Impact of Weight Loss After a Bypass Surgery on Renal Hemodynamic Under Stress Conditions
Condition: Obesity; Bariatric Surgery; Blood Pressure
MeSH terms: Weight Loss
Study type: Observational [Patient Registry]

Summary: 
      The sympathetic nervous (SNS) and the renin angiotensin aldosterone system (RAS) have a
      direct impact on renal hemodynamic, hormonal secretion and vasoactive peptide. Many
      mechanisms including the SNS, RAS and renal sodium handling could explain the pathogenesis of
      hypertension in obese patients. Lifestyle changes and bariatric surgery induce weight loss,
      which is associated with blood pressure lowering in obese patients. A diminution in the renal
      sympathetic stimulation and RAS activation could explain this effect.

      The AIM of this study is to show that weight loss induced by bypass surgery in obese patients
      affects renal salt excretion under " low body negative pressure (LBNP)" conditions .

      Secondary objectives are to investigate the impact of weight loss on renal hemodynamic
      (glomerular filtration rate (GFR), renal plasma flow) and neurohormonal responses under " low
      body negative pressure conditions ". We will also analyse renal blood oxygenation with Blood
      Oxygenation dependant IRM (BOLD-IRM) technique before and after weight loss.

      The population of this study will consist in two groups including 36 patients. The first one
      will include 24 obese patients that are going to undergo a bariatric surgery. The second one
      will include 12 obese patients without any weight loss associated surgery.

      Both group will undergo 3 investigation days. Each patient will have to undergo a screening
      visit that will provide dietary advice to ensure a standardized salt intake (120-180
      mmol/day) for the duration of the study. The first investigation will define baseline, the
      second and third day of investigation will take place after 3 month and 12 month after
      bariatric surgery for surgical patients or after baseline for patients without surgery. One
      to two weeks before phase 1 and 3 patients will perform a BOLD-MRI. The surgery group will
      undergo bariatric surgery between the first investigation phase (baseline) and the second. An
      ambulatory blood pressure and 24-hour urine collection will precede each investigation day.
      An investigation day consists in renal hemodynamics, neurohormonal and natriuretic response
      measurements before, during and after 60 min of LBNP at -30mbar . The duration of the study
      per subject is going to take 12 months.
    


Intervention name(s): bariatric surgery (gastric bypass)
Intervention type(s): Procedure
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Patient will briefly be informed about the study during their follow-up at the obesity
        consultation (Medical Universitary Polyclinic) and the they will be recruited at the
        Nephrology center in CHUV (Lausanne).
      
Keywords: Blood pressure; Obesity; Glomerular filtration rate; Renal Sodium handling