Information Processing and Cardiovascular Control

Abstract

It has previously been reported that an increase in mental task load is accompanied by a decrease in heart rate variability (HRV). In most of the experiments relating mental task load to HRV, the number of signals in paced choice reaction time tasks served as the main loading factor. However, this determinant of task load confounds muscular and mental load. In the present article we scored HRV by computing the power spectrum of the cardiac interval signal. The spectrum contains power related to respiratory activity (usually between 0.20 and 0.40 Hz) and power related to non‐linear processes involved in the control of body temperature and blood pressure (between 0.02 and 0.20 Hz). During performance on cognitive tasks the total power is attenuated, but the spectral power between 0.02 and 0.20 Hz (comprising about 80% of the total spectral energy, i.e. HRV) is particularly affected. Within this latter region we especially investigated the power between 0.06 and 0.14 Hz. The power in this region is believed to originate from processes involved in the dynamic control of mean arterial pressure. In Experiment 1 it was shown that this blood pressure‐related spectral component was rather insensitive to considerable changes in respiratory rate and depth. In Experiments 2 and 3 we kept signal rate constant but varied the cognitive demands of a sentence comprehension task and a working memory task. These experiments indicated that the power of the 0.10 Hz vasomotor oscillations was significantly affected by the processing demands of these tasks. The evidence suggested a decreased baroreflex sensitivity (i.e. a decrease in gain) during mental loading. A method was proposed to non‐invasively determine baroreflex sensitivity.