[Optimal rigidity of the protein structure: three classes of rigidity in the eubacterial RecA protein family].
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Adenosine Triphosphatases↗
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Comparison of RigiScan and formal nocturnal penile tumescence testing in the evaluation of erectile rigidity.
Evaluation of male erectile function ideally should include measurement of axial rigidity expressed as grams force required to produce penile buckling. An axial rigidity more than 550 gm. is generally considered adequate for vaginal penetration. Unfortunately, this test cannot be done frequently and may disrupt sleep. An alternative method of determining rigidity is to use the RigiScan,* which makes repetitive measurements of radial rigidity at the base and tip of the penis expressed as per cent of normal maximum. Previous studies have demonstrated a positive correlation between axial and radial rigidity measurements but they have not been compared in patients with a wide range of erectile function. We performed a prospective study in a consecutive series of patients presenting with impotence comparing axial rigidity measured with a tonometer and radial rigidity measured by RigiScan. Erectile rigidity also was evaluated by a trained, blinded observer. Overall, RigiScan base and tip radial rigidity correlated well with axial rigidity (p < 0.002) and observer ratings (p < 0.003); axial rigidity similarly correlated well with observer ratings (p < 0.0001). However, when RigiScan base and tip radial rigidity exceeded 60% of maximum, there was a poor correlation with axial rigidity and observer ratings (p > 0.1). In this range, the RigiScan failed to discriminate axial rigidities between 450 and 900 gm. buckling force; however, axial rigidity in this same range again correlated well with observer ratings (p < 0.0001). Since an axial rigidity of more than 550 gm. is considered adequate for vaginal penetration, the RigiScan may not be able to detect mild abnormalities in erectile function. Further study is in progress to evaluate the significance of these findings but presently a RigiScan measurement of radial rigidity in excess of 60% of maximum should be interpreted cautiously and not necessarily regarded as normal. In this range further measurements of axial rigidity or observer ratings of rigidity may be necessary to establish the diagnosis.
Erectile Dysfunction↗
[Axial (neck and trunk) rigidity in Parkinson's disease, striatonigral degeneration and progressive supranuclear palsy].
Our previous study showed that the alternating knee tilt test in supine position is a useful method to assess the trunk rigidity. We investigated the progression of axial (neck and trunk) rigidity in Parkinson's disease (PD), striatonigral degeneration (SND), and progressive supranuclear palsy (PSP) by using this method. We assessed rigidity on a scale of 0 (absent) to 3 (severe) on five parts of the body: neck, trunk, wrist, elbow and knee in 57 patients with PD, 13 patients with SND and 18 patients with PSP. In PD patients, the degree of neck and trunk rigidity correlated well with the duration of disease and the staging scale. There was neck rigidity in 27% of PD patients with unilateral involvement of the limbs, but the trunk tonus was normal in them. There was rigidity in the neck and trunk of all PD patients with bilateral involvement of the limbs. When the limb rigidity was predominant on one side, the trunk rigidity was predominant on the opposite side. In SND patients, the degree of neck and trunk rigidity roughly correlated with the duration of disease and the staging scale. In SND patients with unilateral involvement of the limbs, tonus of the neck and trunk was normal. In SND patients with bilateral involvement of limbs, there was rigidity in both the neck and the trunk. In PSP patients, the degree of neck rigidity correlated well with the duration of disease and the staging scale, but the degree of rigidity in the trunk and limb remained relatively mild even at the advanced stage. Accordingly, in PSP patients there was a dissociation of the degree of neck rigidity from that of trunk and limb rigidity. In conclusion, the assessment of axial (neck and trunk) rigidity may be useful for the clinical diagnosis of parkinsonism and the staging scale scoring.
Adult↗
Is there a role of radial rigidity in the evaluation of erectile dysfunction?
RigiScan has been the most widely utilized device for measuring erectile rigidity. However, the use of the RigiScan in the evaluation of erectile dysfunction has questionable because the RigiScan device does not directly determine axial rigidity. The aim of this study is to clarify that radial rigidity measured by RigiScan reflects the intracorporeal pressure and erectile capability efficiently. From January 1998 to May 1999, a total of 23 patients with erectile dysfunction were involved in the study. They were evaluated by RigiScan and duplex ultrasonography after intracorporeal injection of prostaglandin E1. We investigated the relationship between radial rigidity and the resistance index. The results of radial rigidity were also compared with that of the degree of erection. For the entire group, significant correlations were found between radial rigidity and the resistance index (r=0.680, P<0.001 for tip rigidity; r=0.703, P<0.001 for base rigidity). In addition, for 12 patients whose tip rigidity exceeded 60% and for 10 whose base rigidity exceeded 60%, the correlations between radial rigidity and the resistance index remained (r=0.659, P=0.020 for tip rigidity; r=0.759, P=0.011 for base rigidity). Based on the response determined by patients, radial rigidity represented the degree of erection efficiently. Our findings suggest that RigiScan is a useful diagnostic tool. Radial rigidity represents the intracorporeal pressure efficiently and has an acceptable role in the evaluation of erectile dysfunction.
Adult↗
The role of rigid vs. dynamic instrumentation for stabilization of the degenerative lumbosacral spine.
PURPOSE OF THE STUDY: This is a prospective comparative randomised study to compare the immediately postoperative effects of a rigid versus dynamic instrumentation for degenerative spine disease and stenosis on the standing sagittal lumbar spine alignment and to investigate if a dynamic spine system can replace the commonly used rigid systems in order to avoid the above mentioned disadvantages of rigid fixation. MATERIAL & METHODS: 15 randomly selected patients received the rigid instrumentation SCS and an equal number of randomly selected patients the dynamic TWINFLEX device for spinal stenosis associated degenerative lumbar disease. The age of the patients, who received rigid and dynamic instrumentation was 65 +/- 9 years and 62 +/- 10 years respectively. All patients had standing spine radiographs preoperatively and three months postoperatively. The parameters that were measured and compared pre- to postoperatively were: lumbar lordosis (L1-S1), total lumbar lordosis (T12-S1), sacral tilt, distal lordosis (L4-S1), intervertebral angulation, vertebral inclination and disc index. RESULTS: The instrumented levels in the spines that received rigid and dynamic instrumentation were 3.5 +/- 0.53 and 3 +/- 0.7 respectively. The instrumented levels from L3 to L5 were 23, the lumbosacral junction was instrumented in 3 patients of group A and in 4 patients of group B. Lumbar lordosis did not significantly change postoperatively, while total lordosis was significantly (P=0.04) increased in the patients who received the rigid instrumentation, while it was significantly (P=0.012) decreased in the group B. Intervertebral angulation of the non-instrumented level L1-L2 was increased in the group A (P=0.01), while the dynamic instrumentation increased (P=0.02) the intervertebral inclination of the adjacent level L2-L3, immediately above the uppermost instrumented level. Distal lordosis and sacral tilt did not change in any patient in both groups. Both instrumentations did not change the lateral vertebral inclination of L1 to L5 vertebrae. Rigid instrumentation increased the lordotic inclination of L5 (P=0.03) and of S1 (P=0.03). Rigid instrumentation increased (P=0.04) the intervertebral angulation at the uppermost instrumented level L3-L4 The most significant change in vertebral angulation was achieved at the instrumented level L4-L5 by the dynamic (P=0.007) and rigid (0.05). The disc index at the level L2-L3 was increased by both instrumentation [dynamic P=0.007 and rigid (P=0.02)]. The index L3-L4 was increased following dynamic fixation (P=0.0007). The disc index L4-L5 was postoperatively increased by both types of instrumentation (rigid P=0.006, dynamic P=0.02). The disc index L5-S1 did not significantly change postoperatively by either system. CONCLUSION: Both rigid and dynamic instrumentations restored lumbar lordosis, sacral tilt, distal lordosis and increased the foraminal diameter at the level L4-L5 resulting in an indirect decompression of the nerve roots at this level . Both rigid and dynamic instrumentations applied in the lumbosacral spine to treat degenerative disease secured L3 to S1 sagittal spine profile close to preoperative levels, that should theoretically guarantee a pain-free postoperative course. This study supports the belief that the dynamic system can be used with the same indications with the rigid in degenerative lumbar spine because it can offer equally good short-term results regarding sagittal spine alignment while simultaneously it has the previously mentioned advantages (avoidance stress shielding etc).
Aged↗
Relationship between electromyographic activity and clinically assessed rigidity studied at the wrist joint in Parkinson's disease.
The electromyographic (EMG) patterns recorded from wrist muscles during manually applied, repetitive flexion and extension movements of the wrist joint, used for simultaneous clinical assessment of rigidity, were studied in patients with Parkinson's disease and healthy subjects. Recordings were made whilst patients/subjects attempted voluntarily to relax the muscle of the arm whose wrist joint was manipulated. Individual patients were investigated before and at varying times after their routine daily medication as their clinical rigidity underwent associated modulations. It was often possible to induce additional alterations in clinical rigidity by instructing patients to perform an activation or Jendrassik-like manoeuvre (clenching the contralateral fist). In rigid patients, the approximately sinusoidal wrist displacements (60 deg, 1-1.5 Hz) typically elicited pronounced, cyclic modulations of EMG activities in wrist flexors and extensors; increases in EMG activity were phase-locked to the respective periods of muscle stretch. Stretch-related EMG activity reduced or disappeared as rigidity was abolished by drug therapy. The EMG patterns of patients showing cogwheel rigidity featured discrete, phasic bursts superimposed upon more generalized stretch-related increases in activity. In healthy subjects, showing no clinical rigidity, the pronounced cyclic modulations of EMG activity characteristic of rigid patients were absent during similar manually applied wrist displacements. Quantitative EMG measurements for individual patients, made 'on' and 'off' medication and as their rigidity fluctuated, indicated that mild (grade 1) and moderate (grade 2) rigidity was consistently associated with increased stretch-related activity compared with non-rigid conditions. Pair-wise statistical analysis indicated such increases in EMG to be significant. Similarly, the ratios of EMG activities in the stretched versus released muscles were significantly greater for grades 1 and 2 rigidity than in the absence of rigidity. Overall, the present findings support the view that enhancement of stretch reflex activity has a major role in the genesis of parkinsonian rigidity.
Aged↗
Fentanyl-induced rigidity and unconsciousness in human volunteers. Incidence, duration, and plasma concentrations.
BACKGROUND: Muscle rigidity frequently accompanies induction of anesthesia with opioids. The authors sought to determine whether unconsciousness and amnesia occur when humans develop rigidity and apnea after intravenous fentanyl (without other concomitant anesthetics). METHODS: The incidence and duration of rigidity and level of consciousness were evaluated and associated plasma concentrations of fentanyl were measured in 12 healthy adult male volunteers given only intravenous fentanyl. Fentanyl was infused at a rate of 150 micrograms/min until a total of 15 micrograms/kg had been administered. Arterial blood samples for fentanyl assay were drawn and responsiveness, heart rate (HR), and systolic and diastolic arterial blood pressures were determined at frequent intervals during and after infusion. If rigidity was accompanied by an Spo2 < 90%, positive pressure ventilation with 100% O2 with a mask was instituted until spontaneous ventilation resumed. RESULTS: The incidence of muscular rigidity was 50% (6/12). All subjects who developed rigidity were apneic, unresponsive, and had no recall of commands to breathe or of positive pressure ventilation. Subjects not developing rigidity remained awake and responsive. No subject developing rigidity required neuromuscular blockade to allow positive pressure ventilation and adequate oxygenation (Spo2 > 90%). When rigidity occurred, it started 3 +/- 0.9 (range 1-4) min after the peak plasma fentanyl concentration and lasted for 11.5 +/- 5.8 (range 7-23) min. Rigidity started at a plasma fentanyl concentration of 21.5 +/- 4.4 (range 16-28) ng/ml and ended at 6.9 +/- 1.5 (range 5.2-8.7) ng/ml. Baseline HR was less in the subjects who subsequently developed rigidity (56.7 +/- 7.8 vs. 67.2 +/- 7.8 P = 0.04). No differences in fentanyl plasma concentrations or predicted effect site concentrations for rigidity were detected between subjects who developed rigidity and those who did not. CONCLUSIONS: These findings support the hypothesis that unconsciousness occurs in the unstimulated subject during fentanyl-induced apnea and rigidity.
Adult↗
Axial penile buckling forces vs Rigiscan radial rigidity as a function of intracavernosal pressure: why Rigiscan does not predict functional erections in individual patients.
AIM: An improved understanding of the relationship between radial and axial rigdity values would enable better appreciation of the clinical usefulness of RigiScantrade mark, the most widely utilized determination of erectile rigidity testing. Previous studies have shown that axial rigidity (measured by buckling forces) correlated well with radial rigidity (measured by RigiScantrade mark) for radial rigidity values below 60%. For radial rigidity exceeding 60%, there was poor correlation. Heretofore, there has been no physiologic explanation of this phenomenon. METHODS: During dynamic pharmacocavernosometry in 36 impotent patients, we investigated the relationship between axial buckling forces and RigiScan radial rigidity and, for the first time, how they both vary with pressure, (which we varied over over a wide functional range). In addition, we recorded multiple penile length and diameter values enabling us to relate, also for the first time, axial and radial rigidity to individual mechanical erectile tissue and penile geometric properties. RESULTS: Marked differences were found in the manner RigiScan radial rigidity units and axial buckling force magnitudes increased with increases in intracavernosal pressure values in each individual. The former asymptotically approached a maximum finite value while the latter increased continuously towards infinity. Based on data in this study, RigiScan radial rigidity values greater than 55% may be considered a necessary criteria for vaginal intromission capability in all partners but it is not a sufficient one. CONCLUSIONS: Axial and radial rigidity share a common dependency upon intracavernosal pressure, however, they are also dependent upon other unique physical determinants. For axial rigidity, additional dependent variables include cavernosal erectile tissue properties and penile geometry, while for radial rigidity, this may include tunical surface wall tension properties. Clinical devices which assess functional penile rigidity should utilize axial and not radial rigidity testing.
Equipment Design↗
The effect of decerebrate rigidity on intracranial pressure in man and animals.
UNLABELLED: Patients with decerebrate rigidity frequently show intracranial hypertension. The factors responsible for this effect and their inter-relationships were explored in cats and in patients with head injuries. ANIMALS: The factors examined, separately and in combination, were elevation of central venous, intrathoracic, intra-abdominal and systemic arterial pressures. The baselines thus established were used for the investigation of the effects of these factors on the intracranial pressure (ICP) in cats which had been rendered decerebrate by focal stereotactic mesencephalic lesions. Little or no change occurred in the ICP when: Rigidity was mainly unilateral. Bilateral limb rigidity was extreme. Persistent elevation of ICP occurred when: Truncal rigidity resulted in the simultaneous elevation of the intrathoracic and intra-abdominal pressures. Elevation of the systemic arterial pressure occurred in the presence of defective cerebrovascular homeostasis. Human: The dynamics and management of the complex clinical problem posed by decerebrate rigidity were investigated in patients with head injuries who exhibited well-developed bilateral rigidity under conditions of altered cerebral elastance. Rigidity was quantified by measuring the resonant frequency of the wrist induced by a printed-circuit motor. The brain elastance, ICP, intrathoracic and blood pressures were measured throughout the study. The effect of pharmacological muscle paralysis on the ICP and rigidity was examined. It appeared that well-developed decerebrate rigidity increased the ICP. The relationship was direct; the greater the rigidity or cerebral elastance, the greater the rise in ICP and vice versa. The two factors mainly responsible were muscle hypertonicity and cerebral elastance. The rises in ICP were caused by the rigidity and although it may not always be possible to reduce the abnormally increased elastance, the rigidity can certainly be abolished. As long as the cerebral vascular homeostatic mechanisms were intact, spontaneous waning of the rigidity or its abolition by muscle relaxants returned the ICP to its previous resting level. Pancuronium produced much deeper and more lasting relaxation than either diazepam or chlorpromazine. During the period of mechanical ventilation, alterations in ICP were of prognostic value as regards the outcome of the injuries.
Adolescent↗
Picosecond timescale rigid-helix and side-chain motions in deoxymyoglobin.
The contribution of rigid-body motions to the atomic trajectories in a 100 ps molecular dynamics simulation of deoxymyoglobin is examined. Two types of rigid-body motions are considered: one in which the helices are rigid units and one in which the side-chains are rigid units. Using a quaternion-based algorithm, fits of the rigid reference structures are made to each time frame of the simulation to derive trajectories of the rigid-body motions. The fitted trajectories are analysed in terms of atomic position fluctuations, mean-square displacements as a function of time, velocity autocorrelation functions and densities of states. The results are compared with the corresponding quantities calculated from the full trajectory. The relative contribution of the rigid helix motions to the helix atom dynamics depends on which quantity is examined and on which subset of atoms is chosen; rigid-helix motions contribute 86% of the rms helix backbone atomic position fluctuations, but 30% of the helix atom (backbone and side-chain) mean square displacements and only 1.1% of total kinetic energy. Only very low-frequency motions contribute to the rigid-helix dynamics; the rigid-body analysis allows characteristic rigid-helix vibrations to be identified and described. Treating the side-chains as rigid bodies is found to be an excellent approximation to both their diffusive and vibrational mean-square displacements: 96% of side-chain atom mean-square displacements originate from rigid side-chain motions. However, the errors in the side-chain atomic positional fits are not always small. An analysis is made of factors contributing to the positional error for different types of side-chain.
Computer Simulation↗
Comparison of rigid and flexible transbronchial needle aspiration in the staging of bronchogenic carcinoma.
In staging bronchogenic carcinoma by transbronchial needle aspiration (TBNA), rigid histology needles are generally preferred to flexible cytology needles owing to the widespread opinion that rigid needles have higher diagnostic yield and less false-positive results. The objective of this study was to compare the efficacy and safety of the rigid and flexible TBNAs in staging bronchogenic carcinoma to establish whether a flexible cytology needle method can replace the rigid needle. A prospective study was conducted in 138 consecutive patients with extra- or endobronchial masses suggestive of bronchogenic carcinoma and amenable to surgical procedures. All 8 mm and larger paratracheal, carinal, hilar and/or main bronchial lymph nodes determined before bronchoscopy by computed tomography (CT) were sampled by successive 18-gauge rigid and 21-gauge flexible TBNAs in the same session. The anatomic landmarks were followed precisely during TBNAs, and a proper technique applied in sampling and specimen processing. Malignant lymph node involvement was specified in 97 (72%) cases of bronchogenic carcinoma by rigid, and in 89 (66%) by flexible TBNA. There were 4 (100%) benign cases (3 with tuberculosis and 1 with sarcoidosis) of 101 (73%) with positive rigid TBNAs (82 with histological and 19 with cytological specimens). TBNAs determined malignant lymph node involvement in a total of 104 (78%) patients. Of 30 TBNA-negative patients, 14 were proven to have false-negative TBNAs by mediastinoscopy/mediastinotomy/minithoracotomy, and 16 to have true-negative TBNAs by thoracotomy. Thoracotomy confirmed true positivity in 52 rigid and 49 flexible TBNAs, and false negativity in 4 rigid and 7 flexible TBNAs. Further staging was confirmed in these 7 cases. Four had proven false-negative results by both methods. The presence of small cell carcinoma (21) or N3 disease (27) presented a contraindication to thoracotomy in 48 TBNA-positive patients. Adequate-quality and malignant lymph node specimens were more frequently obtained by both techniques at advanced tumor and node stages. However, malignant lymph node invasion was significantly more frequent in rigid and flexible TBNA specimens only in the presence of advanced tumor status and abnormal endoscopic appearance. The sensitivities of rigid and flexible TBNAs were 74 and 70%, respectively (p > 0.05), but both had a specificity of 100%. Neither false-positive results nor serious complications other than hemorrhage of 30-100 ml (rigid: 5%, flexible: 2%) were encountered with either technique. These results indicate that in bronchogenic carcinoma, hilar and mediastinal lymph nodes can be staged by 21-gauge flexible TBNA (76%) as accurately as by 18-gauge rigid TBNA (79%) if a proper technique is applied and anatomic landmarks are followed precisely (p > 0.05).
Adult↗
Objective quantification of resting and activated parkinsonian rigidity: a comparison of angular impulse and work scores.
The clinical assessment of rigidity is influenced by a number of variables which limit the reproducibility of rating scores and the usefulness of comparisons between subjects. We evaluated an objective measure of rigidity which uses unpredictable but reproducible limb perturbations mimicking the waveform, rate, and amplitude of those used in the clinical examination; and evaluates total resistive force, thus avoiding assumptions about the relative influence of elastic, viscous, or inertial components of the measured resistive forces on the genesis of rigidity. We then used this measure to quantify the effects of an activation procedure on parkinsonian rigidity, because this forms an important but poorly understood part of the routine clinical examination. We studied 20 patients with a clinical diagnosis of Parkinson's disease and 10 age-matched control subjects. A torque motor was used to deliver reproducible, transient, sinusoidal perturbations varying between 1.0 and 1.5 Hz. To quantify rigidity, we calculated angular impulse scores, which reflect the relationship between change in total resistive torque and time. Angular impulse scores were compared with work scores, which have previously been found to correlate with clinical assessments of rigidity. All subjects were studied at rest and with activation. Angular impulse scores were more consistently correlated with rigidity and more clearly differentiated between patients and control subjects than work scores. Activation increased both clinical and objective rigidity scores; activated angular impulse scores ranged from approximately 100%-200% of resting values. When plotted against clinical rigidity scores, activated angular impulse scores lay on a continuum with resting values. We conclude that angular impulse is a valid objective measure of parkinsonian rigidity. Activation increases rigidity, but to varying degrees in different patients. To improve the sensitivity and reproducibility of clinical rigidity assessments, parkinsonian rating scales should include separate resting and activated scores.
Aged↗
Comparative clinical performance of rigid versus soft hyper Dk contact lenses used for continuous wear.
PURPOSE: The purpose of this study is to investigate the comparative clinical performance of two hyper Dk contact lenses: a silicone hydrogel lens (Focus Night & Day, Ciba Vision) and a rigid lens (Z-alpha, Menicon Co. Ltd.) when worn for up to 30 days of continuous wear (CW). The rigid lens was worn on an unplanned replacement basis, whereas the soft lens was replaced monthly. METHODS: One hundred subjects were recruited. Fifty neophyte subjects were randomly assigned into one of the lens types (25 subjects per lens type). Twenty-five existing daily wear (DW) rigid lens users wore the rigid study lens and 25 existing DW soft lens users wore the soft study lens. Visual acuity, lens fit, keratometry, refraction, lens surface assessment, physiological response, and subjective response were investigated at baseline and after 1 week of DW and 24 hours, 1 week, and 1, 3, 6, 9, and 12 months of CW. Analysis compared lens type (rigid vs. soft) and subject group (experienced vs. neophyte). RESULTS: Sixty-eight subjects completed the study. Visual acuity was similar for the two lens types and subject groups. Lens fit was judged to be adequate in all subjects. Corneal curvature of subjects in the rigid groups became flatter by 0.13 mm compared with 0.04 mm for subjects in the soft lens groups (F = 14.7, p = 0.0003); the refractive findings mirrored these corneal changes. The increasing rate of deposition on rigid lenses was consistent with the fact that these lenses were not replaced during the study. Conjunctival hyperemia and staining were similar for the two lens types but greater among experienced wearers at baseline (F = 13.8, p = 0.0005; F = 5.3, p = 0.02, respectively). Corneal staining was higher for the rigid lens wearers (F = 5.6, p = 0.02) but this was mainly the result of the initial higher scores in the rigid lens experienced group. The change in papillary conjunctivitis was greater for subjects in the soft lens groups than rigid lens groups (F = 4.6, p = 0.04). Comfort was initially lower for the rigid lens neophyte group (F = 4.2, p = 0.0001), but after the CW phase started, there were no differences between groups. CONCLUSIONS: Notwithstanding subtle differences in physiological responses, continuous wear hyper Dk rigid and soft silicone-containing contact lenses can be successfully worn by both those with previous contact lens experience and those with no history of contact lens wear.
Adult↗
Rigid-cluster models of conformational transitions in macromolecular machines and assemblies.
We present a rigid-body-based technique (called rigid-cluster elastic network interpolation) to generate feasible transition pathways between two distinct conformations of a macromolecular assembly. Many biological molecules and assemblies consist of domains which act more or less as rigid bodies during large conformational changes. These collective motions are thought to be strongly related with the functions of a system. This fact encourages us to simply model a macromolecule or assembly as a set of rigid bodies which are interconnected with distance constraints. In previous articles, we developed coarse-grained elastic network interpolation (ENI) in which, for example, only Calpha atoms are selected as representatives in each residue of a protein. We interpolate distance differences of two conformations in ENI by using a simple quadratic cost function, and the feasible conformations are generated without steric conflicts. Rigid-cluster interpolation is an extension of the ENI method with rigid-clusters replacing point masses. Now the intermediate conformations in an anharmonic pathway can be determined by the translational and rotational displacements of large clusters in such a way that distance constraints are observed. We present the derivation of the rigid-cluster model and apply it to a variety of macromolecular assemblies. Rigid-cluster ENI is then modified for a hybrid model represented by a mixture of rigid clusters and point masses. Simulation results show that both rigid-cluster and hybrid ENI methods generate sterically feasible pathways of large systems in a very short time. For example, the HK97 virus capsid is an icosahedral symmetric assembly composed of 60 identical asymmetric units. Its original Hessian matrix size for a Calpha coarse-grained model is >(300,000)(2). However, it reduces to (84)(2) when we apply the rigid-cluster model with icosahedral symmetry constraints. The computational cost of the interpolation no longer scales heavily with the size of structures; instead, it depends strongly on the minimal number of rigid clusters into which the system can be decomposed.
Algorithms↗
The relationship of penile rigidity and intracavernous vascular resistance in potent men during intracavernous pharmacological testing.
PURPOSE: We studied the relationship of penile rigidity and intracavernous vascular resistance in potent men during intracavernous pharmacological testing. MATERIALS AND METHODS: Enrolled in our study were 19 potent men undergoing intracavernous pharmacological testing for various reasons. Hemodynamic changes in response to the intracavernous injection of 20 microg. prostaglandin E1 were assessed by color Doppler sonography with simultaneous RigiScan (Dacomed Corp., Minneapolis, Minnesota) monitoring of penile rigidity. The relationship of penile rigidity and intracavernous vascular resistance was determined by correlating hemodynamic data with recorded penile rigidity values. RESULTS: Maximal mean rigidity plus or minus standard deviation of the penile tip and base after intracavernous injection of prostaglandin E1 was 76.8% +/- 8.5% and 97.3% +/- 4.7%, respectively. Penile tip and base rigidity correlated positively with the resistive index (r = 0.69 and 0.75, p <0.0001) and negatively with end diastolic velocity (r = -0.62 and -0.70, respectively, p <0.0001). The formula, rigidity = -128 + 195 x resistive index, was derived to describe the linear regression of penile base rigidity and the resistive index. The formula, rigidity = 59.8 - 3.3 x end diastolic velocity, was derived to describe the linear regression of penile base rigidity and end diastolic velocity. CONCLUSIONS: Penile rigidity correlated strongly with intracavernous vascular resistance in potent men during intracavernous pharmacological testing. The resistive index and end diastolic velocity of the cavernous arteries may each be used to estimate penile rigidity quantitatively.
Adult↗
The role of the nucleus raphe pontis and the caudate nucleus in alfentanil rigidity in the rat.
Attempts to eliminate or reduce the rigidity induced with high-dose narcotic anesthesia in the operating room have been only partially successful. Previous investigations of opioid receptor sites mediating this rigidity have implicated two central regions: the nucleus raphe pontis (NRP) within the reticular formation and the caudate nucleus (CN) within the basal ganglia. The present study used systemically administered alfentanil (ALF), a potent, short-acting fentanyl analog, and intracerebrally infused methylnaloxonium (MN), a quaternary derivative of naloxone, to elucidate further the functional role of the NRP and CN in rigidity. ALF (0.5 mg/kg s.c.) produced a reliable model of rigidity, as documented by gastrocnemius electromyography. The onset of this rigidity was within 60 s of ALF administration, with a total duration of approximately 40-50 min. Intracerebroventricular (i.c.v.) injections of 2.0 or 4.0 micrograms of MN 15 min prior to ALF treatment prevented rigidity, while 0.125 or 0.5 microgram had no significant effect on rigidity. MN injected directly into the NRP at doses as low as 0.125 microgram significantly antagonized ALF-induced rigidity, while injections of MN into the caudate nucleus at doses as high as 4.0 micrograms failed to antagonize ALF-induced rigidity. These observations demonstrate that injection of MN into the NRP is at least 16-fold more effective in blocking ALF-induced rigidity than MN injected into the ventricle and, more importantly, at least 32-fold more effective than MN injected into the CN. The results suggest that the NRP may be an important site for the neural control of muscular rigidity associated with high-dose narcotic administration.
Alfentanil↗
Transmission of group II heteronymous pathways is enhanced in rigid lower limb of de novo patients with Parkinson's disease.
A potent heteronymous excitation of quadriceps motoneurones via common peroneal group II afferents has recently been demonstrated in normal subjects. The aim of this study was to investigate whether this group II excitation contributes to rigidity in Parkinson's disease. The early and late facilitations of the quadriceps H reflex elicited by a conditioning volley to the common peroneal nerve (CPN) at twice motor threshold, attributed to non-monosynaptic group I and group II excitations, respectively, were investigated. The comparison was drawn between results obtained in 20 "de novo" patients with Parkinson's disease (hemiparkinsonian, 17; bilateral, three) and 20 age-matched normal subjects. There was no statistically significant effect of "group" (patients/controls), "duration", "global severity" [Unified Parkinson's Disease Rating Scale (UPDRS)] or "side" (unilaterally versus bilaterally affected) factors on either group I or group II facilitations. To further the analysis, the factors of status (affected or non-affected limb), akinesia (lower limb akinesia score) and rigidity (lower limb rigidity score) were entered in a general linear model to explain the variations of the quadriceps H reflex facilitation. Rigidity was the only factor useful in predicting the value of the group II facilitation of the quadriceps H reflex (P < 0.007). Group I and group II facilitation was then compared between the rigid, non-rigid and control lower limbs [multivariate analysis of variance (MANOVA)]. Results are represented as mean +/- SEM (standard error of the mean). Group II facilitation was enhanced in the rigid lower limb of unilaterally affected patients (153.2 +/- 7% of control H reflex) compared with non-rigid lower limbs (124 +/- 4% of control H reflex; P < 0.007) or control lower limbs (126.1 +/- 4.1%; P < 0.01). There was no difference between the non-rigid lower limbs of the unilaterally affected patients and the control lower limbs, but a difference was observed between the rigid lower limbs of unilaterally less affected and bilaterally more affected patients (153.2 +/- 7% and 123.8 +/- 7.5% of control H reflex, respectively; P < 0.04). These results suggest a facilitation of the transmission in the interneuronal pathway activated by group II afferents in rigid lower limb of de novo hemiparkinsonian patients, probably resulting from a change in their descending monoaminergic inhibitory control.
Adult↗
[Muscular rigidity caused by alfentanil: prevention].
We studied three groups of 30 patients each, undergoing minor orthopaedic surgery, anaesthetized with alfentanil (30 micrograms/kg bolus followed by an infusion of 0.3 micrograms/kg/min), thiopental 3 mg/kg and 70% N2O via facial mask. Patients in group I were treated, three minutes before induction, with vecuronium 0.02 mg/kg i.v., while those in group II were premedicated with diazepam 0.15 mg/kg i.m. 30-45 minutes before induction. Group III served as control. Muscular rigidity was evaluated clinically with a subjective score based on a scale of 0 (no rigidity) to 3 (severe rigidity). Diazepam did not give significant protection from muscular rigidity. Vecuronium administration did not significantly reduced the number of patients who became rigid, but significantly decreased the incidence of severe rigidity (p less than 0.005), the mean rigidity score (p less than 0.05) and the incidence of rigidity at the induction of anaesthesia (p less than 0.0005). We also observed a progressively increasing incidence of rigidity with increasing age (not significantly) and body weight (p less than 0.05 total rigidity, p less than 0.01 severe rigidity).
Adolescent↗