Biomedical subjects

A P Shortland

Publications and source records attributed to A P Shortland.

At least 19 recordsLinked to original sources

PubMed2006

The effect of serial casting on gait in children with cerebral palsy: preliminary results from a crossover trial.

Serial casting aims to improve an equinus gait pattern in children with spastic cerebral palsy (SCP). We evaluated the effect of short-term stretch casting on gait in children with SCP, compared to the natural history. A crossover trial, consisting of a control phase and a casting phase, was conducted with children randomised into two groups. Both groups were assessed clinically, and using 3D gait analysis, at 0, 5 and 12 weeks. Subjects in one group had the 3 month casting phase first and in the other had the 3 month control period first. Casts were changed weekly and set at maximum available ankle dorsiflexion. The mean changes at 5 weeks and 12 weeks from baseline measurements in the casting phase were compared with the change within the same time interval in the control phase. Significant improvements in passive ankle dorsiflexion (knee flexed) were found at 5 and 12 weeks. Passive ankle dorsiflexion (knee extended), ankle dorsiflexion in single support, ankle dorsiflexion in swing and minimum hip flexion in stance improved significantly at 5 weeks but not at 12 weeks from baseline. Other kinematic parameters, the score on the Gillette Functional Assessment Questionnaire, and maximum reported walking distance were not changed by casting. Casting to improve range appears to improve passive and dynamic ankle dorsiflexion, but the changes are small, short lived and do not appear to affect function.

Biomechanical Phenomena↗

PubMed2005

Botulinum toxin and cerebral palsy: time for reflection?

Botulinum toxin A (BTX-A) is increasingly being used in early management of spasticity in ambulant children with cerebral palsy (CP), with the aim of improving function, promoting muscle growth, and delaying the need for surgical intervention. However, there is a lack of evidence about the long-term outcome of BTX-A injections. The focus on spasticity as the predominant problem in younger children with spastic CP may not fully consider the associated muscle weakness. It also raises concern that although BTX-A may improve function in the short term, it has the potential to affect muscle growth and function adversely in the long term. A cautious approach to the early use of BTX-A, with the use of objective outcome measures within a specialized multidisciplinary setting, is recommended, particularly in ambulant children with spastic diplegic CP, until further evidence is available on the long-term outcome of early BTX-A injections in children with CP.

Botulinum Toxins, Type A↗

PubMed2004

Lower limb extensor moments in children with spastic diplegic cerebral palsy.

In this retrospective study, we quantified the mean extensor moment at the ankle, knee and hip over the stance period in a group of independently ambulant children with spastic diplegia (n = 90; 167 limbs) and in a group of normally-developing (ND) children (n = 22; 22 limbs). The mean knee extensor moment and the mean support moment demonstrated greater variance in children with diplegia than in normally-developing children (P < 0.0001 and P < 0.001). This was explained by a strong relationship between the mean knee extensor moment and minimum knee flexion in stance (r2 = 0.615; P < 0.0001) in the affected group with a positive mean knee extensor moment for all those children who walked in greater than 20 degrees of knee flexion. We also found a linear relationship between the support moment and knee flexion (r2 = 0.805; P < 0.0001). Our data supported the biomechanical analysis of Hof [Gait Posture, 12 (2000) 196] who suggested that his modified support moment should be a linear function with eccentricity at the knee. Extensor moments at the ankle (r2 = 0.001376; P = 0.641) and hip (r2 = 0.0860; P = 0.000168) bore weak relationships with increasing knee flexion even though there was a strong positive relationship between minimum knee flexion and minimum hip flexion (r2 = 0.316; P < 0.0001). We conclude that children with spastic diplegic cerebral palsy (SDCP) who walk with a crouch gait rely on their knee extensors to prevent collapse of the lower limbs. Intervention directed at redistributing extensor moments between the joints of the lower limbs may slow the increase in knee flexion and prolong reasonable walking function in this group.

Adolescent↗

PubMed2004

Three-dimensional realisation of muscle morphology and architecture using ultrasound.

Two-dimensional B-mode ultrasound imaging and motion tracking were combined to generate three-dimensional reconstructions of the medial gastrocnemius. Architectural and morphological features of this muscle could be visualised. The length of the gastrocnemius belly was measured in normally (ND) developing children and in children with spastic diplegic cerebral palsy (SDCP) who had plantarflexion contractures. Using a random effects linear model we demonstrated that the gastrocnemius muscle bellies of children with SDCP were shorter than those of ND children (P = 0.001) even when corrected for ankle position. The technique described could be used to evaluate muscular deformity before and after an intervention.

Adolescent↗

PubMed2003

Haemodynamic considerations in the design of a skeletal muscle ventricle.

Skeletal muscle ventricles (SMVs) configured to operate as diastolic counterpulsators show promise as cardiac assist devices. In four pigs, SMVs were connected to the aorta by a single-limbed conduit and activated during every third cardiac diastole. During the assisted beats, mean diastolic aortic pressure increased by 30.3 +/- 2.2%, peak diastolic aortic pressure increased by 38.5 +/- 2.7%, the endocardial viability ratio increased by 42.3 +/- 3.4%, and mean left anterior descending coronary artery flow increased by 61.6 +/- 4.5%. Although there are major advantages to making the connection to the aorta by a single-limb conduit, the lack of separation between inlet and outlet means that such devices must be designed carefully to avoid thrombogenesis under chronic conditions. Design rules were developed for this configuration, based on earlier in vitro studies. They addressed the problem of stasis by promoting the development of a propagating vortex that travels the length of the ventricle and ensured proper exchange of blood with the circulation by limiting the volume of the connecting conduit. An SMV compatible with these rules was connected in a pig. At elective termination 1 week later, activation of the SMV increased peak diastolic pressure by 20.1% and reduced left-ventricular stroke work in the post-assisted beat by 10.1%. The SMV was free from thrombus.

Animals↗

PubMed2003

Accurate measurement of muscle belly length in the motion analysis laboratory: potential for the assessment of contracture.

Two-dimensional ultrasound imaging was combined with motion analysis technology to measure distances between remote anatomical landmarks. The length of the belly of the medial gastrocnemius muscle in five normal adults (nine limbs) was estimated using this technique. Our results in vivo were similar to the reported data for the lengths of muscles in cadavers, and were consistent with the expected relationship between muscle belly length and ankle joint angle. Experiments in vitro demonstrated that the accuracy of the device was better than 2 mm over 20 cm. Measurements on the same subject on different occasions showed that the results were repeatable in vivo. Rendering of the reconstructed volume of a foam phantom gave results comparable to photographic images. This validated technique could be used to measure muscle lengths in children with spastic cerebral palsy and indicate which muscles had fixed shortening, and to what extent.

Adult↗

PubMed2001

Architecture of the medial gastrocnemius in children with spastic diplegia.

Ultrasound images were obtained of the medial gastrocnemius at different ankle joint positions with the knee extended. Fascicle length and deep fascicle angle were measured in five normally developing adults (mean age 33 years, age range 24 to 36 years) and in five normally developing children (mean age 7.8 years, age range 7 to 11 years), and in seven children with spastic diplegia (mean age 10 years, age range 6 to 13 years). These architectural variables were similar in the groups of normally developing adults and children. Importantly, no statistical difference could be found between the normally developing children and those with diplegia for fascicle length. Deep fascicle angles were reduced significantly in the clinical group at a particular ankle joint angle but not at the resting angles. The difference in deep fascicle angles is explained as a function of resting muscle length and is not attributed any clinical importance. Our results do not explain the structural origin of muscle contracture explicitly. However, they do indicate that most of the fixed shortness in the medial gastrocnemii of ambulant children with spastic diplegia is not due to reduced muscle fascicle length. We suggest that muscle contracture may be better explained in terms of shortness of the aponeuroses of pennate muscles, such as the medial gastrocnemius, through reduced muscle fascicle diameter.

Adult↗

PubMed2000

Functional assessment of skeletal muscle ventricles after pumping for up to four years in circulation.

BACKGROUND: The successful treatment of cardiac failure by heart transplantation is severely limited by the shortage of donor organs, and alternative surgical approaches are needed. An experimental approach that holds considerable promise is the skeletal muscle ventricle (SMV), an auxiliary blood pump formed from a pedicled graft of latissimus dorsi muscle and connected to the circulation in a cardiac assist configuration. Adaptive transformation, or conditioning, by electrical stimulation enables the skeletal muscle to perform a significant proportion of cardiac work indefinitely without fatigue. METHODS: In 10 dogs, SMVs were constructed from the latissimus dorsi muscle, lined internally with pericardium, and conditioned by electrical stimulation to induce fatigue resistant properties. The SMVs were connected to the descending thoracic aorta via two 12-mm Gore-Tex conduits and the aorta was ligated between the two grafts. The SMV was stimulated to contract during the diastolic phase of alternate cardiac cycles. The animals were monitored at regular intervals. RESULTS: At initial hemodynamic assessment, SMV contraction augmented mean diastolic blood pressure by 24.6% (from 61 +/- 7 to 76 +/- 9 mm Hg). Presystolic pressure was reduced by 15% (from 60 +/- 8 to 51 +/- 7 mm Hg) after an assisted beat. Four animals died early, 1 from a presumed arrhythmia, and 3 during propranolol-induced hypotension. The other 6 animals survived for 273, 596, 672, 779, 969, 1,081, and 1,510 days. Diastolic augmentation was 27.4% at 1 year (93 +/- 9 vs 73 +/- 6 mm Hg; n = 5), 34.7% at 2 years (85 +/- 6 vs 63 +/- 7 mm Hg; n = 3), 21.2% (89 +/- 10 vs 73 +/- 8 mm Hg; n = 2) at 3 years, and 34.5% (78 vs 58 mm Hg; n = 1) after 4 years in circulation. After 4 years, the isolated SMV was able to maintain a pressure of over 80 mm Hg while ejecting fluid at 20 mL/s. No animal showed evidence of SMV rupture or thromboembolism. CONCLUSIONS: The SMVs in this study provided effective and stable hemodynamic assistance over an extended period of time. There was no evidence that the working pattern imposed on the muscular wall of the SMV compromised its viability. Areas of fibrofatty degeneration were suggestive of early damage that future protocols should seek to minimize.

Animals↗

PubMed1999

Computer aided design and fabrication of models for in vitro studies of vascular fluid dynamics.

An integrated computer aided design/computer aided manufacture system has been used to model the complex geometry of blood vessel anastomoses. Computer models are first constructed with key dimensions derived from radiological images of bypass grafts, and from casts of actual blood vessel anastomoses. Physical models are then fabricated in one of two ways: the surface geometry data can be used to control the movement of a three-axis milling machine; alternatively, the same data can be exported in a form that can be interpreted by a stereolithography apparatus. Both methods produce geometrically defined solid investments that can be used in a multistep casting process that yields high-quality physical models for vascular fluid dynamic studies. This technique is useful for parametric studies.

Anastomosis, Surgical↗

PubMed1998

Sodium channel protein expression enhances the invasiveness of rat and human prostate cancer cells.

Expression of Na+ channel protein was analysed in established cell lines of rat and human prostatic carcinoma origin by flow cytometry using a fluorescein-labelled polyclonal antibody. In many cell lines examined, the obtained frequency distribution profiles were bimodal and identified a subpopulation of cells which expressed high levels of Na+ channel protein. A significant positive correlation was demonstrated between the proportion of channel-expressing cells and the functional ability of individual cell lines to invade a basement membrane matrix in vitro. In addition, two transfectant cell lines containing rat prostate cancer genomic DNA were found to express significantly elevated levels of Na+ channel protein when compared with the original benign recipient cell line. Enhanced Na+ channel expression by two metastatic derivatives of these transfectant cells directly correlated with increased invasiveness in vitro. These studies strongly support the hypothesis that expression of Na+ channel protein and the metastatic behaviour of prostatic carcinoma cells are functionally related, either by endowing the membranes of these cells with specialised electrophysiological properties (e.g. enhancing their motility and/or secretory activities) and/or by perturbing endogenous mechanisms regulating ionic homeostasis within the cells.

Animals↗

PubMed1998

Platelet reactions to modified surfaces under dynamic conditions.

The influence of surfaces on the reactions of platelets in whole blood under laminar flow was investigated in a cone and plate viscometer. Citrated whole blood was exposed to steel, PMMA and PMMA modified with PEO at low (500 s(-1)) and high (4000 s(-1)) wall shear rates at room temperature for a period of 100 s. Treated blood samples were fixed with paraformaldehyde, stained with a monoclonal antibody for CD41 (platelet GPIIb/IIIa) conjugated with phycoerythrin and analyzed by flow cytometry. The reactions of platelets (microparticle generation and formation of platelet-platelet, platelet-red blood cell and red blood cell-microparticle aggregates) to these environments were quantified. Additionally, the size of platelet-platelet aggregates was assessed. The percentage platelet aggregation and numbers of microparticles generated were independent of surface type at any shear rate. The composition of the aggregates formed was influenced by the surface: at low and high shear rates PMMA caused the generation of platelet-platelet aggregates of the greatest size. The numbers of red blood cell-platelet and red blood cell-microparticle aggregates also varied depending on the surface. Fewer red blood cell-platelet aggregates were formed at higher shear rates, whereas the reverse was true for red blood cell-microparticle aggregates. It is concluded that these variations may help to explain the differential effects of surfaces to the induction of distant thrombotic events: microparticles may be protected from loss from the blood stream by their association with red blood cells at high shear rates.

Journal Article↗

PubMed1997

The effect of temperature and shear rate on platelet aggregation.

Samples of whole blood were obtained from male volunteers and exposed to combinations of shear rates and temperatures representative of cardiopulmonary bypass (CPB) in a modified computer-controlled concentric cylinder rotational viscometer for a period of 100 s. Blood sampled from the chamber was fixed in paraformaldehyde, stained with CD41 and analysed by flow cytometry. Only platelet-positive particles were acquired, each individual cell, or aggregate of cells, identified by analysis of its fluorescence and forward light scatter characteristics. Little platelet aggregation was observed at shear rates of less than 4000 s(-1) for temperatures of greater than 24 degrees C, but large numbers of aggregates were formed at all temperatures at 4000 s(-1) (p<0.05), with more aggregates forming at 24 and 30 degrees C than at 37 and 42 degrees C (p<0.05). We conclude that the process of aggregation is dependent on both temperature and shear rate. We note that a large number of platelets become involved in aggregates under conditions of temperature and shear-rate typical of CPB.

Journal Article↗

PubMed1997

Activation status of platelet aggregates and platelet microparticles shed in sheared whole blood.

The role of temperature and shear rate in the activation status of aggregating platelets and platelet microparticles (MPs) was investigated in a modified concentric-cylinder rotational viscometer. Whole blood anticoagulated with citrate was exposed to a range of shear rates typical of cardiopulmonary bypass circuits (0, 1000, 2000 and 4000 s(-1)) over four temperatures spanning hypothermic to mildly hyperthermic conditions (24, 30, 37 and 42 degrees C) for short durations (100 s). Aliquots of blood were double-stained for CD41 (platelet GPIIb/IIIa) and CD62 (P-selectin). Platelets, platelet aggregates, MPs and red blood cell-platelet and -MP aggregates were identified by flow cytometry by acquiring only CD41-positive particles and differentiating on a plot of CD41 versus forward light scatter. The activation status of each particle was quantified by measuring CD62 expression (alpha-granule release). A degree of correlation between the shedding of MPs and the formation of platelet-platelet aggregates was observed for the data as a whole (r=0.85 for p<0.01), although this trend was not observed for a shear rate of 4000 s(-1). The mean expression of CD62 on both platelets and MPs was maintained at a very low level for all temperature and shear rate combinations. There was, however, a number of very highly activated MPs associated with red blood cells at high shear rates.

Journal Article↗

PubMed1997

Flow in a simple model skeletal muscle ventricle: comparison between numerical and physical simulations.

Flow patterns generated during ventricular filling have been investigated for three different combinations of flow rate and injection volume. The numerical solutions from a commercially available computational fluid dynamics package were compared with observations made under identical flow conditions in a physical model for the purpose of code validation. Particle pathlines were generated from the numerical velocity data and compared with corresponding flow-visualization pictures. A vortex formed at the inlet to the ventricle in both cases: During the filling phase, the vortex expanded and traveled toward the apex of the ventricle until, at the end of filling, the vortex occupied the full radial extent of the ventricle; the vortex continued to travel once the filling process had ended. The vortices in vitro were more circular in shape and occupied a smaller volume than those generated by the numerical model. Nevertheless, comparison of the trajectories of the vortex centres showed that there was good agreement for the three conditions studied. Postprocessing of velocity data from the numerical solution yielded wall shear-stress measurements and particle pathlines that clearly illustrate the mass-transport qualities of the traveling vortex structure. For the cases considered here, the vortex transit produced a time-dependent shear stress distribution that had a peak value of 20 dynes cm-2, with substantially lower levels of shear stress in those regions not reached by the traveling vortex. We suggest that vortex formation and travel could reduce the residence time of fluid within a skeletal muscle ventricle, provided that the vortex travels the complete length of the ventricle before fluid is ejected at the start of the next cycle.

Blood Flow Velocity↗

PubMed1996

A novel video technique for visualizing flow structures in cardiovascular models.

We describe a video system that produces good quality images of particle trajectories in seeded fluid flows. The operation of a liquid crystal optical shutter and a modified charge-coupled device (CCD) camera were synchronized to generate images of particle trajectories which were stored in a framegrabber before being transferred to S-VHS tape. The camera system is particularly appropriate for visualizing transient or unsteady flows in models of the cardiovascular system as the integration time may be varied to produce particle trajectories of variable length.

Cardiac Output↗

PubMed1996

Formation and travel of vortices in model ventricles: application to the design of skeletal muscle ventricles.

Vortex-ring production was studied in axisymmetric elastomeric ventricles designed to stimulate flow in a cardiovascular assist device. A flow visualization technique was used to investigate the effects of reducing the inlet diameter and predilating the ventricle on vortex travel in two ventricles of different shape and size. In most cases, vortex rings formed during the filling phase. They were bounded by the incoming jet of fluid and the ventricular wall. The velocity of their centres during the filling period was proportional to the inflow velocity. During filling, vortex velocity was substantially independent of the shape and diameter of the two ventricles studied. It was dependent mainly on orifice diameter: a narrower inlet led to greater inflow velocities and proportionately greater vortex velocities. At the end of the filling phase, each vortex increased in size to occupy the full radial extent of the ventricle. This process was associated with a decrease in the axial velocity and strength of the vortex. At low flow rates, these losses resulted in the arrest of the vortex at end filling. Vortex motion in ventricles is particularly important in the design of a cardiovascular device such as the skeletal muscle ventricle (SMV), where small ejection fractions may leave blood at the apex of the ventricle relatively undisturbed. It is suggested that inlet diameter could be selected to favour the formation and travel of vortices, with a resultant reduction in apical residence time and hence a reduced risk of thrombus formation.

Coronary Circulation↗

PubMed1996

Factors influencing vortex development in a model of a skeletal muscle ventricle.

A video technique was used to visualize flow patterns in a pulsatile model of a skeletal muscle ventricle (SMV). The shape and duration of SMV filling/emptying curves were determined by the stroke action of a computer-controlled piston pump. In this way we examined the effect of filling duration and injection volume on the flow structures. To simulate the interaction between the left ventricle and the SMV in the proposed clinical application, two filling/emptying regimes were employed with the period of each SMV cycle being either equal to or twice that of a typical cardiac cycle. Vortex formation at the inlet to the ventricle was a feature of both flow cycles during filling for all the combinations of injection volume and filling duration considered. When a pacing ratio of 1:1 was simulated, SMV filling was immediately followed by ejection, and the formed vortex was expelled. Under this flow regime, fluid in the apical end of the ventricle remained undisturbed. When the pacing ratio was 2:1, however, the quiescent period that followed filling allowed time for the formed vortex to travel a significant distance toward the apical end of the ventricle. Under certain conditions of injection volume and flow rate, the vortex reached the apex by the end of the quiescent period. We suggest that a ventricle connected to the aorta by a single, valveless conduit would require a flow regime that included a significant period of quiescence after filling. This would allow the vortex to reach and displace blood that would otherwise stagnate in the apex, thereby reducing the risk of thrombus formation.

Biomechanical Phenomena↗

PubMed1989

Doppler spectral waveform generation in vitro: an aid to diagnosis of vascular disease.

This paper describes a microcomputer controlled pump which generates pulsatile flows similar to those found in the human peripheral circulation. Continuous wave Doppler ultrasound was used to investigate the flows generated by the pump and the behaviour of diagnostic indices derived from the spectra was examined. Sonograms were recorded from elastic and rigid tubes with various degrees of axisymmetric constriction. Heart rate, stroke volume, severity of vessel constriction, vessel wall elasticity, distal resistance, and systemic peripheral impedance were varied in turn and the resulting Doppler spectra compared. Indices considered were the pulsatility index, spectral broadening index and peck Doppler frequency. In general, the indices lacked the sensitivity to detect low to moderate levels of disease.

Humans↗