Ambulatory heart rate is underestimated when measured by an ambulatory blood pressure device

Objective To test the validity of ambulatory heart rate (HR) assessment wit h a cuff ambulatory blood pressure (ABP) monitor. Design Cross-instrument comparison of HR measured intermittently by a cuff ABP monitor (SpaceLabs, Redmond, Washington, USA), with HR derived from con tinuous electrocardiogram (ECG) recordings (1) in a controlled laboratory e xperiment and (2) during long-term recording in a true naturalistic setting . Participants Six normotensive subjects participated in the laboratory study . A total of 109 male white-collar workers underwent ambulatory monitoring, of which 30 were mildly hypertensive. Methods Four different laboratory conditions (postures: lying, sitting, sta nding, walking), repeated twice, were used to assess the short-term effects of cuff inflation on the HR, To test the actual ambulatory validity, parti cipants simultaneously wore a continuous HR recorder and the ABP monitor fr om early morning to late evening on 2 workdays and one non-workday. Diary a nd vertical accelerometery information was used to obtain periods of fixed posture and (physical) activity across which HR from both devices was compa red, Results. Laboratory results showed that the ABP device reliably detected HR during blood pressure measurement, but that this HR was systematically low er than the HR directly before and after the blood pressure measurement, Th e ambulatory study confirmed this systematic underestimation of the ongoing HR, but additionally showed that its amount increased when subjects went f rom sitting to standing to light physical activity (2.9; 4.3 and 9.1 bpm (b eats/min), respectively). In spite of this activity-dependent underestimati on of HR, the correlation of continuous ECG and intermittent ABP-derived HR was high (median r = 0.81). Also, underestimation was not different for no rmotensives and mild hypertensives. Conclusions A direct effect of cuff inflation leads to the underestimation of ongoing HR during cuff-based ABP measurement. Additional underestimation of HR occurs during periods with physical activity, probably due to behavi oural freezing during blood pressure measurements. HR underestimation was n ot affected by hypertensive state. When its limitations are taken into acco unt, ABP-derived ambulatory HR can be considered a reliable and valid measu re. (C) 2001 Lippincott Williams & Wilkins.