Nanoscale Flow Choking and Spaceflight Effects on Cardiovascular Risk of Astronauts - A New Perspective

摘要

Of late, authors reported conclusively through the state-of-the-art closed-form analytical methodology that the asymptomatic stroke and the transient-ischemic-attack could occur due to the Sanal flow choking (PMCID: PMC7267099). Sanal flow choking leads to the shock wave generation causing arterial stiffening in the arteries particularly with bifurcation regions. At the internal flow choking (biofluid/Sanal flow choking) condition, the systolic-to-diastolic blood pressure ratio (BPR) is a unique function of the blood/biofluid heat capacity ratio (BHCR). The physical situation of internal flow choking in the micro/nanoscale fluid flows in the circulatory system is more susceptible at microgravity condition due to altered variations of blood viscosity, turbulence and the BPR. During a long-term space mission, the major factor that affects cardiovascular dysfunctions is the absence of gravity. Note that microgravity environment decreases plasma volume and increases the hematocrit compared with the situation on the earth surface, which increases the relative viscosity of blood. Since blood viscosity strongly depends on hematocrit there are possibilities of an early Sanal flow choking in microgravity environment due to an enhanced boundary layer blockage. While using the lopsided blood-thinners and/or drugs with anticoagulant property, the dynamic viscosity of blood decreases and as a result Reynolds number increases and the laminar flow could be disrupted and become turbulent and thereby the boundary-layer-blockage factor increases leading to an early internal flow choking. As the pressure of the nanoscale biofluid flows rises, average-mean-free-path diminishes and thus, the Knudsen number lowers heading to a zero-slip wall-boundary condition with compressible viscous flow effect, which increases the risk of internal flow choking in the cardiovascular system at gravity and the microgravity environment. In this paper analytical, in vitro and in silico results are reported to establish the concept of the occurrence of Sanal flow choking in the gravity and micro gravity environment in micro/nanoscale circulatory systems. We could establish herein that the relatively high and the low blood-viscosity are cardiovascular risk factors during the spaceflight. We concluded that for a healthy-life all subjects (human being / animals) in the earth and in the outer space with high BPR necessarily have high BHCR. We also concluded that for reducing the cardiovascular risk, all the astronauts/cosmonauts should maintain the BPR lower than the lower critical hemorrhage index (LCHI) as dictated by the lowest heat capacity ratio (HCR) of the gas generating from the biofluid/blood for prohibiting the internal flow choking during the space travel. We recommend all astronauts/cosmonauts should wear ambulatory blood pressure and thermal level monitoring devices similar to a wristwatch throughout the space travel for the diagnosis, prognosis and prevention of internal flow choking leading to asymptomatic cardiovascular diseases. We concluded without any ex vivo or in vivo studies that suppressing the turbulence level and simultaneously reducing the blood viscosity are the key tasks to prevent internal flow choking for reducing the cardiovascular risk in earth as well as in microgravity conditions. This could be achieved by increasing the thermal tolerance level of blood by increasing the heat capacity ratio of blood and/or decreasing blood pressure ratio.