In extremely preterm infants, the protective capacity for cerebral blood flow (CBF) autoregulation may be impaired or absent, which increases the risk for developing cerebral lesions. The purpose of this study was to quantify the simultaneous influence of several vital parameters, such as mean arterial blood pressure (MABP), PCO2, and PO2, on cerebral blood flow velocity (CBFv), which is used as a measure for CBF. In 16 mechanically ventilated infants of < 33 wk gestation, the CBFv in the internal carotid artery was measured every minute for 1 h by a computer-controlled pulsed Doppler device. MABP and transcutaneous PCO2 and PO2 were recorded as well. A multiple linear regression analysis was performed in each patient to determine the individual MABP, PCO2, and PO2 reactivities as a measure for CBF autoregulation. The medians (and ranges) of the whole group were an MABP reactivity of 7.5% (-12.5 to 20.1%) rise in CBFv/1 kPa rise in MABP, a PCO2 reactivity of 32.7% (-8.1 to 79.5%) rise in CBFv/1 kPa rise in PCO2, and a PO2 reactivity of -3.1% (-14.2 to 7.9%) fall in CBFv/1 kPa rise in PO2. In preterm infants, the individual's capacity for MABP-, PCO2-, and PO2-dependent CBF autoregulation can be estimated by means of the present method, even if the vital parameters change simultaneously.

Summary Direct and immediate recognition of transient unpredictable disturbances of blood perfusion especially for early detection of impairment in the haemodynamics in the brain of neonates requires continous monitoring by dopplersonography. A system for long term monitoring of neonates employing miniaturized doppler transducer, digital recording of spectral data and low energy exposition of the patient has been developed. - miniaturizing of the transducer probe and developement of a fixation for long term monitoring - reduction of energy, ultrasound-exposition of the patient ( < 10% of the AIUM - level accomodation for dopplersonographic exposition) - computer-based data acquisition, analysis, data reduction and archiving.

Acoustic power output levels were measured in four different pulsed Doppler systems (transcranial, Duplex mode, colour mode, miniature for continuous monitoring) currently used for examination of fetal and infant blood flow velocities. The frequencies of the transducers ranged from 2 to 8 MHz. The devices were studied at three to five different intensity settings. The measurements were performed using the radiation force balance of the Fraunhofer-Institut, which was especially adapted for this study. Each of the four devices was tested while running in its commonly used mode, and comparison showed that their acoustic power values varied widely: 96.8 mW (2 MHz, EME TC2-64B), 8.7 mW (5 MHz, ATL Mk 500), 61.9 mW (3.5 MHz, Acuson 128) and 13.5 mW (5 MHz, HP 77020). All transducers had total power output levels below the limits recommended by the American Institute for Ultrasound in Medicine and Biology in the conclusions on a thermal bioeffects mechanism, which were approved in October 1987.

Disorders of cerebral circulation, which are a major risk factor of intracerebral haemorrhage in the preterm baby, can be recognized by Doppler sonography. The development and clinical application of a small miniature Doppler transducer (13 x 9 x 20 mm) is presented which can be fixed onto the infant's fontanel. It is suitable for continuous measurements with a low energy output of only 13 mW.

Für alle diagnostischen Ultraschalluntersuchungen ist nachzuweisen, daß Schädigungen des Gewebes durch die Ultraschallexposition ausgeschlossen werden. Ein wesenthcher Schädigungseffekt ist die lokale Temperaturerhöhung im Gewebe. Um schädigende Temperaturerhöhungen auszuschließen, dürfen Grenzwerte für die Schalleistung nicht überschritten werden. Die akustische Leistungsabgabe von vier Gerätetypen, die zur Untersuchung von fötalen und kindlichen Blutfließgeschwindigkeiten eingesetzt werden transkranieller Doppler, Farbdopp1er, Duplex und Doppler-Monitoring — wurde mittels einer Strahlungsdruckwaage vermessen. Alle Geräte lagen in der Leistungsabgabe unterhalb der vom American Institute of Ultrasound in Medicine (AIUM/1/) angegebenen Grenzwerte; dennoch wurde eine große Variationsbreite festgestellt.

There is no easy comparison of the Doppler spectra. Therefore, determining parameters is necessary for long‐term measurements. A manual analysis is laborious, limits the number of possible examinations, and considerations are restricted to the envelope curve (maximal cerebral blood flow velocity). The applied ultrasonic apparatus (a modified HP 77020AC) determines three waveforms besides the Doppler spectrum: Vmax as maximal, V mean as average, and V mode as the most frequently measured velocity. These data are directly transferred to a PC. Using low Doppler intensity Vmax resulted in values up to 39% lower than determined by manual analysis because of the apparatus' algorithm. By use of higher Doppler intensity this difference was reduced to 19%. Regarding clinical validity, the Vs mean seemed to be the best parameter for further processing. Determining peak systolic velocity (V mean), end‐diastolic velocity (Vd mean), and mean velocity over time (V̄ mean) were selected for standard analysis. The Pourcelot index was not taken into account, first for lack of definition for V mean and secondly for not missing simultaneous changes of the peak systolic and the end‐diastolic velocity.

Continuous monitoring of cerebral blood flow velocities was confined to the Transcranial Doppler Technique, which has its disadvantages: 1) high level of energy output; 2) large size of Doppler probe; 3) big sample volume; 4) lack of duplex scan. We have developed a Transfontanellar Doppler Transducer specified for continuous measurements in very low birth weight infants: 1) miniature pulsed Doppler 5-MHz transducer (13 mm * 9 mm * 25 mm) with a highly flexible cable; 2) variable small sample volume which position is documented by duplex scan; 3) sterilizable silicone/rubber fixation which can easily be attached to the infants head of any size without extra plaster; 4) energy levels reduced to one tenth of the transcranial method; 5) computer program for intermittent long term measurements, so reducing the exposure time of the patient. So far, this device has been used for 100 hours to monitor very low birth weight infants.