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Biomedical subjects

C Shannon

Publications and source records attributed to C Shannon.

At least 37 records · Page 2Linked to original sources
PubMed1998

Electrical potential difference between exocelomic fluid and maternal blood in early pregnancy.

The forces that drive transfer of solutes between maternal blood and embryo in early human pregnancy are poorly understood. The aim of this study was to determine whether there is an electrical potential difference (PD) between maternal blood and the exocelomic cavity and between maternal blood and the amniotic cavity in the normal human conceptus at or before 10 wk of pregnancy. We measured PD between a saline-filled catheter in a forearm vein of women undergoing termination of pregnancy for psychological reasons in the first trimester and a second saline-filled catheter in the exocelomic cavity or amniotic cavity of their conceptus. The mean (+/- SE) maternal blood/exocelomic cavity PD in eight women was 8.7 +/- 1.0 mV and the mean maternal blood/amniotic cavity PD in four of the women was 6.7 +/- 1.3 mV, embryo side negative for both sets of measurement. These data show that there is a PD between maternal and embryonic extracellular fluid in the first trimester that will directly influence exchange of ions between the two compartments.

Amniotic Fluid↗
PubMed1998

Community perceptions of health, illness and care: identifying issues for indigenous communities.

Community meetings, interviews with key informants, and focus groups were used to document major health concerns and problems among Indigenous women in Queensland, as part of the Australian Longitudinal Study on Women's Health. In this article, we analyze understandings of "community" as used in Australian health research and among Indigenous women. We then examine health issues as identified and experienced by women and explore the gaps that exist between community concerns, individual health status, and service delivery.

Adolescent↗
PubMed1997

Types I and III collagen in the tissue capsules of titanium and stainless-steel implants.

Collagen plays an important role in wound healing and as such is present in connective tissue capsules around implanted materials. The proportion of type I collagen to type III collagen is lower during wound healing than that found in normal dermis, but the amount of type I collagen gradually increases and type III decreases as healing continues. The intent of this research was to investigate a possible correlation between implant metals and type I and type III collagen formation in the ensuing soft-tissue capsules. Smooth implants of grade 4 commercially pure titanium and 316L stainless steel were placed via injection needle into the subcutaneous tissue of 12 rats for 6 weeks. The soft-tissue capsule that formed around each implant was evaluated histologically and by immunofluorescence. Although the two metal implant types differ in many respects, they were chosen for their differences in surface conductivity. Titanium oxide is semiconducting, whereas the oxide of stainless steel is conducting. Impedance spectroscopy was used for conductivity analysis of the surface. No qualitative differences were found in amount of type I or type III collagen in the capsules of the two metals. However, the capsules around titanium stained for type I collagen were thicker than capsules around stainless steel. In addition, type I collagen showed evidence of a greater association with densely packed, highly orientated collagen fibers.

Animals↗
PubMed1996

Extrarenal potassium homeostasis with maximal exercise in end-stage renal disease.

Serum potassium levels rise substantially during vigorous exercise as a result of the release of potassium from contracting muscle cells. Widespread use of erythropoietin has allowed for increased exercise capacity in patients with ESRD, raising the concern for severe exertional hyperkalemia. The aim of this study was to determine whether ESRD is associated with alterations in potassium and the neurohumoral mediators of extrarenal potassium disposal with maximal exercise. Eight stable hemodialysis patients (aged 37 +/- 16 yr, mean +/- SE) and eight healthy control subjects (aged 44 +/- 13 yr) exercised to exhaustion, using a graded cycle ergometer. There were no significant differences in exercise performance between groups as assessed by peak work rate, maximal oxygen consumption, and rate pressure product. Although the baseline potassium level was higher in the dialysis group (5.0 +/- 0.2 mEq/L) than in control subjects (4.5 +/- 0.1 mEq/L), both groups had a similar pattern of increase during exercise (with an increment of approximately 1 mEq/L) and a similar return to baseline after exercise. However, the dialysis patients had higher basal norepinephrine levels (820 +/- 104 versus 441 +/- 56 pg/mL, P < 0.01) and a greater response to exercise (3122 +/- 429 versus 1696 +/- 424 pg/mL, P < 0.01), higher basal insulin levels (11 +/- 1 versus 7 +/- 1 microU/mL, P < 0.05), higher insulin post-exercise levels (19 +/- 3 versus 11 +/- 1 microU/mL, P < 0.05), and higher basal aldosterone levels (621 +/- 250 versus 109 +/- 13 pg/mL, P < 0.05) with an increase response to exercise (1100 +/- 350 versus 350 +/- 17 pg/mL, P < 0.05). In summary, despite higher basal potassium, dialysis patients have normal potassium responses to maximal exercise. More vigorous insulin, catecholamine, and aldosterone levels may contribute to the maintenance of extrarenal potassium homeostasis in ESRD.

Adult↗
PubMed1994

Social and cultural differences affect medical treatment.

This paper seeks to identify some of the significant health issues for Aboriginal people and the obstacles they often encounter in assessing the medical system. Clearly, the latter largely result from problems in communication, which can be addressed by seeking to establish good relationships. Whether the Aboriginal patients live in a traditional or remote community, a rural country area, or a large urban setting, an understanding of their conceptualization of their conditions can greatly enhance the communication process. Mobbs points out that this not only improves the clinical encounter, it also helps to overcome barriers of mistrust, misunderstanding and anxiety between the client and the professional.

Australia↗
PubMed1992

Chronic fatigue syndrome. A review from the general practice perspective.

There is no doubt that the chronic fatigue syndrome exists. It is a condition that is debilitating and of unknown cause. Research into chronic fatigue syndrome demonstrates possible psychiatric or organic causes. The truth may be somewhere in between. Evidence for the existence of an ongoing chronic infection is now not convincing. Treatment should be based on supportive counselling, explanation, psychiatric help (both pharmacological and non pharmacological) and a graded programme of increased activity with the eventual aim of resumption of full functioning.

Antibodies, Viral↗
PubMed1992

Ventilators: in-service performance with Biotek ventilator testers.

The assessment of mechanical ventilator performance is a complex task requiring measurement of a number of different transducers under a variety of conditions. The use of dedicated testing equipment can alleviate the complexity of the experimental apparatus. This paper assesses the accuracy and versatility of the Biotek VT-1 and VT-2 dedicated ventilator testers. Results show that the testers perform within the manufacturer's specifications and have the required flexibility to be used in investigating faults reported with ventilators.

Equipment Failure↗
PubMed1989

Normalization of abnormal diurnal weight gain among chronically psychotic geriatric patients. Is abnormal diurnal weight gain a risk factor in chronic psychosis?

We studied 20 geriatric and 87 nongeriatric chronically psychotic male inpatients, 16 acutely psychotic male control subjects, and 14 male normal subjects. The subjects were weighed at 7 a.m. and 4 p.m. weekly for 3 weeks. We normalized the diurnal weight gain (NDWG) as a percentage by subtracting the 7 a.m. weight from 4 p.m. weight, multiplying the difference by 100, and then dividing the result by the 7 a.m. weight. NDWG was .509% +/- .337%, 2.209% +/- 1.529%, .631% +/- .405%, and .533% +/- .410%, among the geriatric men, nongeriatric men, control subjects, and normal subjects respectively. Differences in diagnoses and drugs did not explain these findings. We hypothesize that abnormal diurnal weight gain may be a risk factor for premature death among chronically psychotic inpatients.

Adult↗
PubMed1989

Diurnal weight gain among patients with mental retardation.

We compared the diurnal weight gain of 46 patients with mental retardation to that of 21 patients with organic mental syndromes. They were weighed at 7 a.m. and 4 p.m. weekly for 3 weeks. We normalized the diurnal weight gain as a percentage by subtracting the 7 a.m. weight from the 4 p.m. weight, multiplying the difference by 100, and dividing the result by the 7 a.m. weight. Normalized diurnal weight gain was abnormal among one fourth of patients with mental retardation and two thirds of those with organic mental syndromes. Differences in age, sex, baseline weight, antipsychotic drugs, lithium, carbamazepine, blood pressure, and pulse did not explain our results. We believe that our findings provide additional evidence to separate patients with mental retardation from those with psychosis.

Adult↗
PubMed1987

Atrial tracking (synchronous) pacing in a pediatric and young adult population.

One hundred pediatric and young adult patients underwent implantation of an atrial tracking pacemaker. Seventy-four pacemakers paced in an atrioventricular (AV) sequential mode at the lower rate limit (DDD) while 26 paced in a ventricular demand mode at the lower rate limit (VDD). Five patients required reoperation during follow-up of 1 month to 2.5 years (mean 1.5 years). Six additional patients required programming to ventricular demand (3) or AV sequential (3) pacing, because of development of sinus bradycardia (2), atrial sensing problems (1) or pacemaker-mediated tachycardia (3). Pulse generators that could sense atrial signals less than 1.0 mV and had a programmable atrial refractory period did not require reprogramming out of the atrial tracking mode. No patient developed atrial flutter or fibrillation. Sensing problems during exercise occurred in 37% of the first 60 pacemakers but in none of the last 40, which had improved electronic components. Atrial tracking pacing is feasible in pediatric and young adult patients.

Adolescent↗
PubMed1986

Use of cardiac pacing after the Mustard operation for transposition of the great arteries.

The most frequent complication of the venous redirection (Mustard or Senning) operation for transposition of the great arteries is cardiac arrhythmia. Drug treatment of tachyarrhythmia often worsens bradyarrhythmia. Pacemakers can now treat both arrhythmias. The technique for implantation of pacemakers after redirection for transposition has changed over time from thoracotomy to subxiphoid to transvenous. Atrial pacing is almost always the mode of choice since the electrophysiologic abnormality is sinus node dysfunction with intact atrioventricular conduction. Twenty-nine patients aged 3 to 19 years (mean 9.6) had implantation of a pacemaker a mean of 5.5 years (range 1 to 14) after undergoing the Mustard operation for transposition of the great arteries. Symptoms referable to bradycardia were eliminated in each case. Four patients who received an antitachycardia pacemaker no longer have symptomatic tachycardia. Four patients have required reoperation, three because of lead problems and one because of traumatic erosion of the pacemaker. Pacemakers provide excellent relief of symptoms after the Mustard or Senning operation. Transvenous atrial automatic antitachycardia pacemakers offer the best combination of ease of implantation and symptomatic relief.

Adolescent↗
PubMed1985

Use of atrial pacing in a young population.

Forty pediatric and young adult patients (1-20 years; mean, 11 years of age) had implantation of atrial demand (AAI) pacemakers over a 5.5 year period. Nineteen were implanted by epicardial technique and 21 transvenously. Standard lithium single chamber pulse generators and standard atrial leads were used. Operative stimulation thresholds were better for transvenous leads than for epicardial (0.75 volts vs. 1.5 volts at 0.5 ms) (p less than 0.05). Pulse width thresholds at a mean of 1.5 years were not significantly different (0.11 ms for transvenous vs. 0.18 for epicardial). No patient developed AV block. Eight patients (four epicardial and four endocardial) required reoperation during the mean 3.5 year follow-up--four because of lead problems and four because of persistent tachycardia. Of the six patients who received an automatic antitachycardia pacemaker, only one had persistent symptoms while seven of eight who received a standard unit continued to have symptoms. Twenty-eight of 29 symptomatic patients without tachycardia became asymptomatic. Atrial pacing appears to be a safe and effective therapy for children with sick sinus syndrome.

Adolescent↗
PubMed1984

Long-term follow-up of pulse width threshold of transvenous and myo-epicardial leads.

Postoperative pulse width thresholds were measured at a constant of 5 volts in 140 patients. In 41 patients, transvenous atrial and/or ventricular leads were implanted at a median age of 13 years (3-78 yrs). Myo-epicardial leads were implanted in 99 patients at a median age of 8 3/4 years (1 wk to 76 yrs). The initial rapid rise of threshold was found to persist not longer than to the third follow-up period of 11 days to 5 weeks in all atrial and transvenous ventricular leads; in myo-epicardial ventricular leads it persisted until the period of more than 5 weeks to 6 months. During initial rise, pulse width threshold m + sem did not exceed 0.45 ms. We therefore suggest that a pulse width setting of 0.5 ms at 5 V is a safe setting for this period. In only one patient did a late rise of threshold occur. The comparison of pulse width thresholds of transvenous versus myo-epicardial leads showed lower mean values for transvenous atrial leads in each follow-up period, but the difference was not statistically significant. The pulse width thresholds of transvenous ventricular leads were significantly lower than those of myo-epicardial leads in some follow-up periods. We therefore conclude that transvenous leads have a slight advantage with regard to postoperative pulse width threshold.

Adolescent↗
PubMed1984

The incidence of retrograde conduction in children.

With the increasing use of "physiological" pacemakers in the pediatric age group, retrograde conduction in children has become of clinical importance. Pacemakers which sense atrial depolarization may sense "retrograde" P waves. The pacemaker may then act as the antegrade limb of a reciprocating tachycardia circuit, while the patient's own conduction system acts as the retrograde limb. We reviewed the data of 127 patients who underwent antegrade and retrograde electrophysiologic study at Texas Children's Hospital, with regard to retrograde conduction. Sixty percent of the patients had ventriculo-atrial conduction through the A-V node; the incidence of retrograde conduction in patients after surgical correction of a tetralogy of Fallot was significantly lower (33%). None of the patients with third-degree A-V block had retrograde conduction. The mean retrograde conduction time was 162 ms (range 70-335 ms) at the slowest pacing rate and 257 ms (range 80-475 ms) at the fastest pacing rate. This high incidence of retrograde conduction and the variability of conduction times must be taken into account when "physiological" pacemakers are to be implanted.

Adolescent↗
PubMed1983

Cardiac pacing in children and young adults.

Pacemakers are being used with increasing frequency in children. New pacemakers are smaller, more sophisticated, can be programmed, have output telemetry, are more reliable, and are longer lasting. Implant techniques have been modified, so that they are less traumatic to the patient and result in better electrical measurements. Transvenous implants seem to be the preferred method in children who weigh 13.5 kg or more. Physiologic dual-chamber pacemakers make the patients feel better. The time between hospitalizations for pacemaker replacements or revisions has increased from 14.7 months in 1974 to 22 months in this study.

Adolescent↗