Quantitative aspects of the parenchyma-stroma relationship in experimentally induced cholestasis

In order to quantify changes of the parenchyma/stroma relations in the progression of experimentally induced biliary fibrosis in the rat, localisation of lactate dehydrogenase activity and Sirius Red staining were used as criteria to detect parenchymal cells and collagen fibers, respectively. Blood levels of bilirubin, alkaline phosphatase, anti-thrombin III activity, alpha 2-antiplasmin, factor II and factor X were related to the data obtained by histomorphometric measurements in sections gathered 1, 2, 4 and 6 weeks after the onset of cholestasis in three animals and after 8 weeks in one animal. Histophotometry showed a reduction in volume density of the parenchymal cell mass of 96%, 78%, 76%, 62% and 59% of the control values, respectively. During the same period, the collagen increased 5-fold in 4 weeks time, levelling off afterwards. Newly formed collagen appeared in the portal areas in close association with proliferating ductules, invading with the latter into the parenchymal mass. After 6 weeks, regressive changes were observed in the ductule complexes formed, manifested by a lowering of the epithelium in which extensive apoptotic cell death was observed with the electron microscope. Of the blood parameters analyzed, the clotting factor X showed the best inverse correlation with the Sirius Red readings (rs = -0.84), i.e. the volume density of collagenous fibers.

The blood flow velocity waveform index in the fetal thoracic aorta and its ability to detect fetal compromise in the small for gestational age fetus

In a prospective longitudinal study of 96 patients, mean values of blood velocity waveform indices of the fetal thoracic aorta are established with a combined linear array real-time and pulsed Doppler transducer. The course of the various blood velocity waveforms is elucidated. The most striking finding is the restricted variability of the pulsatility index (PI), resistance index (RI), A/B ratio, acceleration time (AcT) and acceleration time percentage (AcTP) during the last trimester of pregnancy. In 17 proven and evaluable SGA infants the various blood velocity waveform indices were compared with the established mean values. Fourteen of these 17 (82%) infants were proven to be intrauterine growth-retarded (IUGR). Only 3 of these 14 (21%) showed a significant increase in PI values.

Interexaminer variability of fetal Doppler velocity waveforms

A study was made of the interexaminer variability of Doppler velocity waveform determinations of the fetal circulation. Three investigators recorded Doppler ultrasound tracings of the blood velocity in the fetal thoracic and abdominal aorta and umbilical artery in 23 uncomplicated pregnancies. Of these recordings, a hard copy was made, and the pulsatility indices were computed. An analysis of variance was performed and the reliability calculated. The interexaminer variability was nonsignificant in measurements of the three blood vessels under examination. Both thoracic and abdominal aorta measurements showed poor reliability (intraclass correlation coefficient of reliability 0.30 and 0.19, respectively) due to high random errors. Umbilical artery measurements showed a better reliability (intraclass correlation coefficient of reliability 0.61), and, therefore, these hold the greatest clinical applicability.

Pulsatility index and its relationship to placental vascular resistance during partial umbilical venous occlusion: a study in fetal lambs

To study the effect of partial occlusion of the umbilical vein upon umbilical artery velocity waveforms, 4 chronically instrumented pregnant sheep have been subjected to measurement of the relevant haemodynamic parameters, i.e. the arterial inflow pressure, placental venous outflow pressure (Pv), venous blood flow (Quv) and arterial blood velocity waveform. The pulsatility index (PI) of the velocity waveform increases significantly for a Quv reduction of 40% or more (p less than 0.05). The Quv correlates well with the PI (r = 0.61) and the Pv (r = 0.71). The correlation between fetal heart rate (FHR) and Quv, FHR and PI is 0.75 and 0.64, respectively. The placental vascular resistance (R) can be calculated using the Poiseuille equation. There is not significant correlation between R and PI. It can be concluded that the increase in PI in the umbilical artery during partial venous occlusion is very likely caused by an increased Pv rather than a change in R.

Exercise-induced changes in the percentage of free testosterone and estradiol in trained and untrained women

We have studied the effect of exercise on the percentage of free plasma estradiol 17-beta (E2) and testosterone (T) in 13 untrained (UT) and 8 trained (marathon runners, MR) eumenorrheic women. All women performed a standardized bicycle ergometer (UT) or treadmill (MR) test in the follicular and luteal phases of their menstrual cycles (15-min consecutive work loads of 60%, 70%, and 80% VO2 max to exhaustion). Blood was drawn through an indwelling venous catheter at 15 and 2 min before and immediately after exercise. Free E2 and T was assayed by centrifugal ultrafiltration using undiluted plasma at 37 degrees C (basal samples) and 39 degrees C (exercise samples). Statistical analysis was performed by a two-tailed paired t test. In the UT, the basal percentage of free E2 was measured to be 1.55% +/- 0.24% (mean +/- SD) in the follicular phase and 1.62% +/- 0.32% in the luteal phase (differences NS). In the MR, these values were 1.22% +/- 0.25% and 1.25% +/- 0.12% for the follicular and luteal phases, respectively. The differences between the groups were not significant. Exercise did not provoke significant changes in free E2 in either of the groups. Constrastingly, exercise induced a significant (P less than 0.02) increase in the percentage of free T from 1.56% +/- 0.27% to 2.1% +/- 0.36% and from 1.6% +/- 0.27% to 2.12% +/- 0.33% in the UT in the follicular and luteal phases, respectively. In the MR, the free percentage of T increased from 1.04% +/- 0.39% to 1.6% +/-0.16% (follicular phase) and from 1.24% +/- 0.22% to 1.67% +/- 0.18% (P less than 0.02).

Effect of a 3-month endurance training program on metabolic and multiple hormonal responses to exercise

We have investigated the effect of a 3-month endurance training program (running and cycling) on plasma hormone responses during standardized bicycle ergometer work (15-min consecutive work loads of 60%, 70%, 80%, and eventually 90% VO2 max) in eight previously untrained eumenorrheic women. The subjects were investigated before and after training both in the follicular and luteal phases of the menstrual cycle (between the 7th-10th and 20th-25th days of their menstrual cycle, respectively). Blood was obtained 15 and 2 min before the onset of exercise and at the end of each work load from an indwelling catheter. In each sample, the plasma concentrations of estradiol 17 beta (E2), progesterone (P), testosterone (T), androstenedione (delta 4-A), dehydroepiandrosterone sulfate (DHEA-S), prolactin (PRL), and adrenocorticotropic hormone (ACTH) were assayed in duplicate by RIA; lactate was assayed as well. The hormone concentrations were expressed in absolute as well as in relative values. After training basal DHEA-S and ACTH levels were significantly (P less than 0.05) lower in both phases of the menstrual cycle, whereas basal luteal phase E2 and T levels were significantly (0.05 greater than P greater than 0.01) lower after training. Exercise induced significant increments in the relative values of all hormones in both phases (0.05 greater than P greater than 0.001). After training, T and DHEA-S increased relatively more pronounced (0.05 greater than P greater than 0.02) in the follicular and luteal phase, respectively.

Multiple hormonal responses to physical exercise in eumenorrheic trained and untrained women

The aim of the present investigation was to compare the changes in plasma estradiol (E2), progesterone (P), luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), androstenedione (delta 4-A), dehydroepiandrosterone sulfate (DHEA-S), adrenocorticotropic hormone (ACTH), and prolactin (PRL) in standardized tests (15-min consecutive work loads of 60%, 70%, 80% VO2 max to exhaustion) in 13 eumenorrheic untrained (UT) and 8 highly trained women (MR). Blood was obtained 15 and 2 min before exercise and at the end of each work load or each 15 min period. The results showed a significant increase (0.05 greater than P less than 0.001, two-way ANOVA) in plasma E2 P, T delta 4-A, PRL, and ACTH both in UT and MR irrespective of the phase of the menstrual cycle. DHEA S levels increased significantly in the MR, but not in the UT, PRL and ACTH increased linearly with exercise in MR and nonlinearly in UT. In the latter group, only the 80% VO2 max work load was able to elicit significant increments in the plasma levels of these hormones. In the MR plasma T and delta 4-A levels increased relatively more pronounced (P less than 0.05) at comparable work loads and exercise times than in the UT. LH levels decreased with exercise both in the UT and MR, whereas FSH levels remained unchanged (MR) or decreased (UT). These findings suggest that during exercise the ovarian hormones are increased by more unspecific mechanisms such as a decreased metabolic clearance rate, whereas in the MR, adrenal secretion of androgens is enhanced.

Ovulatory disturbances in patients with luteal insufficiency

In order to study ovulatory disturbances in patients with luteal insufficiency we evaluated 210 cycles of 170 women from infertile couples by ultrasonographic follicle measurements and hormonal determinations. Only cycles with evidence of luteinization were included into the study. Mid-luteal progesterone (P) levels were determined in relation to the ultrasonographic ovulation time or, where the follicle failed to rupture, in relation to the LH peak. In spontaneous cycles with a mid-luteal P level below 32 nmol/l (10 ng/ml) a luteinized unruptured follicle (LUF) was found in 71.1% of cycles, whereas in spontaneous cycles with a mid-luteal P level above 32 nmol/l only 7.9% cycles exhibited a failure of the follicle to rupture. The same phenomenon was encountered in cycles in which agents had been given to induce ovulation. The incidence of LUF cycles in an average infertility population could be calculated to be as high as 50% if the mid-luteal P level is below 32 nmol/l and as low as 4% if the mid-luteal P level is above 32 nmol/l. The geometric mean mid-luteal P level in spontaneous LUF cycles was 32.5 nmol/l, compared to 55.2 nmol/l in spontaneous ovulatory cycles (P less than 0.001). We conclude that in patients with luteal insufficiency a high incidence is found of a failure of the follicle to rupture. The entrapment of the oocyte in the unruptured follicle constitutes an important cause of infertility in these patients.

Prospective study of velocity waveforms in the fetal descending thoracic and abdominal aorta in fetuses appropriate for gestational age and in growth-retarded fetuses

Blood velocity waveforms were obtained by a combination of real-time B mode and pulsed Doppler (2 MHz) ultrasound from the fetal descending thoracic and abdominal aorta. In a prospective study 36 patients were studied. Throughout pregnancy 261 tracings of the thoracic aorta and 241 tracings of the abdominal aorta were evaluable for this study. Measurements were performed every 2nd week from a menstrual age of 18 weeks onwards till the 40th week. Reference values for the resistance index (RI), AB ratio and the pulsatility index (PI) were established in 27 patients with uncomplicated pregnancies. Abnormal waveforms were found in the small for gestational age (SGA) group, which consisted of 8 patients. A comparison was made between the 2 sample means of the PI in the abdominal and descending thoracic aorta in the group with appropriate for gestational (AGA) fetuses, as well as between the AGA and SGA groups. With regard to the 95% confidence interval significance is shown between the mean PI in the descending thoracic and abdominal aorta, as well as between the AGA and SGA groups. However, blood velocity measurements of the fetal aorta do not provide additional clinical information compared with measurements of the fetal aorta do not provide additional clinical information compared with measurements in the umbilical artery.

A new administration form of ritodrine. Ritodrine plasma levels with sustained-release capsules in a steady state

A sustained-release administration form of oral ritodrine was introduced to cope with the problem of the short dosage interval inherent to conventional oral ritodrine administration. The bioavailability of this application form was assessed in a clinical study including 11 patients. With a dosage frequency of only 3 times daily and a dosage form index of 1.8, plasma levels of 14.6-26.5 ng/ml ritodrine (equivalent to an infusion rate of approximately 50 micrograms/min) were obtained without serious cardiovascular or metabolic side effects. It was concluded that with this new formulation clinical applicability of orally administered ritodrine in tocolytic therapy has increased.

A prospective study of the umbilical artery waveform in appropriate-for-date and growth-retarded fetuses

Blood velocity waveforms were obtained by a combination of real-time B-mode and pulsed Doppler (2 MHz) ultrasound from the umbilical artery. In a prospective study, velocity waveforms of the umbilical artery were analyzed from 36 patients with single pregnancies. Sonograms were performed every 2nd week from the 18th week menstrual age onwards till labor. A total of 331 velocity profiles were obtained. Reference values were obtained from 27 patients with uncomplicated pregnancies. Abnormal waveforms were found in 9 cases. A comparison was made between the normal and abnormal group with regard to placental impedance indices [resistance index (RI), A/B ratio and pulsatility index (PI)]. The sensitivity, specificity, predictive values of each mentioned index were determined. The sensitivity of the PI and the RI is the same: 77.8%, the sensitivity of the A/B ratio is 66.7%. The specificity is also slightly higher for the PI and RI than for the A/B ratio (81.5, 81.5 and 77.5%, respectively). The same can be said for the predictive values (predictive value with positive result, 58.3, 58.3 and 50.0%, predictive value with negative result, 91.2, 91.2 and 87.5%). On the basis of these results and theoretical considerations, the PI is preferable to the other two placental impedance indices. It was shown once more that, with certain restrictions, this noninvasive transcutaneous technique reflects fetal well-being.

Effect of continuous infusion of fenoterol on maternal pelvic and fetal umbilical blood flow in pregnant sheep

The results from studies on the reactions of the uterine vascular bed upon intravenous administrations of beta-adrenergic drugs to the ewe are not all identical. This can be partly explained by different reactions of the pelvic vasculature on beta-adrenergic receptor stimulation. In order to assess whether any differences in flow reactions existed between the vascular beds of two maternal pelvic vessels upon beta-adrenergic receptor stimulation, we studied the effect of continuous maternal intravenous infusion with fenoterol on the blood flow in the maternal internal iliac and the median uterine artery in seven chronically instrumented pregnant sheep between 104 and 142 days gestation. Furthermore, the effects on umbilical venous blood flow, fetal heart rate, blood pressure and acid-base balance were analyzed. Maternal and fetal blood flows were measured with electromagnetic flow transducers. Fenoterol was administered to the ewe via a continuous intravenous infusion in two sequential periods of 30 minutes duration in a dose of 2 respectively 4 micrograms per minute. The blood flow in the internal iliac artery showed an increase of 10.5% (p less than 0.05) at the end of the infusion period and was still but not significantly elevated during the postinfusion period. No significant changes in median uterine artery blood flow were found during the fenoterol infusion, although an incremental trend was present. Fenoterol infusion to the mother had no effect on umbilical venous blood flow. Fetal pH and PO2 did not change, while fetal PCO2 was reduced (p less than 0.005) at the end of the infusion and recovery period, probably as a result of the concomitant maternal hyperventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Technical aspects of fetal Doppler measurements

Doppler ultrasound may be a valuable tool in the estimation of fetal well-being. Nevertheless, a good understanding of the basic principles of ultrasound and the applied circuitry is necessary to obtain useful information. Some physical principles and limitations of ultrasound are discussed and the basics of the electronic devices are mentioned. Furthermore, the parameters used in obstetrical investigations are reviewed.

Phasic blood flow patterns in the common umbilical vein of fetal sheep during umbilical cord occlusion and the influence of autonomic nervous system blockade

The blood flow pattern in the common umbilical vein is under normal conditions nonpulsatile in contrast to the flow in the fetal inferior vena cava. We observed pulsatile flow patterns in the common umbilical vein of fetal lambs during changes in the fetal hemodynamic equilibrium. These pulsations may influence the mixing of oxygen-rich ductus venosus blood and oxygen-poor inferior vena cava blood. This study deals with the phasic changes in umbilical venous blood flow during cord occlusion. The experiments were performed in eight chronically instrumented fetal lambs between 114 and 133 days gestation (term 146 days). Umbilical venous blood flow was measured with an electromagnetic flow transducer around the intraabdominal common part of both umbilical veins. The fetuses were provided with catheter in the fetal abdominal aorta and with electrodes for monitoring arterial blood pressure and heart rate. Occlusion of the umbilical cord was performed by means of an inflatable balloon occluder around the total cord (occlusion time 20 to 90 seconds). Occlusions were performed in fetuses with an intact autonomic nervous system and after blockade of the alpha-adrenergic, beta-adrenergic or cholinergic part of the autonomic nervous system.

Effect of continuous infusion of norepinephrine on maternal pelvic and fetal umbilical blood flow in pregnant sheep

The effect of continuous maternal intravenous infusion with norepinephrine on the blood flow in the maternal internal iliac and the median uterine artery was studied in ten chronically instrumented pregnant sheep between 104 and 146 days gestation. Furthermore the effects on umbilical venous blood flow, fetal heart rate and acid-base balance were analyzed. Maternal and fetal blood flows were measured with electromagnetic flow transducers. Norepinephrine was administered to the ewe via a continuous intravenous infusion in increasing sequential doses of 15 minutes duration from 4 to 40 micrograms per minute. Variations of often considerable magnitude associated with e. g. micturition, defecation and fear of the ewe occurred in the maternal pelvic blood flow during the steady state period. The blood flow in the maternal vessels substantially decreased immediately following the onset of the norepinephrine infusion but gradually returned towards the preinfusion level despite the continued drug infusion and except one no significant changes in blood flow were found at the end of each sequential infusion period. Umbilical venous blood flow did not change. No significant changes in fetal arterial blood pressure, heart rate and acid base balance were found. It is concluded that the decrease in maternal pelvic blood flow associated with continuous norepinephrine administration gradually abates with time, possibly by the involvement of local factors such as prostaglandin formation and/or by the phenomenon of down-regulation.

Effect of selective occlusion of the umbilical arteries and/or veins on uterine blood flow in sheep

Maternal uterine blood flow was depressed during total umbilical cord occlusion, probably based on an increased fetal cotyledonary tissue pressure (Hasaart and de Haan (1985) Eur. J. Obstet. Gynec. Reprod. Biol., 19, 125-131). This supposed mechanism was further analysed by performing selective occlusions of the umbilical arteries and/or veins (mean occlusion time 35 s). An occluding device which allowed separate occlusion of umbilical veins and arteries was applied to the umbilical cord in 7 chronically prepared fetal lambs between 106 and 135 days gestation. Median uterine artery blood flow (UBF) was measured with an electromagnetic flow meter. During occlusion of both umbilical veins (VV, n = 22) in 6 animals a maximal decrease in UBF to 87.5% of control value (P less than 0.001) was found at the end occlusion, followed by a gradual return to control value in the post occlusion period. Occlusion of both umbilical arteries (AA, n = 29) in 5 animals was accompanied by a slight increase in UBF to 103% of control value (P less than 0.01). Total occlusion of the umbilical arteries and veins simultaneously (n = 17) in 4 animals did not result in any change in UBF. The changes in volume and turgor in the fetal cotyledonary tissue associated with the arterial and venous occlusions should lead to respectively a decrease (AA) and increase (VV) in resistance to maternal flow, causing the changes in uterine blood flow. It is concluded that volume changes in the fetal compartment of the sheep placenta affect maternal uterine blood flow.

Ultrasound increases the prognostic value of the postcoital test

The prognostic value of the postcoital (PC) test was studied in two groups of women in whom the infertility workup differed only in the way the PC test was timed. Fifty patients were investigated in a traditional way. In this group the PC test failed to have any substantial prognostic value. In a second group consisting of 54 patients, the PC test was timed applying ultrasonographic criteria for ovarian follicular development. This resulted in a highly significant prognostic test. Timing of the PC test by ultrasound enhanced both the reliability and the efficacy of the standard fertility investigation.

Effects of fetal breathing movements on umbilical venous blood flow in fetal lambs

The effects of fetal breathing movements on the blood flow pattern in the common umbilical vein were studied in six chronically instrumented fetal lambs between 106 and 143 days gestation. Umbilical venous blood flow was measured with an electromagnetic flow transducer around the intra-abdominal common umbilical vein. Fetal breathing movements were recorded by means of an intratracheal catheter. During rapid irregular breathing movements instantaneous umbilical venous blood flow showed undulations with the frequency of the breathing movements. An inspiratory movement, characterized by a fall in tracheal pressure (mean +/- S.D. = 5.3 +/- 1.7 mmHg) was accompanied by a decrease in instantaneous umbilical venous blood flow (mean +/- S.D. = 10.5 +/- 2.8%). This decrease in umbilical blood flow during inspiration was accompanied by an increase in intra-abdominal pressure. A much greater decrease (mean +/- S.D. = 40.6 +/- 18.4%) in instantaneous umbilical venous blood flow occurred during deep inspiratory efforts (mean pressure drop +/- S.D. = 15.5 +/- 4.3 mmHg), accompanied by marked increases in intra-abdominal pressure. Isolated expiratory efforts resulted in an increase in both tracheal (mean +/- S.D. = 6.3 +/- 2.6 mmHg) and intra-abdominal pressure, while umbilical venous blood flow decreased (mean +/- S.D. = 33.5 +/- 21.3%). These observations show the great influence of fetal respiratory movements on the blood flow pattern in the common umbilical vein. The changes in instantaneous umbilical venous blood flow are possibly brought about by changes in intra-abdominal pressure.

Follicle growth curves and hormonal patterns in patients with the luteinized unruptured follicle syndrome

A prospective longitudinal and standardized study is presented, dealing with ultrasonographic and hormonal characteristics of the luteinized unruptured follicle (LUF) syndrome. Among 600 cycles monitored in 270 infertility patients, 40 cycles in 27 patients showed no evidence of follicle rupture, in spite of signs of luteinization, as reflected by basal body temperature recordings and progesterone determinations. In this study, 20 LUF cycles in 20 infertile patients were compared with 45 ovulatory cycles in 45 control women. During the follicular phase, no substantial difference in follicle growth was found, but after the luteinizing hormone peak, LUF follicles, instead of rupturing, showed a typical accelerated growth pattern. Both mean luteinizing hormone peak levels and midluteal progesterone levels were significantly lower in LUF cycles than in the control cycles. However, the duration of the luteal phase was not affected. Both central and local factors can be held responsible for the lack of follicle rupture. Ultrasound offers new possibilities as a noninvasive method in diagnosing the LUF syndrome.

Depression of uterine blood flow during total umbilical cord occlusion in sheep

The effect of total umbilical cord occlusion upon maternal blood flow in the internal iliac and median uterine arteries was studied in eight chronically instrumented pregnant sheep. Occlusion of the umbilical cord was performed with an inflatable balloon occluder around the total cord. Blood flow was measured with electromagnetic flow transducers. Total umbilical cord occlusion of short duration (mean 40.1 s) caused a significant decrease in the maternal internal iliac and median uterine arteries at the end of the occlusion to respectively 93.9% and 91.7% of the control values. The decrease in internal iliac and median uterine artery blood flow is attributed to an elevated fetal capillary pressure in the placenta, leading to an increased fetal placental tissue pressure which in turn compresses the maternal placental capillaries, resulting in a heightened vascular resistance and a decrease in uterine blood flow.

Computed tomography in staging untreated patients with cervical cancer

In a study to test the accuracy of computed tomography (CT) in staging untreated patients with cervical cancer, the interpretations of the CT scans of pelvis and abdomen of 56 consecutive patients were compared with surgical and/or clinical findings. This study clearly demonstrates that CT is unreliable in diagnosing parametrial tumour invasion and that it is not justified to make the therapeutically important differentiation between a IB or IIB stage with CT. In demonstrating metastatic lymph nodes, the accuracy of CT was only 75%, predominantly due to metastatic deposits in normal-sized nodes. CT was less accurate in diagnosing bladder wall and sigmoid invasion than cystoscopy and sigmoidoscopy, respectively, and was as accurate as urography in diagnosing ureteric obstruction. For these reasons, CT is not indicated as a routine procedure in cervical cancer staging, particularly not in the early stages of the disease. CT may be helpful in the higher clinical stages to measure tumour bulk and to get an impression about the whole extent of the disease.

Predictive value of uterine contractility and the serum levels of progesterone and oestrogens with regard to preterm labour

A longitudinal investigation regarding the serum concentrations of oestradiol, oestriol and progesterone in relation to uterine activity has been performed in 80 healthy primigravid women during the course of pregnancy up to the 37th week of pregnancy. The frequency of uterine contractions was quantitatively objectivated by means of external toco-dynamometry; simultaneously the uterine activity has been recorded by the pregnant women qualitatively. It appears that there is a gradual increase of all the three mentioned hormones during the course of pregnancy. However, there is a large interindividual spread. There exists no relation between the hormonal serum levels and uterine activity (quantitatively as well as qualitatively recorded). Between these two latter there is a poor relation. It is impossible to predict the occurrence of preterm birth based on hormonal serum changes. This holds for the progesterone-oestradiol ratio.

Serum levels of ritodrine during oral maintenance therapy

In order to elucidate some aspects of the efficacy of orally administered ritodrine, serum concentrations of ritodrine were determined during intravenous and oral therapy. Ritodrine serum concentrations during steady-state intravenous therapy (200 micrograms/min) ranged from 91.0 to 123.0 ng/ml. Serum concentrations during maintenance therapy with 120 mg ritodrine per os fluctuate between 3.2 and 30.5 ng/ml, depending on the moment of tablet intake. During oral maintenance therapy a striking correlation was found between the maternal heart rate and the serum concentration of ritodrine. The findings suggest that efficacy of orally administered ritodrine is doubtful on pharmacological grounds.