To attenuate observer variability, an automated oscillometric (Dinamap) method was used for sitting systolic and you can diastolic blood challenges you to had been obtained both at the very first registration otherwise on the day of new bed data. After five full minutes out-of other individuals, step three blood circulation pressure specifications was basically obtained that have five minutes between for each and every dimension. The fresh new mean of those step three strategies was utilized to produce cousin age-, sex-, and you may level-modified systolic and diastolic percentiles centered on auscultatory normative research. 39 Blood circulation pressure percentiles, just like the continuing plenty of fish linear variables, were integrated while the possible confounding parameters from the multivariable studies.
Lab details
Hemoglobin, reticulocytes, lactate dehydrogenase (LDH), and you can plasma arginine-ornithine proportion was indeed received. Hemoglobin account was basically obtained from systematic ideas, having fun with investigation obtained on the day away from sleep investigation or on steady-state next to they. Plasma are obtained in the course of new bed analysis and taken to the new Washington School laboratory to own commitment away from LDH, arginine, and you may ornithine levels. A biochemistry analyzer scanned all of the examples in the 540 nm to help you locate hemoglobin regarding the plasma. None of the products were flagged to have evidence of hemolysis.
Statistical data
Continuous measurements are summarized as mean plus or minus SD. To describe differences between subjects with echocardiograms and those without echocardiograms, ? 2 test or the Wilcoxon 2-sample tests were used to compare categorical and continuous variables, respectively. Exact one-sample binomial tests (for single proportion) and one-sample t tests (for single mean) were used to compare echocardiographic and sleep study data to published normal values, 37,40,41 which were used as the null hypotheses values. 37 Echocardiographic values significantly different from expected values (P < .05), as well as peak tricuspid regurgitant velocity, were defined as dependent variables representing cardiac dysfunction. Spearman univariable coefficients were used to measure the correlation of these dependent cardiac variables with 6 selected sleep variables. The inflated type I error resulting from multiple testing was controlled by the Bonferroni method with the raw P value multiplied by relevant number of tests for the variable of interest. Backward stepwise elimination multivariable analysis was performed using echocardiographic measurements as dependent variables with statistically significant sleep variables as independent variables of main interest. LV E/E? ratio was a dependent variable of interest because of the link between diastolic dysfunction and mortality in individuals with SCD. 17 Elevated tricuspid regurgitation velocity was treated as a nominal dependent variable for backward stepwise logistic regression analysis with a cutoff value of greater than or equal to 2.5 m/sec. If the tricuspid regurgitation velocity was not measurable, it was considered normal for this logistic regression analysis. 5 In addition to sleep variables, other covariates considered in the multivariable analysis were: hemoglobin, LDH, arginine-ornithine ratio, waking oxygen saturation, age, heart rate during the echocardiogram, systolic and diastolic blood pressure percentiles, and body mass index percentile. 42 Oxygen saturation while waking was included as a covariate because prior studies have demonstrated a relationship between waking and nocturnal saturations. 23,25 The arginine-ornithine ratio was a covariate because this ratio is related to elevated tricuspid regurgitant velocity and mortality in adults with SCD. 43 To avoid multicollinearity, separate models were fitted for the 3 independent variables with very high correlation (oxygen saturation waking vs average oxygen saturation asleep or percentage of sleep time with oxygen saturation < 95%, average oxygen saturation asleep vs percentage of sleep time with oxygen saturation < 95%, r values 0.93, ?0.88, and ?0.88, respectively). A correlation coefficient of greater than 0.8 was used as a cutoff for separate models. The final models were chosen based on the maximum r 2 . The significance level for variable retention in multivariable models was set at 10%. The distributional assumptions for the final models (conditional normality and constant variance) were checked by residual plots. The linearity assumption was examined by the added variable plots. 44
