The measurement of extravascular lung density with SPECT imaging and its relationship with ventilatory abnormalities in patients with congestive heart failure

Background. Patients with congestive heart failure (CHF) have increased ventilatory equivalent for carbon dioxide (Ve/VCO2), which may contribute to the symptom of exercise-induced hyperpnea. We have developed a technique in which simultaneous blood volume single photon emission computed tomography imaging and transmission tomography are used to measure extravascular lung density (ELD). We investigated the correlation between Ve/VCO2 and ELD in patients with CHF. Methods and Results. Thirteen patients with stable CHF and eleven control subjects were studied. Attenuation-corrected blood volume emission tomography was acquired with simultaneous transmission tomography to measure pulmonary blood volume and total lung density, respectively. Seven CHF patients underwent maximal exercise treadmill testing with online respiratory gas analysis. ELD was calculated as total lung density minus pulmonary blood volume. SPECT and transmission tomography were repeated immediately after exercise. CHF patients had significantly higher total lung density and ELD compared with normal subjects. No differences in pulmonary blood volume were observed. There was a significant inverse correlation between ELD and left ventricular ejection fraction at rest in CHF patients (r = -0.77, P < .001). A strong correlation was also found between post-exercise ELD and Ve/VCO2, at peak exercise (r = 0.74, P = .008) and at anaerobic threshold (r = 0.67, P = .024). Conclusion. Patients with chronic CHF have increased ELD. The correlation between ELD and Ve/VCO2 suggests that increased lung water may contribute to the ventilatory abnormalities seen in patients with CHF.