Biomedical subjects

J Kavelaars

Publications and source records attributed to J Kavelaars.

3 recordsLinked to original sources

PubMed2001

Hypernatremia in a non insulin dependent (type 2) diabetic patient with central diabetes insipidus.

We describe a patient with central diabetes insipidus who presented with hyperosmolar, non-ketotic hyperglycaemia. The role in this case of reduced thirst sensation with decreased water intake and abnormal AVP production illustrates the importance of these protective mechanisms in normal physiology regarding maintenance of normal plasma osmolality. Despite the complex pathophysiology in this patient, fluid resuscitation aimed at normalisation of the water deficit resulted in full recovery.

Brain Neoplasms↗

PubMed2001

Orientation illusions and heart-rate changes during short-radius centrifugation.

Intermittent short-radius centrifugation is a promising countermeasure against the adverse effects of prolonged weightlessness. To assess the feasibility of this countermeasure, we need to understand the disturbing sensory effects that accompany some movements carried out during rotation. We tested 20 subjects who executed yaw and pitch head movements while rotating at constant angular velocity. They were supine with their main body axis perpendicular to earth gravity. The head was placed at the centrifuge's axis of rotation. Head movements produced a transient elevation of heart-rate. All observers reported head-contingent sensations of body tilt although their bodies remained supine. Mostly, the subjective sensations conform to a model based on semicircular canal responses to angular acceleration. However, some surprising deviations from the model were found. Also, large inter-individual differences in direction, magnitude, and quality of the illusory body tilt were observed. The results have implications for subject screening and prediction of subjective tolerance for centrifugation.

Adult↗

PubMedDate not supplied

Artificial gravity: head movements during short-radius centrifugation.

Short-radius centrifugation is a potential countermeasure to long-term weightlessness. Unfortunately, head movements in a rotating environment induce serious discomfort, non-compensatory vestibulo-ocular reflexes, and subjective illusions of body tilt. In two experiments we investigated the effects of pitch and yaw head movements in participants placed supine on a rotating bed with their head at the center of rotation, feet at the rim. The vast majority of participants experienced motion sickness, inappropriate vertical nystagmus and illusory tilt and roll as predicted by a semicircular canal model. However, a small but significant number of the 28 participants experienced tilt in the predicted plane but in the opposite direction. Heart rate was elevated following one-second duration head turns. Significant adaptation occurred following a series of head turns in the light. Vertical nystagmus, motion sickness and illusory tilt all decreased with adaptation. Consequences for artificial gravity produced by short-radius centrifuges as a countermeasure are discussed. Grant numbers: NCC 9-58.

Adaptation, Physiological↗