Exercise capacity in heart transplant recipients: relation to impaired endothelium-dependent vasodilation of the peripheral microcirculation

Correlation between peripheral endothelial function, oxygen consumption and ventilatory efficiency in heart transplantation recipients

BACKGROUND

Endothelial dysfunction and peak oxygen uptake (VO2peak) are also predictors of increased risk of cardiovascular events in heart transplantation (HTx) recipients. The preservation of endothelial function may contribute to exercise tolerance.

OBJECTIVE

To investigate the correlation between peripheral endothelial function and exercise tolerance through VO2peak and ventilation to carbon dioxide production slope (VE / VCO2 slope) in HTx recipients.

METHODS

A pilot cross-sectional study was conducted with adult individuals aged 18-65 years, HTx ≥ six months after surgery, who had a stable medical condition and no changes over the last three months of immunosuppressive treatment. The patients underwent an assessment of endothelial function through PAT (EndoPAT-2000®) and performed a cardiopulmonary exercise test (CPET).

RESULTS

A total of 41% of the studied population presented endothelial dysfunction. The individuals were divided into two groups: the endothelial dysfunction (GED; n=9) group and the normal endothelial function (GNEF; n=13) group according to the logarithm of the reactive hyperemia index (LnRHI). There was a positive and moderate correlation between the LnRHI and VO2 peak (r=0.659, p=0.013) and a negative and moderate correlation between the LnRHI and VE/VCO2 slope (r= -0.686, p= 0.009) in the GNEF. However, no significant correlations were found in the GED.

CONCLUSION

The results showed that the preservation of peripheral endothelial function is significantly correlated with an increase in exercise tolerance in individuals after HTx. These findings bring important considerations for cardiovascular risk prevention and emphasize that therapeutic strategies with physical training programs must be implemented early.

Exercise-based rehabilitation strategies in heart transplant recipients: Focus on high-intensity interval training

Despite progressive improvement in medical therapy and standard care, the exercise capacity of heart transplant recipients is reduced compared with age-matched healthy individuals. Exercise-based rehabilitation programs have been shown to improve the exercise capacity of transplant patients through a multifactorial effect. In this context, high-intensity interval exercise is a growing field of research, with current evidence suggesting a major benefit in heart transplant recipients compared with a conventional training protocol. Therefore, this study aimed to provide an overview of the mechanisms involved in the reduced exercise capacity of heart transplant patients and a review of current rehabilitation strategies with a special focus on the mechanisms and clinical effects of high-intensity interval training exercise.

Changes in Resting and Exercise Hemodynamics Early After Heart Transplantation: A Simulation Perspective

Introduction: During heart transplantation (HTx), cardiac denervation is inevitable, thus typically resulting in chronic resting tachycardia and chronotropic incompetence with possible consequences in patient quality of life and clinical outcomes. To this date, knowledge of hemodynamic changes early after HTx is still incomplete. This study aims at providing a model-based description of the complex hemodynamic changes at rest and during exercise in HTx recipients (HTxRs). Materials and Methods: A numerical model of early HTxRs is developed that integrates intrinsic and autonomic heart rate (HR) control into a lumped-parameter cardiovascular system model. Intrinsic HR control is realized by a single-cell sinoatrial (SA) node model. Autonomic HR control is governed by aortic baroreflex and pulmonary stretch reflex and modulates SA node activity through neurotransmitter release. The model is tuned based on published clinical data of 15 studies. Simulations of rest and exercise are performed to study hemodynamic changes associated with HTxRs. Results: Simulations of HTxRs at rest predict a substantially increased HR [93.8 vs. 69.5 beats/min (bpm)] due to vagal denervation while maintaining normal cardiac output (CO) (5.2 vs. 5.6 L/min) through a reduction in stroke volume (SV) (55.4 vs. 82 mL). Simulations of exercise predict markedly reduced peak CO (13 vs. 19.8 L/min) primarily resulting from diminished peak HRs (133.9 vs. 169 bpm) and reduced ventricular contractility. Yet, the model results show that HTxRs can maintain normal CO for low- to medium-intensity exercise by increased SV augmentation through the Frank-Starling mechanism. Conclusion: Relevant hemodynamic changes occur after HTx. Simulations suggest that (1) increased resting HRs solely result from the absence of vagal tone; (2) chronotropic incompetence is the main limiting factor of exercise capacity whereby peripheral factors play a secondary role; and (3) despite the diminished exercise capacity, HTxRs can compensate chronotropic incompetence by a preload-mediated increase in SV augmentation and thus maintain normal CO in low- to medium-intensity exercise.

Cardiopulmonary, biomarkers, and vascular responses to acute hypoxia following cardiac transplantation

Previous studies have suggested good adaptation of cardiac transplant (CTx) recipients to exposure to a high altitude. No studies have investigated the cardiopulmonary and biomarker responses to acute hypoxic challenges following CTx. Thirty-six CTx recipients and 17 age-matched healthy controls (HC) were recruited. Sixteen (16) patients (42%) had cardiac allograft vasculopathy (CAV). Cardiopulmonary responses to maximal and submaximal exercise at 21% O₂ , 20-minutes hypoxia (11.5% O₂ ), and following a 10-minute exposure to 11.5% O₂ using 30% of peak power output were completed. Vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), suppression of tumorigenicity 2 (ST2) were measured at baseline and at peak stress. Endothelial peripheral function was assessed using near-infrared spectroscopy. Compared with HC, CTx presented a lesser O₂ desaturation both at rest (-19.4 ± 6.8 [CTx] vs -24.2 ± 6.0% O₂ [HC], P < 0.05) and following exercise (-23.2 ± 4.9 [CTx] vs -26.2 ± 4.7% O₂ [HC], P < 0.05). CTx patients exhibited a significant decrease in peak oxygen uptake. IL-6 and VEGF levels were significantly higher in CTx recipients in basal conditions but did not change in response to acute stress. CTx patients exhibit a favorable ventilatory and overall response to hypoxic stress. These data provide further insights on the good adaptability of CTx to exposure to high altitude.

Meta-analysis of Exercise Training on Vascular Endothelial Function in Cancer Survivors

Cancer and cardiovascular disease (CVD) are leading causes of morbidity and mortality in the United States. Vascular endothelial dysfunction, an important contributor in the development of CVD, improves with exercise training in patients with CVD. However, the role of regular exercise to improve vascular function in cancer survivors remains equivocal. We performed a meta-analysis to determine the effect of exercise training on vascular endothelial function in cancer survivors. We searched PubMed (1975 to 2016), EMBASE CINAHL (1937 to 2016), OVID MEDLINE (1948 to 2016), and Cochrane Central Registry of Controlled Trials (1991 to 2016) using search terms: vascular function, endothelial function, flow-mediated dilation [FMD], reactive hyperemia, exercise, and cancer. Studies selected were randomized controlled trials of exercise training on vascular endothelial function in cancer survivors. We calculated pooled effect sizes and performed a meta-analysis. We identified 4 randomized controlled trials (breast cancer, n=2; prostate cancer, n=2) measuring vascular endothelial function by FMD (n=3) or reactive hyperemia index (n=1), including 163 cancer survivors (exercise training, n=82; control, n=81). Aerobic exercise training improved vascular function (n=4 studies; standardized mean difference [95% CI]=0.65 [0.33, 0.96], I²=0%; FMD, weighted mean difference [WMD]=1.28 [0.22, 2.34], I²=23.2%) and peak exercise oxygen uptake (3 trials; WMD [95% CI]=2.22 [0.83, 3.61] mL/kg/min; I²=0%). Our findings indicate that exercise training improves vascular endothelial function and exercise capacity in breast and prostate cancer survivors.

The association of cardiorespiratory fitness with endothelial or smooth muscle vasodilator function

BACKGROUND

Maximal oxygen consumption (VO2max) is strongly associated with peripheral vasodilator function as determined by exercise-induced vasodilation. However, findings with regard to its relation with non-exercise-stimulated vasodilation are unclear. The purpose of this study was to systematically review published literature reporting associations between VO2max and endothelial function (EF) or smooth muscle function (SMF).

DESIGN AND METHODS

We conducted a systematic search of MEDLINE, Cochrane and Web of Science, since their inceptions until April 2014 for articles reporting the association between (a) VO2max during incremental exercise and (b) endothelium-dependent or -independent vasodilator function, by means of correlation and/or regression analysis.

RESULTS

Fifty-six articles exploring 88 associations between VO2max and vascular EF or SMF were included, involving a total of 4159 healthy and diseased subjects. VO2max was determined by incremental cycle ergometer (64%), treadmill (33%) and cycle ergometer/treadmill (3%) exercise. Vasodilator function variables were assessed in the upper limb (86%), lower limb (10%) and both upper and lower limbs (3%). Most of the evaluated bivariate associations involved EF stimuli such as flow-mediated dilation (FMD) (n = 29) or blood flow occlusion (BFO) (n = 18). VO2max was significantly associated with FMD and BFO in 59% and 67% of bivariate associations and 46% and 33% of age-independent associations, respectively. Explored bivariate associations regarding SMF involved sodium nitroprusside (SNP) iontophoresis (n = 7) and nitrate-mediated dilation (NMD) (n = 4). VO2max was associated with NMD in 50% of bivariate associations and 50% of age-independent associations. VO2max was not associated with SNP iontophoresis. Results were similar for associations including only healthy subjects.

CONCLUSIONS

The association between VO2max and EF or SMF is moderately frequent and independent of health status, despite very few studies having assessed vasodilator function in the lower limb.

Endothelial dysfunction over the course of coronary artery disease

The vascular endothelium regulates blood flow in response to physiological needs. Endothelial dysfunction is closely related to atherosclerosis and its risk factors, and it constitutes an intermediate step on the progression to adverse events throughout the natural history of coronary artery disease (CAD), often affecting clinical outcomes. Understanding the relation of endothelial function with CAD provides an important pathophysiological insight, which can be useful both in clinical and research management. In this review, we summarize the current knowledge on endothelial dysfunction and its prognostic influence throughout the natural history of CAD, from early atherosclerosis to post-transplant management.

Preserved capillary density of dorsal finger skin in treated hypertensive patients with or without type 2 diabetes

OBJECTIVES

Capillary rarefaction is a hallmark of untreated hypertension. Recent data indicate that rarefaction may be reversed by antihypertensive treatment in nondiabetic hypertensive patients. Despite the frequent association of diabetes with hypertension, nothing is known on the capillary density of treated diabetic patients with hypertension.

METHODS

We enrolled 21 normotensive healthy, 25 hypertensive only, and 21 diabetic (type 2) hypertensive subjects. All hypertensive patients were treated with a blocker of the renin-angiotensin system, and a majority had a home blood pressure ≤135/85 mmHg. Capillary density was assessed with videomicroscopy on dorsal finger skin and with laser Doppler imaging on forearm skin (maximal vasodilation elicited by local heating).

RESULTS

There was no difference between any of the study groups in either dorsal finger skin capillary density (controls 101 ± 11 capillaries/mm(2) , nondiabetic hypertensive 99 ± 16, diabetic hypertensive 96 ± 18, p > 0.5) or maximal blood flow in forearm skin (controls 666 ± 114 perfusion units, nondiabetic hypertensive 612 ± 126, diabetic hypertensive 620 ± 103, p > 0.5).

CONCLUSIONS

Irrespective of the presence or not of type 2 diabetes, capillary density is normal in hypertensive patients with reasonable control of blood pressure achieved with a blocker of the renin-angiotensin system.

High-intensity interval training improves peak oxygen uptake and muscular exercise capacity in heart transplant recipients

Heart transplant (HTx) recipients usually have reduced exercise capacity with reported VO(2peak) levels of 50-70% predicted value. Our hypothesis was that high-intensity interval training (HIIT) is an applicable and safe form of exercise in HTx recipients and that it would markedly improve VO(2peak.) Secondarily, we wanted to evaluate central and peripheral mechanisms behind a potential VO(2peak) increase. Forty-eight clinically stable HTx recipients >18 years old and 1-8 years after HTx underwent maximal exercise testing on a treadmill and were randomized to either exercise group (a 1-year HIIT-program) or control group (usual care). The mean ± SD age was 51 ± 16 years, 71% were male and time from HTx was 4.1 ± 2.2 years. The mean VO(2peak) difference between groups at follow-up was 3.6 [2.0, 5.2] mL/kg/min (p < 0.001). The exercise group had 89.0 ± 17.5% of predicted VO(2peak) versus 82.5 ± 20.0 in the control group (p < 0.001). There were no changes in cardiac function measured by echocardiography. We have demonstrated that a long-term, partly supervised and community-based HIIT-program is an applicable, effective and safe way to improve VO(2peak) , muscular exercise capacity and general health in HTx recipients. The results indicate that HIIT should be more frequently used among stable HTx recipients in the future.

Endothelial dysfunction, inflammation, and oxidative stress in obese children and adolescents: markers and effect of lifestyle intervention

With an increasing prevalence, pediatric obesity is often a prelude to adulthood obesity, and represents a major public health issue. Comorbidities are very common and severe in obese adults, justifying the search for earlier markers or risk factors for cardiovascular diseases in obese children. Endothelial dysfunction has been found to be present in the early stages of atherosclerosis, and can be non-invasively assessed with widely accepted and well-standardized techniques at the macrocirculation level. Endothelial dysfunction at the microcirculation level is less documented in obese children. Obesity in children has been repeatedly and independently correlated to endothelial dysfunction, inflammation and oxidative stress markers, although the relationship between these factors remains to be investigated. However, this would not only allow substantial improvements in risk stratification, but also provide essential data regarding the evolution of endothelial dysfunction in childhood obesity, especially during puberty when pro-inflammatory and pro-oxidative changes, with relative insulin resistance, occur. Therapeutic strategies such as lifestyle interventions in early childhood obesity appear all the more necessary, optimally including both exercise and diet because of their known effects on inflammatory and oxidative stress markers, potentially reversing endothelial dysfunction.

The influence of oral magnesium sulfate on skin microvasculature blood flow in diabetic rats

Microvascular disease is a major feature of type1 diabetes and results from long-standing structural and functional changes especially in the skin microvasculature. Magnesium (Mg) deficiency has recently been proposed as a novel factor implicated in the pathogenesis of diabetes complications such as vascular disturbance, but its mechanism of action is not completely elucidated. The present study was designed to determine whether chronic magnesium sulfate administration could control streptozocin-induced diabetes and improve endothelium-dependent and endothelium-independent dilatation, and identify its probable mechanism in the skin microvasculature of diabetic rats. Fifty male Wistar rats (220 ± 10 g) were divided into two diabetic and one control groups. One subgroup of diabetic received magnesium sulfate (10 g/l) in their drinking water, while two other groups had only tap water. Laser Doppler flow meter with iontophoresis was used to measure the relative changes in skin blood flow. We used acetylcholine (Ach), sodium nitroprusside (SNP), and N (w)-nitro-L-arginine (LNNA; NO synthase inhibitor) with magnesium sulfate (0.1 M) in control and experimental animal by microsyringe pump microinjection. SNP- and Ach-induced cutaneous perfusion increased significantly by Mg treatment in the diabetic groups, and local microinjection of magnesium sulfate (0.1 M) increased cutaneous blood flow in all groups (p < 0.01). However, the administration of LNNA prior to magnesium sulfate attenuated (p < 0.05) but not abolished the increase in cutaneous blood flow in diabetic and normal rats. From the results of this study, it may be concluded that Mg could improve skin microvasculature of diabetic rats with potentiation of nitric oxide pathway.

Effect of high intensity exercise on peak oxygen uptake and endothelial function in long-term heart transplant recipients

Coronary allograft vasculopathy is a well-known long-term complication after cardiac transplantation. Endothelial dysfunction is involved and may be prevented by aerobic exercise. The purpose of this study was to examine whether high intensity aerobic exercise improves peak oxygen uptake (VO(2 peak) ) and endothelial function in heart transplant (HT) recipients. Twenty-seven long-term HT recipients were randomized to either 8-weeks high intensity aerobic exercise or no training. Flow mediated dilation of the brachial artery (FMD) was measured by ultrasound and VO(2 peak) by the analysis of expired air. Blood pressure and biomarkers were measured before and after 8 weeks. VO(2 peak) increased significantly in the exercise group (VO(2 peak) 23.9 ± 1.79 to 28.3 ± 1.63 mL/kg/min compared to controls (VO(2 peak) 24.6 ± 1.38 to 23.4 ± 1.58, p < 0.001 exercise vs. control).FMD increased in the exercise group compared to controls (8.3 ± 1.1% to 11.4 ± 1.2% vs. 5.6 ± 1.0% to 5.3 ± 1.7%, p = 0.024). No increase in nitroglycerin-induced vasodilation was observed. Systolic blood pressure fell in the exercise group (142 ±4.2 mmHg to127 ± 3.4 mmHg, p = 0.01) and was unchanged in controls (141 ± 4.2 mmHg to 142 ±6.4 mmHg, NS). High intensity aerobic exercise reduces systolic blood pressure and improves endothelial function in HT recipients.

In vivo functional photoacoustic microscopy of cutaneous microvasculature in human skin

Microcirculation is an important component of the cardiovascular system and can be used to assess systemic cardiovascular health. Numerous studies have investigated cutaneous microcirculation as an indicator of cardiovascular related diseases. Such research has shown promising results; however, there are many limitations regarding the employed measurement techniques, such as poor depth and spatial resolution and measurement versatility. Here we show the results of functional cutaneous microvascular experiments measured with photoacoustic microscopy, which provides high spatial resolution and multiparameter measurements. In a set of experiments, microvascular networks located in the palms of volunteers were perturbed by periodic ischemic events, and the subsequent hemodynamic response to the stimulus was recorded. Results indicate that during periods of arterial occlusion, the relative oxygen saturation of the capillary vessels decreased below resting levels, and temporarily increased above resting levels immediately following the occlusion. Furthermore, a hyperemic reaction to the occlusions was measured, and the observation agreed well with similar measurements using more conventional imaging techniques. Due to its exceptional capability to functionally image vascular networks with high spatial resolution, photoacoustic microscopy could be a beneficial biomedical tool to assess microvascular functioning and applied to patients with diseases that affect cardiovascular health. © 2011 Society of Photo-Optical Instrumentation Engineers.

Chronic cyanosis and vascular function: implications for patients with cyanotic congenital heart disease

In patients with cyanotic congenital heart disease, chronic hypoxaemia leads to important changes in blood vessel function and structure. Some of these alterations are maladaptive and probably contribute to impaired cardiopulmonary performance and an increased incidence of thrombotic and embolic events. Recent evidence suggests that deranged endothelial function, a sequel of chronic cyanosis, could be an important factor in the pathogenesis of cyanosis-associated cardiovascular risk. In this article, we discuss the physiological and mechanical consequences of compensatory erythrocytosis and possible pathophysiological mechanisms of vascular dysfunction in chronic cyanosis.

Moderate Champagne consumption promotes an acute improvement in acute endothelial-independent vascular function in healthy human volunteers

Epidemiological studies have suggested an inverse correlation between red wine consumption and the incidence of CVD. However, Champagne wine has not been fully investigated for its cardioprotective potential. In order to assess whether acute and moderate Champagne wine consumption is capable of modulating vascular function, we performed a randomised, placebo-controlled, cross-over intervention trial. We show that consumption of Champagne wine, but not a control matched for alcohol, carbohydrate and fruit-derived acid content, induced an acute change in endothelium-independent vasodilatation at 4 and 8 h post-consumption. Although both Champagne wine and the control also induced an increase in endothelium-dependent vascular reactivity at 4 h, there was no significant difference between the vascular effects induced by Champagne or the control at any time point. These effects were accompanied by an acute decrease in the concentration of matrix metalloproteinase (MMP-9), a significant decrease in plasma levels of oxidising species and an increase in urinary excretion of a number of phenolic metabolites. In particular, the mean total excretion of hippuric acid, protocatechuic acid and isoferulic acid were all significantly greater following the Champagne wine intervention compared with the control intervention. Our data suggest that a daily moderate consumption of Champagne wine may improve vascular performance via the delivery of phenolic constituents capable of improving NO bioavailability and reducing matrix metalloproteinase activity.

Current concepts in assessment of microvascular endothelial function using laser Doppler imaging and iontophoresis

Effective evaluation of endothelial function is a powerful tool for determining patients at risk of development and progression of cardiovascular disease. As an alternative to invasive tests of endothelial function, several noninvasive methods have been developed, including the use of laser Doppler flowmetry/imaging to measure cutaneous perfusion accompanied by iontophoresis of acetylcholine and sodium nitroprusside. It is clear from previous studies that this technique provides an easy, validated, and reproducible method for investigators to assess and monitor endothelial function in patients with a variety of pathologic conditions, but it may also be used to examine disease progression over time and responsiveness to treatment, thereby facilitating clinical trials. However, a standardization of protocols would help reduce the apparent controversy seen in the literature. With its increasing use by other groups, it is anticipated that further published studies will help to provide a better understanding of the development and progression of cardiovascular disease.

Acute effects of a single dose of phosphodiesterase type 5 inhibitor (sildenafil) on systemic arterial blood pressure during exercise and 24-hour ambulatory blood pressure monitoring in heart transplant recipients

BACKGROUND

Arterial systemic hypertension (SH) can be associated with a decrease in endothelium-dependent nitric oxide (NO). Sildenafil increases cyclic guanosine monophosphate (cGMP), a mediator of NO. However, little is known about the effects of PDE5 inhibition on 24-hour ambulatory pressure (ABP) and exercise blood pressure, noreprinephrine (Nor), and exercise capacity, especially after orthotopic heart transplantation (OHT).

METHODS

We studied 22 OHT patients who on the 1st day underwent a cardiopulmonary (CP) self-controlled treadmill 6' walk test (6') and, then, an ECG monitored CP treadmill maximal exercise test (Ex) within 60 and 90 minutes after oral Sildenafil (Sil; 50 mg) or placebo (Pl) given at random, and ABP. We determined at basal position (b), in the last minute of the 6' and at the peak Ex, the HR (bpm), Systolic blood pressure (SBP), and diastolic blood pressure (DBP), (mm Hg), VO2 (mL/kg/min), Slope VE/VCO2, exercise time (ET, min), distance (D; miles), and Nor (pg/mL). Also, after CP tests, 24-h SBP and DBP, the measurements were repeated on the 2nd day when the cross-over was done.

RESULTS

Sil significantly reduced blood pressure in the basal position and during exercise. It also promoted a significant reduction in SBP and DBP during 24 hours, daytime and nighttime. Sil did not change exercise capacity.

CONCLUSION

The NO-cGMP pathway seems to play a role in blood pressure control in OHT. In addition to antihypertensive therapy, PDE5 inhibition may have potential beneficial effects on hypertensive OHT.

Exercise training attenuates progressive decline in brachial artery reactivity in heart transplant recipients

BACKGROUND

Heart transplantation normalizes central hemodynamics, but endothelial dysfunction persists after transplantation.

METHODS

To investigate the effects of aerobic exercise on arterial function, oxidative stress, lipid profile, and sympathetic nervous system activity, 20 heart transplant recipients (age, 54.3 +/- 9.1 years; 17 men, 3 women) were randomly assigned to 12 weeks of supervised treadmill exercise (Trained; n = 10) or standard medical care (Control; n = 10). Supervised exercise was initiated at 8 weeks after transplant. Brachial artery reactivity was assessed using flow-mediated dilation.

RESULTS

The VO2 peak increased 26% in the Trained patients (15.4 +/- 4.3 vs 19.4 +/- 5.5 ml/kg/min; p < or = 0.05) but did not change in the Controls (16.2 +/- 5.2 vs 16.8 +/- 2.8 ml/kg/min; p > or = 0.05). Brachial artery flow-mediated dilation (10.1% +/- 6.1% vs 9.6% +/- 6.2%) and absolute brachial diameter (0.48 +/- 0.22 vs 0.42 +/- 0.24 mm) did not change in Trained patients, but brachial flow-mediated dilation (10.5% +/- 2.8% vs 7.9% +/- 5.1%) and the absolute change in brachial diameter (0.48 +/- 0.16 vs 0.36 +/- 0.24 mm) decreased significantly (p < or = 0.05) in the Control patients. Resting norepinephrine decreased significantly (p < or = 0.05) after training (0.32 +/- 0.19 vs 0.22 +/- 0.22 ng/ml), but there was a nonsignificant trend toward increased norepinephrine in the Controls (0.26 +/- 0.17 vs 0.53 +/- 0.41 ng/ml; p = 0.07). The lipid profile and marker of oxidative stress did not differ between the groups before or after the intervention.

CONCLUSIONS

To our knowledge, this is the first prospective, randomized study to investigate the effects of heart transplantation and aerobic exercise on peripheral artery function in the same cohort of heart transplant recipients. Brachial artery flow-mediated dilation increased early in the post-operative period. Aerobic exercise preserved but did not improve brachial artery flow-mediated dilation. Heart transplant recipients who did not participate in supervised exercise showed a progressive decline in brachial artery flow-mediated dilation.

Effect of heart transplantation on skeletal muscle metabolic enzyme reserve and fiber type in end-stage heart failure patients

BACKGROUND

Skeletal muscle myopathy is a hallmark of chronic heart failure (HF). Phenotypic changes involve shift in myosin heavy chain (MHC) fiber type from oxidative, MHC type I, towards more glycolytic MHC IIx fibers, reductions in oxidative enzyme activity, and increase in glycolytic enzyme activity. However, it is unknown if muscle myopathy is reversed following heart transplantation. The purpose of this study was to determine the effect of heart transplantation on skeletal muscle metabolic enzyme reserve and MHC fiber type in end-stage HF patients.

METHODS

Thirteen HF subjects were prospectively studied before and two months after heart transplantation and a subgroup (n = 6) at eight months after transplantation. Skeletal muscle biopsy of the vastus lateralis was performed and relative MHC composition was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lactate dehydrogenase (LDH), citrate synthase (CS), and 3-hydroxyacyl-CoA-dehydrogenase (HACoA) enzyme activity assays were performed to assess glycolytic, oxidative, and beta-oxidative metabolic enzyme reserves, respectively.

RESULTS

Lactate dehydrogenase activity (130.5 +/- 13.3 vs. 106.1 +/- 13.2 micromol/g wet wt/min, p < 0.05), CS activity (14.0 +/- 1.2 vs. 9 +/- 0.9 micromol/g wet wt/min, p < 0.05), and HACoA activity (4.5 +/- 0.48 vs. 3.6 +/- 0.3 micromol/g wet wt/min, p < 0.05) decreased two months after heart transplantation. At eight months, LDH activity was restored (139.0 +/- 11 micromol/g wet wt/min), but not CS or HACoA activity compared with before transplantation. There was no significant change in muscle %MHC type I (28.7 +/- 3.5% vs. 25.3 +/- 3.0%, p = NS), %MHC type IIa (33.2 +/- 2.0% vs. 34.6 +/- 1.9%, p = NS), or %MHC type IIx (38.1 +/- 2.8% vs. 40.1 +/- 3.7%, p = NS) fiber type two months after heart transplantation. However, %MHC type I (19.3 +/- 6.6%) was decreased and %MHC type IIx (51.0 +/- 6.5%) was increased at eight months after (p < 0.05) compared with before transplantation.

CONCLUSIONS

Skeletal muscle glycolytic, oxidative, and beta-oxidative enzymatic reserves are diminished early after heart transplantation, with reduced oxidative capacity persisting late in the first year. The myopathic MHC phenotype present in end-stage HF persists early in the post-operative state and declines further by eight months.

Low-frequency oscillations of the laser Doppler perfusion signal in human skin

Spectral analysis of the laser Doppler flow (LDF) signal in the frequency interval from 0.0095-2.0 Hz reveals blood flow oscillations with frequencies around 1.0, 0.3, 0.1, 0.04 and 0.01 Hz. The heartbeat, the respiration, the intrinsic myogenic activity of vascular smooth muscle, the neurogenic activity of the vessel wall and the vascular endothelium influence these oscillations, respectively. The first aim of this study was to investigate if a slow oscillatory component could be detected in the frequency area below 0.0095 Hz of the human cutaneous blood perfusion signal. Unstimulated basal blood skin perfusion and enhanced perfusion during iontophoresis with the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent vasodilator sodium nitroprusside (SNP) were measured in healthy male volunteers and the wavelet transform was computed. A low-frequency oscillation between 0.005 and 0.0095 Hz was found both during basal conditions and during iontophoresis with ACh and SNP. Iontophoresis with ACh increased the normalized amplitude to a greater extent than SNP (P = 0.001) indicating modulation by the vascular endothelium. To gain further insight into the mechanisms for this endothelium dependency, we inhibited nitric oxide (NO) synthesis with N(G)-monomethyl-L-arginine (L-NMMA) and prostaglandin (PG) synthesis by aspirin. L-NMMA did not affect the increased response to ACh vs. SNP iontophoresis in the 0.005-0.0095-Hz interval (P = 0.006) but abolished the difference in the 0.0095-0.021-Hz interval (P = 0.97). Aspirin did not affect the difference in response to ACh and SNP in either of the two frequency intervals. Thus, other endothelial mechanisms, such as endothelium-derived hyperpolarizing factor (EDHF), might be involved in the regulation of this sixth frequency interval (0.005-0.0095 Hz).

Effects of physical training on cardiovascular control after heart transplantation

BACKGROUND

Exercise performance in heart-transplanted patients increases with respect to pre-transplantation but remains subnormal, and it does not improve with time after surgery. Possible causes include persisting denervation, and sympathetic vasoconstriction inducing functional vascular abnormalities that prevent adequate increase in blood flow to the exercising limbs. We tested the effects of physical training on baroreceptors-mediated control of heart rate and blood pressure in recently heart-transplanted subjects.

METHODS

Patients were randomly allocated to physical training (n=13, 30 min cycling at 60-70% of peak oxygen consumption for 5 days/week for 6 months) or to control (n=11). Upright exercise test to exhaustion was performed at the beginning of the study after 3 and 6 months. Reflex changes in RR interval and blood pressure in response to sinusoidal neck suction (6 and 12 cycles/min 0 to -30 mm Hg swing) were considered as evidence of reinnervation and baroreflex control of blood pressure, respectively.

RESULTS

After 6 months peak oxygen consumption (p<0.001), exercise time (p<0.01) and workload (p<0.01) increased in trained patients. Before training RR interval and blood pressure were not modified by neck suction. After physical training systolic (p<0.01) and diastolic blood pressure decreased, RR interval and blood pressure could be modulated (p<0.05) by slow (6 cycles/min) neck suction, indicating initial cardiac sympathetic reinnervation and restored sensitivity to autonomic modulation on the arteries. No changes were observed in controls.

CONCLUSIONS

Physical training improved exercise performance and the control exerted by the autonomic nervous system through the sympathetic nerves at both cardiac and vascular level.

Six months of aerobic exercise does not improve microvascular function in type 2 diabetes mellitus

AIMS/HYPOTHESIS

Adults with type 2 diabetes mellitus have impaired microvascular function. It has been hypothesised that microvascular function may be restored through regular exercise. The aim of this study was to investigate whether 6 months of regular aerobic exercise would improve microvascular function in adults with type 2 diabetes.

MATERIALS AND METHODS

Fifty-nine patients with type 2 diabetes (32 males, age 62.9+/-7.6 years, HbA(1c) 6.8+/-0.9%) were randomised to either a 6-month aerobic exercise programme (30 min, three times a week, 70-80% of maximal heart rate) or a 'standard care' control group. Before and after the intervention period, microvascular function was assessed as the maximum skin hyperaemia to local heating and endothelial and non-endothelial responsiveness following the iontophoretic application of acetylcholine and sodium nitroprusside. Maximal oxygen uptake, as an index of aerobic fitness, was assessed using a maximal exercise test.

RESULTS

No significant improvement was seen in the exercise group compared with the control group for any of the variables measured: maximal oxygen uptake (control pre: 1.73+/-0.53 [means+/-SD] vs post: 1.67+/-0.40; exercise pre: 1.75+/-0.56 vs post: 1.87+/-0.62 l/min, p=0.10); insulin sensitivity (insulin tolerance test) (control pre: -0.17+/-0.06 vs post: -0.17+/-0.06; exercise pre: -0.16+/-0.1 vs post: -0.17+/-0.07 mmol l(-1) min(-1), p=0.97); maximal hyperaemia (control pre: 1.49+/-0.43 vs post: 1.52+/-0.57; exercise pre: 1.42+/-0.36 vs post: 1.47+/-0.33 V, p=0.85); peak response to acetylcholine (control pre: 1.37+/-0.47 vs post: 1.28+/-0.37; exercise pre: 1.27+/-0.44 vs post: 1.44+/-0.23 V, p=0.19) or to sodium nitroprusside (control pre: 1.09+/-0.50 vs post: 1.10+/-0.39; exercise pre: 1.12+/-0.28 vs post: 1.13+/-0.40 V, p=0.98).

CONCLUSIONS/INTERPRETATION

In this group of type 2 diabetic patients with good glycaemic control a 6-month aerobic exercise programme did not improve microvascular function or aerobic fitness.

Serial measurements of peripheral vascular reactivity and exercise capacity in congestive heart failure and after heart transplantation

BACKGROUND

The regulation of nutritive blood flow to skeletal muscles during exercise seems to make an important contribution to exercise capacity. In congestive heart failure (CHF) this regulation seems to be impaired, with attenuated peripheral vasodilatory capacity. The results regarding improvement of peripheral vasoreactivity after heart transplantation (HTx) are conflicting, and the contribution of impaired peripheral vasoreactivity to the observed reduced exercise capacity among heart transplant recipients (HTR) has not been well elucidated. We therefore assessed the reversibility of impaired vasoreactivity in forearm and calf after HTx with relationship to exercise capacity.

METHODS AND RESULTS

The vasoreactivity of both forearm and calf was studied with venous occlusion plethysmography and related to exercise capacity in 64 patients with CHF and in 22 controls. Of these patients, 29 patients underwent HTx, and the same measurements were performed 10 days, 6 months and 1 year after HTx, and in a group of 15 HTR who had undergone HTx several years ago. Our main findings were (1) impaired resting blood flow in patients with CHF improved after HTx and even surpassed levels of controls; (2) peak forearm blood flow remained attenuated early after HTx, but normalized during the first year postoperatively; (3) both forearm and calf minimal resistance remained elevated after HTx; (4) vascular reactivity displays regional variations in forearm and calf both during CHF and after HTx; and (5) peripheral vascular reactivity relate to exercise performance in both patients with CHF and HTR, but the relationship seemed more pronounced in CHF.

CONCLUSION

With impaired vasoreactivity related to limited exercise capacity in CHF, improvement is evident after HTx, but both forearm and calf minimal resistance remains elevated. These findings suggest increased vasoconstrictor drive to both exercising and non-exercising muscles, possibly contributing to persistent physical limitation after HTx.

Physical functional outcomes after cardiothoracic transplantation

The study of patient healthcare outcomes after cardiothoracic transplantation has increased substantially over the last 2 decades. Physical function after heart, lung, and heart-lung transplantation has been studied using both subjective and objective measures. The majority of reports in the literature on physical function after cardiothoracic transplantation are descriptive and observational. The purposes of the article are to review and critique the existing literature on cardiothoracic recipients' subjective and objective physical function, including respiratory function for heart-lung and lung transplant recipients. In addition, the literature on sexual function in cardiothoracic recipients is examined, the gaps in the literature are identified, and recommendations are given for future research.

Peripheral vascular endothelial function correlates with exercise capacity in women

BACKGROUND

Vascular endothelial function has been observed to correlate with exercise capacity in predominantly male populations. Gender-based differences exist in the clinical course of coronary artery disease, and previous studies indicate that estrogen may influence endothelial function. These observations raise the possibility that the relationship between endothelial function and exercise capacity in women may differ from that in men.

HYPOTHESIS

This study aimed to determine whether peripheral vascular endothelial function correlates with exercise capacity in women.

METHODS

Women who were referred for clinically indicated exercise testing with technetium-99 myocardial perfusion imaging were consecutively recruited. To ensure a population free of exercise limitation due to ischemic heart disease, women without myocardial perfusion defects were included for analysis in this study (n = 105). Endothelial function was assessed by brachial artery ultrasound flow-mediated vasodilation (FMD). Exercise capacity was defined as the duration of exercise on a symptom-limited Bruce protocol.

RESULTS

Mean FMD was 11.8 +/- 0.6%, and median FMD was 12%. Subjects with an FMD less than the median of 12% had a significantly shorter exercise time than those with FMD > or = 12% (411 +/- 17 vs. 482 +/- 24 s, p = 0.014). There was a significant correlation between FMD and exercise time (r = 0.34, p < 0.001). Age and body mass index were additional predictors of exercise time; however, the relationship between FMD and exercise time was independent of these variables.

CONCLUSION

Brachial artery FMD correlates with exercise capacity in women, even in the absence of ischemic heart disease.

Chronic But Not Acute Oral L-Arginine Supplementation Delays the Ventilatory Threshold During Exercise in Heart Failure Patients

The purpose of this study was to determine, in heart failure patients (HF), whether acute or chronic L-arginine supplementation (LAS) might delay the ventilatory threshold (VT) and whether chronic LAS might reduce exercise-induced plasma lactate increase. HF patients undertook 4 cardiopulmonary bicycle exercises tests. The first 3 were maximal without (EX1), after acute (EX2), or chronic (EX3) oral LAS (6 gm twice a day for 6 weeks). The 4th test (EX4), performed after chronic LAS, was similar to the first in order to investigate the effect of chronic LAS on circulating lactate levels. Results showed that acute LAS failed to improve both submaximal and maximal exercise capacities. Similarly, maximal exercise capacity remained unmodified after chronic LAS. Nevertheless, chronic LAS delayed significantly the patients' ventilatory threshold. Thus exercise duration prior to VT increased (mean ± SEM) from 6.04 ± 0.9 to 7.7 ± 1.03 min (p = 0.04), resulting in a significant increase in oxygen uptake (1.05 ± 0.08 to 1.24 ± 0.12 L•min−1; p = 0.03), CO2 release (0.94 ± 0.10 to 1.2 ± 0.12 L•min−1; p = 0.018), minute ventilation (29.31 ± 2.8 to 34.5 ± 2.7 L; p = 0.009), and workload (60.7 ± 9.8 to 78.5 ± 10.2 watts; p = 0.034). Furthermore, chronic LAS significantly reduced the exercise-induced increase in postexercise plasma lactate concentration (−21 ± 7%). In conclusion, unlike acute supplementation, chronic LAS significantly delays the ventilatory threshold, and chronic LAS reduces circulating plasma lactate in HF patients. These data suggest that chronic LAS might improve the ability of HF patients to perform their daily-life activities. Key words: maximal exercise, heart device, vasodilator

Time course of physical reconditioning during exercise rehabilitation late after heart transplantation

BACKGROUND

Exercise rehabilitation improves physical capacity in heart transplant recipients. The time course of physical reconditioning and skeletal muscle adaptation late after transplantation are unknown.

METHODS

Twenty-one heart transplant recipients, at 5.2 +/- 2.1 years after transplantation, completed 1 year of an individually tailored home ergometer-training program (2.1 +/- 0.7 sessions weekly with matched heart rates, intensity at 10% below anaerobic threshold). We analyzed time course of physical reconditioning data for each home-training session (n = 2,396). Constant-load tests with consistent blood lactate concentrations were performed quarterly (n = 105) to estimate the time course of skeletal muscle adaptation. Nine heart transplant recipients served as a control group (CG).

RESULTS

After 12 months, exercise capacity for matched heart rates (112 +/- 11 beats/min; CG, 114 +/- 8 beats/min) increased by 35% +/- 19% (from 43 +/- 14 to 58 +/- 18 W; p < 0.001; CG, 53 +/- 18 to 54 +/- 18 W); 24% of the increase was caused by improved skeletal muscle function and 11% by central functioning. Physical reconditioning showed its greatest increase within the first 3 months (+18%; p < 0.001); 50% of the increase consisted of better skeletal muscle or central functioning. Between the 4(th) and 12(th) months, exercise capacity increased continuously (+15%; p < 0.001), mainly because of better skeletal muscle functioning.

CONCLUSIONS

The persistent improvement in exercise capacity along with consistent lactate concentrations during 12 months of training indicates that exercise training could counteract the negative side effects of immunosuppressive treatment on skeletal muscles. Even late after heart transplantation, physical training should be performed regularly to prevent the accelerated decrease in exercise capacity and in skeletal muscle function.

Effect of resistance exercise on skeletal muscle myopathy in heart transplant recipients

The purpose of this study was to determine the efficacy of resistance exercise in reversing skeletal muscle myopathy in heart transplant recipients. Myopathy, engendered by both heart failure and immunosuppression with glucocorticoids, is a post-transplant complication. The sequelae of myopathic disease includes fiber-type shifts and deficits in aerobic metabolic capability. We randomly assigned patients to either 6 months of resistance exercise (training group; n = 8) or a control (control group; n = 7) group. Exercise was initiated at 2 months after transplant. Biopsy of the right vastus lateralis was performed before and after the 6-month intervention. Myosin heavy chain (MHC) composition was assessed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Biochemical assays were performed to determine citrate synthase, 3-hydroxyacyl-CoA-dehydrogenase, and lactate dehydrogenase activity. There were no group differences (p >or=0.05) in MHC composition and enzymatic reserve at baseline. Improvements in the training group for citrate cynthase (+40%), 3-hydroxyacyl-CoA-dehydrogenase (+10%), and lactate dehydrogenase activity (+48%) were significantly greater (p <or=0.05) than in the control group (+10%, -15%, and +20%, respectively). Oxidative type 1 MHC isoform concentration increased significantly in the training group (+73%, p <or=0.05) but decreased in the control group (-28%; p <or=0.05). Glycolytic type 2x MHC isoform increased significantly (17%; p <or=0.05) in the control group but decreased (-33%; p <or=0.05) in the training group. This is the first study to demonstrate that resistance training elicits myofibrillar shifts from less oxidative type II fibers to more oxidative fatigue-resistant type I fibers in heart transplant recipients. Resistance exercise initiated early in the post-transplant period is efficacious in changing skeletal muscle phenotype through increases in enzymatic reserve and shifts in fiber morphology.

Does aerobic fitness influence microvascular function in healthy adults at risk of developing Type 2 diabetes?

AIM

To investigate whether aerobic fitness is associated with skin microvascular function in healthy adults with an increased risk of developing Type 2 diabetes.

METHODS

Twenty-seven healthy normal glucose-tolerant humans with either a previous diagnosis of gestational diabetes or having two parents with Type 2 diabetes and 27 healthy adults who had no history of diabetes were recruited. Maximal oxygen uptake was assessed using an incremental exercise test to exhaustion. Skin microvascular function was assessed using laser Doppler techniques as the maximum skin hyperaemic response to a thermal stimulus (maximum hyperaemia) and the forearm skin blood flow response to the iontophoretic application of acetylcholine (ACh) and sodium nitroprusside.

RESULTS

Maximal oxygen uptake was not significantly different in the 'at-risk' group compared with healthy controls. Maximum hyperaemia was reduced in those 'at risk' (1.29 +/- 0.30 vs. 1.46 +/- 0.33 V, P = 0.047); however, the peak response to acetylcholine or sodium nitroprusside did not differ in the two groups. A significant positive correlation was demonstrated between maximal oxygen uptake and maximum hyperaemia (r = 0.52, P = 0.006 l/min and r = 0.60, P = 0.001 ml/kg/min) and peak ACh response (r = 0.40, P = 0.04 l/min and r = 0.47, P = 0.013 ml/kg/min) in the 'at-risk' group when expressed in absolute (l/min) or body mass-related (ml/kg/min) terms. No significant correlations were found in the control group.

CONCLUSIONS

In this 'at-risk' group with skin microvascular dysfunction maximal oxygen uptake was not reduced compared with healthy controls. However, in the 'at-risk' group alone, individuals with higher levels of aerobic fitness also had better microvascular and endothelial responsiveness.

A Model for Post-Occlusive Reactive Hyperemia as Measured With Laser-Doppler Perfusion Monitoring

To facilitate the quantitative analysis of post-occlusive reactive hyperaemia (PORH), measured with laser-Doppler perfusion monitoring (LDPM) on extremities, we present a flow model for the dynamics of the perfusion of the tissue during PORH, based on three parameters: two time constants (tau1 and tau2) and the ratio of the maximum flux and the resting flux. With these three constants quantitative comparisons between experiments will be possible and, therefore, we propose to adopt this approach as future standard. For this reason, we also developed a computer program to perform the fit of the model to measured data.

Effects of prior moderate exercise on postprandial metabolism and vascular function in lean and centrally obese men

OBJECTIVES

We investigated whether a session of prior exercise could ameliorate postprandial endothelial dysfunction.

BACKGROUND

Endothelial function is impaired after fat ingestion, and this may be related to rises in triglyceride concentrations. Exercise reduces postprandial triglyceride concentrations.

METHODS

Ten lean (waist <90 cm) and 10 centrally obese (waist >100 cm) middle-aged men each underwent two oral fat tolerance tests (blood taken fasting and for 8 h after a high-fat meal containing 80 g fat and 70 g carbohydrate). On the afternoon before one test, subjects performed a 90-min treadmill walk (exercise); no exercise was performed before the control test. Endothelium-dependent and -independent microvascular function was assessed using laser Doppler imaging in the fasted state and at two hourly intervals during the 8-h postprandial period.

RESULTS

Exercise reduced both fasting and postprandial triglyceride concentrations by 25% in both the lean and centrally obese groups (p < 0.0005). For all subjects taken together, exercise improved fasting endothelium-dependent function by 25% (p < 0.05), and, although there was a significant postprandial decrease in both endothelium-dependent and -independent function in both the control and exercise trials (p < 0.01), postprandial endothelium-dependent and -independent function were 15% and 20% higher, respectively, in the exercise trial than the control trial (both p < 0.05).

CONCLUSIONS

A session of prior exercise improves fasting and postprandial vascular function in middle-aged men. This may be one mechanism by which exercise influences cardiovascular risk.

Effects of exercise training and detraining on cutaneous microvascular function in man: the regulatory role of endothelium-dependent dilation in skin vasculature

This study investigated how exercise training and detraining affect the cutaneous microvascular function and the regulatory role of endothelium-dependent dilation in skin vasculature. Ten healthy sedentary subjects cycled on an ergometer at 50% of maximal oxygen uptake (VO(2max)) for 30 min daily, 5 days a week, for 8 weeks, and then detrained for 8 weeks. Plasma nitric oxide (NO) metabolites (nitrite plus nitrate) were measured by a microplate fluorometer. The cutaneous microvascular perfusion responses to six graded levels of iontophoretically applied 1% acetylcholine (ACh) and 1% sodium nitroprusside (SNP) in the forearm skin were determined by laser Doppler. After training, (1) resting heart rate and blood pressure were reduced, whereas VO(2max), skin blood flow and cutaneous vascular conductance to acute exercise were enhanced; (2) plasma NO metabolite levels and ACh-induced cutaneous perfusion were increased; (3) skin vascular responses to SNP did not change significantly. However, detraining reversed these effects on cutaneous microvascular function and plasma NO metabolite levels. The results suggest that endothelium-dependent dilation in skin vasculature is enhanced by moderate exercise training and reversed to the pretraining state with detraining.

Effects of upper extremity exercise training on peak aerobic and anaerobic fitness in patients after transplantation

We found that patients with transplants, regardless of transplant type, and sedentary control subjects experience significant increases in aerobic fitness after 10 weeks of Dragon boat training. However, the magnitude of improvement in aerobic fitness depends on the transplant type, with patients having cardiac transplant experiencing greater relative changes in response to training than patients with noncardiac transplant. It also appears that patients with cardiac and noncardiac transplants have an increased reliance on anaerobic energy systems during exercise conditions compared with healthy control subjects.

Endurance training enhances vasodilation induced by nitric oxide in human skin

Endurance training modifies the thermoregulatory control of skin blood flow, as manifested by a greater augmentation of skin perfusion for the same increase in core temperature in athletes, in comparison with sedentary subjects. In this study, we tested the hypothesis that a component of this adaptation might reside in a higher ability of cutaneous blood vessels to respond to vasodilatory stimuli. We recruited healthy nonsmoking males, either endurance trained or sedentary, in two different age ranges (18-35 y and >50 y). Skin blood flow was measured in the forearm skin, using a laser Doppler imager, allowing to record the vasodilatory responses to the following stimuli: iontophoresis of acetylcholine (an endothelium-dependent vasodilator), iontophoresis of sodium nitroprusside (a nitric oxide donor), and release of a temporary interruption of arterial inflow (reactive hyperemia). There was no effect of training on reactive hyperemia or the response to acetylcholine. In contrast, the increase in perfusion following the iontophoresis of sodium nitroprusside, expressed in perfusion units, was larger in trained than in sedentary subjects (younger: 398 +/- 54 vs 350 +/- 87, p < 0.05; older 339 +/- 72 vs 307 +/- 66, p < 0.05). In conclusion, endurance training enhances the vasodilatory effects of nitric oxide in the human dermal microcirculation, at least in forearm skin. These observations have considerable physiologic interest in view of recent data indicating that nitric oxide mediates in part the cutaneous vasodilation induced by heat stress in humans. Therefore, the augmentation of nitric oxide bioactivity in the dermal microcirculation might be one mechanism whereby endurance training modifies the thermoregulatory control of skin blood flow.

Regulation of human cutaneous circulation evaluated by laser Doppler flowmetry, iontophoresis, and spectral analysis: importance of nitric oxide and prostaglandines

Nitric oxide (NO) and prostaglandines (PGs) are important in regulation of vascular tone and blood flow. Their contribution in human cutaneous circulation is still uncertain. We inhibited NO synthesis by infusing N(G)-monomethyl-L-arginine (L-NMMA) in the brachial artery (16 micromol/min for 5 min) and reversed it by intraarterial infusion of L-arginine (40 micromol/min for 7.5 min). PG synthesis was inhibited by the cyclooxygenase inhibitor aspirin (600 mg over 5 min intravenously). Basal cutaneous perfusion and perfusion responses during iontophoresis with the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent vasodilator sodium nitroprusside (SNP) were recorded by laser Doppler flowmetry (LDF). We performed wavelet transforms of the measured signals. Mean spectral amplitude within the frequency interval from 0.0095 to 1.6 Hz and mean and normalized amplitudes of five intervals around 1, 0.3, 0.1, 0.04, and 0.01 Hz were analysed. The oscillations with frequencies around 1, 0.3, 0.1, and 0.04 Hz are influenced by the heartbeat, the respiration, the intrinsic myogenic activity of vascular smooth muscle, and the neurogenic activity of the vessel wall, respectively. We have previously shown that the oscillation with a frequency around 0.01 Hz is modulated by the vascular endothelium. L-NMMA reduced mean value of the LDF signal by approximately 20% (P = 0.0067). This reduction was reversed by L-arginine. Mean value of the LDF signals during ACh and SNP iontophoresis did not change after infusion of L-NMMA. Aspirin did not affect mean value of the LDF signal or the LDF signal during ACh or SNP iontophoresis. Before interventions the only significant difference between the effects of ACh and SNP was observed in the frequency around 0.01 Hz, where ACh increased normalized amplitude to a greater extent than SNP. L-NMMA abolished this difference, whereas it reappeared after infusion of L-arginine (P = 0.0084). Aspirin did not affect this difference (P = 0.006). We conclude that basal cutaneous blood flow and the endothelial dependency of the oscillation around 0.01 Hz are partly mediated by NO, but not by endogenous PGs. Other aspects of human cutaneous circulation studied are not regulated by NO or PGs.

Involvement of sympathetic nerve activity in skin blood flow oscillations in humans

We have used the wavelet transform to evaluate the time-frequency content of laser-Doppler flowmetry (LDF) signals measured simultaneously on the surfaces of free microvascular flaps deprived of sympathetic nerve activity (SNA), and on adjacent intact skin, in humans. It was thereby possible to determine the frequency interval within which SNA manifests itself in peripheral blood flow oscillations. The frequency interval from 0.0095 to 2 Hz was examined and was divided into five subintervals: I, approximately 0.01 Hz; II, approximately 0.04 Hz; III, approximately 0.1 Hz; IV, approximately 0.3 Hz; and V, approximately 1 Hz. The average value of the LDF signal in the time domain as well as the mean amplitude and total power in the interval from 0.0095 to 2 Hz and amplitude and power within each of the five subintervals were significantly lower for signals measured on the free flap (P < 0.002). The normalized spectral amplitude and power in the free flap were significantly lower in only two intervals: I, from 0.0095 to 0.021 Hz; and II, from 0.021 to 0.052 Hz (P < 0.05); thus indicating that SNA is manifested in at least one of these frequency intervals. Because interval I has recently been shown to be the result of vascular endothelial activity, we conclude that we have identified SNA as influencing blood flow oscillations in normal tissues with repetition times of 20-50 s or frequencies of 0.02-0.05 Hz.

Effects of an enhanced heart rate reserve on aerobic performance in patients with a heart transplant

OBJECTIVE

The aim of this study was to investigate whether a high-intensity warm-up at the start of a graded, symptom-limited exercise test would enhance heart rate reserve and thus improve the aerobic performance of orthotopic heart transplant patients.

DESIGN

Adrenal and cardiorespiratory responses were compared in 10 orthotopic heart transplant patients who performed two graded, symptom-limited exercise tests on an ergocycle.

RESULTS

At the start of the graded, symptom-limited exercise test, high intensity increased the norepinephrine level more than usual intensity between rest and the third minute of exercise. This higher norepinephrine level was followed by a higher heart rate response from the fourth minute of exercise. Heart rate reserve was enhanced during high-intensity exercise, without any significant change in peak oxygen uptake.

CONCLUSIONS

This specific warm-up enhanced heart rate reserve during a graded, symptom-limited exercise test on an ergocycle. Mechanisms more important than limited heart rate reserve are involved in the limitation of exercise tolerance in orthotopic heart transplant patients.

Factors critical to iontophoretic assessment of vascular reactivity: implications for clinical studies of endothelial dysfunction

Skin microvascular responses to iontophoresis of acetylcholine, an endothelium-dependent vasodilator, and sodium nitroprusside, an endothelium-independent vasodilator, were measured using a laser Doppler imager whose software controlled iontophoretic current delivery in an integrated fashion. A novel feature involved monitoring voltage across the iontophoresis chambers during current application (total charge: 8 mC). Both drugs elicited vasodilatation but with differing magnitudes and time courses, whereas current delivery with only vehicle (0.5% NaCl) present was ineffective. During drug delivery a three-to fourfold difference in calculated skin resistance was observed between subjects, with higher resistance being associated with lower dilator responses to both drugs. There was a significant (p < 0.0001) linear inverse correlation between perfusion.time and resistance.time integrals for both acetylcholine ( r = -0.86) and sodium nitroprusside ( r = -0.96). This was corrected in individual subjects by multiplying individual perfusion values by the resistance.time integral, which reduced response variability. Cyclooxygenase inhibition by aspirin apparently attenuated acetylcholine and sodium nitroprusside vasodilator responses but after correcting for skin resistance there was no longer any difference. Monitoring voltage across the iontophoretic circuit is critical, as effective drug delivery in individual subjects is influenced by the circuit resistance that can be corrected for. These findings have implications for clinical studies that use the iontophoresis technique for assessing vascular function.

Comparisons of cutaneous blood flow reactivity to norepinephrine and sodium nitroprusside between patients with heart transplantation and healthy subjects

Heart transplant patients are reported to have impaired regulation of the microvasculature. The purpose of this study was to investigate the cutaneous blood flow and its reactivity to sodium nitroprusside (vasodilator, Nipride 0.1%) and norepinephrine (vasoconstrictor, Levophed 0.1%) in patients after heart transplantation in comparison to normal healthy individuals. Eighteen patients after heart transplantation and 16 healthy, nonsmoking individuals served as subjects of the study. Sodium nitroprusside and norepinephrine were introduced by iontophoresis to the skin of the right and left forearms, respectively. After measuring cutaneous blood flow reactivity in the pre-exercise state by laser Doppler flowmetry, subjects were then asked to close and open their fists for 2 min. The same measurements were repeated after exercise. Comparisons between the groups were carried out by the Wilcoxan signed rank test. The Mann Whitney U-test was used for comparison between pre-exercise and post-exercise states. The results demonstrated that sodium nitroprusside significantly increased forearm cutaneous perfusion at rest but produced only a mild increase after exercise. This reactivity was significantly lower after exercise with no significant differences between groups. Norepinephrine decreased cutaneous blood flow at rest. The transplant patients were significantly less sensitive to norepinephrine before but not after exercise. The changes in norepinephrine reactivity with exercise were significantly different between groups (p < 0.05).

Heart failure etiology affects peripheral vascular endothelial function after cardiac transplantation

OBJECTIVES

The goal of this study was to examine the effect of heart failure etiology on peripheral vascular endothelial function in cardiac transplant recipients.

BACKGROUND

Peripheral vascular endothelial dysfunction occurs in patients with heart failure of either ischemic or nonischemic etiology. The effect of heart failure etiology on peripheral endothelial function after cardiac transplantation is unknown.

METHODS

Using brachial artery ultrasound, endothelium-dependent, flow-mediated dilation (FMD) was assessed in patients with heart failure with either nonischemic cardiomyopathy (n = 10) or ischemic cardiomyopathy (n = 7), cardiac transplant recipients with prior nonischemic cardiomyopathy (n = 10) or prior ischemic cardiomyopathy (n = 10) and normal controls (n = 10).

RESULTS

Patients with heart failure with either ischemic cardiomyopathy or nonischemic cardiomyopathy had impaired FMD (3.6 +/- 1.0% and 5.1 +/- 1.2%, respectively, p = NS) compared with normal subjects (13.9 +/- 1.3%, p < 0.01 compared with either heart failure group). In transplant recipients with antecedent nonischemic cardiomyopathy, FMD was markedly higher than that of heart failure patients with nonischemic cardiomyopathy (13.0 +/- 2.4%, p < 0.001) and similar to that of normal subjects (p = NS). However, FMD remained impaired in transplant recipients with prior ischemic cardiomyopathy (5.5 +/- 1.5%, p = 0.001 compared with normal, p = 0.002 vs. transplant recipients with previous nonischemic cardiomyopathy).

CONCLUSIONS

Peripheral vascular endothelial function is normal in cardiac transplant recipients with antecedent nonischemic cardiomyopathy, but remains impaired in those with prior ischemic cardiomyopathy. In contrast, endothelial function is uniformly abnormal for patients with heart failure, regardless of etiology. These findings indicate that cardiac transplantation corrects peripheral endothelial function for patients without ischemic heart disease, but not in those with prior atherosclerotic coronary disease.

Reproducibility of laser Doppler imaging of skin blood flow as a tool to assess endothelial function

Endothelial dysfunction might be an important and early event in the pathogenesis of major cardiovascular diseases. Therefore, the evaluation of endothelial function in humans may be of great clinical relevance. Usual methods for that purpose are either invasive and/or technically demanding. In the dermal microcirculation, endothelial function may be assessed noninvasively from the laser Doppler measurement of increases in blood flow after either the transdermal application of acetylcholine by iontophoresis, or the release of transient arterial occlusion (reactive hyperemia). An endothelium-independent response may be provided by the iontophoresis of sodium nitroprusside. This approach is notable for technical simplicity, but of uncertain reproducibility. Sixteen young, healthy, nonsmoking males were examined in the fasting state. Changes in skin blood flow were measured with a laser Doppler imager during the iontophoresis of acetylcholine and sodium nitroprusside, as well as during reactive hyperemia, on two different days, at each of two different sites on the volar face of the forearm. Nonspecific effects related to the stimulation of terminal nerve fibers by the iontophoretic current were suppressed by prior surface anesthesia. The iontophoresis of acetylcholine and sodium nitroprusside induced a seven- to eightfold increase in dermal blood flow. The corresponding figure for peak reactive hyperemia was approximately fourfold. The mean coefficients of variation of responses recorded on different days, on the same site, in the same individual were <10% for iontophoresis of acetylcholine and for peak reactive hyperemia, and between 10 and 20% for iontophoresis of sodium nitroprusside. This day-to-day variation was significantly smaller than the site-to-site variation (p < 0.01 for all three responses). Endothelium-dependent and -independent responses of dermal blood flow evaluated with laser Doppler imaging are highly reproducible from day to day, at least in healthy nonsmoking young male subjects, and provided some simple precautions are observed, foremost among which is the strict standardization of the recording site. These observations may have implications for the testing of endothelial function in clinical studies.

Exercise following heart transplantation

During the past 2 decades, heart transplantation has evolved from an experimental procedure to an accepted life-extending therapy for patients with endstage heart failure. However, with dramatic improvements in organ preservation, surgery and immunosuppressive drug management, short term survival is no longer the pivotal issue for most heart transplant recipients (HTR). Rather, a return to functional lifestyle with good quality of life is now the desired procedural outcome. To achieve this outcome, aggressive exercise rehabilitation is essential. HTR present unique exercise challenges. Preoperatively, most of these patients had chronic debilitating cardiac illness. Many HTR have had prolonged pretransplantation hospitalisation for inotropic support or a ventricular assist device. Decrements in peak oxygen consumption (VO2peak) and related cardiovascular parameters regress approximately 26% within the first 1 to 3 weeks of sustained bed rest. Consequently, extremely poor aerobic capacity and cardiac cachexia are not unusual occurrences in HTR who have required mechanical support or been confined to bed rest. Moreover, HTR must also contend with de novo exercise challenges conferred by chronic cardiac denervation and the multiple sequelae resulting from immunosuppression therapy. There is ample evidence that both endurance and resistance training are well tolerated in HTR. Moreover, there is growing clinical consensus that specific endurance and resistance training regimens in HTR can be efficacious adjunctive therapies in the prevention of immunosuppression-induced adverse effects and the reversal of pathophysiological consequences associated with cardiac denervation and antecedent heart failure. For example, some HTR who remain compliant during strenuous long term endurance training programmes achieve peak heart rate and VO2peak values late after transplantation that approach age-matched norms (up to approximately 95% of predicted). These benefits are not seen in HTR who do not participate in structured endurance exercise training. Rather, peak heart rate and VO2peak values in untrained HTR remain approximately 60 to 70% of predicted indefinitely. However, the mechanisms responsible for improved peak heart rate, VO2peak and total exercise time are not completely understood and require further investigation. Recent studies have also demonstrated that resistance exercise training may be an effective countermeasure for corticosteroid-induced osteoporosis and skeletal muscle myopathy. HTR who participate in specific resistance training programmes successfully restore bone mineral density (BMD) in both the axial and appendicular skeleton to pretransplantation levels, increase lean mass to levels greater than pretransplantation, and reduce body fat. In contrast, HTR who do not participate in resistance training lose approximately 15% BMD from the lumbar spine early in the postoperative period and experience further gradual reductions in BMD and muscle mass late after transplantation.