The permeability and the effect of acyl-chain length for phospholipid bilayers containing cholesterol: theory and experiment.

The model of Cruzeiro-Hansson et al. (Biochim. Biophys. Acta (1989) 979, 166-1176) for lipid-cholesterol bilayers at low cholesterol concentrations is used to predict the thermodynamic properties and the passive ion permeability of lipid bilayers as a function of acyl-chain length and cholesterol concentration. Numerical simulations based on the Monte Carlo method are used to determine the equilibrium state of the system near the main gel-fluid phase transition. The permeability is calculated using an ansatz which relates the passive permeability to the amount of interfaces formed in the bilayer when cholesterol is present. The model predicts at low cholesterol contents an increase in the membrane permeability in the transition region both for increasing cholesterol concentration and for decreasing chain length at a given value of the reduced temperature. This is in contrast to the case of lipid bilayers containing high cholesterol concentrations where the cholesterol strongly suppresses the permeability. Experimental results for the Na+ permeability of C15PC and DPPC (C16PC) bilayers containing cholesterol are presented which confirm the theoretical predictions at low cholesterol concentrations.

Management of anticoagulation in outpatients: experience with an anticoagulation service in a municipal hospital setting.

In 66 months, a general hospital's outpatient Anticoagulation Service (ACS) monitored 263 patients who received 280 courses of warfarin sodium totalling 254 patient treatment years. Major hemorrhagic morbidity was 4% of courses and there was no mortality attributable to warfarin therapy. Major hemorrhage occurred in patients with increased anatomic risk of bleeding (diverticulosis, hemorrhoids, cystitis), and was not a function of patient age, sex, anticoagulation control, or medications administered concurrently with warfarin. Control of anticoagulation was not correlated with age or other medications, but was worsened significantly by the presence of congestive heart failure. We attribute a favorable experience with outpatient ACS to careful patient selection, patient education and monitoring, attention to duration of anticoagulation, and continuing communication with primary physicians who retained responsibility for medical care. An ACS offers safety, consistency, efficiency, and a unified approach to outpatient anticoagulation in the general hospital setting.

Outpatient management of anticoagulation.

The Anticoagulation Service insures uniformity of approach to the regulation of anticoagulation for patients of hospital-based primary physicians. There has been no anticoagulant-related mortality in 254 patient treatment-years, and the major complication rate is 4% of treatment courses. There is a relatively low complication rate because of the systematic approach to anticoagulation therapy, recognition of the importance of patient education, communication with the primary physician, and flexibility of drug dosage and patient visit regimens. Achieving the therapeutic range of the prothrombin time with minimum complications is the goal of this Service. The hallmark of adequate control is predictable response of the prothrombin time to adjustments in drug dosage. Statistical analysis of six years' experience has provided support for the thesis that control of anticoagulation and incidence of complications are not significantly altered by patient age, sex, or the presence of concurrent nonthromboembolic medical illness.