Validation of the mean systemic filling pressure assessment with preserved arterial blood flow by comparing two methods of calculation 

Significance: We developed a method for measuring in vivo venular volumes and pressures in the limbs using near-infrared spectroscopy (NIRS). Aim: 36 We aimed to validate the NIRS methodology by comparing two independent methods of calculation based on different physiological approaches.Approach: Pressure-volumes curves were recorded following graded venous occlusion on the forearm. Values from a multi-phase model (method 1) were compared with data derived from a resistor-capacitance calculation model (method 2) based on arterial pressure and venous compliance. We tested these methods on 10 healthy participants at rest and during exercise and on 6 severely ill patients. Results: Pressure-volume curves measured by method 1 were comparable with those calculated by method 2. Venular volumes calculated using method 1 correlated linearly with those calculated using method 2 both in participants (R2 = 0.98, p < 0.001) and in patients (R2 = 0.94, p < 0.001). The Bland-Altman test showed a good agreement between methods with few values out of the range of ± 1.96 SD. Conclusions: Our findings showed that the NIRS methodology may be valid for the assessment of venular bed with no flow interruption. Further research will be required to confirm the relevance of methodology in the clinical setting.