Pediatric research
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Hereditary deficiency of mitochondrial HMG-CoA synthase (mHS, OMIM 600234) is a poorly defined, treatable, probably underdiagnosed condition that can cause episodes of severe hypoketotic hypoglycemia. We present clinical follow-up and molecular analysis of the two known mHS-deficient patients. The diagnosis of mHS deficiency is challenging because the symptoms and metabolite pattern are not specific. ⋯ Similarly, in purified cytoplasmic HS, which in contrast to purified human mHS is stable and can be studied in detail, the corresponding F-->L substitution causes a 10,000-fold decrease in V(max) and a 5-fold reduction in thermal stability. Patient 2 is a genetic compound of a premature termination mutation, R424X, and an as-yet uncharacterized mutant allele that is distinguishable by intragenic single nucleotide polymorphisms that we describe. Molecular studies of mHS are useful in patients with a suggestive clinical presentation.
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Thoracoabdominal asynchrony (TAA) and chest wall distortion (CWD) are commonly seen in preterm infants secondary to a highly compliant rib cage and poor compensation of distorting forces by inspiratory rib cage muscles. Continuous positive airway pressure (CPAP) reduces TAA and CWD by stenting the chest wall. We hypothesized that application of positive airway pressure only during inspiration and in proportion to an infant's inspiratory effort should have a similar but more pronounced effect than CPAP alone. ⋯ Esophageal pressure changes decreased only little with increasing gain. Chest wall excursion increased and abdominal movement decreased, indicating a redistribution of tidal volume between chest and abdomen. We conclude that proportional assist ventilation reduces TAA and CWD by generating a small increase in airway pressure that occurs in synchrony and in proportion to each inspiratory effort.
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Monitoring lung volume is important in the treatment of acute hypoxemic respiratory failure. However, there are no tools available for lung volume measurement to guide ventilator management during high-frequency oscillatory ventilation (HFOV) and during dynamic changes in conventional ventilation (CV). We studied the performance of a new respiratory inductive plethysmograph (RIP) with modified software. ⋯ We conclude that measurements of lung volume in term and preterm lambs by use of modified RIP correlate well with changes in mean airway pressure during HFOV, with static pressure volume curves and with changes in positive end-expiratory pressure during CV. We speculate that this technique may provide clinically useful information about changes in lung volume during HFOV and CV. However, evaluation of the precision and chronic stability of RIP measurements over prolonged periods will require further studies.
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Biography Historical Article
American Pediatric Society John Howland Award 1999: presentation to Abraham Morris Rudolph, MD(1).
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Acute right ventricular (RV) injury is commonly encountered in infants and children after cardiac surgery. Empiric medical therapy for these patients results from a paucity of data on which to base medical management and the absence of animal models that allow rigorous laboratory testing. Specifically, exogenous catecholamines have unclear effects on the injured right ventricle and pulmonary vasculature in the young. ⋯ Infusion of each catecholamine improved preload recruitable stroke work and peak negative derivative of the pressure waveform. Dobutamine and EP both decreased indices of pulmonary vascular impedance, whereas EP was the only inotrope that significantly improved transpulmonary vascular efficiency. Although all three inotropes improved systolic and diastolic RV function, only EP decreased input resistance, decreased pulmonary vascular resistance, and increased transpulmonary vascular efficiency.