A noninvasive method of estimating mean pulmonary artery pressure in the pneumatic total artificial heart.

ABSTRACT

Accurate hemodynamic monitoring is essential for the clinical management of the recipient of a total artificial heart (TAH). The high incidence of pulmonary congestive disorders in this population complicates this already formidable task. Lack of diagnostic pulmonary artery pressure (PAP) information is recognized as a fundamental source of these problems. Because conventional methods of obtaining hemodynamic information are difficult to implement in TAH recipients, improvement of TAH case management depends on the development of innovative monitoring strategies. Noninvasive monitoring techniques have been developed for three (right atrial pressure, left atrial pressure, and aortic pressure) of the four auxiliary circulatory pressures used to quantify hemodynamic performance. Development of the fourth, for PAP, was the subject of this work. We developed a noninvasive, in vitro method of estimating mean PAP in the Jarvik-7 TAH (Symbion, Inc, Salt Lake City, UT) recipient. This information was obtained by analyzing the relationship between the pneumatic right drive pressure (RDP) and PAP waveforms produced by a Jarvik-7 (70 ml) connected to a Donovan mock circulation and driven by a Utahdrive System IIIe Controller (Symbion, Inc, Salt Lake City, UT). Total artificial heart driver parameters (i.e., heart rate, percent systole, and vacuum) were manipulated to produce a range of ventricular filling volumes (FV), from 40 to 60 ml, for three distinct states of the pulmonary vasculature hypotensive, normal, and hypertensive. A unique multiple-linear regression equation was derived for each FV from the RDP-PAP relationship exhibited under these conditions. Comparison of computed estimates of PAP with actual measurements showed overall average correlations of greater than 0.92, with a standard error of the estimate of less than 1.9 mm Hg. The mean difference between actual and computed PAP measurements was -0.03 +/- 2.0 Hg. Estimations were accurate within 8.5% of true PAP values. Additional experimentation revealed that while the RDP-PAP relationships are dependent on FV, they are independent of the manner in which FV was obtained. Estimates proved useful over the clinical operating range of the pneumatic heart driver, as well as over the normal physiologic range of PAP in the human. This method is readily applicable to a computer-based monitoring implementation, although its effectiveness needs to be demonstrated in vivo.