Present-day and future climate pathways affecting Alexandrium blooms in Puget Sound, WA, USA.

This study uses a mechanistic modeling approach to evaluate the effects of various climate pathways on the proliferative phase of the toxin-producing dinoflagellate Alexandrium in Puget Sound, WA, USA. Experimentally derived Alexandrium growth responses to temperature and salinity are combined with simulations of the regional climate and Salish Sea hydrology to investigate future changes in the timing, duration, and extent of blooms. Coarse-grid (100-200km) global climate model ensemble simulations of the SRES A1B emissions scenario were regionally downscaled to a 12-km grid using the Weather Research and Forecasting model for the period 1969-2069. These results were used to: (1) analyze the future potential changes and variability of coastal upwelling winds, and (2) provide forcing fields to a Regional Ocean Model System used to simulate the circulation of the Salish Sea, including Puget Sound, and the coastal ocean. By comparing circa-1990 and circa-2050 climate scenarios for the environmental conditions that promote Alexandrium blooms, we disentangle the effects of three climate pathways: (1) increased local atmospheric heating, (2) changing riverflow magnitude and timing, and (3) changing ocean inputs associated with changes in upwelling-favorable winds. Future warmer sea surface temperatures in Puget Sound from increased local atmospheric heating increase the maximum growth rates that can be attained by Alexandrium during the bloom season as well as the number of days with conditions that are favorable for bloom development. This could lead to 30 more days a year with bloom-favorable conditions by 2050. In contrast, changes in surface salinity arising from changes in the timing of riverflow have a negligible effect on Alexandrium growth rates, and the behavior of the coastal inputs in the simulations suggests that changes in local upwelling will not have major effects on sea surface temperature or salinity or Alexandrium growth rates in Puget Sound.

Evaluating the effects of climate change on summertime ozone using a relative response factor approach for policymakers.

UNLABELLED: The impact of climate change on surface-level ozone is examined through a multiscale modeling effort that linked global and regional climate models to drive air quality model simulations. Results are quantified in terms of the relative response factor (RRF(E)), which estimates the relative change in peak ozone concentration for a given change in pollutant emissions (the subscript E is added to RRF to remind the reader that the RRF is due to emission changes only). A matrix of model simulations was conducted to examine the individual and combined effects offuture anthropogenic emissions, biogenic emissions, and climate on the RRF(E). For each member in the matrix of simulations the warmest and coolest summers were modeled for the present-day (1995-2004) and future (2045-2054) decades. A climate adjustment factor (CAF(C) or CAF(CB) when biogenic emissions are allowed to change with the future climate) was defined as the ratio of the average daily maximum 8-hr ozone simulated under a future climate to that simulated under the present-day climate, and a climate-adjusted RRF(EC) was calculated (RRF(EC) = RRF(E) x CAF(C)). In general, RRF(EC) > RRF(E), which suggests additional emission controls will be required to achieve the same reduction in ozone that would have been achieved in the absence of climate change. Changes in biogenic emissions generally have a smaller impact on the RRF(E) than does future climate change itself The direction of the biogenic effect appears closely linked to organic-nitrate chemistry and whether ozone formation is limited by volatile organic compounds (VOC) or oxides of nitrogen (NO(x) = NO + NO2). Regions that are generally NO(x) limited show a decrease in ozone and RRF(EC), while VOC-limited regions show an increase in ozone and RRF(EC). Comparing results to a previous study using different climate assumptions and models showed large variability in the CAF(CB). IMPLICATIONS: We present a methodology for adjusting the RRF to account for the influence of climate change on ozone. The findings of this work suggest that in some geographic regions, climate change has the potential to negate decreases in surface ozone concentrations that would otherwise be achieved through ozone mitigation strategies. In regions of high biogenic VOC emissions relative to anthropogenic NO(x) emissions, the impact of climate change is somewhat reduced, while the opposite is true in regions of high anthropogenic NO(x) emissions relative to biogenic VOC emissions. Further, different future climate realizations are shown to impact ozone in different ways.

Modeling climate change impacts on overwintering bald eagles.

Bald eagles (Haliaeetus leucocephalus) are recovering from severe population declines, and are exerting pressure on food resources in some areas. Thousands of bald eagles overwinter near Puget Sound, primarily to feed on chum salmon (Oncorhynchus keta) carcasses. We used modeling techniques to examine how anticipated climate changes will affect energetic demands of overwintering bald eagles. We applied a regional downscaling method to two global climate change models to obtain hourly temperature, precipitation, wind, and longwave radiation estimates at the mouths of three Puget Sound tributaries (the Skagit, Hamma Hamma, and Nisqually rivers) in two decades, the 1970s and the 2050s. Climate data were used to drive bald eagle bioenergetics models from December to February for each river, year, and decade. Bald eagle bioenergetics were insensitive to climate change: despite warmer winters in the 2050s, particularly near the Nisqually River, bald eagle food requirements declined only slightly (<1%). However, the warming climate caused salmon carcasses to decompose more rapidly, resulting in 11% to 14% less annual carcass biomass available to eagles in the 2050s. That estimate is likely conservative, as it does not account for decreased availability of carcasses due to anticipated increases in winter stream flow. Future climate-driven declines in winter food availability, coupled with a growing bald eagle population, may force eagles to seek alternate prey in the Puget Sound area or in more remote ecosystems.

A biomechanical analysis of posterior tibial tendon dysfunction, medial displacement calcaneal osteotomy and flexor digitorum longus transfer in adult acquired flat foot.

BACKGROUND: Biomechanical models have been used to study stress in the metatarsals, subtalar motion, lateral column lengthening and subtalar arthroereisis. Posterior tibial tendon dysfunction has been associated with increased loads in the arch of the acquired flat foot. We examine whether a 10 millimeter (mm) medial displacement calcaneal osteotomy and flexor digitorum longus transfer to the navicular reduces these increased loads in the flat foot. METHODS: The response of a normal foot, a foot with posterior tibial tendon dysfunction, and a flat foot to an applied load of 683Newton was analyzed using a multi-segment biomechanical model. The distribution of load on the metatarsals, the moment about each joint, the force on each of the plantar ligaments and the muscle forces were computed. FINDINGS: Posterior tibial tendon dysfunction results in increased load on the medial arch, which may cause the foot to flatten. A 10mm medial displacement calcaneal osteotomy substantially decreases the load on the first metatarsal and the moment at the talo-navicular joint and increases the load on the fifth metatarsal and the calcaneal-cuboid joint. Adding the flexor digitorum longus transfer to the medial displacement calcaneal osteotomy has only a small effect on the flattened foot. INTERPRETATION: Our biomechanical analysis illustrates that when the foot becomes flat, the force on the talo-navicular joint increases substantially from its value for the normal foot, and that medial displacement calcaneal osteotomy can reduce this increased force back toward the value occurring in the normal foot. This study provides a biomechanical rationale for medial displacement calcaneal osteotomy treatments for posterior tibial tendon dysfunction.

A biomechanical analysis of the effect of lateral column lengthening calcaneal osteotomy on the flat foot.

BACKGROUND: Biomechanical models have been used to study the plantar aponeurosis, medial arch height, subtalar motion, medial displacement calcaneal osteotomy, subtalar arthroereisis and the distribution of forces in the normal and flat foot. The objective was to examine the hypothesis that increased load on the medial arch in the adult flat foot can be reduced through a 10mm lateral column lengthening calcaneal osteotomy 10 mm proximal from the calcaneal cuboid joint. METHODS: A three dimensional multisegment biomechanical model was used with anatomical data from a normal foot, a flat foot and a foot corrected with a 10mm lateral column lengthening calcaneal osteotomy. The response of a normal foot, a flat foot and a flat foot with a 10mm lateral column lengthening calcaneal osteotomy to an applied load of 683 N was analyzed using the biomechanical model. Data for the biomechanical model was obtained from a cadaver foot using the direct linear transformation method. Direct linear transformation uses multiple cameras to determine the spatial location of anatomical landmarks. FINDINGS: Load on the first metatarsal increases to 37% body weight in the flat foot compared to 12% for the normal foot and the moment about the talo-navicular joint increases from 5.6 N m to 21.6 N m. Lateral column lengthening shifts the load toward the lateral column, decreasing load on the first metatarsal to 10% and decreasing the moment about the talo-navicular joint to 8.1 N m. INTERPRETATION: The analysis shows that a 10mm lateral column lengthening calcaneal osteotomy reduces the excess force on the medial arch in an adult flat foot and adds biomechanical rationale to this clinical procedure.

The role of counter-current exchange in preventing hypoxia in skeletal muscle.

Mathematical models that describe oxygen transport from a single capillary into a region of surrounding tissue often predict that the tissue is hypoxic, whereas in reality diffusion from more richly perfused nearby capillaries prevents hypoxia from forming in the tissue. In this manuscript, a mathematical model of oxygen transport is presented that is applicable to vascular beds consisting of a large number of non-uniformly perfused parallel capillaries arranged in a manner characteristic of skeletal muscle. The model is used to examine conditions under which counter-current flow and myoglobin-facilitated diffusion provides sufficient oxygen to poorly perfused regions to prevent the occurrence of hypoxia. The method developed here leads to a coupled system of nonlinear ordinary differential equations for the oxygen concentration in the capillaries, and is easy to apply even for vascular beds containing a large number of capillaries.

A biomechanical model of the effect of subtalar arthroereisis on the adult flexible flat foot.

OBJECTIVE: The hypothesis tested was that the increased load on the medial arch in the adult flat foot can be reduced through a 6 mm subtalar arthroereisis. DESIGN: A three-dimensional multisegment biomechanical model was used in conjunction with experimental data and data from the literature. BACKGROUND: Biomechanical models have been used to study the plantar fascia, medial arch height, subtalar motion, medial displacement calcaneal osteotomy and distribution of forces in the foot. METHODS: Responses of a normal foot, a flat foot, and a flat foot with a subtalar arthroereisis to an applied load of 683 N were analyzed and the distribution of support among the metatarsal heads and the moment about various joints were computed. RESULTS: The flattened foot results in an increase in the load on the head of the first metatarsal from 10% to 24% of the body weight, and an increase in the moment about the talo-navicular joint from 3.4 to 11.9 Nm. Insertion of a 6 mm cylinder into the sinus tarsi, subtalar arthroereisis, results in a shift of the load back toward the lateral column, decreasing the load on the first metatarsal to 6% of the body weight and decreasing the moment about the talo-navicular joint to 6.0 Nm. CONCLUSIONS: Our analysis indicates that a 6 mm subtalar arthroereisis in an adult flat foot model decreases the load on the medial arch.

Mathematical analysis of oxygen concentration in a two dimensional array of capillaries.

An approach is presented for modeling transport and exchange in skeletal muscle that can be used to analyze vascular beds consisting of a large number of interacting capillaries. First the oxygen concentration is determined in a functional unit consisting of a single capillary surrounded by a region of tissue in which a flux is prescribed on the outer boundary of the region. This flux, which is a result of the interaction among all of the capillaries comprising the vascular bed, is then found by matching the concentration along the borders between adjacent units. This leads to a system of ordinary differential equations for the oxygen concentration in the capillaries coupled with a system of algebraic equations for the fluxes. The method is illustrated by obtaining the oxygen concentration within an array of capillaries for the case when each capillary has a different initial concentration and for the case when each capillary has a different flow rate.

A biomechanical model of the foot: the role of muscles, tendons, and ligaments.

A biomechanical model of the foot is developed and analyzed to determine the distribution of support under the metatarsal heads, the tension in the plantar aponeurosis, and the bending moment at each of the joints of the foot. This model is an extension of our earlier work to include the role of muscles, tendons, and ligaments. Two cases are presented: in the first the center of gravity of the body is over the mid foot, and in the second, the center of gravity is anterior, over the metatarsals, and no support is provided by the heel. The model shows the extent to which the muscles reduce the force in the supporting ligaments at each of the joints and decrease the tension in the plantar aponeurosis, and that this effect is more pronounced when the center of gravity of the body is moved forward.