A non-invasive continuous method of measuring blood volume during haemodialysis using optical techniques.

Hypotension during haemodialysis and fluid overload between treatments are major problems for haemodialysis patients. Clinical means of assessing hydration state can be relatively imprecise. We describe a non-invasive method of measuring absolute blood volume (BV) during a mock in vitro haemodialysis session which adds objective information to that assessment. As fluid is removed by ultrafiltration, haemoglobin concentration [Hb] rises proportionately with the fall in BV. An optical monitor clamped across the transparent dialysis tubing gives a continuous readout of near infra-red light transmitted through the blood, and this can be converted to [Hb] values. The net change in BV is the difference between the volume of fluid ultrafiltered and the volume which refills the vascular compartment from the extravascular space. By analysing the change in [Hb] and therefore the change in BV at two different rates of fluid removal, the absolute BV can be determined. The accuracy of this method was tested in vitro. This optical method accurately measures the change in BV over a range of [Hb] from 4 to 15 g/dl and blood circulation pump speeds of 150-300 ml/min. A series of 10 in vitro experiments was performed. The mean relative difference between the measured BV and the calculated BV, was 5.7 +/- 2.5%. This readily repeatable technique can accurately measure BV during a mock in vitro haemodialysis session, thus providing information for the clinical assessment of the hydration state. Information from these experiments will assist in future in vivo studies.

Application of volume-selected, two-dimensional multiple-quantum editing in vivo to observe cerebral metabolites.

The volume selection technique SPACE has been combined with a two-dimensional multiple-quantum editing sequence to uniquely detect certain J-coupled cerebral metabolites. In vivo results demonstrating edited glutamate/glutamine and lactate from 0.4 ml of a rat's brain at 4.7 T are presented. The sequence was optimized to balance multiple-quantum generation and signal loss due to T2 relaxation. Without due regard to T2 relaxation little signal is observed.

Training program for a myo-electrically controlled prosthesis with sensory feedback system.

A myo-electrically controlled prosthesis that incorporates a sensory feedback mechanism to provide the wearer with a sense of touch or gripping force in the prosthetic hand was developed for patients with below-elbow amputations. A training protocol was established in which patients were taught to produce myo-electric control signals and to interpret the sensory feedback. The protocol includes functional training in daily living skills. The experiences of four patients trained with these limbs are described.

Fitting below-elbow prostheses which convey a sense of touch.

A myoelectrically controlled electric hand has been modified so that the gripping force between thumb and index finger may be measured. The measurement is used to control a sensory feedback device applied to the surface of the skin within the socket of the prosthesis informing the wearer of the strength of grip exerted. Two people have been fitted with this prosthesis and they report that the sensory feedback gives them reassurance when using the arm. To date there has not been any noticeable adverse tissue reponse from the applied sensory stimulus.

Sensory feedback for artificial limbs.

Over the years various approaches have been made to help solve the problem of replacing mechanical function of a lost limb, but there has been little direct interest in the associated problem of replacing the sensory function also lost in the amputation. Psychological rejection of electrically powered hands (despite their good cosmesis) suggests that greater attention should be given to the provision of sensory feedback on artificial limbs. Myoelectrically controlled electric hands fitted with a sense of touch have been fitted to two patients and in a nine month trial period they reported favourably on these fittings. There has not been any adverse skin reaction to the application of the electrical feedback stimulus and the patients say that because of the feedback they have an increased level of confidence in using the prosthesis.