Effects of flow, perfusion pressure, and oxygen consumption on cardiac capillary exchange.

The roles of blood flow, local oxygen consumption, and perfusion pressure on cardiac transcapillary exchange were characterized in closed-chest anesthetized dogs by use of the multiple-indicator dilution technique. Occlusion of the carotid arteries or injection of dipyridamole increased coronary flow to significantly higher values compared with a group of animals in a basal state obtained in a previous study. Carotid occlusion resulted in a significant increase in perfusion pressure and myocardial oxygen consumption, whereas these two variables were significantly reduced after dipyridamole. For the whole group of animals, the capillary permeability-surface area product for sucrose increased with coronary flow, which appeared to be the important controller for this microcirculatory exchange parameter. Perfusion pressure and myocardial oxygen consumption also regulated permeability-surface area product values, although to a lesser extent than flow. The heterogeneity of transit times in the capillaries was reduced at high coronary flow values, despite large differences in the cardiac utilization of oxygen. The data suggest that cardiac capillary exchange responds mostly to hemodynamic changes originating at the precapillary level.

[Relation between illicit drug use and personal problems related to consumption in students; analysis of a self-administered questionnaire]. / Relation entre l'usage des drogues illicites et les problèmes personnels reliés à la consommation chez les étudiants; analyse d'un questionnaire auto-administré.

An anonymous self-administered questionnaire on psychotropic drugs was completed by 3,212 students, with a response rate of 95.1%. A proportion of 28.1% reported the consumption of illicit drugs during the year preceding the study. The prevalence of personal problems related to psychotropic drugs averaged 13.2% among drug users, compared with 3.8% among those who consumed alcohol only. The percentages of students reporting these problems increased progressively among those who consumed cannabis, hallucinogens, solvents and cocaine, while the proportions of users for these substances decreased respectively in the same order. The inverse relationship observed for these different drugs between the proportion of users and the prevalence of personal problems suggests that a marginal consumption is accompanied by increased difficulties among users. Measurement of the use of different illicit drugs among students could represent an index for the prevalence of personal problems related to drugs.

Microsphere and dilution measurements of flow and interstitial space in dog heart.

The effects of coronary flow on cardiac capillary permeability-surface area products and interstitial spaces were examined at rest and after hemodilution in the canine heart. Multiple-indicator-dilution experiments and left atrial injections of microspheres were carried out in closed-chest anesthetized animals at rest and after plasma expansion with dextran. Plasma expansion was utilized to produce a large increase in coronary perfusion compared with control conditions. Values for plasma flow per unit interstitial space, derived from analysis of the indicator-dilution data, were found to correlate closely with average vascular plasma flow per gram, calculated from the cardiac microsphere data; the one reflects the other. With an increase in flow, cardiac capillary permeability-surface area product values were found to increase substantially, whereas the average sucrose extravascular or cardiac interstitial spaces remained stable. Consequently the dilution parameter, flow per unit interstitial space, which is independent of tracer loss, provided a good reflection of flow per weight of tissue in the heart, without the additional requirement for a flow probe.

Cardiac microcirculatory effects of beta-adrenergic blockade during sympathetic stimulation.

The effects of beta-adrenergic blockade on cardiac transcapillary exchange were examined at rest and during sympathetic stimulation. Multiple indicator dilution experiments were carried out in closed-chest anesthetized dogs at rest and during carotid occlusion, either under basal conditions or after beta-adrenergic blockade with alprenolol. beta-Adrenergic blockade at rest had no effect on coronary flow or transcapillary exchange in comparison with the control situation, but it abolished the increase in coronary flow and in the permeability/surface area product for labeled sucrose produced by carotid occlusion. High coronary resistance values in beta-blocked animals with carotid occlusion were associated with a high degree of heterogeneity in capillary transit times, but the overall relation between coronary flow and the capillary permeability/surface area product was unchanged. The findings indicate that beta-blockade increases coronary resistance during sympathetic stimulation and, simultaneously, decreases the coronary blood flow and capillary permeability/surface area product while increasing the heterogeneity of capillary transit times.