Chest
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We used flexible fiberoptic endoscopy to evaluate 87 patients with potential problems of the airway in a pediatric intensive care unit. Four different-sized bronchoscopes were used to perform 61 diagnostic laryngoscopic procedures, 35 diagnostic bronchoscopic procedures, and eight therapeutic bronchoscopic procedures. ⋯ Morbidity was minimal, and there was no death. Flexible fiberoptic endoscopy proved useful as a bedside technique for critically ill pediatric patients in whom evaluation of the airway in the operating room under general anesthesia would have been difficult.
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To evaluate available clinical methods (self ratings and questionnaire) for rating dyspnea, we (1) compared scores from the recently developed baseline dyspnea index (BDI) with the Medical Research Council (MRC) scale and the oxygen-cost diagram (OCD) in 153 patients with various respiratory diseases who sought medical care for shortness of breath; and (2) evaluated the relationships between dyspnea scores and standard measures of physiologic lung function in the same patients. The dyspnea scores were all significantly correlated (r = 0.48 to 0.70; p less than 0.001). Agreement between two observers or with repeated use was satisfactory with all three clinical rating methods. ⋯ Dyspnea scores were most highly related to spirometric values (r = 0.78; p less than 0.001) for patients with asthma, maximal respiratory pressures (r = 0.34 and 0.35; p less than 0.001) for patients with chronic obstructive pulmonary disease, and PImax (r = 0.51; p = 0.01) and FVC (r = 0.44; p = 0.03) for those with interstitial lung disease. These results show that: (1) the BDI, MRC scale, and OCD provide significantly related measures of dyspnea; (2) the clinical ratings of dyspnea correlate significantly with physiologic parameters of lung function; and (3) breathlessness may be related to the pathophysiology of the specific respiratory disease. The clinical rating of dyspnea may provide quantitative information complementary to measurements of lung function.
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Comparative Study
Work of breathing and airway occlusion pressure during assist-mode mechanical ventilation.
We determined the effect of varying ventilator tidal volume (VT) and inspiratory flow (V) on the inspiratory muscle work (WI) during assist-mode mechanical ventilation (AMV) in four healthy subjects. In another four subjects, under constant chemoreceptor input, we determined the responses of neuromuscular output as assessed by the mouth occlusion pressure (P0.1) to alteration in WI. During AMV, the inspiratory external work of breathing is partitioned between WI and ventilator work. ⋯ Although WI decreased with increasing ventilator V, P0.1 did not decrease significantly. We conclude that during AMV, both ventilator V and to a less extent ventilator VT determine W. In healthy subjects changes in WI do not affect P0.1.
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We evaluated measurements of oxygen saturation from four noninvasive pulse oximeters, and two conventional arterial oximeters. Simultaneous measurements were obtained on each instrument on three different occasions in five healthy subjects breathing gas with an FIO2 of 1.00, 0.50, 0.21, 0.17, 0.15, 0.13 and 0.11. ⋯ Precision was approximately 2 percent for all instruments except one conventional oximeter with a precision of 0.7 percent. In the clinically relevant range, the performance of the noninvasive pulse oximeters was similar to conventional oximeters using arterial samples.
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Comparative Study
Pressure support compensation for inspiratory work due to endotracheal tubes and demand continuous positive airway pressure.
We evaluated the use of pressure support to compensate for the added inspiratory work of breathing due to the resistances of endotracheal tubes and a ventilator demand-valve system for continuous positive airway pressure (CPAP). A mechanical model was used to simulate spontaneous breathing at five respiratory rates through 7-mm, 8-mm, and 9-mm endotracheal tubes with and without a ventilator demand CPAP circuit. Added work was measured as the integral of the product of airway pressure and volume during inspiration. ⋯ For each endotracheal tube and VT/TI, a level of pressure support (range, 2 to 20 cm H2O) was found which eliminated added work in the spontaneously breathing subject. This level correlated well with that predicted from the data derived using the mechanical model. We conclude that when adjusting for an endotracheal tube's diameter and VT/TI, pressure support can be used to compensate for the added inspiratory work due to artificial airway resistances.