[Histomorphological findings in the ascending aorta and inferior vena cava following implantation of ultrasonic Doppler flow transducers and pressure transducers in long-term experiments with rabbits and cats].

We investigated the histological changes of the vessel walls of the carotis dextra, the aorta ascendens and the vena cava inferior following implantation of flow- and pressuretransducers of 17 rabbits and 4 cats. Following correct adaptation of the vessel volumen the implantates were all well tolerated over a prolonged period (up to 58 weeks) and encapsulated by connective tissue. The histological processes are descripted in detail and lesions produced by ultrasound are shown.

[Chronic blood pressure measurements in the rabbit aorta using a novel implantable pressure transducer].

A novel implantable pressure pickup is described for chronical blood pressure measurement at the rabbit aorta, which transmits the intravasal pressure via a short liquid column in a closed foil catheter transmurally to an extravasal pressure transducer. With a natural frequency of 250 Hz, the pressure slope steepness is 1834 kPa/sec. The pickups operate up to 40 kPa linearly with deviation of 2% of the whole scale.

[Vasal flow measurements at the aorta ascendens using the ultrasonic doubler technique in chronic experiments on rabbits].

The conditions under which flow measurements using the ultrasonic doppler technique can be successfully carried out at the Aorta ascendens in chronical experiments were studied in 25 normal rabbits. Pressure necroses of the vascular wall at agar-agar-gel coupling arise only if the implanted pick-off with its inner diameter is less than the outer diameter of the aorta + about 10%. The ultrasonic intensity permissible in a chronic experiment is only about 0.

[Histological findings at the aorta ascendens after measurement of blood flow with ultrasonic doppler technique in chronic experiments with rabbits (author's transl)].

Following implantation of an ultrasonic transducer in the aortic wall of the rabbit, media destructions and pressure necrosis were ascertained when the transducer was fitted closley around the vessel. When the transducer however was fitted widley around the vessel few departures from the normal structure were registered. After ultrasound stress 0.

Decreases of local brain temperature due to convection (local brain blood flow) and increases of local brain temperature due to activity.

The influence of local brain blood flow upon variations of local brain temperature in chronical experiments was investigated in cats. It was found that changes of local brain temperature in chronic experiments are esclusively due to changes of local metabolic heat production as long as the temperature of brain inflowing blood remains constant. Decreases of temperature due to convection (increase of local blood flow) are smaller than increases of temperature due to activity.

[Determination of local brain blood flow by means of switched heating].

It is demonstrated by model experiments that the determination of stationary and instationary data (amplitude and shape of the heating signal) allows the two components of local brain perfusion (flow rate and volume flux) to be measured separately. Since perfusion and temperature are measured at the same site, the convection data are free of variations of the local brain temperature. The dependence of the amplitude of the heating signal on the flow rate is described by the equation Ao = a - e-bv + c, with the parameters a, b, c being represented as a function of the convection-free space around the sensing probe.