Broad-band spectral analysis of 24 h continuous finger blood pressure: comparison with intra-arterial recordings

The present study compares the spectral characteristics of 24-h blood press ure variability estimated invasively at the brachial artery level with thos e estimated by measurement of blood pressure at the finger artery using the non-invasive Portapres device. Broad-band spectra (from 3 x 10(-5) to 0.5 Hz) were derived from both finger and intra-brachial pressures recorded sim ultaneously for 24 h in eight normotensive and twelve hypertensive ambulant subjects. At frequencies lower than 0.07 Hz, higher spectral estimates wer e obtained by Portapres than by intra-brachial measurements. The maximum ov erestimation occurred in systolic pressure at around 10(-2) Hz, where the a mplitude of the oscillations was two times greater when measured by Portapr es. A less pronounced overestimation was found for diastolic pressures. The maximum overestimation was greater during daytime than during night-time. At around 0.1 Hz, invasive and non-invasive spectra were similar. At the re spiratory frequencies (0.15-0.50 Hz), the power spectra were overestimated by Portapres during daytime, and underestimated at night. These results pro vide reference information for the correct interpretation of Portapres data in the estimation of 24-h blood pressure spectral power.