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

The ventilatory response to hypoxia and to hypercarbia was assessed in 36 near-miss sudden infant death syndrome (N-M SIDS) and 23 control infants. Base-line measurements during non-REM 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 (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 (ΔVI/Torr PACO₂) was only 21 ± 1.9 (SE) ml.kg^-1.min^-1 per Torr PACO₂ compared with 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 therefore expressed as the slope of the ΔVI/PAO₂ plot (ml.kg^-1.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). In summary, in comparison to control infants, N-M SIDS infants as a group have a significantly smaller increase in VI in response to hypoxia as well as to hypercarbia.