Skeletal muscle oxygenation and fluid content in upper extremity postthrombotic syndrome: a proof-of-concept study

Little is known about the pathophysiology of upper extremity (UE) postthrombotic syndrome (PTS).

We aimed to investigate the effect of PTS severity on UE muscle oxygen saturation (SmO₂) and fluid content during exercise and recovery in adolescents and young adults.

Eleven cases with unilateral or bilateral UE-PTS who sustained deep vein thrombosis (DVT) in childhood, and 11 age- and sex-matched controls from the general population were recruited for this case-control study. PTS was measured using CAPTSure (0-100-point score). SmO₂ and segmental extracellular fluid content were measured in both UEs using near-infrared spectroscopy (NIRS) and bioimpedance spectroscopy (BIS), respectively. Incremental and constant load UE exercise tests were completed using an ergometer while monitoring NIRS and BIS parameters in both UEs. NIRS and BIS changes throughout exercise and recovery were analyzed using mixed models to account for nested data.

Median age of DVT diagnosis among cases was 5.6 years (quartile [Q]1-Q3, 0.2-16.1 years). At the time of the study, median CAPTSure score in the DVT-affected UE was 39 points (Q1-Q3, 27-55 points); 55% of DVTs were associated with a central venous catheter. Mixed models showed that increasing PTS severity was associated with lower SmO₂ during both incremental and constant load exercise and exercise recovery. We found no evidence of fluid accumulation during exercise.

The lower SmO₂ suggests that UE-PTS severity is associated with muscle microvascular dysfunction and impaired blood flow during and following exercise.