title: Bell-shaped relationship between central blood volume and spontaneous baroreflex function.
abstract: Spontaneous baroreflex function can be altered by acute changes in central blood volume. Both a reduction in spontaneous baroreflex function at central hypovolemia and augmentation at hypervolemia suggest a dose-effect relationship between central blood volume and spontaneous baroreflex function. However, this relationship has not been quantified over stepwise widespread changes in central blood volume. Twelve individuals underwent central hypovolemia at two levels of lower body negative pressure (LBNP) (-15 mm Hg, LBNP15; -30 mm Hg, LBNP30) and hypervolemia with two discrete infusions of normal saline (NS) (15 ml kg(-1), NS15; total 30 ml kg(-1), NS30). Spontaneous baroreflex function was assessed using transfer function analysis and the sequence method between blood pressure and R-R interval. Both central venous pressure (-0.6-7.9 mm Hg) and left ventricular end-diastolic volume (72.4-133.1 ml) decreased during LBNP and increased after saline infusion. Both spontaneous baroreflex indices of high-frequency transfer function gain (LBNP30, 17.4+/-3.2; LBNP15, 22.3+/-3.8; baseline, 25.6+/-4.1; NS15, 28.5+/-4.2 ms mm Hg(-1), ANOVA P=0.001) and of the sequence slope (LBNP30, 14.4+/-2.2; LBNP15, 17.2+/-2.5; baseline, 20.5+/-2.8; NS15, 24.5+/-3.1 ms mm Hg(-1), ANOVA P=0.001) increased stepwise from hypovolemia of LBNP30 to hypervolemia of NS15. However, these indices were lower at NS30 (high-frequency transfer function gain, 22.0+/-2.2 ms mm Hg(-1), post-hoc P=0.071; sequence slope, 17.7+/-1.7 ms mm Hg(-1), post-hoc P<0.05) than NS15 during hypervolemia. These results indicated that the relationship between central blood volume and spontaneous baroreflex function is apparently bell-shaped, with maximal augmentation at moderate hypervolemia.
authors.affiliation: Department of Social Medicine, Division of Hygiene, Nihon University School of Medicine, Tokyo 173-8610, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Saitoh
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Ken
authors.initials: K
authors.lastname: Aoki
authors.forename: Shigeki
authors.initials: S
authors.lastname: Shibata
authors.forename: Akira
authors.initials: A
authors.lastname: Otsubo
authors.forename: Jitsu
authors.initials: J
authors.lastname: Kato
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Iwasaki
mesh_terms: D000704:Analysis of Variance; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D001810:Blood Volume / Q000187:drug effects / Q000502:physiology*; D001811:Blood Volume Determination / Q000379:methods; D002496:Central Venous Pressure / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D020896:Hypovolemia / Q000503:physiopathology*; D007275:Injections, Intravenous; D008150:Lower Body Negative Pressure / Q000379:methods; D008297:Male; D012965:Sodium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D013318:Stroke Volume / Q000187:drug effects / Q000502:physiology; D016683:Supine Position / Q000502:physiology; D055815:Young Adult
chemical_list: D012965:Sodium Chloride