Respiration physiology
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Respiration physiology · Oct 1993
Comparative StudyEffects of beta 2-agonists on the contractility of fatigued canine diaphragm in vivo.
We examined the effects of four beta 2-agonists, clenbuterol, metaproterenol, procaterol, and albuterol, on the contractility of fatigued canine diaphragm. Diaphragmatic contractility was assessed from changes in transdiaphragmatic pressure (Pdi) generated by supramaximal electrical stimulation of the phrenic nerve. Diaphragmatic fatigue was developed by applying an inspiratory resistive load to spontaneously breathing dogs for 30-50 min. ⋯ Albuterol did not change Pdi at any dose. These results suggest that both clenbuterol and metaproterenol have a positive inotropic effect on fatigued canine diaphragm, while procaterol has a negative effect at high doses. Albuterol showed no inotropic effect.
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Respiration physiology · Aug 1993
Comparative StudyEffect of sleep on changes in breathing pattern accompanying sigh breaths.
We studied the effect of sleep on the characteristics of sigh breaths and the associated changes in breathing pattern in breaths following spontaneous sighs in 4 unrestrained dogs with an intact upper airway. The sigh breath was characterized by its large tidal volume (VT), long TI and TE in comparison with the control breath. The volume of the sigh breath was larger in awake sighs than in those recorded during non-REM (NREM) and REM sleep. ⋯ Breathing pattern in the post-sigh period was characterized by a smaller VT and longer TE in the first post-sigh breath in all sleep states (compared with the control breath), but the pattern returned to control level within the second or third post-sigh breath in both NREM and REM sleep. Sighs did not precipitate periodic breathing or other forms of abnormal breathing patterns in either wakefulness or sleep. We conclude that the respiratory control mechanisms stabilizing breathing after a sigh in the awake dog are intact in NREM and REM sleep.
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Respiration physiology · Oct 1992
Mechanical characteristics and functional length of canine expiratory muscles.
The expiratory muscles of the abdominal region actively contribute to breathing. In dogs, the transversus abdominis appears to be the main abdominal muscle of expiration. The in vitro mechanical properties of the transversus abdominis have not been reported to date, and formed the basis of the present investigation. ⋯ In the prone posture, however, we noted that both abdominal muscles were located at similar positions along their length-tension curve, operating at a length of roughly 77% Lo. Since both muscles share common length-tension characteristics, the present results indicate that the tension generating potential of both muscles in prone dogs is equal for a given neural input. However, we conclude that the preferential recruitment of the transversus abdominis in prone animals must be related to factors other than simple tension generation.
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Respiration physiology · Sep 1992
Liquid volume, Na+ and mannitol concentration in a hypertonic mannitol-Ringer hydrothorax.
In anesthetised rabbits with a 2 ml hypertonic mannitol-Ringer hydrothorax in the right space 30 mM/L mannitol were required for an unchanged volume of the hydrothorax after 60 min. [Na+] in the pleural liquid 10, 30 and 60 min after this hydrothorax was 8, 7 and 5 mEq/L, respectively, lower (P less than 0.01) than the initial one and that in a Ringer-hydrothorax. This seems due to the active transport of Na+ out of the pleural space followed by little water because of the osmotic pressure exerted by mannitol. ⋯ From 30 to 60 min 6.5 microM of mannitol left the right space mainly by diffusion. The diffusional permeability of the mesothelium was indirectly assessed from the diffusional outflux of mannitol, the surface of the pleural space, and an estimate of mannitol concentration in the interstitium next to the mesothelium: it is smaller than that found in vitro.
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Respiration physiology · Feb 1992
ReviewHemodynamics of vascular 'waterfall': is the analogy justified?
The concept of 'vascular waterfall' has been used for collapsible vessels in different hemodynamic states which have little similarity to each other from a dynamic standpoint. Examples include (a) flow through large systemic veins entering the thorax, (b) flow through microvessels, such as pulmonary, cardiac, hepatic, cerebral, and (c) flow through the jugular vein of the giraffe. ⋯ Hence, the term waterfall as a metaphor is misleading and unjustified. We suggest that the use of the term be discontinued for describing vascular dynamics.