A Reinforcement Learning approach to study climbing plant behaviour.

A plant's structure is the result of constant adaptation and evolution to the surrounding environment. From this perspective, our goal is to investigate the mass and radius distribution of a particular plant organ, namely the searcher shoot, by providing a Reinforcement Learning (RL) environment, that we call Searcher-Shoot, which considers the mechanics due to the mass of the shoot and leaves. We uphold the hypothesis that plants maximize their length, avoiding a maximal stress threshold. To do this, we explore whether the mass distribution along the stem is efficient, formulating a Markov Decision Process. By exploiting this strategy, we are able to mimic and thus study the plant's behavior, finding that shoots decrease their diameters smoothly, resulting in an efficient distribution of the mass. The strong accordance between our results and the experimental data allows us to remark on the strength of our approach in the analysis of biological systems traits.

A 2D model to study how secondary growth affects the self-supporting behaviour of climbing plants.

Climbing plants exhibit specialized shoots, called "searchers", to cross spaces and alternate between spatially discontinuous supports in their natural habitats. To achieve this task, searcher shoots combine both primary and secondary growth processes of their stems in order to support, orientate and explore their extensional growth into the environment. Currently, there is an increasing interest in developing models to describe plant growth and posture. However, the interactions between the sensing activity (e.g. photo-, gravi-, proprioceptive sensing) and the elastic responses are not yet fully understood. Here, we aim to model the extension and rigidification of searcher shoots. Our model defines variations in the radius (and consequently in mass distribution) along the shoot based on experimental data collected in natural habitats of two climbing species: Trachelospermum jasminoides (Lindl.) Lem. and Condylocarpon guianense Desf.. Using this framework, we predicted the sensory aspect of a plant, that is, the plant's response to external stimuli, and the plant's proprioception, that is, the plant's "self-awareness". The results suggest that the inclusion of the secondary growth in a model is fundamental to predict the postural development and self-supporting growth phase of shoots in climbing plants.

Optimal control of plant root tip dynamics in soil.

This paper aims to propose a novel approach to model the dynamics of objects that move within the soil, e.g. plants roots. One can assume that external forces are significant only at the tip of the roots, where the plant's growth is actuated. We formulate an optimal control problem that minimises the energy spent by a growing root subject to physical constraints imposed by the surrounding soil at the tip. We study the motion strategy adopted by plant roots to facilitate penetration into the soil, which we hypothesize to be a circumnutation movement. By solving the proposed optimal control problem numerically, we validate the hypothesis that plant roots adopt a circumnutation motion pattern to reduce soil penetration resistance during growth. The proposed formalisation could be applied to replicate such a biological behaviour in robotic systems, to adopt the most efficient strategy for autonomous devices in soil exploration.

A General 3D Model for Growth Dynamics of Sensory-Growth Systems: From Plants to Robotics.

In recent years, there has been a rise in interest in the development of self-growing robotics inspired by the moving-by-growing paradigm of plants. In particular, climbing plants capitalize on their slender structures to successfully negotiate unstructured environments while employing a combination of two classes of growth-driven movements: tropic responses, growing toward or away from an external stimulus, and inherent nastic movements, such as periodic circumnutations, which promote exploration. In order to emulate these complex growth dynamics in a 3D environment, a general and rigorous mathematical framework is required. Here, we develop a general 3D model for rod-like organs adopting the Frenet-Serret frame, providing a useful framework from the standpoint of robotics control. Differential growth drives the dynamics of the organ, governed by both internal and external cues while neglecting elastic responses. We describe the numerical method required to implement this model and perform numerical simulations of a number of key scenarios, showcasing the applicability of our model. In the case of responses to external stimuli, we consider a distant stimulus (such as sunlight and gravity), a point stimulus (a point light source), and a line stimulus that emulates twining of a climbing plant around a support. We also simulate circumnutations, the response to an internal oscillatory cue, associated with search processes. Lastly, we also demonstrate the superposition of the response to an external stimulus and circumnutations. In addition, we consider a simple example illustrating the possible use of an optimal control approach in order to recover tropic dynamics in a way that may be relevant for robotics use. In all, the model presented here is general and robust, paving the way for a deeper understanding of plant response dynamics and also for novel control systems for newly developed self-growing robots.

Bicuspid aortic valve repair with hemi-remodeling technique and external ring annuloplasty.

BACKGROUND: Current guidelines recommend root replacement when diameter of the sinuses of Valsalva are superior to 45 mm particularly for bicuspid valve. However, in case of tubular aorta aneurysms with moderate root dilatation (40-45 mm diameter), the approach is still debated regarding the increased risk of coronary reimplantation. We present a modified hemi-remodeling aortic repair technique that includes the replacement of the noncoronary sinus, ascending aorta, and valve repair with external ring annuloplasty in patients with bicuspid aortic valve (BAV) and moderately dilated aortic root. METHODS: Between 2003 and 2017, 18 patients presenting with left-right BAV and an aortic root diameter at 42.3+/-3.3 mm underwent hemi-root and ascending aorta replacement and aortic valve repair with external annuloplasty. RESULTS: Postoperatively, 16 (88.9%) had no aortic insufficiency (AI) and 2 (11.1%) had grade I AI, no patients had grade III or grade IV AI. Overall survival and freedom from grade II AI at 4 years and freedom from aortic valve-related reoperation were 100%. CONCLUSION: The standardized modified hemi-remodeling technique we present is a safe and reproducible procedure, with satisfactory durability at follow-up. This technique represents an interesting alternative to full valve sparing root replacement, as it avoids the operative risk of coronary reimplantation, allows shorter cross-clamping time and a better exposition on the valve for a symmetrical repair, placing the commissure at 180°, compared with valve sparing root replacement.

Does therapeutic plasma exchange have a role in the treatment of prosthetic hip-associated cobalt toxicity? A case report and literature review.

BACKGROUND: Prosthetic hip-associated cobalt toxicity (PHACT) is an uncommon, but potentially devastating, complication for patients with metal-on-metal hip implants (MoMs). Clinical management of PHACT is poorly defined, with primary intervention being MoM explant followed by chelation therapy. Therapeutic plasma exchange (TPE) in cobalt toxicity has not been previously described. Given that cobalt is predominantly albumin bound, it should theoretically be removed by TPE. Here we report a case of PHACT and our experience using TPE to lower plasma cobalt levels. CASE REPORT: A 61-year-old woman developed deafness, blindness, ambulatory dysfunction, and endocrinopathies after MoM implant. Cobalt levels on admission were greater than 1500 µg/L. In an attempt to rapidly lower cobalt levels before MoM explant, hemodialysis and TPE were performed. Hemodialysis removed negligible amounts of cobalt. One session of TPE temporarily removed approximately two-thirds of measurable cobalt, but levels rebounded to pre-TPE values after 8 hours. It was only after MoM removal that cobalt levels plateaued below 300 µg/L and clinical symptoms improved. DISCUSSION: TPE removed cobalt from a PHACT patient, but a durable decrease in cobalt was only achieved after MoM explant. These findings are comparable to reports where chelation was employed in PHACT patients before MoM explant. The observed rebound phenomenon is likely from rapid equilibration between the immense extravascular tissue source (the MoM) and the intravascular compartment. CONCLUSION: TPE may serve as adjunctive therapy for PHACT patients whose cobalt levels remain high after explant, especially in patients with renal failure, in whom chelation is contraindicated.

Surgical anatomy of the aortic annulus: landmarks for external annuloplasty in aortic valve repair.

BACKGROUND: Although reduction of a dilated aortic annulus is becoming an essential parameter for durable valve repair, anatomical descriptions of the annulus and surgical landmarks of the subvalvular plane for an external aortic annuloplasty remain to be defined. METHODS: Twenty hearts with normal anatomy with tricuspid aortic valves were studied. Annulus diameter, cusp geometric height, and interleaflet triangles heights were measured. The aortic root was dissected externally down to the subvalvular plane as to perform an external aortic annuloplasty or reimplantation procedure proximal anastomosis. Tissue thickness and dissection heights relative to the annulus were measured at each cusp nadir and at the middle of each interleaflet triangle. RESULTS: The mean annulus diameter, cusp geometric height, and interleaflet triangle heights were, respectively, 24.9 ± 0.2 mm, 19.7 ± 0.3 mm, and 20.1 ± 0.5 mm. External dissection of the aortic root reached the subvalvular plane below the nadir of left coronary cusp (-2.7 ± 0.4 mm), noncoronary (NC) cusp (-3.1 ± 0.3 mm), and the base of left-NC interleaflet triangle (-2.1 ± 0.4 mm). External dissection remained above the nadir of the right coronary cusp (+1.4 ± 0.4 mm), base of left-right interleaflet triangle (+2.4 ± 0.6 mm), and right-NC interleaflet triangle (+3.4 ± 0.3 mm). Mean tissue thickness between the inner and external side of the subvalvular plane was 2.5 ± 0.1 mm. CONCLUSIONS: External dissection of the aortic annulus allows subvalvular placement of an external aortic ring below the left and NC cusps and below or within 3 mm of the right cusp nadir in 80% of cases. An external aortic annuloplasty would induce at least a 5-mm reduction of annulus diameter, corresponding to tissue thickness. Precise anatomical landmarks are important to standardize aortic valve annuloplasty.

Different clinical pictures of penetrating ulcer of the aorta, an underrated aortic disease.

Penetrating ulcer of the aorta has been recognized as a distinct aortic disorder, defined by the ulceration of an atherosclerotic plaque. The lesion has the potential to evolve acutely into aortic rupture, but chronic pictures are possible. Late evolution into rupture, frank aortic dissection and progressive aortic enlargement have been documented. We discuss different modalities of presentation on the basis of recent clinical cases. As the optimal treatment, either surgical (open or endovascular) or medical, is based on a correct diagnosis, we highlight the importance of including aortic ulcers in the differential diagnosis of chest pain. Although endovascular treatment can be advisable in cases with favorable anatomic condition and in patients with multiple comorbidities, the open surgical option should be available given the heterogeneous location and clinical scenarios of these lesions.

Case series of resection of pelvic leiomyoma extending into the right heart: surgical safeguards and clinical follow-up.

OBJECTIVE: To analyze the clinical features, surgical management and oncologic results of a series of six patients undergoing seven operations for resection of uterine leiomyoma extending into the right cardiac chambers. METHODS: A retrospective review of patients operated on for surgical resection of a pelvic leiomyomatous mass originating from the uterus and extending into the right cardiac chambers was performed. The most common symptoms at presentation were syncope and dyspnea; two patients were asymptomatic. Four patients had been misdiagnosed as having intracardiac thrombus or primary cardiac tumor. The intracardiac and upper intracaval portion was removed under circulatory arrest in moderate hypothermia; the remaining portion was removed by caval incision. In one patient with cardiogenic shock, the sole intracardiac portion of the mass was removed at primary surgery. A mean of 2.8 +/- 1.5 years of follow-up was available, consisting of clinical and radiological tests (computed tomography scan, echocardiography). RESULTS: There were no cases of operative mortality in the present series. No recurrence was observed at the end of the follow-up in all cases of complete resection of the mass from its intracardiac to its pelvic end. Conversely, in the only case in which partial resection was performed due to the patient's clinical condition, recurrence of the intracardiac involvement was observed 6 months after primary surgery. CONCLUSION: Radical resection is curative for uterine leiomyomatosis extending into the right cardiac chambers. Surgery can be afforded with acceptable risks. A high level of suspicion for intracardiac extension of pelvic leiomyomatosis should be retained in the presence of a floating mass within the right cardiac chambers. Such a finding should prompt radiographic evaluation of the abdomen and the pelvis.