Prediction of cardiorespiratory fitness in older men infected with the human immunodeficiency virus: clinical factors and value of the six-minute walk distance.

Human immunodeficiency virus (HIV)-infected patients who receive antiretroviral (ARV) therapy are surviving into older age and are more likely to die from age-associated comorbid conditions than acquired immunodeficiency syndrome (AIDS).1–3 Deterioration in physical function is a consequence of chronic infection and sarcopenia in older adults.4 Aging, HIV infection, and ARV therapy have an additive effect on metabolism, pharmacokinetics, and immune function in older HIV-infected patients,5 but the combined effect on physical function is unknown. Physical function encompasses many parameters, including fitness, strength, balance, and flexibility. In the current treatment era, difficulty with vigorous activities is the predominant functional limitation of HIV-infected patients regardless of their age.6–8 Exercise testing that shows a 42% reduction in cardiorespiratory fitness in adolescent9 and older (mean age 56)10 HIV-infected patients when measured as oxygen consumption during peak exercise performance (VO2peak). Before effective therapy was available, asymptomatic HIV infection frequently progressed to AIDS, resulting in generalized wasting and loss of muscle mass in young adults that was associated with shorter 6-minute walk distance (6-MWD)11 and weaker hand-grip strength.12 Similarly, laboratory markers of HIV disease progression, CD4 cell count, and HIV-1 viral load, were important predictors of physical function.6,13 More recently, in a large cohort of HIV-infected adults that included 447 subjects aged 50 and older it was found that self-reported physical function is associated with cardiac and pulmonary disease, independent of HIV stage and CD4 cell count.8 Although self-reported function provides important insight into physical disability, there may be limitations unique to older HIV-infected adults. Older HIV-infected patients, who represent a survival cohort, could have a different threshold for reporting functional limitations than younger HIV-infected patients or older noninfected patients. Exercise testing offers a laboratory-based measure to investigate the clinical and physiological factors underlying limitations in vigorous activities. 6-MWD is an estimate of submaximal exercise capacity that is easy to administer and predicts physical function and mortality in older adults with congestive heart failure (CHF)14 and chronic obstructive pulmonary disease (COPD)15 but has not been studied in older HIV-infected adults. In particular, the accuracy of the 6-MWD as a surrogate for treadmill testing has not been validated in this population. The objective of the study was to investigate the association between age-associated comorbidity and cardiorespiratory fitness (VO2peak) in older HIV-infected adults receiving ARV therapy. It was hypothesized that cardiac and pulmonary disease contribute to poorer fitness and that current effective HIV treatment minimizes the effects of AIDS and wasting. The secondary goal was to provide objective evidence that the 6-MWD could be used as a safe, easily administered, low-cost alternative to treadmill testing to assess fitness in older HIV-infected adults.