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Doppler ultrasonography of the carotid arteries may be a useful technique for helping to determine brain death in children. Doppler ultrasonography is a kind of ultrasound imaging that analyzes the shift in ultrasonic waves. Seventeen children aged one month to five years with severe brain damage underwent Doppler ultrasonography of the carotid arteries. Seven children were diagnosed as being brain dead by multiple clinical criteria including an EEG. Five of these seven had an abnormal Doppler pattern indicative of brain death. No child who was not diagnosed as brain dead displayed this pattern. The two additional children not identified as brain dead with Doppler ultrasonography had the determining EEG several hours later, suggesting that there may have been further deterioration after the Doppler study. Given the consequences of the diagnosis of brain death, Doppler scans should only be performed and interpreted by skilled vascular ultrasound specialists.

Networks distribute energy, materials and information to the components of a variety of natural and human-engineered systems, including organisms, brains, the Internet and microprocessors. Distribution networks enable the integrated and coordinated functioning of these systems, and they also constrain their design. The similar hierarchical branching networks observed in organisms and microprocessors are striking, given that the structure of organisms has evolved via natural selection, while microprocessors are designed by engineers. Metabolic scaling theory (MST) shows that the rate at which networks deliver energy to an organism is proportional to its mass raised to the 3/4 power. We show that computational systems are also characterized by nonlinear network scaling and use MST principles to characterize how information networks scale, focusing on how MST predicts properties of clock distribution networks in microprocessors. The MST equations are modified to account for variation in the size and density of transistors and terminal wires in microprocessors. Based on the scaling of the clock distribution network, we predict a set of trade-offs and performance properties that scale with chip size and the number of transistors. However, there are systematic deviations between power requirements on microprocessors and predictions derived directly from MST. These deviations are addressed by augmenting the model to account for decentralized flow in some microprocessor networks (e.g. in logic networks). More generally, we hypothesize a set of constraints between the size, power and performance of networked information systems including transistors on chips, hosts on the Internet and neurons in the brain.

We evaluated the effect of elevated airway pressure on the validity of intravascular pressure obtained in the distal inferior vena cava (IVC) as a measure of central venous pressure (CVP) in a group of children receiving mechanical ventilation. The IVC pressure correlated well with CVP in the patients without abdominal distention, but the disparity was wider in those with abdominal distention. Elevated mean airway pressure or positive end-expiratory pressure had no effect on the relationship of IVC to CVP. (J PEDIATR1995;126:961-5)

ANF is an exciting, newly discovered hormone that has significant potential for furthering our understanding of the complex interactions involved in fluid and electrolyte balance. In addition to effects on water and salt balance, it is a potent vasodilator, as well as inhibitor of renin, angiotensin II, aldosterone, and vasopressin. ANF is primarily produced in the atria, but production in the brain is suggestive of action as a neuropeptide and as a potential regulator of CSF production. Receptors are found throughout the heart, vascular tree, kidney, adrenal gland, and brain. The stimulus for release appears to be atrial stretch, which may be secondary to intravascular fluid changes. It causes hemoconcentration and may be an important regulator of interstitial fluid distribution as well as capillary permeability. Patients with CHF and renal failure have been found to have elevated levels that decrease in response to treatment. Potentially, it may be useful as a therapeutic agent in acute renal failure, CHF and other fluid disturbances.

Presents letters to the editor referencing articles and topics discussed in previous issues of "National Review." Article on the Middle East by the author of the book "Witness"; Review of "By Love Possessed"; Comment about the connection of freedom and Christianity.