The American review of respiratory disease
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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.
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Am. Rev. Respir. Dis. · Nov 1991
Comparative StudyGlucocorticoid resistance in chronic asthma. Peripheral blood T lymphocyte activation and comparison of the T lymphocyte inhibitory effects of glucocorticoids and cyclosporin A.
A total of 37 chronic severe asthmatic patients with documented reversible airways obstruction were classified as glucocorticoid sensitive or resistant according to changes in the FEV1 following a course of oral prednisolone. The phenotype and expression of activation molecules on peripheral blood T lymphocytes from these patients just before the course of prednisolone were studied using flow cytometry. The resistant patients had significantly elevated percentages of T lymphocytes expressing the activation molecules IL-2R and HLA-DR compared to the sensitive patients. ⋯ Inhibition of elaboration of interleukin-2 and interferon-gamma by mitogen-stimulated T lymphocytes from sensitive and resistant asthmatic patients was also studied. Dexamethasone (10(-7) mol/L) significantly inhibited the production of interleukin-2 and interferon-gamma by proliferating T lymphocytes isolated from the glucocorticoid-sensitive but not the resistant chronic asthmatic patients. Cyclosporin A (500 ng/ml) inhibited the elaboration of both lymphokines by T lymphocytes derived from both patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)