ObjectivesAcceleration plethysmograms (APGs) are obtained by taking the second derivative of photoplethysmograms (PPGs) and are noninvasive circulatory signals related to risk factors for atherosclerosis with age. There has been growing interest in the development of mobile devices to collect and analyze PPG single features for ambulatory health monitoring. The present study aimed to extract a new feature from the morphologies of APG and PPG signals to classify the dominant indices related to the pulsatile volume of blood in tissue according to age.MethodsTen APG and 14 PPG indices were simultaneously extracted. All indices were compared via Pearson correlation coefficients (r) and a regression analysis. We introduced a combined index extracted from both the PPG and APG indices defined as the inflection point area plus the d_peak (IPAD). The participants included 93 healthy adults aged 36–86 years with a mean ± standard deviation age of 57.43 ± 11.99 years.ResultsThe d_peak and age index for the APG indices were significantly correlated with age (r = −0.408, p < 0.0001 and r = 0.296, p = 0.0039, respectively). Only the A1 time for PPG indices was moderately correlated with age (r = −0.247, p = 0.017). The stiffness index, including individual height information, was not related to age (r = −0.031, p = 0.7713). However, the combined IPAD index was significantly more correlated with age (r = 0.56, p < 0.001) than the other indices.ConclusionsThe proposed index outperformed the other 24 indices for evaluating vascular aging. We suggest that the IPAD is a significant factor related to the clinical information embedded in the PPG waveform.
Mechanical loading such as interstitial fluid shear stress and tensile strain stimulates bone cells, which respond by changing bone mass and structure to maintain optimal skeletal architecture. Bone cells also adapt to bone implants and altered mechanical loading. Osseous integration between host bone and implants is a prerequisite for the stability of implants. Fluctuating fluid pressure and interfacial strains occur between bone cells and implants due to mechanical loading during walking and other daily activities. In this study, we examined the signaling mechanism by which mechanical stimulation activates a novel transcription factor in human and mouse bone cells. Nuclear factor of activated T cells (NFAT) is one of the transcription factors that act downstream of the Ca ++ /Calcineurin (Ca ++ / Cn) network: a well-known pathway of inflammation. In this study, we hypothesized that NFAT2 is activated in response to mechanical stimulation and mediates Cox2 expression. Fluid shear stress and tensile strain results in nuclear translocation of NFAT in cells of the osteoblastic lineage. A peptide inhibitor of the Cn/NFAT axis was found to block the mechanical stimulation-mediated Cox2 induction. Further, chromatin immunoprecipitation assay shows direct interaction between NFAT2 and the human Cox2 promoter region. Additionally, CnAβ knockout calvarial bone cells were found to be less sensitive than control bone cells to mechanical stimulation. Our study provides new evidence for a novel role for NFAT in bone mechanotransduction in the context of cytokine gene induction in bone cells.
ObjectivesRecent studies have emphasized the potential information embedded in peripheral fingertip photoplethysmogram (PPG) signals for the assessment of arterial wall stiffening during aging. For the discrimination of arterial stiffness with age, the brachial-ankle pulse wave velocity (baPWV) has been widely used in clinical applications. The second derivative of the PPG (acceleration photoplethysmogram [APG]) has been reported to correlate with the presence of atherosclerotic disorders. In this study, we investigated the association among age, the baPWV, and the APG and found a new aging index reflecting arterial stiffness for a healthcare device.MethodsThe APG and the baPWV were simultaneously applied to assess the accuracy of the APG in measuring arterial stiffness in association with age. A preamplifier and motion artifact removal algorithm were newly developed to obtain a high quality PPG signal. In total, 168 subjects with a mean ± SD age of 58.1 ± 12.6 years were followed for two months to obtain a set of complete data using baPWV and APG analysis.ResultsThe baPWV and the B ratio of the APG indices were correlated significantly with age (r = 0.6685, p < 0.0001 and r = -0.4025, p < 0.0001, respectively). A regression analysis revealed that the c and d peaks were independent of age (r = -0.3553, p < 0.0001 and r = -0.3191, p < 0.0001, respectively).ConclusionsWe determined the B ratio, which represents an improved aging index and suggest that the APG may provide qualitatively similar information for arterial stiffness.
Bone adapts to its environment. Osteoblasts and osteocytes are subject to mechanical load in vivo. It has been shown that osteoblasts alter cytokine expression in response to mechanical loading. However, signal transduction pathways that mediate bone cell response to mechanical stimuli have not been elucidated. In this study, we report an increase in proinflammatory gene expression in response to fluid shear stress (FSS) in human mesenchymal stem cells (hMSCs) and mouse preosteoblasts. Fluid shear stress (FSS)-induced effect was blocked by the inhibition of the calcineurin-NFATc1 axis, thus implicating a role for nuclear factor of activated T cells (NFAT) signaling in mechanotransduction.
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