Spleen and cardiovascular function during short apneas in divers

Area of Science:

• Cardiovascular Physiology
• Respiratory Physiology
• Diving Medicine

Background:

• The spleen acts as a reservoir for red blood cells, influencing cardiovascular dynamics.
• Short-duration apneas trigger physiological responses, including cardiovascular adjustments.
• The interplay between splenic volume, cardiovascular changes, and respiratory maneuvers is not fully understood.

Purpose of the Study:

• To investigate spleen volume changes during short apneas.
• To correlate splenic responses with cardiovascular changes (heart rate, arterial pressure, cardiac output).
• To explore the roles of baroreflex and lung volume in modulating these responses.

Main Methods:

• Dynamic ultrasound imaging for spleen volume assessment.
• Noninvasive photoplethysmography for cardiovascular measurements.
• Short apneas (15-20s) at rest in trained divers.
• Pharmacological baroreflex manipulation (trinitrosan) and lung volume variations (maximal vs. tidal) with cold stimulation.

Main Results:

• A 20% spleen volume reduction occurred within 3s of apnea onset at maximal lung volume, accompanied by increased heart rate, decreased mean arterial pressure (89.6 to 66.7 mmHg), and reduced cardiac output.
• Trinitrosan administration decreased mean arterial pressure by ~6 mmHg and splenic volume by ~13%.
• At low lung volume, spleen contraction (10-12%) was observed, with mean arterial pressure unchanged or increased (with cold stimulation).

Conclusions:

• Spleen contraction is an early event during apnea, enhanced by cold forehead stimulation.
• At high lung volumes, initial spleen contraction may be facilitated by baroreflex unloading during decreased blood pressure and cardiac output.
• Lung volume significantly influences the relationship between apnea, spleen contraction, and cardiovascular responses.