Abstract
Activation of leg muscles is an important component in the regulation of blood pressure during standing, failure of which could result in syncope and falls. Our previous work demonstrated baroreflex mediated activation of leg muscles (muscle-pump baroreflex) as an important factor in the regulation of blood pressure during standing; however, the effect of aging on the muscle-pump baroreflex of individual leg muscles during standing remains to be understood. Here, the interaction between systolic blood pressure (SBP) and the activation of lateral gastrocnemius (LG), medial gastrocnemius (MG), tibialis anterior (TA), and soleus (SOL) muscles during standing was quantified. Beat-to-beat heart period (RR interval), SBP, electromyography impulse (EMGimp) were derived from continuously acquired electrocardiography, finger blood pressure, and calf-electromyography, respectively. The cardiac baroreflex (SBP→RR) causality (0.88 ± 0.08 vs. 0.94 ± 0.03, p = 0.01), percent time with significant coherence (%SC: 50.95 ± 23.31 vs. 76.75 ± 16.91, p = 0.001), and gain (4.39 ± 4.38 vs. 13.05 ± 8.11, p < 0.001) was lower in older (69 ± 4 years) compared to young (26 ± 2 years) persons. Muscle-pump baroreflex (SBP→EMGimp) causality of LG (0.81 ± 0.08 vs. 0.88 ± 0.05, p = 0.01) and SOL (0.79 ± 0.11 vs. 0.88 ± 0.04, p = 0.01) muscles was lower in older compared to young persons. %SC was lower for all muscles in the older group (LG, p < 0.001; MG, p = 0.01; TA, p = 0.01; and SOL, p < 0.001) compared to young. The study outcomes highlighted impairment in muscle-pump baroreflex with age in addition to cardiac baroreflex. The findings of the study can assist in the development of an effective system for monitoring orthostatic tolerance via cardiac and muscle-pump baroreflexes to mitigate syncope and falls.
Highlights
Falls are debilitating events which occur with increasing frequency with age and cause injuries needing urgent medical attention, degradation in the quality of life, as well as significant financial burden on the healthcare system (Gazibara et al, 2014; Terroso et al, 2014; Do et al, 2015)
In the current work, utilizing data from young, healthy individuals, we investigated the role of muscle-pump baroreflex of individual leg muscles namely the lateral gastrocnemius (LG), medial gastrocnemius (MG), tibialis anterior (TA), and soleus (SOL) toward facilitating venous return to the heart
electromyography impulse (EMGimp) for LG (p = 0.07), MG (p = 0.09), SOL (p = 0.58) muscles were not different in older persons, but it was higher for TA (p = 0.001) muscle compared to young (Table 1)
Summary
Falls are debilitating events which occur with increasing frequency with age and cause injuries needing urgent medical attention, degradation in the quality of life, as well as significant financial burden on the healthcare system (Gazibara et al, 2014; Terroso et al, 2014; Do et al, 2015). With older persons expected to double in the United States by the year 2050 compared to 2012, increase in fall-related incidents are anticipated (Ortman et al, 2014). Orthostatic hypotension is one of the primary causes of falls, affecting older persons, and even more adversely, people with neurological disorders (Allcock et al, 2004; Shaw and Claydon, 2014; Shaw et al, 2015). Blood pressure is regulated during upright stance via a series of reflex mechanisms, of which baroreflex is a key component (Heesch, 1999; Verma et al, 2018). In older persons, due to a decline in the sensitivity of baroreceptor response and the inability to increase vascular resistance via sympathetic outflow, regulating blood pressure can be challenging during standing (Monahan, 2007). Orthostatic hypotension (OH), a physiological condition where blood pressure drops abruptly (i.e., 20 mmHg in systolic blood pressure or 10 mmHg for diastolic blood pressure) within 3-min of assuming upright stance, is frequently experienced by older persons (Senard et al, 1997; Eigenbrodt et al, 2000; Blaber et al, 2013b; Ricci et al, 2015)
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