Spontaneous phrenic nerve activity in the exteriorized fetal lamb

1975 ◽  
Vol 39 (1) ◽  
pp. 124-128 ◽  
Author(s):  
I. Wyszogrodski ◽  
H. W. Taeusch ◽  
R. L. Williams
Keyword(s):  
Neural Activity ◽  
Phrenic Nerve ◽  
High Frequency ◽  
Single Unit ◽  
Nervous Activity ◽  
Nerve Activity ◽  
Phrenic Nerve Activity ◽  
Tracheal Pressure ◽  
Fetal Lamb ◽  
Pressure Changes

Phrenic nerve activity and tracheal pressure changes were recorded in four exteriorized fetal lambs (120–135 days gestation) from lightly anesthetized ewes to study possible mechanisms involved in the establishment of rhythmical breathing patterns. Two types of spontaneous neural activity were found. The first consisted of high-frequency multiunit bursts (mean duration 820 ms; range 450–2,500 ms) that preceded a gasp. Individual units within these bursts reached peak discharge frequencies as high as 40 impulses/s. The second type of neural activity consisted of single-unit, low-frequency (1–14 impulses/s), irregular background discharges lasting up to several seconds without changes in tracheal pressure. Occasionally, higher frequency bursts of single-unit activity were detected that were also unassociated with tracheal pressure changes. The data indicate that the neural correlate of a fetal gasp includes high-frequency synchronized bursting activity in the phrenic nerve. In addition, background phrenic activity can be detected in the exteriorized fetal lamb that reflects central nervous activity in the absence of tracheal pressure changes.

Electrical activity of phrenic nerve and diaphragm in utero

1975 ◽  
Vol 39 (4) ◽  
pp. 513-518 ◽  
Author(s):  
A. Bahoric ◽  
V. Chernick
Keyword(s):  
Phrenic Nerve ◽  
Total Duration ◽  
In Utero ◽  
Respiratory Center ◽  
Nerve Activity ◽  
Recording Time ◽  
Fetal Sheep ◽  
Phrenic Nerve Activity ◽  
Tracheal Pressure ◽  
Pressure Changes

Phrenic nerve activity, diaphragmatic EMG, and tracheal or pleural pressure changes were recorded in a chronic fetal sheep preparation. Three patterns of fetal phrenic nerve activity were observed: 1) a single burst; 2) irregular nonrhythmic bursts; and 3) prolonged rhythmic activity, seen only prior to fetal death. The total recording time was 54.53 h and the total duration of phrenic nerve activity was 65.34 min (2.16%). When an inactive period was defined as the absence of phrenic nerve activity for 60 s or more, active periods occupied 44.7% of the total time. Phrenic nerve activity was present in all fetuses and 97.5% of the time was coupled with diaphragmatic EMG. Both diaphragmatic EMG and intrapulmonary pressure changes occurred in the absence of phrenic nerve activity. In three fetal animals both phrenic nerves were transected. Tracheal pressure changes were seen which were not coupled with corresponding intrauterine pressure changes. Thus, changes in fetal tracheal pressure or diaphragmatic EMG do not necessarily represent the output of the fetal respiratory center. This study suggests that the fetal respiratory center is active in utero, but this activity is minimal and has a different pattern that that present after birth.

Neuromuscular blockade enhances phrenic nerve activity during high-frequency ventilation

1984 ◽  
Vol 56 (1) ◽  
pp. 31-34 ◽  
Author(s):  
S. J. England ◽  
A. Onayemi ◽  
A. C. Bryan
Keyword(s):  
Neuromuscular Blockade ◽  
Phrenic Nerve ◽  
High Frequency ◽  
Intact Animal ◽  
Rhythmic Activity ◽  
High Frequency Ventilation ◽  
Nerve Activity ◽  
Arterial Pco2 ◽  
Phrenic Nerve Activity ◽  
Frequency Ventilation

Phrenic nerve activity was monitored in anesthetized cats during high-frequency ventilation (HFV). Rhythmic phrenic discharge disappeared during HFV in all animals at normal arterial PCO2 levels. Rhythmic activity returned after neuromuscular blockade in the vagally intact animal. Although vagotomy alone also restored phrenic discharge, this activity was further enhanced by subsequent neuromuscular blockade. Therefore we suggest that apnea during HFV results from inspiratory inhibition mediated by both chest wall and vagal afferent mechanisms.

Daily acute intermittent hypoxia enhances phrenic motor output and stimulus-evoked phrenic responses in rats

2021 ◽  
Author(s):  
Raphael Rodrigues Perim ◽  
Michael D. Sunshine ◽  
Joseph F. Welch ◽  
Juliet Santiago ◽  
Ashley Holland ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Phrenic Nerve ◽  
Intermittent Hypoxia ◽  
Neural Control ◽  
Respiratory Cycle ◽  
Evoked Responses ◽  
Nerve Activity ◽  
Synaptic Inputs ◽  
Phrenic Nerve Activity ◽  
The Impact

Plasticity is a hallmark of the respiratory neural control system. Phrenic long-term facilitation (pLTF) is one form of respiratory plasticity characterized by persistent increases in phrenic nerve activity following acute intermittent hypoxia (AIH). Although there is evidence that key steps in the cellular pathway giving rise to pLTF are localized within phrenic motor neurons (PMNs), the impact of AIH on the strength of breathing-related synaptic inputs to PMNs remains unclear. Further, the functional impact of AIH is enhanced by repeated/daily exposure to AIH (dAIH). Here, we explored the effects of AIH vs. 2 weeks of dAIH preconditioning on spontaneous and evoked responses recorded in anesthetized, paralyzed (with pancuronium bromide) and mechanically ventilated rats. Evoked phrenic potentials were elicited by respiratory cycle-triggered lateral funiculus stimulation at C2 delivered prior to- and 60 min post-AIH (or an equivalent time in controls). Charge-balanced biphasic pulses (100 µs/phase) of progressively increasing intensity (100 to 700 µA) were delivered during the inspiratory and expiratory phases of the respiratory cycle. Although robust pLTF (~60% from baseline) was observed after a single exposure to moderate AIH (3 x 5 min; 5 min intervals), there was no effect on evoked phrenic responses, contrary to our initial hypothesis. However, in rats preconditioned with dAIH, baseline phrenic nerve activity and evoked responses were increased, suggesting that repeated exposure to AIH enhances functional synaptic strength when assessed using this technique. The impact of daily AIH preconditioning on synaptic inputs to PMNs raises interesting questions that require further exploration.

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