Comprehensive Analysis of Macrocirculation and Microcirculation in Microgravity During Parabolic Flights

Abstract

Background: Profound knowledge about cardiovascular physiology in the setting of microgravity can help in the course of preparations for human space missions. So far, influences of microgravity on the cardiovascular system have been demonstrated, particularly pertaining to venous fluid shifts. Yet, little is known about the mechanisms of these adaptations on continuous macrocirculatory level and regarding the microcirculation.

Methods: Twelve healthy volunteers were subjected to alternating microgravity and hypergravity in the course of parabolic flight maneuvers. Under these conditions, as well as in normal gravity, the sublingual microcirculation was assessed by intravital sidestream dark field microscopy. Furthermore, hemodynamic parameters such as heart rate, blood pressure, and cardiac output were recorded by beat-to-beat analysis. In these settings, data acquisition was performed in seated and in supine postures.

Results: Systolic [median 116 mmHg (102; 129) interquartile range (IQR) vs. 125 mmHg (109; 136) IQR, p = 0.01] as well as diastolic [median 72 mmHg (61; 79) IQR vs. 80 mmHg (69; 89) IQR, p = 0.003] blood pressure was reduced, and cardiac output [median 6.9 l/min (6.5; 8.8) IQR vs. 6.8 l/min (6.2; 8.5) IQR, p = 0.0002] increased in weightlessness compared to normal gravitation phases in the seated but not in the supine posture. However, microcirculation represented by perfused proportion of vessels and by total vessel density was unaffected in acute weightlessness.

Conclusion: Profound changes of the macrocirculation were found in seated postures, but not in supine postures. However, microcirculation remained stable in all postures.

Keywords: hemodynamic changes; microcirculation; microgravity; parabolic flight; weightlessness.

FIGURE 1

Macrocirculatory parameters in the course of parabolic flights in the seated position. (A) Systolic blood pressure, (B) diastolic blood pressure, (C) heart rate, and (D) cardiac output changes during the course of a parabola in the seated position are shown. Data are presented as median and interquartile range (IQR). Significant differences between groups are shown (Friedman test and Dunn’s multiple comparisons post hoc test). ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, and ^∗∗∗∗p < 0.0001.

FIGURE 2

Macrocirculatory parameters in the course of parabolic flights in the supine position. (A) Systolic blood pressure, (B) diastolic blood pressure, (C) heart rate, and (D) cardiac output changes during the course of a parabola in the supine position are shown. Data are presented as median and interquartile range (IQR). Significant differences between groups are shown (Friedman test and Dunn’s multiple comparisons post hoc test). ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, and ^∗∗∗∗p < 0.0001.

FIGURE 3

Microcirculation in steady flight and acute weightlessness. Comparison of obtained parameters for normal gravity (1 G) and microgravity (0 G) for two variables of sublingual microcirculation, namely, the perfused proportion of vessels [(A) in the supine posture and (B) in the seated posture] and the total vessel density [(C) in the supine posture and (D) in the seated posture]. The test applied in statistical analysis was the Mann–Whitney test. ns, not significant.