Inhalation of the nerve gas sarin impairs ventilatory responses to hypercapnia and hypoxia in rats. Toxicol Appl Pharmacol. 2008;232:440-447. [PMID: 18706921 DOI: 10.1016/j.taap.2008.07.016]

A review of chemical warfare agents linked to respiratory and neurological effects experienced in Gulf War Illness

Over 40% of veterans from the Persian Gulf War (GW) (1990-1991) suffer from Gulf War Illness (GWI). Thirty years since the GW, the exposure and mechanism contributing to GWI remain unclear. One possible exposure that has been attributed to GWI are chemical warfare agents (CWAs). While there are treatments for isolated symptoms of GWI, the number of respiratory and cognitive/neurological issues continues to rise with minimum treatment options. This issue does not only affect veterans of the GW, importantly these chronic multisymptom illnesses (CMIs) are also growing amongst veterans who have served in the Afghanistan-Iraq war. What both wars have in common are their regions and inhaled exposures. In this review, we will describe the CWA exposures, such as sarin, cyclosarin, and mustard gas in both wars and discuss the various respiratory and neurocognitive issues experienced by veterans. We will bridge the respiratory and neurological symptoms experienced to the various potential mechanisms described for each CWA provided with the most up-to-date models and hypotheses.

A critical role of acute bronchoconstriction in the mortality associated with high-dose sarin inhalation: effects of epinephrine and oxygen therapies

Sarin is an organophosphate nerve agent that is among the most lethal chemical toxins known to mankind. Because of its vaporization properties and ease and low cost of production, sarin is the nerve agent with a strong potential for use by terrorists and rouge nations. The primary route of sarin exposure is through inhalation and, depending on the dose, sarin leads to acute respiratory failure and death. The mechanism(s) of sarin-induced respiratory failure is poorly understood. Sarin irreversibly inhibits acetylcholine esterase, leading to excessive synaptic levels of acetylcholine and, we have previously shown that sarin causes marked ventilatory changes including weakened response to hypoxia. We now show that LD50 sarin inhalation causes severe bronchoconstriction in rats, leading to airway resistance, increased hypoxia-induced factor-1α, and severe lung epithelium injury. Transferring animals into 60% oxygen chambers after sarin exposure improved the survival from about 50% to 75% at 24h; however, many animals died within hours after removal from the oxygen chambers. On the other hand, if LD50 sarin-exposed animals were administered the bronchodilator epinephrine, >90% of the animals survived. Moreover, while both epinephrine and oxygen treatments moderated cardiorespiratory parameters, the proinflammatory cytokine surge, and elevated expression of hypoxia-induced factor-1α, only epinephrine consistently reduced the sarin-induced bronchoconstriction. These data suggest that severe bronchoconstriction is a critical factor in the mortality induced by LD50 sarin inhalation, and epinephrine may limit the ventilatory, inflammatory, and lethal effects of sarin.

High-frequency electrical stimulation of cervical vagi reduces airway response to methacholine

AIM: To test whether high-frequency electrical stimulation (HES) of the bilateral cervical vagus nerves reduces the airway responses to methacholine (MCh).

METHODS: Guinea pigs were pretreated with saline (Sal, n = 9) or ovalbumin (Ova, n = 10) aerosol for two weeks (5 min/d, 5 d/wk) and subsequently anesthetized, paralyzed, tracheotomized and artificially ventilated. Both total lung resistance (R_L) and dynamic pulmonary compliance (C_dyn) were recorded. In addition, the effects of vagal low-frequency electrical stimulation (LES, monophasic, 50 Hz) and HES (monophasic and biphasic, 1 and 2.5 kHz) for about 10 s or 2 min on the responses of R_L and C_dyn to MCh aerosol-induced bronchoconstriction were compared in both groups of guinea pigs. In a few guinea pigs, the impact of bivagotomy on the R_L responses to MCh was assessed.

RESULTS: Before MCh challenge, LES, but not HES, significantly increased R_L by about 30% (P < 0.01) and decreased C_dyn by about 20% (P < 0.01) similarly in both groups. MCh aerosol for 2 min elevated R_L and diminished C_dyn more in Ova- than Sal-treated animals (R_L: 313% ± 52% vs 113% ± 17%, P < 0.01; C_dyn: -56% ± 7% vs -21% ± 3%, P < 0.01). During MCh-induced airway constriction, LES further enhanced, but HES decreased R_L and this decrease was greater in Ova- (about 45%) than Sal-treated animals (about 34%, P < 0.01) with little change in cardiovascular activity. On the other hand, LES further reduced whereas HES increased C_dyn more in Ova- (about 20%) than Sal-treated animals (about 13%, P < 0.01). In addition, bivagotomy almost eliminated the R_L and C_dyn responses to MCh.

CONCLUSION: We conclude that vagal HES is able to alleviate the bronchoconstriction induced by MCh in anesthetized guinea pigs, likely via reversible inhibition/blockade of vagal conduction.

Acute Changes in Pulmonary Function Following Microinstillation Inhalation Exposure to Soman in Nonatropenized Guinea Pigs

Barometric whole-body plethysmography (WBP) was used to examine pulmonary functions at 4 and 24 hours postexposure to soman (GD) in guinea pigs without therapeutics to improve survival. Endotracheal aerosolization by microinstillation was used to administer GD (280, 561, and 841 mg/m3) or saline to anesthetized guinea pigs. Significant increases in respiratory frequency (RF), tidal volume (TV), and minute volume (MV) were observed with 841 mg/m3 GD at 4 hours and that were reduced at 24 hours postexposure. A dose-dependent increase in peak inspiration flow and peak expiration flow was present at 4-hour post-GD exposure that was reduced at 24 hours. Time of inspiration and expiration were decreased in all doses of GD exposure at 4 and 24 hours, with significant inhibition at 841 mg/m3. End-expiratory pause (EEP) increased at 280 and 561 mg/m3, but decreased in animals exposed 841 mg/m3 at 24 hours postexposure. Pseudo-lung resistance (Penh) and pause followed similar patterns and increased at 4 hours, but decreased at 24 hours postexposure to 841 mg/m3 of GD compared to control. These studies indicate GD exposure induces dose-dependent changes in pulmonary function that are significant at 841 mg/m3 at 4 hours and remains 24 hours postexposure. Furthermore, at 4 hours, GD induces bronchoconstriction possibly due to copious airway secretion and ongoing lung injury in addition to cholinergic effects, while at 24 hours GD induces bronchodilation a possible consequence of initial compensatory mechanisms.