The association of a simple blood pressure-independent parameter derived from ambulatory blood pressure variability with short-term mortality

Abstract

We explored the predictive ability of the blood pressure variability ratio (BPVR), defined as the ratio of 24-h ambulatory systolic blood pressure variability to diastolic variability, and evaluated its predictable relation with blood pressure and the Ambulatory Arterial Stiffness Index (AASI). A total of 3433 consecutive patients were followed up to 16 years for all-cause mortality. Blood pressure variability was expressed by the standard deviation. BPVR, which is the systolic-on-diastolic slope estimated by a known type of symmetric regression ('reduced major axis'), was compared with other expressions of this slope and with AASI using other regression procedures. Time-dependent Cox proportional hazard models, adjusted for demographics, 24-h mean blood pressure, 24-h pulse pressure and dipping were used to assess the association of BPVR and slope-related parameters with all-cause mortality. We found that Pearson's correlation between BPVR and the symmetric slope was 0.957, and between 1-1/BPVR (an AASI-equivalent expression) and the symmetric version of AASI was 0.973. BPVR was entirely independent of mean arterial pressure (r¼0.013). Systolic and diastolic ambulatory blood pressure variability was not significantly associated with mortality. Over 16 years, BPVR predicted all-cause mortality [hazard ratio¼1.21 (95% CI 1.05-1.40) per 1 s.d. increase]. In time-dependent models, increased BPVR was strongly associated with an 18-month mortality, weakly related to 7 years mortality, showing no effect thereafter. Thus, the ratio between 24-h systolic and diastolic blood pressure variability, readily available from ambulatory monitoring reports, is an easy-to-calculate systolic-on-diastolic slope. It is a blood pressureindependent measure believed to express an arterial property, with prognostic power similar to that of AASI.

Effect of non-drug interventions on arterial properties determined from 24-h ambulatory blood pressure measurements

“…Software commands for this type of regression are found in literature 18 and used here when the estimated error of determination is required. The 'symmetric' S-D slope can be expressed analytically by the ratio between SBP and DBP variability SD(SBP)/SD(DBP) called BP variability ratio (BPVR), 4 where the variability is expressed by the SD of the relevant variable. 18 AASIsym can be expressed by 1À1/BPVR and AASI by 1Àr/BPVR, 4 suggesting that AASI differs from AASIsym mainly at low r-values.…”

“…The 'symmetric' S-D slope can be expressed analytically by the ratio between SBP and DBP variability SD(SBP)/SD(DBP) called BP variability ratio (BPVR), 4 where the variability is expressed by the SD of the relevant variable. 18 AASIsym can be expressed by 1À1/BPVR and AASI by 1Àr/BPVR, 4 suggesting that AASI differs from AASIsym mainly at low r-values. 2,10 As slope-related measures are not meaningful for low r-values, we have excluded from analysis patients, whose r was not 40.25 in any of the phases in the raw data when using method A Abbreviations: BMI, body mass index; DGB, device-guided breathing; SALT, mineral salt diet study; SEASON, winter-to-summer change.…”

“…These measures, called collectively hereafter 'slope-related measures' , include the systolic-on-diastolic slope 2 (S-D slope) and the Ambulatory Arterial Stiffness Index (AASI) defined by 1-(diastolic-on-systolic slope). 3 Both measures were shown to be independent of mean blood pressure (BP) 2,4 and to incorporate clinical and prognostic information; slope-related measures were demonstrated to be independent predictors of cardiovascular and all-cause mortality; 4,5 AASI predicts stroke in the general population, 6 and correlates with target organ damage in hypertension. 7,8 The interpretation of AASI, as a surrogate measure for arterial stiffness, 3 is still debatable.…”

“…7,8 The interpretation of AASI, as a surrogate measure for arterial stiffness, 3 is still debatable. 9 However, a physiological model suggests that S-D slope and AASI, if calculated appropriately using symmetric type of regression procedure, 2,4 express in different but equivalent ways the relative increase in arterial stiffness during the systole. 10 This background suggests that chronic variations in the slope-related measures may have prognostic significance.…”

The relationship between systolic and diastolic blood pressure: a clinically meaningful slope?

“…12 A modified AASI, calculated with symmetric regression, may reduce its dependence on day-night BP changes and on the correlation between SBP and DBP, and has been associated with all-cause mortality. 32,33 The method, however, has not been compared with direct measures of arterial stiffness, and its clinical and prognostic relevance awaits further confirmation. Notably, symmetric AASI is mathematically connected to the ratio between the standard deviation of 24-h SBP and 24-h DBP (BP variability ratio) 12 (Table 1).…”