Cardiovascular adaptation to prolonged in air inspiratory apnea: a cardiac magnetic resonance study in healthy diving athletes

Background: cardiovascular adaptation to extreme acute hypoxemia has been poorly investigated mainly because of lacking technology for assessing cardiac morphology and function during hypoxic stress. Aim: to assess the adaptation of the cardiovascular system to acute hypoxia by the use of cardiac magnetic resonance in healthy diving athletes during maximal in air inspiratory apnea. Methods: 10 male volunteers diving athletes (age 30±6 years) were studied at rest and at peak apnea. O2 saturation (SaO2), heart rate (HR), systolic (S) and diastolic (D) blood pressure (BP), end-diastolic (ED) and end-systolic (ES) left ventricular volumes (LVV), LV ejection fraction (EF), LV stroke volume (SV) and LV systolic wall thickening (SWT) were evaluated. Derived parameters were: systemic vascular resistance (SVR) and SBP/ESLVVratio. Results: The mean apnea time was 215±40 sec. The values of the variables are shown in the table. There was a significant correlation between SaO2 and EDV (R2 0.33, p0.008) and ESV (R2 0.46, p0.001). SBP/ESLVV and LVSWT, indices of global and regional myocardial contractility, showed a marked reduction in systolic function. However, the latter effect as well as increased after-load (DBP) did not impair LVSV thanks to the marked increase in LV pre-load. Conclusion: during prolonged apnea in healthy diving athletes a marked enlargement of the LV chamber occurs. This adaptation allows SV and BP to be maintained in spite of the severe reduction in LV contractile function