The risk of sudden infant death.
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Bedding and Linens↗
Biomedical subjects
B T Thach
Publications and source records attributed to B T Thach.
Ventilatory sparing strategies and swallowing pattern during bottle feeding in human infants.
During feeding, infants have been found to decrease ventilation in proportion to increasing swallowing frequency, presumably as a consequence of neural inhibition of breathing and airway closure during swallowing. To what extent infants decrease ventilatory compromise during feeding by modifying feeding behavior is unknown. We increased swallowing frequency in infants by facilitating formula flow to study potential ventilatory sparing mechanisms. We studied seven full-term healthy infants 5-12 days of age. Nasal air flow and tidal volume were recorded with a nasal flowmeter. Soft fluid-filled catheters in the oropharynx and bottle recorded swallowing and sucking activity, and volume changes in the bottle were continuously measured. Bottle pressure was increased to facilitate formula flow. Low- and high-pressure trials were then compared. With the change from low to high pressure, consumption rate increased, as did sucking and swallowing frequencies. This change reversed on return to low pressure. Under high-pressure conditions, we saw a decrease in minute ventilation as expected. With onset of high pressure, sucking and swallowing volumes increased, whereas duration of airway closure during swallows remained constant. Therefore, increased formula consumption was associated with reduced ventilation, a predictable consequence of increased swallowing frequency. However, when consumption rate was high, the infant also increased swallowing volume, a tactic that is potentially ventilatory sparing as a lower swallowing frequency is required to achieve the increased consumption rate. As well, when consumption rate is low, the sucking-to-swallowing ratio increases, again potentially conserving ventilation by decreasing swallowing frequency much more than if the sucking-to-swallowing ratio was constant.
Bottle Feeding↗
Physical properties of bedding that may increase risk of sudden infant death syndrome in prone-sleeping infants.
Soft bedding has been shown in epidemiologic studies to increase the risk for sudden, unexpected death in prone-sleeping infants. We compared the physical properties of conventional bedding to bedding from two sources: 1) bedding that covered the airways of victims of sudden infant death syndrome (SIDS) lying prone and face down at the time of death; and, 2) bedding associated with increased risk for SIDS in case-control studies (i.e. bedding filled with ti tree bark). Using simple mechanical models and the head from an infant mannequin, we measured the resistance to airflow, malleability, and capacity to limit CO2 dispersal of the bedding. We also describe a technique for quantifying bedding softness. The resistance and malleability were similar for the conventional bedding, the ti tree bedding, and the bedding from SIDS deaths (analysis of variance, p = 0.85 and 0.16). The ti tree bedding and the other bedding from SIDS cases differed from conventional bedding in two physical properties. Both groups were softer (p < or = 0.005) and limited CO2 dispersal to a greater degree (p < or = 0.009). The finding that increased capacity to limit CO2 dispersal is a consistent property of the bedding covering the airways of these SIDS victims and of bedding shown to be an epidemiologic risk factor for SIDS supports rebreathing of expired air as a mechanism underlying the association of certain kinds of bedding with SIDS.
Bedding and Linens↗
Impaired ventilation in infants sleeping facedown: potential significance for sudden infant death syndrome.
Although accidental suffocation has been suggested as a cause of sudden infant death syndrome in infants who are found prone with their faces straight down, the occurrence and effects on breathing of this position in living infants are unknown. We studied prone sleeping infants to see whether they will sleep with their faces straight down; whether they can spontaneously change from this position; the way that thermal stimuli or bedding softness influences this change; and whether rebreathing or airway obstruction occurs. We studied 11 healthy infants, aged 0.2 to 6 months, while they slept on soft and on firm bedding. Most infants slept facedown spontaneously or when turned to this position. All could turn their heads readily but slept facedown for variable periods. All infants put their faces straight down more often after cold than after warm stimuli. Obstructive apnea occurred only once, but rebreathing occurred in all subjects. When the infants were in the facedown position, inspired carbon dioxide was three times greater on soft than on hard bedding. End-tidal carbon dioxide partial pressure rose in all subjects while they were in the facedown position; in one infant, high end-tidal carbon dioxide partial pressure and desaturation occurred without signs of arousal. We conclude that infants sleeping facedown may occasionally have significant asphyxia; this sleep position may have a role in some infant deaths diagnosed as sudden infant death syndrome.
Humans↗
Unintentional suffocation by rebreathing: a death scene and physiologic investigation of a possible cause of sudden infant death.
As part of a 1-year study of sudden unexpected infant deaths in St. Louis, we performed both a specialized death scene investigation and, in selected cases, a physiologic reconstruction of the death scene with a rabbit model. Those cases in which the infant was found face down with nose and mouth covered by bedding were chosen for the physiologic testing; our goal was to assess the potential for lethal rebreathing of expired air. The physiologic studies reconstructed the infants' premortem ventilatory environment by using the head from an infant mannequin positioned on the actual bedding on which an infant had died and a rabbit breathing through the mannequin's nares. The specialized scene investigation was carried out in 31 of 32 deaths from sudden infant death syndrome, diagnosed by the usual methods. Of 31 infants, eight died with their faces downward and covered by bedding, and the bedding was obtained for further study in seven of eight cases. The bedding had low resistance to airflow (6.25 to 22.6 cm H2O/L per second), and caused considerable rebreathing that was lethal to the rabbits in five of seven cases. We conclude that items of bedding in common use are capable of causing lethal rebreathing by prone-sleeping infants whose nose and mouth become covered; suffocation by rebreathing was the probable mechanism of death in a substantial number of these deaths that had been attributed to sudden infant death syndrome.
Animals↗
A sleep position-dependent mechanism for infant death on sheepskins.
OBJECTIVE: To determine whether rebreathing of expired air is a plausible lethal mechanism of sudden death in infants sleeping face down on sheepskins. DESIGN: Case reports of infants who died on sheepskins combined with a controlled study of effects of their respiratory microenvironment at death. SETTING: Research laboratory. MATERIALS: Rabbits used experimentally to assist in simulation of an infant's respiratory microenvironment. Rabbits breathed into sheepskin through the airway of an infant mannequin. INTERVENTION: None. MEASUREMENTS/MAIN RESULTS: Rebreathing of expired air was documented by carbon dioxide analysis of airway gas. Arterial blood gas analysis showed hypoxemia, hypercarbia, and acidosis in all experimental rabbits but not in controls. Rebreathing expired air was lethal for three of four experimental rabbits. CONCLUSIONS: Infants sleeping prone on a sheepskin, with their faces straight down, experience potentially lethal rebreathing of expired air. Avoidance of the prone position would markedly reduce the risk of rebreathing expired air. The pronounced decrease in sudden infant death syndrome in southern New Zealand that followed a campaign to eliminate prone sleeping may have been attributable to reduced fatal rebreathing, as deaths of infants sleeping face down on sheepskins were common before the campaign.
Animals↗
Mechanisms underlying induced autoresuscitation failure in BALB/c and SWR mice.
Mechanisms underlying failure of autoresuscitation from hypoxic apnea were investigated. Failure was induced by repeated exposure to hypoxia. The influence of maturation was studied in adults, weanlings, and 10- and 5-day-old mice. Mice successful at autoresuscitation (BALB/c) as well as those prone to autoresuscitation failure (SWR weanlings) were studied. Hypoxic apnea was induced with 97% N2-3% CO2, and 21% O2 was given at its onset; electrocardiogram and ventilation were recorded. Hypoxic exposure was repeated if autoresuscitation (recovery of eupnea) occurred. Autoresuscitation failure (death) was induced in all mice. Young BALB/c mice tolerated more trials than older mice. SWR weanlings frequently failed to autoresuscitate on the initial exposure and tolerated fewer repeat trials overall than age-matched BALB/c mice. Induced autoresuscitation failure in all mice appeared to be unrelated to gasping regulation, because both gasp number and amplitude were similar during the failed trial and the previous successful trial. In most mice, failure was associated with absent recovery of heart rate during gasping. In BALB/c mice in particular, this persistent bradycardia was usually due to heart block, which occurred in 95% of failed trials. In addition, heart block occurred with increasing frequency on later successful trials, but conversion to sinus rhythm always preceded successful autoresuscitation. Heart block was also frequent in SWR mice and had similar consequences. BALB/c mice exposed to continuous anoxia survived longer than SWR mice, indicating increased endurance of components of the autoresuscitation mechanism not directly related to the ventilatory function of gasping (e.g., cardiovascular components).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Neuromuscular control of upper airway patency.
To understand medical disorders such as obstructive apnea, or pulmonary aspiration, one must understand the many functions performed by the upper airway. These functions include respiration, airway protection at the face, feeding, and regulation of thoracoabdominal pressure. The neuromuscular mechanisms that perform these functions are complex. Many of the upper airway muscles can be classed as either airway constricting or airway dilating. These muscles regulate upper airway functions by regulating the shape of the upper airway.
Airway Resistance↗
Sudden death in infants sleeping on polystyrene-filled cushions.
BACKGROUND: Infants are at risk for both the sudden infant death syndrome (SIDS) and accidental suffocation. On postmortem examination, however, it is difficult to distinguish one from the other without information from the scene of death. Healthy infants are assumed to be able to turn their heads and, if not otherwise restrained, to obtain fresh air. We assessed this assumption in an investigation of infant deaths that occurred during sleep on cushions filled with polystyrene beads. METHODS: We obtained data on 25 deaths from the U.S. Consumer Product Safety Commission. We also used mechanical and animal models to study physiologic aspects of ventilation relevant to these results, by simulating the effects on an infant of breathing into a cushion. We measured the effects of softness, malleability (molding of the cushion about an infant's head), airflow resistance, and rebreathing of expired gases. RESULTS: All 25 study infants were prone when found dead, and at least 88 percent were face down with nose and mouth obstructed by the cushion. SIDS was the diagnosis in 19 of the 23 infants who underwent autopsy. Our findings show, however, that the cushion would have limited movement of the infant's head to obtain fresh air, and the amount of rebreathing we estimated to have occurred in the infants was lethal in a rabbit model. CONCLUSIONS: Accidental suffocation by rebreathing was the most likely cause of death in most of the 25 infants studied. Consequently, there is a need to reassess the cause of death in the 28 to 52 percent of the victims of SIDS who are found with their faces straight down. Safety regulations setting standards for softness, malleability, and the potential for rebreathing are needed for infant bedding.
Air Movements↗
Effect of pentobarbital on spontaneous recovery from hypoxic apnoea in mice.
The effect of pentobarbital anaesthesia on spontaneous recovery from hypoxic apnoea (autoresuscitation) was investigated in SWR/J mice. Experiments were performed in 17 to 23 day old animals, in which the mechanism often fails, and in adults, in which it is usually successful. Mice, matched for age and weight, were injected with pentobarbital (62.5 mg/kg) or saline. Hypoxic apnoea was induced with 97% N2-3% CO2 and air given at its onset. To determine whether the effect of pentobarbital depended on hypothermia, we performed experiments in 17-23-day-olds with and without maintenance of body temperature. In the 'hypothermic' experiments one of 27 mice given pentobarbital died, compared with 10 of 22 controls (P less than 0.005). In the 'isothermic experiments', none of 15 mice given pentobarbital died, compared to 7 of 13 controls (P less than 0.005). All adults in both groups survived. Pentobarbital had a different effect on eupnoea and gasping: resting ventilation was depressed but gasp ventilation increased, and the duty cycle of gasps but not eupnoeic breaths was altered. Pentobarbital may facilitate autoresuscitation because gasping is unimpaired but oxygen consumption and lactate production are reduced, allowing cardiac function and cerebral survival until PO2 is restored.
Animals↗
Mechanism of failure of recovery from hypoxic apnea by gasping in 17- to 23-day-old mice.
The mechanism of failure of autoresuscitation from hypoxic apnea in 17- to 23-day-old (weanling) Swiss Webster related/J mice was investigated by recording electrocardiogram (ECG) and ventilation in adult, weanling, and 11-day-old mice. Hypoxic apnea was induced with 97% N2-3% CO2. O2 (21% or 50% O2) or 97% N2-3% CO2 was given at the onset of apnea. The ECG showed no arrhythmias predictive of failure of autoresuscitation. The first indication of failure was a progressive fall in gasp volume ("run down"). This pattern also occurred in animals given continuous 97% N2-3% CO2 and was significantly different from that in mice that survived. Gasping duration in 97% N2 was longer in weanlings than adults but shorter than in 11 day olds. Respiratory and heart rate recovery were more rapid in adults than in weanlings. Although recovery in high O2 was more rapid, the survival rate was not increased. The lack of effect of high O2 on survival and the virtually identical pattern of gasping in mice dying in 97% N2 and air leads us to conclude that in mice that fail to autoresuscitate little or no O2 reaches the medullary respiratory centers. We speculate that this may be due to increased vulnerability of cardiac muscle to anoxia in 17- to 23-day-old mice, resulting in early and severe heart failure.
Aging↗
Coordination of breathing, sucking, and swallowing during bottle feedings in human infants.
Incoordination of sucking, swallowing, and breathing might lead to the decreased ventilation that accompanies bottle feeding in infants, but the precise temporal relationship between these events has not been established. Therefore, we studied the coordination of sucks, swallows, and breaths in healthy infants (8 full-term and 5 preterm). Respiratory movements and airflow were recorded as were sucks and swallows (intraoral and intrapharyngeal pressure). Sucks did not interrupt breathing or decrease minute ventilation during nonnutritive sucking. Minute ventilation during bottle feedings was inversely related to swallow frequency, with elimination of ventilation as the swallowing frequency approached 1.4/s. Swallows were associated with a 600-ms period of decreased respiratory initiation and with a period of airway closure lasting 530 +/- 9.8 (SE) ms. Occasional periods of prolonged airway closure were observed in all infants during feedings. Respiratory efforts during airway closure (obstructed breaths) were common. The present findings indicate that the decreased ventilation observed during bottle feedings is primarily a consequence of airway closure associated with the act of swallowing, whereas the decreased ventilatory efforts result from respiratory inhibition during swallows.
Bottle Feeding↗
Maturation of cardiorespiratory interactions in spontaneous recovery from hypoxic apnea (autoresuscitation).
The maturation of the process of spontaneous recovery from hypoxic apnea by gasping (autoresuscitation) was characterized in adult, weanling (18-22 d), and infant (5 and 10 d) BALB/c mice. ECG and respiration were recorded and hypoxic apnea was induced with 97% N2-3% CO2. Administration of 21% O2 at onset of hypoxic apnea resulted in successful autoresuscitation in all 63 animals tested. In all mice, three sequential stages occurred: 1) gasping with marked bradycardia, 2) rapid increase in heart rate (cardiac resuscitation), and 3) increase in respiratory rate (respiratory resuscitation). Despite these similar stages, marked maturational differences were apparent. The times to cardiac and respiratory resuscitation were longer in the pups than in the older mice, whereas the gasp frequency before cardiac resuscitation was lower in the infants. Resuscitation time correlated with gasp interval (1/gasp frequency). In addition, the initial bradycardia at onset of gasping was more pronounced in the pups. A 30- or 60-s delay in oxygen administration after onset of hypoxic apnea caused a marked decrease in the adults' ability to autoresuscitate, without affecting that of the pups. A comparison of gasp frequency in 21% O2 versus 97% N2-3% CO2 showed that the presence of oxygen increased gasp frequency in the pups, but had no effect on gasp frequency in the weanlings or adults. We conclude that autoresuscitation is equally effective in both infant and adult BALB/c mice but only when oxygen is available before the onset of hypoxic gasping.(ABSTRACT TRUNCATED AT 250 WORDS)
Aging↗
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.
Apnea↗
Postoperative apnea after caudal anesthesia in an ex-premature infant.
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Anesthesia, Caudal↗
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.
Airway Obstruction↗
Effects of negative upper airway pressure on pattern of breathing in sleeping infants.
Negative upper airway (UAW) pressure inhibits diaphragm inspiratory activity in animals, but there is no direct evidence of this reflex in humans. Also, little is known regarding reflex latency or effects of varying time of stimulation during the breathing cycle. We studied effects of UAW negative pressure on inspiratory airflow and respiratory timing in seven tracheostomized infants during quiet sleep with a face mask and syringe used to produce UAW suction without changing lower airway pressure. Suction trials lasted 2-3 s. During UAW suction, mean and peak inspiratory airflow as well as tidal volume was markedly reduced (16-68%) regardless of whether stimulation occurred in inspiration or expiration. Reflex latency was 42 +/- 3 ms. When suction was applied during inspiration or late expiration, the inspiration and the following expiration were shortened. In contrast, suction applied during midexpiration prolonged expiration and tended to prolong inspiration. The changes in flow, tidal volume, and timing indicate a marked inhibitory effect of UAW suction on thoracic inspiratory muscles. Such a reflex mechanism may function in preventing pharyngeal collapse by inspiratory suction pressure.
Air Pressure↗