A case of cardiogenic shock due to ventricular dyssynchrony resolved by atrial pacing.

We present a case of a man with ischemic cardiomyopathy and single chamber implantable cardioverter-defibrillator who developed sinus arrest creating sudden dependence on right ventricular (RV) pacing. He presented with cardiogenic shock secondary to abrupt onset ventricular dyssynchrony from RV pacing, which required emergent stabilization and completely resolved with atrial pacing. Learning objective: To establish a basic understanding of cardiogenic shock management. To reinforce the adverse effects associated with right ventricular pacing.

Stiffening effects of cortical bone on vertebral cancellous bone in situ.

STUDY DESIGN: This study tested a theory about vertebral cancellous bone stiffness by performing experimental tests and comparing the results with the theoretical predictions. OBJECTIVES: To test experimentally a theoretical prediction that vertebral cancellous bone appears stiffer than would be expected from isolated tests because of the constraining effects of the cortical bone, to measure the magnitude of this strengthening effect and its dependency on tissue composition and density. SUMMARY OF BACKGROUND DATA: Vertebral bodies are composed mainly of cancellous bone surrounded by a thin shell of much stronger cortical bone. Little is known of the ways in which these two materials function synergistically to produce strong but light structures and why sometimes extensive damage to the cancellous bone has apparently little outward effect on vertebral body strength. METHODS: Cancellous bone from 45 lumbar vertebrae from a homogeneous group of pigs was tested in compression both in situ in the vertebral body and as an excised cylinder. The density and composition of the bone were then measured and correlation tested with both of the stiffness measurements. RESULTS: The cancellous bone in situ appears much stiffer than when isolated by a factor of about 4 (range, 1.6-12). No correlation was found between stiffness, either in situ or in isolation, and density, although density is predicted entirely by the volume fractions of water, organic, and mineral phases. CONCLUSIONS: Combining low density cancellous bone with stiffer, more dense cortical bone leads to a lightweight structure that is much stronger than might be expected from the isolated properties of its components.

Validation of a computer model of haemorrhage and transcapillary refill.

A computer model is described which uses blood volume deficit and its duration to simulate the first two hours of haemorrhage, including an estimation of the blood volume added by Starlings transcapillary refill mechanism. Computer prediction of the haematocrit was compared with published data on haemorrhage in animals. There was close correlation with data on the haemodilution caused by Starling's transcapillary refill mechanism in conscious swine (r = 0.84).

Is the objective assessment of cerebral palsy gait reproducible?

It is important to determine the reproducibility of objective measures of gait in children with motor disorders in order that the effect of interventions to improve gait can be monitored. Data for walking velocity and vertical ground reaction force expressed as a percentage of body weight were collected from 15 normal children and 11 with spastic cerebral palsy. Five recordings were obtained for each foot of each child on 3 consecutive days, and calculations of variability made for each set of five recordings. Children with cerebral palsy had slower walking velocities and greater ground reaction force values, and both these parameters had low intraindividual variation for both normal children and those with cerebral palsy (coefficients of variation < 12.5%). This good reproducibility applied to intrasubject and intraday variability; no learning effect was seen over 3 days' recordings. There was no significant difference in variability whether the first three recordings or all five were used. These techniques of gait measurement in children have good reproducibility and a potential role in the objective assessment of medical and surgical interventions.

Electrical impedance tomography: a review of current literature.

Electrical impedance tomography (EIT) is a relatively new imaging technique that has been developed during the past decade. The electrical properties of tissues are imaged by injecting small currents and measuring the resultant voltages. These voltages are then converted into a tomographic image using a reconstructing algorithm. The method has no known hazards and is relatively inexpensive. There are many possible clinical applications of this technique but apart from gastric emptying, most are still at the research stage as there are various technical and practical problems to be overcome. This paper describes the basic principles of EIT and reviews the English literature to try to assess its potential in clinical imaging.

Cervical collars: a potential risk to the head-injured patient.

Interface pressures beneath six types of collar in volunteers were measured. Under certain types of collar mean interface pressures of more than 10 mmHg were obtained, with several individual readings around 30 mmHg. By causing jugular venous obstruction a similar rise in intracranial pressure may be produced inadvertently. The mechanisms of action for this are discussed. Those collars with the least tendency to produce jugular venous obstruction were of the moulded variety which extend support to the occiput, mandible and shoulder girdle. The authors therefore recommend this type of cervical splintage device where injury of the cervical spine is suspected. This paper emphasizes the potential danger to head-injured patients when the other devices are applied too tightly, producing a 'venous tourniquet' effect.

Glass fibre versus non-glass fibre splinting bandages.

We have assessed the current range of synthetic splinting bandages, comparing glass with non-glass fabrics and plaster-of-Paris. Physical and mechanical tests have been carried out and the opinions of patients, volunteers and orthopaedic staff were recorded. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive and potentially more hazardous. However, non-glass bandages are lighter, less brittle, more radiolucent and less hazardous than glass fibre bandages and are preferred by both patients and applicators.

Intracast pressure measurements in Colles' fractures.

Intracast pressures were recorded in conventional plaster-of-Paris below-elbow casts and compared with a new prefabricated brace for the functional treatment of Colles' fractures. Interface pressures were consistently higher in the brace than in the conventional plaster cast throughout the treatment period, and demonstrated more specific loading to the fracture site.

Imaging microbubbles and tissues using a linear focussed scanner operating at 20 MHz: possible implications for the detection of cavitation thresholds.

B-Scan images have been used as a means of detecting the onset of cavitation in tissues. New echoes appearing during simultaneous sonication with therapeutic ultrasound have often been attributed to bubble formation. In this study temperature rises up to 15 degrees C W-1 cm2 in guinea pig leg (post-mortem) were found, which would itself increase the rate of growth of gas bubbles. It is also hypothesized that a temperature dependent attenuation coefficient predicted by Bamber and Hill may, at least in part, account for new echoes appearing in tissues. Possible artefactual echoes in the B-scan images arising from acoustically induced gas bubbles in the coupling medium are also discussed.

On immediate functional bracing of Colles' fracture.

A prospective randomized trial was carried out in 60 consecutive patients with Colles' fractures requiring manipulation. They were treated by either a standard Colles' plaster (control group) or in a functional plaster brace applied immediately after reduction of the fracture. The brace extended from the proximal radius and ulna to the level of the radial styloid and allowed a full range of movement at the radiocarpal joint. Both groups comprised 30 patients and were matched for age, sex and dominance of hand. There was no significant difference in initial severity of fracture or the quality of reduction. Radiological results on cast removal (35-42 days) were significantly better in the brace group compared with those treated with a below-elbow cast (P less than 0.05). Wrist function was also significantly better in the brace treated group at 12 weeks after fracture (P less than 0.05). This brace has a number of advantages over standard plaster treatment, but requires a degree of skill and experience in its application. A prefabricated brace has now been developed with a similar 'built in' three-point loading which will be easier for inexperienced staff to apply.

Modern splinting bandages.

We have assessed the current range of synthetic splinting bandages, using physical and mechanical tests and the subjective opinions of patients, volunteers and orthopaedic staff. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive, and potentially more hazardous.

Radiographic assessment of splinting bandages.

The physical attenuation of X-rays by a variety of splinting bandages was measured and compared with the subjective opinion of nine radiologists. The radiolucency of the bandages and their interference with the interpretation of bony detail on radiographs (using a radiographic knee phantom) was assessed. Plaster-of-Paris (POP) bandages produced the greatest attenuation of X-rays and the greatest interference with interpretation of bony detail. All the polyurethane resin impregnated fabric bandages produced less attenuation than POP, but variations occurred due to the fabric type and knit of the bandage. The lowest attenuation occurred in those bandages using cotton, polyester or polypropylene fabric, and in all but one instance these caused least interference in radiographic interpretation. The exception was the polyester bandage, where the coarse knit of the fabric produced a large difference in X-ray beam absorption between the air spaces and the bandage. The distracting mesh pattern on the radiograph interfered with radiographic visualization. The glass fibre bandages caused intermediate attenuation, being better than POP but not as radiolucent as the non-glass fabrics.

Microcomputer-based system for clinical gait studies.

A microcomputer-based gait recording system is described which can be used to analyse gait routinely in the clinical environment. Foot-ground reaction forces are acquired and processed and the resultant force vector is superimposed on the television image of the subject in real time. A TV-computer interface quantifies the position of reflective markers attached to the joint centres of the lower limb, and moment values, stick-figure diagrams, and joint angle changes can also be displayed shortly after data collection. The system has routine clinical applications in orthotics and prosthetics and is also a valuable tool in teaching the biomechanics of human movement.

Interface pressures in below elbow casts.

Intra-cast pressures were measured in casts worn by patients with Colles' fractures and by volunteers. This study has shown that the loading as determined by the interface pressures in conventional backslab-below elbow casts is low and generally nonspecific. However, moulding the backslab increases the intra-cast pressures and these higher pressures are maintained throughout the period of immobilization as compared with non-moulded casts. There is no evidence of three-point loading in the casts; as a method of applying forces to the fracture site conventional casting does not appear to be particularly effective.

A microcomputer-based video vector system for clinical gait analysis.

A microcomputer-based video vector system has been developed to display the resultant ground reaction force vector on a television image of the subject in real-time. For each television field the force platform signals are acquired and processed and the resultant force vector superimposed on the video image of the walking subject. The force platform results are stored on disc and the composite video signals recorded on video tape for further analysis. The system is easy to set up and use and the results can be readily interpreted. The external moments produced at the joint centers by the ground reaction forces can be observed visually and, if required, quantification of the external moments can be achieved following data collection. The spatial resolution of the system is 0.342% vertically and 0.156% horizontally. The force vector visualization technique has routine applications in orthotics and prosthetics. It is also a useful technique for the teaching of biomechanics.

Determination of stresses in below-knee walking casts.

Glass fibre bandages are now commonly used for definitive below-knee walking casts, in preference to plaster of Paris, since they are better able to withstand the stresses imposed upon them. This paper describes a technique for recording the cast strains in glass fibre bandages and shows typical stress levels in patient and volunteer casts. A typical map of the stress variations in walking casts during gait in a volunteer has been produced. The study shows that the high stresses recorded along the medial and lateral borders of the foot by the strain gauge technique are confirmed by clinical experience, since this is where failure is most commonly seen in below-knee walking casts. It is concluded that the current generation of polyurethane impregnated glass fibre splinting bandages are too brittle in many cases for below-knee walking casts and that a more flexible fabric would reduce the incidence of cast breakdown.

Instrumentation used in clinical gait studies: a review.

This paper reviews the currently available instrumentation used for gait studies and discusses the clinical suitability of the various methods of recording gait parameters. Most of the presently available motion analysis systems appear to be more suited to research than to the routine clinical situation. However the video vector visualization technique appears to be the most useful clinically since it produces a real time display, is simple to operate and interpretation of the data is easier than other systems available. Some further development of the video vector visualization system is necessary to improve its accuracy and to produce quantitative information.

Dust emission during cutting of polyurethane-impregnated bandages.

The airborne dust generated when cutting splinting bandages represents a potential respiratory hazard, particularly to those who regularly remove casts with a power saw. Plaster of Paris (POP) dust is already classified by the Health and Safety Executive as a nuisance dust. This paper reports on a study to determine the nature, size and concentration of dust produced when cutting polyurethane (PU) impregnated bandages using a power saw. It has been shown that, under severe conditions PU bandages produce lower airborne dust concentrations than POP bandage but that all of the bandages tested produced particles small enough to reach the final divisions of the lung. It is therefore recommended that a dust extraction unit be used when cutting all types of bandage.