Estimation of beat-to-beat stroke volume from the pulmonary arterial pressure contour in man

A pressure-contour method for determining the stroke volume (s.v.) from the pulmonaryartery (p.a.) pressure was employed to continuously monitor the cardiovascular status of patients. six patients with ‘normal’ p.a. pressures and three severe pulmonary hypertensives were evaluated during isoproterenol and amyl-nitrite administration, Valsalva manoeuvres and arrhythmias to vary circulatory conditions. The total range of s.v. was 5–157 ml, of heart rate 56–130 beats/min and of mean pulmonary-arterial pressure 6–44 mm Hg. Pressure-contour estimations of s.v. were compared with those simultaneously obtained from the same beat with a catheter-tip electromagnetic velocity transducer. Comparison of the two methods for determining s.v. yielded correlation coefficients ranging from 0·84 to 0·95 and standard errors of the estimate from 4·2 to 10·3 ml for each of two formulas used. Correlation between the true and computed s.v. was better during interventions which only modified cardiac output than during administration of drugs that act on vascular smooth muscle. Results obtained in patients with severe pulmonary hypertension did not differ greatly from those with ‘normal’ pulmonary-artery pressures. Despite relatively high standard errors of the estimate with some interventions the ease, rapidity and simplicity of this method have distinct advantages over standard noncontinuous methods.