Cardiopulmonary function in patients with pulmonary hypertension

A diffuse lung emphysema, severe pulmonary hypertension and lack of airflow limitation

Pulmonary veno-occlusive disease is characterized by remodeling of pulmonary arteries, capillaries and venules. We report a case of diffuse lung emphysema and pulmonary veno-occlusive disease with the characteristic of having no airflow limitation. A very low diffusing capacity for carbon monoxide and results of high-resolution computed tomography of the chest suggested pulmonary veno-occlusive disease. The diagnosis was confirmed on histological analysis after lung transplantation. The combination of results of the computed tomography of the chest and the histological analysis suggested a relationship between diffuse lung emphysema and remodeling of pulmonary vessels. A distinctive pattern of mild-to-moderate airflow limitation in patients with chronic obstructive pulmonary disease and severe pulmonary hypertension has been described. This observation of the combination of diffuse emphysema, pulmonary veno-occlusive disease and no airflow limitation supports further pathophysiological studies on severe pulmonary hypertension in chronic obstructive pulmonary disease.

Lung function in pulmonary hypertension

Breathlessness is a common symptom in pulmonary hypertension (PH) and an important cause of morbidity. Though this has been attributed to the well described pulmonary vascular abnormalities and subsequent cardiac remodelling, changes in the airways of these patients have also been reported and may contribute to symptoms. Our understanding of these airway abnormalities is poor with conflicting findings in many studies. The present review evaluates these studies for the major PH groups. In addition we describe the role of cardiopulmonary exercise testing in the assessment of pulmonary arterial hypertension (PAH) by evaluating cardiopulmonary interaction during exercise. As yet, the reasons for the abnormalities in lung function are unclear, but potential causes and the possible role of inflammation are discussed. Future research is required to provide a better understanding of this to help improve the management of these patients.

Pulmonary vascular diseases

Diseases of the pulmonary vasculature are a cause of increased pulmonary vascular resistance (PVR) in pulmonary embolism, chronic thromboembolic pulmonary hypertension (CTEPH), and pulmonary arterial hypertension or decreased PVR in pulmonary arteriovenous malformations on hereditary hemorrhagic telangiectasia, portal hypertension, or cavopulmonary anastomosis. All these conditions are associated with a decrease in both arterial PO2 and PCO2. Gas exchange in pulmonary vascular diseases with increased PVR is characterized by a shift of ventilation and perfusion to high ventilation-perfusion ratios, a mild to moderate increase in perfusion to low ventilation-perfusion ratios, and an increased physiologic dead space. Hypoxemia in these patients is essentially explained by altered ventilation-perfusion matching amplified by a decreased mixed venous PO2 caused by a low cardiac output. Hypocapnia is accounted for by hyperventilation, which is essentially related to an increased chemosensitivity. A cardiac shunt on a patent foramen ovale may be a cause of severe hypoxemia in a proportion of patients with pulmonary hypertension and an increase in right atrial pressure. Gas exchange in pulmonary arteriovenous malformations is characterized by variable degree of pulmonary shunting and/or diffusion-perfusion imbalance. Hypocapnia is caused by an increased ventilation in relation to an increased pulmonary blood flow with direct peripheral chemoreceptor stimulation by shunted mixed venous blood flow.

Pulmonary vascular complications of liver disease

Hepatopulmonary syndrome and portopulmonary hypertension are two pulmonary vascular complications of liver disease. The pathophysiology underlying each disorder is distinct, but patients with either condition may be limited by dyspnea. A careful evaluation of concomitant symptoms, the physical examination, pulmonary function testing and arterial blood gas analysis, and echocardiographic, imaging, and hemodynamic studies is crucial to establishing (and distinguishing) these diagnoses. Our understanding of the pathobiology, natural history, and treatment of these disorders has advanced considerably over the past decade; however, the presence of either still increases the risk of morbidity and mortality in patients with underlying liver disease. There is no effective medical treatment for hepatopulmonary syndrome. Although liver transplantation can resolve hepatopulmonary syndrome, there appears to be worse survival even with transplantation. Liver transplantation poses a very high risk of death in those with significant portopulmonary hypertension, where targeted medical therapies may improve functional status and allow successful transplantation in a small number of select patients.

Peripheral airway obstruction in primary pulmonary hypertension

BACKGROUND

As there is controversy about changes in lung function in primary pulmonary hypertension (PPH), lung mechanics were assessed with a focus on expiratory airflow in relation to pulmonary haemodynamics.

METHODS

A cross sectional study was performed in 64 controls and 171 patients with PPH (117 women) of mean (SD) age 45 (13) years, pulmonary artery pressure (PAPmean) 57 (15) mm Hg, and pulmonary vascular resistance 1371 (644) dyne.s/cm(5).

RESULTS

Mean (SD) total lung capacity was similar in patients with PPH and controls (98 (12)% predicted v 102 (17)% predicted, mean difference -4 (95% confidence interval (CI) -7.89 to -0.11); residual volume (RV) was increased (118 (24)% predicted v 109 (27)% predicted, mean difference 9 (95% CI 1.86 to 16.14); and vital capacity (VC) was decreased (91 (16)% predicted v 102 (10)% predicted, mean difference -11 (95% CI 15.19 to -6.80). RV/TLC was increased (117 (27)% predicted v 97 (29)% predicted, mean difference 20 (95% CI 12.3 to 27.8)) and correlated with PAPmean (r=0.31, p<0.001). In patients with PAPmean above the median of 56 mm Hg, RV/TLC was further increased (125 (32)% predicted v 111 (22)% predicted, mean difference -14 (95% CI -22.2 to -5.8)). Expiratory flow-volume curves were reduced and curvilinear in patients with PPH.

CONCLUSIONS

Peripheral airway obstruction is common in PPH and is more pronounced in severe disease. This may contribute to symptoms. Reversibility of bronchodilation and relation to exercise capacity need further evaluation.

Pulmonary function test abnormalities in pulmonary vascular disease and chronic heart failure

Diagnostic criteria based on pulmonary function testing for pulmonary vascular disease and CHF are imprecise. Although these tests constitute a necessary part of the work-up of a patient with dyspnea, additional studies are required to obtain a final diagnosis in the setting of cardiopulmonary vascular disease. In contrast, specific pulmonary function tests may offer an objective means of assessing severity of dysfunction resulting from pulmonary hypertension or CHE Serial measurements of pulmonary function offer insight into general and specific patterns of cardiopulmonary vascular disease and are useful in evaluating response to treatment.

Responses to constant work rate bicycle ergometry exercise in primary pulmonary hypertension: the effect of inhaled nitric oxide

OBJECTIVES

The purpose of this study was to investigate the responses of patients with primary pulmonary hypertension (PPH) to constant work rate exercise and to examine the effect of nitric oxide (NO) inhalation.

BACKGROUND

Maximal exercise tolerance is reduced in PPH, but gas exchange responses to constant work rate exercise have not been defined. We hypothesized that increased pulmonary vascular resistance in PPH would reduce the rate of rise of minute oxygen consumption in response to a given work rate. Because NO may lower pulmonary vascular pressures in PPH, we also postulated that inhaled NO might ameliorate gas exchange abnormalities.

METHODS

Nine PPH patients and nine matched normal subjects performed 6-min duration constant work rate cycle ergometry exercise (33.9+/-13.4 W). Patients performed two experiments: breathing air and breathing air with NO (20 ppm). Preexercise right ventricular systolic pressure was assessed by Doppler echocardiography. Normal subjects performed the air experiment only. Gas exchange and heart rate responses were characterized by fitting monoexponential curves.

RESULTS

In PPH patients, resting right ventricular systolic pressure fell after NO inhalation (from 83.8+/-16.9 to 73.9+/-21.6 mm Hg, p<0.01, analysis of variance with Tukey correction), but not after breathing air alone (from 88.0+/-20.8 to 86.7+/-20.6 mm Hg, p = NS). Nitric oxide did not affect any of the gas exchange responses. Minute oxygen consumption was similar by the end of exercise in patients and normals, but increased more slowly in patients (mean response time [MRT]: air, 63.17+/-14.99 s; NO, 61.60+/-15.45 s) than normals (MRT, 32.73+/-14.79, p<0.01, analysis of variance, Tukey test). Minute oxygen consumption kinetics during recovery were slower in patients (MRT air: 82.50+/-29.94 s; NO, 73.36+/-15.87 s) than in normals (MRT, 34.59+/-7.11 s, p<0.01). Heart rate kinetics during exercise and recovery were significantly slower in patients than in normals.

CONCLUSIONS

The cardiac output response is impaired in PPH. Nitric oxide lowered pulmonary artery pressure at rest, but failed to improve exercise gas exchange responses.

Indications for thrombolytic therapy in acute pulmonary embolism

Pulmonary thromboembolism is commonly misdiagnosed and is associated with significant morbidity and mortality both in the early and late stages. A major cause of late morbidity is chronic pulmonary hypertension. Although the incidence of chronic thromboembolic pulmonary hypertension is unknown, there is anatomic and physiologic evidence that it is responsible for a significant degree of the late morbidity and mortality following acute pulmonary embolism. In the absence of underlying cardiopulmonary disease, pulmonary artery pressure is a useful indicator of the severity of acute pulmonary embolism and of the patient's prognosis. Thrombolytic agents accelerate the lysis of the thromboemboli, offer an excellent alternative to emergency embolectomy, and are likely to decrease the incidence of chronic pulmonary hypertension. All currently available agents have been shown to be effective and have similar bleeding-complication profiles. In this review, we discuss the natural history and pathophysiology of pulmonary thromboembolic disease, as well as applications of thrombolytic therapy in the treatment of acute pulmonary embolism.

Pulmonary gas exchange and exercise performance in pulmonary hypertension

Patients with pulmonary hypertension have disordered pulmonary gas exchange and impaired exercise tolerance. The hypoxemia is due to mild ventilation-perfusion (VA/Q) inequality exaggerated by the presence of a low mixed venous PO2 (PvO2) and is accentuated during exercise due to a further fall in PvO2. This in turn may be worsened by vasodilators which increase the degree of VA/Q inequality. Decreased exercise tolerance is due predominantly to cardiac limitation, and thus an improvement in cardiac function subsequent to successful vasodilation can be assessed by improved exercise performance.

Pulmonary mechanical, ventilatory, and gas exchange abnormalities in rats with monocrotaline-induced pulmonary hypertension

Recent clinical studies have suggested that peripheral airways dysfunction contributes to the pathogenesis of idiopathic pulmonary hypertension. To determine whether similar peripheral airways defects occur in a common animal model of pulmonary hypertension, pulmonary function tests were performed in adult male rats rendered pulmonary hypertensive with a single subcutaneous injection of monocrotaline. At 20 days post treatment, animals exhibited well-developed right ventricular hypertrophy coincident with significant changes in lung volumes, pulmonary mechanics, and gas exchange function indicative of a severe combined restrictive and obstructive airways disorder. Morphologic changes in alveolar integrity compatible with such a pulmonary defect also were observed in monocrotaline-treated animals. The specific changes in pulmonary function observed in monocrotaline-treated rats were qualitatively similar to abnormalities reported in patients with idiopathic pulmonary hypertension. These results demonstrate that significant pulmonary mechanical, ventilatory, and gas exchange dysfunction is present in rats with monocrotaline-induced pulmonary hypertension and highlight the suitability of this model for investigating a potential contributory role of pulmonary function abnormalities in the pathogenesis of this disorder.

Exercise induced pulmonary vasoconstriction

Pulmonary vascular resistance normally falls or remains unchanged during exercise. Seven children with pulmonary hypertension were exercised during cardiac catheterisation after operative correction of ventricular septal defect (6) and truncus arteriosus (1). Except for the presence of moderate pulmonary hypertension, resting haemodynamics in these seven children were similar to those of normal children of equal age, but during exercise the postoperative patients showed a rise rather than a fall (+2% vs -18%) in total pulmonary vascular resistance. Two of the seven children had a substantial increase in pulmonary arteriolar resistance during exercise (from 509 to 715 dyne s cm-5 in one patient and from 606 to 828 dyne s cm-5 in the other). These two patients did not differ from normal children in respect of arterial or mixed venous oxygen saturations or of pH with exercise, nor was left atrial pressure related to the rise in pulmonary resistance. These two patients, however, had only a small rise in cardiac output during exercise (6.8% and 43.1%) in spite of a substantial increase in oxygen consumption (121% and 373%). One of the patients with exercise-induced pulmonary vasoconstriction had an 82% increase in resting pulmonary vascular resistance over a five year period subsequent to her first exercise study. Analysis of these data, and those previously reported, suggests that exercise induced pulmonary vasoconstriction may occur in 10 to 25% of patients who survive correction of certain congenital cardiac defects. The vasoconstriction cannot be attributed to abnormal changes in blood gases or left atrial pressure, and may be an early sign of progressive pulmonary hypertension.

Peripheral airways obstruction in idiopathic pulmonary artery hypertension (primary)

The mechanical properties of the lung were studied in ten nonsmokers with idiopathic pulmonary artery hypertension (IPAH) (mean pulmonary artery pressure 65.7 +/- 30 mm Hg). In the routine lung test, residual volume was found to be abnormal (greater than 120 percent of the predicted) in seven patients, and measured airway resistance was normal in eight out of the ten patients. A decreased FEF 75-85 percent, abnormal values for the helium-air flow ratios and increased closing capacities were documented in eight of ten patients in whom lung elastic recoil was normal (six of ten) or increased (four of ten). These features suggest peripheral airways obstruction (PAO) which was also supported by histopathologic findings in three cases (one biopsy and two necropsies). The observed changes in lung compliance could be related to the behavior of the coupling of the air-space and vascular compartments. The etiology of PAO in IPAH patients is not known, but our results indicate that both the peripheral airways and the pulmonary circulation are affected. The knowledge of PAO in IPAH patients could help to better understand the observed V/Q inequality in this entity.

Effects of oxygen breathing on pulmonary vascular input impedance in patients with pulmonary hypertension

The effect of oxygen breathing on the stiffness of the large pulmonary artery has not been elucidated. We analyzed the proximal pulmonary arterial impedance with a multisensor catheter in ten patients with pulmonary arterial hypertension (PAH), eight patients with pulmonary venous hypertension, and six control subjects. The stiffness of the vessel was quantified by the characteristic impedance (Zo) and compared with the plasma norepinephrine level. Ten minutes of high-oxygen breathing decreased the Zo (from 78 +/- 18 to 57 +/- 14 dynes.sec.cm-5, p less than 0.01) and pulmonary arterial resistance in all the cases with PAH. In this group, norepinephrine also decreased (from 381 +/- 89 to 319 +/- 77 pg/ml, p less than 0.01) following the correction of hypoxemia. Yet, those parameters did not change in the other two groups. These results indicate that in patients with PAH, oxygen breathing can reduce the stiffness of the main pulmonary artery because of the sympatholytic effect.

Longterm follow-up of patients with pulmonary thromboembolism. Late prognosis and evolution of hemodynamic and respiratory data

Seventy-six patients with various forms of pulmonary thromboembolic disease were followed-up for 1 to 15 years. All were free of other cardiopulmonary disease at the time of the first examination which was performed at least two months after the last pulmonary embolism. Catheterization was repeated in all survivors on average 4.8 years later. Severe chronic pulmonary hypertension (mean pulmonary artery pressure (PPA greater than 30 mm Hg) did not occur after a single episode of acute embolism, was infrequent after single subacute or recurrent emboli (8 of 9 patients), and was common after occult emboli (12 of 13 patients). Mortality in all clinical groups correlated with PPA and with the presence of right heart failure. In survivors, no correlation was found between the longterm changes of PPA and age, duration of disease, interval between catheterizations, PaO2, or cardiac output. Pulmonary hypertension progressed further in patients with initial PPA greater than 30 mm Hg. In contrast, none of the patients with normal or borderline PPA at the initial examination developed severe pulmonary hypertension during the follow-up. Since the future course of patients could be predicted from the first examination, repeated hemodynamic investigation proved to be of minor prognostic value.

Mechanisms of gas exchange abnormality in patients with chronic obliterative pulmonary vascular disease

We have examined the mechanisms of abnormal gas exchange in seven patients with chronic obliteration of the pulmonary vascular bed secondary to recurrent pulmonary emboli or idiopathic pulmonary hypertension. All of the patients had a widened alveolar-arterial oxygen gradient and four were significantly hypoxemic with arterial partial presssures of oxygen less than 80 torr. Using the technique of multiple inert gas elimination, we found that ventilation-perfusion (VA/Q) relationships were only minimally abnormal with a mean of 10% (range, 2--19%) of cardiac output perfusing abnormal units. These units consisted of shunt and units with VA/Q ratios less than 0.1. In addition, the dead space was found to be normal in each patient. There was no evidence for diffusion impairment, and the widened alveolar-arterial oxygen gradient was completely explained by VA/ inequality. Significant hypoxemia occurred only when VA/Q inequality was combined with a low mixed venous oxygen content.