Insulin resistance is associated with an exaggerated blood pressure response to ischemic rhythmic handgrip exercise in nondiabetic older adults

Abnormal cardiovascular control during exercise: Role of insulin resistance in the brain

During exercise circulatory adjustments to meet oxygen demands are mediated by multiple autonomic mechanisms, the skeletal muscle exercise pressor reflex (EPR), the baroreflex (BR), and by feedforward signals from central command neurons in higher brain centers. Insulin resistance in peripheral tissues includes sensitization of skeletal muscle afferents by hyperinsulinemia which is in part responsible for the abnormally heightened EPR function observed in diabetic animal models and patients. However, the role of insulin signaling within the central nervous system (CNS) is receiving increased attention as a potential therapeutic intervention in diseases with underlying insulin resistance. This review will highlight recent advances in our understanding of how insulin resistance induces changes in central signaling. The alterations in central insulin signaling produce aberrant cardiovascular responses to exercise. In particular, we will discuss the role of insulin signaling within the medullary cardiovascular control nuclei. The nucleus tractus solitarius (NTS) and rostral ventrolateral medulla (RVLM) are key nuclei where insulin has been demonstrated to modulate cardiovascular reflexes. The first locus of integration for the EPR, BR and central command is the NTS which is high in neurons expressing insulin receptors (IRs). The IRs on these neurons are well positioned to modulate cardiovascular responses to exercise. Additionally, the differences in IR density and presence of receptor isoforms enable specificity and diversity of insulin actions within the CNS. Therefore, non-invasive delivery of insulin into the CNS may be an effective means of normalizing cardiovascular responses to exercise in patients with insulin resistance.

Two-week paramedic hospital training augments blood pressure response to isometric handgrip exercise in healthy young men

Persistent stressful situations can have detrimental cardiovascular effects; however, effects on the blood pressure (BP) response to exercise have not been fully examined. This study investigated the impact of a 2-wk stressful situation on the exercise pressor response. Eight healthy male university paramedic trainees underwent a 2-wk paramedic hospital training and a control period study. Pre- and postintervention, BP responses to the exercise test [2-min submaximal isometric handgrip (IHG) exercise followed by postexercise muscle ischemia (PEMI)] and cold pressure test (CPT) were assessed. A stress biomarker, salivary α-amylase (sAA) activity, significantly increased after hospital training (Pre: 8.8 ± 4.6; Post: 15.5 ± 7.3 kU/L; P = 0.036), whereas no significant changes were observed in the control period (Pre: 11.3 ± 3.6; Post: 10.4 ± 4.5 kU/L). Although no significant trial (hospital training vs. control)-by-intervention (pre- vs. post-2-wk period) interactions were detected in the mean arterial pressure (MAP) response to PEMI or CPT, a significant interaction in the MAP response to IHG exercise was noted (Δ48.9 ± 11.2 to Δ55.5 ± 9.1 mmHg, hospital training; Δ53.2 ± 14.1 to Δ51.2 ± 11.9 mmHg, control; P = 0.035). Consequently, changes in the sAA and MAP preintervention to postintervention showed a significant correlation (τ = 0.397, P = 0.036). Results showed that stressful paramedic hospital training augmented BP response to IHG exercise. This suggests that prolonged stressful situations increase pressor response to exercise, particularly in cases involving healthy young men.NEW & NOTEWORTHY Exposure to prolonged stressful situations augmented the blood pressure response to submaximal isometric exercise in healthy young men. This finding suggests that monitoring cardiovascular responses during exercise under chronic stress conditions could be important.

Correlation between triglyceride-glucose index and early neurological deterioration in patients with acute mild ischemic stroke

Objective

The Triglyceride-glucose Index (TyG) index is a dependable metric for assessing the degree of insulin resistance, serving as a standalone predictor of ischemic stroke risk, but its precise relationship with early neurological deterioration (END) remains incompletely expounded within the context of acute mild ischemic stroke patients. This research is to examine the correlation of the TyG index with END among patients experiencing acute mild ischemic stroke in China.

Methods

This retrospective analysis was conducted to systematically gather data regarding patients experiencing their maiden episode of acute mild ischemic stroke and hospitalized at the Neurology Department of Nanjing Meishan Hospital, located in Nanjing, Jiangsu Province, China, over the period extending from January 2020 to December 2022. The severity of stroke was determined through the utilization of the National Institutes of Health Stroke Scale (NIHSS) scores upon their admission. Demographic characteristics were collected, and measurements of fasting blood glucose, blood lipids, and glycosylated hemoglobin Alc levels were taken. END was defined as a one-point rise in the motor item function score on the NIHSS or a two-point increase in the overall score during the initial 72 h of hospitalization. For evaluating the correlation of the TyG index with END, a multivariate logistic regression analysis was carried out. To investigate whether there is a nonlinear relationship between the TyG index and END, smoothed curves were utilized.

Results

The study included 402 patients diagnosed with acute mild ischemic stroke, with a mean age of 66.15 ± 10.04 years. Within this population, 205 were males (51.00%) and 197 were females (49.00%). Among these patients, 107 (26.62%) experienced END within 72 h of admission. Patients who developed END showed higher levels of the TyG index in comparison to those who remained stable (9.18 ± 0.46 vs. 8.87 ± 0.46, p < 0.001). In a comprehensive multivariate logistic regression analysis, the TyG index positively correlates with END (OR = 3.63, 95% CI: 1.75-7.54, p = 0.001). Furthermore, individuals in the fourth TyG index quartile exhibited a 2.36-fold heightened risk of END compared to those in the first quartile (95% CI: 1.38-8.19, p = 0.008). TyG index has a linear correlation with END in the generalized additive model (Log likelihood ratio test, p = 0.525).

Conclusion

Our findings demonstrate that TyG index has a significant, independent, and positive correlation with END in Chinese individuals diagnosed with acute mild ischemic stroke. This underscores the TyG index's potential usefulness as a valuable risk stratification tool for stroke patients.

Glucose metabolism and autonomic function in healthy individuals and patients with type 2 diabetes mellitus at rest and during exercise

Autonomic dysfunction is a common complication of type 2 diabetes mellitus (T2DM). However, the character of dysfunction varies in different reports. Differences in measurement methodology and complications might have influenced the inconsistent results. We sought to evaluate comprehensively the relationship between abnormal glucose metabolism and autonomic function at rest and the response to exercise in healthy individuals and T2DM patients. We hypothesized that both sympathetic and parasympathetic indices would decrease with the progression of abnormal glucose metabolism in individuals with few complications related to high sympathetic tone. Twenty healthy individuals and 11 T2DM patients without clinically evident cardiovascular disease other than controlled hypertension were examined. Resting muscle sympathetic nerve activity (MSNA), heart rate variability, spontaneous cardiovagal baroreflex sensitivity (CBRS), sympathetic baroreflex sensitivity and the MSNA response to handgrip exercise were measured. Resting MSNA was lower in patients with T2DM than in healthy control subjects (P = 0.011). Resting MSNA was negatively correlated with haemoglobin A1c in all subjects (R = -0.45, P = 0.024). The parasympathetic components of heart rate variability and CBRS were negatively correlated with glycaemic/insulin indices in all subjects and even in the control group only (all, P < 0.05). In all subjects, the MSNA response to exercise was positively correlated with fasting blood glucose (R = 0.69, P < 0.001). Resting sympathetic activity and parasympathetic modulation of heart rate were decreased in relationship to abnormal glucose metabolism. Meanwhile, the sympathetic responses to handgrip were preserved in diabetics. The responses were correlated with glucose/insulin parameters throughout diabetic and control subjects. These results suggest the importance of a comprehensive assessment of autonomic function in T2DM.

Age-related alterations in the cardiovascular responses to acute exercise in males and females: role of the exercise pressor reflex

Autonomic adjustments of the cardiovascular system are critical for initiating and sustaining exercise by facilitating the redistribution of blood flow and oxygen delivery to meet the metabolic demands of the active skeletal muscle. Afferent feedback from active skeletal muscles evokes reflex increases in sympathetic nerve activity and blood pressure (BP) (i.e., exercise pressor reflex) and contributes importantly to these primary neurovascular adjustments to exercise. When altered, this reflex contributes significantly to the exaggerated sympathetic and BP response to exercise observed in many cardiovascular-related diseases, highlighting the importance of examining the reflex and its underlying mechanism(s). A leading risk factor for the pathogenesis of cardiovascular disease in both males and females is aging. Although regular exercise is an effective strategy for mitigating the health burden of aging, older adults face a greater risk of experiencing an exaggerated cardiovascular response to exercise. However, the role of aging in mediating the exercise pressor reflex remains highly controversial, as conflicting findings have been reported. This review aims to provide a brief overview of the current understanding of the influence of aging on cardiovascular responses to exercise, focusing on the role of the exercise pressor reflex and proposing future directions for research. We reason that this review will serve as a resource for health professionals and researchers to stimulate a renewed interest in this critical area.

Aging exaggerates blood pressure response to ischemic rhythmic handgrip exercise in humans

Ischemic skeletal muscle conditions are known to augment exercise-induced increases in blood pressure (BP). Aging is also a factor that enhances the pressor response to exercise. However, the effects of aging on the BP response to ischemic exercise remain unclear. We, therefore, tested the hypothesis that aging enhances the BP response to rhythmic handgrip (RHG) exercise during postexercise muscle ischemia (PEMI). We divided the normotensive participants without cardiovascular diseases into three age groups: young (n = 26; age, 18-28 years), middle-aged (n = 23; age, 35-59 years), and older adults (n = 23; age, 60-80 years). The participants performed RHG exercise with minimal effort for 1 min after rest with and without PEMI, which was induced by inflating a cuff on the upper arm just before the isometric handgrip exercise ended; the intensity was 30% of maximal voluntary contraction force. Under PEMI, the increase in diastolic BP (DBP) from rest to RHG exercise in the older adult group (Δ13 ± 2 mmHg) was significantly higher than that in the young (Δ5 ± 2 mmHg) and middle-aged groups (Δ6 ± 1 mmHg), despite there being no significant difference between the groups in the DBP response from rest to RHG exercise without PEMI. Importantly, based on multiple regression analysis, age remained a significant independent determinant of both the SBP and DBP responses to RHG exercise during PEMI (p < 0.01). These findings indicate that aging enhances the pressor response to ischemic rhythmic exercise.

The Impact of Insulin Resistance on Cardiovascular Control During Exercise in Diabetes

Patients with diabetes display heightened blood pressure response to exercise, but the underlying mechanism remains to be elucidated. There is no direct evidence that insulin resistance (hyperinsulinemia or hyperglycemia) impacts neural cardiovascular control during exercise. We propose a novel paradigm in which hyperinsulinemia or hyperglycemia significantly influences neural regulatory pathways controlling the circulation during exercise in diabetes.

Neurovascular Dysregulation During Exercise in Type 2 Diabetes

Emerging evidence suggests that type 2 diabetes (T2D) may impair the ability to properly adjust the circulation during exercise with augmented blood pressure (BP) and an attenuated contracting skeletal muscle blood flow (BF) response being reported. This review provides a brief overview of the current understanding of these altered exercise responses in T2D and the potential underlying mechanisms, with an emphasis on the sympathetic nervous system and its regulation during exercise. The research presented support augmented sympathetic activation, heightened BP, reduced skeletal muscle BF, and impairment in the ability to attenuate sympathetically mediated vasoconstriction (i.e., functional sympatholysis) as potential drivers of neurovascular dysregulation during exercise in T2D. Furthermore, emerging evidence supporting a contribution of the exercise pressor reflex and central command is discussed along with proposed future directions for studies in this important area of research.

TRPV1 (Transient Receptor Potential Vanilloid 1) Sensitization of Skeletal Muscle Afferents in Type 2 Diabetic Rats With Hyperglycemia

[Figure: see text].