Vertebral osteomyelitis: an analysis of 38 surgically treated cases

The purpose of the study was to evaluate the characteristics of patients with vertebral osteomyelitis who were treated by anterior debridement and interbody fusion. Thirty-eight patients with vertebral osteomyelitis, who were treated between 1980 and 1993, were analyzed in terms of age at the occurrence of disease, duration of disease, type of onset symptoms, radiological type of vertebral destruction, species of pathogen, and surgical result. Thirty-one out of 38 patients (82%) were more than 40 years of age. The patients with severe vertebral destruction were significantly older than those with mild vertebral destruction. Vertebral destruction in the thoracic spine was significantly more severe than that in the lumbar spine. Staphylococcus aureus was identified in only six patients (32% of organism-determined cases). In the present patients who required anterior debridement and bone grafting for this disease, the prognosis was quite good after anterior interbody fusion in conjunction with antibiotics therapy.

Capnometry as a tool to unmask silent pulmonary embolism

Because pulmonary embolism is often silent, simple clinical procedures are desirable to identify patients with a low to intermediate probability of pulmonary embolism. Among 19,467 patients managed under general anesthesia, we had one bile tract surgery case and three neurosurgical cases whose silent pulmonary embolism was initially suggested by an increase in the arterial to end-tidal CO2 gradient (from 17 to 27 mmHg) after general anesthesia was induced or their trachea was intubated. During the preoperative assessment, the patients presented no clinical manifestations suggestive of pulmonary embolism. Our initial diagnosis was confirmed by scintigraphy and/or angiography done immediately after the operations. Because capnometry has been shown to be applicable to non-intubated, spontaneously breathing patients, we suggest that measuring the gradient may serve as an additional method for unmasking silent pulmonary embolism in patients at risk or with disturbed consciousness, whether they are scheduled for operations or not.

The addition of phenylephrine contributes to the development of transient neurologic symptoms after spinal anesthesia with 0.5% tetracaine

BACKGROUND

Recent reports indicate that transient neurologic symptoms commonly occur after single-injection spinal anesthesia with lidocaine. Information regarding tetracaine has been limited to a single case report. In addition, little is known about the cause of these symptoms or the cofactors that affect their occurrence. The present study sought to determine whether the presence of phenylephrine or the concentration of glucose in the anesthetic solution affects the incidence of transient neurologic symptoms after spinal anesthesia with 0.5% tetracaine.

METHODS

One-hundred sixty patients classified as American Society of Anesthesiologists physical status I or II who were scheduled for elective surgery on a lower limb or perineum were sequentially assigned to one of four equal groups to receive intrathecal 0.5% tetracaine in 7.5% or 0.75% glucose, with or without 0.125% phenylephrine. Patients were evaluated on postoperative day one for the presence of pain, dysesthesia, or both in the legs or buttocks by an investigator unaware of the drug given.

RESULTS

Symptoms were present in 10 patients (12.5%) receiving a spinal anesthetic containing phenylephrine, but in only one patient (1.3%) receiving spinal anesthesia without phenylephrine. There was no significant difference in the incidence of symptoms between groups receiving 7.5% glucose and those receiving 0.75% glucose (8.8% and 5% of patients, respectively).

CONCLUSIONS

These results suggest that adding phenylephrine to tetracaine for spinal anesthesia increases the potential for transient neurologic symptoms, but that the concentration of glucose does not affect their occurrence.

Juxtalumenal location of plaque necrosis and neoformation in symptomatic carotid stenosis

PURPOSE

The structural features that underlie carotid plaque disruption and symptoms are largely unknown. We have previously shown that the chemical composition and structural complexity of critical carotid stenoses are related to plaque size regardless of symptoms. To further determine whether the spatial distribution of individual plaque components in relation to the lumen corresponds to symptomatic outcome, we evaluated 99 carotid endarterectomy plaques.

METHODS

Indications for operation were symptomatic disease in 59 instances (including hemispheric transient ischemic attack in 29, stroke in 19, and amaurosis fugax in 11) and angiographic asymptomatic stenosis > 75% in 40. Plaques removed after remote symptoms beyond 6 months were excluded. Histologic sections from the most stenotic region of the plaque were examined using computer-assisted morphometric analysis. The percent area of plaque cross-section occupied by necrotic lipid core with or without associated plaque hematoma, by calcification, as well as the distance from the lumen or fibrous cap of each of these features, were determined. The presence of foam cells, macrophages, and inflammatory cell collections within, on, or just beneath the fibrous cap was taken as an additional indication of plaque neoformation.

RESULTS

The mean percent angiographic stenosis was 82% +/- 11% and 79% +/- 13% for the asymptomatic and symptomatic groups, respectively (p > 0.05). The necrotic core was twice as close to the lumen in symptomatic plaques when compared with asymptomatic plaques (0.27 +/- 0.3 mm vs 0.5 +/- 0.5 mm; p < 0.01). The percent area of necrotic core or calcification was similar for both groups (22% vs 26% and 7% vs 6%, respectively). There was no significant relationship to symptom production of either the distance of calcification from the lumen or of the percent area occupied by the lipid necrotic core or calcification. The number of macrophages infiltrating the region of the fibrous cap was three times greater in the symptomatic plaques compared with the asymptomatic plaques (1114 +/- 1104 vs 385 +/- 622, respectively, p < 0.009). Regions of fibrous cap disruption or ulceration were more commonly observed in the symptomatic plaques than in the asymptomatic plaques (32% vs 20%). None of the demographic or clinical atherosclerosis risk factors distinguished between symptomatic and asymptomatic plaques.

CONCLUSIONS

These findings indicate that proximity of plaque necrotic core to the lumen and cellular indicators of plaque neoformation or inflammatory reaction about the fibrous cap are associated with clinical ischemic events. The morphologic complexity of carotid stenoses does not appear to determine symptomatic outcome but rather the topography of individual plaque components in relation to the fibrous cap and the lumen. Imaging techniques that precisely resolve the position of the necrotic core and evidence of inflammatory reactions within carotid plaques should help identify high-risk stenoses before disruption and symptomatic carotid disease.

[Safe levels of hemoglobin concentration in autologous blood transfusion]

It has been generally accepted that an adequate oxygen-carrying capacity can be achieved with a hemoglobin concentration of 7 g/dl, as far as the patient's intravascular volume is sufficient to allow tissue perfusion. To guarantee patient's safety in the operating theater, patient's oxygenation, ventilation, circulation and temperature, which enable oxygen utilization in tissues, should be monitored vigilantly and ensured strictly. This is also true when taking care of anemic patients outside the operating theater, because failure of these functions in anemic patients leads directly to tissue hypoxia. Besides the standard monitoring, measuring oxygen carrying capacity/consumption parameters and gastric/sigmoidal intramucosal pH have been shown to be helpful to estimate tissue oxygenation. Therefore, safe levels of hemoglobin concentration should be determined according to the ability of doctors and nursing staffs to evaluate and to maintain patient's systemic and tissue oxygenation as well as to the patient's pathophysiological conditions.

A Subliminal Effect in a Colour-Discrimination Task and its Modulation by Spatial Attention

Three experiments were performed to examine the effects of masked colour stimuli on the response to masking stimuli. In experiment 1, two coloured squares were presented successively at the same position so that the first one could not be perceived owing to backward masking. The task was to respond to the colour of the second square as quickly as possible. The results showed that the subject's response was affected by the unperceived first square: both error rate and reaction time increased when the two squares had different colours. It was also found that reaction times for wrong responses were shorter than those for correct responses; this suggests that wrong responses occurred when the neural activation representing the first square succeeded in triggering a motor response before being suppressed. In experiment 2 we examined whether spatial attention modulated this effect or not. Eight squares (one coloured and seven white) were displayed and the spatial relation between the coloured square in the first frame (prime) and that in the second frame (target) was varied. The performance of subjects when the target location was pre-cued and when no cue was given was compared. The results indicate that in the no-cue condition the subliminal effect was observed uniformly irrespective of the spatial relation. In contrast, in the pre-cue condition the effect was diminished when prime and target occupied different positions, that is when the prime appeared outside the attended region. The result of experiment 3, with another stimulus configuration, showed a similar attentional modulation. The underlying mechanism is discussed.

Volume Perception with Binocular Viewing

We reported earlier that the binocularly unpaired region plays an essential role in the perception of the volume of a solid object (Idesawa, 1991 Japanese Journal of Applied Physics30-4B L751 - L754). We have investigated this volume perception using both illusory and physical objects. The illusory objects used in the tests were of two types, either with or without binocularly unpaired contours. The physical objects used as stimuli in the present experiments were half-moon-shaped textured cylindrical objects, one with and one without a binocularly unpaired region. A rectangular probe was placed beyond the object, and subjects were asked to adjust its position in depth until they felt that the probe just touched the object.

We found that the chosen depth settings were systematically ‘behind’ the objects with unpaired parts, while they were almost ‘correct’ for the objects without unpaired parts. In the former case, subjects thus had the impression that the volume extended further back. We also found that the rim of an object is important for volume perception, especially for objects without textures. A typical example is an imaginary cone occluding two disks, one a little larger than the bottom surface and placed near the bottom, the other a small one located just beyond the top. A complete illusory cone with volume (just like a ‘Santa cap’) could be seen!

Optimal duration of whole body hyperthermia when combined with cis-diaminne-1,1-cychlobutane dicarboxylate platinum (II) (carboplatin)

Minimizing normal tissue toxicity can enhance the therapeutic gain of thermochemotherapy. For this purpose, we investigated the optimal duration of whole body hyperthermia (WBH) (41.5 degrees C) when administered simultaneously with carboplatin (CBDCA). Using a transplantable fibrosarcoma in Fischer 344 rats, we measured tumor growth delay (TGD) as well as normal tissue toxicities (body weight loss, thrombocytopenia) induced by various durations of WBH (0.5, 1.0, 1.5, 2.0 or 2.5 hours) when combined with CBDCA (30 mg/kg, i.v.). When combined with CBDCA, 1.0 hour WBH increased the TGD compared to 0.5 hour of WBH, but with WBH durations greater than 1.0 hour, the TGD did not further significantly increase. Measuring CBDCA-induced myelosuppression, the platelet count on day 6 post-treatment decreased from a control mean of 6.8 x 10(8)/ml to 1.8 x 10(8)/ml after 2.5 hour WBH exposure in a duration-dependent manner (p < 0.001). To estimate the specific therapeutic efficacy (STE), we calculated a ratio of TGD to myelosuppression (thrombocytopenia). Compared to other WBH exposure times, 1.0 hour duration of WBH combined with CBDCA produced the highest STE (2.8) and over 1.5 hour duration of WBH did not result in any additional increase in STE. We conclude that 1.0 hour WBH exposure is optimal when combined with CBDCA in order to maximize the therapeutic gain.

A case of dilated cardiomyopathy with abnormal atrioventricular conduction 5 years before the appearance of left ventricular systolic dysfunction

The first manifestation of dilated cardiomyopathy is usually dyspnea as a result of left heart failure. In this report we describe an unusual patient with third-degree atrioventricular (AV) block unaccompanied by left ventricular dysfunction. Severe left ventricular dysfunction occurred 5 years after the implantation of a permanent pacemaker. We conclude that AV block should not be overlooked as an initial clinical manifestation of dilated cardiomyopathy.

[Long-term prognosis in patients with exercise-induced ST-segment elevation after myocardial infarction]

The present study investigated whether the exercise-induced ST-segment elevation can predict the prognosis for patients with myocardial infarction. Among 529 patients with myocardial infarction, 411 underwent treadmill exercise testing about 5 weeks after the onset. All patients were followed up (mean [+/-SD] 54 +/- 41 months) to compare the incidence of cardiac events. One hundred and eighteen patients (22%) could not perform the exercise test due to cardiac or noncardiac limitation. Ineligibility for exercise test was most useful for risk stratification. Multivariate analysis showed that elimination from the stress test with cardiac limitation was the most significant predictor for cardiac death. Excluding the 16 patients with bundle branch block, the 395 patients were classified into four groups of ST-segment elevation (107 cases, 27%), ST-segment elevation combined with depression (22 cases, 6%), ST-segment depression (106 cases, 27%), ST-segment unchanged (160 cases, 40%). Among the various stress test abnormalities, only low exercise duration was a predictor for cardiac death. ST-depression and ST-elevation combined with depression were independent risk predictors for all cardiac events. Most patients with ST-elevation had single-vessel disease with excellent exercise capacity and low incidence of cardiac events. ST-segment elevation during exercise 5 weeks after myocardial infarction is not associated with a poor prognosis.

Overexpression of p53 is associated with growth pattern and prognosis in advanced gastric cancer

BACKGROUND/AIMS

The growth pattern of advanced gastric carcinoma, based on volumetric analysis, is closely associated with the biological characteristics of tumors, including DNA ploidy, and is an important prognostic factor. Abnormality of the p53 tumor suppressor gene plays an important role in alteration of cells and possibly leads to cancer development.

MATERIALS AND METHODS

Expression of tumor suppressor gene p53 was investigated immunohistochemically in the primary lesion of 196 patients with advanced gastric cancers, and the relationship of p53 immunopositivity with the growth pattern and prognosis was analyzed.

RESULTS

Positive p53 staining was found in 94 (48%) of the 196 primary carcinomas. Vessel invasions were more frequent and lymph node metastasis was more extensive in p53-positive tumors (p < 0.05), whereas p53 immunopositivity was not associated with depth of cancer invasion nor with the stage of cancer. In the column and mountain type tumors, characterized by vertical or penetrative growth, positive p53 staining was found in 53.8% and 52.9%, respectively. In the funnel type tumor, characterized by superficially spreading growth, positive p53 staining was found in significantly lower incidence (28.9%, p < 0.05). The 5-year survival rates were 44.2% and 25.4% for patients with p53 negative and positive gastric carcinomas, respectively (p < 0.01). Multivariate analysis showed that p53 overexpression was an independent prognostic factor of patients with advanced gastric cancer.

CONCLUSIONS

These findings suggest that p53 gene alteration is associated with less favorable prognosis of advanced gastric cancer, possibly by providing tumors with a potential of vertical growth into the gastric wall.

Mechanism of cardiac involvement in the WBN/Kob rat

The cardiac characteristics of the WBN/Kob rat resemble those of rats with catecholamine-induced myocarditis. To determine the etiology of these WBN cardiac characteristics, we assessed the number and affinity of beta-adrenergic receptors, and investigated adenylate cyclase activity, the cardiac myocyte cyclic adenosine monophosphate (cAMP) concentration and the activity of guanosine triphosphate (GTP)-binding protein in 3-month-old WBN/Kob rats. Age-matched Wistar rats served as controls. The mean number of beta-adrenergic receptors was similar in WBN/Kob and Wistar rats (28.0+/-9.1 v 28.3+/-8.9 fmol/mg protein), and there was no significant difference in beta-adrenergic receptor affinity between groups (1.09+/-0.54 v 1.26+/-0.60 nM). The mean cAMP concentration in cardiac myocytes was significantly higher in WBN/Kob rats than in Wistar rats 1975.6+/-247.8 v 344.9+/-83.6 pmol/g wet tissue), (P=0.0112) as was adenylate cyclase activity (33.61+/-8.32 v 24.3+/-12.78 pmol/mg/min), (P=0.0174). The activity of GTP-binding protein was significantly higher in WBN/Kob rats than in Wistar rats. After a beta-agonist binds to a beta-adrenergic receptor, activated adenylate cyclase produces cAMP in myocytes, which in turn opens the Ca2+ channel, leading to an influx of Ca2+ into myocytes. Our results suggest that the increase in adenylate cyclase activity in WBN/Kob rats have led to an increase in the cAMP concentration in myocytes. This process may have resulted in excessive beta-adrenergic activity due to high activity of GTP binding protein in WBN/Kob rats, which may explain the hypersensitivity of WBN/Kob rats to isoproterenol and the development of catecholamine-induced myocarditis.

The quinolinone derivative vesnarinone potentiates the cytotoxicity of doxorubicin in HL-60 leukemia cells

Vesnarinone, (3,4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1- piperazinyl]-2(1H)-quinolinone), a quinolinone derivative, is a positive inotropic agent. We examined the cytotoxicity either by vesnarinone alone or in combination with doxorubicin (DXR), in vitro. The cytotoxic effect of vesnarinone against HL-60 cells did not increase, even at concentrations as high as (50 mu g/ml). The cytotoxicity of DXR, however, was enhanced after being combined with 30 mu g/ml of vesnarinone. The intracellular level of DXR increased when DXR was administered after incubation with vesnarinone and the efflux of DXR was delayed when the cells were incubated in the presence of vesnarinone after DXR exposure. Flow cytometry showed that the combination of DXR and vesnarinone increased the cell population below the G(0)/G(1) region. Vesnarinone induced DNA ladder formation, but only when these cells were incubated for 72 h, while in addition, when DXR was combined with vesnarinone, the DNA ladder formation was enhanced. Based on the above findings, we thus conclude that the cytotoxicity of DXR was enhanced when combined with vesnarinone.

Comparison of glucose 7.5% and 0.75% with or without phenylephrine for tetracaine spinal anaesthesia

PURPOSE

To investigate whether a marginally hyperbaric tetracaine solution with or without phenylephrine could produce consistent blocks as compared with a conventionally hyperbaric tetracaine solution injected at L3-4 interspace with the patient in the lateral position.

METHODS

We studied 120 ASA I or II patients scheduled for elective surgery to the lower limb. Patients were randomly divided into four equal groups to receive spinal anaesthesia using tetracaine 0.5% in glucose 0.75% or 7.5%, with or without phenylephrine 0.125%. Neural block was assessed in a double-blind manner by cold, pinprick, and touch sensation, and a modified Bromage scale after the injection of the study drug.

RESULTS

The median (10th, 90th percentiles) peak dermatomal level to pinprick obtained by the solutions in glucose 0.75% was T10 (L1, T5), which was lower than that obtained by the solution in glucose 7.5% extending to T5 (T10, T3) and T5 (T10, T2) with or without phenylephrine, respectively (P < 0.0001). The addition of phenylephrine prolonged the time to two-segment regression but did not change the maximum extent of blocks.

CONCLUSIONS

A marginally hyperbaric tetracaine with or without phenylephrine produced consistent blocks with spread restricted to the lower thoracic segments when administered intrathecally at the L3-4 interspace with the patient in the lateral position.

Acute effects of thyroid hormone on inward rectifier potassium channel currents in guinea pig ventricular myocytes

Thyroid hormones play an important role in cardiac electrophysiology. However, the regulation of cardiac ionic channels by thyroid hormones is still unclear. To evaluate the acute effect of 3,3',5-triiode-L-thyronine (T3) on inward rectifier potassium channel (IK1) action potentials, whole-cell IK1 currents and steady-state single IK1 currents were recorded in guinea pig ventricular myocytes. Acute exposure of cells to T3 resulted in shortening of the action potential durations. This effect was initiated at 5-15 min and reached a stable plateau at 25 min. The amplitude of steady-state whole-cell IK1 was significantly increased by T3 at 1 nM to 1 microM concentration rage and with ED50 12 nM/liter. T3 (1 microM) increased IK1 by 68 +/- 7% at -40 mV and 52 +/- 9% at -100 mV. Similar effects were observed with triiodothyroacetic acid, an analogue of T3 that does not stimulate DNA transcription. The single IK1 open probability (Po) was increased 7 +/- 1% by 1 nM T3 (n = 9, P < 0.05) and 42 +/- 6% by 1 microM T3 at -40 mV (n = 18, P < 0.0001). However, the channel unit amplitude, time constants of open and fast-closed time were not changed. T3 shortened interburst duration at each membrane potential but did not change the burst behavior. To elucidate detailed mechanism, we assumed a three-state model (C1 <==> C2 <==> O) and calculated each rate constant. T3 significantly increased the rate constant, k+1, for the transition from the C1 to the C2 state at RP -40 mV (2.84 +/- 0.56 to 7.28 +/- 1.23 sec-1, P < 0.01), RP -20 mV (3.63 +/- 0.95 to 10.17 +/- 2.60 sec-1, P < 0.05) and RP (6.73 +/- 1.20 to 21.94 +/- 4.49 sec-1, P < 0.01). However, the other rate constants were not affected. These results demonstrate that T3 enhances IK1 with the increment in Po, which mainly results from shortening of interburst duration without any changes in burst behavior. Hence, the shortening of interburst duration is due to acceleration of the transition from the C1 to the C2 state. The enhanced IK1 by T3 might be one of the causes for shortened action potential duration in hyperthyroidism.

The difference between the changes in systemic oxygen consumption during orthotopic liver transplantation and those during extracorporeal hepatic resection

Every organ in the body requires oxygen to perform its function. In liver transplantation and extracorporeal hepatic resection, oxygen utilization by the graft or the re-implanted liver is a prerequisite for restoration of liver function. We compared the changes in systemic oxygen consumption in a patient who underwent orthotopic liver transplantation with those in two patients who underwent extracorporeal hepatic resection. The pre-anhepatic systemic oxygen consumption in the patient who underwent orthotopic liver transplantation seemed to be lower than that in the patients who underwent extracorporeal hepatic resection, possibly due to the depressed oxygen utilization which sometimes occurs in cirrhotic patients. The increase in oxygen consumption or the overconsumption of oxygen after reperfusion was more significant in the patient who underwent orthotopic liver transplantation than in the patients who underwent extracorporeal hepatic resection. The possible causes might be the greater hepatic oxygen debt, an associated intestinal oxygen debt, and/or the greater ischemia/reperfusion-induced overproduction of superoxide anion in the patient who underwent orthotopic liver transplantation. The differences between the changes in systemic oxygen consumption during orthotopic liver transplantation and those during extracorporeal hepatic resection further support the usefulness of systemic oxygen consumption to predict the immediate restoration of blood flow and oxygen utilization in the graft or the re-implanted liver. These findings also support the importance of evaluating oxygen consumption to confirm whether the critically ill or unconscious patient can utilize oxygen on demand or not.

Protective effect of NG-monomethyl-L-arginine against hypotension inducted by combined tumour necrosis factor-alpha and whole body hyperthermia in rats

We studied: (a) the adverse effects of tumour necrosis factor-alpha (TNF) given during whole body hyperthermia (WBH) on mean arterial pressure (MAP) and gut mucosa in anaesthetized rats; (b) the potential protective effect of NG-monomethyl-L-arginine (L-NMA), an inhibitor of nitric oxide synthase; and (c) the influence of L-NMA on the antitumour effect of the trimodality therapy, WBH + TNF + Carboplatin (CBDCA). In normothermic rats, TNF alone (10(5) or 10(6) U/kg) did not cause hypotension, but increased MAP (p < 0.05). L-NMA alone (5, 10 and 20 mg/kg) increased MAP moderately and dose-dependently (p < 0.05). WBH (41.5 degrees C for 2 h) increased MAP markedly (from 103 +/- 4 to 161 +/- 4 mm Hg). This increase in MAP was sustained throughout the hyperthermia, but was followed by a transient relative hypotension (MAP = 80 +/- mm Hg) on cessation of WBH and an eventual return to near baseline at 30 min post-WBH (MAP = 94 +/- 5 mm Hg). WBH + TNF (10(5) or 10(6) U/kg) initially increased MAP similarly to WBH alone. During the second hour of WBH, however, MAP decreased towards pre-treatment levels, and cessation of WBH was followed by sustained hypotension. This late hypotensive state was associated with a mortality during the early (first 2 h) post-WBH period of 17 and 100% at TNF dose of 10(5) and 10(6) U/kg TNF, respectively. L-NMA given to rats receiving WBH + TNF (10(6) U/kg) maintained MAP at levels similar to WBH alone during WBH treatment. L-NMA prevented the post-WBH hypotension, and extended the survival beyond the early (first 2 h) post-WBH period. No rat, however, receiving high dose TNF (10(6) U/kg) survived more than 12 h even with L-NMA (totally 40 mg/kg). WBH + TNF (10(5) and 10(6) U/kg) also produced marked histopathological injury to the gut mucosa at 2 h post-treatment. L-NMA substantially protected the gut from this injury. In rats bearing a transplantable fibrosarcoma, L-NMA did not decrease the antitumour effect consisting of WBH + TNF (10(5) U/kg) + CBDCA, while it decreased (p < 0.05) the general toxicity (weight loss, diarrhea and foot oedema) of this combination. We conclude that L-NMA may prevent or ameliorate the early toxicity but not the late lethal effects of WBH + high dose TNF (10(6) U/kg). Additionally, L-NMA reduces some of the toxicity of WBH + TNF (10(5) U/kg) + CBDCA without decreasing the antitumour effect of this trimodality therapy. Inhibitors of nitric oxide synthase such as L-NMA may provide a novel approach to overcoming the toxicity of TNF in combination with WBH.

Dynamic Structural Change of 3-D Illusory Surface Observed with Binocular Viewing

When adequate visual stimuli are suitably arranged, for example, partially along the surface boundary or beyond the covering illusory surface, an opaque or transparent illusory surface can be seen (Idesawa, 1991 Japanese Journal of Applied Physics30-4B L751 – 754; 30-7B L1289). By moving the visual stimuli of the occluding objects which were not physically depicted, several interesting phenomena have been observed.

Dynamic fusion and separation of illusory surfaces have been observed when the visual stimuli were changed continuously between two different conditions; only one illusory surface was perceived in the first condition and two separate illusory surfaces were perceived in the second condition. Hysteresis was recognised in the geometrical positions between fusion and separation of the surfaces.

In addition, elastically distorting illusory surfaces have been observed when the positions of two occluding objects, placed on opposite sides, were moved continuously in a sinusoidal way in opposite phase between two positions where the two illusory surfaces could not be bridged together when they were stationary. The phenomena have been observed both for opaque and for transparent illusory surfaces. They could be interpreted as reflections of the surface-perceiving process in our visual system. Probably our visual system tends to contain the previously perceived structure; then the transition from one structure to another is delayed until the geometrical conditions change sufficiently to break the previously perceived structure.