Gas Exchange in Chronic Thromboembolism after Pulmonary Thromboendarterectomy: Methods (Part 1)
Nine patients with chronic thromboembolic pulmonary hypertension were studied immediately before and approximately one year following thromboendarterectomy. These patients were referred for initial evaluation and potential surgery but were otherwise unselected. They were a subset of a larger preoperative study of 25 subjects reported previously and represent those patients who were able to return for follow-up evaluation. There were no deaths during the follow-up period in the larger study, and follow-up depended upon subject desire. All subjects provided an informed consent, and the study protocol was approved by the UCSD Committee on Human Investigation. buy antibiotics online
Preoperatively, each patient underwent right heart catheterization and pulmonary angiography to establish the diagnosis of chronic thromboembolism, which was later surgically confirmed and returned for a repetition of these studies approximately one year later. The extent of vascular obstruction before and after surgery was estimated angiographically using the method ofTibutt et al. Cardiac output was measured both by thermodilution and using inert gas elimination (see below), and the results were averaged.
During right heart catheterization, the supine resting distribution of Va/Q ratios was measured using the multiple inert gas elimination technique. Briefly, this method estimates the Va/Q ratio distribution from measurements of the simultaneous pulmonary elimination of six physiologically inert gases which are dissolved in saline solution and are infused at a constant rate (2 to 3 ml/min) through a peripheral vein. The six gases used are sulfur hexafluoride, ethane, cyclopropane, enflurane, ether, and acetone.
Samples of blood are obtained from the pulmonary artery and the radial or femoral artery during right heart catheterization, together with simultaneously obtained samples of mixed expired gas. These are analyzed for relative inert gas concentrations using gas chromatography. The data are then expressed as the retention (arterial partial pressure/mixed venous partial pressure) and excretion (mixed expired partial pressure/mixed venous partial pressure) of each inert gas, and the Va/Q ratio distribution is calculated from the relationship of the gas retention and excretion values to the corresponding blood solubilities. Inert gas samples were collected in duplicate.