Measurement of calf muscle oxygenation during light-intensity exercise in patients with post-thrombotic syndrome

Background: Near-infrared spectroscopy (NIRS) provides continuous noninvasive monitoring of changes in the levels of oxygenated hemoglobin (O(2)Hb) and deoxygenated hemoglobin (HHb) in tissues. The purpose of this study was to investigate changes in calf muscle O(2)Hb and HHb levels during standing and exercise in the follow-up of deep venous thrombosis (DVT). Methods: Forty-three patients with a first episode of unilateral proximal DVT were included. Final clinical manifestations were evaluated at a mean follow-up point of 53 months after diagnosis of DVT, and post-thrombotic syndrome (PTS) was considered to be present if the Villalta score was >5. Moreover, to assess the severity of PTS, the revised Venous Clinical Severity Score (VCSS) was employed. NIBS was used to measure changes in the levels of O(2)Hb and HHb in calf muscle. On standing, increases in O(2)Hb and HHb were calculated by subtracting the baseline value from the maximum value (Delta O(2)Hb(st) and Delta HHb(st)). The times taken for the O(2)Hb and HHb concentrations to become maximal ((T)O(2)Hb(st), and (T)HHb(st)) were also measured. During 10 tiptoe movements, the relative change in O(2)Hb was calculated by subtracting the value measured at the end of exercise from the value measured at the beginning of exercise (Delta O(2)Hb(ex)). On the other hand, 10 tiptoe movements produced venous expulsion (Delta HHbE(ex)) and a subsequent retention (Delta HHbR(ex)). The oxygenation index (HbD; HbD = O(2)Hb - HHb) was also calculated at the end of standing and at the end of 10 tiptoe movements (Delta HbD(st), and Delta HbD(ex)). Results: Among the 43 limbs evaluated, 21 had PTS. On standing, the Delta HbD(st) was significantly decreased in patients with PTS relative to the patients without PTS (12 +/- 8, 22 +/- 11 mu mol/L; P = .001). The (T)O(2)Hb(st) was also significantly reduced in patients with PTS relative to those without (43 +/- 41, 107 +/- 58 seconds; P = .001). During 10 tiptoe movements, the Delta HHbE(ex), was significantly reduced in patients with PTS relative to those without (-2 +/- 1, -3 +/- 3 mu mol/L; P = .016). Similarly, the Delta HHbR(ex) was significantly increased in patients with PTS relative to those without (8 +/- 7, 3 +/- 2 mu mol/L; P = .001). Furthermore, falls in Delta HbD(ex) were more pronounced in patients with PTS (-10 +/- 16, 10 +/- 10 mu mol/L; P < .001). NIBS-derived (T)O(2)Hb(st) (r = -0.568; P < .001) and Delta HbD(ex) (r = -0.645; P < .001) showed strong inverse correlations with VCSS. Similarly, NIRS-derived Delta HHbE(ex) (r = 0.409; P < .01) and Delta HHbR(ex) (r = 0.476; P <.01) showed moderate positive correlations and Delta HbD(st) (r = 0.422; P < .01) had a moderate inverse correlation with VCSS. Conclusions: Changes in O(2)Hb and HHb concentrations differ between patients with and without PTS. The reduced (T)O(2)Hb(st) may indicate impairment of the venoarteriolar reflex in patients who have PTS. Furthermore, severe falls in HbD in patients with PTS might reflect the pain of venous claudication. These findings may have implications for investigations of the microcirculation in the context of post thrombotic sequelae.