Age and sex differences in microvascular responses during reactive hyperaemia

Microvascular impairments are typical of several cardiovascular diseases. Near-infrared spectroscopy (NIRS) combined with a vascular occlusion test provides non-invasive insights into microvascular responses by monitoring skeletal muscle oxygenation changes during reactive hyperaemia. Despite increasing interest in the effects of sex and ageing on microvascular responses, evidence remains inconsistent. Therefore, the present study aimed to investigate the effects of sex and age on microvascular responsiveness. Twenty-seven participants (seven young men and seven young women; seven older men and six older women; aged 26 ± 1, 26 ± 4, 67 ± 3 and 69 ± 4 years, respectively) completed a vascular occlusion test consisting of 5 min of arterial occlusion followed by 5 min reperfusion. Oxygenation changes in the vastus lateralis were monitored by near-infrared spectroscopy. The findings revealed that both women (referring to young and older women) and older participants (referring to both men and women) exhibited lower microvascular responsiveness. Notably, both women and older participants demonstrated reduced desaturation (-38% and -59%, respectively) and reperfusion rates (-24% and -40%, respectively) along with a narrower range of tissue oxygenation (-39% and -39%, respectively) and higher minimal tissue oxygenation levels (+34% and +21%, respectively). Women additionally displayed higher values in resting (+12%) and time-to-peak (+15%) tissue oxygenation levels. In conclusion, this study confirmed decreased microvascular responses in women and older individuals. These results emphasize the importance of considering sex and age when studying microvascular responses. Further research is needed to uncover the underlying mechanisms and clinical relevance of these findings, enabling the development of tailored strategies for preserving vascular health in diverse populations.

NIRS-Derived Muscle-Deoxygenation and Microvascular Reactivity During Occlusion-Reperfusion at Rest Are Associated With Whole-Body Aerobic Fitness

Purpose: Near-infrared spectroscopy (NIRS) indices during arterial occlusion-reperfusion maneuver have been used to examine the muscle's oxidative metabolism and microvascular function-important determinants of whole-body aerobic-fitness. The association of NIRS-derived parameters with whole-body VO2max was previously examined using a method requiring exercise (or electrical stimulation) followed by multiple arterial occlusions. We examined whether NIRS-derived indices of muscle deoxygenation and microvascular reactivity assessed during a single occlusion-reperfusion at rest are (a) associated with maximal/submaximal indices of whole-body aerobic-fitness and (b) could discriminate individuals with different VO2max. We, also, investigated which NIRS-parameter during occlusion-reperfusion correlates best with whole-body aerobic-fitness. Methods: Twenty-five young individuals performed an arterial occlusion-reperfusion at rest. Changes in oxygenated- and deoxygenated-hemoglobin (O2Hb and HHb, respectively) in vastus-lateralis were monitored; adipose tissue thickness (ATT) at NIRS-application was assessed. Participants also underwent a maximal incremental exercise test for VO2max, maximal aerobic velocity (MAV), and ventilatory-thresholds (VTs) assessments. Results: The HHbslope and HHbmagnitude of increase (occlusion-phase) and O2Hbmagnitude of increase (reperfusion-phase) were strongly correlated with VO2max (r = .695-.763, p < .001) and moderately with MAV (r = .468-.530; p < .05). O2Hbmagnitude was moderately correlated with VTs (r = .399-.414; p < .05). After controlling for ATT, the correlations remained significant for VO2max (r = .672-.704; p < .001) and MAV (r = .407; p < .05). Individuals in the high percentiles after median and tritile splits for HHbslope and O2Hbmagnitude had significantly greater VO2max vs. those in low percentiles (p < .01-.05). The HHbslope during occlusion was the best predictor of VO2max. Conclusion: NIRS-derived muscle deoxygenation/reoxygenation indices during a single arterial occlusion-reperfusion maneuver are strongly associated with whole-body maximal indices of aerobic-fitness (VO2max, MAV) and may discriminate individuals with different VO2max.

Canagliflozin improves coronary microvascular vasodilation and increases absolute blood flow to the myocardium independent of angiogenesis

OBJECTIVES

Sodium-glucose cotransporter-2 inhibitor, canagliflozin, improves myocardial perfusion to ischemic territory without accompanying changes in vascular density. We aimed to (1) characterize effects on angiogenic pathways, (2) use multiomics to identify gene expression and metabolite profiles relevant to regulation of myocardial blood flow, and (3) investigate drug effect on coronary microvascular reactivity.

METHODS

A nondiabetic swine model of chronic myocardial ischemia and nondiabetic rat model were used to study functional and molecular effects of canagliflozin on myocardium and in vitro microvascular reactivity.

RESULTS

Canagliflozin resulted in increased coronary microvascular vasodilation and decreased vasoconstriction (P < .05) without changes in microvascular density (P > .3). Expression of the angiogenic modulator, endostatin, increased (P = .008), along with its precursor, collagen 18 (P < .001), and factors that increase its production, including cathepsin L (P = .004). Endostatin and collagen 18 levels trended toward an inverse correlation with blood flow to ischemic territory at rest. Proangiogenic fibroblast growth factor receptor was increased (P = .03) and matrix metalloproteinase-9 was decreased (P < .001) with canagliflozin treatment. Proangiogenic vascular endothelial growth factor A (P = .13), Tie-2 (P = .10), and Ras (P = .18) were not significantly altered. Gene expression related to the cardiac renin-angiotensin system was significantly decreased.

CONCLUSIONS

In chronic myocardial ischemia, canagliflozin increased absolute blood flow to the myocardium without robustly increasing vascular density or proangiogenic signaling. Canagliflozin resulted in altered coronary microvascular reactivity to favor vasodilation, likely through direct effect on vascular smooth muscle. Downregulation of cardiac renin-angiotensin system demonstrated local regulation of perfusion. VIDEO ABSTRACT.

Impaired peripheral microvascular reactivity in patients with nonobstructive coronary artery disease

OBJECTIVE

This study aimed to determine whether peripheral microvascular reactivity is impaired in patients with nonobstructive coronary artery disease (NOCAD).

METHODS

Stable patients presenting with angina were recruited and, based on results from coronary angiography, were categorized into OCAD (coronary stenosis of ≥50%) and NOCAD (stenosis <50%) groups. A control group with no history of angina was also recruited. Forearm skin microvascular reactivity was measured using the laser Doppler blood perfusion monitor and the process of postocclusive skin reactive hyperemia (PORH).

RESULTS

Patients were categorized into OCAD (n = 42), NOCAD (n = 40), and control (n = 39) groups. Compared with the control group, the PORH perfusion percent change (PORH% change) was significantly lower in the OCAD and NOCAD groups. No significant differences were noted between the OCAD and NOCAD groups. Additionally, the NOCAD group without any coronary obstruction takes a longer time to reach peak perfusion and had lower PORH% change compared with the nonangina control group.

CONCLUSION

Angina patients with NOCAD have microvascular dysfunction as demonstrated by reduced magnitude of reperfusion with an ischemic stimulus. NOCAD patients without coronary obstruction also displayed a slower response to reperfusion.

Muscle Oxygenation and Microvascular Reactivity Across Different Stages of CKD: A Near-Infrared Spectroscopy Study

RATIONALE & OBJECTIVE

Previous studies in chronic kidney disease (CKD) showed that vascular dysfunction in different circulatory beds progressively deteriorates with worsening CKD severity. This study evaluated muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with different stages of CKD versus controls.

STUDY DESIGN

Observational controlled study.

SETTING & PARTICIPANTS

90 participants (18 per CKD stage 2, 3a, 3b, and 4, as well as 18 controls).

PREDICTOR

CKD stage.

OUTCOME

The primary outcome was muscle oxygenation at rest. Secondary outcomes were muscle oxygenation during occlusion-reperfusion and exercise, and muscle microvascular reactivity (hyperemic response).

ANALYTICAL APPROACH

Continuous measurement of muscle oxygenation [tissue saturation index (TSI)] using near-infrared spectroscopy at rest, during occlusion-reperfusion, and during a 3-minute handgrip exercise (at 35% of maximal voluntary contraction). Aortic pulse wave velocity and carotid intima-media thickness were also recorded.

RESULTS

Resting muscle oxygenation did not differ across the study groups (controls: 64.3% ± 2.9%; CKD stage 2: 63.8% ± 4.2%; CKD stage 3a: 64.1% ± 4.1%; CKD stage 3b: 62.3% ± 3.3%; CKD stage 4: 62.7% ± 4.3%; P=0.6). During occlusion, no significant differences among groups were detected in the TSI occlusion magnitude and TSI occlusion slope. However, during reperfusion the maximum TSI value was significantly lower in groups of patients with more advanced CKD stages compared with controls, as was the hyperemic response (controls: 11.2%±3.7%; CKD stage 2: 8.3%±4.6%; CKD stage 3: 7.8%±5.5%; CKD stage 3b: 7.3%±4.4%; CKD stage 4: 7.2%±3.3%; P=0.04). During the handgrip exercise, the average decline in TSI was marginally lower in patients with CKD than controls, but no significant differences were detected across CKD stages.

LIMITATIONS

Moderate sample size, cross-sectional evaluation.

CONCLUSIONS

Although no differences were observed in muscle oxygenation at rest or during occlusion, the microvascular hyperemic response during reperfusion was significantly impaired in CKD and was most prominent in more advanced CKD stages. This impaired ability of microvasculature to respond to stimuli may be a crucial component of the adverse vascular profile of patients with CKD and may contribute to exercise intolerance.

The Efficacy of Exercise Training for Cutaneous Microvascular Reactivity in the Foot in People with Diabetes and Obesity: Secondary Analyses from a Randomized Controlled Trial

It is unclear if cutaneous microvascular dysfunction associated with diabetes and obesity can be ameliorated with exercise. We investigated the effect of 12-weeks of exercise training on cutaneous microvascular reactivity in the foot. Thirty-three inactive adults with type 2 diabetes and obesity (55% male, 56.1 ± 7.9 years, BMI: 35.8 ± 5, diabetes duration: 7.9 ± 6.3 years) were randomly allocated to 12-weeks of either (i) moderate-intensity continuous training [50−60% peak oxygen consumption (VO2peak), 30−45 min, 3 d/week], (ii) low-volume high-intensity interval training (90% VO2peak, 1−4 min, 3 d/week) or (iii) sham exercise placebo. Post-occlusive reactive hyperaemia at the hallux was determined by laser-Doppler fluxmetry. Though time to peak flux post-occlusion almost halved following moderate intensity exercise, no outcome measure reached statistical significance (p > 0.05). These secondary findings from a randomised controlled trial are the first data reporting the effect of exercise interventions on cutaneous microvascular reactivity in the foot in people with diabetes. A period of 12 weeks of moderate-intensity or low-volume high-intensity exercise may not be enough to elicit functional improvements in foot microvascular reactivity in adults with type 2 diabetes and obesity. Larger, sufficiently powered, prospective studies are necessary to determine if additional weight loss and/or higher exercise volume is required.

[Effects of 12-week Tai Chi exercise on the microvascular reactivity of the middle-aged and elderly patients with mild hypertension and its mechanism]

Objective: To study the effects of 12-week Taijiquan exercise on the microvascular reactivity of middle-aged and elderly patients with mild hypertension and to explore the mechanisms of microvascular reactivity. Methods: Thirty patients with mild hypertension were divided into exercise group (53.8±6.3 years old) and control group (52.6±7.5 years old). The number and gender ratio of the two groups were the same. The exercise group performed Tai Chi exercise for 12 weeks, and the control group maintained the original lifestyle and did not do other regular sports. The two groups of subjects were tested for microvascular reactivity, blood pressure, serum nitric oxide content, and nitric oxide synthase activity before exercise intervention, 6th week and 12th week, respectively. Results: There was no significant difference in the basic values of each index between the two groups of subjects before the test (P＞ 0.05). In the 6th week, the microvascular reactivity (blood flow increase rate), systolic blood pressure, diastolic blood pressure, nitric oxide content, nitric oxide synthase activity of the exercise group did not significantly change from the basic value (P＞0.05). At the 12th week, the microvascular reactivity, nitric oxide content, c nitric oxide synthase activity were significantly higher than those of the base values and the control group (P＜0.05), but the systolic blood pressure and diastolic blood pressure were significantly lower than those of the base values and control group (P＜0.05). In the control group, there were no significant changes in the 6th and 12th week values of each index from the basic value (P＞0.05). Conclusion: Twelve weeks of Taijiquan exercise can improve the microvascular reactivity of middle-aged hypertensive patients, reduce blood pressure, and increase the nitric oxide content and c nitric oxide synthase of patients. The increase of endogenous nitric oxide production is one of the biological mechanisms of Tai Chi exercise to improve the microvascular responsiveness of hypertension patients.

Effects of exenatide on microvascular reactivity in patients with type 2 diabetes and coronary artery disease: A randomized controlled study

OBJECTIVE

We studied the effect of the GLP-1RA exenatide on skin microvascular function in patients with T2DM and CAD.

METHODS

Thirty-five patients with T2DM, CAD, and HbA1C 42-86 mmol/mol were randomized to treatment with exenatide or conventional non-GLP-1-based therapy for 12 weeks. Skin microvascular function was examined in the forearm by LDF and iontophoretic application of acetyl choline and SNP, and by PORH at baseline and after 12 weeks. Blood samples for fasting plasma glucose, HbA1C, and lipid profile were collected.

RESULTS

At 12 weeks, patients on exenatide showed reductions in HbA1C (from 63.5 ± 13 to 60.7 ± 14 mmol/mol, p = .065), body weight (from 92.6 ± 16 to 89 ± 16 kg, p < .001), and systolic blood pressure (from 141 ± 13 to 134 ± 16 mm Hg, p < .05) as compared to the conventionally treated group. There were no significant changes in skin microvascular function between or within the two groups at follow-up.

CONCLUSIONS

Three months' daily treatment with the GLP-1RA exenatide in T2DM patients with CAD showed no significant effects on skin microvascular function or blood glucose control, while this study confirms a reduction in body weight and blood pressure by exenatide, as compared to conventional antidiabetic drug treatment.

Systemic microvascular dysfunction in COVID-19

COVID-19, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), while having lung injury as its most prominent feature, has been increasingly shown to affect endothelial cell function and the microvasculature. In this report, a woman with COVID-19, cardiac valve disease and spherocytosis was assessed with laser Doppler perfusion monitoring. Systemic microvascular reactivity was impaired during a worsening phase of COVID-19, but improved after clinical recovery; microcirculatory dysfunction paralleled systemic inflammation and pulmonary involvement. The assessment of systemic microcirculatory function may therefore provide insights on COVID-19 pathophysiology.

Assessing Renal Microvascular Reactivity by Laser Speckle-Contrast Imaging in Angiotensin-II-Treated Mice

Introduction

The kidney is one of the main organs affected by microvascular damage wrought by hypertension. We developed an approach to investigate renal microcirculatory disturbance in live mice by measuring post-occlusive reactive hyperemia (PORH), a reactivity test exploring endothelial and neuro-microvascular functioning. Laser speckle-contrast analysis (LASCA) assesses microvascular blood flow; it provides real-time images of spatial and temporal blood flow dynamics. We compared basal blood flow and PORH test between control and angiotensin-II-treated mice (Ang-II) to validate the model.

Objective

The study objective was to develop an approach to investigate renal microcirculation, and then to compare microvascular reactivity assessed on LASCA in control versus Ang-II mice.

Methods

Thirty 7-week-old wild-type C57BL/6J mice were allocated into two groups. One received angiotensin-II via osmotic minipumps (Ang-II; n=15); the other served as control (n=15). Basal blood flow was measured on LASCA. The PORH test was then performed in the two groups.

Results

Control mice had significantly lower basal renal microcirculatory flow, expressed in perfusion units (PU), than Ang-II-treated mice (1448 ± 96 vs 1703 ± 185 PU, respectively; P < 0.05). Peak flow was lower in controls than in Ang-II mice (1617±104 vs.1724 ± 205 PU, respectively; P=0.21). Control mice had significantly higher kidney PORH than Ang-II mice (8±3 vs 1±4%, respectively; P < 0.05).

Conclusion

We developed an innovative technique to study renal microcirculation in mice. Ang-II-treated mice showed significantly higher basal blood flow than controls, while PORH was significantly higher in controls than in Ang-II mice.

Impaired microvascular reactivity in gestational diabetes is associated with altered glycemic parameters

OBJECTIVES

To assess microvascular reactivity and glycemic parameters in GDM compared to age and GA matched controls.

METHODS

This study involved 21 GDM patients and 31 controls. Microvascular reactivity was assessed using LDF and PORH. Microvascular parameters; PORH_max , PORH_peak , and time to peak perfusion (Tp) were recorded after the release of 3 minutes' upper arm occlusion. HOMA-IR was performed to evaluate insulin resistance.

RESULTS

Average age and GA for subjects were 32.9 years and 29.2 weeks. Mean FBG and a 2-hour postprandial for GDM and controls were 4.87 ± 0.71 vs 3.99 ± 0.59 mmol/L; P < 0.001 and 9.50 ± 1.8 vs 5.67 ± 1.0 mmol/L; P < 0.001. Fasting insulin (13.88 ± 18.9 vs 8.37 ± 11.0 μLU/mL; P = 0.031) and HOMA-IR (3.14 ± 4.6 vs 1.52 ± 2.2; P = 0.004) were higher in GDM. Tp was prolonged in GDM (16.27 ± 4.3 vs 13.86 ± 2.1 seconds; P = 0.011). Positive correlations were seen between Tp and FBG and 2-hour postprandial levels.

CONCLUSION

Tp was prolonged in GDM compared to age-matched controls, indicating impaired microvascular reactivity.

Enhanced coronary arteriolar contraction to vasopressin in patients with diabetes after cardiac surgery

OBJECTIVE

Cardioplegic arrest (CP) and cardiopulmonary bypass (CPB) are associated with vasomotor dysfunction of coronary arterioles in patients with diabetes (DM) undergoing cardiac surgery. We hypothesized that DM may up-regulate vasopressin receptor expression and alter the contractile response of coronary arterioles to vasopressin in the setting of CP/CPB.

METHODS

Right atrial tissue samples of patients with DM and without (ND) (n = 8 in each group) undergoing cardiac surgery were harvested before and after CP/CPB. The isolated coronary arterioles (80-150 μm) dissected from the harvested right atrial tissue samples were cannulated and pressurized (40 mm Hg) in a no-flow state. The changes in diameter were measured with video microscopy. The protein expression/localization of vasopressin 1A receptors (V1A) and vasopressin 1B receptors (V1B) in the atrial tissue were measured by immune-blotting and immunohistochemistry.

RESULTS

The pre-CP/CPB contractile responses of the coronary arterioles to vasopressin were significantly increased post-CP/CPB in both the ND and DM groups. This effect was more pronounced in the vessels from patients in the DM group than that of vessels from patients in the ND group (P < .05). Vasopressin-induced contractile response of the coronary arterioles was inhibited in the presence of the specific V1A antagonist SR 49059 (10^-7 M) in both ND and DM vessels (P < .05). The post-CP/CPB protein levels of V1A were significantly increased compared with pre-CP/CPB values in both the ND and DM groups (P < .05), whereas this increase was greater in DM than that of ND (P < .05). Immunohistochemistry staining further indicates that V1B were mainly expressed in the myocardium but not in vascular smooth muscle.

CONCLUSIONS

CP/CPB and DM are both associated with up-regulation in V1 receptor expression/localization in human myocardium. Vasopressin may induce coronary arteriolar constriction via V1A. This alteration may lead to increased coronary arteriolar spasm in patients with DM undergoing CP/CPB and cardiac surgery.

Altered distribution of adrenergic constrictor responses contributes to skeletal muscle perfusion abnormalities in metabolic syndrome

PURPOSE

Although studies suggest elevated adrenergic activity paralleling metabolic syndrome in OZRs, the moderate hypertension and modest impact on organ perfusion question the multi-scale validity of these data.

METHODS

To understand how adrenergic function contributes to vascular reactivity in OZR, we utilized a multi-scale approach to investigate pressure responses, skeletal muscle blood flow, and vascular reactivity following adrenergic challenge.

RESULTS

For OZR, adrenergic challenge resulted in increased pressor responses vs LZRs, mediated via α₁ receptors, with minimal contribution by either ROS or NO bioavailability. In situ gastrocnemius muscle of OZR exhibited blunted functional hyperemia, partially restored with α₁ inhibition, although improved muscle performance and VO₂ required combined treatment with TEMPOL. Within OZR in situ cremaster muscle, proximal arterioles exhibited a more heterogeneous constriction to adrenergic challenge, biased toward hyperresponsiveness, vs LZR. This increasingly heterogeneous pattern was mirrored in ex vivo arterioles, mediated via α₁ receptors, with roles for ROS and NO bioavailability evident in hyperresponsive vessels only.

CONCLUSIONS

These results support the central role of the α₁ adrenoreceptor for augmented pressor responses and elevations in vascular resistance, but identify an increased heterogeneity of constrictor reactivity in OZR that is presently of unclear purpose.

Cardiometabolic and traditional cardiovascular risk factors and their potential impact on macrovascular and microvascular function: preliminary data

We studied the relationship between cardiovascular status (CV) and risk factor numbers, macrovascular (flow mediated dilatation: FMD) and microvascular function using near-infrared spectroscopy (NIRS) in adults with different CV status. Seventy adults with different CV status (27 controls, 18 metabolic syndrome (MetS) and 25 coronary heart disease (CHD) patients) underwent a 5-min forearm arterial occlusion in supine position. High-resolution ultrasound examination of the brachial artery was performed during 1 minute at rest and 45 to 120 seconds after cuff release. Oxy, de-oxy and total hemoglobin signals (O2Hb, HHb and tHb) were measured continuously with NIRS on brachio-radialis muscle. FMD was reduced in CHD patients (P<0.05) compared to controls. Max. amplitude of O2Hb and Hmax of tHb were reduced (P<0.05) in MetS patients vs. controls. Post-deflation area under the curve (A.U.C) of O2Hb was lower in CHD (P<0.01) patients vs. controls and MetS patients. Independent predictors of microvascular function (A.U.C of O2Hb) were abdominal obesity and LDL-cholesterol whereas macrovascular function (FMD) was predicted by CV status. Only A.U.C of O2Hb related to CV risk numbers whereas FMD was not. Although macro and microvascular function were impaired in MetS and CHD patients, microvascular function was more strongly related to CV risk factors.

Impact of age and gender on microvascular function

BACKGROUND

Microcirculatory function can be assessed by postocclusive reactive hyperaemia (PORH) using laser Doppler fluxmetry. Previous studies have shown that PORH reveals microvascular damage at an early stage. In particular, at younger ages, PORH might depend on age and gender. To implement PORH into a larger scale of clinical studies, one has to be aware of the influence of age and gender on microcirculation. The aim of this study was to assess the impact of age and gender on microcirculatory function during adolescence.

MATERIALS AND METHODS

Within the scope of an epidemiological project, 896 children and adolescents underwent assessment of PORH by laser Doppler fluxmetry. Microcirculatory parameters during PORH (baseline perfusion, biological zero, peak perfusion, time to peak perfusion and recovery time) were analysed in relation to age (by tertiles) and gender.

RESULTS

Baseline perfusion, biological zero and peak perfusion were lower in children/adolescents in the upper age tertile (12·3-18·1 years) than in the middle (9·8-12·2 years) and lower (4·3-9·7 years) age tertiles (P < 0·0001). In the total of participants, baseline perfusion, biological zero and peak perfusion were higher in males than in females (P < 0·0001). Analysing microcirculatory parameters as a function of age and gender, the sex differences were only apparent in the upper and the middle age tertiles, but not in the lower.

CONCLUSIONS

During adolescence, PORH is a function of age. At higher age, microvascular reactivity considerably depends on gender, whereas no sex differences are present at younger ages.

Effects of acute bouts of endurance exercise on retinal vessel diameters are age and intensity dependent

Alterations of retinal vessel diameters are associated with increased cardiovascular risk. We aimed to investigate changes in retinal vessel diameters in response to acute dynamic exercise of different intensities and whether these changes are age dependent. Seventeen healthy seniors (median (IQR) age 68 (65, 69) years) and 15 healthy young adults (median (IQR) age 26 (25, 28) years) first performed a maximal treadmill test (MTT) followed by a submaximal treadmill test (SMTT) and a resting control condition in randomised order. Central retinal arteriolar (CRAE) and central retinal venular (CRVE) diameter equivalents were measured before as well as 5 (t5) and 40 (t40) minutes after exercise cessation using a static retinal vessel analyser. Both exercise intensities induced a significant dilatation in CRAE and CRVE at t5 compared to the control condition (P < 0.001). At t40, the mean increase in CRAE and CRVE was greater for MTT compared to that for SMTT (CRAE 1.7 μm (95 % confidence interval (CI) -0.1, 3.6; P = 0.061); CRVE 2.2 μm (95 % CI 0.4, 4.1; P = 0.019)). However, the estimated difference at t5 between seniors and young adults in their response to MTT compared to SMTT was 5.3 μm (95 % CI 2.0, 8.5; P = 0.002) for CRAE and 4.1 μm (95 % CI -0.4, 8.6; P = 0.076) for CRVE. Wider arteries and veins after maximal versus submaximal exercise for seniors compared to young adults suggest that myogenic vasoconstriction in response to exhaustive exercise may be reduced in seniors. Age-related loss of vascular reactivity has clinical implications since the arteriolar vasoconstriction protects the retinal capillary bed from intraluminal pressure peaks.

Gender differences in microcirculation: observation using the hamster cheek pouch

OBJECTIVES

Estrogen has been shown to play an important protective role in non-reproductive systems, such as the cardiovascular system. Our aim was to observe gender differences in vivo with regard to the increase in macromolecular permeability and leukocyte-endothelium interaction induced by ischemia/reperfusion as well as in microvascular reactivity to vasoactive substances using the hamster cheek pouch preparation.

METHODS

Thirty-six male and 36 female hamsters, 21 weeks old, were selected for this study, and their cheek pouches were prepared for intravital microscopy. An increase in the macromolecular permeability of post-capillary venules was quantified as a leakage of intravenously injected fluorescein-labeled dextran, and the leukocyte-endothelium interaction was measured as the number of fluorescent rolling leukocytes or leukocytes adherent to the venular wall, labeled with rhodamin G, during reperfusion after 30 min of local ischemia. For microvascular reactivity, the mean internal diameter of arterioles was evaluated after the topical application of different concentrations of two vasoconstrictors, phenylephrine (α1-agonist) and endothelin-1, and two vasodilators, acetylcholine (endothelial-dependent) and sodium nitroprusside (endothelial-independent).

RESULTS

The increase in macromolecular permeability induced by ischemia/reperfusion was significantly lower in females compared with males [19 (17-22) leaks/cm2 vs. 124 (123-128) leaks/cm2, respectively, p<0.001), but the number of rolling or adherent leukocytes was not different between the groups. Phenylephrine-induced arteriolar constriction was significantly lower in females compared with males [77 (73-102)% vs. 64 (55-69)%, p<0.04], but there were no detectable differences in endothelin-1-dependent vasoreactivity. Additionally, arteriolar vasodilatation elicited by acetylcholine or sodium nitroprusside did not differ between the groups.

CONCLUSION

The female gender could have a direct protective role in microvascular reactivity and the increase in macromolecular permeability induced by ischemia/reperfusion.

Cardiovascular reactivity, stress, and physical activity

Psychological stress has been proposed as a major contributor to the progression of cardiovascular disease (CVD). Acute mental stress can activate the sympathetic-adrenal-medullary (SAM) axis, eliciting the release of catecholamines (NE and EPI) resulting in the elevation of heart rate (HR) and blood pressure (BP). Combined stress (psychological and physical) can exacerbate these cardiovascular responses, which may partially contribute to the elevated risk of CVD and increased proportionate mortality risks experienced by some occupations (e.g., firefighting and law enforcement). Studies have supported the benefits of physical activity on physiological and psychological health, including the cardiovascular response to acute stress. Aerobically trained individuals exhibit lower sympathetic nervous system (e.g., HR) reactivity and enhanced cardiovascular efficiency (e.g., lower vascular reactivity and decreased recovery time) in response to physical and/or psychological stress. In addition, resistance training has been demonstrated to attenuate cardiovascular responses and improve mental health. This review will examine stress-induced cardiovascular reactivity and plausible explanations for how exercise training and physical fitness (aerobic and resistance exercise) can attenuate cardiovascular responses to stress. This enhanced functionality may facilitate a reduction in the incidence of stroke and myocardial infarction. Finally, this review will also address the interaction of obesity and physical activity on cardiovascular reactivity and CVD.

Effects of oral administration of different doses of purified micronized flavonoid fraction on microvascular reactivity after ischaemia/reperfusion in the hamster cheek pouch

1. The effects of a purified micronized flavonoid fraction (S5682) on mean internal diameter and blood flow of arterioles and venules, as well as the functional capillary density (FCD) were evaluated in the hamster cheek pouch microvasculature before and after 90 min of total ischaemia. 2. Male hamsters were treated for ten days, twice a day, with oral doses of S5682 (5, 20, 80 and 160 mg kg-1 day-1) or placebo (10% lactose solution). The cheek pouch preparation was placed under an intravital microscope coupled to a closed circuit TV system. Local ischaemia was obtained by a cuff mounted around the neck of the everted pouch where it leaves the mouth of the hamster. 3. Measurements were performed before ischaemia, at the onset of reperfusion and 10, 20, 30, 45 and 60 min thereafter. Diameters were measured by means of an image shearing device. Red blood cell (RBC) velocity was analysed by use of the dual-slit photometric technique. Blood flow was calculated from diameters and RBC velocities. FCD, defined as the number of capillaries with flowing blood per field of observation, was also assessed. 4. During reperfusion, placebo-treated animals showed a significant vasodilatation, a decrease in blood flow and FCD and S5682-treated animals showed a clear trend, dose-dependent, towards maintaining these parameters closer to the value found before ischaemia. 5. In conclusion, our results indicate that S5682 improves the microvascular reactivity and FCD after ischaemia/reperfusion. These data suggest that S5682 could function as an antioxidant, which may explain its beneficial therapeutic effect in chronic venous insufficiency where oxidative stress is involved in the pathological mechanism.