Biomedical subjects

B J Linder

Publications and source records attributed to B J Linder.

7 recordsLinked to original sources

PubMed1995

Effects of optical pitch on oculomotor control and the perception of target elevation.

In two experiments, we used an ISCAN infrared video system to examine the influence of a pitched visual array on gaze elevation and on judgments of visually perceived eye level. In Experiment 1, subjects attempted to direct their gaze to a relaxed or to a horizontal orientation while they were seated in a room whose walls were pitched at various angles with respect to gravity. Gaze elevation was biased in the direction in which the room was pitched. In Experiment 2, subjects looked into a small box that was pitched at various angles while they attempted simply to direct their gaze alone, or to direct their gaze and place a visual target at their apparent horizon. Both gaze elevation and target settings varied systematically with the pitch orientation of the box. Our results suggest that under these conditions, an optostatic response, of which the subject is unaware, is responsible for the changes in both gaze elevation and judgments of target elevation.

Adolescent↗

PubMed1994

The possible role of nystagmus in motion sickness: a hypothesis.

An alternative hypothesis to that provided by conflict theory is formulated to account for motion sickness. The new approach is predicted on the oculocardiac reflex (i.e., bradycardia produced by extra-ocular muscle traction) (18) and empirical evidence that retrobulbar anesthesia significantly lowers the incidence of emesis after strabismus surgery (14). Eye muscle traction is presumed to elicit afferent signals that ultimately stimulate the vagus nerve (15). The same neuromotor sequence is presumed to occur during reflexive eye movements under vestibular control and during more complicated combinations of reflexive and voluntary eye movements. It is proposed that the blocking of afferent signals from extra-ocular muscle in an otherwise intact vestibulo-ocular system will eliminate the signs and symptoms of motion sickness normally produced in a provocative environment.

Eye Movements↗

PubMed1993

Posterior vitreous detachment: a possible complication of noncontact tonometry.

Two patients who underwent conventional screening noncontact tonometry (NCT) were seen after screening for acute onset of floaters, resulting from posterior vitreous detachment. Neither patient had evidence of retinal holes or tears. This observation suggests that NCT rarely may induce posterior vitreous detachment.

Aged↗

PubMed1988

Altering body position affects intraocular pressure and visual function.

Intraocular pressure (IOP) can be altered by changing body position. This report describes two experiments evaluating variations in IOP, as well as neural functioning of the retina and visual cortex (as measured by pattern-reversal electroretinogram and visual evoked potential), associated with whole-body, head-down tilt. The subjects, ten per experiment, were visually normal with IOP less than 19. In the first experiment, IOP elevations were induced by varying the angle of tilt in discrete steps between +90 degrees (upright) and -90 degrees (inverted). In each position IOP was measured and significant elevations (up to 3x baseline) were noted. These elevations were maintained for 1 min during which simultaneous retinal and cortical biopotentials were measured. In the second experiment, 6 degrees head-down tilt was maintained for 2 hr during which time the IOP and both biopotentials were measured repeatedly. Our findings confirm the effect of body position of IOP, while also revealing that head-down tilt produces significant reductions in neurophysiological function at both the retinal and cortical levels. The neural effect is maximized when 6 degrees head-down tilt is maintained for 20 min.

Adult↗

PubMed1987

Simulation of spaceflight with whole-body head-down tilt: influence on intraocular pressure and retinocortical processing.

Cephalad fluid shifts occur in the microgravity environment of spaceflight. Whole-body head-down tilt was used to simulate the influence of these fluid shifts upon intraocular pressure (IOP) and the bioelectrical activity of neural elements in the retinocortical pathway. Noninvasive techniques were used to monitor IOP, pattern reversal electroretinograms (prERGs), and pattern reversal visual evoked cortical potentials (prVEPs) when subjects were oriented either upright or in a head-down position (6 degrees or 90 degrees). The results indicate that there is a significant elevation in IOP when an individual is oriented in a head-down position. Significant alterations of neurophysiological processing in the retinocortical pathway also occur when individuals are oriented in a head-down position.

Adult↗

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↗

PubMed1985

Effects of training on systolic time intervals at rest and during isometric exercise in men and women 61 to 64 years old.

To determine whether regular exercise improves left ventricular (LV) contractile function in persons 60 years and older, systolic time intervals (STIs) were measured in 10 healthy men and women (mean age 62 +/- 1 year [+/- standard deviation]) before and after 6 months of intense endurance training. STIs, systolic and diastolic blood pressure (BP) and heart rate (HR) were determined at rest and in response to isometric handgrip exercise. Systolic BP, diastolic BP and HR increased acutely from rest in response to handgrip (p less than 0.002). The indexes of total electromechanical systole and LV ejection time (ET) index increased (p less than 0.01), preejection period (PEP) index increased (p less than 0.05) or remained unchanged and PEP/LVET did not change from values at rest in response to handgrip. Training resulted in an 18% increase in maximal oxygen uptake (p less than 0.01). After training, systolic and diastolic BP were reduced at rest (p less than 0.002) and, along with HR, were lower in response to handgrip (p less than 0.002). However, training did not alter STIs at rest or during handgrip. These findings indicate that healthy persons in their 60s have a normal LV response to isometric exercise. Prolonged, intense endurance training does not alter LV contractile function at rest or in response to isometric exercise. However, training can significantly reduce BP at rest, and markedly lower the HR-systolic BP product attained during acute isometric stress, even in normotensive older subjects.

Aged↗