Assessment of local changes of cerebral perfusion and blood concentration by near infrared spectroscopy and ultrasound contrast densitometry

The objective of this study is to correlate regional cerebral blood concentration measurements made with near infrared spectroscopy to simultaneous local measurements of ultrasound contrast agent (CA) densitometry. Experiments were performed with piglets (7 kg) under general anesthesia. The cerebral blood flow (CBF) and volume (CBV) were changed by inducing various degrees of hypercapnia. NIRS measurements were performed with a quasi-continuous wave system, using an optode distance of 3-6 cm. The concentration changes in oxygenated and deoxygenated hemoglobin and their sum and difference (cO2Hb, cHHb, ctHb, cHbD) were continuously calculated. Ultrasound contrast agent (SF6) was administered as a short intra-venous bolus. Ultrasound equipment was used in pulse inversion second harmonic gray scale imaging mode at low transmit power setting. Three regions-of-interest (0.25 cm2) were analyzed in each image. Wash-in curves were constructed as spatial mean gray level vs. time. The variables collected with both methods changed according to the induced changes in the physiological condition. Changes in the PaCO2, pH and carotid flow induced highly correlated changes in cO2Hb, cHHb, ctHb and cHbD, and in the variables derived from CA analyses. NIRS and CA methods measure regional, respectively, local changes in CBV and CBF. Moreover, NIRS can yield complementary information about the cerebral oxygenation.