. Purdy, Marina A. James, Paige K. Wakefield, Rachel J. Skow, Sean Van Diepen, Linda E. May, Margie H. Davenport and Craig D. Steinback Maternal cardioautonomic responses during and following exercise throughout pregnancy Appl Physiol Nutr Metab. Published on the web 14 August 2018, doi/10.1139/apnm-2018-0397#.XLiDqpNKhm9
This article is a summary of an article published in Applied Physiology, Nutrition and Metabolism. If you intend to cite any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.