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D Tyler

Publications and source records attributed to D Tyler.

33 records · Page 2Linked to original sources
PubMed1994

A model for the evolution of CO2 on Mars.

We have constructed a model that predicts the evolution of CO2 on Mars from the end of the heavy bombardment period to the present. The model draws on published estimates of the main processes believed to affect the fate of CO2 during this period: chemical weathering, regolith uptake, polar cap formation, and atmospheric escape. Except for escape, the rate at which these processes act is controlled by surface temperatures which we calculate using a modified version of the Gierasch and Toon energy balance model (1973, J. Atmos. Sci. 30, 1502-1508). The modifications account for the change in solar luminosity with time, the greenhouse effect, and a polar and solar equatorial energy budget. Using published estimates for the main parameters, we find no evolutionary scenario in which CO2 is capable of producing a warm (global mean temperatures>250 K) and wet (surface pressures>30 mbar) early climate, and then evolves to present conditions with approximately 7 mbar in the atmosphere, <300 mbar in the regolith, and <5 mbar in the caps. Such scenarios would only exist if the early sun were brighter than standard solar models suggest, if greenhouse gases other than CO2 were present in the early atmosphere, or if the polar albedo were significantly lower than 0.75. However, these scenarios generally require the storage of large amounts of CO2 (>1 bar) in the carbonate reservoir. If the warm and wet early Mars constraint is relaxed, then we find best overall agreement with present day reservoirs for initial CO2 inventories of 0.5-1.0 bar. We also find that the polar caps can a profound effect on how the system evolves. If the initial amount of CO2 is less than some critical value, then there is not enough heating of the poles to prevent permanent caps from forming. Once formed, these caps control how the system evolves, because they set the surface pressure and, hence, the thermal environment. If the initial amount of CO2 is greater than this critical value, then caps do not form initially, but can form later on, when weathering and escape lower the surface pressure to a point at which polar heating is no longer sufficient to prevent cap formation and the collapse of the climate system. Our modeling suggests this critical initial amount of CO2 is between 1 and 2 bar, but its true value will depend on all factors affecting the polar heat budget.

Atmosphere↗
PubMed1990

Subtotal colectomy for familial polyposis. A clinical series and review of the literature.

Familial polyposis is an inherited syndrome in which untreated persons have virtually a 100% incidence of developing colon cancer. Much controversy exists over whether subtotal colectomy with ileoproctostomy is the appropriate procedure in these patients owing to the risk of subsequent cancer in the retained portion of the rectum. At Duke University Medical Center, Durham, NC, a group of 25 patients chose to undergo the subtotal colectomy and ileoproctostomy instead of the definitive total proctocolectomy. Of the 25 patients in this series, invasive adenocarcinoma has developed in the rectal segment in only 1 patient. This patient, the oldest in our series, had carcinoma in situ in her initial operative specimen and has done well following an abdominal perineal resection and 13 years of follow-up. Six other patients have subsequently undergone definitive resections of the rectum because of intractable benign polyps. These results compare favorably with those reported in the literature. We conclude that subtotal colectomy with ileoproctostomy is still a useful and successful mode of treatment for select patients with familial polyposis if they are followed up frequently and aggressively and if the surgeon maintains a low threshold for recommending completion proctectomy.

Adenomatous Polyposis Coli↗
PubMed1990

Spatial updating and training effects in the first year of human infancy.

The ability of infants to locate an invisible target after reorientation in their direction of facing was examined in a series of experiments. In a featureless environment, localization of the target site improved between 4 and 8 months. At 8 months it was shown to be dependent on the training procedure. Infants received either instrumental training in which they were trained to anticipate the occurrence of an event at the site, or association training in which one event immediately followed another regardless of their responses. After instrumental training, localization was dependent on visual cues whereas after association training it occurred whether or not visual cues were provided. Contrary to earlier findings, it was concluded that an updating strategy based on proprioceptive information is operative from the second half of the first year.

Association Learning↗
PubMed1988

Fluoxetine versus trazodone in the treatment of outpatients with major depression.

Fluoxetine and trazodone were compared in a double-blind, randomized, parallel, 6-week trial in 43 outpatients with major depression after a 1-week single-blind placebo period. Thirty-five patients completed at least 3 weeks of active medication, while 25 patients completed all 6 weeks. Response rates, whether defined by end-of-treatment Hamilton Rating Scale for Depression (HAM-D) score less than 10 or by a 50% reduction in HAM-D scores, were equivalent for the two medications. For fluoxetine, HAM-D scores were significantly lower at Weeks 1 and 2 compared with those of trazodone. Trazodone improved sleep significantly more than fluoxetine. Fluoxetine was associated more frequently with weight loss (p = .002) and less frequently with dizziness (p = .04) than trazodone.

Ambulatory Care↗
PubMed1987

Effects of breathing 80% oxygen on water and albumin accumulation in oleic acid-injured rabbit lungs.

This study was done to determine whether breathing 80% oxygen would enhance edema formation in oleic acid (OA) lung injury. Rabbits breathed air (n = 51) or 80% oxygen (n = 51) for 1 to 7 days after OA lung injury (0.09 ml/kg iv). Control groups breathed 80% oxygen (n = 37) or room air (n = 8) without OA injury. Pulmonary vascular permeability was assessed by measuring 131I-albumin (RISA) concentration in extravascular, extracellular lung water (EVECW) relative to plasma (RISAL/RISAPL). EVECW (ml/g dry lung) was measured by 24Na, and total lung water (TLW) by wet/dry weight (g/g dry lung). Air-breathing control values were 4.53 +/- 0.25 (SD) for TLW and 0.40 +/- 0.09 for RISAL/RISAPL. In the air-breathing OA group, TLW and RISAL/RISAPL increased to 8.32 +/- 0.85 and 0.93 +/- 0.16, respectively, 2 h after OA (p less than .001) but by 24 h, were equal to air-breathing controls. TLW and RISAL/RISAPL in the oxygen treated OA group did not differ from the air breathing OA group on days 2 through 7 inclusive, suggesting that 80% oxygen had no effect on edema formation in the OA-injured lung. Breathing 80% oxygen alone, without OA injury, significantly (p less than .005) increased TLW and RISAL/RISAPL on days 5 and 6. Thus, preexisting lung injury had a protective effect against edema formation from a high fraction of inspired oxygen.

Albumins↗
PubMed1986

A study of isoetharine mesylate in patients with chronic bronchial asthma.

We performed a double-blind, random crossover study to investigate the respiratory effects of a single dose isoetharine mesylate (IM), administered by a metered aerosol canister in 19 subjects with mild, stable asthma. In addition, we studied the influence of the dose (number of actuations) and the mode of administration (delay between actuations) on these respiratory effects. The protocol consisted of a screening day and four test days: (1) one inhalation IM (2) two inhalations IM (3) one inhalation placebo (P), and (4) two inhalations P. In addition, the first nine asthmatics paused one minute between inhalations whereas the last ten paused five minutes between inhalations. Lung function was assessed using maximal and partial expiratory flow volume curves. Measurements were taken prior to aerosol delivery and for six hours after aerosol. Significant differences between IM and P were seen for up to two hours. The maximum effect was observed at 15 minutes, corresponding to a 23% and 25% increase in FEV1 from baseline with one and two puffs, respectively (P less than .001). The differences between one and two actuations were, in general, not significant. No significant differences were observed between individuals who waited one versus five minutes between inhalations. We conclude that IM aerosol results in significant improvement compared with placebo for two hours. Differences between one and two inhalations and the interval between two inhalations did not, in general, lead to enhanced effectiveness of this drug in the group of asthmatics studied.

Adolescent↗
PubMed1985

Near-death experiences in a pediatric population. A preliminary report.

Numerous accounts of a unique psychological state associated with near-fatal events have been described in adults; however, we know of no studies in the medical literature of the nature or incidence of such experiences in children. Four of seven children who survived cardiopulmonary arrests or coma associated with trauma, drownings, or hyperosmolar states reported near-death experiences. Their subjective accounts of their experiences included a sense of being out of the body, traveling in a tunnel or staircase, seeing beings dressed in white, and a decisional return to the body. Six patients hospitalized in the intensive care unit for epiglottitis, heart surgery, or Guillain-Barré syndrome, all of whom had mechanical ventilatory support and were treated with anesthetic agents and narcotics, had no memories of the time they were unconscious. Clearly, children report near-death experiences similar to ones previously described in adults. Further systematic study of this phenomenon is indicated.

Adolescent↗
PubMed1985

Cyclosporine and experimental skin allografts. II. Indefinite survival and development of specific immunologic unresponsiveness.

Immunological unresponsiveness toward skin allografts was studied in cyclosporine (CsA)-treated rats. BN skin grafts survive about 22 days and about 34 days in LEW hosts following 7 or 14 days of daily CsA treatment (15 mg/kg/day), respectively; in unmodified hosts grafts are rejected by 9 days. Indefinite (greater than 100 days) survival can, however, be produced by administering maintenance 15 mg/kg CsA every fourth day, following an initial course of the agent for 14 days. Early signs of graft rejection (hair loss, localized epidermal breakdown, and ulcerations) occurring in some animals were reversed by a CsA "pulse" (15 mg/kg/day) for 7 days, reduced gradually to the maintenance dose. CsA was equally effective when started as late as 4 days after grafting, but ineffectual when started after day 4. Once BN grafts were rejected, the agent could not prevent second-set rejection of donor-specific grafts, but significantly prolonged the survival of third-party (WF) skins. Survival of original BN grafts was unchanged by the placement of second BN grafts during both the inductive and maintenance phases; these second grafts survived as long as the original grafts. In contrast, secondary third-party (WF) grafts were promptly rejected; their destruction did not influence survival of the original grafts. Thus, indefinite survival of rat skin allografts is feasible with low maintenance doses of CsA. Graft rejection at later stages can be reversed by resuming daily therapy. Host unresponsiveness is stable and specific both during the early inductive and later maintenance phases.

Animals↗
PubMed1985

Airway reactivity and cotton bract-induced bronchial obstruction.

Most seemingly healthy persons challenged with an aerosol of cotton bract extract develop some degree of bronchospasm. The role of nonspecific reactivity of the airways in this reaction to cotton bract extract is undefined. We examined the relationship between airway responses to cotton bract extract and to methacholine, as well as between airway responses to cotton bract extract and to a bronchodilator. Twenty-two healthy subjects were screened for sensitivity to inhaled cotton bract extract. Pulmonary function was measured using partial expiratory flow-volume curves on which flow at 60 percent of the control vital capacity below total lung capacity was measured (MEF40%[P]) following ten minutes of inhalation of cotton bract extract. In the group screened, 12 were found to be responders to the extract, with drops in MEF40%(P) of 20 percent or more, and ten were found to be nonresponders. On separate days, we measured the responses of our subjects' airways to inhaled metaproterenol and methacholine. The mean threshold dose for methacholine in the responding group was 26.8 mg/ml, as compared to 55.6 mg/ml for the nonresponders (t = 2.52; p less than 0.05). Furthermore, the mean percent increase in MEF40%(P) following inhalation of metaproterenol was 41 percent in responders and 24 percent in nonresponders (t = 2.19; p less than 0.05). We conclude that some responders to cotton bract extract exhibit greater reactivity of the airways than nonresponders.

Adult↗
PubMedDate not supplied

Preoperative chemoradiation for patients with locally advanced adenocarcinoma of the pancreas.

BACKGROUND: Improved resectability is a major theoretical benefit of preoperative chemoradiation for pancreatic cancer. Since 1994, patients at Duke University Medical Center with locally advanced pancreatic cancer have been treated with multimodality preoperative therapy. The purpose of this study was to review our experience with preoperative therapy for locally advanced pancreatic cancer and determine if an aggressive neoadjuvant regimen would not only downstage these tumors pathologically but also improve the odds of complete surgical resection. METHODS: The charts of 25 patients treated with neoadjuvant chemoradiation at Duke University Medical Center with biopsy-proven, locally advanced adenocarcinoma of the pancreas were reviewed. Tumors were defined as locally advanced based on radiographic or intraoperative evidence of disease that abuts the superior mesenteric artery or vein (n = 22) or involves lymph nodes that are within the proposed radiation field (n = 3). All 25 patients received external beam radiotherapy (median dose 4500 cGy) in daily fractions of 180 cGy over 5 weeks. All patients concurrently received 5-fluorouracil (FU), and many also received mitomycin C or cisplatin, or both. Patients were given a 3- to 4-week break before a restaging computed tomographic (CT) scan was performed. Three patients were not restaged: one died from metastatic disease; one was reclassified as having a neuroendocrine tumor; and one was lost to follow-up. RESULTS: On restaging after neoadjuvant therapy, 64% of patients had stable or decreased primary tumor size. Radiographically, two patients appeared potentially resectable, and seven others developed evidence of metastatic disease. Eight patients underwent exploration, but only five could be resected. Of the five patients resected, only one had negative margins and negative lymph nodes. This patient had significant pancreatitis on initial exploration. After neoadjuvant therapy, he had a complete response radiographically, and there was no residual cancer in his resection specimen. Pathologic examination of the other resection specimens suggested that despite significant tumor fibrosis, malignant cells persist even at the periphery of the lesions. CONCLUSION: Although neoadjuvant chemoradiation has many theoretical advantages in managing pancreatic malignancy, true pathologic downstaging of locally advanced lesions into tumors that can be removed with negative nodes and margins appears to be a rare event with currently used therapeutic regimens.

Adenocarcinoma↗
PubMedDate not supplied

Lymphocytic-plasmacytic enteritis in 24 dogs.

Lymphocytic-plasmacytic enteritis (LPE) was diagnosed by intestinal biopsy in 24 dogs with chronic small intestinal diarrhea. Vomiting, weight loss, and reduced appetite were frequent. Breed predispositions were not documented, although four patients were German Shepherd dogs. Hypoproteinemia, hypoalbuminemia, and hypoglobulinemia were common and most likely a result of protein-losing enteropathy. Other biochemical abnormalities were uncommon. Intestinal malabsorption was common. Neutrophilia (sometimes with increased band neutrophils), monocytosis, lymphopenia, and eosinopenia were the most consistent hematologic abnormalities. The severity of the lymphocytic-plasmacytic infiltration was not significantly different (P greater than 0.05) between regions of small intestine. However, the severity of cellular infiltration often varied among different regions of small intestine in the same dog. Changes in villous architecture and lacteal dilation were common. Intestinal nematode infestation was diagnosed in five dogs, and pancreatic exocrine insufficiency was diagnosed in one dog. In the remaining 18 dogs, besides LPE, no other associated or concurrent intestinal disease was diagnosed.

Animals↗