Voluntary control of cardiovascular reactions to demanding tasks

Three groups of 10 normotensives participated in a study exploring voluntary control of cardiovascular reactions to cognitive tasks. Pulse transit time (TT), interbeat interval (IBI), skin conductance level, and respiratory variables were monitored throughout one introductory and four experimental sessions. The groups were matched on the basis of initial TT and IBI responses to the taxing arithmetic and reasoning tasks. During experimental sessions, one group (FB) was provided with visual analogue TT feedback, while the REL group was given detailed relaxation instructions. A third group (CON) performed the same sequence of tasks but was not instructed to modify cardiovascular reactions at any point. Training in voluntary control was carried out in resting (no-task) conditions, and during task administration. Both treatment groups showed lower cardiovascular reactions than controls in task trials. Only REL subjects lengthened TT in no-task conditions, while both FB and REL groups showed smaller cardiovascular reactions than CON during the tasks. Effects were confined to cardiovascular variables, since respiratory and electrodermal reactions during task administration were similar in all groups. The effects of treatments were especially marked among the most reactive subjects.     

Kinematic motion of the anterior cruciate ligament deficient knee during functionally high and low demanding tasks

The purpose of this study was to determine whether mechanical adaptations were present in patients with anterior cruciate ligament (ACL)-deficient knees during high-demand activities. Twenty-two subjects with unilateral ACL deficiency (11 males and 11 females, 19.6 months after injury) performed five different activities at a comfortable speed (level walking, ascending and descending steps, jogging, jogging to a 90-degree side cutting toward the opposite direction of the tested side). Three-dimensional knee kinematics for the ACL-deficient knees and uninjured contralateral knees were evaluated using the Point Cluster Technique. There was no significant difference in knee flexion angle, but an offset toward the knee in less valgus and more external tibial rotation was observed in the ACL-deficient knee. The tendency was more obvious in high demand motions, and a significant difference was clearly observed in the side cutting motions. These motion patterns, with the knee in less valgus and more external tibial rotation, are proposed to be an adaptive movement to avoid pivot shift dynamically, and reveal evidence in support of a dynamic adaptive motion occurring in ACL-deficient knees.     

Changes in indexes of cardiovascular system in different mental tasks

The influence of different types of mental activity on the cardiovascular system was analyzed by following indexes: the heart rate (HR), the variation magnitude (VM), the amplitude of systolic wave (SWA) and the pulse wave transit time (PWTT). A registration of these indexes was conducted when the subjects solved verbal-logical and spatial mental tasks. HR was significantly greater in the spatial tasks than in the verbal-logical tasks, while SWA had an inverse relationship. The time for solving of tasks of the both types did not differ significantly. Therefore, the observed changes in autonomic indexes were not related to a difficulty of the mental tasks, but depended on the specific cognitive processes involved in the mental tasks of different types. Thus, the observed change in HR and the decrease in SWA correlating with the blood pressure rise reflect an influence of the sympathetic nervous system on the heart work during mental tasks of the verbal-logic type. The obtained results suggest that the indexes of HR and a blood pressure may also serve as supporting criteria in a development of new technologies for a determination of different types of mental operations in addition to the rhythms of the brain electrical activity.     

Application of dynamic point process models to cardiovascular control

The development of statistical models that accurately describe the stochastic structure of biological signals is a fast growing area in quantitative research. In developing a novel statistical paradigm based on Bayes' theorem applied to point processes, we are focusing our recent research on characterizing the physiological mechanisms involved in cardiovascular control. Results from a tilt table study point at our statistical framework as a valid model for the heart beat, as generated from complex mechanisms underlying cardiovascular control. The point process analysis provides new quantitative indices that could have important implications for research studies of cardiovascular and autonomic regulation and for monitoring of heart rate and heart rate variability measures in clinical settings.     

Changes in some indices of the cardiovascular system in different mental tasks

In order to study the effects of the type of mental activity on the function of the cardiovascular system in humans, the following indices were used: the heart rate (HR), RR interval, variation magnitude (VM), systolic wave amplitude (SWA), and pulse wave transit time (PWTT). These indices were recorded when the subjects solved verbal-logical or spatial mental tasks. The HR was substantially increased during solving of the spatial tasks as compared to solving of the verbal-logical tasks, whereas the SWA showed the opposite changes. The latencies of the performance of the tasks of various types were similar in the subjects; therefore, the changes in the autonomic indices did not depend on the difficulties of the mental tasks. They rather depended on specific features of the mental processes involved in the performance of the tasks of different types. Thus, changes in the HR and the decreased SWA, which was related to elevated blood pressure, represent the effect of the sympathetic nervous system on the heart function during solving verbal-logical tasks. Our data demonstrate that the HR and blood pressure can be used as additional indices for the development of new techniques for assessment of different types of mental processes together with the indices of electrical brain activity.     

Chemoreceptor reflexes and cardiovascular control

Evidence is presented which indicates that in the absence of other known inputs to the nervous system and during controlled pulmonary ventilation, stimulation of the carotid body chemoreceptors causes bradycardia and selective peripheral vasoconstriction. These responses may be attenuated, however, by concomitant changes in respiration and arterial blood pressure, and by activity of higher parts of the brain stem. Stimulation of the aortic bodies in mammals in which they are functionally active, causes bradycardia or tachycardia and selective peripheral vasoconstriction. The reflex vascular effects from the peripheral arterial chemoreceptors are mediated by alpha-adrenergic sympathetic fibres. A potential mechanism exists therefore whereby the peripheral arterial chemoreceptors could contribute to the neurogenic component of hypertension.     

Human cardiovascular reactions to simulated hypovolaemia, modified by the opiate antagonist naloxone

Six healthy males were exposed to 20 mm Hg lower body negative pressure (LBNP) for 8 min followed by 40 mm Hg LBNP for 8 min. Naloxone (0.1 mg.kg-1) was injected intravenously during a 1 h resting period after which the LBNP protocol was repeated. Systolic, mean, and diastolic arterial blood pressures (SAP, MAP, DAP), and central venous pressure (CVP) were obtained using indwelling catheters. Cardiac output (CO), forearm blood flow (FBF), heart rate (HR), left ventricular ejection time (LVET), and electromechanical systole (EMS) were measured non-invasively. Pulse pressure (PP), stroke volume (SV), total peripheral resistance (TPR), forearm vascular resistance (FVR), systolic ejection rate (SER), pre-ejection period (PEP), PEP/LVET and indices for the systolic time intervals (LVETI, EMSI, PEPI) were calculated. During the second LBNP exposure, only two parameters differed from the pre-injection values: DAP at LBNP = 40 mm Hg increased from 60.0 +/- 4.8 mm Hg to 64.8 +/- 4.1 mm Hg (N = 4, p less than 0.02) and LVETI at LBNP = 20 mm Hg increased from 384.4 +/- 5.2 ms to 396.8 +/- 6.2 ms (N = 6, p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

The neurodynamics underlying attentional control in set shifting tasks

In this work we address key phenomena observed with classical set shifting tasks as the “Wisconsin Card Sorting Test” or the “Stroop” task: Different types of errors and increased response times reflecting decreased attention. A component of major importance in these tasks is referred to as the “attentional control” thought to be implemented by the prefrontal cortex which acts primarily by an amplification of task relevant information. This mode of operation is illustrated by a neurodynamical model developed for a new kind of set shifting experiment: The Wisconsin-Delayed-Match-to-Sample task combines uninstructed shifts as investigated in Wisconsin-like tasks with a Delayed-Match-to-Sample paradigm. These newly developed WDMS experiments in conjunction with the neurodynamical simulations are able to explain the reason for decreased attention in set shifting experiments as well the different consequences of decreased attention in tasks requiring bivalent yes/no responses compared to tasks requiring multivalent responses. Electronic supplementary material  The online version of this article (doi: ) contains supplementary material, which is available to authorized users.

Voluntary control of skin temperature: Role of experimenter presence versus absence

The purpose of the present experiment was to determine whether the physical presence of an experimenter affects biofeedback performance according to social facilitation predictions. A 2(experimenter: presence vs. absence)×2(task directionality: increase vs. decrease) design was employed. It was hypothesized that the presence of an experimenter would hinder the acquiring of skin temperature control in a biofeedback task. Fifty-three subjects were randomly assigned to the four experimental conditions. The results were compatible with social facilitation predictions, i.e., experimenter presence hindered performance.     

Significance and assessment of autonomic indices in cardiovascular reactions.

The purpose of this review was to integrate recent evidence supporting the reliability of noninvasive measures of parasympathetic and sympathetic activity. Literature concerning spectral analysis of heart period (HP) variability is reviewed with special emphasis on works revealing neural mediation of high-frequency and mid-frequency components of HP power spectrum and suggesting their use as a tool to assess autonomic balance. Problems of derivations of autonomic indices based on impedance cardiography and HP variance analysis are discussed. Advantages of parametric time series (autoregressive-AR) models are described with the objective of providing an informed basis for choosing among methodological alternatives. Two original approaches developed in our laboratory are outlined, namely the algorithms for systolic time interval assessment based on impedance cardiogram as well as the AR method developed for heart period power spectral density estimation.