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We present an unobtrusive cuff-less sphygmomanometer based on contact-type and optical pulse sensors for continuous and minimally invasive monitoring of blood pressure (BP). We developed a cuff-less sphygmomanometer that utilizes the pulse arrival time (PAT) to estimate continuous BP. To assess its accuracy, we recruited 10 healthy subjects in whom we carried out BP studies using the cuff-less sphygmomanometer compared with a standard cuff-type device in a stationary sitting patient. Preliminary results showed that the mean difference (MD) of estimated systolic blood pressure and diastolic blood pressure were 0.96 ± 9.6 (mean ± SD) mmHg and 1.14 ± 7.5 mmHg, respectively, compared to the control. The corresponding correlation between the estimated BP values and controls were 0.78 for systolic blood pressure (p < 0.01) and 0.69 for diastolic blood pressure (p < 0.01); thus, there were significant correlations. These results suggest that the developed cuff-less sphygmomanometer has the potential for continuous BP monitoring. Finally, we conducted a preliminary study of simultaneous monitoring of cuff-less BP and near-infrared spectroscopy to evaluate the potential for assessment of autonomic nervous system functions during mental stress tasks.

The incidence of stress-induced psychological and somatic diseases has been increasing rapidly, and it is important to clarify the neurophysiological mechanisms of stress response in order to establish effective stress management methods. We previously reported that the prefrontal cortex (PFC) plays an important role in stress response. In the present study, we employed near-infrared spectroscopy (NIRS) and electroencephalography (EEG) to investigate the characteristics of PFC activity during mental arithmetic tasks. A two-channel NIRS device was used to measure hemoglobin (Hb) concentration changes in the bilateral PFC during a mental arithmetic task (2 min) in normal adults. Simultaneously, EEG was used to also measure bilateral PFC activity during the same task. We evaluated concentration changes of oxy-Hb induced by the task while analyzing α wave changes using power spectrum analysis. It was observed that oxy-Hb in the bilateral PFC increased significantly during the task (p < 0.05), while α wave power in the PFC decreased significantly (p < 0.01). The present results indicate that mental stress tasks caused the activation of the bilateral PFC. Simultaneous measurements of NIRS and EEG are useful for evaluating the neurophysiological mechanism of stress responses in the brain.

Vascular cognitive impairment (VCI) plays an important role in dementia in elderly people, and refers to the contribution of vascular pathology to the entire spectrum of cognitive disorders, ranging from mild cognitive impairment to severe dementia, as well as the pathological spectrum, from 'pure' Alzheimer disease through degrees of vascular comorbidity to 'pure' vascular dementia. In the present study, we investigated the relationship between cognitive dysfunction and systemic metabolic disorders, by employing deep learning (DL). We studied 202 patients (73.4 ± 13.0 years), 94.6% of whom were undergoing treatment for lifestyle diseases, and 68.8% of whom had a history of cerebrovascular disorder. We evaluated cognitive dysfunction by performing a Mini Mental State Examination (MMSE). We performed general blood examination, including Complete Blood Count and Basic Metabolic Panel, and measured cerebral blood oxygenation in the prefrontal cortex (PFC) using time-resolved near infrared spectroscopy (TNIRS). We then used deep neural networks to assess the MMSE scores of the subjects based on the TNIRS parameters and the blood examination data, independently. Next, we compared predicted MMSE scores based on the TNIRS and the blood examination. There was a significant positive correlation between the TNIRS parameters and the blood examination data (r = 0.6, p < 0.01). These observations suggest that cognitive dysfunction in patients with VCI may be caused by combinations of systemic metabolic disorders such as energy and oxygen metabolisms and cerebral circulatory disturbance due to arteriosclerosis resulting from lifestyle-related diseases.

Multi-channel NIRS, so-called optical topography (OT), allows functional mapping of the cortex; however, it takes a long time to set optodes on the head and is relatively expensive. Thus, OT is not suitable as a screening test of brain disorders evaluating many subjects. Recently, a wearable two-channel continuous wave NIRS (CW-NIRS) device has been developed. Such a simple NIRS device may be applicable as a screening test of brain disorders; however, its reliability in measurements of brain function is not yet clear. Here, we tested a two-channel CW-NIRS, which employs single LED (800 nm) for measurement of total hemoglobin (t-Hb) changes. We measured t-Hb changes in the bilateral prefrontal cortex (PFC) during mental arithmetic tasks, employing the CW-NIRS and time-resolve NIRS (TNIRS). The left-right asymmetry of the PFC activity was evaluated by calculating the laterality index (LI; (R-L)/(R + L) of t-Hb), which reflects mental stress. The interval between CW-NIRS and TNIRS measurements was 1-13 days. A significant positive correlation was observed between LI measured by CW-NIRS and TNIRS. These results suggest the reliability of the simple CW-NIRS, and it may be applicable to prevent stress-induced various diseases. Finally, it should be emphasized that the left-right asymmetry of PFC activity is relatively stable.

Near infrared spectroscopy (NIRS) has been applied to measurements of cerebral blood oxygenation (CBO) in normal subjects and patients with various brain disorders including cerebrovascular diseases. However, it is not known whether NIRS allow us to measure CBO correctly in patients with abnormal cortices where optical characteristics such as optical pathlength (OP) may differ from those in normal cortex. In the present study, employing a time-resolved NIRS (TNIRS), we compared baseline hemoglobin (Hb) concentrations and OPs between normal and abnormal cortices in chronic stroke patients. We studied five patients with chronic cerebral infarction (two males, three females, age 59.0 ± 24.2 years) who were admitted to the University Hospital of Fukushima Prefectural Medical University. Employing TNIRS (TRS-20, Hamamatsu Photonics), we measured baseline Hb concentrations and OPs (760, 800, 830 nm) at various positions on the head. We observed that deoxy-Hb concentrations were significantly lower on the affected side (p < 0.01), and the tissue oxygen saturation was significantly higher than that on the affected side (p < 0.01), suggesting that oxygen consumption was reduced on the affected side. In addition, the OPs (760, 800 nm) were significantly longer on the affected side (p < 0.05); these changes might be caused by a possible increase of cerebrospinal fluid layer associated with brain tissue degeneration by ischemia. The present results suggest that NIRS should be performed on patients with abnormal cerebral cortices, giving special consideration to the possible difference in optical characteristics between normal and abnormal brain tissues.