Data on the use of dietary supplements in Danish patients with type 1 and type 2 diabetes.

The data in this article describe the use of dietary supplements in Danish patients with type 1 diabetes (T1D) and type 2 diabetes (T2D). The data were collected from a web-based dietary survey on dietary habits in 774 patients with T1D (n = 426) and T2D (n = 348). The data demonstrate that 99% of the patients with diabetes use dietary supplements with no gender differences. In comparison, only 64% in the general population use dietary supplements [2]. A higher proportion of people in the general population use multivitamin/mineral supplementation as compared to patients with diabetes (48% vs. 34-37%) and a higher proportion of women than men with diabetes use multivitamin/mineral supplementation (T1D: 43% women vs. 26% men and T2D: 45% women vs. 34% men). More patients with diabetes than the general population use supplements such as calcium together with vitamin D, vitamin D, vitamin B, vitamin C, vitamin E, magnesium, calcium, Q10, ginger, garlic, and other herbal supplements.

Allocation to male vs female floral function varies by currency and responds differentially to density and moisture stress.

Allocation of finite resources to separate reproductive functions is predicted to vary across environments and affect fitness. Biomass is the most commonly measured allocation currency; however, in comparison with nutrients it may be less limited and express different environmental and evolutionary responses. Here, we measured carbon, nitrogen, phosphorus, and biomass allocation among floral whorls in recombinant inbred lines of Brassica rapa in multiple environments to characterize the genetic architecture of floral allocation, including its sensitivity to environmental heterogeneity and to choice of currency. Mass, carbon, and nitrogen allocation to female whorls (pistils and sepals) decreased under high density, whereas nitrogen allocation to male organs (stamens) decreased under drought. Phosphorus allocation decreased by half in pistils under drought, while stamen phosphorus was unaffected by environment. While the contents of each currency were positively correlated among whorls, selection to improve fitness through female (or male) function typically favored increased allocation to pistils (or stamens) but decreased allocation to other whorls. Finally, genomic regions underlying correlations among allocation metrics were mapped, and loci related to nitrogen uptake and floral organ development were located within mapped quantitative trait loci. Our candidate gene identification suggests that nutrient uptake may be a limiting step in maintaining male allocation. Taken together, allocation to male vs female function is sensitive to distinct environmental stresses, and the choice of currency affects the interpretation of floral allocation responses to the environment. Further, genetic correlations may counter the evolution of allocation patterns that optimize fitness through female or male function.

Relative validity of a web-based food frequency questionnaire for patients with type 1 and type 2 diabetes in Denmark.

BACKGROUND: Diet has an important role in the management of diabetes. However, little is known about dietary intake in Danish diabetes patients. A food frequency questionnaire (FFQ) focusing on most relevant nutrients in diabetes including carbohydrates, dietary fibres and simple sugars was developed and validated. OBJECTIVES: To examine the relative validity of nutrients calculated by a web-based food frequency questionnaire for patients with diabetes. DESIGN: The FFQ was validated against a 4-day pre-coded food diary (FD). Intakes of nutrients were calculated. Means of intake were compared and cross-classifications of individuals according to intake were performed. To assess the agreement between the two methods, Pearson and Spearman's correlation coefficients and weighted kappa coefficients were calculated. SUBJECTS: Ninety patients (64 with type 1 diabetes and 26 with type 2 diabetes) accepted to participate in the study. Twenty-six were excluded from the final study population. SETTING: 64 volunteer diabetes patients at the Steno Diabetes Center. RESULTS: Intakes of carbohydrates, simple sugars, dietary fibres and total energy were higher according to the FFQ compared with the FD. However, intakes of nutrients were grossly classified in the same or adjacent quartiles with an average of 82% of the selected nutrients when comparing the two methods. In general, moderate agreement between the two methods was found. CONCLUSION: The FFQ was validated for assessment of a range of nutrients. Comparing the intakes of selected nutrients (carbohydrates, dietary fibres and simple sugars), patients were classified correctly according to low and high intakes. The FFQ is a reliable dietary assessment tool to use in research and evaluation of patient education for patients with diabetes.

Observation of forbidden exciton transitions mediated by Coulomb interactions in photoexcited semiconductor quantum wells.

We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the 1s exciton emission, which we attribute to the terahertz-induced 1s-to-2p excitation. Simultaneously, a pronounced enhancement of the 2s exciton emission is observed, despite the 1s-to-2s transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations.

Size-mediated tree transpiration along soil drainage gradients in a boreal black spruce forest wildfire chronosequence.

Boreal forests are crucial to climate change predictions because of their large land area and ability to sequester and store carbon, which is controlled by water availability. Heterogeneity of these forests is predicted to increase with climate change through more frequent wildfires, warmer, longer growing seasons and potential drainage of forested wetlands. This study aims at quantifying controls over tree transpiration with drainage condition, stand age and species in a central Canadian black spruce boreal forest. Heat dissipation sensors were installed in 2007 and data were collected through 2008 on 118 trees (69 Picea mariana (Mill.) Britton, Sterns & Poggenb. (black spruce), 25 Populus tremuloides Michx. (trembling aspen), 19 Pinus banksiana Lamb. (jack pine), 3 Larix laricina (Du Roi) K. Koch (tamarack) and 2 Salix spp. (willow)) at four stand ages (18, 43, 77 and 157 years old) each containing a well- and poorly-drained stand. Transpiration estimates from sap flux were expressed per unit xylem area, J(S), per unit ground area, E(C) and per unit leaf area, E(L), using sapwood (A(S)) and leaf (A(L)) area calculated from stand- and species-specific allometry. Soil drainage differences in transpiration were variable; only the 43- and 157-year-old poorly-drained stands had ∼ 50% higher total stand E(C) than well-drained locations. Total stand E(C) tended to decrease with stand age after an initial increase between the 18- and 43-year-old stands. Soil drainage differences in transpiration were controlled primarily by short-term physiological drivers such as vapor pressure deficit and soil moisture whereas stand age differences were controlled by successional species shifts and changes in tree size (i.e., A(S)). Future predictions of boreal climate change must include stand age, species and soil drainage heterogeneity to avoid biased estimates of forest water loss and latent energy exchanges.

Effects of hydraulic architecture and spatial variation in light on mean stomatal conductance of tree branches and crowns.

In a Pinus taeda L. (loblolly pine) plantation, we investigated whether the response to vapour pressure deficit (D) of canopy average stomatal conductance (G(S)) calculated from sap flux measured in upper and lower branches and main stems follows a hydraulically modelled response based on homeostasis of minimum leaf water potential (Psi(L)). We tested our approach over a twofold range of leaf area index (L; 2-4 m(2) m(-2)) created by irrigation, fertilization, and a combination of irrigation and fertilization relative to untreated control. We found that G(S) scaled well from leaf-level porometery [porometry-based stomatal conductance (g(s))] to branch-estimated and main stem-estimated G(S). The scaling from branch- to main stem-estimated G(S) required using a 45 min moving average window to extract the diurnal signal from the large high-frequency variation, and utilized a light attenuation model to weigh the contribution of upper and lower branch-estimated G(S). Our analysis further indicated that, regardless of L, lower branch-estimated G(S) represented most of the main stem-estimated G(S) in this stand. We quantified the variability in both upper and lower branch-estimated G(S) by calculating the SD of the residuals from a moving average smoothed diurnal. A light model, which incorporated penumbral effects on vertical distribution of direct light, was employed to estimate the variability in light intensity at each canopy level in order to explain the increasing SD of both upper and lower branch-estimated G(S) with light. The results from the light model showed that the upper limit of the variability in individual branch-estimated G(S) could be attributed to incoming light, but not the variation below that upper limit. A porous medium model of water flow in trees produced a pattern of variation below the upper limit that was consistent with the observed variability in branch-estimated G(S). Our results indicated that stems acted to buffer leaf- and branch-level variation and might transmit a less-variable water potential signal to the roots.

Interannual consistency in canopy stomatal conductance control of leaf water potential across seven tree species.

We investigated interannual variability of canopy transpiration per unit ground area (E (C)) and per unit leaf area (E (L)) across seven tree species in northern Wisconsin over two years. These species have previously been shown to be sufficient to upscale stand-level transpiration to the landscape level during one growing season. Our objective was to test whether a simple plant hydraulic model could capture interannual variation in transpiration. Three species, wetland balsam fir (Abies balsamea (L.) Mill), basswood (Tilia Americana L.) and speckled alder (Alnus rugosa (DuRoi) Spreng), had no change in E (C) or E (L) between 2000 and 2001. Red pine (Pinus resinosa Ait) had a 57 and 19% increase in E (C) and E (L), respectively, and sugar maple (Acer saccharum Marsh) had an 83 and 41% increase in E (C) and E (L), respectively, from 2000 to 2001. Quaking aspen (Populus tremuloides Michx) had a 50 and 21% decrease in E (C) and E (L), respectively, from 2000 to 2001 in response to complete defoliation by forest tent caterpillar (Malascoma distria Hüber) and subsequent lower total leaf area index of the reflushed foliage. White cedar (Thuja occidentalis L.) had a 20% decrease in both E (C) and E (L) caused by lowered surface water in wetlands in 2001 because of lower precipitation and wetland flow management. Upland A. balsamea increased E (L) and E (C) by 55 and 53%, respectively, as a result of release from light competition of the defoliated, overstory P. tremuloides. We hypothesized that regardless of different drivers of interannual variability in E (C) and E (L), minimum leaf water potential would be regulated at the same value. Minimum midday water potentials were consistent over the two years within each of the seven species despite large changes in transpiration between years. This regulation was independently verified by the exponential saturation between daily E (C) and vapor pressure deficit (D) and the tradeoff between a reference canopy stomatal conductance (G (S)) and the sensitivity of G (S) to D, indicating that trees with high G (S) must decrease G (S) in response to atmospheric drought faster than trees with low G (S). Our results show that models of forest canopy transpiration can be simplified by incorporating G (S) regulation of minimum leaf water potential for isohydric species.

The extent and distribution of cell death and matrix damage in impacted chondral explants varies with the presence of underlying bone.

Excessive mechanical loading can lead to matrix damage and chondrocyte death in articular cartilage. Previous studies on chondral and osteochondral explants have not clearly distinguished to what extent the degree and the distribution of cell death are dependent on the presence of an underlying layer of bone. The current study hypothesized that the presence of underlying bone would decrease the amount of matrix damage and cell death. Chondral and osteochondral explants were loaded to 30 MPa at a high rate of loading (approximately 600 MPa/s) or at a low rate of loading (30 MPa/s). After 24 hours in culture, matrix damage was assessed by the total length and average depth of surface fissures. The explants were also sectioned and stained for cell viability in the various layers of the cartilage. More matrix damage was documented in chondral than osteochondral explants for each rate of loading experiment. The total amount of cell death was also less in osteochondral explants than chondral explants. The presence of underlying bone significantly reduced the extent of cell death in all zones in low rate of loading tests. The percentage of cell death was also reduced in the intermediate zone and deep zones of the explant by the presence of the underlying bone for a high rate of loading. This study indicated that the presence of underlying bone significantly limited the degree of matrix damage and cell death, and also affected the distribution of dead cells through the explant thickness. These data may have relevance to the applicability of experimental data from chondral explants to the in situ condition.

Rate of blunt impact loading affects changes in retropatellar cartilage and underlying bone in the rabbit patella.

Our laboratory has developed a small animal model using Giant Flemish rabbits to examine chronic degradative changes in joint tissues following a blunt impact. Historically, we observe surface fissuring and decreases in the elastic modulus of retropatellar cartilage along with thickening of the underlying subchondral bone. Previous studies resulted in load insults that peaked in approximately 5ms, while loads that occur during automotive accidents or heavy exercise can produce longer rise times. The objective of the current study was to examine the influence of blunt impact loading rate using our established model. We hypothesized that the extent of fissuring and softening of retropatellar cartilage following impact would not be significantly different for a high (5ms to peak) versus low (50ms to peak) rate of loading experiment. Eight animals were impacted with a high rate of loading blunt impact, while ten animals were subjected to the same impact load at a low rate of loading. An additional eight animals served as a control population. All animals were sacrificed 12 months post-impact. The study yielded unexpected results for the first hypothesis. The high rate of loading experiments generated more surface fissuring of the retropatellar cartilage than the low rate of loading experiments. However, the degree of softening was similar for the two rates, which supported the second hypothesis. Furthermore, the study documented more thickening of bone underlying retropatellar cartilage following the high versus the low rate of loading experiments. The current study suggested that chronic injury mechanisms may be highly dependent on the rate of impact loading. These data could become extremely relevant in the development of high-velocity "safety" devices, such as knee air bags, that are needed to help position an unbelted occupant in an automobile crash.

The extent of matrix damage and chondrocyte death in mechanically traumatized articular cartilage explants depends on rate of loading.

Mechanical loads can lead to matrix damage and chondrocyte death in articular cartilage. This damage has been implicated in the pathogenesis of secondary osteoarthritis. Studies on cartilage explants with the attachment of underlying bone at high rates of loading have documented cell death adjacent to surface lesions. On the other hand, studies involving explants removed from bone at low rates of loading suggest no clear spatial association between cell death and matrix damage. The current study hypothesized that the observed differences in the distribution of cell death in these studies are attributed to the rate of loading. Ninety bovine cartilage explants were cultured for two days. Sixty explants were loaded in unconfined compression to 40 MPa in either a fast rate of loading experiment (approximately 900 MPa/s) or a low rate of loading experiment (40 MPa/s). The remaining 30 explants served as a control population. All explants were cultured for four days after loading. Matrix damage was assessed by measuring the total length and average depth of surface lesions and the release of glycosaminoglycans to the culture media. Explants were sectioned and stained with calcein and ethidium bromide homodimer to document the number of live and dead cells. Greater matrix damage was documented in explants subjected to a high rate of loading, compared to explants exposed to a low rate of loading. The high rate of loading experiments resulted in cell death adjacent to fissures, whereas more dead cells were observed in the low rate of loading experiments and a more diffuse distribution of dead cells was observed away from the fissures. In conclusion, this study indicated that the rate of loading can significantly affect the degree of matrix damage, the distribution of dead cells, and the amount of cell death in unconfined compression experiments on explants of articular cartilage.

Mean canopy stomatal conductance responses to water and nutrient availabilities in Picea abies and Pinus taeda.

We compared sap-flux-scaled, mean, canopy stomatal conductance (GS) between Picea abies (L.) Karst. in Sweden and Pinus taeda (L.) in North Carolina, both growing on nutritionally poor soils. Stomatal conductance of Picea abies was approximately half that of Pinus taeda and the sensitivity of GS in Picea abies to vapor pressure deficit (D) was lower than in Pinus taeda. Optimal fertilization increased leaf area index (L) two- and threefold in Pinus taeda and Picea abies, respectively, regardless of whether irrigation was increased. Although it increased L, fertilization did not increase GS in Picea abies unless irrigation was also provided. In Pinus taeda growing on coarse, sandy soils, the doubling of L in response to fertilization reduced GS sharply unless irrigation was also provided. The reduction in GS with fertilization in the absence of irrigation resulted from the production of fine roots with low saturated hydraulic conductivity. When Pinus taeda received both fertilization and irrigation, the increase in L was accompanied by a large increase in GS. In Pinus taeda, a reference GS (defined as GS at D = 1 kPa; GSR) decreased in all treatments with decreasing volumetric soil water content (theta). In Picea abies, theta varied little within a treatment, but overall, GSR declined with theta, reaching lowest values when drought was imposed by the interception of precipitation. Despite the large difference in GS both between Picea abies and Pinus taeda and among treatments, stem growth was related to absorbed radiation, and stem growth response to treatment reflected mostly the changes in L.

Blunt injuries to the patellofemoral joint resulting from transarticular loading are influenced by impactor energy and mass.

Various impact models have been used to study the injury mechanics of blunt trauma to diarthrodial joints. The current study was designed to study the relationship between impactor energy and mass on impact biomechanics and injury modalities for a specific test condition and protocol. A total of 48 isolated canine knees were impacted once with one of three free flight inertial masses (0.7, 1.5, or 4.8 kg) at one of three energy levels (2, 11, 22 J). Joint impact biomechanics (peak load, loading rate, contact area) generally increased with increasing energy. Injuries were typically more frequent and more severe with the larger mass at each energy level. Histological analyses of the patellae revealed cartilage injuries at low energy with deep injuries in underlying bone at higher energies.

Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere.

Northern mid-latitude forests are a large terrestrial carbon sink. Ignoring nutrient limitations, large increases in carbon sequestration from carbon dioxide (CO2) fertilization are expected in these forests. Yet, forests are usually relegated to sites of moderate to poor fertility, where tree growth is often limited by nutrient supply, in particular nitrogen. Here we present evidence that estimates of increases in carbon sequestration of forests, which is expected to partially compensate for increasing CO2 in the atmosphere, are unduly optimistic. In two forest experiments on maturing pines exposed to elevated atmospheric CO2, the CO2-induced biomass carbon increment without added nutrients was undetectable at a nutritionally poor site, and the stimulation at a nutritionally moderate site was transient, stabilizing at a marginal gain after three years. However, a large synergistic gain from higher CO2 and nutrients was detected with nutrients added. This gain was even larger at the poor site (threefold higher than the expected additive effect) than at the moderate site (twofold higher). Thus, fertility can restrain the response of wood carbon sequestration to increased atmospheric CO2. Assessment of future carbon sequestration should consider the limitations imposed by soil fertility, as well as interactions with nitrogen deposition.

Tissue-engineered rotator cuff tendon using porcine small intestine submucosa. Histologic and mechanical evaluation in dogs.

To determine its efficacy in stimulating the regeneration of a rotator cuff tendon, an implant of 10-ply porcine small intestinal submucosa was used to replace a completely resected infraspinatus tendon in 21 adult mongrel dogs. The contralateral infraspinatus tendon was elevated and then reattached to the greater tubercle with sutures to mimic conventional repair (sham operation). Mechanical evaluations were performed at 0, 3, and 6 months (five specimens at each time period). Histologic comparisons were made at 3 and 6 months (three specimens). At both times, the gross appearance, histologic continuity, and failure mode of the constructs mimicked those of sham-operated and native infraspinatus tendons, thus suggesting host tissue ingrowth and implant remodeling with solid integration of the regenerated tissue to muscular and bony interfaces. Tissue ingrowth occurred without histologic evidence of foreign body or immune-mediated reactions or adhesions to peripheral tissues. Sham operations simulated tendon mobilization and reimplantation procedures routinely performed to treat chronic rotator cuff tendon injuries. Although the ultimate strength of small intestinal submucosa-regenerated tendons was significantly less than that of native infraspinatus tendons (P < 0.001), it was similar to that of reimplanted tendons at 3 (P > 0.05) and 6 months (P > 0.05).

Sensitivity of mean canopy stomatal conductance to vapor pressure deficit in a flooded Taxodium distichum L. forest: hydraulic and non-hydraulic effects.

We measured the xylem sap flux in 64-year-old Taxodium distichum (L.) Richard trees growing in a flooded forest using Granier-type sensors to estimate mean canopy stomatal conductance of the stand (G S). Temporal variations in G S were investigated in relation to variation in vapor pressure deficit (D), photosynthetic photon flux density (Q o), and the transpiration rate per unit of leaf area (E L), the latter variable serving as a proxy for plant water potential. We found that G S was only weakly related to Q o below 500 µmol m-2 s-1 (r 2=0.29), but unrelated to Q o above this value. Above Q o=500 µmol m-2 s-1 and D=0.6 kPa, G S decreased linearly with increasing E L with a poor fit (r 2=0.31), and linearly with lnD with a much better fit (r 2=0.81). The decrease of G S with lnD was at a rate predicted based on a simple hydraulic model in which stomata regulate the minimum leaf water potential. Based on the hydraulic model, stomatal sensitivity to D is proportional to stomatal conductance at low D. A hurricane caused an ~41% reduction in leaf area. This resulted in a 28% increase in G S at D=1 kPa (G Sref), indicating only partial compensation. As predicted, the increase in G Sref after the hurricane was accompanied by a similar increase in stomatal sensitivity to D (29%). At night, G Sref was ~20% of the daytime value under non-limiting light (Q o>500 µmol m-2 s-1). However, stomatal sensitivity to D decreased only to ~46% (both reductions referenced to pre-hurricane daytime values), thus having more than twice the sensitivity expected based on hydraulic considerations alone. Therefore, non-hydraulic processes must cause heightened nighttime stomatal sensitivity to D.

Polysulphated glycosaminoglycan treatments can mitigate decreases in stiffness of articular cartilage in a traumatized animal joint.

A single, blunt impact to the rabbit patellofemoral joint has been shown to decrease the stiffness of retropatellar cartilage and increase the thickness of the underlying bone. Polysulphated glycosaminoglycan treatments, on the other hand, have been shown to inhibit the degradation of articular cartilage and possibly increase synthesis of collagen and glycosaminoglycans in experimental studies on diseased joints. The aim of the current study was to examine the effect of early treatments with polysulphated glycosaminoglycans on cartilage using an in vivo post-trauma animal model. The study used 24 Flemish Giant rabbits in three groups: control, impacted, and impacted with treatment. Treatment consisted of intramuscular injections the day of insult and every 4 days thereafter for 6 weeks. At 30 weeks after trauma, mechanical tests were performed on the retropatellar cartilage to determine its mechanical stiffness. The patellae were also grossly evaluated for surface lesions on the retropatellar cartilage and histologically processed to measure the thickness of the subchondral bone. The rabbits that received no treatment had a statistically significant decrease in stiffness (modulus) for the cartilage of the impacted patellae compared with that of the contralateral, unimpacted patellae and compared with the cartilage of rabbits in the control group. The degradation in mechanical stiffness, however, was not observed in patellae of rabbits in the group receiving treatment. There was also a significant increase in the underlying thickness of the subchondral plate on the impacted patellae compared with that on the contralateral, unimpacted sides for rabbits in both the treated and nontreated groups. In conclusion, the polysulphated glycosaminoglycan treatments minimized a decrease in mechanical stiffness (modulus) of retropatellar articular cartilage 30 weeks after trauma. The mechanism by which the mechanical stiffness of the cartilage was preserved is unknown.

Chronic softening of cartilage without thickening of underlying bone in a joint trauma model.

We have recently developed a trauma model to study degradation of the rabbit patello-femoral joint. Our current working hypothesis is that alterations in retropatellar cartilage and underlying bone in our model are initiated independently by acute overstresses developed in each tissue during blunt insult to the joint, and that the processes of chronic degradation in each tissue are not related in a mechanical sense. The current study was conducted in an attempt to help validate our hypothesis by impacting the patello-femoral joint with a padded interface. Based upon earlier human cadaver experiments, we believe this would reduce the acute overstresses in patellar bone while the stresses developed in the overlying retropatellar cartilage would be sufficient enough to initiate a chronic softening of the tissue. Twenty-four animals received an impact to the patello-femoral joint and were sacrificed at either 0, 4.5, or 12 months post-insult. Three acute animals were impacted to develop a simplified computational model to estimate the stresses in joint tissues. The study showed there was a significant softening of the retropatellar cartilage at 4.5 and 12 months post-trauma, compared to unimpacted controls. However, no thickening of the underlying subchondral bone was documented at any timepoint. This was consistent with a reduction of stress in the bone compared to earlier studies, which document thickened subchondral bone post-insult at the same applied impact load. In conclusion, this study helped validate our hypothesis by documenting chronic softening of cartilage without remodeling of the underlying subchondral bone. Furthermore, this study, along with our earlier studies, suggest that impact load alone, which is currently used by the automobile industry to certify new automobiles, is not a good predictor of chronic injuries to a diarthrodial joint, and that simply the addition of padding to impact interfaces may not be adequate to protect occupants from chronic injuries.

The effect of loading rate on the degree of acute injury and chronic conditions in the knee after blunt impact.

accidents are often overlooked, but can have a profound societal cost. Knee injuries, for example, account for approximately 10% of the total injuries. Fracture of the knee is not only an acute issue but may also have chronic, or long term, consequences. The criterion currently used for evaluation of knee injuries in new automobiles, however, is based on experimental impact data from the 70's using seated human cadavers. These studies involved various padded and rigid impact interfaces that slightly alter the duration of contact. Based on these data and a simple mathematical model of the femur, it appears fracture tolerance increases as contact duration shortens. In contrast, more recent studies have shown mitigation of gross fractures of the knee itself using padded interfaces. The use of padded interfaces, however, result in coincidental changes in contact duration and knee contact area. Therefore, it is difficult to extract the direct effect of loading rate on fracture tolerance of the knee. The object of the current study was to isolate the effect of loading rate alone on fracture tolerance of the human knee joint. Paired experiments were conducted on eight pairs of isolated cadaver knees impacted with a rigid interface to approximately 5 kN at a high (5 ms to peak) or low (50 ms to peak) rate of loading. Gross fracture and occult microfractures of the knee joint were documented. A second part of the study examined some chronic effects of loading rate on "subfracture" injuries in an animal. Thirty-four rabbits were subjected to a "subfracture" knee load at the same rates as used in the human studies. Alterations in the mechanical properties of retropatellar cartilage and thickening of subchondral bone were documented out to one year post "subfracture" trauma to the joint. The current study documented an opposite effect than that expected based on 70's experiments with seated cadavers. There was an increase in the number of gross fractures and occult microfractures in high versus low rate of loading experiments. A similar effect was also seen in the "subfracture" chronic animal experiments, which showed relatively more degradative change in the mechanical properties of cartilage following high versus low rate of loading experiments. There was also a significant increase in subchondral bone thickening underlying cartilage and increased fissuring of cartilage in high versus low rate of loading experiments. The current study suggests a relative decrease in tolerance of the knee at high versus low rates of loading in acute experiments with human cadavers and in the chronic setting with animals. Therefore, it would appear that rate of knee loading may be an important issue in establishing a future injury criterion for the knee itself.

Influence of soil porosity on water use in Pinus taeda.

We analyzed the hydraulic constraints imposed on water uptake from soils of different porosities in loblolly pine (Pinus taeda L.) by comparing genetically related and even-aged plantations growing in loam versus sand soil. Water use was evaluated relative to the maximum transpiration rate (E crit) allowed by the soil-leaf continuum. We expected that trees on both soils would approach E crit during drought. Trees in sand, however, should face greater drought limitation because of steeply declining hydraulic conductivity in sand at high soil water potential (Ψ S). Transport considerations suggest that trees in sand should have higher root to leaf area ratios (A R:A L), less negative leaf xylem pressure (Ψ L), and be more vulnerable to xylem cavitation than trees in loam. The A R:A L was greater in sand versus loam (9.8 vs 1.7, respectively). This adjustment maintained about 86% of the water extraction potential for both soils. Trees in sand were more deeply rooted (>1.9 m) than in loam (95% of roots <0.2 m), allowing them to shift water uptake to deeper layers during drought and avoid hydraulic failure. Midday Ψ L was constant for days of high evaporative demand, but was less negative in sand (-1.6 MPa) versus loam (-2.1 MPa). Xylem was more vulnerable to cavitation in sand versus loam trees. Roots in both soils were more vulnerable than stems, and experienced the greatest predicted loss of conductivity during drought. Trees on both soils approached E crit during drought, but at much higher Ψ S in sand (<-0.4 MPa) than in loam (<-1.0 MPa). Results suggest considerable phenotypic plasticity in water use traits for P. taeda which are adaptive to differences in soil porosity.

The tensile and stress relaxation responses of human patellar tendon varies with specimen cross-sectional area.

In order to provide insight into the mechanical response of the collagen fascicle structures in tendon, a series of constant strain rate and constant displacement, stress relaxation mechanical tests were performed on sequentially sectioned human patellar tendon specimens (protocol 1) and specimens with both small (approximately 1 mm2) and large (approximately 20 mm2) cross-sectional areas (protocol 2). These data described the stress relaxation and constant strain rate tensile responses as a function of cross-sectional area and water content. The experimental data suggested that small portions of tendon exhibit a higher tensile modulus, a slower rate of relaxation and a lower amount of relaxation in comparison to larger specimens from the same location in the same tendon. The decrease in relaxation response and the increase in tensile modulus with decreasing cross-sectional area was nonlinear. These data suggest that there may be structures other than the subfascicle, such as the epitenon and other connective tissue components, which influence the tensile and stress relaxation responses in tendon.