Diminished hypoxic ventilatory responses in near-miss sudden infant death syndrome

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Abstract
The ventilatory response to hypoxia and to hypercarbia was assessed in 36 near-miss sudden infant death syndrome (N-M SIDS) and 23 control human infants. Baseline measurements during REM [rapid eye movement] sleep documented no significant difference in respiratory frequency, alveolar CO2 and O2 partial pressure (PACO2 and PAO2) or tidal volume between the N-M SIDS and control infants. In the N-M SIDS group, mean inspiratory flow and minute ventilation (.ovrhdot.VI) were significantly lower than in the control group (P < 0.001 and P < 0.01, respectively), and the slope of the ventilatory response to hypercarbia (.DELTA..ovrhdot.VI/torr PACO2) was only 21 .+-. 1.9 (SE) ml .cntdot. kg-1 .cntdot. min-1 per torr PACO2 compared to 62 .+-. 3.5 in controls (P < 0.001). For both groups, the increase in ventilation with hypoxia appeared linear within the PAO2 range assessed (65-115 torr) and was expressed as the slope of the .DELTA..ovrhdot.VI/PAO2 plot (ml .cntdot. kg-1 .cntdot. min-1 per torr PAO2). The slope of the hypoxic ventilatory response was significantly less in the N-M SIDS than in the control group, -8.3 .+-. 1.0 vs. -19.9 .+-. 1.5, respectively (P < 0.001). Compared to control infants, N-M SIDS infants as a group have a significantly smaller increase in .ovrhdot.VI in response to hypoxia and to hypercarbia.