On the Intensity of the Microvascular Magnetic Field in Normal State and Septic Shock

<b>Background</b>: Capillary tortuosity is a morphological variant of microcirculation. However, the mechanisms by which tortuous vessels meet metabolic requirements in health and disease remain unknown. We recently reported that capillary tortuosity score (CTS) is significantly higher in patients with septic shock than in steady-state individuals, and that CTS is significantly associated with alveolar-to-arterial oxygen (A-a O₂) gradient and oxygen debt in septic shock patients. <b>Objective</b>: We aimed to investigate the characteristics of the magnetic fields in the sublingual microcirculation of individuals with normal physiology and patients with septic shock. <b>Methods</b>: Systemic hemodynamics were recorded, and sublingual microcirculation was monitored using sidestream dark field (SDF+) imaging. The number of capillary red blood cells (N_RBC), the intensity of the magnetic field of a red blood cell (H_RBC), the intensity of the magnetic field of each capillary (H_CAP), and the intensity with which the magnetic field of a capillary acts on an RBC (F_CAP) were calculated. <b>Results</b>: Significant differences in macro- and microhemodynamic variables were observed between the two groups. Although N_RBC was significantly higher in individuals with steady-state physiology [87.4 (87.12) vs. 12.23 (6.9)], H_RBC was significantly stronger in patients with septic shock [5.9 × 10^-16 (6.9 × 10^-16) A m^-1 vs. 1.6 × 10^-15 (1.4 × 10^-15) A m^-1]. No significant difference was observed in H_CAP [2.16 × 10^-14 (2.17 × 10^-14) A m^-1 vs. 1.34 × 10^-14 (1.23 × 10^-14) A m^-1] and F_CAP [1.66 × 10^-24 (3.36 × 10^-24) A m^-1 vs. 6.44 × 10^-25 (1.1 × 10^-24) A m^-1] between the two groups. In patients with septic shock, H_RBC was associated with De Backer score (rho = -0.608) and venous-arterial carbon dioxide difference (rho = 0.569). In the same group, H_CAP was associated with convective oxygen flow (rho = 0.790) and oxygen extraction ratio (rho = -0.596). Also, F_CAP was significantly associated with base deficit (rho = 0.701), A-a O₂ gradient (rho = 0.658), and oxygen debt (rho = -0.769). <b>Conclusions</b>: Despite the microcirculatory impairment in patients with septic shock, H_RBC was significantly stronger in that group than in steady-state individuals. Also, H_CAP and F_CAP were comparable between the two groups. Tortuous vessels may function as biomagnetic coils that amplify RBC-induced magnetic fields, enhancing perfusion and oxygenation of adjacent tissues.