Manometric brachial arteriography, a new technique for non invasive high-precision blood pressure measurement:development and validation through comparison with intra-arterial blood pressure

Background. Current methods for non invasive automated blood pressure (BP) measurement carry a number of limitations, with important discrepancies between the BP values they yield and those simultaneously recorded intra-arterially. This is the case also for oscillometric measurements, based on the assessment of volume oscillations in air cuff pressure indirectly transmitting to a transducer the brachial artery pulse waves, thus preventing their detailed morphological definition. This emphasizes the static/repetitive nature of the oscillometric method, which focuses on the positive component of artificially detected BP sinusoids only, limiting its assessment to pulse amplitude and disregarding the complex physiological nature of BP waves. Methods. To overcome this limitation, we propose a new method for BP measurement, called Manometric Brachial Arteriography, based on analysis of dynamic brachial artery physiology under the mechanical action of the manometric cuff. Such an analysis was developed under constant comparison with the synchronous homolateral arterial pressure directly recorded through an intra-arterial catheter. The arteriographic technology defines the systolic (S) and diastolic (D) BP points through direct non-traumatic assessment of brachial artery activity, explored by means of miniaturized electro-mechanical cutaneous sensors. The arteriographic trace of the brachial artery offers a complete morphological definition of every pulse wave component, coinciding with the corresponding definition obtained from the intra-arterial signal. Such multiparametric monitoring of subsequent pulse waves, leads to the identification of complex correlations between BP levels, morphological pulse wave details and time, from which the arteriographic manometer derives a measurement of SBP and DBP through two different and independent methods. The first method is based on the identification of the specific chronological latency between a predefined brachial arterial reference wave and the real DBP and SBP levels simultaneously recorded by the intra-arterial catheter. The second BP detection method is based on the assessment of changes in the pressure development speed (mmHg/sec) by the electronic micro-pump inflating the cuff, which occur in concomitance with the increased resistance offered, sequentially during diastolic and systolic phases, by the gradual cuff-induced brachial artery lumen reduction and occlusion. These changes in pump speed were found to coincide with intra-arterial DBP and SBP values simultaneously recorded. The entire procedure leads to detection of SBP and DBP values during the cuff inflation phase only. The accuracy of this method was tested in 120 patients admitted to the intensive care unit of the Sant’Orsola University Hospital in Bologna, in whom intra-arterial blood pressure monitoring was available. In each patient 3 measurements were performed by the device and compared with the homolateral intra-arterial signal simultaneously recorded, for a total of about 720 BP values (360 SBP and 360 DBP). Results. Overall a very high correspondence was found between methods, the mean discrepancy being -4.7 (range +2.8 to -0.6) mmHg for SBP, coefficient of variation 18.7%; and +4.4 (range +2.4 to -4.9) mmHg for DBP, coefficient variation 16.5%. In conclusion, this new method for non invasive automated BP measurement seems to overcome the limitations of available approaches and to offer a much more accurate estimate of actual intra-arterial BP values. Its ability to yield BP values more closely associated with hypertension-related organ damage and cardiovascular events needs to be assessed by ad hoc outcome studies.