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Biomedical subjects

J F Clapp

Publications and source records attributed to J F Clapp.

At least 19 recordsLinked to original sources
PubMed1992

Effect of recreational exercise on midtrimester placental growth.

OBJECTIVE: The purpose of our study was to test the hypothesis that regular recreational exercise increases the rate of growth in placental volume in the midtrimester of human pregnancy. STUDY DESIGN: Serial measurements of placental volume were obtained between the fourteenth and twenty-sixth gestational week in 18 subjects who exercised regularly throughout the midtrimester and in 16 matched controls with an ultrasonographic system equipped with a fixed-base, articulated-arm, 3.5 MHz B-mode transducer. RESULTS: Placental volumes were significantly greater in the women who maintained a regular exercise regimen throughout the midtrimester. At 16 weeks (mean +/- SD) volumes were 141 +/- 34 cm3 and 106 +/- 18 cm3 in the two groups. This difference increased at 20 weeks (265 +/- 67 cm3 vs 186 +/- 46 cm3) and again at 24 (410 +/- 87 cm3 vs 270 +/- 58 cm3) weeks' gestation because of a significant between-group difference in the rate of growth in placental volume over this time interval (34 +/- 8 cm3/wk vs 21 +/- cm3/wk). CONCLUSION: We conclude that the hypothesis is correct and speculate that the change in growth rate represents an adaptive response to the intermittent stimulus of a reduction in regional blood flow.

Adult↗
PubMed1991

The changing glycemic response to exercise during pregnancy.

This study was designed to test the hypothesis that pregnancy reverses the nonpregnant hyperglycemic response to sustained exercise. Serial data were obtained from 75 exercising women. Before pregnancy, exercise produced an intensity-dependent increase in blood glucose that averaged 1.5 mmol/L at high intensities. By the eighth week this response was blunted and blood glucose increased only when exercise intensity exceeded 80% of maximum. At 15 weeks this progressed and was not associated with a change in either the insulin or catecholamine response. By the twenty-third week exercise produced a decrease in blood glucose that was no longer related to exercise intensity. We conclude that the hypothesis is correct and speculate that the early change in the response is related to decreased hepatic glucose release coupled with increased glucose oxidation. In late pregnancy this is probably accentuated by fetoplacental demands.

Adult↗
PubMed1991

The changing thermal response to endurance exercise during pregnancy.

This study was designed to test the hypothesis that the thermal response to endurance exercise is altered by the thermal adaptations to pregnancy. Accordingly, rectal temperature was monitored in 18 recreational athletes before, during, and after 20 minutes of continuous exercise before conception and every 6 to 8 weeks during pregnancy. Mean exercise intensity was 64% of VO2 max before conception and did not change during pregnancy. However, the peak rectal temperature reached during exercise decreased by 0.3 degrees C at 8 weeks and then fell at a rate of 0.1 degrees C per lunar month through the thirty-seventh week. This appeared to be related to changes in resting temperature, thermal mass, sweating threshold, and venous capacitance that began early in pregnancy. These data suggest that the magnitude of any exercise-associated thermal stress for the embryo and fetus is markedly reduced by the maternal physiologic adaptations to pregnancy.

Adult↗
PubMed1991

When do cardiovascular parameters return to their preconception values?

To determine if the postpartum period is reflective of a woman's cardiovascular status before pregnancy, we performed serial studies of 13 women before conception and at 6 and 12 weeks post partum. All pregnancies were singleton without hypertensive complications. Cardiac output, stroke volume, and end-diastolic volume were calculated with M-mode echocardiography from the left ventricular dimensions with subjects in the left lateral position. Systemic vascular resistance was calculated from cardiac output and simultaneous measurements of blood pressure. Stroke volume and end-diastolic volume remained consistently elevated over preconception values at 6 and 12 weeks. Systemic vascular resistance remained decreased, compared with baseline, at 12 weeks. Thus cardiovascular parameters had not returned to the preconception baseline, and previous studies that have used this time period for comparison have underestimated the contribution of stroke volume to the total change in cardiac output during pregnancy.

Adult↗
PubMed1991

The VO2max of recreational athletes before and after pregnancy.

This study was designed to test the hypothesis that pregnancy has an added training effect (increases "absolute" VO2max) in well-conditioned, recreational athletes. VO2max was measured serially in 20 nonpregnant recreational athletes who maintained their exercise within +/- 10% of initial levels over a 15-month period and 20 similar women who conceived and continued exercise at a reduced level during pregnancy with a return to within 20% of initial levels by 12 wk postpartum. Initially the two groups were similar in terms of age (30 +/- 1 vs 30 +/- 2 yr), weight 57.6 +/- 7.2 vs 59.7 +/- 7.5 kg), max pulse rate (189 +/- 8 vs 187 +/- 10 bpm), and absolute (3083 +/- 469 vs 3138 +/- 464 ml.min-1) VO2max. In the nonpregnant group the values obtained 15 months later were unchanged (weight = 57.8 +/- 6.6 kg, max pulse = 191 +/- 7 bpm, VO2max = 2977 +/- 397 ml.min-1) while those who conceived had a significant increase in absolute VO2max that was evident 12-20 wk postpartum and was maintained at the time of final testing 36-44 wk postpartum (3368 +/- 435 ml.min-1). Both weight (60.1 +/- 8.1 kg) and maximum pulse rate (185 +/- 12 bpm) were unchanged. These data indicate that pregnancy is followed by a small but significant increase in VO2max in recreational athletes who maintain a moderate to high level of exercise performance during and after pregnancy.

Adult↗
PubMed1991

Exercise and fetal health.

This is a brief review of current information dealing with the impact of maternal exercise on the well-being of the human embryo and fetus. It discusses the theoretical concerns and exercise variables involved in the interaction between exercise and fetal health and focuses on five areas of fetal health where some information is available describing the interaction in the human. These include embryonic development, fetoplacental growth, prematurity, indices of fetal stress/distress, and condition during labor and at birth. It concludes that well-conditioned women who continue a regular running or aerobics regimen in the peri-conceptual period and throughout pregnancy at levels that exceed current guidelines do not experience an increase in the incidence of failure to conceive, abortion, congenital abnormalities, abnormal placentation, premature rupture of the membranes or preterm labor. Although all their fetuses demonstrate a brisk elevation in heart rate post-exercise throughout pregnancy, they have a significant reduction in the incidence of 4 clinical markers of fetal stress/distress during labor. In addition, at the time of delivery, their % body fat is less than that of the control offspring (11 vs 16%) which accounts for over 70% of the observed 300 g reduction in birthweight. Finally, there is little evidence to suggest that the other exercise regimens studied to date have an adverse effect on fetal health.

Embryo Implantation↗
PubMed1990

The course of labor after endurance exercise during pregnancy.

This study was designed to test the hypothesis that continuation of a regular running or aerobics program, or both, during the latter half of pregnancy would have a negative effect on the course and outcome of labor. The onset, course, and outcome of labor were independently monitored in 131 well-conditioned recreational athletes who had an uneventful first half of pregnancy. Daily exercise performance was quantitated before conception and throughout pregnancy. Comparisons were made between the 87 women who continued to exercise regularly at or above 50% of their preconceptional level throughout pregnancy and the 44 who discontinued their regular exercise regimen before the end of the first trimester. The incidence of preterm labor was similar in the two groups (9%). Labor began significantly earlier in the exercise group (277 +/- 6 vs 282 +/- 6 days). The women who continued to exercise had a lower incidence of abdominal (6% vs 30%) and vaginal (6% vs 20%) operative delivery, and active labor was shorter (264 +/- 149 vs 382 +/- 275 min) in those who were delivered vaginally. Finally, clinical evidence of acute fetal stress (meconium, fetal heart pattern, and Apgar score) was less frequent in the exercise group (50% vs 26%), although birth weight was reduced (3369 +/- 318 vs 3776 +/- 401 gm). These data negate the initial hypothesis and indicate that, in well-conditioned women who regularly perform aerobics or run, continuation of these exercise regimens has a beneficial effect on the course and outcome of labor.

Adult↗
PubMed1990

Neonatal morphometrics after endurance exercise during pregnancy.

This study was designed to test the hypothesis that continuation of a regular running and/or aerobics program during late pregnancy at or above 50% of preconceptional levels limits fetal growth. Accordingly, detailed neonatal morphometric data were gathered in the offspring of two groups: 77 well-conditioned recreational runners and aerobic dancers who were delivered at term after continuing their exercise regimen at or above 50% of the preconceptional level throughout pregnancy and 55 matched controls. Daily exercise performance was quantitated before conception and throughout pregnancy. Significant reductions in birth weight (-310 gm), birth weight percentile (-20), ponderal index (-0.24), its percentile (-30), and the fetoplacental weight ratio (-0.7) were seen in the offspring of the exercise group whereas crown-heel length (51.4 cm) and head circumference (35.0) were similar in the two groups. Reductions in two-site skin-fold thickness (-1.5 mm), skin-fold percentile (-30), calculated percent body fat (-5.0%), and fat mass (-220 gm) in the offspring of the exercise group confirmed the asymmetric pattern of growth restriction and indicated that approximately 70% of the difference in birth weight could be explained by the difference in neonatal fat mass. In runners, the relative level of exercise performance in the last 5 months of pregnancy explained 40% of the variability in birth weight over an 1100 gm birth weight range. We conclude that continuation of a regular aerobic or running program at or above a minimal training level during late pregnancy results in an asymmetric pattern of growth restriction that primarily impacts on neonatal fat mass.

Adult↗
PubMed1989

Cardiovascular changes in early phase of pregnancy.

To assess the magnitude and timing of cardiovascular changes in pregnancy, eight subjects were serially studied before conception and at 8, 16, and 24 weeks' gestation. With the use of M-mode echocardiography, cardiac output, ejection fraction, stroke volume, and end-diastolic volume were calculated from left ventricular dimensions with subjects in the left lateral position. Systemic vascular resistance was calculated with the use of cardiac output and simultaneously obtained measurements of arterial pressure. Cardiac output increased 1 L/min at 8 weeks' gestation, which represented greater than 50% of the total change seen. Cardiac output increased primarily because of stroke volume rather than heart rate. By 8 weeks' gestation, systemic vascular resistance had fallen to 70% of its preconceptional value. Thus when subjects are studied before conception and during the early phase of pregnancy, the majority of the pregnancy-induced changes in these parameters occur during the embryonic period.

Adult↗
PubMed1989

The effects of maternal exercise on early pregnancy outcome.

This study was designed to test the hypothesis that vigorous aerobic exercise during both the periconceptional period and early pregnancy increases the incidence of abnormal early pregnancy outcome. Exercise performance was prospectively monitored before and during pregnancy in 47 recreational runners, 40 aerobic dancers, and 28 physically active, fit controls. Pregnancy was diagnosed by an early test for beta-subunit human chorionic gonadotropin and viability was confirmed by ultrasonography at 40 days' conceptional age. Spontaneous abortion occurred in 19% of the pregnancies. The incidence was 17% in the runners, 18% in the aerobic dancers, and 25% in the controls. At term, one congenital abnormality was detected in each of the three groups. Late pregnancy events, potentially related to abnormalities of placentation, were limited to two cases of mild pregnancy-induced hypertension. We conclude that, in physically fit women, continuation of these types of aerobic activity at intensities between 50% and 85% of maximum during the periconceptional period and early pregnancy does not appreciably alter early pregnancy outcome.

Abortion, Incomplete↗
PubMed1989

Oxygen consumption during treadmill exercise before, during, and after pregnancy.

This study was designed to test the hypothesis that the amount of oxygen required to complete a specific treadmill exercise protocol changes during pregnancy as a function of gestational age, weight gain, and an individual's exercise regimen. The amount of oxygen required to complete a three-step, graded workload treadmill protocol was monitored before, every 6 to 8 weeks during, and after a clinically normal, accurately dated, singleton pregnancy in 18 fit, recreational athletes. Nine subjects continued a moderate- to high-intensity exercise regimen and nine did not. The amount of oxygen required to complete each stage of the protocol decreased significantly (6% to 15%) in both groups in early pregnancy. In the women who continued exercise, the amount of oxygen required remained at or significantly below that required before conception for the remainder of the pregnancy and the initial postpartum period. Conversely, in the women who discontinued regular exercise, the amount of oxygen required for each stage rose progressively throughout the remainder of pregnancy at an average rate of 2% per lunar month. It peaked in the thirty-seventh week and remained significantly elevated 7 weeks post partum. However, when the data were corrected for the additional requirement imposed by pregnancy weight gain, net efficiency was increased in both groups throughout pregnancy. These data support three conclusions. First, the efficacy of low- to moderate-intensity treadmill exercise in physically active women is improved in early pregnancy. Second, this increased efficiency is masked later in pregnancy by the effects of weight gain. Third, the degree of efficiency is enhanced throughout pregnancy in women who continue a regular exercise regimen at or above a basic conditioning level.

Adult↗
PubMed1988

Ovine placental perfusion balance: effect of marijuana smoke.

This study was designed to test the hypothesis that maternal marijuana smoking impairs placental oxygen transfer in late ovine pregnancy by disrupting perfusion balance between the maternal and fetal placental circulations. Placental hemodynamics were assessed in nine chronically prepared ewes 1 hour after exposure to smoke from either a marijuana (n = 5) or a placebo (n = 4) cigarette. When compared with placebo smoke, maternal marijuana smoke exposure resulted in a fall in both uterine and umbilical placental vascular resistance and a 30% improvement in placental perfusion balance at a cotyledonary level. We conclude that maternal marijuana smoking in late ovine pregnancy has a direct relaxant effect on both maternal and fetal placental vascular smooth muscles that decreases the normal heterogeneity of flow and improves macroscopic placental perfusion balance. However, the observed concurrent 6 torr decrease in fetal oxygen tension suggests that perfusion balance is actually disrupted at a microcirculatory level.

Animals↗
PubMed1988

Maternal physiologic adaptations to early human pregnancy.

This study was designed to test the hypothesis that significant maternal physiologic adaptations to pregnancy take place in multiple systems long before they are functionally necessary (during the embryonic period). To test this hypothesis, 20 women were studied serially before pregnancy and in the seventh and fifteenth postconceptional week of an accurately dated, clinically normal, singleton pregnancy. By the seventh week, significant changes were noted in body composition and cardiopulmonary and metabolic functions. Body fat and plasma volume increased 2% and 11%, respectively, accounting for all of the observed 2 kg weight gain. With the patient standing at rest after eating, heart rate increased 13 beats/min (16%) while mean arterial pressure fell 8 mm Hg (9%). Minute ventilation rose 24% and oxygen consumption increased by 27 ml/min, or 10%. The postprandial respiratory exchange ratio also increased, from 0.78 to 0.83; the whole blood glucose level was unchanged at rest, although there was a 15% decrease in whole blood lactate levels. We conclude that our hypothesis is correct, which suggests these adaptations are preparative and may have diagnostic value.

Abortion, Spontaneous↗
PubMed1987

The effects of marijuana smoke on gas exchange in ovine pregnancy.

The effects of marijuana smoke on maternal respiratory rate and gas exchange were examined in nine chronically instrumented, late gestation ewes carrying singletons. The magnitude of exposure was randomly varied producing peak plasma levels of delta-9-tetrahydrocannabinol (delta-9-THC) ranging from 0 to 161 ng/ml. delta-9-THC levels, respiratory rate and arterial blood gas tensions were monitored before and for two hours after inhalational exposure. When compared to placebo, marijuana smoke produced a dose dependent and sustained decrease in maternal respiratory rate and arterial oxygen tension without evidence of either systemic acidosis or carbon dioxide retention. A logarithmic relationship was observed between the blood level of delta-9-THC and the change in respiratory rate. The change plateaued at 30% of control at levels above 80 ng/ml. However, the relationship between the blood level of delta-9-THC and the change in arterial oxygen tension had a linear fit with a maximum decrease of 45% at a blood level of 160 ng/ml. No change was detected in minute ventilation. Fetal oxygen tension fell significantly and remained depressed after maternal values had returned to control levels. We conclude that, in this species, inhalational exposure to marijuana smoke induces a prolonged maternal ventilation/perfusion imbalance and limits fetal oxygen availability by one or more mechanisms.

Animals↗
PubMed1979

Effect of epinephrine infusion on maternal and uterine oxygen uptake in the pregnant ewe.

Ten chronically instrumented pregnant ewes were studied to assess the effect of an epinephrine-induced decrease in uterine blood flow on the oxygen uptake of the uteroplacental-fetal tissue mass. Additional measurements of maternal cardiac output, oxygen uptake, arterial pressure, and hematocrit were obtained. Continuous systemic infusion of epinephrine at a rate of 0.3 to 0.4 microgram per kilogram per minute produced a mean decrease in uterine blood flow of 42 per cent (288 +/- 15 to 157 +/- 8 ml.per kilogram per minute). However, the oxygen uptake of the uteroplacental-fetal tissue mass remained at control levels due to an associated 79 per cent increase in the arteriovenous oxygen content difference across the uterine circulation. The calorigenic and cardiovascular systemic effects of epinephrine (a 22 per cent increase in maternal oxygen uptake and a 43 per cent increase in maternal cardiac output) were not related to the changes in either uterine flow or oxygen uptake. The implications of these observations are discussed.

Animals↗