Biomedical subjects

J M Bissonnette

Publications and source records attributed to J M Bissonnette.

67 records · Page 4Linked to original sources

PubMed1979

Placental diffusing capacity and its relation to fetal growth.

The placental diffusing capacity for carbon monoxide was measured in unanaesthetized monkeys (M. Mulatta). Maternal and fetal blood was sampled from chronically placed catheters while the mother breathed 50 or 100 parts per million of CO. Diffusing was calculated from the amount of CO taken up by the fetus divided by the partial pressure difference across the placenta, it averaged 0.646 plus or minus 0.062 (SEM) ml x min(-1) x torr(-1) x kg(-1) of fetal weight. The significance of this index of respiratory gas exchange in the monkey placenta is discussed with respect to previous measurements in other species and with respect to fetal growth.

Animals↗

PubMed1979

Glucose transfer across the intact guinea-pig placenta.

Experiments were carried out in anaesthetized pregnant guinea-pigs. Following the maternal injection of a bolus containing 14C-hexose and 3H2O, blood was sampled from the fetal umbilical vein during a single circulatory transit. A placental transfer index was calculated from the ratio of the tracers in the fetal whole blood divided by that in maternal plasma. The transfer index for D-glucose, 0.66 +/- 0.03 (SEM), greatly exceeded that for L-glucose, 0.013 +/- 0.004. Elevation of the maternal plasma D-glucose concentration, with unlabelled D-glucose, resulted in saturation of D-glucose transfer with an apparent Km of 1.2 x 10(-2) mol/l mean maternal plasma D-glucose. Phlorizin at maternal plasma concentrations of approximately 10(-3) mol/l inhibited D-glucose transfer by 40%. Phloretin did not affect D-glucose transfer at levels estimated to be 10(-4) mol/l. Specificity studies with substituted D-glucose analogues showed that alpha-methyl-D-glucoside is not transported by a facilitated pathway; 2-deoxy-D-glucose and 3-O-methyl-D-glucose share the D-glucose carrier and D-galactose has a partial affinity for the D-glucose carrier.

Animals↗

PubMed1978

Persistent pulmonary hypertension in the neonate: development of an animal model.

Chronic intrauterine hypoxia was induced in third-trimester lamb fetuses by daily embolization of the maternal side of the placenta with nonradioactive microspheres. After delivery at term, the chronically hypoxic fetuses had significantly increased pulmonary artery pressures when compared to nonhypoxic control measurements. This preparation appears to be a satisfactory model for experimental study of persistent pulmonary hypertension in the neonate.

Animals↗

PubMed1978

Gas exchange of the fertile hen's egg: components of resistance.

The resistance to diffusion of respiratory gases falls by 50% from day 10 to day 18 in the incubating fertile hen's egg (Temple and Metcalfe, 1970). We have calculated the change in the components of this resistance with respect to incubation age. The egg shell resistance remains unchanged. The chorioallantoic membrane (including capillary endothelium) resistance decreases dramatically from day 10 to day 14 and then remains relatively unchanged. The resistance offered by the blood is unchanged from day 10 to day 12, it decreases by day 14 due to an increase in oxygen capacity and continues to decline at days 16 and 18 because of the combined effects of a continued increase in oxygen capacity and an increase in capillary volume.

Allantois↗

PubMed1978

Pulmonary diffusing capacity in lambs during the early neonatal period.

A rebreathing method was used to make 53 measurements of pulmonary diffusing capacity (DLco) and functional residual capacity (FRC) in 17 newborn lambs during the first 2 days of life. DLco, FRC, and DLco/FRC all increased in studies made at 24--48 hr of age compared to those at 2--4 hr of age: DLco 0.86 +/- 0.18 to 1.52 +/- 0.09 ml/min/torr; FRC 37 +/- 10 to 60 +/- 8 ml and DLco/FRC 2.52 +/- 0.75 to 2.89 +/- 0.37 ml/min/torr/ml X 10(-2). DLco measured using 0.005% CO in the test gas was not different than that measured using 0.5% CO.

Animals↗

PubMed1977

Placental diffusing capacity for carbon monoxide in unanesthetized guinea pigs.

In unanesthetized pregnant guinea pigs 5-7 ml of maternal blood which had been equilibrated with carbon monoxide (CO) was reinfused into the sow's carotid artery. Three serial blood samples were withdrawn from the sow and a single terminal fetal sample obtained for determination of CO content and hemoglobin concentration. Transplacental CO uptake (VCO) was determined as the product of fetal blood CO content and fetal CO space (11.8% of fetal weight). Placental diffusing capacity (DPCO) was calculated by dividing VCO by the mean partial pressure difference between maternal and fetal blood. DPCO (ml-min(-1)/torr) increased significantly with gestational age: 45-50 days = 0.0413, 51-57 days = 0.1092 and 58-68 days = 0.1858. This increase paralleled fetal weight but was not related to placental weight.

Animals↗

PubMed1977

Placental diffusing capacities at varied carbon monoxide tensions.

To test the hypothesis that carbon monoxide transfer across the placenta is, in part, a facilitated process, we have looked for evidence of saturation kinetics for carbon monoxide. In eight pregnant ewes, fetal to maternal carbon monoxide transfer was examined in a preparation in which the fetal side of the placenta was perfused with blood. The carboxyhemoglobin concentrations on the fetal side of the placenta were varied from 4.8 to 70% in 23 measurements. At increased carbon monoxide tensions, the transfer from fetus to mother always decreased. The slope of log rate of carbon monoxide transfer vs. log partial pressure gradient across the placenta was significantly different from 1. Placental membrane diffusing capacity was calculated separately from total placental diffusing capacity which includes hemoglobin reaction rates and erythrocyte membrane diffusion. Placental membrane diffusing capacity decreased at increased carbon monoxide tensions. Placental permeability for urea did not change with increasing carbon monoxide tensions. These results are consistent with the hypothesis that carbon monoxide diffusion in the placenta is, in part, carrier mediated.

Animals↗

PubMed1976

Absence of fetal placental waterfall phenomenon in chronically prepared fetal lambs.

An electromagnetic flow sensor was placed on the distal fetal aorta (umbilical flow fraction 78.1 +/- 1.6 SEM, %), an inflatable occluder was tied around the umbilical cord, and catheters were placed in distal branches of an umbilical artery and vein, a uterine vein, and in the amniotic cavity. An inflatalbe occluder was tied around the vagina of some of the ewes. Control values 3 days after surgery were (mean +/- SE): fetal femoral artery pH, 7.37 +/- 0.01; umbilical blood flow, 186 +/- 14 ml-min-1 .kg fetus-1; fetal arterial blood pressure, 39 +/- 3 mmHg; and umbilical venous pressure, 7.4 +/- 1.0 mmHg (above intrauterine pressure). Fetal weight at autopsy was 3.1 +/- 0.3 kg, n = 11. Small increases in umbilical vein pressure caused immediate decreases in placental blood flow without decreases in fetal arterial blood pressure. The relation between venous pressure and umbilical blood flow at constant arterial pressure was that of an inert system, i.e., no evidence of a surrounding pressure (Starling resistor effect or waterfall phenomenon) could be found with increases in venous pressures of 2-40 mmHg. The results were not affected by increases in uterine vein pressure between 2 and 30 mmHg, nor by anesthesia and supine position of the ewe, nor by ganglionic blockade of the fetal ANS. It was concluded that surrounding pressures in the fetal placental circulation could not be demonstrated.

Animals↗

PubMed1975

Control of vascular volume in sheep umbilical circulation.

Vascular and extravascular volumes were measured using a single-injection, double-indicator technique, in a perfused umbilical circulation in which umbilical artery (Pfa) and umbilical vein (Pfv) pressures could be independently varied. At constant Pfv, when Pfa was raised from 25 to 35 mmHg, vascular volume increased 16.1 plus or minus 6 ml (mean plus or minus SD) from a control value of 113 plus or minus 38.3 ml. Extravascular volume increased 25.2 plus or minus 7.7 ml from 128 plus or minus 53.3 ml. During further increases in Pfa to 65 mmHg, vascular volume increased approximately 10 ml for each 10 mm Hg increment, but no change in extravascular volume occurred. At a constant Pfa when Pfv was raised to 15, 20, and 25 mmHg, vascular volume increased 12.2 plus or minus 3.6, 22.2 plus or minus 5.4, and 28 plus or minus 12.5 ml from the measurements at low Pfv. There was no increase in extravascular volume during elevation of Pfv. At the lower values of Pfa (25-35 mmHg) recruitment of previously unperfused channels and distension are seen. Over the higher ranges of Pfa change and during Pfv elevation there is distension of vascular bed.

Animals↗

PubMed1973