VARIATION IN MEAN ARTERIAL PRESSURE AND ITS HEMODYNAMIC COMPONENTS DURING 24-HOUR AMBULATORY PULSE WAVE ANALYSIS: IMPACT OF AGE, RACE, AND GENDER

Abstract

Objective: Blood pressure (BP) is highly variable but the concomitant variations of the underlying hemodynamic components [heart rate (HR), stroke volume (SV), and total vascular resistance (TVR)] are not known. We postulated that covariance (cov) analysis of 24-hour ambulatory pulse wave analysis (PWA) could reveal relevant trends in hemodynamic variability (var) within and between-individuals. Design and method: Ambulatory BP with PWA (Mobil-O-Graph, IEM, Stolzberg, DE) was performed every 20 minutes for 24 hours. Mean arterial pressure (MAP) components were indexed to body surface area: MAP = HR*[SV index (SVI)]*[TVR index (TVRI)] and ln(MAP) = ln(HR) + ln(SVI) + ln(TVRI). For cov analysis, var[ln(MAP)] = cov[ln(HR), ln(MAP)] + cov[ln(SVI), ln(MAP)] + cov[ln(TVRI), ln(MAP)]. Contributions of hemodynamic components to var[ln(MAP)] were expressed as %; other associations were nalysed by correlation and t-test. Results: We studied a convenience sample of 152 people (49% women, 23% black). Data are mean(SD): # readings 57(11), age 59(16) years, BMI 29.9(6.5) kg/m2, systolic BP 135(18) and MAP 106(14) mmHg. Mean 24-hr values were: ln(MAP) 4.64 (0.13), ln(HR) 4.20 (0.15), ln(SVI) -3.32 (0.15), and ln(TVRI) 3.75 (0.18). Relative contributions to 24-hour varMAP were: varTVRI 54(36)%, varHR 33(38)%, and varSVI 13(40)%. The large SDs in these component contributions prompted further analysis: varTVRI correlated with 24-hr mean MAP (r = 0.24, p = 0.003) and was higher (>54%) in males (p = 0.03) and blacks (p = 0.04); varHR was inversely related to MAP (r = -0.26, p = 0.001), age (r = -0.29, p = 0.0003) and BMI (r = -0.17 p = 0.05) and was lower (<33%) in blacks (p = 0.008); varSVI correlated with age (r = 0.31, p < 0.0001) and BMI (r = 0.23, p = 0.005) and was higher (>13%) in women (p = 0.03). Conclusions: Covariance analysis can be used with 24-hr ambulatory PWA to analyze BP and hemodynamic variability in everyday life. Within-individual total varMAP is related to varTVR > varHR > varSV but between-individual factors also affect these trends, including greater influence of varTVR in males and blacks, varHR in younger people, and varSV in younger people and women. HR varies inversely with SV and SVR suggesting counter-regulation. Diagnostic subclassifications or treatment modifications for variation extremes [e.g. vasodilators (TVR), beta-blockers (HR), or diuretics (SV)] may be possible.