Sex-specific vagal and spinal modulation of breathing with chest compression

Abstract

Lung volume is modulated by sensory afferent feedback via vagal and spinal pathways. The purpose of this study was to systematically alter afferent feedback with and without a mechanical challenge (chest compression). We hypothesized that manipulation of afferent feedback by nebulization of lidocaine, extra-thoracic vagotomy, or lidocaine administration to the pleural space would produce differential effects on the motor pattern of breathing during chest compression in sodium pentobarbital anesthetized rats (N = 43). Our results suggest that: 1) pulmonary stretch receptors are not the sole contributor to breathing feedback in adult male and female rats; 2) of our manipulations, chest compression had the largest effect on early expiratory diaphragm activity ("yield"); 3) reduction of spinally-mediated afferent feedback modulates breathing patterns most likely via inhibition; and 4) breathing parameters demonstrate large sex differences. Compared to males, female animals had lower respiratory rates (RR), which were further depressed by vagotomy, while chest compression increased RR in males, and decreased yield in females without changing RR. Collectively, our results suggest that balance between tonic vagal inhibition and spinal afferent feedback maintains breathing characteristics, and that it is important to specifically evaluate sex differences when studying control of breathing.

Sex-specific vagal and spinal modulation of swallow and its coordination with breathing

“…During chest compression conditions, swallows retained an expiratory preference, even when we altered vagal and pleural spinal afferent feedback. In our complementary study [55], chest compression prolonged late expiration duration in female rats. The dominance of swallow during late expiration could be attributed to the large proportion of the respiratory cycle that is spent in expiration, which would ensure adequate time for swallow to occur in safe conditions [14].…”

“…Ages ranged from 8-9 months. Animals were shared with a complementary paper to this study [55]. We recognize that retired breeders are older than the general adult rat, however studies investigating breathing and aging use SD rats with an average of 13 months [56].…”

“…We derived this term from its use in locomotion studies, in which the term describes activation of knee and ankle extensor muscle to cushion the impact of forces on the body as the hips move over the knee [58]. The complementary paper to this study [55] presents a detailed description of this concept in respiration, and hypothesizes that characterizing early expiration as a yield event could aid in interpreting differences in late-I versus early-E activities of breathing.…”

Rapid activation of esophageal mechanoreceptors alters the pharyngeal phase of swallow: Evidence for inspiratory activity during swallow

“…To assess swallow-breathing coordination, a Wilcoxon Signed Rank Test was used. An assigned coding system was used for the breathing phase in which the swallow occurred: inspiration (I; start to peak diaphragm activity) as “1”; early expiration (Yield [ 52 ] or E1; peak to end diaphragm activity) as “2”; and mid/late-expiration (E2; end of diaphragm activity to start of next breath diaphragm activity) as “3”. For all tests a difference was considered significant if the p -value was less than or equal to 0.05.…”

“…To assess swallow-breathing coordination, a Wilcoxon Signed Rank Test was used. An assigned coding system was used for the breathing phase in which the swallow occurred: inspiration (I; start to peak diaphragm activity) as "1"; early expiration (Yield [52] or E1; peak to end diaphragm activity) as "2"; and mid/late-expiration (E2; end of diaphragm activity to start Of note, the first swallow in the combined condition has a swallow occurring in the transition from inspiration to expiration (E1 and/or post-I); all others are during late expiration (E2). Muscle EMGs are displayed as integrated traces, but the cricopharyngeus (UES) and diaphragm display raw EMG traces as well.…”