多変量自己回帰モデルによるヒト神経性循環調節のシステム同定に関する研究

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Closed loop analysis using a multivariate auto-regressive model was applied to time series data for the RR interval (RRI), mean blood pressure (BP), vasomotor sympathetic nerve activity recorded as muscle sympathetic nerve activity (MSNA) and respiration with subjects, to determine integratively the neural control of human systemic circulation at supine rest, during head-up tilt and in elderly subjects. The auto-power spectral density curves showed the existence of Mayor's and respiratory rhythms, in which the coherence indicated a linear linkage among these variables. A noise contribution analysis revealed that Mayer's waves in BP are derived from the combination of both BP and MSNA. At supine rest, impulse responses, when assuming 1 mmHg elevation in BP, showed that MSNA is transiently suppressed (BP-to-MSNA response) and RRI is elongated by 4 ms in the following second (BP-to-RRI response). On the other hand, the MSNA-to-BP response revealed that MSNA discharge induces a prolonged (up to 30 s) elevation in BP, while RRI-to-BP response elicited a transient decrease in BP. During head-up tilt, impulse response analysis showed that MSNA-to-BP response was accentuated and prolonged, and that BP-to-RRI response was suppressed, compared with those in a supine position. RRI-to-BP and BP-to-MSNA were unchanged. In elderly subjects, BP-to-RRI response was diminished, whereas BP-to-MSNA response was unchanged. MSNA-to-BP response was markedly reduced, while RRI-to-BP response was unchanged. These results suggest that closed loop analysis using a multivariate auto-regressive model can describe qualitatively and quantitatively the neural control of human systemic circulation. However, further investigation is necessary to confirm the validity of the method.