Near infrared spectroscopy has been used to assess the effects of bradycardia and hypoxia on the cerebral circulation in the premature neonate. The technique is well tolerated and can be applied in almost any infant. Continuous monitoring of changes in cerebral oxygenated, deoxygenated, and total haemoglobin is possible. Total haemoglobin is analogous to cerebral blood volume; thus information on circulatory changes as well as oxygenation state can be obtained. Twenty five babies had cerebral monitoring carried out using this technique. During episodes of hypoxia, both spontaneous and induced, impairment of haemoglobin oxygenation within the brain was detected together with an overall increase in the total mean haemoglobin concentration, which was 08x 10-2 mmol/l. Bradycardia with apnoea also led to impairment of cerebral oxygenation, and to a rapid fall in the concentration of total mean haemoglobin to 1-4x 10-2 mmoVI, which was followed in some cases by an increase to above the resting value on recovery of the heart rate to a mean of 0-7x102 mmol/l. These disturbances to total haemoglobin concentration represent abnormalities of cerebral blood volume that may be implicated in the pathogenesis of neonatal cerebral injury.

The validation of measurement of cerebral blood volume (CBV) and cerebral blood flow (CBF) using near infrared spectroscopy (NIRS) against jugular venous occlusion plethysmography is described. Repeated measurements in six infants were made using both techniques simultaneously. A close relationship between the two measurements of change in CBV was obtained in five infants. There was also a close relationship for measurement of CBF in four infants. This study confirms the possibility of using NIRS to monitor CBV continuously in the premature infant. This parameter may prove to be of greater clinical value than the intermittent measurement of CBF.

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Cyclical fluctuations of cerebral blood flow velocity have been reported previously using Doppler ultrasound. The same phenomena was detected during investigations of changes in cerebral blood volume using near infrared spectroscopy. Rhythmic fluctuations of cerebral blood volume at a frequency of 3-5 cycles/minute is reported here.

NIRS can be used as a clinical monitor of the cerebral circulation and oxygenation, is safe, non-invasive and can be applied at the bedside. The use of the technique in neonatal, fetal and anaesthetic monitoring is described.