Chest
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We quantified the mechanical work of breathing in six normal subjects during assisted mechanical ventilation. Using two volume-cycled ventilators of different design, we investigated the influence of minute ventilation (VE) and machine settings of trigger sensitivity and flow during CO2-driven hyperventilation to moderate and high levels (12-24 L/min). Work estimates were derived from plots of esophageal and airway pressure against inflation volume. ⋯ During assisted ventilation the subject expended energy equivalent to 33-50 percent of the work of passive inflation, even under the most favorable conditions of VE, sensitivity and flow. Under the least favorable conditions of VE, sensitivity and flow, the subject's inspiratory work of breathing substantially exceeded the energy needed by the ventilator to inflate the passive thorax. These observations imply that exertion of the respiratory muscles continues throughout inflation during assisted mechanical ventilation and call attention to the possibility that inappropriate selection of ventilatory mode or machine settings may contribute to respiratory muscle fatigue and dyspnea.
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A mechanical lung was used to evaluate the pressure and flow characteristics of four demand and two continuous flow intermittent mandatory ventilation (IMV) systems. The amount of negative pressure required to initiate inspiratory flow and peak expiratory resistance were measured. The inspiratory pressure required to initiate flow in the demand mode was also compared to pressures generated in the assist mode. ⋯ There are major differences in the flow and pressure characteristics among demand and continuous flow IMV systems. Systems that impose high inspiratory elastic threshold loads and expiratory flow resistive loads may have a deleterious effect on the mechanics of breathing, and thereby limit weaning success and eventually impair the recovery of certain patients in respiratory failure. The basic methodology, especially the simple technique of inserting an aneroid manometer in line next to a patient's ET tube, for measuring proximal negative inspiratory force (NIF test) can be easily applied to any and all ventilators at any practitioner's individual institution.
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Comparative Study
Comparison of forceps used for transbronchial lung biopsy. Bigger may not be better.
Transbronchial lung biopsy is a useful procedure to obtain an alveolar specimen in the evaluation of diffuse lung infiltrates. Large forceps (cup and alligator) are expected to result in larger specimens and improve diagnostic yield. ⋯ Small and large cup forceps provided equally good results; however, the large open end of the alligator forceps often prevented distal passage through narrowing airways, engaging proximal bifurcating bronchial wall and cartilage rather than lung parenchyma. Small and large cup forceps are more likely to obtain the desired alveolar specimen.
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One hundred young adults with acute pneumonia were prospectively studied to determine the impact of the transtracheal aspiration (TTA) Gram stain on immediate management. Sputum and TTA interpretations by staff and housestaff were compared. After a management plan was elected based on sputum Gram stain interpretation, the TTA was evaluated and the final plan chosen. ⋯ In most cases, paired sputum and TTA Gram stain were both read correctly or incorrectly. When differences occurred, sputum interpretations were as likely to be correct as were TTA interpretations. The TTA Gram stain offered no advantage over sputum Gram stain in the initial management of acute pneumonia in this young adult military population.
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With increasing interest in reducing the cost of oxygen therapy, we recently designed an oxygen-conserving cannula. It reduces the oxygen supply flow necessary to achieve adequate oxygen saturation, but because it requires the use of a reservoir situated under the nose, some patients find it obtrusive. We therefore designed a similar system but displaced the reservoir away from the face and onto the anterior chest wall where it could be hidden from view by the patient's clothing. ⋯ The saturation achieved by the PNC at 0.5 L/min was equivalent to that achieved by the SNC at 1.8 L/min. We conclude that the PNC provides effective oxygen delivery to patients at supply flows substantially less than the SNC. The device is aesthetically acceptable to patients and its widespread use in patients requiring chronic oxygen therapy could bring about significant financial savings.