Physiologic Variations in Venous and Arterial Hemodynamics in Response to Postural Changes at the Thoracic Outlet in Normal Volunteers

Background: Hemodynamic changes in vascular flow and waveforms measured across the thoracic outlet (TO) during positional changes may occur in normal individuals. The aim of this study was to establish the prevalence of significant arterial and venous hemodynamic variation in the limbs of normal volunteers during standardized upper extremity positional changes. Methods: Using Doppler ultrasound and photoplethysmography (PPG), we evaluated arterial and venous flow in 100 limbs of 50 normal volunteers in neutral position and in 5 different standardized arm positions, including 90 degrees arm abduction (with head in neutral position, head turned ipsilaterally, and head turned contralaterally), arm extended above the head at 180 degrees, and arm hyperextended at 200 degrees. Results: There was great variability in the prevalence of abnormal venous and arterial flow changes depending on the arm position. Venous flow anomalies (loss of flow phasicity resulting in continuous, minimally continuous, or absent flow) were demonstrated in 60% of the limbs. The maneuver producing the greatest prevalence of venous flow abnormality was 90 degrees arm abduction with contralateral head turn (34% of limbs), while arm hyperextension produced the least venous flow abnormalities (25% of limbs). In 13% of the limbs arterial flow abnormalities were found by PPG (absent tracings in 10% and dampened wave for min 5%), while 23% of the limbs showed increased arterial velocities (positional to neutral velocity ratio > 2.0). The arm position producing the greatest prevalence of arterial flow anomaly was hyperextension (21% of limbs); while the arm positioning at 90 degrees of abduction with the head in neutral position resulted in no arterial flow abnormalities. Conclusions: The prevalence of upper extremity venous and arterial hemodynamic changes varies substantially in different arm positions. Our data suggest that physiologic anomalies in venous flow across the TO during postural changes are very common, while the absence of finger PPG arterial tracings occur in a very small percentage of the population. Abnormal venous flow across the TO with postural changes should be considered a highly prevalent finding in the normal population, and therefore carries little value in the diagnosis of TO syndrome. On the other hand, absence of arterial waveforms measured at the fingers by PPG testing during positional changes occurs in a small percentage of the normal population, and may represent abnormal compression at the TO in patients with upper extremity symptomatology.