Hand grip strength and postural control among individuals with and without Chronic Obstructive Pulmonary Disease : Epidemiological and motion laboratory studies

Abstract: BackgroundChronic obstructive pulmonary disease (COPD) is estimated to affect approximately 8%–10% of all adults. The disease is considered to be a heterogenic syndrome with systemic effects, in which comorbidities including cardiovascular diseases, muscle dysfunction and fatigue are common. The majority of all individuals with COPD have mild to moderate disease (Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1-2), and only a third are identified by health care, and this under-diagnosis contributes to a lack of knowledge of COPD in the population. COPD is related to skeletal muscle dysfunction, where muscle weakness, frequently assessed with hand grip strength (HGS), is one of the components. Evidence of postural control limitations among individuals with severe or very severe COPD has been emerging during the last decade. These limitations are partly related to muscle weakness, however, research of the other underlying systems of postural control is scarce, and an increased knowledge is of importance for the prevention of falls.AimThe main objective of the thesis was to increase the population-based knowledge about muscle strength, assessed as hand grip strength, and also postural control among individuals with and without COPD. Another objective was to investigate the value of hand grip strength measurements in relation to lower limb muscle strength and postural control among community-dwelling older adults.MethodsPaper I and II are based on the population-based Obstructive Lung disease in Northern Sweden (OLIN) COPD study. All individuals with obstructive lung function impairment (n=993) and an age- and sex-matched group without (n=993) (COPD and non-COPD) were identified after re-examination of population based cohorts during 2002-04. They (n=1,986) have been invited to recurrent examinations including structured interviews and spirometry. Paper I (n=1011) and II (n=831) include data from examinations during 2009-2010 and 2014, respectively, where measurements of HGS (Paper I & II) as well as assessment of fatigue and physical activity (Paper II) were included. Paper III and IV are based on the population-based Balancing Human and Robot (BAHRT) study. Randomly selected individuals over 70 years of age were invited to participate in a study of postural control aspects, in their homes and at the 2 Human Health and Performance Lab- Movement Science, at Luleå University of Technology. The examinations included a structured interview as well as measurements of postural control and sensory and motor systems including HGS, lower limb strength, proprioception, pressure sensitivity, visual acuity, vestibular function and reaction time. Participants in Paper III consisted of communitydwelling individuals over 70 years of age (n=45). Paper IV consisted of individuals with COPD recruited from both the OLIN COPD study as well as the BAHRT-study (n=22), as well as a control group without airway obstruction from the BAHRT-study (n=34).ResultsIn Paper I, there was no differences in mean HGS between the groups with and without COPD. However, HGS was related to disease severity; HGS was lower among those with severe to very severe COPD (GOLD 3-4) compared to nonCOPD, and HGS was associated with forced expiratory volume during 1 second % of predicted value (FEV1 % predicted) in regression models. Five years later, in Paper II, mean HGS was lower in COPD compared to non-COPD. Further, individuals with COPD and clinically relevant fatigue had lower HGS than those without clinically relevant fatigue, significantly so among men and close to among women. There was no clear association between HGS and level of physical activity. In Paper III, there was a strong and valid model showing association between HGS and lower limb strength, where all tested muscle groups were significantly correlated to hand grip strength. The regression model with HGS and postural control was significant, however, the model was weak. In Paper IV, individuals with COPD had worse postural control than those without COPD, significantly so regarding mediolateral amplitude in quiet stance with eyes open on soft/unstable surface, as well as anteroposterior limits of stability. In the COPD group, mediolateral amplitude was related to eye sight and the burden of tobacco smoking assessed as pack-years. Further, muscle strength associated with anteroposterior amplitude in the limits of stability test.ConclusionsIn the population-based OLIN COPD study in 2009-2010, mean HGS was significantly lower among individuals with severe to very severe COPD (GOLD 3-4) than those without COPD. Five years later, mean HGS was lower among all individuals with COPD (GOLD 1-4) compared to those without COPD, which may indicate altered aging process in COPD. HGS was associated to fatigue among individuals with COPD, while there were no associations between HGS and physical activity. HGS is a valid tool for the estimation of lower limb muscle strength among community-dwelling older adults, however, HGS is not 3 appropriate to use as an estimation of postural control. Postural control was impaired among individuals with COPD and different postural control assessments had different demands on the sensory and motor systems. The burden of tobacco smoking and visual acuity might be important for quiet stance trials with visual input, while muscle strength might be important for the more dynamic limits of stability test. Further research regarding the longitudinal aspects of muscle weakness and postural control among individuals with COPD is needed to gain knowledge for appropriate preventive or rehabilitative interventions.