Walking with Non-Invasive Ventilation Does Not Prevent Exercise-Induced Hypoxaemia in Stable Hypercapnic COPD Patients

Background: Non-invasive positive pressure ventilation (NPPV) in addition to supplemental oxygen improves arterial oxygenation, walking distance and dyspnea when applied during exercise in stable hypercapnic COPD patients. The aim of the current study was to investigate whether NPPV without supplemental oxygen is capable of preventing severe exercise-induced hypoxemia in these patients when applied during walking. Methods and Results: 15 stable hypercapnic COPD patients (FEV1 29.9 ± 15.9%) performed two 6-minute walk tests (6MWT) with a rollator in a randomized cross-over design: using either supplemental oxygen

(2.4 ± 0.7 L/min) or NPPV (inspiratory/expiratory positive airway pressure of 28.2 ± 2.8 / 5.5 ± 1.5 mbar) without supplemental oxygen. Results: 10 patients were able to complete both 6MWT. 6MWT with supplemental oxygen resulted in no changes for PO2 (pre: 67.3 ± 11.2 mmHg vs. post: 65.6 ± 12.0 mmHg, p = 0.72) whereas PCO2 increased (pre: 50.9 ± 8.1 mmHg vs. post: 54.3 ± 10.0 mmHg (p < 0.03). During 6MWT with NPPV PO2 significantly decreased from 66.8 ± 7.2 mmHg to 55.5 ± 10.6 mmHg (p < 0.02) whereas no changes occurred in PCO2 (pre: 50.6 ± 7.5 mmHg vs. post: 53.0 ± 7.1 mmHg; p = 0.17). Walking distance tended to be lower in 6MWT with NPPV compared to 6MWT with supplemental oxygen alone (318 ± 160 m vs. 377 ± 108 m; p = 0.08). Conclusion: The use of NPPV during walking without the application of supplemental oxygen does not prevent exercise-induced hypoxemia in patients with stable hypercapnic COPD.     

Effects of Chronic and Acute Pulmonary Hyperinflation on Phrenic Nerve Conduction in Patients with COPD

Abstract

In patients with moderate-to-severe Chronic Obstructive Pulmonary Disorder (COPD), pulmonary hyperinflation can occur at rest and increase during episodes of exacerbation. Among other mechanical constraints, changes in position and configuration of the diaphragm are also induced by increased end-expiratory lung volume. Both descent and flattening of diaphragm might damage the phrenic nerves by stretching their fibers. The study aimed to investigate the phrenic nerve conduction in COPD patients in stable conditions and during COPD exacerbation. In a group of 11 COPD patients without relevant comorbidities in stable conditions and subsequently in another group of 10 COPD patients during in-hospital COPD exacerbation and recovery, measurements of functional respiratory parameters and assessment of phrenic nerves motor conduction by bilateral electric stimulation were performed concurrently. Significant increase in phrenic nerves latency (p?<?0.05), but similar amplitude of motor compound muscle action potential (cMAP) was observed in stable COPD patients vs. matched controls (p?<?0.05). However, in COPD patients with resting pulmonary hyperinflation as reliably detected by substantial Inspiratory Capacity reduction (<80% pred.), the mean bilateral latency was longer vs. COPD patients without pulmonary hyperinflation (p?<?0.02). During COPD exacerbation, in contrast with mean latency, the mean amplitude of phrenic nerves cMAP improved at discharge when compared with in-hospital admission (p?<?0.05). In stable COPD patients the velocity of phrenic nerve conduction was impaired mostly in the presence of pulmonary hyperinflation, while during COPD exacerbation where dynamic pulmonary hyperinflation abruptly occurs, the reversible decrease of cMAP amplitude does suggest a temporary, acute axonal damage of phrenic nerves, potentially contributing to diaphragmatic dysfunction in these circumstances.     

Asincronía e hiperinsuflación en pacientes con enfermedad pulmonar obstructiva crónica durante 2 tipos de ejercicio de las extremidades superiores

Introduction

Occurrence of dynamic hyperinflation during upper-limbs exercises in chronic obstructive pulmonary disease (COPD) patients it is not well established. We hypothesized that dynamic hyperinflation and thoracoabdominal asynchrony occurs in COPD patients accomplishing arms exercises. We assessed the occurrence and association of dynamic hyperinflation and thoracoabdominal asynchrony in COPD patients during the accomplishment of two arm exercises.

Patients and methods

This was a prospective study with 25 COPD patients. A maximal and a sub-maximal upper limbs exercise test with 50% load were performed with the diagonal technique and the arm cycle ergometer technique. Respiratory pattern, thoracoabdominal configuration and dynamic hyperinflation were assessed in the exercise tests.

Results

Thirty per cent and 60% of patients hyperinflated at the end of the sub-maximum exercise tests with the diagonal and cycle ergometer techniques, respectively. Thoracoabdominal asynchrony occurred in 80% and 100% of patients who hyperinflated with the diagonal and cycle ergometer techniques, respectively. For both exercises we found enhancement of pulmonary ventilation, dyspnea, central respiratory drive and shortening of expiratory time (P < .05). Upper-limbs exercises with the diagonal technique presented less number of patients with these alterations.

Conclusions

Dynamic pulmonary hyperinflation and thoracoabdominal asynchrony association occurred in both upper-limbs exercises; however, the diagonal technique developed less dynamic hyperinflation and thoracoabdominal asynchrony in COPD patients than the arm cycle ergometer.     

Continuous positive airway pressure reduces work of breathing and dyspnea during weaning from mechanical ventilation in severe chronic obstructive pulmonary disease

Dynamic hyperinflation and the development of intrinsic positive end-expiratory pressure (PEEPi) are commonly observed in patients with severe chronic obstructive pulmonary disease (COPD) and acute respiratory failure. The presence of intrinsic PEEP acts as an inspiratory threshold load, and contributes significantly to the observed increase in work and oxygen cost of breathing. The present study examined the effects of continuous positive airway pressure (CPAP) (at 5, 10, and 15 cm H2O) and its ability to reduce the mechanical load imposed by PEEPi on breathing pattern, work of breathing, and dyspnea in seven patients with severe COPD during weaning from mechanical ventilation. Tidal volume remained stable at all levels of applied pressure. Breathing frequency was also stable except for a small (12%) decrease during CPAP of 15 cm H2O. Inspiratory pulmonary resistance and elastance were unaltered by the application of CPAP. There were progressive reductions in the inspiratory work of breathing as the level of CPAP increased. At the highest level of CPAP, the amount of inspiratory work performed per minute and per liter of ventilation decreased by 49.8 and 41.8%, respectively. Similar progressive reductions were also obtained in the pressure-time product for the inspiratory muscles and the diaphragm, which amounted to decreases of 42.9 and 42.2%, respectively, at the highest level of CPAP. End-expiratory lung volume remained stable at the lowest level of CPAP, with only modest increases occurring at the higher levels. In addition, all patients reported a reduction in dyspnea during the administration of CPAP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arm exercise and hyperinflation in patients with COPD: effect of arm training

BACKGROUND: Unlike studies on leg exercise, reports on the regulation of dynamic hyperinflation during arm exercise are scanty. We ascertained the following in patients with COPD: (1) whether and to what extent upper-limb exercise results in dynamic hyperinflation, and (2) the mechanism whereby an arm-training program (ATP) reduces arm effort and dyspnea. PATIENTS: Twelve patients with moderate-to-severe COPD were tested during incremental, symptom-limited arm exercise after a non-intervention control period (pre-ATP) and after ATP. METHODS: Exercise testing (1-min increments of 5 W) was performed using an arm ergometer. Oxygen uptake (V(O2)), carbon dioxide output, minute ventilation (Ve), tidal volume, and respiratory rate (RR) were measured continuously during the tests. Inspiratory capacity (IC), exercise dyspnea, and arm effort using a Borg scale were assessed at each step of exercise. RESULTS: Arm exercise resulted in a significant decrease in IC and significant positive relationships of IC with an increase in V(O2) and exercise dyspnea and arm effort. The results of ATP were as follows: (1) a significant increase in exercise capacity (p < 0.001); (2) no change in the relationships of exercise dyspnea and arm effort with Ve and IC, and of IC with V(O2); (3) at a standardized work rate, Ve, exercise dyspnea, and arm effort significantly decreased, while the decrease in IC was significantly less (p < 0.01) than before the ATP; the decrease in Ve was accomplished primarily by a decrease in RR; and (4) at standardized Ve, exercise dyspnea and arm effort decreased significantly. CONCLUSIONS: Arm exercise results in the association of dynamic hyperinflation, exercise dyspnea, and arm effort in COPD patients. An ATP increases arm endurance, modulates dynamic hyperinflation, and reduces symptoms.     

Factors Discriminating Spontaneous Pursed-Lips Breathing Use in Patients with COPD

ABSTRACT

Pursed-lips breathing (PLB) is often spontaneously performed by chronic obstructive pulmonary disease (COPD) patients. The aim of this study was to evaluate spontaneous PLB prevalence and to identify factors discriminating its use. Fifty-seven patients with COPD (FEV₁ = 44.3 ± 17.4%pred) underwent pulmonary function testing and two incremental bicycle exercise tests. Peak workload (Wpeak), oxygen uptake (VO₂peak), breathing pattern, and dyspnea (Borg scale) were measured in the first exercise test and spontaneous PLB performance in the second. Six patients spontaneously performed pursed-lips breathing during rest (PLBrest), exercise and recovery, 18 during exercise and recovery (PLBex), 7 during recovery only (PLBrec), 20 not at all (PLBno), and 6 performed other expiratory resistive maneuvers. PLBrest and PLBex patients exhibited a lower Wpeak, O₂ uptake, and minute ventilation (V_E), greater expiratory flow limitation and higher slopes relating dyspnea to V_E or W (%predicted). PLBrest patients were more hypercapnic, had a lower exercise tolerance and diffusion capacity, and greater flow limitation and hyperinflation. PLBrec and PLBno patients were indistinguishable with regard to pulmonary function, dyspnea, and exercise performance. The most significant independent predictors of spontaneous PLB use during exercise were FEV₁/FVC and the slope relating dyspnea to V_E. Spontaneous PLB is most often performed by COPD subjects when ventilation is stimulated by exercise, and during recovery from exercise. Severity of airflow obstruction and the dyspnea experienced during exercise play an important role in determining whether or not PLB is spontaneously performed by COPD patients.     

Effect of continuous positive airway pressure on respiratory sensation in patients with chronic obstructive pulmonary disease during submaximal exercise

We wished to evaluate the role of dynamic hyperinflation and dynamic airway compression as potential sources of exertional dyspnea in patients with chronic obstructive pulmonary disease (COPD). The rationale was that if such factors contribute importantly, then the administration of continuous positive airway pressure (CPAP), which serves to unload the inspiratory muscles and attenuate dynamic compression on expiration, should improve respiratory sensation. Further partitioning of CPAP into its continuous positive inspiratory pressure (CPIP) and continuous positive expiratory pressure (CPEP) components permitted an assessment of the relative importance of the above factors with respect to respiratory sensation. CPAP, CPIP, and CPEP (4 to 5 cm H2O each) were administered intermittently (for intervals of 40 to 60 s on each occasion) in random order during steady-state submaximal exercise in five patients with COPD (average FEV1, 40% predicted) and in five normal healthy subjects. Changes in the sense of breathing effort during the various pressure applications were assessed by asking the subjects to point to a category scale of -5 to +5, where -5 indicated that breathing was markedly easier and +5 indicated that breathing was markedly harder. CPAP, when administered to the COPD group, resulted in a highly significant (p less than 0.005) reduction in the sense of breathing effort. By contrast, CPAP significantly increased the sense of breathing effort in the normal group (p less than 0.01). CPIP facilitated breathing in both the COPD group and the normal group (p less than 0.05 and p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Response in oxygen uptake and ventilation during stair climbing in patients with chronic heart failure

To examine the level of muscular work and ventilatory response to stair climbing (mobile Stairmaster staircase, 1 step/2.5 s), respiratory gas exchange, ventilation, heart rate and arterial pressure were monitored in patients with chronic heart failure and their response compared with that of normal individuals. Aerobic capacity (maximal oxygen uptake) and anaerobic threshold during treadmill exercise were also determined and used to ascertain the metabolic cost of stair climbing. No differences were observed in the response of mean arterial blood pressure between the 12 patients and 10 normal subjects during exercise or recovery. However, the heart rate and oxygen consumption obtained during exercise were significantly lower in the patients with chronic heart failure than in the normal subjects (p less than 0.05). All patients with a maximal oxygen uptake less than 20 ml/min/kg during treadmill exercise had an oxygen uptake during stair climbing that exceeded their anaerobic threshold and, consequently, they attained a significantly (p less than 0.01) higher level of ventilation during exercise and recovery. This was not the case for those patients with greater aerobic capacity. Therefore, it is concluded that stair climbing for the 12 patients with heart failure and moderate to moderately severe impairment in aerobic capacity represents strenuous anaerobic exercise. The resultant excess ventilation may explain the limiting sensation of dyspnea that is frequently experienced by these patients during and after stair climbing.     

Flow limitation and dynamic hyperinflation during exercise in COPD patients after single lung transplantation

STUDY OBJECTIVE: Using the negative expiratory pressure (NEP) method, we have previously shown that patients receiving single lung transplantation (SLT) for COPD do not exhibit expiratory flow limitation and have little dyspnea at rest. In the present study, we assessed whether SLT patients exhibit flow limitation, overall hyperinflation, and dyspnea during exercise. METHODS: Expiratory flow limitation assessed by the NEP method and inspiratory capacity maneuvers used to determine end-expiratory lung volume (EELV) and end-inspiratory lung volume (EILV) were performed at rest and during symptom-limited incremental cycle exercise in eight SLT patients. RESULTS: At the time of the study, the mean (+/- SD) FEV(1), FVC, functional residual capacity, and total lung capacity (TLC) amounted to 55 +/- 14%, 67 +/- 12%, 137 +/- 16%, and 110 +/- 11% of predicted, respectively. At rest, all patients did not experience expiratory flow limitation and were without dyspnea. At peak exercise, the maximal mechanical power output and maximal oxygen consumption amounted to 72 +/- 20% and 65 +/- 8% of predicted, respectively, with a maximal dyspnea Borg score of 6 +/- 3. All but one patient exhibited flow limitation and dynamic hyperinflation; the EELV and EILV amounted to 74 +/- 5% and 95 +/- 9% TLC, respectively. The patient who did not exhibit flow limitation during exercise had the lowest dyspnea score. CONCLUSION: Most SLT patients for COPD exhibit expiratory flow limitation and dynamic hyperinflation during exercise, whereas maximal dyspnea is variable.     

Effects of Pulmonary Rehabilitation Including Inspiratory Muscle Training in Patients with Chronic Obstructive Pulmonary Disease after Stratification by the Degree of Static Hyperinflation

Background

Inspiratory muscle training (IMT) improves inspiratory muscle strength, exercise capacity and health status in patients with chronic obstructive pulmonary disease (COPD). However, there is no additional effect on top of comprehensive pulmonary rehabilitation (PR). It is unclear whether patients with different baseline degrees of static hyperinflation respond differentially to IMT as part of a PR program. Therefore, the aim was to study the effects of IMT as an add-on on PR after stratification for baseline degrees of static hyperinflation.

Methods

In this single center retrospective study data were extracted between June 2013 and October 2020 of COPD patients who participated in a comprehensive PR program including IMT. IMT was performed twice daily, one session consisted of 3 series of 10 breaths and training intensity was set initially at a load of approximately 50% of patients’ maximal static inspiratory mouth pressure (MIP). The primary outcome measure was MIP. Secondary outcomes were the distance achieved on the 6-min walk test (6MWD), endurance cycling exercise capacity at 75% of the peak work rate (CWRT) and disease-specific health status using the COPD assessment test.

Results

754 patients with COPD were screened for eligibility and 328 were excluded because of repeated PR programs, missing data or baseline residual volume (RV)?>?350%. In total, 426 COPD patients were categorized into RV categories 50–130% (n?=?84), 131–165% (n?=?86), 166–197% (n?=?86), 198–234% (n?=?85) and 235–349% (n?=?85). In the whole sample, MIP, endurance exercise capacity and health status improved significantly. The change in 6MWD was higher in the lowest baseline degree of static hyperinflation [+?39 (9–92) m] compared with the baseline highest degree of static hyperinflation [+?11 (??18–54) m] (p?<?0.05).

Conclusions

IMT as part of a PR program in patients with COPD with different baseline degrees improved MIP irrespective of the degree of static lung hyperinflation. Improvement in functional exercise capacity was significantly higher in the group with the lowest degree of static hyperinflation compared with the patients with the highest degree of static hyperinflation.

     

Does Mechanical Injury of the Peripheral Airways Play a Role in the Genesis of COPD in Smokers?

In the present account it is proposed that in smokers the transition from peripheral airway disease to COPD is characterized by three sequential stages: Stage I, during which the closing volume eventually exceeds the functional residual capacity; Stage II, during which tidal expiratory flow limitation (EFL) is eventually exhibited; and Stage III, during which dynamic hyperinflation progressively increases leading to dyspnea and exercise limitation, which may be considered as markers of overt disease. Presence of airway closure (Stage I) and EFL (Stage II) in the tidal volume range may promote peripheral airway injury and accelerate the abnormalities of lung function. It is such injury that may determine which smoker is destined to develop COPD.     

Effect of dynamic hyperinflation on exertional dyspnea, exercise performance and quality of life in COPD

There is increasing evidence that dynamic hyperinflation (DH) have negative effects on exercise performance and quality of life in chronic obstructive pulmonary disease (COPD) patients. The aim of this study was to investigate effect of dynamic hyperinflation on exertional dyspnea, exercise performance and quality of life in patients with COPD. 72 clinically stable patients with moderate to severe COPD and 30 healthy age-matched control subjects were included in this study. Pulmonary function tests including lung volumes and maximal respiratory muscle forces, arterial blood gas analyses, evaluation of exertional dyspnea with the Borg scale, and The Saint George Respiratory Questionnaire (SGRQ, Turkish version) were performed at rest and after a 6-min walk test. We measured the change in inspiratory capacity (AlphaIC) after exercise to reflect DH. 80% of patients with COPD significantly decreased IC after exercise (DH). AlphaIC were -0.27 +/- 0.26 L in COPD and 0.8 +/- 0.17 L in controls (p= 0.001). A stepwise multiple regression analysis showed that to be a patient with COPD, Basal Dyspnea Index (BDI) and AlphaIC were the best predictors of 6 MWD (r(2)= 0.53, p< 0.001). FEV1 added an additinal 9% to the variance in 6 MWD. Exertional dyspnea (AlphaBorg) correlated with AlphaIC (r= -0.44, p= 0.0001) and BDI (r= 0.34, p= 0.02). AlphaIC significantly correlated with symptom (r= -0.36, p= 0.008), activity (r= -0.31, p= 0.03) and total scores (r= -0.30, p= 0.04) of SGRQ. Dynamic hyperinflation can often occur during exersice in patients with COPD. Extent of dynamic hyperinflation could able to explain exercise capacity limitation, exercise dyspnea, and poor quality of life in patients with COPD.     

Supplemental oxygen prevents exercise-induced oxidative stress in muscle-wasted patients with chronic obstructive pulmonary disease

RATIONALE: Although oxygen therapy is of clear benefit in patients with severe chronic obstructive pulmonary disease (COPD), recent studies have shown that short-term supplementary oxygen may increase oxidative stress and inflammation within the airways. OBJECTIVE: We investigated whether systemic inflammation and oxidative stress at rest and during exercise in patients with COPD are influenced by supplemental oxygen. METHODS: Nine normoxemic, muscle-wasted patients with moderate to very severe COPD were studied. Plasma markers of systemic inflammation (leukocyte counts, interleukin 6 [IL-6]) and oxidative stress (lipid peroxidation, protein oxidation, antioxidant capacity) were measured after treatment with either supplemental oxygen (nasal, 4 L . min(-1)) or compressed air, both at rest (1 h treatment) and after submaximal exercise (40 W, constant work rate). In addition, free-radical production by neutrophils and ATP-degradation products were determined before and after exercise. RESULTS: Short-term oxygen breathing at rest did not influence systemic low-grade inflammation and oxidative stress. The IL-6 response to exercise was attenuated during cycling with supplemental oxygen. Exercise-induced lipid and protein oxidation were prevented by treatment with supplemental oxygen. This was associated with both decreased free-radical production by neutrophils and reduced formation of (hypo)xanthine and uric acid. CONCLUSION: Short-term supplementary oxygen does not affect basal systemic inflammation and oxidative stress but prevents exercise-induced oxidative stress in normoxemic, muscle-wasted patients with COPD, and attenuates plasma IL-6 response. Inhibition of neutrophil activation and ATP degradation appears to be involved in this effect.     

The clinical importance of dynamic lung hyperinflation in COPD

Lung hyperinflation commonly accompanies expiratory flow-limitation in patients with Chronic Obstructive Pulmonary Disease (COPD) and contributes importantly to dyspnea and activity limitation. It is not surprising, therefore, that lung hyperinflation has become an important therapeutic target in symptomatic COPD patients. There is increasing evidence that acute dynamic increases in lung hyperinflation, under conditions of worsening expiratory flow-limitation and increased ventilatory demand (or both) can seriously stress cardiopulmonary reserves, particularly in patients with more advanced disease. Our understanding of the physiological mechanisms of dynamic lung hyperinflation during both physical activity and exacerbations in COPD continues to grow, together with an appreciation of its serious negative mechanical and sensory consequences. In this review, we will discuss the basic pathophysiology of COPD during rest, exercise and exacerbation so as to better understand how this can be pharmacologically manipulated for the patient's benefit. Finally, we will review current concepts of the mechanisms of symptom relief and improved exercise endurance following pharmacological lung volume reduction.     

Pathophysiology of Evolution of Small Airways Disease to Overt COPD

ABSTRACT

Background: The slope of phase III (single breath nitrogen test), an index of ventilation inhomogeneity, has been used for early detection of COPD. Tidal airway closure (cyclic opening and closure of the peripheral airways during tidal breathing; AC_T) and expiratory flow limitation (attainment of maximal expiratory flow during tidal expiration; EFL_T) cause small airways disease (SAD). The relationships of these indices with COPD severity may reflect the progress from SAD to overt COPD. Methods: In this cross-sectional study we have assessed for the first time the phase III slope, AC_T and EFL_T in 10 smokers with normal spirometry (group O) and 40 COPD patients with GOLD scores from I to IV. Results: In most group O smokers the phase III slope was increased, and further increased with GOLD severity (up to 800%pred in GOLD IV). A close correlation was found of slope with GOLD (r = 0.77). AC_T was absent in smokers with normal spirometry and in most patients with mild COPD. EFL_T first appeared in GOLD II patients and its prevalence progressively increased in GOLD III and IV patients. Conclusions: Most group O smokers exhibit increased phase III. With overt COPD there is a progressive increase in phase III and reduction of FEV₁/FVC ratio from GOLD I to IV. A reduction of FEV₁ occurs from GOLD stage II. As the disease progresses from moderate to severe, there is an increasing presence of AC_T. Tidal EFL, with dynamic hyperinflation and severe dyspnea is present only in GOLD III and IV.     

Automatic CPAP Performance in Patients with Sleep Apnea Plus COPD

Abstract

Background: Automatic CPAP devices have demonstrated good results in obtaining optimal fixed CPAP pressure to eliminate respiratory events in patients with sleep apnea-hypopnea syndrome (SAHS). However, automatic CPAP has not been fully studied in patients with COPD plus SAHS. Objectives: To analyse the performance of an automatic CPAP in severe COPD patients compared with SAHS patients with no associated co-morbidity. Methods: We compared 10 consecutive patients with SAHS and no associated co-morbidity and 10 patients with SAHS plus severe COPD who required CPAP titration. Automatic CPAP performance was studied during full-night PSG. Inadequate pressure increase periods, absence of pressure increases in reaction to respiratory events, air leak periods, and pressure behaviour in the face of erratic breathing periods were analysed. Results: The SAHS patients without co-morbidities vs. SAHS plus COPD patients presented: mean sleep efficiency, 80.2 (11.5)% vs. 76.5 (12.1)%; residual AHI, 6.3 (5.2) vs. 5.1 (7.7); residual CT90, 1 (3)% vs. 14 (1)%. The device´s performance demonstrates a mean of 1.2 (1.5) vs. 1.3 (1.2) periods of inadequate pressure increases; absence of pressure increases in reaction to respiratory events, 4.1 (5.4) vs. 0.6 (0.7) times; periods of air leaks, 1.3 (3.8) vs. 13.9 (11.7); mean optimal pressure, 9.1 (1.4) vs. 9.0 (1.9) cm H₂O. Conclusion: Titration with automatic CPAP could be as effective in patients with SAHS plus severe COPD as in patients with SAHS without COPD. However, the presence of more leakages must be taken into account.     

Different COPD Disease Characteristics are Related to Different Outcomes in the 6-minute Walk Test

Abstract

Background: Chronic obstructive pulmonary disease (COPD) can lead to severe disability as the disease advances. The 6-minute walk test (6MWT) is commonly used to measure functional capacity in COPD patients and has three potential outcomes; walking distance, oxygen desaturation, and self-perceived dyspnea assessed by the Borg scale, all reflecting different aspects of COPD. The aim of this study was to identify predictors of all 3 outcomes of 6MWT in patients with COPD. Methods: 370 COPD patients, aged 40–75 yrs, were included from the first phase of the Bergen COPD cohort study. They were examined with spirometry, bioelectrical impedance measurements, 6MWT, Center for Epidemiologic Studies of Depression (CES-D) Scale, Medical Research Council (MRC) dyspnea scale, Charlson index for co-morbidities, self-reported physical activity questionnaire, plasma levels of C-reactive protein (CRP) and arterial blood gases. Results: Significant predictors in the multivariate analyses were sex, age, FEV₁ in% predicted, symptoms of dyspnea (MRC), co-morbidities (Charlson Index) and self-reported physical activity for walking distance, FEV₁ in% predicted and PaO₂ for oxygen desaturation, and body composition, smoking and co-morbidities for self-perceived dyspnea assessed by the Borg scale. Conclusion: Several COPD characteristics have predictive value for the 6MWT, and some COPD characteristics are more strongly related to specific 6MWT outcomes than others.     

A pilot study of inspiratory capacity and resting dyspnea correlations in exacerbations of COPD and asthma

Measurement of inspiratory capacity (IC) as a marker of dynamic lung hyperinflation has been shown to correlate with dyspnea and exercise performance in stable COPD, and is therefore of potential utility in the management of this condition. We have examined whether similar relationships exist during acute exacerbations of COPD and asthma in order to determine whether there is a role for IC monitoring in acute management of these conditions. Eight patients with COPD and ten with asthma requiring hospital admission for acute exacerbations were studied with spirometry (including IC) at admission and at discharge and had concurrent self-perceived resting dyspnea ratings recorded. Over the admission there were significant improvements in resting dyspnea for the COPD group only, and improvements in spirometric indices in the asthma group only. No significant correlations were found between changes in dyspnea and changes in IC, in terms of acute responses to bronchodilator and in response to treatment over the hospital admission. These data suggest that dynamic hyperinflation during acute exacerbations of COPD and asthma is not as sensitive an indicator of resting dyspnea as in stable disease. A role for IC monitoring in the management of acute exacerbations of these diseases has not been identified.     

Reduction of hyperinflation by pharmacologic and other interventions

Hyperinflation of the lungs is associated with activity limitation and reduced quality of life of patients with chronic obstructive pulmonary disease (COPD). Cardiopulmonary exercise testing has proven useful, not only in establishing this link, but also in determining which interventions modify exercise endurance and the mechanisms by which this is achieved. In COPD, dynamic hyperinflation is reduced during exercise by interventions that either increase the potential for expiratory flow or increase the time available for expiration. Two classes of intervention improve exercise tolerance by increasing expiratory flow. Bronchodilators reduce expiratory airflow resistance by increasing the diameter of the airways. An alternative intervention, though less practical, is to reduce the density of the gas exhaled through obstructed airways, such as occurs when breathing a mixture of helium and oxygen (heliox). In contrast, supplemental oxygen and exercise rehabilitation programs improve endurance by reducing respiratory ventilatory drive and, therefore, respiratory rate. The different mechanisms exploited by these interventions to reduce dynamic hyperinflation suggest that combination treatments should yield additive benefits. This has been proven in the case of combinations of rehabilitative exercise training with supplemental oxygen, or with the bronchodilator tiotropium, both of which have been found to yield additive effects. With such interventions, we already have options for improving the mobility of patients with COPD. With a firm understanding of the physiologic basis of exercise limitation, we can focus on defining new and better strategies to improve exercise tolerance.     

Hyperinflation, dyspnea, and exercise intolerance in chronic obstructive pulmonary disease

Expiratory flow limitation is the pathophysiologic hallmark of chronic obstructive pulmonary disease (COPD), but dyspnea (breathlessness) is its most prominent and distressing symptom. Acute dynamic lung hyperinflation, which refers to the temporary increase in operating lung volumes above their resting value, is a key mechanistic consequence of expiratory flow limitation, and has serious mechanical and sensory repercussions. It is associated with excessive loading and functional weakness of inspiratory muscles, and with restriction of normal VT expansion during exercise. There is a strong correlation between the intensity of dyspnea at a standardized point during exercise, the end-expiratory lung volume, and the increased ratio of inspiratory effort to volume displacement (i.e., esophageal pressure relative to maximum: Vt as a % of predicted VC). This increased effort-displacement ratio in COPD crudely reflects the neuromechanical dissociation of the respiratory system that arises as a result of hyperinflation. The corollary of this is that any intervention that reduces end-expiratory lung volume will improve effort-displacement ratios and alleviate dyspnea. In flow-limited patients, bronchodilators act by improving dynamic airway function, thus enhancing lung emptying and reducing lung hyperinflation. Long-acting bronchodilators have recently been shown to reduce hyperinflation during both rest and exercise in moderate to severe COPD. This lung deflation allows greater Vt expansion for a given inspiratory effort during exercise with consequent improvement in dyspnea and exercise endurance.