Biomedical subjects

N A Gibson

Publications and source records attributed to N A Gibson.

21 records · Page 2Linked to original sources

PubMed1989

Severe birth asphyxia and abnormal cerebral blood-flow velocity.

Thirty-four fullterm infants with postasphyxial encephalopathy (PAE) were studied with ultrasound to assess cerebral blood-flow velocity (CBFV). A control group of 126 healthy infants also had CBFV recordings during the first week of life. Measurements for the majority of the asphyxiated group fell into two abnormal patterns in relation to the control group: four had low CBFV (less than 2 SD below the mean) and 17 had high CBFV (greater than or equal to 2 SD above the mean); all had severe PAE. Median age at the first high measurement was 26 hours. There were no statistically significant differences between infants with normal and abnormal CBFV in measurements of PaCO2 or mean arterial blood-pressure. A Pourcelot Resistance Index (PRI) less than 0.55 was common in the presence of high CBFV, but never seen with low measurements. 21 of the 34 infants died of their asphyxial insult and four of the survivors have severe cerebral palsy at a median age of two years. Three of the four with low CBFV died, and no infant with CBFV greater than 3 SD survived without severe impairment. The positive predictive value of CBFV measurements less than 2 SD or greater than 3 SD for death or severe impairment is 94 per cent, compared with 83 per cent for low PRI alone. The authors believe that high CBFV is the result of vasoparalysis of cerebral arterioles and that it represents a form of irreversible cerebral injury.

Asphyxia Neonatorum↗

PubMed1989

Cerebral haemodynamic effects of changes in positive end expiratory pressure in preterm infants.

The effects of changes in positive end expiratory pressure (PEEP) on cerebral blood flow velocity, arterial blood gases, and mean arterial pressure were studied in newborn infants. In mechanically ventilated premature infants with severe respiratory disease, an increase in PEEP from 2 to 6 cm H2O was associated with an increase in cerebral blood flow velocity. There was no significant change in mean arterial blood pressure. There was a significant increase in PaO2 and PaCO2 for every stepwise rise in PEEP. Multivariate regression analysis showed that 72% of the effect on cerebral blood flow velocity was attributable to PaCO2 alone and that any change in blood pressure was not likely to contribute to these changes. There was no evidence that changes in PEEP within the commonly used range adversely affected the neonatal cardiovascular or cerebral circulations.

Blood Flow Velocity↗

PubMedDate not supplied

Somatosensory evoked potentials in the term newborn.

Median nerve somatosensory evoked potentials (SEPs) were recorded from surface electrodes in 40 healthy term infants (range 36.5-43 weeks postmenstrual age). Electrical stimulation at 5 Hz was used, averaging the response to several runs of 1024 stimuli to each median nerve, bandpass 10-3000 Hz, sweeptime 100 msec. Identifiable potentials were collected over the cervical cord on all runs in all 40 infants and from the cortex in at least some runs in 39 out of 40 infants. The cervical response showed little variation and consisted of a clear negative wave with up to 3 peaks, mean latency of the largest 10.2 +/- 0.7 msec, followed by a positive deflection. The cortical response was very variable in form and latency between infants and to a lesser degree within infants. Four types of cortical wave form were found, symmetrical, asymmetrical, plateau and M shaped, of increasing complexity. In 11% of trials the response was absent or indistinct but could usually be uncovered by alteration in stimulus frequency or intensity. In the whole group, the mean latency for N1 was 30.0 +/- 6.8 msec and for the central conduction time 19.8 +/- 6.5 msec. Significant differences were found between the 4 cortical wave forms in the main variables measured, which gave support for form S being the most primitive and form M the most mature response.

Electric Stimulation↗