Impacts Of Prolonged Sitting With Mild Hypercapnia In Healthy Adults

Abstract

Previous research suggests that prolonged sitting attenuates vascular function. It is common for people to sit for prolonged periods of time in places such as offices and classrooms which are accompanied by mild hypercapnic conditions due to poor ventilation. However, the effects of prolonged sitting with mild hypercapnic conditions on vascular function has not been investigated. PURPOSE: The purpose of this study is to investigate the responses in heart rate (HR), blood pressure (BP), vascular function, and autonomic function in healthy young adults to a single bout of prolonged sitting in mild hypercapnic conditions. METHODS: In a randomized crossover design, 12 subjects (6M/6F) sat for 2.5 hours in a control condition (PSIT) or a mild hypercapnic condition (HCAP, CO2=1,500 ppm). During each visit, HR, central and peripheral BP, brachial and popliteal artery endothelial function (flow-mediated dilation, FMD), arterial stiffness (pulse-wave velocity (PWV), augmentation index (AIx)), and heart rate variability (HRV) were assessed before and after prolonged sitting. RESULTS: Both brachial and popliteal FMD were significantly reduced (p<0.05) in HCAP and PSIT, and the reduction in popliteal FMD was significantly greater in HCAP than PSIT (p<0.05). Additionally, there were trends for increased carotid-to-distal (cd) PWV (p=0.083) in HCAP compared to PSIT. HR was significantly reduced (p<0.05) and carotid-to-radial (cr) deceleration time (DT) and cdDT were significantly increased (p<0.05) in HCAP. There were also trends for reduced augmentation pressure (AP) (p=0.07) and LF/HF ratio (p=0.09). AP, AIx, AIx normalized to 75 beats per minute, and crAIx were all significantly reduced (p<0.05) in PSIT. There were no significant changes in BP and HRV in either group (p>0.05). CONCLUSIONS: These results indicate that prolonged sitting in mild hypercapnic conditions attenuate endothelial function to a greater extent than prolonged sitting in normal atmospheric conditions. Our findings suggest that mild hypercapnic conditions in our daily life exacerbate the negative effects of prolonged sitting.