Biomedical subjects

Charles C Della Santina

Publications and source records attributed to Charles C Della Santina.

11 recordsLinked to original sources

PubMed2006

Dynamic visual acuity during passive head thrusts in canal planes.

We sought to determine whether the dynamic visual acuity (DVA) test, which has been used to measure the function of the two horizontal semicircular canals (SCCs), could be adapted to measure the individual function of all six SCCs using transient, rapid, unpredictable head rotation stimuli (head thrusts) in the direction of maximum sensitivity of each SCC. We examined head-thrust DVA (htDVA) performance in 19 healthy control subjects, five patients before and six patients after plugging of one superior SCC for treatment of superior canal dehiscence, and two subjects with unilateral vestibular deafferentation (UVD) by vestibular neurectomy. We compared htDVA results for each SCC to vestibulo-ocular reflex gains measured using 3-D scleral coil recordings during a passive head-thrust-test paradigm. Individuals with normal vestibular function had similar htDVA scores for each of the six directions (canals) tested (mean 0.058 +/- 0.050 LogMAR). Individuals tested after surgical plugging of one superior SCC were similar to normal for all SCCs except the plugged SCC, which had significantly worse htDVA scores (mean 0.270 +/- 0.08 LogMAR). Individuals with UVD had significantly worse htDVA scores for head rotations maximally exciting any of the ipsilesional SCC (mean 0.317 +/- 0.129 LogMAR) and scores similar to normal subjects for contralesional rotations (0.063 +/- 0.051 LogMAR). These findings suggest that the htDVA test, which does not require scleral coil placement, magnetic field coils, or expensive oculography equipment, can provide a useful quantitative measure of individual SCC function.

Adult↗

PubMed2006

Axis of eye rotation changes with head-pitch orientation during head impulses about earth-vertical.

The goal of this study was to assess how the axis of head rotation, Listing's law, and eye position influence the axis of eye rotation during brief, rapid head rotations. We specifically asked how the axis of eye rotation during the initial angular vestibuloocular reflex (VOR) changed when the pitch orientation of the head relative to Earth-vertical was varied, but the initial position of the eye in the orbit and the orientation of Listing's plane with respect to the head were fixed. We measured three-dimensional eye and head rotation axes in eight normal humans using the search coil technique during head-and-trunk (whole-body) and head-on-trunk (head-only) "impulses" about an Earth-vertical axis. The head was initially oriented at one of five pitch angles (30 degrees nose down, 15 degrees nose down, 0 degrees, 15 degrees nose up, 30 degrees nose up). The fixation target was always aligned with the nasooccipital axis. Whole-body impulses were passive, unpredictable, manual, rotations with peak-amplitude of approximately 20 degrees , peak-velocity of approximately 80 degrees /s, and peak-acceleration of approximately 1000 degrees /s2. Head-only impulses were also passive, unpredictable, manual, rotations with peak-amplitude of approximately 20 degrees , peak-velocity of approximately 150 degrees /s, and peak-acceleration of approximately 3000 degrees /s2. During whole-body impulses, the axis of eye rotation tilted in the same direction, and by an amount proportional (0.51 +/- 0.09), to the starting pitch head orientation (P < 0.05). This proportionality constant decreased slightly to 0.39 +/- 0.08 (P < 0.05) during head-only impulses. Using the head-only impulse data, with the head pitched up, we showed that only 50% of the tilt in the axis of eye rotation could be predicted from vectorial summation of the gains (eye velocity/head velocity) obtained for rotations about the pure yaw and roll head axes. Thus, even when the orientation of Listing's plane and eye position in the orbit are fixed, the axis of eye rotation during the VOR reflects a compromise between the requirements of Listing's law and a perfectly compensatory VOR.

Adult↗

PubMed2006

The effect of binocular eye position and head rotation plane on the human torsional vestibuloocular reflex.

We examined how the gain of the torsional vestibulo-ocular reflex (VOR) (defined as the instantaneous eye velocity divided by inverted head velocity) in normal humans is affected by eye position, target distance, and the plane of head rotation. In six normal subjects we measured three-dimensional (3D) eye and head rotation axes using scleral search coils, and 6D head position using a magnetic angular and linear position measurement device, during low-amplitude (approximately 20 degrees ), high-velocity (approximately 200 degrees/s), high-acceleration (approximately 4000 degrees /s2) rapid head rotations or 'impulses.' Head impulses were imposed manually and delivered in five planes: yaw (horizontal canal plane), pitch, roll, left anterior-right posterior canal plane (LARP), and right anterior-left posterior canal plane (RALP). Subjects were instructed to fix on one of six targets at eye level. Targets were either straight-ahead, 20 degrees left or 20 degrees right from midline, at distance 15 or 124 cm from the subject. Two subjects also looked at more eccentric targets, 30 degrees left or 30 degrees right from midline. We found that the vertical and horizontal VOR gains increased with the proximity of the target to the subject. Previous studies suggest that the torsional VOR gain should decrease with target proximity. We found, however, that the torsional VOR gain did not change for all planes of head rotation and for both target distances. We also found a dynamic misalignment of the vertical positions of the eyes during the torsional VOR, which was greatest during near viewing with symmetric convergence. This dynamic vertical skew during the torsional VOR arises, in part, because when the eyes are converged, the optical axes are not parallel to the naso-occipital axes around which the eyes are rotating. In five of six subjects, the average skew ranged 0.9 degrees -2.9 degrees and was reduced to <0.4 degrees by a 'torsional' quick-phase (around the naso-occipital axis) occurring <110 ms after the onset of the impulse. We propose that the torsional quick-phase mechanism during the torsional VOR could serve at least three functions: (1) resetting the retinal meridians closer to their usual orientation in the head, (2) correcting for the 'skew' deviation created by misalignment between the axes around which the eyes are rotating and the line of sight, and (3) taking the eyes back toward Listing's plane.

Adult↗

PubMed2006

Ceravital reconstruction of canal wall down mastoidectomy: long-term results.

OBJECTIVE: To describe long-term outcomes of external auditory canal wall reconstruction using bioactive glass ceramic (Ceravital) after canal wall down mastoidectomy. DESIGN: Retrospective review of a case series over a 21-year period, with a mean +/- SD follow-up of 13.1 +/- 6.7 years (range, 0.2-20.5 years). SETTING: Private otologic practice. PATIENTS: The study population comprised 20 consecutive patients aged 12 to 60 years, who had previously undergone canal wall down mastoidectomy. INTERVENTION: Reconstruction of the canal wall with bioactive glass ceramic. MAIN OUTCOME MEASURES: Incidence, cause, and timing of reconstruction failure; need for additional surgery; change in hearing; frequency of outpatient visits; and incidence of surgical complications. RESULTS: Prosthetic walls have remained intact in 16 patients followed for more than 5 years. One had remained intact at 3 months after surgery, but the patient was lost to follow-up. Prosthesis removal was required in 3 patients (because of infection, displacement, and cholesteatoma in 1 patient each). The only perioperative complications were otorrhea in 4 patients and a 5-dB sensorineural hearing loss in 1 patient. Of the 16 intact patients with long-term follow-up, 4 required no further surgery, while 11 underwent an average of 2 subsequent middle ear procedures each (range, 1-3), including 4 planned reexplorations. The mean +/- SD air bone gap improved 11 +/- 16 dB as of the most recent audiogram (mean +/- SD, 7.7 +/- 5.8 years after operation). CONCLUSION: Canal wall reconstruction using bioactive glass ceramic is a useful option for patients who desire freedom from the frequent mastoid bowl debridements and activity restrictions that may result from canal wall down mastoidectomy.

Adult↗

PubMed2005

Orientation of human semicircular canals measured by three-dimensional multiplanar CT reconstruction.

Analysis of vestibulo-ocular reflex experiments requires knowledge of the absolute orientations (with respect to skull landmarks) of semicircular canals (SCC). Data relating SCC orientations to accessible skull landmarks in humans are sparse, apart from a classic study of 10 skulls, which concluded that the horizontal and anterior SCC are not mutually orthogonal (111 +/- 7.6 degrees). Multiple studies of isolated labyrinths have shown the inter-SCC angles are close to 90 degrees. We hypothesized that a larger sample would yield mean absolute SCC orientations closer to the mutual orthogonality demonstrated for isolated labyrinths. We measured canal orientations with respect to accessible skull landmarks using 3-D multiplanar reconstructions of computerized tomography scans of the temporal bones of 22 human subjects. Images were acquired with 0.5-mm thickness and reconstructed with in-plane resolution of 234 microm. There was no significant difference between the left and a mirror image of the right (p > 0.57 on multiway ANOVA of orientation vector coefficients), so data were pooled for the 44 labyrinths. The angle between the anterior and posterior SCC was 94.0 +/- 4.0 degrees (mean +/- SD). The angle between the anterior and horizontal SCC was 90.6 +/- 6.2 degrees. The angle between the horizontal and posterior SCC was 90.4 +/- 4.9 degrees. The direction angles between a vector normal to the left horizontal SCC and the positive Reid's stereotaxic X (+nasal), Y (+left), and Z (+superior) axes were 108.7 +/- 7.5 degrees, 92.2 +/- 5.7 degrees, and 19.9 +/- 7.0 degrees, respectively. The angles between a vector normal to the left anterior SCC and the positive Reid's stereotaxic X, Y, and Z axes were 125.9 +/- 5.2 degrees, 38.4 +/- 5.1 degrees, and 100.1 +/- 6.2 degrees, respectively. The angles between a vector normal to the left posterior SCC and the positive Reid's stereotaxic X, Y, and Z axes were 133.6 +/- 5.3 degrees, 131.5 +/- 5.1 degrees, and 105.6 +/- 6.6 degrees, respectively. The mean anterior SCC-contralateral posterior SCC angle was 15.3 +/- 7.2 degrees. The absolute orientations of human SCC are more nearly orthogonal than previously reported.

Adult↗

PubMed2005

The vestibulo-ocular reflex response to head impulses rarely decreases after cochlear implantation.

OBJECTIVE: Measure vestibular function using the head impulse test and assess the change in function due to unilateral cochlear implantation. BACKGROUND: Cochlear implantation entails risks to vestibular function in the implanted ear. However, the nature and extent of this risk is not known. The head impulse test uses physiologically relevant stimuli that allow detection of subtle changes in vestibular function of individual semicircular canals. SUBJECTS: Sixteen adults (age, 28-65 years) were recruited for prospective study from the Listening Center at Johns Hopkins. Eleven of these subjects were tested 4 to 6 weeks after cochlear implantation. METHODS: Three-dimensional eye movement recordings were made using the scleral search coil technique. Stimuli were rapid, passive, transient, head-on-body rotations (acceleration approximately 3000 degrees /s) in the direction excitatory for each of the six semicircular canals. RESULTS: Of the 16 subjects measured preoperatively, 6 (36%) had low (< 0.74) VOR gains in one or both of the horizontal canals and 8 (50%) had low (< 0.64) vestibulo-ocular reflex (VOR) gains in one or more of the vertical canals. These preoperative gain deficits were bilateral in six subjects. The VOR gain did not significantly change after implantation in 10 out of the 11 subjects tested postoperatively. The remaining subject suffered a partial loss of function in the implanted ear and was the only subject who experienced transient vertigo and oscillopsia after implantation. CONCLUSIONS: Preoperative vestibular deficits were common among this group of candidates for cochlear implantation; however, significant loss of vestibular function due to cochlear implantation was uncommon.

Acceleration↗

PubMed2004

Responses of irregularly discharging chinchilla semicircular canal vestibular-nerve afferents during high-frequency head rotations.

Mammalian vestibular-nerve afferents innervating the semicircular canals have been divided into groups according to their discharge regularity, gain at 2-Hz rotational stimulation, and morphology. Low-gain irregular afferents terminate in calyx endings in the central crista, high-gain irregular afferents synapse more peripherally in dimorphic (bouton and calyx) endings, and regular afferents terminate in the peripheral zone as bouton-only and dimorphic endings. The response dynamics of these three groups have been described only up to 4 Hz in previous studies. Reported here are responses of chinchilla semicircular canal vestibular-nerve afferents to rotational stimuli at frequencies up to 16 Hz. The sensitivity of all afferents increased with increasing frequency with the sensitivity of low-gain irregular afferents increasing the most and matching the high-gain irregular afferents at 16 Hz. All afferents increased their phase lead with respect to stimulus velocity at higher frequencies with the highest leads in low-gain irregular afferents and the lowest in regular afferents. No attenuation of sensitivity or shift in phase consistent with the presence of a high-frequency pole over the range tested was noted. Responses were best fit with a torsion-pendulum model combined with a lead operator (tau(HF1)s + 1)(tau(HF2)s + 1). The discharge regularity of individual afferents was correlated to the value of each afferent's lead operator time constants. These findings suggest that low-gain irregular afferents are well suited for encoding the onset of rapid head movements, a property that would be advantageous for initiation of reflexes with short latency such as the vestibulo-ocular reflex.

Animals↗

PubMed2004

Inexpensive system for real-time 3-dimensional video-oculography using a fluorescent marker array.

We describe a novel, inexpensive method for real-time measurement of binocular three-dimensional eye position. The method employs consumer-grade digital video cameras ("webcams") to track an array of three fluorescent non-collinear markers affixed to each eye. The instantaneous position of the marker array relative to a reference position is used to construct a rotation matrix describing the eye rotation. The mathematical computation used to determine the rotation matrix is conceptually simpler and computationally more efficient than methods previously described, allowing generation of binocular three-dimensional eye position in real-time during image acquisition. The fluorescent marker is illuminated using a UV-A light source. The light source and reflective artifacts are filtered out to improve the signal to noise ratio. In addition, we present a method to align the camera with the center of eye rotation. When tested in vitro, the video-oculography (VOG) method had a <2.9% positional error (in each component of 3-D eye position) for eye positions within 20 degrees of center. We directly compared this method of VOG to the search coil technique by measuring three-dimensional eye position simultaneously using search coils and VOG in a chinchilla (C. laniger). The in vivo positional difference between the two methods was <3.1% for each component of 3-D eye position.

Algorithms↗

PubMed2002

Changes in the three-dimensional angular vestibulo-ocular reflex following intratympanic gentamicin for Ménière's disease.

The 3-dimensional angular vestibulo-ocular reflexes (AVOR) elicited by rapid rotary head thrusts were studied in 17 subjects with unilateral Ménière's disease before and 2-10 weeks after treatment with intratympanic gentamicin and in 13 subjects after surgical unilateral vestibular destruction (SUVD). Each head thrust was in the horizontal plane or in either diagonal plane of the vertical semicircular canals, so that each head thrust effectively stimulated only one pair of canals. The AVOR gains (eye velocity/head velocity during the 30 ms before peak head velocity) for the head thrusts exciting each individual canal were averaged and taken as a measure of the function of that canal. Prior to intratympanic gentamicin, gains for head thrusts that excited canals on the affected side were 0.91 +/- 0.20 (horizontal canal, HC), 0.78 +/- 0.20 (anterior canal, AC), and 0.83 +/- 0.10 (posterior canal, PC). The asymmetries between these gain values and those for head thrusts that excited the contralateral canals were <2%. In contrast, caloric asymmetries averaged 40% +/- 32%. Intratympanic gentamicin resulted in decreased gains attributable to each canal on the treated side: 0.40 +/- 0.12 (HC), 0.35 +/- 0.14 (AC), 0.31 +/- 0.14 (PC) (p <0.01). However, the gains attributable to contralateral canals dropped only slightly, resulting in marked asymmetries between gains for excitation of ipsilateral canals versus their contralateral mates: HC: 34% +/- 12%, AC: 24% +/- 25%, and PC: 42% +/- 13%. There was no difference in the AVOR gain for excitation of the ipsilateral HC after gentamicin in patients who received a single intratympanic injection (0.39 +/- 0.11, n = 12) in comparison to those who received 2-3 injections (0.42 +/- 0.15, n = 5, p = 0.7). Gain decreases attributed to the gentamicin-treated HC and AC were not as severe as those observed after SUVD. This finding suggests that intratympanic gentamicin causes a partial vestibular lesion that may involve preservation of spontaneous discharge and/or rotational sensitivity of afferents.

Adult↗

PubMed2002

Comparison of head thrust test with head autorotation test reveals that the vestibulo-ocular reflex is enhanced during voluntary head movements.

OBJECTIVES: To compare 2 clinical tests of vestibular function, the head autorotation test (HART) and the head thrust test (HTT), and to determine why they give disparate results in patients with known unilateral vestibular deficiency (UVD) due to labyrinthectomy. METHODS: We used scleral coils to measure the horizontal (yaw) vestibulo-ocular reflex (VOR) in 5 healthy human subjects and in 11 patients who underwent labyrinthectomy. We used 2 paradigms. Using HART, subjects visually fixated a target during self-generated, swept-frequency, sinusoidal, horizontal head rotations. Using HTT, patients fixated the target during horizontal head thrusts delivered randomly in direction and time. RESULTS: In subjects without UVD, eye movements were almost perfectly compensatory for both paradigms. In subjects with UVD, VOR gain for ipsilesional head thrusts was low for both paradigms, but significantly (P<.001) higher (less abnormal) for HART (0.60 +/- 0.13) than for HTT (0.14 +/- 0.13). Contralesional gain was reduced for both, to 0.64 +/- 0.20 for HART and to 0.57 +/- 0.17 for HTT. Because ipsilesional and contralesional gains were not statistically different for HART (P =.69), comparison of VOR gains for half-cycle responses to the HART stimulus could not reliably identify the side of the known lesion. In contrast, HTT consistently identified the side of the lesion for all subjects with UVD. To investigate whether preprogramming contributes to the boost in VOR as measured by HART, we compared the gain and response delay of eye movements during actively self-generated and passively received head thrusts. For subjects without UVD, response delays were shorter for active (6 +/- 1 milliseconds) than for passive (12 +/- 1 milliseconds) HTT. For ipsilesional rotations of subjects with UVD, active HTT yielded a significantly higher gain (0.44 +/- 0.20) (P<.001) and a shorter delay (15 +/- 6 milliseconds) (P<.001) than did passive HTT (0.14 +/- 0.13 and 37 +/- 15 milliseconds, respectively). Contralesional test results revealed a similar performance boost for active head movements. Data are given as mean +/- SD. CONCLUSION: When comparison of half-cycle gains is used to identify the lesion side, self-generated predictable head movement paradigms, such as HART and active HTT, are less accurate than passive HTT in the characterization of UVD, in part because preprogramming can augment the VOR during voluntary head movements.

Adult↗

PubMedDate not supplied

Initial management of total nasal septectomy defects using resorbable plating.

Temporary reconstruction of the nasal skeleton using resorbable plating offers several advantages in management of carefully selected patients undergoing septectomy. These include protection against early soft tissue contracture, lack of interference with postoperative radiation and surveillance imaging, ease of use, and reversibility. This strategy can yield a good functional result and acceptable cosmesis during radiotherapy and a period of surveillance prior to definitive reconstruction. Herein, we describe the use of resorbable plating material for temporary nasal support in staged reconstruction of complex nasal skeletal defects. We managed near-total defects of the nasal cartilaginous and bony skeleton after cancer resection by staged reconstruction, initially using resorbable plating material to provide temporary structural support for nasal soft tissue during a 1-year period of postresection surveillance. The resorbable reconstruction provided adequate support to maintain nasal patency and external contour for a year or more, allowing early return to normal activities. Partial extrusion occurred in a patient who continued heavy smoking.

Female↗