Blood pressure and heart rate of 15 male shift workers were measured every 15 minutes for 24 hours during three work shifts: morning, 4:00 AM to noon; afternoon, noon to 8:00 PM; and night, 8:00 PM to 4:00 AM. For each shift, 24-hour systolic and diastolic blood pressure showed a large "trough" (the low pressure span) and a continuous range of elevated pressure (the high pressure span). Fourier series were used to model the 24-hour blood pressure profiles. A careful examination of the residuals (measured minus predicted pressures) showed that four harmonics were necessary to describe the data accurately. The model enabled localization in each blood pressure profile of the high and low pressure spans that did not coincide with the subject's work and rest periods. The time and slope of blood pressure entering and leaving these spans could also be individually determined. Mean blood pressure during the high pressure span was the same for the three shifts, but mean blood pressure during the low pressure span was lower when the subject worked in the afternoon. During that shift, the systolic blood pressure slopes entering and leaving the low pressure span were steeper than during the two other shifts. The high pressure span was longest during the night shift and shortest during the afternoon shift.Therefore, a change in the working time profoundly perturbed the 24-hour blood pressure profile. We conclude that internal regulation mechanisms, subjects' activities, and the circadian rhythm are the three main factors that govern a 24-hour blood pressure level; a complete change in the time of activities modifies the combined effects of these three factors. (Circulation 1989;80:341-347) S everal noninvasive semiautomatic or automatic devices are presently available that enable blood pressure and heart rate to be measured in ambulatory conditions over 24-hour periods at a frequency arbitrarily set in advance.

Cardiac output, blood pressure, and the characteristics of diastolic pressure decay were studied in 12 normal subjects and 23 sustained hypertensive patients of the same age. In normal subjects and in hypertensives, analysis of the diastolic decay showed that i) the form of the decay approximated a simple monoexponential curve during the last two-thirds of the diastolic segment, and ii) the time constant (t) of the curve was positively correlated with the total peripheral resistance (TPR), with an intercept of nearly zero. The validity of the relationship t = K x TPR was demonstrated both in groups of patients and also in individuals. Using a simple model for the vascular system, the K value was identified as the large arteries compliance and could thus be calculated in each individual. The values of arterial compliance was 1.26 +/- 0.04 ml.mmHg-1.m-2 in normal subjects and was significantly reduced in hypertensive patients (0.88 +/- 0.02 ml.mmHg=1.m-2,. P less than 0.001).

Because the use of spectral powers of blood pressure (BP) and R-R interval (RR) in the low (LF) and high frequencies (HF) to quantify sympathetic and parasympathetic activities is still under debate, we questioned whether nonlinear methods may give better results. The BP signal was recorded for 30 min before and after intravenous injection of hexamethonium (20 mg/kg), atropine (0.5 mg/kg), atenolol (1 mg/kg), and prazosin (1 mg/kg) in conscious, normotensive Wistar-Kyoto rats. Three nonlinear indexes [percentage of recurrence, percentage of determinism, and length index ( L max)] extracted from the recurrence plot method were used to analyze the BP signal. Sympathetic but not parasympathetic blockade reduced BP level and its LF component. RR increased and decreased after β- and α-blockades, respectively. Hexamethonium increased HF, and atropine reduced LF, of RR. Sympathetic blockade and, in particular, α-sympathetic blockade increased nonlinear indexes of BP. In contrast, parasympathetic blockade by atropine increased nonlinear indexes of RR. These results suggest that, compared with spectral indexes, nonlinear indexes may be more specific markers of sympathetic and parasympathetic tones.