Effects of whole-body mechanical stimulation at double the heart rate on the blood pressure waveform in rats.

The effects of mechanical stimulation on hemodynamics, such as due to mechanotransduction in vascular endothelial cells, have been widely discussed recently. We previously proposed a resonance model in which the arterial system is treated as a pressure-transmitting system, and suggested that the application of external mechanical stimulation with frequencies near the heart rate (HR) or harmonics thereof can be sensed by the arterial system and induce hemodynamic changes. In this study, we monitored the effects of external mechanical stimulation at a frequency of double the HR on BPW (blood pressure waveform), HRV (HR variability) and BPHV (blood-pressure-harmonics variability) in rats. A motor beating a waterbed mattress was used to generate pressure variations of 0.5 mmHg to apply onto the rats. The experiments were performed on three groups of rats with different beating frequencies: (A) double the HR, (B) 5% deviation from double the HR and (C) 1.5 times the HR. The experimental procedure was a 15 min control period followed by application of the mechanical stimulation for 15 min and further recording for 15 min (OFF period). During the OFF period, the amplitude of the second harmonic in the BPW significantly increased by >5% in group A with decreased HRV and BPHV. The second harmonic increased less in group B, and decreased in group C. The increase in the second-harmonic amplitude in group A may be due to the filtering properties of the renal arterial structure. This mechanism could be used to improve the local blood supply into the kidneys, and hence provide a new treatment modality for some important diseases, such as renal hypertension or nephrosis.

Raising harmonic variation of arterial pulse in dying rats.

Our previous study revealed that the coefficient of variation of harmonic magnitude (HCV) of radial arterial pulse was significantly raised before the death of cancer patients. In this study, we recorded the caudate arterial pulse of 24 Sprague-Dawley rats that had a fatal dose of urethane injected into their abdomens. Twenty rats were dead within 3 hours after the injection and four survived. We defined the last 100 minutes of each rat's life as the dying process. During the dying process, we found that both the systolic blood pressure and diastolic blood pressure dropped steeply during the last 5 minutes. However, all HCVs, except HCV1, climbed steeply before the last 5 minutes. The HCV1 of the dying rats was significantly higher than that of rats that survived, starting from the first minute (P < 0.01). The HCV2 of the dying rats was significantly higher than that of the survived rats starting from the 52nd minute (P < 0.05). The HCV3 and HCV4 of the dying rats were significantly higher than those of the survived rats until the 70th minute and the 80th minute, respectively (P < 0.05). Furthermore, HCV2-HCV4 proceeded with the dying process and increased gradually. We concluded that HCVs, which failed first in the high-frequency components and then in the low-frequency components, could provide physicians with earlier information to prevent the coming failure of circulatory system, and could reflect quantitatively pathological severity and predict patient outcome. The specific Fourier components in the pulse provide more physiological information than systolic and diastolic blood pressures.

Influencing the heart rate of rats with weak external mechanical stimulation.

The ventricular-arterial coupling is assumed to minimize the expenditure of cardiac energy. From the conjecture of the resonance theory, the arterial system transmits pressure waves and resonates with the heartbeat, therefore, the arterial system is similar to a mechanical resonator. Theoretically, the heart rate can be paced with weak external mechanical stimulation and corresponding blood pressure changes can be observed. A waterbed was activated to generate 0.5-mmHg pressure vibrations as a stimulus and the rate was set to deviate 5% from the control heart rate. Among 13 studies on seven rats, the linear regression between X (stimulation frequency--control heart rate) and Y (actual changes of the heart rate) is Y = 0.992X = 0.062 (Hz) with a correlation coefficient of 0.97 (Y = X implies complete steering). The intercorrelation coefficient between the change in mean blood pressure and the heart rate was 0.79. The study showed that this weak mechanical stimulation influences the heart rate, and the blood pressure changes according to the heart rate. Cardiovascular optimization and the resonance theory may explain the way one may regulate the heart rate and the blood pressure of humans noninvasively in the future.