The American review of respiratory disease
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Am. Rev. Respir. Dis. · Sep 1991
Effect of weight loss on upper airway collapsibility in obstructive sleep apnea.
Previous investigators have demonstrated in patients with obstructive sleep apnea that weight reduction results in a decrease in apnea severity. Although the mechanism for this decrease is not clear, we hypothesize that decreases in upper airway collapsibility account for decreases in apnea severity with weight loss. To determine whether weight loss causes decreases in collapsibility, we measured the upper airway critical pressure (Pcrit) before and after a 17.4 +/- 3.4% (mean +/- SD) reduction in body mass index in 13 patients with obstructive sleep apnea. ⋯ Moreover, decreases in Pcrit were associated with nearly complete elimination of apnea in each patient whose Pcrit fell below -4 cm H2O. In contrast, no significant change in DBR and a minimal reduction in Pcrit from 5.2 +/- 2.3 to 4.2 +/- 1.8 cm H2O (p = 0.031) was observed in the "usual care" group. We conclude that (1) weight loss is associated with decreases in upper airway collapsibility in obstructive sleep apnea, and that (2) the resolution of sleep apnea depends on the absolute level to which Pcrit falls.
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Am. Rev. Respir. Dis. · Sep 1991
Moment analysis of a multibreath nitrogen washout based on an alveolar gas dilution number.
A common method for analyzing a multibreath nitrogen washout (MBNW) is to perform moment analysis and derive the mean dilution number (MDN). A homogeneously mixed alveolar space with zero series dead space (VD = 0) will always result in a MDN = 1, regardless of breathing pattern. A higher MDN implies more inhomogeneity. ⋯ Compared with the MDN, the AMDN showed a significantly wider separation between clinical groups. Also, the AMDN demonstrated an increased variability within both sick groups versus a decrease in the healthy group. We conclude that the AMDN is superior to the MDN because of its decreased sensitivity to breathing pattern but increased sensitivity to degree of disease.
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Am. Rev. Respir. Dis. · Sep 1991
Effects of positive end-expiratory pressure on alveolar recruitment and gas exchange in patients with the adult respiratory distress syndrome.
The effects of different levels of positive end-expiratory pressure (PEEP) (zero to 15 cm H2O) on the static inflation volume-pressure (V-P) curve of the respiratory system and on gas exchange were studied in eight patients with the adult respiratory distress syndrome (ARDS). Alveolar recruitment with PEEP was quantified in terms of recruited volume, i.e., as difference in lung volume between PEEP and zero end-expiratory pressure (ZEEP) for the same static inflation pressure (20 cm H2O) from the V-P curves obtained at the different PEEP levels. ⋯ The results suggest that: (1) in some patients with ARDS the V-P curves determined on ZEEP exhibit an upward concavity reflecting progressive alveolar recruitment with increasing inflation volume, and PEEP results in alveolar recruitment (range of recruited volume at 15 cm H2O of PEEP: 0.11 to 0.36 L); (2) in other patients with ARDS the V-P curves on ZEEP are characterized by an upward convexity, and PEEP results in a volume displacement along this curve without alveolar recruitment and with enhanced risk of barotrauma; (3) the PEEP-induced increase in arterial oxygenation is significantly correlated to the recruited volume but not to the changes in static compliance. The shape of the static inflation V-P curves on ZEEP allows the prediction of alveolar recruitment with PEEP.
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Am. Rev. Respir. Dis. · Sep 1991
Comparative StudyHuman neutrophil elastase and elastase/alpha 1-antiprotease complex in cystic fibrosis. Comparison with interstitial lung disease and evaluation of the effect of intravenously administered antibiotic therapy.
In cystic fibrosis (CF), extracellular lung matrix is progressively damaged, neutrophils invade the air spaces, and activated neutrophils may release large amounts of neutrophil elastase (NE). Although alpha 1-antiprotease (alpha 1-AP) binds and inactivates NE and is the major antielastase of the lower respiratory tract, antielastase defenses may be overwhelmed in CF, leading to progressive lung damage. To determine whether the ability of alpha 1-AP to neutralize NE is impaired in CF, we compared NE activity in bronchoalveolar lavage (BAL) fluid and human neutrophil elastase/alpha 1-antiprotease (NE/alpha 1-AP) complex in both BAL fluid and peripheral blood serum from patients with CF, normal volunteers, and patients with interstitial lung disease. ⋯ Although in interstitial lung disease there was a significant correlation between increased NE/alpha 1-AP complex in BAL or peripheral blood and the degree of neutrophil influx, NE/alpha 1-AP complex was disproportionately low in CF BAL compared with significantly elevated values in serum. These data suggest that in CF, alpha 1-AP-mediated defense against free NE in the lower respiratory tract is significantly impaired, and high levels of uncomplexed, enzymatically active, NE are present in CF respiratory secretions. To determine whether intravenously administered antipseudomonal antibiotic therapy for exacerbations of CF lung disease diminished the amount of free NE in respiratory secretions, we used BAL to investigate the effect of such therapy on neutrophils and NE in patients with CF colonized with pseudomonads.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. Rev. Respir. Dis. · Sep 1991
Effects of positive end-expiratory pressure, lung volume, and inspiratory flow on interrupter resistance in patients with adult respiratory distress syndrome.
Although it has been shown in normal subjects that airway resistance changes significantly with changes in lung volume and inspiratory flow, no studies have as yet examined these phenomena in patients with adult respiratory distress syndrome (ARDS). The effect of positive end-expiratory pressure (PEEP) on airway resistance in ARDS also is unknown. ⋯ This procedure was carried out at four levels of PEEP (0, 5, 10, and 15 cm H2O). We found that (1) at constant inflation volume, Rint,rs did not change significantly with increasing flow; (2) at constant inflation flow, Rint,rs showed an initial decrease followed by a distinct rise with increasing lung volume; (3) on average, PEEP did not significantly change Rint,rs measured during baseline ventilation; and (4) this latter finding occurred because patients behaved differently with application of PEEP, depending on their degree of lung inflation: Rint,rs measured close to full inflation almost invariably exhibited a rise, but values obtained at lower volumes exhibited the characteristic decrease of Rint,rs with increasing inflation volume.