Sympathetic nervous system, defined

NATIONAL INSTRUMENTS, Texas, USA), and were stored on the hard disk of a personal computer. With recorded EGG signal, R-R intervals (RRI) were calculated using a cross-correlation fimetion to detect R waves. And analysis of time series of RRI to estimate heart rate variability (HRV) was performed with STFT as well as analysis of EGG. Indexes of HRV were defined as below. The component of low frequency (LF) and high frequency (HE) were given as area of frequency spectrum from 0.05 to 0.15 Hz and 0.15 to 0.4 Hz respectively, and then ratio of LF to HE (LF/HF) reflects the activity of sympathetic nervous system and HE reflects the activity of parasympathetic nervous system. Obtained time series of HE and LF/HF were divided for sub-periods as well as DP and DF. 

In animals, adrenomedullin dilates resistance vessels in the kidney, brain, lung, hind limbs, and mesentery, resulting in a marked, long-lasting hypotension. The hypotension in turn causes reflex increases in heart rate and cardiac output. Adrenomedullin also acts on the kidneys to increase sodium excretion, and exerts several endocrine effects including inhibition of aldosterone and insulin secretion. Finally it acts on the central nervous system to increase sympathetic outflow. These diverse actions of adrenomedullin are mediated both by CGRP receptors and unique adrenomedullin receptors, the properties of which are incompletely defined. The major second messenger for both receptors is cAMP. 

Further, heart rate does not provide diagnostic information about the soitree of mental workload. O Donnell and Eggemeier (1986) define diagnosticity as the "capability of a technique to discriminate the amount of workload imposed on different operator capacities or resources" (p. 42-3). Backs (1995) offers two reasons for heart rate s limited diagnostic utility. First, heart rate is affected by physical derrtands that may be independent of mental workload. Second, heart rate does not provide information about the separation of the sympathetic and parasympathetic nervous system activity. 

PCA was used to extraet information about the sympathetic and parasympathetic nervous systems eommon aeross the four cardiovascular measures obtained with heart period. A correlation matrix for heart period, RSA, low-frequeney HRV, and residual heart period was eomputed for each task and baseline and then pooled to yield a single correlation matrix. PCA was performed on the pooled eorrelation matrix. One eomponent was expeeted to be defined by the marker variable for sympathetic activity (residual heart period) and the other was expeeted to be defined by the marker variable for parasympathetic activity (RSA). The first two components were rotated to simple strueture using varimax. The eomponent seores for a partieular subjeet in a task were computed as the weighted sum of the subjeef s standardized score for each cardiovascular measure multiplied by the standardized seoring eoeffieient. 

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