Effect of Long-Duration Standing and Sitting On Vascular Function

Background: An increase in sedentary lifestyle is a growing problem as it has a negative impact on vascular function leading to significantly higher risk of myocardial infarction and cardiovascular disease mortality. Both standing and sitting for extended periods of time affect endothelial function in lower leg vasculature. Flow-mediated dilation (FMD) and pulse wave velocity (PWV) are two variables that allow us to quantify endothelial function. Purpose: The purpose of this study was to compare the effects of long-duration sitting versus standing on lower body vasculature as assessed by PWV and FMD. Methodology: This study included 13 men and 13 women ages 18 to 40 yeas old (n=26) and consisted of one familiarization visit as well as two experimental trials. At each experimental trial, subjects either sat or stood for 120 min. Before and after each trial baseline measurements were taken after 20 minutes in a supine position to allow for baseline hemodynamics to return. PWV and FMD were measured using duplex-doppler ultrasound incrementally throughout the trials. PWV was calculated as the direct distance between the sites of the femoral and dorsalis pedis arteries divided by the time delay from the R-wave to the foot of the pulse wave. FMD was recorded at the superficial femoral artery (SFA) on both legs with 2 minutes of baseline data, followed by 5 minutes of occlusion by an automatic blood pressure cuff at 250 mmHg then 3 minutes post-occlusion to measure the vasodilatory response. Other variables measured throughout the trial included mean arterial pressure (MAP) and heart rate (HR). Results: Sitting decreased FMD by [1.41% 95% CI (0.07, 2.74), p = 0.039]. However, standing did not significantly affect FMD, [0.89% 95% CI (-1.21, 2.99)]. Alternatively, there was no change in PWV in the seated trial [-.2 cm/s 95% CI (-45.5,45.5)] but there was an increase in the standing trial [49.6 cm/s 95% CI (1.2,98.1) p = 0.044]. Mean arterial pressure increased by 7 mmHg (SD= 10; p \u3c .01) during the seated trial and increased 10 mmHg (SD=8; p \u3c .001) in the standing trial. HR increased by 10 BPM (SD = 8; p \u3c .01) in the seated trial and 30 BPM (SD = 13; p \u3c .001) in the standing trial. However there were no differences between baseline and post measurements of HR and MAP (supine) for either the seated or standing trial (all p \u3e .05). Discussion: Long-duration sitting reduced FMD, while standing did not. In contrast, PWV increased significantly in the standing trial but was unchanged when seated. Therefore, while there appears to be some benefits of standing (e.g., FMD) there appears to be some negative effects on the arterial compliance (e.g., PWV) over the same period