Comparison of Critical Closing Pressures Extracted from Carotid Tonometry and Finger Plethysmography

Abstract

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 flow velocity. 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.

Cerebral critical closing pressure estimation from Finapres and arterial blood pressure measurements in the aorta

“…Moreover, the Finometer can use a standardized inverse transfer function to obtain estimates of central ABP and it would be of great interest to assess if this can lead to estimates of CrCP and RAP in agreement with the values derived from aortic pressure in this study. Future investigations of noninvasive derivation of CrCP and RAP parameters might also consider other alternatives to the Finapres such as radial (Birch and Morris 2003) or carotid artery tonometry (Hsu et al 2005).…”