Pulmonary function, muscle strength and mortality in old age

Abstract

Numerous reports have linked extremity muscle strength with mortality but the mechanism underlying this association is not known. We used data from 960 older persons without dementia participating in the Rush Memory and Aging Project to test two sequential hypotheses: first, that extremity muscle strength is a surrogate for respiratory muscle strength, and second, that the association of respiratory muscle strength with mortality is mediated by pulmonary function. In a series of proportional hazards models, we first demonstrated that the association of extremity muscle strength with mortality was no longer significant after including a term for respiratory muscle strength, controlling for age, sex, education, and body mass index. Next, the association of respiratory muscle strength with mortality was attenuated by more than 50% and no longer significant after including a term for pulmonary function. The findings were unchanged after controlling for cognitive function, parkinsonian signs, physical frailty, balance, physical activity, possible COPD, use of pulmonary medications, vascular risk factors including smoking, chronic vascular diseases, musculoskeletal joint pain, and history of falls. Overall, these findings suggest that pulmonary function may partially account for the association of muscle strength and mortality.

Associations between muscle strength, spirometric pulmonary function and mobility in healthy older adults

“…Our results support the hypothesis that muscle strength loss initiates the causal chain that contributes to decreased pulmonary function and mobility limitations (Buchman et al 2008). The mechanisms behind age-related changes in muscle tissue are most likely a combination of systemic physiological mechanisms (hormonal and neural changes, increased inflammation, reduced protein synthesis, increased muscle proteolysis, decreased regenerative capacity, motor neuron loss and reduced excitability, decreased central drive, and increased muscle/fat content etc.)…”

“…It has been suggested that a decline in muscle strength initiates a chain of events which leads to reduced pulmonary function and low physical performance and mobility disability (Buchman et al 2008). Reduced chest wall compliance, kyphosis and decreased respiratory muscle strength and endurance are examples of age-related musculoskeletal changes that may have an effect on pulmonary functions (Meyer 2005;Stanojevic et al 2008).…”

Pulmonary Function, Muscle Strength, and Incident Mobility Disability in Elders

“…Then we examined the various combinations of these three factors together, first in combinations and then finally with all three in a single model ( Table 2, Models D-G). In these models, an attenuation of the association of muscle strength with mobility disability when pulmonary function was added into the model would support the hypothesis that muscle strength and mobility disability are linked (mediated) by pulmonary function (8,20). In a final model ( Table 2, Model H), we added terms for a number of potential confounders that might affect these associations with mobility disability.…”

“…Raw scores from each of the three averaged component pulmonary measures were converted to z scores using the means and standard deviations computed from the entire cohort. A composite pulmonary function score was created by converting the raw score from FVC, FEV 1 , and PEF to z scores using the mean and standard deviation from all participants at baseline (Table 1) and averaging z scores for these three measures together as previously described (8).…”

“…In turn, the inadequate energy supply caused by decreased pulmonary function could lead to impaired leg strength, contributing to the development of mobility disability (7). Testing this hypothesized causal sequence requires examining all three of these factors together in the same models (8). However, we are unaware of prior studies that have examined pulmonary function, respiratory muscle strength, and leg strength together to examine how they contribute to the development of mobility disability (9).…”