Motor Current Waveforms as an Index for Evaluation of Native Cardiac Function During Left Ventricular Support with a Centrifugal Blood Pump

Abstract

Control of ventricular assist devices (VADs) for native heart preservation should be attempted, and it could be one strategy for dealing with the shortage of donors in the future. In the application of a nonpulsatile blood pump for ventricular assistance from its apex to the aorta, the bypass flow and hence motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous flow pumps, this study investigated whether or not motor current could be used as an index for continuous monitoring of native cardiac function. In Study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mm Hg, afterload of 40 mm Hg, and left ventricular (LV) systolic pressure of 40 mm Hg was used. The pump rpm were fixed at 1,300, 1,500, and 1,700, and LV systolic pressure was increased up to 140 mm Hg by a step of 20 mm Hg while observing the changes in LV pressure, motor current, pump flow, and aortic pressure. In Study 2, in vivo experiments were performed using 5 sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LV pressure was varied through administration of dopamine while observing the changes in LV pressure, pump flow, motor current, and aortic pressure at 1,500 and 1,700 rpm. An excellent correlation was observed both in vitro and in vivo studies in the relationship between motor current and LV pressure. In Study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1,300, 1,500, and 1,700 rpm, respectively. In Study 2, they were 0.90 (Animal 1), 0.82 (Animal 2), 0.89 (Animal 3), 0.93 (Animal 4), and 0.70 (Animal 5) respectively for 1,500 rpm, and 0.94 (Animal 2), 0.85 (Animal 3), 0.94 (Animal 4), and 0.89 (Animal 5) respectively, for 1,700 rpm. The relationship between motor current and pump flow and LV pressure showed an unstable correlation in an in vivo study. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VADs for native heart preservation.

Measurement for implantable rotary blood pumps

“…This was interpreted as indicating that p lv could be estimated from I motor , although clearly the existence of a correlation does not solve the whole problem of predicting p lv from I motor . He later (Kikugawa 2001) extended these mock-loop experiments to sheep, and found good correlation between I motor amplitude and systolic p lv , except at low speeds. Ohuchi et al (2001) (Kurashiki Medical College, Tokyo Medical & Dental University and Aishin Memorial Hospital Sapporo), also found, in both a mock loop and a goat, a linear correlation between peak p lv and I motor amplitude at a given centrifugal-pump speed.…”

“…These results were obtained with an apico-aortic sealless pivot-supported centrifugal LVAD in two calves. However, Kikugawa (2001) of Kawasaki Medical School, Kurashiki, working both with a mock loop and with sheep, found that the amplitude of Q pump variation did not correlate well with I motor amplitude. He found rather that I motor amplitude was predictive of systolic left ventricular pressure, p lv , except at low speed.…”

“…In a series of papers from 1998 to 2003 (Araki et al 1998, Oshikawa et al 1998, 2000, Endo et al 2000, 2001, 2003, the notably independent-minded group from Miyazaki Medical College, allied in their earlier work with Oita Medical University, have promoted the utility of a motor current pulsatility index (I max -I min )/I mean . Working with their own 'mixed-flow' pump, and plotting this index against ω, they discern two salient points.…”

Left Ventricular Assist Device Management in the ICU

“…Pump power is a direct measurement of watts required by the device to pump blood at the set RPM. Pump power correlates well with blood flow, but there are exceptions (20,28,29) (Table 1).…”

Minimally invasive estimation of cardiac function for patients with rotary VAD support

“…Although this technique can be performed without interrupting VAD operation, the use of indwelling sensors was not completely avoided. Kikugawa [4] and Takahashi et al [5] observed the correlation between motor current waveform and the amplitude of the left ventricular pressure to determine E MAX. Since, left ventricular pressure amplitude is heavily dependant to the pump speed of the VAD, the consistency of using LV pressure to represent cardiac function while the pump speed is changing is still uncertain.…”