Oxygen uptake kinetics in chronic heart failure: clinical and physiological aspects

Skeletal muscle atrophy, regeneration, and dysfunction in heart failure: Impact of exercise training

This review highlights some established and some more contemporary mechanisms responsible for heart failure (HF)-induced skeletal muscle wasting and weakness. We first describe the effects of HF on the relationship between protein synthesis and degradation rates, which determine muscle mass, the involvement of the satellite cells for continual muscle regeneration, and changes in myofiber calcium homeostasis linked to contractile dysfunction. We then highlight key mechanistic effects of both aerobic and resistance exercise training on skeletal muscle in HF and outline its application as a beneficial treatment. Overall, HF causes multiple impairments related to autophagy, anabolic-catabolic signaling, satellite cell proliferation, and calcium homeostasis, which together promote fiber atrophy, contractile dysfunction, and impaired regeneration. Although both wasting and weakness are partly rescued by aerobic and resistance exercise training in HF, the effects of satellite cell dynamics remain poorly explored.

Limited cardiopulmonary capacity in patients with liver cirrhosis when compared to healthy subjects

OBJECTIVES

The present study compared cardiorespiratory capacity between cirrhotic patients and healthy subjects.

METHODS

Nineteen cirrhotic patients and 19 healthy subjects, paired by age and gender, participated in the study. Volunteers performed an incremental cardiopulmonary test with a ramp protocol, a ventilatory and metabolic variables were obtained and analyzed. The recovery was analyzed by calculating the time needed for 50% of oxygen consumption (VO2) recovery to occur as the median between the peak of the exercise and the end of recovery on the VO2 curve (T1/2). The VE/VCO2 slope were performed by the linear regression of ventilation (VE) and carbon dioxide production (VCO2) data.

RESULTS

During resting condition, cirrhotic patients presented significantly higher levels of VO2 compared to healthy subjects. The VE/ VO2 and VE/ VCO2 values were significantly higher in the control group at the anaerobic threshold and at the peak of the test compared to cirrhotic patients. Time under effort was significantly higher for healthy subjects.

CONCLUSIONS

Based on these findings, it is possible to conclude that liver cirrhosis can compromise the patients' quality of life, mainly by inducing metabolic alterations which can impair functional capacity and lead to a sedentary lifestyle.

Proportional Assist Ventilation Improves Leg Muscle Reoxygenation After Exercise in Heart Failure With Reduced Ejection Fraction

Background

Respiratory muscle unloading through proportional assist ventilation (PAV) may enhance leg oxygen delivery, thereby speeding off-exercise oxygen uptake ( V . ⁢ O 2 ) kinetics in patients with heart failure with reduced left ventricular ejection fraction (HFrEF).

Methods

Ten male patients (HFrEF = 26 ± 9%, age 50 ± 13 years, and body mass index 25 ± 3 kg m²) underwent two constant work rate tests at 80% peak of maximal cardiopulmonary exercise test to tolerance under PAV and sham ventilation. Post-exercise kinetics of V . ⁢ O 2 , vastus lateralis deoxyhemoglobin ([deoxy-Hb + Mb]) by near-infrared spectroscopy, and cardiac output (Q _T ) by impedance cardiography were assessed.

Results

PAV prolonged exercise tolerance compared with sham (587 ± 390 s vs. 444 ± 296 s, respectively; p = 0.01). PAV significantly accelerated V . ⁢ O 2 recovery (τ = 56 ± 22 s vs. 77 ± 42 s; p < 0.05), being associated with a faster decline in Δ[deoxy-Hb + Mb] and Q _T compared with sham (τ = 31 ± 19 s vs. 42 ± 22 s and 39 ± 22 s vs. 78 ± 46 s, p < 0.05). Faster off-exercise decrease in Q _T with PAV was related to longer exercise duration (r = -0.76; p < 0.05).

Conclusion

PAV accelerates the recovery of central hemodynamics and muscle oxygenation in HFrEF. These beneficial effects might prove useful to improve the tolerance to repeated exercise during cardiac rehabilitation.

Noninvasive Ventilation Accelerates Oxygen Uptake Recovery Kinetics in Patients With Combined Heart Failure and Chronic Obstructive Pulmonary Disease

PURPOSE

Oxygen uptake (V˙o2) recovery kinetics appears to have considerable value in the assessment of functional capacity in both heart failure (HF) and chronic obstructive pulmonary disease (COPD). Noninvasive positive pressure ventilation (NIPPV) may benefit cardiopulmonary interactions during exercise. However, assessment during the exercise recovery phase is unclear. The purpose of this investigation was to explore the effects of NIPPV on V˙o2, heart rate, and cardiac output recovery kinetics from high-intensity constant-load exercise (CLE) in patients with coexisting HF and COPD.

METHODS

Nineteen males (10 HF/9 age- and left ventricular ejection fraction-matched HF-COPD) underwent 2 high-intensity CLE tests at 80% of peak work rate to the limit of tolerance (Tlim), receiving either sham ventilation or NIPPV.

RESULTS

Despite greater V˙o2 recovery kinetics on sham, HF-COPD patients presented with a faster exponential time constant τ (76.4 ± 14.0 sec vs 62.8 ± 15.2 sec, P < .05) and mean response time (MRT) (86.1 ± 19.1 sec vs 68.8 ± 12.0 sec, P < .05) with NIPPV and greater ΔNIPPV-sham (τ: 5.6 ± 19.5 vs -25.2 ± 22.4, P < .05; MRT: 4.1 ± 32.2 vs -26.0 ± 19.2, P < .05) compared with HF. There was no difference regarding Tlim between sham and NIPPV in both groups (P < .05).

CONCLUSION

Our results suggest that NIPPV accelerated the V˙o2 recovery kinetics following high-intensity CLE to a greater extent in patients with coexisting HF and COPD compared with HF alone. NIPPV should be considered when the objective is to apply high-intensity interval exercise training as an adjunct intervention during a cardiopulmonary rehabilitation program.

Effects of high- and moderate-intensity exercise on central hemodynamic and oxygen uptake recovery kinetics in CHF-COPD overlap

The oxygen uptake (V˙O₂) kinetics during onset of and recovery from exercise have been shown to provide valuable parameters regarding functional capacity of both chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF) patients. To investigate the influence of comorbidity of COPD in patients with CHF with reduced ejection fraction on recovery from submaximal exercise, 9 CHF-COPD male patients and 10 age-, gender-, and left ventricle ejection fraction (LVEF)-matched CHF patients underwent constant-load exercise tests (CLET) at moderate and high loads. The V˙O₂, heart rate (HR), and cardiac output (CO) recovery kinetics were determined for the monoexponential relationship between these variables and time. Within-group analysis showed that the recovery time constant of HR (P<0.05, d=1.19 for CHF and 0.85 for CHF-COPD) and CO (P<0.05, d=1.68 for CHF and 0.69 for CHF-COPD) and the mean response time (MRT) of CO (P<0.05, d=1.84 for CHF and 0.73 for CHF-COPD) were slower when moderate and high loads were compared. CHF-COPD patients showed smaller amplitude of CO recovery kinetics (P<0.05) for both moderate (d=2.15) and high (d=1.07) CLET. Although the recovery time constant and MRT means were greater in CHF-COPD, CHF and CHF-COPD groups were not differently affected by load (P>0.05 in group vs load analysis). The ventilatory efficiency was related to MRT of V˙O₂ during high CLET (r=0.71). Our results suggested that the combination of CHF and COPD may further impair the recovery kinetics compared to CHF alone.

Predicting oxygen uptake responses during cycling at varied intensities using an artificial neural network

Study aim: Oxygen Uptake (VO2) is avaluable metric for the prescription of exercise intensity and the monitoring of training progress. However, VO2 is difficult to assess in anon-laboratory setting. Recently, an artificial neural network (ANN) was used to predict VO2 responses during aset walking protocol on the treadmill [9]. The purpose of the present study was to test the ability of an ANN to predict VO2 responses during cycling at self-selected intensities using Heart Rate (HR), time derivative of HR, power output, cadence, and body mass data.

Material and methods: 12 moderately-active adult males (age: 21.1 ± 2.5 years) performed a50-minute bout of cycling at a variety of exercise intensities. VO2, HR, power output, and cadence were recorded throughout the test. An ANN was trained, validated and tested using the following inputs: HR, time derivative of HR, power output, cadence, and body mass. A twelve-fold hold-out cross validation was conducted to determine the accuracy of the model.

Results: The ANN accurately predicted the experimental VO2 values throughout the test (R2 = 0.91 ± 0.04, SEE = 3.34 ± 1.07 mL/kg/min).

Discussion: This preliminary study demonstrates the potential for using an ANN to predict VO2 responses during cycling at varied intensities using easily accessible inputs. The predictive accuracy is promising, especially considering the large range of intensities and long duration of exercise. Expansion of these methods could allow ageneral algorithm to be developed for a more diverse population, improving the feasibility of oxygen uptake assessment.

Oxygen delivery is not a limiting factor during post-exercise recovery in healthy young adults

Purpose

It is still equivocal whether oxygen uptake recovery kinetics are limited by oxygen delivery and can be improved by supplementary oxygen. The present study aimed to investigate whether measurements of muscle and pulmonary oxygen uptake kinetics can be used to assess oxygen delivery limitations in healthy subjects.

Methods

Sixteen healthy young adults performed three sub-maximal exercise tests (6 min at 40% W_max) under hypoxic (14%O₂), normoxic (21%O₂) and hyperoxic (35%O₂) conditions on separate days in randomized order. Both Pulmonary VO₂ and near infra red spectroscopy (NIRS) based Tissue Saturation Index (TSI) offset kinetics were calculated using mono-exponential curve fitting models.

Results

Time constant τ of VO₂ offset kinetics under hypoxic (44.9 ± 7.3s) conditions were significantly larger than τ of the offset kinetics under normoxia (37.9 ± 8.2s, p = 0.02) and hyperoxia (37±6s, p = 0.04). TSI mean response time (MRT) of the offset kinetics under hypoxic conditions (25.5 ± 13s) was significantly slower than under normoxic (15 ± 7.7, p = 0.007) and hyperoxic (13 ± 7.3, p = 0.008) conditions.

Conclusion

The present study shows that there was no improvement in the oxygen uptake and muscle oxygenation recovery kinetics in healthy subjects under hyperoxic conditions.

Slower TSI and VO₂ recovery kinetics under hypoxic conditions indicate that both NIRS and spiro-ergometry are appropriate non-invasive measurement tools to assess the physiological response of a healthy individual to hypoxic exercise.

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Oxygen uptake kinetics in chronic heart failure: clinical and physiological aspects

One of the hallmark symptoms of patients with chronic heart failure (CHF) is exercise intolerance. Therefore, exercise testing has become an important tool for the evaluation and monitoring of heart failure. Whereas the maximal aerobic capacity (peak VO(2)) is a reliable indicator of the severity and prognosis of heart failure, submaximal exercise parameters may be more closely related to the ability to perform daily activities. As such, oxygen (O(2)) uptake kinetics, describing the rate change of O(2) uptake during onset or recovery of submaximal constant-load exercise (O(2) onset and recovery kinetics, respectively), have been shown to be useful parameters for objectively evaluating the functional capacity of CHF patients. However, their evaluation in this population is not a routine part of daily clinical practice. Possible reasons for this include a lack of standardisation of the assessment methodology and a limited number of studies evaluating the clinical use of O(2) uptake kinetics in CHF patients. In addition, the pathophysiological mechanisms underlying the delay in O(2) uptake kinetics in these patients are not completely understood. This review discusses the current literature on the clinical potency and physiological determinants of O(2) uptake kinetics in CHF patients and provides directions for future research. (Neth Heart J 2009;17:238-44.Neth Heart J 2009;17:238-44.).

Effects of carvedilol on oxygen uptake and heart rate kinetics in patients with chronic heart failure at simulated altitude

Background: The response to moderate exercise at altitude in heart failure (HF) is unknown.

Methods and results: We evaluated 30 HF patients, (NYHA I-III, 25 M/5 F; 59 ± 10 years; LVEF = 39.6 ± 7.1%), in stable clinical conditions, treated with carvedilol at the maximal tolerated dose. We performed a maximal cardiopulmonary exercise test (CPET) with ramp protocol at sea level to evaluate patients’ performance and two moderate intensity constant workload CPETs (50% of peak workload) at sea level (normoxia) and simulated altitude (hypoxia). Oxygen uptake ([Formula: see text]) and heart rate (HR) on-kinetics at constant workload were assessed calculating the time constant (τ) with a monoexponential equation. [Formula: see text] and HR were higher in hypoxia (0.944 ± 0.233 vs 1.031 ± 0.264 l/min; 100 ± 23 vs 108 ± 22 bpm; p < 0.001). On-kinetics showed a different behavior of τ being [Formula: see text] faster in hypoxia (67.1 ± 23.0 vs. 56.3 ± 19.7 s; p = 0.026) and HR faster in normoxia (49.3 ± 19.4 vs. 62.2 ± 22.5 s; p = 0.018). Ten patients, who lowered oxygen kinetics in hypoxia, had greater HR increase during maximal CPET suggesting lower functional betablockade. The higher τ of [Formula: see text] in hypoxia is likely to be due to a peripheral effect of carvedilol mediated either by β- or α-receptor.

Conclusion: HF patients performing moderate exercise at 2000 m simulated altitude have 20% [Formula: see text] increase without trouble at the beginning of exercise when treated with carvedilol.

Progressive chronic heart failure slows the recovery of microvascular O2 pressures after contractions in the rat spinotrapezius muscle

Chronic heart failure (CHF) induces muscle fiber-type specific alterations in skeletal muscle O(2) delivery and utilization during metabolic transitions. As a result, the recovery of microvascular Po(2) (Pmv(O(2))) is prolonged in slow-twitch skeletal muscle but not fast-twitch skeletal muscle in rats with CHF. We tested the hypothesis that CHF slows Pmv(O(2)) recovery in rat skeletal muscle of a mixed fiber-type analogous to human locomotory muscles and that the degree of slowing correlates with central indexes of heart failure. Healthy control [n = 6, left ventricular end-diastolic pressure (LVEDP): 10 ± 1 mmHg], moderate CHF (n = 6, LVEDP: 18 ± 2 mmHg), and severe CHF (n = 4, LVEDP: 34 ± 2 mmHg) female Sprague-Dawley rats had their right spinotrapezius muscles (41% type I, 7% type IIa, and 52% type IIb and d/x) exposed, and Pmv(O(2)) was measured via phosphorescence quenching during 180 s of recovery from 180 s of electrically induced twitch contractions (1 Hz, 4-6 V). CHF progressively slowed the mean response time (MRT; the time to reach 63% of the overall dynamic response) of Pmv(O(2)) recovery (MRT(off); control: 60.2 ± 6.9, moderate CHF: 72.8 ± 6.6, and severe CHF: 109.8 ± 6.6 s, P < 0.05 for all). MRT(off) correlated positively with central hemodynamic (LVEDP: r = 0.76, P < 0.01) and morphological (right ventricle-to-body weight ratio: r = 0.74, P < 0.01; and lung weight-to-body weight ratio: r = 0.79, P < 0.01) indexes of heart failure. The present investigation suggests that slowed Pmv(O(2)) kinetics during recovery in CHF constitutes a mechanistic link between impaired circulatory and metabolic recovery after contractions in CHF.