Comparison of critical closing pressures extracted from carotid tonometry and finger plethysmography

Background: The reliability of critical closing pressure (CrCP) estimates derived from peripheral blood pressure (BP) measurements is unclear. We attempted to evaluate the influences of peripheral circulation on determining CrCP. Methods: Twenty-five young healthy volunteers were studied. BP waves were obtained with plethysmography (Portapres) and carotid applanatory tonometry, respectively, for analysis. Transcranial Doppler was used to monitor cerebral flowvelocity. Using linear regression analysis, beat-to-beat CrCP was calculated at rest, during voluntary hyperventilation and during 5% CO₂ inhalation. Results: Twenty of 25 participants demonstrating satisfactory tonometric tracings for both tests were included in the analysis. The systolic BP measured using plethysmography was higher than that derived from tonometry (139.4 ± 24.7 vs. 105.5 ± 29.6, p < 0.001). CrCP values derived from tonometry were all positive and higher than CrCP values derived from plethysmography (62.9 ± 19.9 vs. 11.1 ± 17.8, p < 0.001). The changes in CrCP induced by 5% CO₂ inhalation and hyperventilation had a correlation between two BP monitoring methods (r = 0.52, p = 0.001). Conclusions: Pressure waveform is an important determinant in calculating CrCP by linear regression analysis. The relative changes in CrCP induced by hemodynamic challenges remained a relevant indicator of cerebrovascular regulation regardless of the methods used for non-invasive BP recording.