Respiratory physiology & neurobiology
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Respir Physiol Neurobiol · Dec 2006
Effects of dexmedetomidine on respiratory mechanics and control of breathing in normal rats.
Dexmedetomidine is a highly selective and specific alpha(2)-adrenergic agonist, with sedative, analgesic, and sympatholytic activities. The aim of the present study was to define the effects of DMED in respiratory mechanics in normal rats. In addition, lung morphometry was studied to determine whether the physiological changes reflected underlying morphological changes defining the sites of action of dexmedetomidine. ⋯ During mechanical ventilation, respiratory mechanical parameters were similar in both groups. These findings were supported by the absence of histological changes. In conclusion, under the conditions studied, dexmedetomidine did not change respiratory mechanical parameters and lung histology, but induced ventilatory depression.
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Respir Physiol Neurobiol · Nov 2006
Flying high: a theoretical analysis of the factors limiting exercise performance in birds at altitude.
The ability of some bird species to fly at extreme altitude has fascinated comparative respiratory physiologists for decades, yet there is still no consensus about what adaptations enable high altitude flight. Using a theoretical model of O(2) transport, we performed a sensitivity analysis of the factors that might limit exercise performance in birds. We found that the influence of individual physiological traits on oxygen consumption (Vo2) during exercise differed between sea level, moderate altitude, and extreme altitude. ⋯ Increases in the temperature effect on P(50) could also be beneficial for high flying birds, provided that cold inspired air at extreme altitude causes a substantial difference in temperature between blood in the lungs and in the tissues. Changes in lung diffusion capacity for O(2), cardiac output, blood Hb concentration, the Bohr coefficient, or the Hill coefficient likely have less adaptive significance at high altitude. Our sensitivity analysis provides theoretical suggestions of the adaptations most likely to promote high altitude flight in birds and provides direction for future in vivo studies.
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Respir Physiol Neurobiol · Aug 2006
Comparative StudySerial respiratory adaptations and an alternate hypothesis of respiratory control in human pregnancy.
This study determined the time course of changes in resting and exercising respiratory responses during the first half of human pregnancy, and examined the potential roles of plasma osmolality and the strong ion difference ([SID]) as mediators of pregnancy-induced increases in ventilation. Healthy active women (n = 11) were studied serially from 7 to 22 weeks gestation. Responses were compared with preconception data from 14 subjects (six of whom were tested in early pregnancy), and with late-gestation resting data from 10 additional women. ⋯ Large correlations (r > 0.5) between resting progesterone and PaCO2 support the traditional theory that circulating progesterone stimulates ventilation during pregnancy. The similar time course of changes and large correlations between raw and delta values of PaCO2 and each of plasma osmolality and [SID] also suggest that both variables may influence respiratory control at rest and during exercise in the first half of pregnancy. Future experiments should continue to explore the hypothesis that osmolality and [SID] contribute to pregnancy-induced respiratory changes.
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Coughing is initiated by activation of mechanically and chemically sensitive vagal afferent nerves innervating the airways. All afferent nerve subtypes innervating the airways can modulate the cough reflex. Rapidly adapting and slowly adapting stretch receptors (RARs and SARs, respectively) innervating the intrapulmonary airways and lung may enhance and facilitate coughing. ⋯ Tracheal and bronchial C-fibers may also interact with other afferents to enhance coughing. Recent studies in anesthetized guinea pigs have identified a myelinated afferent nerve subtype that can be differentiated from intrapulmonary RARs and SARs and play an essential role in initiating cough. Whether these "cough receptors" are the guinea pig equivalent of the irritant receptors described in the extrapulmonary airways of other species is unclear.
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Respir Physiol Neurobiol · May 2006
Comparative StudyMeasuring end-expiratory lung volume and pulmonary mechanics to detect early lung function impairment in rabbits.
We investigated whether end-expiratory lung volume (EELV) or lung mechanical parameters are more sensitive for the detection of a compromised gas exchange during bronchoconstriction and after surfactant depletion. EELV was determined via SF(6) multiple breath wash-outs in mechanically ventilated rabbits while a positive end-expiratory pressure (PEEP) of 1, 3 or 7 cm H(2)O was maintained. Airway resistance (R(aw)) and parenchymal elastance (H) were estimated from the pulmonary input impedance measured at each PEEP level by means of forced oscillations. ⋯ MCh induced marked elevations in R(aw), with no significant change in EELV or H at any PEEP. After lavage, the severity of hypoxia was reflected systematically in significant decreases in EELV at all PEEP levels (-42+/-13%, -26+/-4%, and -18+/-5% at 1, 3 and 7 cm H(2)O, respectively), whereas compromised gas exchange was not associated with consistent changes in the mechanical parameters at a PEEP of 7 cm H(2)O (20+/-9% and 14+/-9% in R(aw) and H, respectively; p=0.2). We conclude that R(aw) is the only sensitive indicator for the detection of a compromised lung function during MCh infusions, whereas the estimation of EELV is necessary to follow the progression of a lung injury when a high PEEP level is applied.