REGIONAL LUNG FUNCTION IN PATIENTS WITH MITRAL STENOSIS STUDIED WITH XENON-133 DURING AIR AND OXYGEN BREATHING

Measurement of regional compliance using 4DCT images for assessment of radiation treatment

PURPOSE

Radiation-induced damage, such as inflammation and fibrosis, can compromise ventilation capability of local functional units (alveoli) of the lung. Ventilation function as measured with ventilation images, however, is often complicated by the underlying mechanical variations. The purpose of this study is to present a 4DCT-based method to measure the regional ventilation capability, namely, regional compliance, for the evaluation of radiation-induced lung damage.

METHODS

Six 4DCT images were investigated in this study: One previously used in the generation of a POPI model and the other five acquired at Henry Ford Health System. A tetrahedral geometrical model was created and scaled to encompass each of the 4DCT image domains. Image registrations were performed on each of the 4DCT images using a multiresolution Demons algorithm. The images at the end of exhalation were selected as a reference. Images at other exhalation phases were registered to the reference phase. For the POPI-modeled patient, each of these registration instances was validated using 40 landmarks. The displacement vector fields (DVFs) were used first to calculate the volumetric variation of each tetrahedron, which represents the change in the air volume. The calculated results were interpolated to generate 3D ventilation images. With the computed DVF, a finite element method (FEM) framework was developed to compute the stress images of the lung tissue. The regional compliance was then defined as the ratio of the ventilation and stress values and was calculated for each phase. Based on iterative FEM simulations, the potential range of the mechanical parameters for the lung was determined by comparing the model-computed average stress to the clinical reference value of airway pressure. The effect of the parameter variations on the computed stress distributions was estimated using Pearson correlation coefficients.

RESULTS

For the POPI-modeled patient, five exhalation phases from the start to the end of exhalation were denoted by P(i), i = 1, ..., 5, respectively. The average lung volume variation relative to the reference phase (P5) was reduced from 18% at P1 to 4.8% at P4. The average stress at phase P(i) was 1.42, 1.34, 0.74, and 0.28 kPa, and the average regional compliance was 0.19, 0.20, 0.20, and 0.24 for i = 1, ..., 4, respectively. For the other five patients, their average R(v) value at the end-inhalation phase was 21.1%, 19.6%, 22.4%, 22.5%, and 18.8%, respectively, and the regional compliance averaged over all six patients is 0.2. For elasticity parameters chosen from the potential parameter range, the resultant stress distributions were found to be similar to each other with Pearson correlation coefficients greater than 0.81.

CONCLUSIONS

A 4DCT-based mechanical model has been developed to calculate the ventilation and stress images of the lung. The resultant regional compliance represents the lung's elasticity property and is potentially useful in correlating regions of lung damage with radiation dose following a course of radiation therapy.

Reduction of mismatch of global ventilation and perfusion on exercise is related to exercise capacity in chronic heart failure

BACKGROUND

The inability to match lung perfusion to ventilation because of a reduced cardiac output on exercise contributes to reduced exercise capacity in chronic heart failure.

OBJECTIVE

To quantify ventilation to perfusion matching at rest and at peak exercise in patients with chronic heart failure and relate this to haemodynamic and ventilatory variables of exercise capacity.

DESIGN

Eight men in New York Heart Association class II underwent maximal bicycle ergometry with expired gas analysis.

MAIN OUTCOME MEASURES

On separate days, ventilation and perfusion gamma camera imaging was performed at rest, and at 80% of previous peak exercise heart rate during bicycle ergometry. The vertical distribution of mismatch between ventilation and perfusion (V/Q) was estimated from subtracted profiles of activity (ventilation and perfusion) to derive a numerical index of global mismatch.

RESULTS

Maximal mean (SD) oxygen consumption on bicycle ergometry was 16.0 (4.5) ml min-1 kg-1. There was a reduction in the global V/Q mismatch index from 23.96 (5.90) to 14.88 (7.90) units (p < 0.01) at rest and at peak exercise. Global V/Q mismatch index at peak exercise correlated negatively with maximal minute ventilation (R = -0.90, p < 0.01) and with maximal mean arterial pressure (R = -0.79, p < 0.05), although no relation was seen with maximal oxygen consumption. The reduction in global V/Q mismatch index from rest to peak exercise correlated with maximal oxygen consumption (R = 0.88, p < 0.01), and with maximal minute ventilation (R = 0.87, p < 0.01).

CONCLUSIONS

During exercise in patients with chronic heart failure, there is a reduction in the global V/Q mismatch index. A lower global V/Q mismatch index at peak exercise is associated with higher maximal ventilation. The reduction in global V/Q mismatch index on exercise correlates well with maximal exercise capacity. This may imply that the inability to perfuse adequately all regions of lung on exercise and match this to ventilation is a factor determining exercise capacity in chronic heart failure.

Regional extravascular lung density and fractional pulmonary blood volume in patients with chronic pulmonary venous hypertension

Using a technique based on positron transmission and emission tomography, we measured regional extravascular lung density (lung tissue and interstitial water per unit thoracic volume) and fractional pulmonary blood volume (volume of blood per unit thoracic volume) in normal subjects and in patients with cardiomyopathy and chronic pulmonary venous hypertension. We found an increase in extravascular lung density in the patients. Extravascular density was increased in all parts of the lung studied, but higher values were seen in the dorsocaudal portion than in the ventrocaudal portion of the lung (average 151% and 130% of normal, respectively). Fractional blood volume was markedly reduced in the dorsocaudal part of the lung (mean 74% of normal). The increase in extravascular density probably reflects structural changes in the lung as well as accumulation of interstitial fluid. The distribution of extravascular density is consistent with previous radiological and morphological studies, and may reflect a higher tendency to oedema formation in the dependent parts of the lung. The measurements of fractional blood volume suggest that intrapulmonary blood volume is reduced in chronic pulmonary venous hypertension. This may reflect a decrease in the distensibility of the pulmonary vessels due to structural abnormalities, as well as functional changes in the pulmonary vasculature.

Regional lung function after pneumonectomy

Hall, D. R. (1974).Thorax, 29, 425-431. Regional lung function after pneumonectomy. Regional lung function was studied with xenon-133 in 10 patients with bronchial carcinoma before and again three to six months after pneumonectomy. It was found that ventilation and perfusion were often considerably reduced in the tumour-bearing lung and that the greater part of the cardiac output had apparently been diverted to the unaffected lung before operation. The regional distribution of ventilation and perfusion in the lung remaining after surgery was essentially unchanged from that measured in the same lung preoperatively and no different from the pattern seen in 10 normal volunteers.

Regional lung function in patients with increased unilateral transradiancy of the lung in the presence of cardiac disease

Regional lung function has been studied with xenon-133 in two patients with unilateral transradiancy of the lung and coincidental cardiac disease. One patient had severe mitral stenosis with pulmonary venous and pulmonary arterial hypertension, the other had a secundum type of atrial septal defect with a pulmonary blood flow which was increased to 25 litres per minute. In both instances the overall perfusion of the transradiant lung was diminished but the regional distribution of blood flow was the same within both the `normal' and the transradiant lung. In the patient with mitral stenosis there was an abnormal increase in upper zone perfusion resulting in a reversal of the normal pattern of pulmonary blood flow while in the patient with an atrial septal defect the blood flow difference between the upper and lower zones was decreased and thus the normal vertical gradient was less. These studies suggest that the hypoplastic pulmonary arteries in the transradiant lung reacted in the same way to alterations in pressure and flow as the vessels in the other lung.

Regional lung function in scoliosis

Radioactive xenon-133 was used to study the pattern of regional lung function in 35 scoliotic patients and 10 normal subjects in the sitting posture. The scoliotic curves were classified into three anatomical sites: high, if the apical vertebra was located between Th1 and Th5; mid, between Th6 and Th10; and low, between Th11 and L4; only the primary curve was considered and in 70% of the patients this measured more than 60°.

The mean pattern of perfusion in patients with low and mid curves was not significantly different from that of the normals, nor was there any significant difference between the convex and concave lungs in these two groups. Patients with high curves showed three distinct patterns: [List: see text]

The mean pattern of ventilation in the three groups of scoliotic patients was not significantly different from that of the normals although there was wide individual variation. The only patients to show a significantly abnormal ventilation/perfusion ratio were the high group.

Regional lung volumes calculated from the equilibration scan indicated that in a majority of scoliotics the lung on the convex side of the curvature was larger than that on the concave side.

Our results suggest that both the anatomical site and the angle of the scoliotic curvature have an effect on regional lung function but that this effect falls equally on the convex and concave lungs.

Regional lung function in patients with hepatic cirrhosis

The lung volume at which the dependent lung zones begin to trap gas as a result of airway closure (i.e., the "closing volume") was measured with (133)Xe in 10 seated patients with hepatic cirrhosis. In all of them the closing volume was increased above normal, and in eight it was greater than the functional residual capacity, indicating the presence of airway closure and gas trapping during resting tidal volume breathing. Direct measurements made with (133)Xe in five cirrhotic patients (a) confirmed the presence of increased gas trapping in the lower lung zones both at residual volume and at functional residual capacity, and (b) indicated that in liver cirrhosis the ventilation-perfusion ratio of the dependent lung zones may be very low, primarily as a result of decreased ventilation due to airway closure. It is concluded that in hepatic cirrhosis, gas trapping in the dependent lung zones may be an important cause of impaired gas exchange within the lungs. It is suggested that the premature airway closure observed in this disease may be due to mechanical compression of small airways by dilated blood vessels and/or interstitial pulmonary edema.

Distribution of pulmonary blood flow after myocardial ischemia and infarction

Regional distribution of pulmonary blood flow and ventilation was determined with the 133 xenon technic in the erect position at the bedside in 15 patients an average of 6 days after uncomplicated myocardial infarction (MI) and in five patients with severe angina in the same coronary care unit. Follow-up studies were repeated within 3 to 25 weeks on six of the patients with MI.

There was marked reduction in perfusion to the lung base after myocardial infarction. Patients with severe angina showed some underperfusion of the lower lung zones, but to a much less degree than those with acute MI. The pattern of pulmonary perfusion reverted toward that seen in angina in the follow-up studies of patients with MI. Distribution of ventilation was normal in all patients.

The results of the study suggest that there are probably chronic changes in the pulmonary vasculature of patients with arteriosclerotic heart disease which lead to redistribution of pulmonary blood flow toward the apex, and that the marked under-perfusion of the lung base demonstrated following acute myocardial infarction reflects an acute increase in the pulmonary venous and interstitial pressures most likely due to occult left ventricular failure.

Regional pulmonary function in patients with mitral stenosis in relation to haemodynamic data

Central haemodynamics in 23 patients with mitral stenosis and 7 control subjects were compared with the results of regional lung perfusion studied by (133)Xe, pulmonary scintigraphy with (99)mTc-labelled macro-aggregates of albumin, and regional ventilation by (133)Xe.A close correlation was found between both methods assessing regional pulmonary perfusion, i.e. pulmonary scintigraphy and (133)Xe. The results show that lower lung zones, when compared with upper zones, have both worse perfusion and worse ventilation. The changed distribution of perfusion and the changed distribution of ventilation correlated significantly with central haemodynamics in these patients. The ventilation gradient can be a valuable diagnostic tool for evaluating the severity of mitral stenosis, especially in long and repeated studies, due to its simplicity for the patient.

Abnormal distribution of pulmonary blood flow in aortic valve disease. Relation between pulmonary function and chest radiograph

Wasted ventilatory volume (V(D)) and its ratio to tidal volume (V(D)/V(T)) were measured at rest and during exertion in 17 patients with aortic valve disease. We considered V(D)/V(T) to indicate abnormal ventilation: perfusion relations if it did not decrease on exertion, or if the exercising value was greater than 40 per cent. Plain chest radiographs were independently examined for evidence of diversion of pulmonary blood to the upper lobes. There was significant agreement (p<0.05) between radiographic and pulmonary function estimations of abnormality. This suggests that the raised pulmonary venous pressure associated with left ventricular failure creates an abnormal pattern of blood flow through the lung, which is responsible for causing inadequate perfusion with respect to ventilation.

Quantitated scintillation scanning for the measurement of lung perfusion

A method using quantitated lung scans is described for the accurate proportioning of lung perfusion. The results obtained by this method have been compared directly with those obtained from bronchospirometry, and a good correlation has been obtained (r = + 0·93).

Effects of acetylcholine on regional pulmonary blood flow in patients with mitral stenosis

The effect of acetylcholine was studied on the region of increased vascular resistance at the lung bases in patients with mitral stenosis. The patients had moderate elevations of pulmonary artery pressure. The distribution of blood flow and ventilation were measured in both lungs of 10 patients using radioactive xenon-133 and a scanning technique. Acetylcholine was then infused into one main pulmonary artery, and the distribution of blood flow and ventilation were measured again. One lung served as a control during the drug infusion. There was a small but significant increase in perfusion to the dependent lung zone during the drug infusion without a change in pulmonary artery pressure indicating localized vasodilation. Relative underperfusion was still present during the acetylcholine administration which indicated that increased vasomotor tone was not the principal pathophysiological mechanism for the increased vascular resistance. There was a decrease in ventilation to the lower zone of the lung receiving acetylcholine.

Alterations in regional pulmonary blood flow in mitral valve disease studied by radioisotope scanning. A simple nontraumatic technique for estimation of left atrial pressure

The distribution of pulmonary blood flow was studied by external scintillation scanning of intravenously injected 131 I-labeled macroaggregates of human serum albumin. The technique, its validation, and the underlying considerations are discussed in detail.

In 13 normal subjects, in whom the indicator was injected while they were in the erect position, the ratio of concentration of radioactivity per unit of lung volume in the upper third of the right lung to that in the lower third (U/L) averaged 0.43±0.08 sd . When 131 I-MAA was injected with the subjects in the supine position, this ratio averaged 0.92±0.05.

In 35 patients with mitral valve disease in whom the injections were made while they were in the erect position, varying abnormalities of the distribution of the pulmonary arterial blood flow were observed, U/L averaging 1.01±0.34. The extent of the abnormality of distribution was found to be a function of the hemodynamic severity of the mitral valve disease, and U/L correlated more closely with the mean left atrial pressure than with any other hemodynamic variable. The potential applicability of the 131 I-MAA technique in the detection and assessment of mitral valve disease was discussed.