A non-invasive cardiovascular index for the quantification of arterial load

Objective - Our aim is to quantify steady and pulsatile components of arterial load in a concise and sensitive way by means of a new non-invasive cardiovascular index (NICI). Methods and results - NICI is based on non-invasively measured pressure (sphygmomanometer), stroke volume index and cardiac index (Doppler echocardiography and ECG) and yields a numerical value (in mmHg). It expresses the difference between the actual arterial load and reference loading conditions as determined in a control group (29 M/35 F, age 34 ± 13 yr.) of healthy subjects, with blood pressure 116/61 mmHg (systolic/diastolic), stroke volume index (SVI) 34 ± 18 ml.m^-2 and cardiac index (CI) 2.1 ± 0.5 l.min^-1.m^-2. NICI was calculated in the control group and in 23 borderline hypertensive subjects (10 M/13 F, age 65 ± 12 yr.) with blood pressure 156/79 mmHg, SVI 36 ± 10 ml.m^-2 and CI 2.4 ± 0.6 l.min^-1.m^-2. NICI was higher in borderline hypertensives (33 ± 51 vs. 0 ± 34 mmHg; P < 0.001) and was strongly correlated with total peripheral resistance index (r = 0.89; P < 0.001) and with the ratio of SVI and pulse pressure (r = -0.89; P < 0.001), expressing the combined effect of both known determinants of cardiac load. NICI was also correlated with effective arterial elastance index (r = 0.89; P < 0.001). Conclusions - NICI quantifies, within a logical biomechanical framework, the arterial load as seen by the ejecting ventricle. It combines steady and pulsatile components of arterial load and has a single control value of zero mmHg.