SPECTRAL AND SEQUENCE-ANALYSIS OF FINGER BLOOD-PRESSURE VARIABILITY - COMPARISON WITH ANALYSIS OF INTRAARTERIAL RECORDINGS

The aim of our study was to assess whether the Finapres device is able to accurately monitor not only average blood pressure values but also blood pressure variability. To examine this issue, we analyzed 30-minute recordings of finger and intra-arterial pressure simultaneously obtained at rest in 14 patients. We compared systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse interval (the reciprocal of heart rate), overall variability (standard deviation), and specific time-domain and frequency-domain components. Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse interval spectral powers were computed by fast Fourier transform over three frequency bands: low frequency (0.025 to 0.07 Hz), midfrequency (0.07 to 0.14 Hz), and high frequency (0.14 to 0.35 Hz). The coherence, ie, the degree of association between blood pressure and pulse interval powers obtained by the two techniques, was also assessed. Standard deviations of diastolic blood pressure, mean arterial pressure, and pulse interval were similar when assessed from the two recordings, whereas standard deviation of systolic blood pressure was overestimated by analysis of finger pressure recordings. All powers of diastolic blood pressure and mean arterial pressure and high-frequency powers of systolic blood pressure estimated from analysis of finger blood pressure tracings were superimposable to those obtained by analyzing invasive recordings. Low-frequency and midfrequency powers of intra-arterial systolic blood pressure were significantly overestimated by the analysis of finger blood pressure tracings (+13.7+/-4.4 mm Hg2, P<.01, and +2.3+/-0.9 mm Hg2, P<.05). Finger and intra-arterial systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse interval powers showed a high coherence in the frequency range considered (0.025 to 0.35 Hz). The coherence of all blood pressure powers became smaller for frequencies greater than 0.35 Hz and lower than 0.025 Hz. The number and slope of hypertension-bradycardia (+pulse interval/+systolic blood pressure) and hypotension-tachycardia (-pulse interval/systolic blood pressure) sequences assessed by time-domain analysis of both recordings were similar. Thus, specific frequency-domain and time-domain components of blood pressure and pulse interval variability seem to be properly assessed by finger blood pressure recordings in most cases, although low-frequency oscillations of systolic blood pressure appear to be magnified by finger blood pressure tracings.