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There has been much lay and medical concern regarding toxic effects of insecticides on the general population. In addition to direct toxic effects, it is suspected that insecticidal application has deleterious physical effects on persons with respiratory diseases. To evaluate some of these problems, the authors have attempted to quantitate actual absorption, symptoms, and laboratory evidence of intoxication in persons with varying degrees of exposure to parathion. By means of controlled observations, the respiratory effect of application of this compound on persons with bronchial asthma was also measured. The results suggest that the effect of this chemical on the general population is negligible.

To the Editor.— It has been estimated that between 1 and 2 million pulmonary artery catheters were inserted for hemodynamic monitoring in the last decade. 1 The prevalence of the procedure has increased substantially over the past few years. It is therefore of interest that the methodology of a clinical hemodynamic measurement, cardiac output by thermodilution, which is made less frequently than blood pressure and heart rate only, be the subject of continued investigation. Some of the errors associated with the early use of this technique have been eliminated by improved technology. For example, those due to alterations in injectate temperature 2 are now minimized by the use of both a proximal and distal thermistor. The question of the importance of the respiratory effect on the measurement of cardiac output appears to have now been settled by a report inThe Journal. 3 The data presented in this article demonstrate

In Reply.— We thank Dr McIntyre for his thoughtful letter in which he states that the importance of the respiratory effect on the measurement of cardiac output appears to have now been settled by our recent article. Dr McIntyre has briefly reviewed several of the critical factors influencing pulmonary interactions with cardiac output. He would have liked data describing respiratory variables included in our article since he thought that the order of initiation of injection at the three different times during the respiratory cycle was not randomized. There is no question that lung compliance, airway pressure, and inspiratory flow wave form all interact with cardiac function. 1 However, we did not include respiratory variables since, in fact, the order of initiation of injection at the three different times during the respiratory cycle was randomized in our study. We utilized the Latin squares' technique. This is so stated in the "Methods"