POWER SPECTRUM ANALYSIS OF CARDIOVASCULAR VARIABILITY MONITORED BY TELEMETRY IN CONSCIOUS UNRESTRAINED RATS

Beat-to-beat variability of arterial pressure and heart period (R-R) w as studied in eight conscious freely-moving adult male rats in which t elemetric recordings of arterial pressure, ECG and respiratory movemen ts were obtained under unrestrained and unstressed conditions. The bea t-to-beat time series of these signals (systolic arterial pressure, di astolic arterial pressure and R-R) were analyzed, in the frequency dom ain, using autoregressive spectral analysis in order to detect and qua ntify the rhythmic components. In basal conditions, the systolic arter ial pressure variability spectrum was characterized by three major spe ctral components which had central frequencies respectively of 0.08 +/ - 0.03 Hz (very low frequency), 0.43 +/- 0.02 Hz (low frequency) and 1 .36 +/- 0.19 Hz (high frequency). Similar rhythmic components were fou nd in R-R signal variability. The very low frequency component include d a higher percentage of total power in R-R variability spectrum (75.3 %) than in systolic arterial pressure variability spectrum (58.4%). Th e low frequency component was more pronounced in both systolic and dia stolic arterial pressure variability spectra. The high frequency compo nent of R-R, systolic and diastolic arterial pressure was synchronous with respiration. Cross-spectral analysis revealed a high statistical coherence between R-R and arterial pressure variabilities in all the t hree frequency bands. An alpha-adrenergic blocker (phentolamine) speci fically abolished the low frequency components of systolic and diastol ic arterial pressure variability spectra, thus suggesting that low fre quency is a marker of sympathetic modulation of vasomotor activity. Th e low frequency component of R-R variability spectrum was also markedl y blunted. We suggest that cardiovascular variability signals, (R-R, s ystolic and diastolic arterial pressure) are composed almost of two ma in rhythms linked to respiration and vasomotor activity. These rhythms can be quantified in conscious unrestrained rats by using telemetry a nd spectral analysis. This approach seems to offer a new powerful tool for pharmacological studies in conscious small animals.