Feasbility of non-invasive arterial blood pressure estimation using inductive plethysmography in anaesthetised rats

Inductive plethysmography (IP) has proven effective in detecting changes in cardiac output and stroke volume, enabling non-invasive hemodynamic monitoring using jacketed telemetry systems. However, the deployment of this modality in safety pharmacology is limited by its current inability to measure arterial blood pressure (AP). Recent studies have demonstrated the feasibility of estimating AP using mathematical formulas describing the relationship between AP and the ‘time delay’ required for a pulse to travel a certain distance in the arterial tree (‘pulse transit time’ or PTT). From a physiological perspective, AP estimated from an average PTT can be correlated with the mean arterial pressure (MAP). The aim of this study was to assess the feasibility of estimating arterial blood pressure (AP’) in rats by measuring PTT between the abdominal and thoracic plethysmographic signals recorded by the DECRO jacketed telemetry device and to compare it with a reference measurement during a pharmacological challenge. The pharmacological protocol consisted of a continuous intravenous (i.v.) infusion of 12.5 μg/ml dobutamine (beta-agonist) administered at increasing infusion rates (4, 6 and 8 ml/h) in six anaesthetised (2 %/2.5 % isoflurane) male Wistar rats (10 weeks, 355 g) under spontaneous ventilation. Arterial pressure was measured with an Edwards probe through a catheter inserted into the left carotid artery, and MAP was calculated. Animals were equipped with the DECRO device and AP’ was estimated from the PTT using a logarithmic model. The two variables were compared using Pearson's correlation coefficient and a Bland-Altman analysis to evaluate agreement and bias. Both methods detected a statistically significant decrease respectively in the AP’ and MAP. The estimation of AP’ by the PTT calculation algorithm adapted to plethysmographic data correlated with the measurement of MAP throughout the pharmacological protocol (correlation coefficient of 0.94). A mean difference of 1.4 % and 95 % limits of agreement ranging from −3.29 % to +6.09 % were found between the two methods. These results demonstrate the potential of this non-invasive modality for estimating blood pressure changes in preclinical situations. Capabilities to conduct a differentiated estimation of Systolic and diastolic pressure changes and implementation in other conditions remain to be explored.