Interstitial Glucose and Physical Exercise in Type 1 Diabetes: Integrative Physiology, Technology, and the Gap In-Between

Abstract

Continuous and flash glucose monitoring systems measure interstitial fluid glucose concentrations within a body compartment that is dramatically altered by posture and is responsive to the physiological and metabolic changes that enable exercise performance in individuals with type 1 diabetes. Body fluid redistribution within the interstitial compartment, alterations in interstitial fluid volume, changes in rate and direction of fluid flow between the vasculature, interstitium and lymphatics, as well as alterations in the rate of glucose production and uptake by exercising tissues, make for caution when interpreting device read-outs in a rapidly changing internal environment during acute exercise. We present an understanding of the physiological and metabolic changes taking place with acute exercise and detail the blood and interstitial glucose responses with different forms of exercise, namely sustained endurance, high-intensity, and strength exercises in individuals with type 1 diabetes. Further, we detail novel technical information on currently available patient devices. As more health services and insurance companies advocate their use, understanding continuous and flash glucose monitoring for its strengths and limitations may offer more confidence for patients aiming to manage glycemia around exercise.

Performance of the Freestyle Libre flash glucose monitoring (flash GM) system in individuals with type 1 diabetes: A secondary outcome analysis of a randomized crossover trial

“…One might assume that physical exercise per se did not deteriorate the performance of the flash GM system, because the rate of change in glucose appeared to result in inaccuracy. In the present study, the MARD during exercise was inherently higher than that with other CGM devices such as Minimed 640G (Medtronic), Dexcom G4 Platinum (Dexcom) or Paradigm Veo Enlite (Medtronic) (mean absolute relative difference/MARD, ~18%) . A systematic overestimation of 2.7 mmol/L might suggest that anticipation of intervention to avoid exercise‐induced hypoglycaemia is required as soon as an interstitial glucose level of 7.2 mmol/L is reached.…”

“…Although the flash GM system demonstrated good efficacy in chronic glucose monitoring settings, the accuracy of acute continuous glucose monitoring (CGM) systems was impaired during periods of high rates of change in glucose . From a physiological point of view, a time lag was observed in the interval needed for glucose to diffuse from the bloodstream into the interstitium .…”

“…Although the flash GM system demonstrated good efficacy in chronic glucose monitoring settings, the accuracy of acute continuous glucose monitoring (CGM) systems was impaired during periods of high rates of change in glucose . From a physiological point of view, a time lag was observed in the interval needed for glucose to diffuse from the bloodstream into the interstitium . In general, use of CGM systems involves a struggle with sensor accuracy during hypoglycaemia and exercise, as shown for both professional (iPro2, Enlite 2, Medtronic, USA) and personal (Minimed 640G, Medtronic; Freestyle Libre 1, Abbott, USA; Dexcom G4 Platinum, Dexcom, USA) CGM systems .…”

Impact of physical exercise on sensor performance of the FreeStyle Libre intermittently viewed continuous glucose monitoring system in people with Type 1 diabetes: a randomized crossover trial

“…To overcome this lag time and to reduce the risk of inadequate therapy decisions, an exercise-related algorithm could improve sensor performance [10]; however, a recent study in people with Type 1 diabetes receiving continuous subcutaneous insulin infusion showed that a 50% reduction in basal rate 1 h before the start of exercise testing did not significantly reduce free circulating insulin during exercise [11]. To overcome this lag time and to reduce the risk of inadequate therapy decisions, an exercise-related algorithm could improve sensor performance [10]; however, a recent study in people with Type 1 diabetes receiving continuous subcutaneous insulin infusion showed that a 50% reduction in basal rate 1 h before the start of exercise testing did not significantly reduce free circulating insulin during exercise [11].…”

“…Additionally, despite it having being shown that blood glucose collected from the earlobe in comparison to the fingertip does not result in clinically relevant differences under resting conditions [13], a sampling-site bias might be present, especially in exercise conditions [14]. Additionally, despite it having being shown that blood glucose collected from the earlobe in comparison to the fingertip does not result in clinically relevant differences under resting conditions [13], a sampling-site bias might be present, especially in exercise conditions [14].…”