The longer the length of a vessel the greater is the resistance to flow
Therefore, there is a correlation between body size / build / height of subject and BP
The tall/obese person will have significantly longer vessels compared to the average person – which increases resistance to flow, impacts on TPR and is reflected in a higher BP, compared to the short/petite individual
Normally, neither vessel length nor haematocrit change much in an individual
However, vessel diameter is subject to frequent alteration and as such has a significant impact on TPR and therefore BP
