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Noninvasive monitoring of β‐adrenergic tone during isoproterenol infusions

Sphygmo‐Recording is a simple, noninvasive technique for analysis of pulse wave contour and timing which has been used to evaluate the change in cardiac dynamics during isoproterenol infusion. The QKd interval, i.e., the time interval between the onset of the QRS complex and the onset of the KorotkojJ sound at the brachial artery when the sphygmomanometer cuff is at diastolic pressure, is normally 205 ± 15 msec. Continuous intravenous infusion of isoproterenol at 0.01, 0.02, and 0.03 ug /kg /min into 12 euthyroia normotensive adult volunteers for 10‐min intervals resulted in decreases of 55, 79, and 89 msec in QKd and increases of heart rate of 14, 27, and 43 beats/min, respectively. The corresponding changes in dP/dt, i.e., slope of the pulse wave upstroke at the brachial artery determined noninvasively from the same records, were 0.65, 1.47, and 2.26 mm Hg/msec. These results confirm previous studies which indicate that the chronotropic response of normal subjects to isoproterenol infusion is comparable to that previously reported in patients with the putative “hyperdynamic β‐adrenergic state.”