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Biomedical subjects

D A Stewart

Publications and source records attributed to D A Stewart.

At least 109 records · Page 6Linked to original sources
PubMed1977

Studies into the transplantation biology of ultraviolet light-induced tumors.

The majority of skin tumors induced in mice by ultraviolet (UV) light are rejected when implanted into normal syngeneic recipients. Subcarcinogenic levels of UV light exposure render the normally resistant mice susceptible to tumor challenge. The immunoregulatory effect of UV light appears to be additive, since the growth rate of a tumor transplant is dependent upon the length of UV exposure administered prior to implantation. This suppressive influence does not appear to be directly mediated by the UV light, because the amputation of UV-irradiated tail skin allows for a retention of tumor resistance in otherwise tumor-susceptible hosts. UV-irradiated mice could also be immunized against UV tumors, which suggests that immune recognition of tumor-specific transplantation antigens has not been inhibited. The ability of UV exposure to alter normal immunological reactivity to UV-induced tumors is possibly an integral factor in the mechanism underlying UV carcinogenesis.

Animals↗
PubMed1976

Cellular protection during myocardial ischemia: the development and characterization of a procedure for the induction of reversible ischemic arrest.

An isolated perfused working rat heart model was used to investigate the extent to which various protective agents, used either singly or in combination, were able to increase the resistance of the heart to periods of transient ischemia. The aim of the studies was to develop a solution which, if infused into the coronary vessels just prior to the onset of ischemia, would rapidly induce arrest and would also counteract several of the deleterious cellular changes known to occur during myocardial ischemia. Agents with induce cardiac arrest, modify cellular ion loss, affect substrate utilization, energy production and energy stores, affect coronary vessel diameter and cell swelling, prevent dysrhythmias, and affect metabolic rate were investigated. The additive effects of these agents were evaluated. An aqueous solution was formulated which contained high concentrations of potassium and magnesium, in combination with adenosine triphosphate, creatine phosphate and procaine. This solution increased the recovery of the ischemic (37 degrees C for 30 min) rat heart from 0% to 93%. The safe period of ischemia could be further increased by the use of hypothermia.

Action Potentials↗
PubMed1976

Myocardial protection during bypass and arrest. A possible hazard with lactate-containing infusates.

Severe myocardial tissue damage may results from the use of prolonged ischemic arrest during cardiac surgery. A number of experimental and clinical studies have been reported in which various protective agents have been infused into the coronary vessels before the onset of ischemia in an attempt to reduce or delay this damage. Although these agents are undoubtedly able to protect the ischemic myocardium, their efficacy may be considerably reduced or enhanced by the composition of the medium in which these agents are dissolved. In experiments with a rat heart model of bypass and ischemic arrest, we found that lactate-based media are detrimental to optimal tissue protection.

Animals↗
PubMed1975

Primary enuresis: relative success of three methods of treatment.

A total of 169 children with primary enuresis were treated by one of three methods--use of a special diet, imipramine, or a waking device (the Mozes detector). Of 64 who received the diet 1 (1.6%) was cured; of 62 who were treated with imipramine 13 (20.9%) were cured; and of 43 who used the detector 23 (53.5%) were cured. Results at follow-up remained substantially unchanged for cure. Improvement rate without cure during treatment was higher for the children treated with imipramine than for those treated with the detector, but at follow-up the reverse was true. Parents of children who received the special diet, because they were unimpressed by the rate of improvement, would not permit their children to continue this form of therapy for longer than 1 or 2 months.

Adolescent↗
PubMed1975

Hypothermic arrest and potassium arrest: metabolic and myocardial protection during elective cardiac arrest.

Hypothermic arrest, potassium arrest, and ischemic arrest, either singly or in combination, with or without coronary perfusion were studied in an isolated perfused rat heart preparation. Procedures that permitted the maintenance of high cellular levels of adenosine triphosphate (ATP) and creatine phosphate during arrest, e.g., coronary perfusion with hypothermic solutions or solutions containing 16.0 mM potassium, produced a fully reversible arrest with complete cardiac recovery. Cardiac arrest and coronary flow were related to the degree of hypothermia and the concentration of potassium in the coronary perfusate, and the minimum conditions required to induce complete cardiac arrest were ascertained. The effects of hypothermia and potassium were additive; total cardiac arrest could be obtained by combining small evaluations of potassium with moderate hypothermia. Under these conditions, cellular high-energy phosphates were maintained, and complete recovery was possible. Under conditions in which arrest was obtained without maintaing coronary perfusion, e.g., ischemic arrest, cellular high-energy phosphates declined rapidly, and the hearts exhibited poor recoveries. Some protection could be afforded to the ischemic myocardium by topical hypothermia or by combining the ischemia with potassium arrest. In both instances, ATP and creatine phosphate were maintained at higher levels, and improved recoveries were observed.

Adenosine Triphosphate↗
PubMed1975

Ischemic damage and metabolism during elective cardiac arrest.

Isolated perfused working rat hearts were subjected to elective cardiac arrest for 20 or 30 min. Various methods of arrest were studied, either singly or in combination and with or without coronary perfusion. The functional recovery of the heart following the termination of arrest was found to be related to the concentration of ATP and creatine phosphate in the myocardium at the end of the period of arrest. In turn, these concentrations were dependent upon the method used to induce arrest. Normothermic ischemic arrest led to a marked reduction in high energy phosphates and a poor functional recovery. In contrast, coronary perfusion with hypothermic solutions or solutions containing high concentrations of potassium, induced arrest without depleting ATP or creatine phosphate. These procedures conferred considerable protection on the myocardium and thus permitted good recoveries. The energy status and recovery associated with ischemic arrest could be improved by combining the ischemia with hypothermia or potassium arrest. The latter, while increasing recovery significantly, still failed to afford complete protection to the myocardium. Potassium chloride gave greater protection than potassium citrate. When topical hypothermia was combined with ischemia, a time and temperature relationship was demonstrated but effective protection could only be obtained with severe topical hypothermia over a relatively short time period. The results stress the importance of maintaining high energy phosphates during arrest, and this requires the provision of a continuous supply of oxygen and nutrient, which may perhaps be best achieved by ensuring continuous and adequate coronary perfusion.

Adenosine Triphosphate↗
PubMed1974

Emergency treatment of petroleum distillate and turpentine ingestion.

A comparative study was made of pulmonary complications following the use of ipecac syrup and gastric lavage for hydrocarbon ingestion. The selected 255 patients had chest radiography when first seen and again two to five days later. Of these patients 74 or 29% had been treated with ipecac syrup, 41 or 16% by gastric lavage. On follow-up radiographs 19% of the ipecac-treated group were unchanged or worsened, compared with 39% of the lavage group, suggesting that pneumonitis was significantly less severe in the ipecac-treated patients. Use of ipecac is preferred over gastric lavage for alert patients who have ingested an excessive amount of hydrocarbon.

Child↗
PubMed1974

Enuresis.

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Adolescent↗
PubMed1972

Are antibiotic drugs needed for the treatment of upper respiratory tract infections in infants?

Much confusion exists about the necessity of using antibiotic drugs to treat upper respiratory tract infections in children, especially infants. In this study the frequency of bacterial causes of such infections was studied in 4746 children under three years of age. Clinical evidence of infection was absent in half of these children and present in the others. There was no practical difference between the frequency of positive cultures from infected and non-infected children, suggesting that antibiotics were not required.

Age Factors↗