Pulse arrival time based indices as surrogates of ankle brachial index for the assessment of peripheral arterial disease

Ankle-Brachial Pressure Index (ABI), the ratio of ankle blood pressure to arm pressure, has been used to assess the severity of peripheral arterial disease (PAD) and to predict major cardiovascular events. This study proposes three indices which can be readily obtained from electrocardiogram and photoplethysmogram, and studies their correlation with ABI in supine and sitting positions. The proposed indices were derived from pulse arrival time (PAT). Specifically, the ratio of PAT measured from the fingertips to PAT measured from the toes of both sides (PAT
_ralio
), and the relative bilateral differences in PAT measured from the toes of the legs, normalised by average PAT from the two legs (PAT
_diff1
) and by the minimal PAT from one side (PAT
_diff2
) were calculated. The results showed that PAT
_ratlo
is better correlated with ABI compared to PAT
_diffl
and PAT
_dff2
. The coefficient of determination (R
²
) between PAT
_ratio
and ABI is 0.57 when measured in sitting posture, indicating its potential role as an alternative index of ABI for PAD diagnosis. Compared with ABI, the advantages of PAT
_ratio
are 1) it can be measured at ease with wearable sensors that are available at a relatively low cost; 2) the PAT-derived indices can be measured in a sitting posture which is more convenient to obtain; and 3) it can potentially provide longer term, continuous monitoring of the vascular function.