American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Nov 1996
Randomized Controlled Trial Comparative Study Clinical TrialPartitioning of inspiratory muscle workload and pressure assistance in ventilator-dependent COPD patients.
To investigate the mechanisms underlying ventilator-dependence in patients with chronic obstructive pulmonary disease (COPD), and to assess the effects of the combination of positive end-expiratory pressure (PEEP) and pressure-support ventilation (PSV) on inspiratory muscle effort, we investigated respiratory mechanics in eight ventilator-dependent COPD patients. The patients' breathing pattern, lung mechanics, diaphragmatic effort (PTPdi), diaphragmatic tension-time index (TTdi), and arterial blood gases were measured during both spontaneous breathing (SB) and ventilatory assistance consisting of PSV alone (15, 20, and 25 cm H2O) and PSV combined with a PEEP of 5 cm H2O (reducing PSV to 10, 15, and 20 cm H2O, respectively, to maintain equivalent inspiratory pressure). The different levels of ventilatory support were delivered in a randomized sequence. ⋯ Application of PEEP during PSV improved ventilatory assistance by further reducing the inspiratory effort (by 17% on average) and by ameliorating patient-ventilator interaction. We conclude that the excessive mechanical load, and in particular the high PEEPi, is the major determinant of ventilator-dependence in COPD patients. Application of PEEP improves the efficiency of PSV in unloading these patients' inspiratory muscles, and can sometimes improve patient-ventilator interaction.
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Am. J. Respir. Crit. Care Med. · Nov 1996
Comparative StudyProportional assist ventilation in acute respiratory failure: effects on breathing pattern and inspiratory effort.
Proportional assist ventilation (PAV) is a new mode of assisted ventilation which, by applying pressure in proportion to volume (volume assist, VA) and flow (flow assist, FA), should specifically reduce the inspiratory effort needed to overcome respiratory system elastance (Ers) and resistance (Rrs), respectively. The aims of this study were to determine (1) the effects of varying the level of VA on breathing pattern, inspiratory effort, and work of breathing, and (2) the interaction between VA and FA. In eight intubated patients with acute respiratory failure, four levels of VA (20 to 80% Ers) with and without a fixed amount of FA (approximately 50% Rrs) were evaluated. ⋯ VA decreased the elastic work of breathing (Wel) whereas resistive work (Wres) tended to increase so that the fall in total work (W/tot) was less than expected. At each VA setting, the addition of FA significantly reduced Wres and, as a result, Wtot. These results demonstrate that PAV can improve breathing pattern while reducing inspiratory effort by specifically decreasing Wel and Wres, and that VA and FA should be used together to optimize reductions in Wtot and the efficacy of assistance provided.
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Am. J. Respir. Crit. Care Med. · Nov 1996
Risk factors for pneumonia, and colonization of respiratory tract and stomach in mechanically ventilated ICU patients.
Risk factors for the development of ventilator-associated pneumonia (VAP) and colonization of the respiratory tract and stomach with enteric gram-negative bacteria (EGB) and Pseudomonadaceae were determined in 141 ventilated patients using univariate analysis and the Cox proportional hazards model. VAP was caused by EGB in 14 patients (10%), and by Pseudomonadaceae in 19 patients (13%). The duration of ventilation was a significant risk factor for VAP caused by EGB and Pseudomonadaceae, and for acquired colonization in oropharynx, stomach, and trachea with these species. ⋯ Preceding colonization of the orophayrnx and of the trachea with Pseudomonadaceae were risk factors for acquired colonization with these species in the stomach. Twelve patients with VAP (46%) and 38 without VAP (33%) died (p = 0.21). In conclusion, duration of ventilation and colonization of the upper respiratory tract are the most important risk factors for VAP caused by EGB or Pseudomonadaceae.
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Am. J. Respir. Crit. Care Med. · Nov 1996
Comparative StudyDescriptors of breathlessness in cardiorespiratory diseases.
The purposes of this study were: to examine the decriptors of breathlessness chosen by a large sample of patients with cardiorespiratory disease; to determine test-retest reliability of a patient's selection of the descriptors; and to assess whether a patient's recall of the experience of breathlessness is the same as that provoked by physical activity. Questionnaire data were collected at an initial visit for patients who complained of breathlessness and at a second visit in a subgroup of patients. A total of 218 patients who sought medical care for difficulty breathing due to one of seven different conditions were recruited from an outpatient pulmonary disease clinic at a university medical center. ⋯ We conclude that patients with different cardiorespiratory conditions experience distinct qualities of breathlessness. Patients' recall of their sensations of breathlessness is reliable and comparable to dyspnea with walking. Employing a questionnaire containing descriptors of breathlessness may help to establish a specific diagnosis and to identify mechanisms whereby a specific intervention relieves dyspnea.
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Am. J. Respir. Crit. Care Med. · Nov 1996
The impact of human immunodeficiency virus infection on drug-resistant tuberculosis.
Infection with human immunodeficiency virus (HIV) has been associated with increased rates of single- and multidrug-resistant (MDR) tuberculosis in the New York City area. In order to examine the relationship of HIV infection to drug-resistant tuberculosis in other selected regions of the United States, we established a registry of cases of culture-proven tuberculosis. Data were collected from sites participating in an NIH-funded, community-based HIV clinical trials group. ⋯ In multiple logistic regression analyses, HIV infection was shown to be a risk factor for drug-resistant tuberculosis, independent of geographic location, history of prior therapy, age, and race. We concluded that HIV infection is associated with increased rates of resistance to antituberculosis drugs in both the New York City area and other geographic areas. MDR tuberculosis is occurring predominantly in the New York City area and is highly correlated with HIV infection.