Acute Toxic Effects of Inhaled Dichlorvos Vapor on Respiratory Mechanics and Blood Cholinesterase Activity in Guinea Pigs

James T. Taylorab, Emily Davisb, Paul Dabischb, Mike Horsmonb, Kathy Matsonb, Charlie Crouseb & Robert Mioduszewskiba National Academy of Sciences-National Research Council, Washington, DC, USAb U.S. Army Edgewood Chemical Biological Center, Aberdeen Proving Ground, Maryland, USAOperational Toxicology Team, U.S. Army Edgewood Chemical Biological Center, ATTN: AMSRD-ECB-RT-TT, 5183 Blackhawk Road, Aberdeen Proving Ground, MD, 21010-5424, USAUsing a modified noninvasive volume-displacement plethysmography system, we investigated the effects of inhaled dichlorvos (2,2-dimethyl dichlorovinyl phosphate, or DDVP) vapor on the respiratory mechanics and blood cholinesterase activity of guinea pigs. Data revealed significant dose-dependent changes in several pulmonary parameters. Animals exposed to a DDVP concentration of 35 mg/m3 did not show any significant changes in frequency, tidal volume, or minute ventilation. However, animals exposed to 55 mg/m3 DDVP showed significantly decreased respiratory frequency and significantly increased tidal volume with no significant changes in minute ventilation. Similarly, animals exposed to 75 mg/m3 DDVP showed significantly decreased respiratory frequency along with significantly increased tidal volume. The decreased respiratory frequency was large enough in the high exposure group to offset the increased tidal volume. This effect resulted in significantly decreased minute ventilation by the end of exposure, which remained attenuated 10 min after exposure. An analysis of whole-blood cholinesterase activity revealed significantly decreased activity for both acetylcholinesterase (AChE) and butylcholinesterase (BChE). Peak inhibition occurred for both enzymes at the end of exposure for all three concentrations and rapidly recovered within several minutes of exposure. Analysis of blood samples using gas chromatography–mass spectroscopy (GC-MS) revealed that minute ventilation may only play a minimal role in the dosimetry of inhaled DDVP vapor.