Investigation of heart rate variability and baroreceptor sensitivity in rats

Scientific studies have traditionally incorporated pharmacological methods to quantify baroreceptor sensitivity (BRS) in both rats and humans. Baroreceptor stimulation has been shown to be efficacious in lowering blood pressure in clinical trials of patients with drug resistant hypertension. Kouchaki et al [1] showed that carotid field stimulation did not alter acute baroreceptor function gain when vasoactive substances were used to induce changes in blood pressure. This thesis aims to compare the spontaneous BRS and heart rate variability (HRV) in carotid stimulated normotensive and hypertensive rats using time and frequency domain methods without the use of pharmacological agents. BRS and HRV were also investigated in normotensive and diabetic induced rats using time and frequency domain methods. The time domain sequence technique for quantifying BRS was used and it was found in all rats that spontaneous baroreceptor function still persisted. There was a significant difference between the BRS in normotensive and diabetic rats (P<0.05). BRS and HRV were quantified using the Welch periodogram (windowed Fast Fourier Transform (FFT)), Non-Uniform Discrete Fourier Transform (NDFT) and the Lomb-Scargle Periodogram (LSP). It was found that the NDFT, Welch periodogram and the Lomb-Scargle periodogram gave similar results. The respiratory, sympathetic & parasympathetic frequencies influence the low frequency peak of the HRV spectrum in rats. The maximum value of frequency was tracked and is most likely due to the oscillating respiratory component in the rat.