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An unconventional analog-to-digital converter and multiplexer is described. The instrument is based on conversion of the analog signals to time intervals between narrow-width pulses by an encoder unit. The coded analog signals may then be transferred on a single line to a decoder unit and/or stored on a single track of an AM magnetic tape recorder for later processing. The signals are digitized in the decoder unit by measuring the time intervals between the pulses by means of a binary counter driven by a 19.8-MHz oscillator. The decoder is directly communicating with the interface of a digital computer, and a software package has been written for the control of data transmission. The performance of the instrument in our version is: eight separate analog inputs, sampling rate 200 Hz, input voltage −1.6 to 1.6 V, resolution capacity 3.2 V/213, noise ≈0.1%, signal bandwidth de to 50 Hz ac.

The strength of aneurysm walls obtained intraoperatively or at autopsy immediately after death was evaluated by measurements of the force response to one-directional stretch and compared to the walls of intracranial arteries. The maximum stress that aneurysm tissue could tolerate was found slightly lower than in arteries, which is most probably due to the amount of immature forms of collagen. The stress resistance of aneurysms and arterial tissue decayed over a period of several hours. The relaxation curve could be approximated by the sum of 2 exponential terms. The half decay times of these terms were found identical in aneurysms and arteries, they appear to be collagen characteristics. The strength measured in vitro was compared to the stress in vivo, which was calculated on the basis of blood pressure and aneurysm radius. The stress tolerated by aneurysm walls over a period of 24 hours was found to be in the range of the stress that is imposed in vivo by the mean blood pressure. Arteries resisted stresses corresponding to pressures 10 to 20 times higher than physiological values. The thickness of the aneurysm walls correlated with the aneurysm radius in a linear fashion. It is suggested that aneurysm growth can be understood as passive yield to blood pressure, and reactive healing and thickening of the wall with increasing aneurysm diameter.

An ultrasonic Doppler method was used to monitor flow velocities in basal cerebral arteries in 21 patients with spontaneous subarachnoid hemorrhage (SAH). The time course of vasospasm as evaluated by this technique was similar to that reported in angiographic studies. In 82% of the patients an increase in intracranial velocities to 120 cm/s or more was found during the second or third week after hemorrhage. (Normal value 62 cm/s). Arterial narrowing giving rise to velocities above 200 cm/s was classified as severe spasm. This occurred in 42% of the cases, and a significant decrease in flow velocity in the extracranial carotid artery was found in this group.