Coherence of cardiac output with rate changes

Area of Science:

• Cardiovascular Physiology
• Hemodynamics

Background:

• Heart rate (HR) influences cardiac output (CO) and stroke volume (SV).
• Circulatory regulators modify CO and SV as HR increases.
• The relationship between SV and HR (dSV/dHR) can characterize circulatory responses.

Purpose of the Study:

• To investigate the predictive capability of the SV-HR relationship (dSV/dHR) under diverse physiological conditions.
• To determine if a single dSV/dHR curve represents cardiac function across various states.
• To resolve apparent contradictions in the literature regarding cardiac output responses to heart rate changes.

Main Methods:

• Atrial pacing was used to increase heart rate in awake or lightly anesthetized dogs.
• The stroke volume-heart rate relationship (dSV/dHR) was analyzed.
• Responses were evaluated under conditions including different body positions, anesthesia, beta-adrenergic stimulation/depression, stellate ganglion/vagal stimulation, volume loading, aortic compression, and ventricular pacing.

Main Results:

• A single dSV/dHR curve consistently predicted circulatory responses to increasing HR across various conditions.
• This relationship appeared to be a fundamental expression of cardiac function.
• The dSV/dHR function demonstrated that higher stroke volumes at lower heart rates correlated with maximum cardiac output occurring at a higher heart rate.
• Specific interventions like stellate ganglion stimulation or ventricular pacing did not follow the same dSV/dHR function.

Conclusions:

• The SV-HR relationship (dSV/dHR) serves as a consistent indicator of cardiac function in response to heart rate changes.
• Understanding this relationship, including its arithmetic basis, clarifies previously contradictory findings in cardiovascular research.
• The dSV/dHR curve provides a unified framework for interpreting cardiac output dynamics under varied physiological circumstances.