Remote ischemic preconditioning alleviates hemodynamic changes induced by acute altitude exposure

To observe the effects of remote ischemic preconditioning (RIPC) on hemodynamic parameters and cerebral oxygen saturation in healthy adults under acute exposure to altitude.

Twenty-four healthy male cadets (24.0±1.7 years old) were recruited from Army Medical University during March and July, 2020, and equally and randomly divided into control and RIPC groups. After the hemodynamic parameters and cerebral oxygen saturation were measured at baseline for all participants, those of the RIPC group were subjected to 7 consecutive days of upper limb ischemic preconditioning with a pneumatic sphygmomanometer, while those of the control group underwent the same procedure but without ischemic treatment. A hypobaric chamber was used to simulate the oxygen partial pressure and atmospheric pressure at an altitude of 4 000 m. The changes of mentioned indexes were observed and compared between the 2 groups, before decompression and 2 h after reaching the simulated altitude. Moreover, blood samples of the participants were collected to determine the levels of norepinephrine and endothelin-1.

There were no significant differences in the baseline values and the values before decompression between the 2 groups. At 2 h after reaching simulated altitude of 4 000 m, systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and systemic vascular resistance (SVR) were all decreased in the control group; while stroke volume (SV), stroke index (SI), and SBP were declined in the RIPC group (P<0.05). Among these changes, the reduction of SVR was remarkably lower in the RIPC group (1 172.8/1 130.9 dyn·s·cm^-5, 3.6%) than the control group (1 225.8/993.0 dyn·s·cm^-5, 19.8%) (P=0.009), whereas the decrease of SV in the RIPC group (99.3/84.3 mL, 17.8%) was higher than that in the control group (82.9/78.8, 4.1%) (P=0.032). All the subjects showed elevated heart rate and reduced pulse oxygen saturation and left and right cerebral oxygen saturations, with significant differences before and after decompression in both groups (P<0.01). However, the RIPC group presented smaller reduction of left cerebral oxygen saturation than the control group [(-6.0±3.5)% vs (-8.6±2.4)%, P=0.049]. Meanwhile, the RIPC group had raised level of norepinephrine when compared with the control group (7 233±1 175 vs 5 995±1 079 pmol·L^-1, P<0.05).

Remote ischemic preconditioning can effectively maintain tissue oxygen supply by relieving the decrease of SVR caused by hypobaric hypoxia, which alleviates the cardiovascular compensatory response to hypobaric hypoxia, and thus improves the early acclimatization in human under acute altitude exposure.