Left ventricular reflex control of venous return and systemic vascular capacitance in dogs

The reflex effects of left ventricular distension on venous return, vascular capacitance, vascular resistance, and sympathetic efferent nerve activity were examined in dogs anesthetized with sodium pentobarbital. In addition, the interaction of left ventricular distension and the carotid sinus baroreflex was examined. Vascular capacitance was assessed by measuring changes in systemic blood volume, using extracorporeal circulation with constant cardiac output and constant central venous pressure. Left ventricular distension produced by balloon inflation caused a transient biphasic change in venous return; an initial small increase was followed by a late relatively large decrease. Left ventricular distension increased systemic blood volume by 3.8 +/- 0.6 mL/kg and decreased systemic blood pressure by 27 +/- 2 mmHg (1 mmHg = 133.3 Pa) at an isolated carotid sinus pressure of 50 mmHg. These changes were accompanied by a simultaneous decrease in sympathetic efferent nerve activity. When the carotid sinus pressure was increased to 125 and 200 mmHg, these responses were attenuated. It is suggested that left ventricular mechanoreceptors and carotid baroreceptors contribute importantly to the control of venous return and vascular capacitance.     

Terrigenous sediment-dominated reef platform infilling: an unexpected precursor to reef island formation and a test of the reef platform size–island age model in the Pacific

Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr⁻¹) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.

     

Catecholamine-induced changes in vascular capacitance and sympathetic nerve activity in dogs.

The effects of three catecholamines, dopamine, epinephrine, and dobutamine, on the systemic circulation, especially on systemic vascular capacitance, were studied using cardiopulmonary bypass in dogs anesthetized with pentobarbital. Venous outflow was divided into three compartments: splanchnic, renal, and other; changes in systemic blood volume (SBV) were calculated from the changes in total venous outflow. To examine the contribution of sympathetic discharge to these vascular responses, sympathetic efferent nerve activity (SENA) from the ventral ansa subclavian nerve was recorded simultaneously. Experiments were done under three conditions: control, after baroreceptor deafferentation, and after hexamethonium injection with low and high doses of each catecholamine. During control and after baroreceptor deafferentation, dopamine- and epinephrine-induced changes in SBV were less than those after hexamethonium, and not significant except with low dose epinephrine. After hexamethonium, dopamine (200 micrograms/kg), epinephrine (10 micrograms/kg), and dobutamine (100 micrograms/kg) reduced SBV by 10.6 +/- 3.4, 13.1 +/- 1.7, and 1.9 +/- 0.3 mL/kg, respectively. Splanchnic outflow increased significantly with dopamine and epinephrine after hexamethonium. High dose dopamine and epinephrine significantly suppressed SENA to 38 +/- 9 and 15 +/- 6% of baseline, respectively. Low dose dopamine decreased arterial pressure and SENA. This suppression in SENA was attenuated but still observed after baroreceptor deafferentation. Dobutamine reduced SBV, but had no effect on SENA. These results suggest that dopamine and epinephrine primarily decrease SBV by venoconstriction in the splanchnic region, however, these effects are greatly modified by basal sympathetic discharge and changes in SENA and vascular tone.     

Antibody profile of pregnant women with antiphospholipid syndrome and pregnancy outcome after treatment with low dose aspirin and low-weight-molecular heparin

The aim of the research was to show our diagnostic and therapeutic experience with antiphospholipid syndrome (APS) in pregnant women. 36 pregnant women suspect on APS were included in the study: 32 with primary antiphospholipd syndrome (PAPS) and 4 with secondary antiphospholipid syndrome (SAPS). All pregnant women received low-molecular-weight-heparin (LMWH) and low dose aspirin (LDA) therapy. Control group represented 26 women with SAPS and previous bad reproductive anamnesis. Average pregnancy lasted 37.06 +/- 0.707 weeks. LMWH and LDA therapy was successful in 97.22%. Lupus anticoagulant (LA) was found to be more frequent in PAPS group (71.87%). Anticardiolipin antibodies (aCL) were found to be more frequent in SAPS (26.66%). For three patients (3.37%), PAPS was diagnosed due to a fact that they had positive antibeta2-glycoproteinl (antibeta-GP1). To make APS diagnosis, it is of great importance to search for all antiphospholipid antibodies. LMWH and low dose of acetylsalicylic acid should be the first choice therapy.