title: Product of heart rate and first heart sound amplitude as an index of myocardial metabolic stress during graded exercise.
abstract: BACKGROUND
  The double product (DP) breakpoint of heart rate (HR) and systolic blood pressure has been identified as coincident with anaerobic threshold (AT), but there are no simple methods for measuring cardiac metabolic stress (CMS) during an exercise test. It was hypothesized that the DP of HR and the amplitude of the first heart sound (AHS1) (DP-AHS1) would reflect CMS, and thus, the breakpoint in the DP-AHS1 (DPBP-AHS1) could be an alternative method for determining AT.
  
  
  RESULTS
  Subjects (age range, 18-73 years) were recruited to perform a graded exercise test on a cycle ergometer with continuous monitoring of DP-AHS1, with left ventricular pressure (LVP; experiment 1, Ex1), plasma catecholamine and blood lactate (experiment 2, Ex2) and gas exchange (experiment 3, Ex3). Ex1: in all subjects there was a strong correlation between AHS1 and LVdP/dtmax (r=0.94-0.98), and between the DP-AHS1 and the triple product of HR, LVdP/dtmax, and max LVP (r=0.98-0.99). Ex2: DP-AHS1 was strongly correlated with adrenaline (r=0.97-1.00) and lactate (r=0.96-1.00) levels in all subjects. Ex3: there was a strong correlation between DPBP-AHS1, AT and maximum oxygen consumption.
  
  
  CONCLUSIONS
  The present simple measure of DP-AHS1 can reflect plasma adrenaline and lactate levels during graded exercise testing. Further, DPBP-AHS1 is a surrogate marker of AT and a good index of functional aerobic capacity.
authors.affiliation: Fukuoka University Institute for Physical Activity, Faculty of Sports and Health Science, Fukuoka University.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Takuro
authors.initials: T
authors.lastname: Matsuda
authors.forename: Takuro
authors.initials: T
authors.lastname: Tobina
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Yamada
authors.forename: Tamiharu
authors.initials: T
authors.lastname: Yamagishi
authors.forename: Hideaki
authors.initials: H
authors.lastname: Sakai
authors.forename: Shigeru
authors.initials: S
authors.lastname: Obara
authors.forename: Yasuki
authors.initials: Y
authors.lastname: Higaki
authors.forename: Akira
authors.initials: A
authors.lastname: Kiyonaga
authors.forename: Peter H
authors.initials: PH
authors.lastname: Brubaker
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D001794:Blood Pressure / Q000502:physiology*; D002395:Catecholamines / Q000097:blood; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006347:Heart Sounds / Q000502:physiology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D015415:Biomarkers; D002395:Catecholamines; D019344:Lactic Acid; D004837:Epinephrine