Automatic System for Noninvasive Blood Pressure Determination in Rotary Pump Recipients

Abstract

In patients with implanted rotary pumps, the arterial pressure pulsatility is usually far lower than in normal individuals. Depending on the remaining degree of pulsatility, cuff-based systems such as the classical Riva-Rocci-determination of arterial blood pressure and correlated sounds or pressure measurements based on cuffpressure oscillations become inaccurate or even impossible. Therefore, a system was developed which evaluates the flow in the radial artery using an ultrasound wristwatch sensor, and this additional information is used for pressure determination. A computerized data acquisition and cuff-control system based on a PC using Matlab software, a wristwatch ultrasound device, and a compressor-driven pressure cuff was set up. The cuff was controlled for automatic inflation and deflation cycles. Cuff pressure and arterial flow was recorded. Several algorithm strategies were developed, which gave data for systolic blood pressure and heart rate together with a reliability index for data quality. Finally, the new algorithms were implemented in a microcontroller system. Comparisons with invasive measurements showed excellent correlation with systolic blood pressure (mean deltaP -0.3 mm Hg, n = 28). During exercise of rotary pump patients and therefore enhanced pulsatility the difference from manual evaluation was -2.1 mm Hg (n = 18). In conclusion, adaptation of the classical cuff-pressure method with ultrasound evaluation of peripheral flow allows reliable determination of blood pressure in patients with low pulsatility resulting from implanted rotary cardiac assist pumps. By development of a wristwatch sensor and an automatic control system a robust method for daily use could be developed.

Renal Failure in Patients with Left Ventricular Assist Devices

“…Myers et al showed that the automatic BP machine provided both systolic and diastolic readings when pulse pressure was .12.864.8 mmHg (76). However, readings obtained using an automatic BP machine are often unreliable because many of them rely on oscillometric pulsations, which are created by the native left ventricular contractions (77,78). Comparison of automatic BP cuff readings with arterial line measurements in 35 patients with a continuous-flow LVAD revealed significant differences in systolic, diastolic, and mean BPs, with the automatic cuff readings of systolic and diastolic measurements consistently lower than those obtained using an arterial catheter (14,76).…”

“…For practical reasons, Doppler audible ultrasonography is a commonly used means to record BP in patients with continuous-flow LVADs, especially when residual left ventricular pulsatility is so low that automated devices have difficulty in displaying a reproducible reading. In these instances, the start of blood flow auscultated with Doppler ultrasonography is commonly regarded as the mean arterial pressure (77). The blood pressure can be measured by placing the Doppler probe over the brachial artery below an inflated blood pressure cuff using the non-access arm of a hemodialysis patient.…”

Physiology of continuous blood flow in recipients of rotary cardiac assist devices

“…The low pulsatility situation can make non-invasive pressure measurement difficult and may require special techniques such as combined pressure cuff ultrasound methods. 38 Typically, patients have a pressure pulsatility of between 5 and 25 mm Hg.…”

Choroidal Microcirculation in Patients With Rotary Cardiac Assist Device

“…Systolic arterial blood pressure (SBP) was measured by a modified Riva-Rocci method using a cuff on the upper arm and a Hartley MDII ultrasound device for determination of systolic flow onset. 8 Heart rate was determined from the pump flow signal by counting the waves in flow.…”