American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Jun 1997
Comparative StudyComparison of assisted ventilator modes on triggering, patient effort, and dyspnea.
In 11 ventilator-dependent patients, we undertook a head-to-head comparison of patient-ventilator interaction during four ventilator modes: assist-control ventilation (ACV), intermittent mandatory ventilation (IMV), pressure support (PS), and a combination of IMV and PS. Progressive increases in IMV rate and PS level each decreased inspiratory pressure-time product (PTP) (p < 0.0001). These reductions in PTP were greater with PS than with IMV at lower but proportional levels of maximal assistance (p < 0.005). ⋯ Ineffective triggering occurred with all modes, and wasted PTP increased with increasing levels of assistance as a result of the accompanying decrease in drive and increase in volume. Breaths preceding nontriggering efforts had shorter respiratory cycle times (p < 0.0005) and expiratory times (p < 0.0001) and higher PEEPi (p < 0.0001), indicating that neural-mechanical asynchrony resulted from inspiratory activity commencing prematurely before elastic recoil pressure had fallen to a level that could be overcome by a patient's muscular effort. Thus, increases in the level of ventilator assistance produced progressive decreases in inspiratory muscle effort and dyspnea,which were accompanied by increases in the rate of ineffective triggering.
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Am. J. Respir. Crit. Care Med. · Jun 1997
Randomized Controlled Trial Clinical TrialInhaled gentamicin reduces airway neutrophil activity and mucus secretion in bronchiectasis.
To investigate whether aerosolized gentamicin (GM) prevents myeloperoxidase (MPO)-mediated airway injury and mucus hypersecretion, a short course of aerosol therapy (3 d) with GM 40 mg or 0.45% saline (saline) twice per day was conducted. Twenty-eight patients with bronchiectasis and mucus hypersecretion after adequate chest care and hydration were enrolled in a randomized, double-blind fashion. MPO levels in sputum collected on arising were determined by fluorometric assay at 655 nm before and after treatment. ⋯ The nocturnal desaturation and the 6-min walking distances were also significantly improved in the GM group (11.2 +/- 3.8 to 0.6 +/- 0.5 min/h; 324.9 +/- 43.1 to 408.1 +/- 25.9 m; p < 0.05; respectively), but not in the saline group. Subjective improvements in the Borg scale and self-sputum assessment were found in the GM group only. In conclusion, aerosolized GM is effective in improving airway hypersecretion and inflammation in patients with bronchiectasis.
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Am. J. Respir. Crit. Care Med. · Jun 1997
Small airway closure and positive end-expiratory pressure in mechanically ventilated patients with chronic obstructive pulmonary disease.
The effects of positive end-expiratory pressure (PEEP) on alveolar recruitment and closing volume were studied in ten supine, sedated, and paralyzed patients with chronic obstructive respiratory disease and acute respiratory failure. We applied PEEP (0, 5, 10, and 15 cm H2O) and constructed inflation static volume-pressure (V-P) curves. In all patients, the static V-P curves obtained at different PEEP levels were superimposed on each other, indicating that with PEEP there was no recruitment of previously atelectatic lung units. ⋯ All patients, however, exhibited dynamic hyperinflation, i.e., with zero PEEP (ZEEP) the end-expiratory lung volume (EELV) was 0.54 L above Vr. Nevertheless, in seven patients the EELV on ZEEP was below Vo, resulting in cyclic reopening and closure of small airways with each breathing cycle, with concomitant mechanical stresses on the peripheral airways that may lead to low-volume barotrauma. Such barotrauma may be prevented by increasing with PEEP the EELV to Vo.
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Am. J. Respir. Crit. Care Med. · Jun 1997
Nasal mask pressure waveform and inspiratory muscle rest during nasal assisted ventilation.
In mechanically ventilated patients, pressure and flow tracings can be used to assess respiratory pump muscle activity or rest. When the ventilation is delivered through an endotracheal tube, the respiratory system can be considered a one-compartment model, and activation of the respiratory muscles results in deformations and variability of the pressure tracings. This is also true when mechanical ventilation is delivered nasally. ⋯ These irregularities were related to significant variations in the glottic width, rather than to the reappearance of transient phasic inspiratory muscle activity. We conclude that during nIPPV, deformations in the mask pressure waveform can be induced by variations in the glottic aperture without activation of the diaphragm. Thus, when mechanical ventilation does not bypass the glottis, the respiratory system does not behave like a one-compartment model, and EMG remains the only reliable technique for assessing diaphragmatic muscle activity.
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Am. J. Respir. Crit. Care Med. · Jun 1997
Randomized Controlled Trial Clinical TrialEffects of inspiratory muscle unloading on the response of respiratory motor output to CO2.
Inspiratory muscle output is downregulated when the mechanical load is reduced in awake humans. It is not known whether this is related to reduction in PCO2 or to removal of load-related neural responses. To address this issue, we did Read CO2 rebreathing tests in 13 normal subjects with and without unloading and compared respiratory output at identical end-tidal PCO2 (PET(CO2)) levels. ⋯ Using a model that allows nonlinearity in the pressure-volume relation and for intrinsic muscle properties (force-length and force-velocity relations), we estimated the expected changes in mean VT and VI when the level of assist used in this study was applied in the absence of any change in neural output response to CO2. The predicted and observed changes in VT and VI were similar. We conclude that when chemical stimuli are rigorously controlled, unloading does not result in downregulation of respiratory muscle activation.