title: A novel approach to mechanical prophylaxis: calf impulse technology mimics natural ambulation more effectively than sequential calf compression.
abstract: BACKGROUND
  The risk of thrombosis can be reduced by mechanical compression, but the optimal device is unknown.
  
  
  OBJECTIVE
  To record the effect of natural ambulation on deep venous flow, providing a reference for evaluating the efficacy of mechanical compression systems, assuming that ambulation is the gold standard against which such systems should be compared; and to compare the hemodynamic effect of the A-V Impulse System CalfPad garment (A-VI) (Orthofix Vascular Novamedix, United Kingdom) with the SCD Express calf compression garment (SCD) (Covidien, USA).
  
  
  METHODS
  Twelve healthy volunteers were recruited and randomly assigned to either A-VI or SCD in a two-device, two-period crossover design. Peak femoral velocity (PFV) was calculated using custom ultrasound software and compared with baseline values. Ultrasound images were recorded.
  
  
  RESULTS
  A-VI augmented the mean (± SD) PFV to 59.79±29.07 cm/s compared with 22.86±5.73 cm/s for SCD. The actual percentage increase from baseline was approximately five times greater for A-VI (mean increase 385%±260%) than SCD (mean increase 81%±53%). Using an analysis of covariance model, with baseline fitted as a covariate, a highly statistically significant difference in favour of A-VI was detected (P=0.0002). Least square (adjusted) means (±95% CIs) were 37.24 cm/s (21.39 cm/s to 64.84 cm/s) for A-VI and 6.71 cm/s (3.86 cm/s to 11.69 cm/s) for SCD, representing more than fivefold greater improvement in PFV from rest with the A-VI device than with the SCD device.
  
  
  CONCLUSIONS
  Pulsatile impulse calf compression (A-VI) more closely mimics PFV of normal ambulation than slow-squeeze sequential compression (SCD). Pulsatile calf compression may provide superior protection against thrombosis in immobile patients.
authors.affiliation: Orthopaedic Surgery, University of Southampton, Southampton, United Kingdom. djwarwick@compuserve.com
authors.forename: David J
authors.initials: DJ
authors.lastname: Warwick
authors.forename: Keith
authors.initials: K
authors.lastname: Dewbury