Cardiopulmonary effects of a halothane/oxygen combination in hypovolemic cats.

The cardiopulmonary effects of a halothane/oxygen combination were studied in eight cats subjected to a 25% whole blood volume loss. Test parameters included cardiac output measured via thermodilution, heart rate, respiratory rate, arterial blood pressure (systolic, diastolic and mean) and blood gas analysis. Values for cardiac index, stroke volume and systemic vascular resistance were calculated from these data. Posthemorrhage cardiac output, cardiac index, stroke volume and measurements of arterial blood pressure were significantly decreased (p less than 0.05). Heart rate remained unchanged. Following induction of halothane anesthesia the above parameters experienced a further significant decline (p less than 0.05) from their immediate preanesthetic (i.e. posthemorrhage) values. Heart rate also significantly decreased (p less than 0.05). Thirty minutes following the cessation of halothane anesthesia these values returned to near-hemorrhage levels, being above their respective preanesthetic values. Systemic vascular resistance initially rose, peaking ten minutes into halothane anesthesia, before gradually falling to prehemorrhage values at the end of halothane anesthesia. Following hemorrhage, respiratory rate demonstrated a transient increase, associated with an arterial CO2 tension fall, before returning to initial values at the preanesthetic time. During halothane anesthesia respiratory rate remained unchanged whereas arterial CO2 tension rose significantly (p less than 0.05) and pH declined slightly from preanesthetic readings. These returned to prehemorrhage values 30 minutes following the cessation of halothane anesthesia.     

Suitability of the ESS laboratory method to determine the equilibrium soil solution composition of agricultural soils,and suggestions for simplification of the experimental procedure

The proper selection of the background electrolyte is of special importance studying element availability and mobility in the laboratory. The determination of the background solution composition can be done with the equilibrium soil solution method ESS (Matschonat and Vogt, 1997). The ESS method is a procedure to find out a salt solution of major cations and anions that does not undergo changes in its composition when brought into contact with a specific soil sample. This composition is experimentally approximated in an iterative procedure until certain quality criteria are fulfilled. We tested if the ESS method, which was developed for forest soils, can successfully be applied also to agricultural soils. The solution composition was confirmed by an independent method. We used samples of a glasshouse and an arable loess soil. Because the ESS method is relatively time and work consuming, we tested modifications which should simplify the procedure: the use of dried and frozen samples instead of field fresh soil, an approximation according to the solution's electric conductivity only, and the modeling of cation exchange to omit iteration steps. The ESS method caused slight overestimation (10–25 %) in cation concentrations, but in general, these were well met. Individual anion concentrations, however, were not buffered in this soil and could not unequivocally be determined. We recommend to adjust the anion concentrations in the ESS procedure according to their proportions in an initial water extract. As ion concentrations are functions of the soil : solution ratio, any method based on addition of water to the soil, like the so‐called soil saturation extract (Germany: Bodensättigungsextrakt), runs a risk to seriously underestimate ion concentrations at field conditions. The ESS method may therefore be especially well suited for soils with a low water content. The use of frozen soil gave good results and the omission of iteration steps by cation exchange modeling was promising and will be explored with the aim to operationalize it in forthcoming work.     

Cardiopulmonary effects of a ketamine hydrochloride/acepromazine combination in healthy cats.

The effect of a ketamine hydrochloride/acepromazine combination on the cardiopulmonary function of 11 healthy cats was studied. Test parameters included cardiac output, measured by thermodilution, heart rate, respiratory rate, arterial blood pressure (systolic, diastolic and mean) and arterial blood gas analysis. Values for systemic vascular resistance, cardiac index and stroke volume were calculated. The cardiac output, cardiac index, stroke volume, arterial blood pressure and arterial blood pH decreased significantly (p less than 0.006). The arterial CO2 increased significantly (p less than 0.006). All changes occurred during the five to 45 minute postinduction time period. The heart rate, respiratory rate, arterial O2 and systemic vascular resistance were not significantly altered. The anesthetic regime maintained an adequate plane of surgical anesthesia for 30-45 minutes.     

Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere

Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of ?0.0063 and ?0.0316 MPa) and with or without addition of ¹³C labelled rye residues (δ¹³C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at ?0.0063 MPa, whereas 41.7% remained on soils at ?0.0316 MPa. Most of the lost litter C was mineralised to CO₂, with 47.9% and 43.4% at ?0.0063 and ?0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.     

Microbial uptake of low‐molecular‐weight organic substances out‐competes sorption in soil

Low‐molecular‐weight organic substances (LMWOS) such as amino acids, sugars and carboxylates, are rapidly turned over in soil. Despite their importance, it remains unknown how the competition between microbial uptake and sorption to the soil matrix affects the LMWOS turnover in soil solution. This study describes the dynamics of LMWOS fluxes (10 µm ) in various pools (dissolved, sorbed, decomposed to CO₂ and incorporated into microbial biomass) and also assesses the LMWOS distribution in these pools over a very wide concentration range (0.01–1000 µm ). Representatives of each LMWOS group (glucose for sugars, alanine for amino acids, acetate for carboxylates), uniformly ¹⁴C‐labelled, were added to sterilized or non‐sterilized soil and analysed in different pools between 1 minute and 5.6 hours after addition. LMWOS were almost completely taken up by microorganisms within the first 30 minutes. Surprisingly, microbial uptake was much faster than the physicochemical sorption (estimated in sterilized soil), which needed 60 minutes to reach quasi‐equilibrium for alanine and about 400 minutes for glucose. Only acetate sorption was instantaneous. At a concentration of 100 µm , microbial decomposition after 4.5 hours was greater for alanine (76.7 ± 1.1%) than for acetate (55.2 ± 0.9%) or glucose (28.5 ± 1.5%). In contrast, incorporation into microbial biomass was greater for glucose (59.8 ± 1.2%) than for acetate (23.4 ± 5.9%) or alanine (5.2 ± 2.8%). Between 10 and 500 µm , the pathways of the three LMWOS changed: at 500 µm , alanine and acetate were less mineralized and more was incorporated into microbial biomass than at 10 µm , while glucose incorporation decreased. Despite the fact that the LMWOS concentrations in soil solution were important for competition between sorption and microbial uptake, their fate in soil is mainly determined by microbial uptake and further microbial transformations. For these substances, which represent the three main groups of LMWOS in soil, the microbial uptake out‐competes sorption.     

Cardiopulmonary effects of a halothane/oxygen combination in healthy cats.

The effects of a halothane/oxygen combination on the cardiopulmonary function of 11 healthy cats were studied. Test parameters included cardiac output, measured via thermo-dilution, heart rate, respiratory rate, arterial blood pressure (systolic, diastolic and mean) and blood gas analysis. Values for systemic vascular resistance, cardiac index and stroke volume were calculated from these data. Cardiac output, cardiac index, heart rate, stroke volume, arterial blood pressure (systolic, diastolic and mean) and arterial blood pH were significantly decreased (p less than 0.001). Respiratory rate was also significantly decreased (p less than 0.007) with arterial CO2 tension being significantly increased (p less than 0.001). Statistically significant changes, where seen, persisted for the duration of the anesthetic period. Arterial O2 tension and systemic vascular resistance remained unchanged. All parameters returned to near pretest values within 30 minutes following cessation of halothane anesthesia.