Peak Exercise Cardiac Power Output Research Articles

Impact of age and sex on heart rate variability and cardiometabolic function in healthy adults

Heart rate variability (HRV) is a non-invasive measure of cardiac autonomic function. A clearer understanding as to whether resting autonomic function represented by HRV could be associated with changes in peak exercise cardiac function remains unanswered. This study evaluated the effect of age and sex on HRV, cardiometabolic function, and determined the correlation between HRV and cardiac function in healthy individuals. Sixty-eight participants (age range: 19–78 years old, females, n = 28) were recruited. Participants were stratified according to age (younger (<40 years old, n = 43, females, n = 17) and older age groups (>55 years old, n = 25, females, n = 11). Firstly, HRV was measured using non-invasive impedance cardiography method (TaskForce, CNSystems, Graz, Austria) and recorded at rest (supine position) for 30 min. HRV measures included: low frequency (LF) power, high frequency (HF) power (both normalised (nu) and absolute units (ms2)) and LF/HF ratio. Participants then completed a progressive cardiorespiratory exercise test using a semi-recumbent cycle ergometer (Corival, Lode, Groningen, Netherlands) with simultaneous gas exchange measurements (Metalyzer 3B, Cortex, Leipzig, Germany). Cardiac function was represented by peak exercise cardiac power output index (CPO). After controlling for body mass index and physical activity, males had significantly higher mean vales of RR interval than females (males = 1043 ± 165; females = 952 ± 128 ms, p = 0.02). There was no significant main effect of age, sex or their interaction on any of the other HRV measures. In younger and older females, resting RR interval had a significant relationship with peak exercise CPO (young females: r = 0.54, p < 0.05; old females: r = 0.81, p < 0.01). There was also a significant relationship between resting HF power and peak exercise CPO in younger females (r = 0.70, p < 0.01). HRV was not influenced by age but RR interval was associated with peak exercise CPO in females regardless of age, whilst HF power was significantly associated with CPO in younger females only.

Haemodynamic determinants of quality of life in chronic heart failure

BackgroundHeart failure patients demonstrate reduced functional capacity, hemodynamic function, and quality of life (QOL) which are associated with high mortality and morbidity rate. The aim of the present study was to assess the relationship between functional capacity, hemodynamic response to exercise and QOL in chronic heart failure.MethodsA single-centre prospective study recruited 42 chronic heart failure patients (11 females, mean age 60 ± 10 years) with reduced left ventricular ejection fraction (LVEF = 23 ± 7%). All participants completed a maximal graded cardiopulmonary exercise test with non-invasive hemodynamic (bioreactance) monitoring. QOL was assessed using Minnesota Living with Heart Failure Questionnaire.ResultsThe average value of QOL score was 40 ± 23. There was a significant negative relationship between the QOL and peak O2 consumption (r = − 0.50, p ≤ 0.01). No significant relationship between the QOL and selected exercise hemodynamic measures was found, including peak exercise cardiac power output (r = 0.15, p = 0.34), cardiac output (r = 0.22, p = 0.15), and mean arterial blood pressure (r = − 0.08, p = 0.60).ConclusionPeak O2 consumption, but not hemodynamic response to exercise, is a significant determinant of QOL in chronic heart failure patients.

Association between heart rate variability and haemodynamic response to exercise in chronic heart failure

Objectives. Heart rate variability (HRV) and haemodynamic response to exercise (i.e. peak cardiac power output) are strong predictors of mortality in heart failure. The present study assessed the relationship between measures of HRV and peak cardiac power output. Design. In a prospective observational study of 33 patients (age 54 ± 16 years) with chronic heart failure with reduced left ventricular ejection fraction (29 ± 11%), measures of the HRV (i.e. R-R interval and standard deviation of normal R-R intervals, SDNN) were recorded in a supine position. All patients underwent maximal graded cardiopulmonary exercise testing with non-invasive (inert gas rebreathing) cardiac output assessment. Cardiac power output, expressed in watts, was calculated as the product of cardiac output and mean arterial blood pressure. Results. The mean RR and SDNN were 837 ± 166 and 96 ± 29 ms, peak exercise cardiac power output 2.28 ± 0.85 watts, cardiac output 10.34 ± 3.14 L/min, mean arterial blood pressure 98 ± 14 mmHg, stroke volume 91.43 ± 40.77 mL/beat, and oxygen consumption 19.0 ± 5.6 mL/kg/min. There was a significant but only moderate relationship between the RR interval and peak exercise cardiac power output (r = 0.43, p = .013), cardiac output (r = 0.35, p = .047), and mean arterial blood pressure (r = 0.45, p = .009). The SDNN correlated with peak cardiac power output (r = 0.42, p = .016), mean arterial blood arterial (r = 0.41, p = .019), and stroke volume (r = 0.35, p = .043). Conclusions. Moderate strength of the relationship between measures of HRV and cardiac response to exercise suggests that cardiac autonomic function is not good indicator of overall function and pumping capability of the heart in chronic heart failure.

Left Ventricular Assist Device as a Bridge to Recovery for Patients With Advanced Heart Failure

BackgroundLeft ventricular assist devices (LVADs) have been used as an effective therapeutic option in patients with advanced heart failure, either as a bridge to transplantation, as destination therapy, or in some patients, as a bridge to recovery. ObjectivesThis study evaluated whether patients undergoing an LVAD bridge-to-recovery protocol can achieve cardiac and physical functional capacities equivalent to those of healthy controls. MethodsFifty-eight male patients—18 implanted with a continuous-flow LVAD, 16 patients with LVAD explanted (recovered patients), and 24 heart transplant candidates (HTx)—and 97 healthy controls performed a maximal graded cardiopulmonary exercise test with continuous measurements of respiratory gas exchange and noninvasive (rebreathing) hemodynamic data. Cardiac function was represented by peak exercise cardiac power output (mean arterial blood pressure × cardiac output) and functional capacity by peak exercise O2 consumption. ResultsAll patients demonstrated a significant exertional effort as demonstrated with the mean peak exercise respiratory exchange ratio >1.10. Peak exercise cardiac power output was significantly higher in healthy controls and explanted LVAD patients compared with other patients (healthy 5.35 ± 0.95 W; explanted 3.45 ± 0.72 W; LVAD implanted 2.37 ± 0.68 W; and HTx 1.31 ± 0.31 W; p < 0.05), as was peak O2 consumption (healthy 36.4 ± 10.3 ml/kg/min; explanted 29.8 ± 5.9 ml/kg/min; implanted 20.5 ± 4.3 ml/kg/min; and HTx 12.0 ± 2.2 ml/kg/min; p < 0.05). In the LVAD explanted group, 38% of the patients achieved peak cardiac power output and 69% achieved peak O2 consumption within the ranges of healthy controls. ConclusionsThe authors have shown that a substantial number of patients who recovered sufficiently to allow explantation of their LVAD can even achieve cardiac and physical functional capacities nearly equivalent to those of healthy controls.

The effect of age on the relationship between cardiac and vascular function

Age-related changes in cardiac and vascular function are associated with increased risk of cardiovascular mortality and morbidity. The aim of the present study was to define the effect of age on the relationship between cardiac and vascular function. Haemodynamic and gas exchange measurements were performed at rest and peak exercise in healthy individuals. Augmentation index was measured at rest. Cardiac power output, a measure of overall cardiac function, was calculated as the product of cardiac output and mean arterial blood pressure. Augmentation index was significantly higher in older than younger participants (27.7±10.1 vs. 2.5±10.1%, P<0.01). Older people demonstrated significantly higher stroke volume and mean arterial blood pressure (P<0.05), but lower heart rate (145±13 vs. 172±10 beats/min, P<0.01) and peak oxygen consumption (22.5±5.2 vs. 41.2±8.4ml/kg/min, P<0.01). There was a significant negative relationship between augmentation index and peak exercise cardiac power output (r=−0.73, P=0.02) and cardiac output (r=−0.69, P=0.03) in older participants. Older people maintain maximal cardiac function due to increased stroke volume. Vascular function is a strong predictor of overall cardiac function in older but in not younger people.

36 Direct Measurement of Cardiac Compensation in Valvular Heart Disease

<h3>Purpose</h3> The natural history of valvular heart disease (VHD) suggests that the heart initially adapts to compensate for valve lesions and thereby maintain physiological function. When these compensatory mechanisms become exhausted, cardiac decompensation commences. We tested the hypothesis that all VHD patients with normal exercise capacity are in the compensatory phase with no symptoms and normal cardiac reserve. <h3>Methods</h3> Unselected consecutive male patients with VHD performed cardiopulmonary exercise (CPX) testing with non-invasive central haemodynamic measurements during symptom-limited treadmill exercise. Exercise capacity was represented by peak oxygen consumption (VO_2max) and cardiac pumping capability by peak exercise cardiac power output (CPO_max). Data are given as mean±SD. <h3>Results</h3> Of the entire VHD patient cohort (n = 215), 81.4% (n = 175) had VO_2max which were within or above the reference range of healthy male sedentary controls (n = 101). This is shown in Figure 1A where individual patient VO_2max is expressed as a percentage of the average VO_2max of age- and sex-matched controls. These 175 patients with normal VO_2max had a mean age of 63.1 ± 14.0 years, and consisted of 98 (56%) who were asymptomatic (NYHA class I) and 77 (44%) who were discordantly symptomatic in NYHA II+ (.001). As shown in Figure 1B, 117 patients (66.9%) had CPO_max within the normal range, of whom 80 (45.7%) were asymptomatic, but 37 (21.1%) were in NYHA II+ despite having normal VO_2max and CPO_max (.001). Conversely, 58 (33.1%) had CPO_max below the normal range, and yet 18 (10.3%) of these were discordantly still in NYHA I (P &lt; 0.001). These patients were classified asymptomatic by their responsible clinicians but our results revealed they had early, objective evidence of cardiac decompensation. <h3>Conclusions</h3> This investigation demonstrates that it is now possible to directly and objectively measure whether patients are in the compensated or decompensated phases of VHD. There were discrepancies between subjective symptomatic statuses and objectively measured cardiac and physical functional statuses. The possibility to determine whether patients are in the compensatory phase or not, might help in the management of difficult VHD cases.

Cardiac power output and its response to exercise in athletes and non‐athletes

Cardiac power output (CPO) is an integrative measure of overall cardiac function as it accounts for both, flow- and pressure-generating capacities of the heart. The purpose of the present study was twofold: (i) to assess cardiac power output and its response to exercise in athletes and non-athletes and (ii) to determine the relationship between cardiac power output and reserve and selected measures of cardiac function and structure. Twenty male athletes and 32 age- and gender-matched healthy sedentary controls participated in this study. CPO was calculated as the product of cardiac output and mean arterial pressure, expressed in watts. Measures of hemodynamic status, cardiac structure and pumping capability were assessed by echocardiography. CPO was assessed at rest and after peak bicycle exercise. At rest, the two groups had similar values of cardiac power output (1·08±0·2W versus 1·1±0·24W, P>0·05), but the athletes demonstrated lower systolic blood pressure (109·5±6·2mmHg versus 117·2±8·2mmHg, P<0·05) and thicker posterior wall of the left ventricle (9·8±1mm versus 9±1·1mm, P<0·05). Peak CPO was higher in athletes (5·87±0·75W versus 5·4±0·69W, P<0·05) as was cardiac reserve (4·92±0·66W versus 4·26±0·61W, P<0·05), respectively. Peak exercise CPO and reserve were only moderately correlated with end-diastolic volume (r=0·54; r=0·46, P<0·05) and end-diastolic left ventricular internal diameter (r=0·48; r=0·42, P<0·05), respectively. Athletes demonstrated greater maximal cardiac pumping capability and reserve than non-athletes. The study provides new evidence that resting measures of cardiac structure and function need to be considered with caution in interpretation of maximal cardiac performance.

Relationship between peak cardiac pumping capability and indices of cardio-respiratory fitness in healthy individuals.

Cardiac power output (CPO) is a unique and direct measure of overall cardiac function (i.e. cardiac pumping capability) that integrates both flow- and pressure-generating capacities of the heart. The present study assessed the relationship between peak exercise CPO and selected indices of cardio-respiratory fitness. Thirty-seven healthy adults (23 men and 14 women) performed an incremental exercise test to volitional fatigue using the Bruce protocol with gas exchange and ventilatory measurements. Following a 40-min recovery, the subjects performed a constant maximum workload exercise test at or above 95% of maximal oxygen consumption. Cardiac output was measured using the exponential CO(2) rebreathing method. The CPO, expressed in W, was calculated as the product of the mean arterial blood pressure and cardiac output. At peak exercise, CPO was well correlated with cardiac output (r=0·92, P<0·01), stroke volume (r=0·90, P<0·01) and peak oxygen consumption (r=0·77, P<0·01). The coefficient of correlation was moderate between CPO and anaerobic threshold (r=0·47, P<0·01), oxygen pulse (r=0·57, P<0·01), minute ventilation (r=0·53, P<0·01) and carbon dioxide production (r=0·56, P<0·01). Small but significant relationship was found between peak CPO and peak heart rate (r=0·23, P<0·05). These findings suggest that only peak cardiac output and stroke volume truly reflect CPO. Other indices of cardio-respiratory fitness such as oxygen consumption, anaerobic threshold, oxygen pulse, minute ventilation, carbon dioxide production and heart rate should not be used as surrogates for overall cardiac function and pumping capability of the heart.

Discrepancy Between Cardiac and Physical Functional Reserves in Stroke

Understanding the physiological limitations to exercise after stroke will assist the development of targeted therapies to improve everyday function. This study defines (1) whether exercise capacity is limited by the cardiovascular system (oxygen supply) or skeletal muscles (oxygen utilization); and (2) cardiac function and pumping capability in people with stroke. Twenty-eight male participants with mild ischemic stroke (70 ± 6 years of age, 18 ± 20 months poststroke) and 25 male, age-matched healthy control subjects performed a graded cardiopulmonary exercise test with gas exchange and noninvasive hemodynamic measurements. Maximal oxygen extraction was calculated as the ratio between peak oxygen consumption and peak cardiac output. Cardiac function and pumping capability were assessed by peak exercise cardiac power output (expressed in watts) and cardiac output. Peak oxygen consumption (18.4 ± 4.6 versus 26.8 ± 5.5 mL/kg/min, P<0.01) and arterial-venous O(2) difference (9.3 ± 2.5 versus 12.6 ± 1.9 mlO(2)/100 mL of blood, P<0.01) were both reduced in stroke participants compared with healthy control subjects. In contrast, peak exercise cardiac power output (4.79 ± 0.79 versus 4.51 ± 0.96 W, P=0.49), cardiac output (16.4 ± 3.1 versus 17.1±2.5 L/min, P=0.41), and the pressure-generating capacity of the heart (127±11 versus 125 ± 14 mm Hg, P=0.97) were similar between stroke participants and healthy control subjects. The ability of skeletal muscles to extract oxygen is diminished after stroke. However, cardiac function and pumping capability are maintained. Appropriate therapies targeting muscle oxygen uptake such as exercise rehabilitation may improve exercise capacity after stroke.

The impact of acute reduction of continuous-flow left ventricular assist device support on cardiac and exercise performance

BackgroundThe use of the HeartMate II continuous-flow left ventricular assist device (LVAD) improves survival, quality of life and functional capacity of patients with advanced heart failure. However, no study so...

002 Can non-pulsatile continuous-flow left ventricular assist devices confer physiologically desirable cardiac and physical functional benefits during peak exercise?

<h3>Introduction</h3> Left ventricular assist devices (LVADs) have been used as an effective therapeutic option in patients with advanced heart failure either as a bridge to transplantation, as destination therapy or as a bridge to recovery. Most recently it has been shown that the use of continuous-flow LVAD (HeartMate II) improves the rate of survival, quality of life, and functional capacity of patients as compared with the pulsatile-flow LVAD. To date, no study has reported how well HeartMate II can improve organ function and patients9 exercise ability. The present project aimed to assess cardiac and exercise performance of patients implanted with continuous-flow LVADs under two conditions: (i) optimal device support, and (ii) reduced device support. These results were compared with those of LVAD explanted (recovered) patients, heart transplant candidates and healthy controls. <h3>Methods</h3> Fifty-eight male patients, 18 implanted with a HeartMate II LVAD, 16 LVAD explanted patients and 24 heart transplant candidates (HTx) and 101 healthy controls performed graded cardiopulmonary exercise test with respiratory gas exchange and noninvasive (rebreathing) haemodynamic measurements. Twelve of the 18 LVAD implanted patients performed an additional cardiopulmonary exercise test with reduced LVAD support (pump speed reduced from optimal 9000–9600 revs/min to 6000 revs/min). <h3>Results</h3> At lower HeartMate II support, peak exercise cardiac power output was 39% lower (1.42±0.41 vs 2.31±0.50 W; p&lt;0.05), peak cardiac output 30% lower (8.6±2.31 vs 12.2±1.55 l/min; p&lt;0.05), and mean blood pressure 13% lower (74±7 vs 85±12 vs mmHg; p&lt;0.05). Exercise capacity was also diminished with 23% lower peak oxygen consumption (14.1±5.3 vs 18.2±4.5 ml/kg/min; p&lt;0.05) and 18% shorter exercise duration (516±179 vs 628±142 s; p&lt;0.05). Peak cardiac power output was significantly higher in the LVAD explanted than in the HTx and the LVAD implanted patients (HTx: 1.31±0.31 W; implanted: 2.31±0.50 W; explanted: 3.39±0.61 W; p&lt;0.01) as was peak cardiac output (HTx: 8.0±1.5; implanted: 12.2±1.55 explanted, 14.6±2.9 l/min; p&lt;0.01). Peak oxygen consumption was higher in the LVAD explanted than the HTx and the implanted patients (HTx, 12.5±2.5; implanted, 18.2±4.5; explanted, 28.2±5.0 ml/kg/min; p&lt;0.05) as was oxygen consumption at anaerobic threshold (p&lt;0.05). In the explanted cohort, 38% achieved peak cardiac power output and 69% peak oxygen consumption within the ranges of healthy controls. <h3>Conclusion</h3> We have shown for the first time that complementary to reported prognostic benefits, non-pulsatile continuous-flow LVAD pumps can confer cardiac functional benefits to patients with end-stage heart failure to derive improved exercise capacity, while those who recovered sufficiently to allow explantation of LVADs can even achieve cardiac and physical functional capacities nearly equivalent to those of healthy controls.

Efficacy of lifestyle intervention on peak exercise cardiac power output and reserve in premenopausal obese females: A randomised pilot study

Background Clinically obese women have a two-fold increased risk for the development of heart failure. Among younger premenopausal females, obesity has been associated with cardiac remodelling and impaired resting systolic and diastolic function. However, few studies have evaluated cardiorespiratory and cardiac responses to maximal exertion among obese premenopausal females. Design A randomised pilot study was conducted to investigate the effects of a 3-month lifestyle intervention programme on weight management and maximal cardiorespiratory function in healthy clinically obese premenopausal females. Within this study, thirteen selected participants performed both graded and single-stage V.˙O 2peak exercise tests, the latter integrating the non-invasive measurement of cardiac output (CO 2 rebreathing method), peak cardiac power output (CPO peak) and physiological cardiac reserve. Six participants were randomly assigned to 3-months of lifestyle intervention and 7 served as waiting list controls. Results Trends were evident for improvement in the traditional weight-adjusted V.˙O 2peak (ml kg − 1 min − 1 ) measure among the lifestyle group compared with a modest reduction in the controls (test for interaction, P = 0.059). CPO peak showed a modest, non-significant increase in the lifestyle group and tended to decrease in the control (test for interaction, P = 0.166). Physiological cardiac reserve also improved (2.63 ± 0.54 to 2.92 ± 0.43 W) in the lifestyle group and declined (2.69 ± 0.24 to 2.56 ± 0.28 W) in the control group (test for interaction, P = 0.091). V.˙O 2peak (ml min − 1 ) increased non-significantly on graded maximal exercise in the lifestyle group compared with control. The larger within group changes in the lifestyle group failed to achieve statistical significance (test for interaction, P = 0.131). Conclusions In the absence of significant weight reduction, clinically obese premenopausal females derived modest benefits in maximal cardiorespiratory capacity and cardiac functional reserve from a 3-month lifestyle intervention incorporating supervised exercise.

How do different indicators of cardiac pump function impact upon the long-term prognosis of patients with chronic heart failure?

The prognosis of patients with mild-moderate chronic heart failure (CHF) over a long-term follow-up period is more difficult to predict than for patients with more severe CHF in the short term. This study assessed the prognostic value of various indicators of cardiac pump function to gain insight into how different aspects of organ function impact upon prognosis. Unselected, consecutive patients with CHF (n = 219, 166 men, mean [+/-SD] age 56 +/- 13 years) who underwent symptom limited cardiopulmonary treadmill exercise testing with noninvasive estimation of cardiac output using carbon dioxide rebreathing techniques were followed up for a median period of 8.6 +/- 1.0 years in survivors. Cardiac power output (CPO) was calculated from the product of cardiac output and mean arterial pressure and cardiac reserve was estimated by subtracting resting from peak exercise CPO or cardiac output (CO). All-cause mortality was 36% (78 deaths). Survivors had a significantly greater cardiac pumping reserve with the greatest difference seen in CPO reserve (+57%) and CO reserve (+49%) (both P < .001). Although various direct and indirect indicators of cardiac function were predictive of outcome on univariate analyses, multivariate analysis using the Cox proportional hazards model identified CO reserve to be the independent variable predictive of all-cause mortality, with a hazard ratio (95% CI) of 0.682 (0.612-0.757, P < .001) for each L/min increase in cardiac output reserve. Survival at 10 years in patients with tertiles of good, moderate, or poor cardiac output reserve was 89%, 63%, and 36.1%, respectively (P < .001). In this long-term follow-up study involving a cohort of unselected ambulatory patients with mild-moderate CHF, cardiac pumping reserve measured noninvasively by cardiopulmonary exercise testing was found to be the strongest independent predictor of prognosis.

210 NYHA class improvement is independent of left ventricular ejection fraction changes in patients treated with resynchronisation therapy for severe congestive heart failure

Results: After CRT implantation, major indicators of prognosis: peak exercise cardiac power output (pCPO), oxygen consumption (pVO2), exercise duration (ExDur) and ventilatory efficiency (VE/VCO2 slope) were significantly improved (see Table). Cardiac pressure-generating capacity (systolic BP at peak exercise, pSBP), flow-generating capacity (peak cardiac output, pCO) and cardiac pumping reserve (CResrv) also increased significantly with CRT. A significant improvement was also seen in NYHA functional class (3.09+-0.3 to 2.554-0.69, P=0.03) and SF-36 score (44.83=t=18.17 to 69.83=t=10.57, P=0.03).

Peak exercise cardiac power output; a direct indicator of cardiac function strongly predictive of prognosis in chronic heart failure.

This study assessed the prognostic value of peak cardiac power output, measured non-invasively during maximal cardiopulmonary exercise testing, against other exercise-derived haemodynamic variables in patients with chronic congestive heart failure. Two hundred and nineteen unselected, consecutive patients with congestive heart failure (166 men, mean (+/-SD) age of 56+/-13 years) who underwent maximal symptom limited cardiopulmonary treadmill exercise testing with non-invasive estimation of cardiac output using carbon dioxide re-breathing techniques, were followed-up for a mean period of 4.64 (4.47--4.82, 95% CI) years. Cardiac power output was calculated from the product of cardiac output and mean arterial blood pressure. All cause mortality was 12.3% (27 deaths). Peak and resting cardiac power output, peak mean arterial blood pressure, peak and resting cardiac output and peak VO(2)were all predictive of outcome on univariate analyses. Peak cardiac power output, either entered continuously or categorically with a cut-off value of 1.96 watts, was the only independent predictor of mortality (P=0.0004 for values < or >1.96 watts and P=0.001 for continuous values) using multivariate analysis. A relative risk ratio of 5.08 (1.94-13.3, 95% CI) was obtained for a cardiac power output <1.96 watts. Peak cardiac power output is an independent predictor of mortality that can be measured non-invasively using cardiopulmonary exercise testing. It can give further prognostic power to a peak VO(2)in the assessment of patients with congestive heart failure.