Regional deformation and deformation rates (TDI and 2DSE) are reduced in the basal RV segment in athletes. This phenomenon is most pronounced in athletes with RV dilatation and should be interpreted as normal when evaluating athletes suspected for RV pathology.

OBJECTIVE -Data on the prevalence of abnormal gastric emptying in diabetic patients are still lacking. The relation between gastric emptying and dyspeptic symptoms assessed during gastric emptying measurement has not yet been investigated. The aim was to investigate the prevalence of delayed gastric emptying in a large cohort of unselected diabetic patients and to investigate the relation between gastric emptying and gastrointestinal sensations experienced in the 2 weeks before and during the test meal, prospectively.RESEARCH DESIGN AND METHODS -Gastric emptying was evaluated in 186 patients (106 with type 1 diabetes, mean duration of diabetes 11.6 Ϯ 11.3 years) using 100 mg 13 C-enriched octanoic acid added to a solid meal.RESULTS -Gastric emptying was significantly slower in the diabetic subjects than in the healthy volunteers (T 50 : 99.5 Ϯ 35.4 vs. 76.8 Ϯ 21.4 min, P Ͻ 0.003; Ret 120 min : 30.6 Ϯ 17.2 vs. 20.4 Ϯ 9.7%, P Ͻ 0.006). Delayed gastric emptying was observed in 51 (28%) diabetic subjects. The sensations experienced in the 2 weeks before the test were weakly correlated with the sensation scored during the gastric emptying test. Sensations assessed during the gastric emptying test did predict gastric emptying to some extent (r ϭ 0.46, P Ͻ 0.0001), whereas sensations experienced in the previous 2 weeks did not.CONCLUSIONS -This prospective study shows that delayed gastric emptying can be observed in 28% of unselected patients with diabetes. Upper gastrointestinal sensations scored during the gastric emptying tests do predict the rate of gastric emptying to some extent and sensation experienced during daily life does not. Diabetes Care 26:3116 -3122, 2003T he prevalence of delayed gastric emptying in patients with diabetes has been subject to debate for several decades. Cross-sectional studies using scintigraphic techniques to measure gastric emptying have shown delayed gastric emptying in patients with diabetes varying from 30 to 60% (1-11). However, there are several important limitations to these studies. First, the vast majority of these studies have been performed in small numbers of patients or in selected patients, which may account for the high percentage of patients showing delayed gastric emptying in some of these studies. Second, none of these studies has been performed during relative euglycemic conditions, whereas recent studies have provided evidence that hyperglycemia has a substantial effect on the rate of gastric emptying (12,13). After taking the aforementioned into account, the prevalence of delayed gastric emptying in diabetic patients who are not selected for gastrointestinal symptoms has yet to be determined.Previous studies have reported a weak association between gastric emptying and upper gastrointestinal symptoms experienced by patients in the period preceding the gastric emptying test, with the exception of the study performed by Jones et al. (10). They studied a large cohort of diabetic subjects over a period Ͼ10 years and reported that abdominal bloating and fullness were as...

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To correct for confounding, the method of instrumental variables (IV) has been proposed. Its use in medical literature is still rather limited because of unfamiliarity or inapplicability. By introducing the method in a nontechnical way, we show that IV in a linear model is quite easy to understand and easy to apply once an appropriate instrumental variable has been identified. We also point out some limitations of the IV estimator when the instrumental variable is only weakly correlated with the exposure. The IV estimator will be imprecise (large standard error), biased when sample size is small, and biased in large samples when one of the assumptions is only slightly violated. For these reasons, it is advised to use an IV that is strongly correlated with exposure. However, we further show that under the assumptions required for the validity of the method, this correlation between IV and exposure is limited. Its maximum is low when confounding is strong, such as in case of confounding by indication. Finally, we show that in a study in which strong confounding is to be expected and an IV has been used that is moderately or strongly related to exposure, it is likely that the assumptions of IV are violated, resulting in a biased effect estimate. We conclude that instrumental variables can be useful in case of moderate confounding but are less useful when strong confounding exists, because strong instruments cannot be found and assumptions will be easily violated.

Propensity score methods give in general treatment effect estimates that are closer to the true marginal treatment effect than a logistic regression model in which all confounders are modelled.