Renal physiology in pregnancy

Mathematical modelling of the maternal cardiovascular system in the three stages of pregnancy

In this study, a mathematical model of the female circulation during pregnancy is presented in order to investigate the hemodynamic response to the cardiovascular changes associated with each trimester of pregnancy. First, a preliminary lumped parameter model of the circulation of a non-pregnant female was developed, including the heart, the systemic circulation with a specific block for the uterine district and the pulmonary circulation. The model was first tested at rest; then heart rate and vascular resistances were individually varied to verify the correct response to parameter alterations characterising pregnancy. In order to simulate hemodynamics during pregnancy at each trimester, the main changes applied to the model consisted in reducing vascular resistances, and simultaneously increasing heart rate and ventricular wall volumes. Overall, reasonable agreement was found between model outputs and in vivo data, with the trends of the cardiac hemodynamic quantities suggesting correct response of the heart model throughout pregnancy. Results were reported for uterine hemodynamics, with flow tracings resembling typical Doppler velocity waveforms at each stage, including pulsatility indexes. Such a model may be used to explore the changes that happen during pregnancy in female with cardiovascular diseases.

Development of PBPK models for PFOA and PFOS for human pregnancy and lactation life stages

Perfluoroalkyl acid carboxylates and sulfonates (PFAA) have many consumer and industrial applications. Developmental toxicity studies in animals have raised concern about potential reproductive/developmental effects of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS); however, in humans conflicting results have been reported for associations between maternal PFAA levels and these outcomes. Risk assessments and interpretation of available human data during gestation and lactation are hindered due to lack of a framework for understanding and estimating maternal, fetal, and neonatal pharmacokinetics (PK). Physiologically based pharmacokinetic (PBPK) models were developed for PFOA and PFOS for the gestation and lactation life stages in humans to understand how the physiological changes associated with development affect pharmacokinetics of these compounds in the mother, fetus, and infant. These models were derived from PBPK models for PFOA/PFOS that were previously developed for adult humans and rats during gestation and lactation and from existing human pregnancy and lactation models developed for other chemicals. The models simulated PFOA and PFOS concentrations in fetal, infant, and maternal plasma and milk, were compared to available data in humans, and also were used to estimate maternal exposure. The models reported here identified several research needs, which include (1) the identification of transporters involved in renal resorption to explain the multiyear half-lives of these compounds in humans, (2) factors affecting clearance of PFOA/PFOS during gestation and lactation, and (3) data to estimate clearance of PFOA/PFOS in infants. These models may help address concerns regarding possible adverse health effects due to PFOA/PFOS exposure in the fetus and infant and may be useful in comparing pharmacokinetics across life stages.

Effects of pregnancy on glomerular dynamics: micropuncture study in the rat

Glomerular dynamics were investigated by micropuncture in 15-day pregnant Munich-Wistar rats. Female non-pregnant rats were used as control. In hydropenia, single nephron glomerular filtration rate (SNGFR) averaged 37.2 nl/min/g kidney weight in pregnant rats, and 26.2 nl/min/g kidney weight in controls (P less than 0.0005). During pregnancy, mean glomerular plasma flow (GPF) rose from 63.0 to 104.5 nl/min (P less than 0.0005), and glomerular capillary hydrostatic pressure (PG) from 44.8 to 50.6 mm Hg (P less than 0.0005). This rise in PG accounted for an increase in effective filtration pressure (EFP). Mean EFP at the efferent end of the glomerulus rose from near zero to 9.7 mm Hg, indicating filtration pressure disequilibrium. After extracellular fluid volume expansion with saline, GPF and EFP were still greater during pregnancy. A filtration pressure disequilibrium occurred also in non-pregnant rats, allowing calculation of definite values of the ultrafiltration coefficient (Kf). During pregnancy, mean Kf was reduced from 0.0332 to 0.0285 nl/(sec X mm Hg) (P less than 0.005). SNGFR was moderately, but not significantly, increased. These results show that during pregnancy glomerular dynamics is characterized by a rise in GPF and EFP, and by a reduction in Kf. Following these changes, a plasma-flow dependent rise in SNGFR occurs in hydropenia. After expansion, instead, SNGFR is unmodified because the dependence of ultrafiltration on plasma-flow declines while the influence of Kf increases at high values of GPF.

Serial changes in 24 hour creatinine clearance during normal menstrual cycles and the first trimester of pregnancy

Serial changes in 24-hour creatinine clearance were determined in 11 women during several menstrual cycles before conception, the conceptional cycle and the first trimester of pregnancy. During the menstrual cycle, a 20 per cent mean increase occurred between the week of menstruation and the late luteal phase. Following conception, this increase continued such that a 45 per cent mean increase was evident by the ninth week of gestation. In two women who aborted spontaneously, the change in 24-hour creatinine clearance in early pregnancy was not as great nor as sustained, this feature being apparent at least three weeks before any clinical abnormality. Possible reasons for the changes in glomerular filtration rate in early pregnancy and its clinical implications are discussed.