Respiration physiology最新文献

In order to investigate the effects of moderate hypoxemia on brain electrical activity and the consequences of an altered cerebro-vascular response to hypoxemia, we recorded changes in electrical activity of the brain in anesthetized rats following unilateral carotid artery ligation (UCAL). In these animals, on the clamped side, cerebral blood flow, whilst normal during normoxia, shows less augmentation during hypoxemia. Six anesthetized (Halothane) Sprague–Dawley rats with UCAL were studied during 20 min periods of baseline (Fi_O2=30%), hypoxemia (Fi_O2=9.5%) and recovery (Fi_O2=30%): mean arterial pressure of oxygen (Pa_O2) achieved was 177.0, 37.6 and 160.1 mmHg, respectively. A significant decrease in the frequencies of the ECoG was observed bilaterally during hypoxemia: centroid frequency (fc)=3.37±0.14 and 2.85±0.13 Hz on the intact and clamped hemisphere respectively during hypoxemia versus fc=4.09±0.20 Hz (mean±S.E.M.) during baseline, which was not reversed during recovery (3.27±0.11 Hz) (ANOVA, P<0.01). The total power of the signal (Pw) was unaffected on the intact hemisphere but diminished on the clamped side during hypoxemia. Our results show that a significant slowing of ECoG is observed during hypoxemia of moderate intensity (40 mmHg) even when cerebro-vascular response to hypoxemia is preserved and that total power of the ECoG signal is severely diminished when the cerebro-vascular response to hypoxemia is impaired.

Following exposure of anesthetized and unanesthetized rats to hypercapnic stress, arginine vasopressin (AVP)-containing neurons of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei were examined for expression of the c-fos gene encoded protein (c-Fos). In addition, we determined whether AVP-containing PVN neurons activated by hypercapnia project to phrenic nuclei. In adult control rats, only scant c-Fos-like immunoreactive neurons were observed within the hypothalamic nuclei. A marked increase in c-Fos positive cells was induced after 2 h of breathing a gas mixture with elevated CO₂ (5% CO₂, 21% O₂ and 74% N₂, or 1 h following breathing of 12% CO_2, 21% O_2, and 67% N₂). Colocalization studies of AVP and c-Fos protein revealed that in the PVN, 75% of AVP-containing cells expressed c-Fos immunoreactivity. c-Fos and AVP were coexpressed in 60% of SON neurons in anesthetized rats. In addition, retrograde labeling studies with cholera toxin b subunit (CTb) revealed that a subpopulation of PVN cells (15%) that project to phrenic nuclei are activated by hypercapnia, as indicated by c-Fos expression. These results indicate that (i) PVN and SON AVP-containing neurons are part of the neuronal networks that react to hypercapnic exposure; and (ii) a subset of CO₂ reactive PVN cells innervate phrenic nuclei.

Upper airway (UA) anatomical abnormalities are frequently observed in obstructive sleep apnea syndrome (OSAS). The correspondence between UA anatomical modifications and UA resistance (UAR) had not been studied. We aimed to determine if cephalometric characteristics could be related to segmental UAR. In twenty-five patients (21 males) (15 OSAS patients, 10 snorers) and 10 control subjects (8 males), segmental UAR were measured in supine position and cephalometry was performed. Inspiratory and expiratory UAR were calculated at peak flow. Length of the soft palate (LP), posterior airway space (PAS), distance from hyoid bone to mandibular plane and to posterior pharyngeal wall were different between the groups (P<0.01). Inspiratory and expiratory, total and segmental, UAR were higher in OSAS (P<0.001). Segmental UAR were correlated with PAS and distance from hyoid bone to mandibular plane and to pharyngeal posterior wall (P<0.05). In conclusion, OSAS patients had higher UAR depending on anatomical variables, especially the place of the hyoid bone.

Adult, conscious rats have been exposed to CO-induced hypoxia for 30 min in normoxia, ambient hypoxia (FI_O2=14%), or hyperoxia (FI_O2=40%). From arterial blood gas analyses, FICO was adjusted in all experimental conditions to obtain final arterial oxygen saturations (Sa_O2) of ∼60%. Oxygen uptake (), ventilation ($\text{V}\text{̇}$) and colonic temperature (Tc) were measured in experiments carried out at an ambient temperature of either 25 or 15 °C. It was found that CO hypoxia induced marked reductions in the hemoglobin O₂ half saturation pressure (P₅₀). Furthermore, isolated reductions in Sa_O2 (with Pa_O2 constant) induced decreases in and Tc and increases in ventilation which, as compared with normoxia, were enhanced in ambient hypoxia and reduced but still significant in hyperoxia. As suggested by previous studies, the interactions between Sa_O2 and Pa_O2 which operate on the control of metabolism and ventilation originate probably in the central nervous system.

Diffusive and perfusive gas conductances of the shell and chorioallantois of avian eggs are not homogeneous, leading to disequilibrium between the air cell gas and chorioallantoic venous blood. This study measured the embryonic ability to maintain oxygen consumption rate and growth under experimentally enhanced inhomogeneity of diffusive conductance, achieved by waxing half of the eggshell and exposing the other half to graded hyperoxia that doubled the oxygen gradient across the shell. Thus, the overall gas conductance was effectively normal but highly inhomogeneous. No differences were observed between the experimental and the control eggs in respiration, residual yolk or embryo growth rate from day 12 until day 20. The embryo was able to utilise the increase of oxygen in the environment to compensate for the loss of about half of its respiratory surface area under the wax. The results indicate that an even distribution of pores in the eggshell and uniformity of chorioallantoic perfusion are not required for successful avian development.

Recently, a circadian oscillation in pulmonary ventilation ($\text{V}\text{̇}$e) was reported in conscious, undisturbed rats [Respir. Physiol. 120 (2000) 179], with a pattern similar to that of body temperature (Tb), oxygen consumption () and activity. The present study explored the relationship between the daily $\text{V}\text{̇}$e pattern and these rhythms. Adult rats (n=23) were instrumented for measurements of Tb and activity by telemetry, and placed in a chamber for measurement of $\text{V}\text{̇}$e by the barometric method and by an open-flow method. Simultaneous recordings were made continuously for 3 consecutive days in a 12-h light:12-h dark (L:D) cycle. All variables showed substantial daily oscillations, with significantly higher values in the D phase, and approximately proportionate changes in $\text{V}\text{̇}$e and . Daily changes in tidal volume (Vt) relative to inspiratory time (Ti), rather than in Ti relative to total breath duration, accounted for the oscillation in $\text{V}\text{̇}$e. The Vt rhythm was phase-advanced relative to those of and Tb. L–D differences in $\text{V}\text{̇}$e persisted when comparison between the phases was made for the same level of either very low or very high activity. We conclude that the oscillation in $\text{V}\text{̇}$e does not depend on the daily changes in activity. Rather, the daily pattern of $\text{V}\text{̇}$e is likely shaped by the oscillations of multiple physiological variables, two of which may be Tb and .