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Byline: Raffaele L. Dellaca (1), Marie Andersson Olerud (2), Emanuela Zannin (1), Peter Kostic (2), Pasquale P. Pompilio (1), Goran Hedenstierna (3), Antonio Pedotti (1), Peter Frykholm (2) Keywords: Forced oscillation technique; ALI/ARDS; Mechanical ventilation; PEEP; Respiratory mechanics Abstract: Purpose ALI and ARDS are associated with lung volume derecruitment, usually counteracted by PEEP and recruitment maneuvers (RM), which should be accurately tailored to the patient's needs. The aim of this study was to investigate the possibility of monitoring the amount of derecruited lung by the forced oscillation technique (FOT). Methods We studied six piglets (26 +- 2.5 kg) ventilated by a mechanical ventilator connected to a FOT device that produced sinusoidal pressure forcing at 5 Hz. The percentage of non-aerated lung tissue (V tiss.sub.NA%) was measured by whole-body CT scans at end-expiration with zero end-expiratory pressure. Respiratory system oscillatory input reactance (X .sub.rs) was measured simultaneously to CT and used to derive oscillatory compliance (C .sub.X5), which we used as an index of recruited lung. Measurements were performed at baseline and after several interventions in the following sequence: mono-lateral reabsorption atelectasis, RM, bi-lateral derecruitment induced by broncho-alveolar lavage and a second RM. Results By pooling data from all experimental conditions and all pigs, C .sub.X5 was linearly correlated to V tiss.sub.NA% (r .sup.2 = 0.89) regardless of the procedure used to de-recruit the lung (reabsorption atelectasis or pulmonary lavage). Separate correlation analysis on single pigs showed similar regression equations, with an even higher coefficient of determination (r .sup.2 = 0.91 +- 0.07). Conclusion These results suggest that FOT and the measurement of C .sub.X5 could be a useful tool for the non-invasive measurement of lung volume recruitment/derecruitment. Author Affiliation: (1) Dipartimento di Bioingegneria, Politecnico di Milano University, Piazza Leonardo da Vinci 32, 20133, Milan, Italy (2) Department of Surgical Sciences, Anaesthesia and Intensive Care, Uppsala University, Uppsala, Sweden (3) Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden Article History: Registration Date: 10/09/2009 Received Date: 19/01/2009 Accepted Date: 02/09/2009 Online Date: 30/09/2009 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1673-3) contains supplementary material, which is available to authorized users.

Scanhead tracking by opto-electronic (OE) systems allows high accuracy in three-dimensional (3-D) freehand ultrasound imaging. In this paper, a new set of methods is proposed and compared with the standard approach [Gram-Schmidt method (GS)]. Three redundancy-based algorithms are introduced to compensate for possible loss of markers during data acquisition: regression plane (RP), multiple Gram-Schmidt (MGS), and center of mass least square (CMLS). When combined with the ultrasound instrument, the root-mean-squared (RMS) uncertainty in locating target points, over a working volume of 420 mm x 490 mm x 100 mm, improved by 7% and 24% using MGS and CMLS method respectively, compared to GS. A lower improvement was obtained with RP methods (5%), using the best marker configuration. In conclusion, CMLS method provides a robust and accurate procedure for 3-D freehand ultrasound scanhead tracking, able to manage possible loss of markers, with interesting perspectives for image fusion and body referenced 3-D ultrasound. Index Terms--Image calibration, opto-electronic motion analysis, reflective markers, scanhead tracking, three-dimensional ultrasound.

Biomechanical study of car driver posture is one of the most referenced aspects for the ergonomic design process of the whole vehicle. The aim of this work is to present a multi-factor method for the analysis of sitting posture and the resulting interactions of the car driver body with the cushion and the backrest. The proposed method, based on the combined use of an optoelectronic system for motion capture and suitable matrices of pressure sensors, has allowed the measurement of a large set of car driver posture parameters and the identification of specific sitting strategies characterising the driving posture, despite the different behaviours of the analysed subjects. Keywords: Car seat; Posture; Pressure map; Ergonomics

A study of eight elderly and eight young hypertensive patients found that elder patients displayed a slight tendency toward a higher 24-h average systolic blood pressure (SBP) compared with young patients. Both groups had no clinical evidence of cardiovascular complications at the time of 24-h blood pressure monitoring. The young have better baroreflex sensitivity and control over heart rate, which is evident at nighttime.

Abstract Background The purpose of this study is to investigate intra-fraction setup variability in hypo-fractionated cranial and body radiotherapy; this is achieved by means of integrated infrared optical localization and stereoscopic kV X-ray imaging. Method and Materials We analyzed data coming from 87 patients treated with hypo-fractionated radiotherapy at cranial and extra-cranial sites. Patient setup was realized through the ExacTrac X-ray 6D system (BrainLAB, Germany), consisting of 2 infrared TV cameras for external fiducial localization and X-ray imaging in double projection for image registration. Before irradiation, patients were pre-aligned relying on optical marker localization. Patient position was refined through the automatic matching of X-ray images to digitally reconstructed radiographs, providing 6 corrective parameters that were automatically applied using a robotic couch. Infrared patient localization and X-ray imaging were performed at the end of treatment, thus providing independent measures of intra-fraction motion. Results According to optical measurements, the size of intra-fraction motion was (median ± quartile) 0.3 ± 0.3 mm, 0.6 ± 0.6 mm, 0.7 ± 0.6 mm for cranial, abdominal and lung patients, respectively. X-ray image registration estimated larger intra-fraction motion, equal to 0.9 ± 0.8 mm, 1.3 ± 1.2 mm, 1.8 ± 2.2 mm, correspondingly. Conclusion Optical tracking highlighted negligible intra-fraction motion at both cranial and extra-cranial sites. The larger motion detected by X-ray image registration showed significant inter-patient variability, in contrast to infrared optical tracking measurement. Infrared localization is put forward as the optimal strategy to monitor intra-fraction motion, featuring robustness, flexibility and less invasivity with respect to X-ray based techniques.

Abstract Background Pulmonary edema induces changes in airway and lung tissues mechanical properties that can be measured by low-frequency forced oscillation technique (FOT). It is preceded by interstitial edema which is characterized by the accumulation of extravascular fluid in the interstitial space of the air-blood barrier. Our aim was to investigate the impact of the early stages of the development of interstitial edema on the mechanical properties of the respiratory system. Methods We studied 17 paralysed and mechanically ventilated closed-chest rats (325–375 g). Total input respiratory system impedance (Zrs) was derived from tracheal flow and pressure signals by applying forced oscillations with frequency components from 0.16 to 18.44 Hz distributed in two forcing signals. In 8 animals interstitial lung edema was induced by intravenous infusion of saline solution (0.75 ml/kg/min) for 4 hours; 9 control animals were studied with the same protocol but without infusion. Zrs was measured at the beginning and every 15 min until the end of the experiment. Results In the treated group the lung wet-to-dry weight ratio increased from 4.3 ± 0.72 to 5.23 ± 0.59, with no histological signs of alveolar flooding. Resistance (Rrs) increased in both groups over time, but to a greater extent in the treated group. Reactance (Xrs) did not change in the control group, while it decreased significantly at all frequencies but one in the treated. Significant changes in Rrs and Xrs were observed starting after ~135 min from the beginning of the infusion. By applying a constant phase model to partition airways and tissue mechanical properties, we observed a mild increase in airways resistance in both groups. A greater and significant increase in tissue damping (from 603.5 ± 100.3 to 714.5 ± 81.9 cmH2O/L) and elastance (from 4160.2 ± 462.6 to 5018.2 ± 622.5 cmH2O/L) was found only in the treated group. Conclusion These results suggest that interstitial edema has a small but significant impact on the mechanical features of lung tissues and that these changes begin at very early stages, before the beginning of accumulation of extravascular fluid into the alveoli.

In health subjects, progressive beat-to-beat increases or decreases in systolic blood pressure (SBP) ramps are not always accompanied by baroreflex-driven lengthening or shortening in pulse interval (PI) ramps, respectively. This phenomenon has been quantified by a new index, the baroreflex effectiveness index (BEI), defined as the ratio between the number of SBP ramps observed in a given time window. Specificity of BEI was shown in eight cats by a -89% reduction of BEI after sinoarotic denervation. In 14 healthy humans, the 24-h average BEI value was 0.21, with a marked day-night modulation ([approximately equals] 0.25 day, [approximately equals] 0.15 night) in counter-phase with modulation of baroreflex sensitivity (BRS). Our analysis indicates that 1) in normal subjects, arterial baroreflex can induce beat-by-beat PI changes in response to only 21% of all SBP ramps, possibly because of central inhibitory influences or of interferences at sinus node level by nonbaroreflex mechanisms and 2) BEI provides information on the baroreflex function that is complementary to BRS.

We describe a novel capacitive position sensor using micromachining to achieve high sensitivity and large range of motion. These sensors require a new theoretical framework to describe and optimize their performance. Employing a complete description of the electrical fields, the sensor should deviate from the standard geometries used for capacitive sensors. By this optimization, the sensor gains a twofold increase in sensitivity. Results on a PC board 10x model imply that the micromachined sensor should achieve a sensitivity of less than 10 nm over 500-[micro]m range of travel. Some bioengineering applications are addressed, including positioning of micromirrors for laser surgery and dose control for implantable drug delivery systems. Index Terms--Capacitive sensor, microelectromechanical systems (MEMS), microtechniques, position sensor.