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Biomedical subjects

M Bonnet

Publications and source records attributed to M Bonnet.

At least 55 records · Page 3Linked to original sources
PubMed1996

Brain activation induced by estimation of duration: a PET study.

Duration information about a visual stimulus requires processing as do other visual features such as size or intensity. Using positron emission tomography, iterative H215O infusions, and statistical parametric mapping, we investigated the neural correlates of time processing. Nine normal subjects underwent six serial rCBF. Three tasks were studied: (a) A temporal generalization task (D task) in which the subjects had to judge (by pressing one of two keys) whether the duration of the illumination of a green LED was equal to or different from that of a previously presented standard; (b) An intensity generalization task (I task) in which the judgment concerned the intensity of the LED; and (c) A control task (C task) in which the subjects had to press one of the two keys at random in response to LED illumination. A significant increase in rCBF during the D task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, anterior cingulate cortex, vermis, and a region corresponding to the left fusiform gyrus. A significant increase in rCBF during the I task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, right extrastriate cortex, anterior cingulate cortex, left inferior parietal lobule, vermis, and two symmetrical regions corresponding to the fusiform gyri. No significant activation was observed in the D task when compared to that in the I task. We propose that these cortical maps are best explained by the recruitment of visual attention and memory structures, which play a major role in prospective time judgements as indicated by behavioral studies. The data also suggest that the temporal dimension of a visual stimulus is processed in the same areas as other visual attributes.

Adult↗
PubMed1996

Cryopexy in primary rhegmatogenous retinal detachment: a risk factor for postoperative proliferative vitreoretinopathy?

PURPOSE: To evaluate the role of cryopexy in the stimulation of postoperative proliferative vitreoretinopathy (PVR) in primary rhegmatogenous retinal detachment. MATERIALS AND METHODS: A series of 595 eyes of 554 patients with primary rhegmatogenous retinal detachment, referred before any failed surgery, were prospectively evaluated. Univariate and multivariate statistical analyses of the data were conducted. RESULTS: The incidence of postoperative PVR in relation to the methods used for retinopexy was dependent on the types and anatomy of retinal breaks associated with retinal detachment. The incidence of postoperative PVR was nil in retinal detachments due to atrophic holes in lattice, oral dialyses, and macular holes, regardless of the retinopexy methods. Postoperative PVR occurred solely in retinal detachments due to horseshoe tears (incidence 4.42%), paravascular tears of the postequatorial region (18.18%), and giant tears (24.6%) (P < 0.00001). The incidence of postoperative PVR was 0.5% in eyes with horseshoe tears with mobile posterior edges vs 9.72% in eyes with horseshoe tears with curled posterior edges, regardless of the retinopexy methods (P < 0.00001). In retinal detachments due to horseshoe tears with mobile posterior edges the incidence of postoperative PVR (0.5%) was not influenced by the retinopexy methods. In contrast, in retinal detachments due to horseshoe tears with curled posterior edges the incidence of postoperative PVR was higher in eyes managed with cryopexy (14.77%) than in eyes managed with laser retinopexy (1.78%) (P < 0.02). In retinal detachments due to giant tears the incidence of postoperative PVR was not statistically significantly greater in eyes managed with cryopexy (33.3%) than in eyes managed with laser retinopexy (15.6%). In tears 180 degrees and over in size, however, the incidence of postoperative PVR was significantly higher in eyes managed with cryopexy (9/11 eyes) than in eyes managed with laser retinopexy (5/17 eyes) (P = 0.006). CONCLUSIONS: Cryopexy is not a stimulating factor for postoperative PVR in primary rhegmatogenous retinal detachments due to atrophic holes in lattice, oral dialyses, macular holes, or horseshoe tears with mobile posterior edges. In contrast, cryopexy probably is a stimulating factor for postoperative PVR in retinal detachments due to horseshoe tears with curled posterior edges or to retinal tears 180 degrees and over.

Adolescent↗
PubMed1996

Preoperative vitreous hemorrhage associated with rhegmatogenous retinal detachment: a risk factor for postoperative proliferative vitreoretinopathy?

BACKGROUND: We conducted a prospective clinical study to elucidate the role of preoperative vitreous hemorrhage in the development of postoperative proliferative vitreoretinopathy (PVR) in primary rhegmatogenous retinal detachment. MATERIALS AND METHODS: We prospectively evaluated 409 eyes of 390 patients affected by primary rhegmatogenous retinal detachment referred before any failed attempt to reattach the retina. Single and multiple logistic regression analysis were used to test 14 categories of variables. RESULTS: Postoperative PVR occurred in 48 (11.7% of 409 eyes). Postoperative PVR developed in 41 (11.8%) of the 347 eyes with no preoperative vitreous hemorrhage, and 7 (11.3%) of the 62 eyes with preoperative vitreous hemorrhage (P = 0.90). The results of multiple logistic regression analysis showed that only four variables were significant factors which had independently and jointly an effect on the risk of postoperative PVR: (1) 90 degrees or greater circumferential extent of the retinal tears; (2) preoperative PVR grade B; (3) preoperative PVR grade C-D; and (4) the use of cyrotreatment as the method of retinopexy. CONCLUSION: With the surgical techniques currently used, mild preoperative vitreous hemorrhage is not an independent risk factor for postoperative PVR in primary rhegmatogenous retinal detachment. The role of moderate and severe vitreous hemorrhage remains to be fully evaluated in a larger series of eyes.

Adolescent↗
PubMed1996

Accurate mapping of the "acid meat" RN gene on genetic and physical maps of pig chromosome 15.

It has been shown that a major gene, called RN, is responsible for the RTN technological yield, a meat quality porcine trait. Experimental families informative for the segregation of RN gene were constituted from animals belonging to the Laconie composite line. We have previously mapped the RN gene to Chromosome (Chr) 15 (Milan et al. Genet. Sel. Evol. 27, 195-199, 1995). A Chr 15 map was established with 16 markers. The RN gene was found to be located between markers Sw120 and Sw936, at 2 cM from Sw936 (LOD = 38.1). In addition, by localizing Sw936 at 15q21-22 using DISC-PCR, we also located RN on the physical map.

Animals↗
PubMed1996

The "short-long" reaction time effect in duration programming.

The programming processes concerned with response duration were studied in a precueing and in a priming reaction time (RT) paradigm. Participants had to produce a motor response of a specified duration as soon as possible after a response signal (RS) preceded by a warning signal (WS), which could deliver information on 2 response parameters (duration and effector). In Experiment I (precueing; N = 12), 3 effectors (the right hand, the left hand, or the knees) and 3 durations (.7, 2.5, or 5.5 s) were contrasted. Two responses differing in their biomechanical features were required in 2 blocks of trials: Subjects had to accurately time the duration of either a sustained button press or an interval between 2 brief presses. The RT patterns revealed a short-long effect: Shorter RTs were produced before the short duration than before the longer, provided that the duration was not precued. This short-long effect occurred whatever type of response and effector were involved. Two conclusions were reached. First, response duration was included in the motor program elaborated before execution, whatever the biomechanical features of the response; and, second, the program for the short duration was activated on all trials and was used as a basis for programming longer durations when needed. These conclusions were tested in Experiment 2 (priming; N = 12), in which a small proportion of invalid trials concerning duration was provided. Thus, the duration required by the RS differed from that primed by the WS. Two durations (.7 or 2.5 s) and 2 effectors (the index or the middle finger) were involved. In the invalid trials, the responses of short and long durations did not yield any RT differences, thus confirming the particular status of the short duration. This suggests that deprogramming operations (which lengthen the RT) are needed after a RS to produce short response durations but not after a RS to produce long response durations in the invalid trials.

Journal Article↗
PubMed1996

[Risk factors of postoperative proliferative vitreoretinopathy in giant tears].

BACKGROUND: In eyes with giant retinal tears, the rate of severe postoperative PVR and failure to permanently reattach the retina remains especially high in spite of technical advances in surgical management. This study was conducted to elucidate the clinical and surgical risk factors for severe postoperative PVR in such eyes. PATIENTS AND METHODS: We reviewed the records of 68 consecutive patients (69 eyes) with giant retinal tears. Univariate and multivariate statistical analyses were used to evaluate the risk factors for severe PVR. RESULTS: The rate of severe postoperative and failure to permanently reattach the retina were 43.5% (30/69 eyes). It was influenced at a statistically significant level by two independent risk factors: 1) the presence and severity of preoperative PVR and 2) the use of cryotreatment as compared to the use of ALP treatment. Severe postoperative PVR occurred in 63.6% (14/22 eyes) of eyes managed with cryotreatment versus 31.1% (14/45 eyes) of eyes managed with ALP treatment (P < 0.02). The rate of severe postoperative PVR was 64% (16/25 eyes) in eyes with grade C-D PVR preoperatively versus 31.8% (14/44 eyes) in eyes with no PVR or grade B PVR preoperatively (P < 0.01). In eyes managed with the use of ALP treatment the rate of severe postoperative PVR remained influenced at a statistically significant level (P < 0.005) by the presence of grade C-D PVR preoperatively. Grade C-D PVR was significantly more frequent preoperatively in patients with visual symptoms of 3 week-duration or more at initial examination (23/24 patients, 95.8%), than in those with visul symptoms under 3 week-duration (8/41 patients, 19.5%) (P: 0.0005). CONCLUSION: The results suggest that the high incidence of severe postoperative PVR in giant retinal tears may be decreased by 1) early management before the occurrence of PVR and 2) the use of argon laser photocoagulation rather than cryotreatment as the method of creating a chorioretinal scar.

Adult↗
PubMed1996

-Choroidal detachment associated with rhegmatogenous retinal detachment: a risk factor for postoperative PVR?.

PURPOSE: To determine whether preoperative choroidal detachment associated with primary rhegmatogenous retinal detachment is an independent risk factor for postoperative PVR. MATERIAL AND METHODS: One hundred eighty nine primary rhegmatogenous retinal detachments in 187 consecutive patients, initially operated on by the same surgeon, were enrolled in a prospective study. Ten eyes showed preoperative choroidal detachment associated with retinal detachment. Owing to the small number of eyes with preoperative choroidal detachment, we conducted the statistical analysis using the calculation of relative risk. RESULTS: The correlation between preoperative choroidal detachment and preoperative PVR grade C-D was statistically significant (RR: 9.03; confidence interval: 2.91-28). Postoperative PVR occurred, or recurred, in one of the 10 eyes with preoperative choroidal detachment (10%), and 10 of the 179 eyes with no choroidal detachment (5.58%). The difference between the two groups is not statistically significant (RR: 1.79; confidence interval: 0.25-12.64). All eyes which developed postoperative PVR showed one or two recognized independent risk factors for postoperative PVR (preoperative PVR grade C-D and/or retinal tears > or = 90 degrees). CONCLUSION: With the treatment modalities used in the present series (preoperative and postoperative steroids, and vitreoretinal microsurgery) preoperative choroidal detachment associated with primary rhegmatogenous retinal detachment no longer appears to be an independent risk factor for postoperative PVR.

Adult↗
PubMed1996

[Retinal detachment caused by macular holes in patients with severe myopia: results of intravitreal injection of pure C3F8].

PURPOSE: To evaluate the long-term anatomic and visual results of intravitreal injection of pure C3F8 in the management of retinal detachments due to macular holes in myopic eyes. MATERIALS AND METHODS: Twenty one highly myopic eyes (19 patients) with retinal detachments due to macular holes were initially managed by intravitreal injection of pure C3F8. The postoperative follow-up ranged from 6,5 to 45 months (median: 27.5 months). RESULTS: Total retinal reattachment was achieved in 16 eyes (76.2%). Anatomic success was obtained with a single C3F8 injection in 15 eyes, and two injections in one eye. The 5 eyes which failed to reattach after gas injection underwent reoperation using choroidal irritation in the macular area associated with gas injection. The retina was reattached in all eyes. Eleven of the 16 eyes (68.7%) in which the retina was reattached solely with intravitreal gas injection had a nearly normal final near reading visual acuity. In contrast, none of the eyes reattached with the use of choroidal irritation had measurable final visual acuity. CONCLUSION: The results achieved in the present series of patients confirm that intravitreal injection of pure C3F8 is a valuable alternative in the management of retinal detachments due to macular holes in myopic eyes. We recommend this treatment approach as the initial surgical procedure, since more than half of eyes successfully operated on recover useful central vision.

Adult↗
PubMed1996

[Has the incidence of postoperative PVR in rhegmatogenous retinal detachment decreased?].

PURPOSE: To determine whether the incidence of severe postoperative PVR in primary rhegmatogenous retinal detachment has decreased over the last twelve years. MATERIALS AND METHODS: We prospectively evaluated 595 eyes of 554 consecutive patients with primary rhegmatogenous retinal detachment, referred before any failed attempt to reattach the retina, managed by the same surgeon between March 1983 and December 1994. The eyes were divided into two consecutive series: 275 eyes operated on from March 1983 through February 1988 (series no. 1), and 320 eyes operated on from February 1988 through December 1994 (series no. 2). We conducted univariate and multivariate statistical analyses to compare the incidence of postoperative PVR in the two consecutive series. RESULTS: The overall incidence of postoperative PVR was 8.72% (24/275 eyes) in series no. 1, versus 2.81% (9/320 eyes) in series no. 2 (p < 0.01). The incidence of postoperative PVR in retinal detachments due to atrophic holes in lattice degeneration, oral dialyses, and macular holes in myopic eyes, was nil in both series. The incidence of postoperative PVR in retinal detachments due to horseshoe tears with mobile posterior edges was 1.16% (1/86 eyes) in series no. 1, and 0% (0/109 eyes) in series no. 2. The incidence of postoperative PVR in retinal detachments associated with horseshoe tears with curled posterior edges was 21.15% (11/52 eyes) in series no. 1 versus 3.2% (3/93 eyes) in series no. 2 (p < 0.001). The incidence of postoperative PVR in giant tears was 35.5% (11/31 eyes) in series no. 1. and 14.7% (5/34 eyes) in series no. 2 (chi square = 3.77; at the limit of significance). The incidence of postoperative PVR in retinal detachments du to paravascular tears of the post-equatorial region in myopic eyes was 25% (1/4 eyes) in series no. 1, and 14% (1/7 eyes) in series no. 2. CONCLUSION: In our own experience, the incidence of postoperative PVR in primary rhegmatogenous retinal detachment has decreased at a statistically significant level since 1988. We believe that the decreased incidence of postoperative PVR in our most recent series is mainly related to the use of laser photocoagulation retinopexy rather than cryopexy in the management of high risk eyes (retinal detachments associated with horseshoe tears with curled posterior edges, and giant tears).

Adolescent↗
PubMed1995

Multi-slice, breathhold imaging of the lung with submillisecond echo times.

The signal from the lungs is heavily attenuated by T2 and T2 decay in standard MR images of the thorax. The authors utilized the capabilities of a prototype fast gradient system to develop a multi-slice gradient echo sequence that can obtain images with an echo time of 0.7 ms. Images acquired in a single breath-hold are free from respiratory motion artifacts and clearly display signal from lung parenchyma. The use of fast gradients makes short echo times possible without the use of nonstandard RF pulses and spatial encoding techniques and their associated limitations.

Artifacts↗
PubMed1995

Surgical risk factors for severe postoperative proliferative vitreoretinopathy (PVR) in retinal detachment with grade B PVR.

BACKGROUND: Previous studies have shown that grade B proliferate vitreoretinopathy (PVR) is a considerable risk factor for the development of severe postoperative PVR. We conducted a prospective study to elucidate which surgical procedures used in retinal detachment management may stimulate the PVR process in such eyes. MATERIALS AND METHODS: The study included 156 eyes of 152 consecutive patients with rhegmatogenous retinal detachment complicated by grade B PVR referred before any failed surgery and operated on between 1983 and 1993. The parameters evaluated by multivariate statistical analysis included the cumulative circumferential extent of the retinal tears, the extent of the scleral buckle, gas injection, vitrectomy, the method used for retinopexy, and the time of surgical management during the period of the study. RESULTS: The incidence of severe postoperative PVR was 25.8% in eyes managed with cryotreatment versus 2.2% in eyes managed with argon laser photocoagulation (P = 0.001). The rate of severe postoperative PVR was not influenced by the other surgical variables. CONCLUSION: We conclude that cryotherapy may be a risk factor for the development of severe postoperative PVR in retinal detachments associated with grade B PVR.

Adolescent↗
PubMed1995

Programming the duration of a motor sequence: role of the primary and supplementary motor areas in man.

Event-related potentials were recorded in a reaction time (RT) paradigm, where the duration of a learned interval (either 0.7 s or 2.5 s) delimited by two brief button-presses was to be accurately controlled. A preparatory signal (PS) either did not give or gave prior information concerning the duration of the following response (neutral condition or primed conditions, respectively). In the latter case, the information was either validated (valid condition) or invalidated (invalid condition) by the response signal (RS). When duration was not known in advance (invalid and neutral conditions), RTs were longer before a response of short than long duration. This difference was not found under the valid condition. During the preparatory period (PP), the amplitude of the contingent negative variation (CNV) was larger when the duration was primed than when it was not. A larger CNV appeared when the PS primed a short rather than a long duration. This effect occurred in the early part of the PP over the supplementary motor area (SMA) and in its latest part over the primary motor area (MI). The RT and the electrophysiological pattern were interpreted as revealing the occurrence of programming operations regarding the temporal dimension of the response. The time course of the CNV over the SMA and MI suggested that these two areas were hierarchically organized. Between the RS and the onset of the response, differences probably related to programming effects were still found over MI: the activities were larger under the valid than under the neutral condition. However, no sign of deprogramming (expected in the invalid condition) was observed: similar amplitudes were found under the neutral and invalid conditions. Deprogramming operations seemed to be postponed during response execution where the invalid condition evoked larger activities than the two other conditions over the SMA. Finally, MI but not the SMA yielded a Bereitschaftpotential before the second press ending the response (i.e., during response execution). These results suggest that the duration of a motor response can be a part of the motor program and that the SMA plays a major role in programming processes but not in response execution, contrary to MI.

Algorithms↗
PubMed1995

Modulation of spinal reflexes: arousal, pleasure, action.

The human startle reflex is reliably modulated by the affective valence of foreground pictures, with larger reflexes elicited when viewing unpleasant relative to pleasant scenes. If this modulation is due to priming of the defensive startle reflex by an aversive foreground, a different pattern should occur for a reflex that is not inherently defensive in nature. In the current study, affective modulation was investigated using the spinal tendinous (T) reflex, which is well documented as sensitive to differences in arousal and is involved in actions that are both appetitively defensively motivated. As such, T reflexes elicited during unpleasant pictures were not expected to be augmented relative to those elicited in the context of pleasant pictures. Results showed that T reflexes were facilitated during processing of arousing stimuli-either pleasant or unpleasant relative to low-arousal neutral materials. These effects of emotional stimuli on T-reflex amplitude are consistent with hypothesis that motivational priming underlies affective reflex modulation.

Adult↗
PubMed1995

[Myasthenia induced by tiopronin in the treatment of rheumatoid arthritis].

Myasthenia gravis (MG) is a well known side-effect of D-Penicillamine used in the treatment of rheumatoid polyarthritis. Tiopronin is another drug available in France, which can also induce MG. Drug-induced MG are characterized by frequent involvement of facial and oropharyngeal muscles. Moreover, the generalization is scarce and the outcome always quite good. No thymoma is present, anti-acetylcholine receptors antibodies are often highly positive. Furthermore, some HLA phenotypes are most frequently found among patients with drug-induced MG suggesting a genetic predisposition. This observation underlines the interest of careful management of patients treated by tiopronin.

Aged↗