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Investigation of in vivo measurement of cerebral cytochrome-c-oxidase redox changes using near-infrared spectroscopy in patients with orthostatic hypotension

Department of Medical Physics and Bioengineering, Malet Place Engineering Building, University College London, Gower Street, London, UK.
Physiological Measurement (Impact Factor: 1.62). 03/2007; 28(2):199-211. DOI: 10.1088/0967-3334/28/2/008
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ABSTRACT We have previously used a continuous four-wavelength near-infrared spectrometer to measure changes in the cerebral concentrations of oxy-haemoglobin (Delta[HbO(2)] and deoxy-haemoglobin (Delta[HHb]) during head-up tilt in patients with primary autonomic failure. The measured changes in light attenuation also allow calculation of changes in the concentration of oxidized cytochrome-c-oxidase (Delta[(ox)CCO]), and this paper analyses the Delta[(ox)CCO] during the severe episodes of orthostatic hypotension produced by this experimental protocol. We studied 12 patients during a passive change in position from supine to a 60 degrees head-up tilt. The challenge caused a reduction in mean blood pressure of 59.93 (+/-26.12) mmHg (Mean (+/-SD), p < 0.0001), which was associated with a reduction in the total concentration of haemoglobin (Delta[HbT] = Delta[HbO(2)] + Delta[HHb]) of 5.02 (+/-3.81) microM (p < 0.0001) and a reduction in the haemoglobin difference concentration (Delta[Hb(diff)] = Delta[HbO(2)] - Delta[HHb]) of 14.4 (+/-6.73) microM (p < 0.0001). We observed a wide range of responses in Delta[(ox)CCO]. Six patients demonstrated a drop in Delta[(ox)CCO] (0.17 +/- 0.15 microM); four patients demonstrated no change (0.01 +/- 0.12 microM) and two patients showed an increase in Delta[(ox)CCO] (0.21 +/- 0.01 microM). Investigation of the association between the changes in concentrations of haemoglobin species and the Delta[(ox)CCO] for each patient show a range of relationships. This suggests that a simple mechanism for crosstalk, which might produce artefactual changes in [(ox)CCO], is not present between the haemoglobin and the (ox)CCO NIRS signals. Further investigation is required to determine the clinical significance of the changes in [(ox)CCO].

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    • "Using a four-channel continuous-wave near-infrared spectroscope (Oxymon M III, Artinis Medical Systems, BV, The Netherlands), O 2 Hb and HHb were determined by measuring light attenuation at 760 and 864 nm wavelengths that was analyzed using algorithms based on the modified Beer–Lambert law. Detailed descriptions of NIRS methodology are described elsewhere (van der Sluijs et al., 1997; Grassi et al., 1999; Kirkpatrick et al., 1998; Tachtsidis et al., 2007). Two variables were calculated from O 2 Hb, and HHb: (1) tHb = O 2 Hb + HHb, and (2) the difference between changes of O 2 Hb and HHb concentrations (Hb diff ) = O 2 Hb − HHb. "
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