Avoidance of Nonanadromous Fish Passage Impedance Caused by Highway Culverts

Highway culverts may hinder the normal migrations of various trout species in wild trout streams through increased flow velocity, shallow water depths, increased turbulence, and perching. This can impede migrational movements, affecting the genetic diversity and long-term survival of some species. Often, the proper installation of culverts can reduce the adverse effects on fish while maintaining hydraulic efficiency. This study characterized the problems with existing culverts to develop guidelines for the future use of culverts in areas with high gradient streams. Installation criteria will ideally limit the use of bridges where culverts are appropriate, and eliminate the use of culverts where they would create fish passage problems. This will reduce installation, maintenance, and retrofitting costs. The study concluded that culverts can be considered the primary option for crossing trout streams if the culvert can be placed on the same slope as that of the streambed, the slope of the stream is less than 3 percent, the flow velocity does not exceed 1.2 m/sec under normal flow conditions, and the barrel of the culvert can be properly countersunk at the outlet to prevent perching. Bridges should be used at these crossings if any of these criteria cannot be met. The study also concluded that baffles should not be used to control streamflow velocities in newly installed culverts, and concrete aprons should not be used at culvert outlets.

Download Full-text

Abstract 2212: Computational Model of Exercise Effects on Fontan Hemodynamics Demonstrates Favorable Energetics In Extracardiac Fontans When Compared to Lateral Tunnel

Circulation ◽

10.1161/circ.116.suppl_16.ii_481 ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Kevin K Whitehead ◽

Kerem Pekkan ◽

Ravi Doddasomayajula ◽

Hiroumi D Kitajima ◽

Kartik S Sundareswaran ◽

...

Keyword(s):

Computational Model ◽

Flow Condition ◽

Power Loss ◽

Resistance Index ◽

Flow Conditions ◽

Term Survival ◽

Lateral Tunnel ◽

Significant Difference ◽

Fontan Patients

Background: Previous computational experiments using anatomically correct Fontan geometries have suggested that extracardiac Fontans (EC) have lower power loss compared to lateral tunnel intracardiac (IC) Fontans. Differences in exercise performance may also be important in the long term morbidity of Fontan patients. We have previously developed a computational model for studying exercise conditions. Hypothesis: It is our hypothesis that the EC total cavopulmonary connection (TCPC) is more hemodynamically favorable and demonstrates significantly lower resistance at exercise. Methods: We performed steady flow CFD simulations on 3-D anatomical reconstructions of TCPC from 9 Fontan patients using cardiac magnetic resonance imaging (CMR) data, 5 with EC and 4 with IC. Caval flows were determined using CMR velocimetry and outlet pulmonary artery pressures tuned to obtain flow splits corresponding to equal vascular lung resistance (EVLR) of 2 Woods units for each lung. Simulated exercise conditions of twice (2x) and three times (3x) baseline MRI flow were performed by increasing IVC flow. Power loss calculations using control volume analysis were performed for each TCPC and each flow condition studied. Power losses were normalized to calculate a resistance index and the two groups compared using the Student t-test for independent groups. Results: Resistance index was significantly greater in IC compared to EC Fontans for all three flow conditions. This difference was magnified at exercise flow conditions. At baseline flow, EC TCPC resistance index was 0.14 compared to 0.49 Woods units for IC (p = 0.001). This rose to 0.29 and 0.81 for EC and IC TCPC respectively for the 2x exercise condition (p = 0.002), and to 0.44 and 1.2 for the 3x condition (p = 0.008). There was no significant difference in cardiac output between EC and IC pts, but the EC pts were significantly younger. Conclusions: CFD modeling of 3-D anatomical reconstructions demonstrates significant differences in power loss between EC and IC TCPC which are magnified at exercise conditions. The differences are hemodynamically significant, as high as 0.76 Woods units at the highest exercise flow condition, and are thus likely important in the long-term survival and quality of life of patients with TCPC.

Download Full-text

Caspases and apoptosis

Essays in Biochemistry ◽

10.1042/bse0380009 ◽

2002 ◽

Vol 38 ◽

pp. 9-19 ◽

Cited By ~ 121

Author(s):

Guy S Salvesen

Keyword(s):

Cysteine Proteases ◽

Signalling Pathways ◽

Term Survival ◽

Mature Adult ◽

Intracellular Signalling Pathways ◽

Adult Cell ◽

Caspase Family ◽

Cell Fragments ◽

Pro Inflammatory Cytokines

The ability of metazoan cells to undergo programmed cell death is vital to both the precise development and long-term survival of the mature adult. Cell deaths that result from engagement of this programme end in apoptosis, the ordered dismantling of the cell that results in its 'silent' demise, in which packaged cell fragments are removed by phagocytosis. This co-ordinated demise is mediated by members of a family of cysteine proteases known as caspases, whose activation follows characteristic apoptotic stimuli, and whose substrates include many proteins, the limited cleavage of which causes the characteristic morphology of apoptosis. In vertebrates, a subset of caspases has evolved to participate in the activation of pro-inflammatory cytokines, and thus members of the caspase family participate in one of two very distinct intracellular signalling pathways.

Download Full-text