Biomedical subjects

Robert Guardo

Publications and source records attributed to Robert Guardo.

3 recordsLinked to original sources

PubMed2006

Electrical impedance tomography's correlation to lung volume is not influenced by anthropometric parameters.

STUDY OBJECTIVES: Electrical impedance tomography (EIT) is able to reflect physiological parameters such as real-time changes in global and regional lung volume. EIT can aid in the assessment of lung recruitment, and its use has been validated in preliminary studies monitoring mechanical ventilation at the bedside. ICU patients vary widely in their body habitus, and obesity is becoming more prevalent. Our primary research purpose was to establish whether anthropometric parameters influence EIT's reliability. Our secondary question was whether body position alters its correlation to spirometric measurements. SUBJECTS: 22 healthy adult volunteers (12 male, 10 female) with broadly variable anthropometric parameters. INTERVENTIONS: Simultaneous measurements of changes in lung volume using EIT imaging and a pneumotachograph were obtained with two breathing patterns (quiet and deep breathing) and in four body positions (standing, sitting, semi-reclining and supine). MEASUREMENTS AND RESULTS: Correlation between measurements of changes in lung volume using EIT imaging and a pneumotachograph was excellent. Variations attributable to anthropometric measurements accounted for at most a 1.3% difference. CONCLUSIONS: Anthropometric variability and body position do not adversely influence the EIT estimation of changes in lung volume. These data suggest EIT could be used to monitor critically ill mechanically ventilated adults with variable body habitus regardless of position.

Adult↗

PubMed2006

A method for modelling and optimizing an electrical impedance tomography system.

Electrical impedance tomography (EIT) image reconstruction is an ill-posed problem requiring maximum measurement precision. Recent EIT systems claim 60 to 80 dB precision. Achieving higher values is hard in practice since measurements must be performed at relatively high frequency, on a living subject, while using components whose tolerance is usually higher than 0.1%. To circumvent this difficulty, a method for modelling the electronic circuits of an EIT system was developed in order to optimize the circuits and incorporate the model in the reconstruction algorithms. The proposed approach is based on a matrix method for solving electrical circuits and has been applied to the scan-head which contains the front-end electronic circuits of our system. The method is used to simulate the system characteristic curves which are then optimized with the Levenberg-Marquardt method to find optimal component values. A scan-head was built with the new component values and its simulated performance curves were compared with network analyser measurements. As a result of the optimization, the impedance at the operating frequency was increased to minimize the effects of variations in skin/electrode contact impedance. The transconductance and gain frequency responses were also reshaped to reduce noise sensitivity and unintended signal modulation. Integrating the model in the reconstruction algorithms should further improve overall performance of an EIT system.

Algorithms↗

PubMed2005

A parametric model of the relationship between EIT and total lung volume.

Spirometry and electrical impedance tomography (EIT) data from 26 healthy subjects (14 males, 12 females) were used to develop a model linking contrast variations in EIT difference images to lung volume changes. Eight recordings, each 64 s long, were made for each subject in four postures (standing, sitting, reclining at 45 degrees, supine) and two breathing modes (quiet tidal and deep breathing). Age, gender and five anthropometric variables were recorded. The database was divided into four subsets. The first subset, data from 22 subjects (12 males, 10 females) recorded in deep breathing mode, was used to create the model. Validation was done with the other subsets: data recorded during quiet tidal breathing in the same 22 subjects, and data recorded in both breathing modes for the other four subjects. A quadratic equation in DeltaV(P) (lung volume changes recorded by the spirometer) provided a very good fit to total contrast changes in the EIT images. The model coefficients were found to depend on posture, gender, thoracic circumference and scapular skin fold. To validate the model, the quadratic equation was inverted to estimate lung volume changes from the EIT images. The estimated changes were then compared to the measured volume changes. Validations with each data subset yielded mean standard errors ranging from 9.3% to 12.4%. The proposed model is a first step in enabling inter individual comparisons of EIT images since: (1) it provides a framework for incorporating the effects of anthropometric variables, gender and posture, and (2) it references the images to a physical quantity (volume) verifiable by spirometry.

Adult↗