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At least 109 records · Page 6Linked to original sources
PubMed1992

The influence of head position and head reorientation on the axis of eye rotation and the vestibular time constant during postrotatory nystagmus.

Reorienting the head with respect to gravity during the postrotatory period alters the time course of postrotatory nystagmus (PRN), hastening its decline and thereby reducing the calculated vestibular time constant. One explanation for this phenomenon is that the head reorientation results in a corresponding reorientation of the axis of eye rotation with respect to head coordinates. This possibility was investigated in 10 human subjects whose eye movements were monitored with a three-dimensional magnetic field - search - coil technique using a variety of head reorientation paradigms in a randomized order during PRN following the termination of a 90 degrees/s rotation about earth vertical. Average eye velocities were calculated over two time intervals: from 1 s to 2 s and from 7 s to 8 s after cessation of head rotation. The time constant was estimated as one third of the duration of PRN. For most conditions, a reorientation of the head with respect to gravity 2 s after the rotation had stopped did not significantly alter the direction of the eye velocity vector of PRN with respect to head coordinates. This strongly indicates that, in humans, PRN is mainly stabilized in head coordinates and not in space coordinates, even if the otolith input changes. This finding invalidates the notion that the shortening of PRN due to reorientation of the head could be due to a change of the eye velocity vector towards a direction (torsion), which is not detectable with the eye recording methods (electrooculography) used in earlier studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

[Noninvasive head fixation for external irradiation of tumors of the head-neck area].

PURPOSE: To fully utilize the technical capabilities of radiation diagnostics and planning, a precise and reproducible method of head fixation is a prerequisite. METHOD: We have adapted the Vogele-Bale-Hohner (VBH) head holder (Wellhöfer Dosimetrie, Schwarzenbruck, Germany), originally designed for frameless stereotactic operations, to the requirements of external beam radiotherapy. A precise and reproducible head fixation is attained by an individualized vacuum upper-dental cast which is connected over 2 hydraulic arms to an adjustable head- and rigid base-plate. Radiation field and patient alignment lasers are marked on a relocatable clear PVC localization box. RESULTS: The possibility of craniocaudal adjustment of the head plate on the base plate allows the system to adapt to the actual position of the patient on the radiotherapy couch granting tensionless repositioning. The VBH head holder has proven itself to be a precise yet practicable method of head fixation. Duration of mouthpiece production and daily repositioning is comparable to that of the thermoplastic mask. CONCLUSION: The new head holder is in routine use at our hospital and quite suitable for external beam radiation of patients with tumors of the head and neck.

Equipment Design↗
PubMed2003

Role of routine nonenhanced head computed tomography scan in excluding orbital, maxillary, or zygomatic fractures secondary to blunt head trauma.

The purpose of this paper is to determine the necessity of a dedicated facial bone/orbital computed tomography (CT) scan for fracture surveillance in patients who have suffered blunt head trauma and whose routine nonenhanced head CT scan is negative. It is based on a retrospective review of 115 patients presenting to the Emergency Department at a level I trauma center after blunt head trauma. Included patients underwent both a nonenhanced head CT scan and a dedicated facial bone or orbit CT. Standard nonenhanced head CT protocol was followed for each patient as per department protocol. A positive head CT scan is defined to include either an air-fluid level within the paranasal sinuses or fracture of the maxillary, orbital, or zygomatic osseous structures. A negative scan demonstrates none of these findings. Intracranial/parenchymal pathology was not evaluated in this study. Sixty-five of the 115 patients had a negative head CT scan as defined above. Of these 65 patients, none subsequently had a positive facial bone or orbit CT scan. The sensitivity and negative predictive values of a negative routine nonenhanced head CT scan for fracture surveillance are both 100%. In the setting of blunt trauma, a negative nonenhanced head CT scan precludes the need for a dedicated facial bone or orbital CT scan in the evaluation for orbital, maxillary, or zygomatic fractures. This saves the patient unnecessary radiation exposure, health care costs, and time spent in the emergency radiology department.

Adult↗
PubMed2001

The Canadian CT Head Rule Study for patients with minor head injury: rationale, objectives, and methodology for phase I (derivation).

Head injuries are among the most common types of trauma seen in North American emergency departments, with an estimated 1 million cases seen annually. "Minor" head injury (sometimes known as "mild") is defined by a history of loss of consciousness, amnesia, or disorientation in a patient who is conscious and talking, that is, with a Glasgow Coma Scale score of 13 to 15. Although most patients with minor head injury can be discharged without sequelae after a period of observation, in a small proportion, their neurologic condition deteriorates and requires neurosurgical intervention for intracranial hematoma. The objective of the Canadian CT Head Rule Study is to develop an accurate and reliable decision rule for the use of computed tomography (CT) in patients with minor head injury. Such a decision rule would allow physicians to be more selective in their use of CT without compromising care of patients with minor head injury. This paper describes in detail the rationale, objectives, and methodology for Phase I of the study in which the decision rule was derived. [Stiell IG, Lesiuk H, Wells GA, McKnight RD, Brison R, Clement C, Eisenhauer MA, Greenberg GH, MacPhail I, Reardon M, Worthington J, Verbeek R, Rowe B, Cass D, Dreyer J, Holroyd B, Morrison L, Schull M, Laupacis A, for the Canadian CT Head and C-Spine Study Group. The Canadian CT Head Rule Study for patients with minor head injury: rationale, objectives, and methodology for phase I (derivation). Ann Emerg Med. August 2001;38:160-169.]

Adolescent↗
PubMed1994

Subcortical contributions to head movements in macaques. II. Connections of a medial pontomedullary head-movement region.

1. In the companion article, a variety of head movements were elicited by stimulation in, and adjacent to, the gigantocellular reticular nucleus (Cowie and Robinson 1994). We refer to this area, caudal to the abducens nucleus, as the gigantocellular head movement region. In the present paper, the anatomical connections of this region, as determined by injections of wheat-germ agglutinin conjugated horseradish peroxidase (WGA-HRP), are reported. The majority of efferent and afferent connections were with areas related to head movements. 2. Efferent fibers from the region projected via two paths to the caudal medulla and upper cervical spinal cord. Labeled fibers descended in the anterolateral funiculus of the ipsilateral spinal cord to terminate in lateral parts of the ventral horn. A second pathway descended bilaterally in the medial longitudinal fasciculus to the anterior funiculi and medial portions of the ventral gray. These efferents paralleled the head-movement topography demonstrated physiologically. Other projections included efferents to the interstitial nucleus of Cajal, caudal field H of Forel, paramedian pontine reticular formation, and caudal vestibular nuclei. Other efferent fibers projected to the trigeminal, facial, and hypoglossal nuclei, as well as to the parvocellular reticular field, which contains interneurons for these motor groups. However, no efferent or afferent labeling involved the ocular motor nuclei. 3. Afferents to the gigantocellular head movement region arose mainly from head-movement areas. In all animals, labeled cells were found in the intermediate and deep layers of the caudal superior colliculus. Labeled neurons also were found in the caudal field H of Forel, interstitial nucleus of Cajal, pontine medial tegmentum including the pontine paramedian reticular formation, nucleus subcoeruleus, and vestibular nuclear complex. Caudally, filled cells were located in the parvocellular, magnocellular, dorsal, and ventral reticular nuclei, the supraspinal nucleus, and the upper cervical ventral horn. 4. In one animal, the ipsilateral frontal cortex contained retrogradely labeled neurons. These cells were found in layer V of cortical areas 4 and 6. Other afferent cells were found consistently in the periventricular and periaqueductal gray matter. 5. A control injection into the caudal vestibular nuclear complex showed projections to the gigantocellular reticular formation and labeled cells in the vestibular and parvocellular reticular nuclei. These observations show that the connections of the gigantocellular region are not typical of all head movement sites. 6. These data indicate that the gigantocellular head-movement region has the requisite efferent and afferent connections to function in the subcortical control of head, but not eye, movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Analysis of primate IBN spike trains using system identification techniques. III. Relationship To motor error during head-fixed saccades and head-free gaze shifts.

The classic model of saccade generation assumes that the burst generator is driven by a motor-error signal, the difference between the actual eye position and the final "desired" eye position in the orbit. Here we evaluate objectively, using system identification techniques, the dynamic relationship between motor-error signals and primate inhibitory burst neuron (IBN) discharges (upstream analysis). The IBNs presented here are the same neurons whose downstream relationships were characterized during head-fixed saccades and head-free gaze shifts in our companion papers. In our analysis of head-fixed saccades we determined how well IBN discharges encode eye motor error (epsilone) compared with downstream saccadic eye movement dynamics and whether long-lead IBN (LLIBN) discharges encode epsilone better than short-lead IBNs (SLIBNs), given that it is commonly assumed that short-lead burst neurons (BNs) are closer than long-lead BNs to the motor output and thus further from the epsilone signal. In the epsilone-based models tested, IBN firing frequency B(t) was represented by one of the following: 1) model 1u, a nonlinear function of epsilone; 2) model 2u, a linear function of epsilone [B(t) = rk + a1epsilone(t)] where the bias term rk was estimated separately for each saccade; 3) model 3u, a version of model 2u wherein the bias term was a function of saccade amplitude; or 4) model 4u, a linear function of epsilone with an added pole term (the derivative of firing rate). Models based on epsilone consistently produced worse predictions of IBN activity than models of comparable complexity based on eye movement dynamics (e.g., eye velocity). Hence, the simple two parameter downstream model 2d [B(t) = r + b1(t)] was much better than any upstream (epsilone-based) model with a comparable number of parameters. The link between B(t) and epsilone is due primarily to the correlation between the declining phases of B(t) and epsilone; motor-error models did not predict well the rising phase of the discharge. We could improve substantially the performance of upstream models by adding an e term. Because e = -, this process was equivalent to incorporating terms into upstream models thereby erasing the distinction between upstream and downstream analyses. Adding an e term to the upstream models made them as good as downstream ones in predicting B(t). However, the epsilone term now became redundant because its removal did not affect model accuracy. Thus, when is available as a parameter, epsilone becomes irrelevant. In the head-free monkey the ability of upstream models to predict IBN firing during head-free gaze shifts when gaze, eye, or head motor-error signals were model inputs was poor and similar to the upstream analysis of the head-fixed condition. We conclude that during saccades (head-fixed) or gaze shifts (head-free) the activity of both SLIBNs and LLIBNs is more closely linked to downstream events (i.e., the dynamics of ongoing movements) than to the coincident upstream motor-error signal. Furthermore, SLIBNs and LLIBNs do not differ in their characteristics; the latter are not, as is usually hypothesized, closer to a motor-error signal than the former.

Animals↗
PubMed1992

The transmission of translational seat vibration to the head: the effect of measurement position at the head.

Head motion has been measured in six axes on twelve subjects exposed to vertical seat vibration in the frequency range 0.5-25 Hz. The subjects sat on a rigid flat seat in two postures: 'back-off' (no backrest) and 'back-on' (subject's back in contact with the seat backrest). Translational acceleration has been calculated for various locations on the head and transmissibilities between vertical seat vibration and translational head motion determined for each location and all axes. The translational motion of the head was most affected by pitch motion of the head. This caused variations in fore-and-aft motion with position along the vertical axis of the head and variations in vertical motion with position along the fore-and-aft axis of the head. These variations are illustrated for each subject in both postures. The individual data allow the identification of various modes of vibration and show that seat-to-head transmissibility is greatly affected by pitch modes of the head and neck. The magnitude of motion occurring in some modes is dependent on body posture.

Adolescent↗
PubMed1988

[Hygienic aspects of pig's head meat. 2. Mechanical separation of pigs' heads].

Deboning pigs' heads is a labour-intensive process. According to information supplied by the industry, mechanical separation of pigs' heads offers good prospects. Data on the hygienic implications of this process were not known. These were studied more closely in an experimental design. The bacteriological and sensory qualities as well as the chemical and histological composition of the product were compared with those of manually obtained pig's head meat. In addition, the yield of the process of separation was determined. Three groups of heads were mechanically separated, viz. untreated heads and heads which had previously been dipped in water having an initial temperature of 100 degrees C for one minute and five minutes respectively. These studies served to verify the fact that mechanical separation of pigs' heads is technically possible. Previous dipping of the heads in water at a temperature of 100 degrees C produced a considerable improvement of the yield in meat, which was due to setting of the rind. The chemical composition of the product was roughly identical with that of manually obtained head meat. However, tissue composition and structure of the tissues differed markedly. An important drawback is the higher count of Enterobacteriaceae in the product. These bacteria are probably released on compression from sites which are difficult of access such as the nose, the pharyngeal cavity and the alveoli. In addition, they may be possibly protected by a covering layer of mucus. Therefore, mechanical separation is not regarded as acceptable from the point of view of hygiene.

Animals↗
PubMed1986

Adapted head- and eye-movement responses to added-head inertia.

Adaptation to inertia added to the head was studied in man by mounting masses on a rigidly attached helmet. Two- to ten-fold increases of inertia were thus produced, while an overhead suspension compensated for the weights. Eye and head positions and corresponding velocities were simultaneously recorded during eye-head tracking of a target stepping at 0.2 Hz in the horizontal direction. Without added inertia, fast gaze movements are type III, the accelerated head movement coming early and the resulting VOR truncating the simultaneous eye movement saccade in both amplitude and velocity. Head oscillations are fast and overcompensated by higher gain VOR. With added inertia, the adapted head movement is slowed and delayed. This permits the eye movement saccade to be completed before head movement begins and to escape truncation; the saccade is normal or slightly increased in amplitude. Head oscillations are slow and compensated by normal gain VOR. Either truncation of the saccade or overcompensation of the VOR leads to eye movement and gaze position error that is corrected for by secondary corrective saccades. These same two errors in gaze coordination could explain the cause of the perceived oscillopsia. Oscillopsia, or continual displacement or instability of the visual worlds, is a symptom of breakdown of space constancy, and was prominent and consistent in perceptual reports of our subjects. Adaptation resulting from adding inertia to the head occurred much faster than that induced by adding prisms or lenses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1985

Inter-individual variation in blood supply of the optic nerve head. Its importance in various ischemic disorders of the optic nerve head, and glaucoma, low-tension glaucoma and allied disorders.

There is no one standard pattern of the blood supply of the optic nerve head in all human eyes. There is a marked inter-individual variation in the blood supply of the optic nerve head, and the various factors which produce this include variations in (I) the anatomical pattern of blood supply, (II) the pattern of posterior ciliary artery (PCA) circulation (the main source of blood supply to the optic nerve head), and (III) the blood flow. The variations in the pattern of PCA circulation include the variations in (a) number of PCAs supplying an eye, (b) area of supply to the optic nerve head by each PCA, (c) location of the watershed zones between the various PCAs in relation to the optic nerve head, and (d) blood pressure in various PCAs as well as short PCAs. The variations in the blood flow in the optic nerve head can be produced by changes in (i) the intraocular pressure, (ii) mean blood pressure in the capillaries of the optic nerve head and (iii) peripheral vascular resistance. These variations are discussed in detail. A lack of appreciation of these complexities of the blood supply of the optic nerve head in health and disease is responsible for many of the current problems in the understanding of the role of vascular disturbances in anterior ischemic optic neuropathy, glaucoma, low-tension glaucoma and various ischemic disorders of the optic nerve head.

Adolescent↗
PubMed1998

[Duodenum-preserving resection of the pancreas head in treatment of benign tumors of the pancreas head].

Benign tumors of the pancreatic head are normally treated by a partial duodenopancreatectomy. This operation has been developed for the treatment of malignant alterations in the pancreatic head and includes resection of the gastric bowel, duodenum and common bile duct. The aim of this study was to evaluate whether the less radical duodenum-preserving pancreatic head resection is a suitable surgical procedure in the treatment of benign pancreatic head tumors. From May 1982 to December 1996, seven patients underwent surgical treatment for benign pancreatic head tumors. Two patients suffered from gastrinoma of the pancreatic head, four exhibited a serous or mucinous cystadenoma, and one patient suffered from an intraductal papillary-mucinous tumor in this region. All patients were treated by duodenum-preserving pancreatic head resection. The operation was easily performed with little blood loss and a low rate of complications. None of the patients had to be reoperated upon due to postoperative surgical complications. After a follow-up period of a median 3 years, six of seven patients were had no recurrence of the disease and were symptom-free. One patient who had initially been operated on for gastrinoma still exhibited high gastrin values postoperatively. The endocrine and exocrine pancreatic function was not impaired in the early and late postoperative phase as compared to the preoperative assessment. From our results, it is concluded that duodenum-preserving pancreatic head resection is an adequately radical, yet organ-preserving procedure for the treatment of benign tumors of the pancreatic head without compromising endocrine and exocrine function.

Cystadenoma, Mucinous↗
PubMedDate not supplied

Metatarsal head resection in the rheumatoid foot: 5-year follow-up with and without resection of the first metatarsal head.

Twenty-nine patients (45 feet) who underwent metatarsal head resections for rheumatoid forefoot deformities were reviewed retrospectively at a mean follow-up of 6.57 years (range, 5-9.3 years). Resections were confined to the lesser metatarsal heads in 16 feet because of a lack of involvement in the first metatarsal head. In the remaining 29 feet, all metatarsal heads were resected. A questionnaire was provided to assess subjective outcomes. Thirty-three feet (73.3%) had no pain or only mild pain, 5 feet (11%) had moderate pain, and 7 (15.5%) had severe pain. Among the 29 feet with panmetatarsal head resections, 5 (17%) required revision of metatarsal stumps at an average follow-up of 55.2 months (range, 17-84 months; standard deviation, 26.88). Among the 16 feet with only lesser metatarsal head resections, 7 (43.75%) required subsequent first metatarsal head resections at an average follow-up period of 33.14 months (range, 13-56 months; standard deviation, 16.54). In conclusion, metatarsal head resection is a simple procedure that gives long-term pain relief in over two thirds of the patients who have rheumatoid forefoot deformities. A high rate of recurrence of pain and subsequent resection of first metatarsal head is noted if it is not resected primarily. We recommend a low threshold for the inclusion of some form of primary reconstruction of the first metatarsophalangeal joint when resection arthroplasty is performed on the lesser toes.

Adult↗
PubMed2001

Phosphorylation-dependent regulation is absent in a nonmuscle heavy meromyosin construct with one complete head and one head lacking the motor domain.

To understand the domain requirements of phosphorylation-dependent regulation, we prepared three recombinant constructs of nonmuscle heavy meromyosin IIB containing 1) two complete heads, 2) one complete head and one head lacking the motor domain, and 3) one complete head and one head lacking both motor and regulatory domains. Steady-state ATPase measurements showed that phosphorylation did not alter the affinity for actin by more than a factor of 2 for any construct. Phosphorylation increased V(max) by a factor of 10 for construct 1 and 1.5-3 for construct 2 but had no effect for construct 3. Single turnover measurements, a better measure of slow rates inherent to unphosphorylated regulated myosins, showed that the single-headed construct 2, like construct 3 retains less than 1% of the regulatory properties of the double-headed construct 1 (300-fold activation). Therefore, a complete head cannot be down-regulated by a regulatory domain (without the motor domain) on the partner head. Two motor domains are required for regulation. This result is predicted by a structural model (Wendt, T., Taylor, D., Messier, T., Trybus, K. M., and Taylor, K. A. (1999) J. Cell Biol. 147, 1385-1390) showing interaction between the motor domains for unphosphorylated smooth muscle myosin, if motor-motor interaction is the basis for down-regulation.

Animals↗
PubMed1976

Bacteriophage T4 head morphogenesis. VII. Terminal stages of head maturation.

Several aspects of the terminal stages of T4 head maturation were investigated using ts and am mutants blocked at single steps of the assembly pathway. We had previously found that cells infected with mutants of gene 13, e.g., tsN38 and amE609, accumulated both stable (10 to 20%)- and fragile (80%)-filled head precursors (Hamilton and Luftig, 1972). Here we showed the following for such gene 13-defective, mutant-infected cells. (i) Using thin-section analysis the pool of phage precursor structures observed under nonpermissive conditions was one-third of that observed when the cells were cultured under permissive conditions. (ii) In order for complete conversion of the precursors into viable phage to occur, there were apparent requirements of metabolic energy, protein, and DNA synthesis. (iii) The intracellular DNA pool under nonpermissive conditions exhibited a 50% distribution between 63S (mature size) and 200 S (concatenate size) DNA, with the latter DNA serving as a precursor pool. Further, this DNA pool when spread onto a protein monolayer exhibited a dispersed array of DNA, strands around a core, which was less dense than that found for the greater than 1,000S DNA concatenate isolated from gene 49-defective infected cells. (iv) When precuations were taken to stabilize the head precursors, such as lysis of the cells into glutaraldehyde, there was a 30% increase in the yield of 1,200S filled heads. Correlating these results and previous results concerning gene 49-defective unfilled heads, we propose that there are several forms of gene 13 fragile head precursors which serve as intermediates between gene 49 unfilled heads and gene 13 stable filled heads. We cannot, however, rule out the possibility that all gene 13-defective heads represent a single class of unstable particles, which decay slowly. In either case, we have shown that gene 13-defective particles are unstable to some degree inside the cell and are highly unstable outside the cell; yet all particles can still be efficiently converted to phage in vivo.

Chloramphenicol↗