Baseline physical performance, health, and functioning of participants in the Frequent Hemodialysis Network (FHN) trial

Abstract

Background: Self-reported physical health and functioning and direct measures of physical performance are decreased in hemodialysis patients and are associated with mortality and hospitalization.

Study design: We determined baseline cross-sectional associations of physical performance, health, and functioning with demographics, clinical characteristics, nutritional indexes, laboratory benchmarks, and measures of body composition in participants in the Frequent Hemodialysis Network (FHN) trial.

Setting & participants: 375 persons enrolled in the FHN with data for physical performance, health, and functioning.

Predictors: Explanatory variables were categorized into fixed factors of age, race, comorbid conditions (diabetes mellitus, heart failure, and peripheral arterial disease) and potentially modifiable factors of dialysis dose, phosphorus level, hemoglobin level, equilibrated normalized protein catabolic rate (enPCR), body composition, body mass index, phase angle, and ratio of intracellular water volume to body weight (calculated from bioelectrical impedance).

Outcomes: Scores on tests of physical performance, health, and functioning.

Measurements: Physical performance measured using the Short Physical Performance Battery, self-reported physical health and functioning using the 36-Item Short Form Health Survey (SF-36). Body composition (body mass index and bioimpedance analysis) and laboratory data were obtained from affiliated dialysis providers.

Results: Relative to population norms, scores for all 3 physicality metrics were low. Poorer scores on all 3 metrics were associated with diabetes mellitus and peripheral arterial disease. Poorer scores on the SF-36 Physical Functioning subscale and Short Physical Performance Battery also were associated with age, lower ratio of intracellular water volume to body weight, and lower enPCR. Black race was associated with poorer scores on the Short Physical Performance Battery.

Limitations: This was a cross-sectional study of individuals agreeing to participate in the FHN study and may not be generalizable to the general dialysis population.

Conclusions: Hemodialysis patients show markedly impaired physical performance, health, and functioning relative to population norms. Although some factors associated with these impairments are not modifiable, others may change with improvement in nutritional status or body composition.

Figure 1

Flow chart of derivation of analytic cohort. Abbreviation: FHN, Frequent Hemodialysis Network.

Figure 2

Distribution of Short Physical Performance Battery (SPPB) scores of patients enrolled in the Frequent Hemodialysis Network trial. Lower-extremity function was measured empirically using the SPPB, which measured: (1) gait speed for a 4-m walk, (2) chair stand with a goal of standing unassisted without use of arms 5 times within 60 seconds, and (3) balance score, which measures the capacity to stand with feet together for 10 seconds. Each exercise was scored from 0-4, with higher scores representing fewer limitations. SPPB score was the sum of these component scores. For composing this figure, scores were grouped by 2.

Figure 3

Distribution of physical health composite scores in patients enrolled in the Frequent Hemodialysis Network Trial. The minimum score achieved was 18.

Figure 4

Distribution of Physical Functioning subscale scores measured in patients enrolled in the Frequent Hemodialysis Network Trial. The Physical Functioning subscale is composed of 10 questions about mobility (moving a table, pushing a vacuum, lifting or carrying groceries, climbing several flights of stairs, climbing 1 flight of stairs, bending or stooping, walking 1 mile, walking several blocks, and walking 1 block) and self-care (bathing or dressing oneself). These scales are scored from 0-100, with higher scores indicating better function. For composing this figure, scores were grouped by 5.

Figure 5

Multivariable associations with physical performance subscale score. Values are shown as odds ratios and 99% confidence limits for independent associations with the Short Physical Performance Battery score. Empty circles represent odds ratio estimates in which maximized fitting to the data from our cohort is offset through penalization methods. These estimates may be more generalizable.

Figure 6

Multivariable associations with self-reported physical health. Values are shown as regression coefficients and 99% confidence limits for independent associations with the 36-Item Short Form Health Survey physical health composite scores. Empty circles represent regression coefficient estimates in which maximized fitting to the data from our cohort is offset through penalization methods. These estimates may be more generalizable.

Figure 7

Multivariable associations with self-reported physical functioning. Values are shown as regression coefficients and 99% confidence limits for independent associations with the 36-Item Short Form Health Survey Physical Functioning subscale score. Empty circles represent regression coefficient estimates in which maximized fitting to the data from our cohort is offset through penalization methods. These estimates may be more generalizable. Abbreviation: enPCR, equilibrated normalized protein catabolic rate.