Respiratory changes induced by prolonged laryngeal stimulation in awake piglets

Abstract

To examine the role of the laryngeal reflex in modulating cardiorespiratory function, we stimulated the superior laryngeal nerves (SLN) bilaterally in unanesthetized, chronically instrumented piglets (n = 10, age 5-14 days). The SLN were placed in cuff electrodes and wires were exteriorized in the neck for stimulation. A cannula placed in the aorta was used for blood pressure recording and arterial blood sampling. During each experiment, 1-2 days after surgery, ventilation was recorded using whole-body plethysmography, and electroencephalogram and electrocardiogram were recorded after acute subcutaneous electrode placement. After base-line recordings, the SLN were electrically stimulated for 1 h. During this period, mean respiratory frequency decreased by 40-75% and apneas of 10-15 s were regularly interspersed between single breaths or clusters of breaths. Periods of breathing were always associated with opening of the eyes and generally with head and body movements, an awakening that occurred every 10-15 s. At 1 h into the stimulus period, minute ventilation had decreased by 57 +/- 7% (mean +/- SE), arterial partial pressure of O2 (PaO2) by 68 +/- 3 Torr, and arterial partial pressure of CO2 (PaCO2) had increased by 19 +/- 2 Torr. Throughout the entire stimulus period, mean blood pressure and average heart rate were maintained within 12% of base line. We suggest that: low-threshold SLN afferents exert primarily respiratory effects and only minor cardiovascular effects; breathing during laryngeal reflex activation is sustained by an arousal system; and the laryngeal reflex does not pose an imminent threat to the unanesthetized, awake, young animal.

Cardiovascular and Neurophysiologic Changes during Graded Duration of Apnea in Piglets

“…reflexes evoked regardless of the cause of the apnea. Furthermore, we have previously shown that SLN stimulation in unanesthetized piglets resulted in no significant change in heart rate or blood pressure (28). Similarly, herein SLN stimulation in the presence of hyperoxia had a negligible effect on heart rate or blood pressure (Table 2).…”

Chronic Electrical Stimulation of the Superior Laryngeal Nerve in the Rat: A Potential Therapeutic Approach for Postmenopausal Osteoporosis

“…This result is consistent with a study in unanesthetized rabbits in which SLN stimulation, with intensity at 1.2-1.5 times the threshold for inducing swallowing reflex (0.2 ms, 0.2-0.65 mA, 30 Hz), that did not affect the behavior of the animal [14]. In unanesthetized piglets, when SLNs were stimulated (0.5 ms, 10 Hz) with an intensity near threshold for respiratory changes, which were lower than that for producing discomfort behavior, mean respiratory frequency decreased by 57% during stimulation period of 5 min or 1 h [6,7]. When SLN electrical stimulation was applied to conscious humans, sensation of touch and pain were induced, depending on stimulation parameters [15].…”

“…The purpose of this study was to progress from acute stimulation in anaesthetized animals and to establish a conscious experimental animal model to translate results obtained in anesthetized animals for potential clinical application in osteoporosis. The SLN is known to include afferent nerve fibers that can inhibit respiration [6][7][8]. Therefore, it is necessary to identify parameters that do not adversely affect respiratory measures by SLN stimulation.…”

Cough and Other Reflexes on Irritation of Airway Mucosa in Man

“…Preferential suppression of expiratory efforts by increasing depth of anesthesia is similarly imminent threat to the unanesthetized awake animals. 19 This apnoeic response to airway irritation observed in anesthetized subjects whose tracheas were stimulated with water injection. 4 Therefore, the types appears to be more pronounced in neonatal animals than adult animals.…”