Protons at the speed of sound: Predicting specific biological signaling from physics.

Local changes in pH are known to significantly alter the state and activity of proteins and enzymes. pH variations induced by pulses propagating along soft interfaces (e.g. membranes) would therefore constitute an important pillar towards a physical mechanism of biological signaling. Here we investigate the pH-induced physical perturbation of a lipid interface and the physicochemical nature of the subsequent acoustic propagation. Pulses are stimulated by local acidification and propagate - in analogy to sound - at velocities controlled by the interface's compressibility. With transient local pH changes of 0.6 directly observed at the interface and velocities up to 1.4 m/s this represents hitherto the fastest protonic communication observed. Furthermore simultaneously propagating mechanical and electrical changes in the lipid interface are detected, exposing the thermodynamic nature of these pulses. Finally, these pulses are excitable only beyond a threshold for protonation, determined by the pKa of the lipid head groups. This protonation-transition plus the existence of an enzymatic pH-optimum offer a physical basis for intra- and intercellular signaling via sound waves at interfaces, where not molecular structure and mechano-enyzmatic couplings, but interface thermodynamics and thermodynamic transitions are the origin of the observations.

The efficacy of color duplex sonography in preoperative assessment of anterolateral thigh flap.

The anterolateral thigh (ALT) flap has become a workhorse in reconstructive surgery of the head and neck region and the extremities. However, its inconsistent vascular anatomy and frequent intramuscular course of perforators often cause difficulties during the dissection of this versatile flap. Hence, reliable preoperative perforator mapping and identification of vascular anomalies may render the raising of the flap easier and safer. The aim of this study was to evaluate the use of Color Duplex sonography and whether it allows the distinction between septocutaneous and musculocutaneous perforators. For this purpose, the thighs of 13 patients undergoing reconstruction with ALT flaps were examined preoperatively, and results were compared to intraoperative findings. A total of 30 perforators could be detected preoperatively, of which 29 were confirmed during flap dissection. Preoperative Color Duplex sonography correctly predicted the course of all perforators as either running through the vastus lateralis muscle or the intermuscular septum. In our investigations, Color Doppler sonography had a 96.7% positive predictive value and a 96.7% true positive rate in detecting perforators. Color Duplex sonography is a highly reliable tool in the preoperative assessment of ALT flaps. Localization and course of perforators can be determined accurately and vascular anomalies can be identified.