title: A potential early physiological marker for CNS oxygen toxicity: hyperoxic hyperpnea precedes seizure in unanesthetized rats breathing hyperbaric oxygen.
abstract: Hyperbaric oxygen (HBO(2)) stimulates presumptive central CO2-chemoreceptor neurons, increases minute ventilation (V(min)), decreases heart rate (HR) and, if breathed sufficiently long, produces central nervous system oxygen toxicity (CNS-OT; i.e., seizures). The risk of seizures when breathing HBO(2) is variable between individuals and its onset is difficult to predict. We have tested the hypothesis that a predictable pattern of cardiorespiration precedes an impending seizure when breathing HBO2. To test this hypothesis, 27 adult male Sprague-Dawley rats were implanted with radiotelemetry transmitters to assess diaphragmatic/abdominal electromyogram, electrocardiogram, and electroencephalogram. Seven days after surgery, each rat was placed in a sealed, continuously ventilated animal chamber inside a hyperbaric chamber. Both chambers were pressurized in parallel using poikilocapnic 100% O(2) (animal chamber) and air (hyperbaric chamber) to 4, 5, or 6 atmospheres absolute (ATA). Breathing 1 ATA O(2) initially decreased V(min) and HR (Phase 1 of the compound hyperoxic ventilatory response). With continued exposure to normobaric hyperoxia, however, V(min) began increasing toward the end of exposure in one-third of the animals tested. Breathing HBO2 induced an early transient increase in V(min) (Phase 2) and HR during the chamber pressurization, followed by a second significant increase of V(min) ≤8 min prior to seizure (Phase 3). HR, which subsequently decreased during sustained hyperoxia, showed no additional changes prior to seizure. We conclude that hyperoxic hyperpnea (Phase 3 of the compound hyperoxic ventilatory response) is a predictor of an impending seizure while breathing poikilocapnic HBO(2) at rest in unanesthetized rats.
authors: Department of Molecular Pharmacology & Physiology, Hyperbaric Biomedical Research Laboratory, University of South Florida, Morsani College of Medicine, Tampa, FL 33612, USA.
authors: Raffaele
authors: R
authors: Pilla
authors: Carol S
authors: CS
authors: Landon
authors: Jay B
authors: JB
authors: Dean
mesh_terms: D000009:Abdominal Muscles / Q000503:physiopathology*; D000818:Animals; D001921:Brain / Q000503:physiopathology*; D058256:Brain Waves; D016292:Procedural Sedation; D003964:Diaphragm / Q000503:physiopathology*; D004195:Disease Models, Animal; D018450:Disease Progression; D004562:Electrocardiography; D004569:Electroencephalography; D004576:Electromyography; D006339:Heart Rate; D006931:Hyperbaric Oxygenation; D018496:Hyperoxia / Q000139:chemically induced* / Q000503:physiopathology; D008297:Male; D020258:Neurotoxicity Syndromes / Q000209:etiology* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D012119:Respiration; D012640:Seizures / Q000139:chemically induced* / Q000503:physiopathology; D013686:Telemetry; D013997:Time Factors