An association between vasomotion and oxygen extraction

Abstract

Vasomotion is defined as a spontaneous local oscillation in vascular tone whose function is unclear but may have a beneficial effect on tissue oxygenation. Optical reflectance spectroscopy and laser Doppler fluximetry provide unique insights into the possible mechanisms of vasomotion in the cutaneous microcirculation through the simultaneous measurement of changes in concentration of oxyhemoglobin ([HbO(2)]), deoxyhemoglobin ([Hb]), and mean blood saturation (S(mb)O(2)) along with blood volume and flux. The effect of vasomotion at frequencies <0.02 Hz attributed to endothelial activity was studied in the dorsal forearm skin of 24 healthy males. Fourier analysis identified periodic fluctuations in S(mb)O(2) in 19 out of 24 subjects, predominantly where skin temperatures were >29.3°C (X(2) = 6.19, P < 0.02). A consistent minimum threshold in S(mb)O(2) (mean: 39.4%, range: 24.0-50.6%) was seen to precede a sudden transient surge in flux, inducing a fast rise in S(mb)O(2). The integral increase in flux correlated with the integral increase in [HbO(2)] (Pearson's correlation r(2) = 0.50, P < 0.001) and with little change in blood volume suggests vasodilation upstream, responding to a low S(mb)O(2) downstream. This transient surge in flux was followed by a sustained period where blood volume and flux remained relatively constant and a steady decrease in [HbO(2)] and equal and opposite increase in [Hb] was considered to provide a measure of oxygen extraction. A measure of this oxygen extraction has been approximated by the mean half-life of the decay in S(mb)O(2) during this period. A comparison of the mean half-life in the 8 normal subjects [body mass index (BMI) <26.0 kg/m(2)] of 12.2 s and the 11 obese subjects (BMI >29.5 kg/m(2)) of 18.8 s was statistically significant (Mann Whitney, P < 0.004). The S(mb)O(2) fluctuated spontaneously in this saw tooth manner by an average of 9.0% (range 4.0-16.2%) from mean S(mb)O(2) values ranging from 30 to 52%. These observations support the hypothesis that red blood cells may act as sensors of local tissue hypoxia, through the oxygenation status of the hemoglobin, and initiate improved local perfusion to the tissue through hypoxic vasodilation.

Rapid calculation of diffuse reflectance from a multilayered model by combination of the white Monte Carlo and adding-doubling methods

“…The average values of C m and C th were 6.24 ± 0.06% and 0.211 ± 0.008%, respectively, in pre-occlusion (normal), which are close to typical values for Japanese subjects reported in the literatures [10,21,22]. The average value of 44.3 ± 3.4% for StO 2 in pre-occlusion agrees with the mean blood oxygen saturation of normal human subjects (range 30.2-52.4%) reported in the literatures [23]. During cuff occlusion, C oh and C dh decreased and increased, respectively.…”

Normal Muscle Oxygen Consumption and Fatigability in Sickle Cell Patients Despite Reduced Microvascular Oxygenation and Hemorheological Abnormalities

“…Vasomotion is a form of spontaneous localized oscillations induced by spontaneous contraction and relaxation of the smooth muscle components in the small blood vessel walls which generate rhythmic changes in their diameter. Although vasomotion mechanisms are still under debate [12], several studies demonstrated that vasomotion may have beneficial effects on tissue oxygenation [13], [14], [15]. Therefore the hypothesis of a reduced muscle microvascular oxygenation in SCD patients, due to abnormal hemorheology, compensated by a greater vasomotion activity needs to be tested.…”

Age, waist circumference, and blood pressure are associated with skin microvascular flow motion

“…Since flow motion has predominantly been observed in participants with a skin temperature above 29.38C [3], the laser-Doppler probe was set at 308C. The LDF output was recorded for 25 min with a sample rate of 32 Hz, which gives a semi-quantitative assessment of skin microvascular blood perfusion expressed in arbitrary perfusion units (i.e.…”

“…In fact, these rhythmic oscillations regulate microvascular flow distribution so that various tissue regions are intermittently perfused [1,2]. Indeed, theoretical and experimental studies demonstrate that an increase in vasomotion can increase total blood flow by 40-60% [3,4]. In addition, when active and passive vessels with the same average diameter are compared, active vessels have a lower vascular resistance (according to Poiseuille's law) [5,6], that is, vasomotion decreases arterial pressure by 20% [7].…”