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Biomedical subjects

M Eng

Publications and source records attributed to M Eng.

At least 37 records · Page 2Linked to original sources
PubMed1986

Erythropoietic reserve in marrow-transplanted dogs.

The effect of marrow transplantation on erythropoiesis was studied in three normal dogs (T0), three irradiated dogs receiving compatible marrow (T1), and three irradiated dogs (T2) who donated their marrow to a recipient animal and then at a later date underwent a marrow transplant from the initial marrow recipient. Plasma iron turnover was measured (a) under basal conditions, (b) after plasma iron was elevated by iron infusion, and (c) after hemolytic anemia had been produced by phenylhydrazine. Basal plasma iron turnover in T0, T1, and T2 animals averaged 1.3, 1.0, and 1.3 mg/dl whole blood/day. Turnover of the three groups increased to 7.1, 6.2, and 6.4 mg/dl whole blood/day after the induction of anemia by phenylhydrazine. These values were converted from the transferrin saturation present at the time of the measurement to the calculated turnover at 100% saturation, thereby expressing the maximum capacity of tissues to assimilate iron. After this correction, the calculated maximum uptake was shown to be increased over basal by 3.7, 4.0, and 3.8 times. To validate this approach, an additional comparison was made between baseline turnovers at elevated levels of plasma iron and anemic animals at similarly elevated plasma iron levels. The increment of the three groups was shown to be 3.7, 3.9, and 4.0 times basal. These studies illustrate the use of a refined method of ferrokinetic evaluation of erythropoiesis and indicate that the proliferative reserve in transplanted animals is unimpaired.

Anemia↗
PubMed1985

Transferrin saturation, plasma iron turnover, and transferrin uptake in normal humans.

The relationship between plasma iron, transferrin saturation, and plasma iron turnover was studied in 53 normal subjects whose transferrin saturation varied between 17% and 57%, in 25 normal subjects whose transferrin saturation was increased by iron infusion to between 67% and 100%, and in five subjects with early untreated idiopathic hemochromatosis whose transferrin saturation was continually elevated to between 61% and 86%. The plasma iron turnover of all of these subjects ranged from 0.45 to 1.22 mg/dL whole blood/d. The mean values for the above-mentioned three groups were 0.71 +/- 0.17, 1.01 +/- 0.11, and 1.01 +/- 0.13 mg/dL whole blood/d, respectively. Most of this variation, estimated at 72% by regression analysis, was due to a direct relationship between transferrin saturation and plasma iron turnover. This effect was attributed to a competitive advantage of diferric over monoferric transferrin in delivering iron to tissues. This was confirmed by the demonstration of a more rapid clearance of diferric as compared to monoferric transferrin in an additional group of eight normal subjects. Calculations were made of the amount of transferrin reacting with membrane receptors per unit time. Allowance was made for the noncellular (extravascular) exchange and for the 4.2:1 preference of diferric over monoferric transferrin demonstrated in vitro. The amount of iron-bearing transferrin leaving the plasma to bind to tissue receptors for 53 subjects with a transferrin saturation between 17% and 57% was 71 +/- 13; for 25 subjects with a saturation from 67% to 100%, 72 +/- 12; and for five subjects with early idiopathic hemochromatosis, 82 +/- 11 mumol/L whole blood/d. There were no significant differences among these groups. These studies indicate that while the number of iron atoms delivered to the tissues increases with increasing plasma iron and transferrin saturation, the number of iron-bearing transferrin molecules that leave the plasma per unit time to bind to tissue receptors is relatively constant and within the limits studied, independent of transferrin saturation.

Adult↗
PubMed1982

Effect of transfused reticulocytes on iron exchange.

A animal model was developed whereby reticulocyte-rich blood was introduced into normal rats by exchange transfusion. Measurements of plasma iron turnover was made at similar plasma iron concentrations before and after exchange transfusions. High reticulocyte blood obtained from animals rendered iron deficient by diet or by treatment with phenylhydrazine resulted in a mean increase of 86% in internal iron exchange, while the plasma iron turnover was unaffected by exchange with normal red cells. Since iron input from reticuloendothelial cells could have increased due to breakdown of transfused cells, iron absorption was also measured. Within 1 hr and for a least 6 hr after exchange with high reticulocyte blood, mean absorption in six groups of animals was increased over control animals by 50%-130%. The increased plasma iron turnover and absorption was not mediated by a decrease in plasma iron or an increase in unsaturated iron-binding capacity. Indeed, a higher plasma iron and transferrin saturation augmented the movement of iron into the plasma from iron-donating tissues. It is proposed that the donation of iron by transferrin in some way immediately facilitates the procurement of more iron by transferrin.

Animals↗
PubMed1978

Plasma radioiron kinetics in man: explanation for the effect of plasma iron concentration.

The plasma iron turnover was measured in 19 normal subjects. A correlation was found between plasma iron concentration and plasma iron turnover. In addition to the turnover of 55Fe at normal plasma iron concentration (predominantly monoferric transferrin), a second turnover in which the labeled plasma was saturated with iron (to produce predominantly diferric transferrin) was studied with 50Fe. It was demonstrated that diferric transferrin had a greater rate of iron turnover but that the distribution between erythroid and non-erythroid tissues was unchanged. It was concluded that plasma iron turnover is dependent on the monoferric/diferric transferrin ratio in the plasma but that the internal distribution of iron is unaffected.

Adult↗
PubMed1978

Aortic valve mechanics. Part II: a stress analysis of the porcine aortic valve leaflets in diastole.

The stress analysis of the porcine aortic valve leaflets in diastole at 80 mm Hg pressure in-vitro is presented. Incorporation of local geometrical asymmetry, material inhomogeneity, anistropy and non-linearity are applied. The stress theory used is a modified form of the thin membrane stress theory for a homogeneous linearly elastic and orthotropic lamina. Modifications are made so that the Hooke's law constitutive equations of stress may be applied to the inhomogeneous, non-lineary elastic and orthotropic thin (membrane) aortic valve leaflets. Stress calculations are made on the premise that the valve is in pre-transition (i.e. low elastic modulus) in the circumferential direction and post-transition (i.e. high elastic modulus) in the radial direction. It is shown that sigmaCIR less than 1 gm/mm2, and for most of the noncoronary leaflet, 0 less than sigmaRAD less than 30 gm/mm2. The areas of highest stress concentrations are in the areas of mutual leaflet coaptation near the Node of Arantii. A progressive increase of radial stresses from the sinus-annulus edge toward the node is observed.

Animals↗
PubMed1976

A comparison of the effects of the inhalation of 4% and 8% fluroxene in the pregnant primate.

A comparison was made of the effects of inhalation of 4% fluroxene (n = 5) and 8% fluroxene (n = 5) in pregnant monkeys. Measurements of maternal arterial blood pressure, heart rate, cardiac output, total peripheral resistance, uterine blood flow, fetal heart rate and arterial blood pressure, and maternal and fetal blood gas levels were made. Inhalation of 4% fluroxene for 20 minutes produced little change in maternal hemodynamics and was well tolerated by the fetus. Fluroxene 8% inhaled for a similar 20-minute-period produced a significant decrease in maternal blood pressure (--27%), total peripheral resistance (--32%), and uterine blood flow (--27%) and lowered the level of maternal fetal exchange.

Anesthesia, Inhalation↗
PubMed1975

Respiratory function in pregnant obese women.

Lung volumes and other ventilatory variables were measured in 10 women with a mean age of 28 years, a mean height of 163 cm., and weights which were 50 to 140 per cent above the normal. Measurements were made during the last trimester of pregnancy and after the second month postpartum. Mean values of lung volumes in liters during these two time periods were: vital capacity (VC), 3.7 and 3.92; expiratory reserve volume (ERV), 0.79 and 0.94; functional residual capacity (FRC), 2.06 and 2.14; and forced expiratory volume at one second (FEV1) 3.2 and 3.3. Mean blood gas values were as follows: pH, 7.44 during both times; PaCO2, 29.7 and 35 torr; standard bicarbonate, 22 and 28.8 mEq; base excess, -4.2 and 0.03 PaO2 breathing air, 85 and 86 and breathing 100 per cent oxygen, 527 and 515 torr; AaDO2, 162 and 167 torr. We conclude that, with the exception of FRC, pregnant obese women who are 50 to 140 per cent overweight develop respiratory changes similar to those seen in normal-weight gravidas. These findings suggest that obesity of this magnitude does not exaggerate changes in ventilation induced by pregnancy as generally believed. Why in this obese population the decrease in FRC during pregnancy did not occur to the same degree as that seen in normal-weight gravidas cannot be defined from our study. Evidence is presented for a ventilation/perfusion imbalance in obese subjects which is not corrected during pregnancy.

Adult↗
PubMed1975

Respiratory depression in newborn monkeys at Caesarean section following ketamine administration.

Ketamine, currently being evaluated as an obstetric anaesthetic agent, is said to provide analgesia without depression of the protective airway reflexes or depression of the respiratory or cardiovascular systems. We have studied the effects of ketamine on the uterine blood flow, the foetus and the newborn in five monkeys (Macaca nemistrina). Uterine blood flow, (UBF) was measured by the steady-state infusion technique using tritiated water as the indicator. All of the variables were measured during a control period and again at 10 and 90 min after the administration of ketamine in doses of 2 mg/kg in three monkeys or 1 mg/kg in two. Maternal respiration was maintained at normal physiological levels without significant variation. The maternal mean arterial pressure (MAP), cardiac output (CO), and stroke volume (SV) did not change significantly, but heart rate (HR) did increase significantly following the injection of ketamine and remained increased for the duration of the study. UBF, a-v oxygen difference, and the oxygen consumption of the uterus and its contents remained stable throughout. During the intrauterine period the foetus did not seem to be affected by the two doses of ketamine. However, the three newborn monkeys delivered of the mothers who had reveived ketamine 2 mg/kg had profound respiratory depression. This was not seen in the two infants delivered from mothers receiving 1 mg/kg. Others have shown that neonatal depression is dose- and time-related. We conclude that ketamine should be administered to obstetric patients in small single doses or by continuous infusion in very low concentrations.

Anesthesia, Obstetrical↗
PubMed1975

Maternal and fetal responses to halothane in pregnant monkeys.

Maternal cardiac output, blood pressure, heart rate, fetal blood pressure, heart rate and respiratory blood gases, and uterine blood flow were measured in six pregnant monkeys during halothane-nitrous oxide and oxygen anesthesia and compared to theses same parameters observed during nitrous oxide and oxygen anesthesia. Halothane 1.5% was associated with a decrease in maternal arterial pressure (54%), heart rate (10%), cardiac output (17%), total peripheral resistance (40%), and uterine blood flow (38%). Mean fetal heart rate decreased 18% and mean fetal blood pressure 22%. These changes in fetal hemodynamics were probably related to a direct depression of the fetal cardiovascular system and its usual compensatory mechanism as well as the fetal asphyxia secondary to the decrease in uterine blood flow.

Anesthesia, General↗