Distinct mechanisms of relaxation to bioactive components from chamomile species in porcine isolated blood vessels.

German chamomile (Matricaria recutita L.), a widely-used herbal medicine, has been reported to have a wide range of biological effects, including smooth muscle relaxation. The aim of this study was to compare the effects of representative compounds from chamomile (apigenin, luteolin, (-)-α-bisabolol, farnesene, umbelliferone; 3-30 µM) on vascular tone using porcine coronary and splenic arteries mounted for isometric tension recording in isolated tissue baths and precontracted with the thromboxane-mimetic U46619. Apigenin, luteolin, and (-)-α-bisabolol produced slow, concentration-dependent relaxations in both the coronary and splenic arteries that were not blocked by inhibition of nitric oxide synthase or potassium channels. Removal of extracellular calcium inhibited the relaxations to all three compounds, and these compounds also inhibited calcium re-addition-evoked contractions, indicating that the relaxation response may be mediated through inhibition of calcium influx. Apigenin and luteolin, but not (-)-α-bisabolol, enhanced the relaxation to the nitric oxide donor sodium nitroprusside, indicating that apigenin and luteolin may act to regulate cyclic GMP levels. Umbelliferone produced a rapid, transient relaxation in the splenic artery, but not the coronary artery, that was inhibited by L-NAME and removal of the endothelium, suggesting an influence on nitric oxide production. Farnesene, at concentrations up to 30 µM, was without effect in either blood vessel. In conclusion, hydroxylated compounds (apigenin, luteolin and (-)-α-bisabolol) found in chamomile all caused a slow relaxation of isolated blood vessels through an effect on calcium influx. Umbelliferone, on the other hand, produced a rapid, transient relaxation dependent upon release of nitric oxide from the endothelium.

Post-acute stroke patients use brain-computer interface to activate electrical stimulation.

Through certain mental actions, our electroencephalogram (EEG) can be regulated to operate a brain-computer interface (BCI), which translates the EEG patterns into commands that can be used to operate devices such as prostheses. This allows paralyzed persons to gain direct brain control of the paretic limb, which could open up many possibilities for rehabilitative and assistive applications. When using a BCI neuroprosthesis in stroke, one question that has surfaced is whether stroke patients are able to produce a sufficient change in EEG that can be used as a control signal to operate a prosthesis.

Influence of visual feedback and speed on micromanipulation accuracy.

Accuracy in micromanipulation tasks is limited and it is important to identify various factors affecting it. This paper studies the effect of visual magnification, speed and handedness to micromanipulation accuracy using microscope and LCD screen for feedback. Magnification of visual feedback increases the accuracy, but large magnification does not provide further improvement beyond 16x. Further, we observed a trade off between speed and accuracy in tracing a circular path, i.e. faster speed reduces the speed control ability of the hand. Finally, dominant/non-dominant hand is found to affect accuracy in motion.

Automatic control of mechanical forces acting on cell biomembranes using a vision-guided microrobotic system in computer microscopy.

A prototype for automatic control of mechanical forces acting on cell biomembranes is proposed in this paper. This prototype consists of vision-guided position control of the holder and micro-force sensor, automatic mechanical property characterization of cell biomembranes and automatic control of mechanical forces acting on cell biomembranes. A template-free calibration method and autofocusing of multiple objects are introduced in the vision-guided position control to minimize external biological contamination and position the cell, holder and micro-force sensor into the same focal plane, respectively. A third-order polynomial modified from biomembrane point-load model describing the relationship between the measured mechanical force and the deformations of biomembranes is proposed. This simplified model is easily identified and inversed to facilitate the automatic control of mechanical forces. Experimental results based on zebrafish embryos demonstrate the feasibility of the proposed prototype.

Self-calibration method for vision-guided cell micromanipulation systems.

A new self-calibration method for a piezoelectric actuator-based vision-guided cell micromanipulation system is proposed. This method consolidates all the system parameters' uncertainties into a matrix instead of classifying into intrinsic and extrinsic. The position difference of the micromanipulator tip in the image plane between the measured and estimated output which is based on estimations of relevant parameters is assumed to be caused by the matrix. This matrix is estimated by means of collecting several pairs of known input and the corresponding output differences. Matrix standard deviation and gray-value based matching are applied to identify the output differences. Biological contamination is reduced since a calibration template is not required. This self-calibration is particularly suitable for cell micromanipulation systems where the micromanipulator is frequently dismounted and mounted.

Design and implementation of a two degree-of-freedom micromanipulation assessment system.

A two degree-of-freedom (DOF) micro motion sensing system to assess micromanipulation accuracy and physiological tremor has been developed. The system employs a position sensitive detector (PSD) module and a laser diode placed inside an instrument used in micromanipulation. A laser light is shined from the laser diode onto the PSD surface which is faced upward. The PSD detects the centroid position of the laser light spot falling onto its surface. A few markers are overlaid in a circular pattern on the PSD surface as reference for path dependent tests. Ambient light disturbance is eliminated by modulating the laser light on and off. Advantages and limitation of the system comparing to other similar systems are described.

A study of a hand-held instrument's angular motion due to physiological tremor in micromanipulation tasks.

Angular motion of a hand-held instrument due to physiological tremor during micromanipulation tasks was recorded with a six degree-of-freedom accelerometer-based sensing unit placed in the instrument. Methods to get angular velocities and angular accelerations from the acceleration readings of accelerators in the sensing unit are described. Statistics of angular velocity and angular acceleration of the instrument due to the tremor obtained from ten normal subjects are reported. Assumption of very small tremor angular velocities in micromanipulation tasks to calculate tremor angular accelerations analytically is validated.

System to assess accuracy of micromanipulation.

The authors had previously developed an optical micro motion sensing system (M2S2) using a pair of orthogonally placed position sensitive detectors (PSD) to track 3D displacement of the tip of a microsurgical instrument in real-time. In the M2S2 system, an infrared (IR) diode is used to illuminate the workspace. A ball is attached to the tip of an intraocular shaft to reflect IR rays onto the PSDs. Instrument tip position is then calculated from the centroid position of reflected IR light on the PSDs. The M2S2 system together with a test platform is used as an evaluation system to assess the accuracy and physiological tremor of subjects performing micromanipulation tasks. Since the need to use the ball at the instrument tip prevents the subjects from performing the manipulation tasks precisely, a laser light is provided as a guide for the subjects to aim at the target precisely. A laser diode module is placed inside the instrument to provide the required laser light. The instrument intraocular shaft is replaced with a same-sized hollow tube to let the laser light from the instrument pass through down to the target. The laser light spot position on the platform is used to access the performance of the subjects. The laser light spot position is calculated from the tilt angle information provided by an accelerometer placed inside the instrument, and the instrument tip position information given by M2S2.

Bandlimited multiple Fourier linear combiner for real-time tremor compensation.

Surgical accuracy of the hand-held instruments depends on the active compensation of disturbance and tremor. Physiological tremor is one of the main causes for imprecision in micro-surgery procedures. One of the popular tremor compensation methods is based on weighted-frequency Fourier linear combiner (WFLC) algorithm, that can adapt to the changes in frequency as well as amplitude of the tremor signal. WLFC estimates the dominant frequency and the amplitude. For the case of tremor with frequency variation or comprising of two or three frequencies close in spectral domain, the WFLC performance is degraded. In this paper, we present a bandlimited multiple Fourier linear combiner that can track the modulated signals with multiple frequency components. We also discuss the tremor sensing with accelerometers. Using the proposed algorithm the drift caused by the accelerometers is also eliminated. The proposed filter is tested in real-time for 1-DOF cancellation of tremor.