Journal of applied physiology
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Pulmonary hypertension in rats, induced by an injection of monocrotaline, is associated with changes in the wall structure of the pulmonary arterial bed. We have studied the effects of this remodeling on mechanical properties of cylindrical pulmonary artery segments from rats 21 days after monocrotaline (MCT) injection. Resting and active (KCl induced) circumference-tension relationships were established for segments of extrapulmonary and intrapulmonary arteries isolated from the hilum and the fifth lateral branch from the axial pathway (all preacinar). ⋯ Resting and active stress were also calculated. The study shows that active circumferential tension and active stress are reduced in vessels from MCT-treated rats. Based on our findings, it is unlikely that altered contractile function of preacinar arteries contributes significantly to the increased vascular resistance seen in this model.
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Positive end-expiratory pressure (PEEP) has generally been withheld from the treatment of patients with chronic airflow obstruction (CAO), in view of the risk of hyperinflation and lack of documented benefit. We studied 10 mechanically ventilated patients with exacerbated CAO and air trapping to determine the impact of PEEP on lung mechanics, alveolar pressure, and the work of breathing. PEEP levels of 5 and 10 cmH2O were applied to patients whose end-expiratory alveolar pressures were documented to be positive when breathing against ambient pressure (the auto-PEEP effect). ⋯ The difference between the end-expiratory values of alveolar and central airway pressure narrowed as PEEP increased. Adding PEEP improved the effective triggering sensitivity of the ventilator, diminished ventilatory drive, and reduced the mechanical work of breathing during the machine-assisted ventilatory cycle. Our results indicate that low levels of PEEP may improve lung mechanics and reduce the effort required of mechanically ventilated patients with severe airflow obstruction, without substantially increasing the hazards of hyperinflation.
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Cough and bronchoconstriction are airway reflexes that protect the lung from inspired noxious agents. These two reflexes can be evoked both from the larynx and tracheobronchial tree and also from some extrarespiratory sites. Within the airways, certain sites are particularly sensitive to stimulation of cough (larynx and points of proximal airway branching), whereas bronchoconstriction can be triggered from the whole of the tracheobronchial tree. ⋯ C-fiber endings (bronchial and pulmonary) mediate bronchoconstriction. Inhalation of so-called "selective" C-fiber stimulants induces cough, but excitation of RARs has not been eliminated, and the possibility also exists that the cough is secondary to other lung actions mediated by these nerve endings. Although cough and bronchoconstriction may be mediated by the same type of receptor, they seem to have separate afferent neural pathways.
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We investigated respiratory reflex responses to tracheal mucosa stimulation induced by injection of distilled water in 13 female patients under three different depths of enflurane anesthesia (0.7, 1.0, and 1.3 minimum alveolar concentration). Detailed analysis of the types of reflex responses revealed that there are at least six different responses: 1) the apneic reflex, 2) the expiration reflex, 3) spasmodic, panting breathing, 4) the cough reflex, 5) slowing of breathing, and 6) rapid, shallow breathing. Among these reflex responses, the cough reflex was the most sensitive and the apneic reflex followed by slowing of breathing was the most resistant to deepening anesthesia, whereas the sensitivity of other types of reflex responses was in between. Our results indicate that the types of respiratory reflex responses to tracheal mucosa stimulation are associated with depths of anesthesia and that the differences in sensitivity to anesthesia may be a valuable sign in clinical assessment of depth of anesthesia.
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The effects of endurance training on vascular responsiveness to an alpha 1-agonist and the associated changes in baroreflex modulation of heart rate and vascular resistance were studied. Graded dosages of phenylephrine were given to eight treadmill-trained dogs and to eight untrained dogs; both groups were chronically instrumented and were sedated and resting when tested. These dosages were repeated after ganglionic blockade. ⋯ The unblocked resistance slopes were reduced with respect to the blocked slopes by 77 (untrained) and 79% (trained). The slope of the heart rate-aortic pressure response was reduced, but not significantly, by endurance training. We conclude that 6 wk of endurance training in dogs resulted in a doubling of the vascular responsiveness to an alpha 1-agonist, with no significant change in the baroreflex regulation of resistance or heart rate.