Post-sigh breathing behavior and spontaneous pauses in the C57BL/6J (B6) mouse

Abstract

The purpose was to examine sighs and spontaneous pauses in regard to the stability of resting breathing in the B6 strain, compared to the A/J strain. A 5-HT 1A receptor agonist (buspirone) and a chromosomal substitution strain (B6a1) were used to further alter breathing patterning. Tenminute recordings of room air breathing were collected from unanaesthetized B6, A/J, and B6a1 mice. Despite no differences between strains in the magnitude and incidence of sighs, post-sigh apneas, the variation for duration of expiration (Te) after sighs, and the number of spontaneous pauses were greater in the B6, while Shannon Entropy (nonlinear metrics) for Te after sighs was lower in B6, compared to the other strains. Buspirone and chromosomal substitution eliminated post-sigh apneas and decreased spontaneous pauses. A greater irregularity and the lower complexity of post-sigh breathing in B6 are reversed by elements on A/J Chromosome 1 and by increased 5-HT 1A serotonergic tone.

Hypocapnia increases the prevalence of hypoxia-induced augmented breaths

“…Augmented breaths are known to precipitate instability in the breathing cycle (4,23,28,29,60,81). Therefore, the unusually high prevalence of augmented breaths during hypocapnia predisposes the respiratory system to transient disturbances and instability more frequently than is the case in other respiratory backgrounds.…”

“…Augmented breaths are often followed by a period of apnoea (25,28,60,81). Even when apnoea does not result, these large breaths will alter the depth and rate of breathing for several subsequent respiratory cycles (4,10,23,28,29,60,81). Normally, the respiratory system is stable enough to resume a normal rhythmic pattern of breathing shortly after an augmented breath.…”

Acetazolamide suppresses the prevalence of augmented breaths during exposure to hypoxia

“…On cessation of acetazolamide treatment, the prevalence of augmented breaths during exposure to hypocapnic hypoxia returned toward pretreatment levels. Since augmented breaths are transient respiratory disturbances that often lead to respiratory instability and apneas (4,13,17,18,42,60), this effect of acetazolamide may reveal a novel means by which acetazolamide exerts a stabilizing effect on breathing rhythm.…”

“…On the other hand, augmented breaths represent a respiratory disturbance in the eupneic breathing cycle and are often followed by a period of apnea (14,17,42,60) or, at least, a change in tidal volume and/or frequency of breathing that may last for many subsequent breath cycles (4,9,13,17,18,42,60). Whether this perturbation in breathing rhythm is due to an acute alteration in arterial blood gas composition or a central respiratory phenomenon related to the generation of eupneic breathing rhythm remains unclear.…”

Effects of Hydrogen Sulfide Synthesis Inhibitors on Posthypoxic Ventilatory Behavior in the C57BL/6J Mouse

“…The primary endpoint of our study was the presence or absence of one or more apneas during the first minute of reoxygenation, with apneas being defined as an absence of breathing activity, as measured by plethysmography, lasting longer than two breaths. The CV for respiratory frequency has been used previously as a marker of respiratory stability in rodents [13][14][15] and was calculated for each animal at rest and during the posthypoxic/reoxygenation period. CV and the presence or absence of apneic episodes were compared between saline and each HSSI group.…”