Effect of exercise stress on carotid, uterine, and iliac blood flow in pregnant and nonpregnant ewes

Exercise as a therapeutic intervention to optimize fetal weight

The Developmental Origins of Health and Disease suggest the in utero environment programs offspring obesity and cardiovascular disease. Therefore, there is a need to implement safe therapeutic interventions that do not involve the intake of medications or biological products during pregnancy that can improve maternal and fetal health. Prenatal exercise is established to promote maternal and fetal health. It is generally recommended that women accumulate at least 150 min per week of moderate-intensity exercise. It has been demonstrated that prenatal exercise maintains healthy weight gain and improves maternal glucose control, maternal cardiac autonomic control, placental efficiency (increases angiogenesis, downregulates genes involved in fatty acid transport and insulin transport across the placenta, and upregulates genes involved in amino acid transport across the placenta), and oxidative stress. These adaptations following exercise improve maternal metabolism and provide adequate uteroplacental perfusion. In this review, we will focus on exercise as a therapeutic intervention to optimize fetal weight. It has been established that prenatal exercise does not increase the risk of having a small for gestational age baby. To the contrary, prenatal exercise has been associated with the prevention of excessive fat accumulation in the newborn and the maintenance of fetal muscle mass.

Cerebral blood flow regulation, exercise and pregnancy: why should we care?

Cerebral blood flow (CBF) regulation is an indicator of cerebrovascular health increasingly recognized as being influenced by physical activity. Although regular exercise is recommended during healthy pregnancy, the effects of exercise on CBF regulation during this critical period of important blood flow increase and redistribution remain incompletely understood. Moreover, only a few studies have evaluated the effects of human pregnancy on CBF regulation. The present work summarizes current knowledge on CBF regulation in humans at rest and during aerobic exercise in relation to healthy pregnancy. Important gaps in the literature are highlighted, emphasizing the need to conduct well-designed studies assessing cerebrovascular function before, during and after this crucial life period to evaluate the potential cerebrovascular risks and benefits of exercise during pregnancy.

Umbilical artery flow velocity waveforms following maternal exercise

The effect of acute exercise on pregnant women in the last trimester of pregnancy and the changes in fetal umbilical artery flow velocity waveforms were studied. One hundred and forty-three healthy pregnant women underwent an acute exercise test. The exercise was performed on an upright bicycle ergometer for 5 minutes, followed by 30 minutes of recovery. The baseline control values of umbilical artery velocity waveforms were compared with those after exercise. The mean exercise intensity achieved was 67.4% (55-90%) of submaximal exercise. Maternal heart rate rose significantly from a mean of 89 (68-120) beats per minute at rest to a mean of 144 (116-200) beats per minute after exercise (P<0.001). Maternal blood pressure rose significantly after exercise from a mean systolic of 112 (80-150) mmHg to a mean of 147 (120-200) mmHg (P<0.001), and from a mean diastolic of 67 (40-85) mmHg to a mean of 84 (70-100) mm Hg (P<0.001). The mean fetal umbilical pulsatility index (PI) was shown to decrease significantly following exercise at 2 and 4 minutes of recovery. It is concluded that (1) an acute exercise test of this intensity causes a significant decrease in PI index after 2 and 4 minutes of recovery; (2) an exercise intensity between 55 and 75% causes a decrease in the PI after exercise while exercise of 76-90% of submaximal exercise causes a rebound increase after an initial decrease at 2 minutes; (3) it may be possible to use this pattern of exercise as an exercise test to differentiate between low- and high-risk pregnancies. Studies on high-risk pregnancies are being prepared for publication.

Effects of Pregnancy on Maternal Work Tolerance

This review summarizes current information on the tolerance of healthy pregnant women and their fetuses to acute strenuous exertion. Maximal aerobic power, expressed in L•min−1, is not significantly affected in women who maintain an active lifestyle, whereas values expressed in mlùkg−1ùmin−1 decline with advancing gestational age in relation to maternal/fetal weight gain. Efficiency during standard exercise testing and the ventilatory anaerobic threshold (Tvent) also appear to be unaffected by pregnancy, but the ability to utilize carbohydrate and exercise anaerobically during brief strenuous exercise may be reduced. Fetal responses to short strenuous exercise are usually moderate and revert to baseline values within approximately 30 min postexercise. Future studies should examine alveolar gas exchange kinetics at the start of exercise and during recovery from both moderate and strenuous exertion. Existing studies of the responses of pregnant women to prolonged exercise have focused primarily on substrate utilization and glucose homeostasis. Other maternal responses to prolonged exercise that should be examined include acid-base regulation, temperature regulation, fluid and electrolyte balance, and perception of effort. Fetal reactions should also be examined in relation to maternal responses. Until evidence-based, occupation-specific guidelines become available, it is recommended that pregnant women use the Joint SOGC/CSEP Clinical Practice Guideline: Exercise in Pregnancy and the Postpartum Period, published by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology (2003). Key words: human gestation, maximal exercise, prolonged exercise, fetal well-being

Effects on fetal and maternal body temperatures of exposure of pregnant ewes to heat, cold, and exercise

We exposed Dorper-cross ewes at approximately 120-135 days of gestation to a hot (40 degrees C, 60% relative humidity) and a cold (4 degrees C, 90% relative humidity) environment and to treadmill exercise (2.1 km/h, 5 degrees gradient) and measured fetal lamb and ewe body temperatures using previously implanted abdominal radiotelemeters. When ewes were exposed to 2 h of heat or 30 min of exercise, body temperature rose less in the fetus than in the mother, such that the difference between fetal and maternal body temperature, on average 0.6 degrees C before the thermal stress, fell significantly by 0.54 +/- 0.06 degrees C (SE, n = 8) during heat exposure and by 0.21 +/- 0.08 degrees C (n = 7) during exercise. During 6 h of maternal exposure to cold, temperature fell significantly less in the fetus than in the ewe, and the difference between fetal and maternal body temperature rose to 1.16 +/- 0.26 degrees C (n = 9). Thermoregulatory strategies used by the pregnant ewe for thermoregulation during heat or cold exposure appear to protect the fetus from changes in its thermal environment.

Exercise and pregnancy: a review

The effects of pregnancy on the maternal cardiorespiratory system include increases in oxygen consumption, cardiac output, heart rate, stroke volume, and plasma volume. The increase in oxygen reserve seen in early pregnancy is reduced later, suggesting that maternal exercise may present a greater physiologic stress in the third trimester. Evidence suggests that weight-bearing exercise produces a greater decrease in oxygen reserve than nonweight-bearing exercise. Furthermore, to maintain a heart rate below 140 beats per minute during pregnancy, the intensity of weight-bearing exercise must be reduced. Nonweight-bearing, water-based exercise results in smaller fetal heart rate changes and a lower maternal heart rate than the same exercise performed on land. Exercising in the supine position in late pregnancy has raised concerns because cardiac output in the supine position is lower than in the lateral position at rest, presumably because the gravid uterus partially obstructs the inferior vena cava. Sustained exercise produces a training effect on the mother, although reported associations between this effect and the experience of labor are not consistent. Short-term changes in fetal heart rate provide circumstantial evidence that physical activity can influence the fetus. Acute effects of exercise that can potentially affect the fetus include hyperthermia, changes in uteroplacental flow, reduced levels of maternal glucose, and increased uterine contractions. Moderate to high levels of sustained maternal exercise have been associated with reduced birthweight. Much research remains to be done on the effects of specific exercise regimens during pregnancy, the effects on previously sedentary women, and the long-term health consequences to the offspring of women who perform vigorous exercise during pregnancy.

The effect of maternal exercise on fetal umbilical artery waveforms

Twenty-one nulliparous women in the last trimester of pregnancy gave their informed verbal consent to undergo an acute exercise test. Fetal umbilical artery velocimetry waveforms were measured to monitor the effect of exercise on fetal umbilical artery blood flow. The mean gestational age was 32 weeks (range 28-37 weeks). The mean exercise intensity was 71% of submaximal exercise (range 67-74%). Maternal heart rate rose significantly (P less than 0.001) from a mean of 83 to 138 beats per min. Following moderate exercise, the systolic over the diastolic ratio (S/D) decreased significantly (P less than 0.001) after 2 and 20 min. This indicates a decrease in umbilical blood flow resistance and an improved placental circulation following exercise in healthy women. We conclude that maternal exercise does not appear to be harmful to the mother or her fetus at this level of exercise intensity in healthy individuals.

[Physical activity in pregnancy]

The author reviews works dealing with the effects of physical activity during pregnancy on the maternal and fetal organism. Considering the great controversy existent in the literature comments on the tendency to recommend more vigorous activity to pregnant woman is examined.

Doppler sonographic evaluation of exercise-induced blood flow velocity and waveform changes in fetal, uteroplacental and large maternal vessels in pregnant women

The aim of this study was the evaluation by Doppler sonography of blood flow velocity and waveforms in maternal (Femoral artery and vein, carotid artery, uteroplacental) and fetal (Umbilical artery) vessels before and after exercise. Thirteen healthy women with uncomplicated pregnancies (and outcomes) participated in the study between the 36th and 40th gestational week. Each proband underwent 5 exercise tests in a sitting position on a bicycle ergometer with a work load of 100 Watts during 3 minutes. The Doppler measurements were performed with Acuson 128. In the femoral and carotid arteries, peak velocities (systolic and end-diastolic, and for the femoral artery also post-systolic) as well as the mean blood flow velocities were measured. Mean blood flow velocity was also measured in the femoral vein. For the measurements of the arterial diameters, the M-Mode technique, for the femoral vein diameter, the B-Mode technique was used. The uteroplacental and umbilical blood flow waveforms were analysed by the Resistance and Pulsatility Indices. The maternal heart rate as well as systolic and diastolic blood pressures increased after each of the exercise tests. The mean blood flow velocity increased in both the femoral artery and vein while the vessel diameter remained constant. In the carotid artery, however, the velocity remained constant. An analysis of the velocity waveforms for the femoral artery showed in increase in the systolic and end-diastolic velocities as well as a reversal of the post-systolic flow, where the velocity is negative in a state of rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of aerobic and strength conditioning on pregnancy outcomes

This study evaluated the effects of a physical conditioning program on pregnancy outcomes and the subjective pregnancy experience. Pregnancy outcomes included length of labor, mode of delivery, length of hospitalization, and gestational age, birth weight, and Apgar scores of newborn infants. Subjective data included level of tension, general physical comfort, and self-image. The 845 subjects in the study were divided into a control group (n = 393) and into groups of low, medium, and high levels of exercise (n = 82, 309, and 61, respectively). Exercise sessions consisted of treadmill or bicycle warm-up, individually prescribed exercises on weight-lifting equipment for arms, legs, abdomen, and back, and 1- to 2-mile workout on bicycle ergometer. Pregnancy outcomes were more favorable in the exercise groups, particularly the high-exercise group. Significant data included length of hospitalization, incidence of cesarean section, and Apgar scores. All patients reported positive subjective responses to the conditioning program.

Reproductive hazards in the workplace: a case study of women firefighters

Recent attention has focused on the difficulties of providing equal employment opportunities for women while ensuring reproductive health in the workplace. This paper examines the potential hazards faced by pregnant firefighters and recommends a policy that seeks a reasonable accommodation between employment and fetal and maternal health. The potential hazards faced by firefighters include physical exertion, hyperthermia, and exposure to carbon monoxide and other toxic gases. The ideal policy option for improving reproductive health is to make the workplace safe for all employees. Where this cannot be accomplished and a unique reproductive hazard exists to women during pregnancy, temporary positions should be found that remove the pregnant woman from the hazard while allowing her to continue work.

The interactions of exercise and pregnancy: a review

Increasing numbers of women engage in relatively strenuous exercise during pregnancy. The interaction of the increased metabolic demands of physical activity with those of pregnancy is poorly understood. We review what is known and what is not known of the extent to which pregnancy affects a woman's ability to perform strenuous activity and the degree to which exercise affects the pregnant woman, the fetus, and the infant.

Catecholamine physiology in the ovine fetus. III. Maternal and fetal response to acute maternal exercise

A study was made of the effects of maternal exercise on fetal plasma concentrations of catecholamines in nine ewes with chronically catheterized singleton fetuses at 125 to 137 days' gestation. The ewes were subjected to acute treadmill exercise of 2.5 mph for 45 minutes with continuous recording of maternal and fetal blood pressures. Samples of arterial blood were obtained for measurement of catecholamines, glucose, and blood gases. Changes in blood flow in fetal organs in response to maternal exercise were assessed by injection of radioactive microspheres. The maternal plasma catecholamine responses were related to the severity of the exercise stress as indicated by the index of cardiac effort. The fetal responses did not correlate with maternal cardiac effort. A significant decrease in fetal Po2 with a moderate alkalosis occurred, accompanied by a significant elevation in circulating levels of norepinephrine. At the peak of exercise, there was an increase in fetal renal, adrenal, and placental blood flows, as compared to the control period.

Current controversies: exercising during pregnancy

The current emphasis on physical fitness has motivated many women to participate in a variety of exercise programs. Increased participation by pregnant women is also occurring in the form of self-directed activities and/or as recommended by physicians in an effort to shorten labor and improve pregnancy outcome. Whether exercise improves or presents a potential hazard to the mother and fetus is a concern. The implications for the "trained" woman as well as the "untrained" exerciser are unclear and need definitive study.

Serum testosterone concentration during two hours of moderate intensity treadmill running in trained men and women

The purpose of this study was to determine alterations in testosterone concentration in women during 2 hours of moderate intensity running, and to compare this response to that seen in men. Maximal oxygen uptake (VO2 max) and anaerobic threshold (AT) were determined in 11 men and 9 women. These subjects subsequently ran for 2 hours on a motor-driven treadmill at 10% below the AT which was approximately 70% VO2 max. Blood samples were drawn at 0, 30, 60, 90 and 120 minutes of exercise and testosterone was measured by specific radioimmunoassay. Serum testosterone concentration was significantly increased (41%, P less than .01) after 30 minutes of exercise in the men. In the women, testosterone was not significantly increased from pre-exercise concentrations until 120 minutes of exercise (48%, P less than .01). At this time the testosterone concentration in the men had decreased and was no longer significantly elevated from the pre-exercise concentration. The magnitude of the increases in serum testosterone concentration can probably be accounted for by decreases in the metabolic clearance rate of sex-steroids known to occur during exercise. Differences in the testosterone response between men and women during prolonged aerobic exercise are of interest and may imply that different mechanisms of control are involved.

Fetal heart rate reactivity before and after maternal jogging during the third trimester

A paucity of data exists concerning the fetal effects of exercise during pregnancy. Seven women who jogged at least 1.5 miles three times per week prior to and during pregnancy were studied during the third trimester of pregnancy (28 to 38 weeks' gestation). Fetal status was evaluated by the nonstress test (NST) before and immediately after maternal jogging of at least 1.5 miles. The seven pregnant women had a total of 30 NSTs--15 prior to and 15 immediately after jogging. All 30 tests were reactive, and there was no significant difference in the monitoring time required to obtain a reactive NST before and after jogging. The prejogging fetal heart rate (FHR) ranged from 140 to 150 bpm, and the postjogging FHR ranged from 180 to 204 in nine of the 15 NSTs. It took a mean of 22 minutes (range, 12 to 30 minutes) for the FHR to return to the prejogging baseline.

Respiratory and hemodynamic effects of methadone in pregnant women

Minute ventilation, end-tidal PCO2, O2 and CO2 concentrations in expired air, pulse rate and arterial blood pressure were measured in the last half of pregnancy in eight women taking methadone daily. Measurements were made with the subjects seated at rest, during the steady state of 50-watt bicycle exercise, and during recovery. Calculations of O2 consumption. CO2 production, alveolar ventilation and oxygen debt were made. Studies were repeated in five subjects postpartum. Methadone diminishes the normal hyperventilation of pregnancy and its effect persists for more than 24 h. When comparisons are made of pregnant and postpartum values, some respiratory stimulation during pregnancy is apparent. Maternal oxygen debt following standard exercise during pregnancy is diminished after the daily dose of methadone and the maternal heart rate response to exercise is diminished concurrently. The maternal hypoventilation induced by methadone and maintained during exercise may be relevant to the low birth weights and high incidence of sudden infant death syndrome observed by others in the offspring of methadone-dependent women.

Maternal physical activity, birth weight and perinatal mortality

As a result of the acquisition of upright posture, adaptation to muscular exercise seems to be unique in man. It involves a redistribution of the cardiac output mediated by the sympathetic system towards priority organs which apparently do not include the pregnant uterus. This could explain the poor tolerance of the human fetus to maternal exercise. The hypothesis is supported by the independence of a detrimental effect of work from the effect of maternal nutrition and by an influence of maternal posture in late pregnancy on its outcome. Possible relations between maternal activity before and during late pregnancy and perinatal mortality are discussed in the context of this hypothesis.

Acute exercise stress in the pregnant ewe

In the near-term pregnant ewe, acute treadmill exercise produced significant changes in maternal and fetal parameters only with the onset of maternal exhaustion which was unrelated to the degree or duration of maternal exercise. With exercise to exhaustion the rate of both uterine and umbilical blood flow fell but uterine and umbilical oxygen uptakes were unchanged. Although maternal lacticemia developed and fetal PO2 fell no excess lactate was produced by the uteroplacental tissues or fetus. The increase in maternal heart rate during exercise was directly related to the decrease in uterine blood flow.

A randomized controlled trial of bed rest and sedation or normal activity and non-sedation in the management of non-albuminuric hypertension in late pregnancy

One hundred and thirty-five patients took part in a randomized controlled trial designed to determine whether bed rest and sedation are of any general benefit to either the mother or the baby in pregnancies complicated by mild non-albuminuric and non-symptomatic hypertension after the 28th week. The results suggest that they are not.