Effect of propranolol on myocardial oxygen consumption and its hemodynamic correlates during upright exercise

Quantitatively Predicting Effects of Exercise on Pharmacokinetics of Drugs Using a Physiologically Based Pharmacokinetic Model

Exercise significantly alters human physiological functions, such as increasing cardiac output and muscle blood flow and decreasing glomerular filtration rate (GFR) and liver blood flow, thereby altering the absorption, distribution, metabolism, and excretion of drugs. In this study, we aimed to establish a database of human physiological parameters during exercise and to construct equations for the relationship between changes in each physiological parameter and exercise intensity, including cardiac output, organ blood flow (e.g., muscle blood flow and kidney blood flow), oxygen uptake, plasma pH and GFR, etc. The polynomial equation P = ΣaiHRi was used for illustrating the relationship between the physiological parameters (P) and heart rate (HR), which served as an index of exercise intensity. The pharmacokinetics of midazolam, quinidine, digoxin, and lidocaine during exercise were predicted by a whole-body physiologically based pharmacokinetic (WB-PBPK) model and the developed database of physiological parameters following administration to 100 virtual subjects. The WB-PBPK model simulation results showed that most of the observed plasma drug concentrations fell within the 5th-95th percentiles of the simulations, and the estimated peak concentrations (Cmax) and area under the curve (AUC) of drugs were also within 0.5-2.0 folds of observations. Sensitivity analysis showed that exercise intensity, exercise duration, medication time, and alterations in physiological parameters significantly affected drug pharmacokinetics and the net effect depending on drug characteristics and exercise conditions. In conclusion, the pharmacokinetics of drugs during exercise could be quantitatively predicted using the developed WB-PBPK model and database of physiological parameters. SIGNIFICANCE STATEMENT: This study simulated real-time changes of human physiological parameters during exercise in the WB-PBPK model and comprehensively investigated pharmacokinetic changes during exercise following oral and intravenous administration. Furthermore, the factors affecting pharmacokinetics during exercise were also revealed.

Clinical Care for Cardiovascular Disease in Patients With Williams-Beuren Syndrome

Williams-Beuren syndrome (WBS) is a congenital multisystem disorder affecting the cardiovascular, central nervous, and musculoskeletal systems. Cardiovascular abnormalities, which consist principally of vascular stenoses, occur in approximately 80% of people with WBS and are the predominant cause of early morbidity and mortality. Supravalvar aortic stenosis and peripheral pulmonary artery stenosis are the most common stenotic lesions in WBS, though other stenoses often occur, including stenoses of the coronary arteries. Approximately one-third of people with WBS undergo cardiovascular interventions. The risk of sudden cardiac death is markedly higher than the general population, with most events occurring in the periprocedural period. Because of the rarity of WBS and the often-complex nature of the cardiovascular abnormalities, most physicians, including cardiologists, have limited experience in caring for patients with WBS. Further, heretofore, clinical cardiovascular management guidelines based on international expert consensus have not been available. This state-of-the-art review provides a comprehensive synopsis of the cardiovascular abnormalities in WBS and presents clinical management guidelines based on the authors' expert consensus.

Changes in oxygen supply-demand balance during induction of general anesthesia: an exploratory study using remimazolam

PURPOSE

This study was performed to evaluate the changes in oxygen supply-demand balance during induction of general anesthesia using an indirect calorimeter capable of measuring oxygen consumption (VO2) and carbon dioxide production (VCO2).

METHODS

This study included patients scheduled for surgery in whom remimazolam was administered as a general anesthetic. VO2 and VCO2 were measured at different intervals: upon awakening (T1), 15 min after tracheal intubation (T2), and 1 h after T2 (T3). Oxygen delivery (DO2) was calculated simultaneously with these measurements. VO2 was ascertained using an indirect calorimeter and further calculated using vital signs, among other factors. DO2 was derived from cardiac output and arterial blood gas analysis performed with an arterial pressure-based cardiac output measurement system.

RESULTS

VO2, VCO2, and DO2 decreased significantly from T1 to T2 and T3 [VO2/body surface area (BSA) (ml/min/m2): T1, 130 (122-146); T2, 107 (83-139); T3, 97 (93-121); p = 0.011], [VCO2/BSA (ml/min/m2): T1, 115 (105-129); T2, 90 (71-107); T3, 81 (69-101); p = 0.011], [DO2/BSA (ml/min/m2): T1, 467 (395-582); T2, 347 (286-392); T3, 382 (238-414); p = 0.0020]. Among the study subjects, a subset exhibited minimal reduction in VCO2. Although the respiratory frequency was titrated on the basis of end-tidal CO2 levels, there was no significant difference between the groups.

CONCLUSION

General anesthetic induction with remimazolam decreased VO2, VCO2, and DO2.

Ascending aortic impedance in young endurance athletes: a time-resolved phase-contrast MRI study

Ventricular-vascular coupling in endurance athletes remains incompletely understood. The purpose of this study was to determine the ascending aortic impedance in endurance athletes and explore its associations with traditional cardiovascular measurements. In 15 young male endurance runners and 19 young healthy men, time-resolved (CINE) two-dimensional (2-D) phase-contrast MRI quantified the ascending aortic flow while the pressure waveform was simultaneously collected via a generalized transfer function. The aortic impedance modulus and phase were calculated in the frequency domain while characteristic impedance (ZcF) was calculated by averaging moduli between the 4th and 8th heart rate (HR) harmonics. Stroke volume (SV), left ventricular (LV) morphometry, double product, aortic compliance, and total peripheral resistance (TPR) were also measured. Endurance athletes had higher SV, slower HR, greater LV end-diastolic volume and mass, and lower double product than sedentary participants (all P < 0.05). ZcF was significantly lower in athletes than in sedentary participants (73.3 ± 19.2 vs. 93.4 ± 19.0 dyn·s/cm5, P = 0.005). Furthermore, ZcF was negatively correlated with SV (r = -0.691) and aortic compliance (r = -0.601) but was positively correlated with double product (r = 0.445) and TPR (r = 0.458; all P < 0.05). Multivariate analysis revealed that ZcF was the strongest predictor of SV followed by TPR and HR (adjusted R2 = 0.788, P < 0.001). Therefore, our findings collectively suggest that LV afterload quantified by aortic ZcF is significantly lower in endurance athletes than in sedentary adults. The lower pulsatile LV afterload may contribute to greater SV in endurance athletes.NEW & NOTEWORTHY This is the first study to investigate aortic impedance with the noninvasive, simultaneous recordings of aortic pressure using SphygmoCor XCEL and flow using phase-contrast MRI. We found that the characteristic impedance (Zc) is significantly lower in endurance athletes than sedentary adults, is the strongest predictor of stroke volume (SV), and is inversely associated with aortic compliance. These findings suggest that aortic impedance is a key determinant of the ventricular-vascular coupling adapted to long-term training in endurance athletes.

Physiological Function during Exercise and Environmental Stress in Humans-An Integrative View of Body Systems and Homeostasis

Claude Bernard's milieu intérieur (internal environment) and the associated concept of homeostasis are fundamental to the understanding of the physiological responses to exercise and environmental stress. Maintenance of cellular homeostasis is thought to happen during exercise through the precise matching of cellular energetic demand and supply, and the production and clearance of metabolic by-products. The mind-boggling number of molecular and cellular pathways and the host of tissues and organ systems involved in the processes sustaining locomotion, however, necessitate an integrative examination of the body's physiological systems. This integrative approach can be used to identify whether function and cellular homeostasis are maintained or compromised during exercise. In this review, we discuss the responses of the human brain, the lungs, the heart, and the skeletal muscles to the varying physiological demands of exercise and environmental stress. Multiple alterations in physiological function and differential homeostatic adjustments occur when people undertake strenuous exercise with and without thermal stress. These adjustments can include: hyperthermia; hyperventilation; cardiovascular strain with restrictions in brain, muscle, skin and visceral organs blood flow; greater reliance on muscle glycogen and cellular metabolism; alterations in neural activity; and, in some conditions, compromised muscle metabolism and aerobic capacity. Oxygen supply to the human brain is also blunted during intense exercise, but global cerebral metabolism and central neural drive are preserved or enhanced. In contrast to the strain seen during severe exercise and environmental stress, a steady state is maintained when humans exercise at intensities and in environmental conditions that require a small fraction of the functional capacity. The impact of exercise and environmental stress upon whole-body functions and homeostasis therefore depends on the functional needs and differs across organ systems.

Effects of pre-exercise acupuncture stimulation on heart rate response during short-duration exercise

Background

The purpose of the present study was to investigate the effects of bradycardia induced by pre-exercise acupuncture on heart rate responses during short-duration exercise.

Methods

A total of 29 healthy subjects underwent two protocols: protocol 1 assessed the effects of manual acupuncture on heart rate response during rest, and protocol 2 tested the hypothesis that the bradycardic effects induced by pre-exercise acupuncture continue during low- and high-intensity exercise. Their average age, height, weight, and body mass index were 21.2 ± 2.0 years, 167.2 ± 8.8 cm, 63.8 ± 12.8 kg, and 22.7 ± 3.5 kg/m², respectively. In acupuncture stimulations for protocols 1 and 2, an acupuncture needle was inserted into the lower leg and manual acupuncture stimulation was performed at 1 Hz.

Results

In protocol 1 (resting condition), acupuncture stimulation induced a bradycardic response, which continued for 4 min after the cessation of acupuncture stimulation (p < 0.05). In protocol 2, the bradycardic response induced by pre-exercise acupuncture stimulation remained during low-intensity exercise and in the beginning of high-intensity exercise performed immediately after the cessation of acupuncture stimulation (p < 0.05). However, the effects disappeared when post-acupuncture exercise was performed when the heart rate was approximately 140 beats/min during high-intensity exercise. The rating of perceived exertion after exercise differed significantly between the acupuncture stimulation task (7.9 ± 1.6) and no-stimulation task (8.5 ± 2.0) (p = 0.03) only in the low intensity group.

Conclusion

This study may provide new insights into the effect of acupuncture stimulation on psycho-physiological conditions during exercise.

Development of an automated closed-loop β-blocker delivery system to stably reduce myocardial oxygen consumption without inducing circulatory collapse in a canine heart failure model: a proof of concept study

Beta-blockers are well known to reduce myocardial oxygen consumption (MVO₂) and improve the prognosis of heart failure (HF) patients. However, its negative chronotropic and inotropic effects limit their use in the acute phase of HF due to the risk of circulatory collapse. In this study, as a first step for a safe β-blocker administration strategy, we aimed to develop and evaluate the feasibility of an automated β-blocker administration system. We developed a system to monitor arterial pressure (AP), left atrial pressure (P_LA), right atrial pressure, and cardiac output. Using negative feedback of hemodynamics, the system controls AP and P_LA by administering landiolol (an ultra-short-acting β-blocker), dextran, and furosemide. We applied the system for 60 min to 6 mongrel dogs with rapid pacing-induced HF. In all dogs, the system automatically adjusted the doses of the drugs. Mean AP and mean P_LA were controlled within the acceptable ranges (AP within 5 mmHg below target; P_LA within 2 mmHg above target) more than 95% of the time. Median absolute performance error was small for AP [median (interquartile range), 3.1% (2.2–3.8)] and P_LA [3.6% (2.2–5.7)]. The system decreased MVO₂ and P_LA significantly. We demonstrated the feasibility of an automated β-blocker administration system in a canine model of acute HF. The system controlled AP and P_LA to avoid circulatory collapse, and reduced MVO₂ significantly. As the system can help the management of patients with HF, further validations in larger samples and development for clinical applications are warranted.

Cardiovascular Responses and Cardiac Work of Selected Daily Activities in Young Healthy Indian Participants

BACKGROUND

Studies suggest that habitual daily activities may result in significant cardiovascular responses that might have implications for individuals with coronary artery disease. This study determined the cardiac work for various activities of daily living among healthy young participants.

METHODS

We evaluated cardiovascular responses in 42 young adults (21 male, 21 female) to graded activities. Subjects were divided into three groups. In each group, one light, one moderate, and one heavy activity were performed based on published METS. Cardiovascular responses were evaluated using impedance cardiography (BOMED Instruments, USA) and automated blood pressure monitor (Welch Allyn, USA). Cardiac work was computed as the double product (heart rate × systolic blood pressure) and triple product (systolic blood pressure × cardiac output [stroke volume × heart rate]). Perceived exertion was evaluated using Borg's scale.

RESULTS

There was high inter-individual variability in cardiovascular responses for each activity. There were, by and large, no gender differences across the activities. Cardiac work was significantly higher with heavy activities than light activities using both indices; however, the triple product showed greater discriminatory ability in evaluating differences in cardiac work across all categories of activities.

CONCLUSION

The data suggest a need to develop a compendium of cardiac work related to habitual activities to guide doctors and patients.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Esmolol infusion versus propranolol infusion: effects on heart rate and blood pressure in healthy volunteers

Despite its widespread clinical use, the β1-adrenergic receptor antagonist esmolol hydrochloride is not commonly used in human physiology research, and the effective dose of esmolol (compared with the nonselective β-blocker propranolol) is unclear. In four separate studies we used cycle ergometry exercise and infusions of isoproterenol and epinephrine to test the heart rate (HR)-lowering effect of esmolol compared with propranolol and saline in healthy humans. In cohort 1, both esmolol (ΔHR 57 ± 6 beats/min) and propranolol (ΔHR 56 ± 7 beats/min) attenuated exercise tachycardia compared with saline (ΔHR 88 ± 17 beats/min). In cohort 2, we found that the HR response to exercise was similar at 5 min (ΔHR 57 ± 9 beats/min) and 60 min (ΔHR 55 ± 9 beats/min) after initiation of the esmolol maintenance infusion. In cohort 3, we confirmed that the HR-lowering effect of esmolol disappeared 45 min after termination of the maintenance infusion. In cohort 4, changes in femoral blood flow and hematological parameters in response to epinephrine infusion were not different between esmolol and saline infusion, indicating that our esmolol infusion paradigm does not block β2-receptors. Collectively, our data indicate that infusion of ~160 mg of esmolol (range 110-200 mg in the 5 min before exercise) acutely and selectively blocks β1-receptors in healthy humans. Additionally, β1-receptors remain blocked 60 min later if a maintenance infusion of ~0.2 mg·kg total body mass-1·min-1 continues. The current data lay the foundation for future studies to evaluate β1- vs. β2-receptor control of the circulation in humans.NEW & NOTEWORTHY We used cycle ergometry exercise and infusions of isoproterenol and epinephrine to test the heart rate-lowering effect of esmolol compared with propranolol and saline in healthy humans. Collectively, our data indicate that infusion of ~160 mg of esmolol (range 110-200 mg in the 5 min before exercise) acutely and selectively blocks β1-adrenergic receptors. These infusion parameters can be used in future experiments to evaluate β1- vs. β2-receptor control of the circulation in humans.

β1-Blockade increases maximal apnea duration in elite breath-hold divers

We hypothesized that the cardioselective β₁-adrenoreceptor antagonist esmolol would improve maximal apnea duration in elite breath-hold divers. In elite national-level divers (n = 9), maximal apneas were performed in a randomized and counterbalanced order while receiving either iv esmolol (150 μg·kg^-1·min^-1) or volume-matched saline (placebo). During apnea, heart rate (ECG), beat-by-beat blood pressure, stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were measured (finger photoplethysmography). Myocardial oxygen consumption (MV̇o₂) was estimated from rate pressure product. Cerebral blood flow through the internal carotid (ICA) and vertebral arteries (VA) was assessed using Duplex ultrasound. Apnea duration improved in the esmolol trial when compared with placebo (356 ± 57 vs. 323 ± 61 s, P < 0.01) despite similar end-apnea peripheral oxyhemoglobin saturation (71.8 ± 10.3 vs. 74.9 ± 9.5%, P = 0.10). The HR response to apnea was reduced by esmolol at 10-30% of apnea duration, whereas MAP was unaffected. Esmolol reduced SV (main effect, P < 0.05) and CO (main effect; P < 0.05) and increased TPR (main effect, P < 0.05) throughout apnea. Esmolol also reduced MV̇o₂ throughout apnea (main effect, P < 0.05). Cerebral blood flow through the ICA and VA was unchanged by esmolol at baseline and the last 30 s of apnea; however, global cerebral blood flow was reduced in the esmolol trial at end-apnea (P < 0.05). Our findings demonstrate that, in elite breath-hold divers, apnea breakpoint is improved by β₁-blockade, likely owing to an improved total body oxygen sparring through increased centralization of blood volume (↑TPR) and reduced MV̇o₂NEW & NOTEWORTHY The governing bodies for international apnea competition, the Association Internationale pour le Développment de l'Apnée and La Confédération Mondaile des Activités Subaquatiques, have banned the use of β-blockers based on anecdotal reports that they improve apnea duration. Using a randomized placebo-controlled trial, we are the first to empirically confirm that β-blockade improves apnea duration. This improvement in apnea duration coincided with a reduced myocardial oxygen consumption.

Benefits of exercise training on coronary blood flow in coronary artery disease patients

Every 34 seconds an American experiences a myocardial infarction or cardiac death. Approximately 80% of these coronary artery disease (CAD)-related deaths are attributable to modifiable behaviors, such as a lack of physical exercise training (ET). Regular ET decreases CAD morbidity and mortality through systemic and cardiac-specific adaptations. ET increases myocardial oxygen demand acting as a stimulus to increase coronary blood flow and thus myocardial oxygen supply, which reduces myocardial infarction and angina. ET augments coronary blood flow through direct actions on the vasculature that improve endothelial and coronary smooth muscle function, enhancing coronary vasodilation. Additionally, ET promotes collateralization, thereby, increasing blood flow to ischemic myocardium and also treats macrovascular CAD by attenuating the progression of coronary atherosclerosis and restenosis, potentially through stabilization of atherosclerotic lesions. In summary, ET can be used as a relatively safe and inexpensive way to prevent and treat CAD.

Recovery mismatch between myocardial blood flow and cardiac workload after physical exercise: a positron emission tomography study

AIMS

We studied the interrelation between oxygen consumption and myocardial blood flow (MBF) during recovery. MBF is directly dependent on oxygen consumption. The latter is linearly related to the heart rate-blood pressure product (RPP, bpm × mmHg), an index reflecting external cardiac work. In the immediate post-exercise period, cardiac output decreases considerably. This is expected to be paralleled by a rapid fall in oxygen demand, rendering ischaemia unlikely. Thus, the phenomenon of ST-segment depression during recovery remains unexplained.

METHODS AND RESULTS

(15)O-labelled water and positron emission tomography were used to measure MBF in 14 young healthy volunteers (mean age 27 ± 3 years) during the following study conditions: (i) at rest, (ii) during a steady submaximal supine bicycle exercise stress within the scanner, and (iii) during recovery immediately after cessation of exercise. During recovery, RPP decreased by 43% (18 768 ± 1337 vs. 11 652 ± 3224, P < 0.001). In contrast, the associated decrease in MBF (2.52 ± 0.52 vs. 1.93 ± 0.50 mL/min/g, P < 0.001) and perfusion reserve (2.68 ± 0.51 vs. 2.03 ± 0.42, P < 0.001) was significantly less pronounced (-24%, P < 0.01), indicating a relative delay in MBF recovery compared with cardiac work load.

CONCLUSION

The mismatch between a rapid decrease in cardiac workload but preserved hyperaemic response early after cessation of physical exercise suggests an uncoupling of cardiac work and MBF during recovery.

β-Adrenergic blockade enhances coronary vasoconstrictor response to forehead cooling

Forehead cooling activates the sympathetic nervous system and can trigger angina pectoris in susceptible individuals. However, the effect of forehead cooling on coronary blood flow velocity (CBV) is not well understood. In this human experiment, we tested the hypotheses that forehead cooling reduces CBV (i.e., coronary vasoconstriction) and that this vasoconstrictor effect would be enhanced under systemic β-adrenergic blockade. A total of 30 healthy subjects (age range, 23-79 years) underwent Doppler echocardiography evaluation of CBV in response to 60 s of forehead cooling (1°C ice bag on forehead). A subset of subjects (n = 10) also underwent the procedures after an intravenous infusion of propranolol. Rate pressure product (RPP) was used as an index of myocardial oxygen demand. Consistent with our first hypothesis, forehead cooling reduced CBV from 19.5 ± 0.7 to 17.5 ± 0.8 cm/s (P < 0.001), whereas mean arterial pressure increased by 11 ± 2 mmHg (P < 0.001). Consistent with our second hypothesis, forehead cooling reduced CBV under propranolol despite a significant rise in RPP. The current studies indicate that forehead cooling elicits a sympathetically mediated pressor response and a reduction in CBV, and this effect is augmented under β-blockade. The results are consistent with sympathetic activation of β-receptor coronary vasodilation in humans, as has been demonstrated in animals.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

The influence of aerobic exercise training on the double product break point in low-to-moderate risk adults

The double product is the product of the heart rate and systolic blood pressure. The double product break point (DPBP) is a physiologic threshold that occurs at similar exercise intensities to that of the ventilatory threshold (VT). The influence of aerobic exercise training on the DPBP has not yet been examined. The purpose of this study was to examine whether aerobic exercise training (ET) increases the exercise intensity at which the DPBP occurs, and whether it increases in a similar fashion to the VT. Seven males and 11 females, all sedentary (mean ± SD: age = 29.9 ± 10.5 years) underwent supervised cardiopulmonary exercise testing using a cycle ergometer ramp protocol at baseline and after 8 weeks of vigorous ET on a cycle ergometer. The VT was determined by gas analysis and the V-slope method. Experienced observers using standardized instructions visually determined the DPBP. Following ET, VO(2 peak), maximal workload, and body composition variables all showed significant positive changes. The VO(2) at which the DPBP and VT occurred increased significantly from baseline to follow-up (P < 0.001). At baseline and at follow-up, the DPBP and VT did not differ. The DPBP and VT were significantly correlated to each other at both time points. Results suggest that the DPBP responds to ET in a similar fashion to that of the VT, and may be an easier and more useful marker of the VT for exercise training purposes.

Both beta1- and beta2-adrenoceptors contribute to feedforward coronary resistance vessel dilation during exercise

During exercise, beta-feedforward coronary vasodilation has been shown to contribute to the matching of myocardial oxygen supply with the demand of the myocardium. Since both beta(1)- and beta(2)-adrenoceptors are present in the coronary microvasculature, we investigated the relative contribution of these subtypes to beta-feedforward coronary vasodilation during exercise as well as to infusion of the beta(1)-agonist norepinephrine and the beta(1)- and beta(2)-agonist isoproterenol. Chronically instrumented swine were studied at rest and during graded treadmill exercise (1-5 km/h) under control conditions and after beta(1)-blockade with metoprolol (0.5 mg/kg iv) and beta(1)/beta(2)-blockade with propranolol (0.5 mg/kg iv). The selectivity and degree of beta-blockade of metoprolol and propranolol were confirmed using isoproterenol infusion (0.05-0.4 microg. kg(-1).min(-1)) under resting conditions. Isoproterenol-induced coronary vasodilation was mediated through the beta(2)-adrenoceptor, whereas norepinephrine-induced coronary vasodilation was principally mediated through the beta(1)-adrenoceptor. Exercise resulted in a significant increase in left ventricular norepinephrine release and epinephrine uptake. beta(1)-Adrenoceptor blockade with metoprolol had very little effect under resting conditions. However, during exercise, metoprolol attenuated the increase in myocardial oxygen supply in excess of the reduction in myocardial oxygen demand, as evidenced by a progressive decrease in coronary venous Po(2). Consequently, metoprolol caused a clockwise rotation of the relationship between myocardial oxygen consumption and coronary venous Po(2). Additional beta(2)-adrenoceptor blockade with propranolol further inhibited myocardial oxygen supply during exercise, resulting in a further clockwise rotation of the relationship between myocardial oxygen consumption and coronary venous Po(2). In conclusion, both beta(1)- and beta(2)-adrenoceptors contribute to the beta-feedforward coronary resistance vessel dilation during exercise.

Deep breathing, Valsalva, and tilt table tests in diabetics with and without symptoms of autonomic neuropathy

Autonomic neuropathy (AN) test results (Valsalva manoeuvre, deep breathing, and tilting) are frequently impaired in diabetics without symptoms of AN, particularly in those with peripheral neuropathy (PN). We have investigated 24 asymptomatic diabetics with PN, 17 diabetics with symptoms of AN and 24 healthy controls. The heart rate reactions to the three tests were impaired in both patient groups. The Valsalva manoeuvre could not distinguish between the patient groups. The heart rate reaction to deep breathing, estimated as the expiration/inspiration (E/I) ratio, was slightly more disturbed in patients with AN than those with PN (1.04 vs. 1.09, p less than 0.05) but the frequency of abnormally low E/I ratios was high in both groups (76.5 vs. 54.2%, NS). The immediate heart rate reaction to tilting, estimated as the brake index, clearly separated the patient groups. An abnormally low brake index was shown in 82.3% of AN patients and in 33.3% of PN patients (p less than 0.01). The study shows that the deep breathing test is sensitive for AN but an impaired immediate heart rate reaction to tilting is more specific for symptomatic AN.

Regulation of Coronary Blood Flow During Exercise

Exercise is the most important physiological stimulus for increased myocardial oxygen demand. The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate, myocardial contractility, and ventricular work. The approximately sixfold increase in oxygen demands of the left ventricle during heavy exercise is met principally by augmenting coronary blood flow (∼5-fold), as hemoglobin concentration and oxygen extraction (which is already 70–80% at rest) increase only modestly in most species. In contrast, in the right ventricle, oxygen extraction is lower at rest and increases substantially during exercise, similar to skeletal muscle, suggesting fundamental differences in blood flow regulation between these two cardiac chambers. The increase in heart rate also increases the relative time spent in systole, thereby increasing the net extravascular compressive forces acting on the microvasculature within the wall of the left ventricle, in particular in its subendocardial layers. Hence, appropriate adjustment of coronary vascular resistance is critical for the cardiac response to exercise. Coronary resistance vessel tone results from the culmination of myriad vasodilator and vasoconstrictors influences, including neurohormones and endothelial and myocardial factors. Unraveling of the integrative mechanisms controlling coronary vasodilation in response to exercise has been difficult, in part due to the redundancies in coronary vasomotor control and differences between animal species. Exercise training is associated with adaptations in the coronary microvasculature including increased arteriolar densities and/or diameters, which provide a morphometric basis for the observed increase in peak coronary blood flow rates in exercise-trained animals. In larger animals trained by treadmill exercise, the formation of new capillaries maintains capillary density at a level commensurate with the degree of exercise-induced physiological myocardial hypertrophy. Nevertheless, training alters the distribution of coronary vascular resistance so that more capillaries are recruited, resulting in an increase in the permeability-surface area product without a change in capillary numerical density. Maintenance of α- and ß-adrenergic tone in the presence of lower circulating catecholamine levels appears to be due to increased receptor responsiveness to adrenergic stimulation. Exercise training also alters local control of coronary resistance vessels. Thus arterioles exhibit increased myogenic tone, likely due to a calcium-dependent protein kinase C signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, training augments endothelium-dependent vasodilation throughout the coronary microcirculation. This enhanced responsiveness appears to result principally from an increased expression of nitric oxide (NO) synthase. Finally, physical conditioning decreases extravascular compressive forces at rest and at comparable levels of exercise, mainly because of a decrease in heart rate. Impedance to coronary inflow due to an epicardial coronary artery stenosis results in marked redistribution of myocardial blood flow during exercise away from the subendocardium towards the subepicardium. However, in contrast to the traditional view that myocardial ischemia causes maximal microvascular dilation, more recent studies have shown that the coronary microvessels retain some degree of vasodilator reserve during exercise-induced ischemia and remain responsive to vasoconstrictor stimuli. These observations have required reassessment of the principal sites of resistance to blood flow in the microcirculation. A significant fraction of resistance is located in small arteries that are outside the metabolic control of the myocardium but are sensitive to shear and nitrovasodilators. The coronary collateral system embodies a dynamic network of interarterial vessels that can undergo both long- and short-term adjustments that can modulate blood flow to the dependent myocardium. Long-term adjustments including recruitment and growth of collateral vessels in response to arterial occlusion are time dependent and determine the maximum blood flow rates available to the collateral-dependent vascular bed during exercise. Rapid short-term adjustments result from active vasomotor activity of the collateral vessels. Mature coronary collateral vessels are responsive to vasodilators such as nitroglycerin and atrial natriuretic peptide, and to vasoconstrictors such as vasopressin, angiotensin II, and the platelet products serotonin and thromboxane A2. During exercise, ß-adrenergic activity and endothelium-derived NO and prostanoids exert vasodilator influences on coronary collateral vessels. Importantly, alterations in collateral vasomotor tone, e.g., by exogenous vasopressin, inhibition of endogenous NO or prostanoid production, or increasing local adenosine production can modify collateral conductance, thereby influencing the blood supply to the dependent myocardium. In addition, vasomotor activity in the resistance vessels of the collateral perfused vascular bed can influence the volume and distribution of blood flow within the collateral zone. Finally, there is evidence that vasomotor control of resistance vessels in the normally perfused regions of collateralized hearts is altered, indicating that the vascular adaptations in hearts with a flow-limiting coronary obstruction occur at a global as well as a regional level. Exercise training does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. In addition to ischemia, the pressure gradient between vascular beds, which is a determinant of the flow rate and therefore the shear stress on the collateral vessel endothelium, may also be important in stimulating growth of collateral vessels.

Exercise hyperaemia in the heart: the search for the dilator mechanism

Coronary blood flow is tightly coupled to myocardial oxygen consumption to maintain a consistently high level of myocardial oxygen extraction over a wide range of physical activity. This tight coupling has been proposed to depend on periarteriolar oxygen tension, signals released from cardiomyocytes (adenosine acting on K(ATP) channels) and the endothelium (prostanoids(,) nitric oxide, endothelin) as well as neurohumoral influences (catecholamines, endothelin), but the contribution of each of these regulatory pathways, and their interactions, to exercise hyperaemia in the human heart are still incompletely understood. Thus, in the human heart, nitric oxide, prostanoids, adenosine and K(ATP) channels each contribute to resting tone, but evidence for a critical contribution to exercise hyperaemia is lacking. In dogs K(ATP) channel activation together with adenosine and nitric oxide contribute to exercise hyperaemia in a non-linear redundant fashion. In contrast, in swine nitric oxide, adenosine and K(ATP) channels contribute to resting coronary resistance vessel tone control in a linear additive manner, but are not mandatory for exercise hyperaemia in the heart. Rather, exercise hyperaemia in swine appears to involve K(Ca) channel opening that is mediated, at least in part, by exercise-induced beta-adrenergic activation, possibly in conjunction with exercise-induced blunting of an endothelin-mediated vasoconstrictor influence. In view of these remarkable species differences in coronary vasomotor control during exercise, future studies are required to determine whether exercise hyperaemia in humans follows a canine or porcine control design.

Myocardial perfusion during exercise in endurance-trained and untrained humans

Because of technical challenges very little is known about absolute myocardial perfusion in humans in vivo during physical exercise. In the present study we applied positron emission tomography (PET) in order to 1) investigate the effects of dynamic bicycle exercise on myocardial perfusion and 2) clarify the possible effects of endurance training on myocardial perfusion during exercise. Myocardial perfusion was measured in endurance-trained and healthy untrained subjects at rest and during absolutely the same (150 W) and relatively similar [70% maximal power output (W(max))] bicycle exercise intensities. On average, the absolute myocardial perfusion was 3.4-fold higher during 150 W (P < 0.001) and 4.9-fold higher during 70% W(max) (P < 0.001) than at rest. At 150 W myocardial perfusion was 46% lower in endurance-trained than in untrained subjects (1.67 +/- 0.45 vs. 3.00 +/- 0.75 ml x g(-1) x min(-1); P < 0.05), whereas during 70% W(max) perfusion was not significantly different between groups (P = not significant). When myocardial perfusion was normalized with rate-pressure product, the results were similar. Thus, according to the present results, myocardial perfusion increases in parallel with the increase in working intensity and in myocardial work rate. Endurance training seems to affect myocardial blood flow pattern during submaximal exercise and leads to more efficient myocardial pump function.

Development of cardiovascular function in the horse fetus

In mammals, the mechanisms regulating an increase in fetal arterial blood pressure with advancing gestational age remain unidentified. In all species studied to date, the prepartum increase in fetal plasma cortisol has an important role in the maturation of physiological systems essential for neonatal survival. In the horse, the prepartum elevation in fetal cortisol and arterial blood pressure are delayed relative to other species. Hence, the mechanisms governing the ontogenic increase in arterial blood pressure in the horse fetus may mature much closer to term than in other fetal animals. In the chronically instrumented pony mare and fetus, this study investigated how changes in fetal peripheral vascular resistance, in plasma concentrations of noradrenaline, adrenaline and vasopressin, and in the maternal-to-fetal plasma concentration gradient of oxygen and glucose relate to the ontogenic changes in fetal arterial blood pressure and fetal plasma cortisol concentration as term approaches. The data show that, towards term in the horse fetus, the increase in arterial blood pressure occurs together with reductions in metatarsal vascular resistance, elevations in plasma concentrations of cortisol, vasopressin, adrenaline and noradrenaline, and falls in the fetal : maternal ratio of blood P(a,O(2)) and glucose concentration. Correlation analysis revealed that arterial blood pressure was positively related with plasma concentrations of vasopressin and noradrenaline, but not adrenaline in the fetus, and inversely related to the fetal : maternal ratio of blood P(a,O(2)), but not glucose, concentration. This suggests that increasing vasopressinergic and noradrenergic influences as well as changes in oxygen availability to the fetus and uteroplacental tissues may contribute to the ontogenic increase in fetal arterial blood pressure towards term in the horse.

Plasma volume expansion does not increase maximal cardiac output or VO2 max in lowlanders acclimatized to altitude

With altitude acclimatization, blood hemoglobin concentration increases while plasma volume (PV) and maximal cardiac output (Q̇max) decrease. This investigation aimed to determine whether reduction of Q̇max at altitude is due to low circulating blood volume (BV). Eight Danish lowlanders (3 females, 5 males: age 24.0 ± 0.6 yr; mean ± SE) performed submaximal and maximal exercise on a cycle ergometer after 9 wk at 5,260 m altitude (Mt. Chacaltaya, Bolivia). This was done first with BV resulting from acclimatization (BV = 5.40 ± 0.39 liters) and again 2–4 days later, 1 h after PV expansion with 1 liter of 6% dextran 70 (BV = 6.32 ± 0.34 liters). PV expansion had no effect on Q̇max, maximal O2 consumption (V̇o2), and exercise capacity. Despite maximal systemic O2 transport being reduced 19% due to hemodilution after PV expansion, whole body V̇o2 was maintained by greater systemic O2 extraction ( P < 0.05). Leg blood flow was elevated ( P < 0.05) in hypervolemic conditions, which compensated for hemodilution resulting in similar leg O2 delivery and leg V̇o2 during exercise regardless of PV. Pulmonary ventilation, gas exchange, and acid-base balance were essentially unaffected by PV expansion. Sea level Q̇max and exercise capacity were restored with hyperoxia at altitude independently of BV. Low BV is not a primary cause for reduction of Q̇max at altitude when acclimatized. Furthermore, hemodilution caused by PV expansion at altitude is compensated for by increased systemic O2 extraction with similar peak muscular O2 delivery, such that maximal exercise capacity is unaffected.

Walking performance and cardiovascular response: associations with age and morbidity--the Health, Aging and Body Composition Study

BACKGROUND

The long-distance corridor walk is a timed 400-meter walk test used to assess walking endurance in well-functioning men and women aged 70-79 in the Health, Aging and Body Composition Study.

METHODS

We examined walking time along with heart rate and blood pressure response in relationship to prevalent chronic conditions, weight, physical activity, and markers of subclinical disease. Of 3075 participants, 2324 (76%) completed the test with heart rate and blood pressure responses in the range expected for a moderate level of exertion.

RESULTS

Slower walking time was influenced by both clinical and subclinical disease, and also was strongly related to both low and high body weight and low self-reported physical activity. Heart rate and blood pressure responses were higher with several clinical and subclinical diseases, but heart rate response and recovery were more strongly related to walking time than to disease. Higher body mass index and lower physical activity were associated with greater heart rate response and recovery.

CONCLUSIONS

The independent contribution of both clinical and subclinical disease to walking time supports the use of walking tests as a summary measure of disease in older adults. The independent association of walking time with physical activity suggests that it is sensitive to levels of fitness as well. Together these findings show that walking performance is a valid indicator of physiologic reserve in older adults.

Change in double product during stepwise incremental exercise

The purpose of this study was to observe the change in double product with increases in the intensity of bicycle exercise. Eleven young male adults participated in this study. The subjects performed graded bicycling exercise increasing 20 watts every 2 min from 0 watts until the heart rate (HR) reached 170 beats.min(-1). During exercise systolic blood pressure (SBP) and HR were continuously measured. Initially SBP gradually increased with the increase in workload, but when the intensity of exercise became even higher, the rate of increase slowed. On the other hand, the increase in HR was very small during the initial 5 min of exercise and when the intensity of exercise increased, the rate of increase of HR became higher. The polygonal regression analyses on the relation of double product to elapsed time revealed clear break-points. On average, the break-point of double product was 6.6 min (56 watts). These results clearly showed that the break-point of double product with an increase in workload appeared even though the workload was relatively low.

Periconceptional nutrition programs development of the cardiovascular system in the fetal sheep

It has been proposed that fetal adaptations to intrauterine nutrient deprivation permanently reprogram the cardiovascular system. We investigated the impact of restricted periconceptional nutrition and/or restricted gestational nutrition on fetal arterial blood pressure (BP), heart rate, rate pressure product, and the fetal BP responses to ANG II and the angiotensin-converting enzyme inhibitor captopril during late gestation. Restricted periconceptional nutrition resulted in an increase in fetal mean arterial BP between 115 and 125 days gestation (restricted 41.5 +/- 2.8 mmHg, n = 12; control 38.5 +/- 1.5 mmHg, n = 13) and between 135 and 147 days gestation (restricted 50.5 +/- 2.2 mmHg, n = 8; control 42.5 +/- 1.9 mmHg, n = 10) as well as an increase in the rate pressure product in twin, but not singleton, fetuses between 115 and 147 days gestation. Mean BP and fetal plasma ACTH were also positively correlated in twin, but not singleton, fetuses. This is the first demonstration that maternal undernutrition during the periconceptional period results in an increase in fetal arterial BP. This increase occurs concomitantly with an increase in fetal ACTH but is not dependent on activation of the fetal renin-angiotensin system.

Feedforward sympathetic coronary vasodilation in exercising dogs

The hypothesis that exercise-induced coronary vasodilation is a result of sympathetic activation of coronary smooth muscle beta-adrenoceptors was tested. Ten dogs were chronically instrumented with a flow transducer on the circumflex coronary artery and catheters in the aorta and coronary sinus. During treadmill exercise, coronary venous oxygen tension decreased with increasing myocardial oxygen consumption, indicating an imperfect match between myocardial blood flow and oxygen consumption. This match was improved after alpha-adrenoceptor blockade with phentolamine but was significantly worse than control after alpha + beta-adrenoceptor blockade with phentolamine plus propranolol. The response after alpha-adrenoceptor blockade included local metabolic vasodilation plus a beta-adrenoceptor vasodilator component, whereas the response after alpha + beta-adrenoceptor blockade contained only the local metabolic vasodilator component. The large difference in coronary venous oxygen tensions during exercise between alpha-adrenoceptor blockade and alpha + beta-adrenoceptor blockade indicates that there is significant feedforward beta-adrenoceptor coronary vasodilation in exercising dogs. Coronary venous and estimated myocardial interstitial adenosine concentrations did not increase during exercise before or after alpha + beta-adrenoceptor blockade, indicating that adenosine levels did not increase to compensate for the loss of feedforward beta-adrenoceptor-mediated coronary vasodilation. These results indicate a meaningful role for feedforward beta-receptor-mediated sympathetic coronary vasodilation during exercise.

Development of normative values for resting and exercise rate pressure product

PURPOSE

The purpose of this study was to develop multivariate models to quantify resting, submaximal, and maximal rate pressure products (RPP).

METHODS

A validation sample (N = 1623) was randomly selected from a clinically healthy population, and four cross-validation samples were randomly selected from a clinical cohort. The cross-validation samples were patients who had a negative exercise ECG with (Neg-Med, N = 179) and without cardiovascular drug (Neg-NoMed, N = 350), and patients who had a positive exercise ECG with (Pos-Med, N = 60) and without cardiovascular drug (Pos-NoMed, N = 75). Men made up 83% of the validation sample (mean age = 44.2+/-8.7) and women 17% (mean age = 39.7+/-10.1). The validation sample was used to develop multiple regression equations to quantify resting, submaximal, and maximal RPP.

RESULTS

Results indicated that gender, body mass index (BMI), and physical activity level (Ex-code) were significantly related with resting RPP. Gender, age, BMI, and Ex-code were significantly related with maximal RPP. Gender, age, BMI, Ex-code, and percent of maximal heart rate at submaximal exercise (%HRmax) were significantly related with submaximal RPP. The multiple correlations for the resting, submaximal, and maximal models were 0.29 (SE = 16.75 beats x min(-1) x mm Hg), 0.87 (SE = 29.04 beats x min(-1) x mm Hg), and 0.31 (SE = 42.41 beats x min(-1) x mm Hg), respectively. The accuracy of the models was confirmed when applied to the Neg-NoMed and Pos-NoMed samples but not the Neg-Med and Pos-Med samples. This result suggest that the regression models developed from this study can be generalized to other populations where patients were not taking cardiovascular medication. Microcomputer programs were suggested to evaluate RPP at rest, maximal exercise, and submaximal exercise.

CONCLUSION

Normative RPP for resting and exercise relies on multiple fitness parameters. Practical regression models are developed and can be applied to patients without cardiovascular medication.

Effect of maternal undernutrition in early gestation on ovine fetal blood pressure and cardiovascular reflexes

Human epidemiological and animal experimental studies suggest that maternal undernutrition during pregnancy may alter cardiovascular development of the offspring. The extent to which these effects involve changes in fetal cardiovascular function and whether they are necessarily linked to reduced fetal growth is unknown. In sheep, we investigated the effect of a 15% reduction in maternal global nutrition for the first 70 days of gestation (term = 147 days) on fetal blood pressure development, baroreflex control of fetal heart rate (FHR), and cardiovascular responses to acute hypoxemia in late gestation. Basal mean arterial pressure (P < 0.05), systolic blood pressure (P < 0.05), diastolic blood pressure (P < 0.05), and rate-pressure product (P < 0.001) were significantly lower in fetuses of nutritionally restricted ewes (R) compared with controls (C). FHR was not altered. The operating point for the fetal baroreflex was significantly lower in R fetuses compared with C (P < 0.01), but there was no difference between the groups in the cardiovascular response to hypoxemia. We conclude that mild maternal undernutrition alters fetal cardiovascular development, producing low blood pressure and resetting of baroreflex control mechanisms. This effect occurs without any changes in fetal growth or blood gas status.

A critical appraisal of the rate pressure product as index of myocardial oxygen consumption for the study of metabolic coronary flow regulation

For the assessment of metabolic coronary vasodilatation, changes in systolic rate pressure product (RPP) are frequently used to estimate the pacing- or exercise induced changes in myocardial oxygen consumption (MVO2). The present study was designed to test whether this is justified in patients with coronary artery disease. To study the relation between RPP and changes in MVO2 under different conditions, we used data from 21 patients who participated in two previous studies investigating the effect of nitroglycerin (NTG) and anaesthesia on metabolic coronary flow regulation. At control, during administration of NTG 1 microg/kg/min (n=11), and during anaesthesia (n=10), coronary sinus blood flow, MVO2 and RPP were measured at sinus rhythm and during atrial pacing (30 bpm above sinus rate) and the relation between the percentage increase in RPP (delta%RPP) and MVO2 delta%MVO2) was analysed, using standard linear regression analysis. Although a significant relation between delta%MVO2 and delta%RPP was found at control and during anaesthesia, prediction intervals were very wide and only 40% and 60% of the variation in delta%MVO2, respectively, could be explained by the variation in delta%RPP. During administration of NTG 1 microg/kg/min no significant relation was found between delta%MVO2 and delta%RPP. Thus, for the study of metabolic coronary flow regulation, pacing induced changes in MVO2 cannot be predicted accurately from changes in RPP.

Estrogen replacement, vascular distensibility, and blood pressures in postmenopausal women

The pathogenesis of blood pressure (BP) rise in aging women remains unexplained, and one of the many incriminating factors may include abnormalities in arteriolar resistance vessels. The aim of this study was to determine the effects of unopposed estrogen on arteriolar distensibility, baroreceptor sensitivity (BRS), BP changes, and rate-pressure product (RPP). We tested the hypotheses that estrogen replacement therapy (ERT) enhances arteriolar distensibility and ameliorates BRS, which leads to decreases in BP and RPP. Postmenopausal women participated in a single-blind crossover study; the participants of this study, after baseline measurements, were randomly assigned to receive estrogen (ERT) or a drug-free treatment with a 6-wk washout period between treatments. The single-blind design was instituted because subjects become unblinded due to physiological changes (i.e., fluid shifts, weight gain, and secretory changes) associated with estrogen intake. However, investigators and technicians involved in data collection and analyses remained blind. After each treatment, subjects performed identical autonomic tests, during which electrocardiograms, beat-by-beat BPs, and respiration were recorded. The area under the dicrotic notch of the BP wave was used as an index of arteriolar distensibility. The magnitude of the reflex bradycardia after a precipitous rise in BP was used to determine BRS. Power spectral analysis of heart rate variability was used to assess autonomic activity. BPs were recorded from resistance vessels in the finger using a beat-by-beat photoplethysmographic device. RPP, a noninvasive marker of myocardial oxygen consumption, was calculated. Repeated-measures analyses of variance revealed a significantly enhanced arteriolar distensibility and BRS after ERT (P < 0.05). A trend of a lower sympathovagal balance at rest was observed after ERT, however, this trend did not reach statistical significance (P = 0.061) compared with the other treatments. The above autonomic changes produced significantly lower systolic and diastolic BP changes and RPPs (P < 0.05) at rest and during isometric exercise. We conclude that short-term unopposed ERT favorably enhances arteriolar distensibility, BRS, and hemodynamic parameters in postmenopausal women. These findings have clinical implications in the goals for treating cardiovascular risk factors in aging women.

Neuromuscular fatigue in prostate cancer patients undergoing radiation therapy

OBJECTIVE

To determine the etiology of fatigue in prostate cancer patients undergoing radiation therapy (RT).

METHODS

Thirteen prescreened men (60 to 76 years in age, 58 to 130 kg in body weight) were evaluated for neuromuscular fatigue (NMF) of the tibialis anterior (TA) muscle, cardiopulmonary fatigue (CPF), and psychological-subjective fatigue (PSF) at 1 to 2 weeks before RT (Pre), at the end of 8 weeks of RT (RT), and at 5 to 6 weeks after completion of RT (Post).

OUTCOME MEASURES

For NMF, the TA muscle was fatigued by sustained isometric contraction at 80% of maximum voluntary contraction for 60 seconds on a force dynamometer. Neuromuscular efficiency (NME) expressed as a ratio of isometric force (in Newtons) and respective integrated electromyograms were measured. For CPF, stress testing was performed on a treadmill using the modified Bruce protocol. Piper Fatigue Scale, Beck Depression Inventory, and Epworth Sleepiness Scale were administered to evaluate PSF.

DATA ANALYSIS

Paired t tests, single factor analysis of variance, and nonparametric analysis.

RESULTS

At RT, there was a significant decline in NME of TA at the beginning (18.4%, p < .01) and the end (29.2%, p < .001) of sustained muscle contraction for 60 seconds. Post values were lower but nonsignificant in comparison with Pre values. NME recovered within 5 to 6 weeks after RT. No abnormalities were detected in CPF or PSF. No correlation was found between the decline in NME and psychological status of the patients.

CONCLUSION

Results provide definitive evidence of transient decline in NME in prostate cancer patients at the completion of RT. The effect seems to be specific for neuromuscular performance alone and is independent of the cardiovascular or psychological status of the patients.

Double product response is accelerated above the blood lactate threshold

Catecholamine concentrations are known to increase sharply in the blood at work rates above the blood lactate threshold (LT); thus, we hypothesized that the double product (DP, heart rate-systolic blood pressure product) may also abruptly increase at work rates above the LT. Ninety healthy students performed a stepwise incremental test on a cycle ergometer. The slopes of the two regression lines below and above the LT for the heart rate (HR), the indirectly measured systolic blood pressure (SBP), and the DP, respectively, were compared using VO2 as an independent variable. For all three parameters the slope of the regression line above the LT was significantly higher than that below the LT. Although either the same or a lower slope was found in the HR (N = 23) or SBP (N = 22) responses in some subjects above the LT as compared with that below the LT, a steeper DP slope above the LT was evident in all 90 subjects. The same results were also obtained during 4-min constant work rate exercise sessions at a variety of submaximal intensities performed in a random order in seven subjects. In addition, we established the DP break point (DPBP) determining protocol with a fairly good test-retest reliability (r = 0.951) and a correlation coefficient between the DPBP and the LT (r = 0.900). These results suggest that the DP increases more steeply above the LT, and, as a result, the DPBP is considered to be a valid and useful parameter as a marker of the LT.

Low efficiency of oxygen utilization during exercise in hyperthyroidism

STUDY OBJECTIVE

The mechanism of exercise intolerance in hyperthyroidism has not been fully elucidated. This study was undertaken to determine if hyperthyroidism reduced the efficiency of sub-maximal exercise.

STUDY DESIGN

We measured cardiorespiratory variables up to the anaerobic threshold (AT) during ramp-loading cycle ergometry in 12 patients (New York Heart Association functional class II or III). Studies were performed in the hyperthyroid state and repeated in the euthyroid state after 10 months of medical treatment. In 10-W steps from rest to the AT, we measured oxygen uptake (VO2) as a measure of total body work rate, and pressure rate product (PRP) as a measure of cardiac work rate. Loading watts at AT divided by the increment of Vo2 from rest to the AT (delta Watt/delta VO2) was calculated as an index of work efficiency (where delta means the increment of each value from rest to the AT).

RESULTS

VO2 and PRP at the AT were not significantly different between hyperthyroid and euthyroid states (VO2, 16.6 +/- 3.0 vs 17.5 +/- 2.3 mL/min/kg; PRP, 229 +/- 41 vs 218 +/- 28 x 10(2) mm Hg/min). However, loading watts at the AT were significantly lower in the hyperthyroid than the euthyroid state (28 +/- 22 vs 60 +/- 14 W: p < 0.01). VO2 and PRP while hyperthyroid were significantly higher than when euthyroid at every 10-W step during ramp-loading exercise. Furthermore, delta Watt/delta VO2 was significantly lower in hyperthyroid than euthyroid states (p < 0.001). There was a significant inverse correlation-ship between triiodothyronine and delta Watt/delta Vo2 (r = -0.654, p < 0.001).

CONCLUSION

Hyperthyroidism causes low work efficiency, which may limit exercise tolerance.

Heart rate adjustment of ST segment depression and performance of the exercise electrocardiogram: a critical evaluation

Analysis of the rate-related change in exercise-induced ST segment depression using the exercise ST segment/heart rate slope and ST segment/heart rate index can improve the accuracy of the exercise electrocardiogram (ECG) for the identification of patients with coronary artery disease, recognition of patients with anatomically or functionally severe coronary obstruction and detection of patients at increased risk for future coronary events. These methods provide a more physiologic approach to analysis of the ST segment response to exercise by adjusting the apparent severity of ischemia for the corresponding increase in myocardial oxygen demand, which in turn can be linearly related to increasing heart rate. Solid-angle theory provides a model for the linear relation of ST segment depression to heart rate during exercise and a framework for understanding the relation of the ST segment/heart rate slope to the presence and extent of coronary artery disease. False positive and false negative test results of the heart rate-adjusted methods are well known in selected populations and require further clarification. Application of these methods is also highly dependent on the type of exercise protocol, number of ECG leads examined, timing of ST segment measurement relative to the J point and accuracy and precision of ST segment measurement. These methodologic details have been an important limitation to test application when traditional protocols and measurement procedures are required. When applied with attention to required details, the heart rate-adjusted methods can improve the usefulness of the exercise ECG in a range of clinically relevant populations.

Solid-angle theory and heart rate adjustment of ST-segment depression for the identification and quantification of coronary artery disease

Determinants of the ST-segment response to exercise can be mathematically modeled by solid-angle theory, and heart rate adjustment of the magnitude of exercise-induced ST-segment depression can remodel the solid-angle relationship to provide a theoretic and practical basis for application of heart rate-adjusted indexes of ST depression in exercise electrocardiography. Solid-angle theory indicates that the magnitude of ST depression recorded at a surface electrode (epsilon) can be described as the product of spatial and nonspatial determinants: epsilon = (omega/4 pi).(delta Vm).K (equation 1), where omega is the solid angle subtending the boundary of the ischemic territory, delta Vm is the difference in transmembrane voltage between the ischemic and adjacent nonischemic regions, and K is a term correcting for differences in intracellular and extracellular conductivity and changes in end-plate conductance. As a consequence, the magnitude of ST depression recorded by a surface electrode will be proportional both to the area of ischemic territory subtended by the recording electrode, which reflects the solid angle, and to the local transmembrane potential difference, which in turn reflects the electric consequences of the metabolic severity of ischemia at the level of the myocardial cell. It follows from equation 1 that the amplitude of ST depression can accurately reflect the area of ischemic boundary only when the severity of ischemia is constant or otherwise controlled, and differences in ST depression will only reflect varying areas of underlying ischemia when similar severity of ischemia is present. During exercise the severity of ischemia is directly proportional to changes in myocardial oxygen demand and coronary blood flow, which in turn are directly related to increasing heart rate (delta HR). Because the change in transmembrane voltage across the ischemic boundary is linearly proportional to delta HR, delta Vm/delta HR remains constant as ischemia develops. Dividing the solid-angle relationship in equation 1 by delta HR and making the appropriate substitution for a constant delta Vm/delta HR then indicates that epsilon/delta HR = (omega/4 pi).(c . K) [equation 2], where c is the new constant. Under conditions where changes in conductance are proportional or small, this simplified relationship reduces to delta ST/delta HR = c'.omega [equation 3], where delta ST reflects the magnitude of ST depression recorded by the surface electrode, delta HR the change in heart rate during developing ischemia, and c' the resulting empiric constant.

Effect of antianginal agents on the relationship between rate-pressure product and myocardial oxygen uptake

To evaluate the effects of antianginal agents on the correlation between rate-pressure product and myocardial oxygen uptake, multistage supine leg exercise tests were performed by 21 patients with stable effort-induced angina pectoris before and after administration of antianginal drugs (a calcium channel blocker of the dihydropyridine class [10 mg of nisoldipine orally] in 11 patients and a beta-blocker [0.2 mg/kg of propranolol intravenously] in 10 patients). The rate-pressure product was closely correlated with myocardial oxygen uptake before and after administration of each drug. However, the slope of the regression line of rate-pressure product (X) and myocardial oxygen uptake (Y) became significantly steeper after the calcium channel blocker administration, and the Y-intercept was significantly increased by administration of the beta-blocker. Myocardial oxygen uptake was increased after administration of the calcium channel blocker and the beta-blocker compared with control values at corresponding rate-pressure product. These observations should be considered when the rate-pressure product is used to predict myocardial oxygen uptake in patients with angina pectoris who are receiving antianginal drugs.

Value and limitations of heart rate-adjusted ST segment depression criteria for the identification of anatomically severe coronary obstruction: test performance in relation to method of rate correction, definition of extent of disease, and beta-blockade

Performance of the linear regression-based ST/HR (heart rate) slope, the simple ST/HR index, and ST segment depression alone for the identification of anatomically severe coronary obstruction was examined in relation to the definition of the extent of disease and the presence or absence of beta-blockade during treadmill exercise using the Cornell protocol in 172 catheterized patients. Whether severe disease was defined by three-vessel obstruction, by Gensini scores partitioned at 35 or at 48, or by Duke jeopardy scores exceeding 6, the 83% to 100% sensitivities of an ST/HR slope criterion of 6.0 microV/beat/min were each significantly higher than the corresponding 65% to 80% sensitivities of 150 microV of ST segment depression closely matched specificities. The ST/HR slope was significantly more sensitive than a simple ST/HR index criterion of 3.4 microV/beat/min for detection of high Gensini scores, but despite consistently intermediate performance trends, in no case did sensitivity of the simple ST/HR index criterion significantly exceed that of ST depression alone. Each method performed better and with comparable sensitivity in patients not receiving beta-blockers. In contrast, the 82% to 100% sensitivities of the ST/HR slope for identification of severe disease were significantly higher than the 63% to 77% sensitivities of ST depression in patients taking beta-blocking drugs; however, simple heart rate adjustment using the ST/HR index had intermediate performance that in no case was significantly more sensitive than ST segment depression alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of carbon monoxide on myocardial ischemia

The purpose of this study was to determine whether low doses of carbon monoxide (CO) exacerbate myocardial ischemia during a progressive exercise test. The effect of CO exposure was evaluated using the objective measure of time to development of electrocardiographic changes indicative of ischemia and the subjective measure of time to onset of angina. Sixty-three male subjects (41-75 years) with well-documented coronary artery disease, who had exertional angina pectoris and ischemic ST-segment changes in their electrocardiograms, were studied. Results from three randomized, double-blind test visits (room air, low and high CO) were compared. The effect of CO exposure was determined from the percent difference in the end points obtained on exercise tests performed before and after a 1-hr exposure to room air or CO. The exposures resulted in postexercise carboxyhemoglobin (COHb) levels of 0.6% +/- 0.3%, 2.0% +/- 0.1%, and 3.9% +/- 0.1%. The results obtained on the 2%-COHb day and 3.9%-COHb day were compared to those on the room air day. There were 5.1% (p = 0.01) and 12.1% (p less than or equal to 0.0001) decreases in the time to development of ischemic ST-segment changes after exposures producing 2.0 and 3.9% COHb, respectively, compared to the control day. In addition, there were 4.2% (p = 0.027) and 7.1% (p = 0.002) decreases in time to the onset of angina after exposures producing 2.0 and 3.9% COHb, respectively, compared to the control day. A significant dose-response relationship was found for the individual differences in the time to ST end point and angina for the pre- versus postexposure exercise tests at the three carboxyhemoglobin levels. These findings demonstrate that low doses of CO produce significant effects on cardiac function during exercise in subjects with coronary artery disease.

Propionyl carnitine in stable effort angina

The aim of this study was to investigate the anti-ischemic activity of propionyl carnitine (PC) in 18 informed, volunteer male patients, aged 37-70, suffering from a typical stable effort angina. The study design was randomized, balanced, crossover, and double blinded. The study lasted 75 days. In the first 15 days of washout the patients performed two maximal symptom-limited bicycle tests to verify the repeatability of the parameters examined. Then one group received PC for 30 days 500 mg three times a day, and the other group received placebo (PL) three times a day. At the end of 30 days the groups exchanged treatments. At the end of each period, 2 hours after the last oral administration, the patients performed a maximal symptom-limited bicycle exercise test with increased loads of 10 watts/min. No significant differences were observed between the two tests performed during the wash-out period, for a 1 mm ST-segment depression time, for the time to the end of exercise, and for the rate x pressure product at the same experimental time. The oral administration of PC in coronary patients increased both the 1 mm ST-segment depression time and the time to the end of exercise. Furthermore, the drug reduced the ischemic depression of ST at maximal common work and at maximal work. After PC, the rate x pressure product was not significantly different in relation to placebo at submaximal and maximal exercise. Thus PC seems to have an antiischemiclike effect, probably related to its metabolic activity.

Short-term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease

Patients with atherosclerotic cardiovascular disease may be adversely affected by the presence of carboxyhemoglobin, even at low concentrations. We investigated the effects of carbon monoxide exposure on myocardial ischemia during exercise in 63 men with documented coronary artery disease. On each test day, subjects performed two symptom-limited incremental exercise tests on a treadmill; the tests were separated by a recovery period and 50 to 70 minutes of exposure to either room air or air containing one of two concentrations of carbon monoxide (117 +/- 4.4 ppm or 253 +/- 6.1 ppm). The order of exposure was assigned randomly. On each occasion, neither the subjects nor the study personnel knew whether the subjects had been exposed to room air or to one of the concentrations of carbon monoxide. Exposure to room air resulted in a mean carboxyhemoglobin level of 0.6 percent, exposure to the lower level of carbon monoxide resulted in a carboxyhemoglobin level of 2.0 percent, and exposure to the higher level of carbon monoxide resulted in a level of 3.9 percent. An effect of carbon monoxide on myocardial ischemia was demonstrated objectively by electrocardiographic changes during exercise. We observed a decrease of 5.1 percent (90 percent confidence interval, 1.5 to 8.7 percent; P = 0.02) and a decrease of 12.1 percent (90 percent confidence interval, 9.0 to 15.3 percent; P less than or equal to 0.0001) in the length of time to a threshold ischemic ST-segment change (ST end point) after carbon monoxide exposures that produced carboxyhemoglobin levels of 2.0 percent and 3.9 percent, respectively. The length of time to the onset of angina decreased by 4.2 percent (90 percent confidence interval, 0.7 to 7.9 percent; P = 0.054) at the 2.0 percent carboxyhemoglobin level and by 7.1 percent (90 percent confidence interval, 3.1 to 10.9 percent; P = 0.004) at the 3.9 percent carboxyhemoglobin level. Significant dose-response relations were found in both the change in the length of time to the ST end point (P less than or equal to 0.0001) and the change in the length of time to the onset of angina (P = 0.02). We conclude that low levels of carboxyhemoglobin exacerbate myocardial ischemia during graded exercise in subjects with coronary artery disease.

Efficacy and safety of oral nadolol for exercise-induced ventricular arrhythmias

Sixty-four patients with reproducible exercise-induced ventricular arrhythmias were enrolled in an open-label, multicenter study to assess the efficacy and safety of oral nadolol therapy. There were 53 men and 11 women ranging in age from 19 to 75 years (mean 53.9). The severity of arrhythmias varied from frequent ventricular premature beats to nonsustained and sustained ventricular tachycardias. Using serial treadmill exercise tests, patients underwent dose titration for 1 month and were followed up for 3 to 6 months. Depending on drug tolerance and response to treadmill exercise testing, the single daily required dose of oral nadolol ranged from 20 to 240 mg (average 66). Twenty-three (36%) of the patients experienced a total of 30 adverse effects of nadolol therapy; however, only 9 (14%) patients had to be withdrawn from the study. The adverse effects observed were those commonly associated with beta-adrenergic blocking agents, and all were dose-dependent and reversible. At the last patient visit, the severity of exercise-induced ventricular arrhythmias was significantly decreased compared with pretreatment in 36 (75%) of 48 evaluable patients. Eighteen (38%) of the patients demonstrated total suppression of arrhythmias. This was accompanied by significant increases from pretreatment in both the mean duration of symptom-limited exercise (+1.02 +/- 0.41 minutes, p less than 0.05) and the mean time of exercise required for arrhythmia induction (+1.80 +/- 0.66 minutes, p less than 0.01), a significant decrease from pretreatment in the mean peak exercise double-product (-4,775, p less than 0.001) and a decrease in the incidence of exercise-induced ST-segment depression (-33%).(ABSTRACT TRUNCATED AT 250 WORDS)