Pulmonary Mechanics in Early Infancy. Sublinical Grunting in Low-Birth-Weight Infants

Abstract

SummaryPulmonary mechanics were studied with the constant pressure body plethysmograph method in 78 infants during the first year of life. Registrations of breathing frequency, tidal volume, minute volume, dynamic compliance, pulmonary functional resistance, and end-expiratory resistance were made at rest and during carbon dioxide-induced hyperventilation. Data from 70 infants demonstrated strong correlations (P < 0.001) between all pulmonary function parameters and length. Carbon dioxide-induced hyperventilation was achieved mainly by an increased tidal volume. Pulmonary functional resistance did not change with hyperventilation, indicating wider airways during forced ventilation.A special breathing pattern called "subclinical grunting" was found in 16 of 45 infants who were low birth weight but without clinical signs of hyaline membrane disease. The pattern was characterized by a high resistance during most of the prolonged expiration. It was identical to that previously described in cases of hyaline membrane diseases. All re-examined low-birth-weight infants with subclinical grunting developed a normal breathing pattern. SpeculationSublinical grunting found in preterm low-birth-weight infants might be a phenomenon of postnatal lung adaptation which can be registered by pulmonary mechanics examination.

Fetal pH and postnatal adaptation in preterm vaginal deliveries

“…3). This might be an expression of postnatal pulmonary adaptation mechanisms in order to clear, the airways from fetal water and prevent atelectases, by subclinical grunting as described previously in such infants (13,16). The most preterm infants with low fetal pH (Group B) also had low beat-to-beat heart rate variability on CRG.…”

Breathing Patterns in Preterm and Term Infants Immediately After Birth

“…3) and amplitude than grunting. Grunting has been recognized as a dynamic braking of expiration by the larynx (11,13), but crying has not been described earlier as a braking mechanism. The most likely reason for this is that in earlier studies breaths were excluded from analysis if the infant was crying (7,11).…”

“…This is known as expiratory braking and helps to develop and maintain functional residual capacity (FRC) during the immediate newborn period when the lung is partially liquid filled and the chest wall is very compliant (9,10). Although this respiratory pattern has also been observed in preterm and term infants later in life (11)(12)(13)(14)(15), there are no data describing the breathing pattern of very preterm infants immediately after birth.…”

Spontaneous Breathing Patterns of Very Preterm Infants Treated With Continuous Positive Airway Pressure at Birth

“…The second is by closure or narrowing of the larynx (19,21-23). The expiratory noise associated with vocal cord adduction, i.e., grunting has been recognized as a dynamic braking of expiration by the larynx (22,38). In absence of an audible grunt, the larynx still maintains a dynamic role in slowing expiration (27).…”