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Heart rate variability in 1-day-old infants born at 4330 m altitude
J P Mortola1, F León-Velarde, L Aguero
1Department of Physiology, McGill University, Montreal, Quebec H3G 1Y6, Canada.
Insights
Newborn infants born at high altitude show similar heart rate variability to low-altitude infants. However, high-altitude newborns may have altered heart rate control responses to cooling.
Area of Science:
- Physiology
- Neonatal Medicine
- Altitude Physiology
Background:
- Heart rate variability (HRV) in fetuses and newborns is affected by hypoxia.
- Altitude exposure presents a chronic hypoxic environment.
- Understanding HRV differences in high-altitude newborns is crucial for assessing adaptation.
Purpose of the Study:
- To compare heart rate variability between infants born at high altitude and those born at low altitude.
- To investigate the impact of thermal stress (cooling) on HRV in these two groups.
Main Methods:
- Short-term (4-5 min) inter-beat interval recordings were collected from 19 infants in Lima (50 m) and 15 in Cerro de Pasco (4330 m).
- Recordings were taken during quiet rest in warm (35°C) and cool (26°C) conditions.
- Heart rate variability was analyzed using time-domain and frequency-domain methods on 512 consecutive intervals.
Main Results:
- No significant differences in HRV were observed between high-altitude and low-altitude infants at warm ambient temperature.
- During cooling, heart rate increased only in the low-altitude group.
- The high-frequency power of HRV, indicative of vagal activity, was greater in high-altitude infants during cooling.
Conclusions:
- Gestation at high altitude does not significantly impact newborn heart rate variability under resting conditions.
- Differences in heart rate response to cooling suggest potential limitations in cardiac autonomic control in high-altitude newborns that warrant further investigation.
Abstract:
In fetuses and newborn infants heart rate variability changes in conditions of acute and chronic hypoxia; we therefore asked whether heart rate variability of infants born at high altitude differed from that of low-altitude infants. Short-term recordings (4-5 min) of inter-beat intervals were obtained in 19 infants in Lima (50 m altitude) and in 15 infants in Cerro de Pasco (4330 m, barometric pressure approximately 450 mmHg, inspired oxygen pressure approximately 94 mmHg) during quiet rest in warm conditions (ambient temperature, Ta, approximately 35 degrees C). In 12 infants from each group recordings were also obtained during cooling (Ta approximately 26 degrees C). Heart rate variability was evaluated from 512 consecutive inter-beat intervals, with analysis based on time-domain and frequency-domain methods. At warm Ta, heart rate variability did not differ between the two groups. During cooling, heart rate increased only in the low-altitude group. As in the warm, during cooling most parameters of heart rate variability did not differ between the two groups. The only exception was the inter-beat interval power of the high-frequency range of the spectrum (0.15-0.4 Hz), which, at least in adults, is believed to be a reflection of vagal activity, and was greater in the high-altitude group. It is concluded that gestation at high altitude, despite its blunting effects on fetal growth, does not have a major impact on heart rate variability of the newborn. Nevertheless, the possibility that differences in response to cooling may reflect some limitation in heart rate control needs to be examined further.