Fear and pulmonary stress behaviors to an asphyxial threat across cognitive states.

Abstract

<italic>Purpose.</italic> To identify respiratory distress behaviors in response to an asphyxial threat across cognitive states in a naturally occurring clinical context. <italic>Theoretical framework.</italic> Nociceptive responses activated by an asphyxial threat produce measurable behaviors from subcortical brain areas. Since most studies of respiratory distress have rapidly induced asphyxia in healthy subjects and cognitively intact patients the naturally occurring graded behaviors in cognitively impaired patients are not well understood. <italic>Subjects.</italic> A convenience sample of 12 adult men and women were recruited from a medical intensive care unit. Subjects were scheduled to undergo a weaning trial from mechanical ventilation producing an opportunity to measure respiratory distress. The subjects were experiencing acute vs. chronic respiratory failure and were cognitively intact vs. impaired. <italic>Method.</italic> A descriptive, comparative, time-series design was used. Mediating variables that may alter the development or expression of respiratory distress were measured, including peripheral oxygen saturation, end-tidal carbon dioxide, asphyxial threat severity, and benzodiazepine use. Respiratory distress behaviors (heart and respiratory rates) were recorded using a capnograph/oximeter. Simultaneously, a video camera recorded the subject's fear, accessory muscle use, paradoxical breathing pattern and nasal flaring. After the weaning trial subjects were asked to point to an emotion photo that characterized their experience during weaning. <italic>Results.</italic> Exposure to an asphyxial threat produced a mixed picture of autonomic, pulmonary stress, and fear behaviors. Behaviors had the same appearance in subjects with varying cognitive states. Asphyxial severity had an effect on paradoxical breathing and benzodiazepine administration suppressed respiratory rate and paradoxical breathing. Fear was activated for most subjects; gender differences characterized fear reporting. Hypercarbia was strongly predictive of activation of fear behaviors. <italic>Conclusions.</italic> An asphyxial threat activated and mediated respiratory distress behaviors. Cognitive state did not influence behaviors. Subject variances probably resulted from differences in asphyxial thresholds, adaptation to chronic disease and benzodiazepine administration. The behavior sequence suggests that activation of compensatory brainstem responses precede activation of fear. Asphyxia may induce an innate array of pulmonary stress and fear behaviors that cannot be volitionally controlled and will have the same appearance across cognitive states. Behaviors that signify respiratory distress may be more reliable than patient report.