Sažetak
In many terrestrial and aquatic mammals, including humans, spleen contains a significant volume of a thick blood, which is partly released to active circulation during increased physical activity or diving. However, human spleen con-tains relatively few adrenergic fibers and it was suggested that spleen volume changes following an increase in sym-pathetic activity represent a passive collapse, secondary to reduced splenic arterial blood flow, rather than active contraction (Allsop et al). We tested this hypothesis in apnea diving by measuring the diving induced changes in spleen volume, arterial inflow and venous outflow. Three trained apnea divers underwent a single simulated apnea dive with face immersion in cold water, lasting 150 seconds. The spleen volume and blood flows were measured ultrasonographically at baseline, during apnea, and after apnea, up to the full recovery of spleen volume. Heart rate and arterial oxygen saturation were measured with pulse oximetry. We have shown that in simulated apnea diving reduction of spleen volume is fast and in presence of conserved flow in the splenic artery, which rules out the possibility of passive collapse. The spleen contracts immediately upon the onset of apnea, in parallel with simultaneous increase in heart rate, when arterial blood gases are yet unaffected. This rapidity of the splenic response to apnea diving argues against peripheral triggers and favors the existence of the centrally mediated feed-forward mechanism.
