Vibrotactile stimulators and virtual 3-D audio countermeasures, training and motion sickness symptoms with a simulated graveyard spin illusion.

The vestibular system by itself is incapable of effectively compensating for the graveyard spin illusion. We examined two countermeasures, i.e.

Multisensory cueing for enhancing orientation information during flight.

The U.S. Air Force still regards spatial disorientation (SD) and loss of situational awareness (SA) as major contributing factors in operational Class A aircraft mishaps ($1M in aircraft loss and/or pilot fatality).

Acceleration in other axes affects +Gz tolerance: dynamic centrifuge simulation of agile flight.

Background: Modern, thrust-vectored jet aircraft have the capability of developing multi-axis accelerations, especially during the performance of "supermaneuvers." These "agile" aircraft are capable of unconventional flight. The human consequences of this agile flight environment are unknown.

The effect of brief headward acceleration on human G tolerance.

Objective: To generate, on a multi-axial centrifuge, a negative to positive acceleration profile that reproduces the physiological reaction and subjective symptoms experienced by agile aircraft pilots. Previous research will be summarized and current status of research described.

Methods: Experiments have been accomplished with the Dynamic Environment Simulator (DES) using different profile generating techniques.

Echocardiographic evaluation of female centrifuge subjects for chronic changes in cardiac function.

Background: High sustained G exposure as experienced in flying high performance aircraft can affect cardiac function. Numerous studies, mostly on male pilots, have evaluated the chronic effects of exposure to high G. To date, none of these studies has revealed significant positive findings in cardiac function as a result of long-term high G exposure.

Female exposure to high G: performance of simulated flight after 24 hours of sleep deprivation.

Background: Ground-based research has investigated the loss of cognitive function in the extreme conditions of G-induced loss of consciousness, however, little is known about pilots' abilities to maintain cognitive performance throughout prolonged conscious exposure in the high-G environment. The effects of fatigue and G layoff on performance during exposure to high G are mostly unknown for the female population.

Methods: This research was conducted on the centrifuge Dynamic Environment Simulator.

Female exposure to high G: echocardiographic evaluation for chronic changes in cardiac function.

Background: Significant changes in cardiac preload and afterload are generated by a number of factors present during the operation of high performance aircraft. These include high levels of +Gz, positive pressure breathing and anti-G straining maneuvers. Centrifuge subjects are exposed to these same factors in doses that are comparable to their operational counterparts.

Effect of G suit type on cognitive performance.

Background: Sustained acceleration protection ensembles are being developed to help pilots of high performance aircraft endure high G exposures for longer periods of time. It has been assumed that better G endurance confers better pilot task performance. This premise was studied on the Armstrong Laboratory Dynamic Environment Simulator centrifuge.

Development of space motion sickness in a ground-based human centrifuge.

Adaptation of the vestibular system, specifically the otolith organs, to a non-terrestrial environment can result in space motion sickness-like symptoms when the human is reintroduced to the normal, 1 Gz, terrestrial environment. This premise was investigated by exposing nine subjects to 90 min of sustained 2 Gz acceleration in a human centrifuge and then observing and evaluating them at 1 Gz. Five of the subjects developed slight SMS symptoms, three developed moderate, and one developed frank sickness.

The effect of head tilt on perception of self-orientation while in a greater than one G environment.

The effect of head tilt on the perception of self-orientation while in a greater than one G environment was studied in nine subjects using the Armstrong Laboratory Dynamic Environment Simulator. After a 12-s stabilization period at a constant head tilt and G level, subjects reported their perception of the horizon by placing their right hand in a position they believed to be horizontal. Head tilt conditions ranged from -30 degrees to +45 degrees pitch over each of three head yaw positions.

Non-invasive sensing systems for acceleration-induced physiologic changes.

The status of a system under development for detection of gravity-induced loss of consciousness (G-LOC) and subsequent recovery is presented. The physiological factors under investigation for use in the loss-of-consciousness monitoring system (LOCOMS) effort are eye blink rate, head slumping, head-level arterial pulsations, and spectral shift in EEG frequency. Also being studied for inclusion in the LOCOMS are a means of detecting the presence/quality of the anti-G straining maneuver and anti-G suit functions, and a system for voice-synthesized query for interrogating the pilot prior to intervention in aircraft control.

Molecular recognition and molecular sensors.

Enzyme-substrate recognition provides a convenient and powerful basis on which to construct molecular sensors. In direct enzyme electrodes the rate of the enzyme reaction is transduced into a current using an electrode made of a conducting organic salt. In vivo microelectrodes designed to measure glucose have been constructed and used in the brain of the freely moving rat.

Inhibited enzyme electrodes. Part 3. A sensor for low levels of H2S and HCN.

It is shown that an inhibited enzyme electrode, using cytochrome oxidase, will respond to H2S, HCN and azide ion. For all three inhibitors the kinetics of the inhibiton and recovery processes have been analysed using the theoretical model presented previously (Albery et al., 1990a).

Inhibited enzyme electrodes. Part 2: The kinetics of the cytochrome oxidase system.

An inhibition enzyme electrode to measure toxic gases can be constructed using the respiratory enzyme cytochrome oxidase. The rate of enzyme turnover is followed by reducing cytochrome c on a gold electrode modified with the mediator bis(4-pyridyl) disulphate. The kinetics and mechanism of the system have been measured.

Inhibited enzyme electrodes. Part 1: Theoretical model.

A theoretical model is developed for an electrochemical sensor for toxic substances which works by measuring the inhibition of the enzyme activity. The enzyme is assumed to follow Michaelis-Menten kinetics and the diffusion kinetic equation describing the concentration profile of the enzyme's substrate in the electrolyte layer between the electrode and the membrane covering the electrode is solved. A complete set of analytical solutions is found which corresponds to a number of different rate limiting processes.

Evolutionary optimization of the catalytic effectiveness of an enzyme.

The kinetic and thermodynamic features of reactions catalyzed by present-day enzymes appear to be the consequence of the evolution of these proteins toward maximal catalytic effectiveness. These features are identified and analyzed (in detail for one substrate-one product enzymes) by using ideas that link the energetics of the reaction catalyzed by an enzyme to the maximization of its catalytic efficiency. A catalytically optimized enzyme will have a value for the "internal" equilibrium constant (Kint, the equilibrium constant between the substrates and the products of the enzyme when all are bound productively) that depends on how close to equilibrium the enzyme maintains its reaction in vivo.

The effect of sustained acceleration and noise on workload in human operators.

Biodynamic stressors such as acceleration, vibration, heat, and cold can affect pilot performance. The objective of this research was to determine the individual effect of two of these stressors, sustained acceleration or high intensity pink noise, on workload in human operators. Combined stressors were not investigated.

Amperometric enzyme electrodes.

Three different types of amperometric enzyme electrode are described. The first type uses a conducting organic-salt electrode to oxidize NADH. Results for sensors for ethanol and for bile acids are presented.

Energetics of enzyme catalysis. II. Oversaturation, case diagrams, reversible and irreversible behaviour.

Most enzymes react in vivo under reversible conditions where the substrate and product concentrations are not far removed from equilibrium values. Under these conditions when the concentration of substrate is increased, in addition to the usual unsaturated and saturated behaviour we find a third type of kinetic regime at high substrate concentration-oversaturation. In this regime the rate limiting transition state involves interconversion of free enzyme forms.

Energetics of enzyme catalysis. I. Isotopic experiments, enzyme interconversion, and oversaturation.

An enzyme-catalyzed interconversion of one substrate, S, and one product P, by an enzyme that exists in two forms E1 and E2 where E1 binds S and E2 binds P, is considered S + E1 in equilibrium E1S in equilibrium E2P in equilibrium E2 + P. Under reversible conditions (where the concentrations of S and P are not far removed from their equilibrium values) it is shown that, in addition to the usual unsaturated and saturated behaviour there exists a third regime at high substrate concentration: the oversaturated region. In this region, the rate-limiting transition state is the interconversion of the unliganded forms of the enzyme: E1 and E2.

An amperometric enzyme electrode for monitoring brain glucose in the freely moving rat.

Brain glucose concentration was measured with an amperometric enzyme electrode using glucose oxidase (EC 1.1.3.

Energetics of proline racemase: racemization of unlabeled proline in the unsaturated, saturated, and oversaturated regimes.

The interconversion of L- and D-proline catalyzed by proline racemase has been studied. The entire time course of the approach to equilibrium has been followed. After a short time the product concentration is significant, and the reaction runs under reversible conditions.

Energetics and mechanism of proline racemase.

The results from the previous six papers are collated so as to allow the construction of the complete free energy profile for the reaction catalyzed by proline racemase. This profile includes the step that involves the isomerization of the two forms of free enzyme, which can become rate limiting at very high substrate levels (in "oversaturation"). The mechanism of the reaction has been defined, the results being best accommodated by a route that involves a transition state or unstable intermediate in which the proline carbanion is flanked by the two catalytic thiols of the enzyme.

Energetics of proline racemase: rates, fractionation factors, and buffer catalysis in the oversaturated region. Nature of the interconversion of the two forms of free enzyme.

To probe the nature of the interconversion of the two unliganded forms of proline racemase, a number of experiments have been performed under oversaturating conditions where the rate of the enzymic reaction is mainly limited by the rate of this interconversion. Competitive deuterium washout experiments, where an equimolar mixture of D- and L-proline (in which some or all of one enantiomer is specifically deuterated at the 2-position) is allowed to reach chemical and isotopic equilibrium mediated by the enzyme, have been followed in four ways. The size and the rate of achievement of the maximum perturbation in the optical rotation have been measured, the deuterium content of the substrate at this maximum has been determined, and the final approach to equilibrium after the perturbation maximum has been followed.