R. Totaro et al., EVALUATION OF POTENTIAL FACTORS AFFECTING THE MEASUREMENT OF CEREBROVASCULAR REACTIVITY BY NEAR-INFRARED SPECTROSCOPY, Clinical science, 95(4), 1998, pp. 497-504
1. Near-infrared (IR) spectroscopy is based on the relative transparen
cy of skin, skull and brain to the light in the near-IR region (700-11
00 nm) and on the oxygen-dependent tissue absorption changes of haemog
lobin. 2. We evaluated the most relevant factors (reproducibility, ven
ous return, age and sex) that might affect reliability of near-IR spec
troscopy to test CO2 cerebrovascular reactivity. 3. Thirty-four health
y volunteers were enrolled in the study. The protocol consisted of a 3
-min baseline, a 3-min hypercapnia (5% CO2 in air) and a 2-min recover
y. Transcranial Doppler sonography measurements were simultaneously pe
rformed. The CO2 reactivity test was repeated on 27 subjects after 1 h
to assess reproducibility. CO2 reactivity was also evaluated at diffe
rent body positions (supine, 35 degrees Trendelenburg and 35 degrees r
everse Trendelenburg), and over a gradual increase of the inspired CO2
. 4. Changes in near-IR spectroscopy and transcranial Doppler sonograp
hy parameters were significantly correlated with variations of end-tid
al CO2 (P < 0.005). A significant correlation between the reactivity i
ndexes of near-IR spectroscopy parameters and flow velocity was also f
ound (P < 0.01). A high reproducibility was also found for deoxyhaemog
lobin (r(i) = 0.76), oxyhaemoglobin (r(i) = 0.68) and flow velocity (r
(i) = 0.60) reactivity indexes. No significant differences between the
reactivity indexes of different body positions were found (P > 0.05).
The reactivity index of oxyhaemoglobin and deoxyhaemoglobin decreased
(P < 0.05) and increased (P < 0.01) with age respectively. 5. We foun
d that near-IR spectroscopy is a reliable and reproducible method for
the evaluation of cerebrovascular reactivity and might be considered,
after appropriate validation, for the assessment of patients with cere
brovascular disease.