Biomedical subjects
Publications and source records attributed to M H Carr.
An international flotilla of spacecraft are to be sent to Mars over the next decade in an effort to understand the planet's geology and climate history, and to determine whether some form of life ever started there. At least two spacecraft will be sent at each launch opportunity, and at times up to four spacecraft may be operating simultaneously at the planet.
Polar processes can be sensitive indicators of global climate, and the geological features associated with polar ice caps can therefore indicate evolution of climate with time. The polar regions on Mars have distinctive morphologic and climatologic features: thick layered deposits, seasonal CO2 frost caps extending to mid latitudes, and near-polar residual frost deposits that survive the summer. The relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained, mainly by the limited spatial resolution of the available data. In particular, it has not been known if the residual caps represent simple thin frost cover or substantial geologic features. Here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography; this is very different from the residual cap on the north pole, which grades into the underlying layered materials. These findings indicate that the differences between the caps are substantial (rather than reflecting short-lived differences in frost cover), and so support the idea of long-term asymmetry in the polar climates of Mars.
As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of approximately 10(6) km2 and total as much as 3-4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young--preserving a record of the seasonal and climatic cycling of atmospheric CO2, H2O, and dust over the past approximately 10(5)-10(8) years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet--documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason--providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding.
The martian surface shows large outflow channels, widely accepted as having been formed by gigantic floods that could have occurred under climatic conditions like those seen today. Also present are branching valley networks that commonly have tributaries. These valleys are much smaller than the outflow channels and their origins and ages have been controversial. For example, they might have formed through slow erosion by water running across the surface, either early or late in Mars' history, possibly protected from harsh conditions by ice cover. Alternatively, they might have formed through groundwater or ground-ice processes that undermine the surface and cause collapse, again either early or late in Mars' history. Long-duration surface runoff would imply climatic conditions quite different from the present environment. Here we present high-resolution images of martian valleys that support the view that ground water played an important role in their formation, although we are unable as yet to establish when this occurred.
Infrared wavelength observations of Io by the Galileo spacecraft show that at least 12 different vents are erupting lavas that are probably hotter than the highest temperature basaltic eruptions on Earth today. In at least one case, the eruption near Pillan Patera, two independent instruments on Galileo show that the lava temperature must have exceeded 1700 kelvin and may have reached 2000 kelvin. The most likely explanation is that these lavas are ultramafic (magnesium-rich) silicates, and this idea is supported by the tentative identification of magnesium-rich orthopyroxene in lava flows associated with these high-temperature hot spots.
High-resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms. Dunes, sandsheets, and drifts are prevalent and exhibit a range of morphology, composition (inferred from albedo), and age (as seen in occurrences of different dune orientations at the same location). Steep walls of topographic depressions such as canyons, valleys, and impact craters show the martian crust to be stratified at scales of a few tens of meters. The south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non-volatile components. Low resolution regional views of the planet provide synoptic observations of polar cap retreat, condensate clouds, and the lifecycle of local and regional dust storms.
Ground-based spectroscopy of Jupiter's moon Europa, combined with gravity data, suggests that the satellite has an icy crust roughly 150 km thick and a rocky interior. In addition, images obtained by the Voyager spacecraft revealed that Europa's surface is crossed by numerous intersecting ridges and dark bands (called lineae) and is sparsely cratered, indicating that the terrain is probably significantly younger than that of Ganymede and Callisto. It has been suggested that Europa's thin outer ice shell might be separated from the moon's silicate interior by a liquid water layer, delayed or prevented from freezing by tidal heating; in this model, the lineae could be explained by repetitive tidal deformation of the outer ice shell. However, observational confirmation of a subsurface ocean was largely frustrated by the low resolution (>2 km per pixel) of the Voyager images. Here we present high-resolution (54 m per pixel) Galileo spacecraft images of Europa, in which we find evidence for mobile 'icebergs'. The detailed morphology of the terrain strongly supports the presence of liquid water at shallow depths below the surface, either today or at some time in the past. Moreover, lower-resolution observations of much larger regions suggest that the phenomena reported here are widespread.
The ice-rich surface of the jovian satellite Europa is sparsely cratered, suggesting that this moon might be geologically active today. Moreover, models of the satellite's interior indicate that tidal interactions with Jupiter might produce enough heat to maintain a subsurface liquid water layer. But the mechanisms of interior heat loss and resurfacing are currently unclear, as is the question of whether Europa has (or had at one time) a liquid water ocean. Here we report on the morphology and geological interpretation of distinct surface features-pits, domes and spots-discovered in high-resolution images of Europa obtained by the Galileo spacecraft. The features are interpreted as the surface manifestation of diapirs, relatively warm localized ice masses that have risen buoyantly through the subsurface. We find that the formation of the features can be explained by thermally induced solid-state convection within an ice shell, possibly overlying a liquid water layer. Our results are consistent with the possibility that Europa has a liquid water ocean beneath a surface layer of ice, but further tests and observations are needed to demonstrate this conclusively.
Images obtained by the Voyager spacecraft revealed dark, wedge-shaped bands on Europa that were interpreted as evidence that surface plates, 50-100 km across, moved and rotated relative to each other. This implied that they may be mechanically decoupled from the interior by a layer of warm ice or liquid water. Here we report similar features seen in higher resolution images (420 metres per pixel) obtained by the Galileo spacecraft that reveal new details of wedge-band formation. In particular, the interior of one dark band shows bilateral symmetry of parallel lineaments and pit complexes which indicates that plate separation occurred in discrete episodes from a central axis. The images also show that this style of tectonic activity involved plates < 10 km across. Although this tectonic style superficially resembles aspects of similar activity on Earth, such as sea-floor spreading and the formation of ice leads in polar seas, there are significant differences in the underlying physical mechanisms: the wedge-shaped bands on Europa most probably formed when lower material (ice or water) rose to fill the fractures that widened in response to regional surface stresses.
OBJECTIVE: Recommendations for the use of antenatal antibiotics in obstetrics have increased in the past few years, especially for prophylaxis against group B streptococci, for prolongation of the latency time in patients with preterm premature rupture of the membranes, and as an adjuvant treatment in preterm labor. Our objective was to determine whether the use of antenatal ampicillin affects the incidence of and resistance of early-onset neonatal sepsis with organisms other than group B streptococci. STUDY DESIGN: A prospective cohort study was performed between January 1, 1991, and December 31, 1996. Every case of blood culture-proven neonatal sepsis was prospectively surveyed. The type of bacteria isolated, drug resistance, antenatal antibiotic use and treatment indication, gestational age at delivery, and other antenatal and outcome variables were gathered. Early-onset neonatal sepsis was defined as disease onset within 7 days after birth. RESULTS: A total of 42 cases of early-onset neonatal sepsis among 29,897 neonates delivered were found during the 6-year period. Of these, 15 cases were due to group B streptococci and 27 were the result of non-group B streptococcal organisms (21 gram-negative rods and 6 gram-positive cocci). Among the 27 non-group B streptococcal cases, 15 mothers had received antenatal ampicillin and 13 of the 15 bacterial isolates from these neonates (87%) were resistant to ampicillin, versus only 2 ampicillin-resistant isolates (17%) among the 12 cases in which no antenatal antibiotics were administered (P = .0004). Of the 15 mothers who were treated with ampicillin, 13 received more than 1 dose. In evaluating each year of the study, the overall administration of antibiotics to pregnant women in the antenatal period increased from <10% in 1991 to 16.9% in 1996. The incidence of early-onset neonatal sepsis with group B streptococci decreased during this time, whereas the incidence of early-onset sepsis with non-group B streptococcal organisms, especially Escherichia coli, increased. CONCLUSIONS: The increased administration of antenatal ampicillin to pregnant women may be responsible for the increased incidence of early-onset neonatal sepsis with non-group B streptococcal organisms that are resistant to ampicillin. At this time penicillin G, rather than ampicillin, is therefore recommended for prophylaxis against group B streptococci. In addition, future studies are needed to determine whether alternate approaches, such as immunotherapy or vaginal washing, could be of benefit.
The Martian surface shows abundant evidence of water erosion. Liquid water is unstable under present climatic conditions but conditions may have been different in the past. The planet has been volcanically active throughout its history. The combination of water and volcanism must have commonly resulted in hydrothermal environments similar to those in which grow the most primitive terrestrial life-forms.
Large flood channels, valley networks and a variety of features attributed to the action of ground ice indicate that Mars emerged from heavy bombardment 3.8 Ga ago, with an inventory of water at the surface equivalent to at least a few hundred metres spread over the whole planet, as compared with 3 km for the Earth. The mantle of Mars is much drier than that of the Earth, possibly as a result of global melting at the end of accretion and the lack of plate tectonics to subsequently reintroduce water into the interior. The surface water resided primarily in a porous, kilometres-thick megaregolith created by the high impact rates. Under today's climatic conditions groundwater is trapped below a thick permafrost zone. At the end of heavy bombardment any permafrost zone would have been much thinner because of the high heat flows, but climatic conditions may have been very different then, as suggested by erosion rates 1000 times higher than subsequent rates. Water trapped below the permafrost periodically erupted onto the surface to form large flood channels and lakes. Given abundant water at the surface and sustained volcanism, hydrothermal activity must have frequently occurred but we have yet to make the appropriate observations to detect the results of such activity.
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Prosthetic small-caliber vascular grafts give poorer patency rates than autogenous vein grafts, possibly because the former never spontaneously form endothelium. Animal studies have shown that endothelialization of prosthetic grafts can be encouraged by seeding endothelial cells into the graft at the time of surgery, resulting in improved patency. Information regarding the attachment characteristics of adult human endothelial cells to prosthetic grafts is, however, sparce. Laboratory experiments were performed by use of cell culture techniques to compare the attachment characteristics of adult human endothelial cells to expanded polytetrafluoroethylene graft material, both untreated and treated, with one of four protein substrates--preclotted blood, fibronectin, laminin, and type 4 collagen. Attachment characteristics were compared quantitatively by use of attachment assays and qualitatively by scanning electron microscopy. Attachment to untreated expanded polytetrafluoroethylene was poor but could be greatly improved by preclotting or precoating with any of the proteins, particularly fibronectin. In preclotted grafts seeded endothelial cells formed a virtually confluent monolayer after 1 hour. Cell attachment to the other grafts coated with protein was patchy and inconsistent. It is concluded that a rapid confluent endothelial lining within a prosthetic vascular graft is possible, and of the substrates examined, preclotted blood best encourages cell attachment to expanded polytetrafluoroethylene.
Mouse serosal mast cells (SMCs) and Kirsten sarcoma virus-immortalized mast cells store large amounts of mast cell carboxypeptidase A and serine proteases in their secretory granules. Secretory granule proteins from 2.6 x 10(6) purified SMCs were separated by NaDodSO4/PAGE, trans-blotted to poly(vinylidine difluoride) membranes, and subjected to amino-terminal amino acid sequencing. Four distinct mast cell serine proteases were identified. With mast cell carboxypeptidase A, these serine proteases comprise the major proteins of mouse SMC secretory granules. Each of the four SMC serine proteases was distinct from the two serine proteases present in mucosal mast cells in the intestines of helminth-infected mice. The secretory granules of a Kirsten sarcoma virus-immortalized mast cell line contained three of the SMC-derived serine proteases and one of the mucosal mast cell-derived serine proteases. Thus, the family of mouse mast cell secretory granule serine proteases has at least six distinct members that can be expressed in different combinations in different mast cell populations.
Principal science goals for exploration of Mars are to establish the chemical, isotopic, and physical state of Martian material, the nature of major surface-forming processes and their time scales, and the past and present biological potential of the planet. Many of those goals can only be met by detailed analyses of atmospheric gases and carefully selected samples of fresh rocks, weathered rocks, soils, sediments, and ices. The high-fidelity mineral separations, complex chemical treatments, and ultrasensitive instrument systems required for key measurements, as well as the need to adapt analytical strategies to unanticipated results, point to Earth-based laboratory analyses on returned Martian samples as the best means for meeting the stated objectives.
This is the first study to assess the risk of clinically apparent DVT in pregnant women placed in the hospital at prolonged bedrest. The outcome is discussed with reference to the risks associated with heparin. Information, including delivery data, length of hospital stay, and discharge diagnoses were extracted from a prospectively collected computerized data bank of all deliveries that occurred over a 5.5-year period at Long Beach Memorial Women's Hospital in Long Beach, California, and at St. Joseph's Hospital in Milwaukee, Wisconsin. One group consisted of all pregnant women who had been hospitalized at prolonged antepartum bedrest, as defined by 3 weeks or more. The other group consisted of the remaining population of women whose deliveries occurred during the same time period. There were 48,525 deliveries during the study period, and 266 (0.5%) women were hospitalized at prolonged antepartum bedrest. The mean number of days in the hospital for these women was 34.6 +/- 14 (range 21-82 days). Of these women, one received prophylactic heparin for a prior history of DVT. There were no cases of DVT in the 265 women who did not receive heparin, risk = 0.0 (CI = 0.00-0.99). Of these 265 women, 234 were hospitalized up to the day of delivery. Of these 234 women, 154 (65.8%) underwent cesarean section and no case of DVT occurred in the postoperative period, risk = 0.0 (CI = 0.0-1.7). Out of the remaining 48,259 women who were not hospitalized at prolonged bedrest, there were 18 cases of clinically apparent DVT, and the longest antepartum hospitalization was 4 days. A conservative risk of complications with prophylactic heparin therapy is 1.0% or greater. Although the risk of DVT in pregnant women hospitalized at prolonged bedrest is not zero, our study indicates that it is very low (< 1.0%). Whereas a risk of DVT of at least 1.0% could warrant heparin prophylaxis, even with 265 patients at prolonged bedrest and 48,525 controls, this risk could not be demonstrated. Using a power analysis with an alpha of 0.05 and a power of 80% to demonstrate this risk, one would need 247 cases and approximately 49,000 controls, which were clearly achieved in this study. In view of the risks associated with heparin, routine antenatal prophylaxis is not recommended unless other risk factors for DVT are present.
Sixteen patients with severe occlusive vascular disease of the lower extremities were randomised to receive a five day course of combined intravenous and oral Pentoxifylline followed by three months oral treatment only, or identical treatment with a matching placebo. Nine patients received active Pentoxifylline, and 7 placebo, Follow-up by regular clinical examination and haemoreological assessment revealed a marked improvement in claudication distance and an increase in red cell deformability in those receiving Pentoxifylline, there being no change in those receiving placebo. Although both of the above parameters were improved by the treatment, there did not appear to be a direct correlation between red cell deformability and claudication distance in individual patients. A combination of intravenous and oral Pentoxifylline therapy results in an increase in both claudication distance and red cell deformability, but the former may not te a direct consequence of the latter.