Beat-to-beat stroke volume estimation from aortic pressure waveform in conscious rats: comparison of models

Several methods for estimating stroke volume (SV) were tested in conscious, freely moving rats in which ascending aortic pressure and cardiac flow wer e simultaneously (beat-to-beat) recorded. We compared two pulse-contour mod els to two new statistical models including eight parameters extracted from the pressure waveform in a multiple linear regression. Global as well as i ndividual statistical models gave higher correlation coefficients between e stimated and measured SV (model 1, r = 0.97; model 2, r = 0.96) than pulse- contour models (model 1, r = 0.83; model 2, r = 0.91). The latter models as well as statistical model 1 used the pulsatile systolic area and thus coul d be applied to only 47 +/- 17% of the cardiac beats. In contrast, statisti cal model 2 used the pressure-increase characteristics and was therefore es tablished for all of the cardiac beats. The global statistical model 2 appl ied to data sets independent of those used to establish the model gave reli able SV estimates: r = 0.54 +/- 0.07, a small bias between -8% to + 10%, an d a mean precision of 7%. This work demonstrated the limits of pulse-contou r models to estimate SV in conscious, unrestrained rats. A multivariate sta tistical model using eight parameters easily extracted from the aortic wave form could be applied to all cardiac beats with good precision.