Upright head roll test: A new contribution for the diagnosis of lateral semicircular canal benign paroxysmal positional vertigo

Diagnosing the affected side in Benign Paroxysmal Positional Vertigo (BPPV) involving the Lateral Semicircular Canal (LSC) is often challenging and uncomfortable in patients with recent onset of vertigo and intense autonomic symptoms. The Minimum Stimulus Strategy (MSS) aims to diagnose side and canal involved by BPPV causing as little discomfort as possible to the patient. The strategy applied for LSC-BPPV includes the evaluation of pseudo-spontaneous nystagmus and oculomotor responses to the Head Pitch Test (HPT) in upright position, to the seated-supine test and to the Head Yaw Test (HYT) while supine. Matching data obtained by these tests enables clinicians to diagnose the affected side in LSC-BPPV. The purpose of this preliminary study is to propose a new diagnostic test for LSC-BPPV complimentary to the HPT, the Upright Head Roll Test (UHRT), to easily determine the affected ear and the involved arm in the sitting position and to evaluate its efficiency. Our results suggest that the UHRT can increase the sensitivity of the MSS without resorting to the HYT, thus reducing patient’s discomfort.

Human path navigation in a three-dimensional world

Jeffery et al. propose a non-uniform representation of three-dimensional space during navigation. Fittingly, we recently revealed asymmetries between horizontal and vertical path integration in humans. We agree that representing navigation in more than two dimensions increases computational load and suggest that tendencies to maintain upright head posture may help constrain computational processing, while distorting neural representation of three-dimensional navigation.

Abstract 3315: Therapeutic Implications of Sympathetic Stimulus in Orthostatic Patients: Measured by Spectral Domain Analysis

Upon assuming an upright, head up posture, a sympathetic surge is expected. Sympathetic Withdrawal (SW) is abnormal and can differentiate Orthostasis. SW, with blood pressure (BP) and heart rate (HR), can fully define the continuum that is Orthostasis, including pre-clinical forms: Orthostatic Hypotension (OH-), Orthostatic Intolerance (OI), Orthostatic Hypertension (OH+), and Postural Orthostatic Tachycardia Syndrome (POTS). Our objective was to test the therapeutic implications of SW in Orthostatic patients. Autonomic profiling of 210 consecutive Orthostatic patients recruited from ambulatory clinics was performed using the ANX-3.0 Autonomic Monitoring System (Ansar, Inc., Philadelphia, PA). The cohort (age=58.9±11.6; 30 Diabetics; 132 Females, 28 Controls) was followed over a two year period. Autonomic profiling was based on patient responses to a standard clinical study that includes a resting baseline and periods of deep (relaxed) breathing, short Valsalva maneuvers, and quick stand immediately followed by quiet standing. The control group were patients with known diagnoses. The experimental group were prescribed 2.5 mg Midodrine once a day around dinner. Control patients were administered Flourinef, or support hose, or when possible were requested to modify their diets to add salt and build fluid volume. Patients with dysautonomia, with symptoms of elevated BP when supine were omitted from the study. In 89% of the experimental cases, SW was reversed in approximately 6 months and weaned from the medication. The remaining cases were reversed and weaned before the end of the two year follow up. In the control group, 46% of the patients on Flourinef, 4% of the support hose patients and 12% of the diet modification patients corrected SW within the two year period. The application of an alpha-adrenergic agonist seems to have greater efficacy than a mineralo-corticoid, mechanical intervention, or dietary modification in correcting SW associated with Orthostasis.

Changes in the perceived head transversal plane and the subjective visual horizontal induced by Coriolis stimulation during gondola centrifugation

For studying the influence of the vertical semicircular canals on spatial orientation in roll, the subjective visual horizontal (SVH) and the subjective transversal plane of the head (STP) were measured in a situation where the vertical canals sense a roll-velocity stimulus while the otolith organs persistently signal that the head is upright in roll. During gondola centrifugation (resultant gravitoinertial force vector 2.5 G, gondola inclination 66 degrees) subjects were exposed to controlled rotational head movements (angular speed 27 degrees/s, magnitude 40 degrees) about the yaw (body z-) axis, produced by means of a motor-driven helmet. This causes a roll-plane Coriolis stimulus to the canals, while the otoliths persistently sense upright head position in roll. The subjects reported intense sensations of rotation and tilt in the roll plane. This was reflected in tilts of both the SVH and STP. The initial tilt of the SVH was 13.0 ± 9.7 degrees (mean ± S.D., n=10). {The STP was changed in the opposite direction}. The initial tilt was 23.8 ± 12.2 degrees (mean ± S.D., n=5). {The changes in the SVH and STP were not of equal magnitude.} A few subjects who had almost no deviations in the SVH showed pronounced tilts of the STP. The time constant for exponential decay of the tilts of the SVH and STP was on average approximately 1 minute. These findings indicate that a difference in activity of the vertical canals in the right versus left ear may cause substantial tilts of the SVH even if there is no asymmetry in the activity of the otolith system. Further, the canal stimulus may induce a tilt of the fundamental egocentric frame of reference.

Further Evaluation of Microswitch Clusters to Enhance Hand Response and Head Control in Persons with Multiple Disabilities

This study was a further evaluation of microswitch clusters (combinations of two microswitches) to improve adaptive responding together with correct head position in two persons with multiple disabilities. The two participants were 19.7 and 6.6 yr. old and had profound intellectual disabilities, spastic tetraparesis, and visual impairment. They were initially taught an adaptive hand response that activated a pressure microswitch and produced favorite stimulation. Thereafter, their performance of the hand response produced favorite stimulation only when it was combined with a correct head position (detected through a mercury microswitch). Analysis showed that both participants increased the frequency of the hand response and, subsequently, the percentage of times they emitted this response in combination with correct (upright) head position. In essence, they were able to coordinate constructive occupation with exercise of appropriate posture. Performance was maintained at a 2-mo. postintervention check.

Motor Strategy in Rapid Sequential Swallowing

This study examined the physiological properties and movement strategies of normal, rapid sequential swallowing during simultaneous videofluoroscopy (VFS) and submental surface electromyography (EMG). Ten subjects performed discrete (5 and 15 cc) and sequential (150 cc in tilted and upright head postures) swallowing tasks. Analyses included VFS event timing, movement/bolus passage characteristics, EMG amplitude waveforms, and peak and offset EMG amplitudes. Results revealed that sequential swallows were significantly shorter than discrete swallows in several VFS event durations, but significantly longer in pharyngeal transit and stage transition times. The hyolaryngeal system exhibited a cyclical "rise and partial fall" movement pattern during sequential swallows on VFS, corresponding to a repetitive "activation and partial deactivation" characteristic on EMG. Greater peak EMG amplitude for sequential than discrete swallows was found in 6/10 subjects. Pharyngeal bolus merging, preparatory laryngeal gestures, and penetration without aspiration were also observed in some subjects on VFS. Intersubject differences were significant in timing measures and EMG amplitude. Our findings of individual variability and subject-specific strategies for task accommodation support the notion of built-in plasticity in the deglutitive motor complex.

Resistance reflex that maintains upright head posture in the flesh fly neobellieria bullata (Sarcophagidae)

In flesh flies Neobellieria bullata, we investigated a resistance reflex that maintains upright head posture around the roll axis relative to the thorax. The gain of the reflex depends upon the fly's behavioral state: moving flies immediately correct 90 % of the amplitude of experimentally imposed roll perturbations, returning the head almost to the fully upright position; motionless flies allow perturbations to persist for minutes before correcting only 70 % of perturbation amplitude. To investigate the role of various neural pathways, we examined the control of head posture after sectioning relevant propriosensory or motor nerves. Excision of the prosternal chordotonal organ causes no decrements in the control of head posture. Unilateral deafferentation of a cervical propriosensory organ, the prosternal organ, induces roll towards the cut side. Unilateral section of the frontal nerve, a mixed motor nerve that supplies the neck depressors and levators, leads to unilateral deficits in correcting perturbations towards the contralateral side. After bilateral propriosensory or frontal motor nerve section, approximately 40 % of perturbation amplitude is still corrected. To determine the contributions of the passive elastic properties of the neck skeleto-muscular system, flies were tested under reversible nitrogen anesthesia. They immediately corrected 40 % of perturbation amplitude. Taken together, the results demonstrate that passive elasticity plus active prosternal nerve afference to contralateral depressors innervated by the frontal nerve in combination constitute a sufficient and necessary reflex loop to control head roll posture.

Hypoxaemia following Sustained Low-Volume Venous Air Embolism in Sheep

In six upright (head above thorax) anaesthetised sheep, serial blood gas measurements were made over a 100-minute period during which repeated small-volume air emboli were injected intravenously to lower and maintain the end-tidal CO 2 concentration approximately 0.5% below its initial baseline level. With constant volume ventilation and an inspired N 2 O:O 2 ratio of 2:1, the arterial PCO 2 progressively increased and the arterial PO 2 progressively decreased with significant arterial hypoxaemia ensuing in three out of the six animals. It is suggested that during neurosurgery performed in the sitting position and with an inspired oxygen concentration of 33%, the degree of cardio-respiratory disturbance caused by venous air embolism should be assessed by continuous monitoring not only of end-tidal CO 2 concentration but also of arterial oxygen saturation using pulse oximetry.