Effect of Weight Loss on Myocardial Metabolism and Cardiac Relaxation in Obese Adults

Experimental: Diet

Participants who received counseling and instruction about weight loss through diet and exercise

Conductual: Diet

Participants attended 20 group behavioral modification sessions led by a behaviorist, a registered dietician, and a physical therapist. The meal plans ranged from 1200 to 1500 kilocalories per day, depending on subject sex and BMI, and were designed to achieve ≤1% body weight loss/week. Participants completed daily food records, and were taught a variety of weight management skills. The exercise component included strength, flexibility, balance, and endurance instruction, gradually increasing to 30 minutes of exercise 5 days/week.

Experimental: Gastric bypass surgery

Participants who received gastric bypass surgery

Procedimiento: Gastric bypass surgery

The same surgeon performed all bypass procedures using standard techniques. A small (~20 ml) proximal gastric pouch was created by stapling the stomach, and a 75-cm Roux-en-Y limb was constructed by transecting the jejunum distal to the ligament of Treitz, and creating a jejunojejunostomy 75 cm distal to the transection.

Total Myocardial Oxygen Consumption (MVO2)

The evening before an imaging study, all participants were given a meal containing 12 kcal/kg adjusted body weight (=ideal body weight + ((actual body weight-ideal body weight) x 0.25)). Participants fasted until their imaging studies were completed. Myocardial oxygen consumption (MVO2) was measured using positron emission tomography (PET) following injection of 1-^11C-acetate. Total MVO2 was calculated by multiplying the MVO2 measure by left ventricular weight.

Total Myocardial Fatty Acid (FA) Utilization

The evening before an imaging study, all participants were given a meal containing 12 kcal/kg adjusted body weight (=ideal body weight + ((actual body weight-ideal body weight) x 0.25)). Participants fasted until their imaging studies were completed. Myocardial blood flow was measured using positron emission tomography (PET) following injection of ^30O-water. Myocardial fatty acid (FA) utilization was measured using PET after injection of 1-^11C-palmitate. The calculations that describe the relationship between the different measures of myocardial FA metabolism are: FA utilization/gram = blood flow/gram × FA uptake/gram × [average plasma free FA at the time of the 1-11C-palmitate injection]; FA utilization/gram = FA oxidation/gram + esterification/gram. Total fatty acid utilization was calculated by multiplying the fatty acid utilization rate by left ventricular weight.

Total Myocardial Fatty Acid (FA) Oxidation

The evening before an imaging study, all participants were given a meal containing 12 kcal/kg adjusted body weight (=ideal body weight + ((actual body weight-ideal body weight) x 0.25)). Participants fasted until their imaging studies were completed. Myocardial fatty acid utilization was measured using positron emission tomography (PET) after injecting 1-^11C-palmitate. Total fatty acid oxidation was calculated by multiplying the fatty acid oxidation rate by left ventricular weight.

Left Ventricular (LV) Relaxation (E')

Immediately following MVO2 measurement, complete two-dimensional, M-mode, and Doppler echocardiographic studies were performed using second harmonic imaging. Left ventricular relaxation (E') was measured at the lateral annulus. All reported measurements represent the average of three consecutive cardiac cycles. A single investigator blinded to all clinical parameters evaluated all echocardiograms.

Septal Ratio (E/E')

Immediately following MVO2 measurement, complete two-dimensional, M-mode, and Doppler echocardiographic studies were performed using second harmonic imaging. The early diastolic (E) velocity was measured, left ventricular relaxation (E') was measured at the lateral mitral annulus, and the E/E'(septal) ratio was calculated. All reported measurements represent the average of three consecutive cardiac cycles. A single investigator blinded to all clinical parameters evaluated all echocardiograms. The normal septal ratio from the lateral mitral annulus is <5, a ratio from 5 to 10 is indeterminate, and a ratio of >10 indicates elevated left atrial pressure.

Left Ventricular (LV) Mass

Immediately following MVO2 measurement, complete two-dimensional, M-mode, and Doppler echocardiographic study were performed using second harmonic imaging. Left ventricular (LV) mass was measured using the area-length method. All reported measurements represent the average of three consecutive cardiac cycles. A single investigator blinded to all clinical parameters evaluated all echocardiograms.

Mean Heart Rate

Heart rate was measured at scheduled physical examinations.

Mean Arterial Pressure

Mean arterial pressure was measured at scheduled physical examinations.

Mean Body Mass Index

Participant weight and height was measured at scheduled physical examinations. Body mass index was calculated as participant body weight in kilograms divided by their height in meters squared.

Mean Total Serum Cholesterol and Triglycerides

Blood testing was conducted at scheduled times during the study. Serum cholesterol and triglycerides were measured by the enzymatic method (Roche Diagnostics).

Mean Homeostasis Model Assessment of Insulin Resistance

The homeostasis model assessment of insulin resistance (HOMA) was used to calculate insulin resistance using the first AM, fasting glucose and insulin levels. Plasma insulin levels were measured by radioimmunoassay, and glucose levels were measured by automated hexokinase assay. A HOMA score of <3 represents normal insulin resistance, a score between 3 and 5 moderate insulin resistance, and a score of 5 or higher represents severe insulin resistance.