A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions.

In spite of many modifications to decompression algorithms, the incidence of decompression sickness (DCS) in scuba divers has changed very little. The success of stage, compared to linear ascents, is well described yet theoretical changes in decompression ratios have diminished the importance of fast tissue gas tensions as critical for bubble generation. The most serious signs and symptoms of DCS involve the spinal cord, with a tissue half time of only 12.5 minutes. It is proposed that present decompression schedules do not permit sufficient gas elimination from such fast tissues, resulting in bubble formation. Further, it is hypothesized that introduction of a deep stop will significantly reduce fast tissue bubble formation and neurological DCS risk. A total of 181 dives were made to 82 fsw (25 m) by 22 volunteers. Two dives of 25 min and 20 min were made, with a 3 hr 30 min surface interval and according to 8 different ascent protocols. Ascent rates of 10, 33 or 60 fsw/min (3, 10, 18 m/min) were combined with no stops or a shallow stop at 20 fsw (6 m) or a deep stop at 50 fsw (15 m) and a shallow at 20 fsw (6 m). The highest bubbles scores (8.78/9.97), using the Spencer Scale (SS) and Extended Spencer Scale (ESS) respectively, were with the slowest ascent rate. This also showed the highest 5 min and 10 min tissue loads of 48% and 75%. The lowest bubble scores (1.79/2.50) were with an ascent rate of 33 fsw (10 m/min) and stops for 5 min at 50 fsw (15 m) and 20 fsw (6 m). This also showed the lowest 5 and 10 min tissue loads at 25% and 52% respectively. Thus, introduction of a deep stop significantly reduced Doppler detected bubbles together with tissue gas tensions in the 5 and 10 min tissues, which has implications for reducing the incidence of neurological DCS in divers.     

Chromatic pattern-reversal electroretinograms (ChPERGs) are spared in multiple system atrophy compared with Parkinson’s disease

Abstract Idiopathic Parkinson’s disease (IPD) patients have abnormal visual evoked potentials (VEPs) and pattern electroretinograms (PERGs), attributed to dopaminergic transmission deficiency in visual pathway, probably the retina. VEP abnormalities are not reported in multiple system atrophy (MSA). The aim of this study was to investigate and compare chromatic (Ch) red-green (R-G) and blue-yellow (B-Y), and luminance yellow-black (Y-Bk) PERGs in patients with MSA and IPD. We investigated 6 MSA patients (mean age: 62±7.4 years) not undergoing any pharmacological treatment, as well as 12 early IPD patients (mean age: 60.1±8.3 years) and 12 age-matched normal observers. ChPERGs were recorded monocularly in response to full-field equiluminant R-G, B-Y and Y-Bk horizontal gratings. In MSA only responses to R-G stimuli showed minimal insignificant changes (slight but not significant amplitude reduction without any significant latency delay); no significant abnormality was detected for B-Y and luminance Y-Bk stimuli. By contrast, in IPD all responses were reduced in amplitude and delayed in latency, above all for B-Y stimuli. Present data indicate that both chromatic and achromatic PERGs are virtually unaffected in MSA, whereas in early IPD they are clearly impaired, suggesting different pathogenic retinal mechanisms and a useful simple tool for distinguishing MSA from IPD.     

Pharmacokinetics and pharmacodynamics of L-Dopa after acute and 6-week tolcapone administration in patients with Parkinson's disease

Tolcapone, a central and peripheral catechol O-methyltransferase (COMT) inhibitor, reduces the conversion of L-Dopa into 3-O-methyl-Dopa (3-OMD), thus leading to more stable and sustained L-Dopa plasma levels. This study was designed to evaluate the effects of acute and 6-week tolcapone administration on L-Dopa pharmacokinetics and pharmacodynamics in Parkinson's disease (PD) patients with predictable motor fluctuations. Tapping test, walking time, and tremor, as well as L-Dopa and 3-OMD plasma levels, were assessed before and for 5 hours after the administration of a single L-Dopa dose, alone or in combination with 200 mg tolcapone, in seven patients with PD. This clinical and pharmacokinetic study was repeated after 6 weeks of tolcapone therapy (200 mg three times daily). It was observed that tolcapone, after both acute and chronic administration, prolonged the motor improvement induced by L-Dopa. As a result, at week 6 of tolcapone therapy, the daily hours spent "off" were significantly decreased. Tolcapone significantly increased the area under the curve of L-Dopa plasma levels by slowing down the elimination of L-Dopa from plasma, whereas the maximal concentration of L-Dopa was not modified. 3-OMD levels decreased significantly after acute tolcapone administration, and after 6 weeks of tolcapone therapy, they were approximately one sixth of pre-tolcapone values. The data confirm that tolcapone decreases L-Dopa clearance and prolongs motor response in PD patients with motor fluctuations, and that this effect is maintained after 6 weeks of tolcapone therapy.     

Paroxetine in Parkinson's disease: effects on motor and depressive symptoms

Selective serotonin reuptake inhibitors have been used in the treatment of depression in patients with PD. Conflicting data as to whether selective serotonin reuptake inhibitors worsen parkinsonian motor symptomatology have been reported. In this study, the additional 6 months therapy with paroxetine 20 mg/d in a group of depressed patients with PD did not modify parkinsonian motor function (Unified Parkinson's Disease Rating Scale scores); however, in one patient, fully reversible worsening of tremor was observed. Depression, as evaluated by Beck Depression Inventory and Hamilton Depression Rating Scale, improved from baseline to final visit (p < 0.05 by analysis of variance).     

Validity and metric of MiniMental Parkinson and MiniMental State Examination in Parkinson’s disease

The MiniMental Parkinson (MMP) has been derived from the MiniMental State Examination (MMSE) for the screening of cognitive impairment in Parkinson’s disease by adding subtests that were focused on executive and visuo-spatial impairment more than on memory or language deficits. In this multicenter study, the psychometric and validity properties of the MMP have been evaluated in 69 cognitively intact and 52 cognitively impaired patients with Parkinson’s disease, classified according to their performance at the Dementia Rating Scale. The MMP showed better metrics and convergent validity, and higher screening ability. However, its performance was not fully satisfying in terms of data distribution, coefficient of variation and specificity, and Receiver Operating Characteristic curves did not show clear cut superiority of either scale at their best sensitivity–specificity trade off. The MMP seems to be slightly preferable to the MMSE only at a cut off that favours sensitivity with respect to specificity, for screening purposes. The test is simple and quick, but has limitations in terms of validity.     

Comparison of 3T and 7T Susceptibility-Weighted Angiography of the Substantia Nigra in Diagnosing Parkinson Disease

BACKGROUND AND PURPOSE:Standard neuroimaging fails in defining the anatomy of the substantia nigra and has a marginal role in the diagnosis of Parkinson disease. Recently 7T MR target imaging of the substantia nigra has been useful in diagnosing Parkinson disease. We performed a comparative study to evaluate whether susceptibility-weighted angiography can diagnose Parkinson disease with a 3T scanner.MATERIALS AND METHODS:Fourteen patients with Parkinson disease and 13 healthy subjects underwent MR imaging examination at 3T and 7T by using susceptibility-weighted angiography. Two expert blinded observers and 1 neuroradiology fellow evaluated the 3T and 7T images of the sample to identify substantia nigra abnormalities indicative of Parkinson disease. Diagnostic accuracy and intra- and interobserver agreement were calculated separately for 3T and 7T acquisitions.RESULTS:Susceptibility-weighted angiography 7T MR imaging can diagnose Parkinson disease with a mean sensitivity of 93%, specificity of 100%, and diagnostic accuracy of 96%. 3T MR imaging diagnosed Parkinson disease with a mean sensitivity of 79%, specificity of 94%, and diagnostic accuracy of 86%. Intraobserver and interobserver agreement was excellent at 7T. At 3T, intraobserver agreement was excellent for experts, and interobserver agreement ranged between good and excellent. The less expert reader obtained a diagnostic accuracy of 89% at 3T.CONCLUSIONS:Susceptibility-weighted angiography images obtained at 3T and 7T differentiate controls from patients with Parkinson disease with a higher diagnostic accuracy at 7T. The capability of 3T in diagnosing Parkinson disease might encourage its use in clinical practice. The use of the more accurate 7T should be supported by a dedicated cost-effectiveness study.

Parkinson disease (PD) is a common neurodegenerative disease whose pathologic substrate is nigrostriatal dopaminergic degeneration due to the neuronal loss in the pars compacta of the substantia nigra (SN).¹On the basis of the correlation between MR signal intensity at conventional field strengths and Perls staining for iron distribution, the medial portion of the midbrain with lower MR signal is attributed to the pars reticulata of the substantia nigra, and the lateral region (with higher MR signal), to the substantia nigra pars compacta.² However, Perls staining and T2WI signal hypointensity do not match precisely,³ and the hypointense area on T2WI does not match the substantia nigra pars reticulata.⁴ Moreover, conventional MR imaging techniques, including segmented inversion recovery ratio imaging,⁵ fail to distinguish the inner structure of the substantia nigra.⁶ More advanced and recently proposed SN-derived biomarkers such as relaxometry,^7,8 DTI,⁹ and neuromelanin imaging¹⁰ are currently not yet accepted in evaluating patients with PD in clinical practice.¹¹Recently, by using high-resolution 3D susceptibility-weighted angiography (SWAN),¹² the ultra-high-field (UHF) anatomy of the SN with its inner organization has been described¹³ as a 3-layer structure of different signal intensities along the posterior-anterior axis of the midbrain, resembling the dorsal and ventral components of the substantia nigra pars compacta and the substantia nigra pars reticulata, respectively. By using calbindin immunostaining, one can distinguish calbindin-positive (matrix) and calbindin-negative structures (nigrosomes)¹⁴ within the substantia nigra. In a recent MR imaging study at 7T,¹⁵ nigrosome 1, the largest and highly attenuated cluster of calbindin-negative neurons within the substantia nigra pars compacta ventralis, corresponded to the round hyperintense area observed in the intermediate and lateral portion of the substantia nigra pars compacta.¹⁶In patients with PD the 3-layer organization and the hyperintense lateral spot within the SN (nigrosome 1) are lost, and this radiologic sign distinguishes patients with PD from healthy subjects (HS) on an individual basis with high accuracy.¹³The diagnostic gain provided by 7T imaging is a prerequisite for the clinical acceptance of UHF, but until now, 7T MR imaging examinations have been confined to the research environment. The neuroimaging-based diagnosis of PD might constitute an important addition to the clinical diagnosis of extrapyramidal disorders. Therefore, the diagnostic role of SWI performed with a clinical MR imaging scanner at 3T has been tested recently,^17,18 with promising results. A direct comparison of 3T and 7T evaluation of the SN is mentioned in a pilot experience including 2 patients with PD.¹⁵Here, we describe a comparative study with a case control design that prospectively evaluates the diagnostic accuracy of SWAN at 3T and 7T.