Submaximal Exercise Levels Research Articles

Correlation of Hemodynamic and Respiratory Parameters in Invasive Cardiopulmonary Exercise Testing (iCPET).

Background: Invasive cardiopulmonary exercise testing (iCPET) is an integral part in the advanced diagnostic workup of pulmonary hypertension (PH). Our study evaluated the relation between hemodynamic and respiratory parameters at two different resting conditions and two defined low exercise levels with a close synchronization of measurements in a broad variety of dyspnea patients. Subjects and methods: We included 146 patients (median age 69 years, range 22 to 85 years, n = 72 female) with dyspnea of uncertain origin. Invasive hemodynamic and gas exchange parameters were measured at rest, 45° upright position, unloaded cycling, 25 and 50 W exercise. All measurements were performed in a single RHC procedure. Results: Oxygen uptake (VO/body mass) correlated significantly with cardiac index (all p ≤ 0.002) at every resting and exercise level and with every method of cardiac output measurement (thermodilution, method of Fick). Mean pulmonary arterial pressure (PAPmean) correlated with all respiratory parameters (respiratory rate, partial end-tidal pressures of oxygen and carbon dioxide [petCO and petO], ventilation/carbon dioxide resp. oxygen ratio [VE/VCO, VE/VO], and minute ventilation [VE], all p < 0.05). These correlations improved with increasing exercise levels from rest via unloaded cycling to 25 W. There was no correlation with right atrial or pulmonary arterial wedge pressure. Summary: In dyspnea patients of different etiologies, the cardiac index is closely linked to VO at every level of rest and submaximal exercise. PAPmean is the only pressure that correlates with different respiratory parameters, but this correlation is highly significant and stable at rest, unloaded cycling and at 25 W.

Unmasking Pulsus Alternans In Patients With Heart Failure With Reduced Ejection Fraction. The Importance Of Upright Exercise

<h3>Background</h3> : Pulsus alternans (PA), typically observed in a supine resting position, is a poor prognostic indicator among patients with heart failure with reduced ejection fraction (HFrEF). We tested the hypothesis that PA may not be present in the supine position, but only when upright. <h3>Methods</h3> : 27 patients with severe HFrEF completed invasive cardiopulmonary exercise testing (CPET) with Swan-Ganz and radial arterial catheters. Hemodynamics were recorded in supine and upright resting positions. During exercise on upright cycle ergometry, hemodynamics were collected at two submaximal levels of exercise below ventilatory threshold (Steady-States 1 and 2) and peak effort. Breath-by-breath gas-exchange parameters were measured by indirect calorimetry. <h3>Results</h3> : Baseline characteristics are displayed in <b>Table 1</b>. Twenty-one participants showed no evidence of PA in either supine or upright position. However, six participants were found to have PA when in an upright resting but not supine resting position (<b>Figure 1</b>). Exercise hemodynamics and gas exchange parameters are displayed in <b>Table 2</b>. Maximal oxygen uptake (VO₂Max) was severely reduced, the cardiac output response to exercise was blunted, and exertional cardiac filling pressures were abnormal in both groups. <h3>Conclusions</h3> : PA, a poor prognostic indicator, may manifest in an upright but not supine position among patients with HFrEF. As human beings are upright and bipedal, this novel finding reinforces the importance of upright exertional hemodynamic assessments to guide risk-stratification and management.

Right Ventricular Performance During Exercise In Patients With Heart Failure

<h3>Purpose</h3> : To characterize resting and exertional right ventricular (RV) function during exercise among patients with heart failure with reduced ejection fraction (HFrEF). <h3>Methods</h3> : Six patients (five males, 60±9yrs) completed invasive cardiopulmonary exercise testing (CPET) on upright cycle ergometry with conductance catheters for real-time RV pressure-volume (PV) analysis, as well as radial arterial catheterization for blood pressure monitoring. Data were collected at rest, two submaximal levels of exercise (Steady-States 1, 2) below ventilatory threshold, and peak effort. Breath-by-breath gas-exchange parameters were determined by indirect calorimetry. Cardiac output (Qc) was determined by direct Fick. <h3>Results</h3> : Cohort characteristics are displayed in <b>Table 1</b>. VO2Max was severely reduced (11.8±5.0) and ventilatory efficiency was severely abnormal (46±15). Exercise Qc increased from rest to Steady-State 1, but there were no increases thereafter at higher workloads or at peak effort. Exercise myocardial energetics (stroke work) were also blunted with a modest increase from rest to Steady-State 2. Diastolic reserve (dpdt_min) increased modestly from rest to Steady-State 1 only. <b>Table 2</b> displays exercise hemodynamics and gas-exchange parameters. An example figure of hemodynamics and RV PV loops during exercise is displayed in <b>Figure 1</b>. <h3>Conclusion</h3> : HFrEF patients experience impairments in RV contractile and lusitropic reserve, and energy utilization during exercise. These findings demonstrate how exertional RV dysfunction contributes to impairments in functional capacity.

Right ventricular function and cardiopulmonary performance among patients with heart failure supported by durable mechanical circulatory support devices

Patients with continuous-flow left ventricular assist devices (CF-LVADs) experience limitations in functional capacity and frequently, right ventricular (RV) dysfunction. We sought to characterize RV function in the context of global cardiopulmonary performance during exercise in this population. A total of 26 patients with CF-LVAD (aged 58 ± 11 years, 23 males) completed a hemodynamic assessment with either conductance catheters (Group 1, n = 13) inserted into the right ventricle to generate RV pressure‒volume loops or traditional Swan‒Ganz catheters (Group 2, n = 13) during invasive cardiopulmonary exercise testing. Hemodynamics were collected at rest, 2 sub-maximal levels of exercise, and peak effort. Breath-by-breath gas exchange parameters were collected by indirect calorimetry. Group 1 participants also completed an invasive ramp test during supine rest to determine the impact of varying levels of CF-LVAD support on RV function. In Group 1, pump speed modulations minimally influenced RV function. During upright exercise, there were modest increases in RV contractility during sub-maximal exercise, but there were no appreciable increases at peak effort. Ventricular‒arterial coupling was preserved throughout the exercise. In Group 2, there were large increases in pulmonary arterial, left-sided filling, and right-sided filling pressures during sub-maximal and peak exercises. Among all participants, the cardiac output‒oxygen uptake relationship was preserved at 5.8:1. Ventilatory efficiency was severely abnormal at 42.3 ± 11.6. Patients with CF-LVAD suffer from limited RV contractile reserve; marked elevations in pulmonary, left-sided filling, and right-sided filling pressures during exercise; and severe ventilatory inefficiency. These findings explain mechanisms for persistent reductions in functional capacity in this patient population.

Abstract 14369: Assessment of Hemodynamic Response to Exercise in Patients With Advanced Heart Failure

Introduction: Among patients suffering from HFrEF, outcomes are closely associated with quality-of-life and functional capacity. Data are limited regarding exertional cardiopulmonary performance measures in these patients. The objective of this study was to complete a comprehensive analysis of cardiac function among patients with advanced HFrEF during submaximal and peak exercise through an invasive cardiopulmonary exercise test (CPET) on an upright cycle ergometer. Methods: Thirty-five participants with advanced HFrEF (age 59 ± 12) underwent invasive hemodynamic assessment with Swan-Ganz catheter during CPET. Group 1 comprised individuals not on inotropes (N=23, 66%); group 2 was comprised of individuals on inotropes (N=12, 34%). Data were obtained at supine and upright rest, two submaximal levels (steady-states 1-2) of exertion below the ventilatory threshold (VT), and peak exercise. Results: Cohort characteristics are displayed in table 1 . VO 2 max for the overall cohort was severely reduced (11.8 ± 3.3), and was similar between group 1 and 2 (12.1 ± 3.2 v. 10.1 ± 3.5 ml/kg/min, P= 0.71). As displayed in figure 1 , pulmonary arterial and left-sided filling pressures increased dramatically even during submaximal exercise. Cardiac output increased minimally, with only an ~2-fold change from rest to peak exercise for both groups. Conclusions: Among patients with advanced HFrEF, exercise is limited by severe increases in cardiac and pulmonary filling pressures, even during submaximal levels of exercise that mimic real-world activities of daily living, as well as severely impaired inotropic reserve. Inotropes do not appear to improve exertional hemodynamics.

Cardiopulmonary Exercise Metrics Demonstrate that CF-LVAD Patients Suffer from Residual Heart Failure

Background Continuous flow left ventricular assist devices (CF-LVADs) improve survival and quality-of-life for patients with heart failure with reduced ejection fraction (HFrEF), but exercise capacity remains reduced. While resting and exertional cardiovascular performance is described in the setting of CF-LVAD support, data on pulmonary performance are limited. The primary objective of this study was to describe changes in metrics of cardiopulmonary performance during exercise among HFrEF patients before and after CF-LVAD implantation. Methods 11 HFrEF patients completed submaximal and symptom-limited cardiopulmonary exercise testing (CPET) on three separate visits. Visit 1 involved CPET testing ∼2-4 weeks prior to CF-LVAD implantation. Visit 2 involved CPET testing ∼3 months post-LVAD at a constant pump speed. Visit 3 involved CPET testing ∼4-5 months post-LVAD with progressive increases in LVAD pump speed during exercise. Exercise involved two levels of submaximal exercise below the ventilatory threshold (steady-states 1-2) and peak exercise on an upright cycle ergometer. Breath-by-breath gas exchange parameters (oxygen uptake [VO2], carbon dioxide production [VCO2], minute ventilation [VE]) were recorded by indirect calorimetry. Results Clinical characteristics are summarized in table 1. There was no improvement in submaximal or peak VO2 following LVAD implantation (figure 1) regardless of whether individuals exercised at constant speed (visit 2) or exercised with progressive pump speed increases (visit 3). Ventilatory efficiency improved modestly on visits 2 and 3, but remained severely impaired. Oxygen uptake efficiency slope (OUES) was largely unchanged post-LVAD. Changes in end-tidal carbon dioxide during exercise were similar on all three visits. Conclusions HFrEF patients suffer from severe impairments in functional capacity as measured by oxygen uptake following CF-LVAD implantation, which does not improve with modulations in pump speed. CF-LVAD patients also suffer from severe impairments in ventilatory efficiency. These data suggest that CF-LVAD patients suffer from residual heart failure that is precipitated by submaximal exercise and not alleviated by modulations in pump speed.

New insights into resting and exertional right ventricular performance in the healthy heart through real-time pressure-volume analysis.

Despite growing interest in right ventricular form and function in diseased states, there is a paucity of data regarding characteristics of right ventricular function - namely contractile and lusitropic reserve, as well as ventricular-arterial coupling, in the healthy heart during rest, as well as submaximal and peak exercise. Pressure-volume analysis of the right ventricle, during invasive cardiopulmonary exercise testing, demonstrates that that the right heart has enormous contractile reserve, with a three- or fourfold increase in all metrics of contractility, as well as myocardial energy production and utilization. The healthy right ventricle also demonstrates marked augmentation in lusitropy, indicating that diastolic filling of the right heart is not passive. Rather, the right ventricle actively contributes to venous return during exercise, along with the muscle pump. Ventricular-arterial coupling is preserved during submaximal and peak exercise in the healthy heart. Knowledge of right ventricular (RV) function has lagged behind that of the left ventricle and historically, the RV has even been referred to as a 'passive conduit' of lesser importance than its left-sided counterpart. Pressure-volume (PV) analysis is the gold standard metric of assessing ventricular performance. We recruited nine healthy sedentary individuals free of any cardiopulmonary disease (42±12years, 78±11kg), who completed invasive cardiopulmonary exercise testing during upright ergometry, while using conductance catheters inserted into the RV to generate real-time PV loops. Data were obtained at rest, two submaximal levels of exercise below ventilatory threshold, to simulate real-world scenarios/activities of daily living, and maximal effort. Breath-by-breath oxygen uptake was determined by indirect calorimetry. During submaximal and peak exercise, there were significant increases in all metrics of systolic function by three- to fourfold, including cardiac output, preload recruitable stroke work, and maximum rate of pressure change in the ventricle (dP/dtmax ), as well as energy utilization as determined by stroke work and pressure-volume area. Similarly, the RV demonstrated a significant, threefold increase in lusitropic reserve throughout exercise. Ventricular-arterial coupling, defined by the quotient of end-systolic elastance and effective arterial elastance, was preserved throughout all stages of exercise. Maximal pressures increased significantly during exercise, while end-diastolic volumes were essentially unchanged. Overall, these findings demonstrate that the healthy RV is not merely a passive conduit, but actively participates in cardiopulmonary performance during exercise by accessing an enormous amount of contractile and lusitropic reserve, ensuring that VA coupling is preserved throughout all stages of exercise.

Determinants of Oxygen Uptake (VO2) among Patients with CF-LVADs

Characterize individual components of VO2 (cardiac output [Qc] and (A-V)O2 difference) at rest and during submaximal and peak exercise among CF-LVAD patients. Thirteen CF-LVAD participants (56±12 yrs, 12 male) and 9 healthy controls 42±12 yrs, 7 male) completed invasive cardiopulmonary exercise testing on a stationary upright cycle ergometer. Hemodynamic data and gas-exchange parameters were collected at rest, two submaximal levels of exercise below the ventilatory threshold, and peak workload. Swan-Ganz catheterization was performed to determine baseline hemodynamics. A conductance catheter was then used to calculate Qc at each stage of exercise. VO2was recorded on a breath-by-breath basis by indirect calorimetry. Blood pressure was continuously monitored by arterial line. Musculoskeletal performance was assessed by calculating the (A-V)O2 difference at each stage of exercise. Cohort characteristics and baseline demographics are demonstrated in table 1. Peak VO2 among CF-LVAD participants was severely reduced compared to healthy controls. When CF-LVAD participants were matched to healthy controls by workload according to VO2 quartiles, the CF-LVAD participants had a hypotensive response to exercise, as well as a blunted rise in Qc, with modest increases only from rest to submaximal exercise (figure 1). As a result, (A-V)O2 difference was higher for CF-LVAD participants than healthy controls at each VO2 quartile. Due to impairments in contractile reserve, CF-LVAD participants exhibit a greater (A-V)O2 difference than healthy individuals when exercising at similar workloads.

Guidance to the Interpretation of Cardiopulmonary Exercise Testing

Cardiorespiratory fitness has been established as an independent overall predictor of morbidity and mortality. However, patients' symptoms or stated levels of exercise intolerance correlate only poorly with resting functional and imaging tests. Cardiopulmonary exercise testing (CPET) is the gold standard for the integrative assessment of the cardiocirculatory, pulmonary and metabolic response to exercise and can help identify the source of exercise limitation, monitor disease progression, evaluate treatment responsiveness and inform about prognosis. Though CPET offers more valuable and pertinent information with slightly more expenditure of time compared to other methods even at submaximal exercise levels, it remains underutilized for various reasons such as costs, reimbursement and expertise. CPET can be seen as a complex, but not necessarily difficult tool. The objective of this review was to provide a description of the underlying principles of physiology, and an easy-to-follow guidance to indications, methodology, and interpretative strategies of CPET.

Laboratory Validation of Hexoskin Biometric Shirt at Rest, Submaximal Exercise, and Maximal Exercise While Riding a Stationary Bicycle.

Evaluate Hexoskin performance on a stationary bike against "gold standard" laboratory equipment and develop adjustment models for future use in field settings. Compared respiratory rate (RR), tidal volume (VT), minute ventilation (VE), and heart rate (HR) measured by the Hexoskin shirt to simultaneous spirometry and full 12-lead electrocardiogram during a laboratory based incremental exercise test on a stationary bicycle. Data from 17 participants demonstrated Hexoskin VT and VE had the best agreement in the submaximal exercise level (discrepancies less than or equal to 5.3%) with larger discrepancies observed at rest (less than or equal to 15.3%) and at maximal exercise level (less than or equal to 11.7%). The discrepancies for HR and RR were lower at all levels (less than 10%). Adjusting for sex and body weight allowed for a single VE algorithm across the entire range of effort (r = 0.89). These discrepancies are acceptable for field use in comparison to the ranges typical of bicycle commuting.

Oral versus Nasal Breathing during Moderate to High Intensity Submaximal Aerobic Exercise

Introduction: When comparing oral breathing versus nasal breathing, a greater volume of air can be transported through the oral passageway but nasal breathing may also have benefits at submaximal exercise intensities. Purpose: The purpose of this study was to determine breathing efficiency during increasing levels of submaximal aerobic exercise. Methods: Nineteen individuals (males N=9, females N=10) completed a test for maximal oxygen consumption (VO2max) and on separate days 4-min treadmill runs at increasing submaximal intensities (50%, 65%, and 80% of VO2max) under conditions of oral breathing or nasal breathing. Respiratory (respiration rate [RR], pulmonary ventilation [VE]), metabolic (oxygen consumption [VO2], carbon dioxide production [VCO2]) and efficiency measures (ventilatory equivalents for oxygen [Veq×O2-1] and carbon dioxide [Veq×CO2-1] were obtained. Data were analyzed utilizing a 2 (sex) x 2 (condition) x3 (intensity) repeated measures ANOVA with significance accepted at p≤0.05. Results: Significant interactions existed between breathing mode and intensity such that oral breathing resulted in greater RR, VE, VO2, and VCO2 at all three submaximal intensities (p&lt;.05). Veq×O2-1 and Veq×CO2-1 presented findings that nasal breathing was more efficient than oral breathing during the 65% and 80% VO2max intensities (p&lt;0.05). Conclusion: Based on this analysis, oral breathing provides greater respiratory and metabolic volumes during moderate and moderate-to-high submaximal exercise intensities, but may not translate to greater respiratory efficiency. However when all variables are considered together, it is likely that oral breathing represents the more efficient mode, particularly at higher exercise intensities.

Heterogeneity of blood flow and metabolism during exercise in patients with chronic obstructive pulmonary disease

The study investigated whether the capacity to regulate muscle blood flow (Q) relative to metabolic demand (VO2) is impaired in COPD. Using six NIRS optodes over the upper, middle and lower vastus lateralis in 6 patients, (FEV1:46±12%predicted) we recorded from each: a) Q by indocyanine green dye injection, b) VO2/Q ratios based on fractional tissue O2 saturation and c) VO2 as their product, during constant-load exercise (at 20%, 50% and 80% of peak capacity) in normoxia and hyperoxia (FIO2:1.0). At 50 and 80%, relative dispersion (RD) for Q, but not for VO2, was greater in normoxia (0.67±0.07 and 0.79±0.08, respectively) compared to hyperoxia (0.57±0.12 and 0.72±0.07, respectively). In both conditions, RD for VO2 and Q significantly increased throughout exercise; however, RD of VO2/Q ratio was minimal (normoxia: 0.12–0.08 vs hyperoxia: 0.13–0.09). Muscle Q and VO2 appear closely matched in COPD patients, indicating a minimal impact of heterogeneity on muscle oxygen availability at submaximal levels of exercise.

Effects of a Dietary Beetroot Juice Treatment on Systemic and Cerebral Haemodynamics- A Pilot Study.

Beetroot Juice (BJ) contains dietary nitrates that increase the blood Nitric Oxide (NO) level, decrease Blood Pressure (BP), increase athletic performance and improve cognitive functions but the mechanism remains unclear. Ultrasonographic measurement of middle cerebral artery blood flow velocity with computation of Cerebral Augmentation Index (CAIx) is a measure of the reflected flow signal, modulated by changes in cerebrovascular resistance and compliance. This pilot study tests the hypothesis that ingestion of an amount of BJ sufficient to raise the blood NO level two-to three-fold, decreases Transcranial Doppler (TCD) measured CAIx. Ten healthy young-adult African-American women were studied at two levels of submaximal exercise, 40% and 80% of their predetermined peak oxygen consumptions. The subjects ingested nitrate-free orange juice (OJ, control) and an isocaloric BJ beverage (1.5 mg/mL nitrate, 220 Cal), on different days, 1-2 weeks apart. The BJ treatment increased blood NO and decreased systolic BP at rest and at the two levels of exercise. The BJ treatment decreased CAIx only at the two levels of exercise (from 79 ± 2% to 62 ± 2% and from 80 ± 2% to 60 ± 3%, p<0.05). Exercise increased TCD-measured resistance and pulsatility indices (RIx, PIx) without changing AIx. The BJ treatment had no effect on RIx and PIx. These findings suggest that decreased CAIx associated with aerobic exercise reflects the change in cerebral haemodynamics resulting from dietary nitrate supplementation. Future studies should determine whether the BJ-induced decrement in CAIx is correlated with an improvement in brain function.

Aerobic Fitness Affects the Exercise Performance Responses to Nitrate Supplementation.

Dietary nitrate supplementation has been shown to reduce O2 cost of submaximal exercise, improve exercise tolerance, and enhance performance in moderately trained individuals. In contrast, data have been provided that elite athletes do not benefit from nitrate supplementation. The aim of this study was to evaluate the effects of short-term nitrate supplementation on endurance performance in subjects with different levels of aerobic fitness. Twenty-one subjects (mean age, 22.7 ± 1.8 yr) with different aerobic fitness level (V˙O2peak value ranging from 28.2 to 81.7 mL·kg·min) participated in a crossover double-blind placebo-controlled study. Subjects were tested after 6 d of supplementation with either 0.5 l per day of nitrate (5.5 mmol)-containing water (NITR) or nitrate-free water (PLA). Participants performed an incremental running test until exhaustion and four repetitions of 6-min submaximal (approximately 80% of gas exchange threshold) constant load exercise on a motorized treadmill. Moreover, subjects performed a 3-km running time trial on the field. After NITR, a negative correlation between reduction of O2 cost of submaximal exercise and individual aerobic fitness level was observed (r = 0.80; P < 0.0001). A significant inverse correlation was also found between aerobic fitness level and improvement in performance for 3-km time trial after NITR (r = 0.76; P < 0.0001). Additionally, subjects responded differently to dietary nitrate supplementation according to aerobic fitness level with higher-fit subjects showing a lower increase in plasma [NO3] (r = 0.86; P < 0.0001) and [NO2] (r = 0.75; P < 0.0001). The results of the present study suggest that the individual aerobic fitness level affects the ergogenic benefits induced by dietary nitrate supplementation. The optimal nitrate loading regimen required to elevate plasma [NO2] and to enhance performance in elite athletes is different from that of low-fit subjects and requires further studies.

The effect of lifelong exercise dose on cardiovascular function during exercise

An increased "dose" of endurance exercise training is associated with a greater maximal oxygen uptake (Vo2max), a larger left ventricular (LV) mass, and improved heart rate and blood pressure control. However, the effect of lifelong exercise dose on metabolic and hemodynamic response during exercise has not been previously examined. We performed a cross-sectional study on 101 (69 men) seniors (60 yr and older) focusing on lifelong exercise frequency as an index of exercise dose. These included 27 who had performed ≤ 2 exercise sessions/wk (sedentary), 25 who performed 2-3 sessions/wk (casual), 24 who performed 4-5 sessions/wk (committed) and 25 who performed ≥ 6 sessions/wk plus regular competitions (Masters athletes) over at least the last 25 yr. Oxygen uptake and hemodynamics [cardiac output, stroke volume (SV)] were collected at rest, two levels of steady-state submaximal exercise, and maximal exercise. Doppler ultrasound measures of LV diastolic filling were assessed at rest and during LV loading (saline infusion) to simulate increased LV filling. Body composition, total blood volume, and heart rate recovery after maximal exercise were also examined. Vo2max increased in a dose-dependent manner (P < 0.05). At maximal exercise, cardiac output and SV were largest in committed exercisers and Masters athletes (P < 0.05), while arteriovenous oxygen difference was greater in all trained groups (P < 0.05). At maximal exercise, effective arterial elastance, an index of ventricular-arterial coupling, was lower in committed exercisers and Masters athletes (P < 0.05). Doppler measures of LV filling were not enhanced at any condition, irrespective of lifelong exercise frequency. These data suggest that performing four or more weekly endurance exercise sessions over a lifetime results in significant gains in Vo2max, SV, and heart rate regulation during exercise; however, improved SV regulation during exercise is not coupled with favorable effects on LV filling, even when the heart is fully loaded.

Cardiorespiratory function associated with dietary nitrate supplementation

The advent of medical nutrition therapy and nutritional physiology affords the opportunity to link diet to specific cardiovascular mechanisms, suggesting novel treatments for cardiovascular disease. This study tests the hypothesis that beetroot juice increases the plasma nitric oxide (NO) concentration, which is associated with improvements in cardiorespiratory function at rest and during submaximal aerobic exercise. The subjects were 12 healthy, young adult, normotensive African-American females, with a body mass of 61 ± 2 kg, body fat of 28% ± 4%, and peak oxygen consumption of 26 ± 3 mL·kg(-1)·min(-1). The subjects were studied at rest and during cycle ergometer exercise at 40%, 60%, and 80% of peak oxygen consumption. Plasma NO concentration, respiratory quotient (RQ), minute ventilation, systolic and diastolic blood pressure (SBP and DBP), heart rate, and oxygen consumption were compared between isocaloric, isovolumetric placebo control orange juice and experimental beetroot juice treatments on separate days. The beetroot juice treatment increased plasma NO concentration and decreased oxygen consumption, SBP, and the heart rate-SBP product at rest and at 40%, 60%, and 80% of peak oxygen consumption in the absence of significant effects on RQ, minute ventilation, heart rate, and DBP. These findings suggest that, in healthy subjects, beetroot juice treatments increase plasma NO concentration and decrease cardiac afterload and myocardial oxygen demand at rest and during 3 submaximal levels of aerobic exercise. Future studies should determine the cellular and molecular mechanisms responsible for the improvement in cardiorespiratory function associated with dietary nitrate supplementation and whether they translate into better cardiovascular function and exercise tolerance in individuals with a compromised cardiovascular system.

The physiological basis of rehabilitation in chronic heart and lung disease

Cardiopulmonary rehabilitation is recognized as a core component of management of individuals with congestive heart failure (CHF) or chronic obstructive pulmonary disease (COPD) that is designed to improve their physical and psychosocial condition without impacting on the primary organ impairment. This has lead the scientific community increasingly to believe that the main effects of cardiopulmonary rehabilitative exercise training are focused on skeletal muscles that are regarded as dysfunctional in both CHF and COPD. Accordingly, following completion of a cardiopulmonary rehabilitative exercise training program there are important peripheral muscular adaptations in both disease entities, namely increased capillary density, blood flow, mitochondrial volume density, fiber size, distribution of slow twitch fibers, and decreased lactic acidosis and vascular resistance. Decreased lactic acidosis at a given level of submaximal exercise not only offsets the occurrence of peripheral muscle fatigue, leading to muscle task failure and muscle discomfort, but also concurrently mitigates the additional burden on the respiratory muscles caused by the increased respiratory drive, thereby reducing dyspnea sensations. Furthermore in patients with COPD, exercise training reduces the degree of dynamic lung hyperinflation leading to improved arterial oxygen content and central hemodynamic responses, thus increasing systemic muscle oxygen availability. In patients with CHF, exercise training has beneficial direct and reflex sympathoinhibitory effects and favorable effects on normalization of neurohumoral excitation. These physiological benefits apply to all COPD and CHF patients independently of the degree of disease severity and are associated with improved exercise tolerance, functional capacity, and quality of life.

Comparison of intra-arterial and manual auscultation of blood pressure during submaximal exercise in humans

Blood pressure (BP) is a key measure of cardiovascular function, and accurate measurement is important to ensure proper clinical evaluation, diagnosis, and treatment. We compared intra-arterial (direct) and cuff auscultation (manual) measurement techniques at rest and during 2 levels of submaximal constant-load exercise (9 min at 40% and 75% maximum watts). Sixty-four adults (aged 29.0 ± 0.7 years; 48% male; height, 173.7 ± 1.2 cm; mass, 73.0 ± 1.7 kg; body mass index, 24.1 ± 0.4 kg·m(-2); body surface area, 1.87 ± 0.03 m(2)) participated in the study. At rest, low, and moderate intensity, direct measurement demonstrated higher systolic BP (SBP) and diastolic BP (DBP) (bias for SBP: 22, 31, and 27 mm Hg and for DBP: 5, 7, and 17 mm Hg; rest, low-, and moderate-intensity, respectively; p < 0.01). At rest, the correlation and agreement between the 2 methods was modest (SBP: r = 0.56, bias = +22.1 mm Hg; DBP: r = 0.53, bias = +4.9 mm Hg; p < 0.001). There was good correlation and agreement with SBP at low and moderate intensity; however, DBP demonstrated a weaker relationship (SBP: r = 0.74 and 0.74, bias = +30.2 and +26.8 mm Hg; DBP: r = 0.39 and 0.28, bias = +7.1 and +13.4 mm Hg; for low and moderate intensity, respectively; p < 0.001). Further, manual measurement demonstrated a greater slope from rest to moderate exercise for the relationship between pulse pressure (PP) and cardiac output (13.6 ± 0.4 vs 12.3 ± 0.4, p = 0.03). As exercise intensity increases, manual DBP tends to bias low compared with direct DBP, which, when combined with parallel increases in SBP, leads to no differences in PP between methods at moderate exercise. Because PP is used to calculate other cardiovascular parameters (mean arterial pressure, systemic vascular resistance), measurement technique and exercise intensity should be considered when using cardiovascular variables as outcome measures.

Exercise efficiency is reduced by mitochondrial uncoupling in the elderly

A reduction in exercise efficiency accompanies ageing in humans. Here we evaluated the impact of changes in the contractile-coupling and mitochondrial-coupling efficiencies on the reduction in exercise efficiency in the elderly. Nine adult (mean, 38.8 years old) and 40 elderly subjects (mean, 68.8 years old) performed a cycle ergometer test to measure O2 uptake and leg power output up to the aerobic limit ( ). Reduced leg power output per unit O2 uptake was reflected in a drop in delta efficiency (εD) from 0.27 ± 0.01 (mean ± SEM) in adults to 0.22 ± 0.01 in the elderly group. Similar declines with age were apparent for both the leg power output at and the ATP generation capacity (ATPmax) determined in vivo using (31)P magnetic resonance spectroscopy. These similar declines resulted in unchanged contractile-coupling efficiency values (εC) in the adult (0.50 ± 0.05) versus the elderly group (0.58 ± 0.04) and agreed with independent measures of muscle contractile-coupling efficiency in human quadriceps (0.5). The mitochondrial-coupling efficiency calculated from the ratio of delta to contractile-coupling efficiencies in the adults (εD/εC = 0.58 ± 0.08) corresponded to values for well-coupled mitochondria (0.6); however, εD/εC was significantly lower in the elderly subjects (0.44 ± 0.03). Conversion of ATPmax per mitochondrial volume (ATPmax/Vv[mt,f]) reported in these groups into thermodynamic units confirmed this drop in mitochondrial-coupling efficiency from 0.57 ± 0.08 in adults to 0.41 ± 0.03 in elderly subjects. Thus, two independent methods revealed that reduced mitochondrial-coupling efficiency was a key part of the drop in exercise efficiency in these elderly subjects and may be an important part of the loss of exercise performance with age.

Noninvasive Cardiac Output Measurement at Rest and During Exercise in Pediatric Patients After Interventional or Surgical Atrial Septal Defect Closure

In the majority of patients, secundum atrial septal defects (ASDs) are treated interventionally or surgically, before the onset of clinical symptoms, between 3 and 6 years of age. Because right-ventricular dimensions usually normalize after ASD closure, it has been assumed that cardiac function and exercise performance also normalize at long-term follow-up. The aim of our study was to determine cardiac index (CI) at rest and during exercise at medium-term follow-up of children who had undergone surgical or interventional closure of ASD because no such reports have been published thus far. Seventeen patients (age range 8.8-17.3 years) who underwent surgical correction were included together with 17 subjects who received an interventional procedure with Amplatzer and Helex occluders (age range 12.2-17.3 years). The study was performed after a median interval of 8.6 years (range 6.5-11.6) after the procedure. Twelve healthy children of comparable age served as controls. CI measurements were performed based on the inert gas-rebreathing method with the Innocor system. For exercise testing, the standard treadmill protocol of the German Society of Pediatric Cardiology was used. CI, stroke volume (SV), and heart rate (HR) were determined at rest and at two standardized submaximal exercise levels (levels 3 and 6). CI increased in all subjects under exercise conditions. Neither SV nor HR displayed significant differences between the three groups either at rest or under exercise conditions. Although HR increased continuously, no increase of indexed SV occurred beyond level 3. Noninvasive determination of CI at rest and during exercise with the IGR method is feasible in the pediatric age group. At medium-term follow-up, we found no significant differences between patients who underwent surgical or interventional ASD closure compared with normal controls.