Battery powered neuromuscular stimulator circuit for use during simultaneous recording of myoelectric signals

Surface Functional Electrical Stimulation (FES) requires high stimulation voltages. A step-up transformer in the output stage of the stimulation circuit is often used. In the present technical paper a voltage controlled current source (VCCS) is presented as an alternative to the transformer coupling. Two (master–slave) coupled transconductance amplifiers (TAs)—in series with pre-charged capacitors—are used to drive the output current. After each stimulation pulse the capacitors are recharged to a high voltage by a switch mode power supply (SMPS). A multiplexer in the output stage is used to provide biphasic output. Output rise-time (10–90%) was less than 2 μs at 100 mA output. Biphasic charge balanced stimulation current can be produced with a net current to ground of less than 20 nA, thus virtually separated from ground. The circuit permits recording of the volitional myoelectric signal from the stimulated muscle. It is part of a portable myoelectrically controlled FES system powered by 2 AA batteries and currently used in clinical trials.     

Water-immersion wrinkling is due to vasoconstriction

The underlying mechanism of the water-immersion skin wrinkling test, which is used as a test of sympathetic nerve function, remains elusive. We investigated changes of blood circulation in the hand occurring with water-immersion wrinkling by measuring the velocity of ulnar and digital artery blood flow, and of digit skin blood flow, in healthy subjects before and during wrinkling. Wrinkling was accompanied by significant reduction in blood flow velocity in all vessels, with a maximum in digital vessels. Our data show that water-immersion wrinkling is a function of digit pulp vasoconstriction. This test of sympathetic function can now be quantified using parameters of blood flow velocity, enabling its more widespread and accurate use.     

Vasomotor dysfunction in carpal tunnel syndrome

Little attention has been paid to small-fiber dysfunction in carpal tunnel syndrome (CTS) although its symptoms are common. This study investigates vasomotor dysfunction, which is controlled by small nerve fibers, in patients with CTS compared with control subjects. Vasomotor function was quantified by measuring, with laser Doppler velocimetry, skin vasoconstriction induced by a eutectic mixture of local anesthetic (EMLA) cream over digit tips 3, 4, and 5. Hands with CTS (n = 32) compared with controls (n = 19) demonstrated significantly reduced vasoconstriction in digits 3 and 4, but not digit 5. A blood flow ratio (digit 3/5) of less than 0.73 identified CTS in 69% with 68% specificity. Testing for vasomotor dysfunction in CTS allows for more comprehensive neurophysiological testing, which is heavily biased towards large nerve fibers.