Regional specificity of peak hyperemic response in patients with congestive heart failure: correlation with peak aerobic capacity

Vascular Adaptation to Exercise in Humans: Role of Hemodynamic Stimuli

On the 400th anniversary of Harvey's Lumleian lectures, this review focuses on "hemodynamic" forces associated with the movement of blood through arteries in humans and the functional and structural adaptations that result from repeated episodic exposure to such stimuli. The late 20th century discovery that endothelial cells modify arterial tone via paracrine transduction provoked studies exploring the direct mechanical effects of blood flow and pressure on vascular function and adaptation in vivo. In this review, we address the impact of distinct hemodynamic signals that occur in response to exercise, the interrelationships between these signals, the nature of the adaptive responses that manifest under different physiological conditions, and the implications for human health. Exercise modifies blood flow, luminal shear stress, arterial pressure, and tangential wall stress, all of which can transduce changes in arterial function, diameter, and wall thickness. There are important clinical implications of the adaptation that occurs as a consequence of repeated hemodynamic stimulation associated with exercise training in humans, including impacts on atherosclerotic risk in conduit arteries, the control of blood pressure in resistance vessels, oxygen delivery and diffusion, and microvascular health. Exercise training studies have demonstrated that direct hemodynamic impacts on the health of the artery wall contribute to the well-established decrease in cardiovascular risk attributed to physical activity.

Skeletal Muscle Changes in Chronic Cardiac Disease and Failure

Peak exercise performance in healthy man is limited not only by pulmonary or skeletal muscle function but also by cardiac function. Thus, abnormalities in cardiac function will have a major impact on exercise performance. Many cardiac diseases affect exercise performance and indeed for some cardiac conditions such as atherosclerotic heart disease, exercise testing is frequently used not only to measure functional capacity but also to make a diagnosis of heart disease, evaluate the efficacy of treatment, and predict prognosis. Early in the course of cardiac diseases, exercise performance will be minimally affected but with disease progression impairment in exercise capacity will become apparent. Ejection fraction, that is, the percent of blood volume ejected with each cardiac cycle is often used as a measure of cardiac performance but frequently there is a dissociation between the ejection fraction and exercise capacity in patients with heart disease. How abnormalities in cardiac function impacts the muscles, vasculature, and lungs to impact exercise performance will here be reviewed. The focus of this work will be on patients with systolic heart failure as the incidence and prevalence of heart failure is reaching epidemic proportions and heart failure is the end result of many other chronic cardiac diseases. The prognostic role of exercise and benefits of exercise training will also be discussed.

Flow-mediated dilation normalization predicts outcome in chronic heart failure patients

BACKGROUND

Reduced flow-mediated dilation (FMD) is a known prognostic marker in heart failure (HF), but may be influenced by the brachial artery (BA) diameter. Aiming to adjust for this influence, we normalized FMD (nFMD) by the peak shear rate (PSR) and tested its prognostic power in HF patients.

METHODS AND RESULTS

BA diameter, FMD, difference in hyperemic versus rest brachial flow velocity (FVD), PSR (FVD/BA), and nFMD (FMD/PSR × 1000) were assessed in 71 HF patients. At follow-up (mean 512 days), 19 HF (27%) reached the combined endpoint (4 heart transplantations [HTs], 1 left ventricle assist device implantation [LVAD], and 14 cardiac deaths [CDs]). With multivariate Cox regression analysis, New York Heart Association functional class ≥III (hazard ratio [HR] 9.36, 95% confidence interval [CI] 2.11-41.4; P = .003), digoxin use (HR 6.36, 95% CI 2.18-18.6; P = .0010), FMD (HR 0.703, 95% CI 0.547-0.904; P = .006), PSR (HR 1.01, 95% CI 1.005-1.022; P = .001), FVD (HR 1.04, 95% CI 1.00-1.06; P = .02), and nFMD (HR 0.535, 95% CI 0.39-0.74; P = .0001) were predictors of unfavorable outcome. Receiver operating characteristic curve for nFMD showed that patients with nFMD >5 seconds had significantly better event-free survival than patients with nFMD ≤5 seconds (log-rank test: P < .0001).

CONCLUSIONS

nFMD is a strong independent predictor of CD, HT, and LVAD in HF with left ventricular ejection fraction <40%. Patients with nFMD >5 seconds have a better prognosis than those with lower values.

Age and sex influence the balance between maximal cardiac output and peripheral vascular reserve

We evaluated the influence of age and sex on the relationship between central and peripheral vasodilatory capacity. Healthy men (19 younger, 12 older) and women (17 younger, 17 older) performed treadmill and knee extensor exercise to fatigue on separate days while maximal cardiac output (Q, acetylene uptake) and peak femoral blood flow (FBF, Doppler ultrasound) were measured, respectively. Maximal Q was reduced with age similarly in men (Y: 23.6 +/- 2.7 vs. O: 17.4 +/- 3.5 l/min; P < 0.05) and women (Y: 17.7 +/- 1.9 vs. O: 12.3 +/- 1.6 l/min; P < 0.05). Peak FBF was similar between younger (Y) and older (O) men (Y: 2.1 +/- 0.5 vs. O: 2.2 +/- 0.7 l/min) but was lower in older women compared with younger women (Y: 1.9 +/- 0.4 vs. O: 1.4 +/- 0.4 l/min; P < 0.05). Maximal Q was positively correlated with peak FBF in men (Y: r = 0.55, O: r = 0.74; P < 0.05) but not in women (Y: r = 0.34, O: r = 0.10). Normalization of cardiac output to appendicular muscle mass and peak FBF to quadriceps mass reduced the correlation between these variables in younger men (r = 0.30), but the significant association remained in older men (r = 0.68; P < 0.05), with no change in women. These data suggest that 1) aerobic capacity is associated with peripheral vascular reserve in men but not women, and 2) aging is accompanied by a more pronounced sex difference in this relationship.

Transit delay and flow quantification in muscle with continuous arterial spin labeling perfusion-MRI

PURPOSE

To test the hypothesis that flow measurements using continuous arterial spin labeling (CASL) magnetic resonance imaging (MRI) in muscle depend upon transit delay, and examine the repeatability of CASL measurements.

MATERIALS AND METHODS

A total of 23 healthy subjects underwent CASL imaging of the calf, foot, and forearm with varying postlabeling delay (PLD = 1000, 1500, and 1900 msec). Experiments were conducted on a 3.0T system. An orthopedic tourniquet system was employed to create a five-minute period of ischemia followed by a transient hyperemic flow. Imaging commenced two minutes prior to cuff inflation and ended three minutes after cuff release.

RESULTS

CASL was found able to well resolve the time course of the hyperemic flow pattern with an effective TR of 16 seconds, although we were unable to establish that a plateau had been reached in the flow measurements even at a PLD as long as 1900 msec. Peak hyperemic flow measurements compared favorably with those obtained with contrast-enhanced (CE) MRI following a similar period of ischemia. Region-of-interest (ROI)-based repeated measurements varied by approximately 20% over a period of one hour.

CONCLUSION

In all anatomic regions studied, flow measurements were found to increase with PLD, suggesting the prolonged transit delay in muscle.

Central haemodynamics and peripheral muscle function during exercise in patients with chronic heart failure

In this narrative review of the current literature, we examine the central and peripheral mechanisms responsible for the exercise intolerance of chronic heart failure and highlight briefly the benefits of exercise training in the treatment of this debilitating disorder. Specifically, we identify the common finding of reduced cardiac output reserve during exercise conditions leading to decreased exercise tolerance. We also reveal that the stroke volume response to exercise varies depending on the individual patient, the presence of mitral regurgitation, and the aetiology of heart failure. Chronic heart failure patients with left ventricular systolic dysfunction appear able to use the Frank-Starling mechanism to compensate (in part) for their decreased contractile reserve. Patients with left ventricular diastolic dysfunction have normal contractile function; however, they are unable to make use of the Frank-Starling mechanism during exercise conditions. We also reveal that pericardial constraint may limit diastolic filling and exercise capacity in patients with chronic heart failure. It appears that interventions that reduce pericardial constraint and mitral regurgitation enhance diastolic filling and increase exercise tolerance. A series of peripheral muscle changes also occur, including changes in muscle mass, cellular structure, energy metabolism, and blood flow. Each of these factors is associated with decreased exercise capacity and the symptoms of chronic heart failure. Exercise training has been shown to improve both central haemodynamics and peripheral muscle function leading to improvements in exercise capacity, functional status, and overall quality of life in patients with chronic heart failure.

Vasoconstrictive Response in the Vascular Beds of the Non-Exercising Forearm During Leg Exercise in Patients With Mild Chronic Heart Failure

BACKGROUND

Reduced exercise capacity may be related to decreased redistribution of blood flow from the non-exercising tissues to the exercising skeletal muscle in patients with mild chronic heart failure (CHF).

METHODS AND RESULTS

In the present study 14 patients with mild CHF and 10 healthy subjects (N) underwent symptom-limited multistage-ergometer exercise, during which forearm vascular resistance (FVR), cardiac index (CI), systemic vascular resistance index (SVRI), and oxygen uptake (VO(2)) were measured non-invasively using the plethysmograph, impedance, and respiratory gas analysis methods, respectively. The VO(2) and CI at peak exercise were lower (p<0.01 each), and SVRI and FVR at both rest and peak exercise were higher in the CHF group than in N. However, both the percent increase in FVR and percent decrease in SVRI from the resting state to peak exercise were lower in CHF than N, and both of them correlated with not only peak VO(2), but also the corresponding resting value of FVR and SVRI (p<0.01 each).

CONCLUSIONS

Redistribution of blood flow from the non-exercising tissues to the working skeletal muscles, which may participate in exercise capacity, can be blunted in CHF. The decreased vasoconstrictive response in the non-exercising tissues is intimately related to the increased resting vascular tone in CHF.

Is There a Difference in Vascular Reactivity of the Arms and Legs?

The arterial vessels within the arms and legs are exposed to different hydrostatic pressures and blood-flow demands during the course of daily life. There is compelling indirect evidence that arterial reactivity differs in the arms and legs of humans; greater blood-flow responses to physiological vasodilator stimuli are generally reported in the arms of healthy younger subjects, whereas greater sympathetically mediated vasoconstrictor responsiveness is generally observed in the legs. Limb blood-flow responses to local arterial infusions of vasoactive agents reveal a similar pattern of heterogeneity in human arms versus legs. The advantages and assumptions of these pharmacological approaches for evaluating limb arterial reactivity are discussed, and methodological issues pertaining to the normalization and interpretation of vascular responses in the human arm and leg are critically examined. The article concludes with recent data from our laboratory indicating that limb-specific variation in arterial function may be age-, sex-, and physical activity dependent.

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.

Cardiovascular Adaptations to Exercise Training After Uncomplicated Acute Myocardial Infarction

OBJECTIVE

This study examined the cardiovascular adaptations of an exercise training program and evaluated the role of peripheral vasodilator capacity in contributing to these adaptations after myocardial infarction.

DESIGN

A total of 44 consecutive patients with uncomplicated myocardial infarction underwent 3 wks of exercise training. Controls (n = 12) with comparable myocardial infarction were selected from our database and were restricted to a program with minimal activity. All patients performed cardiopulmonary exercise testing with hemodynamic measurements. Forearm and calf reactive hyperemic flow were measured by venous occlusive plethysmography as indices of peripheral vasodilator capacity.

RESULTS

Despite no change in arteriovenous oxygen difference at peak exercise after training, training resulted in significant increases in oxygen consumption, cardiac output, and stroke volume and a significant decrease in systemic vascular resistance at peak exercise (overall, P < 0.05). Calf reactive hyperemic flow increased significantly after training (P < 0.001), but forearm reactive hyperemic flow did not. Furthermore, increase in calf reactive hyperemic flow after training had a positive correlation with increases in peak cardiac output, stroke volume, and oxygen consumption after training and an inverse correlation with peak systemic vascular resistance.

CONCLUSIONS

Exercise training improved exercise tolerance by improving hemodynamic responses to exercise after myocardial infarction. This improved exercise performance was linked to a training-induced increase in calf vasodilator capacity.

Muscle metaboreflex is blunted with reduced vascular resistance response of nonexercised limb in patients with chronic heart failure

BACKGROUND

Exercise-mediated muscle metaboreflex (MMR) activates the sympathetic nervous system afferently and may play an important role in the reduction in blood flow in nonexercised limb, thus enhancing exercised skeletal muscle blood flow (ie, normal regional blood flow redistribution during exercise). However, few data are available to describe the relationship between MMR and peripheral vascular control during exercise in congestive heart failure (CHF). The aim of this study was to determine whether MMR is impaired in CHF, and, if so, whether MMR is related to clinical severity of CHF and to changes in nonexercised limb vascular resistance in CHF.

METHODS AND RESULTS

Eleven CHF patients and 9 healthy age- and gender-matched controls were examined. All subjects performed a rhythmic handgrip exercise test at 50% of maximal voluntary contraction for 3 minutes on 2 occasions with and without postexercise upper arm regional circulatory occlusion (RCO/non-RCO). Changes in systolic blood pressure were measured and plotted against protocol time for both RCO and non-RCO. The area under each curve was estimated, and the calculating difference in the area between RCO and non-RCO was regarded as MMR. In addition, changes in calf vascular resistance were measured continuously by plethysmography after the handgrip test and the area differences between the RCO and non-RCO data was taken to represent MMR-provoked resistance changes in the nonexercised limb. During the handgrip exercise, systolic blood pressure increased similarly on the 2 occasions for both groups. MMR was significantly lower in CHF patients than in controls (68.2 +/- 23.1 versus 160.4 +/- 29.6 arbitrary units; P < .05). Decrease in MMR activity was related to clinical severity of CHF (controls, 160.4 +/- 29.6; New York Heart Association class II, 87.6 +/- 29.8; New York Heart Association class III, 34.3 +/- 34.8 arbitrary units; P < .05). The increase in calf vascular resistance between RCO and non-RCO protocols in the control group was significant (+146.5 +/- 38.0 arbitrary units; P < .05), whereas the difference in the CHF group was not significant (-72.9 +/- 126.9 arbitrary units; not significant).

CONCLUSIONS

Exercise-induced MMR control in mild to moderate CHF is impaired in association with a blunted increase in nonexercised limb vascular resistance. This suggests that blunted MMR activity impairs regional blood flow redistribution and may contribute in part to exercise intolerance in this disorder.

Forearm reactive hyperemic blood flow and arm-cranking exercise capacity in healthy and heart failure subjects

BACKGROUND

The relationship between lower limbs maximal vasodilatory capacity and exercise capacity in congestive heart failure (CHF) and healthy subjects has been well-documented. However, the relationship between upper limbs maximal vasodilatory capacity and exercise is less well-established.

METHODS AND RESULTS

Twelve patients with CHF, 16 age-matched normal subjects, and 11 very fit individuals underwent an arm-cranking exercise test using maximal oxygen uptake (arm VO(2max)) and measurements of peak forearm reactive hyperemic blood flow. Despite similar forearm strength, arm VO(2max) was significantly reduced in patients with CHF when compared to normal and very fit individuals (13.9 +/- 2.9, 23.5 +/- 4.8, and 36.4 +/- 8.5 mL/kg/min, respectively, P <.05). Similarly, peak reactive hyperemia was lower in CHF patients as compared to normal and very fit individuals (18.6 +/- 5.9, 24.3 +/- 5.8, and 41.1 +/- 8.1 mL/100 mL/min, respectively, P <.05). There was a strong relationship between peak reactive hyperemic blood flow and arm VO(2max) (r =.75; P <.001) in all subjects.

CONCLUSIONS

These results suggest a significant relationship between forearm vasodilatory capacity and arm-cranking VO(2max) in CHF patients, sedentary, and very fit individuals.

Vascular dysfunction and heart failure: epiphenomenon or etiologic agent?

Endothelial function plays a key role in the local regulation of vascular tone. Alterations in endothelial function may result in impaired release of endothelium-derived relaxing factors or increased release of endothelium-derived contracting factors. Heart failure may impair endothelial function by means of reduced synthesis and release of nitric oxide (NO) or by increased degradation of NO and increased production of endothelin-1. Endothelial dysfunction may worsen heart function by means of peripheral effects, causing increased afterload and central effects such as myocardial ischemia and inducible nitric oxide synthase (iNOS)-induced detrimental effects. Evidence from clinical studies has suggested that there is a correlation between decreased endothelial function and increasing severity of congestive heart failure (CHF). Treatments that improve heart function may also improve endothelial dysfunction. The relationship between endothelial dysfunction and heart failure may be masked by the stage of endothelial dysfunction, the location of vessels being tested, and the state of endothelial-dependent vasodilatation response.

Short-term physical training improves vasodilatory capacity in cardiac patients

There have been no previous studies that clearly demonstrate the effects of training on the relation between exercise capacity and vasodilatory capacity in skeletal muscle. This study was performed to clarify the effects of short-term, moderate-intensity physical training on exercise tolerance and vasodilatory capacity in cardiac patients. We studied 21 patients after acute myocardial infarction, coronary artery bypass grafting, or valve replacement. Each patient performed symptom-limited incremental exercise tests before and after a 2-week training program of moderate-intensity exercise. A cycle ergometer was used for both the training and exercise tests. Blood pressure measurement and respiratory gas analysis were continuously performed during the tests. Cardiac output was also measured using a dye-dilution method at rest and every 2 minutes during incremental exercise. Reactive hyperemic calf blood flow was measured at rest. After the training program, the subjects attained a significant decrease in systemic vessel resistance and significant increases in oxygen uptake and cardiac output at peak exercise. Changes in reactive hyperemic calf blood flow were significantly correlated with the changes in cardiac output, systemic vascular resistance, and the kinetics of oxygen uptake during warm-up exercise. By improving the peripheral vasodilatory capacity in these patients, short-term, moderate-intensity physical training was found to improve the cardiovascular adaptation not only at peak exercise, but also during the onset of exercise.

Evaluation of the severity of chronic heart failure by the reactivity of peripheral vessels

We developed a method to evaluate the severity of chronic cardiac failure by Doppler image analysis. Doppler images of the whole arterial lumen were consecutively recorded on video tape and the power spectrum (sum of intensity multiplied by frequency) of each frame was considered as an index of the blood flow volume (VI). The right brachial artery was occluded for 15-60 seconds by a occluding cuff, and was released quickly. The VI was determined until the VI returned to the level at rest and total VI was calculated as an O2 repayment. The O2 repayment rate (R-Rate) was calculated as a ratio of the O2 repayment divided by total VI during interruption. The cardiac function was evaluated by sub-maximal exercise using bicycle ergometer and was compared with the R-Rate. The subjects were 22 patients (18 males and 4 females) with chronic cardiac failure of NYHA class I (9), class II (6), class III (4), class IV (3) and 12 healthy controls. R-Rate was almost unchanged by the duration of occlusion and showed positive correlation with exercise capacity. R-Rate decreased as the class of NYHA advanced. In conclusion, determination of reactive hyperemia can be used for objectively evaluating the severity of cardiac failure. Doppler sonography; cardiac failure; reactive hyperemia; peripheral circulation

Acetylcholine-mediated vasodilation in the forearm circulation of patients with heart failure: indirect evidence for the role of endothelium-derived hyperpolarizing factor

Vasomotor responses to intraarterial administration of acetylcholine are mediated by release of nitric oxide, prostaglandins, and an unidentified hyperpolarizing factor from vascular endothelial cells. The contribution of endothelium-derived hyperpolarizing factor (EDHF) to the vasodilatory response to acetylcholine in the skeletal muscle circulation of patients with congestive heart failure (CHF) has not been previously characterized. Accordingly, to specifically assess the role of EDHF, the regional vascular effects of sequential administration of acetylcholine and nitroglycerin in the brachial artery were determined in the forearm circulation with strain-gauge venous occlusion plethysmography in patients with CHF and in normal subjects during combined systemic inhibition of cyclooxygenase activity with indomethacin and regional inhibition of nitric oxide synthase activity with l-N(G)-monomethylarginine (l-NMMA). After administration of indomethacin, infusion of l-NMMA significantly decreased the forearm blood flow response to acetylcholine in normal subjects (5.4 +/- 1.2 to 3.5 +/- 0.6 ml/min/100 ml, p < 0.05) but not in patients with CHF (5.7 +/- 1.3 to 5.7 +/- 1.4 ml/min/100 ml). Infusion of l-NMMA did not change forearm blood flow responses to nitroglycerin in either group. The presence of a noncyclooxygenase, non-nitric-oxide relaxing factor indicates that EDHF, rather than nitric oxide, may be the predominant endothelium-derived substance mediating vasodilation in response to acetylcholine in patients with CHF.

Alterations in the peripheral circulation in patients with mild heart failure

OBJECTIVE

In patients with severe heart failure, compensatory mechanisms fail to provide adequate blood supply to the peripheral circulation, especially when the metabolic need is increased. The aim of this study was to assess alterations in the peripheral circulation in patients with mild heart failure using ultrasound Doppler.

METHODS

In 19 controls and in 11 patients with mild heart failure, Doppler spectra were recorded from the carotid, the brachial and the femoral artery at rest and, from the latter two arteries, during post-occlusive reactive hyperemia. Parameters derived from these Doppler spectra were used to make comparisons between both groups.

RESULTS

At rest, the duration of the acceleration of blood was shorter in controls, the acceleration was steeper in controls and the deceleration duration was longer in controls as compared to the patients. Differences in the response to reactive hyperemia were only observed in the common femoral artery.

CONCLUSIONS

In patients with mild heart failure, significant alterations in the peripheral circulation were observed especially for the femoral artery. These changes are caused by the impairment of the left ventricular function and by adjustments in the compensatory mechanism of the peripheral circulation.

Vascular reactivity in acromegalic patients: preliminary evidence for regional endothelial dysfunction and increased sympathetic vasoconstriction

BACKGROUND AND OBJECTIVES

Hypertension is found in one-third of acromegalic patients. An heterogenous distribution of cardiac output has been recently demonstrated in acromegalic patients with an increased blood flow at the level of the upper limb, suggesting that acromegalic patients may have some degree of endothelial dysfunction. Elsewhere, studies involving hypopituitary GH-deficient adults have shown that GH and/or IGF-I may have direct effect on endothelial function.

SUBJECTS AND METHODS

We thus compared cutaneous vasoreactivity responses in 10 normotensive patients with active acromegaly (A) (six women and four men) aged 25-59 (mean, 43.2 years), whose basal GH and IGF-I levels ranged from 7.4 to 158 mU/l and from 401 to 1690 microg/l, respectively, and in 10 normal age- and sex-matched controls (NC) by means of Laser Doppler flowmetry at the levels of the palm and the dorsum of the right hand. Circulatory skin velocities were studied basally and after increasing skin temperature to 44 degrees C (in order to study direct nonspecific vasodilatation response which is independent of endothelial or autonomous nervous system and reflects normal vascular muscle function), after shear-stress (known to produce flow-dependent vasodilatation, mediated by nitric oxyde (NO) originating from endothelial cells) and after cold-stress applied on the opposite hand (known to produce vaso-constriction mediated by the sympathetic nervous system).

RESULTS

The warm test induced a significant (P<0.001) and similar increase in both dorsal and palmar skin perfusion in A (mean +/- SD) (240+/-96 and 238+/-134%, respectively) and NC (232+/-137 and 233+/-73, respectively). Ischaemia release induced a significant increase in both dorsal and palmar skin blood flows in the two groups (P<0.001), but reactivities in acromegalic patients were about one half of those measured in controls (22.9+/-16.2% (A) vs. 46.9 25% (NC), 2P<0.02, at the level of the dorsum; and 45.0+/-43.6% (A) vs. 104.7+/-40.1 (NC), 2P<0.01, at the level of the palm). Cold pressor test resulted in significant decreases in both cutaneous flows (P<0.01) in the two groups, with a larger vasoconstriction (that did not reach statistical significance) in acromegalic patients as compared with controls (P< 0.10).

CONCLUSION

Vascular smooth cell ability to produce skin vasodilatation is normal but endothelium-dependent vasodilatation appears to be impaired while sympathetic-mediated vasoconstrictive response might be increased in acromegaly. This endothelial dysfunction may contribute to hypertension and represent a risk factor for cardiovascular complications in acromegaly.

Exercise skeletal muscle blood flow is related to peripheral microvascular stiffness in idiopathic dilated cardiomyopathy

Peripheral microvascular function plays an important role in congestive heart failure (CHF). Decreased exercise blood flow and microvascular dysfunction have been described in CHF and both factors are regarded as parameters that might influence exercise capacity in these patients. Whether these factors are related to or can be characterized in clinical severity of CHF has not been elucidated in this population. Skeletal muscle blood flow (SMBF) was measured continuously noninvasively, by means of the local isotope washout technique using (133)Xenon, in musculus tibialis anterior during graded maximal supine bicycle exercise. The distensibility in skeletal muscle was measured in a papaverine-relaxed vascular bed using (99m)Tc-pertechnetate. The investigation included 20 patients with moderate CHF (NYHA II), 11 patients with severe CHF (NYHA III, IV) due to idiopathic dilated cardiomyopathy (IDCM), and 31 age-matched healthy subjects. The maximal SMBF level was significantly lower in severe CHF (3.6 +/- 2.5 (ml x (100 g x min)(-1))) compared with moderate CHF (8.6 +/- 5.1 (ml x (100 g x min)(-1)); P < 0.005) and controls (11.0 +/- 4.1 (ml x (100 g x min)(-1)); P < 0.0001), but similar between moderate CHF and controls. Distensibility in skeletal muscle was decreased in severe CHF (12 +/- 8%) compared with controls (44 +/- 17%; P < 0.0001 vs severe CHF) and decreased with increasing severity of CHF (moderate CHF, 23 +/- 14%; P < 0.0005 vs controls). In CHF patients, a relationship was demonstrated between skeletal muscle distensibility and the maximal SMBF (P < 0.0001; r = 0.70). Moreover, maximal SMBF correlated directly to exercise time (P < 0.005; r = 0.54). Patients with CHF have reduced exercise SMBF, which may be a limiting factor for the reduced maximal exercise capacity. Moreover, microvascular distensibility in skeletal muscle is reduced and correlates to maximal exercise SMBF. Furthermore, maximal SMBF correlates to exercise time. This implies that increased skeletal muscle microvascular stiffness may contribute to the reduced blood flow during exercise and SMBF may partly limit exercise performance in CHF patients due to IDCM.

The role of exercise testing in the evaluation and management of heart failure

The clinical syndrome of heart failure has been investigated so extensively that it may now almost be regarded as a metabolic disorder. Although an initial insult reduces cardiac pump efficacy, the resultant physiological response culminates in complex neurohormonal dysfunction. This has created confusion and prevented the acceptance of a universal definition of cardiac failure. With much current research concentrating on the pharmacological modification of neuroendocrine imbalance, it is easy to lose sight of the fundamental principles behind heart failure management, namely, to improve cardiac function. In attempting to achieve this, the issues of morbidity and mortality must be addressed jointly; they are not mutually exclusive entities. Discrepant results between mortality studies and changes in exercise capacity have undermined the value of exercise testing. Because a treatment enhances longevity we should not ignore its effect on symptomatic status, and likewise we should not discard a therapy, which improves function because adverse events result in occasional premature deaths. Informed patient choice must exist. Historically, exercise testing has been quintessential in our understanding and evaluation of heart failure. Peak oxygen consumption remains the best overall indicator of symptomatic status, exercise capacity, prognosis and hospitalisation. Unfortunately, muddling of surrogate and true end-points has confused many of these issues. Improved comprehension may be gained by applying the concept of cardiac reserve which has been described in a variety of heart conditions and used in cardiac failure patients to provide an indication of prognosis and functional capacity.

Influence of high-intensity exercise training on the ventilatory response to exercise in patients with reduced ventricular function

BACKGROUND

Exercise training increases exercise capacity in patients with reduced ventricular function in part through improved skeletal muscle metabolism, but the effect training might have on abnormal ventilatory and gas exchange responses to exercise has not been clearly defined.

METHODS

Twenty-five male patients with reduced ventricular function after a myocardial infarction were randomized to either a 2-month high-intensity residential exercise training program or to a control group. Before and after the study period, upright exercise testing was performed with measurements of ventilatory gas exchange, lactate, arterial blood gases, cardiac output, and pulmonary artery and wedge pressures.

RESULTS

In the exercise group, peak VO2 and VO2 at the lactate threshold increased 29 and 39%, respectively, whereas no increases were observed among controls. Maximal cardiac output increased only in the exercise group (1.7 L x min(-1), P < 0.05), and no changes in rest or peak exercise pulmonary pressures were observed in either group. At baseline, modest inverse relationships were observed between pulmonary wedge pressure and peak VO2 both at rest (r = -0.56, P < 0.05) and peak exercise (r = -0.43, P < 0.05). Maximal VE/VCO2 was inversely related to maximal cardiac output (r = -0.72, P < 0.001). Training did not have a significant effect on these relationships. Training lowered VE/VO2, heart rate, and blood lactate levels at matched work rates throughout exercise and tended to lower maximal Vd/Vt. The slope of the relationship between VE and VCO2 was reduced after training in the exercise group (0.33 pre vs 0.27 post, P < 0.01), whereas control patients did not differ.

CONCLUSIONS

Exercise training among patients with reduced left ventricular function results in a systematic improvement in the ventilatory response to exercise. Training increased maximal cardiac output, tended to lower Vd/Vt, and markedly improved the efficiency of ventilation. Peak VO2 and ventilatory responses to exercise were only modestly related to pulmonary vascular pressures, and training had no effect on the relationships between exercise capacity, ventilatory responses, and pulmonary pressures.

Peripheral vascular remodeling in chronic heart failure: clinical relevance and new conceptualization of its mechanisms

Increased peripheral vascular tone is a critical factor in the deterioration of clinical stage and symptoms in chronic congestive heart failure (CHF) because of increased cardiac afterload and decreased nutritive skeletal muscle blood flow. Endothelial function as represented by nitric oxide (NO) production shows significant attenuation with the progression of clinical severity of CHF as determined by New York Heart Association class and exercise capacity parameters. This endothelial dysfunction emerges in the early stages of CHF. In the advanced stage of the condition, both endothelium-dependent and endothelium-independent dilator mechanisms are impaired in limb resistance vessels. This occurs because vascular endothelial function, especially NO production, is an important factor in the regulation of vasodilatory function, as well as making an important contribution to vascular structure. Furthermore, although such vasodilatory circulating factors as natriuretic polypeptides and newly discovered adrenomedullin are increased in heart failure, the vasodilatory potency of these polypeptide hormones in the limb vascular bed is significantly blunted. These observations suggest that peripheral circulatory failure in CHF is caused not only by simple arterial muscle constriction, but also by structural and functional changes, including receptor and postreceptor levels in the vasculature. This vascular remodeling may be an important mechanism underlying vasodilatory failure in both limb conduit and intraskeletal muscle vessels and may contribute significantly to left ventricular dysfunction and exercise intolerance in patients with heart failure.

Effects of L-arginine on lower limb vasodilator reserve and exercise capacity in patients with chronic heart failure

OBJECTIVE

To determine whether the reactive hyperaemic response of the lower limb increases with improved exercise capacity after acute supplementation with L-arginine, the precursor of nitric oxide, in patients with chronic heart failure.

METHODS

19 patients with chronic heart failure were enrolled in the study. Rest calf blood flow and femoral occlusion induced calf blood flow changes were measured by venous occlusion plethysmography before and after intravenous infusion of 10% L-arginine solution (5 ml/kg for 30 minutes) or placebo. Postexercise calf blood flow was also measured after the experimental infusion. During both postinfusion periods, several exercise capacity indices were determined by a symptom limited cardiopulmonary exercise test using a bicycle ergometer.

RESULTS

Baseline calf blood flow, systemic blood pressure, and heart rate showed no significant changes in either of the two experimental conditions. However, the occlusion induced blood flow response was significantly enhanced by L-arginine infusion (mean (SEM) peak flow, 19.6 (1.5) v 28.9 (3.1) ml/min/dl calf tissue; p < 0.01), but not by placebo (peak flow, 19.1 (1.4) v 20.9 (1.8) ml/min/dl calf tissue; NS). Calf blood flow response after exercise was also higher after L-arginine infusion than after placebo (peak flow, 4.8 (0.4) v 6.0 (0.8) ml/min/dl calf tissue; p < 0.05). L-arginine infusion had no significant effect compared with placebo on exercise capacity indices such as peak oxygen uptake (17.1 (1.0) v 15.8 (1.1) ml/min/kg; NS), anaerobic threshold (10.5 (0.6) v 10.4 (0.7) ml/min/kg; NS), and exercise time (296 (23) v 283 (22) s; NS).

CONCLUSIONS

Acute supplementation with the nitric oxide precursor L-arginine increased lower limb reactive hyperaemia but did not lead to any significant improvement in exercise capacity in patients with chronic heart failure.

Effect of intensive therapy for heart failure on the vasodilator response to exercise

OBJECTIVES

The purpose of the study was to evaluate the lower extremity vascular responsiveness to metabolic stimuli in patients with heart failure and to determine whether these responses improve acutely after intensive medical therapy.

BACKGROUND

Metabolic regulation of vascular tone is an important determinant of blood flow, and may be abnormal in heart failure.

METHODS

The leg blood flow responses were measured in 11 patients with nonedematous class III-IV heart failure before and after inpatient medical therapy and in 10 normal subjects. Venous occlusion plethysmography was used to measure peak blood flow and total hyperemia in the calf after arterial occlusion and also after isotonic ankle exercise. Measurements were repeated following short-term inpatient treatment with vasodilators and diuretics administered to decrease right atrial pressure (18+/-2 to 7+/-1 mm Hg), pulmonary wedge pressure (32+/-3 to 15+/-2 mm Hg), and systemic vascular resistance (1581+/-200 to 938+/-63 dynes.s.cm(-5), all p < 0.02).

RESULTS

Leg blood flow at rest, after exercise, and during reactive hyperemia was less in heart failure patients than in control subjects. Resting leg blood flow did not increase significantly after medical therapy, but peak flow after the high level of exercise increased by 59% (p = 0.009). Total hyperemic volume in the recovery period increased by 73% (p = 0.03). Similarly, the peak leg blood flow response to ischemia increased by 88% (p = 0.04), whereas hyperemic volume rose by 98% (p = 0.1).

CONCLUSIONS

The calf blood flow responses to metabolic stimuli are blunted in patients with severe heart failure, and improve rapidly with intensive medical therapy.

Improved exercise tolerance after losartan and enalapril in heart failure: correlation with changes in skeletal muscle myosin heavy chain composition

BACKGROUND

In congestive heart failure, fatigue-resistant, oxidative, slow type I fibers are decreased in leg skeletal muscle, contributing to exercise capacity (EC) limitation. The mechanisms by which ACE inhibitors and AII antagonists improve EC is still unclear. We tested the hypothesis that improvement in EC is related to changes in skeletal muscle composition toward type I fibers.

METHODS AND RESULTS

Eight patients with congestive heart failure, NYHA classes I through IV, were treated for 6 months with enalapril (E) 20 mg/d, and another 8 with losartan (L) 50 mg/d. EC was assessed with maximal cardiopulmonary exercise testing at baseline and after treatment. Myosin heavy chain (MHC) composition of the gastrocnemius was studied after electrophoretic separation of slow MHC1, fast oxidative MHC2a, and fast glycolytic MHC2b isoforms from needle microbiopsies obtained at baseline and after 6 months. EC improved in both groups. Peak V(O2) increased from 21.0+/-4.7 to 27.6+/-4.3 mL . kg-1 . min -1 (P=0.011) in the L group and from 17.5+/-5.0 to 25.0+/-5.5 mL . kg-1 . min -1 (P=0.014) in the E group. Similarly, ventilatory threshold changed from 15.0+/-4.0 to 19.9+/-4.9 mL (P=0. 049) with L and from 12.0+/-1.9 to 15.4+/-3.5 mL (P=0.039) with E. MCH1 increased from 61.2+/-11.2% to 75.4+/-7.6% with L (P=0.012) and from 60.6+/-13.1% to 80.1+/-10.9% (P=0.006) with E. Similarly, MHC2a decreased from 21.20+/-9.5% to 12.9+/-4.4% (P=0.05) with L and from 19.9+/-7.8% to 11.8+/-7.9% (P=0.06) with E. MHC2b changed from 17. 5+/-6.5% to 11.7+/-5.2% (P=0.07) with L and from 19.5+/-6.4% to 8. 1+/-4.6% (P=0.0015) with E. There was a significant correlation between net changes in MHC1 and absolute changes in peak V(O2) (r2=0.29, P=0.029) and a trend to significance for MHC2a and 2b.

CONCLUSIONS

Six months' treatment with L and with E produces an improvement in EC of similar magnitude. These changes are accompanied by a reshift of MHCs of leg skeletal muscle toward the slow, more fatigue-resistant isoforms. Magnitude of MHC1 changes correlates with the net peak V(O2) gain, which suggests that improved EC may be caused by favorable biochemical changes occurring in the skeletal muscle.

Importance of intrinsic calf vasodilator capacity in determining distribution of skeletal muscle perfusion during supine bicycle exercise in patients with left ventricular dysfunction

BACKGROUND

Distribution of skeletal muscle perfusion during exercise is an important factor in determining exercise capacity and is markedly impaired in patients with cardiac disease. This study examined the importance of intrinsic calf vasodilator capacity in determining distribution of skeletal muscle perfusion during supine bicycle exercise in patients with left ventricular dysfunction.

METHODS

We studied 19 patients with left ventricular dysfunction (left ventricular ejection fraction <45%) after myocardial infarction. All the patients underwent cardiopulmonary exercise testing with measurements of central hemodynamics, leg blood flow (LBF), and the percentage of cardiac output distributed to both legs (%LBF). Calf reactive hyperemic flow (RH) was measured by venous occlusive plethysmography at supine rest.

RESULTS

LBF at peak exercise was closely related to peak cardiac output and RH. Furthermore, %LBF at peak exercise had modest correlation with peak cardiac output and good correlation with RH. Although peak cardiac output and RH were independent determinants of LBF at peak exercise by multiple regression analysis, RH had higher correlation with %LBF at peak exercise than peak cardiac output. Despite marked changes in other hemodynamic variables, nonleg blood flow during exercise was constantly maintained at a level identical to resting value.

CONCLUSIONS

Calf vasodilator capacity, which was the major determinant of distribution of skeletal muscle perfusion during exercise, may have contributed to maintaining perfusion of important nonexercising regions during exercise in patients with left ventricular dysfunction.

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

OBJECTIVES

The aim of this study was to examine the responses to endothelium-dependent and -independent vasodilators on the peripheral microcirculation in heart transplant recipients in relation to exercise capacity compared with that in healthy controls.

BACKGROUND

Impaired endothelium-dependent vasodilation of the microcirculation may play an important role in the limitation of exercise capacity after heart transplantation.

METHODS

Microvascular perfusion responses to four graded levels of iontophoretically applied 1% acetylcholine (endothelium-dependent vasodilator) and 1% sodium nitroprusside (SNP) (endothelium-independent) in the forearm skin of 42 transplant recipients and 16 age-matched controls were determined by laser Doppler perfusion measurements. Maximal exercise capacity was assessed by peak oxygen uptake (peak VO2) during progressive, symptom-limited, upright bicycle exercise.

RESULTS

With similar baseline perfusion levels in transplant recipients and controls (4.2 +/- 0.4 vs 4.6 +/- 0.6 arbitrary units [AU]), the increases in perfusion to acetylcholine, but not to SNP, were significantly attenuated in the transplant recipients: 7.0 +/- 1.0 vs 11.0 +/- 2.0, 12.7 +/- 1.5 vs 21.0 +/- 2.8, 21.0 +/- 1.9 vs 32.7 +/- 2.4, and 28.0 +/- 1.6 vs 39.2 +/- 2.4 AU, respectively (all p < 0.01). Peak VO2 was significantly lower in the transplant recipients (22.4 +/- 1.0 vs 38.0 +/- 2.9 ml/kg/min; p < 0.01). Furthermore, acetylcholine responses of the transplant recipients correlated closely to their peak VO2, irrespective of level of application (r = 0.63; p < 0.001, all four acetylcholine responses taken together), whereas no such correlation was found for SNP responses. In the control group, no relation was observed in acetylcholine/SNP responses to peak VO2.

CONCLUSIONS

Exercise limitation in transplant recipients appears strongly associated with attenuated endothelium-dependent vasodilation of the peripheral microcirculation.

Effects of exercise training on limb blood flow in patients with reduced ventricular function

BACKGROUND

Among the factors that contribute to limiting exercise tolerance in chronic heart failure are reduced peripheral blood flow and impaired vasodilatory capacity. Exercise training improves vasodilatory capacity in normal subjects, but controlled studies of exercise training evaluating upper and lower limb blood flow rates have not been performed in patients with reduced ventricular function. Improved vasodilatory capacity could help explain how training increases exercise capacity in these patients.

METHODS

Twenty patients (mean age 55 +/- 6 years) with reduced left ventricular function (mean ejection fraction 32% +/- 6%) after a myocardial infarction were randomized to a 2-month high-intensity residential rehabilitation program or to a control group and were monitored over the subsequent year. Both groups were treated according to current practice with angiotensin-converting enzyme inhibition therapy. Training began 1 month after myocardial infarction. Baseline and postischemic flow rates were measured by plethysmography in both the upper and lower limbs 1 month, 3 months, and 1 year after the infarction. Peak oxygen uptake (VO2) and cardiac output were measured before and after training, and peak VO2 was determined again after 1 year.

RESULTS

After 2 months of training peak VO2 increased 25%, VO2 at the lactate threshold increased 40%, and maximal cardiac output increased from 12.1 +/- 1.6 L/min to 13.9 +/- 2.4 L/min in the exercise group (all p < 0.05), whereas no differences were observed in the control group. At the 1-year follow-up no further increases in peak VO2 were noted in either group, but the higher value persisted in the trained group. However, changes in limb flow rates were poorly related to changes in both peak VO2 and maximal cardiac output. Improvements in baseline and postischemic flow rates occurred mainly in the lower limbs and were observed in the two groups to a similar degree.

CONCLUSION

Exercise training is highly effective in improving exercise capacity in patients with reduced ventricular function after myocardial infarction. These improvements parallel an increase in maximal cardiac output, but they are unrelated to vasodilatory capacity. In patients with reduced ventricular function after myocardial infarction, lower limb vasodilatory capacity improves gradually over the subsequent year, and these improvements occur irrespective of exercise training.

Special article: non-invasive measurement of endothelial function

1. Endothelial dysfunction, due to reductions in nitric oxide (NO) action, is an early feature of macrovascular disease. 2. Non-invasive measurement of endothelial function may be assessed by postischaemic dilation of forearm vessels, using plethysmography, or flow-mediated dilatation of the brachial artery, using ultrasound. 3. Brachial flow-mediated dilatation reflects NO release and/or action more than forearm hyperaemia. 4. These techniques have been used as surrogate measures of coronary endothelial function. 5. Methodological, physiological and clinical aspects of the techniques are discussed.

Muscular performance in heart failure

BACKGROUND

Some of the major symptoms in patients with chronic heart failure are muscle weakness and fatigue. However, not much is known about muscle performance in these patients compared to healthy controls.

METHODS AND RESULTS

Activity level, gait speed, hand grip strength, muscle performance of the knee extensors and flexors along with the plantar and dorsal flexors of the foot were evaluated. Muscle biopsies from the lateral vastus lateralis were taken. Sixteen patients in New York Heart Association class II or III were tested and compared to 112 reference subjects. Compared to the reference subjects, there was a reduction in activity level, gait speed, isometric and isokinetic peak torque for knee extension at different velocities, hand grip strength, peak torque for plantar and dorsal flexion of the ankle and isometric and isokinetic endurance for the knee extension. Recovery was faster. There were small differences in fiber composition. 3-Hydroxy-acylCoA-dehydrogenase and citrate synthase were lower, and lactate dehydrogenase was increased.

CONCLUSIONS

Muscle performance is affected in terms of both strength and endurance, which might affect performance in everyday activities. The more pronounced reduction in hand grip compared to the other muscles tested could be an indication of intrinsic abnormalities in the skeletal muscle.

Myocardial reactive hyperemia in experimental chronic heart failure: evidence for the role of K+ adenosine triphosphate-dependent channels and cyclooxygenase activity

BACKGROUND

Several studies suggest that coronary perfusion is abnormal in heart failure. The fact that these deficits may results in an altered coronary reserve remains controversial. Therefore, coronary adaptability to short-duration ischemia and the resultant myocardial reactive hyperemia were investigated in a model of chronic heart failure.

METHODS AND RESULTS

Experiments were performed in normal and failing hamster hearts (UM-X7.1, aged > 225 days). Heart rate, left ventricular developed pressure, and coronary flow were recorded continuously before and after each 30-second ischemia in isolated perfused heart preparations. Studies were conducted under control conditions and in the presence of four inhibitors of potential mediators of the reactive hyperemia response: the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (30 microM), the adenosine antagonist 8-(p-sulfophenyl)theophylline (50 microM), the K+ cyclic adenosine triphosphate-dependent channel antagonist glibenclamide (10 microM), and the cyclooxygenase inhibitor indomethacin (10 microM). Baseline hemodynamic parameters were all significantly impaired in failing hearts. Under control conditions, failing hearts were able to respond adequately to a 30-second ischemia: repayment-to-debt ratio averaged 1.02 +/- 0.09 as compared with 1.10 +/- 0.09 in normal hearts (P = NS). All inhibitors significantly reduced basal coronary perfusion except for indomethacin. Of the four inhibitors of potential mediators of the myocardial reactive hyperemic response, only glibenclamide and indomethacin impaired the repayment-to-debt ratio. In their presence, repayment-to-debt ratio was reduced by 40% of the baseline response (P < .01) without significant difference between normal and failing hearts. On the contrary, NG-nitro-L-arginine methyl ester and 8-(p-sulfophenyl)theophylline did not alter the repayment-to-debt ratio.

CONCLUSIONS

These observations demonstrate the capacity of the failing heart to tolerate short-duration ischemia despite the presence of significant alterations in its basal coronary perfusion. In addition, results suggest that activation of K+ adenosine triphosphate-dependent channels and the presence of cyclooxygenase by-products are important determinants of coronary adaptation to short-duration ischemia in this model of chronic heart failure.

Nonselective beta-adrenergic blockade with carvedilol does not hinder the benefits of exercise training in patients with congestive heart failure

BACKGROUND

Long-term beta-adrenergic blockade does not appear to be associated with drug-induced training in patients with congestive heart failure (CHF); whether exercise training can increase peak aerobic capacity in patients with CHF who are treated with beta-adrenergic blockers is currently unknown.

METHODS AND RESULTS

We studied 23 patients with CHF who were treated with carvedilol or propranolol in addition to ACE inhibitors, furosemide, and digoxin. Of the patients treated with carvedilol, 8 underwent exercise training and 8 remained sedentary. All 7 patients treated with propranolol underwent exercise training. Peak oxygen consumption (mL.kg-1.min-1) was serially measured in trained and sedentary patients. Peak reactive hyperemia (mL.min-1.100 mL-1) was determined in the calf and forearm immediately before and after 12 weeks of training. The peak oxygen consumption of trained patients treated with either carvedilol or propranolol increased from 12.9 +/- 1.4 to 16.0 +/- 1.6 (P < .001) and 12.4 +/- 1.0 to 15.7 +/- 0.9 (P < .001) mL.kg-1.min-1, respectively, whereas it did not change in the sedentary patients. Peak reactive hyperemia increased significantly in the calves but not the forearms of trained patients.

CONCLUSIONS

Long-term, nonselective beta-adrenergic blockade with carvedilol or propranolol does not prevent patients with CHF from deriving systemic and regional benefits from physical training.

Relation of functional improvement in congestive heart failure after quinapril therapy to peripheral limitation

Angiotensin-converting enzyme inhibitors have been shown to increase maximal muscle blood flow in parallel to peak VO2 in patients with congestive heart failure (CHF). Whether this increase shifts factors limiting peak aerobic capacity from periphery (skeletal muscle or vessels) to central factors (cardiac or respiratory) is unknown. Comparison of peak oxygen consumption (VO2) obtained during leg cycling (VO2 leg) with peak VO2 obtained during combined leg cycling and arm cranking (VO2 arm + leg) allows determination of the relative role of central or peripheral factors. We compared VO2 leg with VO2 arm + leg before and after 3 months of therapy with quinapril 40 mg in 16 patients with CHF (age 53 +/- 13 years) due to left ventricular systolic dysfunction (ejection fraction 0.25 +/- 0.07). Before quinapril, VO2 arm + leg was significantly higher than VO2 leg (19.0 +/- 3.3 vs 16.9 +/- 3.8 ml/kg/min, p < 0.001), whereas after therapy these 2 values were similar (20.3 +/- 4.3 vs 21.0 +/- 4.3 ml/kg/min; p = NS), indicating that patients were no longer limited by peripheral factors. Besides, VO2 leg increase after therapy was higher in patients in whom difference between VO2 arm + leg and VO2 leg was the greatest (i.e., in patients who were initially more limited by peripheral factors). Simultaneously, calf peak reactive hyperemia and circumference significantly increased, indicating an improvement in vascular dilating capacity and an increase in skeletal muscle mass. No significant modification occurred in the forearm. Thus, patients who improved the most after 3 months of quinapril therapy were those who were initially limited by peripheral factors. The restricting role of these factors was reduced after quinapril therapy.

Muscular blood flow response to submaximal leg exercise in normal subjects and in patients with heart failure

Blood flow to working skeletal muscle is usually reduced during exercise in patients with congestive heart failure. An intrinsic impairment of skeletal muscle vasodilatory capacity has been suspected as a mechanism of this muscle underperfusion during maximal exercise, but its role during submaximal exercise remains unclear. Therefore, we studied by transcutaneous Doppler ultrasonography the arterial blood flow in the common femoral artery at rest and during a submaximal bicycle exercise in 12 normal subjects and in 30 patients with heart failure. Leg blood flow was lower in patients than in control subjects at rest [0.29 +/- 0.14 (SD) vs. 0.45 +/- 0.14 l/min, P < 0.01], at absolute powers and at the same relative power (2.17 +/- 1.06 vs. 4.39 +/- 1.4 l/min, P < 0.001). Because mean arterial pressure was maintained, leg vascular resistance was higher in patients than in control subjects at rest (407 +/- 187 vs. 247 +/- 71 mmHg.l-1.min, P < 0.01) and at the same relative power (73 +/- 49 vs. 31 +/- 13 mmHg.l-1.min, P < 0.01) but not at absolute powers. Although the magnitude of increase in leg blood flow corrected for power was similar in both groups (31 +/- 10 vs. 34 +/- 10 ml.min-1.W-1), the magnitude of decrease of leg vascular resistance corrected for power was higher in patients than in control subjects (5.9 +/- 3.3 vs. 1.9 +/- 0.94 mmHg.l-1.min.W-1, P < 0.001). These results suggest that the ability of skeletal muscle vascular resistance to decrease is not impaired and that intrinsic vascular abnormalities do not limit vasodilator response to submaximal exercise in patients with heart failure.

Interrelationship of oxidative metabolism and local perfusion demonstrated by NMR in human skeletal muscle

Using nuclear magnetic resonance (NMR), we have examined the relationship of high-energy phosphate metabolism and perfusion in human soleus and gastrocnemius muscles. With 31P-NMR spectroscopy, we monitored phosphocreatine (PCr) decay and recovery in eight normal volunteers and four heart failure patients performing ischemic plantar flexion. By using echo-planar imaging, perfusion was independently measured by a local [inversion-recovery (T1-flow)] and a regional technique (NMR-plethysmography). After correction for its pH dependence, PCr recovery time constant is 27.5 +/- 8.0 s in normal volunteers, with mean flow 118 +/- 75 (soleus and gastrocnemius T1-flow) and 30.2 +/- 9.7 ml.100 ml-1.min-1 (NMR-plethysmography-flow). We demonstrate a positive correlation between PCr time constant and local perfusion given by y = 50 - 0.15x (r2 = 0.68, P = 0.01) for the 8 normal subjects, and y = 64 - 0.24x (r2 = 0.83, P = 0.0001) for the 12 subjects recruited in the study. Regional perfusion techniques also show a significant but weaker correlation. Using this totally noninvasive method, we conclude that aerobic ATP resynthesis is related to the magnitude of perfusion, i.e., O2 availability, and demonstrate that magnetic resonance imaging and magnetic resonance spectroscopy together can accurately assess muscle functional status.

Exercise-induced vasodilation in forearm circulation of normal subjects and patients with congestive heart failure: role of endothelium-derived nitric oxide

OBJECTIVES

This study was undertaken to investigate the role of endothelium-derived nitric oxide in the regulation of forearm blood flow during exercise in normal subjects and patients with congestive heart failure.

BACKGROUND

Nitric oxide-mediated vasodilation in response to muscarinic stimulation is impaired in the peripheral circulation of patients with congestive heart failure. Whether nitric oxide-mediated vasodilation during exercise is also impaired in patients with congestive heart failure is unknown.

METHODS

Forearm blood flows (ml/min per 100 ml) were determined during rhythmic hand grip exercise at 15%, 30% and 45% of maximal voluntary contraction by venous occlusion plethysmography before and after regional inhibition of nitric oxide synthesis with administration of L-NG-monomethylarginine (L-NMMA) in the brachial artery of 17 patients with congestive heart failure (mean age 49 years, mean left ventricular ejection fraction 0.22) and 10 age-matched normal subjects.

RESULTS

Before administration of L-NMMA in the brachial artery, forearm blood flows in patients with congestive heart failure during rhythmic hand grip exercise at 15%, 30% and 45% of maximal voluntary contraction were slightly but not significantly lower than that of normal subjects ([mean +/- SE] 6.8 +/- 1.0, 8.5 +/- 1.0 and 12.9 +/- 1.7 ml/min per 100 ml, respectively, in patients with congestive heart failure vs. 6.6 +/- 1.2, 11.6 +/- 1.9 and 16.2 +/- 1.9 ml/min per 100 ml, respectively, in normal subjects, p = NS). After administration of L-NMMA in the brachial artery, forearm blood flows in normal subjects significantly decreased by 10% to 21% during hand grip exercise but did not change during exercise in patients with congestive heart failure.

CONCLUSIONS

Regional inhibition of nitric oxide synthase with administration of L-NMMA in the brachial artery significantly decreased forearm blood flows during rhythmic hand grip exercise in normal subjects but not in patients with congestive heart failure. These findings suggest that nitric oxide-mediated vasodilation during submaximal exercise is impaired in the forearm circulation of patients with congestive heart failure.

Influence of intrinsic limb vasodilator capacity on exercise tolerance in patients with recent myocardial infarction

To investigate the influence of intrinsic limb vasodilator capacity on exercise performance, limb reactive hyperemic flows and their relations to exercise capacity during upright bicycle exercise were examined in 52 patients with recent myocardial infarction. Reactive hyperemic flow was measured in the forearm and the calf by venous occlusive plethysmography after 5 min of arterial occlusion. Calf reactive hyperemic flow correlated significantly with cardiac output, systemic vascular resistance, and oxygen consumption at peak exercise, whereas flow in the forearm did not. In patients with preserved exercise capacity (group 1, n = 20) compared with those with exercise impairment (group 2, n = 32), calf reactive hyperemic flow was significantly augmented, but forearm flow was similar in the two groups. There were no significant differences in hemodynamic parameters at rest between the two groups. At peak exercise, however, cardiac output was lower and systemic vascular resistance was higher in group 2 than in group 1, whereas arterial blood pressure was maintained identically in the two groups. Thus, intrinsic calf but not forearm vasodilator capacity was linked to exercise hemodynamic responses and exercise capacity in patients with recent myocardial infarction. In addition, reduced calf vasodilation and concomitant enhanced vascular tone seemed to be useful for preserving arterial blood pressure in the setting of decreased cardiac output response to exercise in patients with exercise impairment.

The role of endothelium-derived vasoactive substances in the pathophysiology of exercise intolerance in patients with congestive heart failure

The vascular endothelium releases vasoactive substances that appear to play an important role in the normal regulation of peripheral vasomotor tone. Nitric oxide, endothelins, prostaglandins, and other endothelium-derived vasodilating and vasoconstricting factors are released by the vascular endothelium in response to a diverse array of hormonal, pharmacologic, chemical, and physical stimuli. Shear stress, produced by pulsatile blood flow at the endothelial cell luminal surface, alters endothelial production of several endothelium-derived vasoactive substances, which may contribute to regional regulation of skeletal muscle blood flow during exercise. Abnormal vascular endothelium function has been shown in both experimental and clinical heart failure. Preliminary data suggest that abnormalities of endothelial function may contribute to increased peripheral vasomotor tone during exercise in patients with congestive heart failure.

Peripheral factors in the management of congestive heart failure

Maladaptive changes in the periphery largely account for the symptomatology of patients with congestive heart failure (CHF). A decline in the systolic function of the left ventricle precipitates activation of neural and humoral systems to provide circulatory support. These include sympathetic release of norepinephrine, increases in angiotensin II, elevated levels of circulating arginine vasopressin, and impairment of the counterregulatory function of atrial natriuretic peptide. The resultant circulatory changes are ultimately responsible for the declining function of the peripheral vasculature and skeletal muscles of patients with CHF. In the peripheral vasculature, impaired vasodilatory capacity results from excess vessel wall stiffness, endothelial dysfunction, and structural abnormalities. The skeletal muscles develop poor aerobic capacity as a result of a change in predominant fiber type and excess reliance on glycolytic metabolic pathways. Physical deconditioning induced by symptoms tends to further promote these peripheral changes. Therapeutic interventions with symptomatic and prognostic benefits have essentially been targeted at the periphery. Angiotensin converting enzyme inhibitors may act by normalizing electrolyte and water balance, improving vascular endothelial function, and reversing structural changes in peripheral vessels. Exercise training appears to exert its benefit at the level of the vascular endothelium. Advances in the therapy of CHF depend on a greater understanding of changes in the periphery.