CD4 and pulmonary hypertension: Previous studies with echocardiography data have been cross-sectional; as a result, IRs and associations between viral control over time and future risk of pulmonary hypertension have not been previously reported.21-24 Finally, we considered HIV viral control metrics (CD4 count and viral load) as time-varying covariates, which allowed us to account for fluctuation in these factors over time rather than assuming they were constant.