Noninvasive index of cardiac contractility during stress testing: a collaborative study

Area of Science:

• Cardiology
• Exercise Physiology

Background:

• The first heart sound (S1) amplitude correlates with left ventricular pressure acceleration.
• Catecholamines influence both left ventricular pressure and S1 amplitude.
• Exercise induces catecholamine secretion and sympathetic reflexes.

Purpose of the Study:

• To investigate changes in S1 amplitude during physical exertion in healthy young adults.
• To assess the reliability of S1 amplitude as an indicator of cardiac contractility during exercise.

Main Methods:

• Simultaneous recordings of blood pressure, heart rate, electrocardiograph, and phonocardiograph in 34 subjects.
• Cardiac output measurement using impedance cardiography in 10 subjects.
• Standardized exercise protocols to induce varying levels of exertion.

Main Results:

• S1 amplitude routinely increased 4-5 times above baseline during exercise, with some subjects showing up to a 15-fold increase.
• The extent of S1 increase generally correlated with exercise intensity and duration, as well as other physiological parameters.
• Observed variations in S1 response were attributed to complex hormonal and neural influences and differential receptor activation.

Conclusions:

• S1 amplitude serves as a dependable index for monitoring cardiac contractility shifts during exercise.
• The study recommends incorporating S1 amplitude measurement into routine stress testing protocols alongside other physiological parameters.