Relationship between blood pressure and heart rate while awake and asleep in patients with mild essential hypertension.

Blood pressure (BP) and heart rate (HR) (BP waveforms) are affected by external stress during waking and BP is reduced to its lowest level (base BP) during sleep. This study investigated the relationship between BP waveforms while awake and base BP waveforms during sleep. The intra-arterial BPs of 64 inpatients (34 males and 30 females, age: 42 +/- 11, mean +/- SD) with mild essential hypertension were measured for 24 h by the telemetry method. The average ln (SBP/DBP) (m) while awake and the m at base BP (ln: natural logarithm, SBP: systolic BP, DBP: diastolic BP) had approximately the same values in each patient (mean difference: -0.02 +/- 0.07). The product of the RR interval (60/HR) and DBP (RR x DBP) while awake and at base BP had almost the same value (mean difference: -3.2 +/- 10 mmHg.sec). According to the Windkessel model, the RR interval during which blood-flow volume in relation to the m value is at its highest can be inferred as S (em-1)/(em-m-1) (S: systolic time). Using this formula, we developed a formula to estimate base RR from waking m, BP, and RR. Calculations with this estimate formula produced a very slight difference (0.0 +/- 0.1 sec) between estimated and actual values for base RR. For the most part, it was possible to infer the base DBP value from the estimated base RR using RR x DBP while awake (mean difference: -3.7 +/- 7.0 mmHg). These results suggest that the base BP waveform may be the most efficient pattern, and that waking BP waveforms change based on the base BP waveform during sleep.