Factors affecting regional pulmonary blood flow in left heart valvular disease

Pulmonary hypertension leads to a loss of gravity dependent redistribution of regional lung perfusion: a SPECT/CT study

OBJECTIVE

Pre-capillary pulmonary hypertension (PHT) is characterised by progressive pulmonary vascular obliteration and loss of vascular reserves. In health, regional lung perfusion redistributes under the influence of gravity due to the presence of recruitable vessels. We investigated a combined single photon emission computed tomography/CT (SPECT/CT) method for assessing the pulmonary circulation by quantifying the gravity dependent redistribution of lung perfusion.

DESIGN

Characterisation of patients versus healthy controls.

PATIENTS

15 patients with pre-capillary PHT and 11 healthy controls.

SETTING

University hospital clinic.

INTERVENTION

Regional lung perfusion was measured using SPECT/CT in two different postures (supine vs upright). A perfusion redistribution index (PRI) was used to quantify the cranial-caudal shift in regional lung perfusion resulting from gravitational (postural) change.

MAIN OUTCOME MEASURE

PRI was compared between cases and controls, and correlated with markers of disease severity in cases.

RESULTS

Patients with pre-capillary PHT had notably reduced PRI compared to controls (0.02±0.06 vs. 0.28±0.15 normalised perfusion/cm, p<0.0001). PRI was significantly associated with prognostic parameters such as 6 min walk distance (r=0.60, p=0.018), functional class (p=0.008), and tricuspid annular plane systolic excursion (r=0.58, p=0.022). The receiver operating characteristic curve showed that PRI differentiated patients with pre-capillary PHT from controls with AUC=0.94 (p<0.001).

CONCLUSIONS

With SPECT/CT, gravity dependent redistribution of lung perfusion can be quantified using the PRI derived from supine and upright perfusion analysis. The potential utility of PRI for the non-invasive detection of PHT and assessment of disease severity warrants further study.

Pulmonary hypertension secondary to left-sided heart disease: a cause for ventilation-perfusion mismatch mimicking pulmonary embolism

Ventilation-perfusion (V/Q) scans are commonly performed in patients with suspected pulmonary thromboembolism (PE). V/Q mismatch is typically attributed to PE. We describe a case in which a V/Q scan performed on a patient with advanced hypertrophic obstructive cardiomyopathy showed large areas of V/Q mismatch not due to PE. The mismatch was due to pulmonary hypertension secondary to left-sided heart disease. The pathophysiology is briefly reviewed.

Efficient lung scintigraphy

Lung scintigraphy is a first-choice method to diagnose lung embolism. The clinical routine in most centres is a perfusion study complemented with a ventilation study when judged necessary. We describe a routine with ventilation scintigraphy preceding perfusion scintigraphy, which is completed within one hour. Furthermore, the data acquired allow the determination of lung clearance of the tracer 99mTc-DTPA (diethylene triamine penta-acetate) used for the ventilation scintigraphy. An aerosol generator charged once a day with 99mTc-DTPA solution is used for all inhalations during the day. Inhalation is monitored with a counter and interrupted when the count rate corresponds to about 20 MBq. The ventilation imaging starts and ends with posterior projections. This allows calculation of lung clearance of 99mTc-DTPA. Perfusion scintigraphy is performed in a standard fashion with 100 MBq of 99mTc-MAA (macro-aggregated albumin). The ventilation study was considered to give some diagnostic information in the majority of the patients. The clearance determination allows detection of inflammatory lung disease. The background activity caused by the ventilation study comprised only 13% of the activity in the perfusion scintigraphy and did not significantly interfere with interpretation of the perfusion scan. The cost for the investigation is low because of the rational system for aerosol administration and the short time for a complete study.

Radiographic inversion of pulmonary blood flow in acute asthma

Chest radiographs are obtained routinely in children hospitalized with asthma but are considered to be of low utility. We describe a previously unreported radiographic inversion of pulmonary artery flow patterns in the chest films of a majority of children and young adults hospitalized for asthma. Seventy-five hospital records of 65 patients aged 2 to 25 years (mean 9.2) admitted for asthma during the calendar year 1991 were reviewed. As compared with the normal pattern, patients with inverted vascularity were younger (mean age 6.75 years), tended to be admitted through the emergency department, and had significantly more signs of labored breathing, such as tachypnea, retractions, nasal flaring, and tachycardia. We propose that the exaggerated respiratory effort in these children raises the transmural pulmonary artery pressure, impeding pulmonary blood flow. This results in distension of the right ventricle, which then compresses the left ventricle in the confines of the pericardium by posterior displacement of the interventricular septum. The resultant loss of left-sided compliance raises the left atrial and pulmonary venous pressures, leading to inversion of vascular markings through the same mechanism as seen in left-heart failure. We conclude that attention to this easily recognized sign will detect presence of the hemodynamically significant respiratory obstruction in asthmatic patients.

Estimation of pulmonary hypertension by perfusion lung scintigraphy: gravitational effect of postural changes between the lateral decubitus positions

To estimate pulmonary hypertension in patients with various heart diseases, we devised a new method using perfusion lung scintigraphy with technetium-99m-labelled macroaggregated albumin. In this method, changes in the distribution of pulmonary perfusion caused by gravitational effects, namely, changes in the total count ratios of the right lung against the left lung between right and left lateral decubitus positions (rt/lt), were assessed in 62 patients and in 10 normal subjects. The rt/lt ratios were calculated as indices of the above changes. They correlated significantly with mean pulmonary arterial pressure (mPAP) (gamma = -0.62, P less than 0.001), pulmonary capillary wedge pressure (gamma = -0.63, P less than 0.001) and pulmonary arteriolar resistance (gamma = 0.50, P less than 0.001) in all subjects. In 17 patients with valvular heart diseases, the ratio correlated significantly with mPAP (gamma = -0.84, P less than 0.001). In 10 patients with various heart diseases, the U/S ratio, i.e. the index of changes in the count ratios of the upper field against the lower field for the right lung following postural change from the upright to the supine position, was also obtained as well as the rt/lt ratio. The latter evidenced a better correlation with mPAP (gamma = -0.90, P less than 0.001) than the former (gamma = -0.64, P less than 0.05). We conclude that this method is valuable as a noninvasive approach for the estimation of pulmonary hypertension.

Pulmonary embolism in neurosurgical patients: diagnosis and treatment

Pulmonary embolism was suspected in 45 neurosurgical patients who were treated between January, 1980, and December, 1981. Hypoxemia with respiratory alkalosis and sudden tachycardia gave rise to this suspicion more often than any other sign or symptom. Perfusion lung scanning confirmed the presence of pulmonary embolism in 23 of these cases. A retrospective analysis of the clinical course of these 23 patients suggested that one or more previous episodes of pulmonary embolism had occurred in 16 cases (69.6%), and had been either overlooked or misdiagnosed. Treatment was started immediately after diagnosis. Twenty-one patients were given heparin; however, two could not be treated because of contraindication to using anticoagulant drugs. Two patients died during treatment. The 21 surviving patients were assessed and 11 of them submitted again to perfusion lung scanning 1 week after diagnosis: 14 had improved, but seven did not show significant changes either clinically or on perfusion lung scanning. Nine treated patients developed hemorrhage, but it was readily controlled. In two of the nine patients, hemorrhage involved the surgical area. It is stressed that pulmonary embolism may be suspected and diagnosed in neurosurgical patients at an early stage. Heparin may be given and the survival rate appears to be better than previously reported figures.

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.

Postural changes in pulmonary blood flow in pulmonary hypertension: a noninvasive technique using ventilation-perfusion scans

To determine whether postural changes in ratio of upper to lower (U:L) zone pulmonary blood flow reflect pulmonary arterial pressures, we used pulmonary perfusion photoscintigraphy to study 12 normal subjects and 10 patients with precapillary pulmonary hypertension (eight classified as "primary" and two as thromboembolic). All patients underwent right-heart catheterization and measurement of pulmonary arterial systolic, diastolic, mean and capillary (wedge) pressures. The distribution of perfusion was then assessed in the supine and erect positions after i.v. injection of technetium-99m-labeled, macroaggregated albumin. Perfusion distribution was corrected for lung volume by xenon-133 equilibrium ventilation scans. In normal subjects, the U:L lung zone perfusion ratio decreased by 70.7 +/- 12.2% with the change in position. The patient group differed (p less than 0.0001) from normal subjects in that there was only a 19 +/- 17.4% shift of U:L ratio with the postural change. The mean pulmonary arterial pressure in the patient groups was 50 +/- 24.2 mm Hg. The postural change in U:L zone ratio correlated significantly with the mean pulmonary arterial pressure (r = -0.84, p less than 0.01) pulmonary arterial systolic (r = -0.83, p less than 0.01) and diastolic pressures (r = -0.72, p less than 0.05) and with the pulmonary vascular resistance (r = -0.74, p less than 0.02). No correlation was found with other hemodynamic, spirometric or blood gas data. We conclude that the postural shift in U:L ratio warrants further exploration as a noninvasive approach for detecting and quantifying pulmonary hypertension.

Pulmonary perfusion imaging applied to prediction of pulmonary vascular pressures in mitral and aortic valve disease

Radionuclide lung perfusion imaging was performed on 27 patients with valvular disease of the left heart. The ratio of upper to total counts for the lungs, determined by computer, was correlated against pulmonary vascular mean pressures. A close correlation (r = 0.91) was obtained against pulmonary wedge pressure. After corrective cardiac surgery upper/total ratios fell towards normal in four patients in whom pulmonary vascular pressures were measured and the correlation persisted. This simple non-invasive index can be used to follow changes in pulmonary venous hypertension.

Clinical ventilation-perfusion scintigraphy

Ventilation-perfusion scintigraphy is an established procedure for the investigation of lung disease. Perfusion scans are commonly obtained with a gamma-camera following injection of 99mTc-labelled microspheres. For the assessment of regional lung ventilation, a number of techniques are now being employed, i.e. 133Xe and 127Xe single breath/washout studies, continuous inhalation of 81mKr and inhalation of radioactive aerosols. The latter two methods are now gaining consideration in clinical practice. Lung perfusion scanning is highly sensitive for detection of regional abnormalities of blood flow; the diagnosis of pulmonary embolism remains the most important clinical application of the technique. In this context, the use of a ventilation scan is required in order to increase the specificity of the procedure. In general, lung ventilation-perfusion scintigraphy is of great value for the management of patients with both primary lung disease and heart disease, by providing pathophysiological information of importance for the diagnosis, follow up and the functional evaluation of the patient.