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Biomedical subjects

T Kiserud

Publications and source records attributed to T Kiserud.

At least 19 recordsLinked to original sources
PubMed2006

Umbilical vein constriction at the umbilical ring: a longitudinal study.

OBJECTIVE: It has been suggested that constriction of the umbilical vein (UV) at the umbilical ring has hemodynamic effects. We aimed to determine the occurrence and extent of such constriction in serial observations. METHODS: This was a prospective longitudinal study of UV velocities at the umbilicus measured at approximately 4-week intervals between 19 and 42 weeks' gestation in 129 low-risk singleton pregnancies. Each participant was examined three to five times. Multilevel modeling was used to construct the reference ranges and to test associations between variables. RESULTS: Gestational age-specific reference percentiles of UV velocities at the umbilicus were established based on 469 observations. Fetuses were able to alter the UV velocities considerably during the second half of pregnancy, signifying a varying degree of UV constriction. Of a total of 129 fetuses, 56 (43.4%) never had high UV blood velocity (i.e. > 46 cm/s, the highest quartile), 42 (32.6%) fetuses had high UV blood velocity on one occasion and 31 (24.0%) fetuses on two or more occasions. In 36 (27.9%) fetuses the UV velocity at the umbilical ring was > 300% of the mean gestational age-specific reference value at the intra-abdominal section on at least one occasion. Constriction of the UV at the umbilical ring did not affect the pulsatility of the umbilical artery, and was not associated with adverse perinatal outcome in this study. CONCLUSIONS: Low-risk fetuses may well constrict the UV at the abdominal wall with velocities extending over wide ranges on one or more occasions during the second half of pregnancy. Rather than being a risk for complications, the constriction seems to be part of physiological development and possibly a regulatory mechanism.

Adult↗
PubMed2006

Ductus venosus shunting in growth-restricted fetuses and the effect of umbilical circulatory compromise.

OBJECTIVE: To determine the degree of ductus venosus (DV) shunting in fetuses with intrauterine growth restriction (IUGR) and the effect of various degrees of umbilical circulatory compromise. METHODS: This was a cross-sectional observational study. Sixty-four fetuses with IUGR (estimated weight < or = 2.5(th) percentile) underwent ultrasound examination. The diameter, velocity, and blood flow were determined in the DV and intra-abdominal umbilical vein (UV), and the fraction of shunting and DV : UV diameter ratios were calculated. Placental compromise was classified according to either normal umbilical artery (UA) pulsatility index (PI), UA-PI > 97.5(th) percentile, or absent or reversed end-diastolic flow velocity (A/REDV). Regression analysis was used to construct mean values, and SD scores were used to determine differences compared with a reference population (n = 212) after ln- or power-transformation. RESULTS: In the 64 growth-restricted fetuses, the average DV shunting was 39% compared with 25% in the reference group (overall P < 0.0001). The corresponding values in the subgroups with normal UA-PI, UA-PI > 97.5(th) percentile, and A/REDV were 31%, 35%, and 57%, respectively. Fetuses with IUGR and normal UA-PI (SD score: mean, 0.48; 95% CI, 0.04-0.92) did not shunt significantly more than did the reference fetuses (SD score: mean, 0.0; 95% CI, - 0.15 to 0.15), but those with UA-PI > 97.5(th) percentile (SD score: mean, 0.85; 95% CI, 0.41-1.29), and particularly those with A/REDV (SD score: mean, 1.56; 95% CI, 1.0-2.12) did shunt significantly more. With more DV shunting, these fetuses distributed correspondingly less umbilical blood to the liver, one of the mechanisms being a lower perfusion pressure as reflected in the lower DV blood velocity (P < 0.0001). CONCLUSIONS: DV shunting is higher and the umbilical blood flow to the liver is less in fetuses with IUGR, particularly in those with the most severe umbilical hemodynamic compromise.

Blood Flow Velocity↗
PubMed2006

Fetal cardiac output, distribution to the placenta and impact of placental compromise.

OBJECTIVES: Intrauterine growth restriction is a common clinical problem, but the underlying hemodynamic changes are not well known. Our aim was to determine the normal distribution of fetal cardiac output to the placenta during the second half of pregnancy, and to assess the changes imposed by growth restriction with various degrees of placental compromise. METHODS: A cross-sectional study of 212 low-risk pregnancies with a gestational age of 18-41 weeks constituted the reference population. A second group of 64 pregnancies with an estimated fetal weight 97.5th percentile, or absent/reversed end-diastolic velocity. Regression analysis and Z-score (SD-score) statistics were used to establish normal ranges and to compare groups. RESULTS: During gestational weeks 18-41 the normal CCO/kg was on average 400 mL/min/kg and the fraction directed to the placenta was on average 32%, while after 32 weeks it was 21%. In intrauterine growth restriction the CCO/kg was not significantly different, but the fraction to the placenta was lower (P < 0.001). This effect was more pronounced in severe placental compromise (P < 0.001). CONCLUSIONS: Normally, one third of the fetal CCO is distributed to the placenta in most of the second half of pregnancy, and one fifth near term. In placental compromise this fraction is reduced while CCO/kg is maintained at normal levels, signifying an increased recirculation of umbilical blood in the fetal body.

Aorta↗
PubMed2006

Effect of umbilical ring constriction on Wharton's jelly.

OBJECTIVE: The turgor of Wharton's jelly depends on osmotic and hydrostatic pressures. We tested the hypothesis that umbilical ring constriction has an impact on umbilical venous hemodynamics and thus on the volume of Wharton's jelly. METHODS: In a cross-sectional study of 237 low-risk singleton pregnancies, the cross-sectional area of the fetal end of the umbilical cord was determined using sonography at 20-41 weeks of gestation. The inner area of the two arteries and the vein was also measured and subtracted from the cord area to calculate the area of Wharton's jelly. Based on the Bernoulli equation, the degree of vein constriction at the umbilical ring was assessed using the blood velocity increment at the abdominal inlet. Regression analysis and SD-score statistics were used to construct mean values and to assess the effects. The dataset was also analyzed for gender-specific effects. RESULTS: The umbilical cord cross-sectional area increased with gestational age during the period 20-31 weeks, remaining essentially stable thereafter. The Wharton's jelly increased with gestational age from 20 until 31-32 weeks of gestation and remained at the same level for the rest of the pregnancy. At mid-gestation, on average 70% of the cord cross-sectional area was occupied by Wharton's jelly; at 31 weeks and later this value was 60%. Umbilical vein constriction was associated with reduced umbilical cord cross-sectional area and Wharton's jelly in female fetuses (P = 0.0007 and P = 0.003, respectively), but not in male fetuses. CONCLUSIONS: Under physiological conditions, umbilical ring constriction affects umbilical vein hemodynamics, with corresponding effects on the umbilical cord cross-sectional area and the amount of Wharton's jelly. Interestingly, the effects are gender-specific.

Abdominal Wall↗
PubMed2006

Longitudinal reference ranges for ductus venosus flow velocities and waveform indices.

OBJECTIVES: Serial Doppler measurements of the ductus venosus are used increasingly for monitoring fetuses at risk of hemodynamic compromise, but existing reference ranges are based on cross-sectional studies and thus are less suitable for comparison with serial measurements. We aimed to establish longitudinal reference ranges for ductus venosus flow velocities and waveform indices and to provide the necessary terms for calculating conditional reference ranges for serial measurements. METHODS: This was a longitudinal study of 160 low-risk pregnancies. Pulsed Doppler ultrasound was used to record ductus venosus blood flow velocities at 4-week intervals from 20-22 weeks of gestation onwards. RESULTS: With a success rate of 93%, 547 measurements (four or five in each fetus) were used to establish reference ranges. The time-averaged maximum velocity was 50 cm/s at 21 weeks of gestation, increased to 60 cm/s at 32 weeks, and remained so until term. Similarly, the peak systolic velocity increased from 59 cm/s at 21 weeks to 71 cm/s at 31 weeks and remained so until term. The end-diastolic velocity showed a continuous increase from 31 cm/s at 21 weeks to 43 cm/s at 40 weeks. The pulsatility index for veins decreased from 0.57 at 21 weeks to 0.44 at 40 weeks. When conditioned by a previous measurement, the reference ranges for the next observation became narrower and commonly shifted compared with those of the entire population. CONCLUSION: The new longitudinal reference ranges presented here reflect the development of the ductus venosus flow velocities and velocity indices and are thus appropriate for serial measurements, particularly if conditional terms are included.

Adult↗
PubMed2005

Hormone replacement therapy, body mass index and asthma in perimenopausal women: a cross sectional survey.

BACKGROUND: Hormone replacement therapy (HRT) and obesity both appear to increase the risk of asthma. A study was undertaken to investigate the association of HRT with asthma and hay fever in a population of perimenopausal women, focusing on a possible interaction with body mass index (BMI). METHODS: A postal questionnaire was sent to population based samples in Denmark, Estonia, Iceland, Norway, and Sweden in 1999-2001, and 8588 women aged 25-54 years responded (77%). Pregnant women, women using oral contraceptives, and women <46 years were excluded. Analyses included 2206 women aged 46-54 years of which 884 were menopausal and 540 used HRT. Stratified analyses by BMI in tertiles were performed. RESULTS: HRT was associated with an increased risk for asthma (OR 1.57 (95% CI 1.07 to 2.30)), wheeze (OR 1.60 (95% CI 1.22 to 2.10)), and hay fever (OR 1.48 (95% CI 1.15 to 1.90)). The associations with asthma and wheeze were significantly stronger among women with BMI in the lower tertile (asthma OR 2.41 (95% CI 1.21 to 4.77); wheeze OR 2.04 (95% CI 1.23 to 3.36)) than in heavier women (asthma: p(interaction) = 0.030; wheeze: p(interaction) = 0.042). Increasing BMI was associated with more asthma (OR 1.08 (95% CI 1.05 to 1.12) per kg/m2). This effect was only found in women not taking HRT (OR 1.10 (95% CI 1.05 to 1.14) per kg/m2); no such association was detected in HRT users (OR 1.00 (95% CI 0.92 to 1.08) per kg/m2) (p(interaction) = 0.046). Menopause was not significantly associated with asthma, wheeze, or hay fever. CONCLUSIONS: In perimenopausal women there is an interaction between HRT and BMI in the effects on asthma. Lean women who were HRT users had as high a risk for asthma as overweight women not taking HRT. It is suggested that HRT and overweight increase the risk of asthma through partly common pathways.

Adult↗
PubMed2005

Doppler-derived umbilical artery absolute velocities and their relationship to fetoplacental volume blood flow: a longitudinal study.

OBJECTIVES: To construct reference ranges for serial measurements of the umbilical artery (UA) absolute blood flow velocities in the second half of pregnancy and to test the hypothesis that significant associations exist between UA velocities and placental volume blood flow assessed from umbilical vein blood flow velocities and diameter. METHODS: This was a prospective longitudinal study of the umbilical circulation. UA absolute velocities and umbilical vein blood flow were measured at 4-weekly intervals between 19 and 42 weeks' gestation in 130 low-risk singleton pregnancies. A total of 511 observations were used to construct the reference ranges and assess the association between UA absolute velocities and placental volume flow using multilevel modeling. RESULTS: Both UA absolute velocities and placental volume blood flow showed a steady increase throughout the second half of pregnancy. However, the gestational age-related increase in the UA end-diastolic velocity (EDV) was greater than the corresponding increase in the peak systolic velocity (PSV). The time-averaged intensity-weighted mean velocity (TAWMV)/time-averaged maximum velocity (TAMXV) was 0.6 indicating probably not a completely parabolic velocity profile. There was a significant positive association (P < 0.00001) between UA absolute velocities and placental volume blood flow, but this association was modified by the gestational age. The intraobserver coefficients of variation for the UA PSV, EDV, TAMXV and TAWMV and placental volume blood flow were 10.17%, 16.29%, 11.46%, 18.18% and 8.61%, respectively. CONCLUSION: We have established new reference ranges for the UA absolute velocities based on longitudinal data. They show a significant association with fetoplacental volume blood flow and may have a clinical value in the assessment of the umbilical circulation.

Adult↗
PubMed2005

Reference ranges for serial measurements of blood velocity and pulsatility index at the intra-abdominal portion, and fetal and placental ends of the umbilical artery.

OBJECTIVE: To construct reference ranges for serial measurements of umbilical artery (UA) blood flow velocity and pulsatility index (PI) at standardized insonation sites during the second half of pregnancy. METHODS: This was a prospective longitudinal study of the umbilical circulation. UA blood flow velocities were measured at the intra-abdominal portion, fetal end and placental end at 4-weekly intervals at 19-42 weeks of gestation in 130 low-risk singleton pregnancies. A total of 513 observations were used to construct the reference ranges using regression statistics and multilevel modeling. RESULTS: UA blood velocities and PI were higher at the intra-abdominal portion and fetal end than at the placental end. The gestational age-related increase of end-diastolic velocity was greater than the corresponding increase of the peak systolic velocity at all locations. The mean differences (delta values) of UA blood velocities between the fetal and placental ends increased and that of PI decreased with advancing gestational age. CONCLUSION: UA Doppler parameters vary significantly at different locations. We have established new reference ranges for the UA velocities and PI at standardized locations based on longitudinal observations, which should be useful for the surveillance of fetuses with repeated observations.

Blood Flow Velocity↗
PubMed2004

Foramen ovale changes in growth-restricted fetuses.

OBJECTIVE: In animal experiments hypoxemia induces an increased shunting through the fetal foramen ovale (FO). Based on the hypothesis that the FO is expanded to permit more flow, the aim of this study was to determine the size of the FO in growth-restricted human fetuses. METHODS: Thirty-one women with singleton pregnancies complicated with growth-restriction (< 5th percentile) were examined at 24-39 weeks of gestation. The diameter between the FO valve and the atrial septum was determined during maximum excursion in a horizontal transverse section of the fetal heart, and the transverse diameter of the right atrium (RA) was noted. The pulsatility index (PI) was determined in the umbilical artery (UA) and absent or reversed end-diastolic flow velocity was noted. The measurements were compared with a reference population using Z-scores. RESULTS: In comparison with normally grown fetuses, the growth-restricted fetuses had a normal RA size (P = 0.08) but a smaller FO (P = 0.002), particularly when expressed as a relative size by the ratio FO/RA (P < 0.0001). This effect on the FO and FO/RA was seen mainly at < 32 weeks of gestation (P = 0.003 and P < 0.0001, respectively), and was not significant later in pregnancy. There was a tendency towards a negative relationship between relative size of the FO (FO/RA) and progressive placental compromise (overall P < 0.0001). CONCLUSIONS: Growth-restricted fetuses maintain a normally grown heart (expressed by the RA diameter) but a reduced FO diameter. The effect is seen before 32 weeks and tends to be more marked in fetuses with pronounced hemodynamic compromise of the placenta. This supports the theory that FO shunting is impaired in severely premature fetuses with placental compromise.

Blood Flow Velocity↗
PubMed2004

Portal and umbilical venous blood supply to the liver in the human fetus near term.

OBJECTIVES: To determine the contribution of the umbilical (UV) and portal (PV) veins to blood supply to the human fetal liver in a low-risk population near term, and to assess the distribution between the left and right lobes. METHODS: In 91 low-risk pregnancies with normally grown fetuses at 36 weeks of gestation we measured the distribution of blood in the UV and PV to the right and left hepatic lobes using ultrasound imaging and Doppler techniques. RESULTS: The median (10(th), 90(th) centile) total UV return was 205 (127, 294) mL/min, of which 25% (13, 47%) was shunted through the ductus venosus, 55% (35, 66%) was distributed to the left hepatic lobe, and 20% (11, 30%) was distributed to the right hepatic lobe. While the left lobe was supplied exclusively by the UV, the right lobe received 50% (20, 70%; 37 (16, 65) mL/min) of its venous blood supply from the PV. The total venous blood supply to the liver parenchyma was 185 (114, 277) mL/min; 21% (8, 34%) came from the PV supply to the right lobe and the remainder came from the UV supply to both lobes. CONCLUSIONS: The venous supply to the left lobe is from nutrient-rich UV blood; for the right lobe, half is from UV blood and half from nutrient-poor PV blood. This watershed between the portal and umbilical venous flows to the fetal liver suggests a corresponding functional dichotomy; this may be modified by hemodynamic influences, with long-term consequences.

Adult↗
PubMed2004

The effect of vascular constriction on umbilical venous pulsation.

OBJECTIVES: Umbilical venous pulsation is an important sign of hemodynamic compromise, but is also found under normal physiological conditions. Mathematical modeling suggests that vascular compliance is a determinant for pulsation, and we tested this by studying velocity pulsation at three sites on the umbilical vein. METHODS: In a cross-sectional study of 279 low-risk pregnancies (20-40 weeks' gestational age) blood flow velocity in the umbilical vein was determined before, within and after the umbilical ring in the fetal abdominal wall, and the incidence and magnitude of pulsation (the difference between the maximum and minimum velocity during a pulse, and pulsatility index) were noted. Based on the fact that the vessel cross-sectional area is an important determinant of compliance, we measured the diameter and time-averaged maximum velocity to reflect variation in diameter and compliance at the three sites. RESULTS: The incidence of umbilical venous pulsation was higher at the umbilical ring in the abdominal wall (242/279, 87%, 95% CI 82-90) than in the cord (43/198, 22%, 95%CI 16-27) or intra-abdominally (84/277, 30%, 95% CI 25-36) (P < 0.001). When pulsation was observed intra-abdominally, the pulsatility was not different from that at the umbilical ring (P = 0.16). However, the lowest pulsatility was found in the cord vein (P < 0.0001), where the largest vein diameter was found. CONCLUSION: The high incidence of venous pulsation at the umbilical ring where diameter and compliance are low supports the suggestion that local compliance is an important factor influencing pulsation in fetal veins.

Constriction, Pathologic↗
PubMed2003

Venous pulsation in the fetal left portal branch: the effect of pulse and flow direction.

OBJECTIVE: To determine whether the waveform in the left portal branch is reciprocal to the waveform found in the ductus venosus and umbilical vein due to difference in pulse direction compared to flow. METHODS: Ten fetuses (gestational age, 18-33 weeks), six with intrauterine growth restriction, three with non-immune hydrops and one with sacrococcygeal teratoma, were examined using ultrasound imaging and pulsed Doppler. Techniques were adjusted to record simultaneously the waveform from neighboring sections of the veins, relate wave components to each other and determine degree of pulsatility. The corresponding vessel diameters were determined. ANOVA with t-test or Wilcoxon signed rank test was used to compare paired measurements. RESULTS: Pulsation in the left portal branch was noted in all fetuses. The pulsatility index was higher than in the umbilical vein (P = 0.005) and the diameter smaller (P = 0.001). In the left portal branch the atrial contraction wave appeared as a velocity peak while there was a nadir during ventricular systole. Simultaneous recordings showed that the waveform was reciprocal to that found in the ductus venosus and umbilical vein. In three cases an augmented pulsatility represented a pendulation of blood in the left portal branch with time-averaged velocity near zero. CONCLUSIONS: The velocity waveform recorded in the left portal vein is an inverse image of that in the ductus venosus, proving that pulse wave and blood flow run in the same direction in the left portal vein. Low compliance (i.e. small diameter) is probably a main reason for the high incidence of pulsation in this vein. Time-averaged velocity near zero recorded in three fetuses indicates that this area acts also as a watershed.

Analysis of Variance↗
PubMed2001

[Fetal circulation--from passive knowledge to current hemodynamics].

BACKGROUND: Modern technology, especially ultrasound, has made foetal medicine a rapidly expanding field. The aim of the present review is to focus at the traditional knowledge of foetal circulation, which has recently been reassessed and expanded to serve our new patient, the human foetus. MATERIAL AND METHODS: Based on literature published mainly over the last 10 years, specific mechanisms of the foetal circulation are discussed, particularly the three foetal shunts and the placental circuit. RESULTS: The foetal circulation has capacity to compensate for considerable cardiovascular abnormalities and to redistribute circulation to meet shortage in resources. The circulatory mechanisms described in animal foetuses also operate in the human foetus, but with notable differences. The ductus venosus shunts 20-30% of the umbilical blood in the human foetus compared to 50% in the foetal lamb. The foramen ovale receives less (18-34% of the combined cardiac output) and the lungs more blood (13-25%) in the human foetus than in the foetal lamb. The isthmus aortae represents a watershed area reflecting the redistribution of blood during increased peripheral impedance and hypoxemia. INTERPRETATION: The expanded knowledge in human foetal circulation promises a more differentiated evaluation than the Doppler examination of the umbilical and middle cerebral artery offers at the moment.

Animals↗
PubMed2001

A randomized, controlled trial comparing effect of oral misoprostol and intravenous syntocinon on intra-operative blood loss during cesarean section.

BACKGROUND: Oxytocics are routinely used in an attempt to prevent excessive blood loss during cesarean section. Misoprostol, a potent uterotonic agent, has been reported to be useful in the prevention and treatment of postpartum hemorrhage by several investigators but its use during cesarean section has not been described. The objective of this study was to randomly compare the effectiveness of oral misoprostol with intravenous syntocinon on blood loss during elective cesarean sections under regional anesthesia. METHODS: Sixty pregnant women were randomized either to receive misoprostol 400 micrograms orally or syntocinon 10 IU intravenously during cesarean section. The primary outcome measure was intra-operative blood loss as estimated by physicians, and by values of preoperative and postoperative hemoglobin concentration and hematocrit. Demographic characteristics of the subjects and outcomes were compared using chi-square test for categorical and two-sample t-test for continuous data. RESULTS: Baseline characteristics in terms of age, body weight, parity, gestational age and indications for cesarean section were similar in both groups. The estimated blood loss was 545 ml (CI 476-614) in misoprostol group and 533 ml (CI 427-639) in syntocinon group (p = 0.85). Differences in preoperative and postoperative hemoglobin and hematocrit values were also similar in both groups. Two women in the misoprostol group and three in the syntocinon group (p=0.64) required additional oxytocics. One patient in each group required blood transfusion. No serious side effects were noted in either group. CONCLUSION: Oral misoprostol appears to be safe and as effective as intravenous syntocinon in reduction of intra-operative blood loss during elective cesarean section under regional anesthesia and merits further investigation.

Administration, Oral↗
PubMed2001

Ultrasound assessment of the fetal foramen ovale.

OBJECTIVES: Based on the assumption that the horizontal area between the fetal foramen ovale valve and the atrial septum (the outlet) represents the limiting structure for the foramen ovale flow, our objective was to determine the normal size of this section during the second half of pregnancy. METHODS: One hundred and thirty-eight women with low-risk singleton pregnancies were examined in a cross-sectional study between 18 and 42 weeks of gestation. Using ultrasound imaging and M-mode, the area and diameter between the foramen ovale valve and the atrial septum were determined in a four-chamber view of the fetal heart above the foramen ovale limbus. The inferior vena cava cross section and right atrial width were also determined. RESULTS: The mean foramen ovale width increased from 3 mm at 18 weeks to 6 mm at term. Correspondingly, the horizontal area grew from 15 to 50 mm2. The mean ratio between this area and the area of the inferior vena cava fell from 1 at 18 weeks to 0.5 at term. The ratio between the transverse width of the foramen ovale and the right atrium remained at average 0.45-0.50 until 32 weeks, when a slight reduction was observed towards term. CONCLUSIONS: Normal values for the horizontal cross section and transverse diameter of the foramen ovale outlet were established for the second half of pregnancy. In particular, the horizontal transverse diameter and its ratio to the right atrial width are easy to determine, and use of these measurements is thus suggested for the assessment of the fetal foramen ovale.

Adult↗