Restoring ATBF: Dreaming the impossible dream? Commentary on: Subcutaneous adipose tissue blood flow and vasomotion in morbidly obese patients: Long term effect of gastric bypass

Dear Sir: Knowledge of the longterm effect of weight loss on adipose tissue blood flow (ATBF) is scarce. We read with great interest the paper by Rossi et al. [3], reporting the results of a study using laser-Doppler flowmetry (LDF), where baseline thigh ATBF was lower in morbidly obese subjects compared to ageand sex-matched controls (4.8 vs. 79.9 perfusion units /PU). These results confirm several previous studies [4]. After one-year follow-up subsequent to Roux-en Y gastric bypass (RYGB) in obese patients, they observed a meaningful weight loss (−40 kg, e.g.−28%). This weight loss was associated with a slight but nevertheless significant increase in ATBF (up to 10.0 PU) although patients remained obese. The main limitations of the Rossi et al. study are linked to the inherent drawbacks of the LDF method, relating mainly to calibration, multiple Doppler shifts, tissue optical properties, motion artefacts, biological zero and impossibility to express the results in absolute values [2]. The gold-standard for ATBF measurement is the 133 xenon wash-out method, which should be combined with LDF in order to validate data obtained therewith [1]. Anemia, a frequent complication of RYGB, and antihypertensive drugs, which may influence adipose tissue perfusion [4], could also interfere with LDF measurements. However, no indication relating to these specific issues was provided in the paper. Additionally, the chosen site of measurement stands out as another scientific issue, because subcutaneous adipose tissue in the thigh is known to be much less active than in abdomen [4]. Rossi et al.’s conclusion to the effect that the slight increase in ATBF, observed one year after RYGB, is rather negligible, is sustained by another study [5] reporting on ATBF following a very low-calorie diet