Delayed chemoreceptor responses in infants with apnoea

Abstract

Aims: To test the hypothesis that apnoea of infancy (AOI) is due to a deficit in chemoreception.

Methods: Tests were performed on 112 infants: 43 healthy control infants, 28 infants with periodic breathing or central apnoea (PBCA), and 41 infants with obstructive apnoea (OA) on overnight polysomnography. Chemoreceptor responses to hypercapnia (4% and 6% CO2 in air) for 6-8 minutes and hyperoxia (100% O2) for 60 seconds were expressed in terms of response strength and reaction time. Age at birth (gestational week 37-41) and age at test (2-34 postnatal weeks) were comparable across groups (median, min-max value). A total of 70 CO2 and 71 O2 tests were analysed.

Results: The strongest and fastest CO2 responders were control infants: their median increase in ventilation was 291%/kPaCO2 and their reaction time 16 breaths. In infants with PBCA and OA, the increase in ventilation was 41% and 130%/kPaCO2, and reaction time 64 and 54 breaths, respectively. There was a significant negative correlation between CO2 response strength and response time. In response to hyperoxia there was a comparable decrease in ventilation in all infants (12-20%), but a significantly longer response time in infants with apnoea (20 v 12 breaths). There was no correlation between the response strength and response time to O2 and CO2.

Conclusion: An inappropriate central control of respiration is an important mechanism in the pathogenesis of apnoea of infancy.

Figure 1

Description of the infant study population.

Figure 2

(A) Polysomnographic recording of CO₂ challenge test in one infant: note the progressive increase in chest and abdominal excursion and air flow. (B) Polysomnographic recording of O₂ challenge test in one infant. Note the decrease in amplitude of chest and abdominal excursions preceding the increase in transcutaneous PO₂.

Figure 3

The response strength to CO₂ in healthy controls, in infants with periodic breathing/central apnoeas (PBCA) and obstructive apnoeas (OA). The medians are indicated by bold horizontal lines. The rectangles contain 50% of the values—that is, all values between the lower and upper quartiles. The bars extend out to the minimal and maximum values, while the values below or above 1.5 times the interquartile (outliers) are indicated as small squares (box and whisker plot).

Figure 4

The response time to CO₂ inhalation, expressed in number of breaths in healthy controls, in infants with periodic breathing/central and obstructive apnoeas. The medians are indicated by bold horizontal lines. The rectangles contain 50% of the values—that is, all values between the lower and upper quartiles. The bars extend out to the minimal and maximum values, while the values below or above 1.5 times the interquartile (outliers) are indicated as small squares (box and whisker plot).