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This Article Full Text Full Text (PDF) All Versions of this Article: 90/3/367    most recent expphysiol.2004.029496v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gulli, G. Articles by Hainsworth, R. Search for Related Content PubMed PubMed Citation Articles by Gulli, G. Articles by Hainsworth, R. Related Collections Cardiovascular control

¹ Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT

In addition to the gain, the time delay in the input–output response in a feedback system is crucial for the maintenance of its stability. Patients with posturally related (vasovagal) syncope have inadequate control of blood pressure and one possible explanation for this could be prolonged latency of the baroreflex. We studied 14 patients with histories of syncope and poor orthostatic tolerance (assessed by a progressive orthostatic stress test) and 16 healthy controls. We performed spontaneous sequence analysis of the fluctuations of R–R period (ECG) and systolic arterial pressure (SAP, Finapres) recorded during a 20 min supine period and during 20 min 60 deg head-up tilt (HUT). The baroreflex latency was determined by identifying the lag between the changes in SAP and in R–R interval from which the highest correlation coefficient was obtained. During the supine period, 74% of sequences in control subjects and 54% in patients occurred with zero beats of delay (i.e. R–R interval changed within the same R–R interval). The remaining sequences occurred with delays of up to four beats. HUT shifted the baroreflex delay to be approximately one heartbeat slower and again patients showed more sequences with prolonged response. The delay in heartbeats was transformed into delay in time. In control subjects, 75% of baroreflex responses occurred within 1 s. In patients, 75% of baroreflex responses took more than 2 s to occur. The results showed that syncopal patients with poor orthostatic tolerance have increased baroreflex latency. This may lead to instability and inadequate blood pressure control and may predispose to vasovagal syncope.

(Received 13 November 2004; accepted after revision 21 January 2005; first published online 21 January 2005)
Corresponding author G. Gulli: Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT. Email: giosuegulli{at}yahoo.it

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