Investigating the dielectric response of blood to dissolved nitrogen

This study explores the relationship between dissolved nitrogen in blood and its complex permittivity, with the aim of evaluating the feasibility of developing a non-invasive biosensor for detecting dissolved nitrogen. Such a sensor would enable decompression profile calculation to be based on real-time physiological data rather than a one-size-fits-all algorithm. Experiments were carried out on human blood samples extracted at hyperbaric air pressures of up to 3 bar absolute within a hyperbaric chamber. A custom measurement setup was developed to facilitate data acquisition in this environment. Two measurement techniques were employed: a broadband open-ended coaxial probe and a resonant complementary split ring resonator (CSRR) sensor, covering a frequency range from 0.5 to 6.5 GHz. The coaxial probe showed no significant changes in the complex permittivity of blood across different pressure levels. The CSRR sensor exhibited more pronounced shifts in resonant frequency, though these changes lacked consistency and reproducibility, and therefore could not be reliably linked, as yet, to dissolved nitrogen concentration. • Dielectric characterisation of freshly extracted blood was performed under hyperbaric conditions. • Measurements were conducted inside a hyperbaric chamber using a coaxial probe and a novel CSRR sensor. • Changes observed using the coaxial probe were within the associated measurement uncertainty. • The CSRR sensor exhibited more pronounced shifts in resonant frequency, although these lacked consistency and reproducibility. • Although shifts in the dielectric response of blood were observed, they could not be reliably correlated, as yet, with dissolved nitrogen concentration.