megavideolinks
Joined: 19 Nov 2011
Posts: 273
|
 Posted: Sat Nov 26, 2011 11:22 am Post subject: Endothelial-Dependent FMD and NIRS Imaging |
 |
|
Each subject was placed in a supine position on the exam
table with the arm supported and immobilized in a Vac-Lok
pillow (Medtech, Orange City, IA). Brachial artery FMD and
forearm muscle microcirculation were assessed prior to and for
3 min after 4 min of artery occlusion, which was evoked using
a sphygmomanometer cuff on the upper arm inflated to 280
mm Hg. The brachial artery was imaged above the antecubital
fossa in the longitudinal plane using two-dimensional gray-scale
imaging (Sonosite Titan, SonoSite, Inc. Bothell, WA). Images
were captured at rest and at 40, 60, and 100 after cuff deflation.
The average of four measurements at each time point image
was used to derive the maximal FMD. FMD was expressed as a
percentage of postocclusion vessel diameter relative to precuff
occlusion vessel diameter.
Change in near-infrared light absorption by oxygenated and
deoxygenated hemoglobin (Hb) and myoglobin (Mb) in the
forearm muscle was evaluated using two-channel continuouswavelength NIRS at a sampling frequency of 4 Hz (cwNIRS;
NIMS, Philadelphia, PA). The NIRS unit was fitted with a probe
consisting of one LED (light-emitting diode) light source and
two photodiode detectors. The optical probe was positioned on
the medial aspect of the right forearm muscle. The location of
the probe was recorded by noting distances from anatomical
landmarks to ensure identical probe placement during all trials.
Wavelengths of 730 and 850 nm were used to monitor relative
change in oxy/deoxy-Hb/Mb. Oxy-Hb/Mb of muscle tissue was
estimated by changes in the difference in signal strength at those
wavelengths. Although individual contributions of Hb and Mb
cannot be distinguished by NIRS because of similar absorption
spectra for the respective oxygenated and deoxygenated chromophores, the contribution of myoglobin in skeletal muscle has
been shown to account for less than 10% of the NIRS signal
(Chance et al., 1988). Since [Hb] and [HbO2] in large vessels
are sufficient to maximally absorb NIR light, the signal reflects
Hb/HbO2 in muscle arterioles, capillaries, and venules (Mancini
et al., 1994). Reperfusion rate after cuff ischemia following each
session was computed as the slope of reoxygenation to baseline
signal
_______________
14k white gold charms
Free Music Download |
|
