Noninvasive assessment and monitoring of the pulmonary circulation

In pulmonary vascular disease, changes in the pulmonary vascular bed will lead to altered pulmonary haemodynamics. This review describes the application of several physiological principles to measure these changes noninvasively by means of novel techniques. Flow characteristics of blood through the pulmonary vascular bed alter in pulmonary vascular disease. Recent developments in magnetic resonance imaging and computed tomography make it possible to visualise and quantify these abnormal flow patterns. Information regarding pulmonary perfusion can also be obtained by measuring the electrical impedance changes in the lung by electrical impedance tomography. A more indirect approach to measure the pulmonary blood flow is the measurement of the absorption of acetylene, a perfusion limited gas. Information on the pulmonary vascular bed can also be obtained by the measurement of exhaled products of the pulmonary vascular endothelium, such as nitric oxide. Although all the techniques described offer new ways to diagnose or monitor pulmonary vascular disease, clinical data on these techniques are limited. Further improvement and evaluation of the clinical value of these techniques are therefore obligatory before they can be used in clinical practice.

Angiotensin-converting enzyme genotype and the ventilatory responseto exertional hypoxia

The "insertion" (I) rather than "deletion" (D) variant of the human angiotensin-converting enzyme (ACE) gene is associated with both lower tissue ACE activity and elite performance at high altitude. Three genotypes, II, ID and DD, are thus represented in the population. The authors examined whether an improved ventilatory response to hypoxic exercise may contribute to this effect. Subjects (n=60; 37 male, mean+/-SEM age 23.6+/-0.6 yrs, 14 II, 30 ID, 16 DD) underwent incremental cardiopulmonary exercise testing to establish maximal oxygen uptake and ventilatory threshold (VT). Four hours later, subjects exercised for 6 mins at 50% of the workload at VT. The protocol was repeated 15 mins later while breathing 12.5+/-0.5% oxygen in nitrogen. All subject characteristics were independent of genotype, as were data during normoxic exercise. However, the hypoxia-induced rise in minute ventilation was significantly greater among those of II genotype (39.6+/-4.1% versus 27.9+/-2.0% versus 28.4+/-2.2% for II versus ID versus DD, respectively). These data are supported by a significantly greater decrease in end tidal carbon dioxide (consistent with an increase in alveolar ventilation) among those homozygous for the I allele (II -18.7+/-1.3%, ID -15.7+/-0.4%, DD -15.1%+/-1.1). The ventilatory response to hypoxic exercise is influenced by angiotensin-converting enzyme genotype. Potential implications concern high altitude performance and the pathogenesis and management of hypoxic lung disease.

Ventricular mass index using magnetic resonance imaging accurately estimates pulmonary artery pressure

Magnetic resonance imaging (MRI) can provide accurate anatomical measurements of the cardiac ventricles. This study investigated whether a calculated ventricular mass index (VMI) would provide an accurate means of estimating pulmonary artery pressure noninvasively, and compared the results with conventional Doppler echocardiography and invasive measurement. A total of 26 subjects referred for investigation of pulmonary hypertension were studied by MRI and echocardiography within 2 weeks of cardiac catheterisation. The correlations for mean pulmonary artery pressure were as follows: VMI (ratio of right ventricular mass over left ventricular mass) r=0.81; pulmonary artery systolic pressure (echocardiography) r=0.77. The confidence intervals for the VMI were narrower than for echocardiography. Sensitivity and specificity for pulmonary hypertension were 84 and 71% respectively for the VMI compared with 89 and 57% for echocardiography. The calculated ventricular mass index provides an accurate and practical means of estimating pulmonary artery pressure noninvasively in pulmonary hypertension and may provide a more accurate estimate than Doppler echocardiography. This may be because it reflects the right ventricular response to sustained pulmonary hypertension over a long period and is not influenced by short-term physiological variables affecting echocardiography, such as heart rate, posture, hydration status and oxygen supplementation.

Ambulatory pulmonary artery pressure monitoring during sleep and exercise in normal individuals and patients with COPD

BACKGROUND

Pulmonary hypertension is a common complication of chronic obstructive airways disease (COPD) and its presence implies a poor prognosis. However, it is difficult to measure and its specific contribution to symptoms is difficult to quantify. A micromanometer tipped pulmonary artery catheter was used to measure pulmonary artery pressure (PAP) during sleep and on exercise.

METHODS

Ten patients (five with COPD receiving long term oxygen therapy and five normal individuals) were studied. Pulmonary artery pressure was recorded continuously during two periods of sleep (breathing oxygen followed by air for the COPD group) and during exercise.

RESULTS

In the COPD group PAP during sleep on oxygen was significantly lower than PAP during sleep breathing air (mean (SD) difference 9.6 (5.3) mm Hg, 95% CI 4.9 to 14.3, p= 0.016). PAP during exercise was not significantly different from PAP during sleep breathing air (mean (SD) difference 0.8 (8.9) mm Hg, 95% CI -7.0 to 8.6, p= 0.851). In normal individuals the group mean (SD) PAP was 15 (5.9) mm Hg for the first nocturnal period and 15 (5.7) mm Hg for the second nocturnal period. PAP during exercise was not significantly different from PAP during sleep breathing air (mean (SD) difference 3.3 (2.2) mm Hg, 95% CI 1.1 to 5.5, p= 0.061).

CONCLUSION

In patients with COPD, PAP rose significantly during sleep to levels similar to those measured during exercise, but this could be reversed with oxygen.

Build your own infection control link nurse: an innovative study day

Infection control is everyone's business and it is important that all members of staff observe good infection control practice. An effective infection control link nurse system has been shown to support and develop this approach. The strength of ward-based infection control link nurses depends upon their effectiveness as role models and their ability to influence practice on their wards and beyond. In addition, the degree of respect they command from their peers and colleagues and the amount and quality of knowledge they possess is crucial. This paper describes an innovative approach taken in Mid-Essex, which allowed infection control link nurses to assess their capabilities and limitations in communicating with and influencing colleagues. In addition, we show how quantitative measures may be made available by this approach. Such measures may be used to explain to management how particular areas of infection control practice (e.g. the need for infection control link nurses to have more authority and more 'muscle') may be important.

Chronic hypoxia induces constitutive p38 mitogen-activated protein kinase activity that correlates with enhanced cellular proliferation in fibroblasts from rat pulmonary but not systemic arteries

Pulmonary hypertension occurs commonly in patients with chronic hypoxic lung disease and is characterized by the remodeling of the pulmonary artery walls. The molecular mechanisms underlying such remodeling are unknown but we have recently shown that the stress-activated (Jnk and p38) mitogen-activated protein (MAP) kinases are activated in pulmonary artery fibroblasts following acute hypoxia. We now show that Erk and p38 MAP kinases are constitutively activated in fibroblasts derived from the remodeled pulmonary, but not the systemic circulation from rats exposed to chronically hypoxic conditions. Moreover, we find that such fibroblasts show sustained enhanced proliferative capacities relative to pulmonary artery fibroblasts derived from normoxic rats or to aortic fibroblasts from either normoxic or hypoxic rats. Finally, abrogation of p38, but not Erk MAP kinase activity by use of specific inhibitors, prevents the enhanced proliferative capacity exhibited by pulmonary artery fibroblasts. Taken together, these data suggest that enhanced p38 MAP kinase activity provides a molecular mechanism to explain the proliferation of pulmonary artery fibroblasts required for remodeling of the pulmonary vasculature.

Pulmonary artery pressure measurement during exercise testing in patients with suspected pulmonary hypertension

It is recognized that exercise produces abnormally large increases in pulmonary artery pressure in patients with pulmonary vascular disease as a consequence of a variety of disorders, but the relationship between pressure and cardiopulmonary exercise performance is poorly understood. This lack of understanding is due (in part) to difficulty making measurements of pulmonary haemodynamics using conventional fluid filled catheters. This article seeks to improve understanding by comparing variables measured during formal exercise testing with simultaneous measurements of pulmonary artery pressure using a micro-manometer tipped catheter. Ten patients with suspected pulmonary hypertension were studied using a micromanometer tipped pulmonary artery catheter, during cardiopulmonary exercise testing. Ventilatory equivalents for oxygen and carbon dioxide correlated with the pulmonary artery pressure measured on exercise, but oxygen pulse and oxygen uptake did not. Ventilatory equivalents, noninvasively measured during exercise, may merit further study as potential surrogates of pulmonary artery pressure and hence be useful in identifying individuals at risk of developing pulmonary hypertension.

The effect of amlodipine on respiratory and pulmonary vascular responses to hypoxia in mountaineers

Calcium antagonists are known to reduce the incidence of high-altitude pulmonary oedema, but the mechanism is unclear. The aim of this study was to examine the effects of the calcium antagonist, amlodipine, on cardiac and respiratory responses in normoxia and hypoxia. Fourteen normal subjects aged 31+/-4 yrs who had climbed to altitudes of 5,000-7,500 m without problems were randomly assigned to a double-blind crossover trial of amlodipine versus placebo, using sea-level inspiratory hypoxia to simulate altitude. Doppler echocardiographic estimates of resting pulmonary haemodynamics and cycle ergometer test results of cardiorespiratory responses to exercise were recorded in normoxia and hypoxia. It was found that, although hypoxic pulmonary vasoconstriction (HPV) was not significantly reduced by amlodipine, the effect of the drug on HPV was inversely related to the serum level of amlodipine. Amlodipine did not alter left ventricular function measured echocardiographically. During exercise, amlodipine increased breathlessness, measured using standard scales, in both normoxia and hypoxia but had no effect on ventilatory variables. It was concluded that amlodipine has the potential to block hypoxic pulmonary vasoconstriction as evidenced by a drug concentration-related decrease in resting tricuspid regurgitation jet velocity without any change in resting myocardial contractility. However, with amlodipine, the subjects felt more breathless during exercise. The reasons for this increase in breathlessness are not clear.

Is pulmonary embolism a common cause of chronic pulmonary hypertension? Limitations of the embolic hypothesis

The hypothesis that chronic thromboembolic pulmonary hypertension results from unresolved pulmonary embolism has strongly influenced the diagnosis and management of this disease since the 1960s. However, it is nearly impossible to induce chronic pulmonary hypertension in any animal species by means of repeated embolization of thrombotic material. The haemodynamic effects of thrombotic pulmonary embolism of different degrees of magnitude have also been studied in humans and there is little to suggest that chronic pulmonary hypertension is a likely long term outcome. Furthermore many conditions which predispose to venous thromboembolism do not appear to cause thromboembolic pulmonary hypertension. Other arteriopathic and atherosclerotic risk factors, are found in patients with chronic thromboembolic pulmonary hypertension, but not in those with venous thrombosis, suggesting that these may be unrelated conditions. Thrombosis in situ of the pulmonary arteries is common in severe pulmonary hypertension of any cause. Such thrombosis cannot usually be distinguished from pulmonary embolism. It is hypothesized that in situ thrombosis and pulmonary arteriopathy are common causes of vascular occlusion which is usually diagnosed as "chronic thromboembolic pulmonary hypertension" and that venous thromboembolism is unlikely to be a common cause of chronic pulmonary hypertension. It is further hypothesized that pulmonary embolism is seldom the sole cause of "chronic thromboembolic pulmonary hypertension".

Hypoxia enhances cellular proliferation and inositol 1,4, 5-triphosphate generation in fibroblasts from bovine pulmonary artery but not from mesenteric artery

When pulmonary hypertension occurs in the face of hypoxia there is remodeling of all three layers of the pulmonary vessels, but in particular, there is an increase in number of adventitial fibroblasts. Hypoxia causes vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation. We hypothesized that there are fundamental differences in oxygen sensing and cell signaling between systemic and pulmonary artery cells in response to hypoxia. Here, we determined the effect of hypoxia either alone or in combination with known growth factors such as serum, endothelin-1 (ET-1), and platelet-derived growth factor (PDGF) on the proliferative responses of bovine pulmonary artery and mesenteric artery fibroblasts. Fibroblasts were obtained from primary cultures. Growth was assessed by [3H]thymidine incorporation. Inositol 1,4,5-triphosphate (IP3) generation was measured using a competitive binding assay. Hypoxia alone increased proliferation of pulmonary artery fibroblasts (611 +/- 24%), but not in those from the mesentery. Furthermore, hypoxia had the effect of increasing the replicative response of pulmonary fibroblasts to serum and PDGF, but no change was observed in the mesenteric cells. ET-1 had no effect on growth of either cell type. PDGF gave rise to a significant elevation in IP3 production under hypoxic conditions in the pulmonary artery cells (234%), but not in the mesenteric cells. ET-1 caused no change in IP3 production in any cell type. These data suggest that hypoxia sensitizes pulmonary artery fibroblasts to the proliferative effect of mitogens through a pathway that is not present, or is present but repressed, in the mesenteric cells.

Pulmonary artery pressure variation in patients with connective tissue disease: 24 hour ambulatory pulmonary artery pressure monitoring

BACKGROUND

The specific contribution of secondary pulmonary hypertension to the morbidity and mortality of patients with underlying lung disease can be difficult to assess from single measurements of pulmonary artery pressure. We have studied patients with secondary pulmonary hypertension using an ambulatory system for measuring continuous pulmonary artery pressure (PAP). We chose to study patients with connective tissue disease because they represent a group at high risk of pulmonary vascular disease, but with little disturbance of lung function.

METHODS

Six patients (five with progressive systemic sclerosis and one with systemic lupus erythematosis) were studied. They underwent preliminary cardiopulmonary investigations followed by Doppler echocardiography, right heart catheterisation, and ambulatory pulmonary artery pressure monitoring to measure changes in pressure over a 24 hour period including during a formal exercise test.

RESULTS

All patients had pulmonary hypertension as measured by Doppler echocardiography with estimated pulmonary artery systolic pressures of 40-100 mm Hg. Pulmonary function testing revealed virtually normal spirometric values (mean FEV1 86.9% predicted) but marked reduction in CO gas transfer factor (KCO 57.8% predicted). Exercise responses were impaired with mean VO2max 50.6% predicted. Ambulatory PAP monitoring indicated significant changes in pressures with variation in posture and activity throughout 24 hours. Resting PAP did not predict the change in PAP seen on exercise.

CONCLUSION

Conventional methods of assessment of the pulmonary circulation based on single measurements in the supine position may underestimate the stresses faced by the right side of the circulation. This ambulatory system allows monitoring of pulmonary haemodynamics continuously over 24 hours during normal activities of daily living. These measurements may increase our understanding of the contribution made by secondary pulmonary hypertension to the morbidity and mortality of the underlying lung disease.

Hypoxic stimulation of the stress-activated protein kinases in pulmonary artery fibroblasts

Pulmonary hypertension in response to chronic hypoxia is invariably accompanied by remodeling of the pulmonary vessels but the mechanism by which hypoxia increases the replication of vascular cells is unknown. To investigate the hypothesis that hypoxia stimulates intracellular kinase cascades we measured the activity of "classic" mitogen-activated protein (MAP) kinase pathways and "stress- activated" MAP kinase pathways in bovine pulmonary artery fibroblasts subjected to hypoxia for up to 30 h. Hypoxia (1% O2) stimulated strongly the stress-activated protein kinases, c-Jun NH2-terminal kinase (JNK) and p38 MAP kinase. Two peaks of p38 MAP kinase activity at 6 and 24 h were associated with an increase in the activity of mitogen-activated protein kinase-activated protein (MAPKAP) kinase-2, the immediate downstream target of p38 MAP kinase. Furthermore, the second phase of p38 MAP kinase activity could be reversed if cells were reoxygenated after 12 h. These data suggest that hypoxic stimulation of pulmonary artery cells is mediated by activation of the stress-activated protein kinases.

Investigation of pleural effusion: an evaluation of the new Olympus LTF semiflexible thoracofiberscope and comparison with Abram's needle biopsy

STUDY OBJECTIVES

Recently, pulmonologists have performed thoracoscopy under local anesthesia using rigid thoracoscopes or flexible bronchoscopes. The latter allow greater access within the pleural cavity but are difficult to manipulate. The Olympus LTF semiflexible fiberoptic thoracoscope combines features of both instruments, having a solid body and a flexible terminal section. In the first study with this instrument, we evaluated ease of use and compared diagnostic yield with closed needle biopsy.

PATIENTS

Twenty-four patients with pleural effusion were investigated.

SETTING

Scottish University Hospital.

DESIGN

Thoracoscopy was performed in the bronchoscopy suite after premedication with atropine and papaveretum. Following a standard Abram's needle biopsy, the LTF thoracoscope was inserted through a flexible introducer (Olympus Optical Co Ltd; Tokyo, Japan). The pleura was inspected and biopsy specimens were taken of suspicious areas.

RESULTS

The final diagnosis was malignant pleural effusion in 16 of 24 patients. Ten of 16 were positive by Abram's biopsy, giving a sensitivity of 62%. Thirteen of 16 were positive by fiberoptic thoracoscopy, giving an improved sensitivity of 81%. The LTF thoracoscope was easy to use for pulmonologists experienced in rigid thoracoscopy and flexible bronchoscopy. Excellent views of the pleura were obtained from a single entry point. The procedure was well tolerated and no complications were encountered.

CONCLUSION

The LTF thoracoscope allows excellent pleural access but a larger biopsy channel (currently 2 mm) might increase the accuracy of diagnosis.

The acute effects of prostacyclin on pulmonary hemodynamics in patients with pulmonary hypertension secondary to systemic sclerosis

OBJECTIVE

To determine whether patients with isolated pulmonary hypertension secondary to systemic sclerosis (SSc) have a pulmonary vasculature that is responsive to treatment with vasodilators.

METHODS

Seven SSc patients with pulmonary hypertension underwent right heart catheterization. Pulmonary pressures and cardiac output were measured before and during a systemic intravenous infusion of prostacyclin.

RESULTS

Both pulmonary arterial mean pressure and pulmonary vascular resistance decreased significantly with prostacyclin infusion (median decrease 11% and 32%, respectively), with a concomitant increase in cardiac output (median increase 26%). No adverse hemodynamic effects were noted during the infusion.

CONCLUSION

Vasospasm contributes to the pulmonary hypertension complicating SSc. This feature may be amenable to treatment with vasodilators.