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Biomedical subjects

W E Thornton

Publications and source records attributed to W E Thornton.

At least 19 recordsLinked to original sources
PubMed1992

Changes in leg volume during microgravity simulation.

Little published information exists regarding the magnitude and time course of cephalad fluid shift resulting from microgravity simulations. Six subjects were exposed to 150 min each at horizontal bed rest, 6 degrees head-down tilt, and horizontal water immersion. Fluid shift was estimated by calculating leg volumes from eight serial girth measurements from groin to ankle before, during, and after exposure. Results were compared with data from the first 3 h of spaceflight. By the end of exposure, total leg volume for the six subjects decreased by 2.6 +/- 0.8%, 1.7 +/- 1.2%, and 4.0 +/- 1.6% for horizontal, head-down, and immersion, respectively. Changes had plateaued for horizontal and head-down and had slowed for immersion. Relatively more fluid was lost from the lower leg than the thigh for all three conditions, particularly head-down. During the first 3 h of spaceflight, total leg volume decreased by 8.6%, and relatively more fluid was lost from the thigh than the lower leg. The difference in volume changes in microgravity and simulated microgravity may be caused by the small transverse pressures still present in ground-based simulations and the extremely nonlinear compliance of tissue.

Adult↗
PubMed1990

Ambulatory blood pressure monitoring in hypertensive adolescents.

The purpose of this study was to determine the ability of ambulatory blood pressure monitoring to identify youths with chronic blood pressure elevation. Nineteen adolescent boys were studied, ten had 5-year average systolic or diastolic pressures above the 95th percentile, nine had normal pressure. A Del Mar Avionics Pressurometer III system recorded an average of 121 readings on each subject. The coefficients of variation for pressure were similar for hypertensive and normotensive individuals. During classes, eight of the ten hypertensive youths had elevated pressures in over half of the measurements. Also during these classes eight of ten hypertensive boys had average systolic or diastolic pressure above the 95th percentile, whereas only one of nine normotensive boys had average pressures above this level. We suggest that schooltime ambulatory pressures may be most useful in classifying the blood pressure trend in a youth.

Adolescent↗
PubMed1989

Studies of the horizontal vestibulo-ocular reflex in spaceflight.

Changes in the vestibulo-ocular reflex (VOR) during space flight have been suspected of contributing to space motion sickness. The horizontal VOR was studied in nine subjects on two space shuttle missions. Active unpaced head oscillation at 0.3 Hz was used as the stimulus to examine the gain and phase of the VOR with and without visual input, as well as the visual suppression of the reflex. No statistically significant changes were noted inflight in the gains or phase shifts of the VOR during any test condition, or between space motion sickness susceptible and nonsusceptible populations. Although VOR suppression was unaffected by spaceflight, the space motion sickness-susceptible group tended to exhibit greater error in the suppression than the nonsusceptible group. It is concluded that at this stimulus frequency, VOR gain is unaffected by spaceflight, and any minor individual changes do not seem to contribute to space motion sickness.

Adult↗
PubMed1987

Clinical characterization and etiology of space motion sickness.

An inflight, clinically-oriented investigation of SMS was begun on STS-4 and revealed the following: compared to motion sickness on Earth, autonomic signs are significantly different in space motion sickness (SMS) vs. motion sickness (MS) in that sweating is not present, pallor or flushing may be present, and vomiting is episodic, sudden, and brief. Nausea may be present but is more often absent. Onset ranges from minutes to hours, plateaus, and rapidly resolves in 8-72 h with 36 h as average. Postflight reactions have been mild unless deliberately provoked in the early period of re-exposure to gravity. Postflight there is a period of resistance to all forms of motion sickness. There is some evidence for individual reduction in sensitivity on repeated flights. Etiology could not be proven objectively; however, the sensitivity to angular motion, often pronounced in pitch, and theoretical considerations make an intravestibular conflict the most likely cause. Electro-oculogram (EOG), audio-evoked potentials, measurement of fluid shifts, and other studies are inconsistent with a transient vestibular hydrops or increased intracranial pressure as a cause.

Electrooculography↗
PubMed1987

Gastrointestinal motility in space motion sickness.

Gastrointestinal (Gl) symptoms in space motion sickness (SMS) are significantly different from those in ordinary motion sickness (MS). Vomiting is sudden, often unexpected, infrequent, never prolonged and usually without nausea. Inflight bowel sounds are absent in those with SMS but present after recovery and in those not affected. Recording and tabulation of sounds was the only technique that could be used as a measure of motility during spaceflight operations. There were 17 subjects, 6 unaffected by SMS, who made ambulatory recordings pre- and inflight. With one exception, all those affected had sharply reduced sounds while those unaffected had increases or moderate reductions. The mechanism of vomiting in SMS appears to be secondary to this ileus in contrast to vomiting in ordinary MS, where the emesis center is thought to be directly triggered by the vestibular system. This ileus appears to be the only consistent and reliable indicator for SMS to date.

Auscultation↗
PubMed1987

Fluid shifts in weightlessness.

Studies of leg volumes in space by multiple girth measurements showed reductions of 1.9 L (12.8% of leg volume) with 1.1 L from the non-dominant leg on Skylab 4. On landing, 65% of postflight leg volume increase was complete at 1.5 h. Measurement of the dominant leg during the equivalent period on Shuttle showed a mean loss of 0.9 L which was 90% complete at 150 min. Postflight increases were 87% complete at 1.5 h postlanding. Mass measurements during and after Skylab 4 showed a loss of 2.5 kg over the first 4 d on-orbit with a gain of 2.7 kg over the first 4 d of recovery. These changes are assumed to be tissue fluids secondary to changes in hydrostatic pressures and are much greater than those seen in bed rest. Rate and magnitude of inflight and postflight changes have significant operational impact.

Arm↗
PubMed1987

Space shuttle inflight and postflight fluid shifts measured by leg volume changes.

This is a study of the inflight and postflight leg volume changes associated with spaceflight on Space Shuttle missions. The results of this study show an inflight volume loss of 2 L from lower extremities, 1 L from each leg, representing an 11.6% volume change. The vast majority of this change appears to be a shift in body fluids, both intravascular and extravascular. The fluid shift occurs rapidly on Mission Day 1 (MD-1), with it being essentially complete by 6 to 10 h. The regional origin of shift and leg volume change shows a far greater absolute volume (708 ml vs. 318 ml) and percentage (69% vs. 31%) of the total change coming from the thigh as compared to the lower leg. Postflight, the return of fluid to the lower extremities occurs rapidly with the majority of volume return complete within 1.5 h postlanding. At 1 week postflight there is a residual leg volume decrement of 283 ml or 3.2% that is probably due to tissue loss secondary to atrophic deconditioning and weight loss.

Body Fluids↗
PubMed1979

Tricyclic antidepressant and cardiovascular drug interactions.

Tricyclic antidepressants have anticholinergic, adrenolytic and quinidine-like activity. These actions result in a variety of cardiac and blood pressure effects. Tricyclic antidepressants can reverse the antihypertensive effect of guanethidine and clonidine. Orthostatic hypotension may be increased with diuretics and hydralazine. Myocardial depression may occur with lidocaine, phenytoin or propranolol. Dangerous additive effects may result from concomitant use of a tricyclic antidepressant and either quinidine or procainamide.

Adrenergic beta-Antagonists↗
PubMed1978

Modulation of gastrin release by acute changes in plasma calcium.

Gastrin release was studied in 5 hypergastrinemic patients, both during calcium infusion and EDTA infusion. In each patient, gastrin decreased in conjunction with the fall in plasma calcium, and increased during calcium infusion. Plasma gastrin and calcium levels were strongly correlated.

Achlorhydria↗
PubMed1978

Folic acid, mental function, and dietary habits.

The combination of biochemical theory, case studies, and patient population surveys suggests that the water soluble vitamin, folic acid, is relevant to mental functions. Several studies demonstrate a clinical correlation between folate deficiency and psychiatric hospitalization. The role of dietary deficiency to these observations has needed further examination. After reviewing the serum folate values of 269 psychiatric hospital admissions, the incidence of serum folates below 5.9 ng./ml. was found to be greater than a control group. A dietary rating for all admissions revealed a high frequency of deficiency in all patients with no greater prevalence among the low folate group. These observations agree that psychiatric patients are more likely to have low serum folate values, and suggest that poor diet does not explain the increased likelihood.

Adult↗