Internal structure and early thermal evolution of Mars from Mars Global Surveyor topography and gravity.

Topography and gravity measured by the Mars Global Surveyor have enabled determination of the global crust and upper mantle structure of Mars. The planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy: a region of crust that thins progressively from south to north and encompasses much of the southern highlands and Tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and Arabia Terra. The strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history. The thickness of the elastic lithosphere increases with time of loading in the northern plains and Tharsis. The northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing.

The global topography of Mars and implications for surface evolution.

Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.

Assessing intervention effects in the Minnesota Heart Health Program.

The Minnesota Heart Health Program is a 13-year research and demonstration project to reduce morbidity and mortality from coronary heart disease in whole communities in the upper Midwest. Six communities were selected for the study: three intervention and three comparison sites, matched to increase baseline comparability. After 2-4 years of baseline observations, a 5- to 6-year program of intensive intervention was introduced in the three intervention communities. Periodic cross-sectional and cohort surveys provided data on risk factors and related behaviors. Regression adjustments within and between communities reduced the confounding influences of important covariates and the variance inflation associated with the nesting of individuals within communities and surveys. Post hoc stratification allowed exploration of the main and strata-specific effects of the intervention program. Finally, the intervention effect was modeled as a departure from the trend line fit to the nonintervention city-year means. Together, these procedures explicitly acknowledged the component of variance associated with communities, and so avoided a major source of bias created in the usual analysis when that variation is ignored. They also increased the interpretability of the analyses and reduced the mean square errors used to assess the treatment effects.

Management of common femoral artery occlusion. A report of ten cases.

Complete occlusion or high-grade stenosis of the common femoral artery (CFA) occurs infrequently, whether as an isolated lesion or associated with similar lesions in other arteries. Ten patients with this condition comprise this report. Three had severe claudication, while seven required treatment for limb salvage. Two of the patients with claudication and one with critical ischemia had isolated CFA lesions. The remaining seven had CFA disease in tandem with either inflow aortoiliac disease or associated distal occlusions. Physical examination and vascular laboratory studies failed to suggest the diagnosis in every instance. Angiography was definitive in revealing the location and extent of pathology. Patients with localized disease were treated by patch angioplasty, balloon dilatation, or by graft replacement and profundaplasty. All others required more extensive reconstructions, with important variations from standard technique being necessary because of the CFA lesion. Amelioration of symptoms was achieved in all patients.

Hemodynamics of an anastomotic arteriovenous fistula.

Various vascular surgical techniques have been employed to increase both graft patency and limb survival when the prognosis for limb salvage in arteriosclerotic patients is especially poor due to a diseased outflow tract. Ibrahim et al described the creation of an anastomotic arteriovenous fistula in distal tibial bypasses as the reconstructive procedure of choice in severely ischemic extremities unsalvageable by more conventional methods. This study presents the hemodynamics of an anastomotic arteriovenous fistula under such circumstances. Four adult mongrel dogs were anesthesized, and a femoral artery and vein were exposed from the groin to the knee. The femoral artery was ligated in midthigh, and the ligated segment was than bypassed using an umbilical vein graft. The distal anastomosis included an arteriovenous fistula. Flow was measured electromagnetically, and pressure was measured with intravascular catheters attached to strain gauges. The creation of an anastomotic arteriovenous fistula rapidly leads to a reversal of flow in the distal artery, distal arterial hypotension, and distal venous hypertension. Its clinical use in contraindicated as a result of our experimental observations.

Management of bilateral internal jugular venous injuries.

We report the case of a 16-year-old boy admitted to hospital because of multiple stab wounds. Exploration under general anaesthesia revealed bilateral simultaneous injuries of the internal jugular vein. The management of these injuries is discussed. Optimal treatment requires preservation of at least one internal jugular vein. Both veins may be ligated but this can result in facial oedema and permanent cosmetic defects, and even in death due to cerebral oedema.

Patterns of mortality in a surgical intensive care unit.

Mortalities in a surgical intensive care unit during a three year period were reviewed. The over-all mortality was 8.2 per cent. Sixty-four per cent of the deaths followed nontraumatic surgical illness and 36 per cent followed trauma. Eighty-one per cent of patients died as a direct result of traumatic injuries, while only 19 per cent died of sepsis or multiple organ failure. On the other hand, 62 per cent of the nontrauma related deaths were a consequence of sepsis or multiple organ failure. Further research into cellular support is needed to reverse the problem of sepsis related organ failure.

The effect of pH of resuscitative fluids in treatment of severe hemorrhagic shock.

Commercially available Ringer's lactate solution has a pH of approximately 6.5. In a situation such as shock, which is normally accompanied by a metabolic acidosis, this additional acid load could have an adverse effect on resuscitation when massive amounts of fluid are required. We prepared a similar solution with a pH of 7.4 and compared the two solutions. Fourteen dogs were shocked according to a Wiggers' hemorrhagic shock model. Six dogs (43%) died during shock, 8 dogs survived the model, 4 were resuscitated over a 150-minute observation period to a pulmonary capillary wedge pressure (PCWP) of 8-12 mmHg with Ringer's lactate with a pH of 7.4. The cardiac output, lactate levels, amount of fluid required to maintain the PCWP, and arterial and mixed venous pH were measured at 30, 60, 90, 120, and 150 minutes. No significant differences were found except for occasionally higher arterial pH values in the group treated with Ringer's lactate with a pH of 7.4. There was no difference between the groups in any measurement at the end of the observation period or in survival. All dogs died within 12 hours of the end of the shock period. Our data indicate that the somewhat acidic pH of standard Ringer's lactate does not adversely affect the adequacy of resuscitation. There is no advantage to using Ringer's lactate with a pH of 7.4.

Effects of endotoxin in murine burns.

Previous studies in our laboratory have demonstrated the protective effect of the spleen in murine burns. Since the spleen is a reservoir of the reticuloendothelial system (RES) and since small doses of endotoxin stimulate RES activity, the purpose of this investigation was to perform studies to determine whether endotoxin administration will further augment burn protection in splenectomized and nonsplenectomized animals. Swiss white mice were randomly assigned to one of two groups. One group was splenectomized and the other received a sham splenectomy. Twelve weeks later, under pentobarbital anesthesia, all animals were burned uniformly on the lower back. Log doses of Escherichia coli endotoxin or an equal volume of saline were administered intraperitoneally immediately after thermal injury. Severity of burns at 24 hours was assessed from gross and microscopic appearances using a grading scale of 0 (normal) to 4 (severe). Splenectomized controls receiving saline had more severe burns than the sham-splenectomized controls. Endotoxin decreased burn severity in both splenectomized and non-splenectomized mice. However, endotoxin afforded greater burn protection in the splenectomized mice when compared with the non-splenectomized animals.