Canadian journal of physiology and pharmacology
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Can. J. Physiol. Pharmacol. · Jun 1996
Central venous pressure during exercise: role of muscle pump.
Central venous pressure (CVP) gives the integral result of changes in cardiac and peripheral factors. Thus, the sudden increase in CVP observed at the onset of dynamic exercise has been attributed to the action of the muscle pump but is also affected by reflex changes in cardiac response. To determine which predominates at the onset of exercise, we compared the change in CVP from rest to onset of upright exercise and after 3 min of exercise in four healthy normal subjects (N) and six patients following heart transplantation (HT), who thus had a delayed cardiac response. ⋯ The immediate increase in CVP with leg movement in both groups supports an initial central shift in blood volume because of muscle contractions. During the first minute of exercise, muscle blood flow most likely continues to increase and CVP increased further in HT but not in N, which had adequate reflex cardiac adjustment. We conclude that the muscle pump increases CVP at exercise onset, but the interaction between cardiac response and circuit function determines CVP as exercise continues.
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Can. J. Physiol. Pharmacol. · Apr 1996
ReviewModulation of corticospinal influence over hand muscles during gripping tasks in man and monkey.
Transcranial magnetic brain stimulation (TMS) was used to investigate corticospinal influences during a task in which human subjects had to reach out and grasp and lift an object. TMS applied to the hand area of the motor cortex was delivered during eight different phases of the task. There was a striking phase-related modulation in the amplitude of the short-latency EMG responses elicited by TMS in six arm and hand muscles. ⋯ THe enhanced corticospinal influence that this represents probably contributes to the powerful, short-latency boosting in grip force observed when the object was suddenly subjected to an external load. Recording of corticospinal cells in the primary motor cortex of the awake monkey suggests that the phasic modulation observed with TMS may reflect the phasic-tonic pattern of corticomotoneuronal cell discharge during the task. Since the activation of corticospinal cells by low-intensity TMS is dependent upon their level of excitability, EMG responses evoked by TMS during the performance of skilled tasks in man may, in part, reflect changes in the excitability of these cells.
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Can. J. Physiol. Pharmacol. · Dec 1995
Strychnine-dependent allodynia in the urethane-anesthetized rat is segmentally distributed and prevented by intrathecal glycine and betaine.
The blockade of spinal glycine receptors with intrathecal strychnine produces a reversible allodynia-like state in the rat. Thus, hair deflection, in the presence of intrathecal strychnine, induces cardiovascular and motor withdrawal responses comparable with those evoked by noxious thermal, mechanical, or chemical stimulation in the absence of strychnine. In the present study, we mapped the cutaneous sites of abnormal sensitivity to hair deflection throughout the strychnine time course to investigate the segmental distribution of strychnine-induced allodynia. ⋯ There was no difference in the effect of betaine on sensory-evoked cardiovascular and motor responses. Cortical electroencephalographic activity was not affected by intrathecal glycine or betaine, consistent with a spinal locus of action in reversing strychnine-induced allodynia. These results support the hypothesis that removal of spinal glycinergic modulation from low threshold afferent input with intrathecal strychnine results in segmentally localized, tactile-evoked allodynia.
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Can. J. Physiol. Pharmacol. · Nov 1995
Vascular capacitance and cardiac output in pacing-induced canine models of acute and chronic heart failure.
The relationship between stressed and total blood volume, total vascular capacitance, central blood volume, cardiac output (CO), and pulmonary capillary wedge pressure (Ppcw) was investigated in pacing-induced acute and chronic heart failure. Acute heart failure was induced in anesthetized splenectomized dogs by a volume load (20 mL/kg over 10 min) during rapid right ventricular pacing at 250 beats/min (RRVP) for 60 min. Chronic heart failure was induced by continuous RRVP for 2-6 weeks (average 24 +/- 2 days). ⋯ Cardiac output was increased when stressed and unstressed blood volumes increased proportionately as during volume loading alone. When CO was reduced and Ppcw increased, as during chronic RRVP or acute RRVP plus a volume load, stressed blood volume was increased and unstressed blood volume was decreased. Thus, interventions that reduced CO and increased Ppcw also increased stressed and reduced unstressed blood volume and total vascular capacitance.
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Can. J. Physiol. Pharmacol. · Jul 1995
ReviewPlasticity of calcitonin gene related peptide neurotransmission in the spinal cord during peripheral inflammation.
Injection of complete Freund's adjuvant (CFA; 75 microL) into the plantar surface of the hind paw of the rat results in a mild inflammation that lasts for several days and is accompanied by hyperalgesia. Multiple components of calcitonin gene related peptide (CGRP) neurotransmission in the spinal cord are altered during the course of this peripheral inflammation. The content of immunoreactive (i) CGRP in the dorsal horn of the spinal cord, where primary afferent neurons terminate, is significantly decreased within 2 days after injection of CFA but increases to a level greater than that of the control at 8 days. ⋯ Measurements of the binding of 125I-labelled CGRP in the dorsal spinal cord indicate that high affinity binding sites for CGRP are downregulated at 4 days after injection of CFA. In total, these data support the hypothesis that the activity of CGRP-containing primary afferent neurons is increased during peripheral inflammation. CGRP released from primary afferent neurons in the spinal cord may contribute to cellular changes that accompany peripheral inflammation.