Non-invasive vs. invasive beat-to-beat monitoring of blood pressure.

The present study focuses on the accuracy in tracing fast beat-to-beat changes in blood pressure using a non-invasive technique. The measurements using a commercially available apparatus (Finapres, Ohmeda, USA) were compared to ipsilateral intra-arterial radial pressure. Eight patients were studied at rest, during deep breathing with a fixed rate of 6 breaths min-1, and during an exercise test on an ergometer cycle. A total of 900 systolic pressure values were included for statistical evaluation, covering a pressure range of 86-266 mmHg. On average the systolic correlation coefficient for the whole material was 0.97, with a range of 0.94-0.996. For mean pressure the correlation coefficient was on average 0.97, and for diastolic pressure 0.93. No systematic difference between the non-invasive and the invasive method was found, although for each individual patient a difference between direct and indirect measured blood pressure existed that could be relatively large (systolic pressure: average difference = 0.8 mmHg, SD = 16 mmHg). We found the method easy to handle and consider it excellently suited to track relative changes in blood pressure.