Noninvasive optical polarimetric glucose sensing using a true phase measurement technique.

The focus of this paper was to describe the development and testing of a noninvasive true phase optical polarimetry sensing system to monitor in vivo glucose concentrations. To demonstrate the applicability of this optical sensor for glucose measurement, we first calibrated the system and then tested it in vitro using both a glass test cell filled with glucose solution in the physiologic range, with a path length of 0.9 cm to approximate one centimeter path length present in the anterior chamber of the eye, and then on an excised human eye. Our technique used helium neon laser light which was coupled through a rotating linear polarizer along with two stationary linear polarizers and two detectors to produce reference and signal outputs whose amplitudes varied sinusoidally with a frequency of twice the angular velocity of the rotating polarizer, and whose phase was proportional to the rotation of the linear polarization vector passing through the glucose solution.

Amplitude-modulated tone encoding behavior of cochlear nucleus neurons: modeling study.

A recent study of amplitude-modulated (AM) tone encoding behavior of dorsal and posteroventral cochlear nucleus (DCN and PVCN) neurons by Kim et al. [Hear. Res. 45, 95-113, 1990] observed that certain neurons (e.g., pause/build type-III neurons and chop-S neurons) tended to exhibit band-pass modulation transfer functions (MTFs) and intrinsic oscillations (IOs) whereas certain other neurons (e.g., chop-T neurons) tended to exhibit low-pass MTFs and no IOs. The goal of the present study was to develop models of these response characteristics in an attempt to understand the underlying neuronal mechanisms. We hypothesized that chopper neurons corresponded to stellate cells and pause/build neurons corresponded to fusiform cells. We also hypothesized that, with right input combination, appropriate models of a single stellate and fusiform cell could account for band-pass and low-pass MTFs as well as the associated IOs. The neuron models developed by Arle and Kim [Biol. Cybern. 64, 273-283, 1991] for the stellate and fusiform cells were used in this study. The models are modified versions of MacGregor type neuron model incorporating cell-specific nonlinear voltage-dependent conductances. The AM tone excitation via the auditory nerve fibers was represented by a current at the soma of the neuron model, which consisted of dc, ac and a zero-mean Gaussian noise. The dc, ac and noise represent a high-frequency carrier beyond the neuron's phase-locking limit, an envelope, and randomness of the system, respectively. With systematic variation of dc, ac and noise amplitudes, we observed the following: the band-pass MTF behaviors of pause/build and chop-S neurons were reproduced by the fusiform cell model and the stellate cell model with a strong dc/noise ratio, respectively. The low-pass MTF behavior of a chop-T neuron was reproduced by the stellate cell model with a weak dc/noise ratio. It was observed that the stellate cell model was more susceptible to the noise, in the sense that an increase in noise tended to abolish the IO and change the MTF of the model from band-pass to low-pass more readily in the stellate cell model than in the fusiform cell model. Kim et al. (1990) observed a close correlation between the IO frequency and the best envelope frequency (BEF). In the models, a similar correlation was observed between the two measures for both the stellate and fusiform cell models.(ABSTRACT TRUNCATED AT 400 WORDS)

A new approach to the modeling and control of postoperative pain.

The objective of this paper has been to explore contributions which the technology of control engineering can make to the relief of postoperative pain. A human-operated, closed-loop, analgesic drug injection system has been designed to alleviate chronic pain. In this system, a patient presses a button when pain relief is required. A computer interfaces the button to the patient's drug injection pump. A patient pain model has been developed to describe the dynamics of the human physiological and psychological responses to chronic pain. A pharmacokinetic model of analgesia is also included. The pain model has been validated by adjusting its parameters so that its behavior mimics actual button-pressing records of self-administered analgesia. A modified Smith delay compensator and IPFM controller are used to compensate for the inherent nonlinearity of the system and to obtain the high performance required. The results of this simulation study are promising. The nonlinear patient pain model represents a contribution to the description of the dynamics and quantification of pain. The control algorithms proposed have shown, through modeling studies, an improvement in the performance of self-administered analgesia systems. The simulated patients obtained good pain relief without excessive button-pressing, and without undesirable high concentrations of opioids being observed. The SDC/IPFM controller architecture has been found to be robust in the presence of pain noise and pharmacokinetic plant parameter changes.