Henrique Silva

The MEDUSA class of autonomous marine vehicles and their role in EU projects

This paper describes a new class of autonomous marine vehicles named Medusa and highlights their role in a number of EU projects addressing multiple vehicle scenarios. The MEDUSA vehicles, with surface and diving versions, were designed and built at the Institute for Systems and Robotics, IST, Univ. de Lisboa, Portugal as a result of an effort aimed at affording researchers and practitioners of marine robotics tools to: i) assess the efficacy of cooperative motion control and navigation algorithms and ii) seamlessly execute scientific and commercial missions with multiple robots at sea. We first define the problem of designing the MEDUSA-class of vehicles by describing the desired functional requirements that motivated their development and then present our solution. Mechanical and electrical design considerations that relate to the requirements are explained, and the software architecture is described. This includes a brief overview of the navigation system, the main lower-level control loops which other features can build upon, and some of the higher-level algorithms for multiple-vehicle cooperative missions. We also illustrate the functionality of the mission control system, a dedicated software suite that allows operators to seamlessly program and follow the state of execution of cooperative missions involving multiple vehicles, possibly running different operations or missions in parallel. Finally, we summarize the participation of IST and the MEDUSA vehicles in a number of representative EC-funded Marine Robotics-related projects.

Regarding the quantification of peripheral microcirculation — Comparing responses evoked in the in vivo human lower limb by postural changes, suprasystolic occlusion and oxygen breathing

The human skin is an interesting model to explore microcirculation, particularly if using noninvasive technologies such as LDF (Laser Doppler Flowmetry) and tc (transcutaneous) gasimetry and methods as near as possible from the normal physiological state. In this study, we combined those technologies with three classical approaches--leg raising from supine, suprasystolic occlusion (in the ankle), and normobaric oxygen breathing to explore distal peripheral circulation in the foot. These methods are often cited, but a comparative assessment has not been done. The goal of this study was to identify relevant flow related descriptors, method-related advantages and pitfalls, and eventually, to find the best experimental approach. Volunteers (both genders, 22.1 ± 3.7 years old) were subjected to these methods and variables registered during basal, challenge and stabilization phases. Descriptive and comparative statistics were obtained, adopting a 95% confidence level. All flow-related quantitative descriptors potentially useful for the analysis were identified and compared. As expected, male patients consistently showed higher LDF levels and transepidermal water loss (TEWL) and lower tcpO2 values. However, lower results were recorded in the supine position, suggesting a postural dependence. Both leg raising and suprasystolic occlusion produced a hyperemic response after provocation, although different in magnitude, significantly reducing LDF and tcpO2 during provocation. The oxygen breathing method provided the most patient-friendly protocol, consistently reducing LDF (potentially by the inhibition of production of local vasodilators). TEWL increased during the provocation phase in all protocols, although not significantly. Baseline tcpO2 was found to correlate positively with the peak tcpO2 during oxygen breathing and basal LDF with peak flow during leg raising and suprasystolic occlusion. No statistical correlation between TEWL and LDF could be demonstrated under the current experimental conditions. We conclude that although equally useful considering the purpose, these methods involve very different practicalities and do not provide the same information. Also noteworthy, LDF is a highly sensitive indicator that could be further explored to look deeper into blood flow regulating mechanisms.

Observations on the perfusion recovery of regenerative angiogenesis in an ischemic limb model under hyperoxia

This study combines two well‐known vascular research models, hyperoxia and hind limb ischemia, aiming to better characterize capacities of the hyperoxia challenge. We studied two groups of C57/BL6 male mice, a control (C) and a hind limb ischemia (HLI) group. Perfusion from both limbs was recorded in all animals by laser Doppler techniques under an oxygen (O2) saturated atmosphere, once for control and, during 35 days for the HLI group. We used a third set of normoxic animals for HLI morphometric control. The expected variability of responses was higher for the younger animals. In the HLI group, capillary density normalized at Day 21 as expected, but not microcirculatory physiology. In the operated limb, perfusion decreased dramatically following surgery (Day 4), as a slight reduction in the non‐operated limb was also noted. Consistently, the response to hyperoxia was an increased perfusion in the ischemic limb and decreased perfusion in the contralateral limb. Only at Day 35, both limbs exhibited similar flows, although noticeably lower than Day 0. These observations help to understand some of the functional variability attributed to the hyperoxia model, by showing (i) differences in the circulation of the limb pairs to readjust a new perfusion set‐point even after ischemia, an original finding implying that (ii) data from both limbs should be recorded when performing distal measurements in vivo. Our data demonstrate that the new vessels following HLI are not functionally normal, and this also affects the non‐operated limb. These findings confirm the discriminative capacities of the hyperoxia challenge and suggest its potential utility to study other pathologies with vascular impact.

About the in vivo quantitation of skin anisotropy

Human skin anisotropy is difficult to quantify. The Cutiscan®, is allegedly, the first biometrical system to provide information on the elastic and viscoelastic properties, as well as on anisotropy and directionality of the human skin in vivo. Thus, this study aims to contribute to characterize this new device and its applicability, and to compare its behavior with two other well‐known devices—the Cutometer® and the Reviscometer®.

The Venoarteriolar Reflex Significantly Reduces Contralateral Perfusion as Part of the Lower Limb Circulatory Homeostasis in vivo

Perfusion at microvascular level involves the contribution of both local and central regulators, under a complex vascular signaling frame. The venoarteriolar reflex (VAR) is one of such regulatory responses, of particular relevance in the lower limb to prevent edema. Although known for quite some time, many of the complex interactions involving all of these regulatory mechanisms still need clarification. Our objective was to look deeper into VAR through modern photoplethymography (PPG). Twelve healthy subjects (both sexes, 26.0 ± 5.0 y.o.) were enrolled in this study after informed written consent. Subjects were submitted to a leg lowering maneuver while lying supine to evoke the VAR, involving three phases–10 min baseline register, both legs extended, 10 min challenge, with one randomly chosen leg (test) pending 50 cm below heart level, while the contralateral (control) remained in place, and 10 minutes recovery, resuming the initial position. PPG signals were collected from both feet and treated by the wavelet transform (WT) revealing six spectral bands in frequency intervals comprising the cardiac [1.6–0.7 Hz], respiratory [0.4–0.26 Hz], myogenic [0.26–0.1 Hz], neurogenic/sympathetic [0.1–0.045 Hz], endothelial NO-dependent (NOd) [0.045–0.015 Hz], and NO-independent (NOi) [0.015–0.007 Hz] activities. For the first time, this approach revealed that, with VAR, perfusion significantly decreased in both limbs, although the change was more pronounced in the test foot. Here, a significant decrease in myogenic, neurogenic and NOd, were noted, while the control foot recorded a decrease in neurogenic and an increase in NOd. These results confirm the utility of WT spectral analysis for flowmotion. Further, it strongly suggests that VAR results from a complex cooperation between local myogenic-endothelial responses, where a central neurogenic reflex might also be involved.

Cooperative navigation and control: The EU MORPH project

The EU MORPH project advances the use of a formation of five autonomous marine vehicles for mapping and scientific surveying of challenging, unstructured underwater environments as a means to overcome the limitations imposed by current single-vehicle based technology. We describe the test scenarios envisioned in the project and the requirements and constraints that they impose on the cooperative navigation and control systems that enable the concerted operation of the vehicle formation. We then provide a high-level description of each of the blocks that compose the final navigation and formation control architecture, developed at ISR/IST. We highlight how the systems take into account specific mission-related requirements and applications (e.g., typical trajectories employed for mapping and surveying). We describe the results of several trials at sea (involving multiple partners in the project and a group of heterogeneous vehicles) that illustrate the applicability of the MORPH concept in real operational scenarios as well as the limitations of the systems developed.