Carpal tunnel syndrome: correlations between pressure measurement and intraoperative electrophysiological nerve study. In 19 carpal tunnel syndrome (CTS) patients and 4 control subjects a catheter was introduced into the carpal tunnel and slowly retracted in 5 mm steps. Pressure was measured with the continuous infusion technique. In the same group of patients and controls, median nerve antidromic sensory action potential (aSAP) was detected intraoperatively stimulating proximally (S1), in the center (S2), and distally (S3) to the carpal tunnel and recording from the third finger (R). Sensory conduction velocity (SCV) and aSAP amplitude were considered in S1-S2, S2-S3 and S3-R segments. The intracarpal tunnel pressure was significantly higher in CTS patients than in controls, with the highest values located between 25 and 35 mm distal to the proximal border of the flexor retinaculum. SCV and aSAP amplitude were also decreased most often in the distal part (S2-S3) of the carpal tunnel. 