Cardiorespiratory responses elicited by right atrial injections of iodinated contrast media. Comparative evaluation of four agents.

Rationale and Objectives: The purpose of this study is three-fold: 1) to quantify the cardiorespiratory responses to rapid right atrial injections of meglumine/sodium diatrizoate, ioxaglate, iotrolan, and iopamidol; 2) to compare the effects of each contrast medium to that of its corresponding vehicle and saline; and 3) to evaluate the role of the vagus nerve in the cardiorespiratory responses.
Methods: Seventeen anesthetized dogs, breathing spontaneously, were used. Injections of 2.0 mL/kg were given into the right atrium in 2 seconds. Each contrast medium, along with its vehicle and saline, was tested on 4 dogs (5 dogs for diatrizoate). Blood pressure, air flow, tidal volume, upper airway pressure, esophageal pressure, mean arterial pressure and heart rate, breathing frequency, dynamic lung compliance, upper airway resistance, and total lung resistance were recorded or calculated.
Results: Diatrizoate and its vehicle caused a significant increase in blood pressure, tidal volume, esophageal pressure, and a decrease in mean arterial pressure with an increase in heart rate. These responses were not mediated by vagal afferents. Ioxaglate and iotrolan, but not their vehicles, increased breathing frequency; this response was abolished by vagal block. Ioxaglate decreased mean arterial pressure and increased heart rate; the decrease in mean arterial pressure was still present during vagal block. Iopamidol and its vehicle did not alter respiratory parameters. Iopamidol, but not its vehicle, caused only a minimal and transient increase in mean arterial pressure before and during vagal block. None of the contrast media changed upper airway resistance, total lung resistance, and dynamic lung compliance.
Conclusion: Both diatrizoate and its vehicle elicited the largest changes in respiratory and cardiovascular functions, not mediated by vagal afferents and caused by osmolality of the solution. Ioxaglate, iotrolan, and iopamidol induced smaller cardiorespiratory changes, mediated by vagal afferents. Their respective vehicles did not cause any effects, which suggests that the chemical structure plays a role. Nonionic contrast media elicited only minor and transient cardiorespiratory alterations.