Cardiovascular reactivity to stressors: Effect of time of day?

Abstract

Reduced cardiovagal baroreflex sensitivity and a peak in the incidence of cardiovascular events in the hours immediately after waking from nocturnal sleep suggest that cardiovascular control is impaired in the morning compared with other times of day. Previous research indicates that diurnal variation exists in acute blood pressure (BP) responses to exercise. However, the effect of time of day on activities such as cognitive tasks and "passive coping" physical tasks has yet to be established. Therefore, the primary aim of this study was to explore cardiovascular responses to physical and mental stressors at two times of day that have previously been associated with differing levels of cardiovascular control. In addition, the effect of the chronotype was examined to identify possible interactions between morningness/eveningness, time of day and responses to stressors. Fourteen healthy, young subjects completed a morning (08:30 h) and an afternoon (13:30 h) trial on separate days. Subjects performed a mental arithmetic task and a cold pressor test while beat-to-beat measurements of BP and heart rate were recorded continuously. Reactivity was determined using mean change scores in systolic BP, diastolic BP, mean arterial pressure, heart rate and rate-pressure product (RPP) from a period of rest recorded immediately prior to the task. There was no significant difference in cardiovascular reactivity between the morning and afternoon (p > 0.05). The time course of the responses and subsequent recovery were also consistent between the two times of day (p > 0.05). There was a significant interaction between time of day and chronotype, although this was apparent only for heart rate and RPP reactivity (p < 0.05); subjects tending towards "morningness" exhibited greater heart rate and RPP reactivity in the afternoon, and subjects tending towards "eveningness" exhibited greater heart rate and RPP reactivity in the morning. No interactions were observed between time of day and chronotype for BP reactivity (p > 0.05). Despite effects of time of day on heart rate that are dependent upon chronotype, this study suggests that BP control during mental and passive physical stress is not altered between the morning and afternoon.

Rate of rise in diastolic blood pressure influences vascular sympathetic response to mental stress

“…Consistent with previous studies (Carter & Ray, ; Yang et al . ; Dunn & Taylor, ), mental stress was associated with significant increases in blood pressure and heart rate. However, in contrast to physical stressors, there was considerable inter‐individual variability in MSNA responses to mental stressors.…”

Morningness-eveningness analysis in high performance young athletes

“…Además, encontrarían un momento del día donde su acrofase biorrítmica encajaría con un momento de máxima demanda de actividad (los matutinos en clase del colegio y los vespertinos en el entrenamiento). De esta manera podría no producirse el desajuste que algunos autores (Collado-Mateo et al, 2013;De Almondes & Araújo, 2003;Díaz-Morales & Sánchez, 2008;Dunn & Taylor, 2014;Nebel et al, 1996;Willis et al, 2005) proponen como facilitador de ansiedad.…”

“…Al respecto, los estudios con población general tienden a indicar que la ansiedad se relaciona positivamente con la vespertinidad, el cual se ve más acentuado en las mujeres (Collado-Mateo et al, 2013;Díaz-Morales & Sánchez, 2008). Estos resultados se ven reforzados por los trabajos que indican que los matutinos muestran una menor tasa cardíaca por las mañanas como indicador de ansiedad ante tareas estresantes, mientras que los vespertinos lo hacen por las tardes ( De Almondes & Araújo, 2003;Dunn & Taylor, 2014;Nebel et al, 1996;Willis, O´Connor & Smith, 2005). Los autores indican que la asociación ansiedad-vespertinidad se debe al desajuste entre los ritmos biológicos y los horarios impuestos por la sociedad (e. g, una persona vespertina que tiene que levantarse todos los días a las 7.30 am para entrenar a las 9.00 am), ya que estos están estructurados principalmente para las personas matutinas, en las que sus necesidades biorrítimicas no cuadran con los horarios establecidos, pudiendo generar ansiedad en la persona debido a que su organismo tal vez no esté en condiciones óptimas para hacer frente a las diferentes demandas por la mañana.…”

Blood pressure reactivity at onset of mental stress determines sympathetic vascular response in young adults

“…In order to assess whether BP responses to stressors differed between positive and negative responders, the following comparisons were made between groups: Peak changes : The peak changes in systolic BP, DBP and MAP were compared between positive and negative responders during the first minute of the task. The first minute was chosen because evidence suggests that the majority of the increase in BP during mental stress occurs within the first minute, after which it typically plateaus (Dunn and Taylor ). Peak change (mmHg) was defined as the highest BP value during the first minute of the task minus the BP value of the first cardiac cycle of the task. Time of peak : The time of the peak changes in systolic BP, diastolic BP, and MAP during the first minute of the task were compared between positive and negative responders.…”

“…Peak changes: The peak changes in systolic BP, DBP and MAP were compared between positive and negative responders during the first minute of the task. The first minute was chosen because evidence suggests that the majority of the increase in BP during mental stress occurs within the first minute, after which it typically plateaus (Dunn and Taylor 2014). Peak change (mmHg) was defined as the highest BP value during the first minute of the task minus the BP value of the first cardiac cycle of the task.…”