Estimating exercise stroke volume from asymptotic oxygen pulse in humans

Area of Science:

• Cardiovascular Physiology
• Exercise Science
• Biomedical Engineering

Background:

• Noninvasive methods for estimating cardiac output (Q) during exercise often interfere with natural breathing and gas exchange.
• Existing techniques necessitate vascular cannulation, which is invasive.

Purpose of the Study:

• To test the hypothesis that exercise stroke volume (SV) and cardiac output (Q) can be accurately estimated from the response patterns of oxygen uptake (VO2) and heart rate (HR).
• To develop a nonintrusive method for assessing cardiovascular function during exercise.

Main Methods:

• Utilized the Fick equation and the concept of a constant product of Q and mixed venous O2 content during steady-state exercise.
• Derived a method to predict SV from the slope (S) of the linear VO2-HR relationship and arterial O2 content (CaO2).
• Validated the prediction against direct measurements in 23 healthy subjects undergoing incremental cycle ergometry.

Main Results:

• The predicted SV closely correlated with the directly measured SV (r = 0.80).
• Demonstrated that the oxygen pulse (O2-P) changes hyperbolically with HR, approaching an asymptote related to SV.
• Established that exercise SV can be estimated as approximately five times the slope (S) of the VO2-HR relationship in normal subjects.

Conclusions:

• Exercise stroke volume (SV) can be accurately estimated noninvasively using the linear relationship between oxygen uptake (VO2) and heart rate (HR).
• This simplified method provides a practical alternative to invasive techniques for assessing cardiac function during exercise.
• The findings support the use of VO2 and HR responses for estimating SV and cardiac output in healthy individuals.