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Relationship between heart rate, left ventricular output, and stroke volume in preterm infants during fluctuations in
1Department of Pediatrics, Karolinska Institute, St. Göran's Children's Hospital, Stockholm, Sweden.
Insights
In preterm infants, heart rate changes had little effect on left ventricular output. Instead, stroke volume significantly varied, often inversely with heart rate, closely regulating cardiac function.
Area of Science:
- Neonatal Cardiology
- Pediatric Physiology
Background:
- Assessing cardiovascular function in preterm infants is crucial.
- Understanding the interplay between heart rate, stroke volume, and cardiac output is key for managing these vulnerable patients.
Purpose of the Study:
- To investigate the relationship between heart rate, left ventricular output, and left ventricular stroke volume in preterm infants.
- To determine how changes in heart rate affect cardiac output and stroke volume in this population.
Main Methods:
- Utilized range-gated Doppler to measure aortic blood flow velocity.
- Employed cross-sectional and M-mode echocardiography to determine aortic cross-sectional area.
- Calculated left ventricular output and stroke volume in 18 preterm infants.
Main Results:
- Left ventricular output showed a poor correlation with heart rate (r² = 0.17).
- Stroke volume varied substantially (exceeding 25% in 13/18 infants) and closely related to left ventricular output.
- Increased heart rate was often associated with decreased stroke volume, leading to increased left ventricular output.
Conclusions:
- Heart rate is not the primary determinant of left ventricular output variability in preterm infants.
- Stroke volume plays a significant role in regulating cardiac output in this age group.
- A reciprocal relationship exists between afterload and left ventricular output.
Abstract:
The relationship between changes in heart rate, left ventricular output, and left ventricular stroke volume was studied in 18 preterm infants, with mean gestational age 29 wk (range 26-33 wk) and mean postnatal age 10 d (range 1-21 d). To yield left ventricular output, the blood flow velocity in the ascending aorta was measured by range-gated Doppler technique and multiplied by the aortic cross-sectional area measured by cross-sectional and M-mode echocardiography. Stroke volume was calculated by dividing left ventricular output by heart rate. The individual mean left ventricular output correlated poorly with heart rate (r2 = 0.17), and, accordingly, there was a closer relationship between stroke volume and left ventricular output. In only four of the 18 infants was a significant correlation between heart rate changes and left ventricular output found. Substantial changes in stroke volume were seen in most infants, and in 13 of the 18 infants the changes exceeded 25%. These variations in stroke volume were closely related to left ventricular output. In 15 of the 18 infants, the maximum heart rate change was associated with a stroke volume change in the opposite direction. The group average of the maximum heart rate increase in each individual, 24 bpm (18%), corresponded to a decrease in stroke volume of 0.15 mL.kg-1 (9%) (p less than 0.05) and an increase in left ventricular output of 22.7 mL.min-1.kg-1 (9%) (p less than 0.05). A reciprocal relationship was seen between afterload and left ventricular output.(ABSTRACT TRUNCATED AT 250 WORDS)