Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease.

Several ultrasonic and Fourier-domain optical coherence tomography (FD-OCT) pachymeters are used to measure corneal thickness in canine patients and research subjects. This study assessed the reliability of and consistency between two ultrasonic pachymetry (USP) devices, Pachette 3 and Accupach VI, as well as automated and manual measurements obtained using FD-OCT in dogs with and without corneal disease. Corneal thickness measurements were compiled from 108 dogs and analyzed using mixed effects linear regression, with Bonferonni adjustments for post-hoc comparisons, to determine the effects of age, weight and disease state. Data are presented as predicted mean±standard error. Canine corneal disease can result in marked increases in thickness that frequently exceed the upper limits of measurement of some pachymetry devices developed for human use. In this study, the corneas of dogs with endothelial disease or injury frequently exceeded the upper limits of quantitation of 999 and 800µm for the Accupach VI and automated FD-OCT pachymeters, respectively. Using values <800µm, the Pachette 3 generated significantly greater values for central corneal thickness (CCT) than the Accupach VI, manual FD-OCT and automated FD-OCT at 625±7.0, 615±7.2, 613±7.2, and 606±7.4µm respectively (P<0.001). Of the two devices where measurements >1000µm were obtained, manual FD-OCT demonstrated less variability than the Pachette 3. Corneal thickness increased linearly with age and weight with an increase of 6.9±1.8µm/year and 1.6±0.8µm/kg body weight (P<0.005 and P=0.038, respectively).

Effects of high condensed-tannin substrate, prior dietary tannin exposure, antimicrobial inclusion, and animal species on fermentation parameters following a 48 h in vitro incubation.

Condensed tannins (CT), prior dietary CT exposure, animal species, and antimicrobial inclusion effects on 48 h extent of in vitro fermentation were measured in an experiment with a 3 × 2 × 2 × 3 factorial arrangement of treatments. Treatments included species of inoculum donor (Bos taurus, Ovis aries, or Capra hircus; n = 3/species), prior adaptation to dietary CT (not adapted or adapted), culture substrate (low-CT or high-CT), and antimicrobial additive (none, bacterial suppression with penicillin + streptomycin, or fungal suppression with cycloheximide). Low-CT or high-CT substrates were incubated in vitro using inoculum from animals either not exposed (period 1) or previously exposed to dietary CT (period 2). The extent of IVDMD after 48 h of incubation was greater (P < 0.001) for cultures with low-CT substrate (21.5%) than for cultures with high-CT substrate (16.5%). Cultures with high-CT substrate or with suppressed bacterial activity had less (P < 0.001) gas pressure than cultures with low-CT substrate or cultures with suppressed fungal activity. Total VFA concentrations were greater (P < 0.001) in low-CT cultures when inoculum donors were without prior CT exposure (83.7 mM) than when inoculum was from CT-exposed animals (79.6 mM). Conversely, total VFA concentrations were greater (P < 0.001) in high-CT cultures with tannin-exposed inoculum (59.4 mM) than with nonexposed inoculum (52.6 mM). As expected, CT and suppression of bacterial fermentative activities had strong negative effects on fermentation; however, prior exposure to dietary CT attenuated some negative effects of dietary CT on fermentation. In our experiment, the magnitude of inoculum-donor species effects on fermentation was minor.

Modeling of two-phase flow in membranes and porous media in microgravity as applied to plant irrigation in space.

In traditional applications in soil physics it is convention to scale porous media properties, such as hydraulic conductivity, soil water diffusivity, and capillary head, with the gravitational acceleration. In addition, the Richards equation for water flux in partially saturated porous media also contains a gravity term. With the plans to develop plant habitats in space, such as in the International Space Station, it becomes necessary to evaluate these properties and this equation under conditions of microgravitational acceleration. This article develops models for microgravity steady state two-phase flow, as found in irrigation systems, that addresses critical design issues. Conventional dimensionless groups in two-phase mathematical models are scaled with gravity, which must be assigned a value of zero for microgravity modeling. The use of these conventional solutions in microgravity, therefore, is not possible. This article therefore introduces new dimensionless groups for two-phase models. The microgravity models introduced here determined that in addition to porous media properties, important design factors for microgravity systems include applied water potential and the ratio of inner to outer radii for cylindrical and spherical porous media systems.

Recent advances in technologies required for a "Salad Machine".

Future long duration, manned space flight missions will require life support systems that minimize resupply requirements and ultimately approach self-sufficiency in space. Bioregenerative life support systems are a promising approach, but they are far from mature. Early in the development of the NASA Controlled Ecological Life Support System Program, the idea of onboard cultivation of salad-type vegetables for crew consumption was proposed as a first step away from the total reliance on resupply for food in space. Since that time, significant advances in space-based plant growth hardware have occurred, and considerable flight experience has been gained. This paper revisits the "Salad Machine" concept and describes recent developments in subsystem technologies for both plant root and shoot environments that are directly relevant to the development of such a facility.

Approaches in the determination of plant nutrient uptake and distribution in space flight conditions.

The effective growth and development of vascular plants rely on the adequate availability of water and nutrients. Inefficiency in either the initial absorption, transportation, or distribution of these elements are factors which impinge on plant structure and metabolic integrity. The potential effect of space flight and microgravity conditions on the efficiency of these processes is unclear. Limitations in the available quantity of space-grown plant material and the sensitivity of routine analytical techniques have made an evaluation of these processes impractical. However, the recent introduction of new plant cultivating methodologies supporting the application of radionuclide elements and subsequent autoradiography techniques provides a highly sensitive investigative approach amenable to space flight studies. Experiments involving the use of gel based 'nutrient packs' and the radionuclides calcium-45 and iron-59 were conducted on the Shuttle mission STS-94. Uptake rates of the radionuclides between ground and flight plant material appeared comparable.

Hydrophilic membrane-based humidity control.

A dehumidification system for low gravity plant growth experiments requires the generation of no free-liquid condensate and the recovery of water for reuse. In the systems discussed in this paper, the membrane is a barrier between the humid air phase and a liquid-coolant water phase. The coolant water temperature combined with a transmembrane pressure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared different hydrophilic membranes for humidity control. In a direct comparison of the hydrophilic membranes, hollow fiber cellulose ester membranes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up, and stability. However, cellulose ester membranes were inferior to metal membranes in one significant category, durability. Dehumidification systems using mixed cellulose ester membranes failed after operational times of only hours to days. We propose that the ratio of fluid surface area to membrane material area (approximately = membrane porosity) controls the relative performances among membranes. In addition, we clarified design equations for operational parameters such as the transmembrane pressure differential. This technology has several potential benefits related to earth environmental issues including the minimization of airborne pathogen release and higher energy efficiency in air conditioning equipment. Utilizing these study results, we designed, constructed, and flew on the space shuttle missions a membrane-based dehumidification system for a plant growth chamber.

An autonomous module for supporting mice during spaceflight.

The Animal Module for Autonomous space Support (A-MASS) was developed to enable 30-day spaceflight for mice on the first Commercial Experiment Transporter mission. Because space hardware did not previously exist to support mice without astronaut intervention, the A-MASS presented considerable technical and animal care challenges. The technical challenges included maintaining a 42.5l payload volume and 20-g structural conformance while providing 30 days of autonomous mouse support. Sensors, video, a pressurized oxygen supply system and an internal data logging system were incorporated. The A-MASS met NIH guidelines for temperature, humidity, food and water access, oxygen supply, air quality and odor control. These technical and animal care challenges, along with power and mass constraints, were addressed using a novel design which ensures a fresh food and water supply, a clean view path into the cage for the camera system, and removal of the wastes from the air supply. The payload was successfully tested in an enclosed chamber and passed animal health, vibrational, mechanical, and electrical tests. The physiological, tactical and animal support information gathered will be applicable to the development of mouse support modules for the Shuttle Middeck and Space Station Freedom Express Rack environments.

Plant-module for autonomous space support (P-MASS).

A wide variety of technical and science questions arise when attempting to envision the long-term support of plants, algae and bacteria in space. Currently, spaceflight data remain elusive since there are no U.S. carriers for investigating either the germane technical or scientific issues. The first flight of the Commercial Experiment Transporter (COMET) will provide a nominal 30 day orbital opportunity to evaluate such issues. The P-MASS is a small payload that is designed to meet the mass (40 lbs.), volume (1.5 cu.ft.), and power (120 W) constraints of one of several COMET payloads while enabling flight evaluations of plants, algae and bacteria. Various P-MASS subsystems have been subjected to extensive ground tests as well as KCl35 tests. Various biological sub-systems have been similarly evaluated. Through a variety of sensors coupled with color video, the P-MASS performance and the supported biological systems will be compared for terrestrial controls versus spaceflight materials. This small, low cost payload should return valuable information regarding the requirements for hardware and biological systems needed to move toward bioregenerative life support systems in space. In addition, it should be possible to accurately identify major unresolved difficulties that may arise in the long-term, spaceflight support of various biological systems. Finally, this generic spaceflight capability should enable a variety of plant research programs focused on the use of microgravity to modulate and exploit plant products for commercial applications ranging from new agricultural products to pharmacological feedstocks and new controlled agricultural strategies.

Characterization of fluid distribution through a porous substrate under dynamic g conditions.

Dedicated electronic hardware has been constructed to monitor fluid distributions inside a plant rooting/nutrient substrate (Rockwool). With this hardware the effect of dynamically varying gravity states, from enhanced 2g to reduced 0.01g, on solution distributions inside a cube of substrate was monitored aboard the NASA KC-135 reduced gravity research aircraft. The 8 vertices and the center of the cube were used to place sinusoidal voltage sources (electrodes), emitting different fixed frequencies, inside the substrate. Using another set of 9 electrodes the voltage fields were detected across all frequencies. Since the substrate cannot conduct, those frequencies which appeared on any detector (sensor) were indicative of the conductive liquid pathways inside the substrate. An analysis algorithm was developed to visualize the fluid distributions under g-level conditions. Even though the duration of the experiment was short, gravity induced changes in fluid position were readily and reliably detected. Since fluids carry the nutrients necessary for plant growth these data and techniques can lead to the development of a uniform nutrient supply system supportive of optimal plant growth in space.

Leaf orientation and the response of the xanthophyll cycle to incident light.

Leaves from two species, Euonymus kiautschovicus and Arctostaphylos uva-ursi, with a variety of different orientations and exposures, were examined in the field with regard to the xanthophyll cycle (the interconversion of three carotenoids in the chloroplast thylakoid membranes). East-, south-, and west-facing leaves of E. kiautschovicus were sampled throughout the day and all exhibited a pronounced and progressive conversion of violaxanthin to zeaxanthin, followed by a reconversion of zeaxanthin to violaxanthin later in the day. Maximal levels of zeaxanthin and minimal levels of violaxanthin were observed at the time when each leaf (orientation) received the maximum incident light, which was in the morning in east-facing, midday in southfacing, and in the afternoon in west-facing leaves. A very slight degree of hysteresis in the removal of zeaxanthin compared to its formation with regard to incident light was observed. Leaves with a broader range of orientations were sampled from A. uva-ursi prior to sunrise and at midday. All of the examined pigments (carotenoids and chlorophylls) increased somewhat per unit leaf area with increasing total daily photon receipt. The sum of the carotenoids involved in the xanthophyll cycle, violaxanthin + antheraxanthin + zeaxanthin, increased more strongly with increasing growth light than any other pigment. In addition, the amounts of zeaxanthin present at midday also increased markedly with increasing total daily photon receipt. The percentage of the xanthophyll cycle that was converted to zeaxanthin (and antheraxanthin) at peak irradiance was very large (approximately 80%) in the leaves of both E. kiautschovicus and A. uva-ursi. The daily changes in the components of the xanthophyll cycle that paralleled the daily changes in incident light in the leaves of E. kiautschovicus, and the increasing levels of the xanthophyll cycle components with total daily photon receipt in the leaves of A. uva-ursi, are both consistent with the involvement of zeaxanthin (i.e. the xanthophyll cycle) in the photoprotection of the photosynthetic apparatus against damage due to excessive light.