The American review of respiratory disease
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Am. Rev. Respir. Dis. · Jan 1992
Clinical TrialProportional assist ventilation. Results of an initial clinical trial.
The response to proportional assist ventilation (PAV) was tested in four normal subjects during heavy exercise and in five ventilator-dependent patients recovering from assorted medical disorders. The apparatus consisted of a rolling-seal piston coupled to a motor that generated pressure in proportion to inspired flow and inspired volume, with the gains adjusted such that the proportionality between airway pressure (Paw) and instantaneous patient-generated pressure (Pmus) was approximately 1:1 (i.e., machine-amplified patient effort by a factor of 2). Normal subjects responded to PAV by decreasing their own effort, as judged from esophageal pressure, such that the changes in ventilation and breathing pattern were rather small (VE: 64.8 +/- 3.6 during PAV versus 56.0 +/- 4.3, p less than 0.01; VT: 2.39 +/- 0.24 versus 2.02 +/- 0.17, p less than 0.05; f: 27.5 +/- 1.9 versus 28.0 +/- 2.2, NS). ⋯ After a period of observation during synchronized intermittent mechanical ventilation (SIMV) the patient was switched to PAV and maintained on it for 1 to 3 h. No patient had to be replaced on SIMV because of discomfort or deterioration in any of the monitored variables. During PAV peak airway pressure was less than half the value observed with the IMV breaths (16.6 +/- 2.4 versus 35.4 +/- 3.4 cm H2O, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. Rev. Respir. Dis. · Jan 1992
Observer agreement for respiratory signs and oximetry in infants hospitalized with lower respiratory infections.
To determine observer agreement for a clinical score and oximetry in lower respiratory infection in children less than 2 yr of age, a convenience sample of 56 infants hospitalized with bronchiolitis or pneumonia was assessed independently by two observers. A total of 12 infants had chronic lung disease of prematurity or congenital heart disease. Infants in whom oxygen supplementation could not be discontinued for at least 5 min were excluded. ⋯ The median difference between oximetry readings was 1. The correlation coefficient between total score and oximetry was -0.04. The limited agreement for clinical signs makes comparison of patient illness severity between studies difficult.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. Rev. Respir. Dis. · Dec 1991
Centrilobular and panlobular emphysema in smokers. Two distinct morphologic and functional entities.
In order to investigate the hypothesis that different morphologic patterns of disease might correspond to different mechanical properties of the lung in emphysema, pulmonary function tests and lung mechanics were measured in 34 subjects undergoing lung resection for peripheral lung tumors. Using standard microscopic criteria, pure or predominant centrilobular (n = 18) or panlobular (n = 16) emphysema was diagnosed in lungs. The degree of emphysema measured by the mean linear intercept (Lm) was not significantly different between the two groups. ⋯ CLE also had a higher proportion of airways less than 400 microns in diameter than did PLE (p less than 0.05). Static compliance, specific compliance, and the exponential constant (K) were significantly lower (p less than 0.005, p less than 0.001, and p less than 0.05, respectively) in CLE than in PLE. FEV1/FVC was significantly correlated with SAD in CLE (r = -0.69, p less than 0.01) but not in PLE (r = 0.29 p greater than 0.05); conversely, FEV1/FVC was significantly correlated with elasticity (K) in PLE (r = -0.72, p less than 0.01) but not in CLE (r = 0.08, p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. Rev. Respir. Dis. · Dec 1991
Airway insufflation. Increasing flow rates progressively reduce dead space in respiratory failure.
We have previously shown that airway insufflation (AI) reduces dead space (VD) and minute ventilation (VL) in patients with respiratory failure, and when used chronically leads to lowered and more stable arterial PCO2. The present study was designed to measure the effect of increasing AI flow rate on VD and other aspects of gas exchange in respiratory failure in order to examine the hypothesis that AI exerts its main physiologic effect by progressive reductions of VD. Five patients with varying degrees of respiratory failure caused by either restrictive or obstructive lung disease were studied by means of the specialized techniques we developed to analyze gas exchange during AI. ⋯ Contrary to our previous study, some of these patients accompanied the decrease in VD with not only decreases in VL but with slight rises in alveolar ventilation (VA) and decrements in arterial PCO2. The greatest percentile decreases in VD and VL occurred in those with the smallest initial control values for each of these parameters. In summary, AI exerts its main effects on gas exchange through the reductions in VD that it produces, and the accompanying decreases in VL and/or slight increases in VA seem to stem from the latter.
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Am. Rev. Respir. Dis. · Nov 1991
Comparative StudyRole of airway mechanoreceptors in the inhibition of inspiration during mechanical ventilation in humans.
The purpose of this study was to demonstrate a neuromechanical inhibitory effect on respiratory muscle activity during mechanical ventilation and to determine whether upper and lower airway receptors provide this inhibitory feedback. Several protocols were completed during mechanical ventilation: (1) positive and negative pressure changes in the upper airway, (2) airway anesthesia to examine the consequences of receptor blockade on respiratory muscle activity, (3) increasing FRC with positive end-expiratory pressure to study the effect of hyperinflation or stretch on respiratory muscle activity, and (4) use of heart-lung transplant patients to determine the effects of vagal denervation on respiratory muscle activity. All subjects were mechanically hyperventilated with positive pressure until inspiratory muscle activity was undetectable and the end-tidal PCO2 decreased to less than 30 mm Hg. ⋯ Neuromechanical feedback caused significant inspiratory muscle inhibition during mechanical ventilation, as evidenced by the difference between PCO2RT and PETCO2 during spontaneous eupnea (45 +/- 4 versus 39 +/- 4 mm Hg) and a lower PCO2RT when tidal volume was reduced with a constant frequency and fraction of inspired CO2. Recruitment threshold was unchanged during positive and negative pressure ventilation, during upper and lower airway anesthesia, and in vagally denervated lung transplant patients. These findings demonstrate that neuromechanical feedback causes highly significant inhibition of inspiratory muscle activity during mechanical ventilation; upper and lower airway receptors do not appear to mediate this effect.