Abstract:
RATIONALE:Brief recurrent apneas in preterm infants and adults can precipitate rapid and severe arterial O(2) desaturation for reasons that remain unclear. OBJECTIVES:We tested a mathematically derived hypothesis that when breathing terminates apnea, mixed-venous hypoxemia continues into the subsequent apnea; as a result, there is a surge in pulmonary O(2) uptake that rapidly depletes the finite alveolar O(2) store, thereby accelerating arterial O(2) desaturation. METHODS:Recurrent apneas were simulated in an experimental lamb model. Pulmonary O(2) uptake was calculated from continuously measured arterial and mixed-venous O(2) saturation and cardiac output. MEASUREMENTS AND MAIN RESULTS:Direct measurements revealed that asynchrony in the desaturation and resaturation of arterial and venous blood gave rise to dips and surges in O(2) uptake. After desaturation to 50%, a typical nadir in preterm infants, O(2) uptake surged to a peak of 176.9 ± 7.8% of metabolic rate. During subsequent apneas, desaturation rate was increased two- to threefold greater than during isolated apneas, in direct proportion to the magnitude of the surge in O(2) uptake (P < 0.001; R(2) = 0.897). Application of our mathematical model to a published recording of cyclic apneas in a preterm infant precisely reproduced the accelerated desaturation rates of up to 15% · s(-1) observed clinically. CONCLUSIONS:Rapid depletion of alveolar O(2) stores by surges in O(2) uptake almost completely explains the acceleration of desaturation that occurs during recurrent apnea. This powerful mechanism is likely to explain the severity of intermittent hypoxemia that is associated with neurocognitive and cardiovascular morbidities in preterm infants and adults.
journal_name
Am J Respir Crit Care Medauthors
Sands SA,Edwards BA,Kelly VJ,Skuza EM,Davidson MR,Wilkinson MH,Berger PJdoi
10.1164/rccm.201003-0477OCsubject
Has Abstractpub_date
2010-10-01 00:00:00pages
961-9issue
7eissn
1073-449Xissn
1535-4970pii
201003-0477OCjournal_volume
182pub_type
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journal_title:American journal of respiratory and critical care medicine
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