Time course of cardiovascular responses induced by mental and orthostatic challenges

Abstract

Cardiovascular responses to single stressors diminish over time. Interaction of different stressors influencing hemodynamic variables, indicative of stress-induced reactivity and physiological responses are, however, poorly understood. We investigated time course of mental (using mental arithmetic, MA) and orthostatic (using head up tilt, HUT) challenges induced responses in 16 males. Three protocols were used: HUT, MA and MA + HUT, with sessions randomized and two weeks apart. Hemodynamic responses were compared for 30 s epochs of stress application (stress T1 , stress T2 …). Compared to baseline, HUT, HUT + MA and MA applications affected heart rate (HR) (+ 15.1 ± 8.0 bpm, + 20.0 ± 9.2 bpm, + 11.9 ± 7.2 bpm, all p's b .001, respectively) and stroke volume (SV) (− 22.3 ± 8.1 ml, − 22.0 ± 10.4 ml, − 7.6 ± 8.7 ml, all p's b .001, respectively). HUT and MA + HUT induced HR increases were higher in stress T2 compared to stress T1 (p b .05) and reached maximum at stress T2 . HUT and MA + HUT further reduced SV in stress T2 as compared to stress T1 (p b .001); lowest SV was in stress T2 . Mean arterial pressure reached its minimum in stress T1 during HUT and MA + HUT (− 6.0 ± 8.5 mm Hg, p b .001, − 4.4 ± 9.7 mm Hg, p b .01, respectively) but increased in MA (+ 4.3 ± 3.7 mm Hg, p b .01). Combination of MA + HUT resulted in different time courses of blood pressure responses as compared to HUT alone. We conclude that application of single or combined stress challenges lead to stressor-and time dependent-initial changes in cardiovascular responses. Our findings provide novel insights regarding the duration a stressor must be applied to elicit maximal cardiovascular responses.

Delaying orthostatic syncope with mental challenge: A pilot study

“…Column 1: Average of orthostatic tolerance times (OTT, in min) of presyncopal run 1 (PS1), presyncopal run 2 (PS2); Column 2: Improvements in OTT (measured by subtracting from mental arithmetic induced orthostatic tolerance the averages of PS1 and PS2); Column 3: Proportional improvements in OTT derived by dividing improvements in OTT (Column 2) with the corresponding baseline (Column 1). than with mental arithmetic (MA) or head up tilt (HUT) alone [4]. As shown in the Fig.…”

“…The interaction between these stressors when applied together, however, is poorly understood. Since the mechanisms of cardiovascular regulation have been reported to be different in orthostatic and mental stresses, we previously investigated the modulation of head up tiltinduced orthostatic responses by mental challenge, applied using mental arithmetic [4]. We observed that mental arithmetic (adding or subtracting six or seven from two or three digit numbers) increased mean arterial pressure and prevented the decrease in cardiac output when it was done while standing up [4].…”

“…Mental challenge was applied using mental arithmetic: Participants were asked to add or subtract continuously the numbers 6 or 7, randomly, from a 2 or 3 digit numbers and to state the correct answers. In study [4], participants did only 10 min of head up tilt, with and without 10 min mental arithmetic. In the present study, subjects were driven up to presyncope and mental arithmetic was applied only for 2-3 min preceding presyncope.…”

“…Mental challenge was applied by using mental arithmetic: Participants were asked to add or subtract continuously the numbers 6 or 7, randomly, from a 2 or 3 digit number [4] and to state the correct answer. A new number combination was provided every 5 s on a computer screen fixed at level of the eye of the participant.…”

“…Being a primary capacitance area of the body, the venous system can exert great changes in venous return and cardiac preload when its capacity is altered. In a previous study, in which we studied the effects of mental challenge on orthostatic responses [4], mental challenge-induced sympathetic activity increased cardiac output, being sustained perhaps by a greater increase in venous tone, increased mean circulatory filling pressure and thus increased venous return (see Guyton's analysis [20]). Our results are supported by observations of Kuipers et al that mental challenge induces splanchnic vasoconstriction [3].…”