## Abstract

Background. The time constant of isovolumic relaxation (τ) is an important parameter of ventricular diastolic function, but the need for invasive measurement with high-fidelity catheters has limited its use in general clinical cardiology. The Doppler mitral regurgitant velocity spectrum can be used to estimate left ventricular (LV) pressure throughout systole and may provide a new noninvasive method for estimating τ. Methods and Results. Mitral regurgitation was produced in nine dogs, and ventricular relaxation was adjusted pharmacologically and with hypothermia. High-fidelity ventricular pressures were recorded, and τ was calculated from these hemodynamic data (τ_{H}) assuming a zero-pressure asymptote. Continuous-wave mitral regurgitant velocity profiles were obtained, and the ventriculo-atrial (VA) pressure gradient was calculated by the simplified Bernoulli equation; τ was calculated from the Doppler data from the time of maximal negative dP/dt until LV-LA pressure crossover. Three methods were used to correct the Doppler VA gradient to better approximate the LV pressure before calculating τ: 1) adding actual LA V wave pressure (to yield τ_{LA}); 2) adding 10 mm Hg (τ_{10}); and 3) no adjustment at all (actual VA gradient used to calculate τ_{0}). The agreement between τ_{H} and the three Doppler estimates of τ was assessed by linear regression and by the mean and standard deviation of the error between the measurements (Δτ). τ_{H} ranged from 29 to 135 msec. Without correction for LA pressure, the Doppler estimate of τ seriously underestimated τ_{H}: τ_{0}=0.30τ_{H}+9.4, r=0.79, Δτ=-35±18 msec. This error was almost completely eliminated by adding actual LA pressure to the VA pressure gradient: τ_{LA}=0.927τ_{H}+7.6, r=0.95, Δτ=2±7 msec. Addition of a fixed LA pressure estimate of 10 mm Hg to the VA gradient yielded an estimate that was almost as good: τ_{10}=0.89τ_{H}+4.9, τ=0.88, Δτ=-2±12 msec. In general, τ was overestimated when actual LA pressure was below this assumed value, and vice versa. Numerical analysis demonstrated that assuming LA pressure to be 10 mm Hg should yield estimates of τ accurate to ±15% between true LA pressures of 5 and 20 mm Hg. Conclusions. This study demonstrates that the Doppler mitral regurgitant velocity profile can be used to provide a direct and noninvasive measurement of τ. Because mitral regurgitation is very common in cardiac patients, this method may allow more routine assessment of τ in clinical and research settings, leading to a better understanding of the role of impaired ventricular relaxation in diastolic dysfunction and the effect of therapeutic interventions.

Original language | English (US) |
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Pages (from-to) | 272-278 |

Number of pages | 7 |

Journal | Circulation |

Volume | 86 |

Issue number | 1 |

DOIs | |

State | Published - Jul 1992 |

## Keywords

- Diastolic function
- Doppler echocardiography
- Tau

## ASJC Scopus subject areas

- Cardiology and Cardiovascular Medicine
- Physiology (medical)