The American review of respiratory disease
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Am. Rev. Respir. Dis. · Aug 1985
Alveolar pressure magnitude and asynchrony during high-frequency oscillations of excised rabbit lungs.
One possible advantage of high-frequency ventilation (HFV) over conventional mechanical ventilation is that adequate pulmonary ventilation may be established with lower pressure swings. Pressure swings measured at the airway opening may not accurately reflect pressure swings in the alveoli, however. Furthermore, little is known about the synchrony of alveolar filling during HFV. ⋯ These results, when compared with earlier results on excised canine lungs, show that the amplification of PA during HFO is lung-size dependent. The observed degree of phase differences in pressure swings between peripheral alveolar locations implies substantial asynchrony of alveolar filling. This in turn suggests interregional gas transport as an important contributor to gas mixing during HFV.
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Am. Rev. Respir. Dis. · Aug 1985
Acute cigarette smoke exposure increases alveolar permeability in rabbits.
We measured lung clearance of aerosolized technetium-labeled diethylenetriamine pentaacetic acid (99mTcDTPA) as an index of alveolar epithelial permeability in rabbits exposed to cigarette smoke. Eighteen rabbits were randomly assigned to 3 equal-size groups: control, all smoke exposure (ASE), and limited smoke exposure (LSE). Cigarette or sham smoke was delivered by syringe in a series of 5, 10, 20, and 30 tidal volume breaths with a 20-min counting period between each subset of breaths to determine 99mTcDTPA biologic half-life (T1/2). ⋯ We observed a significant difference at 20 and 30 breath exposures between the control and ASE group mean values (% baseline) for T1/2, arterial blood pressure, and peak airway pressure. A combination of light and electron microscopy showed focal alveolar edema and hemorrhage in the ASE and LSE groups but no alveolar-capillary membrane damage. In summary, acute cigarette smoke exposure increases alveolar permeability as measured by 99mTcDTPA clearance, but there was no detectable ultrastructural alteration of the alveolar-capillary membrane.
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Am. Rev. Respir. Dis. · Aug 1985
Effects of aminophylline, isoproterenol, and neostigmine on hypercapnic depression of diaphragmatic contractility.
We investigated the effects of aminophylline, isoproterenol, and neostigmine on decreased diaphragmatic contractility induced by hypercapnia. With the thorax open, the animal receiving mechanical ventilation, and a plaster cast around the abdomen, constant length and geometry of the diaphragm were maintained. Contractility was assessed by analysis of transdiaphragmatic pressure (Pdi) generated during supramaximal phrenic stimulation at different frequencies. ⋯ Low and high doses of all 3 drugs significantly reversed this effect by improving peak twitch tension to values equal with or greater than control values (p less than 0.05). In addition, aminophylline (40 mg/kg) and neostigmine (0.25 and 1.0 mg) significantly increased time to peak tension of the twitch (p less than 0.05) and isoproterenol (5 and 20 micrograms/min) significantly decreased twitch half relaxation time (p less than 0.05). We conclude that aminophylline and neostigmine improve diaphragmatic contractility during hypercapnia by virtue of their potentiating effect on twitch amplitude, whereas isoproterenol does not increase contractility because the process underlying the decrease in twitch duration masks the effect of an improved twitch amplitude.
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Am. Rev. Respir. Dis. · Aug 1985
The effect of a gas leak around the endotracheal tube on the mean tracheal pressure during mechanical ventilation.
Infants requiring mechanical ventilation are usually intubated with uncuffed endotracheal tubes, which permit gas to leak between the tube and the trachea. This gas leak may alter the mean pressure transmitted to the trachea by changing the pattern of airway flow and modifying the resistive behavior of the endotracheal tube. To test this hypothesis, we measured mean tracheal pressure, gas flow through the endotracheal tube, and resistance of the tube in rabbits ventilated with and without a leak. ⋯ A ventilatory pattern of short inspiratory times and high peak pressures was associated with a proportionally greater decrease in mean tracheal pressure caused by the leak. These findings suggest that the mean proximal airway pressure, measured at the ventilator, may overestimate the mean tracheal pressure in the presence of a gas leak around the tube. Furthermore, the decrease in mean tracheal pressure caused by the leak may decrease oxygenation despite a constant mean proximal airway pressure.