Canadian journal of physiology and pharmacology
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Can. J. Physiol. Pharmacol. · Apr 1995
Clinical TrialDifferential effects of a flexor nerve input on the human soleus H-reflex during standing versus walking.
A conditioning (C) stimulus at group I strength was delivered during standing to the common peroneal (CP) nerve before a test (T) stimulus at several C-T intervals ranging from 0 to 150 ms. At sufficiently long C-T intervals (100-120 ms) the soleus H-reflex was strongly inhibited despite little, or no change, in the background level of EMG activity. This finding indicates that a significant portion of the inhibition occurs at a premotoneuronal level, likely via presynaptic inhibition of the Ia-afferent terminals. ⋯ Firstly, during walking the intraspinal terminals of the afferent fibres (group Ia and Ib) conducting the conditioning volley may be presynaptically inhibited, or their input gated at the interneuronal level. Secondly, on the assumption that the conditioning stimulus is acting via the presynaptic inhibitory network in the spinal cord, it is possible that during walking this network is saturated as a result of increased central or peripheral synaptic inputs. Finally, it seems unlikely that differences in the refractoriness of the CP nerve between the tasks may be involved; the reasons for this are presented in the discussion.
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Can. J. Physiol. Pharmacol. · Nov 1994
ReviewPotential role for phenotypic modulation of bronchial smooth muscle cells in chronic asthma.
Asthma is considered to be a chronic inflammatory disease of the airways and is highlighted by excessive airway narrowing in response to various stimuli. Subepithelial fibrosis and increased airway smooth muscle mass are characteristic pathological features of the disease. Airway remodelling in asthma involves cellular hyperplasia and hypertrophy of bronchial myocytes. ⋯ Recruitment and modulation of smooth muscle cells to functionally different phenotypes, which contribute to fibrosis by secreting extracellular matrix materials and promote cellular hyperplasia by producing growth factors, are known to occur in atherogenic blood vessels; and evidence suggests that airway smooth muscle cells might play a similar role in asthma. We report the identification of markers of differentiation for airway smooth muscle cells. These markers should be useful tools in the elucidation of phenotypic heterogeneity of smooth muscle in asthmatic airways and, thereby, allow for the definition of a clearer role for bronchial smooth muscle cells in the pathogenesis of chronic asthma.
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Can. J. Physiol. Pharmacol. · May 1992
Influence of pregnancy on mean systemic filling pressure and the cardiac function curve in guinea pigs.
To assess the degree of circulatory fullness and to evaluate the influence of peripheral and cardiac factors in the regulation of cardiac output during pregnancy, the following studies were conducted using pentobarbital-anesthetized, open-chest nonpregnant and late term pregnant guinea pigs. Mean circulatory filling pressure was taken as the equilibrium pressure when the pulmonary artery was constricted. Total vascular compliance was assessed by +/- 5-mL changes in blood volume performed while this constriction was maintained. ⋯ The cardiac function curve was shifted upwards in pregnant animals. The resistance to venous return, as determined from the slope of the venous return curves, was not changed. These data suggest that the circulation of the pregnant guinea pig is slightly overfilled.(ABSTRACT TRUNCATED AT 250 WORDS)
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Can. J. Physiol. Pharmacol. · May 1991
ReviewThe pain-adaptation model: a discussion of the relationship between chronic musculoskeletal pain and motor activity.
Articles describing motor function in five chronic musculoskeletal pain conditions (temporomandibular disorders, muscle tension headache, fibromyalgia, chronic lower back pain, and postexercise muscle soreness) were reviewed. It was concluded that the data do not support the commonly held view that the pain of these conditions is maintained by some form of tonic muscular hyperactivity. Instead, it seems clear that in these conditions the activity of agonist muscles is often reduced by pain, even when this does not arise from the muscle itself. ⋯ As a consequence of these changes, force production and the range and velocity of movement of the affected body part are often reduced. To explain how such changes in the behaviour come about, we propose a neurophysiological model based on the phasic modulation of excitatory and inhibitory interneurons supplied by high-threshold sensory afferents. We suggest that the "dysfunction" that is characteristic of several types of chronic musculoskeletal pain is a normal protective adaptation and is not a cause of pain.
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Muscle pain and poor sleep commonly occur together. Whether pain induces poor sleep or vice versa is difficult to know. Muscle pain is also observed in the presence of some types of dyskinesia or movement disorders. The interaction between sleep, movement disorders, and some musculoskeletal pain appears to be complex and may be influenced by various concomitant psychological and (or) biological factors.