Right ventricular diastolic relaxation in conscious dog models of pressure overload, volume overload, and ischemia

Abstract

Objective: Limitations in clinical understanding of right ventricular relaxation can be attributed to the paucity of information from basic studies in animal models of right ventricular disease. This study examined, in the conscious state, right ventricular relaxation dynamics under normal conditions (n = 15) and in subacute (2-5 weeks) canine models of right ventricular pressure overload (n = 6), volume overload (n = 7), and free wall ischemia (n = 7).

Methods: Right-heart micromanometric measurements were obtained by using multisensor catheters. A new algorithm was developed to obtain representative ensemble averages of hemodynamic waveform data sets. Right ventricular relaxation was analyzed by using an exponential model with 3 parameters: P(0), tau, and P(b). Significant changes versus control values were determined by means of analysis of variance and the Student unpaired t test with Bonferroni's adjustment.

Results: In the state of pressure overload, right ventricular pressure decay exhibits an increased P(0) (56.2 +/- 19.1 vs 13.1 +/- 5.1 mm Hg [mean +/- SD]) and prolonged tau (57.1 +/- 2.8 vs 27.8 +/- 3.9 ms); there is also a decreased P(b) (-7.9 +/- 1.5 vs 0.28 +/- 1.8 mm Hg). The only significant change in volume overload is an increased asymptote, P(b) (5.3 +/- 2.9 mm Hg). In right ventricular ischemia, prolongation of tau (41.4 +/- 13.0 ms) and decreased P(b) (-1.95 +/- 1.1 mm Hg) attain high significance.

Conclusions: Distinctive abnormalities in right ventricular relaxation dynamics accompany pressure overload, volume overload, and ischemia and may contribute to clinical right ventricular dysfunction.

Figure 1

Comparison of TE and EC algorithms. The top panels show application of the TE algorithm to 3 waveforms: the second and third were extrapolated and truncated, respectively. The bottom panels show application of the EC algorithm to the same waveforms: all 3 beats preserve their original shapes.

Figure 2

Steady-state RV pressure pulses under control conditions (A), pressure overload (B), volume overload (C), and ischemia (D). Peak systolic pressure is greatly increased under pressure overload, slightly increased under volume overload, and slightly decreased under ischemia.

Figure 3

Tracings of RV isovolumic pressure decay under control conditions (A), pressure overload (B), volume overload (C), and ischemia (D). Dots denote every other point in the digital ensemble average of the measured waveforms. The line shows the exponential fit. Arrows indicate the last points used in regression.

Figure 4

Descriptive statistics of the exponential model coefficients. CTRL, Control condition; PO, pressure overload; VO, volume overload; IS, ischemia.