Specific heating power of fatty acid and phospholipid stabilized magnetic fluids in an alternating magnetic field

Magnetic fluids (MFs) with a similar narrow size distribution of the iron oxide core were stabilized with lauric acid (MF 1), oleate (MF 2) or, after dialysis in the presence of liposomes, with phospholipid molecules (MF 3 and MF 4, respectively). The hydrodynamic sizes of the MF 1 and MF 3 were half those found for MF 2 and MF 4. The MFs were exposed to inductive heating in an alternating magnetic field at a frequency of 200 kHz and a maximum magnetic field strength of 3.8 kA m(-1). Specific absorption rates (SAR) of 294 ± 42 (MF 1), 214 ± 16 (MF 2), 297 ± 13 (MF 3) and 213  ± 6 W g(-1) Fe (MF 4) were obtained. The data for MF 2 and MF 4 were identical to those found for the commercially available ferucarbotran. The biomedical relevance of the phospholipid-coated MFs is briefly discussed.

Synthesis, physicochemical characterization and MR relaxometry of aqueous ferrofluids

The synthesis and characterization of ferrofluid based MR contrast agents, which offer R2* versatility beyond that of ferucarbotran, is described. Ferrofluids were formed after stabilizing magnetite cores with dodecanoic acid (a), oleic acid (b), dodecylamine (c), citric acid (d) or tartaric acid (e). Core sizes were deduced from TEM micrographs. Magnetic properties were determined by SQUID magnetometry. Hydrodynamic particle diameters were determined by dynamic light scattering measurements. Zeta potentials were measured by combining laser Doppler velocimetry and phase analysis light scattering. Iron contents were evaluated colorimetrically. MR relaxometry including R1 and R2* was conducted in vitro using homogeneous ferrofluid samples. The average core diameters of ferrofluids a, b and c equaled 9.4 +/- 2.8 nm and approximately 2 nm for ferrofluids d and e. Magnetization measurements at 300 K revealed superparamagnetic behaviour for the dried 9 nm diameter cores and paramagnetic-like behaviour for the dried cores of ferrofluids d and e. Iron contents were between 32-75 mg Fe/mL, reflecting the ferrofluids' high particle concentrations. Hydrodynamic particle diameters equaled 100-120 nm (a, b and c). For the ferrofluids a, b, d and e coated with anions, strong negative zeta potential values between -27.5 mV and -54.0 mV were determined and a positive zeta potential value of +33.5 mV was found for ferrofluid c, covered with cationic dodecylammonium ions. MR relaxometry yielded R1-values of 1.9 +/- 0.3 (a), 4.0 +/- 0.8 (b), 5.2 +/- 1.0 (c), 0.124 +/- 0.002 (d) and 0.092 +/- 0.005 s(-1) mM(-1) (e), and R2*-values of 856 +/- 24 (a), 729 +/- 16 (b), 922 +/- 29 (c), 1.7 +/- 0.05 (d) and 0.49 +/- 0.05 s(-1) mM(-1) (e). Thus, the synthesized ferrofluids reveal a broad spectrum of R2* relaxivities. As a result, the various MR contrast agents have a great potential to be used in studies dealing with malignant tissue targeting or molecular imaging.

New strategies for automated differential diagnosis of degenerative brain disorders

New strategies are considered for automated, single-subject differential diagnosis of independent degenerative brain disorders characterized by similar clinical symptoms using functional imaging. The methodology of these strategies is described and its application in parkinsonian movement disorders is illustrated for PET data. Using an automated diagnostic Topographic Profile Rating (TPR) technique based on the Scaled Subprofile Model (SSM-PCA), single-subject score values for different conditions are compared with reference values to predict diagnosis. The discriminatory parameters of reference score sets associated with significant SSM principal components referred to as group invariant subprofiles (GIS networks) are examined. It is shown that the extraction of exclusive sub-networks that stem from contrasting image features between conditions can be an effective tool for optimization that does not require expert knowledge.

Hierarchical role of fetuin-A and acidic serum proteins in the formation and stabilization of calcium phosphate particles

The serum protein fetuin-A is a potent systemic inhibitor of soft tissue calcification. Fetuin-A is highly effective in the formation and stabilization of protein-mineral colloids, referred to as calciprotein particles (CPPs). These particles ripen in vitro in a two-step process, indicated by a morphological conversion from spheres to larger prolate ellipsoids. Using a combined light scattering and electron microscopic imaging approach we determined that the second-stage particles resulted from a highly anisotropic outgrowth of the first-stage particles. Electron microscopy of ascites fluid from a patient with calcifying peritonitis revealed particles reminiscent of secondary CPPs. Thus, CPPs form in the body and undergo the two-step ripening at least in pathological conditions. Unlike in vitro generated CPPs, ascites-derived CPPs contained little fetuin-A but large amounts of albumin. This prompted us to study the role of fetuin-A combined with other serum proteins in CPP formation. Fetuin-A was indispensable for primary CPP formation. Albumin and acidic proteins in general greatly enhanced the fetuin-A triggered formation of secondary CPPs and, thus, substituted substantial amounts of fetuin-A without loss of inhibition of calcium phosphate precipitation. Thus, direct mineral deposition from solute in the body is unlikely even at low fetuin-A serum levels as long as sufficient bulk acidic protein is available. Collectively fetuin-A and other acidic bulk plasma proteins may be considered as mineral chaperones mediating the stabilization, safe transport, and clearance in the body of calcium and phosphate as colloidal complexes, thus, preventing ectopic calcification.

Assessment of the progression of Parkinson's disease: a metabolic network approach

BACKGROUND

Clinical research into Parkinson's disease has focused increasingly on the development of interventions that slow the neurodegeneration underlying this disorder. These investigations have stimulated interest in finding objective biomarkers that show changes in the rate of disease progression with treatment. Through radiotracer-based imaging of nigrostriatal dopaminergic function, a specific class of biomarkers to monitor the progression of Parkinson's disease has been identified, and these biomarkers were used in the clinical trials of drugs with the potential to modify the course of the disease. However, in some of these studies there was discordance between the imaging outcome measures and blinded clinical ratings of disease severity. Research is underway to identify and validate alternative ways to image brain metabolism, through which the efficacy of new therapies for Parkinson's disease and related disorders can be assessed.

RECENT DEVELOPMENTS

During recent years, spatial covariance analysis has been used with (18)F-fluorodeoxyglucose PET to detect abnormal patterns of brain metabolism in patients with neurodegenerative disorders. Rapid, automated, voxel-based algorithms have been used with metabolic imaging to quantify the activity of disease-specific networks. This approach has helped to characterise the unique metabolic patterns associated with the motor and cognitive features of Parkinson's disease. The results of several studies have shown correction of abnormal motor, but not cognitive, network activity by treatment with dopaminergic therapy and deep brain stimulation. The authors of a longitudinal imaging study of early-stage Parkinson's disease reported substantial differences in the development of these metabolic networks over a follow-up of 4 years. WHERE NEXT?: Developments in network imaging have provided the basis for several new applications of metabolic imaging in the study of Parkinson's disease. A washout study is currently underway to determine the long-duration effects of dopaminergic therapy on the network activity related to Parkinson's disease, which will be useful to plan future trials of disease-modifying drugs. Network approaches are also being applied to the study of atypical parkinsonian syndromes. The characterisation of specific patterns associated with atypical parkinsonian syndromes and classic Parkinson's disease will be the basis for a fully automated imaging-based procedure for early differential diagnosis. Efforts are underway to quantify the networks related to Parkinson's disease with less invasive imaging methods. Assessments of network activity with perfusion-weighted MRI show excellent concordance with measurements done with established radiotracer techniques. This approach will ultimately enable the assessment of abnormal network activity in people who are genetically at risk of Parkinson's disease.

Regional metabolic changes in Parkinsonian patients with normal dopaminergic imaging

Dopaminergic imaging has been found to be normal in approximately 15% of parkinsonian patients enrolled in neuroprotective trials. We used (18)F-fluorodeoxyglucose positron emission tomography (FDG PET) to determine the metabolic basis for this finding. We reviewed scans from 185 patients with clinical signs of Parkinson's disease (PD) who underwent (18)F-fluorodopa PET imaging for diagnostic confirmation. Of this group, 27 patients (14.6%) had quantitatively normal scans; 8 of these patients were additionally scanned with FDG PET. Pattern analysis was performed on an individual scan basis to determine whether the metabolic changes were consistent with classic PD. Computer-assisted single-case assessments of the FDG PET scans of these 8 patients did not disclose patterns of regional metabolic change compatible with classical PD or an atypical parkinsonian variant. Similarly, network quantification revealed that PD-related pattern expression was not elevated in these patients as it was in an age- and duration-matched cohort with classical PD (P < 0.0001). None of these patients developed clinical signs of classical PD or of an atypical parkinsonian syndrome at a follow-up visit conducted 3 years after imaging. The results suggest that parkinsonian subjects with normal dopaminergic imaging do not have evidence of classical PD or an atypical parkinsonian syndrome.

Quantification of Parkinson's disease-related network expression with ECD SPECT

PURPOSE

Spatial covariance analysis has been used with FDG PET to identify a specific metabolic network associated with Parkinson's disease (PD). In the current study, we utilized a new, fully automated voxel-based method to quantify network expression in ECD SPECT images from patients with classical PD, patients with multiple system atrophy (MSA), and healthy control subjects.

METHODS

We applied a previously validated voxel-based PD-related covariance pattern (PDRP) to quantify network expression in the ECD SPECT scans of 35 PD patients, 15 age- and disease severity-matched MSA patients, and 35 age-matched healthy control subjects. PDRP scores were compared across groups using analysis of variance. The sensitivity and specificity of the prospectively computed PDRP scores in the differential diagnosis of individual subjects were assessed by receiver operating characteristic (ROC) analysis.

RESULTS

PDRP scores were significantly increased (p < 0.001) in the PD group relative to the MSA and control groups. ROC analysis indicated that the overall diagnostic accuracy of the PDRP measures was 0.91 (AUC). The optimal cutoff value was consistent with a sensitivity of 0.97 and a specificity of 0.80 and 0.71 for discriminating PD patients from MSA and normal controls, respectively.

CONCLUSION

Our findings suggest that fully automated voxel-based network assessment techniques can be used to quantify network expression in the ECD SPECT scans of parkinsonian patients.

Increased pre–SMA activation in early PD patients during simple self–initiated hand movements

The slowness of movement, termed bradykinesia, is one of the main symptoms of Parkinson's disease (PD). This symptom may be due to the inability of PD patients to maximise the speed of internally driven movements. The mesial premotor areas and in particular the pre-supplementary motor area (pre-SMA) seem to play a crucial role in the temporal initiation of movements in humans and animals. However, this activation seems to be debatable in imaging studies of PD patients. We performed a motor paradigm with temporally self-initiated movements in nine de novo PD patients before and after initiation of dopaminergic medication. The main finding was an increased activation of the pre-SMA in de novo PD patients compared with healthy age-matched control subjects. This result indicates the contribution of the pre-SMA in the temporal initiation of self-generated movements and in the disease pathology of PD. Increased bilateral activation of the superior cerebellum, mainly on the ipsilateral side, and a decreased activation of the ipsilateral inferior cerebellum in PD patients were also present. These findings provide new insights into the activation pattern of the cerebellum in PD patients.

Neuroimaging and therapeutics in movement disorders

In this review, we discuss the role of neuroimaging in assessing treatment options for movement disorders, particularly Parkinson's disease (PD). Imaging methods to assess dopaminergic function have recently been applied in trials of potential neuroprotective agents. Other imaging methods using regional metabolism and/or cerebral perfusion have been recently introduced to quantify the modulation of network activity as an objective marker of the treatment response. Both imaging strategies have provided novel insights into the mechanisms underlying a variety of pharmacological and stereotaxic surgical treatment strategies for PD and other movement disorders.

FDG PET in the differential diagnosis of parkinsonian disorders

The differential diagnosis of parkinsonian disorders can be challenging, especially early in the disease course. PET imaging with [(18)F]-fluorodeoxyglucose (FDG) has been used to identify characteristic patterns of regional glucose metabolism in patient cohorts with idiopathic Parkinson's disease (PD), as well as variant forms of parkinsonism such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBGD). In this study, we assessed the utility of FDG PET in the differential diagnosis of individual patients with clinical parkinsonism. 135 parkinsonian patients were referred for FDG PET to determine whether their diagnosis could be made accurately based upon their scans. Imaging-based diagnosis was obtained by visual assessment of the individual scans and also by computer-assisted interpretation. The results were compared with 2-year follow-up clinical assessments made by independent movement disorders specialists who were blinded to the original PET findings. We found that blinded computer assessment agreed with clinical diagnosis in 92.4% of all subjects (97.7% early PD, 91.6% late PD, 96% MSA, 85% PSP, 90.1% CBGD, 86.5% healthy control subjects). Concordance of visual inspection with clinical diagnosis was achieved in 85.4% of the patients scanned (88.4% early PD, 97.2% late PD, 76% MSA, 60% PSP, 90.9% CBGD, 90.9% healthy control subjects). This study demonstrates that FDG PET performed at the time of initial referral for parkinsonism accurately predicted the clinical diagnosis of individual patients made at subsequent follow-up. Computer-assisted methodologies may be particularly helpful in situations where experienced readers of FDG PET images are not readily available.

The role of functional neuroimaging in the differential diagnosis of idiopathic Parkinson's disease and multiple system atrophy

Parkinsonism is a symptom of a number of neurodegenerative disorders in the elderly. Even though clinical criteria for various parkinsonian disorders have been developed recently, the differential diagnosis of parkinsonian disorders based on clinical symptoms remains unsatisfactory, particularly in early disease stages. Early differential diagnosis on the other hand is important as prognosis and treatment options differ substantially. Multiple system atrophy (MSA) is one of the major differential diagnoses of idiopathic Parkinson's disease (PD). Radiotracer-based imaging methods such as positron emission tomography (PET) remain the established method for differential diagnosis of parkinsonian disorders. The following paper provides a review of different PET imaging methods for the differential diagnosis of PD and MSA patients.

Differentiation of idiopathic Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, and healthy controls using magnetization transfer imaging

The differentiation of multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) from idiopathic Parkinson's disease (IPD) is difficult. Magnetization transfer imaging (MTI), a measure that correlates with myelination and axonal density, was employed in this study in the attempt to distinguish between these disorders. Measurements were carried out in 15 patients with IPD, 12 patients with MSA, 10 patients with PSP, and in 20 aged-matched healthy control subjects. The main finding was a change in the magnetization transfer ratio in the globus pallidus, putamen, caudate nucleus, substantia nigra, and white matter in IPD, MSA, and PSP patients, matching the pathological features of the underlying disorder. Furthermore, stepwise linear discriminant analysis provided a good classification of the individual patients into the different disease groups. All IPD patients and control subjects were correctly separated from the MSA and PSP cohort, and all PSP patients and 11 of 12 MSA patients were correctly separated from the IPD and control cohort. There was also a fairly good discrimination of IPD patients from control subjects and of MSA from PSP patients. In conclusion, MTI revealed degenerative changes in patients with different parkinsonian syndromes matching the underlying pathological features of the different diseases, underlining the high potential of this method in distinguishing MSA and PSP from IPD.

The effect of free polymer on the interactions and the glass transition dynamics of microgel colloids

By studying the phase behaviour and the short range order of polystyrene microgel colloids in a good solvent we demonstrated that these particles can be considered as hard spheres or nearly hard spheres if the internal cross link density is made sufficiently high. A binary mixture of 1:50 crosslinked (1 crosslink per 50 monomers) particles with a size ratio R(small)/R(large) = 0.83 and a number ratio N(small)/N(large) = 2.7 was characterized with respect to the short range order and glass transition dynamics. We found that this mixture can be mapped onto a one-component hard sphere system with an effective polydispersity of 11%, even though for the particle interactions an inverse power potential u(r) alpha r(-35) was established. The only significant difference observed was a shift of the glass transition to a higher volume fraction of 0.595. Thus, the binary mixture was used as a non-crystallizing reference system to study the effect of free polymer on interactions and glass transition dynamics. Addition of linear polystyrene with a size ratio delta = R(g,polymer)/R(colloid) = 0.054 induced short-ranged depletion attractions between microgel particles. In the case of a glassy sample already a rather small amount of polymer leads to melting of the glass and a re-entrant glass transition is observed at high polymer content. From the difference of the line shapes of the density autocorrelation functions on approaching the different transition lines. measured over the full dynamic range, a change of the freezing mechanism from a packing-driven glass transition at low polymer content to a bonding-driven glass transition at high polymer content was deduced.

Re-entrant glass transition in a colloid-polymer mixture with depletion attractions

Performing light scattering experiments we show that introducing short-ranged attraction to a colloid suspension of nearly hard spheres by addition of a free polymer produces new glass-transition phenomena. We observe a dramatic acceleration of the density fluctuations amounting to the melting of a colloidal glass. Upon increasing the strength of the attractions the system freezes into another nonergodic state sharing some qualitative features with gel states occurring at lower colloid packing fractions. This re-entrant glass transition is in qualitative agreement with recent theoretical predictions.

Motivation for smoking cessation: what role do doctors play?

PRINCIPLES

Cigarette smoking causes an estimated 13% of all deaths in Switzerland. Though most smokers will eventually become ex-smokers of their own volition, physicians play an important role in accelerating the process of quitting among smoking patients. Even brief advice from physicians is effective in doing so. The purpose of this study was to investigate which smokers were asked about their smoking habits, and how often, whether they received advice to quit, and how this correlates with the patient's desire to quit.

METHODS

Telephone interviews were carried out with a random sample of smokers and ex-smokers from the German-speaking Swiss population (n = 993). We collected information on personal characteristics, smoking habits, and recall of physicians' advice. Data was analysed descriptively and by logistic regression.

RESULTS

88% recalled being asked by a doctor about their smoking habits. In contrast, only 34% of smoking patients recalled being advised to stop. Women, older people and those in poor subjective health were asked more frequently. Heavier smokers and those in poor subjective health were advised more frequently. Current smokers more frequently express the desire to quit if they are heavier smokers and have been advised to quit by their physician, compared with those who have not received such advice.

CONCLUSIONS

Similarly to the international findings, smoking patients in Switzerland receive brief advice with insufficient frequency. Action should therefore be taken to encourage health professionals not only to question all smoking patients but to advise and motivate them to quit smoking.

Motivation for smoking cessation: what role do doctors play?

PRINCIPLES

Cigarette smoking causes an estimated 13% of all deaths in Switzerland. Though most smokers will eventually become ex-smokers of their own volition, physicians play an important role in accelerating the process of quitting among smoking patients. Even brief advice from physicians is effective in doing so. The purpose of this study was to investigate which smokers were asked about their smoking habits, and how often, whether they received advice to quit, and how this correlates with the patient's desire to quit.

METHODS

Telephone interviews were carried out with a random sample of smokers and ex-smokers from the German-speaking Swiss population (n = 993). We collected information on personal characteristics, smoking habits, and recall of physicians' advice. Data was analysed descriptively and by logistic regression.

RESULTS

88% recalled being asked by a doctor about their smoking habits. In contrast, only 34% of smoking patients recalled being advised to stop. Women, older people and those in poor subjective health were asked more frequently. Heavier smokers and those in poor subjective health were advised more frequently. Current smokers more frequently express the desire to quit if they are heavier smokers and have been advised to quit by their physician, compared with those who have not received such advice.

CONCLUSIONS

Similarly to the international findings, smoking patients in Switzerland receive brief advice with insufficient frequency. Action should therefore be taken to encourage health professionals not only to question all smoking patients but to advise and motivate them to quit smoking.

[Blood titanium levels before and after oral administration titanium dioxide]

The normal titanium levels in the blood of males between 24 and 66 years of age were found to be 11.2 micrograms/l (rsd 4.1). After oral administration of titanium dioxide containing capsules or as powder (anatas) it could be observed that the material can be absorbed from the gastro-intestinal tract. If two titanium dioxide qualities, having different mean particle sizes (0.16 micron and 0.38 micron), are administered orally, the latter shows less absorption, most likely due to agglomeration phenomena. The blood concentration/time correlation shows the type of curves which are characteristic for a persorption mechanism of absorption and reveal a high individual fluctuation. An increase of the administered dose by twice the amount shows only a tendentious response in the corresponding blood levels. The method of analysis was ICP-AES. A pretreatment of the samples in order to eliminate the organic matrix is necessary.

The effect of combined oestrogen and progesterone replacement on the renal responses to oxytocin and vasopressin in ovariectomized rats

OBJECTIVE

Renal responsiveness to the neurohypophyseal hormones, oxytocin and vasopressin, has been shown in the rat to vary during pregnancy and lactation. A study was performed to determine whether ovarian steroids could contribute to the observed changes.

DESIGN

Using a previously validated method, fluid excretion during infusion of oxytocin or vasopressin was monitored in ovariectomized animals with and without chronic administration of oestrogen and progesterone.

METHODS

After 14 days treatment with vehicle or 12.5 mg hydroxyprogesterone caproate and 0.25 mg oestradiol valerate injected every 3 days, rats were infused with 0.077 mol/l NaCl for an equilibration period of approximately 2.5h. Timed urine collections for the determination of volume and electrolytes were then made during a control period of at least 45 min and for 60 min while the infusate was supplemented with vasopressin (40 fmol/min) or oxytocin (50 fmol/min). Further observations were made for a final 90 min of hypotonic saline infusion. In control infusions saline alone was given.

RESULTS

Treatment with ovarian steroids did not affect the volume of urine excreted during hormone infusion. Electrolyte excretion, however, was affected with lower concentrations of sodium and chloride on oxytocin infusion being seen in the steroid-treated animals. During vasopressin infusion, peak electrolyte concentrations were also achieved later in this group of animals.

CONCLUSION

The increased circulating concentrations of oestrogen and progesterone seen during pregnancy could contribute to variations in the natriuretic response to neurohypophyseal hormones observed in the rat.

Tight binding of bulky fluorescent derivatives of adenosine to the low affinity E2ATP site leads to inhibition of Na+/K+-ATPase. Analysis of structural requirements of fluorescent ATP derivatives with a Koshland-Némethy-Filmer model of two interacting ATP sites

A Koshland-Némethy-Filmer model of two cooperating ATP sites has previously been shown to explain the kinetics of inhibition of Na+/K+-ATPase (EC 3.6.1.37) by dansylated ATP (Thoenges, D., and Schoner, W. (1997) J. Biol. Chem. 272, 16315-16321). The present work demonstrates that this model adequately describes all types of interactions and kinetics of a number of ATP analogs that differ in their cooperativity of the high and low affinity ATP binding sites of the enzyme. 2',3'-O(2,4,6-trinitrophenyl)ATP binds in a negative cooperative way to the E1ATP site (Kd = 0.7 microM) and to the E2ATP site (Kd = 210 microM), but 3'(2')-O-methylanthraniloyl-ATP in a positive cooperative way with a lower affinity to the E1ATP binding site (Kd = 200 microM) than to the E2ATP binding site (Kd = 80 microM). 3'(2')-O(5-Fluor-2,4-dinitrophenyl)-ATP, however, binds in a noncooperative way, with equal affinities to both ATP binding sites (Kd = 10 microM). In a research for the structural parameters determining ATP site specificity and cooperativity, we became aware that structural flexibility of ribose is necessary for catalysis. Moreover, puckering of the ring atoms in the ribose is essential for the interaction between ATP sites in Na+/K+-ATPase. A number of derivatives of 2'(3')-O-adenosine with bulky fluorescent substitutes bind with high affinity to the E2ATP site and inhibit Na+/K+-ATPase activity. Evidently, an increased number of interactions of such a bulky adenosine with the enzyme protein tightens binding to the E2ATP site.

Suspected malignant hyperthermia in a 13-month-old: today's "typical" episode--a case report

A case of suspected malignant hyperthermia in a 13-month-old female, to whom succinylcholine was not administered, is presented. The patient presented for a repair of the right radial nerve under general anesthesia. Induction was accomplished with halothane, nitrous oxide, and oxygen. Tracheal intubation was facilitated with intravenous vecuronium. Controlled ventilation was initiated, and anesthesia was maintained with isoflurane, nitrous oxide, oxygen, morphine sulfate, and vecuronium. At the conclusion of the surgical procedure, an abrupt increase in ETCO2, an elevation in body temperature, and a mixed acidosis was observed. Resolution of symptoms followed the administration of dantrolene sodium. The patient underwent an uneventful postoperative recovery and was discharged home. It was felt that the patient was too young to undergo a muscle biopsy for a caffeine-halothane stimulation test.

[Outcome of corneal astigmatism after pars plana vitrectomy with or without simultaneous cataract extraction]

Changes in corneal astigmatism induced by pars plana vitrectomy (PPV) (group I, 44 eyes) and PPV combined with no-stitch cataract surgery (group II, 20 eyes) were studied prospectively for a period of at least 3 months. The amount and orientation of the keratometric cylinder and the surgically induced astigmatism (according to the methods of Jaffe and Clayman or Naeser) were analysed. In the first postoperative week both groups exhibited a marked against-the-rule to oblique astigmatism (in group I up to 3.65 +/- 1.40 D, in group II up to 3.05 +/- 1.60 D, according to Jaffe). After 3 months this had declined in group I to 0.40 +/- 0.27 D, whereas a slight induced astigmatism (0.97 +/- 0.41 D) persisted in group II. Gas endotamponade did not significantly aggravate the postoperative astigmatism in either group. Computerized video-keratography generally revealed an asymmetric bowtie pattern during the first week. Our results show that PPV alone induces no appreciable long-term corneal astigmatism. Optical rehabilitation, however, can be delayed by a marked short-term postoperative astigmatism. PPV with simultaneous no-stitch cataract surgery, by contrast, was found to induce a persisting slight astigmatism against the rule.

[Micelle formation as the origin of the cut-off phenomenon in a homologous series of local anesthetics]

On the example of the surface anaesthetic homologous series of 4-alkoxybenzoic-diethylaminoethylester-HCl (parethoxycaine) the so-called "cut off"-effect was studied. The "cut off"-effect is the phenomenon, that a weaker efficiency or an inefficiency is observed on the higher homologues of therapeutic substances. It is demonstrated that the "cut off"-effect is referred to the micellisation and aggregation of the higher homologues of the local anaesthetics in aqueous solution. This has the consequence, that the higher homologues cannot diffuse on the pain receptors and so the efficiency is reduced. By the addition of urea the aggregation will be reduced and the chain length-efficiency curve will take a different course.