Acta physiologica Scandinavica
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Acta Physiol. Scand. · Nov 1998
Albumin infusion in humans does not model exercise induced hypervolaemia after 24 hours.
We rapidly infused 234 +/- 3 mL of 5% human serum albumin in eight men while measuring haematocrit, haemoglobin concentration, plasma volume (PV), albumin concentration, total protein concentration, osmolality, sodium concentration, renin activity, aldosterone concentration, and atrial natriuretic peptide concentration to test the hypotheses that plasma volume expansion and plasma albumin content expansion will not persist for 24 h. Plasma volume and albumin content were expanded for the first 6 h after infusion (44.3 +/- 1.9-47.2 +/- 2.0 mL kg-1 and 1.9 +/- 0.1-2.1 +/- 0.1 g kg-1 at pre-infusion and 1 h, respectively, P < 0.05), but by 24 h plasma volume and albumin content decreased significantly from 1 h post-infusion and were not different from pre-infusion (44.8 +/- 1.9 mL kg-1 and 1.9 +/- 0.1 g kg-1, respectively). Plasma aldosterone concentration showed a significant effect of time over the 24 h after infusion (P < 0.05), and showed a trend to decrease at 2 h after infusion (167.6 +/- 32.5(-1) 06.2 +/- 13.4 pg mL-1, P = 0.07). These data demonstrate that a 6.8% expansion of plasma volume and 10.5% expansion of plasma albumin content by infusion does not remain in the vascular space for 24 h and suggest a redistribution occurs between the intravascular space and interstitial fluid space.
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Acta Physiol. Scand. · Oct 1997
Effects of scorpion venom on central and peripheral circulatory response in an open-chest dog model.
Scorpion venom can induce in dogs severe haemodynamic changes leading to rapid rise in systemic blood pressure and cardiac output, followed by reduction of cardiac output and blood pressure within 1 h. The decrease in cardiac output is not related to myocardial dysfunction (Tarasiuk et al. 1994). We hypothesized that scorpion venom affects cardiac output by reducing venous return to the heart. ⋯ This study indicates that, in dogs, scorpion venom affects cardiac output by modifying the determinants of venous return. The initial increase in cardiac output is related to increased mean circulatory pressure since resistance to venous return did not change. The later fall in cardiac output is related to the reduction of mean circulatory pressure and increased resistance to venous return.
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Acta Physiol. Scand. · Feb 1997
Heterogeneous blood flow response in the foot on dependency, assessed by laser Doppler perfusion imaging.
The exact nature of the decrease in foot skin blood flow seen after a change in posture remains unsettled. This mechanism has previously been examined by non-invasive techniques such as the laser Doppler perfusion monitor (laser Doppler flowmetry). Taking into account the shortcomings of laser Doppler perfusion monitoring when applied to the determination of skin blood flow, which normally shows substantial heterogeneity, we have applied an emerging technology, the laser Doppler perfusion imager (LDPI). ⋯ As the LDPI technique readily records skin perfusion during variations in venous stasis and posture, as well as information on flow distribution changes. It appears promising for future application in stimuli-response studies of skin blood flow. The difference in flow distribution seen between increased venous pressure and dependency suggests an additive regulatory mechanism to the veni-vasomotor reflex during a change in posture.
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Acta Physiol. Scand. · Nov 1996
N-methyl-D-aspartate receptor antagonists potentiate morphine's antinociceptive effect in the rat.
The interaction between morphine and three antagonists of the N-methyl-D-aspartate (NMDA) receptor. MK-801 (non-competitive channel blocker), dextromethorphan (clinically available non-competitive antagonist) and CGS19755 (competitive receptor antagonist), was examined in rats with the hot plate test. ⋯ However, pretreatment with the NMDA antagonists at these doses 30 min prior to subcutaneous injection of 5 mg kg-1 morphine significantly potentiated the antinociceptive effect of morphine, with strongest effect observed with dextromethorphan. It is suggested that blockade of NMDA receptors enhances the antinociceptive effect of morphine and NMDA antagonists may improve the analgesic efficacy of morphine in the clinic.
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Acta Physiol. Scand. · Sep 1995
Facilitation of the human nociceptive reflex by stimulation of A beta-fibres in a secondary hyperalgesic area sustained by nociceptive input from the primary hyperalgesic area.
Hyperalgesia was induced in healthy volunteers by topical capsaicin applied on the dorsum of the foot within the receptive field of the sural nerve. Under presence of hyperalgesia different normally non-noxious conditioning stimuli were applied to the hyperalgesic area and the polysynaptic nociceptive spinal reflex and pain ratings were used to assess central excitability. The nociceptive reflex was measured in the knee extensor and flexor muscles evoked by electrical stimulation of the sural nerve trunk at an intensity of 1.5 times the initial reflex threshold (an intensity above the pain threshold). ⋯ The same measurement without prior thermal conditioning stimulation of the primary area resulted in no reflex facilitation, indicating rapid changes in the central excitability with existence of on-going nociceptive activity. This indicates that the development and maintenance of secondary hyperalgesia are dependent on sustained peripheral nociceptive activity. The study also shows that a central summation of nociceptive and non-nociceptive afferent activity can occur once secondary hyperalgesia is present.