Response of heart rate to atropine and left ventricular function in Chagas' heart disease.

Chagasic patients may have a normal or abnormal response of heart rate to atropine. To determine if this response to atropine is related to the degree of left ventricular dysfunction, we studied 33 patients with a positive complement fixation test for Chagas' disease. Eleven subjects, with atypical chest pain and negative complement fixation test, were used as controls (sero-negative).

Valsalva maneuver: a test of the functional state of cardiac innervation in Chagasic myocarditis.

The ratio between maximal and minimal R-R intervals measured during the Valsalva maneuver is an adequate means of studying the functional state of the cardiac parasympathetic nervous system. We studied the changes in heart rate evoked during the Valsalva maneuver in 49 asymptomatic Chagasic patients with different degrees of myocardial involvement. The Chagasic patients were divided in three groups.

Mathematical treatment of absorbance versus pH graphs of polybasic acids.

Mathematical relationships determining the shape of absorbance vs. pH graphs of polybasic acids are derived, and new graphical and numerical techniques for evaluating the acidity constants of two-step overlapping equilibria are examined.

Spectrophotometric methods for the evaluation of acidity constants--II: Numerical methods for two-step overlapping equilibria.

A brief review of the numerical methods employed in the evaluation of acidity constants of two step overlapping equilibria is given. A new alternative to the method of three equations developed by Thamer is also proposed in this paper. Taking into account the Gauss-elimination method, several variants to the original method of Thamer are devised.

Spectrophotometric methods for the evaluation of acidity constants-I Numerical methods for single equilibria.

The spectrophotometric methods applicable to the numerical evaluation of acidity constants of monobasic acids are briefly reviewed. The equations are presented in a form suitable for easy calculation with a programmable pocket calculator. The aim of this paper is to cover a gap in the education analytical literature.