Mid- and Long-Term Effects of Wildfire and Debris Flows on Stream Ecosystem Metabolism

Wildfire is an important and prevalent agent of disturbance in vegetated landscapes across much of the Earth’s surface, including forested watersheds in the arid western USA. Between 1992 and 2003, \u3e40% of the watersheds in the upper reaches of the Boise River watershed in central Idaho burned. The purpose of our study was to investigate the legacy effects of wildfire on stream ecosystems by analyzing the relationship between wildfire and resulting debris flows and their joint effects on stream ecosystem metabolism in 31 streams. The watersheds of ∼½ of these streams burned within the last 11 y, and some of these burned watersheds also experienced large-scale debris flows 1 y postfire. Streams with burned watersheds recovered quickly, and estimates of photosynthetically active radiation, gross primary production, and ecosystem respiration were indistinguishable from those in streams draining unburned watersheds. However, streams that experienced debris flows after their watersheds burned were remarkably different. They exhibited higher production and incident light and lower ecosystem respiration. Debris flows resulted in nearly complete removal of streamside vegetation, slowed recovery of the riparian canopy, and altered stream ecosystem metabolism. Our results suggest a synergistic interaction between wildfire and associated geomorphological processes whereby debris flows delay succession of stream ecosystems, possibly resulting in altered recovery trajectories, communities, and foodweb interactions

An Irrigation Canal as a Lotic Mesocosm: Examining the Relationship Between Macroinvertebrate Benthos and Drift

We explored the notion that small canals could be good experimental proxies of streams by documenting physiochemical parameters and macroinvertebrate community development in an aridland irrigation canal. Further, we tested the production-compensation hypothesis between benthic invertebrates and invertebrates in the water column (drift). If the hypothesis held, invertebrates in the drift would be low until the benthic carrying capacity was reached; then organisms in the drift would increase as individuals avoided overcrowded conditions in the substrate. In a small, naturalized freshwater canal, we sampled macroinvertebrates in the substrate and those in the drift once every 2 weeks over 170 days (May–October). We placed macroinvertebrates into functional feeding groups (FFG) and examined these groups along with total density and taxa richness. We found no density-dependent relationship either in FFG or total density between the benthos and invertebrates in the drift. Our negative results might indicate that the stream benthos did not reach carrying capacity (partially affected by adult emergence in the autumn), the invertebrate dynamics in the canal did not adequately represent those occurring in a natural stream, or the duration of our study was too short. However, the invertebrate community in the canal did follow community buildup patterns for small streams reported in the literature, and it also resembled the community in a nearby natural stream. We suggest that naturalized canals could be used as “mesocosms,” mimicking small natural streams, in which highly manipulative experiments could be conducted. In addition, the effects of temporary and permanent canals across the arid western landscape have been understudied and represent a new area of ecological research

Present Effects of Past Wildfires on Leaf Litter Breakdown in Stream Ecosystems

We investigated the present effects from a 10-year-old wildfire on leaf litter breakdown rates in 3 headwater streams in central Idaho. These systems experienced a massive debris flow one year after the fire. Based on soil instability and burn patterns, we identified 3 stream conditions: unburned, burned only, and burned/scoured. We placed leaf bags containing willow leaves (Salix sp.) in each stream type and removed bags at various time intervals until all bags were collected 100 days after their introduction. Leaf material was dried and weighed, and decay rate coefficients were calculated. Macroinvertebrates colonizing the bags were enumerated and identified, and selected taxa were placed into trophic groups. We found that the unburned stream had the fastest leaf litter breakdown rate, the lowest level of incident light reaching the stream, and the largest amount of benthic organic matter. The burned/scoured stream was nearly opposite in all respects. Numbers of 2 detritivore invertebrate taxa, Serratella tibialis and Zapada oregonensis, were highest in the unburned stream but lowest in the burned/scoured stream. A third taxon, Baetis sp., showed the opposite relationship. Presence of predatory invertebrates did not affect detritivore abundance or leaf decay rate in the bags. Our research suggests that recovery response variables of some stream systems may not have returned to prefire levels even a decade after the initial wildfire. In this study, the recovery of our streams appears to be connected to the return of the riparian zone, though fire-induced debris flows may slow or alter final recovery of the stream system

Microcirculatory blood flow as a tool to select ICU patients eligible for fluid therapy

The aim of this study is to assess the incidence of sublingual microcirculatory flow alterations, according to a predefined arbitrary cutoff value, in patients with "clinical signs of impaired organ perfusion". Secondary endpoints were the changes in microvascular flow index (MFI), "clinical signs of impaired organ perfusion", and stroke volume (SV) after fluid administration, and the differences between groups. Prospective, single-center, observational study in a 22-bed mixed intensive care unit (ICU). Patients a parts per thousand yen18 years with invasive hemodynamic monitoring and "clinical signs of impaired organ perfusion" as the principal reason for fluid administration were included. Before and after fluid challenge, systemic hemodynamics and direct in vivo observation of the sublingual microcirculation with sidestream dark-field imaging were obtained. Microvascular flow index (MFI) 2.6 at baseline, MFI and clinical signs changed insignificantly [2.8 (2.8-2.9) versus 2.8 (2.7-3), p = 0.45, respectively, 1 (1-2) versus 1 (1-2), p <0.32]. These changes were not restricted to patients with a rise in SV a parts per thousand yen10 %. These data add to the understanding that noninvasive assessment of microvascular blood flow may help to identify patients eligible for fluid therapy, and to evaluate its effec

Hemodynamic Characteristics of Mechanically Ventilated COVID-19 Patients: A Cohort Analysis

Background. Solid data on cardiovascular derangements in critically ill COVID-19 patients remain scarce. The aim of this study is to describe hemodynamic characteristics in a cohort of COVID-19-related critically ill patients. Methods. A retrospective observational cohort study in twenty-eight consecutive mechanically ventilated COVID-19 patients. Pulse contour analysis-derived data were obtained from all patients, using the PiCCO® system. Results. The mean arterial pressure increased from 77 ± 10 mmHg on day 1 to 84 ± 9 mmHg on day 21 (p=0.04), in combination with the rapid tapering and cessation of norepinephrine and the gradual use of antihypertensive drugs in the vast majority of patients. The cardiac index increased significantly from 2.8 ± 0.7 L/min/m2 on day 1 to 4.0 ± 0.8 L/min/m2 on day 21 (p<0.001). Dobutamine was administered in only two patients. Mean markers of left ventricular contractility and peripheral perfusion, as well as lactate levels, remained within the normal range. Despite a constant fluid balance, extravascular lung water index decreased significantly from 17 ± 7 mL/kg on day 1 to 11 ± 4 mL/kg on day 21 (p<0.001). Simultaneously, intrapulmonary right-to-left shunt fraction (Qs/Qt) decreased significantly from 27 ± 10% in week 1 to 15 ± 9% in week 3 (p=0.007). PaO2/FiO2 ratio improved from 159 ± 53 mmHg to 319 ± 53 mmHg (p<0.001), but static lung compliance remained unchanged. Conclusions. In general, this cohort of patients with COVID-19 respiratory failure showed a marked rise in blood pressure over time, not accompanied by distinctive markers of circulatory failure. Characteristically, increased extravascular lung water, vascular permeability, and intrapulmonary shunt diminished over time, concomitant with an improvement in gas exchange

Effects of nitroglycerin on sublingual microcirculatory blood flow in patients with severe sepsis/septic shock after a strict resuscitation protocol:a double-blind randomized placebo controlled trial

OBJECTIVES: Microcirculatory alterations have been associated with morbidity and mortality in human sepsis. Such alterations occur despite pressure-guided resuscitation. Earlier data suggested that impaired microcirculatory blood flow could be corrected with intravenous nitroglycerin in these patients. We tested this concept after fulfillment of preset systemic hemodynamic resuscitation end points in the early phase of sepsis. DESIGN: Prospective, single center, randomized, placebo-controlled, double-blind clinical trial. SETTING: Closed-format 22-bed mixed intensive care unit in a tertiary teaching hospital. PATIENTS: Patients > or =18 yrs with sepsis, according to international criteria, and at least one early sign of organ dysfunction, as the principal reason for intensive care unit admission, were eligible for enrollment. INTERVENTIONS: Patients were randomly assigned to receive nitroglycerin (n = 35) or placebo (n = 35) after fulfillment of protocol-driven resuscitation end points. This trial is registered with ClinicalTrials.gov as NCT00493415. MEASUREMENTS AND MAIN RESULTS: Primary outcome was sublingual microcirculatory blood flow of small vessels, as assessed by side-stream dark field imaging. After protocolized resuscitation, we observed recruitment of sublingual microcirculation in both groups, as indicated by a significant improvement in the microcirculatory flow index after 24 hrs, in comparison to baseline. However, no difference in the sublingual microvascular flow index was observed between groups. The median microvascular flow index in sublingual small-sized vessels was 2.71 (1.85-3) in the nitroglycerin group and 2.71 (1.27-3), p = .80, in the placebo group. In medium-sized vessels, the respective values were 3 (2.75-3) vs. 2.86 (2.19-3), p = .21, and in large-sized vessels, 3 (3-3) vs. 3 (2.89-3), p = .06. In-hospital mortality, as a secondary outcome, was 34.3% in the nitroglycerin group and 14.2% in the placebo group, p = .09. CONCLUSIONS: In the context of a strict resuscitation protocol, based upon fulfillment of systemic hemodynamic end points in patients with early-phase severe sepsis or septic shock, we conclude that intravenous nitroglycerin does not promote sublingual microcirculatory blood flow

Serum drug levels and anti-drug antibodies in the context of dose tapering by interval prolongation of adalimumab, etanercept and ustekinumab in psoriasis patients: results of the CONDOR trial

Background: Biologics for psoriasis are registered in standard dosages. In patients with low disease activity, reduction of the dose by interval prolongation can prevent overtreatment, and lower risks and costs. However, fear for increased anti-drug antibody (ADA) formation due to interval prolongation of biologics is an important barrier. Objective: To investigate the course of serum drug concentrations, ADA levels, and predictors for successful dose reduction of adalimumab, ustekinumab, and etanercept for psoriasis. Methods: Patients were randomized to dose reduction (DR) or usual care (UC) and followed for one year. The course and extent of detectable ADA levels were expressed as proportions/relative risks for DR vs. UC. Association of baseline characteristics with successful tapering was investigated with log-binomial regression analysis. Results: In total, 118 patients were included. In adalimumab-treated patients, no significant difference in the proportion of patients with relevant ADA levels in DR vs. UC was seen. For ustekinumab, relevant ADA development was absent in both groups. Baseline trough levels were not predictive for successful DR. Conclusions: Immunogenicity may not increase by interval prolongation in psoriasis patients with low disease activity. This pilot provides important and reassuring insight into the pharmacological changes after dose tapering of adalimumab, etanercept, and ustekinumab