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Biomedical subjects

A B Lewis

Publications and source records attributed to A B Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1985

Update on infections involving permanent pacemakers. Characterization and management.

From January, 1974, to December, 1983, 75 patients with infections related to permanent pacemakers were successfully treated. Demographic characterization, mode of presentation, types of infecting organisms, potential predisposing factors, significance of a retained infected pacemaker lead, and various medical and surgical treatment methods were analyzed. Likely infecting organisms depended on the mode of presentation and the time of the infection. Dermatologic diseases accounted for a significant number of secondary infections. Removal of the entire infected pacing system was required for eradication of infection in 74 of 75 patients. In 31 patients, the infected system was removed at the same time that the new system was implanted. In 26 patients, a two-stage procedure was used that included a period of temporary pacing between explantation of the old system and implantation of the new. No difference in complications or incidence of reinfection was found between these two groups. Infections occurring within 2 weeks after operation accounted for 15% of the cases. In these patients, Staphylococcus aureus was the most common organism. In patients with later infections, Staphylococcus epidermidis was the most common.

Adult↗
PubMed1984

Cardiovascular and catecholamine responses to successive episodes of hypoxemia in the fetus.

The cardiovascular and plasma catecholamine responses to successive episodes of hypoxemia were evaluated in 5 fetal lambs in utero (greater than or equal to 0.7 gestation). Fetal heart rate (HR) and blood pressure (BP) were monitored continuously and specimens obtained for arterial blood gases, plasma norepinephrine (NE) and epinephrine (E) during a baseline control period, during each of 5 hypoxemic episodes and during 4 intervening recovery periods. Hypoxemia (PO2 = 9.8-13.7 Torr) was produced by gradual, controlled constriction of the umbilical cord by a silicone rubber cuff. HR fell from 176 +/- 9 beats/min (means +/- SE) to between 105 +/- 11 and 119 +/- 5 (p less than 0.01) and BP increased from 71 +/- 2/49 +/- 1 mm Hg to between 79 +/- 2/55 +/- 2 and 90 +/- 3/66 +/- 3 (p less than 0.01) during the hypoxic periods. There was no evidence of waning in the magnitude of the hypertensive response over the course of successive hypoxemic episodes. Baseline plasma NE and E rose from 278 +/- 65 and 28 +/- 8 pg/ml, respectively, to between a mean of 4,982 and 17,060 pg/ml for NE and 2,217 to 9,471 pg/ml for E. No attenuation in the rise of NE and E was observed throughout the 5 hypoxic periods. Thus, the late gestation fetus appears capable of sustaining appropriate cardiovascular and catecholamine responses to multiple successive episodes of hypoxemia.

Animals↗
PubMed1984

Fetal cardiovascular and catecholamine responses to hypoxemia after chemical sympathectomy.

Chemical sympathectomy was performed in fetal lambs in utero by daily intravenous administration of 6-hydroxydopamine (6HD) until a total dose of 60-70 mg/kg was reached. The completeness of adrenergic denervation was confirmed by the absence of any cardiovascular response to tryamine infusion. Baseline plasma catecholamine concentrations in normoxemic, sympathectomized fetuses were slightly higher than controls but the differences were not statistically significant. The concentration of norepinephrine (NE) was 313 +/- 73 pg/ml after 6HD administration compared with 259 +/- 25 pg/ml in control animals. Similarly, the concentration of epinephrine (E) was 39 +/- 15 pg/ml (6HD) versus 21 +/- 4 pg/ml (control). These mildly elevated catecholamine levels were accompanied by a small but significant increase in resting blood pressure (BP) (P less than 0.05). Heart rate (HR), however, was no different from control. Hypoxemia induced a marked increase in plasma catecholamines in control animals (NE, 2416 +/- 419 pg/ml and E, 2017 +/- 749 pg/ml) along with hypertension and bradycardia. Sympathectomized fetuses maintained a profound NE response to hypoxemia (NE, 1550 +/- 261 pg/ml) but a significant reduction in peak E response was observed (E, 244 +/- 42 pg/ml, P less than 0.05). HR and BP responses to hypoxemia were generally similar to control animals though there appeared to be a brief 1-3 min lag period between the nadir of the bradycardia and the peak of the BP response. We conclude that the generalized chemical sympathectomy after 6HD administration in the fetal lamb in utero is useful in evaluating the interaction of the autonomic nervous system and adrenal medullary function on the regulation of the fetal cardiovascular system.

Animals↗
PubMed1984

Sibling correlations for cranial measurements from serial radiographs.

Sibling correlations are presented for nine craniofacial measurements from lateral cephalometric radiographs of participants in the Fels Longitudinal Study of Growth and their siblings. Because the data were collected serially, measurements on sibs at the same age can be compared at one-year intervals. Sibling correlations are generally lowest during the first year of life and highest as adulthood is approached, but no interpretable pattern is established during the intervening years. Most of the correlations are significantly greater than zero, and many exceed 0.5, the value expected for a completely heritable polygenic trait. This suggests that common sibling environment contributes to sibling resemblance for craniofacial dimensions in our sample.

Adolescent↗
PubMed1983

Evaluation and surgical treatment of pulmonary atresia and intact ventricular septum in infancy.

The initial surgical approach to the infant with pulmonary atresia and intact ventricular (PA-IVS) is to establish an adequate source of pulmonary blood flow and, when possible, relieve right ventricular (RV) outflow obstruction. The selection of patients for pulmonary valvotomy, alone or in combination with a systemic-pulmonary arterial shunt, depends on the presence of an RV outflow tract and the adequacy of the RV chamber. To evaluate the size of the RV cavity in PA-IVS, an RV index (RVI) was developed using biplane angiographic measurements of the sum of the tricuspid valve annulus and the RV inflow and the RV outflow tracts. The RVI was normalized by relating it to the aortic diameter (Ao) at the diaphragm (RVI/Ao). The RVI/Ao was 13.5 +/- 1.4 in 20 control subjects and only 7.3 +/- 2.6 in 26 PA-IVS patients (p less than 0.001), and was within the normal range in only two of the 26. Since 1976, pulmonary valvotomy plus a Blalock-Taussig shunt has been performed in 10 infants, with one death. Serial cardiac catheterizations in five of nine survivors demonstrated substantial RV growth in all, with the RVI/Ao increasing from an average of 8.0 to 12.5. In contrast, patients who underwent a shunt alone had no change in RV cavity size. We conclude that pulmonary valvotomy may be performed successfully in most PA-IVS patients, but usually must be combined with a systemic-pulmonary shunt. In a small minority of patients, a normal RV cavity, as evidenced by an RVI/Ao greater than or equal to 11, appears to be sufficient to sustain adequate pulmonary blood flow after valvotomy alone. The RVI/Ao ratio is a simple method of quantitatively evaluating RV cavity size and is helpful in planning the initial surgical approach for these infants.

Cardiac Catheterization↗
PubMed1982

A factor analysis of cranial base and vault dimensions in children.

Lengths within the cranial base and vault were measured in cephalometric radiographs of 220 boys and 177 girls ranging in age from 0 to 15 years; all these children are participants in The Fels Longitudinal Growth Study. The present study is based on mixed longitudinal data derived from 1640 radiographs for boys and 1260 radiographs for girls. Factor analysis was applied separately for boys and girls for each age group; i.e., 0-3, 4-6, 7-9, 10-12, and 13-15 years. For the 0-3 year age group, two factors were extracted in each sex, whereas four factors were extracted in the rest of the age groups. The factor structures are similar in the three older age groups of boys (7-9, 10-12, and 13-15 years). The first four factors for these groups are labelled, respectively: cranial vault size, posterior cranial base length, presphenoid length, and basisphenoid length. The order of the third and fourth factors is reversed in the 7-9 year olds. For girls, the factors extracted were also the same in both the 7-9 and 10-12 year age groups, even though the order of factors was different between age groups; i.e., anterior cranial base length, cranial vault size, basisphenoid length, and basioccipital length. Differential growth rates among cranial base dimensions probably cause changes in factor patterns. Obliteration of the spheno-occipital synchondrosis is suggested as the mechanism responsible for the change of factor pattern in the girls. closure of this synchondrosis would have occurred too late to affect the patterns in boys.

Adolescent↗
PubMed1982

Growth of the mandible during pubescence.

Annual cephalometric radiographs of 67 children were used to analyze mandibular growth during pubescence. Annual increments were calculated for articulare-gonion (Ar-Go), articulare-gnathion (Ar-Gn) and gonion-gnathion (Go-Gn). Pubertal spurts were recorded for annual increments within two years of peak height velocity (PHV) that exceeded the immediately preceding increment by at least 1 mm (corrected for enlargement). Such spurts in mandibular dimensions are common but not universal. They were more common in the boys, but occurred about 1.5 years earlier in the girls. They tended to be larger in boys, although the mean increments in the two sexes were similar before and after the spurts. First pubertal spurts usually occur before PHV, but there was considerable variation in this relationship. Almost all first pubertal spurts occur after ulnar sesamoid ossification and before menarche. The variability of their timing was less in relation to PHV than in relation to skeletal age, menarche or ulnar sesamoid ossification. It can be desirable to determine whether a spurt has occurred in an individual patient. For this purpose, Greulich-Pyle skeletal age may be only slightly more meaningful than chronological age, and neither is sufficiently precise for many clinical applications.

Adolescent↗
PubMed1982

Plasma catecholamine responses to hypoxemia in fetal lambs.

The plasma catecholamine responses to hypoxemia were evaluated in 10 chronically catheterized fetal lambs in utero from 0.77 gestation to term using a highly sensitive radioenzymatic assay. Hypoxemia was produced by gradual constriction of the umbilical cord by an implanted cuff occluder. Fetal carotid arterial PO2 fell from 23 to 12 torr and was accompanied by an exponential increase in catecholamine concentration. Plasma norepinephrine (NE) increased from 256 +/- 31 to 1,888 +/- 384 pg/ml while epinephrine rose from 24 +/- 5 to 1,159 +/- 433 pg/ml. Fetal arterial PO2 returned to normal within 1 min of deflating the cuff occluder. Simultaneously, NE and epinephrine levels declined rapidly but, nevertheless, remained mildly elevated compared to controls. There was no maturational change in baseline NE levels during the last quarter of gestation, where as epinephrine was significantly higher after 125 days than between 115 and 125 days (37 +/- 7 vs. 16 +/- 6 pg/ml, p less than 0.05). However, maturation had no significant effect upon the magnitude of the epinephrine or NE response to hypoxemia. In conclusion, the late gestation fetal lamb is capable of manifesting a profound catecholamine response to hypoxemia which appears to play a major role in the compensatory cardiovascular adjustment to severe stress.

Animals↗
PubMed1981

Side effects of therapy with prostaglandin E1 in infants with critical congenital heart disease.

The case reports of 492 infants with critical congenital cardiac disease treated with prostaglandin E1 (PGE1) were reviewed to determine the nature and incidence of intercurrent medical events. Forty-three percent of the infants had at least one such event, but only half of these were related to PGE1 and the majority required only minor changes in management. Cardiovascular events were the most common (18% incidence), with cutaneous vasodilation and edema occurring more frequently during intraaortic infusion than during i.v. infusion. Central nervous system events were reported in 16% of the patients. Respiratory depression was reported in 12%, and was particularly common in infants weighing less than 2.0 kg at birth (42%). Hematologic, infectious and renal events appeared for the most part to be unrelated to PGE1. The overall mortality (excluding 19 patients with hypoplastic left-heart syndrome) was 31%; the mortality for the patients with critical coarctation or interruption of the aortic arch was nearly twice that for the cyanotic infants (50% vs 27%). No death was attributed to PGE1 administration. During infusion of PGE1, arterial blood pressure and respiratory activity should be monitored carefully and appropriate supportive steps taken if hypotension or respiratory depression occurs. The development of fever or jitteriness may require reduction of the infusion rate and, in view of the possible increased incidence of infections, the prophylactic use of antibiotics is recommended.

Bacterial Infections↗
PubMed1981

Recovery of left ventricular function following discontinuation of anthracycline chemotherapy in children.

Echocardiographic evaluation of left ventricular (LV) performance was performed in 41 children during and following anthracycline chemotherapy. Prior to treatment LV function was normal in all patients; LV shortening fraction was 35.2 +/- 0.7% and percent of predicted velocity of circumferential fiber shortening was 110 +/- 20%. However, the indices measured concurrent with the final anthracycline dose (mean = 308 +/- 16 mg/sq m) demonstrated a significant decline in LV function. The LV shortening fraction had decreased to 29.5 +/- 0.8% and percent of predicted velocity of circumferential fiber shortening decreased to 94 +/- 4% (P less than .01). Four of the eight patients with evidence of significant LV dysfunction had received thoracic or upper abdominal irradiation. Following cessation of anthracycline therapy, LV function improved within one to six months and had returned to normal in all but two patients, both of whom received irradiation. Echocardiography is useful for the identification of anthracycline-induced LV dysfunction. With discontinuation of further anthracycline administration the functional decline in LV performance appears to be reversible.

Adolescent↗
PubMed1980

Cardiovascular responses to autonomic blockade in hypoxemic fetal lambs.

The cardiovascular responses of 11 fetal lambs in utero to hypoxemia were evaluated before and after autonomic blockade. Hypoxemia was produced by lowering the maternally inspired oxygen or by progressive constriction of the umbilical cord by a cuff occluder. The animals were studied serially from 112 days' gestation to term. Fetal carotid arterial pO2 fell from 24 to 12 torr and was accompanied by a 35% decline in heart rate and 32% rise in blood pressure. Parasympathetic blockade with atropine produced a 114% increase in heart rate in the hypoxemic fetuses compared to 26% in the normoxemic controls. Pretreatment with atropine prevented the hypoxemia-induced bradycardia without altering the hypertensive response. alpha-Adrenergic blockade resulted in a 22% decrease in blood pressure in the hypoxemic group, three times greater than the controls. Pre-hypoxemia alpha-blockade prevented the hypertension without affecting the fall in fetal heart rate. It is concluded that fetal bradycardia in response to hypoxemia is due to a direct increase in parasympathetic activity rather than secondary to a hypertension-induced baroreflex. The alpha-mediated increase in systemic vascular resistance and blood pressure may be a compensatory mechanism to maintain placental blood flow despite the decline in combined ventricular output.

Animals↗
PubMed1978

Administration of prostaglandin E1 in neonates with critical congenital cardiac defects.

Prostaglandin E1 was administered to 12 neonates and young infants in whom pulmonary or systemic blood flow was entirely or significantly dependent upon persistent patency of the ductus arteriosus. Nine neonates responded favorably to PGE1 infusion; their mean age was 2.8 days. Three infants who failed to respond were 10 days, 14 days, and 9 weeks of age, respectively. Six neonates with right ventricular outflow obstruction had a mean increase in arterial PO2 of 136% following administration of PGE1. In three patients in whom systemic flow was ductus dependent, PGE1 infusion was followed by improvement in arterial blood pressure, peripheral perfusion, and urine output. Complications included pyrexia, vasodilatation, and myoclonic jerks (or focal seizures). Three side effects were easily reversible by decreasing the infusion rate or altering the site of administration. PGE1 is a highly effective agent in stabilizing critically ill neonates with ductus dependent congenital cardiac lesions.

Blood Pressure↗
PubMed1978

Cardiovascular responses to autonomic blockade in brain-injured fetal lambs.

The cardiovascular responses to autonomic blockade were investigated in 15 late-gestation fetal lambs in utero. 4 animals had normal brains and 11 had hydranencephalic-like cerebral injury secondary to bilateral carotid artery obstruction (BCO). Following atropine administration, heart rate increased only 0.7 +/- 0.7% in the BCO lambs compared to 25.7 +/- 5.2% in the controls. alpha-Blockade with phentolamine resulted in a small decrease in systolic (2.2 +/- 0.8%) and diastolic (1.8 +/- 1.4%) blood pressure, and beta-blockade with propranolol produced a small decrease in heart rate (2.5 +/- 0.8%) as compared to control fetuses. Post mortem examination revealed extensive destruction of the cerebrum but normal hypothalamus and brain stem. These data suggest that supramedullary modification of autonomic cardiovascular control involves the cerebrum.

Animals↗