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Biomedical subjects

G Gregory

Publications and source records attributed to G Gregory.

At least 37 records · Page 2Linked to original sources
PubMed1991

Maximizing the informational content of vectorial data in the electrocardiogram.

Scalar electrocardiograms contain a great deal of vectorial data. The informational content of these data can be maximized by treating each angle as a point on a plane whose distance from the origin is equal to the magnitude of its vector. These points can be resolved into their horizontal and vertical coordinates. The coordinates are linear values and can therefore be subjected to standard statistical methodology.

Adolescent↗
PubMed1989

Sexual maturity rating: a marker for effects of pubertal maturation on the adolescent electrocardiogram.

The heart is known to participate in the adolescent growth spurt. A peak increase in transverse diameter coincides with peak height velocity during pubertal maturation. The effects of maturation on the adolescent ECG were explored using sexual maturity rating (SMR) as a marker. ECGs were obtained from 751 patients 8 to 20 years of age seen for routine physical examinations. A total of 33 standard ECG measures were analyzed, with subjects separated by sex and SMR. Different trends were seen in boys and girls during the course of maturation for the majority of R and S wave amplitude measurements. Lower mean amplitudes were seen consistently in more mature (SMR 4 and 5) girls than less mature girls and all boys. The clinical implication of these findings is illustrated by analysis of the sum of RV5 and SV2, one of the criteria for left ventricular hypertrophy, by sex and SMR. No significant difference in the sum is noted for boys across five SMR groups. Girls, in contrast, show a steady decrease in the sum with advancing maturation. These trends are not as clearly shown when subjects are grouped by broad chronologic age ranges, as had been the practice in developing current adolescent ECG tables. These findings suggest that development of standard ECG tables in which SMR and sex have been taken into account might enhance interpretation during adolescence.

Adolescent↗
PubMed1988

The relationship between sexual maturity rating, age, and increased blood pressure in adolescents.

Blood pressure values are known to vary with age and body size. The effect of sexual maturity was explored in 746 patients in an adolescent clinic. Systolic blood pressure for boys and girls showed an increase with a change from Tanner stage 2 to 3. Diastolic blood pressure did not increase. Both systolic and diastolic blood pressures showed a weight effect that was generally maintained within the Tanner stages. The gradual increase in blood pressure for large groups of adolescents would appear to be the result of the aggregate increase in size (weight) resulting from the asynchronous growth spurts of individuals studied. Consequently, those individuals with a strikingly early or late onset of maturation may have erroneous interpretations of their blood pressure. As biologic outliers, the borderline hypertensive who matures early may be overidentified, while the late maturer might go unrecognized.

Adolescent↗
PubMed1988

Field independence and simultaneous processing in preschool children.

The present study examined the relations between field independence and simultaneous processing of preschool children as measured by the Preschool Embedded Figures Test (PEFT) and subtests from the Kaufman Assessment Battery for Children (K-ABC), respectively. Data partially supported the assumption that field-independent children would perform significantly better on simultaneous processing tasks in general. Significant age and sex differences on field-independence/field-dependence and simultaneous-processing abilities were found among the embedded figures task and selected portions of the K-ABC. Analysis of embedded figures further indicated age differences, but no significant sex differences.

Achievement↗
PubMed1987

Effects of bicarbonate on arterial and brain intracellular pH in neonatal rabbits recovering from hypoxic lactic acidosis.

We used 31P spectroscopy to determine whether administration of a neutralizing dose of bicarbonate in rabbits with lactic acidosis caused a paradoxical brain intracellular acidosis. Ten 10- to 16-day-old rabbits were anesthetized with 0.75% halothane/oxygen and their lungs mechanically ventilated. Metabolic acidosis was induced by decreasing PaO2 to 25 to 35 mm Hg for 1 to 2 hours until the base deficit was 10 to 15 mEq/L. Cerebral ischemia was prevented by maintaining arterial blood pressure at +/- 20% of control value with a venous infusion of epinephrine. Hypoxia was then terminated by administration of 100% oxygen, which was continued for the remainder of the study. After 15 minutes 100% oxygen, 5 mEq/kg 4.2% bicarbonate was administered to five animals; 5 minutes later the same dose was repeated. Control rabbits were given equal volumes of saline solution. In all animals, arterial pH decreased from 7.43 +/- 0.06 to 7.25 +/- 0.08 (SE) during hypoxia, and brain intracellular pH from 7.22 +/- 0.06 to 7.09 +/- 0.09 (SE). Both pH values remained low during reoxygenation. Bicarbonate administration normalized arterial pH (7.41 +/- 0.03), whereas treatment with saline solution did not (7.23 +/- 0.01, P less than 0.05). PaCO2 rapidly increased by 10 mm Hg in the bicarbonate group, and remained elevated; it was unaffected by saline solution administration. Brain intracellular pH in the bicarbonate group increased by 0.12 U over 40 minutes, but intracellular pH in the saline solution group decreased 0.05 pH U (P less than 0.05) over the same period. We conclude that administering a total dose of 10 mEq/kg sodium bicarbonate to neonatal rabbits recovering from hypoxic lactic acidosis increases arterial pH, brain intracellular pH, and PaCO2; it does not produce paradoxical intracellular acidosis in the brain.

Acidosis, Lactic↗
PubMed1986

Acidemia impairs autoregulation of cerebral blood flow in newborn lambs.

Cerebral blood flow (CBF) and autoregulation of cerebral blood flow were assessed in newborn lambs before and after inducing metabolic acidemia. CBF was measured by xenon washout and autoregulation by the change in CBF after increasing mean arterial pressure (MAP) 30 per cent with 0.02 per cent phenylephrine hydrochloride. After surgical preparation, stabilization, and demonstration of the presence of autoregulation, six lambs received 10 mg X kg-1 of lactic acid intravenously over 30 minutes. Arterial pH decreased from 7.35 +/- 0.01 (mean +/- SEM) during the control period to 6.96 +/- 0.02 (p less than 0.01) at the end of the lactic acid infusion. Arterial blood gases, MAP's, and heart rates did not change. Prior to lactic acid infusion, CBF before and after raising MAP were 53 +/- 3 ml/100 g/min and 56 +/- 4 ml/100 g/min respectively. After lactic acid infusion, CBF increased from 54 +/- 2 ml/100 g/min to 62 +/- 3 ml/100 g/min (p less than 0.05) following phenylephrine induced rise in MAP. Five control lambs showed no significant change in any of these variables, including CBF, over the same time periods. These data indicate that metabolic acidosis per se does not alter CBF, but that metabolic acidosis impairs cerebral vascular autoregulation in hyperoxic lambs. Similar changes in human neonates might result in intracranial haemorrhage.

Acidosis↗
PubMed1986

Impairment of cerebral blood flow autoregulation in the newborn lamb by hypoxia.

Autoregulation of cerebral blood flow has been demonstrated in both fetal and newborn animal models under normoxic conditions. In the present experiments we have attempted to define the minimal hypoxic insult which impairs autoregulation in the newborn lamb and to assess the time to recovery. We measured cerebral blood flow by the intracarotid 133Xe method in fifteen 4- to 9-day-old lambs and tested autoregulation of cerebral blood flow by increasing blood pressure 20-30% with phenylephrine. Autoregulation was tested in the control state and at successive time intervals after an hypoxic stress (PaO2 of 30 mm Hg) of 10 or 20 min. We found that cerebral autoregulation was abolished after 20 min of hypoxia and recovered within 7 h. Since this model identifies the minimal hypoxic insult to abolish autoregulation it might be used to study means to protect autoregulation or to hasten its recovery after hypoxia.

Animals↗
PubMed1985

Indium-111 oxine platelet survival in dogs: effect of doxorubicin and Dacron grafts.

The cytotoxic chemotherapeutic agent doxorubicin was found to acutely decrease platelet survival times in beagle dogs as determined using platelets labeled with [111In]oxine. Recovery was rapid, with platelet survival times returning to normal within 3 wk of cessation of treatment. Doxorubicin (1.5 mg/kg i.v. every 3 wk for a total of four doses) also delayed the return of platelet survival times to normal when given to beagle dogs following placement of thoracoabdominal aortic Dacron grafts. It is not known whether or not this may have clinical significance.

Animals↗
PubMed1982

Preservation of fetal brain blood flow relative to other organs during hypovolemic hypotension.

The asphyxiated newborn is particularly vulnerable to hypotension, which contributes to hypoxic brain damage by reducing cerebral perfusion. During asphyxia, cerebral blood flow (CBF)( is pressure passive, that is, CBF autoregulation is abolished. It is important to know if the nonasphyxiated fetus and newborn are similarly vulnerable to hypotension. In the present study, we have measured acute responses of organ blood flow to a hypovolemic/hypotensive stress in the normoxic near term sheep fetus. Changes in brain flow were compared to changes in other organs. Eight chronically prepared fetal lambs were studied. Organ blood flows were measured by the microsphere technique during a control period, after a 20% blood volume reduction, and again after reinfusion of that volume. Hypovolemia was accompanied by a 21% decrease in blood pressure and a 4 torr increase in PCO2; after reinfusion blood pressure increased 16% above control. Control measurements of organ perfusion were similar to those reported by other investigators. Cardiac output and flow to all organs, with the exception of the brain, were reduced 30-56% during hypovolemia. Brain blood flow was insignificantly reduced by 9%. If a correction is applied for the increase in PCO2, CBF corrected to control PCO2 would have have been significantly reduced by 18%. After reinfusion, flow to all organs increased to near control levels. We conclude that the normoxic fetal lamb shows evidence of CBF autoregulation, and is able to preserve relative constancy of CBF within a blood pressure range of +/- 20% of normal. However, the evidence presented in this study suggests that autoregulation may be less effective in response to a hypotensive stress, even though CBF is better preserved than flow to most other organs.

Animals↗