Systolic and Diastolic Functions After a Brief Acute Bout of Mild Exercise in Normobaric Hypoxia

Abstract

Acute hypoxia (AH) is a challenge to the homeostasis of the cardiovascular system, especially during exercise. Research in this area is scarce. We aimed to ascertain whether echocardiographic, Doppler, and tissue Doppler measures were able to detect changes in systolic and diastolic functions during the recovery after mild exercise in AH. Twelve healthy males (age 33.5 ± 4.8 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (W_max). On separate days, participants performed randomly assigned two exercise sessions consisting in 3 min pedalling at 30% of W_max: (1) one test was conducted in normoxia (NORMO) and (2) one in normobaric hypoxia with FiO₂ set to 13.5% (HYPO). Hemodynamics were assessed with an echocardiographic system. The main result was that the HYPO session increased parameters related to myocardial contractility such as pre-ejection period and systolic myocardial velocity with respect to the NORMO test. Moreover, the HYPO test enhanced early transmitral filling peak velocities. No effects were detected for left ventricular volumes, as end-diastolic, end-systolic, and stroke volume were similar between the NORMO and the HYPO test. Results of the present investigation support the hypothesis that a brief, mild exercise bout in acute normobaric hypoxia does not impair systolic or diastolic functions. Rather, it appears that stroke volume is well preserved and that systolic and early diastolic functions are enhanced by exercise in hypoxia.

Keywords: blood pressure; cardiac pre-load; echocardiography; myocardial contractility; tissue Doppler.

Figure 1

Scatter plot graphs of levels of blood O₂ saturation (SO₂, panel A), heart rate (HR, panel B), mean arterial pressure (MAP, panel C), pre-ejection period (PEP, panel D), ventricular ejection time (VET, panel E), and diastolic time (DT, panel F) during the recovery from sessions of exercise in normoxia (NORMO) and in normobaric hypoxia with a FiO₂ of 13.5% (HYPO). N = 12. *p < 0.05 vs. NORMO test.

Figure 2

Scatter plot graphs of levels of end-systolic volume (ESV, panel A), end-diastolic volume (EDV, panel B), ejection fraction (EF, panel C), and stroke volume (SV, panel D) during the recovery from sessions of exercise in normoxia (NORMO) and in normobaric hypoxia with a FiO₂ of 13.5% (HYPO). N = 12.

Figure 3

Scatter plot graphs of levels of early transmitral filling peak velocity (Evel, panel A), late transmitral filling peak velocity (Avel, panel B), their ratio (E/A, panel C), and early diastolic mitral valve motion velocity (Em, panel D) during the recovery from sessions of exercise in normoxia (NORMO) and in normobaric hypoxia with a FiO₂ of 13.5% (HYPO). N = 12. *p < 0.05 vs. NORMO test.

Figure 4

Scatter plot graphs of levels of late diastolic mitral valve motion velocity (Am, panel A), ratio between early and late diastolic mitral valve motion velocities (Em/Am, panel B), systolic myocardial velocity (Sm, panel C), and ratio between early transmitral filling peak and early mitral valve diastolic velocities (Evel/Em, panel D) during the recovery from sessions of exercise in normoxia (NORMO) and in normobaric hypoxia with a FiO₂ of 13.5% (HYPO). N = 12. *p < 0.05 vs. NORMO test.