Increased pulmonary vascular resistance and reduced stroke volume in association with CO2 retention and inferior vena cava dilatation

Increased pulmonary vascular resistance and reduced stroke volume in association with CO2 retention and inferior vena cava dilatation. J Appl Physiol 101: 866-872, 2006. First published May 25, 2006; doi: 10.1152/japplphysiol.00759.2005.-Changes in cardiovascular parameters elicited during a maximal breath hold are well described. However, the impact of consecutive maximal breath holds on central hemodynamics in the postapneic period is unknown. Eight trained apnea divers and eight control subjects performed five successive maximal apneas, separated by a 2-min resting interval, with face immersion in cold water. Ultrasound examinations of inferior vena cava (IVC) and the heart were carried out at times 0, 10, 20, 40, and 60 min after the last apnea. The arterial oxygen saturation level and blood pressure, heart rate, and transcutaneous partial pressures of CO2 and O-2 were monitored continuously. At 20 min after breath holds, IVC diameter increased (27.6 and 16.8% for apnea divers and controls, respectively). Subsequently, pulmonary vascular resistance increased and cardiac output decreased both in apnea divers (62.8 and 21.4%, respectively) and the control group (74.6 and 17.8%, respectively). Cardiac output decrements were due to reductions in stroke volumes in the presence of reduced end-diastolic ventricular volumes. Transcutaneous partial pressure of CO2 increased in all participants during breath holding, returned to baseline between apneas, but remained slightly elevated during the postdive observation period (similar to 4.5%). Thus increased right ventricular afterload and decreased cardiac output were associated with CO2 retention and signs of peripheralization of blood volume. These results indicate that repeated apneas may cause prolonged hemodynamic changes after resumption of normal breathing, which may suggest what happens in sleep apnea syndrome.