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Using a new method to measure the hardness of pericranial muscles, the role of muscle factors in tension-type headache was evaluated. In 223 normal healthy subjects, the hardness of trapezius muscles was 82 +/- 15 kPa/cm (mean +/- SD). The muscle hardness in women, 92 +/- 17 kPa/cm, was significantly greater than that in men, 74 +/- 14 kPa/cm (P < 0.01). Trapezius muscles were significantly harder than paraspinal posterior neck muscles measured at the level of the fifth cervical vertebra (71 +/- 13 kPa/cm; n = 26) but a significant correlation in muscle hardness did exist between these two muscle groups (r = 0.89, P < 0.001). Muscle hardness did not show a significant correlation with advancing age, blood pressure or subjective feeling of stiffness in the shoulder. A significant correlation was noted between the muscle hardness measured by the present method and the stiffness scores evaluated by manual palpation. In patients with tension-type headache (n = 60), the hardness of trapezius muscles, 114 +/- 24 kPa/cm (mean +/- SD), was significantly greater than that in normal subjects (P < 0.01). Twenty-six patients (43% of the total) showed significantly high values which exceeded the mean +/- 2 SD (113 kPa/cm) of the normal value, while the remaining patients (57%) constituted a high normal group. The hardness of posterior neck muscles measured in 27 patients (99 +/- 21 kPa/cm) was also significantly greater than that in normal subjects (P < 0.01). There was no significant difference in muscle hardness between episodic tension-type headache and chronic tension-type headache.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocerebral inactivity for the determination of cerebral death is defined as no findings of EEG greater than the amplifier's inherent internal noise level when recording at increased sensitivity. A surface biopotential electrode contains two interfaces composed of skin gel (electrolyte) and gel electrode (metal), each forming a noise source. The power spectral density, S(f), of extremely low noise signals was obtained by means of autocorrelation and fast Fourier transformation. Interelectrode resistance, R(f), was measured with synchronous rectification. The formula of equivalent noise resistance R(n) = S(f)/4kT, where k is the Boltzmann constant and T is room temperature in Kelvin, gives a resistance that generates the thermal noise corresponding to the measured S(f). Rn/R is a parameter derived from normalization by R. When Rn/R = 1, measured noise contains thermal noise only. Meanwhile, Rn/R > 1 indicates presence of excess noise, such as 1/f, and tissue noise in addition to the thermal noise. Mean square root (Rn/R) of the scalp noise was 10.8 at 10 Hz, showing existence of excess noise. The study results suggest that it is necessary to take excess noise into consideration in the measurement of low-amplitude EEG for the determination of cerebral death.