Contribution of tissue lipid to long xenon residence times in muscle.

Experiments demonstrate that the mean residence time of an inert gas in tissue is longer than that predicted by a single-compartment model of gas exchange. Also the relative dispersion (RD, the standard deviation of residence times divided by the mean) is 1 according to this model, but RDs in real tissues are closer to 2, suggesting that a multiple-compartment model might be more accurate. The residence time of a gas is proportional to its solubility in the tissue. Although the noble gases in particular are 10 times more soluble in lipid than in nonlipid tissues, models of gas exchange generally do not incorporate measurements of the lipid in tissue, which may lead to error in the predicted gas residence times. Could a multiple-compartment model that accounts for the lipid in tissue more accurately predict the mean and RD of gas residence times? In this study, we determined the mean and RD of Xe residence times in intact and surgically isolated muscles in a canine model. We then determined the lipid content and the perfusion heterogeneity in each tissue, and we used these measurements with a multiple-compartment model of gas exchange to predict the longest physiologically plausible Xe residence times. Even so, we found the observed Xe mean residence times to be twice as long as those predicted by the model. However, the predicted RDs were considerably larger than the observed RDs. We conclude that lipid alone cannot account for the residence times of Xe in tissue and that a multiple-compartment model is not an accurate representation of inert gas exchange in tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Paraneoplastic digital thrombosis: a case report.

Persistent digital ischemia is an uncommon paraneoplastic syndrome. We describe a 71-year-old man whose only manifestation of an underlying adenocarcinoma was digital ischemia. His symptoms responded dramatically to bilateral dorsal sympathectomies. A thorough search for the mechanism producing the ischemia failed to provide an explanation. We assume that unknown neurohumoral factors produced by the tumor were responsible.

Sinus node dysfunction in pediatric and young adult patients: treatment by implantation of a permanent pacemaker in 39 cases.

To examine the clinical course of sinus node dysfunction that necessitates permanent pacing in the pediatric and young adult populations, we studied the records of the 39 patients 40 years of age or younger (mean age, 23 years) who underwent implantation of a permanent pacemaker for treatment of this disorder at our medical center between 1960 and 1983. The tachycardia-bradycardia syndrome was the most common rhythm disturbance, and syncope was the most frequent initial symptom. All symptomatic patients noted resolution of symptoms after pacemaker implantation. Twenty-five of the 39 patients (64%) had associated cardiovascular disease, most commonly transposition of the great arteries. In each of the 11 patients with this anomaly, sinus node dysfunction developed after a surgical procedure for correction of the defect. Of the total patient population, 20 patients (51%) had previously undergone a cardiac operation. The mean interval between pacemaker implantation and the previous operation was 105 months. After a mean follow-up of 50.5 months, the patients with no obvious underlying heart disease have done well. Each of the eight patients who have died had underlying cardiovascular disease. None of the deaths was thought to be pacemaker related. Sinus node dysfunction should be considered in the differential diagnosis of young patients with syncope or dizziness, especially if they have undergone a reparative cardiac surgical procedure. If symptomatic sinus node dysfunction is confirmed, permanent pacing is an effective therapeutic modality. In the absence of associated heart disease, the prognosis seems to be excellent.