Biomedical subjects

Laura Roa

Publications and source records attributed to Laura Roa.

4 recordsLinked to original sources

PubMed2004

A novel mathematical method based on urea kinetic modeling for computing the dialysis dose.

A novel normalized single pool urea kinetic model (nspUKM) for the quantification of the urea removal, dialyzer urea clearance and urea generation rate during a dialysis session, is presented. Its major goal is the computation of an accurate estimate of the fractional dialyzer urea clearance (dKt/V), which is denoted nKt/V, in contrast to the equilibrated Kt/V (eKt/V). This work clarifies the significance of dKt/V as a complement to eKt/V in hemodialysis (HD) prescription and quantification. This new model emerges from a generalization of the standard single pool urea kinetic model (spUKM) of the US National Cooperative Dialysis Study (NCDS), identified as gspUKM. Due to their significance, the standard single pool Kt/V (spKt/V) and the eKt/V are also analyzed from gspUKM in this work, with the aim of achieving a better interpretation of the results. Indices nKt/V, eKt/V and spKt/V have been compared with the dKt/V computed from a published and validated two-pool urea kinetic model (2pUKM). We present the results obtained from a clinical study carried out on a group of 30 end stage renal disease (ESRD) patients. The limits of agreement (mean+/-2S.D. (standard deviation) of the difference) between nKt/V and 2pKt/V were -0.077+/-0.72% (percentage of the dKt/V mean), while between eKt/V and 2pKt/V were -13.75+/-17.39% and between spKt/V and 2pKt/V were -1.61+/-6.54%. These scores prove that the nspUKM model is able to provide a very accurate estimate of 2pKt/V and thus dKt/V, even with high flux (HF) HD. The presented method joins the simplicity of single-pool models to the accuracy of double-pool models, when the target is the identification of the dialyzer urea clearance, urea removal and urea generation rate, although it does not provide a good prediction of the urea dynamics. Finally, we think that our analytical and experimental findings throw light on the behavior and applicability of the different Kt/V indices analyzed.

Blood Urea Nitrogen↗

PubMed2003

A kinetic study of blinking responses in cats.

Reflexively evoked and eye-related eyelid responses were recorded using the search coil in a magnetic field technique in alert cats. The downward phase of a blink was a large (up to 21 deg), fast (up to 2000 deg s-1) eyelid displacement in the closing direction, with an almost fixed rise time duration (15-20 ms); its maximum velocity was achieved in ~10 ms. Upward eyelid motion was separated into two phases. The first phase consisted of a fast eyelid displacement, with a short duration (approximately 30 ms) and a maximum velocity up to 900 deg s-1. The second phase had an exponential-like form, lasting for 200-400 ms, and a maximum velocity ranging between 30 and 250 deg s-1. Maximum blink velocity in the downward direction was linearly related to maximum velocity of the first upward phase. The first phase in the upward direction was never observed if the eyelid stayed closed for a long period (> 50 ms) or moved slowly in the closing direction before it started to open. In these two cases, the upswing motion of the blink reflex contained only the exponential-like movement characteristic of the second upward phase, and maximum velocity in the downward direction was not related to that of the eyelid upward displacement. Mean duration of eyelid downward saccades was approximately 130 ms, and their peak velocities ranged between 50 and 440 ms. A physiological model is presented explaining the active and passive forces involved in both reflex and saccadic eyelid responses. A second-order system seems to be appropriate to describe the postulated biomechanical model.

Air↗

PubMed2003

Renal telehealthcare system based on a patient physiological image: a novel hybrid approach in telemedicine.

This paper presents a novel renal telemedicine system, Virtual Center for Renal Support (VCRS), focused on the end-stage renal disease (ESRD) population. The VCRS design modifies the telemedicine paradigm, currently centered on communication technologies and monitoring devices, by emphasizing the way that biosignals are used to extract on-line knowledge to be used by physicians to solve current needs of this population. We begin with an ESRD review, from which a summary of major limitations of current renal health assistance programs is obtained. This is used to form the basis for the VCRS. This work is focused on a theoretical description of the technological architecture of VCRS, followed by a simulation experiment showing some preliminary results from a prototype of a patient physiologic image (PPI) computer component, the major knowledge creator of VCRS. Preliminary results show that PPI technology provides the ability to supervise internal variables representing the patient's dynamic behavior. The demonstrated relation between adequate control of extracellular volume and blood pressure suggests that VCRS is able to generate hypovolemia warnings before their occurrence during a hemodyalysis session delivered remotely. However, PPI is not restricted to kinetic models, which were initially chosen because of their successful results in the provision of dialysis. Preliminary results suggest the ability of this telemedicine system to enhance remote patient supervision and care.

Adult↗

PubMed2002

Virtual center for renal support: technological approach to patient physiological image.

The patient physiological image (PPI) is a novel concept which manages the knowledge of the virtual center for renal support (VCRS), currently being developed by the Biomedical Engineering Group of the University of Seville. PPI is a virtual "replica" of the patient, built by means of a mathematical model, which represents several physiological subsystems of a renal patient. From a technical point of view, PPI is a component-oriented software module based on cutting-edge modeling and simulation technology. This paper provides a methodological and technological approach to the PPI. Computational architecture of PPI-based VCRS is also described. This is a multi-tier and multi-protocol system. Data are managed by several ORDBMS instances. Communications design is based on the virtual private network (VPN) concept. Renal patients have a minimum reliable access to the VCRS through a public switch telephone network--X.25 gateway. Design complies with the universal access requirement, allowing an efficient and inexpensive connection even in rural environments and reducing computational requirements in the patient's remote access unit. VCRS provides support for renal patients' healthcare, increasing the quality and quantity of monitored biomedical signals, predicting events as hypotension or low dialysis dose, assisting further to avoid them by an online therapy modification and easing diagnostic tasks. An online therapy adjustment experiment simulation is presented. Finally, the presented system serves as a computational aid for research in renal physiology. This is achieved by an open and reusable modeling and simulation architecture which allows the interaction among models and data from different scales and computer platforms, and a faster transference of investigation models toward clinical applications.

Aged↗