Determinants of the exercise endurance capacity in patients with chronic obstructive pulmonary disease. The power-duration relationship

How to interpret a cardiorespiratory fitness assessment - Key measures that provide the best picture of health, disease status and prognosis

Graded exercise testing is a widely accepted tool for revealing cardiac ischemia and/or arrhythmias in clinical settings. Cardiopulmonary exercise testing (CPET) measures expired gases during a graded exercise test making it a versatile tool that helps reveal underlying physiologic abnormalities that are in many cases only present with exertion. It also characterizes one's health status and clinical trajectory, informs the therapeutic plan, evaluates the efficacy of therapy, and provides submaximal and maximal information that can be used to tailor an exercise intervention. Practitioners can also modify the mode and protocol to allow individuals of all ages, fitness levels, and most disease states to perform a CPET. When used to its full potential, CPET can be a key tool used to optimize care in primary and secondary prevention settings.

Invited review: The speed-duration relationship across the animal kingdom

The parameters of the hyperbolic speed-duration relationship (the asymptote critical speed, CS, and the curvature constant, D') provide estimates of the maximal steady state speed (CS) and the distance an animal can run, swim, or fly at speeds above CS before it is forced to slow down or stop (D'). The speed-duration relationship has been directly studied in humans, horses, mice and rats. The technical difficulties with treadmill running in dogs and the relatively short greyhound race durations means that, perhaps surprisingly, it has not been assessed in dogs. The endurance capabilities of lizards, crabs and salamanders has also been measured, and the speed-duration relationship can be calculated from these data. These analyses show that 1) raising environmental temperature from 25 °C to 40 °C in lizards can double the CS with no change in D'; 2) that lungless salamanders have an extremely low critical speed due, most likely, to O₂ diffusion limitations associated with cutaneous respiration; and 3) the painted ghost crab possesses the highest endurance parameter ratio (D'/CS) yet recorded (470 s), allowing it to maintain high speeds for extended periods. Although the speed-duration relationship has not been measured in fish, the sustainable swimming speed has been quantified in a range of species and is conceptually similar to the maximal steady state in humans. The high aerobic power of birds and low metabolic cost of transport during flight permits the extreme feats of endurance observed in bird migrations. However, the parameters of the avian speed-duration relationship have not been quantified.

Interaction of Factors Determining Critical Power

The physiological determinants of high-intensity exercise tolerance are important for both elite human performance and morbidity, mortality and disease in clinical settings. The asymptote of the hyperbolic relation between external power and time to task failure, critical power, represents the threshold intensity above which systemic and intramuscular metabolic homeostasis can no longer be maintained. After ~ 60 years of research into the phenomenon of critical power, a clear understanding of its physiological determinants has emerged. The purpose of the present review is to critically examine this contemporary evidence in order to explain the physiological underpinnings of critical power. Evidence demonstrating that alterations in convective and diffusive oxygen delivery can impact upon critical power is first addressed. Subsequently, evidence is considered that shows that rates of muscle oxygen utilisation, inferred via the kinetics of pulmonary oxygen consumption, can influence critical power. The data reveal a clear picture that alterations in the rates of flux along every step of the oxygen transport and utilisation pathways influence critical power. It is also clear that critical power is influenced by motor unit recruitment patterns. On this basis, it is proposed that convective and diffusive oxygen delivery act in concert with muscle oxygen utilisation rates to determine the intracellular metabolic milieu and state of fatigue within the myocytes. This interacts with exercising muscle mass and motor unit recruitment patterns to ultimately determine critical power.

Impaired regenerative capacity contributes to skeletal muscle dysfunction in chronic obstructive pulmonary disease

Locomotor skeletal muscle dysfunction is a relevant comorbidity of chronic obstructive pulmonary disease (COPD) and is strongly associated with worse clinical outcomes including higher mortality. Over the last decades, a large body of literature helped characterize the process, defining the disruptive muscle phenotype caused by COPD that involves reduction in muscle mass, force-generation capacity, fatigue-tolerance, and regenerative potential following injury. A major limitation in the field has been the scarcity of well-calibrated animal models to conduct mechanistic research based on loss- and gain-of-function studies. This article provides an overall description of the process, the tools available to mechanistically investigate it, and the potential role of mitochondrially driven metabolic signals on the regulation muscle regeneration after injury in COPD. Finally, a description of future avenues to further expand on the area is proposed based on very recent evidence involving mitochondrial metabolic cues affecting myogenesis.

Exertional ventilation/carbon dioxide output relationship in COPD: from physiological mechanisms to clinical applications

There is well established evidence that the minute ventilation (V′_E)/carbon dioxide output (V′_CO2) relationship is relevant to a number of patient-related outcomes in COPD. In most circumstances, an increased V′_E/V′_CO2 reflects an enlarged physiological dead space (“wasted” ventilation), although alveolar hyperventilation (largely due to increased chemosensitivity) may play an adjunct role, particularly in patients with coexistent cardiovascular disease. The V′_E/V′_CO2 nadir, in particular, has been found to be an important predictor of dyspnoea and poor exercise tolerance, even in patients with largely preserved forced expiratory volume in 1 s. As the disease progresses, a high nadir might help to unravel the cause of disproportionate breathlessness. When analysed in association with measurements of dynamic inspiratory constraints, a high V′_E/V′_CO2 is valuable to ascertain a role for the “lungs” in limiting dyspnoeic patients. Regardless of disease severity, cardiocirculatory (heart failure and pulmonary hypertension) and respiratory (lung fibrosis) comorbidities can further increase V′_E/V′_CO2. A high V′_E/V′_CO2 is a predictor of poor outcome in lung resection surgery, adding value to resting lung hyperinflation in predicting all-cause and respiratory mortality across the spectrum of disease severity. Considering its potential usefulness, the V′_E/V′_CO2 should be valued in the clinical management of patients with COPD.

The minute ventilation/carbon dioxide production relationship is relevant to a number of patient-related outcomes in COPD. Minute ventilation/carbon dioxide production, therefore, should be valued in the clinical management of these patients.https://bit.ly/3df2upH

Endurance cycle ergometry tests performed at a sub-maximal work rate elicit peak physiological and symptom responses in adults with cystic fibrosis

Time to symptom limitation (T_lim ) achieved during constant work rate tests is considerably more responsive to change than measures commonly recorded during ramp-based tests, such as peak rate of oxygen uptake and maximal work rate (W_max ). There is limited literature on the use of, and physiological and symptom responses to, constant work rate cycle ergometry tests in people with cystic fibrosis (CF). The results of this study provide evidence that the constant work rate cycle ergometry test, when conducted at 80% of the W_max , elicits peak physiological and symptom responses and appears to be safe in adults with CF. For clinicians prescribing exercise at an intensity approaching or equivalent to 80% of the W_max in a non-laboratory-based setting, consideration needs to be given to the level of supervision and patient monitoring required.

Influence of muscular contraction on vascular conductance during exercise above versus below critical power

We tested the hypothesis that limb vascular conductance (LVC) would increase during the immediate recovery phase of dynamic exercise above, but not below, critical power (CP) indicating a threshold for muscular contraction-induced impedance of limb blood flow (LBF). CP (115 ± 26 W) was determined in 7 men and 7 women who subsequently performed ∼5 min of near-supine cycling exercise both below and above CP. LVC demonstrated a greater increase during immediate recovery and remained significantly higher following exercise above, compared to below, CP (all p < 0.001). Power output was associated with the immediate increases in LVC following exercise above, but not below, CP (p < 0.001; r = 0.85). Additionally, variance in percent LBF impedance was significantly lower above (CV: 10.7 %), compared to below (CV: 53.2 %), CP (p < 0.01). CP appears to represent a threshold above which the characteristics of LBF impedance by muscular contraction become intensity-dependent. These data suggest a critical level of LBF impedance relative to contraction intensity exists and, once attained, may promote the progressive metabolic and neuromuscular responses known to occur above CP.

Correlates of variability in endurance shuttle walk test time in patients with chronic obstructive pulmonary disease

Background

The endurance shuttle walk test (ESWT) is used to evaluate exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). The recommended pre-intervention tolerated duration (Tlim) is between 3–8 minutes for optimal interpretation of treatment effects. However, this window may be exceeded and factors determining ESWT Tlim are not completely understood. Therefore, we aimed to determine whether pulmonary function, physical and incremental shuttle walk test (ISWT) performance measures are associated with ESWT Tlim in COPD patients.

Methods

Assessment data from patients eligible for pulmonary rehabilitation was retrospectively analyzed. Inclusion criteria were: diagnosis of COPD and complete data availability regarding ESWT and ISWT. Patients performed an ESWT at 85% of ISWT speed and were divided into three groups (ESWT Tlim: <3 minutes, 3–8 minutes, >8 minutes). Subject characteristics, severity of complaints, pulmonary function, physical capacity and activity, exercise tolerance and quadriceps muscle strength were evaluated.

Results

245 COPD patients (FEV₁ 38 (29–52)% predicted) were included. Median ESWT Tlim was 6.0 (3.7–10.3) minutes, 41 (17%) patients walked <3 minutes and 80 (33%) patients walked >8 minutes. Body mass index, maximal oxygen consumption, Tlim on constant work rate cycle test, physical activity level, maximal ISWT speed, dyspnoea Borg score at rest and increase of leg fatigue Borg score during ISWT independently predicted Tlim in multivariate regression analysis (R² = 0.297, p<0.001).

Conclusion

This study reported a large variability in ESWT Tlim in COPD patients. Secondly, these results demonstrated that next to maximal ISWT speed, other ISWT performance measures as well as clinical measures of pulmonary function, physical capacity and physical activity were independent determinants of ESWT Tlim. Nevertheless, as these determinants only explained ~30% of the variability, future studies are needed to establish whether additional factors can be used to better adjust individual ESWT pace in order to reduce ESWT Tlim variability.

Exertional Desaturation in Idiopathic Pulmonary Fibrosis: The Role of Oxygen Supplementation in Modifying Cerebral-Skeletal Muscle Oxygenation and Systemic Hemodynamics

BACKGROUND

In patients with idiopathic pulmonary fibrosis (IPF) with isolated exertional desaturation, there are limited data regarding the effectiveness of oxygen supplementation during exercise training; the underlying mechanisms that contribute to these responses are unknown.

OBJECTIVES

To examine in these IPF patients the effects of oxygen supplementation during submaximal exercise (vs. medical air) on cerebral/skeletal muscle oxygenation and systemic hemodynamics.

METHODS

In this randomized, cross-over, placebo-controlled trial, IPF patients (n = 13; 63.4 ± 9.6 years) without resting hypoxemia but a significant desaturation during maximal cardiopulmonary exercise testing underwent 2 steady-state exercise trials (65% peak-work-load), breathing either oxygen-enriched or medical air. Cerebral/skeletal muscle oxygenation (near-infrared spectroscopy) and beat-by-beat hemodynamics (photoplethysmography) were monitored.

RESULTS

In the air protocol, from the initial minutes of submaximal exercise, patients exhibited a marked decline in cerebral oxygenated hemoglobin (O2Hb) and an abrupt rise in deoxygenated hemoglobin (HHb). Oxygen supplementation alleviated desaturation, lessened dyspnea, and prolonged exercise duration (p < 0.01). Oxygen supplementation during exercise (i) attenuated cerebral deoxygenation (cerebral-HHb: 0.7 ± 1.9 vs. 2.5 ± 1.5 μmol/L, O2 and air protocol; p = 0.009) and prevented cerebral-Hbdifference decline (2.1 ± 2.7 vs. -1.7 ± 2.0 μmol/L; p = 0.001), (ii) lessened the decline in muscle O2-saturation index, and (iii) at isotime exercise, it resulted in lower muscle-HHb (p = 0.05) and less leg fatigue (p < 0.05). No differences between protocols were observed in exercise cardiac output and vascular resistance.

CONCLUSIONS

IPF patients with isolated exertional hypoxemia exhibit an inability to increase/maintain cerebral oxygenation during submaximal exercise. Correcting desaturation with O2 supplementation prevented the decline in brain oxygenation, improved muscle oxygenation, and lessened dyspnea, suggesting an efficacy of acute oxygen supplementation during exercise training in protecting brain hypoxia in these IPF patients.

The anaerobic threshold: 50+ years of controversy

The anaerobic threshold (AT) remains a widely recognized, and contentious, concept in exercise physiology and medicine. As conceived by Karlman Wasserman, the AT coalesced the increase of blood lactate concentration ([La^- ]), during a progressive exercise test, with an excess pulmonary carbon dioxide output ( V ̇ C O 2 ). Its principal tenets were: limiting oxygen (O₂ ) delivery to exercising muscle→increased glycolysis, La^- and H⁺ production→decreased muscle and blood pH→with increased H⁺ buffered by blood [HCO₃ ^- ]→increased CO₂ release from blood→increased V ̇ C O 2 and pulmonary ventilation. This schema stimulated scientific scrutiny which challenged the fundamental premise that muscle anoxia was requisite for increased muscle and blood [La^- ]. It is now recognized that insufficient O₂ is not the primary basis for lactataemia. Increased production and utilization of La^- represent the response to increased glycolytic flux elicited by increasing work rate, and determine the oxygen uptake ( V ̇ O 2 ) at which La^- accumulates in the arterial blood (the lactate threshold; LT). However, the threshold for a sustained non-oxidative contribution to exercise energetics is the critical power, which occurs at a metabolic rate often far above the LT and separates heavy from very heavy/severe-intensity exercise. Lactate is now appreciated as a crucial energy source, major gluconeogenic precursor and signalling molecule but there is no ipso facto evidence for muscle dysoxia or anoxia. Non-invasive estimation of LT using the gas exchange threshold (non-linear increase of V ̇ C O 2 versus V ̇ O 2 ) remains important in exercise training and in the clinic, but its conceptual basis should now be understood in light of lactate shuttle biology.

The effect of dietary nitrate supplementation on the speed-duration relationship in mice with sickle cell disease

Sickle cell disease (SCD) causes exercise intolerance likely due to impaired skeletal muscle function and low nitric oxide (NO) bioavailability. Dietary nitrate improves hemodynamic and metabolic control during exercise in humans and animals. The purpose of this investigation was to assess the impact of nitrate supplementation on exercise capacity as measured by the running speed to exercise duration relationship [critical speed (CS)]in mice with SCD. We tested the hypothesis that nitrate supplementation via beetroot juice (BR) would attenuate the exercise intolerance observed in mice with SCD. Ten wild-type (WT) and 18 Berkley sickle-cell mice (BERK) received water (WT: n = 10, BERK: n = 10) or nitrate-rich BR (BERK+BR: n = 8, nitrate dose 1 mmol/kg/day) for 5 days. Following the supplementation period, all mice performed 3-5 constant-speed treadmill tests that resulted in exhaustion within 1.5 to 20 min. Time to exhaustion vs. treadmill speed was fit to a hyperbolic model to determine CS. CS was significantly lower in BERK vs. WT and BERK+BR with no significant difference between WT and BERK+BR (WT: 36.6 ± 1.6, BERK: 23.8 ± 1.5, BERK+BR: 31.1 ± 2.1 m/min, P < 0.05). Exercise tolerance, measured via CS, was significantly lower in BERK mice relative to WT. However, BERK mice receiving 5 days of nitrate supplementation exhibited no difference in exercise tolerance when compared with WT. These results support the potential utility of a dietary nitrate intervention to improve functionality in SCD patients.NEW & NOTEWORTHY Sickle cell disease compromises muscle O₂ delivery resulting in exercise intolerance. Dietary nitrate supplementation increases skeletal muscle blood flow during exercise and may improve exercise capacity in a mouse model of sickle cell disease. We investigated the effects of dietary nitrate supplementation on exercise tolerance in a mouse model of sickle cell disease using the treadmill speed-duration relationship (critical speed). Mice with sickle cell disease provided with a dietary nitrate supplement had a critical speed not significantly different from healthy wild-type mice.

Are the “critical” inspiratory constraints actually decisive to limit exercise tolerance in COPD?

Exercise intolerance is characteristically multi-factorial in patients with chronic obstructive pulmonary disease (COPD) [1]. At least in symptomatic patients with moderate-to-severe airflow limitation, higher operating lung volumes assume a relevant role in decreasing patients’ tolerance to sustain “prolonged” exercise. As a consequence of the dynamic increase in the end-expiratory lung volume, tidal volume (VT) occurs close to total lung capacity (TLC), thereby reducing the room for further lung–chest wall expansion. The combination of low dynamic lung compliance and a severely reduced inspiratory reserve volume causes a mismatch between a growing respiratory neural drive and the resulting lung–chest wall displacement [2]. It has been postulated that such critical inspiratory constraints (CIC) lead to a plateau in VT, and a concomitant increase in dyspnoea as a function of ventilation (V′_E) [3]. Accordingly, patients change their perception of the uncomfortable respiratory sensations from “laboured breathing” to “insufficient inspiration”, prompting early exercise termination [4].

The concept of critical inspiratory constraints is key to the modern understanding of exercise pathophysiology in patients with moderate-to-severe COPDhttps://bit.ly/2A6bCxD

Greater exercise tolerance in COPD during acute interval, compared to equivalent constant-load, cycle exercise: physiological mechanisms

KEY POINTS

Exercise intolerance is common in chronic obstructive pulmonary disease (COPD) patients. In patients with COPD, we compared an interval exercise (IE) protocol (alternating 30 s at 100% peak work rate (WR_peak ) with 30 s at 50% WR_peak ) with moderate-intensity constant-load exercise (CLE) at 75% WR_peak , which yielded the same work rate. Exercise endurance time and total work output were almost twice as high for IE than CLE. At exercise isotime (when work completed was the same between IE and CLE), IE was associated with less dynamic hyperinflation, lower blood lactate concentration, and greater respiratory and locomotor muscle oxygenation, but there were no differences in ventilation or cardiac output. However, at the limit of tolerance for each modality, dynamic hyperinflation was not different between IE and CLE, while blood lactate remained lower and muscle oxygenation higher with IE. Taken together, these findings suggest that dynamic hyperinflation and not muscle-based factors dictate the limits of tolerance in these COPD patients.

ABSTRACT

The relative importance of ventilatory, circulatory and peripheral muscle factors in determining tolerance to exercise in patients with chronic obstructive pulmonary disease (COPD) is not known. In 12 COPD patients (forced expiratory volume in one second: 58 ± 17%pred.) we measured ventilation, cardiac output, dynamic hyperinflation, local muscle oxygenation, blood lactate and time to exhaustion during (a) interval exercise (IE) consisting of 30 s at 100% peak work rate alternating with 30 s at 50%, and (b) constant-load exercise (CLE) at 75% peak work rate, designed to produce the same average work rate. Exercise time was substantially longer during IE than CLE (19.5 ± 4.8 versus 11.4 ± 2.1 min, p = 0.0001). Total work output was therefore greater during IE than CLE (81.3 ± 27.7 versus 48.9 ± 23.8 kJ, p = 0.0001). Dynamic hyperinflation (assessed by changes from baseline in inspiratory capacity, ΔIC) was less during IE than CLE at CLE exhaustion time (isotime, p = 0.009), but was similar at exhaustion (ΔIC_CLE : -0.38 ± 0.10 versus ΔIC_IE : -0.33 ± 0.12 l, p = 0.102). In contrast, at isotime, minute ventilation, cardiac output and systemic oxygen delivery did not differ between protocols (P > 0.05). At exhaustion in both protocols, the vastus lateralis and intercostal muscle oxygen saturation were higher in IE than CLE (p = 0.014 and p = 0.0002, respectively) and blood lactate concentrations were lower (4.9 ± 2.4 mmol l^-1 versus 6.4 ± 2.2 mmol l^-1 , p = 0.039). These results suggest that (1) exercise tolerance with COPD is limited by dynamic hyperinflation; and (2) cyclically lower (50%) effort intervals in IE help to preserve muscle oxygenation and reduce metabolic acidosis compared with CLE at the same average work rate; but these factors do not appear to determine time to exhaustion.

Transcapillary PO2 gradients in contracting muscles across the fibre type and oxidative continuum

KEY POINTS

Within skeletal muscle the greatest resistance to oxygen transport is thought to reside across the short distance at the red blood cell-myocyte interface. These structures generate a significant transmural oxygen pressure (PO₂ ) gradient in mixed fibre-type muscle. Increasing O₂ flux across the capillary wall during exercise depends on: (i) the transmural O₂ pressure gradient, which is maintained in mixed-fibre muscle, and/or (ii) elevating diffusing properties between microvascular and interstitial compartments resulting, in part, from microvascular haemodynamics and red blood cell distribution. We evaluated the PO₂ within the microvascular and interstitial spaces of muscles spanning the slow- to fast-twitch fibre and high- to low-oxidative capacity spectrums, at rest and during contractions, to assess the magnitude of transcapillary PO₂ gradients in rats. Our findings demonstrate that, across the metabolic rest-contraction transition, the transcapillary pressure gradient for O₂ flux is: (i) maintained in all muscle types, and (ii) the lowest in contracting highly oxidative fast-twitch muscle.

ABSTRACT

In mixed fibre-type skeletal muscle transcapillary PO₂ gradients (PO₂ mv-PO₂ is; microvascular and interstitial, respectively) drive O₂ flux across the blood-myocyte interface where the greatest resistance to that O₂ flux resides. We assessed a broad spectrum of fibre-type and oxidative-capacity rat muscles across the rest-to-contraction (1 Hz, 120 s) transient to test the novel hypotheses that: (i) slow-twitch PO₂ is would be greater than fast-twitch, (ii) muscles with greater oxidative capacity have greater PO₂ is than glycolytic counterparts, and (iii) whether PO₂ mv-PO₂ is at rest is maintained during contractions across all muscle types. PO₂ mv and PO₂ is were determined via phosphorescence quenching in soleus (SOL; 91% type I+IIa fibres and CSa: ∼21 μmol min^-1 g^-1 ), peroneal (PER; 33% and ∼20 μmol min^-1 g^-1 ), mixed (MG; 9% and ∼26 μmol min^-1 g^-1 ) and white gastrocnemius (WG; 0% and ∼8 μmol min^-1 g^-1 ) across the rest-contraction transient. PO₂ mv was higher than PO₂ is in each muscle (∼6-13 mmHg; P < 0.05). SOL PO₂ is_area was greater than in the fast-twitch muscles during contractions (P < 0.05). Oxidative muscles had greater PO₂ is_nadir (9.4 ± 0.8, 7.4 ± 0.9 and 6.4 ± 0.4; SOL, PER and MG, respectively) than WG (3.0 ± 0.3 mmHg, P < 0.05). The magnitude of PO₂ mv-PO₂ is at rest decreased during contractions in MG only (∼11 to 7 mmHg; time × (PO₂ mv-PO₂ is) interaction, P < 0.05). These data support the hypothesis that, since transcapillary PO₂ gradients during contractions are maintained in all muscle types, increased O₂ flux must occur via enhanced intracapillary diffusing conductance, which is most extreme in highly oxidative fast-twitch muscle.

CRITICAL VS ESTIMATED HEART RATE IN ELDERLY SUBJECTS

ABSTRACT Introduction: Heart rate (HR) has been a simple and easy-to-use physiological parameter widely used to determine exercise intensity. The critical power fatigue limit model, known as the critical heart rate (CHR), can be extrapolated to HR. However, an estimate for a CHR mathematical model has not yet been extrapolated for upper limb exercise in the elderly. Objective: To compare the mathematical model previously used to estimate CHR with the heart rate values at the critical power (CP) during arm-ergometer exercises in elderly subjects. Methods: After an initial maximum-incremental exercise test on a cycle arm-ergometer, seven elderly people performed four high-intensity constant-load tests to the limit of tolerance (Tlim), to determine CP and critical heart rate (CHR). For each power output, the heart rate of the last five seconds (HRlim) and total time to exhaustion (in minutes) were obtained. The slope coefficients of the regression lines between HRlim and Tlim were defined as CHR, and between Wlim and Tlim as CP. A square-wave test was performed on a different day, in the power determined as equivalent to CP, and the heart rate at CP (CPHR) was assessed. Results: The HR-Tlim relationship was found to be hyperbolic in all subjects, who were able to sustain upper-limb exercise at CP for 20 min. CP attained 66.8±9.4% of peak work rate in the ramp test. The real average HR measured in the CP test was strikingly similar to the CHR calculated by the mathematical model of PC (137.6±16.9 versus 139.7±13.3bpm, respectively, p=0.53). There was strong correlation between the real and the estimated CHR. Conclusion: This study indicated that the maximal sustainable exercise intensity can be based on a physiological variable such as HR, and the CHR test can define exercise endurance, which can be useful in performance assessment and training prescription. Level of evidence II; Diagnostic studies – Investigating a diagnostic test.

Critical power for the upper limb in patients with chronic obstructive pulmonary disease: A pilot study

PURPOSE

To investigated the impact of the ventilatory constraints in the power-duration relationship for upper limbs exercise in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Eight patients with COPD and eight healthy subjects performed an arm incremental test on cycle ergometer and four constant workload tests (100%, 90%, 80% and 70% of peak workload). The power-duration (or critical power - CP) estimative was determined. The inspiratory capacity was measured before and after each test.

RESULTS

There was no significant difference in the CP between patients and controls. Also, the curvature constant (W_AT, work do able above CP) was similar between patients and control subjects. Finally, the limits of tolerance for all constant workload tests in the patients with COPD were closely associated with the presence of dynamic hyperinflation and ventilatory reserve.

CONCLUSION

Despite patients typically showed more ventilatory stress compared with control subjects, the ventilatory constraints did not limit the sustained upper limbs exercise at the critical power.

Central and peripheral factors mechanistically linked to exercise intolerance in heart failure with reduced ejection fraction

Exercise intolerance is a primary symptom of heart failure (HF); however, the specific contribution of central and peripheral factors to this intolerance is not well described. The hyperbolic relationship between exercise intensity and time to exhaustion (speed-duration relationship) defines exercise tolerance but is underused in HF. We tested the hypotheses that critical speed (CS) would be reduced in HF, resting central functional measurements would correlate with CS, and the greatest HF-induced peripheral dysfunction would occur in more oxidative muscle. Multiple treadmill-constant speed runs to exhaustion were used to quantify CS and D' (distance coverable above CS) in healthy control (Con) and HF rats. Central function was determined via left ventricular (LV) Doppler echocardiography [fractional shortening (FS)] and a micromanometer-tipped catheter [LV end-diastolic pressure (LVEDP)]. Peripheral O₂ delivery-to-utilization matching was determined via phosphorescence quenching (interstitial Po₂, Po_2 is) in the soleus and white gastrocnemius during electrically induced twitch contractions (1 Hz, 8V). CS was lower in HF compared with Con (37 ± 1 vs. 44 ± 1 m/min, P < 0.001), but D' was not different (77 ± 8 vs. 69 ± 13 m, P = 0.6). HF reduced FS (23 ± 2 vs. 47 ± 2%, P < 0.001) and increased LVEDP (15 ± 1 vs. 7 ± 1 mmHg, P < 0.001). CS was related to FS (r = 0.72, P = 0.045) and LVEDP (r = -0.75, P = 0.02) only in HF. HF reduced soleus Po_2 is at rest and during contractions (both P < 0.01) but had no effect on white gastrocnemius Po_2 is (P > 0.05). We show in HF rats that decrements in central cardiac function relate directly with impaired exercise tolerance (i.e., CS) and that this compromised exercise tolerance is likely due to reduced perfusive and diffusive O₂ delivery to oxidative muscles.NEW & NOTEWORTHY We show that critical speed (CS), which defines the upper boundary of sustainable activity, can be resolved in heart failure (HF) animals and is diminished compared with controls. Central cardiac function is strongly related with CS in the HF animals, but not controls. Skeletal muscle O₂ delivery-to-utilization dysfunction is evident in the more oxidative, but not glycolytic, muscles of HF rats and is explained, in part, by reduced nitric oxide bioavailability.

Dyspnea and the Varying Pathophysiologic Manifestations of Chronic Obstructive Pulmonary Disease Evaluated by Cardiopulmonary Exercise Testing With Arterial Blood Analysis

Background: Patients with chronic obstructive pulmonary disease (COPD) show varying mechanisms of exertional dyspnea with different exercise capacities. Methods: To investigate the pathophysiologic conditions related to exertional dyspnea, 294 COPD patients were evaluated using cardiopulmonary exercise testing (CPET) with arterial blood analyses, with the patients classified into two groups according to their exercise limitation: the leg fatigue group (n = 58) and the dyspnea group (n = 215). The dyspnea group was further subdivided into four groups based on peak oxygen uptake ( V ° O 2 in mL/min/kg): group A (< 11), group B (11 to < 15), group C (15 to < 21), and group D (≥21). Results: In the dyspnea group, group A (n = 28) showed the following findings: (i) the forced expiratory volume in 1 s was not correlated with the peak V ° O 2 (p = 0.288), (ii) the arterial oxygen tension (PaO₂) slope (peak minus resting PaO₂/Δ V ° O 2 ) was the steepest (p < 0.0001) among all subgroups, (iii) reduced tidal volume (V_T) was negatively correlated with respiratory frequency at peak exercise (p < 0.0001), and (iv) a break point in exertional V_T curve was determined in 17 (61%) patients in group A. In these patients, there was a significant negative correlation between bicarbonate ion ( HCO 3 - ) levels at peak exercise and V_T level when the V_T-break point occurred (p = 0.032). In group D (n = 46), HCO 3 - levels were negatively correlated with plasma lactate levels (p < 0.0001). In all subgroups, the HCO 3 - level was negatively correlated with minute ventilation. The dyspnea subgroups showed no significant differences in the overall mean pH [7.363 (SD 0.039)] and Borg scale scores [7.4 (SD, 2.3)] at peak exercise. Conclusions: During exercise, ventilation is stimulated to avoid arterial blood acidosis and hypoxemia, but ventilatory stimulation is restricted in the setting of reduced respiratory system ability. These conditions provoke the exertional dyspnea in COPD. Although symptom levels were similar, the exertional pathophysiologic conditions differed according to residual exercise performance; moreover, COPD patients showed great inter-individual variability. An adequate understanding of individual pathophysiologic conditions using CPET is essential for proper management of COPD patients.

Effectiveness of Pulmonary Rehabilitation in Patients With Chronic Obstructive Pulmonary Disease With Different Degrees of Static Lung Hyperinflation

OBJECTIVE

To evaluate the effect of pulmonary rehabilitation (PR) on exercise performance and quality of life in patients with chronic obstructive pulmonary disease (COPD) with different degrees of static lung hyperinflation (LH).

DESIGN

Retrospective cohort study.

SETTING

PR network.

PARTICIPANTS

A cohort of 1981 patients with COPD (55% men; age: 66.8±9.3y; forced expiratory volume in the first second%: 50.7±19.5; residual volume [RV]%: 163.0±49.7).

INTERVENTION

An interdisciplinary PR program for patients with COPD consisting of 40 sessions.

MAIN OUTCOME MEASURES

Participants were stratified into 5 quintiles according to baseline RV and were evaluated on the basis of pre- and post-PR 6-minute walk distance (6MWD), constant work rate test (CWRT), and Saint George's Respiratory Questionnaire (SGRQ), among other clinical parameters.

RESULTS

With increasing RV quintile, patients were younger, more frequently women, had lower forced expiratory volume in the first second%, lower body mass index and fat-free mass index, shorter 6MWD, shorter CWRT, and worse SGRQ scores (P<.01). All RV strata improved after PR in all 3 outcomes (P<.001). Nevertheless, higher, compared to lower RV categories, had lower ΔCWRT (P<.01) but similar Δ6MWD (P=.948) and ΔSGRQ (P=.086) after PR.

CONCLUSIONS

LH in COPD is related to younger age, female sex, lower body weight, worse exercise capacity and health status, but did not prevent patients from benefitting from PR. LH, however, influences walking and cycling response after PR differently.

A Simplified Approach to Select Exercise Endurance Intensity for Interventional Studies in COPD

Time to exercise limitation (Tlim) in response to constant work rate (CWR) is sensitive to interventions in chronic obstructive pulmonary disease (COPD). This is particularly true when the pre-intervention test lasts between 3 and 8 min (Tlim_3'-8'). There is, however, no simple method to select a work rate which is consistently associated with Tlim_3'-8' across the spectrum of COPD severity. We assessed 59 GOLD stages II-IV patients who initially cycled to Tlim at 75% peak. In case of short (<3 min, low-endurance) or long (>8 min, high-endurance) tests, patients exercised after 60 min at 50% or 90%, respectively (CWR_{50%⇐75%⇒90%}). Critical mechanical constraints and limiting dyspnea at 75% were reached within the desired timeframe in 27 "mid-endurance" patients (46%). Increasing work rate intensity to 90% hastened the mechanical-ventilatory responses leading to Tlim_3'-8' in 23/26 (88%) "high-endurance" patients; conversely, decreasing exercise intensity to 50% slowed those responses leading to Tlim_3'-8' in 5/6 (83%) "high-endurance" patients. Repeating the tests at higher (60%) or lower (80%) intensities fail to consistently produce Tlim_3'-8' in "low-" and "high-endurance", respectively (p > 0.05). Compared to a fixed work rate at 75%, CWR_{50%⇐75%⇒90%} significantly decreased Tlim's coefficient of variation; consequently, the required N to detect 100 s or 33% improvement in Tlim decreased from 82 to 26 and 41 to 14, respectively. This simplified approach to individualized work rate adjustment (CWR_{50%⇐75%⇒90%}) might allow greater sensitivity in evaluating interventional efficacy in improving respiratory mechanics and exercise tolerance while simultaneously reducing sample size requirements in patients with COPD.

Exertional dyspnoea in COPD: the clinical utility of cardiopulmonary exercise testing

Activity-related dyspnoea is often the most distressing symptom experienced by patients with chronic obstructive pulmonary disease (COPD) and can persist despite comprehensive medical management. It is now clear that dyspnoea during physical activity occurs across the spectrum of disease severity, even in those with mild airway obstruction. Our understanding of the nature and source of dyspnoea is incomplete, but current aetiological concepts emphasise the importance of increased central neural drive to breathe in the setting of a reduced ability of the respiratory system to appropriately respond. Since dyspnoea is provoked or aggravated by physical activity, its concurrent measurement during standardised laboratory exercise testing is clearly important. Combining measurement of perceptual and physiological responses during exercise can provide valuable insights into symptom severity and its pathophysiological underpinnings. This review summarises the abnormal physiological responses to exercise in COPD, as these form the basis for modern constructs of the neurobiology of exertional dyspnoea. The main objectives are: 1) to examine the role of cardiopulmonary exercise testing (CPET) in uncovering the physiological mechanisms of exertional dyspnoea in patients with mild-to-moderate COPD; 2) to examine the escalating negative sensory consequences of progressive respiratory impairment with disease advancement; and 3) to build a physiological rationale for individualised treatment optimisation based on CPET.

Pulmonary rehabilitation for COPD improves exercise time rather than exercise tolerance: effects and mechanisms

BACKGROUND

COPD patients undergoing pulmonary rehabilitation (PR) show various responses. The purpose of this study was to investigate the possible mechanisms and predictors of the response to PR in COPD patients.

METHODS

Thirty-six stable COPD patients underwent PR including a 4-week high-intensity exercise training program, and they were evaluated by cardiopulmonary exercise testing. All patients (mean age 69 years, severe and very severe COPD 94%) were classified into four groups by whether the exercise time (T_ex) or the peak oxygen uptake [Formula: see text] increased after PR: two factors increased (both the T_ex and the peak [Formula: see text] increased); two factors decreased; time only increased (the T_ex increased, but the peak [Formula: see text] economized); and [Formula: see text] only increased (the T_ex decreased, but the peak [Formula: see text] increased). Within all patients, the relationships between baseline variables and the post-to-pre-change ratio of the time-slope, T_ex/(peak minus resting [Formula: see text]), were investigated.

RESULTS

Compared with the two factors increased group (n=11), in the time only increased group (n=18), the mean differences from pre-PR at peak exercise in 1) minute ventilation [Formula: see text] (P=0.004), [Formula: see text] (P<0.0001), and carbon dioxide output [Formula: see text] (P<0.0001) were lower, 2) [Formula: see text]/ [Formula: see text] (P=0.034) and [Formula: see text]/ [Formula: see text] (P=0.006) were higher, and 3) the dead space/tidal volume ratio (V_D/V_T) and the dyspnea level were similar. After PR, there was no significant difference in the ratio of the observed peak heart rate (HR) to the predicted peak HR (220 - age [years]) between the two groups. A significant negative correlation with the baseline time-slope (r=-0.496, P=0.002) and a positive correlation with the baseline body mass index (BMI) (r=0.496, P=0.002) were obtained.

CONCLUSIONS

PR in COPD patients improves T_ex rather than exercise tolerance, economizing oxygen requirements, resulting in reduced ventilatory requirements without cardiac loads followed by reduced exertional dyspnea. In addition, the time-slope and BMI could be used to predict PR responses beforehand.

Physiological and clinical relevance of exercise ventilatory efficiency in COPD

Exercise ventilation (V'_E) relative to carbon dioxide output (V'_CO2 ) is particularly relevant to patients limited by the respiratory system, e.g. those with chronic obstructive pulmonary disease (COPD). High V'_E-V'_CO2 (poor ventilatory efficiency) has been found to be a key physiological abnormality in symptomatic patients with largely preserved forced expiratory volume in 1 s (FEV₁). Establishing an association between high V'_E-V'_CO2 and exertional dyspnoea in mild COPD provides evidence that exercise intolerance is not a mere consequence of detraining. As the disease evolves, poor ventilatory efficiency might help explaining "out-of-proportion" breathlessness (to FEV₁ impairment). Regardless, disease severity, cardiocirculatory co-morbidities such as heart failure and pulmonary hypertension have been found to increase V'_E-V'_CO2 In fact, a high V'_E-V'_CO2 has been found to be a powerful predictor of poor outcome in lung resection surgery. Moreover, a high V'_E-V'_CO2 has added value to resting lung hyperinflation in predicting all-cause and respiratory mortality across the spectrum of COPD severity. Documenting improved ventilatory efficiency after lung transplantation and lung volume reduction surgery provides objective evidence of treatment efficacy. Considering the usefulness of exercise ventilatory efficiency in different clinical scenarios, the V'_E-V'_CO2 relationship should be valued in the interpretation of cardiopulmonary exercise tests in patients with mild-to-end-stage COPD.

Critical Power: An Important Fatigue Threshold in Exercise Physiology

: The hyperbolic form of the power-duration relationship is rigorous and highly conserved across species, forms of exercise, and individual muscles/muscle groups. For modalities such as cycling, the relationship resolves to two parameters, the asymptote for power (critical power [CP]) and the so-called W' (work doable above CP), which together predict the tolerable duration of exercise above CP. Crucially, the CP concept integrates sentinel physiological profiles-respiratory, metabolic, and contractile-within a coherent framework that has great scientific and practical utility. Rather than calibrating equivalent exercise intensities relative to metabolically distant parameters such as the lactate threshold or V˙O2max, setting the exercise intensity relative to CP unifies the profile of systemic and intramuscular responses and, if greater than CP, predicts the tolerable duration of exercise until W' is expended, V˙O2max is attained, and intolerance is manifested. CP may be regarded as a "fatigue threshold" in the sense that it separates exercise intensity domains within which the physiological responses to exercise can (CP) be stabilized. The CP concept therefore enables important insights into 1) the principal loci of fatigue development (central vs. peripheral) at different intensities of exercise and 2) mechanisms of cardiovascular and metabolic control and their modulation by factors such as O2 delivery. Practically, the CP concept has great potential application in optimizing athletic training programs and performance as well as improving the life quality for individuals enduring chronic disease.

Skeletal muscle power and fatigue at the tolerable limit of ramp-incremental exercise in COPD

Muscle fatigue (a reduced power for a given activation) is common following exercise in chronic obstructive pulmonary disease (COPD). Whether muscle fatigue, and reduced maximal voluntary locomotor power, are sufficient to limit whole body exercise in COPD is unknown. We hypothesized in COPD: 1) exercise is terminated with a locomotor muscle power reserve; 2) reduction in maximal locomotor power is related to ventilatory limitation; and 3) muscle fatigue at intolerance is less than age-matched controls. We used a rapid switch from hyperbolic to isokinetic cycling to measure the decline in peak isokinetic power at the limit of incremental exercise ("performance fatigue") in 13 COPD patients (FEV₁ 49 ± 17%pred) and 12 controls. By establishing the baseline relationship between muscle activity and isokinetic power, we apportioned performance fatigue into the reduction in muscle activation and muscle fatigue. Peak isokinetic power at intolerance was ~130% of peak incremental power in controls (274 ± 73 vs. 212 ± 84 W, P < 0.05), but ~260% in COPD patients (187 ± 141 vs. 72 ± 34 W, P < 0.05), greater than controls (P < 0.05). Muscle fatigue as a fraction of baseline peak isokinetic power was not different in COPD patients vs. controls (0.11 ± 0.20 vs. 0.19 ± 0.11). Baseline to intolerance, the median frequency of maximal isokinetic muscle activity, was unchanged in COPD patients but reduced in controls (+4.3 ± 11.6 vs. -5.5 ± 7.6%, P < 0.05). Performance fatigue as a fraction of peak incremental power was greater in COPD vs. controls and related to resting (FEV₁/FVC) and peak exercise (V̇_E/maximal voluntary ventilation) pulmonary function (r² = 0.47 and 0.55, P < 0.05). COPD patients are more fatigable than controls, but this fatigue is insufficient to constrain locomotor power and define exercise intolerance.

Use of exercise testing in the evaluation of interventional efficacy: an official ERS statement

This document reviews 1) the measurement properties of commonly used exercise tests in patients with chronic respiratory diseases and 2) published studies on their utilty and/or evaluation obtained from MEDLINE and Cochrane Library searches between 1990 and March 2015.

Exercise tests are reliable and consistently responsive to rehabilitative and pharmacological interventions. Thresholds for clinically important changes in performance are available for several tests. In pulmonary arterial hypertension, the 6-min walk test (6MWT), peak oxygen uptake and ventilation/carbon dioxide output indices appear to be the variables most responsive to vasodilators. While bronchodilators do not always show clinically relevant effects in chronic obstructive pulmonary disease, high-intensity constant work-rate (endurance) tests (CWRET) are considerably more responsive than incremental exercise tests and 6MWTs. High-intensity CWRETs need to be standardised to reduce interindividual variability. Additional physiological information and responsiveness can be obtained from isotime measurements, particularly of inspiratory capacity and dyspnoea. Less evidence is available for the endurance shuttle walk test. Although the incremental shuttle walk test and 6MWT are reliable and less expensive than cardiopulmonary exercise testing, two repetitions are needed at baseline. All exercise tests are safe when recommended precautions are followed, with evidence suggesting that no test is safer than others.

Lack of independent effect of type 2 diabetes beyond characteristic comorbidities and medications on small muscle mass exercising muscle blood flow and exercise tolerance

Persons with type 2 diabetes (T2D) are believed to have reduced exercise tolerance; this may be partly due to impaired exercising muscle blood flow (MBF). Whether there is an impact of T2D on exercising MBF within the typical constellation of comorbidities (hypertension, dyslipidemia, obesity) and their associated medications has not been investigated. We tested the hypothesis that small muscle mass exercise tolerance is reduced in persons with T2D versus Controls (matched for age, body mass index, fitness, comorbidities, non-T2D medications) and that this is related to blunted MBF. Eight persons with T2D and eight controls completed a forearm critical force (fCF_impulse) test as a measure of exercise tolerance (10-min intermittent maximal effort forearm contractions; the average contraction impulse in the last 30 sec quantified fCF_impulse). Forearm blood flow (FBF; ultrasound) and mean arterial pressure (MAP; finger photoplethysmography) were measured; forearm vascular conductance (FVK) was calculated. Data are means ± SD, T2D versus Control. fCF_impulse was not different between groups (136.9 ± 47.3  N·sec vs. 163.1 ± 49.7 N·sec, P = 0.371) nor was the ΔFBF from rest to during exercise at fCF_impulse (502.9 ± 144.6 vs. 709.1 ± 289.2 mL/min, P = 0.092), or its determinants ΔFVK and ΔMAP (both P > 0.05), although there was considerable interindividual variability. ΔFBF was strongly related to fCF_impulse (r = 0.727, P = 0.002), providing support for the relationship between oxygen delivery and exercise tolerance. We conclude that small muscle mass exercising MBF and exercise tolerance are not impaired in representative persons with T2D versus appropriately matched controls. This suggests that peripheral vascular control impairment does not contribute to reduced exercise tolerance in this population.

Test-retest reliability of lower limb isokinetic endurance in COPD: A comparison of angular velocities

Background

The purpose of this study was to determine and compare the test-retest reliability of quadriceps isokinetic endurance testing at two knee angular velocities in patients with chronic obstructive pulmonary disease (COPD).

Methods

After one familiarization session, 14 patients with moderate to severe COPD (mean age 65±4 years; forced expiratory volume in 1 second (FEV₁) 55%±18% predicted) performed two quadriceps isokinetic endurance tests on two separate occasions within a 5–7-day interval. Quadriceps isokinetic endurance tests consisted of 30 maximal knee extensions at angular velocities of 90° and 180° per second, performed in random order. Test-retest reliability was assessed for peak torque, muscle endurance, work slope, work fatigue index, and changes in FEV₁ for dyspnea and leg fatigue from rest to the end of the test. The intraclass correlation coefficient, minimal detectable change, and limits of agreement were calculated.

Results

High test-retest reliability was identified for peak torque and muscle total work at both velocities. Work fatigue index was considered reliable at 90° per second but not at 180° per second. A lower reliability was identified for dyspnea and leg fatigue scores at both angular velocities.

Conclusion

Despite a limited sample size, our findings support the use of a 30-maximal repetition isokinetic muscle testing procedure at angular velocities of 90° and 180° per second in patients with moderate to severe COPD. Endurance measurement (total isokinetic work) at 90° per second was highly reliable, with a minimal detectable change at the 95% confidence level of 10%. Peak torque and fatigue index could also be assessed reliably at 90° per second. Evaluation of dyspnea and leg fatigue using the modified Borg scale of perceived exertion was poorly reliable and its clinical usefulness is questionable. These results should be useful in the design and interpretation of future interventions aimed at improving muscle endurance in COPD.

Guidelines for the evaluation and treatment of muscle dysfunction in patients with chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD), skeletal muscle dysfunction is a major comorbidity that negatively impacts their exercise capacity and quality of life. In the current guidelines, the most recent literature on the various aspects of COPD muscle dysfunction has been included. The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) scale has been used to make evidence-based recommendations on the different features. Compared to a control population, one third of COPD patients exhibited a 25% decline in quadriceps muscle strength, even at early stages of their disease. Although both respiratory and limb muscles are altered, the latter are usually more severely affected. Numerous factors and biological mechanisms are involved in the etiology of COPD muscle dysfunction. Several tests are proposed in order to diagnose and evaluate the degree of muscle dysfunction of both respiratory and limb muscles (peripheral), as well as to identify the patients' exercise capacity (six-minute walking test and cycloergometry). Currently available therapeutic strategies including the different training modalities and pharmacological and nutritional support are also described.

An official American Thoracic Society/European Respiratory Society statement: update on limb muscle dysfunction in chronic obstructive pulmonary disease

BACKGROUND

Limb muscle dysfunction is prevalent in chronic obstructive pulmonary disease (COPD) and it has important clinical implications, such as reduced exercise tolerance, quality of life, and even survival. Since the previous American Thoracic Society/European Respiratory Society (ATS/ERS) statement on limb muscle dysfunction, important progress has been made on the characterization of this problem and on our understanding of its pathophysiology and clinical implications.

PURPOSE

The purpose of this document is to update the 1999 ATS/ERS statement on limb muscle dysfunction in COPD.

METHODS

An interdisciplinary committee of experts from the ATS and ERS Pulmonary Rehabilitation and Clinical Problems assemblies determined that the scope of this document should be limited to limb muscles. Committee members conducted focused reviews of the literature on several topics. A librarian also performed a literature search. An ATS methodologist provided advice to the committee, ensuring that the methodological approach was consistent with ATS standards.

RESULTS

We identified important advances in our understanding of the extent and nature of the structural alterations in limb muscles in patients with COPD. Since the last update, landmark studies were published on the mechanisms of development of limb muscle dysfunction in COPD and on the treatment of this condition. We now have a better understanding of the clinical implications of limb muscle dysfunction. Although exercise training is the most potent intervention to address this condition, other therapies, such as neuromuscular electrical stimulation, are emerging. Assessment of limb muscle function can identify patients who are at increased risk of poor clinical outcomes, such as exercise intolerance and premature mortality.

CONCLUSIONS

Limb muscle dysfunction is a key systemic consequence of COPD. However, there are still important gaps in our knowledge about the mechanisms of development of this problem. Strategies for early detection and specific treatments for this condition are also needed.

Characteristics and determinants of endurance cycle ergometry and six-minute walk distance in patients with COPD

Background

Exercise tolerance can be assessed by the cycle endurance test (CET) and six-minute walk test (6MWT) in patients with Chronic Obstructive Pulmonary Disease (COPD). We sought to investigate the characteristics of functional exercise performance and determinants of the CET and 6MWT in a large clinical cohort of COPD patients.

Methods

A dataset of 2053 COPD patients (43% female, age: 66.9 ± 9.5 years, FEV₁% predicted: 48.2 ± 23.2) was analyzed retrospectively. Patients underwent, amongst others, respiratory function evaluation; medical tests and questionnaires, one maximal incremental cycle test where peak work rate was determined and two functional exercise tests: a CET at 75% of peak work rate and 6MWT. A stepwise multiple linear regression was used to assess determinants.

Results

On average, patients had impaired exercise tolerance (peak work rate: 56 ± 27% predicted, 6MWT: 69 ± 17% predicted). A total of 2002 patients had CET time of duration (CET-T_end) less than 20 min while only 51 (2.5%) of the patients achieved 20 min of CET-T_end . In former patients, the percent of predicted peak work rate achieved differed significantly between men (48 ± 21% predicted) and women (67 ± 31% predicted). In contrast, CET-T_end was longer in men (286 ± 174 s vs 250 ± 153 s, p < 0.001). Also, six minute walking distance (6MWD) was higher in men compared to women, both in absolute terms as in percent of predicted (443 m, 67%predicted vs 431 m, 72%predicted, p < 0.05). Gender was associated with the CET-T_end but BMI, FEV₁ and FRC were related to the 6MWD highlighting the different determinants of exercise performance between CET and 6MWT.

Conclusions

CET-T_end is a valuable outcome of CET as it is related to multiple clinical aspects of disease severity in COPD. Gender difference should temper the interpretation of CET.

Treadmill endurance during 2-year treatment with tiotropium in patients with COPD: a randomized trial

BACKGROUND

Disease progression in COPD is associated with a decline in exercise performance over time. We assessed whether tiotropium might mitigate this by determining its effect on treadmill endurance time (ET) over 2 years.

METHODS

This was a randomized, double-blind, placebo-controlled trial of tiotropium, 18 μg daily, in patients with COPD (FEV1/FVC &lt; 70%; postbronchodilator FEV1 &lt; 65%). The primary end point was ET at 90% of baseline maximum work rate at 96 weeks. Secondary end points were ET at other visits, ET by smoking status, spirometry, and St. George's Respiratory Questionnaire (SGRQ).

RESULTS

A total of 519 patients were randomized (tiotropium 260, placebo 259). Mean age was 65 years, 77% were men, 34% were continuing smokers, and mean FEV1 was 1.25 L (44% predicted). Significantly more patients discontinued placebo (hazard ratio [95% CI], 0.61 [0.44-0.83]). Baseline ET was 301 s (improvement tiotropium/placebo was 13% overall; P = .009; 18% at 48 weeks, P = .004; 13% at 96 weeks, P = .106). In patients with baseline ET between 2 and 10 min (n = 404), improvement at 96 weeks was 19% (P = .04). Current smokers had higher ET with tiotropium vs placebo (P = .018). FEV1/FVC improved with tiotropium (P &lt; .01). SGRQ total score at 96 weeks improved with tiotropium vs placebo by 4.03 units (P = .007).

CONCLUSIONS

Treadmill ET was numerically greater over 2 years with tiotropium vs placebo. However, the 96-week difference was not statistically significant. Spirometry and health status also improved with tiotropium over 2 years, attesting to the benefits of long-acting bronchodilator therapy.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT00525512; URL: www.clinicaltrials.gov.

Factors limiting exercise tolerance in chronic lung diseases

The major limitation to exercise performance in patients with chronic lung diseases is an issue of great importance since identifying the factors that prevent these patients from carrying out activities of daily living provides an important perspective for the choice of the appropriate therapeutic strategy. The factors that limit exercise capacity may be different in patients with different disease entities (i.e., chronic obstructive, restrictive or pulmonary vascular lung disease) or disease severity and ultimately depend on the degree of malfunction or miss coordination between the different physiological systems (i.e., respiratory, cardiovascular and peripheral muscles). This review focuses on patients with chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD) and pulmonary vascular disease (PVD). ILD and PVD are included because there is sufficient experimental evidence for the factors that limit exercise capacity and because these disorders are representative of restrictive and pulmonary vascular disorders, respectively. A great deal of emphasis is given, however, to causes of exercise intolerance in COPD mainly because of the plethora of research findings that have been published in this area and also because exercise intolerance in COPD has been used as a model for understanding the interactions of different pathophysiologic mechanisms in exercise limitation. As exercise intolerance in COPD is recognized as being multifactorial, the impacts of the following factors on patients' exercise capacity are explored from an integrative physiological perspective: (i) imbalance between the ventilatory capacity and requirement; (ii) imbalance between energy demands and supplies to working respiratory and peripheral muscles; and (iii) peripheral muscle intrinsic dysfunction/weakness.

Selecting constant work rates for endurance testing in COPD: the role of the power-duration relationship

Constant work rate (CWR) exercise testing is highly responsive to therapeutic interventions and reveals physiological and functional benefits. No consensus exists, however, regarding optimal methods for selecting the pre-intervention work rate. We postulate that a CWR whose tolerated duration (tlim) is 6 minutes (WR6) may provide a useful interventional study baseline. WR6 can be extracted from the power-duration relationship, but requires 4 CWR tests. We sought to develop prediction algorithms for easier WR6 identification using backward stepwise linear regression, one in 69 COPD patients (FEV1 45 ± 15% pred) and another in 30 healthy subjects (HLTH), in whom cycle ergometer ramp incremental (RI) and CWR tests with tlim of ∼6 minutes had been performed. Demographics, pulmonary function, and RI responses were used as predictors. We validated these algorithms against power-duration measurements in 27 COPD and 30 HLTH (critical power 43 ± 18W and 231 ± 43W; curvature constant 5.1 ± 2.7 kJ and 18.5 ± 3.1 kJ, respectively). This analysis revealed that, on average, only corrected peak work rate ( = WRpeak-1 min × WRslope) in RI was required to predict WR6 (COPD SEE = 5.0W; HLTH SEE = 5.6W; R(2) > 0.96; p < 0.001). In the validation set, predicted and actual WR6 were strongly correlated (COPD R(2) = 0.937; HLTH 0.978; p < 0.001). However, in COPD, unlike in HLTH, there was a wide range of tlim values at predicted WR6: COPD 8.3 ± 4.1 min (range 3.6 to 22.2 min), and HLTH 5.5 ± 0.7 min (range 3.9 to 7.0 min). This analysis indicates that corrected WRpeak in an incremental test can yield an acceptable basis for calculating endurance testing work rate in HLTH, but not in COPD patients.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

The Physiologic Effects of an Acute Bout of Supramaximal High-Intensity Interval Training Compared with a Continuous Exercise Bout in Patients with COPD

This study compared physiological responses and work performed during a supramaximal high-intensity interval exercise training session (HIIT) and a constant work rate (CWR) exercise session. Fourteen patients with COPD (mean FEV1   53±13% predicted (±SD)) completed an incremental cardiopulmonary exercise test (CPET) and a steep ramp anaerobic test (SRAT) and then two exercise bouts to symptom limitation on separate days, in random order: (1) a CWR trial at 80% of CPET peak work rate (mean 63±15 W) and (2) a HIIT trial using repeats of 30 s at 70% of SRAT peak work rate (mean 112±29 W) followed by 90 s at 20% of CPET peak work rate. Subjects ceased exercise primarily due to dyspnea for both HIIT and CWR (64% vs. 57%, resp.). End-exercise VE, HR, dyspnea, and leg fatigue were similar between the two exercise protocols. Average work rate was lower in HIIT than CWR (32 vs. 63 W, P<0.05); however, subjects performed HIIT longer (542 vs. 202 s, P<0.05) and for greater total work (23.3 vs. 12.0 kJ, P<0.05). The supramaximal HIIT protocol was well tolerated and demonstrated similar maximal physiologic responses to constant work rate exercise, but with greater leg muscle work performed and greater peak exercise intensity.

Sinusoidal high-intensity exercise does not elicit ventilatory limitation in chronic obstructive pulmonary disease

During exercise at critical power (CP) in chronic obstructive pulmonary disease (COPD) patients, ventilation approaches its maximum. As a result of the slow ventilatory dynamics in COPD, ventilatory limitation during supramaximal exercise might be escaped using rapid sinusoidal forcing. Nine COPD patients [age, 60.2 ± 6.9 years; forced expiratory volume in the first second (FEV(1)), 42 ± 17% of predicted; and FEV(1)/FVC, 39 ± 12%] underwent an incremental cycle ergometer test and then four constant work rate cycle ergometer tests; tolerable duration (t(lim)) was recorded. Critical power was determined from constant work rate testing by linear regression of work rate versus 1/t(lim). Patients then completed fast (FS; 60 s period) and slow (SS; 360 s period) sinusoidally fluctuating exercise tests with mean work rate at CP and peak at 120% of peak incremental test work rate, and one additional test at CP; each for a 20 min target. The value of t(lim) did not differ between CP (19.8 ± 0.6 min) and FS (19.0 ± 2.5 min), but was shorter in SS (13.2 ± 4.2 min; P < 0.05). The sinusoidal ventilatory amplitude was minimal (37.4 ± 34.9 ml min(-1) W(-1)) during FS but much larger during SS (189.6 ± 120.4 ml min(-1) W(-1)). The total ventilatory response in SS reached 110 ± 8.0% of the incremental test peak, suggesting ventilatory limitation. Slow components in ventilation during constant work rate and FS exercises were detected in most subjects and contributed appreciably to the total response asymptote. The SS exercise was associated with higher mid-exercise lactate concentrations (5.2 ± 1.7, 7.6 ± 1.7 and 4.5 ± 1.3 mmol l(-1) in FS, SS and CP). Large-amplitude, rapid sinusoidal fluctuation in work rate yields little fluctuation in ventilation despite reaching 120% of the incremental test peak work rate. This high-intensity exercise strategy might be suitable for programmes of rehabilitative exercise training in COPD.

Dynamics of chest wall volume regulation during constant work rate exercise in patients with chronic obstructive pulmonary disease

This study evaluated the dynamic behavior of total and compartmental chest wall volumes [(V CW) = rib cage (V RC) + abdomen (V AB)] as measured breath-by-breath by optoelectronic plethysmography during constant-load exercise in patients with stable chronic obstructive pulmonary disease. Thirty males (GOLD stages II-III) underwent a cardiopulmonary exercise test to the limit of tolerance (Tlim) at 75% of peak work rate on an electronically braked cycle ergometer. Exercise-induced dynamic hyperinflation was considered to be present when end-expiratory (EE) V CW increased in relation to resting values. There was a noticeable heterogeneity in the patterns of V CW regulation as EEV CW increased non-linearly in 17/30 "hyperinflators" and decreased in 13/30 "non-hyperinflators" (P < 0.05). EEV AB decreased slightly in 8 of the "hyperinflators", thereby reducing and slowing the rate of increase in end-inspiratory (EI) V CW (P < 0.05). In contrast, decreases in EEV CW in the "non-hyperinflators" were due to the combination of stable EEV RC with marked reductions in EEV AB. These patients showed lower EIV CW and end-exercise dyspnea scores but longer Tlim than their counterparts (P < 0.05). Dyspnea increased and Tlim decreased non-linearly with a faster rate of increase in EIV CW regardless of the presence or absence of dynamic hyperinflation (P < 0.001). However, no significant between-group differences were observed in metabolic, pulmonary gas exchange and cardiovascular responses to exercise. Chest wall volumes are continuously regulated during exercise in order to postpone (or even avoid) their migration to higher operating volumes in patients with COPD, a dynamic process that is strongly dependent on the behavior of the abdominal compartment.

Mechanisms of physical activity limitation in chronic lung diseases

In chronic lung diseases physical activity limitation is multifactorial involving respiratory, hemodynamic, and peripheral muscle abnormalities. The mechanisms of limitation discussed in this paper relate to (i) the imbalance between ventilatory capacity and demand, (ii) the imbalance between energy demand and supply to working respiratory and peripheral muscles, and (iii) the factors that induce peripheral muscle dysfunction. In practice, intolerable exertional symptoms (i.e., dyspnea) and/or leg discomfort are the main symptoms that limit physical performance in patients with chronic lung diseases. Furthermore, the reduced capacity for physical work and the adoption of a sedentary lifestyle, in an attempt to avoid breathlessness upon physical exertion, cause profound muscle deconditioning which in turn leads to disability and loss of functional independence. Accordingly, physical inactivity is an important component of worsening the patients' quality of life and contributes importantly to poor prognosis. Identifying the factors which prevent a patient with lung disease to easily carry out activities of daily living provides a unique as well as important perspective for the choice of the appropriate therapeutic strategy.

A single test for the determination of parameters of the speed-time relationship for running

A validated expeditious method is needed to determine critical speed (CS) and the finite distance that can be covered above CS (D'). We tested the hypothesis that a single all-out 3-min running test would accurately determine CS and D'. Seven healthy subjects completed three constant-speed runs on a treadmill for the determination of CS and D', as well as an all-out 3-min test on a track for the determination of end-test speed (ES) and the distance above end-test speed (DES). ES (13.4 ± 2.8 km h(-1)) was not significantly different from the speed-1/time model CS (13.3 ± 2.8 km h(-1)). While DES (141 ± 34 m) was not significantly different from D' (204 ± 103 m), it underestimated D' in 5 of 7 subjects. Thus, the speed-1/time model CS can be accurately determined using a single 3-min test, while caution should be used in relating DES to D'.