Blood Rheology Adjustments in Rats after a Program of Intermittent Exposure to Hypobaric Hypoxia

Abstract

Intermittent hypobaric hypoxia (IHH) exposure induces a rise in hemoglobin concentration and an increase in erythrocyte mass in both rats and humans. Although this response increases blood oxygen transport capacity, paradoxically, it could impair blood flow and gas exchange because of the blood viscosity alterations associated with the rising hematocrit. In the present study, male rats were subjected to an IHH program consisting of a daily 4-h session for 5 days/week until they had completed 22 days of hypoxia exposure in a hypobaric chamber at a simulated altitude of 5000 m. Blood samples were taken at the end of the exposure period (H) and at 20 (P20) and 40 (P40) days after the end of the program and were compared to control (C) maintained at sea- level pressure. Apparent blood viscosity (eta(a)) and plasma viscosity (eta(p)) were measured in a cone-plate microviscometer. Although the hematocrit significantly increased in the H group, blood apparent viscosity did not differ among groups, ranging from 7.67 to 6.57 mPa*sec at a shear rate of 90 sec(-1). Relative blood viscosity showed a clear increase (about 27%) in H rats, mainly due to the significant decrease in plasma viscosity. This finding could be interpreted as a compensatory response, which reduced the effect of increased erythrocyte mass volume on whole-blood viscosity. Oxygen delivery index and blood oxygen potential transport capacity remained unchanged in all groups. These data indicate that the IHH program has a deep but transitory effect on red cell parameters and a moderate effect on blood rheological behavior.

Physiological Effects of Intermittent Passive Exposure to Hypobaric Hypoxia and Cold in Rats

“…The hematological responses already took place after the shorter exposure period (9 days) and lasted while the hypoxic stimulus was present at least until day 21 (Figure 2). These results agree with previous studies where similar intermittent exposure protocols were applied (Casas et al, 2000;Esteva et al, 2009;Núñez-Espinosa et al, 2014. It has been widely known that exposure to high altitude per se produces an increase of oxygen transport capacity both in humans and animals except for those adapted to life at high altitude (Vinegar and Hillyard, 1972;León-Velarde et al, 1993;Heinicke et al, 2003;Zhang H. et al, 2018;Laguë et al, 2020).…”

Physiological and Biological Responses to Short-Term Intermittent Hypobaric Hypoxia Exposure: From Sports and Mountain Medicine to New Biomedical Applications

“…Our group took an in-depth look at the physiological responses to intermittent exposure to hypobaric hypoxia (IEHH) in hypobaric (low barometric pressure) chambers. A detailed study of the precise mechanisms that underlie these adaptive responses (erythropoiesis, angiogenesis and the release of circulating stem cells) in humans and in an experimental rodent model encouraged us to explore the possibilities of applying IEHH programs with biomedical and therapeutic purposes (Panisello et al, 2007 , 2008 ; Esteva et al, 2009 ; Viscor et al, 2009 ; Corral et al, 2014b ). Thus, we recently demonstrated the efficacy of applying IEHH programs (passive exposure only or combined with exercise protocols) in the recovery of a range of injuries (Corral et al, 2014a ; Núñez-Espinosa et al, 2014 ; Rizo-Roca et al, 2017a , b ).…”

Acetazolamide and chronic hypoxia: effects on haemorheology and pulmonary haemodynamics

“…However, no data are currently available regarding the effects of acetazolamide on blood viscosity. The changes in PVR observed in chronic hypoxia could be related to several mechanisms, such as pulmonary vascular remodelling [2,8], haemorheological changes [9,10], hypoxic vasoconstriction [11] or greater nitric oxide scavenging by erythrocytes as a consequence of the rise of Hct [12]. Polycythaemia in various models (mice, rats and guinea pigs) appears to be involved in pulmonary hypertension by increasing blood viscosity [13].…”