Pulmonary arterial pressure during rest and exercise in healthy subjects: a systematic review

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.

Pulmonary arterial hypertension in patients treated by dasatinib

BACKGROUND

The French pulmonary hypertension (PH) registry allows the survey of epidemiological trends. Isolated cases of precapillary PH have been reported in patients who have chronic myelogenous leukemia treated with the tyrosine kinase inhibitor dasatinib.

METHODS AND RESULTS

This study was designed to describe incident cases of dasatinib-associated PH reported in the French PH registry. From the approval of dasatinib (November 2006) to September 30, 2010, 9 incident cases treated by dasatinib at the time of PH diagnosis were identified. At diagnosis, patients had moderate to severe precapillary PH with functional and hemodynamic impairment. No other incident PH cases were exposed to other tyrosine kinase inhibitors at the time of PH diagnosis. Clinical, functional, or hemodynamic improvements were observed within 4 months of dasatinib discontinuation in all but 1 patient. Three patients required PH treatment with endothelin receptor antagonist (n=2) or calcium channel blocker (n=1). After a median follow-up of 9 months (min-max 3-36), the majority of patients did not demonstrate complete clinical and hemodynamic recovery, and no patients reached a normal value of mean pulmonary artery pressure (≤20 mm Hg). Two patients (22%) died at follow-up (1 of unexplained sudden death and 1 of cardiac failure in the context of septicemia, respectively, 8 and 12 months after dasatinib withdrawal). The lowest estimate of incident PH occurring in patients exposed to dasatinib in France was 0.45%.

CONCLUSIONS

Dasatinib may induce severe precapillary PH fulfilling the criteria of pulmonary arterial hypertension, thus suggesting a direct and specific effect of dasatinib on pulmonary vessels. Improvement is usually observed after withdrawal of dasatinib.

Pulmonary complications of sickle cell disease

Sickle cell disease (SCD) is a common monogenetic disorder with high associated morbidity and mortality. The pulmonary complications of SCD are of particular importance, as acute chest syndrome and pulmonary hypertension have the highest associated mortality rates within this population. This article reviews the pathophysiology, diagnosis, and treatment of clinically significant pulmonary manifestations of SCD, including acute chest syndrome, asthma, and pulmonary hypertension in adult and pediatric patients. Clinicians should be vigilant in screening and treating such comorbidities to improve patient outcomes.

Modulation of pulmonary vascular resistance as a target for therapeutic interventions in Fontan patients: focus on phosphodiesterase inhibitors

Despite advancements in surgical techniques over the past 20 years, Fontan patients have decreased exercise capacity as a consequence of an inherent inability to adequately increase cardiac output during exercise. They are also affected by several complications that are associated with considerable morbidity and mortality. As the systemic and pulmonary circulations are placed in series without a subpulmonary ventricle propelling blood through the pulmonary vasculature, the systemic venous pressure and the respiratory mechanics are the only forces driving pulmonary blood flow. In Fontan circulation, pulmonary vascular resistance is the single most important factor involved in the limitation of cardiac output and treatments able to decrease pulmonary vascular resistance might conversely improve cardiac output and exercise capacity. In this article we discuss the initial experience with the use of sildenafil in Fontan patients and we discuss the possible mechanisms through which sildenafil might positively act in Fontan circulation.

Pulmonary circulation at exercise

The pulmonary circulation is a high-flow and low-pressure circuit, with an average resistance of 1 mmHg/min/L in young adults, increasing to 2.5 mmHg/min/L over four to six decades of life. Pulmonary vascular mechanics at exercise are best described by distensible models. Exercise does not appear to affect the time constant of the pulmonary circulation or the longitudinal distribution of resistances. Very high flows are associated with high capillary pressures, up to a 20 to 25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40 to 50 mmHg, which can be achieved at maximal exercise, may correspond to the extreme of tolerable right ventricular afterload. Distension of capillaries that decrease resistance may be of adaptative value during exercise, but this is limited by hypoxemia from altered diffusion/perfusion relationships. Exercise in hypoxia is associated with higher pulmonary vascular pressures and lower maximal cardiac output, with increased likelihood of right ventricular function limitation and altered gas exchange by interstitial lung edema. Pharmacological interventions aimed at the reduction of pulmonary vascular tone have little effect on pulmonary vascular pressure-flow relationships in normoxia, but may decrease resistance in hypoxia, unloading the right ventricle and thereby improving exercise capacity. Exercise in patients with pulmonary hypertension is associated with sharp increases in pulmonary artery pressure and a right ventricular limitation of aerobic capacity. Exercise stress testing to determine multipoint pulmonary vascular pressures-flow relationships may uncover early stage pulmonary vascular disease.

Lung neovascularity in pulmonary arterial hypertension associated with congenital heart defects and idiopathic pulmonary arterial hypertension: study of 198 patients

OBJECTIVES

To correlate the severity of lung neovascularity (Sheehan vessels) with the cause and haemodynamic severity of pulmonary arterial hypertension (PAH), pulmonary artery (PA) size and heart disease type in patients with PH associated with congenital heart diseases (PAH-CHD) and idiopathic PH (IPAH).

METHODS

We reviewed the HRCT and CT pulmonary angiography studies of 87 patients with PAH-CHD and 111 with IPAH; all had undergone right heart catheterisation. We evaluated the PA size and severity of neovascularity on CT.

RESULTS

Neovascularity, which was found in 72% of PAH-CHD (56% with Eisenmenger's syndrome) and in 22% of IPAH patients, is significantly related to the severity of PH and all patients with severe neovascularity had intermediate or high PH. All PAH-CHD patients had a dilated PA with a greater risk of developing severe dilatation (diameter >5 cm). The neovascularity correlated with the PA size only in IPAH.

CONCLUSIONS

Neovascularity even if not pathognomonic for PAH-CHD, is significantly more common in these patients, especially in Eisenmenger's syndrome. It is often the first CT sign to indicate the severity of PH in PAH-CHD and IPAH. A neovascularity ≥5 on CT indicates a intermediate or high PH.

KEY POINTS

• Large retrospective studying specific lung disorders in patients with pulmonary arterial hypertension. • Neovascularity is often the first CT sign indicating the severity of pulmonary hypertension Alterations of lung parenchyma on CT in pulmonary hypertension are described • The first study to assess the severity of pulmonary hypertension by CT • If substantiated, CT might eventually replace some cardiac catheterisation for evaluating PH.

Pulmonary embolism: predicting disease severity

Pulmonary embolism (PE) is the most common cause of acute pulmonary hypertension, yet it is commonly undiagnosed, with risk of death if not recognized promptly and managed accordingly. Patients typically present with hypoxemia and hypomania, although the presentation varies greatly, being confounded by co-morbidities such as pre-existing cardio-respiratory disease. Previous studies have demonstrated variable patient outcomes in spite of similar extent and distribution of pulmonary vascular occlusion, but the path physiological determinants of outcome remain unclear. Computational models enable exact control over many of the compounding factors leading to functional outcomes and therefore provide a useful tool to understand and assess these mechanisms. We review the current state of pulmonary blood flow models. We present a pilot study within 10 patients presenting with acute PE, where patient-derived vascular occlusions are imposed onto an existing model of the pulmonary circulation enabling predictions of resultant haemodynamic after embolus occlusion. Results show that mechanical obstruction alone is not sufficient to cause pulmonary arterial hypertension, even when up to 65 per cent of lung tissue is occluded. Blood flow is found to preferentially redistribute to the gravitationally non-dependent regions. The presence of an additional downstream occlusion is found to significantly increase pressures.

Diagnosis and assessment of pulmonary vascular disease by Doppler echocardiography

Pulmonary hypertension (PH) is a relatively misunderstood disease, partly related to the fact that many perceive PH to be a singular diagnosis. An unintended consequence of this is the misapplication of the role of the Doppler-Echocardiographic (DE) examination, as well as an underappreciation for its ability to help discern PH pathophysiology prior to right heart catheterization. Since DE often serves as the "gatekeeper" to invasive right heart catheterization, misinterpretation of the DE can lead to missed or delayed diagnosis with devastating consequences. Too often, the primary or nearly exclusive focus of the DE examination is placed on the pulmonary artery pressure estimation. Two main issues with this approach are that Doppler pressure estimations can be inaccurate and even when accurate, without integration of additional 2-D and Doppler information, the clinician will often still not appreciate the pathophysiology of the PH nor its clinical significance. This review will focus on the 2-D and Doppler features necessary to assess pulmonary vascular disease (PVD), discern the salient differences between PVD and pulmonary venous hypertension (PVH), and how to integrate these key DE parameters such that PH pathophysiology can be determined noninvasively and early in the patient workup. Overreliance on any single DE metric, and especially PA pressure estimation, detracts from the overall diagnostic potential of the DE examination. Integrating the relative balance of right and left heart findings, along with proper Doppler interpretation provides a wealth of clinical and pathophysiologic insight prior to invasive hemodynamic assessment. The end results are heightened awareness and improved identification of which patients should be referred for further invasive testing, as well the use of the DE information to compliment the findings from invasive testing.

Exercise oscillatory ventilation in systolic heart failure: an indicator of impaired hemodynamic response to exercise

BACKGROUND

Exercise oscillatory ventilation (EOV) is a noninvasive parameter that potently predicts outcomes in systolic heart failure (HF). However, mechanistic insights into EOV have been limited by the absence of studies relating EOV to invasive hemodynamic measurements and blood gases performed during exercise.

METHODS AND RESULTS

Fifty-six patients with systolic HF (mean±SEM age, 59±2 years; left ventricular ejection fraction, 30±1%) and 19 age-matched control subjects were studied with incremental cardiopulmonary exercise testing. Fick cardiac outputs, filling pressures, and arterial blood gases were measured at 1-minute intervals during exercise. We detected EOV in 45% of HF (HF+EOV) patients and in none of the control subjects. The HF+EOV group did not differ from the HF patients without EOV (HF-EOV) in age, sex, body mass index, left ventricular ejection fraction, or origin of HF. Univariate predictors of the presence of EOV in HF, among measurements performed during exercise, included higher right atrial pressure and pulmonary capillary wedge pressure and lower cardiac index (CI) but not Paco2 or Pao2. Multivariate logistic regression identified that low exercise CI is the strongest predictor of EOV (odds ratio, 1.39 for each 1.0-L · min(-1) · m(-2) decrement in CI; 95% confidence interval, 1.14-1.70; P=0.001). Among HF patients with EOV, exercise CI was inversely related to EOV cycle length (R=-0.71) and amplitude (R=-0.60; both P<0.001). In 11 HF+EOV subjects treated with 12 weeks of sildenafil, EOV cycle length and amplitude decreased proportionately to increases in CI.

CONCLUSION

Exercise oscillatory ventilation is closely related to reduced CI and elevated filling pressures during exercise and may be an important surrogate for exercise-induced hemodynamic impairment in HF patients. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00309790.

Diagnosis and treatment of pulmonary hypertension: an update

Over the last five years, knowledge in the field of pulmonary hypertension has grown consistently and significantly. On the basis of various clinical studies showing the usefulness of new diagnostic tools, as well as the efficacy of new medications and drug combinations, new diagnostic and treatment algorithms have been developed. Likewise, in order to simplify the clinical management of patients, the classification of pulmonary hypertension has been changed in an attempt to group the various forms of pulmonary hypertension in which the diagnostic and therapeutic approaches are similar. The objective of this review was to discuss these modifications, based on the 2005 Brazilian guidelines for the management of pulmonary hypertension, emphasizing what has been added to the international guidelines.

Commentary on symptom experience of pulmonary arterial hypertension (PAH) patients

Pulmonary arterial hypertension (PAH) is a complex and rapidly progressing illness with few long-term treatment options to prolong life and improve quality of life. The complexity of the disease predisposes patients to a multitude of symptoms that have an effect on their biopsychosocial well-being. McDonough et al. have taken a qualitative approach to examine the dimensions of PAH symptomology. Using a telephone survey approach, 10 patients were questioned regarding their symptoms. Following coding and categorization of the responses, two main themes were found, "holding back" and redefining life.” The primary symptom associated with holding back was breathlessness. This symptom largely governed fears and behaviors associated with subthemes found within this main theme. Breathlessness also featured in the redefining life category; however, practical issues associated with medication and treatment were also assigned importance in this category by the study respondents. Symptoms of anxiety and depression were counteracted in many instances by a positive and sometimes stoic attitude toward the illness. This study presents important foundational information which will help direct further development of theoretical hypothesis related to PAH symptomology, as well as help focus clinical research toward venues that will enhance nursing care of this complex disease.

Early detection of pulmonary vascular disease in pulmonary arterial hypertension: time to move forward

Pulmonary arterial hypertension (PAH) can be a rapidly progressive disorder and is associated with high rate of mortality, despite medical intervention. With the availability of effective therapy, early disease detection is an important strategic objective to improve treatment outcomes. Resting echocardiography is currently the recommended screening modality for high-risk population groups. However, it is clear that derangements in resting haemodynamics (and symptoms) are late sequelae of the pathobiological processes that begin in the distal pulmonary arteries. Exercise stress may unmask early pulmonary vascular dysfunction but the definition, clinical significance, and natural history of 'exercise PAH' remain undefined. We will review the currently available and potential future strategies aimed at early disease detection, and propose that ultimately the way forward is to detect disease at a stage prior to the rise in resting pulmonary artery pressure.

Time-resolved magnetic resonance angiography: evaluation of intrapulmonary circulation parameters in pulmonary arterial hypertension

PURPOSE

To determine whether pulmonary arterial and venous transit times measured by time-resolved magnetic resonance angiography (MRA) can be used as a diagnostic tool for pulmonary arterial hypertension (PAH).

MATERIALS AND METHODS

Twelve patients with confirmed PAH and 10 healthy volunteers were scanned with Institutional Review Board (IRB) approval. Time-resolved MRA and 2D phase contrast flow images of the pulmonary vasculature were acquired. Pulmonary arterial and venous transit times (PaTT and PvTT) and pulmonary valve flow (PVF) were obtained. Pulmonary arterial and pulmonary venous blood volumes (PaBV and PvBV) were calculated as the product of flow and transit time.

RESULTS

Patients with PAH showed statistically significant increases in PaTT and PvTT (P < 0.0004, P < 0.05, respectively) compared to controls. PaBV (165.2 ± 92.0 mL) was significantly higher in PAH subjects than controls (97.0 ± 47.1 mL) (P < 0.04), whereas PvBV (127.9 ± 148.9 mL) of PAH subjects had no significant increase from those of healthy controls (142.5 ± 104.1 mL) (P < 0.38).

CONCLUSION

Pulmonary arterial transit times measured using time-resolved MRA can be used as a simple, noninvasive metric for detection of altered hemodynamics in PAH.

Exercise-induced pulmonary hypertension associated with systemic sclerosis: four distinct entities

OBJECTIVE

Exercise-induced pulmonary hypertension (PH) may represent an early but clinically relevant phase in the spectrum of pulmonary vascular disease. There are limited data on the prevalence of exercise-induced PH determined by right heart catheterization in scleroderma spectrum disorders. We undertook this study to describe the hemodynamic response to exercise in a homogeneous population of patients with scleroderma spectrum disorders at risk of developing pulmonary vascular disease.

METHODS

Patients with normal resting hemodynamics underwent supine lower extremity exercise testing. A classification and regression tree (CART) analysis was used to assess combinations of variables collected during resting right heart catheterization that best predicted abnormal exercise physiology, applicable to each individual subject.

RESULTS

Fifty-seven patients who had normal resting hemodynamics underwent subsequent exercise right heart catheterization. Four distinct hemodynamic groups were identified during exercise: a normal group, an exercise-induced pulmonary venous hypertension (ePVH) group, an exercise out of proportion PH (eoPH) group, and an exercise-induced PH (ePH) group. The eoPH and ePVH groups had higher pulmonary capillary wedge pressure (PCWP) than the ePH group (P < 0.05). The normal and ePH groups had exercise PCWP ≤18 mm Hg, which was lower than that in the ePVH and eoPH groups (P < 0.05). During submaximal exercise, the transpulmonary gradient and pulmonary vascular resistance (PVR) were elevated in the ePH and eoPH groups as compared with the normal and ePVH groups (P < 0.05). CART analysis suggested that resting mean pulmonary artery pressure (mPAP) ≥14 mm Hg and PVR ≥160 dynes/seconds/cm(-5) were associated with eoPH and ePH (positive predictive value 89% for mPAP 14-20 mm Hg and 100% for mPAP >20 mm Hg).

CONCLUSION

We characterized the exercise hemodynamic response in at-risk patients with scleroderma spectrum disorders who did not have resting PH. Four distinct hemodynamic groups were identified during exercise. These groups may have potentially different prognoses and treatment options.

Modulating the nitric oxide - cyclic GMP pathway in the pressure-overloaded left ventricle and group II pulmonary hypertension

Group II pulmonary hypertension (PH) commonly occurs in the setting of a pressure-overloaded left ventricle (LV) which is also conducive to the development of heart failure with preserved ejection fraction. Population trends and a high prevalence of underlying causative conditions, such as essential hypertension or aortic stenosis, have increased the awareness of the pressure-overloaded LV and associated group II pulmonary hypertension. Patients often exhibit poor exercise tolerance and signs of heart failure indistinguishable from systolic heart failure; but effective medical treatments in this area have been lacking. Recent preclinical work has shed light on how the down-regulated nitric oxide - cyclic GMP pathway (within the myocardium and pulmonary vasculature) contributes to the pathophysiology of these associated conditions. This article will discuss the impact of the nitric oxide - cyclic GMP pathway on the pathogenesis of the pressure-overloaded LV and group II pulmonary hypertension, and will also introduce the potential therapeutic value of modulating this pathway.

Pulmonary vascular response patterns during exercise in left ventricular systolic dysfunction predict exercise capacity and outcomes

BACKGROUND

Elevated resting pulmonary arterial pressure (PAP) in patients with left ventricular systolic dysfunction (LVSD) purports a poor prognosis. However, PAP response patterns to exercise in LVSD and their relationship to functional capacity and outcomes have not been characterized.

METHODS AND RESULTS

Sixty consecutive patients with LVSD (age 60±12 years, left ventricular ejection fraction 0.31±0.07, mean±SD) and 19 controls underwent maximum incremental cardiopulmonary exercise testing with simultaneous hemodynamic monitoring. During low-level exercise (30 W), LVSD subjects, compared with controls, had greater augmentation in mean PAPs (15±1 versus 5±1 mm Hg), transpulmonary gradients (5±1 versus 1±1 mm Hg), and effective pulmonary artery elastance (0.05±0.02 versus -0.03±0.01 mm Hg/mL, P<0.0001 for all). A linear increment in PAP relative to work (0.28±0.12 mm Hg/W) was observed in 65% of LVSD patients, which exceeded that observed in controls (0.07±0.02 mm Hg/W, P<0.0001). Exercise capacity and survival was worse in patients with a PAP/watt slope above the median than in patients with a lower slope. In the remaining 35% of LVSD patients, exercise induced a steep initial increment in PAP (0.41±0.16 mm Hg/W) followed by a plateau. The plateau pattern, compared with a linear pattern, was associated with reduced peak Vo(2) (10.6±2.6 versus 13.1±4.0 mL · kg(-1) · min(-1), P=0.005), lower right ventricular stroke work index augmentation with exercise (5.7±3.8 versus 9.7±5.0 g/m(2), P=0.002), and increased mortality (hazard ratio 8.1, 95% CI 2.7 to 23.8, P<0.001).

CONCLUSIONS

A steep increment in PAP during exercise and failure to augment PAP throughout exercise are associated with decreased exercise capacity and survival in patients with LVSD, and may therefore represent therapeutic targets.

CLINICAL TRIAL INFORMATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00309790.

The Nuts and Bolts of Interpreting Hemodynamics in Pulmonary Hypertension Associated With Diastolic Heart Failure

With the widespread application of transthoracic echocardiography as a screening tool for pulmonary hypertension (PH), we have come to appreciate the prevalence of PH associated with diastolic heart failure. Diastolic heart failure (DHF, sometimes called heart failure with preserved, or normal, left ventricular ejection fraction [HFpEF]) is quite common, and PH appears to be a fairly frequent component of DHF.1–3 The epidemiology of these conditions is described in the article by Dr Soto in this issue of Advances. There is a complex relationship between DHF and PH: the 2 may exist independent of each other or in combination; and when they exist in combination, the PH may be in proportion or out of proportion to the DHF. Cardiac catheterization is critical in differentiating among these patterns, and this distinction may lead to important modifications in treatment strategy. This requires, however, a full understanding of the proper performance and interpretation of cardiac catheterization, as well as the potential pitfalls that can limit the utility of the procedure. This article will discuss these aspects of cardiac catheterization as they pertain to patients with pulmonary arterial hypertension (PAH) and PH associated with DHF. A number of important aspects of cardiac catheterization are not covered here due to space limitations but can be obtained in a more detailed text.4

Effects of inhaled nitric oxide at rest and during exercise in idiopathic pulmonary fibrosis

Patients with idiopathic pulmonary fibrosis (IPF) usually develop hypoxemia and pulmonary hypertension when exercising. To what extent endothelium-derived vasodilating agents modify these changes is unknown. The study was aimed to investigate in patients with IPF whether exercise induces changes in plasma levels of endothelium-derived signaling mediators, and to assess the acute effects of inhaled nitric oxide (NO) on pulmonary hemodynamics and gas exchange, at rest and during exercise. We evaluated seven patients with IPF (6 men/1 woman; 57 ± 11 yr; forced vital capacity, 60 ± 13% predicted; carbon monoxide diffusing capacity, 52 ± 10% predicted). Levels of endothelin, 6-keto-prostaglandin-F(1α), thromboxane B(2), and nitrates were measured at rest and during submaximal exercise. Pulmonary hemodynamics and gas exchange, including ventilation-perfusion relationships, were assessed breathing ambient air and 40 ppm NO, both at rest and during submaximal exercise. The concentration of thromboxane B(2) increased during exercise (P = 0.046), whereas levels of other mediators did not change. The change in 6-keto-prostaglandin-F(1α) correlated with that of mean pulmonary arterial pressure (r = 0.94; P < 0.005). Inhaled NO reduced mean pulmonary arterial pressure at rest (-4.6 ± 2.1 mmHg) and during exercise (-11.7 ± 7.1 mmHg) (P = 0.001 and P = 0.004, respectively), without altering arterial oxygenation or ventilation-perfusion distributions in any of the study conditions. Alveolar-to-capillary oxygen diffusion limitation, which accounted for the decrease of arterial Po(2) during exercise, was not modified by NO administration. We conclude that, in IPF, some endothelium-derived signaling molecules may modulate the development of pulmonary hypertension during exercise, and that the administration of inhaled NO reduces pulmonary vascular resistance without disturbing gas exchange.

Current therapeutic approaches to pulmonary arterial hypertension

Pulmonary hypertension is a heterogeneous hemodynamic and pathophysiological state that is observed in a number of clinical conditions, which have been divided into six diagnostic groups. Although the increase in pulmonary pressure observed in these clinical groups may be similar, underlying disease mechanisms, diagnostic methods, and prognostic and therapeutic consequences are completely different. Pulmonary arterial hypertension is associated with several rare conditions that have comparable clinical and hemodynamic characteristics and exhibit virtually identical anatomical and pathological alterations in the lung microcirculation. These conditions include idiopathic and familial forms of the disease and disease forms associated with connective tissue disease, congenital heart defects involving systemic-to-pulmonary arterial shunts, portal hypertension, and HIV infection. It has been shown that treatment with specific drugs (e.g. prostanoids, endothelin-receptor antagonists and phosphodiesterase type-5 inhibitors) is effective in these patients and that these drugs can also be administered in various combinations. An evidence-based treatment algorithm has been developed for these patients. In patients with pulmonary hypertension due to left heart disease or lung disease, treatment focuses on the underlying condition and there is no convincing evidence that agents approved for pulmonary arterial hypertension are effective. For patients with chronic thromboembolic pulmonary hypertension, the treatment of choice is pulmonary endarterectomy. However, drugs intended specifically for the treatment of pulmonary arterial hypertension may be considered in inoperable cases or after suboptimal surgery.

Pulmonary hypertension in systemic sclerosis

OBJECTIVES

To discuss the clinical subtypes, pathogenesis, pathology, diagnostic evaluation, treatment options, and prognosis of pulmonary hypertension in systemic sclerosis (SSc-PH) and highlight its fundamental differences from idiopathic pulmonary arterial hypertension (IPAH).

METHODS

A Medline search for articles published between January 1969 and June 2010 was conducted using the following keywords: scleroderma, systemic sclerosis, pulmonary hypertension, pulmonary arterial hypertension, pulmonary veno-occlusive disease, pathogenesis, pathology, investigation, treatment, and prognosis. The essential differences from IPAH in pathogenesis and histopathologic findings were highlighted and the limitations of some of the investigations used were emphasized. The differences in response to currently accepted therapy and prognosis were also reviewed.

RESULTS

In scleroderma, pulmonary hypertension can be present in isolation or along with interstitial lung disease and left heart disease. In SSc-PH, the unique histopathologic findings in the lungs include intimal fibrosis, absence of plexiform lesions, and a high prevalence of pulmonary veno-occlusive disease-like lesions. Both "6-minute walk test" and NT-proBNP have their limitations in the evaluation of SSc-PH. For treatment, calcium channel blockers are ineffective and anticoagulation should be used with caution. Currently approved therapies are not as effective and prognosis is much worse in SSc-PH compared with IPAH.

CONCLUSIONS

SSc-PH is a complex condition with poorer response to therapy and worse outcome compared with that of IPAH. Recent findings have shed some light about the pathophysiology and pathogenesis of SSc-PH. Further research in this area is warranted to better understand the complex pathogenesis and devise better therapeutic strategies.

The pulmonary circulation and exercise responses in the elderly

Aging is associated with a progressive deterioration in the structure and function of the pulmonary circulation. Remodeling of the pulmonary vasculature occurs from maturity to senescence that is characterized by an increase in pulmonary vascular stiffness, pulmonary vascular pressures, and pulmonary vascular resistance along with increased heterogeneity of alveolar ventilation and pulmonary perfusion and decreased pulmonary capillary blood volume and membrane diffusing capacity that is consistent with a reduction in alveolar-capillary surface area. In theory, the aforementioned age-related changes in the pulmonary circulation may conspire to make elderly individuals more susceptible to gas exchange abnormalities during exercise. However, despite the erosion in ventilatory reserve with aging, the healthy older adult appears able to maintain alveolar ventilation at a level that allows maintenance of arterial blood gases within normal limits, even during heavy exercise. This ability to maintain adequate gas exchange likely occurs because age-related reductions in the maximal metabolic demand of exercise occur at a rate equal to or greater than the rate of deterioration in ventilatory reserve. A more prominent aspect of aging is the loss of lung elastic recoil that is associated with a modest reduction in the expiratory boundary of the maximal flow-volume envelope. This in turn increases the severity of expiratory airflow limitation and induces dynamic lung hyperinflation during exercise. The consequences of this age-associated decrease in elastic recoil on the pulmonary circulation are speculative, but an age-associated decline in elastic recoil may influence pulmonary vascular resistance and cardiac output, in addition to its impact on the work and oxygen cost of breathing.

What Limits Cardiac Performance during Exercise in Normal Subjects and in Healthy Fontan Patients?

Exercise is an important determinant of health but is significantly reduced in the patient with a univentricular circulation. Normal exercise physiology mandates an increase in pulmonary artery pressures which places an increased work demand on the right ventricle (RV). In a biventricular circulation with pathological increases in pulmonary vascular resistance and/or reductions in RV function, exercise-induced augmentation of cardiac output is limited. Left ventricular preload reserve is dependent upon flow through the pulmonary circulation and this requires adequate RV performance. In the Fontan patient, the reasons for exercise intolerance are complex. In those patients with myocardial dysfunction or other pathologies of the circulatory components, it is likely that these abnormalities serve as a limitation to cardiac performance during exercise. However, in the healthy Fontan patient, it may be the absence of a sub-pulmonary pump which limits normal increases in pulmonary pressures, trans-pulmonary flow requirements and cardiac output. If so, performance will be exquisitely dependent on pulmonary vascular resistance. This provides a potential explanation as to why pulmonary vasodilators may improve exercise tolerance. As has recently been demonstrated, these agents may offer an important new treatment strategy which directly addresses the physiological limitations in the Fontan patient.

Physical activity and right ventricular structure and function. The MESA-Right Ventricle Study

RATIONALE

Intense exercise in elite athletes is associated with increased left ventricular (LV) and right ventricular (RV) mass and volumes. However, the effect of physical activity on the RV in an older community-based population is unknown.

OBJECTIVES

We studied the association between levels of physical activity in adults and RV mass and volumes.

METHODS

The Multi-Ethnic Study of Atherosclerosis (MESA) performed cardiac magnetic resonance imaging on community-based participants without clinical cardiovascular disease. RV volumes were determined from manually contoured endocardial margins. RV mass was determined from the difference between epicardial and endocardial volumes multiplied by the specific gravity of myocardium. Metabolic equivalent-minutes/day were calculated from the self-reported frequency, duration, and intensity of physical activity.

MEASUREMENTS AND MAIN RESULTS

The study sample (n = 1,867) was aged 61.8 ± 10 years, 48% male, 44% white, 27% African American, 20% Hispanic, and 9% Chinese. Higher levels of moderate and vigorous physical activity were linearly associated with higher RV mass (P = 0.02) after adjusting for demographics, anthropometrics, smoking, cholesterol, diabetes mellitus, hypertension, and LV mass. Higher levels of intentional exercise (physical activity done for the sole purpose of conditioning or fitness) were nonlinearly associated with RV mass independent of LV mass (P = 0.03). There were similar associations between higher levels of physical activity and larger RV volumes.

CONCLUSIONS

Higher levels of physical activity in adults were associated with greater RV mass independent of the associations with LV mass; similar results were found for RV volumes. Exercise-associated RV remodeling may have important clinical implications.

Current diagnostic and prognostic assessment of pulmonary Hypertension

Recently, our view of pulmonary hypertension has been changed by the significant progress made in understanding the pathobiology, epidemiology and prognosis of the disease. The increasing number of different conditions now associated with pulmonary hypertension and the appearance of new diagnostic techniques have led to a need for a systematic diagnostic approach and a new disease classification. This review article presents an update on developments in the epidemiology and pathobiology of pulmonary hypertension, on changes in the clinical classification of the disease, and on alterations in the diagnostic algorithm. In addition, it contains detailed descriptions of the treatment recommended for patients in whom an elevated systolic pulmonary pressure is discovered on echocardiography, of the differential diagnosis of pulmonary arterial hypertension and pulmonary hypertension associated with left heart disease, and of multifactorial approaches to determining prognosis, which are three of the most actively debated topics today. Finally, a care program for patients with pulmonary arterial hypertension is proposed.

The right heart and pulmonary circulation (III). The pulmonary circulation in heart failure

Pulmonary hypertension due to left heart disease is a pathophysiological and hemodynamic state which is present in a wide range of clinical conditions that affect left heart structures. Although the pulmonary circulation has traditionally received little attention, it is reasonable to say that today it is a fundamental part of cardiological evaluation. In patients with heart failure, the most important clinical factors are the presence of pulmonary hypertension and right ventricular function. These factors are also essential for determining prognosis and must be taken into account when making some of the most important therapeutic decisions. The pathophysiological process starts passively but later transforms into a reactive process. This latter process, in turn, has one component that can be reversed with vasodilators and another component that is fixed, in which the underlying mechanism is congestive vasculopathy (i.e. essentially medial hypertrophy and pulmonary arterial intimal fibrosis). Currently no specific therapy is available for this type of pulmonary hypertension and treatment is the same as for heart failure itself. The drugs that have been shown to be effective in pulmonary arterial hypertension have generally had a neutral effect in clinical trials. Nevertheless, we are involved in the clinical development of a number of groups of pharmacological compounds that will enable us to make progress in the near future.

Right ventricular oscillatory power is a constant fraction of total power irrespective of pulmonary artery pressure

RATIONALE

Pulmonary hypertension (PH) is characterized by increased arterial load requiring more right ventricular (RV) hydraulic power to sustain adequate forward blood flow. Power can be separated into a mean and oscillatory part. The former is associated with mean and the latter with pulsatile blood flow and pressure. Because mean power provides for net blood flow, the ratio of oscillatory to total power (oscillatory power fraction) preferably should be small. It is unknown whether this is the case in pulmonary arterial hypertension (PAH).

OBJECTIVES

To derive components of power generated by the right ventricle in PAH.

MEASUREMENTS AND MAIN RESULTS

Thirty-five patients with idiopathic PAH (IPAH) and 14 subjects without PH were included. The patients were divided in two groups, "moderate" and "high," based on pulmonary artery (PA) pressure. PA pressures were obtained by right heart catheterization and PA flows by magnetic resonance imaging. Total hydraulic power (Power(total)) was calculated as the integral product of pressure and flow. Mean hydraulic power (Power(mean)) was calculated as mean pulmonary artery pressure times mean flow. Their difference is oscillatory power (Power(oscill)). Total hydraulic power in subjects without PH compared with moderate and high IPAH was 0.29 ± 0.10 W (n = 14), 0.52 ± 0.14 W (n = 17), and 0.73 ± 0.24 W (n = 18), respectively. The oscillatory power fraction is approximately 23% and not different between groups.

CONCLUSIONS

In this study, oscillatory power fraction is constant at 23% in non-PH and IPAH, implying that a considerable amount of power is not used for forward flow, making the RV less efficient with respect to its arterial load. Our findings emphasize the need to develop new therapy strategies to optimize RV power output in PAH.

Age-related prolongation of phase I of VO2 on-kinetics in healthy humans

Data are lacking regarding age-related modifications of phase I (PhI) of pulmonary Vo(2) on-kinetics during moderate-intensity exercise. We studied three groups (aged 20-30, 40-50, and 60-70 years) of 10 normal subjects, who underwent one incremental and four below-gas exchange threshold constant-power cardiopulmonary exercise tests. Data from constant-power tests were time-aligned and averaged, and the PhI-phase II transition (PhI-IItr) determined when a sharp decrease from baseline of respiratory exchange ratio occurred. The Vo(2) phase II time constant (tau) was obtained by an exponential fitting starting 1) from PhI-IItr ("experimental" fitting strategy) and 2) after 20 s from exercise onset ("fixed-duration" fitting strategy). Assuming estimated arterial-venous O(2) concentration difference not to change with respect to resting value, cardiac output (CO) values at rest and PhI-IItr were obtained according to Fick's principle. Average pulmonary flow acceleration (AFA) during PhI was calculated as the ratio between CO increase during PhI and PhI duration. PhI duration was related to age (r = 0.74, P < 0.0001), increasing from 21 +/- 3 s to 27 +/- 3 s to 32 +/- 4 s in the 20-30, 40-50, and 60-70 age groups, respectively, and to AFA (r = -0.60, P < 0.001), but not to CO increase during PhI. With respect to the experimental fitting strategy, the fixed-duration strategy overestimated Vo(2) phase II tau the more the higher the subject's age, with a lower goodness of fit in the 60-70 group (SE 0.035 vs. 0.056, P < 0.01). In conclusion, PhI duration is related to age in healthy male humans and is linked to CO acceleration-rather than to increase-during PhI. A significant overestimation of phase II tau thus may occur in healthy elderly subjects and patients with a pathologically induced longer PhI duration when fitting data where the PhI-PhIItr was not experimentally determined but assumed to be a set value (i.e., 20 s).

Effects of hyperoxia on ventilation and pulmonary hemodynamics during immersed prone exercise at 4.7 ATA: possible implications for immersion pulmonary edema

Immersion pulmonary edema (IPE) can occur in otherwise healthy swimmers and divers, likely because of stress failure of pulmonary capillaries secondary to increased pulmonary vascular pressures. Prior studies have revealed progressive increase in ventilation [minute ventilation (Ve)] during prolonged immersed exercise. We hypothesized that this increase occurs because of development of metabolic acidosis with concomitant rise in mean pulmonary artery pressure (MPAP) and that hyperoxia attenuates this increase. Ten subjects were studied at rest and during 16 min of exercise submersed at 1 atm absolute (ATA) breathing air and at 4.7 ATA in normoxia and hyperoxia [inspired P(O(2)) (Pi(O(2))) 1.75 ATA]. Ve increased from early (E, 6th minute) to late (L, 16th minute) exercise at 1 ATA (64.1 +/- 8.6 to 71.7 +/- 10.9 l/min BTPS; P < 0.001), with no change in arterial pH or Pco(2). MPAP decreased from E to L at 1 ATA (26.7 +/- 5.8 to 22.7 +/- 5.2 mmHg; P = 0.003). Ve and MPAP did not change from E to L at 4.7 ATA. Hyperoxia reduced Ve (62.6 +/- 10.5 to 53.1 +/- 6.1 l/min BTPS; P < 0.0001) and MPAP (29.7 +/- 7.4 to 25.1 +/- 5.7 mmHg, P = 0.002). Variability in MPAP among subjects was wide (range 14.1-42.1 mmHg during surface and depth exercise). Alveolar-arterial Po(2) difference increased from E to L in normoxia, consistent with increased lung water. We conclude that increased Ve at 1 ATA is not due to acidosis and is more consistent with respiratory muscle fatigue and that progressive pulmonary vascular hypertension does not occur during prolonged immersed exercise. Wide variation in MPAP among healthy subjects is consistent with variable individual susceptibility to IPE.

Pulmonary Vascular Response Patterns to Exercise: Is there a Role for Pulmonary Arterial Pressure Assessment during Exercise in the Post-Dana Point Era?

Pulmonary hypertension (PH) is often diagnosed late in its course when it purports a particularly poor prognosis. Exercise effectively unmasks early forms of several cardiopulmonary diseases but the role of performing pulmonary arterial pressure measurements during exercise in the evaluation of PH remains unclear. Whether pulmonary arterial pressure-flow relationships during exercise may provide a window into earlier diagnosis of functionally significant pulmonary arterial hypertension and left ventricular dysfunction,¹ or add incrementally to our armentarium of diagnostic tests and prognostic indicators in PH, is the topic of active ongoing investigation. Evidence is emerging that abnormal pulmonary arterial pressure response patterns to exercise, when properly indexed to increased blood flow, may help to identify early forms of heart failure and pulmonary arterial hypertension. This article will discuss approaches to performing hemodynamic measurements during exercise as well as the potential clinical utility of identifying normal and abnormal pulmonary vascular response patterns to exercise.