Reduced Work Capacity in Individuals with Down Syndrome

Abstract

Low work capacity and V˙O2peak commonly are described phenomena in Down syndrome. This is accompanied by chronotropic incompetence and a high incidence of obesity. Although many causes of low work capacity in Down syndrome have been proposed, little scientific support exists. Our working hypothesis is that autonomic dysfunction is the major contributor to the low levels of work capacity in this population.

Difference of catecholamine responses to exercise in men with trisomy 21, with or without chronotropic incompetence

“…This could be related to both depressed sympathetic tone and response as incomplete vagal withdrawal [3,19]. Fernhall et al [19] have demonstrated that chronotropic incompetence in persons with DS limits exercise performance, consistent with findings in other clinical observations where chronotropic incompetence is a significant contributor to exercise intolerance [20]. Alterations in the sympathetic and parasympathetic modulation of heart rate are indicative of dysautonomia [21,22].…”

“…The pathophysiological links between chronotropic incompetence and DS remain unclear but some impaired exercise-induced adrenomedullary and sympathetic responses have been proposed [3,9,18]. This could be related to both depressed sympathetic tone and response as incomplete vagal withdrawal [3,19]. Fernhall et al [19] have demonstrated that chronotropic incompetence in persons with DS limits exercise performance, consistent with findings in other clinical observations where chronotropic incompetence is a significant contributor to exercise intolerance [20].…”

“…In persons with DS, an impairment of heart rate variability is observed especially since decreased parasympathetic tone is related to autonomic nervous system imbalance, and this could help to confirm the dysautonomia in this population. The relationship between autonomic imbalance and chronotropic incompetence in DS was also mentioned by others [18,19,36]. These authors found a blunted autonomic control during sympathetic stimulation (tilt test or isometric handgrip test), and explained it by a blunted sympathetic activation [18,37], a reduced vagal withdrawal [3] or alterations in both branches of the autonomic nervous system and baroreflex cardiac modulation [18] during physiological maneuvers.…”

Impact of obesity and Down syndrome on peak heart rate and aerobic capacity in youth and adults

“…In addition to high rates of overweight and obesity among individuals with DS, this population commonly exhibits very low peak aerobic capacities coupled with lower than expected peak heart rates (HR peak ) (Balic, Mateos, Blasco, & Fernhall, 2000;Fernhall et al, 2009;Fernhall, Mendonca, & Baynard, 2013). While lack of motivation and understanding do not explain low work capacities achieved among individuals with DS when appropriate testing and familiarization protocols are followed (Fernhall et al, 2013), physical activity levels do not further explain this phenomenon either with activity being similar to the general population (Mendonca, Pereira, & Fernhall, 2010).…”

Acute effects of cycling exercise on post-exercise blood pressure in individuals with Down syndrome

“…In addition, DS patients exhibit reduced work capacity, which is attributable to an attenuated heart rate (Hr) response to exercise as well as to sympathoexcitatory challenges [11,12]. Studies suggest that such attenuated Hr and blood pressure (BP) responses in individuals with DS may be coupled with a lesser reduction in baroreflex sensitivity, which is related to a blunted sympathetic activation and to a parasympathetic withdrawal [13,14]. On the other hand, individuals with DS have an elevated arterial stiffness [15] and risk of stroke [16] so that BP control through exercise interventions could be an interesting strategy to apply in this population.…”