title: Assessment of cardiac baroreflex function during fixed atrioventricular pacing using baroreceptor-stroke volume reflex sensitivity.
abstract: Baroreflex sensitivity in paced patients.
  
  
  BACKGROUND
  The baroreceptor-heart rate (HR) reflex has prognostic value in cardiovascular medicine. However, it cannot be used in chronotropically incompetent or paced patients. In healthy subjects, the baroreceptor-stroke volume (SV) reflex, with power spectral analysis of SV and blood pressure (BP) variations in the low-frequency band, serves as an alternate measure of the baroreceptor-cardiac reflex. This study examined the baroreceptor-stroke volume (SV) reflex sensitivity in the supine and 60 degrees upright positions in paced patients.
  
  
  RESULTS
  We studied 16 recipients of dual-chamber pacemakers paced at a fixed rate. The hemodynamics and baroreceptor-SV reflex sensitivity were measured during atrioventricular (AV) sequential pacing every 5 minute in the supine and 60 degrees upright positions. Mean SV decreased from 42.0+/-20.1 mL in the supine to 36.6+/-16.1 mL in the upright position (P<0.05), whereas BP and total peripheral resistance did not change. A significant fall in baroreceptor-SV reflex sensitivity from 29.2+/-18.0%/mmHg to 19.5+/-15.5%/mmHg was observed during upright tilt (P<0.005).
  
  
  CONCLUSIONS
  Fixed-rate AV sequential pacing did not blunt the decrease in baroreceptor-SV reflex sensitivity consistent with the arterial baroreflex gain response to upright posture. The decreased baroreceptor-SV reflex sensitivity occurring with the upright posture may reflect a baroreflex-induced inotropic effect secondary to vagal withdrawal and sympathetic activation.
authors.affiliation: First Department of Medical Technology, School of Health Sciences, University of Occupational and Environmental health, Kitakyushu, Japan.
authors.forename: Tomiya
authors.initials: T
authors.lastname: Yasumasu
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Abe
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Oginosawa
authors.forename: Kazuo
authors.initials: K
authors.lastname: Takahara
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Nakashima
mesh_terms: D000368:Aged; D001283:Atrioventricular Node / Q000503:physiopathology*; D017704:Baroreflex; D002304:Cardiac Pacing, Artificial; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D011311:Pressoreceptors / Q000503:physiopathology*; D012119:Respiration; D013318:Stroke Volume; D016683:Supine Position