Exercise Improves Function and Quality of Life for ESRD Patients

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Exercise may benefit patients with end stage renal disease (ESRD) by improving their functional independence, resistance to disability, and survival of acute stressors.

Exercise is often broken down into endurance exercise, such as walking or running, and resistance exercise. Endurance exercise can be quantified as peak oxygen uptake or aerobic capacity. Resistance exercise is more about strength or muscle power.

Kathy Sietsema, MD, professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles, and chief of respiratory and critical care medicine at Harbor-UCLA Medical Center in Torrance, Calif., explained that energy production in muscles depends on the body getting oxygen from the atmosphere into the lungs, to the bloodstream, into muscles, and to the mitochondria.

“There are multiple points in this system where patients with renal disease can have impairments, and impairment anywhere along the line can reduce the maximum rate of oxygen uptake or the maximum level of exercise that can be sustained,” she said. Sietsema spoke on “Exercise Interventions in ESRD: Can We Improve Function, Quality of Life, or Survival?” at the symposium “Exercise, Physical Function, and Quality of Life in Patients with ESRD.”

Oxygen uptake (VO2) is measured as mL/min/kg. Maximal VO2 decreases with age even in healthy people, “so that [when] you get up to the 80s, you might see people with peak VO2s around 18 or 20 mL/min/kg,” Sietsema said.

Several studies have reported maximal VO2 levels in people with end stage renal disease. Epoetin treatment has tended to have an effect on peak VO2 in a number of studies, “but it didn’t normalize exercise capacity, and it didn’t even increase exercise capacity as much as one might expect it to if the sole limitation to exercise function were the anemia or the cardiovascular system,” Sietsema said. In a study of 193 ESRD patients from about age 20 to 80 years on hemodialysis, the majority had a peak VO2 <20 mL/min/kg across the entire age range. This value is close to that of an 80-year-old healthy but sedentary woman.

The clinical implications are apparent. “Exercise capacity is related to both survival and to function,” she said. Among patients with ESRD, 35 percent of patients reported exercising “almost never or never.” In a year’s follow-up, “the investigators found that mortality rate was considerably higher in those who answered the question that way than in patients who answered it in any other way,” Sietsema said, “suggesting that exercise behavior is related to survival in this population.”

In another study of 175 high-functioning ESRD patients, those above the median VO2 value of 17.5 mL/min/kg had significantly better survival than patients below the median over a period of almost 1600 days.

Neither of the two studies says whether changing exercise behavior would have any effect on survival. Besides exercise capacity, physical functioning was also found to correlate strongly with peak VO2 among community dwelling elderly adults.

Studies have shown that frailty and disability are dynamic states, and “people move not only to higher levels of disability, but it’s also possible to move in the other direction,” Sietsema said. Periods of decreased physical activity, such as hospitalization, are among the most common causes of a shift to a lower level of function or increased frailty. “One of the best predictors of the ability to recover independence after a period of disability was the preceding habitual activity level,” she said. While this concept may seem self-evident, it provides a scientific basis for the field of rehabilitation.

Exercise interventions can prevent disability. Sietsema cited a study in which patients with osteoarthritis of the knee were assigned to a control group or to aerobic or resistance exercise groups. Over 18 months, about half of the control group lost at least one activity of daily living whereas only about 30 percent of patients in the exercise groups did so (P = 0.03 for resistance exercise group versus control; P = 0.01 for aerobic exercise versus control; and P = 0.006 for both exercise groups versus control). “This study is important because it is one of the few that actually demonstrates that an intervention can change the natural history of disability,” Sietsema concluded.

In a review of studies of endurance exercise training in ESRD patients, Kirsten Johansen of the San Francisco VA Medical Center showed that the vast majority of the studies demonstrated a significant increase in peak VO2 associated with the training intervention (J Am Soc Nephrol 2007; 18:1845–1854). The question of clinical significance remains since Johansen calculated that the average peak increase in VO2 was only 17 percent.

In a small pilot study of intradialytic cycling exercise three times a week, Storer et al. (Nephrology, Dialysis Transplantation 2005; 20:1429–1437) showed that this intervention significantly improved “strength, fatigability, and power.” An additional finding was an increase in strength, contrary to general findings in healthy people, where strength and endurance training are viewed as very separate processes.

It turns out that increasing peak VO2 by a small amount (e.g., 17 percent), can increase the endurance exercise time greatly. In daily living, this increase may translate into a patient being able to walk to a bus stop, shop in a warehouse store, or even play golf.

“I think that there are correlations between what we measure in the lab and what people really care about, the activities that people do,” Sietsema said. “And there’s beginning to be literature that suggests that we can improve these distal endpoints that really matter by the things that we learn from basic exercise physiology.”