Degrees-7 Degrees Research Articles

MACULAR TELANGIECTASIA

By analyzing the patterns of macular pigment (MP) in type 2 idiopathic telangiectasia eyes, different stages in the changes reflecting the extent of disease can be observed. The purpose of this study was to determine whether the amount and the pattern of MP can be influenced by supplementation. Eleven patients with type 2 idiopathic telangiectasia received 12 mg lutein and 0.6 mg zeaxanthin (Ocuvite Lutein AMD) daily for 9 months. For a period of 12 months, MP concentration was determined every 3 months by autofluorescence (2 excitation wavelengths: 488 and 514 nm). When central accumulation of MP was similar to that in healthy subjects (with segment of reduced MP in the temporal fovea: MP Class I), supplementation enriched the MP at 0.5 degrees, 2 degrees, and 5 degrees to 6 degrees. In MP Class II (reduced concentration of MP centrally), accumulation could be detected at 2 degrees and 5 degrees to 6 degrees but not centrally. In MP Class III (oval-shaped effacement of MP centrally, surrounding oval-shaped ring of MP at 5 degrees-7 degrees eccentricity), supplementation promoted MP accumulation only at 5 degrees to 6 degrees. After oral supplementation with lutein/zeaxanthin, an increase in the MP was detected only in areas where the MP was present at baseline. Supplementation did not produce an increase in the area where the MP was absent. Degenerative processes causing an impairment in transport and storage of lutein and zeaxanthin may play a leading role in the pathogenesis of type 2 idiopathic telangiectasia.

Correction for Resolution Nonuniformities Caused by Anode Angulation in Computed Tomography

Most X-ray tubes comprise a rotating anode that is bombarded with electrons to produce X-rays. A substantial amount of heat is generated, and to increase the area of the anode exposed to the electrons, without increasing the apparent size of the focal spot, the focal track of the anode is generally beveled with a very shallow angle (typically 5 degrees-7 degrees in a computed tomography (CT) tube). Due to the line focus principle, this allows a fairly large area of the focal track to be exposed to electrons while retaining a fairly small effective projected focal spot. One side effect of anode angulation is that the focal spot appears different from different positions in the detector array; the effective focal spot size at a constant distance from the tube will be larger for a peripheral detector channel than for a central one. These differences in the effective size of the focal spot across the field-of-view lead to worse resolution in the periphery than in the center of reconstructed images. In this work we describe a method for achieving more uniform resolution in fanbeam CT images by correcting for these focal spot angulation effects. We do so by modeling the effects as a series of local blurrings in the space of transmitted CT intensities and determining the effective coefficients of the corresponding discrete convolutions. The effect of these blurrings can then be compensated for in the sinogram domain through the use of a penalized-likelihood sinogram restoration model we have recently developed.

Heat Generated by Knee Prostheses

Temperature sensors were placed in 50 knees in 25 patients who had one or both joints replaced. Temperature recordings were made before walking, after walking, and after cycling. The heat generated in healthy, arthritic, and replaced knees was measured. The knee replacements were done using eight different prostheses. A rotating hinge knee prosthesis generated a temperature increase of 7 degrees C in 20 minutes and 9 degrees C in 40 minutes. An unconstrained ceramic femoral prosthesis articulating with a polyethylene tibial prosthesis generated a temperature increase of 4 degrees C compared with a healthy resting knee. The other designs using a cobalt-chrome alloy and high-density polyethylene had temperature increases of 5 degrees-7 degrees C with exercise. Frictional heat generated in a prosthetic knee is not immediately dissipated and may result in wear, creep, and other degenerative processes in the high-density polyethylene. Extended periods of elevated temperature in joints may inhibit cell growth and perhaps contribute to adverse performance via bone resorption or component loosening. Prosthetic knees generate more heat with activity than healthy or arthritic knees. More-constrained knee prostheses generate more heat than less-constrained prostheses. A knee with a ceramic femoral component generates less heat than a knee with the same design using a cobalt-chromium alloy.

Extraocular muscle proprioception and eye position.

In the lamb, acute unilateral section of the ophthalmic branch induced in the ipsilateral eye occasional oscillations of the resting position and misalignment of the horizontal vestibulo-ocular reflex (HVOR) with respect to the stimulus. Additional electrolytic lesion of the cells innervating the proprioceptors of the medial rectus muscle, or of the lateral rectus muscle in the contralateral semilunar ganglion, provoked a 4 degrees-7 degrees consensual eye deviation towards and away from the lesioned side, respectively. The optokinetic beating field was similarly deviated. Under these experimental conditions, HVOR showed enhanced gain and marked misalignment in both eyes. Therefore, the selective suppression of muscular proprioceptive input deviated both eyes towards the direction opposite to the muscle whose gangliar proprioceptive representation has been destroyed.

Blockade of noradrenaline‐induced constrictions by yohimbine and prazosin differs between consecutive segments of cutaneous arteries in guinea‐pig ears

1. The study has examined the receptors mediating constriction produced by brief local application of noradrenaline (NA) to cutaneous arteries and arterioles in the ear vasculature of anaesthetized guinea-pigs. The innervation of the corresponding vascular segments has been examined immunohistochemically at the conclusion of the pharmacological experiments. 2. Small arteries of branch order 4 (4 degrees, 40-110 microns internal diameter) were more sensitive to the vasoconstrictor action of NA than were more proximal arteries of branch order 3 (3 degrees, 60-150 microns internal diameter), or more distal arteries and arterioles of branch orders 5 to 7 (5 degrees-7 degrees, 18-85 microns internal diameter). This higher sensitivity of 4 degrees arteries was maintained after blockade of neuronal uptake with desipramine (1 microM), and after blockade of beta-adrenoceptors with propranolol (1 microM). 3. NA-induced vasoconstrictions of distal arterioles (5 degrees-7 degrees) were abolished or greatly reduced by yohimbine (1 microM). The blockade by yohimbine decreased progressively with increasing vessel diameter of proximal arteries, while the blockade by prazosin (1 microM) increased progressively in arteries > 40 microns diameter. 4. In 3 degrees and 4 degrees arteries, a substantial component (approximately 50%) of NA-induced vasoconstrictions remained after combined treatment with yohimbine and prazosin, in the presence or absence of desipramine. These constrictions were not further reduced by benextramine (1-10 microM), but were abolished by dihydroergotamine (1-10 microM). Constrictions induced by ATP (0.1-1 mM) were not affected by dihydroergotamine. 5. 5-Hydroxytryptamine (3-100 microM) had a variable effect on 3 degree and 4 degree arteries including: concentration dependent constrictions (n = 3); small constrictions at some concentrations, and dilatations or no change in diameter at other concentrations (n = 6); concentration-dependent dilatations only (n = 3). The 5-HT2 receptor antagonist, ketanserin (0.1-0.3 micro M), did not affect NA-induced constrictions.6. In 16 arterial segments ranging from 3 degree arteries to 60 arterioles, there was a significant correlation between the presence of neuropeptide Y-immunoreactive (NPY-IR) sympathetic axons and the degree of blockade of NA-induced constrictions by yohimbine, prazosin and dihydroergotamine.7. These results demonstrate marked differences in the postsynaptic adrenoceptors mediating vasoconstriction to a bolus of NA applied briefly to the adventitial surface of different segments of the cutaneous vasculature of the guinea-pig ear. Furthermore, the presence or absence of adrenoceptors sensitive to blockade by yohimbine or prazosin is related to the proportion of sympathetic axons innervating each vascular segment which contain NPY-IR.

PROFOUND HYPOTHERMIA (<10°C) COMPARED TO DEEP HYPOTHERMIA (15°C) IMPROVES NEUROLOGIC OUTCOME IN DOGS AFTER 2 HOURS CIRCULATORY ARREST INDUCED TO ENABLE RESUSCITATIVE SURGERY

Deaths from uncontrollable hemorrhage might be prevented by arresting the circulation under protective hypothermia to allow resuscitative surgery to repair these injuries in a bloodless field. We have shown previously that in hemorrhagic shock, circulatory arrest of 60 minutes under deep hypothermia (tympanic membrane temperature, Ttm = 15 degrees C) was the maximum duration of arrest that allowed normal brain recovery. We hypothesize that profound cerebral hypothermia (Ttm less than 10 degrees C) could extend the duration of safe circulatory arrest. In pilot experiments, we found that the cardiopulmonary system did not tolerate arrest at a core (esophageal) temperature (Tes) of less than 10 degrees C. Twenty-two dogs underwent 30-minute hemorrhagic shock (mean arterial pressure 40 mm Hg), rapid cooling by cardiopulmonary bypass (CPB), blood washout to a hematocrit of less than 10%, and circulatory arrest of 2 hours. In deep hypothermia group 1 (n = 10), Ttm was maintained at 15 degrees C during arrest. In profound hypothermia group 2 (n = 12), during cooling with CPB, the head was immersed in ice water, which decreased Ttm to 4 degrees-7 degrees C. The Tes was 10 degrees C in all dogs during arrest. Reperfusion and rewarming were by CPB for 2 hours. Controlled ventilation was to 24 hours, intensive care to 72 hours. In the 20 dogs that followed protocol, best neurologic deficit scores (0% = normal, 100% = brain death) at 24-72 hours were 23% +/- 19% in group 1 and 12% +/- 8% in group 2 (p = 0.15). Overall performance categories and histologic damage scores were significantly better in group 2 (p = 0.04 and p less than 0.001, respectively). We conclude that profound cerebral hypothermia with CPB plus ice water immersion of the head can extend the brain's tolerance of therapeutic circulatory arrest beyond that achieved with deep hypothermia.

Orientation illusions induced by briefly flashed plaids.

Orientation illusions which occur when a vertical grating is surrounded by a plaid can be induced either by one of the plaid's orthogonal component gratings or by a virtual axis of symmetry of the plaid, whichever is nearest vertical. In six experiments in which such illusion displays were flashed for durations between 15 and 405 ms, it was found that when these two-dimensional illusions are induced by a component grating (direct effects) the illusions increase monotonically as duration decreases, from 1 degree-2 degrees to about 6 degrees-7 degrees, over this range. Effects induced by axes of symmetry (indirect effects), in contrast, begin to occur only at longer durations: for short exposures, illusions are directionally opposite and large, similar to direct effects. These results suggest that only plaid-component-selective mechanisms operate at the shortest exposure durations and that additional time is required to extract more global higher-order pattern structure. The data are discussed in relation to sustained and transient mechanisms and also with respect to recent reports of more global processing mechanisms in extrastriate cortex and related data on one-dimensional tilt illusions.

An Analysis of Ocular Counter-rolling Measured with Search Coils

Ocular counter-rolling (OCR) was studied by using a scleral search coil magnetic system in normal subjects and in pathological cases. Normal ocular counter-rolling was 2.7 degrees-7 degrees when the head was tilted 10 to 30 degrees. In most cases of benign paroxysmal positional vertigo, the OCR to the ipsilateral side was reduced, while that to the contralateral side was normal or only slightly reduced. Soon after unilateral labyrinthectomy, the OCR to the ipsilateral side was reduced or was 0, whereas OCR to the contralateral side was normal or slightly reduced. Some 3-5 years after the operation, however, the OCR seemed to depend on the compensation achieved. In cases of acoustic neurinoma, OCR to both sides was reduced, that to the ipsilateral side being more strongly impaired than the OCR to the contralateral side.