Conventional near infrared spectroscopy (NIRS), introduced by Jobsis in 1977, can be considered as a reliable trend monitor for cerebral oxygenation. Quantisation, however, is complex and cumbersome. Recently a relatively simple system for cerebral oximetry (INVOS 3100, Somanetics Corporation, USA) was developed, measuring the regional oxygen saturation (rSo,) in the capillary bed of the cerebrum, presented as a numerical figure for easy interpretation. In this study a comparison was made between a conventional NIRS instrument and the new INVOS instrument, in order to obtain information about sensitivity and usefulness of the INVOS system. Changes in cerebral haemodynamics were induced by a moderate decrease of the arterial oxygen saturation (S,oZ) and by varying the arterial carbon dioxide level (P,CO,). This will result in a higher (hypercapnia) or lower (hypocapnia) cerebral blood flow and subsequent change of both NIRS signals and INVOS signal. Healthy volunteers were used for this study. It was found that the steady state value for rSo, was 70 * 6% (mean r SD).During the lowering of arterial saturation a poor correlation was found between rSo, and S,o, (r=0.37). Increased cerebral blood flow induced by hypercapnia was detected by both conventional NIRS and the INVOS. Decreased cerebral blood flow induced by hypocapnia could only be detected by conventional NIRS. It was concluded that due to the variation in displayed rSo, and the high amount of averaging in the algorithm the INVOS instrument does not yet provide more information than conventional NIRS. E 0 R. Quantitation of cerebral blood volume in newborn human infants by near infrared spectroscopy. J Appl Physiol 1990 68: 1086-1091. Skov L, Pryds 0, Greissen G. Estimating cerebral blood flow in newborn infants: comparison of near infrared spectroscopy and '33Xe clearance. Ped Res 1991: 30: 570-573.
Near infrared spectroscopy (NIRS) is an optical technique that provides information on cerebral tissue oxygenation and hemodynamics on a continuous, direct, and noninvasive basis. It is used to determine cerebral blood volume (CBV) and cerebrovascular CO 2 reactivity during normoxic hyper-and hypocapnia in a group of 28 healthy volunteers aged 20 to 83 years. The main focus is on to the age dependency of the measured variables. The influence of changes in minute ventilation during normocapnia on the cerebral oxygenation was also studied. The mean CBV (ϮSD) in age was, for 20 to 30 years, 2.14Ϯ0.51 ml/100 g of brain tissue; for 45 to 50 years, 1.92Ϯ0.40 ml/100 g; and for 70 to 83 years, 1.47Ϯ0.55 ml/100 g. The CBV showed a significant decrease with advancing age. No influence was found for a change in minute ventilation on cerebral oxygenation. During hypercapnia cerebral blood flow (CBF) significantly increased in all age groups, with a factor of 1.31Ϯ0.17 kPa −1 , 1.64Ϯ1.39 kPa −1 , and 2.4Ϯ1.7 kPa −1 , respectively, for the three age groups. The difference in change among the age groups was not statistically significant (pϭ0.09). The trend seen was an increased change in CBF with advancing age. During hypocapnia, the CBF significantly decreased in all age groups, with a factor of 0.89Ϯ0.08 kPa −1 , 0.89Ϯ0.04 kPa −1 , and 0.85Ϯ0.11 kPa −1 , respectively. There was no significant difference among the age groups (pϭ0.50).
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