American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Jun 1994
Comparative StudyEffects of inspired carbon dioxide on ventilation-perfusion matching in normoxia, hypoxia, and hyperoxia.
We studied the effect of low concentrations (2 to 4%) of inspired CO2 on gas exchange and ventilation-perfusion (VA/Q) relationships in healthy normocapnic anesthetized dogs during constant mechanical ventilation by the multiple inert gas elimination technique (MIGET). One group was studied at normal tidal volumes (12 to 14 ml/kg) and rates (13 to 15/min) in normoxia, and the other in mild hyperoxia (FIO2 = 0.50) and hypoxia (FIO2 = 0.15). In normoxic dogs there were progressive increases in arterial PO2 and reductions in the alveolar-to-arterial PO2 and arterial-to-mixed expired PCO2 differences in response to increases in FICO2. ⋯ In the second group, the effects of 3% inspired CO2 were of comparable magnitude in both mild hypoxia and hyperoxia. In this group (taking hyperoxic values as baseline), there were improved gas exchange and less VA/Q heterogeneity with inspired hypoxia, both with and without inspired CO2. In contrast to the effects of added inspired CO2, improved VA/Q matching with hypoxia was characterized by reductions in both log SDV and log SDQ.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Jun 1994
ReviewDeterminants of susceptibility to cigarette smoke. Potential roles for neuroendocrine cells and neuropeptides in airway inflammation, airway wall remodeling, and chronic airflow obstruction.
There is a subgroup of cigarette smokers who are more susceptible than others to the deleterious effects of cigarette smoke and to chronic airflow obstruction. The study of histopathologic and physiologic differences between these "susceptible" smokers and "resistant" smokers, who do not develop clinically significant airflow obstruction, may lead to better understanding of host factors that determine individual susceptibility to cigarette smoke. This report puts forth the hypothesis that individual differences in number or function of pulmonary neuroendocrine cells may play an important role in determining whether cigarette smokers develop chronic airflow obstruction and perhaps other smoking-related disorders. In this context, pulmonary neuroendocrine cells and bombesin-like peptides are discussed, emphasizing those aspects most relevant to the pathobiologic consequences of cigarette smoking.
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Am. J. Respir. Crit. Care Med. · Jun 1994
Randomized Controlled Trial Comparative Study Clinical TrialLong-term effects of two different ventilatory modes on oxygenation in acute lung injury. Comparison of airway pressure release ventilation and volume-controlled inverse ratio ventilation.
A total of 18 patients with acute lung injury (ALI) were sequentially ventilated with two different modes of mechanical ventilation, each applied for a period of 24 h: (1) volume-controlled inverse ratio ventilation (VC-IRV), (2) airway pressure release ventilation (APRV). The individual sequence of both ventilatory modes was randomized. Ventilatory minute volume was adjusted for a PaCO2 of 35 to 45 mm Hg at the beginning of the study during the first ventilatory mode and then kept constant within preset limits. ⋯ During APRV AaDO2/FIO2 and venous admixture improved significantly with time after more than 8 h (AaDO2/FIO2: 487 versus 414 mm Hg; p < 0.01; venous admixture: 20.6 versus 13.9%; p < 0.01; medians of onset versus end). The improvement was significantly different between both ventilatory modes (p < 0.01). We conclude that this indicates a progressive alveolar recruitment over time during ventilation with APRV.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Jun 1994
Soluble TNF receptors (TNF-sR55 and TNF-sR75) in lung allograft recipients displaying cytomegalovirus pneumonitis.
Two distinct types of tumor necrosis factor receptors (TNF-R) have been identified (TNF-R55 and TNF-R75). Both TNF-R also exist in soluble forms (TNF-sR), resulting from the release of the extracellular domains (TNF-sR55 and TNF-sR75). TNF-sR may play an important role in vivo as they can bind to TNF alpha and prevent ligand binding to the cellular TNF-R, thus acting as naturally occurring inhibitors of TNF alpha. ⋯ Serum TNF alpha concentration was low in case of rejection or in control subjects (< 20 pg/ml). Conversely increased levels of TNF alpha were detected in the serum of six out of the 12 patients with CMV pneumonitis (p < 0.03 versus rejection and control subjects). Ganciclovir treatment of CMV pneumonitis led to a dramatic decrease of TNF alpha, TNF-sR55, and TNF-sR75 serum levels.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. J. Respir. Crit. Care Med. · Jun 1994
Comparative StudyExtracorporeal carbon dioxide removal technique improves oxygenation without causing overinflation.
Extracorporeal CO2 removal combined with low frequency positive pressure ventilation (ECCO2R-LFPPV) improves gas exchange and decreases peak pressures, respiratory rates, and tidal volumes in animals and in humans. Recent evidence suggests that pulmonary barotrauma results from lung overinflation rather than from high pressures. This study was to test the hypothesis whether ECCO2R-LFPPV could improve gas exchange without causing lung overinflation, despite the use of higher levels of PEEP, when compared with conventional mechanical ventilation. ⋯ By contrast, no evidence of persistent lung overinflation could be detected by either static P-V curves or dynamic measurements in nine of 11 patients who were treated by ECCO2R-LFPPV. The two remaining patients had severe airway obstruction because of bleeding, and they remained ventilated with persistent risk of barotrauma. We conclude that ECCO2R-LFPPV improves gas exchange without causing lung overinflation in a majority of patients with ARDS.