Pediatric research
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We studied the activity of the diaphragm and of the genioglossus at the onset and at the end of obstructive sleep apnea in children. Seven children (mean age 46 months, range 15-87) with obstructive sleep apneas mainly due to enlarged tonsils were tested during natural sleep. ⋯ Compared to the preceding unoccluded breaths, genioglossus and diaphragm EMG data showed that 1) at the onset of obstructive apnea there was no significant decrease in genioglossus and/or diaphragm EMG, contrasting with published data for obese adults, and 2) at the end of obstructive apnea, significant preferential increase in genioglossus EMG, not related to the decrease in transcutaneous partial pressure of oxygen, was found as in obese adults. This study showed that different mechanisms may control the onset of obstructive apnea in children as compared to adults, whereas children and obese adults share the same preferential increase in genioglossus EMG at the end of obstructive apnea.
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Three to five measurements of fetal cardiac output and its distribution were made using radiolabeled microspheres in each of 12 sheep fetuses in whom fetal plasma insulin concentration was varied by exogenous infusion of insulin to the fetus. Blood concentrations of oxygen and glucose as well as blood gases, pH, hematocrit, and plasma insulin concentrations were also measured. Both fetal arterial oxygen content and whole blood glucose concentration fell as fetal insulin concentration rose. ⋯ As plasma insulin concentration rose, the percentage of the cardiac output distributed to the fetal heart and upper carcass increased; that distributed to the fetal brain, lungs, liver, stomach, intestines, and lower carcass remained unchanged; while that distributed to the kidneys, spleen, and placenta decreased. When expressed as a fraction of cardiac output, an additional 7% (from 39 to 46%) of the cardiac output was distributed to carcass over the range of insulin concentrations studied. Most of the increased portion of the fetal cardiac output distributed to the fetal carcass during hyperinsulinemia was accounted for by a decrease in the percentage of fetal cardiac output perfusing the placenta.
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Ten anesthetized, paralyzed adult cats were ventilated by high frequency chest wall compression (HFCWC) at 3, 5, 7, and 9 Hz by means of a single chamber cuff enclosing the thorax from the axillae to the xyphisternum. The effects of HFCWC in terms of gas exchange, end-expiratory lung volume, and respiratory system compliance were compared to conventional intermittent positive pressure ventilation (IPPV) (30 breaths/mn). HFCWC and IPPV were compared at three levels of matched end-expiratory airway pressure [continuous positive airway pressure (CPAP)/positive end-expiratory pressure/(PEEP) of 0, 2, and 5 cm H2O]. ⋯ Peak cuff pressures between 14 and 17 cm H2O generated oscillary tidal volumes between 4.5 and 2.1 ml/kg. The size of the oscillatory volume was significantly affected by increasing frequencies (decrease in tidal volume) and increasing levels of positive airway pressure (increase in tidal volume). We conclude that in cats with normal lungs, HFCWC can provide for normal gas exchange, provided that it is combined with low level CPAP in order to prevent the occurrence of airway closure associated with HFCWC alone.
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Comparative Study
Selective elevation of systemic blood pressure by epinephrine during sepsis-induced pulmonary hypertension in piglets.
In a piglet model of group B beta Streptococci (GBS)-induced pulmonary hypertension, we have determined hemodynamic responses to epinephrine (EPI) infusion in both the systemic and pulmonary circulations. Three groups of piglets (GBS + EPI, n = 6; GBS + placebo, n = 6; placebo, n = 6) were studied. GBS, infused intravenously at approximately 5 X 10(7) organisms/kg/min, reduced cardiac index and stroke volume index while elevating pulmonary artery pressure and pulmonary vascular resistance index. ⋯ Systemic acid/base status and PaO2 did not differ among piglets who received GBS + EPI, GBS alone, or placebo. Extrapolation of these data to human infants must be approached with extreme caution. However, selective elevation of systemic blood pressure may be a feasible strategy for some infants to impede right-to-left shunting of blood often associated with sepsis-induced pulmonary hypertension.
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The measurement of tidal volume during high-frequency jet ventilation is difficult due to the high-frequency components of the inspiratory flow. To validate tidal volume measured with a screen pneumotachograph placed on the expiratory limb, we simultaneously determined tidal volume with a body plethysmograph in seven anesthetized normal adult New Zealand rabbits before and after saline lung lavage. Four to six comparisons of tidal volume were obtained by varying peak inspiratory pressures at each combination of frequency (120, 240, and 480/min) and inspiratory to expiratory time ratio (1:1, 1:3, 1:5, 1:9). ⋯ There was unidirectional outward flow at the pneumotachograph during inspiration when both normal and saline lavaged lungs were being ventilated, suggesting a lack of gas entrainment. We conclude that a pneumotachograph on the expiratory limb may be used to measure tidal volume and gas entrainment in vivo during high-frequency jet ventilation. Determination of tidal volume may serve to optimize ventilator settings during high-frequency jet ventilations and facilitate an understanding of the mechanism involved in gas exchange.