Accelerating fishes increase propulsive efficiency by modulating vortex ring geometry.

Swimming animals need to generate propulsive force to overcome drag, regardless of whether they swim steadily or accelerate forward. While locomotion strategies for steady swimming are well characterized, far less is known about acceleration. Animals exhibit many different ways to swim steadily, but we show here that this behavioral diversity collapses into a single swimming pattern during acceleration regardless of the body size, morphology, and ecology of the animal. We draw on the fields of biomechanics, fluid dynamics, and robotics to demonstrate that there is a fundamental difference between steady swimming and forward acceleration. We provide empirical evidence that the tail of accelerating fishes can increase propulsive efficiency by enhancing thrust through the alteration of vortex ring geometry. Our study provides insight into how propulsion can be altered without increasing vortex ring size and represents a fundamental departure from our current understanding of the hydrodynamic mechanisms of acceleration. Our findings reveal a unifying hydrodynamic principle that is likely conserved in all aquatic, undulatory vertebrates.

Fish prey change strategy with the direction of a threat.

Predation is a fundamental interaction between species, yet it is unclear what escape strategies are effective for prey survival. Classical theory proposes that prey should either escape in a direction that conforms to a performance optimum or that is random and therefore unpredictable. Here, we show that larval zebrafish (Danio rerio) instead use a mixed strategy that may be either random or directed. This was determined by testing classic theory with measurements of the escape direction in response to a predator robot. We found that prey consistently escaped in a direction contralateral to the robot when approached from the side of the prey's body. At such an orientation, the predator appeared in the prey's central visual field and the contralateral response was consistent with a model of strategy that maximizes the distance from the predator. By contrast, when the robot approached the rostral or caudal ends of the body, and appeared in the prey's peripheral vision, the escape showed an equal probability of a contralateral or ipsilateral direction. At this orientation, a contralateral response offered little strategic advantage. Therefore, zebrafish larvae adopt an escape strategy that maximizes distance from the threat when strategically beneficial and that is otherwise random. This sensory-mediated mixed strategy may be employed by a diversity of animals and offers a new paradigm for understanding the factors that govern prey survival.

Surgical management of infective endocarditis complicated by ischemic stroke.

Embolism to the central nervous system is a frequent and important complication of infective endocarditis. While early surgery improves outcomes in many groups of patients with infective endocarditis, ischemic stroke secondary to septic embolism carries the risk of hemorrhagic transformation and neurological deterioration with heparinization and cardiopulmonary bypass. We review the literature regarding the surgical management of infective endocarditis in patients with cerebral emboli.

Speciation through the lens of biomechanics: locomotion, prey capture and reproductive isolation.

Speciation is a multifaceted process that involves numerous aspects of the biological sciences and occurs for multiple reasons. Ecology plays a major role, including both abiotic and biotic factors. Whether populations experience similar or divergent ecological environments, they often adapt to local conditions through divergence in biomechanical traits. We investigate the role of biomechanics in speciation using fish predator-prey interactions, a primary driver of fitness for both predators and prey. We highlight specific groups of fishes, or specific species, that have been particularly valuable for understanding these dynamic interactions and offer the best opportunities for future studies that link genetic architecture to biomechanics and reproductive isolation (RI). In addition to emphasizing the key biomechanical techniques that will be instrumental, we also propose that the movement towards linking biomechanics and speciation will include (i) establishing the genetic basis of biomechanical traits, (ii) testing whether similar and divergent selection lead to biomechanical divergence, and (iii) testing whether/how biomechanical traits affect RI. Future investigations that examine speciation through the lens of biomechanics will propel our understanding of this key process.

Refuging rainbow trout selectively exploit flows behind tandem cylinders.

Fishes may exploit environmental vortices to save in the cost of locomotion. Previous work has investigated fish refuging behind a single cylinder in current, a behavior termed the Kármán gait. However, current-swept habitats often contain aggregations of physical objects, and it is unclear how the complex hydrodynamics shed from multiple structures affect refuging in fish. To begin to address this, we investigated how the flow fields produced by two D-shaped cylinders arranged in tandem affect the ability of rainbow trout (Oncorhynchus mykiss) to Kármán gait. We altered the spacing of the two cylinders from l/D of 0.7 to 2.7 (where l=downstream spacing of cylinders and D=cylinder diameter) and recorded the kinematics of trout swimming behind the cylinders with high-speed video at Re=10,000-55,000. Digital particle image velocimetry showed that increasing l/D decreased the strength of the vortex street by an average of 53% and decreased the frequency that vortices were shed by ∼20% for all speeds. Trout were able to Kármán gait behind all cylinder treatments despite these differences in the downstream wake; however, they Kármán gaited over twice as often behind closely spaced cylinders (l/D=0.7, 1.1, and 1.5). Computational fluid dynamics simulations show that when cylinders are widely spaced, the upstream cylinder generates a vortex street that interacts destructively with the downstream cylinder, producing weaker, more widely spaced and less-organized vortices that discourage Kármán gaiting. These findings are poised to help predict when fish may seek refuge in natural habitats based on the position and arrangement of stationary objects.

Predictors of long-term outcomes in patients with significant myxomatous mitral regurgitation undergoing exercise echocardiography.

BACKGROUND: Significant myxomatous mitral regurgitation leads to progressive left ventricular (LV) decline, resulting in congestive heart failure and death. Such patients benefit from mitral valve surgery. Exercise echocardiography aids in risk stratification and helps decide surgical timing. We sought to assess predictors of outcomes in such patients undergoing exercise echocardiography. METHODS AND RESULTS: This is an observational study of 884 consecutive patients (age, 58 ± 14 years; 67% men) with grade III+ or greater myxomatous mitral regurgitation who underwent exercise echocardiography between January 2000 and December 2011 (excluding functional mitral regurgitation, prior valvular surgery, hypertrophic cardiomyopathy, rheumatic valvular disease, or greater than mild mitral stenosis). Clinical and echocardiographic data (mitral regurgitation, LV ejection fraction, LV dimensions, right ventricular systolic pressure) and exercise variables (metabolic equivalents, heart rate recovery at 1 minute after exercise) were recorded. Composite events of death, myocardial infarction, stroke, and progression to congestive heart failure were recorded. Mean LV ejection fraction, indexed LV end-systolic dimension, resting right ventricular systolic pressure, peak stress right ventricular systolic pressure, metabolic equivalents achieved, and heart rate recovery were 58 ± 5%, 1.6 ± 0.4 mm/m(2), 31 ± 12 mm Hg, 46 ± 17 mm Hg, 9.6 ± 3, and 33 ± 14 beats, respectively. During 6.4 ± 4 years of follow-up, there were 87 events. On stepwise multivariable Cox analysis, percent of age/sex-predicted metabolic equivalents (hazard ratio, 0.99; 95% confidence interval, 0.98-0.99; P=0.005), heart rate recovery (hazard ratio, 0.29; 95% confidence interval, 0.17-0.50; P<0.001), resting right ventricular systolic pressure (hazard ratio, 1.03; 95% confidence interval, 1.004-1.05; P=0.02), atrial fibrillation (hazard ratio, 1.91; 95% confidence interval, 1.07-3.41; P=0.03), and LV ejection fraction (hazard ratio, 0.96; 95% confidence interval, 0.92-0.99; P=0.04) predicted outcomes. CONCLUSIONS: In patients with grade III+ or greater myxomatous mitral regurgitation undergoing exercise echocardiography, lower percent of age/sex-predicted metabolic equivalents, lower heart rate recovery, atrial fibrillation, lower LV ejection fraction, and high resting right ventricular systolic pressure predicted worse outcomes.

Renin-angiotensin system blockade therapy after surgical aortic valve replacement for severe aortic stenosis: a cohort study.

BACKGROUND: Data are lacking on the effect of renin-angiotensin system (RAS) blockade therapy with angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers after surgical aortic valve replacement (SAVR) for severe aortic stenosis (AS). OBJECTIVE: To investigate the association between RAS blockade therapy and outcomes after SAVR for severe AS. DESIGN: Retrospective study. SETTING: Single tertiary referral care center. PATIENTS: Patients who were prescribed angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers after SAVR for severe AS between 1991 and 2010 who had at least 2 refills 90 days apart and at least a 6-month follow-up constituted the RAS blockade group (n = 741). Patients who did not receive these prescriptions were in the untreated group (n = 1011). Unadjusted and propensity-matched analyses (594 matched pairs of treated and untreated patients) were performed. MEASUREMENTS: The primary outcome was survival rates after SAVR. Secondary end points were changes in left ventricular mass index, left ventricular ejection fraction, and left atrial size. RESULTS: Overall unadjusted estimated survival rates at 1, 5, and 10 years were significantly greater in the RAS blockade group than in the non-RAS blockade group (99%, 90%, and 60% vs. 99%, 81%, and 53%, respectively; P < 0.001). Among propensity-matched patients, estimated survival rates at 1, 5, and 10 years remained significantly greater in the RAS blockade group than in the non-RAS blockade group (99%, 90%, and 71% vs. 96%, 78%, and 49%, respectively; P < 0.001). For the matched cohorts, the groups did not significantly differ in the change in left ventricular mass index (P = 0.37), left ventricular ejection fraction (P = 0.67), or left atrial size (P = 0.43) after SAVR on echocardiographic analysis. LIMITATION: Retrospective, single-center analysis. CONCLUSION: Renin-angiotensin system blockade therapy is associated with increased survival rates in patients after SAVR for severe AS. A randomized trial of RAS blockade therapy after SAVR should be considered. PRIMARY FUNDING SOURCE: None.

Predictors of mortality and outcomes of therapy in low-flow severe aortic stenosis: a Placement of Aortic Transcatheter Valves (PARTNER) trial analysis.

BACKGROUND: The prognosis and treatment of patients with low-flow (LF) severe aortic stenosis are controversial. METHODS AND RESULTS: The Placement of Aortic Transcatheter Valves (PARTNER) trial randomized patients with severe aortic stenosis to medical management versus transcatheter aortic valve replacement (TAVR; inoperable cohort) and surgical aortic valve replacement versus TAVR (high-risk cohort). Among 971 patients with evaluable echocardiograms (92%), LF (stroke volume index ≤35 mL/m(2)) was observed in 530 (55%); LF and low ejection fraction (<50%) in 225 (23%); and LF, low ejection fraction, and low mean gradient (<40 mm Hg) in 147 (15%). Two-year mortality was significantly higher in patients with LF compared with those with normal stroke volume index (47% versus 34%; hazard ratio, 1.5; 95% confidence interval, 1.25-1.89; P=0.006). In the inoperable cohort, patients with LF had higher mortality than those with normal flow, but both groups improved with TAVR (46% versus 76% with LF and 38% versus 53% with normal flow; P<0.001). In the high-risk cohort, there was no difference between TAVR and surgical aortic valve replacement. In patients with paradoxical LF and low gradient (preserved ejection fraction), TAVR reduced 1-year mortality from 66% to 35% (hazard ratio, 0.38; P=0.02). LF was an independent predictor of mortality in all patient cohorts (hazard ratio, ≈1.5), whereas ejection fraction and gradient were not. CONCLUSIONS: LF is common in severe aortic stenosis and independently predicts mortality. Survival is improved with TAVR compared with medical management and similar with TAVR and surgical aortic valve replacement. A measure of flow (stroke volume index) should be included in the evaluation and therapeutic decision making of patients with severe aortic stenosis. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrial.gov. Unique identifier: NCT0053089.4.

Prey fish escape by sensing the bow wave of a predator.

Prey fish possess a remarkable ability to sense and evade an attack from a larger fish. Despite the importance of these events to the biology of fishes, it remains unclear how sensory cues stimulate an effective evasive maneuver. Here, we show that larval zebrafish (Danio rerio) evade predators using an escape response that is stimulated by the water flow generated by an approaching predator. Measurements of the high-speed responses of larvae in the dark to a robotic predator suggest that larvae respond to the subtle flows in front of the predator using the lateral line system. This flow, known as the bow wave, was visualized and modeled with computational fluid dynamics. According to the predictions of the model, larvae direct their escape away from the side of their body exposed to more rapid flow. This suggests that prey fish use a flow reflex that enables predator evasion by generating a directed maneuver at high speed. These findings demonstrate a sensory-motor mechanism that underlies a behavior that is crucial to the ecology and evolution of fishes.

Passively stuck: death does not affect gecko adhesion strength.

Many geckos use adhesive toe pads on the bottom of their digits to attach to surfaces with remarkable strength. Although gecko adhesion has been studied for hundreds of years, gaps exist in our understanding at the whole-animal level. It remains unclear whether the strength and maintenance of adhesion are determined by the animal or are passively intrinsic to the system. Here we show, for the first time, that strong adhesion is produced passively at the whole-animal level. Experiments on both live and recently euthanized tokay geckos (Gekko gecko) revealed that death does not affect the dynamic adhesive force or motion of a gecko foot when pulled along a vertical surface. Using a novel device that applied repeatable and steady-increasing pulling forces to the foot in shear, we found that the adhesive force was similarly high and variable when the animal was alive (mean ± s.d. = 5.4 ± 1.7 N) and within 30 min after death (5.4 ± 2.1 N). However, kinematic analyses showed that live geckos are able to control the degree of toe pad engagement and can rapidly stop strong adhesion by hyperextending the toes. This study offers the first assessment of whole-animal adhesive force under extremely controlled conditions. Our findings reveal that dead geckos maintain the ability to adhere with the same force as living animals, disproving that strong adhesion requires active control.

Comparison of soft toothbrush and new ultra-soft cleaner in ability to remove plaque from teeth.

In this single-blind, crossover study, the difference between a brushless tooth cleaner and a soft toothbrush was studied to compare plaque removal efficiency. The sample was composed of 15 human subjects who were categorized into two groups. Group 1 was composed of subjects randomly assigned to the brushless tooth cleaner for the first two weeks. Group 2 was composed of those randomly assigned to begin the study using the soft toothbrush. After two weeks of brushing with their assigned device, subjects returned to their normal modality to brush their teeth for one week. For the last two weeks of the study, subjects were told to brush with the opposite device they were originally assigned to at the beginning of the trial. Investigators recorded the subjects' gingival indices (based on probe depths) and Quigley scores (based on plaque indices using disclosing solution) at the beginning of week one, the end of week two, the end of week three and the end of week five. The main outcomes in this study were the Silness Loe Index (SLI) and the Quigley Hein Index (QHI). The SLI was assessed on the buccal, lingual, mesial and distal surfaces of six teeth, for a total of 24 surfaces. The QHI was assessed on the buccal and lingual surfaces of six teeth, for a total of 12 surfaces. Each index was measured at each visit by the sum total score divided by the total number of surfaces. The data were analyzed separately using a mixed-effects repeated measures analysis of variance (RMANOVA) for crossover designs. Results indicate that, according to the SLI, there is no significant difference between the two treatments after the first or second weeks. However, based on the QHI, statistically significant differences existed between the two treatments after week one and two. After week one, the soft toothbrush use had a higher QHI than the brushless tooth cleaner. After week two, the brushless tooth cleaner had a higher QHI than the soft toothbrush.

Percutaneous coronary intervention in patients with severe aortic stenosis: implications for transcatheter aortic valve replacement.

BACKGROUND: With the availability of transcatheter aortic valve replacement, management of coronary artery disease in patients with severe aortic stenosis (AS) is posing challenges. Outcomes of percutaneous coronary intervention (PCI) in patients with severe AS and coronary artery disease remain unknown. We sought to compare the short-term outcomes of PCI in patients with and without AS. METHODS AND RESULTS: From our PCI database, we identified 254 patients with severe AS who underwent PCI between 1998 and 2008. Using propensity matching, we found 508 patients without AS who underwent PCI in the same period. The primary end point of 30-day mortality after PCI was similar in patients with and without severe AS (4.3% [11 of 254] versus 4.7% [24 of 508]; hazard ratio, 0.93; 95% confidence interval, 0.51-1.69; P=0.2). Patients with low ejection fraction (≤30%) and severe AS had a higher 30-day post-PCI mortality compared with those with an ejection fraction >30% (5.4% [7 of 45] versus 1.2% [4 of 209]; P<0.001). In addition, AS patients with high Society of Thoracic Surgeons score (≥10) had a higher 30-day post-PCI mortality than those with a Society of Thoracic Surgeons score <10 (10.4% [10 of 96] versus 0%; P<0.001). CONCLUSIONS: PCI can be performed in patients with severe symptomatic AS and coronary artery disease without an increased risk of short-term mortality compared with propensity-matched patients without AS. Patients with ejection fraction ≤30% and Society of Thoracic Surgeons score ≥10% are at a highest risk of 30-day mortality after PCI. This finding has significant implications in the management of severe coronary artery disease in high-risk severe symptomatic AS patients being considered for transcatheter aortic valve replacement.

Zebrafish larvae evade predators by sensing water flow.

The ability of fish to evade predators is central to the ecology and evolution of a diversity of species. However, it is largely unclear how prey fish detect predators in order to initiate their escape. We tested whether larval zebrafish (Danio rerio) sense the flow created by adult predators of the same species. When placed together in a cylindrical arena, we found that larvae were able to escape 70% of predator strikes (mean escape probability P(escape)=0.7, N=13). However, when we pharmacologically ablated the flow-sensitive lateral line system, larvae were rarely capable of escape (mean P(escape)=0.05, N=11). In order to explore the rapid events that facilitate a successful escape, we recorded freely swimming predators and prey using a custom-built camera dolly. This device permitted two-dimensional camera motion to manually track prey and record their escape response with high temporal and spatial resolution. These recordings demonstrated that prey were more than 3 times more likely to evade a suction-feeding predator if they responded before (P(escape)=0.53, N=43), rather than after (P(escape)=0.15, N=13), a predator's mouth opened, which is a highly significant difference. Therefore, flow sensing plays an essential role in predator evasion by facilitating a response prior to a predator's strike.

Big MAC: caseous calcification of the mitral annulus referred for possible cardiac tumor.

A 73-year-old woman was found to have a 1.4 × 3.0 cm heterogeneous echodensity with smooth borders and central echolucency associated with a dynamic left ventricular outflow tract gradient and episodic chest pain. Although mitral annular calcification is a common manifestation, this case represents caseous calcification of the mitral annulus, which is a rare variant with an estimated prevalence of 0.068%. It should not be misinterpreted as an intracardiac tumor, abscess or cyst, as was the initial assumption in this case. The implications of the dynamic left ventricular outflow tract obstruction as the etiology of her episodic chest pain and potential dynamic changes in structure with calcium levels are further elucidated in this case.

Sensing the strike of a predator fish depends on the specific gravity of a prey fish.

The ability of a predator fish to capture a prey fish depends on the hydrodynamics of the prey and its behavioral response to the predator's strike. Despite the importance of this predator-prey interaction to the ecology and evolution of a diversity of fish, it is unclear what factors dictate a fish's ability to evade capture. The present study evaluated how the specific gravity of a prey fish's body affects the kinematics of prey capture and the signals detected by the lateral line system of the prey during the strike of a suction-feeding predator. The specific gravity of zebrafish (Danio rerio) larvae was measured with high precision from recordings of terminal velocity in solutions of varying density. This novel method found that specific gravity decreased by ∼5% (from 1.063, N=8, to 1.011, N=35) when the swim bladder inflates. To examine the functional consequences of this change, we developed a mathematical model of the hydrodynamics of prey in the flow field created by a suction-feeding predator. This model found that the observed decrease in specific gravity due to swim bladder inflation causes an 80% reduction of the flow velocity around the prey's body. Therefore, swim bladder inflation causes a substantial reduction in the flow signal that may be sensed by the lateral line system to evade capture. These findings demonstrate that the ability of a prey fish to sense a predator depends crucially on the specific gravity of the prey.

Hydrodynamic fin function of brief squid, Lolliguncula brevis.

Although the pulsed jet is often considered the foundation of a squid's locomotive system, the lateral fins also probably play an important role in swimming, potentially providing thrust, lift and dynamic stability as needed. Fin morphology and movement vary greatly among squid species, but the locomotive role of the fins is not well understood. To begin to elucidate the locomotive role of the fins in squids, fin hydrodynamics were studied in the brief squid Lolliguncula brevis, a species that exhibits a wide range of fin movements depending on swimming speed. Individual squid were trained to swim in both the arms-first and tail-first orientations against currents in a water tunnel seeded with light-reflective particles. Particle-laden water around the fins was illuminated with lasers and videotaped so that flow dynamics around the fins could be analyzed using digital particle image velocimetry (DPIV). Time-averaged forces generated by the fin were quantified from vorticity fields of the fin wake. During the low swimming speeds considered in this study [<2.5 dorsal mantle lengths (DML) per second], L. brevis exhibited four unique fin wake patterns, each with distinctive vortical structures: (1) fin mode I, in which one vortex is shed with each downstroke, generally occurring at low speeds; (2) fin mode II, an undulatory mode in which a continuous linked chain of vortices is produced; (3) fin mode III, in which one vortex is shed with each downstroke and upstroke, and; (4) fin mode IV, in which a discontinuous chain of linked double vortex structures is produced. All modes were detected during tail-first swimming but only fin modes II and III were observed during arms-first swimming. The fins produced horizontal and vertical forces of varying degrees depending on stroke phase, swimming speed, and swimming orientation. During tail-first swimming, the fins functioned primarily as stabilizers at low speeds before shifting to propulsors as speed increased, all while generating net lift. During arms-first swimming, the fins primarily provided lift with thrust production playing a reduced role. These results demonstrate the lateral fins are an integral component of the complex locomotive system of L. brevis, producing lift and thrust forces through different locomotive modes.

Determinants of recurrent or residual functional tricuspid regurgitation after tricuspid annuloplasty.

BACKGROUND: The durability of tricuspid valve (TV) repair by annuloplasty is limited. Identification of mechanisms of recurrent or residual tricuspid regurgitation (TR) after annuloplasty is necessary to improve results of TV repair. The purpose of this study was to investigate echocardiographic determinants of mid-term outcome after TV annuloplasty. METHODS AND RESULTS: This study consisted of 39 patients with functional TR who had echocardiography preoperatively, early postoperatively (5+/-2 days), and >1 year (20+/-6 months) after TV annuloplasty. Detailed echocardiographic measurements were performed, including TR severity, TV annular dimension, TV leaflet displacement, left ventricular (LV) function, and right ventricular (RV) function and pressures. Preoperative leaflet tethering height and area predicted early and mid-term outcome of annuloplasty. Early postoperative LV ejection fraction and TR severity influenced degree of TR >1 year after surgery. In addition, increased RV pressure was related to worse TR during late follow-up. CONCLUSIONS: Although TV tethering is an important determinant of recurrent or residual TR, LV and RV function and pressures impact repair durability. These factors identify patients at risk for repair failure; such individuals require development of additional surgical strategies to improve results of tricuspid valve repair and close surveillance after surgery.

Quantitative assessment of severity of mitral regurgitation by serial echocardiography in a multicenter clinical trial of percutaneous mitral valve repair.

The aims of the echocardiographic substudy of this multicenter trial were to evaluate the use of quantitative assessment of mitral regurgitation (MR) severity using serial echocardiography and to assess the efficacy of percutaneous mitral valve repair. Previous surgical repair studies did not use quantitative echocardiographic methods. Results of a percutaneous mitral valve repair clip device in a core echocardiographic laboratory were evaluated. Published parameters for quantifying MR were used in a systematic protocol to qualify patients for study entry and evaluate treatment efficacy at discharge and 6 months after clip repair. Baseline results were presented for 55 patients, and follow-up results, for 49. Ninety-eight percent of required echocardiographic studies were submitted to the core laboratory, and >85% of required measurements were possible. At baseline, mean regurgitant volume was 54.8 +/- 24 ml, regurgitant fraction was 46.9 +/-16.2%, effective regurgitant orifice area was 0.71 +/- 0.40 cm(2), and vena contracta width was 0.66 +/- 0.20 cm. Based on a severity scale of 1 to 4, mean color flow grade was 3.4 +/- 0.7, and mean pulmonary vein flow was 2.8 +/- 1.2. In patients with a clip at 6 months, all measurements of MR severity were significantly decreased versus baseline, with mean regurgitant volume decreased from 50.3 to 27.5 ml (change -22.8 ml; p <0.0001), regurgitant fraction from 44.6% to 28.9% (change -15.7%; p <0.0001), color flow grade from an average of 3.4 to 1.8 (change -1.6; p <0.0001), and pulmonary vein flow from 2.8 to 1.8 (change -1.0; p <0.0018). In conclusion, quantitative assessment of MR is feasible in a multicenter trial, and percutaneous mitral repair with the MitraClip produces a sustained decrease in MR severity to moderate or less for > or =6 months.