Tunable stiffness enables fast and efficient swimming in fish-like robots.

Fish maintain high swimming efficiencies over a wide range of speeds. A key to this achievement is their flexibility, yet even flexible robotic fish trail real fish in terms of performance. Here, we explore how fish leverage tunable flexibility by using their muscles to modulate the stiffness of their tails to achieve efficient swimming. We derived a model that explains how and why tuning stiffness affects performance. We show that to maximize efficiency, muscle tension should scale with swimming speed squared, offering a simple tuning strategy for fish-like robots. Tuning stiffness can double swimming efficiency at tuna-like frequencies and speeds (0 to 6 hertz; 0 to 2 body lengths per second). Energy savings increase with frequency, suggesting that high-frequency fish-like robots have the most to gain from tuning stiffness.

Future Tail Tales: A Forward-Looking, Integrative Perspective on Tail Research.

Synopsis Tails are a defining characteristic of chordates and show enormous diversity in function and shape. Although chordate tails share a common evolutionary and genetic-developmental origin, tails are extremely versatile in morphology and function. For example, tails can be short or long, thin or thick, and feathered or spiked, and they can be used for propulsion, communication, or balancing, and they mediate in predator-prey outcomes. Depending on the species of animal the tail is attached to, it can have extraordinarily multi-functional purposes. Despite its morphological diversity and broad functional roles, tails have not received similar scientific attention as, for example, the paired appendages such as legs or fins. This forward-looking review article is a first step toward interdisciplinary scientific synthesis in tail research. We discuss the importance of tail research in relation to five topics: (1) evolution and development, (2) regeneration, (3) functional morphology, (4) sensorimotor control, and (5) computational and physical models. Within each of these areas, we highlight areas of research and combinations of long-standing and new experimental approaches to move the field of tail research forward. To best advance a holistic understanding of tail evolution and function, it is imperative to embrace an interdisciplinary approach, re-integrating traditionally siloed fields around discussions on tail-related research.

Swimming Turned on Its Head: Stability and Maneuverability of the Shrimpfish (Aeoliscus punctulatus).

The typical orientation of a neutrally buoyant fish is with the venter down and the head pointed anteriorly with a horizontally oriented body. However, various advanced teleosts will reorient the body vertically for feeding, concealment, or prehension. The shrimpfish (Aeoliscus punctulatus) maintains a vertical orientation with the head pointed downward. This posture is maintained by use of the beating fins as the position of the center of buoyancy nearly corresponds to the center of mass. The shrimpfish swims with dorsum of the body moving anteriorly. The cross-sections of the body have a fusiform design with a rounded leading edge at the dorsum and tapering trailing edge at the venter. The median fins (dorsal, caudal, anal) are positioned along the venter of the body and are beat or used as a passive rudder to effect movement of the body in concert with active movements of pectoral fins. Burst swimming and turning maneuvers by yawing were recorded at 500 frames/s. The maximum burst speed was 2.3 body lengths/s, but when measured with respect to the body orientation, the maximum speed was 14.1 body depths/s. The maximum turning rate by yawing about the longitudinal axis was 957.5 degrees/s. Such swimming performance is in line with fishes with a typical orientation. Modification of the design of the body and position of the fins allows the shrimpfish to effectively swim in the head-down orientation.

La natación al revés: estabilidad y maniobrabilidad del pez Aeoliscus punctulatus (Swimming Turned on Its Head: Stability and Maneuverability of the Shrimpfish (Aeoliscus punctulatus)) La orientación típica de un pez neutralmente flotante es con la abertura hacia abajo y la cabeza apuntando hacia delante a lo largo del eje longitudinal. Sin embargo, varios teleósteos avanzados reorientarán el cuerpo verticalmente para comer, ocultarse o agarrarse. El pez Aeoliscus punctulatus mantiene una orientación vertical con la cabeza apuntando hacia abajo. Esta postura se mantiene mediante golpes de las aletas mientras la posición del centro de flotabilidad casi corresponde al centro de masa. El pez nada con el dorso del cuerpo en movimiento anterior. Las secciones transversales del cuerpo tienen un diseño fusiforme con un borde delantero redondeado en el dorso y un borde posterior que se estrecha en la abertura. Las aletas medianas (dorsales, caudales, anales) se colocan a lo largo de la abertura del cuerpo y se golpean o se usan como un timón pasivo para efectuar el movimiento del cuerpo en concierto con los movimientos activos de las aletas pectorales. Se registraron maniobras de natación en ráfaga y de vueltas por guiñada a 500 cuadros/s. La velocidad máxima natación en ráfaga fue de 2, 3 longitudes corporales/s, pero cuando se midió con respecto a la orientación corporal, la velocidad máxima fue de 14, 1 profundidades corporales/s. La velocidad máxima de vuelta por desviarse alrededor del eje longitudinal fue de 957, 5 grados/s. Tal rendimiento de natación está en línea con los peces con una orientación típica. La modificación del diseño del cuerpo y la posición de las aletas permite que el pez Aeoliscus punctulatus nade efectivamente en la orientación de cabeza hacia abajo. Translated to Spanish by YE Jimenez (yordano_jimenez@brown.edu).

A natação de cabeça para baixo: Estabilidade e manobrabilidade do peixe-camarão (Aeoliscus punctulatus) (Swimming Turned on Its Head: Stability and Maneuverability of the Shrimpfish (Aeoliscus punctulatus)) A orientação típica de um peixe de flutuação neutra é com o ventre para baixo e a cabeça apontada anteriormente ao longo do eixo de oscilação longitudinal. No entanto, vários teleósteos derivados reorientam o corpo verticalmente para alimentação, ocultação ou prensão. O peixe-camarão (Aeoliscus punctulatus) mantém uma orientação vertical com a cabeça apontada para baixo. Essa postura é mantida pelo batimento das nadadeiras, já que a posição do centro de empuxo quase corresponde ao centro de massa. O peixe-camarão nada com o dorso do corpo movendo-se anteriormente. As seções transversais do corpo têm um desenho fusiforme com uma borda de ataque arredondada no dorso e uma de fuga no ventre. As nadadeiras medianas (dorsal, caudal e anal) são posicionadas ao longo do ventre e são batidas ou usadas como um leme passivo para efetuar o movimento do corpo em conjunto com os movimentos batidos das nadadeiras peitorais. As manobras explosivas de natação e de guinada foram registradas a 500 quadros por segundo. A velocidade máxima de explosão foi de 2, 3 comprimentos de corpo por segundo, mas quando medida em relação à orientação do corpo, a velocidade máxima foi de 14, 1 vezes a profundidade do corpo por segundo. A taxa máxima de rotação através da guinada em torno do eixo longitudinal foi de 957, 5 graus por segundo. Esse desempenho de natação está de acordo com peixes com uma orientação típica. A modificação do desenho do corpo e a posição das barbatanas permitem que os peixes-camarão nadem efetivamente de cabeça para baixo. Translated to Portuguese by G Sobral (gabisobral@gmail.com).

Body Flexibility Enhances Maneuverability in the World's Largest Predator.

Blue whales are often characterized as highly stable, open-ocean swimmers who sacrifice maneuverability for long-distance cruising performance. However, recent studies have revealed that blue whales actually exhibit surprisingly complex underwater behaviors, yet little is known about the performance and control of these maneuvers. Here, we use multi-sensor biologgers equipped with cameras to quantify the locomotor dynamics and the movement of the control surfaces used by foraging blue whales. Our results revealed that simple maneuvers (rolls, turns, and pitch changes) are performed using distinct combinations of control and power provided by the flippers, the flukes, and bending of the body, while complex trajectories are structured by combining sequences of simple maneuvers. Furthermore, blue whales improve their turning performance by using complex banked turns to take advantage of their substantial dorso-ventral flexibility. These results illustrate the important role body flexibility plays in enhancing control and performance of maneuvers, even in the largest of animals. The use of the body to supplement the performance of the hydrodynamically active surfaces may represent a new mechanism in the control of aquatic locomotion.

Congenital long-QT syndrome caused by a novel mutation in a conserved acidic domain of the cardiac Na+ channel.

BACKGROUND: Congenital long-QT syndrome (LQTS) is an inherited condition of abnormal cardiac excitability characterized clinically by an increased risk of ventricular tachyarrhythmias. One form, LQT3, is caused by mutations in the cardiac voltage-dependent sodium channel gene, SCN5A. Only 5 SCN5A mutations have been associated with LQTS, and more work is needed to improve correlations between SCN5A genotypes and associated clinical syndromes. METHODS AND RESULTS: We researched a 3-generation white family with autosomal dominant LQTS who exhibited a wide clinical spectrum from mild bradycardia to sudden death. Molecular genetic studies revealed a single nucleotide substitution in SCN5A exon 28 that caused the substitution of Glu1784 by Lys (E1784K). The mutation occurs in a highly conserved domain within the C-terminus of the cardiac sodium channel containing multiple, negatively charged amino acids. Two-electrode voltage-clamp recordings of a recombinant E1784K mutant channel expressed in Xenopus oocytes revealed a defect in fast inactivation characterized by a small, persistent current during long membrane depolarizations. Coexpression of the mutant with the human sodium channel beta1-subunit did not affect the persistent current, even though we did observe shifts in the voltage dependence of steady-state inactivation. Neutralizing multiple, negatively charged residues in the same region of the sodium channel C-terminus did not cause a more severe functional defect. CONCLUSIONS: We characterized the genetics and molecular pathophysiology of a novel SCN5A sodium channel mutation, E1784K. The functional defect exhibited by the mutant channel causes delayed myocardial repolarization, and our data on the effects of multiple charge neutralizations in this region of the C-terminus suggest that the molecular mechanism of channel dysfunction involves an allosteric rather than a direct effect on channel gating.

Heart rate and blood pressure response to upright tilt in young patients with unexplained syncope.

Syncope in apparently normal patients has been attributed to an inhibitory reflex originating in cardiac sensory receptors. The reflex may be elicited by upright tilt with or without isoproterenol infusion. In this study, an upright 90 degree tilt protocol was evaluated in 20 young patients aged 7 to 22 years with syncope but with normal cardiac and neurologic evaluations. The electrocardiogram and blood pressure were noninvasively recorded at 1 min intervals while the patient was supine (5 to 10 min) and during tilt (15 min) in the baseline state. The protocol was repeated during isoproterenol infusion at increasing doses until symptoms of syncope or near syncope were provoked or the maximal isoproterenol dose was achieved (0.07 to 0.1 microgram/kg per min). Mean heart rate, mean blood pressure and RR interval variability, expressed as the standard deviation and the mean of the absolute difference between consecutive RR intervals, were assessed. Symptoms were elicited during tilt in 16 of the 20 patients (in 4 at baseline and in 12 with isoproterenol infusion); no symptoms were induced in 4 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid-eluting epicardial pacing leads in pediatric patients: encouraging early results.

OBJECTIVES: This study evaluated the pacing and sensing characteristics of a new porous-tipped steroid-eluting epicardial lead in a group of pediatric patients. BACKGROUND: Pacing in children may be complicated by small patient size, patient growth and the prevalence of structural congenital heart disease in children requiring pacing. Epicardial pacing has been associated with a high incidence of problems with sensing and capture, prompting the use of transvenous endocardial pacing when possible. In some children, epicardial pacing may still be desirable because of small patient size, potential for caval obstruction, previous cardiac surgery limiting transvenous access to the heart, or the need to repair congenital heart disease at the time of pacemaker insertion. METHODS: Twelve patients aged 3 weeks to 18 years underwent placement of 23 epicardial pacing leads (8 atrial, 15 ventricular). Pulse width thresholds, sensing thresholds and lead impedance were measured weekly for 6 weeks, then at 3, 6, 12 and 18 months after pacemaker implantation. The median duration of follow-up was 12 months. RESULTS: Ventricular pulse width thresholds did not change over time, whereas atrial pulse width thresholds improved significantly. At 6 months, the mean pulse width threshold at 2.5 V for the atrial and ventricular leads was 0.10 +/- 0.03 and 0.19 +/- 0.09 ms, respectively. The thresholds were slightly lower at 12 and 18 months. At the most recent follow-up, all atrial leads sensed appropriately at 2.5 mV and all ventricular leads at 5 mV. CONCLUSIONS: These encouraging early results suggest that steroid-eluting epicardial pacing leads may be an attractive option for children needing epicardial pacing. Their excellent pacing and sensing characteristics may allow reliable dual-chamber pacing in infants who are too small for transvenous pacing.

Proarrhythmia, cardiac arrest and death in young patients receiving encainide and flecainide. The Pediatric Electrophysiology Group.

The potential for proarrhythmic responses to the class IC sodium channel-blocking drugs encainide and flecainide has not been well described in young patients. Therefore, data were retrospectively collected from 36 institutions regarding 579 young patients who were administered encainide or flecainide for treatment of supraventricular tachycardias (encainide 86 patients, flecainide 369 patients) or ventricular arrhythmias (encainide 21 patients, flecainide 103 patients) to assess the frequency of proarrhythmia, cardiac arrest and death during therapy (adverse events). The two drugs were similar in regard to efficacy (flecainide 71.4%, encainide 59.8%) and rate of proarrhythmic responses (flecainide 7.4%; encainide 7.5%). However, patients receiving encainide more frequently experienced cardiac arrest (encainide 7.5% vs. flecainide 2.3%, p less than 0.05) or died during treatment (encainide 7.5% vs. flecainide 2.1%, p less than 0.05). Detailed data were provided for 44 patients experiencing one or more adverse events. Patient age, previous drug trials, concomitant therapy and days of inpatient monitoring were similar for patients receiving encainide or flecainide. However, echocardiographic left ventricular shortening before treatment was lower among patients receiving encainide (0.23 +/- 0.09) than among those receiving flecainide (0.34 +/- 0.06, p less than 0.05). Plasma drug concentrations were rarely elevated. Cardiac arrest (12 patients) and deaths (13 patients) occurred predominantly among patients with underlying heart disease, particularly among patients receiving flecainide for supraventricular tachycardia (8.3% vs. 0.3%, p less than 0.001). Fifteen patients with an ostensibly normal heart and normal ventricular function experienced proarrhythmia during treatment for supraventricular tachycardia, but only 3 of the 15 had a cardiac arrest or died. The relatively high incidence of adverse events should be considered when contemplating treatment with encainide or flecainide, particularly among patients with underlying heart disease.

Biomechanical model of batoid (skates and rays) pectoral fins predicts the influence of skeletal structure on fin kinematics: implications for bio-inspired design.

Growing interest in the development of bio-inspired autonomous underwater vehicles (AUVs) has motivated research in understanding the mechanisms behind the propulsion systems of marine animals. For example, the locomotive behavior of rays (Batoidea) by movement of the pectoral fins is of particular interest due to their superior performance characteristics over contemporary AUV propulsion systems. To better understand the mechanics of pectoral fin propulsion, this paper introduces a biomechanical model that simulates how batoid skeletal structures function to achieve the swimming locomotion observed in nature. Two rays were studied, Dasyatis sabina (Atlantic ray), and Rhinoptera bonasus (cownose ray). These species were selected because they exhibit very different swimming styles (undulation versus oscillation), but all use primarily their pectoral fins for propulsion (unlike electric rays or guitarfishes). Computerized tomography scans of each species were taken to image the underlying structure, which reveal a complex system of cartilaginous joints and linkages. Data collected from these images were used to quantify the complete skeletal morphometry of each batoid fin. Morphological differences were identified in the internal cartilage arrangement between each species including variations in the orientation of the skeletal elements, or radials, and the joint patterns between them, called the inter-radial joint pattern. These data were used as the primary input into the biomechanical model to couple a given ray skeletal structure with various swimming motions. A key output of the model is an estimation of the uniaxial strain that develops in the skeletal connective tissue in order for the structure to achieve motions observed during swimming. Tensile load tests of this connective tissue were conducted to further investigate the implications of the material strain predictions. The model also demonstrates that changes in the skeletal architecture (e.g., joint positioning) will effect fin deformation characteristics. Ultimately, the results of this study can be used to guide the design of optimally performing bio-inspired AUVs.

Novel KCNQ1 mutations associated with recessive and dominant congenital long QT syndromes: evidence for variable hearing phenotype associated with R518X.

Congenital long QT syndrome may be transmitted as either an autosomal dominant or recessive trait. Two families with the autosomal recessive Jervell and Lange-Nielsen syndrome (JLNS), and one family with the autosomal dominant Romano-Ward syndrome (RWS) were evaluated for mutations in KCNQ1. Two different novel frameshift mutations were discovered in one of the JLNS families (1188delC) and in the RWS family (504delG). A third allele (R518X) was observed in the second JLNS family. The R518X allele was previously associated with recessive long QT syndrome without deafness, but was present in a congenitally deaf proband in our study. These data extend the range of known KCNQ1 mutations associated with both recessive and dominant forms of congenital long QT syndrome, and demonstrate that the R518X allele may be associated with or without congenital deafness.

Interaction between soluble immune complexes and glass-fiber filters.

The two components of soluble antigen--antibody complexes, at the antigen excess, exhibit an increase in their binding ability to glass-fiber filters. This is demonstrated in two systems. In the 125I-BSA--anti-BSA system the proportion of 125I-BSA bound to the filter is markedly increased in the presence of anti-BSA antibodies. More than 80% of the antibody bound BSA can be removed by passage through the filter. In the other system, mouse gamma globulin (MGG)--125I-anti-MGG, the proportion of antibody bound to the filter increases with the increase in antigen concentration, whilst the presence of another, non-related, gamma globulin has little effect on the binding. The possible mechanisms for the binding of soluble complexes to the glass fibers are suggested and discussed.

The effects of erythrocyte-absorbed H-2 alloantisera on mixed lymphocyte culture reactions.

One-way mixed lymphocyte culture reactions were inhibited by the addition of H-2 alloantisera directed against the stimulator cell type. The sera retained their original inhibitory activity after the removal from them of conventional H-2K antibodies by exhaustive absorption with erythrocytes. The absorbed antisera had specificity for Ia but not H-2 antigens thereby indicating that the inhibitory activity of the sera is a function of antibodies against I region products. H-2 and Ia alloantisera directed against the responder cell type did not specifically inhibit culture reactions: they either had no effect or they apparently increased stimulation. This increase appeared to be immunologically specific, at least in part, and to require some heat-labile normal serum component for its elicitation. It is concluded that treatment of responder cells inactivates or destroys some normally inactive or inhibitory subpopulation such that the remaining cells respond better to allogeneic stimulation. Both the anti-stimulator and the anti-responder effects were seen with either whole serum or crude immunoglobulin preparations when one of these was added to the culture or used for pretreating cells before establishing the culture.

Reproducibility of a symptomatic response to upright tilt in young patients with unexplained syncope.

Serial upright tilt testing has been advocated as a possible therapeutic end point in treating patients with recurrent syncope, but the reproducibility of such testing has not been well-established in the absence of therapy. In 21 patients with recurrent syncope and a symptomatic response to upright tilt testing, tilt was repeated following a 25- to 30-minute recovery. Syncope or presyncope was reproduced in 14 of 21 patients on repeat tilt; 4 of 21 patients experienced milder symptoms, and 3 of 21 patients remained entirely asymptomatic on repeat tilt. The pattern of physiologic response was different during initial and repeat tilt in 7 of the 21 patients. Blood pressure and heart rate (before and during symptoms) were similar for the group on initial and repeat tilt. The abnormal physiologic response and associated symptoms elicited during upright tilt testing for unexplained syncope can be reproduced on immediate repeat tilt testing in most patients. However, the frequently attenuated response during repeat testing may limit its use as a therapeutic end point in individual patients.

Characteristics and management of chaotic atrial tachycardia of infancy.

Chaotic atrial tachycardia was observed in 7 infants without underlying structural heart disease. Clinical presentation and approach to management are discussed, with particular attention to the use of propafenone for this uncommon pediatric arrhythmia.

Randomized comparison of atenolol and fludrocortisone acetate in the treatment of pediatric neurally mediated syncope.

Overall, these results indicate that oral treatment of neurally mediated syncope is safe and efficacious. Further randomized trials in children will be required to determine the significance of a placebo effect, as well as potential differences in results related to the mechanism of syncope.

Detection of genotoxic substances in cancer patients receiving antineoplastic drugs.

A short-term bacterial mutation test, the SOS Chromotest, has been used to detect the excretion in urine of genotoxic metabolites of antineoplastic drugs administered to cancer patients. In this test, the damage to the DNA of the test bacteria is expressed by the production of beta-galactosidase, which can be quantitatively assessed and is proportional to the concentration of the drug. Kinetic curves of excretion for adriamycin, bleomycin, dacarbazine, cis-platinum and vincristine and their mixtures have been constructed from standard curves relating the intensity of the beta-galactosidase response to the concentration of drugs dissolved in normal urine. Comparative data on extraction and concentration of the drugs from urine or serum by means of selective resin or silica columns are presented.

Hydroplaning by ducklings: overcoming limitations to swimming at the water surface

Rapid escape behavior by mallard (Anas platyrhynchos) ducklings is restricted to burst swimming at the water surface. Maximum speed may be limited because of the pattern of waves created as the duckling's body moves through the water (hull speed). Burst speeds for 9-day-old ducklings were compared with predicted hull speeds, based on the waterline length of ducklings either resting in water or actively swimming. Kinematic analysis of video tapes showed a mean maximum burst speed of 1.73 m s-1, which was four times greater than the predicted hull speed. At burst velocities, stroke frequency was 1.9 times higher than the stroke frequency measured during steady low-speed paddling. Transition to burst speeds from steady paddling occurred near predicted hull speed. The paddling motions of the webbed feet were used to generate both thrust and lift. By using lift to raise the body above the water surface, the influence of waves in restricting maximum swimming speed is negated. The duckling's body becomes a planing type of hull and skims on the water surface.

Opercular jetting during fast-starts by flatfishes

When attacked by predators, flatfishes perform fast-starts that result in a rapid take-off from the ocean bottom on which they lie. High-speed video recordings of the blind side of flatfishes indicate that they expel a coherent jet of water from the blind-side opercular valve during take-off. Buccal pressure recordings in winter flounder (Pseudopleuronectes americanus) show that a buccal pressure pulse begins 0­20 ms before the beginning of the fast-start and has a range of mean magnitudes for three individuals of 1.6­10.7 kPa. We hypothesize that one function of the opercular jet in flatfishes may be to reduce the effects of Stefan adhesion. Stefan adhesion occurs as the fish lifts its head up rapidly from the ocean bottom, when water must flow into the space forming beneath the fish. Water viscosity opposes this rapid shear, and a suction pressure develops under the fish, making it more difficult for the fish to escape from the bottom. To estimate the magnitude of Stefan adhesion, we simulated fast-starts using a physical model in which a dead flounder was pulled upwards with an acceleration of 95 m s-2. Results from the physical model indicate that up to 35 % of the total force required to lift the head at 20 ms into the start can be attributed to Stefan adhesion. Despite this large adhesion force, previous work has shown that live flatfish do not show improved fast-start performance when Stefan adhesion has been eliminated by starting the fish from an open wire grid. Thus, live fishes are likely to be using behavioral mechanisms to reduce the adhesion force. Both the timing and location along the body of the opercular jet indicate that it is ideally suited to attenuate the effects of Stefan adhesion. Propping the body up on the median fins may also reduce adhesion by increasing the initial distance between the fish and the ocean floor.

MR magnetization transfer measurements in temporal lobe epilepsy: a preliminary study.

MR magnetization transfer ratio was measured in both hippocampi of three patients with temporal lobe epilepsy, and in two control subjects. The magnetization transfer ratio in each section was significantly lower on the affected side than on the contralateral side and in control subjects. Magnetization transfer ratio measurements are relatively fast and precise, this preliminary study shows that they may provide useful presurgical information.

Hydrodynamic design of the humpback whale flipper.

The humpback whale (Megaptera novaeangliae) is reported to use its elongate pectoral flippers during swimming maneuvers. The morphology of the flipper from a 9.02-m whale was evaluated with regard to this hydrodynamic function. The flipper had a wing-like, high aspect ratio planform. Rounded tubercles were regularly interspersed along the flipper's leading edge. The flipper was cut into 71 2.5-cm cross-sections and photographed. Except for sections near the distal tip, flipper sections were symmetrical with no camber. Flipper sections had a blunt, rounded leading edge and a highly tapered trailing edge. Placement of the maximum thickness placement for each cross-section varied from 49% of chord at the tip to 19% at mid-span. Section thickness ratio averaged 0.23 with a range of 0.20-0.28. The humpback whale flipper had a cross-sectional design typical of manufactured aerodynamic foils for lift generation. The morphology and placement of leading edge tubercles suggest that they function as enhanced lift devices to control flow over the flipper and maintain lift at high angles of attack. The morphology of the humpback whale flipper suggests that it is adapted for high maneuverability associated with the whale's unique feeding behavior.