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UBC Theses and Dissertations

Left ventricular twisting mechanics during incremental exercise : the influence of aerobic fitness and venous return Drury, Chipman Taylor


The role left ventricular (LV) twisting mechanics play in the stroke volume response to incremental exercise is unknown. Furthermore, the influences of aerobic fitness and venous return on LV twisting mechanics during vigorous exercise have not been investigated previously. To examine this issue, LV twisting mechanics and haemodynamics were assessed in eight endurance-trained (VO₂ max = 68.1 ± 5.6 mL∙kg⁻¹∙min⁻¹) and eight normally active (VO₂ max = 50.1 ± 5 mL∙kg⁻¹∙min⁻¹) males during incremental upright and supine exercise at rest and during heart rates of 110, 130, 150, and 170 bpm. LV twisting mechanics were measured via echocardiography, while haemodynamic measures were collected using impedance cardiography. During both incremental protocols, cardiac output increased continuously in both groups. Stroke volume (SV) and end-diastolic volume increased to a greater extent in endurance-trained athletes compared to normally active individuals during exercise in both postural positions (e.g., SV at 170 bpm supine: ET, 45%; NA, 30.5%; SV at 170 upright: ET, 44.7%; NA, 33.8%; p < 0.05). No differences in the response of LV twisting mechanics to incremental exercise in either posture existed between groups. During supine exercise, SV and LV systolic and diastolic twisting mechanics reached a plateau during sub-maximal exercise (110 – 150 bpm). During upright exercise, LV systolic twisting mechanics increased with each exercise stage until maximum, while LV diastolic twisting mechanics plateaued at approximately 110 bpm. These results indicate that aerobic fitness has minimal influence on LV twisting mechanics during exercise, while changes in cardiac loading resulting from changes in posture have a significant effect. It appears that at higher intensity exercise, LV twisting mechanics play a reduced role in maintaining cardiac function as compared to low to moderate intensity exercise, regardless of aerobic fitness and venous return

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