Biomedical subjects

D T O'Keeffe

Publications and source records attributed to D T O'Keeffe.

5 recordsLinked to original sources

PubMed2002

A versatile drop foot stimulator for research applications.

Drop Foot Stimulators are used to correct hemiplegic drop foot by synchronising the application of Functional Electrical Stimulation (FES) of the Common Peroneal Nerve (CPN) to the swing phase of the gait cycle. A research Drop Foot Stimulator (DFS) has been developed with a very flexible architecture to enable the investigation of a variety of gait-correction strategies. The portable unit has been carefully designed to optimise functionality while keeping its size and power consumption to a minimum. The device has two channels of stimulation, with all parameters of stimulation for each channel independently programmable. Four analogue and four digital sensor input channels are provided with a wide variety of sensor types possible. A microcontroller core is utilised to enable the implementation of different control algorithms. A PC-based user interface enables easy programming of the system configuration.

Electric Stimulation Therapy↗

PubMed2001

Stimulus artifact removal using a software-based two-stage peak detection algorithm.

The analysis of stimulus evoked neuromuscular potentials or m-waves is a useful technique for improved feedback control in functional electrical stimulation systems. Usually, however, these signals are contaminated by stimulus artifact. A novel software technique, which uses a two-stage peak detection algorithm, has been developed to remove the unwanted artifact from the recorded signal. The advantage of the technique is that it can be used on all stimulation artifact-contaminated electroneurophysiologic data provided that the artifact and the biopotential are non-overlapping. The technique does not require any estimation of the stimulus artifact shape or duration. With the developed technique, it is not necessary to record a pure artifact signal for template estimation, a process that can increase the complexity of experimentation. The technique also does not require the recording of any external hardware synchronisation pulses. The method avoids the use of analogue or digital filtering techniques, which endeavour to remove certain high frequency components of the artifact signal, but invariably have difficulty, resulting in the removal of frequencies in the same spectrum as the m-wave. With the new technique the signal is sampled at a high frequency to ensure optimum fidelity. Instrumentation saturation effects due to the artifact can be avoided with careful electrode placement. The technique was fully tested with a wide variety of electrical stimulation parameters (frequency and pulse width) applied to the common peroneal nerve to elicit contraction in the tibialis anterior. The program was also developed to allow batch processing of multiple files, using closed loop feedback correction. The two-stage peak detection artifact removal algorithm is demonstrated as an efficient post-processing technique for acquiring artifact free m-waves.

Action Potentials↗

PubMed1982

The autoreducible cytochromes c of the methylotrophs Methylophilus methylotrophus and Pseudomonas AM1.

The two types of soluble cytochrome c (cytochrome cH and cytochrome cL) found in methylotrophs are completely distinct proteins; one type is not a dimer or degradation product of the other. Free thiol groups are probably not involved in the unusually rapid autoreduction of the cytochromes at high pH. The axial ligands to the haem iron, histidine and methionine, are the same as in other low-spin cytochromes c. The methionine ligand is displaced at high pH by an alternative strong-field ligand. This displacement does not occur on reduction of cytochrome cL by methanol dehydrogenase, but this does not rule out the possibility that the autoreduction mechanism is involved in the interaction of the dehydrogenase and cytochrome c.

Alcohol Oxidoreductases↗

PubMed1980

The two cytochromes c in the facultative methylotroph Pseudomonas am1.

It was previously suggested that there is only one soluble cytochrome c in Pseudomonas AM1, having a molecular weight of 20000, a redox midpoint potential of about +260mV and a low isoelectric pint [Anthony (1975) Biochem. J.146, 289-298; Widdowson & Anthony (1975) Biochem. J.152, 349-356]. A more thorough examination of the soluble fraction of methanol-grown Pseudomonas AM1 has now revealed the presence of two different cytochromes c. These were both purified to homogeneity by acid treatment, ion-exchange chromatography, gel filtration, chromatography on hydroxyapatite and preparative isoelectric focusing. Molecular weights were determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis; midpoint redox potentials were determined directly by using platinum and calomel electrodes; isoelectric points were estimated by electrophoresis and by the behaviour of the two cytochromes on ion-exchange celluloses. The more abundant cytochrome c(H) (lambda(max.) 550.5nm) had a low molecular weight (11000), a midpoint potential of about +294mV and a high isoelectric point, not being adsorbed on DEAE-cellulose in 20mm-Tris/HCl buffer, pH8.0. The less abundant cytochrome c(L) (lambda(max.) 549nm) was about 30% of the total; it had a high molecular weight (20900), a midpoint potential of about +256mV and a low isoelectric point, binding strongly to DEAE-cellulose in 20mm-Tris/HCl buffer, pH8.0. The pH-dependence of the midpoint redox potentials of the two cytochromes c were very similar. There were four ionizations affecting the redox potentials in the pH range studied (pH4.0-9.5), two in the oxidized form (pK values about 3.5 and 5.5) and two in the reduced form (pK values about 4.5 and 6.5), suggesting that the ionizing groups involved may be the two propionate side chains of the haem. Neither of the cytochromes c was present in mutant PCT76, which was unable to oxidize or grow on C(1) compounds, although still able to grow well on multicarbon compounds such as succinate. Whether or not these two cytochromes c have separate physiological functions is not yet certain.

Carbon Monoxide↗

PubMed1980

The interaction between methanol dehydrogenase and the autoreducible cytochromes c of the facultative methylotroph Pseudomonas AM1.

Cytochromes cH and cL were autoreduced at high pH (pK greater than 10) and the autoreduced cytochromes reacted with CO. The autoreduction was first-order with respect to oxidized cytochrome c and was reversible by lowering the pH. Pure methanol dehydrogenase reduced cytochrome c (in the absence of methanol) by lowering the pK for autoreduction to less than 8.5. A mechanism is proposed for the autoreduction of cytochrome c and its involvement in the reaction with methanol dehydrogenase.

Alcohol Oxidoreductases↗