Right ventricular function at rest and during exercise in chronic obstructive pulmonary disease

Semi-quantitative analysis of Right Ventricular Myocardial First-pass Perfusion Using Cardiac Magnetic Resonance Imaging in Systemic Sclerosis and Pulmonary Arterial Hypertension

BACKGROUND

Right ventricular (RV) myocardial perfusion has been touted as a primary mechanism to understand impairment in RV function in patients with pulmonary arterial hypertension (PAH). However, measuring RV perfusion presents technical challenges. In this study, our aim is to employ a semi-quantitative approach using cardiac magnetic resonance (CMR) imaging to measure RV free wall first-pass perfusion in patients with PAH and controls, and to evaluate the intra- and inter-reader reproducibility of this approach.

METHODS

This study included 37 subjects (mean age 58.2±12 years, 72.9% female), 8 with idiopathic pulmonary arterial hypertension (IPAH), 10 with systemic sclerosis (SSc) and pulmonary arterial hypertension (PAH), 12 with SSc without PAH, and seven healthy controls. All participants underwent rest and adenosine stress perfusion CMR imaging using a 3 T scanner as part of a research protocol for evaluating pulmonary hypertension. Two readers delineated three regions of interest (ROIs) within the visible RV myocardium and manually traced contours of endocardial and epicardial borders of the left ventricle (LV) in two planes. Semi-quantitative perfusion analysis was performed with dedicated software for the measurement of first-pass myocardial perfusion. Concordance correlation coefficients (CCC) assessed inter- and intra-reader agreement of measurements.

RESULTS

Patients had an RV Ejection fraction (EF) of 50.9±11.3% and LVEF of 63.8±6.4 % and controls had an RVEF of 61.3±6.7 % and LVEF of 65.5±5.1 %. RV myocardial perfusion measurements at rest and stress were similar between the two readers (2.29±1.17 (mL/g × min) and 2.77±1.44 (mL/g × min) at rest, 4.02±2.45 (mL/g × min) and 4.35±2.72 (mL/g × min) during stress. The agreement was best for stress phase (0.90), followed by rest phase (0.83), and myocardial perfusion reserve index (MPRI) (0.72). The agreement was higher between readers for LV perfusion measurements (rest phase: 0.97, stress phase: 0.99, and MPRI: 0.89). RV MPRI was significantly higher in controls (2.62±0.73) as compared to all patients (1.63±0.75). The differences remained when controls were compared to patients with PAH.

CONCLUSION

Semi-quantitative first-pass RV perfusion reserve measures are technically feasible and show excellent inter-reader agreement. RV perfusion reserve index was lower in patients with PAH compared to healthy controls.

Right Heart Catheterization During Exercise in Patients with COPD-An Overview of Clinical Results and Methodological Aspects

While right heart catheterization (RHC) at rest is the gold standard to assess pulmonary hemodynamics in patients with chronic obstructive pulmonary disease (COPD) and pulmonary hypertension (PH), the invasive measurement of exercise hemodynamics is less well established in this group. Since exercise hemodynamics are increasingly recognized as important clinical information in patients with PH, our goal was to review the literature in this field to provide a basis for clinical use, further studies, and future recommendations. We identified 69 studies (published since 1968) reporting RHC data in 2819 patients with COPD, of whom 2561 underwent exercise testing. Few studies simultaneously measured gas exchange during exercise. Overall, these studies showed large variations in the patient populations and research questions studied and the methods and definitions employed. Despite these limitations, the data consistently demonstrated the presence of precapillary PH at rest in up to 38% of patients with COPD. With exercise, a relevant proportion of patients developed an abnormal hemodynamic response, depending on the definition used. Furthermore, some studies assessed right ventricular function during exercise and showed a blunted increase in right ventricular ejection fraction. Drug effects and the impact of interventional procedures were also studied. Again, due to large variations in the patients studied and the methods used, firm conclusions are difficult to derive. Despite the limitations of this dataset, several recommendations with respect to technical aspects (body position, exercise protocol, and data acquisition) can be inferred for this challenging patient population and may be helpful for further studies or recommendations.

Near-infrared spectroscopy using indocyanine green dye for minimally invasive measurement of respiratory and leg muscle blood flow in patients with COPD

Reliability of near-infrared spectroscopy, measuring indocyanine green (ICG) for minimally invasive assessment of relative muscle blood flow during exercise has been examined in fit young individuals but not in chronic obstructive pulmonary disease (COPD). Here we ask whether it could be used to evaluate respiratory and locomotor muscle perfusion in COPD patients. Vastus lateralis muscle blood flow (MBF, the reference method calculated from arterial and muscle ICG concentration curves) and a blood flow index [BFI, calculated using only the (same) muscle ICG concentration curves] were compared in 10 patients (forced expiratory volume in 1 s: 51 ± 6% predicted) at rest and during cycling at 25, 50, 75, and 100% of peak work rate (WR_peak). Intercostal muscle MBF and BFI were also compared during isocapnic hyperpnea at rest, reproducing ventilation levels up to those at WR_peak. Intercostal and vastus lateralis BFI increased with increasing ventilation during hyperpnea (from 2.5 ± 0.3 to 4.5 ± 0.7 nM/s) and cycling load (from 1.0 ± 0.2 to 12.8 ± 1.9 nM/s), respectively. There were strong correlations between BFI and MBF for both intercostal ( r = 0.993 group mean data, r = 0.872 individual data) and vastus lateralis ( r = 0.994 group mean data, r = 0.895 individual data). Fold changes from rest in BFI and MBF did not differ for either the intercostal muscles or the vastus lateralis. Group mean BFI data showed strong interrelationships with respiratory and cycling workload, and whole body metabolic demand ( r ranged from 0.913 to 0.989) simultaneously recorded during exercise. We conclude that BFI is a reliable and minimally invasive tool for evaluating relative changes in respiratory and locomotor muscle perfusion from rest to peak exercise in COPD patient groups. NEW & NOTEWORTHY We show that noninvasive near-infrared spectroscopic (NIRS) detection of indocyanine green dye (ICG) after peripheral venous injection adequately reflects intercostal and locomotor muscle perfusion during exercise and hyperpnea in patients with chronic obstructive pulmonary disease (COPD). Mean, individual, and fold change responses from rest to exercise or hyperpnea correlated closely with the reference method, which requires arterial sampling. NIRS-ICG is a reliable, robust, and essentially noninvasive tool for assessing relative changes in intercostal and locomotor muscle perfusion in COPD patient groups.

Positive end-expiratory pressure attenuates hemodynamic effects induced by an overload of inspiratory muscles in patients with COPD

BACKGROUND

Inspiratory muscle training (IMT) using a Threshold^® device is commonly used to improve the strength and endurance of inspiratory muscles. However, the effect of IMT, alone or with positive end-expiratory pressure (PEEP), on hemodynamic parameters in patients with chronic obstructive pulmonary disease (COPD) remains unknown.

OBJECTIVE

To assess the effects of an overload of inspiratory muscles using IMT fixed at 30% of the maximal inspiratory pressure (MIP), and IMT associated with 5 cmH₂O of PEEP (IMT + PEEP), on the echocardiographic parameters in healthy subjects and patients with COPD.

METHODS

Twenty patients with COPD (forced expiratory volume in 1 second 53.19±24.71 pred%) and 15 age-matched healthy volunteers were evaluated using spirometry, MIP, the COPD assessment test (CAT), and the modified Medical Research Council (mMRC) dyspnea scale. The E- (fast-filling phase) and A- (atrial contraction phase) waves were evaluated at the tricuspid and mitral valves during inspiration and expiration in the following sequence: at basal conditions, using IMT, and using IMT + PEEP.

RESULTS

Patients with COPD had reduced MIPs versus the control group. Ten patients had CAT scores <10 and 12 patients had mMRC scores <2. E-wave values at the mitral valve were significantly decreased with IMT during the inspiratory phase in both groups. These effects were normalized with IMT + PEEP. During the expiratory phase, use of IMT + PEEP normalized the reduction in E-wave values in the COPD group. During inspiration at the tricuspid valve, reduction in E-wave values during IMT was normalized by IMT + PEEP in COPD group. During the expiratory phase, the value of the E-waves was significantly reduced with overload of the inspiratory muscles in both groups, and these effects were normalized with IMT + PEEP. A-waves did not change under any conditions.

CONCLUSION

Acute hemodynamic effects induced by overloading of the inspiratory muscles were attenuated and/or reversed by the addition of PEEP in COPD patients.

Diagnostic and Prognostic Implications of Exercise Treadmill and Rest First-Pass Radionuclide Angiography in Patients With Pulmonary Hypertension

PURPOSE

Pulmonary hypertension (PH) is characterized by abnormally increased pulmonary vascular pressure, leading to deteriorated right ventricular function and premature death. Pulmonary mean transit time (PMTT) and biventricular function response to exercise in first-pass radionuclide angiography (FP-RNA) may provide early detection and timely disease monitoring of PH. This study aimed to investigate the diagnostic and prognostic values of this imaging modality in PH patients.

METHODS

Left and right ventricular ejection fraction (LVEF/RVEF) and PMTT at rest and immediately after exercise treadmill test were measured by FP-RNA in 77 consecutive patients with clinical presentations suggestive of PH (aged 46 ± 15 years, 33 men), mostly with symptoms of unexplained progressive dyspnea. These parameters, along with other clinical variables, were correlated with right-sided heart catheterization data and clinical outcomes.

RESULTS

Fifty patients (64.9%) were diagnosed as having definite PH. Besides higher N-terminal pro-B-type natriuretic peptide levels, right atrial pressure, and pulmonary vascular resistance, PH patients had significantly longer PMTT, lower LVEF after exercise and rest, and lower poststress RVEF (all P < 0.05), compared with non-PH subjects. Moreover, PH patients exhibited stress-induced right ventricular dysfunction and stationary poststress PMTT. Poststress PMTT and echocardiography had comparable diagnostic utility (area under the curve, 0.80 vs 0.84, respectively). Eighteen patients died during a median follow-up period of 380 days. Failure of exercise treadmill test, lower peak heart rate response, and stress/rest LVEF ratio of less than 90% using exercise treadmill FP-RNA were independent predictors of mortality in PH patients.

CONCLUSIONS

Exercise treadmill and rest FP-RNA provided diagnostic value and had prognostic implications in patients with PH.

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.

Ventilatory and cardiocirculatory exercise profiles in COPD: the role of pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is a well-recognized complication of COPD. The impact of PH on exercise tolerance is largely unknown. We evaluated and compared the circulatory and ventilatory profiles during exercise in patients with COPD without PH, with moderate PH, and with severe PH.

METHODS

Forty-seven patients, GOLD (Global Initiative for Chronic Obstructive Lung Disease)stages II to IV, underwent cardiopulmonary exercise testing and right-sided heart catheterization at rest and during exercise. Patients were divided into three groups based on mean pulmonary artery pressure (mPAP) at rest: no PH (mPAP, < 25 mm Hg), moderate PH (mPAP, 25-39 mm Hg),and severe PH (mPAP, ≥ 40 mm Hg). Mixed venous oxygen saturation (S VO 2 ) was used for evaluating the circulatory reserve. Pa CO 2 and the calculated breathing reserve were used for evaluation of the ventilatory reserve.

RESULTS

Patients without PH (n = 24) had an end-exercise S VO 2 of 48%± 9%, an increasing Pa CO 2 with exercise, and a breathing reserve of 22% ± 20%. Patients with moderate PH (n = 14) had an exercise S VO 2 of 40% ± 8%, an increasing Pa CO 2 , and a breathing reserve of 26% ± 15%. Patients with severe PH (n =9) had a significantly lower end-exercise S VO 2 (30% ± 6%), a breathing reserve of 37% ± 11%, and an absence of Pa CO 2 accumulation.

CONCLUSION

Patients with severe PH showed an exhausted circulatory reserve at the end of exercise.A profile of circulatory reserve in combination with ventilatory impairments was found inpatients with COPD and moderate or no PH. The results suggest that pulmonary vasodilation might only improve exercise tolerance in patients with COPD and severe PH.

Right ventricular ejection fraction during exercise as a predictor of mortality in patients awaiting lung transplantation: a cohort study

OBJECTIVE

The occurrence of right ventricular dysfunction is a well-known indicator of poor prognosis in patients with chronic cardiopulmonary disease. The role of right ventricular ejection fraction (RVEF) at rest and during exercise as predictors of outcome in patients awaiting lung transplantation (LTx) is unclear.

DESIGN

We performed a retrospective analysis of lung transplant candidates who had undergone equilibrium radionuclide angiography (ERNA), to determine baseline and exercise RVEF. Lung function, gas exchange and pulmonary haemodynamics were also assessed.

PATIENTS AND MAIN OUTCOME MEASURES

152 patients (mean age 47±11 years; 59% women) were included in the study. Primary endpoint was death on the waiting list for LTx. Main diagnoses were α-1 antitrypsin deficiency (n=35), chronic obstructive pulmonary disease (n=41), cystic fibrosis (n=10), interstitial lung disease (n=34) and pulmonary arterial hypertension (n=32). Twenty-five patients died (16, 4%). LTx was performed in 121 patients. The mean RVEF at rest was equal to mean RVEF during exercise (38±12%). In univariate analysis RVEF at rest, RVEF during exercise, heart rate and forced volume capacity (FVC) % of predicted were factors significantly associated with risk of death. In multivariate analysis RVEF during exercise and FVC% of predicted were independent predictors of death.

CONCLUSIONS

In lung transplant candidates, right ventricular function during exercise is a stronger predictor of outcome than right ventricular function at rest. RVEF during exercise assessed by ERNA could be incorporated into priority-based allocation algorithms for LTx.

Heliox increases quadriceps muscle oxygen delivery during exercise in COPD patients with and without dynamic hyperinflation

Some reports suggest that heliox breathing during exercise may improve peripheral muscle oxygen availability in patients with chronic obstructive pulmonary disease (COPD). Besides COPD patients who dynamically hyperinflate during exercise (hyperinflators), there are patients who do not hyperinflate (non-hyperinflators). As heliox breathing may differently affect cardiac output in hyperinflators (by increasing preload and decreasing afterload of both ventricles) and non-hyperinflators (by increasing venous return) during exercise, it was reasoned that heliox administration would improve peripheral muscle oxygen delivery possibly by different mechanisms in those two COPD categories. Chest wall volume and respiratory muscle activity were determined during constant-load exercise at 75% peak capacity to exhaustion, while breathing room air or normoxic heliox in 17 COPD patients: 9 hyperinflators (forced expiratory volume in 1 s = 39 ± 5% predicted), and 8 non-hyperinflators (forced expiratory volume in 1 s = 48 ± 5% predicted). Quadriceps muscle blood flow was measured by near-infrared spectroscopy using indocyanine green dye. Hyperinflators and non-hyperinflators demonstrated comparable improvements in endurance time during heliox (231 ± 23 and 257 ± 28 s, respectively). At exhaustion in room air, expiratory muscle activity (expressed by peak-expiratory gastric pressure) was lower in hyperinflators than in non-hyperinflators. In hyperinflators, heliox reduced end-expiratory chest wall volume and diaphragmatic activity, and increased arterial oxygen content (by 17.8 ± 2.5 ml/l), whereas, in non-hyperinflators, heliox reduced peak-expiratory gastric pressure and increased systemic vascular conductance (by 11.0 ± 2.8 ml·min(-1)·mmHg(-1)). Quadriceps muscle blood flow and oxygen delivery significantly improved during heliox compared with room air by a comparable magnitude (in hyperinflators by 6.1 ± 1.3 ml·min(-1)·100 g(-1) and 1.3 ± 0.3 ml O(2)·min(-1)·100 g(-1), and in non-hyperinflators by 7.2 ± 1.6 ml·min(-1)·100 g(-1) and 1.6 ± 0.3 ml O(2)·min(-1)·100 g(-1), respectively). Despite similar increase in locomotor muscle oxygen delivery with heliox in both groups, the mechanisms of such improvements were different: 1) in hyperinflators, heliox increased arterial oxygen content and quadriceps blood flow at similar cardiac output, whereas 2) in non-hyperinflators, heliox improved central hemodynamics and increased systemic vascular conductance and quadriceps blood flow at similar arterial oxygen content.

Pulmonary hypertension in critical care

PURPOSE OF REVIEW

To review the contemporary management of patients with pulmonary hypertension in critical care.

RECENT FINDINGS

The normal mean pulmonary artery pressure (mPAP) at rest is 14±3  mmHg and pulmonary hypertension is considered when mPAP is greater than or equal to 25  mmHg at rest. The classification of pulmonary hypertension has been redefined recently and updated in 2009 and could help to guide the management of patients with pulmonary hypertension in critical care. The management of pulmonary hypertension in ICU is based on expert opinion. Among the diagnostic and monitoring tools available, echocardiography provides useful information noninvasively, although pulmonary artery catheter must be used in case of complicated situations. Calcium sensitizers, a new class of inotrope, have inotropic effects and induce dilatation of the pulmonary, systemic, and coronary vasculature and thus could be useful in case of right ventricular failure (RVF), particularly in patients with acute respiratory distress syndrome (ARDS). By increasing the pulmonary vasodilator response to inhaled nitric oxide and preventing the rebound pulmonary vasoconstriction which occurs following cessation of nitric oxide breathing, selective type 5 isoform of phosphodiesterase inhibitors could be useful in critically ill patients.

SUMMARY

This article reviews recent and key findings on the management of pulmonary hypertension in critically ill patients.

On- and off-exercise kinetics of cardiac output in response to cycling and walking in COPD patients with GOLD Stages I-IV

Exercise-induced dynamic hyperinflation and large intrathoracic pressure swings may compromise the normal increase in cardiac output (Q) in Chronic Obstructive Pulmonary Disease (COPD). Therefore, it is anticipated that the greater the disease severity, the greater would be the impairment in cardiac output during exercise. Eighty COPD patients (20 at each GOLD Stage) and 10 healthy age-matched individuals undertook a constant-load test on a cycle-ergometer (75% WR(peak)) and a 6min walking test (6MWT). Cardiac output was measured by bioimpedance (PhysioFlow, Enduro) to determine the mean response time at the onset of exercise (MRTon) and during recovery (MRToff). Whilst cardiac output mean response time was not different between the two exercise protocols, MRT responses during cycling were slower in GOLD Stages III and IV compared to Stages I and II (MRTon: Stage I: 45±2, Stage II: 65±3, Stage III: 90±3, Stage IV: 106±3s; MRToff: Stage I: 42±2, Stage II: 68±3, Stage III: 87±3, Stage IV: 104±3s, respectively). In conclusion, the more advanced the disease severity the more impaired is the hemodynamic response to constant-load exercise and the 6MWT, possibly reflecting greater cardiovascular impairment and/or greater physical deconditioning.

Mechanisms of non-pharmacologic adjunct therapies used during exercise in COPD

Individuals with chronic obstructive pulmonary disease (COPD) are often limited in their ability to perform exercise due to a heightened sense of dyspnea and/or the occurrence of leg fatigue associated with a reduced ventilatory capacity and peripheral skeletal muscle dysfunction, respectively. Pulmonary rehabilitation programs have been shown to improve exercise tolerance and health related quality of life. Additional therapeutic approaches such as non-invasive ventilatory support (NIVS), heliox (He-O(2)) and supplemental oxygen have been used as non-pharmacologic adjuncts to exercise to enhance the ability of patients with COPD to exercise at a higher exercise-intensity and thus improve the physiological benefits of exercise. The purpose of the current review is to examine the pathophysiology of exercise limitation in COPD and to explore the physiological mechanisms underlying the effect of the adjunct therapies on exercise in patients with COPD. This review indicates that strategies that aim to unload the respiratory muscles and enhance oxygen saturation during exercise alleviate exercise limiting factors and improve exercise performance in patients with COPD. However, available data shows significant variability in the effectiveness across patients. Further research is needed to identify the most appropriate candidates for these forms of therapies.

Effect of helium breathing on intercostal and quadriceps muscle blood flow during exercise in COPD patients

Emerging evidence indicates that, besides dyspnea relief, an improvement in locomotor muscle oxygen delivery may also contribute to enhanced exercise tolerance following normoxic heliox (replacement of inspired nitrogen by helium) administration in patients with chronic obstructive pulmonary disease (COPD). Whether blood flow redistribution from intercostal to locomotor muscles contributes to this improvement currently remains unknown. Accordingly, the objective of this study was to investigate whether such redistribution plays a role in improving locomotor muscle oxygen delivery while breathing heliox at near-maximal [75% peak work rate (WR(peak))], maximal (100%WR(peak)), and supramaximal (115%WR(peak)) exercise in COPD. Intercostal and vastus lateralis muscle perfusion was measured in 10 COPD patients (FEV(1) = 50.5 ± 5.5% predicted) by near-infrared spectroscopy using indocyanine green dye. Patients undertook exercise tests at 75 and 100%WR(peak) breathing either air or heliox and at 115%WR(peak) breathing heliox only. Patients did not exhibit exercise-induced hyperinflation. Normoxic heliox reduced respiratory muscle work and relieved dyspnea across all exercise intensities. During near-maximal exercise, quadriceps and intercostal muscle blood flows were greater, while breathing normoxic heliox compared with air (35.8 ± 7.0 vs. 29.0 ± 6.5 and 6.0 ± 1.3 vs. 4.9 ± 1.2 ml·min(-1)·100 g(-1), respectively; P < 0.05; mean ± SE). In addition, compared with air, normoxic heliox administration increased arterial oxygen content, as well as oxygen delivery to quadriceps and intercostal muscles (from 47 ± 9 to 60 ± 12, and from 8 ± 1 to 13 ± 3 mlO(2)·min(-1)·100 g(-1), respectively; P < 0.05). In contrast, normoxic heliox had neither an effect on systemic nor an effect on quadriceps or intercostal muscle blood flow and oxygen delivery during maximal or supramaximal exercise. Since intercostal muscle blood flow did not decrease by normoxic heliox administration, blood flow redistribution from intercostal to locomotor muscles does not represent a likely mechanism of improvement in locomotor muscle oxygen delivery. Our findings might not be applicable to patients who hyperinflate during exercise.

Heliox improves oxygen delivery and utilization during dynamic exercise in patients with chronic obstructive pulmonary disease

RATIONALE

Normoxic heliox (mixture of 79% He and 21% O(2)) may enhance exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). It remains to be determined whether part of these beneficial effects could be ascribed to increased O(2) delivery (O(2)DEL) to locomotor muscles.

OBJECTIVES

To investigate the effects of heliox on peripheral O(2)DEL and utilization during exercise in moderate to severe COPD.

METHODS

Twelve mildly hypoxic or nonhypoxemic men (FEV(1) = 45.0 +/- 13.0% predicted) underwent constant-work rate tests (70-80% peak) to the limit of tolerance while receiving heliox or room air. Near-infrared spectroscopy determined changes (Delta) in leg muscle deoxygenation (deoxyhemoglobin concentration [HHb], an index of fractional O(2) extraction), and surface electromyography estimated muscle fiber recruitment (n = 5). Q and Sp(O(2)) were monitored by impedance cardiography and pulse oximetry, respectively.

MEASUREMENTS AND MAIN RESULTS

Heliox significantly decreased dynamic hyperinflation and increased exercise tolerance compared with room air (640 +/- 95 s vs. 371 +/- 100 s; P < 0.01). Heliox also accelerated on-exercise dynamics of Q, which were accompanied by faster O(2) uptake kinetics and slower Delta[HHb] responses (P < 0.05). During steady-state exercise, Sp(O(2))-corrected Delta[HHb] values decreased with heliox despite no significant changes in cardiac output. Muscle fiber recruitment and leg effort scores were also diminished (P < 0.05). On a multiple regression analysis, reductions in dynamic hyperinflation, dyspnea, and Delta[HHb] were independently related to improvements in exercise tolerance with heliox (R(2) = 0.91; P < 0.01).

CONCLUSIONS

Heliox increases lower limb O(2)DEL and utilization during dynamic exercise in patients with moderate to severe COPD. These effects enhance exercise tolerance in this patient population.

What role does the right side of the heart play in circulation?

Right ventricular failure (RVF) is an underestimated problem in intensive care. This review explores the physiology and pathophysiology of right ventricular function and the pulmonary circulation. When RVF is secondary to an acute increase in afterload, the picture is one of acute cor pulmonale, as occurs in the context of acute respiratory distress syndrome, pulmonary embolism and sepsis. RVF can also be caused by right myocardial dysfunction. Pulmonary arterial catheterization and echocardiography are discussed in terms of their roles in diagnosis and treatment. Treatments include options to reduce right ventricular afterload, specific pulmonary vasodilators and inotropes.

Acute right ventricular failure--from pathophysiology to new treatments

The right ventricle (RV) provides sustained low-pressure perfusion of the pulmonary vasculature, but is sensitive to changes in loading conditions and intrinsic contractility. Factors that affect right ventricular preload, afterload or left ventricular function can adversely influence the functioning of the RV, causing ischaemia and right ventricular failure (RVF). As RVF progresses, a pronounced tricuspid regurgitation further decreases cardiac output and worsens organ congestion. This can degenerate into an irreversible vicious cycle. The effective diagnosis of RVF is optimally performed by a combination of techniques including echocardiography and catheterisation, which can also be used to monitor treatment efficacy. Treatment of RVF focuses on alleviating congestion, improving right ventricular contractility and right coronary artery perfusion and reducing right ventricular afterload. As part of the treatment, inhaled nitric oxide or prostacyclin effectively reduces afterload by vasodilating the pulmonary vasculature. Traditional positive inotropic drugs enhance contractility by increasing the intracellular calcium concentration and oxygen consumption of cardiac myocytes, while vasopressors such as norepinephrine increase arterial blood pressure, which improves cardiac perfusion but increases afterload. A new treatment, the calcium sensitiser, levosimendan, increases cardiac contractility without increasing myocardial oxygen demand, while preserving myocardial relaxation. Furthermore, it increases coronary perfusion and decreases afterload. Conversely, traditional treatments of circulatory failure, such as mechanical ventilation and volume loading, could be harmful in the case of RVF. This review outlines the pathophysiology, diagnosis and treatment of RVF, illustrated with clinical case studies.

Functional assessment of the right ventricle with gated myocardial perfusion SPECT

BACKGROUND

The evaluation of right ventricular function can provide valuable information in a variety of cardiac and noncardiac conditions. Functional assessment of the right ventricle is difficult because of its anatomy and geometry. The authors describe a method for assessing right ventricular function using gated myocardial perfusion SPECT.

METHODS

In 20 patients, right and left ventricular ejection fractions (RVEF, LVEF) were determined using gated blood-pool scintigraphy (GBPS) and gated myocardial perfusion SPECT (GSPECT). To avoid contamination with right atrial activity, the two-frame method was adopted for gated blood-pool data when RVEF was measured. In nine patients with normal right ventricles, an index of wall thickening for the right ventricle was derived from the peak systolic and diastolic counts in the free wall.

RESULTS

Linear correlation between the two methods adopted for calculation of LVEF and RVEF was good. Bland-Altman analysis revealed good agreement between the two methods with no specific bias. The mean LVEF was 47.9 +/- 12% (GBPS) and 47.3 +/- 12.4 (GSPECT). The mean RVEF was 43.2 +/- 9.6% (GBPS) and 44.2 +/- 8.5% (GSPECT). In both cases, the values were not significantly different. The mean wall motion index was 35%. There was no correlation between the wall thickness index and ejection fraction, but the index was greater in patients with a normal right ventricle compared with those with reduced RVEF.

CONCLUSIONS

Gated SPECT offers an alternative to GBPS for the functional assessment of the right ventricle. Using GSPECT will allow the simultaneous assessment of both the right and left ventricles.

Cardiovascular limitations in chronic pulmonary disease

Chronic lung disease has significant impact on cardiovascular function. Much of this effect is because of increased right ventricular afterload caused by increased pulmonary vascular resistance resulting from structural changes in the pulmonary circulation, and because of hypoxic pulmonary vasoconstriction. In the case of chronic obstructive diseases, there may be additional increases in afterload resulting from dynamic hyperinflation. These processes can lead to structural changes in the heart (cor pulmonale), including right ventricular dilatation and hypertrophy, to maintain right ventricular output. In most ambulatory patients with chronic obstructive disease, it appears that cardiac output may be maintained at levels that are similar to normal both at rest and during exercise, with no consistent improvement in maximal exercise function afforded by interventions that increase blood flow. In contrast, diseases characterized by fibrosis or infiltration of the lung parenchyma may be associated with a disproportionate increase in pulmonary vascular resistance and more pronounced cardiovascular impairment, particularly with exercise.

Echocardiographic Detection of Occult Cor Pulmonale During Exercise in Patients with Chronic Obstructive Pulmonary Disease

We tested the ability of cycle ergometer exercise echocardiography to detect cases of occult cor pulmonale among 25 patients with chronic obstructive pulmonary disease (COPD). The M-mode echocardiographic ventricular septal motion, left ventricular shape determined by short-axis two-dimensional (2-D) echocardiography, and right and left ventricular pressure curves were recorded at rest and during exercise and were compared between patients. The ventricular septal motion was normal at rest in all of the patients. In nine patients (dip group), there was marked downward ventricular septal motion in early diastole during exercise, indicating distortion of the left ventricular shape. There were no distinct changes in the remaining 16 patients (non-dip group). At rest, the cardiac index was significantly lower, and right ventricular systolic and mean pulmonary artery pressures were significantly higher in the dip group than in the non-dip group. However, no significant difference was noted in the right ventricular end-diastolic pressure between the two groups at rest. The right ventricular systolic and end-diastolic pressures were greater during exercise in the dip group than in the non-dip group. In all of the patients in the dip group, the right ventricular pressure exceeded the left ventricular pressure only in early diastole, coinciding with the early diastolic dip of the ventricular septum, during exercise. In conclusion, occult cor pulmonale can be diagnosed accurately by the appearance of an early diastolic dip of the ventricular septum and distorted left ventricular shape during exercise in patients with COPD.

Effects of theophylline withdrawal in severe chronic obstructive pulmonary disease

To determine the value of theophylline in the maintenance therapy of patients with severe chronic obstructive pulmonary disease (COPD), we conducted a trial of theophylline therapy withdrawal in 38 clinically stable patients with severe COPD (FEV1 < 60 percent) predicted. Symptoms, lung function, blood gases, and 6-min walking distance were assessed on days 1 and 2. Quality of life and overall dyspnea were scored using four different clinical rating scales. Theophylline therapy was continued in 20 patients and replaced by placebo from day 3 on in the remainder; measurements were repeated on days 5 and 6. Withdrawal of theophylline therapy resulted in significant (p < 0.05) deterioration in lung function, exercise performance, and two indices of overall dyspnea, and a significant increase in scoring of symptoms and auscultation findings. Individual analysis revealed a clinically relevant deterioration in 72 percent of patients from whom theophylline therapy was withdrawn, while only 15 percent of patients receiving theophylline exhibited deterioration. No major side effects were observed. Our data show that about half of the patients with severe COPD can be considered as theophylline responders. The response of these patients to withdrawal of theophylline therapy suggests that the clinical effectiveness of this drug cannot be explained exclusively by bronchodilation. Due to the inherent difficulties in predicting response to theophylline, its effectiveness in patients with severe COPD should be determined individually, including assessment of exercise performance and ratings of dyspnea.