The main goal of this study was to develop tools for the detection of malfunctions in the autonomic control of hypertensive subjects, and in those at risk of developing hypertension. Previous investigations, using spectral analysis of heart (HR) and blood pressure (BP) fluctuations, have led to the detection of autonomic alterations in hypertensive patients. We wanted to investigate whether still normotensive offspring of at least one hypertensive parent showed similar autonomic dysfunction. Differences in autonomic control that are not observed during steady state conditions can be unmasked by autonomic provocation. Use of the Wavelet transform enables the extension of typical HRV analysis to non steady-state conditions. This time dependent spectral analysis of heart rate enables quantification of different spectral components reflecting the sympathetic and parasympathetic activity during rapid transitions such as an active change in posture.
Thirteen normotensive young adults (YN) (29±3) and 10 normotensive individuals with one hypertensive parent (KHT) (28± 4 y) were recruited for the study. All subjects gave their informed consent to participate in the study. All subjects were studied between 8-10:00 am, following a light breakfast after an overnight fast. Subjects were asked to refrain from caffeine containing beverages on the day of the study and to refrain from intense physical activity and alcohol consumption in the 24 hours prior to the study. The following signals were continuously recorded: ECG from the MP 100 Biopac System, continuous, noninvasive BP with a Portapres device, and respiration from a Respitrace pneumoplethysmograph. All signals were sampled simultaneously online, at a sampling rate of 500HZ, using a Biopac multi-channel device with Acknowledge software. Subjects rested supine in a thermo-neutral environment for 30 minutes, performed 3 Valsalva maneuvers, each followed by a 2 min rest period, performed a mental arithmetic task, held 30% MVC isometric handgrip to fatigue, rested 10 min, then transitioned actively from supine to stand followed by a 5 min stand.
The experimental groups were similar at baseline, however they differ in their response to provocation. During the 30 second period after transition to stand, KHT demonstrated significantly higher (p<0.05) integrals in the low frequency (0.04-0.15) content of heart rate fluctuations. Additionally, they demonstrated significantly higher (p<0.05) integrals in the LF/total power, although the high frequency (0.18-0.4) content of HR fluctuations was not different. This indicates a stronger sympathetic response to a rapid change in posture in KHT, possibly pointing to the existence of autonomic abnormality at a pre-hypertensive stage.
We are continuing the analysis of the data obtained during this study and expect to publish our results in a respectable scientific journal. Any publication of this information will acknowledge support by the Slezak Foundation, and the foundation will be sent copies of the resulting publications.
