title: Heart rate increases linearly in response to acute isovolemic anemia.
abstract: BACKGROUND
  The cardiovascular response to acute isovolemic anemia in humans is thought to differ from that of other species. Studies of anesthetized humans have found either no change or a decreased heart rate. A previous study showed that in 32 healthy unmedicated humans, heart rate increased during acute isovolemic anemia. The hypothesis that heart rate in humans increases in response to acute isovolemic anemia and that the increase is affected by gender was tested.
  
  
  METHODS
  Acute isovolemic anemia to a Hb concentration of approximately 5 g per dL in 95 unmedicated healthy humans was produced by simultaneous withdrawal of blood and IV replacement with 5-percent HSA and autologous platelet-rich plasma. The relationship between heart rate and Hb concentration was examined using a mixed-effects linear regression model that allowed each person to have a fitted line with its own slope and intercept. Cubic and quadratic terms were added to determine if these improved the goodness of fit. The effect of gender was tested by including it and its interactions with Hb in the mixed model.
  
  
  RESULTS
  The relationship between heart rate and Hb concentration was linear (p < 0.001) and consistent among the population studied: heart rate = 116.0-4.0 [Hb] (slope 95% CI: -4.2 to -3.8 beats/min/g Hb). Adding a cubic or quadratic term did not significantly improve the goodness of fit of the mathematical expression to the data, confirming the linear nature of the relationship between heart rate and Hb concentration. For women, the slope of the heart rate response was significantly greater than it was for males (difference +/- SE: 0.70 +/- 0.23, p < 0.005).
  
  
  CONCLUSIONS
  In 95 unmedicated, healthy humans, heart rate was a linear function of Hb during acute isovolemic anemia. Females had a significantly greater slope of increase in heart rate with decreasing Hb concentration than did males. The relationship is consistent among individuals, is similar to that reported for conscious dogs, and differs from that found previously in anesthetized humans.
authors.affiliation: Department of Anesthesia, The Cardiovascular Research Institute, University of California, San Francisco, California 94122, USA. weiskopf@anesthesia.ucsf.edu
authors.forename: Richard B
authors.initials: RB
authors.lastname: Weiskopf
authors.forename: John
authors.initials: J
authors.lastname: Feiner
authors.forename: Harriet
authors.initials: H
authors.lastname: Hopf
authors.forename: Maurene K
authors.initials: MK
authors.lastname: Viele
authors.forename: Jessica J
authors.initials: JJ
authors.lastname: Watson
authors.forename: Jeremy
authors.initials: J
authors.lastname: Lieberman
authors.forename: Scott
authors.initials: S
authors.lastname: Kelley
authors.forename: Pearl
authors.initials: P
authors.lastname: Toy
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D000740:Anemia / Q000503:physiopathology*; D001810:Blood Volume; D002320:Cardiovascular Physiological Phenomena; D005260:Female; D006339:Heart Rate; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D012737:Sex Factors
chemical_list: D006454:Hemoglobins