Cardiac output during exercise measured by acetylene rebreathing, thermodilution, and Fick techniques

C. C W Hsia, L. F. Herazo, M. Ramanathan, R. L. Johnson

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


In dogs during exercise, respiratory rate can reach 200 breaths/min, blood temperature can exceed 42°C, and hematocrit can approach 60%. To determine whether these changes significantly affect the measurement of cardiac output by the acetylene rebreathing method (Q̇c(RB)), we compared estimates of Q̇c(RB) with those measured by thermodilution and Fick (Q̇c(FI)) techniques in nine dogs at rest and during steady-state exercise on a treadmill up to near-maximal workloads. Solubility of acetylene in blood was corrected to the simultaneously measured blood temperature and hematocrit. Results were also adjusted for mixing efficiency. Up to a Q̇c(FI) of 20 1/min, Q̇c(RB) was not significantly different from Q̇c(FI) (P > 0.05). However, cardiac output measured by thermodilution was consistently higher than those measured by the other techniques (P < 0.0001). We conclude that the overall agreement between Q̇c(RB) and Q̇c(FI) estimates supports the validity of the rebreathing technique under exercise conditions where body temperature and hematocrit are changing rapidly and the breathing pattern is unrestrained. Systematic error by the thermodilution technique may be related to a variety of methodological issues as well as possible dissipation of cooling into the myocardial tissue and subsequent incomplete washout.

Original languageEnglish (US)
Pages (from-to)1612-1616
Number of pages5
JournalJournal of applied physiology
Issue number4
StatePublished - 1995


  • acetylene
  • dog
  • hematocrit correction
  • mixing efficiency
  • pulmonary blood flow
  • temperature correction

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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