Impact of dialysis modality and acidosis on nutritional status

Experimental evidence suggests that acidosis may have a deleterious effect on protein metabolism. We evaluated 124 chronic dialysis patients (59 +/- 17 years) and defined acidosis as an anion gap >18 meq/L. A direct correlation (p < 0.0001 was found between anion gap and serum albumin (R = 0.402), BUN (R = 0.488), and serum creatinine (R = 0.473) concentrations. Acidotic patients (43%), when compared with nonacidotic patients, had greater serum albumin concentrations (3.95 +/- 0.50 vs. 3.60 +/- 0.48 g/dl, p = 0.0001, respectively), higher normalized protein catabolic rates (1.12 +/- 0.27 vs. 0.96 +/- 0.26 g/kg/d, respectively; p = 0.0004), and higher BUN (70 +/- 19 vs. 55 +/- 17 mg/dl, p = 0.0001) and serum creatinine (11.1 +/- 3.4 vs. 8.3 +/- 3.2, p = 0.0001 mg/dl) concentrations. However, no differences in midarm muscle circumference, fat free mass, or body cell mass were noted between groups when assessed by dialysis modality or acidosis status. In conclusion, mild chronic metabolic acidosis, likely caused by increased dietary protein intake, does not independently and adversely impact nutritional status in chronic dialysis patients.

Hemodynamic responses to acute carboxyhemoglobinemia in the rat

The effects of carbon monoxide on the hemodynamics of the adult rat were investigated. A number of parameters were measured using an open-chest, chloralose-urethan anesthetized preparation. Our experiments showed this anesthetic agent to have several advantages over pentobarbital sodium. One group inhaled 150 ppm CO for 0.5-2 h, carboxyhemoglobin (HbCO) reaching 16%. Heart rate, cardiac output, cardiac index, dF/dtmax (aortic), and stroke volume rose significantly; mean arterial pressure, total peripheral resistance, and left ventricular systolic pressure fell, whereas stroke work, left ventricular dP/dtmax, and stroke power changed little. These effects were evident at a HbCO saturation as low as 7.5% (0.5 h). A second group inhaled 500 ppm CO for 5-48 h, HbCO reaching 35-38%. The same parameters changed in the same direction as in the first group, with mean arterial pressure and peripheral resistance remaining depressed, while heart rate, cardiac output, cardiac index, and stroke volume remained elevated. Heart rate and arterial systolic pressure were also monitored in conscious rats; rats in one group inhaled 500 ppm CO for 24 h, and rats in a second group were injected with a bubble of pure CO ip. In both cases heart rate was sharply elevated and blood pressure depressed as HbCO saturation increased. Both parameters recovered on CO washout. There was no significant difference between the response to inhaled vs. injected CO.

The impact of insect herbivory on biogeochemical cycling in broadleaved forests varies with temperature

Herbivorous insects alter biogeochemical cycling within forests, but the magnitude of these impacts, their global variation, and drivers of this variation remain poorly understood. To address this knowledge gap and help improve biogeochemical models, we established a global network of 74 plots within 40 mature, undisturbed broadleaved forests. We analyzed freshly senesced and green leaves for carbon, nitrogen, phosphorus and silica concentrations, foliar production and herbivory, and stand-level nutrient fluxes. We show more nutrient release by insect herbivores at non-outbreak levels in tropical forests than temperate and boreal forests, that these fluxes increase strongly with mean annual temperature, and that they exceed atmospheric deposition inputs in some localities. Thus, background levels of insect herbivory are sufficiently large to both alter ecosystem element cycling and influence terrestrial carbon cycling. Further, climate can affect interactions between natural populations of plants and herbivores with important consequences for global biogeochemical cycles across broadleaved forests.

Leaf spectroscopy of resistance to Ceratocystis wilt of 'Ōhi'a

Plant pathogens are increasingly compromising forest health, with impacts to the ecological, economic, and cultural goods and services these global forests provide. One response to these threats is the identification of disease resistance in host trees, which with conventional methods can take years or even decades to achieve. Remote sensing methods have accelerated host resistance identification in agricultural crops and for a select few forest tree species, but applications are rare. Ceratocystis wilt of 'ōhi'a, caused by the fungal pathogen Ceratocystis lukuohia has been killing large numbers of the native Hawaiian tree, Metrosideros polymorpha or 'Ōhi'a, Hawaii's most common native tree and a biocultural keystone species. Here, we assessed whether resistance to C. lukuohia is detectable in leaf-level reflectance spectra (400-2500 nm) and used chemometric conversion equations to understand changes in leaf chemical traits of the plants as indicators of wilt symptom progression. We collected leaf reflectance data prior to artificially inoculating 2-3-year-old M. polymorpha clones with C. lukuohia. Plants were rated 3x a week for foliar wilt symptom development and leaf spectra data collected at 2 to 4-day intervals for 120 days following inoculation. We applied principal component analysis (PCA) to the pre-inoculation spectra, with plants grouped according to site of origin and subtaxon, and two-way analysis of variance to assess whether each principal component separated individuals based on their disease severity ratings. We identified seven leaf traits that changed in susceptible plants following inoculation (tannins, chlorophyll a+b, NSC, total C, leaf water, phenols, and cellulose) and leaf chemistries that differed between resistant and early-stage susceptible plants, most notably chlorophyll a+b and cellulose. Further, disease resistance was found to be detectable in the reflectance data, indicating that remote sensing work could expedite Ceratocystis wilt of 'ōhi'a resistance screenings.

Impacts of insect frass and cadavers on soil surface litter decomposition along a tropical forest temperature gradient

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q 10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Impact of peritoneal dialysis modality and acidosis on nutritional status in peritoneal dialysis patients

Continuous ambulatory (CAPD) and continuous cyclic peritoneal dialysis (CCPD) differ in solute transport, and variances in mass balance could impact nutritional parameters. Chronic acidosis may decrease albumin synthesis and increase catabolism. We prospectively studied 50 peritoneal dialysis patients (age: 55 +/- 16 yrs; CAPD = 33; CCPD = 17) over 24 months. Acidosis was defined by an anion gap > 18 mEq/L. Bioimpedance analysis was used to estimate body cell mass and fat-free mass. Patients on CAPD had a lower body mass index than CCPD patients (27 +/- 5 kg/m2 vs. 29 +/- 9 kg/m2 respectively; P = 0.039). However no differences were observed in body cell mass (25 +/- 8 kg vs. 26 +/- 9 kg respectively; P = 0.787) or fat-free mass (53 +/- 14 kg vs. 50 +/- 18 kg respectively; P = 0.404). Urea kinetic modeling showed no differences in Kpt/V or nPCR (0.26 +/- 0.06 vs. 0.24 +/- 0.07; P = 0.709 and 0.67 +/- 0.29 g/kg per day vs. 0.65 +/- 0.23 g/kg per day; P = 0.709 for CAPD and CCPD respectively). When categorized by the presence of acidosis no differences were observed in body cell mass (24 +/- 8 kg vs. 27 +/- 9 kg respectively; P = 0.131) or fat-free mass (54 +/- 15 kg vs. 50 +/- 16 kg respectively; P = 0.348), while body mass index was greater in acidotic than nonacidotic individuals (30 +/- 8 kg/m2 vs. 26 +/- 6 kg/m2 respectively; P = 0.005). Dietary protein intake assessed as nPCR was similar in both groups (0.64 +/- 0.26 vs. 0.71 +/- 0.28 g/kg per day; P = 0.319, for CAPD and CCPD respectively). We conclude that over a 24-month period neither peritoneal dialysis modality nor the presence of acidosis has a detrimental influence on nutritional parameters in well dialyzed patients.