Biomedical subjects

B S Shender

Publications and source records attributed to B S Shender.

7 recordsLinked to original sources

PubMed2001

Dynamic strength capabilities of small-stature females to eject and support added head weight.

BACKGROUND: Naval Air Warfare Center Aircraft Division investigated the abilities of small-stature females (< or = 120 lb) to fly under G-stress using the Dynamic Flight Simulator (DFS) and its tactical fight/attack cockpit, displays and controls. OBJECTIVES: Determine ability to exert NACES ejection seat actuation pull force under static, acceleration and simulated flight conditions; support up to 5 lb of added head weight (AHW) under catapult, arrestment, and aerial combat maneuver G-loads; and reach all controls. METHODS: Seven female subjects (six small and one medium stature) participated. The AHW task included three helmet weights, 3.5 lb (standard configuration), 4.25 lb and 5 lb and subjects were tasked to accurately read cockpit displays. Muscular exertion and fatigue (arm, shoulder, neck) assessment used electromyography (EMG). Limits in overall reach and throttle and stick movements were measured. RESULTS: Subjects successfully ejected using a two-hand grip under G-stress. Subjects read all displays supporting 5 lb under +6 Gz. Most small-stature subjects could not fully support their heads wearing 3.5 lb helmet during flat spin conditions. CONCLUSIONS: Within the scope of these tests, small-stature subjects demonstrated the strength to safely initiate ejection during severe physically-taxing dynamic conditions but had difficulty supporting AHW under -Gx stress. Human factors deficiencies were noted in the areas of torso harness fit, inertia reel placement relative to shoulder width, and the ability maintain a full range of stick motion.

Adult↗

PubMed2001

Dynamic strength capabilities of small-stature females to perform high-performance flight tasks.

BACKGROUND: Naval Air Warfare Center Aircraft Division investigated the abilities of small-stature females (< or = 120 lb.) to fly under G-stress using the Dynamic Flight Simulator (DFS) and its tactical fight/attack cockpit, displays and controls. The objective was to determine if these individuals possess sufficient upper-body muscular endurance to perform tasks required during fighter-pilot training, aerial combat maneuvers, and failure modes. METHODS: Five female subjects (four small-stature and one medium) participated. DFS tasks featured bombing runs, surface-to-air missile (SAM) avoidance, and single engine failure. Muscular exertion and fatigue (arm, shoulder, neck) were assessed using electromyography. RESULTS: During the most physically taxing simulation (SAM avoidance), flight performance did not significantly degrade over time. No statistically significant increase in muscular fatigue was found during the bombing simulation, though there was some evidence of degraded fine muscle control. Evidence of flexor and extensor muscular fatigue was associated with the single-engine-failure simulation. CONCLUSIONS: Within the scope of these tests, small-stature individuals demonstrated the strength and endurance to safely fly physically strenuous missions. However, a larger subject sample is necessary to increase the statistical power of the results.

Adult↗

PubMed2001

Human tolerance to Gz acceleration loads generated in high-performance helicopters.

BACKGROUND: As the Gz capabilities of tactical helicopters increase, the risk to unprotected helicopter aircrew resulting from the physiologic response to transitions from -1 Gz (push) to +4.5 Gz (pull) loads needs to be addressed. METHODS: There were 9 volunteers who participated in a study conducted at the Veridian Operations Centrifuge Facility in Warminster, PA. A 1-h mission scenario consisting of nine helicopter maneuvers, based on inflight G measurements (push-pull mission, PPM), simulated both current (CM: -0.2 to +3.5 Gz) and projected future platform capabilities (FM: -1 Gz to +4.5 Gz). Additional scenarios were run in which push transitions were limited to +1 Gz (GM). Measurements included blood pressure (BP), heart rate (HR), loss of vision, and subjective fatigue. RESULTS: Visual decrements were minimal during CM while muscular tensing was required to avoid blackout during FM. Light loss typically occurred during the transition from -Gz to +Gz. Within the scope of these tests, subjects tolerated the range of Gz stresses associated with current U.S. Navy rotary wing platforms. When subjected to FM G-loads (typical of current U.S. Army high-performance platforms), cardiovascular stress significantly increased, Gz tolerance dropped as much as 1.2 G, and HR increased as much as 67 bpm. Cardiovascular changes were significantly greater during FM PPM relative to GM. Four subjects reported Almost-Loss of Consciousness (A-LOC) symptoms during FM. CONCLUSIONS: While G-stress experienced by aircrew generated by current helicopters does not appear to present a high risk, G-awareness training is recommended to reduce risks to aircrew exposed to G-loads generated by more aggressive helicopters. Future studies are required to determine the impact of longer mission times and dehydration.

Acceleration↗

PubMed1996

High performance supine flight assessment using the NAWC dynamic flight simulator.

INTRODUCTION: To determine the feasibility of high-performance supine flight, the USAF Canopy Escape Module (65 degree seat-back-angle) was modified and deployed into the Naval Air Warfare Center Dynamic Flight Simulator. METHODS: Seven male subjects performed a flight syllabus consisting of instrument flight maneuvers (high-G level turns, ILS task, vertical S-2, Half Cuban Eight). Subjects were trained and performed under both 1 g (static) and dynamic conditions in supine and upright postures. Data were assessed to determine the effects of motion (G) and seat position. A weighted objective performance grading scheme was devised based on the ability to achieve specified flight parameters. RESULTS: This paper presents the analysis of the first two tasks. During the turns, motion effects did not effect the ability to maintain specified G loads when supine, whereas there were significant differences when upright. Also, there were lower error rates under static, as compared to dynamic, conditions. Even though subjects demonstrated lower error rates during dynamic turns when upright, there were few significant differences referable to body position. Overall, subjects with the most flight experience performed better upright than supinated, while a naive subject flew significantly better supine. Notably, one subject did experience a G-induced loss of consciousness (G-LOC) and an almost LOC event during a supinated high-G turn. Body position or motion effects did not significantly alter ILS task performance. CONCLUSIONS: High performance supine flight is feasible and additional study is warranted. Important and unanticipated performance-related decrements were discovered only through the use of dynamic flight simulation.

Aerospace Medicine↗

PubMed1995

Cold water immersion simulations using the Wissler Texas Thermal Model: validation and sensitivity analysis.

BACKGROUND: Wissler's Texas Thermal Model (TM) has been used to simulate the effects of thermal stresses on individuals under a variety of conditions. As part of a U.S. Navy effort to develop integrated protection garments, TM was modified to predict tolerance to cold water immersion (CWI) with garments with clo values less than 0.1 (15). METHODS: With these modifications, TM predictions were validated using experimental data obtained from 39 males and females during anti-exposure suit CWI assessments. Data analyses were based on changes in rectal (Tre) and various skin temperatures (Tsk). A sensitivity analysis was also performed to determine which TM parameters were most affected during simulated CWI. The condition tested was head-out immersion in 4.4 degrees C water by a 72.6 kg man (10 mm mean skinfold thickness). RESULTS: For most of the subject pool, the estimated change in Tre, chest, thigh, calf, and arm temperatures were not statistically different from experimental values. However, TM predictions were less accurate with respect to female responses. Based on thermal end points, TM predictions indicated that the following body segments were most sensitive to changes in insulation level (ordered from most to least important): chest and abdomen, leg, head, and arm. The physical parameters mean skinfold thickness, basal metabolic rate, body weight, and exercise metabolic rate had the most impact on TM predictions. CONCLUSIONS: The relative benefit of increased insulation on individual body segments was identified to aid garment design. Further, the relative importance of model physical parameters was identified so that judicious initial conditions could be selected to ensure that only garment design changes would be reflected in model predictions.

Abdomen↗

PubMed1994

Contribution of cerebrospinal fluid to rheoencephalographic waveforms during hypoxic and +Gz stress.

Acceleration (G) forces generated by high performance aircraft induce a redistribution of blood and cerebrospinal fluid (CSF) in the head resulting in decreased visual function, and may lead to G-induced loss of consciousness (G-LOC). CSF provides a critical support function to the brain by equalizing the pressure changes occurring throughout the skull under G-stress, particularly to the venous system. While it has been acknowledged that understanding this role of the CSF system is essential in order to enhance G-tolerance, no such studies have been conducted since the 1940's, due to technical difficulties. We have shown that these can be surmounted through the development of rheoencephalography (REG), or impedance plethysmography of the head, to noninvasively monitor shifts in CSF under both hypoxic (oxygen deprivation in the laboratory) and actual +Gz stress (small centrifuge) conditions. Using surgical and physiologic techniques on New Zealand White rabbits, we have established the following: 1) REG contains information concerning the function of the vascular, CSF, and respiratory systems as they influence both beat-to-beat and bulk movement of cephalic fluids; 2) respiratory effects on cerebral blood volume and CSF pressure can be monitored with the REG; 3) REG waveforms obtained from rabbits under laboratory and +Gz stress conditions were similar to those obtained during human +Gz centrifuge exposures; 4) using (i) brief occlusions of blood flow into the head and (ii) withdrawals of CSF, it was estimated that the relative volumetric contributions of blood and CSF to the REG were 70% and 30%, respectively; and 5) physiologic responses to stress are reflected in changes in the frequency content of the REG.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗

PubMed1993

The opticogravic nerve: eye-level anatomic relationships within the central nervous system.

The anatomic relationships between arterial blood supply and key structures within the central nervous system (CNS) are important in comprehending the neurophysiological effects of acceleration (+Gz) stress, including +Gz-induced loss of consciousness (G-LOC). An accurate understanding of the location of the vascular and neurologic structures at eye-level is vital, since it is possible to determine precisely when visual symptoms occur. Cerebral perfusion is supported by the pressure-equalizing effects provided by the cerebrospinal fluid. While brain and brain stem are protected by this pressure compensation, the eye is not. Decreased visual function results when retinal perfusion is compromised. G-LOC generally occurs following loss of visual function. The exact location(s) of altered perfusion within the CNS that results in G-LOC is currently unknown. To thoroughly understand G-LOC, it will be necessary to understand which CNS structures must be affected by +Gz-induced ischemia to cause G-LOC. Based on previous theoretical considerations of loss of consciousness as a protective mechanism, it is possible to consider the eye (visual system) as a dual sensor for both vision and gravitational (acceleration) stress. Due to this expanded definition of the sensory functions of the second cranial nerve, it would therefore be more appropriate to describe it as the "opticogravic" nerve. This manuscript discusses some of these considerations and the eye-level neuroanatomic relationships of vital importance for the acceleration medical subspecialist.

Acceleration↗