LOS ANGELES – Hand grip strength is independently predictive of risk for respiratory events in smokers who have or are at risk for chronic obstructive pulmonary disease, results from a single-center study showed.
“Measures of lung function, including spirometry, are used as the main descriptors of COPD severity and prognosis,” Carlos H. Martinez, MD, MPH, said in an interview in advance of the annual meeting of the American College of Chest Physicians. “These measurements, as important as they are, need to be improved, in order to develop better risk and prognostic models of the disease, to identify subgroups at higher risk of poor outcomes ... With our work, we have proved that simple physical tests could be part of future prognostic models.”
Dr. Carlos H. Martinez
Interest has grown in developing multidimensional models to predict respiratory prognosis. Such models include BODE (body mass index, airflow obstruction, dyspnea and exercise capacity), ADO (age, dyspnea and airflow obstruction), and DOSE (dyspnea, airflow obstruction, smoking status, and exacerbation frequency).
In patients with or at risk for COPD, Dr. Martinez, of the University of Michigan Health System, Ann Arbor, and his colleagues tested the associations of hand grip strength with measures of body composition such as pectoralis muscle area and extent of subcutaneous fat, imaging phenotypes, and lung function.
The researchers obtained demographic, clinical, lung function, hand grip strength, and imaging data from 441 smokers with and without COPD participating in the Genetic Epidemiology of COPD Study (COPDGene) at the National Jewish Health in Denver. Imaging methods used in the study were developed by George R. Washko, MD, and his associates at Brigham and Women’s Hospital, Boston, to evaluate patients’ body composition, including chest CTs to obtain measures of airway thickness, emphysema percentage, pectoralis muscle area, and subcutaneous adipose tissue area.
Correlations between measures of lung function, imaging phenotypes, body composition, and hand grip strength were analyzed in univariate analysis and in multivariate linear models. The association between hand grip strength and exacerbations was analyzed at enrollment and during an average follow-up of 2.6 years.
Hand grip strength was similar across groups categorized by spirometry severity and was not associated with emphysema severity.
After adjustment for demographics, smoking history, smoking intensity, comorbidities and lung imaging phenotypes, however, grip strength was associated with pectoralis muscle area (increase of 3.9 kg per one standard deviation of pectoral muscle area) and subcutaneous adipose tissue (a decrement of 5.1 kg per one standard deviation of subcutaneous adipose tissue). These associations were independent of body mass index and the presence of emphysema.
During follow-up, hand grip strength was associated with exacerbations (risk ratio 0.94 per one kg increment on grip strength) and incident exacerbations (incident risk ratio 0.92 per one kg increment on grip strength) in models adjusted for other factors known to be associated with exacerbations.
Research in body composition has mostly relied on dual absorptiometry and bioelectrical impedance, tools not routinely used in clinical practice, Dr. Martinez said. “We were surprised by the ability to show similar results using imaging data that are available from regular chest CTs.”
“We have confirmed prior hypotheses that it is not just weight or BMI that matters (to risk of exacerbations), but how much muscle and how much fat are contributing to our patient’s high or low BMI,” Dr. Martinez said.
Hand grip testing can be challenging in this patient population, he said. Still, “asking relevant questions about (patients’) physical fitness will help us to understand better our patients’ needs. We can also give more attention to the extrapulmonary structures included in the numerous chest CT scans that we order for our patients. These imaging studies, besides the information that they provide about parenchymal and mediastinal structures, include important and easy to discover clues to identify patients at higher risk of exacerbations – those with low muscle and low hand grip could benefit from close follow-up.”
Dr. Martinez acknowledged certain limitations of the study, including the selection of the measures of body composition. “We used analysis of chest CTs, instead of the gold standard of dual absorptiometry (DXA) or other methods such as bioelectrical impedance,” he said. “A final limitation is that we tested a selected group of participants in a cohort study, not a representative sample of the population, [with a] low burden of emphysema and fewer African American participants.”
Dr. Martinez disclosed that his work is supported by the National Institutes of Health and that COPDGene also receives NIH funding. He acknowledged the support and effort of all COPDGene investigators and participants.