Linkage mechanics and power amplification of the mantis shrimp's strike.

Mantis shrimp (Stomatopoda) generate extremely rapid and forceful predatory strikes through a suite of structural modifications of their raptorial appendages. Here we examine the key morphological and kinematic components of the raptorial strike that amplify the power output of the underlying muscle contractions. Morphological analyses of joint mechanics are integrated with CT scans of mineralization patterns and kinematic analyses toward the goal of understanding the mechanical basis of linkage dynamics and strike performance. We test whether a four-bar linkage mechanism amplifies rotation in this system and find that the rotational amplification is approximately two times the input rotation, thereby amplifying the velocity and acceleration of the strike. The four-bar model is generally supported, although the observed kinematic transmission is lower than predicted by the four-bar model. The results of the morphological, kinematic and mechanical analyses suggest a multi-faceted mechanical system that integrates latches, linkages and lever arms and is powered by multiple sites of cuticular energy storage. Through reorganization of joint architecture and asymmetric distribution of mineralized cuticle, the mantis shrimp's raptorial appendage offers a remarkable example of how structural and mechanical modifications can yield power amplification sufficient to produce speeds and forces at the outer known limits of biological systems.

Should status II patients be removed from the pediatric heart transplant waiting list? A multi-institutional study.

BACKGROUND: The survival benefit of cardiac transplantation (CTx) among Status 2 (stable outpatient) adult recipients has been questioned, but few studies have addressed this issue in pediatric patients. This study examined the following hypothesis: "Status 2 pediatric recipients have a survival benefit with CTx." METHODS: Between 1993 and 2003, 2,375 patients were listed for CTx at 24 institutions; 614 (26%) of these patients were Status 2. By multivariate competing outcomes hazard function analysis, death after listing and post-transplant survival were analyzed. RESULTS: A single-phase hazard function described the risk of death after listing, with 20% actual mortality within 2 months after Status 1 listing. The "natural history" of Status 2-listed patients was estimated by the risk of death, whereas waiting and risk of deterioration to Status 1 at CTx (weighted by the probability of death at 3 months after Status 1 listing). At 4 months after CTx, survival with CTx exceeded the predicted "natural Hx" survival in all diagnostic categories out to 4 years of follow-up. CONCLUSIONS: Pediatric patients currently listed as Status 2 have a survival benefit with transplant out to at least 4 years. A pediatric allocation system restricted to Status 1 patients could only be justified if the vast majority of such patients could be transplanted within 1 to 2 months.

Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus.

Mantis shrimp are renowned for their unusual method of breaking shells with brief, powerful strikes of their raptorial appendages. Due to the extreme speeds of these strikes underwater, cavitation occurs between their appendages and hard-shelled prey. Here we examine the magnitude and relative contribution of the impact and cavitation forces generated by the peacock mantis shrimp Odontodactylus scyllarus. We present the surprising finding that each strike generates two brief, high-amplitude force peaks, typically 390-480 micros apart. Based on high-speed imaging, force measurements and acoustic analyses, it is evident that the first force peak is caused by the limb's impact and the second force peak is due to the collapse of cavitation bubbles. Peak limb impact forces range from 400 to 1501 N and peak cavitation forces reach 504 N. Despite their small size, O. scyllarus can generate impact forces thousands of times their body weight. Furthermore, on average, cavitation peak forces are 50% of the limb's impact force, although cavitation forces may exceed the limb impact forces by up to 280%. The rapid succession of high peak forces used by mantis shrimp suggests that mantis shrimp use a potent combination of cavitation forces and extraordinarily high impact forces to fracture shells. The stomatopod's hammer is fundamentally different from typical shell-crushing mechanisms such as fish jaws and lobster claws, and may have played an important and as yet unexamined role in the evolution of shell form.

Biomechanics: deadly strike mechanism of a mantis shrimp.

Stomatopods (mantis shrimp) are well known for the feeding appendages they use to smash shells and impale fish. Here we show that the peacock mantis shrimp (Odontodactylus scyllarus) generates an extremely fast strike that requires major energy storage and release, which we explain in terms of a saddle-shaped exoskeletal spring mechanism. High-speed images reveal the formation and collapse of vapour bubbles next to the prey due to swift movement of the appendage towards it, indicating that O. scyllarus may use destructive cavitation forces to damage its prey.

Sensory adaptation. Tunable colour vision in a mantis shrimp.

Systems of colour vision are normally identical in all members of a species, but a single design may not be adequate for species living in a diverse range of light environments. Here we show that in the mantis shrimp Haptosquilla trispinosa, which occupies a range of depths in the ocean, long-wavelength colour receptors are individually tuned to the local light environment. The spectral sensitivity of specific classes of photoreceptor is adjusted by filters that vary between individuals.

HIV-1 Tat represses transcription from the mannose receptor promoter.

The mannose receptor is expressed on mature macrophages and immature dendritic cells, and functions to mediate phagocytosis of pathogens and capture of Ags for delivery to MHC class II-containing intracellular compartments. It has been previously reported that HIV-1-infected macrophages have reduced functions associated with the mannose receptor, including impaired Pneumocystis carinii phagocytosis and mannosylated albumin uptake. Several HIV-1-derived proteins including the Tat protein have been shown to transcriptionally repress host cell genes. The present study was undertaken to define the role of the HIV-1-derived protein Tat in HIV-mediated mannose receptor down-regulation. Cotransfection of the human macrophage cell line U937 with a Tat expression vector and a mannose receptor promoter-luciferase reporter construct resulted in down-regulation of mannose receptor promoter activity. This repression was targeted to the basal promoter. Expression of either one- or two-exon Tat resulted in decreased promoter activity. The addition of the transactivation response element (TAR) sequence enhanced the Tat-mediated repression. Down-regulation was also seen when transfected cells were treated with exogenously added Tat protein. These results are consistent with a mechanism whereby Tat reduces mannose receptor promoter activity by interfering with the host transcriptional initiation machinery, potentially resulting in decreased levels of surface mannose receptor available for Ag or pathogen capture.

Spectral tuning and the visual ecology of mantis shrimps.

The compound eyes of mantis shrimps (stomatopod crustaceans) include an unparalleled diversity of visual pigments and spectral receptor classes in retinas of each species. We compared the visual pigment and spectral receptor classes of 12 species of gonodactyloid stomatopods from a variety of photic environments, from intertidal to deep water (> 50 m), to learn how spectral tuning in the different photoreceptor types is modified within different photic environments. Results show that receptors of the peripheral photoreceptors, those outside the midband which are responsible for standard visual tasks such as spatial vision and motion detection, reveal the well-known pattern of decreasing lambdamax with increasing depth. Receptors of midband rows 5 and 6, which are specialized for polarization vision, are similar in all species, having visual lambdamax-values near 500nm, independent of depth. Finally, the spectral receptors of midband rows 1 to 4 are tuned for maximum coverage of the spectrum of irradiance available in the habitat of each species. The quality of the visual worlds experienced by each species we studied must vary considerably, but all appear to exploit the full capabilities offered by their complex visual systems.

Two living species of coelacanths?

During the period of September 1997 through July 1998, two coelacanth fishes were captured off Manado Tua Island, Sulawesi, Indonesia. These specimens were caught almost 10,000 km from the only other known population of living coelacanths, Latimeria chalumnae, near the Comores. The Indonesian fish was described recently as a new species, Latimeria menadoensis, based on morphological differentiation and DNA sequence divergence in fragments of the cytochrome b and 12S rRNA genes. We have obtained the sequence of 4,823 bp of mitochondrial DNA from the same specimen, including the entire genes for cytochrome b, 12S rRNA, 16S rRNA, four tRNAs, and the control region. The sequence is 4.1% different from the published sequence of an animal captured from the Comores, indicating substantial divergence between the Indonesian and Comorean populations. Nine morphological and meristic differences are purported to distinguish L. menadoensis and L. chalumnae, based on comparison of a single specimen of L. menadoensis to a description of five individuals of L. chalumnae from the Comores. A survey of the literature provided data on 4 of the characters used to distinguish L. menadoensis from L. chalumnae from an additional 16 African coelacanths; for all 4 characters, the Indonesian sample was within the range of variation reported for the African specimens. Nonetheless, L. chalumnae and L. menadoensis appear to be separate species based on divergence of mitochondrial DNA.

Should pediatric echocardiography be performed in adult laboratories?

OBJECTIVES: Current health care management has resulted in a change in referral patterns. The present study was undertaken to define the efficacy and value of pediatric echocardiography performed and interpreted in adult laboratories. METHODS: We reviewed the findings in 100 consecutive pediatric patients 1 month to 18 years of age referred for possible heart disease and evaluated previously by echocardiography performed in an adult laboratory. Technical adequacy and interpretation of the echocardiogram at the outside facility was correlated with our final diagnosis. RESULTS: Of the studies, 32 (32%) were performed in hospital laboratories, and 68 (68%) in physician offices. A total of 52 (52%) of the 100 patients arrived with an outside diagnosis in agreement with our final diagnosis. Technical difficulties were reported in 14 (14%) studies by the original laboratory; we felt that 32 (32%) studies were inadequate. Interpretation or communication between the outside echocardiography laboratory, primary care physicians, and patients' family was erroneous in 32 (32%) cases. Repeat echocardiography was necessary in 38 (38%) patients (6 because of planned surgery). If initial referral had been to our own institution, 25 to 30 patients would not have undergone echocardiography. CONCLUSIONS: Slightly more than half of echocardiography studies performed in pediatric patients in adult laboratories were technically adequate and interpreted correctly with proper physician-family communication. Many patients require repeat studies on further referral. A significant number would be spared echocardiography if they were sent to a pediatric cardiology center initially.

Doppler derivation of complete pulmonary artery pressure curves in patent ductus arteriosus.

Doppler echocardiography can be used in patients with a patent ductus arteriosus to generate complete pulmonary artery pressure curves. This technique provides a dynamic evaluation of changes in pulmonary artery pressures throughout the cardiac cycle and provides more hemodynamic information than single-point Doppler velocity methods of estimating pulmonary artery pressures.

Surgical management of hypoplastic left heart syndrome.

BACKGROUND: The treatment of infants with hypoplastic left heart syndrome has been challenging and controversial. METHODS: To assess the operative management and intermediate-term outcome, we retrospectively analyzed our surgical experience with 50 newborns with hypoplastic left heart syndrome operated on between January 1989 and June 1995. RESULTS: Surgical palliation with a first-stage Norwood operation was offered to 28 patients. The remaining 22 infants were initially listed for heart transplantation, and 15 underwent the operation. Ten of the 15 recipients are alive, and all are in New York Heart Association class I. Seven infants underwent a Norwood procedure after being on the list for transplantation for 12 to 42 days. A total of 34 patients underwent Norwood procedures with one operation aborted because of inoperable anatomy. Two infants who survived the first-stage Norwood operation underwent subsequent heart transplantation and are currently doing well. The 1-year mortality rate for heart transplantation was 18% (3/17) versus 50% (17/34) for the Norwood procedure. Risk factors for early mortality after a Norwood procedure include longer circulatory arrest time (> 50 minutes), preoperative acidosis (pH < 7.20), larger systemic-pulmonary artery shunt (> or = 4 mm), diminutive ascending aorta (< or = 2.0 mm), and anatomic subtype of aortic and mitral atresia. The 1-year survival rate for the Norwood procedure improved from 36% for the patients operated on during 1989 through 1992 to 75% during 1993 to mid-1995 (p = 0.005). Of the 17 survivors of a first-stage Norwood operation, 10 have undergone the second stage (bidirectional Glenn procedure), and 7 have completed a Fontan procedure. Heart transplantation results have also improved, with no deaths since 1992. CONCLUSIONS: Both the Norwood procedure and heart transplantation have encouraging early to intermediate results in infants with hypoplastic left heart syndrome. Hypoplastic left heart syndrome should be managed selectively on the basis of cardiac morphology, donor availability, and family wishes. Development of a flexible program involving the use of both procedures may aid in the successful management of infants with hypoplastic left heart syndrome.

Right ventricular systolic function in adolescents and young adults after Mustard operation for transposition of the great arteries.

This study evaluates long-term ( > 10 years since surgery) right ventricular (RV) systolic function in patients who had previously undergone intraatrial baffle surgery for transposition of the great arteries. Studies suggest these patients are clinically stable and lead satisfactory lifestyles, but long-term ventricular performance is not known. Radionuclide angiocardiography was used to estimate RV ejection fraction in 58 patients a mean of 14 years after the Mustard operation. Repeat studies were performed in 32 patients. The absolute RV ejection fraction of 0.53 +/- 0.10 in our patients did not differ from normal values. Nine patients had a value < 0.42, placing them > 2 SDs below normal. Repeat RV ejection fraction decreased from 0.54 +/- 0.11 to 0.51 +/- 0.11 (p < 0.1) in 32 patients, and > 0.10 in 6. Thus, RV ejection fraction was abnormal in 9 of 58 patients (16%) evaluated > 10 years after a Mustard operation. Repeat studies demonstrate worsening in at least 6 of 32 patients (19%). These postoperative Mustard patients require continued evaluation, even in the absence of overt symptomatology.

Short-term survivors of pediatric heart transplantation: an autopsy study of their pulmonary vascular disease.

BACKGROUND: The most common indications for heart transplantation in children are congenital heart disease and cardiomyopathy. Intracardiac lesions that vary widely in morphology may have a similar impact on pulmonary vascular morphology; for example, any lesion that increases left-sided intracardiac pressure will affect pulmonary venous pressure and morphology and, if long-standing, may affect pulmonary arteries also. METHODS: The lungs of eight children who died 2 days to 7 months after receiving a heart transplant at ages 8 days to 4 years were examined at autopsy with particular regard to the pulmonary arteries and veins. Arteries were evaluated for medial thickness, intimal proliferation, and peripheral extension of muscle; veins for medial thickness and mural elastic tissue configuration; and lymphatics for degree of dilation. RESULTS: The main pulmonary arteries of the children with congenital heart disease showed an abnormal elastic tissue pattern, similar to the pattern of the aorta, indicating that pulmonary arterial hypertension was present in these children at birth. In contrast, the pulmonary trunk of a child who had myocarditis beginning at age 2 years had a normal pulmonary elastic tissue pattern, consistent with normal neonatal pulmonary pressure. Five children with morphologic evidence of early pulmonary arterial hypertension had a left-to-right atrial shunt before the operation and elevated pulmonary artery pressure immediately after transplantation. The pulmonary arteries of all five patients had medial hypertrophy or peripheral extension of muscle; the most advanced pathologic condition occurred in the arteries of the oldest child, who was 5 months of age, at the time of transplantation who died 2 days after the operation with pulmonary arterial hypertension. In the lungs of all eight patients, pulmonary veins showed medial hypertrophy and excess elastic tissue fibers (arterialization), consistent with venous hypertension. The most impressive venous changes in the lungs of the children with hypoplastic left heart syndrome occurred in the two children who had the smallest left ventricles (4 x 6 mm and 8 x 8 mm), and in another child with hypoplastic and anomalous extrapulmonary pulmonary veins. The most impressive lymphangiectasis occurred in the lungs of the child with hypoplastic left heart syndrome who was oldest at the time of transplantation and in the lungs of a child with obstructed venous drainage. CONCLUSIONS: Pulmonary vasculopathy in children who require heart transplantation because of congenital heart disease or long-standing congestive heart failure may involve arteries, veins, and lymphatics. Among the eight patients in this autopsy study of children who died less than a year after heart transplantation, arterial vasculopathy associated with congenital heart disease appeared more pronounced in the five who survived less than 30 days compared with the two longer survivors. The lack of morphologic progression in short-term survivors of pulmonary arterial vasculopathy after heart transplantation correlates with clinical follow-up of long-term survivors who do not have problematic pulmonary arterial hypertension. Pulmonary venous vasculopathy is determined by the degree of pretransplantation left-sided obstruction caused by congenital or acquired disease and may be more persistent morphologically than arterial vasculopathy. This morphologic study of the pulmonary vasculature of short-term survivors of heart transplantation supports the concept that palliative surgical procedures may benefit children awaiting heart transplantation, especially infants with hypoplastic left heart syndrome for whom suitable donors are scarce.

Specialization of retinal function in the compound eyes of mantis shrimps.

Visual function and its specialization at the level of the retina were studied in 13 species of stomatopod crustaceans, representing three superfamilies: Gonodactyloidea, Lysiosquilloidea, and Squilloidea. We measured attenuation and irradiance spectra in the environment of each species, at the actual depths and times of activity where we observed individuals. We also characterized the intrahabdomal filters of all study species and determined the absolute spectral sensitivity functions and approximate photon capture rates of all photoreceptor classes below the level of the 8th retinular cell in seven of these species. Shallow-water gonodactyloid species have four distinct classes of intrarhabdomal filters, producing photoreceptors that are relatively insensitive but which have the broadest spectral coverage of all. Deep-water gonodactyloids and all lysiosquilloids have filters that are spectrally less diverse. These species often discard the proximal filter classes of one or more receptor types. As a result, their retinas are more sensitive but have reduced spectral range or diversity. The single squilloid species has the most sensitive photoreceptors of any we observed, due to the lack both of intrarhabdomal filters and tiered photoreceptors. Photon absorption rates, at the times of animal activity, were similar in most photoreceptor classes of all species, whether the receptors were tiered or untiered, or filtered or unfiltered. Thus, the retinas of stomatopods are specialized to operate at similar levels of stimulation at the times and depths of actual use, while evidently maintaining the greatest possible potential for spectral coverage and discrimination.

The intrarhabdomal filters in the retinas of mantis shrimps.

The intrarhabdomal filters in the photoreceptors of compounds eyes of 32 species of mantis shrimps (Crustacea: Stomatopoda), representing seven families within the superfamilies Lysiosquilloidea and Gonodactyloidea, were surveyed by microspectrophotometry of filters in fresh cryosections of the retina. A total of up to four classes of filters exist in stomatopods: two each in Rows 2 and 3 of the midband. All lysiosquilloid species lacked the proximal filter in Row 3; a few also lacked the proximal Row 2 class. While most gonodactyloid species had all four possible classes, in some species the proximal filters of Row 3 and (in one case) Row 2 were missing. In all, at least 11 distinct spectral classes of pigments were found. Absorption spectra suggested that the filter pigments were probably carotenoids or carotenoproteins, although the distal filter of Row 3 was often exceptional, appearing to contain a mixture of pigments. While the types of pigments found in the filters of the various species generally followed taxonomic lines, numerous exceptions were found that were apparently related to the ecological requirements of the various species.

Rings, slings and such things: diagnosis and management with special emphasis on the role of echocardiography.

Vascular anomalies of the aorta and pulmonary artery that cause tracheal, esophageal, or tracheoesophageal compression form an important group of congenital cardiovascular malformations. The diagnostic approach to the patient with possible vascular ring is variable. This article presents a systematic approach to the evaluation and management of this fascinating group of malformations, with special emphasis on the role and limitations of echocardiography. Using this approach between September 1990 and March 1992, we identified and defined vascular anomalies of aorta and pulmonary artery in eight children.

Ventricular function in the single ventricle before and after Fontan surgery.

To better delineate the importance of ventricular function in patients with a single ventricle and assess its relation to outcome after the Fontan procedure, 47 patients with a single ventricle were studied. Ventricular ejection fraction was estimated by radionuclide angiocardiography. Before Fontan surgery, ejection fraction was 0.57 +/- 0.10 (mean +/- standard deviation). This differed significantly from the normal mean left ventricular ejection fraction of 0.68 +/- 0.09 (p less than 0.001) derived in our laboratory by radionuclide angiocardiographic methods. Age, ventricular morphology and the presence of pulmonary artery band or systemic to pulmonary artery shunts had no statistical relation to ventricular ejection fraction in patients with a single ventricle. Serial preoperative evaluation in 15 patients over 3.8 +/- 1.3 years revealed no significant change in ventricular ejection fraction; however, increased atrioventricular valve regurgitation was documented in 4 of these 15. Modified Fontan procedure was performed in 24 of the 47 study patients; 7 have died, 1 has undergone cardiac transplantation and 1 faces possible transplantation. No difference was noted in preoperative ejection fraction between survivors and nonsurvivors. Ventricular morphology, age at Fontan surgery and operative factors such as bypass and cross-clamp time were not related to functional outcome. Preoperative ejection fraction of 0.52 +/- 0.08 decreased to 0.39 +/- 0.11 (p less than 0.001) when evaluated 1.16 +/- 0.44 years after Fontan surgery. In patients with a single ventricle (1) ventricular ejection fraction is less than that of the normal systemic ventricle; (2) during childhood, ejection fraction is not related to age or ventricular morphology; and (3) ventricular ejection fraction frequently decreases after a Fontan repair.(ABSTRACT TRUNCATED AT 250 WORDS)