Biomedical subjects
D L Pickens
Publications and source records attributed to D L Pickens.
Characterization of prolonged apneic episodes associated with respiratory syncytial virus infection.
We used high-speed polygraphic recordings to document in detail the sequence of events during prolonged apneic spells in two infants with respiratory syncytial viral (RSV) infection. Also, we elicited upper airway reflexes by stimulating the airway with saline during sleep. Spontaneous prolonged apneic spells were recorded in both infants, and these consisted of two distinctly different apnea types. A number of similarities between apnea of prematurity, upper airway reflex apnea and the apneas in these two infants with RSV infection suggests the possibility that these various kinds of apnea may have related causal mechanisms.
Pharyngeal fluid clearance and aspiration preventive mechanisms in sleeping infants.
We sought to characterize ventilatory and airway protective responses to pharyngeal stimulation in young infants during sleep. We studied the various responses with respect to frequency of occurrence, effect of increased stimulus intensity, and relation of stimulus fluid to laryngeal structures. Two groups of infants were studied: healthy full-term infants (n = 5) and preterm infants with a history of prolonged apnea (n = 9). We used a nasopharyngeal catheter to deliver small boluses of warm saline (0.02-0.35 ml) to the oropharynx. Responses repeatedly observed in both infant groups included swallows, obstructed respiratory efforts, brief apnea, prolonged apnea, and cough. In both infant groups, swallows and obstructed breaths occurred frequently and cough and prolonged apnea infrequently. The functional significance of some response patterns was clear, whereas that of others was obscure. Larger stimulus volumes yielded more frequent responses (P less than 0.01), and preterm infants responded much more frequently than full-term infants (P less than 0.01). Prolonged apnea was a composite of the other responses and was much more common in preterm than full-term infants (P less than 0.01). The stimulus technique was performed under direct visualization of the airway in two deceased infants. The findings suggested that the relation of the piriform fossae to the interarytenoid notch is important in determining response frequency. Implications for regulation of the removal of upper airway secretions during sleep are discussed.
Influence of upper airway negative pressure reflex on response to airway occlusion in sleeping infants.
Artificially produced upper airway suction inhibits the diaphragm in animals and infants; however, the effects of spontaneously generated suction in humans are unknown. We studied nine tracheostomized infants because separation of the upper from the lower airway allowed us to channel suction created by an occluded inspiratory effort to both upper and lower airways (upper + lower airway occlusions) or to the lower airway only (lower airway occlusion). The tracheostomy airway was briefly occluded at end expiration during quiet sleep. In upper + lower airway occlusions, peak airway pressure of the first occluded breath was less negative and rate of pressure decrease slower than that of lower airway occlusions, indicating that upper airway suction inhibits thoracic inspiratory muscles. The threshold for this response was less than or equal to 4 cmH2O suction pressure. The effect on inspiratory time was variable. A decrease in slope of the inspiratory pressure waveform occurring at approximately 0.12 s after inspiration onset was more marked in upper + lower airway occlusions. We conclude that infants have an upper airway reflex response to inspiratory pressure that alters not only the peak and slope but also the shape of the inspiratory pressure waveform.
Prolonged apnea associated with upper airway protective reflexes in apnea of prematurity.
We examined the hypothesis that most idiopathic prolonged apneic spells in preterm infants originate as a form of upper airway protective reflex. We elicited a previously described upper airway reflex in 10 sleeping preterm infants with apnea of prematurity by instilling physiologic saline into the oropharynx and recording respiration, heart rate, and swallowing. Immediately after a small pharyngeal bolus of warm saline, one or more of several characteristic airway reflex responses occurred with most stimulus trials. These responses included brief central apnea, swallowing, and obstructed inspiratory efforts. Intermittently, this response pattern was more extensive and resulted in prolonged apnea. We compared the frequency of prolonged apnea immediately after saline boluses with spontaneously occurring prolonged apnea and found that apnea frequency after saline was greater than spontaneous apnea frequency in all 10 infants (p less than 0.0025). Also, the incidence of prolonged apnea occurring immediately after saline stimuli was significantly greater than that after randomly delivered control stimuli (p less than 0.005). These observations indicate that saline can induce prolonged apnea. Swallowing, a distinctive feature of the chemoreflex, occurred during 76% of spontaneous prolonged apnea spells. Spontaneous and postsaline prolonged apnea were nearly identical with respect to general features and frequency of specific airway protective responses. We conclude that the majority of spontaneous prolonged apneic spells in preterm infants have multiple features that are characteristic of an exaggerated airway protective response to an upper airway fluid stimulus. Circumstantial evidence suggests that endogenous upper airway secretions may be an important source of stimuli-inducing apneic spells in preterm infants.