American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Nov 1996
Mechanisms for diaphragmatic fatigue following high-intensity leg exercise.
Diaphragmatic fatigue can occur following high-intensity leg exercise to exhaustion. Exercise-induced diaphragmatic fatigue may be due to changes in the milieu to which the diaphragm is exposed (i.e., acidosis, etc.) and/or to increases in diaphragmatic activity during exercise. The purpose of this study was to determine whether changes in milieu are responsible for exercise-induced diaphragmatic fatigue. ⋯ In both groups, a significant lactic acidosis developed during exercise and the magnitude of this acidosis was similar for the two groups. The adductor pollicis muscle (a nonexercising muscle during cycle exercise) is exposed to the same milieu as the diaphragm. Because adductor pollicis twitch force was unchanged postexercise while twitch Pdi fell, changes in milieu cannot be solely responsible for exercise-induced diaphragmatic fatigue.
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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
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
Comparative StudyImproved arterial oxygenation after oleic acid lung injury in the pig using a computer-controlled mechanical ventilator.
We compared computer-controlled mechanical ventilation programmed for biologic variability of respiratory rate (RR) and tidal volume (VT) with conventional intermittent positive-pressure ventilation (IPPV) in an oleic acid (OA) lung injury model. Seventeen pigs were ventilated with an Ohio 7000 anesthesia ventilator. Minute ventilation (VE) was adjusted to maintain PaCO2 at 30 to 35 mm Hg at baseline and was not altered further. ⋯ By 180 min, respiratory system compliance (Crs) was significantly lower in the control group. The wet:dry lung weight ratios were greater in the control group. Thus, in a porcine model of OA lung injury, computer-controlled mechanical ventilation, which is programmed for biologic variability, resulted in improved blood oxygenation without increasing mean airway pressures when compared with conventional IPPV.