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Biomedical subjects

T Hertzberg

Publications and source records attributed to T Hertzberg.

22 records · Page 2Linked to original sources
PubMed1987

Postnatal sensitivity of the peripheral chemoreceptors in newborn infants.

The peripheral chemoreflex was tested in healthy term infants by measuring the ventilatory response to 100% oxygen over 30 seconds. Minute ventilation did not change when studied two to six hours after birth. By contrast, at 2-6 days of age a mean decrease of 9.8% was noted, the difference between the groups being highly significant. There were no significant changes in respiratory rate. It is concluded that the chemoreflex is less active immediately after birth than it is a few days later, possibly due to a resetting of the sensitivity of the peripheral chemoreceptors from the fetal state, with its relatively low arterial oxygen tension to the higher postnatal concentrations.

Chemoreceptor Cells↗
PubMed1987

Ventilatory and metabolic responses to acute hypoxia in infants assessed by transcutaneous gas monitoring.

Transcutaneous PO2, transcutaneous PCO2 and respiratory pattern were monitored during acute mild hypoxia (15% O2) in quiet sleep. Eighteen healthy infants were studied sequentially at 1-5 days, 4-8 weeks and 10-14 weeks of age. The transcutaneous PCO2 changes (delta PCO2) related to the transcutaneous PO2 fall, were used as an index of the total ventilatory and metabolic response during the test. This calculated index was related to the occurrence of arousal and periodic breathing. Transcutaneous PCO2 increased above control levels in infants 1-5 days old, decreased markedly in infants 4-8 weeks of age, and decreased slightly or remained unchanged in the 10-14 weeks old infants. The changes in response pattern were significant (P less than 0.006). These differences in response were not reflected in the lowest values of transcutaneous PO2 attained during the test. The lowest transcutaneous PO2 levels did not differ significantly between the age groups, indicating that the mechanisms maintaining PO2 during hypoxia may change during development. Periodic breathing was always associated with a decrease in transcutaneous PCO2 and in 8 out of 10 tests where it occurred it commenced at the lowest transcutaneous PCO2 level recorded. These results do not support the concept that periodic breathing is a sign of hypoventilation. Arousal was observed in less than half of the infants and was not related to the degree of hypoxaemia. We conclude that hypoxic arousal in infants may not be the important escape mechanism as suggested previously.

Arousal↗
PubMedDate not supplied

Autonomic reflexes in preterm infants.

Some autonomic nervous reflexes often tested in adult medicine have been studied in 21 preterm infants (25-37 gestational weeks). The aim was to develop such tests for preterm infants and see if there were any differences in babies with recurrent apnea and bradycardia and babies who had been exposed to sympathicolytic drugs before birth. To test sympathetic nervous activity the peripheral vascular resistance was measured before and during 45 degrees of head-up tilting. To test parasympathetic nervous activity the degree of bradycardia was measured in response to cold face test (application of an ice-cube on the fore-head) and laryngeal stimulation with saline. Finally the heart rate changes after a sudden noise (85 dB) were studied as an indicator of both sympathetic and vagal activity. The peripheral resistance was found to be relatively low in these preterm infants, particularly in some infants tested at the postnatal age of about two months. Heart rate and mean blood pressure did not change during tilting, while the peripheral resistance increased significantly mainly due to lowered limb blood flow. The median decrease of the heart rate during the cold face test was 20.0% and during laryngeal receptor stimulation 23.7%. The sudden noise usually caused a biphasic heart rate response. An autonomic nervous reflex score was calculated and found to be negative (parasympathetic) in infants with recurrent prolonged apnea and bradycardia and positive in infants with clinical signs of increased sympathetic nervous activity.

Apnea↗