Non-Gaussian distribution of arterial pressure and heart rate during sleep and waking in hypertensive and normotensive subjects.

For statistical analysis of 24-hour recordings of arterial pressure (AP) and heart rate (HR), it is necessary to establish a theoretical probability density function of the distributions. In the present study, 24-hour recordings of direct AP and HR were performed in 15 normotensives (NT) and 39 patients with essential hypertension (EH) by means of a new portable device with a digital memory for analyzing frequency histograms. In both NT and EH, frequency histograms of AP (systolic and diastolic AP) and HR during a 24-hour period showed bi-modal curves, whereas those made during sleep and waking produced asymmetrical patterns resembling Gamma distribution. From the AP and HR histograms made for each subject during sleep and waking, such parameters as mean (M), standard deviation, mode (Mo), skewness (Sk), kurtosis (K) and minimum values (Mi) were calculated. The Sk and M minus Mo were positive, and K was greater than 3 in both HR and AP histograms; the AP and HR histograms during sleep can be more correctly analyzed with Gamma distribution (mean parameter errors were less than 7.3%) than with Gaussian distribution (in this: S = O, M minus Mo = O, K = 3). The Mi would accord with the location parameter of the Gamma distribution.