T-WAVE AMPLITUDE - RELATIONSHIPS TO PHASIC RSA AND HEART PERIOD CHANGES

T-Wave Amplitude (TWA) has been suggested as an indicator of sympathet ic influence on myocardial performance, but critics have argued that T WA is confounded by parasympathetic influence or that it is a non-spec ific feature of tachycardia. To help clarify the issue, we examined TW A as a function of parasympathetic activity, using cardiac vagal contr ol as measured by high frequency components of heart period variabilit y (respiratory sinus arrhythmia) and of interbeat intervals (IBI), acr oss several stressful tasks. Sixteen male subjects were exposed to Val salva, Serial Subtraction and Cold-Presser tasks. After controlling fo r between-person variance, it was found that RSA did not contribute to TWA and that IBI contributed dependably to TWA only during the Valsal va maneuver, when heart rate was driven very high. In light of these r esults, we recommend that TWA continue to be considered a candidate in dicator of sympathetic influence on myocardial performance, although c aution should be used if heart rate is dramatically elevated. (C) 1998 Elsevier Science B.V. All rights reserved.