The 24 hour relation between R-R interval and diastolic blood pressure measured by ambulatory blood pressure monitoring.

THE 24 HOURS RELATION BETWEEN RR INTERVAL AND DIASTOLIC BLOOD PRESSURE CHANGES ±MEASURED BY AMBULATORY BLOOD PRESSURE MONITORING G. Recordati, A. Zanchetti. Centro Fisiologia Clinica ed Ipertensione. Universita’ degli Studi ed Ospedare Maggiore. Milano. Italy Background: The day and night circadian rhythm is accompanied by reciprocal changes in vagal and sympathetic dominance which may be quantified by measuring the R-R interval (R-R) and diastolic blood pressure (DBP) changes relation with ambulatory blood pressure monitoring (ABPM). Methods: ABPM was performed using Spacelabs monitors in 60 healthy young subjects (30 females and 30 males aged 21.8±1.0) with readings every 15 min (day) and 20 min (night). The collected variables were copied to a software program (Diadem. National Instruments) and R-R values obtained by dividing 60.000 by heart rate in beats/min. The following measurements were made: 1) night and day means ± SD: 2) night less day R-R (Δy, msec) and DBP (Δx. mmHg) differences and Δy/Δx ratios (ms/mmHg): 3) percent :Δy, Δx changes over day mean values and their ratio and 4) slope (b _24h) and r coefficient (r_24h) of the regression of R-R over DBP 24 hours values. Results: With respect to day. night was characterized by lengthenirg of R-R and lowering of DSP values in all subjects. The R-R and DBP day and night means ± SD. the night less day differences and the Δy/Δx ratios, both actual and percent. and the b_24h were different and characteristic for each subject. The r _24h reached statistical significance in all subjects Subjects were classified according to their proportionality ratios between R-R and DBP changes: two subjects had a Δy/Δx ratio below -5, 18 between -5 and -10, 28 between -10 and -20 and 12 above -20 ms/mmHg (range: -41.1 to -4.6. mean -14.6 ms/mmHg). The percent Δy/Δx ratio ranged from -32 to -0.5, mean -1.3 and the slope, b_24h, ranged from -14.28 to -3.14, mean -9.12 ms/mmHg. Conclusions: Results indicate that the ABPM may allow to quantify the individual's day—night autonomic reciprocity and that the subjects with steeper proportionality ratios have a higher 24h period vagal tone. This novel approach may thus be helpful to study the autonomic balance in several patients groups and the individual effects of different pharmacologjcal treatments.