EXPERIMENTAL ACUTE-HYPOXIA IN HEALTHY-SUBJECTS - EVALUATION OF SYSTOLIC AND DIASTOLIC FUNCTION OF THE LEFT-VENTRICLE AT REST AND DURING EXERCISE USING ECHOCARDIOGRAPHY

To clarify whether or not systolic and diastolic function of the human left ventricle (LV) were decreased during acute hypoxia, at rest and with exercise, 14 healthy male volunteers [age 25.9 (SD 3.0) years, he ight 182.9 (SD7.1) cm, body mass 75.9 (SD 6.9)kg] were examined using M-mode and 2D-mode echocardiography to determine the systolic LV funct ion as well as Doppler-echocardiography for the assessment of diastoli c LV function on 2 separate test days. In random order, the subjects b reathed either air on 1 day (N) or a gas mixture with reduced oxygen c ontent on the other (H; oxygen fraction in inspired gas 0.14). Measure ments on either day were made at rest, several times during incrementa l cycle exercise in a supine position (6-min increments of 50 W, maxim al load 150 W) and in 6th min of recovery. Corresponding measurements during N and H were compared statistically. Arterial O-2 tension (PaO2 ) was normal on N-day. All subjects showed a marked acute hypoxia at r est [PaO2, 54.5 (SD 4.6) mmHg], during exercise and recovery on N-day. The latter was associated with tachycardia compared to N-day. All ech ocardiographic measurements at rest were within the limits of normal v alues on both test days. Ejection time, end-systolic and end-diastolic left ventricular dimensions as well as the thickness of left posterio r wall and of interventricular septum showed no statistically signific ant influence of H either at rest or during exercise. Stroke volume an d cardiac output were always higher on H-day, which could be attribute d to a slight reduction in end-systolic volume with unaffected end-dia stolic volume as well as to increased heart rates. Among the indices o f systolic LV function the fractions of thickening in the left ventric ular posterior wall and interventricular septum showed no differences between H and N at rest or during exercise. However, fibre shortening, ejection fraction and mean circumferential fibre shortening were incr eased on H-day on all occasions. The mitral-valve-Doppler ratio, the i ndex of diastolic LV function, was decreased with H at rest, showed a more pronounced reduction during exercise and was still lower in 6th m in of recovery compared to N-day. It was concluded that with acute hyp oxia of the severity applied in this study left ventricular systolic f unction in our healthy subjects showed a pronounced improvement and le ft ventricular diastolic function was reduced, both at rest and with e xercise.