Essential hypertension as a result of increased exposure to high gravitational stress associated with regular prolonged sitting typical for modern lifestyle

Contribuição dos grandes vasos arteriais na adaptação cardiovascular a ortostase

“…As the aortic length is related to body height, the arterial refl ection wave occurs later in taller individuals 121 , and it would not be incongruous to suppose that, in young individuals, especially females, those who present lower basal levels of arterial pressure, the presence of a more elongated aorta could interfere with the return of the refl ected component to the proximal aortic portions in an optimized way, which could result in the activation of refl exes related to the genesis of the syncope (for instance, the Bezold-Jarisch refl ex). Another aspect that supports this hypothesis is, as previously discussed, the importance of height (h) in gravitational stress 24 . Therefore, in young individuals, the premature return of the refl ected component of the pulse wave caused by the increment of the PWV during orthostasis would act together with the barorefl ex and other regulatory mechanisms of the arterial pressure, allowing an immediate adaptation to orthostatism 95 .…”

“…Thus, based on the equation established for the gravitational stress, the mass of blood displaced by infl uence of gravity, M, is a function of time, GS=U gr x M (t) = g x h x M (t). This means that gravitational stress can increase not only through the gravity force increase, but also depending on the duration of the orthostatic posture period 24 . Hence, remaining an excessive period of time in orthostasis requires a more advanced stage of anti-gravitational response with higher sympathetic hyperactivity, hypervolemia and arterial pressure increment, similarly to what would occur with an increment of the gravitation force.…”

“…The direction of the Earth's gravitational fi eld close to the surface is vertical, and the distance r is equal to the system height: U gr =gz x h. That explains why the effect of gravity is signifi cant only in the orthostatic posture. In the horizontal posture, the height of the human body, h, is too little, making U gr negligible, but it increases several fold during orthostasis 24 .…”

“…Therefore, the fi nal equation of gravitational stress can be expressed as follows: GS = g x h x M (t) / R p x H per , where R p is the peripheral resistance and H per is the work of the "peripheral venous heart" 24 .…”

Sitting and endothelial dysfunction: The role of shear stress

“…It could be hypothesized that repeated sedentary activity presents a chronic stimuli in the lower extremity which promotes the development of atherosclerosis. In the seated posture, blood pools in the leg, and both peripheral resistance and blood pressure in the leg increase [52,53,64]. As previously mentioned, Padilla and colleagues [51] observed changes in popliteal artery shear following 30 minutes of sitting; however, these changes were not detected in the post-intervention popliteal artery FMD, even after normalizing FMD to the shear stimulus.…”