Impact of Gravity on Cardiac Hemodynamics

Gravitational force affects both the cardiac mass and the thoracic compartment. However, few studies in humans have explored whether the relationship between cardiac function and load-dependence varies according to the orientation of the heart in space (e.g. between the upright and supine positions) and therefore according to gravitational stress.

Thirty-two volunteers (16 healthy subjects and 16 subjects with type I diabetes) will be included in the study. Each subject will be analysed over half a day in the Inserm COMETE laboratory. Measurements of the intra-cardiac hydrostatic pressure gradient (reflecting gravitational force) and indicators of cardiac function will be analysed by transthoracic echocardiography using dedicated post-processing software. These measurements will be compared at identical pre-load on the basis of the relationship between thoracic impedance and angle of vertical inclination using a Tilt Test on the one hand and between thoracic impedance and Lower Body Negative Pressure (LBNP) depression in the supine position on the other. In the supine position, the echocardiogram will be repeated for each subject with different levels of intensity of preload decrease by LBNP up to a maximum of -50 torr, and compared with different angles of vertical inclination head up up to +80° on the Tilt Test.

The study aims to compare the contribution of intra-cardiac hydrostatic force to cardiac filling and ejection mechanics in a population of healthy volunteers and subjects with diabetes.

The goal is to define and compare the pre-load dependence of the cardiac function indices studied according to the anatomical supine posture with zero intra-cardiac hydrostatic gradient with the standing posture during which the hydrostatic force is expressed between the cardiac base and apex. The hypothesis is that cardiac filling and ejection are improved when the longitudinal axis of the heart is anatomically oriented in the standing position compared with the supine position, by restoring the intraventricular hydrostatic pressure gradient. Comparing a group of healthy subjects with a group of subjects with diabetes will enable to assess whether the dependence of cardiac function on the orientation of the heart in space is more marked in the presence of subclinical impairment of myocardial function.

Inclusion criteria

• Affiliated to the social security system
• Patient informed of the study and having signed an informed consent form
• Type 1 diabetes for at least 10 years followed at Caen University Hospital, equipped with a continous glucose monitoring system

Exclusion criteria

• Trained athletes (≥ 6 hours of sustained physical exercise >70% VO2max per week for > 6 months)
• Chronic cardiovascular disease or cardiovascular treatment
• Personal history of chemotherapy and/or thoracic radiotherapy
• Cerebral and/or spinal disease
• Inclusion of the subject in another biomedical research protocol of interventional type (during the study or in the 3 months prior to inclusion)
• Pregnant, breast-feeding or parturient women
• Adults under legal protection (guardianship, curators) or unable to express their consent or deprived of their freedom