Mitja Veber

Regulation of human cutaneous circulation evaluated by laser Doppler flowmetry, iontophoresis, and spectral analysis: importance of nitric oxide and prostaglandines

Nitric oxide (NO) and prostaglandines (PGs) are important in regulation of vascular tone and blood flow. Their contribution in human cutaneous circulation is still uncertain. We inhibited NO synthesis by infusing N(G)-monomethyl-L-arginine (L-NMMA) in the brachial artery (16 micromol/min for 5 min) and reversed it by intraarterial infusion of L-arginine (40 micromol/min for 7.5 min). PG synthesis was inhibited by the cyclooxygenase inhibitor aspirin (600 mg over 5 min intravenously). Basal cutaneous perfusion and perfusion responses during iontophoresis with the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent vasodilator sodium nitroprusside (SNP) were recorded by laser Doppler flowmetry (LDF). We performed wavelet transforms of the measured signals. Mean spectral amplitude within the frequency interval from 0.0095 to 1.6 Hz and mean and normalized amplitudes of five intervals around 1, 0.3, 0.1, 0.04, and 0.01 Hz were analysed. The oscillations with frequencies around 1, 0.3, 0.1, and 0.04 Hz are influenced by the heartbeat, the respiration, the intrinsic myogenic activity of vascular smooth muscle, and the neurogenic activity of the vessel wall, respectively. We have previously shown that the oscillation with a frequency around 0.01 Hz is modulated by the vascular endothelium. L-NMMA reduced mean value of the LDF signal by approximately 20% (P = 0.0067). This reduction was reversed by L-arginine. Mean value of the LDF signals during ACh and SNP iontophoresis did not change after infusion of L-NMMA. Aspirin did not affect mean value of the LDF signal or the LDF signal during ACh or SNP iontophoresis. Before interventions the only significant difference between the effects of ACh and SNP was observed in the frequency around 0.01 Hz, where ACh increased normalized amplitude to a greater extent than SNP. L-NMMA abolished this difference, whereas it reappeared after infusion of L-arginine (P = 0.0084). Aspirin did not affect this difference (P = 0.006). We conclude that basal cutaneous blood flow and the endothelial dependency of the oscillation around 0.01 Hz are partly mediated by NO, but not by endogenous PGs. Other aspects of human cutaneous circulation studied are not regulated by NO or PGs.

Wavelet analysis of blood flow dynamics:effect on the individual oscillatory components of iontophoresis with pharmacologically neutral electrolytes

Iontophoresis currents are used in the transcutaneous delivery of vasoactive substances for noninvasive assessment of skin vascular properties. The blood flow rate can be recorded by laser Doppler flowmetry (LDF), its average value and the amplitudes of its oscillatory components being used to evaluate the effect of the drugs. Because non-drug-specific, current-induced, vasodilation could confound the interpretation of the response, we have investigated the effect of currents of both polarities on the spectral components of the LDF signal in the absence of vasoactive substances. It was recorded for healthy volunteers with both high conductance (5 mol/l NaCl) and low conductance (deionized water) electrolytes. The oscillatory components were analysed by wavelet transform within 0.0095-1.6 Hz, divided into five sub-intervals. Only cathodal iontophoresis with deionized water increased the oscillatory energy and amplitude. It did so at all frequencies, but none of the sub-intervals associated with vasodilation (0.0095-0.145 Hz) was selectively affected compared to the others.

Assessment of human hand kinematics

In the paper we propose a method for assessment of hand motion which is based on optical tracking system and parametric model of a hand. The model was scaled according to hand external dimensions of each individual. Optical tracking device was used for model validation which was made for middle and index finger. The algorithms for calculation of hinge joint axis of rotation and ball joint center of rotation were employed. The joint angles were obtained in two ways, from known centers of joint rotation and by solving inverse kinematics for finger from given positions of fingertips. The lengths of finger segments, calculated by using data from statistical anthropometry, do not differ notably from the lengths obtained from calculated centers of rotation of joints. The angles obtained by inverse kinematics are comparable to the angles obtained from estimated centers of rotation. Minimalistic approach makes the method suitable for calibration of a sensor glove

Using computer vision in a rehabilitation method of a human hand

We developed this program for the purpose of a rehabilitation method that requires a patient to move an object around with his hand. Using a black and white firewire camera the program determines the position and orientation of a black rectangle on a white plane. The user must enter the length and width of the rectangle before the start. With this information the position is determined even if a part of the rectangle is obscured by a user’s hand. The program works in real-time (15 to 20 frames per second).

Assessment of hand kinematics and its control in dexterous manipulation

The aim of our work was to design a method for assessment and training of human hand dexterity while manipulating an object. A virtual environment was used to display a target object in various poses. The target poses were first recorded for a single person – a virtual trainer. The poses of a real object, held by the subjects included in the investigation, were assessed by a motion tracking device and displayed within the virtual environment. The subjects were asked to align the 3D images of real object and the target object. The target poses were normalized with respect to the different sizes of arms and hands. In this way all subjects were able to reach the desired target postures. Satisfactory repeatability of hand movements was observed in a single subject and across a group of twelve unimpaired subjects.