Biomedical subjects
Publications and source records attributed to R S Simons.
The synthesis of a dicationic imidazolium-linked cyclophane and a dimeric silver-N-heterocyclic carbene complex, that is the first silver complex with a N-heterocyclic carbene ligand involved in a pi-bonding interaction, is reported.
The function of the lateral hypaxial muscles during locomotion in tetrapods is controversial. Currently, there are two hypotheses of lateral hypaxial muscle function. The first, supported by electromyographic (EMG) data from a lizard (Iguana iguana) and a salamander (Dicamptodon ensatus), suggests that hypaxial muscles function to bend the body during swimming and to resist long-axis torsion during walking. The second, supported by EMG data from lizards during relatively high-speed locomotion, suggests that these muscles function primarily to bend the body during locomotion, not to resist torsional forces. To determine whether the results from D. ensatus hold for another salamander, we recorded lateral hypaxial muscle EMGs synchronized with body and limb kinematics in the tiger salamander Ambystoma tigrinum. In agreement with results from aquatic locomotion in D. ensatus, all four layers of lateral hypaxial musculature were found to show synchronous EMG activity during swimming in A. tigrinum. Our findings for terrestrial locomotion also agree with previous results from D. ensatus and support the torsion resistance hypothesis for terrestrial locomotion. We observed asynchronous EMG bursts of relatively high intensity in the lateral and medial pairs of hypaxial muscles during walking in tiger salamanders (we call these 'alpha-bursts'). We infer from this pattern that the more lateral two layers of oblique hypaxial musculature, Mm. obliquus externus superficialis (OES) and obliquus externus profundus (OEP), are active on the side towards which the trunk is bending, while the more medial two layers, Mm. obliquus internus (OI) and transversus abdominis (TA), are active on the opposite side. This result is consistent with the hypothesis proposed for D. ensatus that the OES and OEP generate torsional moments to counteract ground reaction forces generated by forelimb support, while the OI and TA generate torsional moments to counteract ground reaction forces from hindlimb support. However, unlike the EMG pattern reported for D. ensatus, a second, lower-intensity burst of EMG activity ('beta-burst') was sometimes recorded from the lateral hypaxial muscles in A. tigrinum. As seen in other muscle systems, these beta-bursts of hypaxial muscle coactivation may function to provide fine motor control during locomotion. The presence of asynchronous, relatively high-intensity alpha-bursts indicates that the lateral hypaxial muscles generate torsional moments during terrestrial locomotion, but it is possible that the balance of forces from both alpha- and beta-bursts may allow the lateral hypaxial muscles to contribute to lateral bending of the body as well.
The mechanics of lung ventilation in frogs and aquatic salamanders has been well characterized, whereas lung ventilation in terrestrial-phase (post-metamorphic) salamanders has received little attention. We used electromyography (EMG), X-ray videography, standard videography and buccal and body cavity pressure measurements to characterize the ventilation mechanics of adult (post-metamorphic) tiger salamanders (Ambystoma tigrinum). Three results emerged: (i) under terrestrial conditions or when floating at the surface of the water, adult A. tigrinum breathed through their nares using a two-stroke buccal pump; (ii) in addition to this narial two-stroke pump, adult tiger salamanders also gulped air in through their mouths using a modified two-stroke buccal pump when in an aquatic environment; and (iii) exhalation in adult tiger salamanders is active during aquatic gulping breaths, whereas exhalation appears to be passive during terrestrial breathing at rest. Active exhalation in aquatic breaths is indicated by an increase in body cavity pressure during exhalation and associated EMG activity in the lateral hypaxial musculature, particularly the M. transversus abdominis. In terrestrial breathing, no EMG activity in the lateral hypaxial muscles is generally present, and body cavity pressure decreases during exhalation. In aquatic breaths, tidal volume is larger than in terrestrial breaths, and breathing frequency is much lower (approximately 1 breath 10 min(-)(1 )versus 4-6 breaths min(-)(1)). The use of hypaxial muscles to power active exhalation in the aquatic environment may result from the need for more complete exhalation and larger tidal volumes when breathing infrequently. This hypothesis is supported by previous findings that terrestrial frogs ventilate their lungs with small tidal volumes and exhale passively, whereas aquatic frogs and salamanders use large tidal volumes and and exhale actively.
Despite the acknowledged importance of the locomotory and respiratory functions associated with hypaxial musculature in salamanders, variation in gross morphology of this musculature has not been documented or evaluated within a phylogenetic or ecological context. In this study, we characterize and quantify the morphological variation of lateral hypaxial muscles using phylogenetically and ecologically diverse salamander species from eight families: Ambystomatidae (Ambystoma tigrinum), Amphiumidae (Amphiuma tridactylum), Cryptobranchidae (Cryptobranchus alleganiensis), Dicamptodontidae (Dicamptodon sp.), Plethodontidae (Gyrinophilus porphyriticus), Proteidae (Necturus maculosus), Salamandridae (Pachytriton sp.), and Sirenidae (Siren lacertina). For the lateral hypaxial musculature, we document 1) the presence or absence of muscle layers, 2) the muscle fiber angles of layers at mid-trunk, and 3) the relative dorsoventral positions and cross-sectional areas of muscle layers. Combinations of two, three, or four layers are observed. However, all species retain at least two layers with opposing fiber angles. The number of layers and the presence or absence of layers vary within species (Necturus maculosus and Siren lacertina), within genera (e.g., Triturus), and within families. No phylogenetic pattern in the number of layers can be detected with a family-level phylogeny. Fiber angle variation of hypaxial muscles is considerable: fiber angles of the M. obliquus externus range from 20-80 degrees; M. obliquus internus, 14-34 degrees; M. transversus abdominis, 58-80 degrees (acute angles measured relative to the horizontal septum). Hypaxial musculature comprises 17-37% of total trunk cross-sectional area. Aquatic salamanders show relatively larger total cross-sectional hypaxial area than salamanders that are primarily terrestrial.
The relative motion of the visceral mass may be important to ventilation during running. A visceral piston hypothesis predicts that, during galloping, cranial motion of the liver during expiration and caudal motion of the liver during inspiration may characterize efficient quadrupedal mammalian locomotion. Although a theoretical model based on vibration mechanics casts doubt on this prediction, only limited direct measurements of visceral mass motion during galloping have been reported. In the present study, mechanical interactions between running, breathing and liver oscillations in the domestic rabbit are recorded using synchronized videographic, cineradiographic and pneumotachographic techniques. The analysis focuses on the variation in locomotor-respiratory coupling (LRC) and on the relative position of the liver. Results from running rabbits show (1) variation in phase angle between the locomotor and respiratory periods that is inconsistent with the 1:1 LRC ratio that has been reported for other galloping mammals; (2) a tendency towards a 1:1 LRC ratio at higher speeds and stride frequencies; and (3) that the relative motion of the liver is caudal during expiration and cranial during inspiration, which is inconsistent with the visceral piston hypothesis. The data presented here are generally consistent with the theoretical vibration mechanics model for liver motion and with a pneumatic stabilization hypothesis that the lungs serve an important role in the stabilization of the thorax during locomotion.
Gross lung morphology is examined in representative species from four genera within the order Lagomorpha (Lepus californicus, Sylvilagus nuttalli, Oryctolagus cuniculus, Ochotona princeps), and compared with a representative rodent out-group (Spermophilus richardonsii). Examination of pulmonary morphology reveals several correlations between the thoracic morphology and locomotor behavior. Lepus, the most cursorial species, exhibits a distinct suite of characteristics: 1) tissue of the right cranial lobe interposed between the heart and sternum; 2) well-defined grooves in the lung tissue for both the aorta and ribs; 3) a fibrous pericardial attachment to the sternum; 4) relatively large heart and lung mass. Sylvilagus, a sprinter, exhibits these features to a lesser degree, whereas Oryctolagus and Ochotona, non-cursorial species, lack most of these features. This same suite of pulmonary features is also observed in a wide range of unrelated cursorial taxa (including selected Artiodactlya, Perissodactyla, Carnivora). Corrosion casts of the internal airways demonstrate that the cursorial and non-cursorial taxa examined here have similar branching patterns despite their variable external morphologies. The juxtaposition of pulmonary lobes, heart, and ribs leads to the hypothesis that the lungs themselves provide mechanical support of the heart and visceral mass during locomotion. Analyses of cineradiographic and pneumotachographic data obtained from Oryctolagus tend to support a pneumatic stabilization hypothesis: the lungs themselves, intimately associated with the chest walls and positively pressurized during landing, may provide some mechanical support to the viscera. This mechanism may be important in stabilizing the relatively large hearts of the most cursorial species during running.
In a prospective study 568 patients admitted to a mixed medical and surgical intensive therapy unit (ITU) were assessed using the Apache II severity of illness score to predict outcome. Their outcome was also predicted subjectively by a doctor and nurse on admission. There were 260 deaths in the group. The subjective predictions were compared with the Apache II predictions using logistic regression analysis and receiver-operating-characteristic curve measurement. The subjective assessments were found to be a more powerful predictor of outcome in this group of patients than the Apache II scores and predicted risk of death. Although the predictions could be successfully applied to the population as a whole, none of the tests were suitable for predicting outcome on an individual patient.
Preregistration house officers need to be able to manage the first 5-10 minutes of a cardiac arrest. A course has been designed based on the recommendations of the Resuscitation Council UK 1984 and the format of the American Heart Association advanced cardiac life support course. Fifty-nine newly qualified doctors from the same medical school class were studied in two consecutive groups: Group 1 (n = 31) were commencing their first post and Group 2 (n = 28), whose first preregistration post had been at other hospitals without practical resuscitation training, were commencing their second post. They were pretested and taught in three 2-hour sessions. Five months later they were tested to measure retention of knowledge and skills. Before training there was no difference in knowledge between the two groups but Group 1 were more skilled. The knowledge and skills of both groups immediately after training were significantly improved and at 5 months skills were subject to modest decay only. Experience of managing cardiac arrests was not a substitute for formal practical training.
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Five- to ten-cell embryos and expanded blastocysts from 68 patients were thawed in an attempt to establish pregnancy. Three fresh embryos had been replaced unsuccessfully in these patients. Forty-five patients had intact freeze-thawed embryos replaced and 12 became clinically pregnant. Ten of these pregnancies have now advanced beyond week 24. The preliminary results presented here demonstrate that significantly more expanded blastocysts survive cryopreservation than cleaving embryos. Faster-growing embryos did not survive better than slowly growing embryos, but the incidence of implantation was higher with faster-developing embryos. Significantly more blastocysts with a "normal" morphology survived cryostorage than those scored as "irregular" (77 versus 7%). A similar trend was observed when normal and irregular cleaving embryos were frozen, but the difference was not significant. The severity of contraction of blastocysts upon the addition of cryoprotectant increased the incidence of survival. The proportion of patients whose embryos had holes in the zona pellucida following cryopreservation was significantly higher when embryos were frozen at the cleaving stage (39%) rather than the expanded blastocyst stage (16%). Almost all embryos with damaged zonae degenerated. The proportion of cleaving embryos that survived cryostorage was inversely correlated with the number of follicles aspirated.
A simple test rig was developed to assess the force applied during the application of cricoid pressure. Anaesthetists and paramedical personnel familiar with Sellick's manoeuvre were tested yielding results which indicate an unacceptably wide variation in performance in each group. The mean force was 46.4 N but 47% failed to reach a force of 44 N. In addition a survey was undertaken of trained anaesthetic staff to identify the current status of the manoeuvre. Of those sampled 78% routinely employed Sellick's manoeuvre and over 70% had experienced a problem with its application which exposed the patient to the risk of regurgitation.
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