Digital blood flow measurement via finger plethysmography

The PAT (Itamar-Medical, Israel) device was used to measure digital arterial pulse wave amplitude continuously during rest and the MS test, as previously described [18, 19]. The device uses a modified form of plethysmography to measure pulsatile blood volume changes (Supplementary Figure 1). The probe is applied on the index finger and applies a constant subdiastolic pressure over the distal two-thirds of the finger to prevent distal venous blood stasis, unload arterial wall tension, and stabilize the probe to reduce noise. As a result, the changes in pulsatile volume only reflect changes in digital arterial blood perfusion. Pulsatile pressure changes from the probe are registered from a pressure transducer, and then fed into a specialized software which filters, amplifies, stores, and analyzes the signal in an operator independent manner. The baseline pulse wave amplitude during rest is determined by averaging the last 3 min of recording that preceded the MS test. The pulse wave amplitude during the MS test is determined visually as the area of maximum vasoconstriction during the MS task (Supplementary Figure 2). The stress/rest PAT ratio (sPAT) was calculated as the ratio of the pulse wave amplitude of the digit during MS compared to the resting amplitude, where a value <1 signifies vasoconstriction. This method has previously been validated to reflect vasoconstriction with MS testing [15, 18, 19, 32].