Respiratory physiology & neurobiology
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Respir Physiol Neurobiol · Apr 2005
Comparative StudyGlutamatergic receptors of the rostral ventrolateral medulla are involved in the ventilatory response to hypoxia.
Rostral ventrolateral medulla (RVLM) is a region in the brainstem that is involved in the physiologic responses to hypoxia (i.e. hyperventilation and regulated hypothermia) and contains l-glutamate receptors. Therefore, we examined the effects of blocked of glutamatergic receptors in the RVLM on hypoxic hyperventilation and regulated hypothermia. ⋯ KYN or MCPG into the RVLM did not change V(E) and T(b) under normoxia, but reduced the hypoxic hyperventilation due to a lower tidal volume, although regulated hypothermia persisted. These data suggest that glutamatergic receptors in the RVLM are involved in the ventilatory response to hypoxia, exercising an excitatory modulation of the RVLM neurons, but play no role in hypoxia-induced hypothermia.
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Respir Physiol Neurobiol · Apr 2005
Comparative Study Clinical TrialCough determinants in patients with neuromuscular disease.
Neuromuscular disease leads to cough impairment. Cough augmentation can be achieved by mechanical insufflation (MI) or manually assisted coughing (MAC). Many studies have compared these two methods, but few have evaluated them in combination. ⋯ We measured vital capacity and PCF in 10 neuromuscular patients during cough augmentation by MI, MAC, or both. MI or MAC significantly improved VC and PCF (p<0.01) as compared to the basal condition and VC and PCF were higher during MI plus MAC than during MAC or MI alone (p<0.01). In conclusion, combining MAC and MI is useful for improving cough in neuromuscular patients.
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Respir Physiol Neurobiol · Jan 2005
Comparative Study Clinical TrialHow does lobeline injected intravenously produce a cough?
In order to examine, whether the lobeline-induced cough is a true reflex or a voluntary effort to get rid of its irritating sensations in the upper respiratory tract, we systematically studied the cough response to lobeline, of subjects who were unable to make conscious discriminations i.e. were either comatose (n=4) or anaesthetized (n=5). 8 microg/kg lobeline injected into the right atrium of one and 29 microg/kg intravenously (i.v.) into another evenly and spontaneously breathing comatose subject produced a cough after 4s and 12s, respectively. Cough was repeatable and showed a dose response relationship i.e., its latency decreasing and its duration/intensity increasing with the dose. In a third subject, capable only of weak spontaneous respiration, a relatively high dose injected into the right atrium (44 microg/kg) generated a pronounced cough-like respiratory movement superimposed on the artificial ventilation and also during the apnoea after disconnecting the pump. ⋯ It may be noted that neither the later dose nor the latency or duration of cough that it produced were significantly different from the pre anaesthesia values (P>0.05). These two sets of results show unequivocally that the lobeline-induced cough is evoked reflexly; its magnitude in the conscious state could vary by subjective influences. We discuss the likelihood of its origin from juxtapulmonary capillary receptors.
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Respir Physiol Neurobiol · Jan 2005
Comparative StudyOn the interaction between respiratory compartments during passive expiration in ARDS patients.
Relaxed expiratory volume-time profile has been frequently analysed by fitting exponential functions of time to one- or two-compartment models. In the latter case, the two exponential constants are assumed as representing the time constants of both compartments. Least-square fittings on the experimental data of five consecutive mechanically ventilated supine patients with acute respiratory distress syndrome (ARDS) were performed using rate-constants (flow/volume ratio) as parameters in order to obtain the model matching. ⋯ Model matching was optimal with significant, reliable parameter values. As a result, the use of a PEEP in ARDS patients: (a) delayed expiration; (b) decreased the percentage initial volume contribution of the slow-emptying compartment; and, (c) modified the interaction between compartments. The volume-time profile of the second compartment was found to increase at the beginning of expiration, and, then, progressively decayed towards zero, showing a maximum, although the overall curve decreased throughout expiration.
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Respir Physiol Neurobiol · Oct 2004
Comparative StudyDistribution of ventilation in young and elderly adults determined by electrical impedance tomography.
To determine the effect of age and posture on regional lung ventilation, eight young (26 +/- 1 years, mean +/- S. D.) and eight old (73 +/- 5 years) healthy men were studied by electrical impedance tomography in four body positions (sitting, supine, right and left lateral). The distribution of gas into the right and left lung regions was determined in the chest cross-section during tidal breathing at the resting lung volume, near residual volume and total lung capacity, as well as forced and slow vital capacity maneuvers. ⋯ In the older subjects, the contribution of the right lung to global ventilation fell with the transition from sitting to supine posture during both full expiration maneuvers. During forced vital capacity, the high flow rate and early airway closure in the dependent lung, occurring at higher volumes in the elderly, minimized the posture-dependency in gas distribution which was present during the slow maneuver. Our study revealed the significant effect of age on posture-dependent changes in ventilation distribution.