Lack Of Paradoxical Breathing Movements
Date: Tue, 29 Oct 1996 04:35:03 -0800
The above is abstracted from a paper by two Japanese investigators, J.Kohyama and Y.Iwakawa...Brain & Development 11(3):186-190.1989 The authors report having examined the polygram of a SIDS victim ,and serial polygraphic observations of 4 ALTE infants. Reference to the original paper would be indicated ,since the method of selection of the records is not explained in the abstract. What seems to have happened is that they noticed something in the record of the SIDS victim which motivated them to follow 4 ALTE infants to see how things showed up in their recordings over time, and apparently 1 infant of the 4 had a similar reading as the SIDS infant. But I cannot be sure since I cannot access the full report. However ,they state as follows: "Normal paradoxical motions between chest and abdominal wall during active sleep period (AS) were completely abolished in the record of SIDS and 1 ALTE." This is the only reference to the absence of this paradoxical movement in infants during REM sleep (AS) that appears in the literature. Paradoxical movement has been receiving increasing attention over the past few years, and is regarded as a respiratory feature during this phase of sleep. However, this may be a collateral effect and it may be related more directly to tense arousal during dreaming, much in the same way as it occurs when we listen to a story or awaiting the punch line of a joke. Elevation of the sympathetic nervous system occurs as we await the outcome. This is part of the vigilance/survival/fight/flight system. The absence of this abdominal contraction in infants might well be an indicator of a higher than usual parasympathetic tone during REM, and a possible means of early identification of an infant with autonomic irregularity. It would be doubtful if visual assessment of a sleeping infant would yield reliable conclusions about this phenomenon, but professionals having access to a sleep laboratory facility should be able to investigate it further in relation to SIDS/ALTE cases...apparently it has never received any attention since the time of the above mentioned analyses by the two Japanese investigators. It might be worth a look...?
In regard to SIDS infants found in the prone position, if they had pressure on their chests and could not breathe would not this result in the autonomic system still attempting to maintain a ventilatory response, and would the end result not be unlike suffocation and detectable at the autopsy?
Date: Tue, 29 Oct 1996 12:06:37 -0800
In response to Ed O'Hagan's comments about a Japanese study showing "lack of paradoxical breathing movements in a SIDS victim and in 4 ALTE infants":
Paradoxical rib cage motion is a very common phenomenon in infants. When a baby breathes, the diaphragm is the major muscle of breathing. As this contracts, it descends, pushing abdominal contents out. Thus, the baby's belly rises during inspiration. The rib cage of an infant is not as stable or rigid as in a child or adult. Thus, when the diaphragm contracts, it causes a negative pressure (vacuum) in the chest. Because the ribs are still cartilaginous (instead of bony), they bend, and rib cage volume actually decreases. This is especially pronounced during REM sleep, when dreaming occurs. Although REM sleep accounts for only 15%-20% of sleep time in adults, it is about 40%-50% of sleep time in infants. The result is that as the belly rises with diaphragmatic contraction, the rib cage is drawn inward (paradoxical motion).
Absence of paradoxical motion can occur with the following "normal"
Brainstem dysfunction, and consequent autonomic nervous system dysfunction, is a leading hypothesis about the cause of SIDS. I think that SIDS research is increasingly focusing on markers of brainstem and/or autonomic dysfunction to try and understand SIDS better. I am not sure whether absence of paradoxical motion would actually represent abnormal autonomic nervous system function. However, the CHIME monitor is capable of detecting paradoxical motion (and we see a lot of it), as are most Sleep Laboratory systems. I think these are being investigated.
Tom, thank you for your response. I agree. In addition, it is difficult to say very much based on just 1 SIDS infant and 4 ALTE. Several ongoing projects are addressing the issues of sleep state, obstructive apnea, and other indices of brain stem function, including the CHIME project. We can thus expect better insights in the future.
Carl E. Hunt, M.D.
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