Blood flow restriction therapy: The essential value of accurate surgical-grade tourniquet autoregulation

Abstract

Blood flow restriction (BFR) therapy, in which arterial blood flow into a subject’s limb is restricted by a pressurized tourniquet cuff during prescribed therapy, has been shown to induce significant improvements in muscle strength, hypertrophy and endurance. However, differences in equipment and methodology have led to inconsistent restrictions of blood flow (‘inconsistent BFR pressure stimuli’).  This prevents meaningful comparisons of results and identification of optimal therapy protocols and outcomes. We conducted a pilot study to evaluate the ability of five common BFR systems to accurately maintain and autoregulate the actual BFR cuff pressure near target BFR pressure throughout prescribed exercise periods. For effectiveness and safety, accurate autoregulation for BFR was defined to be the same as for surgical tourniquet systems:  automatic and rapid self-regulation of cuff pressure to within ±15 mmHg of the target pressure, within one second in the presence of transient pressure changes associated with exercise. Fifteen subjects (8 male; 7 female) completed a standard 30/15/15/15 BFR protocol at 2-second eccentric and 2-second concentric cadence on a horizontal leg press for each BFR system. Target pressures followed manufacturers’ recommendations and actual BFR cuff pressures were recorded at 100 samples per second for the duration of BFR exercise periods.  The percentage of time BFR systems provided accurate surgical-grade autoregulation of BFR cuff pressure were: 36.6% ± 41.9% (B Strong), 100% ± 0.0% (Delfi), 45.2% ± 33.6% (Saga), 35.3% ± 34.6% (Smart Tools), and 62.1% ± 26.7% (Suji). At the end of prescribed exercise periods, actual BFR cuff pressures in 3/5 systems differed from target pressures among subjects by more than 15 mmHg and 4/5 systems demonstrated standard deviations of more than 15 mmHg.  In view of the pilot results, it is recommended that BFR systems having accurate surgical-grade autoregulation be used to achieve consistent, safe and effective BFR therapy.