Haemodynamic Enhancement in Perforator Flaps: The Inversion Phenomenon — A 2006 Study Revisited

In 2006, Rubino et al. published a study1 in JPRAS examining the haemodynamic differences between perforator flaps and normal systemic circulation. Twenty years later, their findings remain relevant and point toward several unexplored research directions.

What They Did

The team studied 10 patients undergoing free perforator flap reconstruction (ALT, DIEP, and S-GAP flaps). Using echo-colour-Doppler, they measured vessel diameter, blood velocity (Vmax, Vmin, Vmean), and calculated flow rates at both the pedicle artery and skin perforator artery levels, pre-operatively (normal anatomy) and post-operatively (perforator flap configuration, 4–10 weeks after surgery). Flow rates were derived from a mathematical model based on a modified Hagen–Poiseuille equation that accounts for tapering vessel radius. Statistical comparison used the Wilcoxon matched pairs signed sum rank test.

What They Found

The key finding was what the authors termed the "inversion phenomenon." Pre-operatively, blood velocity in the perforator was lower than in the pedicle, consistent with normal branching circulation. Post-operatively, this relationship reversed — velocity in the perforator exceeded that in the pedicle (P<0.01). The explanation lies in the altered vascular architecture: ligation of all side branches converts the normal parallel resistance system into a single series conduit with decreasing calibre, and by the continuity equation, velocity must increase as cross-section narrows.

Flow data showed a corresponding shift. The proportion of pedicle flow reaching the perforator increased dramatically after surgery — from as low as 4–5% pre-operatively to 23–89% post-operatively (P<0.01). In essence, the skin receives a much greater share of total pedicle blood flow in a perforator flap than in normal anatomy.

The authors concluded that perforator flaps exhibit a form of "haemodynamic enhancement" — higher blood velocity and proportionally greater flow at the skin level — which may explain their robust clinical perfusion and support their use as alternatives to muscle flaps even where abundant vascularity is needed.

Possible Future Directions

This study established the fundamental hemodynamic principle with the tools available in 2006. Several areas remain open for further investigation:

Patient-specific computational fluid dynamics. The original model used a simplified tapered-cylinder approximation. Modern CFD simulations based on patient-specific CTA vascular reconstructions could predict the degree of haemodynamic enhancement before surgery and potentially guide perforator selection.

Intraoperative hemodynamic monitoring. The study measured haemodynamics pre-op and weeks post-op. Current imaging technologies (ICG angiography, laser speckle contrast imaging, micro-Doppler) could track the inversion phenomenon in real time during and immediately after surgery, and correlate the degree of velocity inversion with clinical outcomes.

Venous side of the equation. The study addressed only arterial haemodynamics. The same parallel-to-series conversion applies to venous drainage, and venous congestion remains the most common cause of early flap compromise. Characterising the venous inversion phenomenon could have significant clinical impact.

Multi-perforator configurations. The study examined single-perforator flaps. Many modern reconstructions use multiple perforators. How the inversion phenomenon behaves with shared inflow — including potential competitive flow or steal between perforators — has not been systematically studied.

Large-scale validation with outcome correlation. The original cohort was 10 patients. Multicentre studies with larger samples could validate the findings and determine whether pre-operative or intraoperative Perf/Ped ratios have predictive value for flap complications.

Integration with machine learning. Combining haemodynamic parameters (velocity ratios, flow ratios, vessel diameters) with patient and surgical variables in predictive models could move toward data-driven decision-making in perforator flap surgery.

  1. Rubino C, Coscia V, Cavazzuti AM, Canu V. Haemodynamic enhancement in perforator flaps: the inversion phenomenon and its clinical significance. A study of the relation of blood velocity and flow between pedicle and perforator vessels in perforator flaps. J Plast Reconstr Aesthet Surg. 2006;59(6):636-43. doi: 10.1016/j.bjps.2005.07.010. PMID: 16817260. ↩