Types of Interference Effects on the Autonomic-Cardiovascular Response to the Simultaneous Performance of Active Orthostatic and Cold Face Tests

Abstract

In 25 healthy subjects we assessed the effects of cold face test (CFT) IntroductionIt is commonly accepted that active orthostatic test (AOT) provokes an increase in sympathetic activity with baroreflex involvement [1,2] and that cold face test (CFT) elicits a non-baroreflex sympatho-vagal coactivation [2,3]. However, when we recently compared the time course of the autonomic cardiovascular effects of CFT and AOT, we found that their response patterns are quite opposite, because, while CFT elicits great increases in vagal activity, baroreflex sensitivity (BRS) and respiratory sinus arrhythmia sensitivity (RSAS), AOT shows a 7 times greater sympathetic activation, and BRS and RSAS reductions [4,5]. If CFT and AOT were performed simultaneously (CFAOT), how would the minimal sympathetic activity of the former interfere with the sympathetic predominance of the latter? And how would the minimal vagal outflow of AOT interfere with the great vagal activation of CFT? To answer these questions, we modified an experimental strategy that has been employed to evaluate the suppressive and facilitatory interactions in the electrical response of sensory cortical areas [6,7]. Recently, we studied the interference effects between regions of the autonomic nervous system when stimulated by complex respiratory maneuvers [8].Our methodological strategy was to compare the responses to two different maneuvers applied separately and simultaneously, testing the assumption that, if the response to the simultaneous maneuver equals the sum of the separate responses, no functional interference effects (FIE) are produced, so, there is no convergence of inputs. Thus, we assessed the time course of FIE provoked by CFAOT relative to the sum of the separate effects of CFT and AOT (CFT+AOT) on the instantaneous spectral measures derived from heart rate and arterial pressure (AP) variabilities, BRS and RSAS. Methods SubjectsTwenty-five healthy, normotensive and sedentary subjects, 14 men and 11 women, were studied. Mean age, height and weight were 22.2±2.2 years, 167±8 cm and 69.1±10.4 kg respectively. Their written informed consent was requested to participate. ProtocolVolunteers visited the laboratory twice, first to evaluate their health status and anthropometric values, and second to carry out the experimental stage. Subjects