Noninvasive baroreflex sensitivity assessment in geriatric patients: feasibility and role of the coherence criterion

In baroreflex sensitivity (BRS) assessment by the blood pressure to heart rate transfer function modulus in the 0.05-0.15 Hz band, low coherence spectral components are normally rejected. This criterion has, however, no sound theoretical basis. We studied the impact of this criterion in low BRS low coherence subjects. Eleven geriatric patients with cardiac and/or pulmonary disease participated. Five measurement sessions were held. In only 8 measurements (in 5 subjects) there were coherence-components >0.7. Using all frequency components, BRS was 7.9/spl plusmn/5.1 ms/mmHg and coherence was 0.43/spl plusmn/0.14. Using only frequency components with coherence >0.7, BRS was 11.1/spl plusmn/11.3 ms/mmHg (NS) and coherence was 0.75/spl plusmn/0.06 (P<0.01). Our study demonstrates that the coherence criterion often precludes BRS assessment in patients. Our study suggests that application of the criterion introduces the risk of BRS bias (overestimation).