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Dynamic characteristics of respiratory central chemoreflex in normal rats
Author(s) -
Tohyama Takeshi,
Saku Keita,
Tsutsui Hiroyuki,
Sunagawa Kenji
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.1072.6
Subject(s) - central chemoreceptors , hyperventilation , ventilation (architecture) , respiration , respiratory system , medulla , peripheral , anesthesia , control of respiration , peripheral chemoreceptors , chemoreceptor , chemistry , medicine , anatomy , physics , receptor , thermodynamics
Background Central chemoreflex is the dominant regulator of respiration. Central chemoreceptors are located on the ventral surface of the medulla, respond primarily to changes in arterial carbon dioxide content (PaCO2). It is well known that increasing in PaCO2 linearly increases minute ventilation (VE) and increasing in VE decreases PaCO2 with hyperbolic manner. Thus, central chemoreflex consists of a negative feedback loop to maintain PaCO2 around 40 mmHg. Although the static characteristics of central chemoreflex have been well examined in both animals and human, the dynamic characteristics, which is prerequisite to understand how quickly and how stably central chemoreflex operates to regulate ventilation and PaCO2, has not been elucidated. The purpose of this investigation is to characterize the dynamic characteristics of central chemoreflex control of ventilation and PaCO2 with a system identification techniques based on a white noise approach. Methods We divided the central chemoreflex system into two components: central controller (EtCO2‐VE relationship) and peripheral plant (VE‐EtCO2 relationship) ( Fig. 1). In eleven anesthetized rats, we measured respiratory end tidal CO2 (EtCO2) as a surrogate of PaCO2, and VE. To estimate central controller, we randomly switched inhaled gas from 0% to 5% CO2 every 10 sec for an hour and recorded spontaneous VE ( Fig. 2A). To evaluate the peripheral plant, we randomly switched VE from hypoventilation to hyperventilation every 0.8 sec for an hour and simultaneously recorded EtCO 2 under mechanical respiratory condition ( Fig. 2B). We calculated the transfer functions of central controller and peripheral plant in the frequency domain. Results The gain of central controller was flat up to 0.005 Hz and then decreased with frequencies. The phase was in phase at the lowest frequency and gradually delayed in higher frequencies ( Fig. 3A). In the peripheral plant, the gain gradually decreased from the lowest frequency to 0.1Hz and then sharply decreased. Its phase has out of phase at the lowest frequency and gradually delayed in higher frequencies ( Fig. 3B). Transfer functions of both subsystems represented as a low‐pass filter characteristic with dead time. High coherence values suggested that the input‐output relationships of the central controller and peripheral plant were predominately governed by this framework. Conclusions We characterized the dynamic properties of the central controller and peripheral plant of the central chemoreflex in normal rats with the white noise system identification method. These systematic analysis of chemoreflex dynamics would help us understand the respiratory regulation in physiological condition.