Cardiac performance in humans during breath holding

Area of Science:

• Physiology
• Cardiovascular Research
• Diving Science

Background:

• Breath-hold diving involves voluntary cessation of breathing, impacting cardiovascular function.
• Intrathoracic pressure changes during breath-holding can influence cardiac performance.
• The diving response, including circulatory adjustments, is complex and influenced by factors like lung volume and water temperature.

Purpose of the Study:

• To investigate the effects of high and low intrathoracic pressures from breath-holding at large and small lung volumes on cardiac performance.
• To differentiate the effects of breath-holding maneuvers from the cold-induced diving response.

Main Methods:

• Cardiac index and systolic time intervals were measured using impedance cardiography in six resting subjects.
• Measurements were taken under both nonimmersed and immersed conditions in a thermoneutral environment (air 28°C, water 35°C).
• Subjects performed breath-holding at large and small lung volumes.

Main Results:

• Cardiac performance was enhanced during immersion compared to nonimmersion.
• Breath-holding at a large lung volume significantly depressed cardiac performance.
• This depression was evidenced by a decrease in cardiac index (24.1% immersed, 20.9% nonimmersed) and altered systolic time intervals (shortened ejection time, lengthened pre-ejection period).

Conclusions:

• In a thermoneutral environment, breath-holding at large lung volumes, typical for breath-hold divers, tends to reduce cardiac performance.
• This reduction in cardiac performance is likely due to impeded venous return caused by high intrathoracic pressure.
• These findings help isolate the mechanical effects of breath-holding from the physiological diving response.