Connection between RR-interval length and the pulsatile microcirculatory flow.

The present study used laser Doppler flowmetry (LDF) to investigate the connection between skin microcirculatory flow and the length of the RR interval (LRR). Local heating was performed on healthy volunteers to further elucidate its effect on LDF index. ECG and LDF signals were measured in 102 trials on seven volunteers. Each experiment involved a 5 min control and a 5 min heating-effect sequence. Each laser Doppler flux pulse was categorized into four groups according to its LRR compared with the 5 min average LRR. Synchronized averaging analysis was applied to the four groups of pulses to obtain their averaged waveforms, from which four flux parameters were calculated. The ac component of the flux increased significantly with increasing LRR, and the differences therein between the groups with LRR more than 4% smaller and more than 4% larger than the average LRR increased from 15.8% during the control period to 23.9% during the heating period. Understanding of the different flux responses between the control and local-heating experiments may aid the development of a new index, which helps to avoid LDF's main drawback of providing only qualitative measurement.

Effects of angiotensin II on flux rise time in rats (a time index of laser Doppler flowmetry) and its relation with microvascular structures.

Laser Doppler flowmetry (LDF) is a popular method for monitoring the microcirculation, but it does not provide absolute measurements on local area with small size microvessels. Instead, the mean flux response is generally compared between before and after stimulus. In this study, we proposed a new dimension for comparing the LDF signals. The flux rise time (FRT), a time index with absolute physical quantity, was extracted from noisy LDF signals using a pulsatile-based synchronized-averaging method. We investigated the changes of FRT and its relation to the microvascular resistance (MVR) under the selective effects of angiotensin II (Ang II) on the kidney and the plantar palm. Ang II was infused into anesthetized Wistar Kyoto rats via the femoral vein for 1 h. Using the heartbeat as a self-trigger, we calculated the FRT and MVR from the renal cortical flux, plantar palm flux, and abdominal aortic blood pressure recorded before, during, and after Ang II infusion. The control FRT values were similar in the two vascular beds. Ang II decreased the renal cortical flux but significantly increased the FRT and MVR of both beds. The effects on the renal FRT and renal MVR were selectively larger than those on the palm FRT and palm MVR. The results indicate that the changes of FRT and MVR are similarly physiologically linked with microvascular structures. As an MVR-related absolute physical quantity, the FRT could be developed as a monitoring tool in physiological, pathological, and pharmacological investigations.

Study on the microcirculatory blood velocity of acupoint monitored by laser Doppler signal.

Meridian system composed of acupoints is the most fundamental concept to build oriental medicine. In this study, we employ LDF measurement to compare the microcirculatory blood velocity of acupuncture point and its surrounding tissues. Measurements were performed around an important acupoint in oriental medicine, Hoh-Ku (Li4, on the hand), in healthy volunteers. The study presented has shown that the acupoints have significantly slower mean blood velocity than their surrounding tissues (p all < 0.005). This finding facilitates the detection of the position of acupuncture point and helps us to provide a possible connection between microcirculatory physiology and the underlying mechanism of acupoints.

Evaluation of stationarity of laser Doppler signal in the pulse-based synchronized-averaging analysis.

Pulse parameters calculated from the LDF waveform based on time-domain synchronized averaging analysis were shown to be able to discriminate the difference in microvascular resistance, however its applicability depends seriously on the assumption of signal stationarity. In this study, our aim is to investigate the effect of pulse number, which may destroy the signal stationarity, on the pulse LDF parameters. The study presented here has established the criteria for pulse number to achieve the signal stationarity so that the microcirculatory discriminability of the pulse-based time-averaging analysis on LDF signal can be improved. The proposed quantitative method to verify the assumption of signal stationarity when utilizing time-averaging can also be applied to analysis of other bio-signals.

Microcirculatory characteristics of acupuncture points obtained by laser Doppler flowmetry.

Acupuncture points (acupoints) form part of the meridian system that constitutes the most fundamental concept in oriental medicine, but their physiological basis has not been clarified. In this study we employed laser Doppler flowmetry (LDF) to extract the microcirculatory characteristics of acupoints and their surrounding tissues, and we interpreted the results from the viewpoint of microcirculatory physiology. Three groups of measurements were performed focusing on the following two important acupoints in oriental medicine in healthy volunteers (n = 13 for group A and n = 9 for groups B and C, respectively): Hoh-Ku (Li4, on the hand) and Ching-Ku (B64, on the foot). The two groups of measurements around Hoh-Ku (Groups A and B) were so designed as to examine the effect of the direction of the nonacupoint away from the acupoint, whereas comparison between the Hoh-Ku and the Ching-Ku measurements was to verify whether the phenomenon was consistent in the upper and the lower extremities. We found that the mean LDF signals were significantly larger at the acupoints than in their surrounding tissues (all p < 0.05), which indicates a larger blood supply into the microvascular beds of acupoints. The results indicate that the physical properties of the vascular structure of acupoints may affect the perfusion resistance, and thereby modulate the microcirculatory perfusion in accordance with tissue needs. This finding facilitates the localization of acupoints, helps in identifying the connection between microcirculatory physiology and responses to acupoint stimulation, and introduces an objective research method for understanding the mechanisms that underlie oriental medicine.

Organ-specific ligation-induced changes in harmonic components of the pulse spectrum and regional vasoconstrictor selectivity in Wistar rats.

It has been shown previously that the amplitudes of the harmonic components of the pulse spectrum vary in specific patterns when the arteries leading to different organs are ligated, with the variations in the harmonics being linearly additive. Since ligation can be regarded as a vast increase in organ resistance, the present study examined the potential of using these ligation-induced variations in the pulse spectrum as reference parameters for an increase in vascular resistance and for regional vasoconstrictor selectivity. A vasoconstrictor, either arginine vasopressin (AVP) or angiotensin II (Ang II), was infused into anaesthetized Wistar rats via the femoral vein for 1 h. The distinct harmonic-specific drug effects on the pulse spectrum were simulated by combining renal artery and superior mesenteric artery ligations in different ratios, the ratio with the lowest mean square difference determining the regional drug selectivity. The ratios indicated that the effect of AVP on the pulse spectrum was attributable to the combined effect of ligating the renal and superior mesenteric arteries, while the effect of Ang II was attributable to ligation of the renal artery. The results are comparable with those of investigations of regional vascular resistance performed using traditional methods. Our findings indicate that the ligation-induced variations in the pulse spectrum can be used to determine regional increases in vascular resistance. This implies that blood pressure can be used as the sole parameter to determine which arterial bed has been affected by the vasoconstrictor, and how seriously.

Three-block electrical model of renal impedance.

In this study, we measured the characteristic renal impedance profiles of Wistar rats and simulated the profiles using an electrical model with three series connected Windkessel blocks containing inductance. It is expected that a complete renal impedance profile ought to provide better physical properties information and have more diagnostic power than the pulsatility (PI) and resistive indices (RI) as a result of frequency dependency. A characteristic peak value at the third harmonic on the renal impedance amplitude curve was observed and the phase curve decreased with increasing harmonic numbers. From least mean square fitted parameters, the three blocks were given distinct physical properties and identified as: (1) the renal artery, (2) the small arteries plus the afferent arteriole and (3) the residual kidney (i.e., the efferent arteriole plus the post glomerular capillary structures). These allocations were made according to respective physical properties reported in previous research. These classifications were further confirmed when we compressed the kidney or infused Ang II. Variations in electrical parameters concurred with the likely affected blood vessels reported. This model describes renal impedance characteristics well; and it provides useful hints on the physical properties of the renal vascular system as well as allows for distinctions in possible physiologically affected locations during functional disturbance. It has potential for development as a clinical non-invasive diagnostic tool.

Pulse Analysis as a Possible Real-Time Biomarker Complementary to SGPT and SGOT for Monitoring Acute Hepatotoxicity.

Based on the resonance theory, the pressure wave of the arterial system could reflect the physical condition of the internal organs. Experimental evidence indicates that the physical condition of organs is related to various Fourier components of the pressure pulse. We have proved that the first harmonic of the pressure-wave spectrum is closely related to the liver. In this study, Wistar rats given massive doses of acetaminophen were examined. The amplitude of the first harmonic of the blood pressure pulse, A1, was analyzed and correlated with the blood liver function indexes that examine serum glutamate pyruvate transaminase (SGPT) and serum glutamic oxaloacetic transaminase (SGOT). When A1 was below 3650 and SGPT was above 90, the kappa value was about 0.6; the probability is greater than. 999 based on a chi-square test. When A1 was below 3650 and SGOT was above 380, the kappa value was around 0.5; the probability is greater than. 999. Our results indicate that A1 may be used as a simple, real-time biomarker that is complementary to the commonly used first-line liver indicators, SGPT and SGOT levels, for monitoring acute hepatotoxicity. It promises a noninvasive, real-time liver-function monitoring method.