Craig P. Black

Development and Metabolism during Hypoxia in Embryos of High Altitude Anser indicus versus Sea Level Branta canadensis Geese

The yolk-free body mass, the mass of selected organs, the rates of oxygen consumption, and the air cell gas tensions were measured throughout incubation in embryos of the bar-headed goose, Anser indicus, and the Canada goose, Branta canadensis. The embryo mass for both species increased exponentially with incubation time to a stage just prior to pipping when growth appeared to stop. The rates of oxygen consumption for the embryos paralleled the rate of growth for the first 40%-50% of the increase in embryo mass, followed by a period when the rate of oxygen consumption plateaued at a value of 43.9 ± 0.7 cm³ O₂/h for the embryos of the Canada goose and 39.1 ± 1.7 cm³ O₂/h for the embryos of the bar-headed goose. The oxygen tensions in the air cell decreased with time concomitant with the increase in oxygen consumption to a value of 96.3 ± 2.0 torr for the Canada goose and 88.0 ± 1.0 torr for the bar-headed goose. The lower air cell oxygen tensions in the bar-headed goose reflect a lower eggshell permeability and smaller egg size. When acutely exposed to hypoxic hypoxia, the normoxic embryos of the bar-headed goose were able to maintain rates of oxygen consumption at significantly lower oxygen tensions than were the embryos of the Canada goose. However, the embryos of the Canada goose were able to acclimate to incubation under conditions of hypoxic hypoxia as evidenced by a shift to the left in the oxygen tension necessary to reduce the rate of oxygen consumption.

Influence of incubation water content on oxygen uptake in embryos of the Burmese python (Python molurus bioittatus)

Flexible-shelled reptilian eggs exchange water via two routes; 1) diffusive water vapor loss through shell interstices and 2) liquid water imbibition from incubation substrate in response to a water potential gradient. Uptake of liquid water may result in the filling of some of the shell interstices which would in turn increase shell O2 diffusion resistance. We measured whole-egg mass changes, water vapor conductance (\({G_{{H_2}O}}\)), O2 consumption, trans-shell \({P_{{O_2}}}\) gradient, incubation period, and hatchling weights in four groups of Burmese python (Python molurus bivittatus) eggs incubated in substrates with estimated water potentials of −360, −220, −130 and −80 kPa respectively. O2 consumption among the four groups did not differ significantly throughout incubation. Trans-shell \({P_{{O_2}}}\) gradients measured during the periods of maximum O2 consumption varied from 34 ± 6 (s.e.) torr in eggs incubated in the driest substrate to 64 ± 9 torr in eggs incubated in the wettest substrate, and O2 conductance values calculated from trans-shell \({P_{{O_2}}}\) and O2 consumption data were only about one-tenth of that predicted from \({G_{{H_2}O}}\). Thus, the incubating Burmese python egg has a functional water layer in the shell, and the embryos are subject to hypoxia comparable to that observed in developing chicken embryos. This does not appear to compromise tissue O2 delivery, however, because hatchling weights and O2 consumption are not adversely affected by increased incubation substrate water content.

Plastic Bronchitis in Children

Cast or plastic bronchitis (PB) is an unusual disorder that is rarely encountered in children. Plastic bronchitis is characterized by widespread formation of casts in the tracheobronchial tree with partial or complete airway obstruction. The pathologist may receive bronchial casts that have been removed by bronchoscopy for gross and histopathologic analysis. We describe two children with PB in the setting of an apparent lower respiratory tract infection, where the bronchoscopic removal of major cast segments was associated with a favorable outcome. Patients’ clinical and radiographic features and gross anatomic and histopathologic characteristics of casts are presented.

DEFINING POLYCYTHEMIA: A REAPPRAISAL

The first cases of neonatal polycythemia were described over 25 years ago. To date, controversy still exists as to what critical level of hematocrit (hct) should be utilized to define this syndrome. The most common definition has been a venous hct of 65% or greater. Values as low as 60% or as high as 70% have also been suggested. In addition, the relationship between polycythemia and hyperviscosity is poorly described. We re-evaluated the definition of polycythemia based on neonatal symptoms and long-term outcome at 1-2 yrs of age and evaluated the relationship between hct and viscosity. The subjects were infants referred for further screening because of high hcts. Viscosity measurements were made using the methods and standards of Gross et al. (1973). Viscosity and venous hct were coded for 225 infants. Follow-up was available on 158 (70%). Among infants studied, elevated viscosity measurements were not limited to those with venous hct of 65% or greater. Eleven percent of infants had an abnormal viscosity, although hct was less than 65%. The enrollment mechanism did not permit identification of the lowest hct at which abnormal viscosity could be found. Infants whose venous hcts were between 65 and 69% were as likely to have neonatal symptoms as infants with hcts between 60 and 64%. Infants with markedly abnormal hcts (>69%) had similar neonatal courses. Infants with symptoms in more than one organ system varied from 26-30% of each group. Similarly, outcome measurements were not different among the three groups. No evidence of long-term sequelae was found in 44-65% of the children. In conclusion, determinations of a critical level of hct does not fully account for the effects of neonatal hyperviscosity. It is also likely that additional factors influence peripheral blood flow and must be considered when attempting to predict which infants with elevated hcts will have neonatal symptoms or long-term sequelae.

835 RELATIONSHIP BETWEEN DEXTROSTIX, PLASMA AND WHOLE BLOOD GLUCOSE IN THE RANGE 0 - 100 MG|[sol]|DL

Two laboratory measurements frequently made in the newborn period are Dextrostix (Ames) and hematocrit; yet the relationship between Dextrostix, plasma glucose and whole blood glucose values has not been described. Umbilical vein and peripheral vein blood samples were studied for whole blood, plasma and red cell glucose (YSI Model 23A) and were compared to values obtained using the Dextrostix read by eye. Dextrostix predicted whole blood glucose (R = .83, slope of regression = 1.1, not significantly different from 1.0). Plasma glucose was underestimated by the Dextrostix (R = .64, slope = .70 in the range measured in vivo (30-100 mg.dl−1). Measurements in vitro were carried out using umbilical vein blood during incubation with and without added glucose to determine the relationship between plasma and whole blood glucose at the lower glucose levels. No statistically significant difference was observed between plasma and whole blood glucose at these low levels. Dextrostix reflected both of these levels. No clinically significant error would have been made using the Dextrostix.In vivo, red cell glucose fell more quickly than plasma glucose at values greater than 100. Below that level, plasma and red cell glucose fell at similar rates. However, preliminary data from infants with polycythemia/hyperviscosity reveal red cell glucose values lower than would be predicted by the plasma glucose value alone.