Biomedical subjects

William H Paloski

Publications and source records attributed to William H Paloski.

6 recordsLinked to original sources

PubMed2006

Space motion sickness: incidence, etiology, and countermeasures.

Space motion sickness is experienced by 60% to 80% of space travelers during their first 2 to 3 days in microgravity and by a similar proportion during their first few days after return to Earth. Space motion sickness symptoms are similar to those in other forms of motion sickness; they include: pallor, increased body warmth, cold sweating, malaise, loss of appetite, nausea, fatigue, vomiting, and anorexia. These are important because they may affect the operational performance of astronauts. Two hypotheses have been proposed to explain space motion sickness: the fluid shift hypothesis and the sensory conflict hypothesis. The fluid shift hypothesis suggests that space motion sickness results from the cranial shifting of body fluids resulting from the loss of hydrostatic pressure gradients in the lower body when entering microgravity. The cranial fluid shifts lead to visible puffiness in the face, and are thought to increase the intracranial pressure, the cerebrospinal-fluid pressure or the inner ear fluid pressures, altering the response properties of the vestibular receptors and inducing space motion sickness. The sensory conflict hypothesis suggests that loss of tilt-related otolith signals upon entry into microgravity causes a conflict between actual and anticipated signals from sense organs subserving spatial orientation. Such sensory conflicts are thought to induce motion sickness in other environments. Space motion sickness is usually treated using pharmaceuticals, most of which have undesirable side effects. Further studies elucidating the underlying mechanism for space motion sickness may be required for developing new treatments.

Antiemetics↗

PubMed2006

Age associated differences in postural equilibrium control: a comparison between EQscore and minimum time to contact (TTC(min)).

Increased postural instability and the subsequent elevation in fall incidence with increasing age are important contributors for hip fractures and developing frailty. When testing for such instability, most studies characterize balance in terms of center-of-mass (COM) deviation from a finite point, the "equilibrium point", located at the center of a subject's stance. For example, the clinically accepted equilibrium score (EQscore) represents instability as the maximum peak-to-peak sway about the "equilibrium point". An alternative theory views balance as being controlled within a "stability margin" in which all corrective actions are based on the time to contact (TTC) of the body's COM with that margin. This study examines the differences offered by evaluating balance control using the EQscore and TTC approach across several age groups and sessions. Consenting subjects from the Baltimore Longitudinal Study of Aging were recruited (N=155) from each age decade (20s-80s) who were generally healthy and free from neurological diagnoses. Results showed TTC tests detected significant variations in eyes open versus eyes closed testing that were unpredictable by EQscore. Further, TTC produced differences in age-related stability threats not seen using EQscore. The TTC data also provided a discriminating difference between subjects who fell in the difficult tests and those who maintained posture. Overall, these data suggest EQscore might not sufficiently account for dynamic control components the body may be using to maintain balance. TTC may offer a more accurate estimate of postural stability (functional ability) than EQscore based on its inclusion of a velocity component to detect dynamic changes.

Accidental Falls↗

PubMed2005

Destabilization of human balance control by static and dynamic head tilts.

To better understand the effects of varying head movement frequencies on human balance control, 12 healthy adult humans were studied during static and dynamic (0.14, 0.33, 0.6 Hz) head tilts of +/- 30 degrees in the pitch and roll planes. Postural sway was measured during upright stance with eyes closed and altered somatosensory inputs provided by a computerized dynamic posturography (CDP) system. Subjects were able to maintain upright stance with static head tilts, although postural sway was increased during neck extension. Postural stability was decreased during dynamic head tilts, and the degree of destabilization varied directly with increasing frequency of head tilt. In the absence of vision and accurate foot support surface inputs, postural stability may be compromised during dynamic head tilts due to a decreased ability of the vestibular system to discern the orientation of gravity. This instability may compound the risk of falling following recovery from balance disorders or adaptation to altered gravity conditions such as space flight. Thus, dynamic head tilts may improve the diagnostic sensitivity of computerized dynamic posturography, particularly for healthy subjects recovering from temporary balance control deficits.

Adaptation, Physiological↗

PubMed2004

Postflight balance control recovery in an elderly astronaut: a case report.

OBJECTIVE: To examine the sensorimotor adaptive response of a 77-year-old man exposed to the gravito-inertial challenges of orbital space flight. STUDY DESIGN: Prospective case study with retrospective comparisons. SETTING: NASA Neurosciences Laboratory (Johnson Space Center) and Baseline Data Collection Facility (Kennedy Space Center). PRIMARY PARTICIPANT: One 77-year-old male shuttle astronaut. INTERVENTION: Insertion into low Earth orbit was used to remove gravitational stimuli and thereby trigger sensorimotor adaptation to the microgravity environment. Graviceptor stimulation was reintroduced at landing, and sensorimotor readaptation to the terrestrial environment was tracked to completion. MAIN OUTCOME MEASURES: Computerized dynamic posturography tests were administered before and after orbital flight to determine the magnitude and time course of recovery. RESULTS: The elderly astronaut exhibited balance control performance decrements on landing day; however, there were no significant differences between his performance and that of younger astronauts tested on the same shuttle mission or on previous shuttle missions of similar duration. CONCLUSIONS: These results demonstrate that the physiological changes attributed to aging do not necessarily impair adaptive sensorimotor control processes.

Adaptation, Physiological↗

PubMed2004

Sensorimotor recovery following spaceflight may be due to frequent square-wave saccadic intrusions.

Square-wave jerks (SWJs) are small, involuntary saccades that disrupt steady fixation. We report the case of an astronaut (approximately 140 d on orbit) who showed frequent SWJs, especially postflight, but who showed no impairment of vision or decrement of postflight performance. These data support the view that SWJs do not impair vision because they are paired movements, consisting of a small saccade away from the fixation position followed, within 200 ms, by a corrective saccade that brings the eye back on target. Since many returning astronauts show a decrement of dynamic visual function during postflight locomotion, it seems possible that frequent SWJs improved this astronaut's visual function by providing postsaccadic enhancement of visual fixation, which aided postflight performance. Certainly, frequent SWJs did not impair performance in this astronaut, who had no other neurological disorder.

Astronauts↗

PubMed2002

A statistical model for interpreting computerized dynamic posturography data.

Computerized dynamic posturography (CDP) is widely used for assessment of altered balance control. CDP trials are quantified using the equilibrium score (ES), which ranges from zero to 100, as a decreasing function of peak sway angle. The problem of how best to model and analyze ESs from a controlled study is considered. The ES often exhibits a skewed distribution in repeated trials, which can lead to incorrect inference when applying standard regression or analysis of variance models. Furthermore, CDP trials are terminated when a patient loses balance. In these situations, the ES is not observable, but is assigned the lowest possible score--zero. As a result, the response variable has a mixed discrete-continuous distribution, further compromising inference obtained by standard statistical methods. Here, we develop alternative methodology for analyzing ESs under a stochastic model extending the ES to a continuous latent random variable that always exists, but is unobserved in the event of a fall. Loss of balance occurs conditionally, with probability depending on the realized latent ES. After fitting the model by a form of quasi-maximum-likelihood, one may perform statistical inference to assess the effects of explanatory variables. An example is provided, using data from the NIH/NIA Baltimore Longitudinal Study on Aging.

Adult↗