Temporal (in)stability of suboptimal toe-brachial indices

To be effective in screening, prognostic, and monitoring contexts, the toe-brachial index (TBI) should not be susceptible to large sporadic fluctuations from one time to another. In order to identify whether those fluctuations exist in people who have suboptimal TBIs, the temporal stability of their TBIs was examined in detail across 6 months.

TBI readings from SysToe and Omron automated devices were taken from 21 participants at baseline and at 2- and 6-month timepoints subsequently. The primary inclusion criterion was that participants had at least one of three baseline TBIs on either foot ≤0.65 if a standard 25-mm wide occlusion cuff was used, or ≤0.85 if a 15-mm occlusion cuff was used.

After excluding five participants because of their extremely high TBI fluctuations, TBI stability within the remaining 16 participants was examined. Ipsilateral TBIs changed by ≥0.10 on at least one foot for 11 participants across the initial 2-month timespan (maximum difference 0.26) and for same number of participants across the full 6-month timespan (maximum difference 0.36), with the composition of the 11-person groups differing slightly for the two timespans. Contralateral differences were ≥0.10 for five participants across the 2-month timespan (maximum difference 0.26) and for nine participants across the 6-month timespan (maximum difference 0.42), again with some group overlap. The foot with the higher TBI at baseline remained so across the 6 months.

For many people with suboptimal TBIs there might be inherent ipsilateral and contralateral inconsistency among TBI readings. This threatens the effectiveness of TBIs for screening, prognostic, and monitoring purposes. In order to maximize the prospects of the TBI as a valuable metric, adherence to standard protocols should be observed and other prospects for the TBI to assess vascular supply to the foot more effectively should be considered.