Decrease In PCO2 Research Articles

The physiology of overwintering in a turtle that occupies multiple habitats, the common snapping turtle (Chelydra serpentina).

Common snapping turtles, Chelydra serpentina (Linnaeus), were submerged in anoxic and normoxic water at 3 degrees C. Periodic blood samples were taken, and PO(2), PCO(2), pH, [Na(+)], [K(+)], [Cl(-)], total Ca, total Mg, [lactate], [glucose], hematocrit, and osmolality were measured; weight gain was determined; and plasma [HCO(3)(-)] was calculated. Submergence in normoxic water caused a decrease in PCO(2) from 10.8 to 6.9 mmHg after 125 d, partially compensating a slight increase in lactate and allowing the turtles to maintain a constant pH. Submergence in anoxic water caused a rapid increase in lactate from 1.8 to 168.1 mmol/L after 100 d. Associated with the increased lactate were decreases in pH from 8.057 to 7.132 and in [HCO(3)(-)] from 51.5 to 4.9 mmol/L and increases in total Ca from 2.0 to 36.6 mmol/L, in total Mg from 1.8 to 12.1 mmol/L, and in [K(+)] from 3.08 to 8.45 mmol/L. We suggest that C. serpentina is tolerant of anoxic submergence and therefore is able to exploit habitats unavailable to some other species in northern latitudes.

Impact of alcohol intoxication on hemodynamic, metabolic, and cytokine responses to hemorrhagic shock.

Alcohol intoxication is associated with a high incidence of traumatic injury, particularly in the young healthy population. The impact of alcohol intoxication on the immediate pathophysiologic response to injury has not been closely examined. We hypothesized that acute alcohol intoxication would aggravate the immediate outcome from hemorrhagic shock by impairing homeostatic counterregulation to blood loss. Chronically catheterized male Sprague-Dawley rats were randomized to receive an intragastric infusion of ethyl alcohol (1.75 g/kg followed by 250-300 mg/kg/h) or isocaloric dextrose (3-mL bolus + 0.375 mL/h) for 15 hours. Before initiating fixed-pressure hemorrhage followed by fluid resuscitation, an additional intragastric bolus of ethyl alcohol (1.75 g/kg) was administered. Hemodynamic, metabolic, cytokine, and acid-base parameters were assessed during the hemorrhage period and at completion of resuscitation. Lungs were obtained for cytokine determinations. Basal mean arterial pressure was significantly lower in alcohol-intoxicated (blood-alcohol concentration, 135 +/- 12 mg/dL) animals than in controls during baseline (20%) and after the initial fluid resuscitation period (30%). Hemorrhage decreased arterial HCO3 and Pco2, and increased Po2 without significant alteration in arterial blood pH. Alcohol intoxication blunted the decrease in Pco2 and increase in Po2 and decreased blood pH during baseline and throughout the course of the hemorrhage period. Hemorrhage produced marked and progressive elevations in plasma glucose and lactate levels in controls, and this was inhibited by alcohol intoxication. Hemorrhage elevated plasma tumor necrosis factor-alpha (TNF-alpha) (686 +/- 252 pg/mL) and interleukin (IL)-10 (178 +/- 25 pg/mL), and did not alter IL-6 and IL-1 levels. Alcohol blunted the hemorrhage-induced rise in plasma TNF-alpha (142 +/- 48 pg/mL) and enhanced the hemorrhage-induced increase in IL-10 (678 +/- 187 pg/mL). Hemorrhage produced a two- to threefold increase in lung content of TNF-alpha, IL-1alpha, and IL-6 without significantly altering lung IL-10. Alcohol exacerbated the hemorrhage-induced increase in lung TNF-alpha, and did not alter the IL-1alpha, IL-6, and IL-10 lung responses. These results indicate marked alterations in the hemodynamic and metabolic responses to hemorrhagic shock by alcohol intoxication. Furthermore, our findings suggest that alcohol modulates the early proinflammatory responses to hemorrhagic shock. Taken together, these alterations in metabolic and inflammatory responses to hemorrhage are likely to impair immediate outcome and predispose to tissue injury.

Water column anoxia, enhanced productivity and concomitant changes in δ13C and δ34S across the Frasnian–Famennian boundary (Kowala — Holy Cross Mountains/Poland)

The investigation of the trace element and organic geochemistry of the Frasnian–Famennian boundary section at Kowala (Holy Cross Mountains/Poland) shows that the lower water column was oxygen-deficient during late Frasnian and early Famennian times. The abundance and carbon isotopic composition of diaryl isoprenoids, biomarkers indicative for green sulfur bacteria, prove that euxinic waters reached into the photic zone, at least episodically. Total organic carbon (TOC) contents show two maxima that are time-equivalent to the Kellwasser horizons deposited in shallower water settings. Enhanced TOC concentrations are explained by a higher primary productivity, presumably as a consequence of an enhanced nutrient supply from the continent. The increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to TOC increased at the Frasnian–Famennian transition. The sulfur isotopic composition of pyritic- and organically bound sulfur shows a +27‰ excursion across the boundary. The observation that the δ 34S values of organic-bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source, likely early diagenetic sulfide. A change in the δ 13C of total dissolved inorganic carbon as a consequence of an enhanced burial of 12C-enriched organic carbon is indicated by a +3‰ excursion measured for TOC as well as for individual n-alkanes and isoprenoids. The burial of large amounts of organic carbon is expected to result in a decrease in pCO 2 and should affect the photosynthetic carbon isotope fractionation ( ε p). The fact that we observe no change in ε p can be explained by the circumstance that ε p was most probably at maximum values, as a consequence of high atmospheric and oceanic-dissolved CO 2 concentrations during the Devonian.

Long-haul flights may induce respiratory changes similar to ventilatory acclimatisation to altitude.

Ventilatory acclimatisation to altitude is associated with a progressive increase in ventilation, a progressive decrease in end-tidal PCO2 (PETCO2)1 and a progressive increase in the acute ventilatory sensitivity to hypoxia (AHVR)2. The duration and severity of hypoxia generally associated with these changes are both substantially greater than those associated with commercial airline flight. Nevertheless, commercial airline flight normally involves some reduction in cabin pressure, and this study sought to determine whether the associated reduction in inspired PO2 could also induce acclimatisation.

Anion uptake and acid-base and ionic effects during isolated and combined exposure to hypercapnia and nitrite in the freshwater crayfish, Astacus astacus.

Nitrite influx into crayfish showed saturation kinetics, supporting a carrier-mediated uptake. Addition of 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS: at 10(-5), 10(-4) and 10(-3) M) and bumetanide (at 10(-5) M and 10(-4) M) to the ambient water did not significantly affect nitrite influx. Rather than suggesting that neither Cl-/HCO3- exchange nor K+/Na+/2Cl- cotransport were involved in the transport, this may reflect that the gill cuticle has a low permeability to the pharmacological agents, or that the sensitivity of the transport mechanism to the inhibitors is low. Nitrite accumulation in the haemolymph was significantly decreased during hypercapnic conditions compared to normocapnic conditions. This supports the idea that an acid-base regulatory decrease in Cl-(influx)/HCO3- (efflux) induced by hypercapnia should decrease NO2- uptake if NO2- and Cl- share this uptake route. The respiratory acidosis caused by exposure to hypercapnia alone was partially compensated by HCO3- accumulation in the haemolymph. Combined exposure to hypercapnia and nitrite improved pH recovery, mainly by augmenting the [HCO3-] increase, but also by decreasing haemolymph PCO2. Exposure to nitrite in normocapnic water induced an initial increase in haemolymph [HCO3-] and later also a decrease in PCO2. Thus, the improved acid-base compensation during combined hypercapnia and nitrite exposure was an amplification of this nitrite-induced response. Haemolymph base excess rose much more than haemolymph [Ca], suggesting that transfer of acid-base equivalents between animal and water was more important than H+ buffering by exoskeletal CaCO3 in mediating the increase in haemolymph [HCO3-].

Evaluation of cerebrovascular reactivity in children [corrected] with chronic renal failure.

Developmental disturbances and encephalopathy have been observed in children with chronic renal failure (CRF). The aim of this study was to investigate the efficiency of the cerebral circulation in uremic children. The study group consisted of 10 children with CRF on conservative treatment, 8 children on continuous ambulatory peritoneal dialysis (CAPD), and 8 children on maintenance hemodialysis (HD). Examination was performed using a TC2-64B, EME Doppler flowmeter machine and capnograph Datex, Normocap. Blood flow velocity in both middle cerebral arteries (MCA), at rest and after spontaneous hyperventilation for 30 s, was analyzed. The vascular reactivity coefficient was calculated as the percentage ratio of decline of blood flow velocity in MCA to PCO2 decrease. Baseline mean blood flow velocities of MCA in euvolemic children under conservative treatment and on CAPD were significantly higher than those in children on HD and healthy control children. The highest value of the vascular reactivity coefficient was significantly higher in the group of children with CRF on conservative and CAPD treatment, than in children on HD and healthy controls. We suggest that hyperreactivity of the cerebral circulation could be the result of impaired autoregulation of blood flow. Evaluation of cerebrovascular reactivity in uremic children requires further examination.

Heliox improves ventilation during high-frequency oscillatory ventilation in pediatric patients.

OBJECTIVE: To describe improved ventilation during high-frequency oscillatory ventilation when a nitrogen-oxygen gas mixture is replaced by a helium-oxygen gas mixture. DESIGN: Case series. SETTING: A tertiary pediatric intensive care unit. PATIENTS: Five patients with hypoxemic respiratory failure who developed persistent respiratory acidosis during treatment with high-frequency oscillatory ventilation. INTERVENTIONS: Introduction of helium-oxygen into a conventional high-frequency oscillatory ventilation circuit. MEASUREMENTS AND MAIN RESULTS: Blood gas values (pH, Pco2, and Po2) were compared in these patients during treatment with high-frequency oscillatory ventilation with nitrogen-oxygen gas flow and then for several hours after a change in treatment to helium-oxygen gas flow. An initial 24% decrease in Pco2 was documented, and an ultimate 43% decrease in Pco2 was observed. The mechanism for this improved ventilation may be related to improved gas flow properties as well as increased CO2 diffusion resulting from helium's low-mass density. Oxygenation was not adversely affected in any way. CONCLUSION: In patients with hypoxemic respiratory failure and in whom respiratory acidosis develops during high-frequency oscillatory ventilation, the use of helium-oxygen rather than nitrogen-oxygen may improve ventilation and decrease ventilator-related trauma. Further investigation is needed to validate these findings and to elucidate the mechanisms of improved ventilation.

A preliminary study of the comfort of paced respiration

In order to obtain basal information about what type of externally paced respiration is comfortable, 25 male and 25 female undergraduate students were asked to practice self‐paced respiration. After a 1‐min rehearsal following instructions on comfortable self‐paced respiration, subjects carried out 2 min of self‐paced respiration and rated their level of comfort on a scale of 1–5. This was repeated (up to a maximum of seven times) until the subject recorded a high rating. Results indicated that self‐paced respiration was most comfortable, irrespective of sex, when a respiratory pattern was attained of half the respiratory rate and nearly twice the tidal volume of the trainee's resting condition. Although respiratory sinus arrhythmia and heart rate were indicative of a decrease in cardiac vagal activity and end‐tidal PCO2 was suggestive of a reduction in anxiety, these effects were small. The results have implications for the utilization of externally paced respiration.

Doxapram accentuates white matter injury in neonatal rats following bilateral carotid artery occlusion

The effect of the respiratory stimulant, doxapram, on white matter damage was investigated in neonatal rats under cerebral ischemia. Five-day-old rats underwent bilateral carotid artery occlusion with or without 50 mg/kg i.p. of doxapram. Their brains were neuropathologically examined 48 h later. Doxapram induced about a 20% decrease of PCO 2 for 90 min, but did not cause any neuropathological abnormalities. Bilateral carotid artery occlusion resulted in mild cerebrocortical lesions in 67% of pups, and white matter lesions in the internal capsule in 44%. Doxapram, in addition to bilateral carotid artery occlusion, produced more severe white matter injury in the internal capsule (injury score; 0.67±0.87 vs. 1.70±0.48, P<0.05) and in the subcortical white matter (0.33±0.67 vs. 1.10±0.54, P<0.05). These results demonstrated that the use of doxapram under an ischemic condition accentuates white matter damage in neonatal rats.

Biological pump and vertical mixing in the southern ocean: Their impact on atmospheric CO2

A global box model simulating nitrogen and carbon cycling in the ocean has been developed. The distinctive feature of the model is the detailed description of the seasonal cycles of the oceanic upper mixed layer (UML) ecosystem. Unlike other ocean regions, phytoplankton productivity in the Southern Ocean is assumed to be limited by low iron availability, leading to twofold decrease in the phytoplankton growth rate. Calculated ecosystem and carbon cycle characteristics are in a good agreement with available observational data and conceptual models of generalized phytoplankton seasonal cycles in the world ocean. The model estimates of the global ocean new production outside of shelf regions and the preindustrial atmospheric pCO2 are 9.9 Gt C/yr and 282 ppm, respectively. Results of numerical experiments with the model showed that the potential new production which might be reached by allowing phytoplankton maximum growth rate to increase is 29 Gt C/yr (76% of this increase is contributed by the Southern Ocean) and corresponds to an atmospheric pCO2 of 205 ppm; however, this would require an unrealistic tenfold increase in growth rate. The large contribution of the Southern Ocean is accounted for by the high‐nutrient, low‐chlorophyll (HNLC) conditions existing in this region caused by the high dissolved inorganic nitrogen concentrations below the UML, deep mixing during the austral summer, and iron limitation of phytoplankton productivity. A realistic (twofold) increase in the phytoplankton growth rate in the Southern Ocean which can be considered as a maximal effect of iron fertilization results in the lowering of atmospheric pCO2 by only 10 ppm. Changes in the UML depth in the Southern Ocean (a wintertime shallowing and summertime deepening of the UML in comparison with preindustrial conditions) could lead to a decrease of atmospheric pCO2 by 15 ppm at the most. The combined effect of iron fertilization and these changes in vertical mixing might constitute about 30–35 ppm, that is, less than one half of the lowering of 80 ppm during the last glaciation.

Partition of plasma hydrogen ion concentration changes during repeated sprints.

Increases in blood [H+] and lactic acid [La-] attend fatigue. We applied Stewart's physiological model of acid-base status and simple regressions to assess the importance of independent variables and [La-] on [H+] during repeated sprints. Eight well-conditioned Arabians performed 9 sprints. Plasma from jugular vein samples was analysed for pH, PCO2, Na+, K+ and Cl-. Plasma [La-] was calculated from blood [La-], plasma [H+] from pH, SID from Na+, K+, Cl- and La-, Atot from pH, PCO2 and SID. Peaks for SID, PCO2 and [H+] were reached at sprint 1, -2 and -3, respectively. At sprint 3, the 5.7 nmol/l peak in [H+] was partitioned into 2.3, 2.7 and 0.7 nmol/l for Atot, PCO2 and SID, respectively. From sprint 3 to sprint 9, increases in Atot and decreases in SID tended to increase [H+] but were counteracted by a steady decrease in PCO2 that determined the progressive decrease in [H+]. Therefore PCO2 was the dominant determinant of [H+] during 9 repeated sprints, and the expected major effect of [La-] was moderated in the SID by opposing increases in [Na+] and [K+]. In the work-adapted phase (sprints 3-9), decreasing [H+] was correlated positively with PCO2 (r = 0.997, P < 0.001) but negatively with La- (r = -0.986, P < 0.001). Respiration was therefore completely compensating for the effects of metabolism on [H+]. During the transition from rest to sprint 3 (peak plasma [H+]), increasing [H+] was highly correlated (r = 0.99, P = 0.011) with [La-] but no other variable. The empirical and physiological analyses were consistent with one another during the work-adapted phase, but emphasis was placed on [La-] by the regression analysis, in contrast to PCO2 by the Stewart analysis, during the rest-work transition.

Miocene evolution of atmospheric carbon dioxide

Changes inpCO2or ocean circulation are generally invoked to explain warm early Miocene climates and a rapid East Antarctic ice sheet (EAIS) expansion in the middle Miocene. This study reconstructs late Oligocene to late MiocenepCO2from εpvalues based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from Deep Sea Drilling Project sites 588 and 608 and Ocean Drilling Program site 730. Our results indicate that highestpCO2occurred during the latest Oligocene (∼350 ppmv) but decreased rapidly at ∼25 Ma. The early and middle Miocene was characterized by lowpCO2(260–190 ppmv). Lower intervals ofpCO2correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle Miocene. There is no evidence for either highpCO2during the late early Miocene climatic optimum or a sharppCO2decrease associated with EAIS growth. Paradoxically,pCO2increased following EAIS growth and obtained preindustrial levels by ∼10 Ma. Although we emphasize an oceanographic control on Miocene climate, lowpCO2could have primed the climate system to respond sensitively to changes in heat and vapor transport.

Interactions of calcareous suspended sediment with glacial meltwater: a field test of dissolution behaviour

Abstract Dissolution of calcite and associated interactions of suspended sediment with aqueous solution were investigated in a tributary-free 600 m reach of the main meltstream draining the Tsanfleuron glacier, Switzerland, over a 24-h cycle during which solute concentrations varied inversely with discharge. Downflow, solute calcium, strontium, and alkalinity increased because of calcite dissolution. Using flow-through times from salt-dilution gauging, a consistent small sulphate excess at the downstream site was observed. Given the slowness of sulphate supply by pyrite oxidation, this excess sulphate can be attributed to mixing of around 1% of ion-rich water (seeping from till banks) with the main meltstream. Calcite dissolution is normally directly proportional to exposed surface area of the mineral, yet only a small increase in calcite dissolution was observed when suspended sediment increased by a factor of 25 to 1.3 g/l at peak flow. The suspended sediment displays little variation in size distribution with total suspended load, and contains 30–40% calcite with a minimum specific surface area (S) of 0.25 m2/g sediment. Application of the Plummer–Wigley–Parkhurst (PWP) model predicts dissolution rates broadly similar to those found at lower suspended sediment concentrations given this value of S. At higher suspended sediment loads predicted dissolution rates are too high. This discrepancy is reduced by use of the Buhmann–Dreybrodt (B–D) model which takes explicit account of the slowness of hydration of aqueous carbon dioxide, and the problem of mass transfer of H2CO3 given the surface area of calcite to volume of solutions considered. The remaining discrepancy implies less interaction than expected of suspended sediment particles with turbulent meltwater at high suspended sediment concentrations. The effects of proglacial modification of meltstream geochemistry in this case is a strong decrease in PCO2 accompanied by an increase in total ion load, but decreases in Mg/Ca and Sr/Ca, from the high values characteristic of low water–rock ratio interactions in subglacial environments and till. Nevertheless, the distinctive chemical imprint in meltstream chemistry of non-congruent mineral dissolution in low water–rock ratio glacial weathering environments remain. In contrast, in terrains where calcite is scarce, it will tend to dissolve congruently, contributing significantly to total solutes, and its dissolution will be less limited by CO2 reaction kinetics.

A global oceanic sediment model for long‐term climate studies

A chemically reactive 10‐layer sediment module was coupled to a geochemical ocean general circulation model (the Hamburg Oceanic Carbon Cycle Model). The sediment model includes four solid sediment components (CaCO3, opal, organic carbon, and clay), and five pore water substances (dissolved inorganic carbon, total alkalinity, PO43−, O2, Si(OH)4) plus corresponding species containing 13C and 14C instead of 12C. The processes, namely, particle deposition, pore water reactions, pore water diffusion and interaction with the open water column, vertical sediment advection, sediment accumulation, and bioturbation, are simulated through basic parametrizations. For the water column part the Si and C cycles are coupled by a formulation of the “rain ratio” Si:C(CaCO3):C(POC), where POC is particulate organic carbon, in biogenic particle export production, with CaCO3 frustrule production growing in parallel to a weakening of opal production during progressing deficiency of dissolved silicate in the surface layer. For two preindustrial velocity fields the model reproduces major features of observed water column and sediment tracer distributions parallel to a correct preindustrial CO2 level close to 280 ppm. The model reacts sensitively to the formulation of the POC flux parametrization, the rain ratio, as well as the solubility of opal but is fairly insensitive to changes in the bioturbation rate as well as the amount of clay deposition. A simulation of the sediment distribution by use of a velocity field, which represents the ocean at conditions during the last glacial maximum, yields realistic glacial‐interglacial changes for the Atlantic Ocean, while discrepancies remain for the Indo‐Pacific region. A significant decrease of the atmospheric pCO2 could be achieved through an additional change of water column inventories by a change in weathering input of Si and alkalinity.

Effects of hyperthermia on uterine blood flow and shunting through uterine arteriovenous anastomoses in the late-pregnant ewe

The effect of maternal hyperthermia on uterine blood flow (UBF) through the two main uterine arteries and on the proportion of UBF shunted through uterine arteriovenous anastomoses (AVAs) was investigated. Eight late-pregnant ewes were exposed to normothermic (22-23 degrees C) or hyperthermic (approximately 39 degrees C) ambient conditions for 8 h. UBF was measured in the left and right uterine arteries using flow probes and microspheres were injected into the uterine artery before, during and after the experimental period. The distribution of microspheres between the uterus and lungs was determined to calculate changes in capillary and AVA blood flows. Hyperthermia produced a significant (P<0.05) increase in maternal core temperature (+1.5 degrees C), increase in maternal blood pH (+0.21; P<0.05) and decrease in maternal pCO2 (-16.2 mmHg; P<0.05). Blood flow to the uterine horn ipsilateral to the corpus luteum (CL) remained unchanged during hyperthermia, whereas total UBF and blood flow to the contralateral uterine horn were significantly decreased (P<0.05), by 23.1% and 20.8%, respectively, of pre-heat control values. The proportion of UBF shunted through uterine AVAs during hyperthermia was not significantly different from values observed in normothermic ewes (21.9 +/- 0.7%). Mild to moderate hyperthermia in late-pregnant sheep induces respiratory alkalosis and decreases total blood flow to the uterus, brought about by a decrease in blood flow to the uterine horn contralateral, but not ipsilateral to the CL. Heat treatment does not alter the proportion of UBF traversing uterine AVAs.

Cerebral hemodynamic response to generalized spike-wave discharges.

Data in the literature concerning metabolic demand during generalized spike-wave activity (gSW) are conflicting. We investigated instantaneous changes in cerebral blood flow velocities (CBFV) in both middle cerebral arteries (MCAs) by transcranial Doppler sonography (TCD) during gSW paroxysms recorded by scalp EEG. In 13 patients, CBFVs in both MCAs were averaged, time-locked to the occurrence of the gSW; respiratory rate (RR) and end-expiratory pco2 were measured in one patient. Nine patients showed significant changes in CBFV during gSW. Four had biphasic flow changes with an initial increase (p < 0.05) and a subsequent decrease (p < 0.01). This was partially paralleled by an increase in RR (p < 0.01) and a decrease in pco2 (p < 0.01). In three patients, an increase in CBFV that preceded the onset of gSW by several seconds was observed, followed by a decrease in CBFV. Two patients showed a significant decrease only of CBFV. Only gSWs of a median duration of >0.8 s were associated with significant changes in CBFV. We were able to demonstrate that gSWs of several seconds duration lead to cortical perfusion changes. We suggest that the initial increase of CBFV demonstrated in some patients reflects neuronal activation, whereas the subsequent decrease might in part be due to hyperventilation-induced hypocapnia.

A Late Cambrian positive carbon-isotope excursion in the Southern Appalachians; relation to biostratigraphy, sequence stratigraphy, environments of deposition, and diagenesis

ABSTRACT A positive carbon-isotope excursion is recorded within the Upper Cambrian sedimentary succession in the southern Appalachians that consists of the Nolichucky Shale, the Maynardville Formation, and the Copper Ridge Dolomite. The lower part of the succession contains Aphelaspis zone fauna (Early Steptoean). The extensively dolomitized and poorly fossiliferous nature of the upper part of the succession precludes any detailed biostratigraphic determinations. Correlation with similar positive carbon-isotope excursions in coeval successions elsewhere suggests that this excursion represents a perturbation in the global cycling of carbon. Comparison of excursions at different localities in North America provides a means for the application of carbon-isotope stratigraphy. In the southern Appalachians the excursion started during deposition of the upper Nolichucky Shale. Maximum 13C values (4 to 5o/oo PDB) are associated with the conformable interval at the Maynardville/Copper Ridge Dolomite transition, which has been interpreted as a correlative conformity in sequence-stratigraphic terms. The excursion ended during deposition of the lower Copper Ridge Dolomite. In western North America the excursion started at the base of the Pterocephaliid Biomere (near the base of the Aphelaspis Zone). This well-documented excursion ended prior to the end of the Pterocephaliid Biomere, with the maximum excursion at the Sauk II/Sauk III unconformity. This supports the correlation between Late Steptoean (Dresbachian/Franconian) sea-level fall and the sequence boundary at the end of Cambrian Grand Cycle deposition in the southern Appalachians. The cause of this carbon-isotope excursion remains unclear. The excursion most likely reflects the enhanced burial of organic carbon promoted by ocean stratification, a warm nonglacial climate, and a sea-level maximum during the early Late Cambrian. The onset of regression may have contributed to the maximum carbon-isotope excursion by enhancing sedimentation rates, and by increasing organic productivity because of increased nutrient availability. The removal of carbon from the ocean surface may have caused a decrease in pCO2 of the atmosphere. The resulting cooling episode could have triggered an oceanic overturn bringing 12C-enriched bottom waters to the surface, which in conjunction with oxidation of organic matter during the sea-level fall, ended the carbon-isotope excursion. Comparison of 13C and 18O values of matrix samples to the associated cement phases provides insights into the relationship between isotope variations and depositional and diagenetic environments. 13C values of peritidal dolomicrite define a rather smooth stratigraphic variation curve, whereas the values for subtidal micrite have significant scatter resulting from involvement of organic matter in diagenesis. Fibrous to bladed calcite cement from the subtidal deposits has 13C and 18O values comparable to the associated micrite, suggesting precipitation from marine water and similar diagenetic modifications. Meteoric diagenesis may be responsible for the depletion of 13C and 18O in equant calcite cement relative to the micrite. For saddle dolomite cement, the depletion of 18O and 13C values similar to those for the peritidal dolomicrite, are consistent with formation during burial at elevated temperatures in a rock-dominated system. This study demonstrates the potential of applying carbon-isotope stratigraphy, developed in highly fossiliferous successions, to stratigraphic intervals with poorly constrained biostratigraphy. Such studies require evaluation of the effects of depositional environments and diagenesis upon the preservation of marine isotope signatures.

Variability of pCO2 on diel to seasonal timescales in the Sargasso Sea near Bermuda

Continuous underway measurements of atmospheric and surface seawater pCO2 were collected on numerous cruises in the Sargasso Sea (32°N, 64°W) near Bermuda from June 1994 to November 1995. We observed that seawater pCO2 was highly variable on different timescales, ranging from diel to seasonal. On diel timescales, pCO2 changes of 5–25 μatm occurred in response to diurnal warming and cooling associated with solar heat fluxes. Over longer timescales, pCO2 was influenced by atmospheric forcing and tropical cyclones. For example, a surface cooling of 3°C and decrease in pCO2 of 45–50 μatm occurred after Hurricane Felix passed near Bermuda in August 1995. The decrease in pCO2 was significant considering the annual change was 90–100 μatm. Over all timescales, temperature was the dominant control on pCO2 variability. We found that surf ace pCO2 conditions were accurately predicted from temperatures with small errors (4–9 μatm) if seasonal pCO2‐temperature relationships were established. In future synthesis of regional pCO2 data it should be feasible to use surface temperature, remotely sensed from space, as a tool for extrapolation over wider spatial scales in the North Atlantic subtropical gyre. Net annual fluxes of CO2 for 1994 and 1995 (−0.25 to −0.6 mol CO2 m−2 yr−1) were directed from atmosphere to ocean and were similar to values reported for 1989–1993 by Bates et al. [1996b]. We found that short‐term variability of pCO2 (diel warming and cooling or atmospheric forcing), frequency of sampling (every 3–4 days or monthly), or use of temperature‐derived pCO2 did not affect estimates of net yearly CO2 fluxes by more than 10–20%. However, strong winds associated with hurricanes decreased the net annual flux of CO2 into the ocean by 19–28% in 1995. The major sources of error for air‐sea gas exchange was uncertainty associated with gas transfer‐wind speed relationships and differences in the types of wind speed data used (daily averaged versus climatological). Such uncertainties make it difficult to quantify the contribution of gas exchange to the carbon cycle and the balance of carbon import and export terms in the upper ocean of the Sargasso Sea.

Effects of antivenom serotherapy on hemodynamic pathophysiology in dogs injected with L. quinquestriatus scorpion venom

In dogs, scorpion venom causes an immediate increase in cardiac output that declines below baseline values within one hour. We tested the hypotheses that antivenom given before venom injection may prevent changes in cardiac output, while antivenom given after the inotropic stage of envenomation cannot reverse cardiac output decline. Twenty-five anesthetized, mechanically ventilated dogs were given 0.1 mg/kg IV venom of the scorpion Leiurus quinquestriatus. The dogs were randomized into 4 groups: 5 dogs were given venom alone (control group) and 6 dogs were given 6 ml of antivenom one minute before venom injection while 8 and 6 dogs were given 6 ml of antivenom 20 and 60 min after venom injection, respectively. Parameters reflecting respiratory and circulatory functions were measured for 180 min after venom injection. Scorpion venom caused a gradual decrease in heart rate, an initial elevation of systemic and pulmonary blood pressure and cardiac output followed by a decline in these parameters. PO 2, pH and HCO 3 − gradually decreased, while PCO 2 gradually increased from baseline. Antivenom given before venom injection prevented all the effects induced by the venom. Antivenom given at 20 and 60 min after venom injection had no effect on cardiac output and HCO 3 − decline, but caused an increase in heart rate, PO 2 and pH and a decrease in PCO 2. We assume that antivenom clears free toxins from the circulation, and since cardiac output and HCO 3 − did not improve after this clearance, we conclude that following intravenous venom injection, heart and circulation are rapidly affected by the toxins or by other substances released by the venom which do not respond to antivenom. Improvements in respiration and heart rate with antivenom given after venom injection may be secondary to reversion of cholinergic effects of the venom. Improvement in respiration may be also explained by reversion of the toxic effects on Ca 2+ activated K + channels of bronchial smooth muscle. All these effects may be secondary to clearance of toxins by the antivenom.

Effects of vasodilators and perfusion pressure on coronary flow and simultaneous release of nitric oxide from guinea pig isolated hearts.

The aims were to validate the use of a direct reading NO electrode, to compare the effects of diverse acting drugs on altering coronary flow (CF) and NO release, and to examine the effects of altered perfusion pressure on flow-induced changes in NO concentration [NO] in the hemoglobin free effluent of guinea pig isolated hearts. Hearts were isolated and perfused initially at a constant perfusion pressure (55 mmHg) with a modified Krebs-Ringer's solution equilibrated with 97% O2 and 3% CO2 at 37 degrees C. Heart rate, left ventricular pressure, CF, and effluent pH, pCO2, pO2, and NO generated current were monitored continuously on-line. Effluent was sampled for L-citrulline. Percent O2 extraction and O2 consumption were calculated. [NO] was quantitated with a sensitive amperometric sensor (sensitivity > or = 1 nmol/l approximately 3 pA) and a selective gas permeable membrane. The electrode was not sensitive to changes in solution pO2, flow, or pressure. The electrode was sensitive to pCO2 (-0.50 nmol/l/mmHg) and temperature (+24.5 nmol/l/degree C), so coronary effluent pCO2 was measured to compensate for a small decrease in pCO2 that occurred with an increase in coronary flow, and effluent temperature was rigidly controlled. Serotonin, bradykinin, and nitroprusside increased NO release along with CF, whereas nifedipine, butanedione monoxime, zaprinast, and bimakalim comparably increased CF but did not increase [NO] or NO release. Increases in CF (ml/g/min) and NO release (pmol/g/min), respectively, were 5.0 +/- 1 and 100 +/- 17 for 1 mumol/l serotonin, 7.5 +/- 1 and 148 +/- 18 for 100 nmol/l bradykinin, and 7.8 +/- 1 and 173 +/- 28 for 100 mumol/l nitroprusside. The increases in effluent NO by bradykinin were proportional to the increases in L-citrulline. Tetraethylammonium decreased CF, but did not change NO release, indomethacin changed neither CF nor NO release, and NG-nitro-L-arginine methyl ester (L-NAME) reduced CF by 2.6 +/- 1 ml/g/min and NO release by 25 +/- 8 pmol/g/min. An increase of CF of 8.0 +/- 0.3 ml/g/min, produced by increasing perfusion pressure from 25 to 90 mmHg, increased [NO] by 30 +/- 4 nmol/l; L-NAME but did not reduce the pressure-induced increase in CF, but reduced the increase in [NO] to 10 +/- 5 nmol/l. This study demonstrates in intact hearts real-time release of NO by several vasodilator drugs and by pressure-induced increases in flow (shear stress) and attenuation of these effects by L-NAME.