The Effect of Breaking up Prolonged Sitting on Cerebral Blood Flow

Abstract

Prolonged sitting has a detrimental effect on peripheral conduit artery endothelial function, whilst breaking up prolonged sitting time can prevent such impairments. The effect of prolonged sitting and breaking up sitting time on cerebral blood flow (CBF) is currently unknown. Importantly, decreased CBF is related to lower cognitive functioning and increased risk of cognitive impairment and dementia. PURPOSE:To determine the effect of uninterrupted sitting and breaking up sitting time with light intensity walking on CBF in healthy subjects. METHODS: Thirteen healthy participants (8 male, 37.3±10.1 years old, BMI: 25.6±3.4 kg/m2) completed, on separate days, three 4 hr conditions in a counterbalanced order: a) uninterrupted sitting, b) sitting with 2-min light intensity walking breaks every 30 mins, or c) sitting with 8-min light intensity walking breaks every 2 hrs. Middle cerebral artery blood flow velocity (MCAv) was measured using transcranial Doppler in a supine position at BASELINE, 2HRS and 4HRS. Beat-to-beat blood pressure was assessed (Finometer), enabling the calculation of cerebrovascular conductance (CVC). Between each measurement participants remained seated and were permitted to complete desk-based tasks. RESULTS:There was no change over time in MCAv (BASELINE: 57.3±2.4 cm/s, 2HRS: 56.5±2.3 cm/s, 4HRS: 56.3±2.1 cm/s; p=0.77) or CVC (BASELINE: 0.71±0.04 cm/s/mmHg, 2HRS: 0.70±0.04 cm/s/mmHg, 4HRS: 0.67±0.03 cm/s/mmHg; p=0.18), or between the conditions (MCAv: p=0.18; CVC: p=0.11). Moreover, there was no interaction between condition and time for MCAv (p=0.56) or CVC (p=0.64). CONCLUSIONS:Contrary to previous findings which indicate that prolonged sitting can reduce peripheral endothelial function, our data suggest that neither CBF velocity nor CVC are altered following prolonged sitting for 4 hrs. Additionally, breaking up this sitting time with walking breaks did not further affect CBF velocity or CVC. Whilst our data indicate unaltered CBF following uninterrupted sitting, changes in cerebrovascular function may occur independent of changes in blood flow. Further research is therefore needed to determine whether measures of cerebrovascular function, including autoregulation and reactivity, are influenced by prolonged sitting. Supported by BBSRC Grant BB/L017237/1