Estimation of the prevalence of isolated inter-scalenic compression from simultaneous arterial and venous photoplethysmography in patients referred for suspected thoracic outlet syndrome.

In patients with suspected thoracic outlet syndrome (TOS), diagnosing inter-scalenic compression could lead to minimally invasive treatments. During photo-plethysmography, completing a 30-sec 90° abduction, external rotation ("surrender" position) by addition of a 15-sec 90° antepulsion "prayer" position, allows quantitative bilateral analysis of both arterial (A-PPG) and venous (V-PPG) results. We aimed at determining the proportion of isolated arterial compression with photo-plethysmography in TOS-suspected patients. &#xD;Approach: We studied 116 subjects recruited over 4 months (43.3+/-11.8 years old, 69% females). Fingertip A-PPG and forearm V-PPG were recorded on both sides at 125 Hz and 4 Hz respectively. A-PPG was converted to PPG amplitude and expressed as percentage of resting amplitude (%rest). V-PPG was expressed as percentage of the maximal value (%max) observed during the "Surrender-Prayer" maneuver. Impairment of arterial inflow during the surrender (As+) or prayer (Ap+) phases were defined as a pulse-amplitude either < 5%rest, or < 25%rest. Incomplete venous emptying during the surrender (Vs+) or prayer (Vp+) phases were defined as V-PPG values either <70%max, or <87%max. &#xD;Main results: Of the 16 possible associations of encodings, As-Vs-Ap-Vp- was the most frequent observation assumed to be a normal response. Isolated arterial inflow without venous outflow (As+Vs-) impairment in the surrender position was observed in 10.3% [95%CI: 6.7-15.0%] to 15.1% [95%CI: 10.7 - 20.4%] of limbs. &#xD;Significance: Simultaneous A-PPG and V-PPG can discriminate arterial from venous compression and then potentially inter-scalenic from other levels of compressions. As such, it opens new perspectives in evaluation and treatment of TOS.&#xD.