Even when health status appears normal, hidden changes in oxygen use and microvascular function may already be present in adolescents with type 1 diabetes.
Study: Cardiovascular and autonomic nervous system responses to graded exercise in adolescents with type 1 diabetes. Image credit: Iren_Geo/Shutterstock.com
New research published in Frontiers of endocrinology reveal that type 1 diabetes is associated with subtle changes in oxygen utilization and peripheral microvascular function in response to graded exercise in adolescents. However, this chronic metabolic state is not expected to significantly impact cardiovascular function or overall exercise capacity.
Early vascular changes may begin in diabetic adolescence
Type 1 diabetes is a chronic autoimmune disease characterized by the destruction of pancreatic beta cells, which produce the hormone insulin. The condition usually manifests in childhood, with peak diagnosis in adolescence. The global prevalence of this disease is estimated at 9.5 million people.
Lifelong insulin replacement therapy is key to avoiding chronic hyperglycemia (high blood sugar levels) and preventing health complications such as cardiovascular disease, kidney disease, eye disease, and peripheral neuropathy. However, there is evidence to suggest that young people with type 1 diabetes may already be experiencing early signs of vascular dysfunction and atherosclerosis.
Physical activity is considered an effective intervention for children and adolescents with diabetes to positively modulate blood lipid profile, glucose metabolism, and endothelial function. However, there are limited studies investigating the effects of type 1 diabetes on maximal exercise capacity and exercise-induced physiological changes in children and adolescents.
Given this gap in the literature, researchers at the University of Ljubljana in Slovenia conducted a small observational study comparing cardiovascular, respiratory, metabolic, and microvascular responses to cardiopulmonary exercise testing (CPET) in adolescents with type 1 diabetes and healthy adolescents. CPET is a test widely used in sports medicine to accurately assess the physiological response to short-term maximal exercise.
Adolescents were tested during rest, exercise, and recovery periods
A total of 8 adolescents with type 1 diabetes and 8 healthy adolescents were enrolled in the study. All participants underwent CPET on a bicycle ergometer, followed by a 10-min recovery period.
To assess participants’ cardiorespiratory, metabolic, and microvascular responses to graded exercise, several physiological parameters were assessed before (rest), during, and after (recovery) CPET.
Oxygen usage efficiency varies despite normal peak performance
The analysis showed that young people with type 1 diabetes showed subtle differences in the amount of oxygen they used during maximal exercise. They showed a lower slope of oxygen consumption per unit of output (VO2/PO) and a higher ventilatory equivalent of oxygen (VE/VO2). However, other measurements, including the slope of oxygen uptake efficiency, were not significantly different from healthy people.
There were no significant differences in peak power output (peak workload achieved, measured in watts) or peak oxygen consumption between groups. Cardiovascular responses, including heart rate and heart rate variability, were also similar throughout the exercise test.
In contrast, peripheral microvascular responses were different. Adolescents with type 1 diabetes had reduced skin blood flow in the fingertips and reduced skin vascular conductance at rest and during post-exercise recovery. These microvascular measurements were not assessed during vigorous exercise.
Changes in peripheral blood vessels appear before physical strength declines
This study shows that young people with type 1 diabetes have comparable exercise capacity and cardiovascular function to non-diabetic young people when performing graded exercise. However, they may already indicate early changes in oxygen utilization during exercise, changes in peripheral microvascular function at rest and during post-exercise recovery. These findings suggest that any differences are likely caused by peripheral mechanisms rather than central cardiovascular limitations.
Comparable cardiovascular parameters between groups indicate that cardiovascular autonomic function is preserved in these adolescents. However, previous studies have reported mixed results. Some studies have shown a reduced cardiovascular response to exercise in patients with type 1 diabetes, while others have reported no differences.
This variation can be influenced by factors such as duration of illness, blood sugar control, fitness level, and specific exercise conditions.
Of note, this study found that skin blood flow was significantly reduced in the fingertips, but not the forearm, among diabetic participants. Similarly, significant reductions in cutaneous vascular conductance and differences in skin temperature (lower fingertip temperatures observed in diabetic participants) were observed only at the fingertips and not at the forearm.
These findings suggest that early stage microangiopathy of glabrous skin (smooth skin without hair on the palms of the hands and soles of the feet) or endothelial dysfunction may already be present in patients with type 1 diabetes. With dense sympathetic innervation and abundant arteriovenous connections, glabrous skin, such as the skin on fingertips, plays a central role in temperature regulation, rapidly regulating skin blood flow and promoting heat dissipation. Taken together, these findings suggest altered peripheral microvascular regulation and impaired thermoregulatory capacity in adolescents with type 1 diabetes.
The observed early signs of peripheral microvascular dysfunction highlight the need for continuous monitoring of vascular function even in young diabetic patients without obvious health complications. Future studies are needed to investigate the factors and mechanisms that cause microvascular dysfunction in this vulnerable population.
Given the limited number of participants, the researchers noted that these findings should be interpreted as preliminary evidence and require confirmation in a larger and more representative cohort.
Furthermore, the study did not collect or systematically analyze detailed information such as the content and timing of pre-exercise meals, blood sugar levels over time, and insulin doses. These factors may influence the physiological response to exercise and therefore need to be evaluated as within-subject determinants of CPET response in larger cohorts.
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