In clinical practice, subjective pain evaluations, e.g., the visual analogue scale and the numeric rating scale, are generally employed, but these are limited in terms of their ability to detect inaccurate reports, and are unsuitable for use in anesthetized patients or those with dementia. We focused on the peripheral sympathetic nerve activity that responds to pain, and propose a method for evaluating pain sensation, including intensity, sharpness, and dullness, using the arterial stiffness index. In the experiment, electrocardiogram, blood pressure, and photoplethysmograms were obtained, and an arterial viscoelastic model was applied to estimate arterial stiffness. The relationships among the stiffness index, self-reported pain sensation, and electrocutaneous stimuli were examined and modelled. The relationship between the stiffness index and pain sensation could be modelled using a sigmoid function with high determination coefficients, where R2 ≥ 0.88, p < 0.01 for intensity, R2 ≥ 0.89, p < 0.01 for sharpness, and R2 ≥ 0.84, p < 0.01 for dullness when the stimuli could appropriately evoke dull pain.
This paper proposes a novel technique to monitor peripheral vascular conditions by using biological signals, such as electrocardiogram, arterial pressure, and pulse oximetric plethysmogram. A second-order log-linearized model (called the log-linearized peripheral arterial viscoelastic model) is used to describe the nonlinear viscoelastic relationship between the blood pressure waveform and the transillumination plethysmographic waveform. The proposed index is able to estimate the changes of stiffness of peripheral arterial wall induced by sympathetic nervous activity, and the validity of the proposed method is then discussed by monitoring peripheral vascular conditions during arm position tests and during endoscopic thoracic sympathectomies (ETSs). As results of the arm position tests, the stiffness was arm position-independent (Up: 4.0 [%], Down: 5.5 [%]). Then, as results of the ETSs, the variation of the stiffness was significantly changed between before and during the ETS procedure (p < 0.01), and between during and after the ETS procedure (p < 0.01). The above experimental results clearly show that the proposed method can assess changes in the sympathetic nervous activity during ETSs.
This paper proposed a novel objective pain intensity assessment technique using the change of peripheral arterial stiffness β, which reacts to a peripheral sympathetic nervous activity. The stiffness β is calculated from continuous arterial pressures and photo-plethysmograms beat-by-beat based on the log-linearized peripheral arterial model. In the experiment, the validity of the proposed method was examined by comparing estimated normalized arterial stiffness βn with simultaneously-measured numeric rating scale (NRS) as a general index of pain intensity when electrocutaneous stimuli were applied to the healthy subjects. The results showed the maximum amplitude of electrocutaneous current Imax has linear correlation with the normalized stiffness βn (R 2 = 0.77, p < 0.05). In addition, both the maximum amplitude of electrocutaneous current Imax and the normalized stiffness βn strongly correlated with NRS values by sigmoidal curves (Imax v.s. NRS: R 2 = 0.91, p < 0.01; βn v.s. NRS: R 2 = 0.92, p < 0.01). It was therefore concluded that the proposed method can assess pain intensity objectively.
The flow-mediated dilation (FMD) test is a method of evaluating the vascular endothelial function and has been popular as it is noninvasive and readily performed by a skillful ultrasound technician. The FMD test, however, evaluates only the maximal increase in vascular diameter mediated by the increases in blood flow after the release of the occlusive cuff and does not evaluate the arterial viscoelastic properties. Therefore, this paper proposes a new index, called log-linearlized viscoelasticity, to evaluate the arterial viscoelastic properties using the arterial diameter and blood pressure measured in a beat-to-beat manner during the FMD test. To six healthy people, we performed the FMD test to measure the arterial diameter and blood pressure with ultrasound diagnostic imaging equipment and noninvasive continuous arterial blood pressure monitor. As a result, the maximal vasodilatation ratio of FMD (%FMD) was obtained after cuff occlusion. In comparison with the arterial viscoelastic characteristics before FMD test, the stiffness of the arterial wall β and the viscosity of the artery η temporarily decreased and increased, respectively. The change of log-linearlized viscoelasticity after cuff occlusion may be caused by vascular endothelial function. Vascular endothelial function might thus be estimated using the arterial viscoelasticity β and η.
This paper proposes a novel non-invasive method for assessing the vascular endothelial function of lower-limb arteries based on the dilation rate of air-cuff plethysmograms measured using the oscillometric approach. The principle of evaluating vascular endothelial function involves flow-mediated dilation. In the study conducted, blood flow in the dorsal pedis artery was first monitored while lower-limb cuff pressure was applied using the proposed system. The results showed blood flow was interrupted when the level of pressure was at least 50 mmHg higher than the subject’s lower-limb systolic arterial pressure and that blood flow velocity increased after cuff release. Next, values of the proposed index, %ezFMDL, for assessing the vascular endothelial function of lower-limb arteries were determined from 327 adult subjects: 87 healthy subjects, 150 subjects at high risk of arteriosclerosis and 90 patients with cardiovascular disease (CAD). The mean values and standard deviations calculated using %ezFMDL were 30.5 ± 12.0% for the healthy subjects, 23.6 ± 12.7% for subjects at high risk of arteriosclerosis and 14.5 ± 15.4% for patients with CAD. The %ezFMDL values for the subjects at high risk of arteriosclerosis and the patients with CAD were significantly lower than those for the healthy subjects (p < 0.01). The proposed method may have potential for clinical application.
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