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We analyzed the spectral components of RR interval variability under controlled respiration (15 location of diseased coronary arteries. In these studies, the vagal cardiac function has been assessed by heart rate responses to tilting, the Valsalva maneuver, facial water immersion, or deep breathing. These conventional methods inflict a temporary imbalance on the cardiovascular system,9 and the data can be considerably affected by many hemodynamic control factors other than the vagal cardiac function. The purpose of this study was to investigate the relation between the autonomic cardiac function and the clinical and angiographic features of CAD. We evaluated the autonomic cardiac function by power spectral analysis of heart rate variability.9-14 Heart rate power spectral density in humans contains two major components, reflecting respiratory sinus arrhythmia (RSA) and a 0.04-0.

Although fast sodium current (INa) plays a major role in the generation and conduction of the cardiac impulse, the electrophysiological characteristics of INa in isolated human ventricular myocytes have not yet been fully described. We characterized the human ventricular INa of enzymatically isolated myocytes using whole cell voltage-clamp techniques. Sixty myocytes were isolated from ventricular specimens obtained from 22 patients undergoing open-heart surgery. A low temperature (17 degrees C) and Na+ concentration in the external solution (5 or 10 mM) allowed good voltage control and facilitated the measurement of INa. Cs+ was substituted for K+ in both internal and external solutions to block K+ currents, and F- was added to the internal solution to block Ca2+ current. INa was activated at a voltage threshold of approximately -70 mV, and maximal inward current was obtained at approximately -30 mV (holding potential = -140 mV). The voltage dependence of steady-state INa availability (h infinity) was sigmoidal with half inactivation occurring at -97.3 +/- 1.1 mV and a slope factor of 5.77 +/- 0.10 mV (n = 60). We did not detect any significant differences in these parameters in cells from patients with a variety of disease states, with or without congestive heart failure. The overlap in voltage dependence of h infinity and Na+ conductance suggested the presence of a Na+ "window" current. An inactivation time course was voltage dependent and was fitted best by the sum of two exponentials. The rate of recovery from inactivation also was voltage dependent and fitted by the sum of two exponentials.(ABSTRACT TRUNCATED AT 250 WORDS)