ORIGINAL ARTICLES   

The Journal of Sports Medicine and Physical Fitness 1998 June;38(2):158-63

Copyright © 1998 EDIZIONI MINERVA MEDICA

language: English

Prolonged exercise alters cardiac chronotropic responsiveness in endurance athletes

Douglas P. S. ¹, O’Toole M. L. ², Katz S. E. ¹

¹ Cardiovascular Division, Beth Israel Deaconess Medical Center, Harvard Medical School, Harvard-Thorndike Laboratory, 330 Brookline Avenue, Boston, MA 02215, USA; ² Department of Orthopaedic Surgery, University of Tennessee, Memphis, USA

Objective. To deter­mine wheth­er exhaus­tive exer­cise ­alters car­diac adre­ner­gic chron­o­trop­ic respon­sive­ness in endu­rance-­trained ath­letes.
Methods. Fifteen ath­letes ­were stud­ied pros­pec­tive­ly 2-4 ­days ­before and with­in 3.3 ­hours ­after com­plet­ing the Hawaii Ironman Triathlon (3.9 km ­swim, 180.2 km ­bike, 24.2 km run). Increasing intra­ve­nous bolus­es of iso­pro­ter­e­nol ­were giv­en ­until the ­rise in ­heart ­rate was >30 bpm (n=3-6 dos­es). A log ­dose ­heart ­rate ­response ­curve was con­struct­ed, and the ­dose ­required to ­increase ­heart ­rate by 15 and 25 bpm esti­mat­ed. Left ven­tric­u­lar ­size and func­tion ­were ­also ­assessed by ech­o­car­di­og­ra­phy.
Results. After ­race fin­ish, ­left ven­tric­u­lar vol­ume (98 vs 83 cc), ejec­tion frac­tion (56 vs 46%) and dia­stol­ic fill­ing ­rate (3.86 vs 3.12 edv/sec) ­were ­reduced (all p<0.01). Resting ­heart ­rate ­rose ­from 54±7 bpm to 70±10 bpm. The iso­pro­ter­e­nol ­dose ­required to ­increase ­heart ­rate by 15 bpm ­rose ­from 0.6 to 1.7 μg and by 25 bpm ­rose ­from 1.8 to 4.0 μg, ­both p<0.01. The lin­e­ar rela­tion­ship ­between ­change in ­heart ­rate and log iso­pro­ter­e­nol ­dose was pre­served.
Conclusions. Cardiac chron­o­trop­ic respon­sive­ness is ­reduced fol­low­ing an Ironman tri­ath­lon.