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Air Movement in the Human Sleeping Environment
and Sudden Infant Death

J. A. Corbyn

Department of Biological and Environmental Science
Murdoch University, Murdoch, Western Australia

Cataloguing data:-
Corbyn, John Andrew 1944-

Air Movement in the Human Environment and Sudden Infant Death with tables, illustrations and bibliography. Murdoch University, Murdoch, Western Australia 1997.

Subjects to which research report is relevant:-

  1. Medicine and child care
  2. Sudden infant death
  3. Ventilation engineering
  4. Meteorology (at scales of the order of 1 mm to 1m)
  5. Fluid mechanics
  6. Ventilation in confined spaces
  7. Health and safety
  8. Design of housing and housing standards
  9. Design of cots, beds and bedding standards
  10. Child care practice
  11. Care of old persons
  12. Indoor environment

Abstract

The microclimate near the face of a sleeping human is examined. It is found that exhaled air can accumulate near the face of a sleeping infant in certain circumstances; this air can become vitiated by having an excess of carbon dioxide and a deficiency of oxygen. Model studies and direct measurements are used to study the composition of air in the facial region of a sleeping infant. It is shown that the carbon dioxide content of inhaled air in certain sleeping environments can be above the industrial thresh hold limit value of 0.5% with values of over 2% occurring. Apparatus for simulating infant sleeping environments is described: this apparatus is also suitable for studying environments that may be hazardous to infant health.

Transport of carbon dioxide from and oxygen to the face of a sleeping infant is found to be affected by air movement caused by jet action of the nose, density contrasts between exhaled air and ambient air and other factors.

The physiology of exposure of an infant to a sleeping environment with an excess of carbon dioxide and a deficiency of oxygen is discussed. It is found that mechanisms exist such that a re-breathing of vitiated air can account for a proportion of sudden infant deaths: in particular a sleeping infant acclimatized to a hypercarbic atmosphere may suffer from a reduced lung ventilation rate1 on subsequent exposure to a normal atmosphere.

The statistics of sudden infant death are reviewed and it is found that the environmental associations of SIDS are also those where accumulations of exhaled air at the face are likely.

Safety recommendations are derived from the work: in particular that sleeping infants should have good ventilation at the face and there should not be bulky bedding or other obstructions to air flow near the face.

Principal Findings

(1) In certain environmental conditions mass transport of carbon dioxide from and oxygen to the face of a sleeping infant is insufficient to maintain a safe and healthy sleeping environment. Carbon dioxide levels in inhaled air in excess of 2% exist in certain situations.

(2) Potentially dangerous environmental conditions are those where exhaled air is not carried clear of the face by the stream of air issuing from the mouth or nose. If or not a dangerous situation develops depends on the microclimate at the face. Environmental aspects which affect the accumulation of exhaled air at the face include atmospheric pollution, temperature, humidity, bedding arrangement, sleeping position, interaction between the infant and the sleeping environment. Changes to child care practice to improve the sleeping environment of infants would be expected to eliminate or reduce SIDS deaths due to breathing exhaled air.

(3) Physiological mechanisms can be identified that provide explanation for sudden infant death as a result of prolonged exposure to a hypercarbic atmosphere.

(4) Physical mechanisms can be shown to exist that explain the environmental associations of sudden infant death in terms of the accumulation of exhaled air at the face.

(5) The presently used (1996) safety precautions regarding sudden infant death require modification to give effect to the concept that inhaled air should not mix with exhaled air. There appears to be no dangers in the proposed modifications to advice on infant care.

(6) Industrial standards regarding the properties and usage of infant beds and bedding require to be revised.

(7) Investigations of cases of possible sudden infant death should include study of the sleeping environment using a physical model in the form of a breathing environment simulator. Designs of such a simulator are given by the present author. It is essential that such simulators include control of the microclimate of the sleeping environment, chest motion and composition control of exhaled air.

Previous Publications Describing the Work

Corbyn, J.A. Atmospheric Carbon Dioxide Levels in the Vicinity of Sleeping Infants and Sudden Infant Death. Trans. of Multi-Disciplinary Engineering of Institution of Engineers, Australia. Vol. GE 15 No. 1 August 1991 pages 9 to 13.

Corbyn J.A., Matthews P. Environmental Causes of Sudden Infant Death. Western Technical Press, PO Box 195, Fremantle, Western Australia 1992. ISBN 0 646 097970

Corbyn J.A. Sudden Infant death due to Carbon Dioxide and other Pollutant accumulation at the face of a sleeping baby. Med. Hypotheses 1993a 41(6) pp 484-495

Corbyn J.A. Excess Carbon Dioxide and other contaminants in inhaled air as a general explanation of sudden infant death. Paper 101 Third International SIDS Conference, Stavanger, Norway 1994a ISBN 82-91154-13-9

Corbyn J.A. The Causes and Prevention of Sudden Infant Death. Western Technical Press, PO Box 195, Fremantle, Western Australia 1994b. ISBN 0 9524255 0 5

Corbyn J.A. The Relationship between air composition at the face of a sleeping infant and sudden infant death. Clean air ’94: Proceedings of the clean air society of Australia and New Zealand 12 Int. Conf. Perth Western Australia 1994. pp535-555. The Clean Air Society of Australia and New Zealand 1994c. ISBN 1 86308 024 4

Sudden infant death, Crib death, Cot death and Overlaying

Sudden infant death, cot death, crib death (U.S.A. term for cot death) and overlaying (where baby dies in bed with mother) have been found to be similar and are now all described as SIDS. These deaths have been found to be more common during periods of low temperature, high humidity and atmospheric pollution.

Explanation for a proportion of these deaths can be made in terms of the accumulation of exhaled air with excess carbon dioxide at the face during sleep. The result of continued sleeping in this environment is that the infant becomes acclimatized to a high carbon dioxide level in inspired air and the control of breathing becomes abnormal. Exhaled air from other persons or animals sleeping close to the face of the infant may also contribute.

Diagram of safe and unsafe conditions
POSSIBLE DANGER SAFE
Conditions that make the retention of exhaled air at the face more likely Conditions that make the retention of exhaled air at the face less likely
Soft or bulky bedding Hard bed
Bulky bedding at the face or neck No bulky bedding at face or neck
No draughts Dry bedding (note B)
Face down position Face up position
Damp or wet bedding Draughts
Confined cot, pram or bed No bottles, toys or obstructions
Unventilated mattress Not sleeping through the night
Infant under bedding Not exposed to breath of others (note C)
High humidity (see note A) Not sleeping between adults
Tobacco smoke, air pollution Not to sleep against a wall
Exhaled air directed into bed Mattress not to be permeable
Permeable or porous mattress Breath to direct air away from the face
Sleeping on a bean bag Breath not directed into the bed

Note A: High humidity can result from climatic influences, unflued gas or kerosene heaters and evaporative air conditioners. Note B: Bedding should have good “wickability” so that any moisture moves away from the face, ordinary cotton sheets are satisfactory. Note C: If in bed with adults the infant must not be down in the bed and exposed to a pool of exhaled air from the adults.

Always make sure that there is a clear space around the head and neck so that the baby has access to fresh air. Breath coming from the mouth or nose should not be obstructed and move freely away from the face. Making sure that the baby gets fresh air will provide protection against the dangers of exhaled air at the face even if other conditions are bad.

Extract from:- “Air Movement in the Human Sleeping Environment and Sudden Infant Death” Research Report by J.A. Corbyn, Dept. of Biological and Environmental Science, Murdoch University, Murdoch, Western Australia, 1997 (in preparation). See also “Environmental Causes of Sudden Infant Death” by J.A. Corbyn and P. Matthews published by Western Technical Press, PO Box 195, Fremantle, Western Australia.


1 …rate In medical terms a reduced minute volume.