RESUMO
The feasibility of measuring blood pressure (BP) variability by a noninvasive beat-to-beat finger arterial BP device (Finapres) was assessed in preterm infants. By application of the finger cuff around the infant's wrist, time and frequency domain (spectral power) analysis of noninvasive beat-to-beat BP signals were compared with intra-arterial measurements. A fast Fourier Transform was used to compute the spectral power density from 128-s periods. The low-frequency band (LF; 0.04-0.15 Hz) is partly associated with baroreflex activity. The high-frequency band (HF; 0.4-1.5 Hz) is associated with respiratory activity. In eight subjects above 1000 g, reliable signals could be obtained. We observed a high correlation between noninvasive and intra-arterial beat-to-beat systolic BP values (mean r value +/- SD, 0.87 +/- 0.11), with a gain close to 1 (mean gain +/- SD, 1.0 +/- 0.4 mm Hg/mm Hg). Finapres estimated beat-to-beat systolic BP changes more accurately than diastolic values. We found a very high amount of linear coupling, expressed as coherence function, between the power spectra of noninvasive and intra-arterial systolic BP measurements. For systolic BP, the (pooled) group mean +/- SEM coherence values were 0.93 +/- 0.00 and 0.91 +/- 0.01 for LF and HF fluctuations, respectively (NS). The wrist method of Finapres in neonates has limited value in estimating absolute BP but is useful in a clinical research situation, where identification of beat-to-beat changes in systolic BP is more important. Finapres provides a noninvasive tool for investigating autonomic cardiovascular regulation (baroreflex sensitivity, spectral analysis of BP fluctuations) in neonates.
