| الوصف: |
Impact of repeated breath-holds on cardiac output and venous blood flow remains controversial. We hypothesized that CO2 retention after series of apneas can dilate veins, reduce venous return and decrease cardiac output. Eight trained apnea divers and eight control subjects performed 5 successive maximal apneas with face immersion in cold water, which were separated with 2 minutes intervals. Echocardiographic measurements were carried out instantaneously upon completion of last apnea, and at 10, 20, 40, and 60 minute during observation period. Transcutaneous partial pressure of CO2 and arterial pressure were continuously monitored and recorded on personal computer. Echocardiographic measurements show increase in vena cava diameter (37.5% and 11.6%, for apnea divers and controls, respectively) and decrease in vena cava flow (37.4% and 22.6%). Subsequently, there was a decrease in cardiac output in apnea diver (25%) and control group (18.7%). CO2 partial pressure increased in all participants during breath holding, returned to baseline in between apneas, but remained slightly elevated during observed post diving period. Arterial pressure increased during repeated apneas, but normalized quickly after last breath-hold. The results are showing that repeated apneas initiate venodilation, which can be explained by prolonged CO2 retention. Consequently we observed significant decrease in cardiac output. All responses were more pronounced in trained apnea diver compared to control subjects. Supported by Croatian Ministry of Science, Education and Sport measure |