To attenuate observer variability, an automatic oscillometric (Dinamap) strategy was applied to possess resting systolic and you may diastolic blood pressures that have been gotten sometimes from the 1st enrollment otherwise on the day off the fresh sleep research. Immediately after five full minutes of rest, 3 hypertension measurements was in fact gotten that have 5 minutes between for every single dimension. The fresh new imply ones 3 methods was applied to produce https://www.sugardaddydates.net/sugar-daddies-canada/regina relative age-, sex-, and level-adjusted systolic and you can diastolic percentiles centered on auscultatory normative investigation. 39 Blood pressure percentiles, just like the proceeded linear parameters, were provided while the prospective confounding parameters on multivariable data.
Laboratory parameters
Hemoglobin, reticulocytes, lactate dehydrogenase (LDH), and you will plasma arginine-ornithine proportion were received. Hemoglobin accounts have been taken from medical details, using studies acquired at the time of sleep data otherwise at steady-state close to they. Plasma was gotten during the time of the newest bed research and provided for the fresh new Arizona University laboratory to own commitment out of LDH, arginine, and you may ornithine levels. A biochemistry analyzer read all samples at 540 nm so you can detect hemoglobin on plasma. Nothing of one’s products had been flagged to possess proof of hemolysis.
Statistical analysis
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
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