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Biomedical subjects

T Wheeler

Publications and source records attributed to T Wheeler.

At least 55 records · Page 3Linked to original sources
PubMed1997

MRI quantitative myocardial perfusion with compartmental analysis: a rest and stress study.

K1 (first-order transfer constant from arterial plasma to myocardium for Gd-DTPA) and Vd (distribution volume of Gd-DTPA in myocardium) were measured in vivo in a canine model (n = 5) using MRI-derived myocardial perfusion curves and a compartmental model. Perfusion curves were obtained after a bolus injection of Gd-DTPA (0.04 mM/kg) with an inversion-prepared fast gradient echo sequence. Myocardium and blood signal intensity were converted to a concentration of Gd-DTPA, according to a model appropriate for short (<1 s) interimage intervals characteristic of cardiac-triggered acquisitions. Before dipyridamole-induced stress, K1 and Vd, obtained from the fit of the MRI-derived perfusion curves, were 6.2 +/- 1.4 (mHz) and 17.5 +/- 4.2%, respectively. After dipyridamole infusion, a K1 increase of a factor of 2.82 +/- 0.72 was measured (P = 0.003). No change was observed in Vd (P = 0.98). These results suggest that the K1 increase after dipyridamole reflects a flow-related effect that can be useful to quantify the MRI-derived perfusion curves.

Animals↗
PubMed1997

Maternal serum vascular endothelial growth factor during early pregnancy.

1. The objectives of the study were: (i) to investigate the serum concentrations of vascular endothelial growth factor (VEGF) in pregnant and non-pregnant women; and (ii) to study the relationship between the levels of maternal serum VEGF and the serum concentrations of human chorionic gonadotrophin (hCG) and progesterone during the first trimester. 2. Total immunoreactive VEGF was measured by competitive RIA using recombinant human VEGF165 and a polyclonal antiserum. Serum VEGF was measured in 60 non-pregnant women of childbearing age. These data were compared with serum VEGF measured in 363 women between 41 and 91 days of gestation. 3. The median serum VEGF concentration was 1.10 micrograms/l (interquartile range 0.91-1.30) in the nonpregnant women and 2.13 micrograms/l (interquartile range 1.62-2.77) in the pregnant women. Serum levels of VEGF were significantly higher among the pregnant cohort (P < 0.0001). Serum VEGF concentration was positively correlated with gestational age, increasing until ten completed weeks of pregnancy. Serum VEGF was negatively correlated with maternal height and weight, and positively correlated with serum hCG and serum progesterone (P < or = 0.0001 in all cases). Serum VEGF was lower in the pregnant women who smoked (P = 0.06). 4. Our data show a positive and highly significant correlation between maternal serum levels of VEGF and hormones reflecting placental function (hCG, progesterone). We speculate that VEGF production is increased by progesterone and hCG, and that VEGF has a positive influence on trophoblast development. VEGF may also be involved in the initiation of the maternal cardiovascular adaptation to pregnancy.

Adult↗
PubMed1997

Variation in detection of VEGF in maternal serum by immunoassay and the possible influence of binding proteins.

Using radioimmunoassay (RIA) and a polyclonal antibody we have shown that maternal serum vascular endothelial growth factor (VEGF) is elevated during pregnancy. In contrast, a commercial VEGF ELISA utilizing a sandwich two-site immunoassay was unable to detect VEGF in 19 of the 20 maternal serum samples analysed. In addition, the recovery of exogenous VEGF added to the pregnancy samples was low or not recordable with the ELISA. Using RIA, 82-101% of the added VEGF was recovered. These differing results could be explained by the formation of VEGF-protein complexes that are detectable using RIA but undetectable with the ELISA. Our data imply that there is a substantial increase in circulating VEGF binding proteins during pregnancy. The increase in VEGF and its binding proteins during pregnancy may reflect important physiological events in the mother and feto-placental unit.

Blood Proteins↗
PubMed1996

Peripheral blood leukocyte populations in the elderly with and without periodontal disease.

Periodontal disease in the elderly has not been characterized. Initial reports suggest that the disease is common and severe. Deficiencies in the immune response have also been reported to occur in the elderly. Consequently it was hypothesized that aging-related changes in the immune response may contribute to the severity and occurrence of periodontal disease in the elderly. To test that hypothesis, the % and number of leukocytes and leukocyte subsets in the peripheral blood of elderly (65-75 years) subjects were tested and used as indicators of the immune potential of those individuals. Age and gender effects on several of the parameters tested were identified. With the exception of increased number of leukocytes in the elderly group with severe periodontal disease, no other alteration in the leukocyte parameters tested were identified. These results suggest that periodontal disease in the elderly was not associated with obvious changes in the leukocyte and leukocyte subsets in the peripheral blood due to aging.

Adult↗
PubMed1995

Angiogenesis and the placental environment.

Rapid growth and vascularization of the human placenta are characteristic of early pregnancy and are accomplished in an unusually hypoxic environment. Stimulation of placental growth through hypoxia-induced angiogenesis may therefore be of particular importance. We have previously found that several varieties of vascular endothelial growth factor (VEGF) mRNA, including VEGF165, are present in cultured placental fibroblasts. We hypothesized that hypoxia would increase the transcription and translation of VEGF by these cells and provide one mechanism linking placental development with its environment. Placental fibroblasts were grown in aerobic or anaerobic atmospheric conditions for 72 h. By 24 h the oxygen tension of the anaerobic culture media was significantly less than that of the aerobic cultures. RNA was extracted from the cells at 24, 48 and 72 h. Following reverse transcription polymerase chain reaction (RT-PCR) stronger signals for VEGF were always found in the anaerobic cultures and this was confirmed by competitive PCR. mRNA for VEGF165 was represented most strongly but the anaerobic cultures also showed clearly mRNA for VEGF121, VEGF189 and VEGF206. The VEGF protein was also measured in the aerobic and anaerobic culture medium. By 72 h the average concentration of VEGF was significantly higher (P = 0.01) in the anaerobic culture medium. VEGF production is one mechanism through which oxygen supply may influence placental development. Examples of this may include the compensatory placental hypertrophy associated with maternal anaemia and with reproduction at high altitude.

Alternative Splicing↗
PubMed1995

Relationships between the uterine environment and maternal plasma concentrations of insulin-like growth factor binding protein-1 and placental protein 14 in early pregnancy.

Blood was obtained from 218 women between 6 and 13 weeks of gestation. Measurements of serum insulin-like growth factor binding protein-1 (IGFBP-1) and placental protein 14 (PP14) concentrations were compared with maternal weight and height, maternal smoking habit, indices of maternal haematological status and two placental hormones [human chorionic gonadotrophin (HCG) and human placental lactogen (HPL)]. IGFBP-1 concentration was negatively correlated with maternal weight (P < 0.001) and body mass index (P < 0.001); PP14 concentration was not correlated with these measurements. PP14 concentration was negatively correlated with maternal haemoglobin concentration (P = 0.010), mean corpuscular volume (P = 0.003) and serum ferritin concentration (P = 0.016). The concentrations of PP14 were significantly less among smokers (P < 0.001); IGFBP-1 concentrations were uninfluenced by smoking. IGFBP-1 concentration was positively correlated with maternal serum HCG (P = 0.003) and maternal serum HPL (P = 0.002). PP14 concentration was positively correlated with maternal serum HCG (P < 0.0001) but not with HPL. These findings demonstrate that the maternal environment has an early influence on both endometrial and placental function.

Body Mass Index↗
PubMed1995

The influence of maternal haemoglobin and ferritin on mid-pregnancy placental volume.

OBJECTIVE: To investigate whether low maternal haemoglobin and ferritin levels are associated with increased placental volume by mid-pregnancy. DESIGN: Prospective study of women attending hospital for shared antenatal care. SETTING: A teaching hospital in the south of England. SUBJECTS: Five hundred and sixty-eight women booking for delivery in the hospital. MAIN OUTCOME MEASURES: Placental volume measured by ultrasound at 18 weeks gestation. RESULTS: At 14 weeks gestation 9% of women had haemoglobin levels < or = 11 g/dl and 26% had ferritin levels < 13 micrograms/l. Placental volume at 18 weeks was inversely related to the maternal haemoglobin and ferritin levels. The influence of haemoglobin and ferritin concentrations was independent of maternal social class, parity, smoking, and weight. Larger placentae were found in taller women, those who had previously been pregnant, and in those who were smoking more than 15 cigarettes daily at the time of their last menstrual period. CONCLUSION: These data suggest that placental development is influenced from early in pregnancy by the intrauterine environment provided by the mother. In conjunction with other studies they support the proposal that, as a result of these changes, programming of adult blood pressure may be initiated in early pregnancy.

Adolescent↗
PubMed1995

Antibody responses to suspected periodontal pathogens in elderly subjects with periodontal disease.

Little is known about the relationship of aging to periodontal disease. The immune response undergoes aging-related changes resulting in loss of functional capacity. The aim of this study was to investigate the relationship between levels of serum IgG antibodies against suspected periodontal pathogenic microorganisms to the presence or absence of periodontal disease in an elderly (65-75 yrs) population. From this study, we obtained information concerning: (1) the ability to differentiate elderly individuals without disease from those with disease by their levels of antibodies against periodontal pathogens and (2) which periodontal pathogen(s) triggered those responses. IgG anti- Porphyromonas gingivalis (strains W83 and 381) levels in the serum of elderly patients with severe periodontal disease were the only antibody responses measured which were elevated compared to the elderly control group of subjects with no periodontal disease. Anti- Prevotella intermedia IgG levels in both elderly patient groups were depressed compared to anti- P. intermedia levels in the young normal control subjects. Serum IgG antibody levels to six other plaque microorganisms did not differentiate between diseased and normal, elderly or young subjects. This data suggested that P. gingivalis was associated with periodontal disease in this elderly group of individuals and that those elderly individuals were able to respond with a normal IgG immune response.

Adult↗
PubMed1995

The effect of uterine contractions on the T/QRS ratio of the fetal electrocardiogram.

The aim of this study was to establish whether the T/QRS ratio of the fetal electrocardiogram (ECG) was influenced by uterine contractions. Data was collected from 55 women during labour using a purpose built computer which also measured background noise. The T/QRS ratio was measured on individual complexes and the measurements averaged. Measurements made during periods of excessive noise were excluded. The average T/QRS ratio during contractions showed a small but significant increase of 1.02% (principally in the second half of the contraction). The significance of this small increase is uncertain and for most fetuses the ratio would remain in the normal range during contractions. The higher T/QRS ratios, recorded in the noisy records, draw attention to the importance of accounting for this problem when fetal ECG data are reported.

Electrocardiography↗
PubMed1994

Relation between maternal haemoglobin and placental hormone concentrations in early pregnancy.

Environmental factors that influence placental development are of particular interest because of the reported association between adult hypertension, low birthweight, and large placental size. Maternal anaemia is one environmental factor that is associated with an increase in placental size at birth. We have examined the relation between haematological status and plasma concentrations of chorionic gonadotropin (hCG) and placental lactogen (hPL) in 175 women at about 10 weeks of pregnancy. There were significant negative correlations between maternal haemoglobin concentration and the levels of hCG (p = 0.03) and hPL (p = 0.02). Although 21% of women had low iron stores (ferritin < 13 micrograms/L), no relation was found between serum ferritin and the two placental hormones. There was no association between plasma volume (calculated from maternal weight and height) and hCG or hPL concentrations. We conclude that our observations reflect an influence of the maternal environment on the placenta. The fact that negative correlations with placental hormone concentrations exist across the normal haemoglobin range suggest that they reflect a normal aspect of placental development. We speculate that placental growth is, in part, determined by maternal factors that prevail before conception. One possibility is that these factors modify angiogenesis within the trophoblastic villi.

Adolescent↗
PubMed1994

Measurement of placental volume with real-time ultrasound in mid-pregnancy.

A new method to measure placental volume in mid-pregnancy using real-time ultrasound is described. The method is an adaptation of the B-mode parallel planimetric technique. The mean error of in vitro measurements on 45 balloons (mean volume 186 mL range: 88-485 mL) was -2.24 mL, standard deviation 6.76 mL. The error standard deviation of in vivo placental volume measurements was 16.4 mL (volume range: 173-396.5 mL). Placental measurements were made on 175 women between 14.3 weeks and 21.4 weeks, menstrual age (MA) and a smooth centile curve derived. Median volume increased linearly from 144 to 329 mL. The size of the ultrasound probe limits the technique to use before 20 weeks, MA.

Female↗