Non‐invasive blood pressure monitoring during head‐up tilt using the Penaz principle

Continuous blood pressure measurement by a non-invasive means is of clinical utility in many situations where changes in cardiovascular hemodynamics and blood volume distribution are likely to occur. We have compared blood pressure measurements using the Penaz principle (Finapres, Ohmeda) to an intra-arterial catheter system during head-up tilt (reverse Trendelenburg's position) which models central hypovolemia. Twelve healthy volunteers were raised to a 60 degree head-up tilt position for 60 min or until presyncope occurred. Seven subjects developed presyncopal symptoms at a mean time of 38 +/- 6 min with blood pressure measured by the Penaz principle falling from 140 +/- 8/72 +/- 4 to 82 +/- 10/54 +/- 6 mmHg (18.7 +/- 1.1/9.6 +/- 0.5 to 10.9 +/- 1.3/7.2 +/- 0.8 kPa) (P less than 0.01), at which point they were returned to a horizontal position with an immediate rise in blood pressure. During the maximal drop in blood pressure, heart rate decreased from 82 +/- 7 to 45 +/- 5 (P less than 0.01). Overall, the non-invasive system had a correlation coefficient of 0.98 as compared to the intra-arterial method and ECG for blood pressure and heart rate in all 12 subjects during rest, tilt, and recovery. We conclude that the Penaz principle apparatus is a useful monitor of symptomatic hypotension during central hypovolemia.