K. D. Mueller-Glaser

Noninvasive, real time laser Doppler flowmetry in perfusion regions and larger vessels

This paper describes an enhanced noninvasive continuous laser Doppler system for real time blood flow measurement in perfusion regions and larger vessels. The system consists of a miniaturized sensor, a fast digital signal processing (DSP) unit and a PC for signal visualization. The sensor comprises an IR laser diode to illuminate tissue through a short optical fiber with a variable spot size of 400 micrometers to 1000 micrometers and a photodetector which can be positioned 3 mm to 7 mm from the laser spot. The DSP of the system uses a parametric estimation of the laser Doppler power spectrum density based on a first order autoregressive process model AR (1) to calculate the first weighted moment. This algorithm is approximately ten times faster and as accurate as equivalent FFT-based algorithms. With a sampling rate of 390 kHz, it is possible to calculate and visualize 85 flow values per second. Model measurements prove very high linear correlations (r >= 0.99) between calculated first moments and flow velocities in a range from 1 mm/s up to 120 mm/s. Furthermore, in vivo measurement of blood flow both in perfusion regions and larger arteries, such as the a. radialis, were successfully performed in real time.

Noninvasive and nonocclusive determination of blood pressure using laser Doppler flowmetry

This report describes an approach determining blood pressure noninvasively without cuff. Regarding an elastic, fluid-filled tube as a model of an arterial segment, the solution of the Navier Stokes differential equations delivers a relation between the pressure and velocity pulse. There, simulations prove a minimal sensitivity of blood pressure concerning blood density, blood viscosity and damping. Hence, these parameters can be regarded interindividually as constants. Blood pressure is essentially sensitive on the pulse wave velocity, the velocity pulse, the arterial diameter and the reflection coefficient. To perform measurements, a system was built up comprising at least one laser Doppler blood flow sensor, a high performance DSP hardware and a PC. After individual initial Riva Rocci calibration, arterial diameter and reflection coefficient can be determined. Flow and pulse wave velocity and thus blood pressure can be calculated measuring continuously at least one velocity pulse with the laser Doppler flow sensor at a superficial artery like the a. radialis and simultaneously another cardiovascular signal like an ECG or another flow pulse at a different site of the artery. As a first result, high linear correlations between systolic blood pressure and pulse transit time were obtained.

Noncontact measurement of intraocular pressure using a modified Michelson interferometer

This paper describes a new method to examine the intraocular pressure (IOP) without any contact with the eye. In our new approach the IOP is determined indirectly from the acoustic properties of the eye, as the resonance frequencies of the bulbus are shifting with increasing IOP. In a first step simulations were made with the Finite Element Method to explore the correlation between the IOP and the acoustic properties of the bulbus. The results showed a significant rise of the resonance-frequencies with increasing IOP. Simultaneously a in-vitro measurement system was built comprising a modified michelson interferometer to measure the vibrations, a transducer to stimulate the eye and a controlling PC. With this system measurements were made with artificial eyes and enucleated pig eyes to prove the correlation experimentally. The eyes were stimulated both contacting the eye with a transducer by a stick and contactless with sonic waves. Several series of measurements showed a proportional constant of 1,25 Hz/mmHg in average, which can be detected easily. The standard deviation measuring different pig eyes was 4,5 mmHg. Next a in-vivo system was developed to study the acoustic behavior of the human eye in the real environment. The in-vivo system consists of a miniaturized semiconductor-laser interferometer complying laser safety requirements, an automatic positioning unit and an excitation unit to stimulate vibrations of the eye. Sub-micrometer vibrations of the eye can be measured in-vivo with this system.

Web based Teletherapy System for Telemonitoring and Remote Control of Therapeutic Devices

Health Monitoring is a growing field of research and development that gets more and more attention. Monitoring of patients at home by means of telemedical devices is a great chance to reduce costs for the healthcare system and increases the quality of life. Expanding the idea of health monitoring, a system is presented which not only monitors patient’s vital data, but also enables the physician to adapt the therapy from afar by remote controlling the therapeutic device at the patient’s site. Taking therapy of pain with infusion pumps as an example, the shortcomings of current treatment are discussed and optimizations using a teletherapeutic system are shown. The presented system consists of a webserver with webservice interface, which allows bidirectional, secure and fault tolerant communication between the physician and the devices of the patient.

Securely control Infusion Pumps via Internet for efficient Remote Therapy of Pain

Pain therapy is an important part of the current health care system and will become even more significant in future, because of the demographic changes. Though there are shortfalls in medical care of patients with pain. There are not enough specialized clinics and most of the patients do not get adequate therapy. In this paper the authors present a system that can solve these problems in pain therapy and enables specialized clinics to increase their efficiency in order to increase the capacity for pain care. The system combines telemonitoring of patients with the ability to remote control the patient’s infusion pump from afar. The physician is able to adapt the therapy of a patient without the need to visit him personally. Because of the fact, that the infusion pump applies analgesics that are able to cause vital harm, special interest is taken in the security and safety of the teletherapy system.

Design and realization of a handheld vibrometer system for noncontact in-vivo detection of microvibrations of the human eye to determine the intraocular pressure (IOP)

To allow measurements of the intraocular pressure (IOP) by glaucoma patients themselves (self-tonometry) a handheld-interferometer system for non-contact in vivo measurements of microvibrations of the human eye was realized. The measurement principle is based on the dependence of the resonance frequencies of the human eye on the IOP. To analyze this, the human eye is stimulated by ultrasonic waves and the induced microvibrations are measured with a vibrometer and processed by a DSP unit. Beside a stabilized diode laser and a low noise photodetector an exact three-dimensional positioning system had to be developed to guarantee reliable measurements. To investigate the corresponding requirements a camera-based system for the detection of human eye movements was developed and test series with several persons were made. Based on these results an adjustment unit was integrated in a miniaturized interferometer system: After a short self-adjusting procedure lateral to the setup by overlaying two targets of a highly sensitive optical system the correct measuring distance between the cornea and the vibrometer parallel to the optical axis is determined automatically by an astigmatic auto-focus system. With this handheld-vibrometer in vivo measurements with several test persons were made with very good results concerning the reliability and handling capability.

Noncontact tonometry using laser interferometry

This paper describes a new method to examine the intraocular pressure (IOP) without any contact to the eye. In our new approach the IOP is determined indirectly from the acoustic properties of the eye as the resonance frequencies of the bulbus are shifting with increasing IOP. Simulations with the Finite Element Method were done to explore the coherence between the IOP and the acoustic properties of the bulbus. A three-dimensional model of the eye was developed comprising the elastic cornea and sclera and the vitreous body. The results showed a significant rise of the resonance-frequencies with increasing IOP. This shift is enlarging for higher modes. In parallel measurements were performed on artificial eyes and on enucleated pig eyes to prove this correlation experimentally. A measuring system existing of a transducer to excite the bulbus, a miniaturized laser-vibrometer and PC was built. The eyes were stimulated both contacting the eye with a transducer by a stick and contactless with sonic waves. Several series of measurements were done to examine the pressure dependency of the acoustic behavior. The measurements showed a proportional constant of 1.25 Hz/mmHg in average, which can be detected easily. The standard deviation measuring different pig eyes was 4.5 mmHg.

Design flow for the reconfigurable HW platform XPP

Due to an increasing technology progress in the configurable hardware sector, which is currently dominated by FPGAs, new approaches like very fast re-configurable devices with ALU level granularity are on the rise. However, these coprocessor devices can not be programmed with conventional HW nor SW design approaches. To solve this dilemma, a combination is needed. This approach is described in this paper. Furthermore, an example how to program a re-configurable device is illustrated. This example consists of parts of an MPEG-4 decoder, which is running on the re-configurable processor platform XPP. The partitioning of these decoding algorithms into modules and the means of interaction between these modules is highlighted. In addition, the embedding of this algorithm in a XPP system is outlined.

Evaluation of laser Doppler flowmetry system with fast signal processing using an autoregressive process model

This report describes the evaluation of a noninvasive laser Doppler system comprising a sensor, a digital signal processor (DSP) unit and a visualizing PC for continuous blood flow measurements. The first weighted moment of the power spectrum density of the laser Doppler sensor signal is a linear measure for blood flow. In order to estimate the power spectrum densities in real time, a first order autoregressive process model was developed. Due to this very fast signal processing, the system allows measurements both in microcirculation and of higher blood flows in larger vessels with a signal bandwidth of up to 200 kHz, e.g. in superficial arteries. Since the analytical dependency of blood flow and first spectral moment is only valid for tissue perfusion, Monte Carlo simulations were performed to evaluate this dependency also for higher blood flow velocities in larger vessels. A multilayered, semi- infinite tissue model essentially comprising epidermis, dermis and a blood vessel with a parabolic profile of constant blood flow was used varying different parameter like vessel diameter and skin thickness. Furthermore, model measurements were performed using a Delrine slab with a drilling through which constant flow of whole blood was provided. Both the Monte Carlo simulations and model measurements prove very high linear correlations between the calculated spectral moments and flow velocities.

Design and fabrication of a microstructured bifocal intraocular lens

Intraocular lenses IOLs allow the vision restoration of cataract patients. However the ability of accommodation is lost after cataract surgery. Multifocal lenses show two or more foci with different refractive powers. Far and near objects can be at focus simultaneously. No additional spectacles are necessary. Bifocal lenses can be fabricated as multizone or as diffractive lenses. Diffractive multifocal lenses show in contrast to multi zone multifocal lenses no change of the brightness ratio for the far and near focus with change of the pupil diameter. Diffractive lenses show a saw tooth like microscopic shape with a geometrical height of the teeth in the order of microns. The lens was fabricated with a mold technique in a flexible silicone material. The molds have been lathed in metal with a ultra precision diamond lathe machine. For the test of the optical performance a MTF-measurement machine was constructed for multifocal lenses. With this machine the imaging quality and the intensity ratio of the two foci were measured. The optical quality of the lens turned out to be diffraction limited. At the University Hospital of Giessen, Germany a first clinical evaluation with 23 patients has been performed and proved for the high quality of the manufactured IOLs.