THE BLOOD PRESSURE REDUCTION AFTER GASTRIC BYPASS SURGERY IS EXPLAINED BY A DECREASE IN CARDIAC OUTPUT

Background: Blood pressure (BP) decreases in the first weeks after Roux-and-Y gastric bypass surgery. Yet, the pathophysiology of the BP lowering effects observed after gastric bypass surgery are incompletely understood. Methods: We evaluated BP, systemic hemodynamics and baroreflex sensitivity in 15 obese women (mean age 42±7 yrs, body mass index 45±6 kg/m²) two weeks before and six weeks following Roux-and-Y gastric bypass surgery. Results: Six weeks after gastric bypass surgery mean body weight decreased by 13±5 kg (10%, p<0.001). Office blood pressure (BP) decreased from 137±10/86±6 to 128±12/81±9 mmHg (p<0.001, p<0.01), while daytime ambulatory BP decreased from 128±14/80±9 to 114±10/73±6 mmHg (p=0.01, p=0.05), whereas night-time BP decreased from 111±13/66±7 to 102±9/62±7 mmHg (p=0.04, p<0.01). The decrease in BP was associated with a 1.6±1.2 L/min (20%, p<0.01) decrease in cardiac output (CO), while systemic vascular resistance increased (153±189 dyn.s/cm⁵, 15%, p<0.01). The maximal rise in systolic blood pressure decreased (192 mmHg/s, 19%, p=0.01), suggesting a reduction in left ventricular contractility. Baroreflex sensitivity increased from 9.0 [6.4-14.3] to 13.8 [8.5-19.0] ms·mmHg^-1 (median [IQR]; p<0.01) and was inversely correlated with the reductions in heart rate (R= -0.64, p=0.02) and CO (R= -0.61, p=0.03). In contrast, changes in body weight were not correlated with changes in either BP or CO. Conclusions: The BP reduction following Roux-and-Y gastric bypass surgery is correlated with a decrease in CO independent of changes in body weight. The contribution of heart rate to the reduction in CO together with enhanced baroreflex sensitivity suggests a shift towards increased parasympathetic cardiovascular control.

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