Increase In Breathing Frequency Research Articles

Conditional activity of parabrachial Tac1 neurons turns on rapid breathing

Breathing is regulated automatically to preserve homeostasis. This reflex regulation of breathing is achieved through neural circuits that function as negative feedback loops. Similar to how a thermostat regulates temperature in a room, the activity of these circuits can be adjusted up or down to fine tune breathing and restore a homeostatic set-point. Yet, breathing is also conditionally altered by behaviors and emotions, requiring dissociation of breathing frequency and pattern from its underlying automatic control. Relatively little is known about the circuits that mediate this “state-dependent'' control. We previously found that optogenetic activation of a Tac1, but not Calca, expressing subpopulation of lateral parabrachial (PBN) neurons drives breathing frequencies that far exceed those relevant for the homeostatic control of breathing. Here, we combine cell-type-specific silencing and multi-unit recording approaches to further test the hypothesis that this circuit plays an important role in state-dependent, but not automatic, respiratory control. To render Tac1 PBN neurons non-functional, the PBN of adult Tac1Cre mice was injected bilaterally with an AAV that drives Cre-dependent expression of tetanus light chain. After allowing ~4 weeks for viral expression, plethysmography did not reveal any differences in breathing frequency or pattern compared to mice injected with control AAV. Changes in breathing were also absent during acute optogenetic inhibition of Tac1+; Calca- neurons following injection of AAV that expresses iC++ in neurons that contain Cre but not FlpO in the PBN of Tac1Cre; CalcaFlpO mice. To assess the spiking activity of Tac1 PBN neurons relative to ongoing breathing patterns, the PBN of Tac1Cre; CalcaFlpO mice was injected with an AAV that expresses ChRmine in neurons containing Cre but not FlpO, a cranial window was created dorsal to the PBN and a head bar secured to the skull. After 2 weeks, mice were head-fixed and a high-density neuropixels probe was inserted into the PBN via the cranial window. Multi-unit activity was recorded from awake, freely breathing mice during simultaneous recording of respiratory pattern. Illumination of the cranial window with red light was suffcient for ChRmine mediated deep brain activation of Tac1+;Calca- PBN neurons, producing a robust increase in breathing frequency. Recorded PBN units were then optically tagged by assessing their response latency and fidelity to repeated 10 ms light pulses. Based on our preliminary observations, “optotagged” Tac1+; Calca- neurons were mostly quiescent during resting breathing but switched to tonic spiking during bouts of sniffng/rapid breathing. Thus, we predict that Tac1 PBN neurons do not regulate breathing via thermostat-like changes in activity similar to breathing reflexes. Instead, Tac1 PBN neurons represent a switch-like mechanism where these neurons are primarily inactive with minimal respiratory role under normal conditions, but when activated they turn on rapid breathing. R01HL166317. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

HELMINTHIASIS IN DOMESTIC MALE CAT

Helminthiasis is also known as parasitic helminth infectious disease. Gastrointestinal helminth parasitic infection is a common disease diagnosed in cats. Some types are known to be zoonotic. The writing of this article aims to report cases of helminthiasis in cats based on history, clinical symptoms, physical examination, and supporting examinations. A four-year-old cat was examined at the Teaching Animal Hospital, Faculty of Veterinary Medicine, Udayana University with complaints of anorexia and diarrhea like paste to yellowish liquid. In feces found the presence of two types of adult worms. Checking the status of the presens obtained Capillary Refill Time (CRT) of more than 2 seconds and an increase in breathing frequency. On physical examination, it was found that the abdomen of the case cat had a slight distention and there was residual feces attached to the anus. When the cat's abdomen is palpated, it shows signs of discomfort and sounds of borborygmus when occulted. Anemis oral mucosa, anus, and conjunctiva. The results of fecal examination with the native method found Toxocara cati worm eggs. The results of hematological examination showed that the case cat had hypochromic microcytic anemia and thrombocytopenia. Case cats were diagnosed with helminthiasis with the discovery of eggs of Toxocara cati worms, and adult worms of nematodes and cestodes in feces. The prognosis of this case is fausta. Therapy is carried out by administering anthelmintic drugs containing fenbendazole, pyrantel pamoat, and praziquantel (1 tablet / 10 kg body weight, PO) twice with a repeat interval of 14 days and vitamin B complex (1 tablet, PO) for 7 days. Treatment with Caniverm tablets gave good results characterized by significant improvement in clinical condition, fecal intensity from grade 6 to grade 5, and no worm eggs were found on native examination and adult worms on macroscopic examination of feces. Regular deworming of cats is important, and make sure the cat is free of ectoparasites which are intermediate hosts of disease agents.

The Effect of Caffeine on Heart Rate Variability in Newborns: A Pilot Study.

Neonatal apnoea can be treated with caffeine, which affects the central nervous and cardiovascular systems. Heart rate variability (HRV) reflects the activity of the autonomic nervous system (ANS) and might be used as a measure of ANS maturation in newborns. We aimed to establish the effect of caffeine on HRV in newborns and investigated the potential correlation between HRV and postmenstrual age (PMA). In 25 haemodynamically stable newborns hospitalized due to apnoea and treated with caffeine (2.5 mg/kg), we assessed breathing frequency, arterial oxygen saturation, body temperature, and the heart rate while they were sleeping. We assessed HRV by spectral analysis using fast Fourier transformation. The same protocol was reapplied 100 h after caffeine withdrawal to assess the control parameters. Caffeine increased breathing frequency (p = 0.023) but did not affect any other parameter assessed including HRV. We established a positive correlation between postmenstrual age and HRV during treatment with caffeine as well as after caffeine had been withdrawn (total power: p = 0.044; low-frequency band: p = 0.039). Apparently, the maintenance dose of caffeine is too low to affect the heart rate and HRV. A positive correlation between PMA and HRV might reflect maturation of the ANS, irrespective of caffeine treatment.

Impact of High-Flow Nasal Cannula Use in Subjects With COVID-19 ARDS at High Altitudes: Clinical Presentation and Prognostic Factors.

High-flow nasal cannula (HFNC) reduces the need for intubation in adult subject with acute respiratory failure. Changes in hypobaric hypoxemia have not been studied for subject with an HFNC in ICUs at altitudes > 2,600 m above sea level. In this study, we investigated the efficacy of HFNC treatment in subjects with COVID-19 at high altitudes. We hypothesized that progressive hypoxemia and the increase in breathing frequency associated with COVID-19 in high altitudes affect the success of HFNC therapy and may also influence the performance of the traditionally used predictors of success and failure. This was a prospective cohort study of subjects >18 y with a confirmed diagnosis of COVID-19-induced ARDS requiring HFNC who were admitted to the ICU. Subjects were followed up during the 28 d of HFNC treatment or until failure. One hundred and eight subjects were enrolled. At admission to the ICU, FIO2 delivery between 0.5-0.8 (odds ratio 0.38 [95% CI 0.17-0.84]) was associated with a better response to HFNC therapy than oxygen delivery on admission between 0.8-1.0 (odds ratio 3.58 [95% CI 1.56-8.22]). This relationship continued during follow-ups at 2, 6, 12, and 24 h, with a progressive increase in the risk of failure (odds ratio 24 h 13.99 [95% CI 4.32-45.26]). A new cutoff for the ratio of oxygen saturation (ROX) index (ROX ≥ 4.88) after 24 h of HFNC administration was demonstrated to be the best predictor of success (odds ratio 11.0 [95% CI 3.3-47.0]). High-altitude subjects treated with HFNC for COVID-19 showed a high risk of respiratory failure and progressive hypoxemia when FIO2 requirements were > 0.8 after 24 h of treatment. In these subjects, personalized management should include continuous monitoring of individual clinical conditions (such as oxygenation indices, with cutoffs adapted to those corresponding to high-altitude cities).

Seven days of ischemic preconditioning augments hypoxic exercise ventilation and muscle oxygenation in recreationally trained males.

This investigation sought to assess whether single or repeated bouts of ischemic preconditioning (IPC) could improve oxyhemoglobin saturation ([Formula: see text]) and/or attenuate reductions in muscle tissue saturation index (TSI) during submaximal hypoxic exercise. Fifteen healthy young men completed submaximal graded exercise under four experimental conditions: 1) normoxia (NORM), 2) hypoxia (HYP) [oxygen fraction of inspired air ([Formula: see text]) = 0.14, ∼3,200 m], 3) hypoxia preceded by a single session of IPC (IPC1-HYP), and 4) hypoxia preceded by seven sessions of IPC, one a day for 7 consecutive days (IPC7-HYP). IPC7-HYP heightened minute ventilation (V̇e) at 80% HYP peak cycling power output (Wpeak) (+10.47 ± 3.35 L·min-1, P = 0.006), compared with HYP, as a function of increased breathing frequency. Both IPC1-HYP (+0.17 ± 0.04 L·min-1, P < 0.001) and IPC7-HYP (+0.16 ± 0.04 L·min-1, P < 0.001) elicited greater oxygen consumption (V̇o2) across exercise intensities compared with NORM, whereas V̇o2 was unchanged with HYP alone. [Formula: see text] was unchanged by either IPC condition at any exercise intensity, yet the reduction of muscle TSI during resting hypoxic exposure was attenuated by IPC7-HYP (+9.9 ± 3.6%, P = 0.040) compared with HYP, likely as a function of reduced local oxygen extraction. Considering all exercise intensities, IPC7-HYP attenuated reductions of TSI with HYP (+6.4 ± 1.8%, P = 0.001). Seven days of IPC heightens ventilation, posing a threat to ventilatory efficiency, during high-intensity submaximal hypoxic exercise and attenuates reductions in hypoxic resting and exercise muscle oxygenation in healthy young men. A single session of IPC may be capable of modulating hypoxic ventilation; however, our present population was unable to demonstrate this with certainty.

Intercostal muscle oxygenation and expiratory loaded breathing at rest: Respiratory pattern effect

In patients with airway obstruction, an increase in breathing frequency at rest is commonly associated with a dynamic hyperinflation (DH). In such a situation, intercostal muscle oxygenation may be disturbed. This hypothesis was examined in a context of simulated airway obstruction in healthy subjects.After a control period of 5 min, twelve participants (20 ± 2 years) breathed at rest through a 20-cmH2O expiratory threshold load, either by increasing or reducing their respiratory rate (ETLF+ or ETLF). Tissue saturation index (TSI) and concentration changes in oxyhaemoglobin (oxy[Hb+Mb]) were measured as well as cardiorespiratory variables.Inspiratory capacity was decreased in ETLF+ (p < 0.001) and correlated with dyspnea. An increase in oxy[Hb+Mb] occurred in ETLF+ that was higher than in ETLF (p < 0.01). TSI was not different between conditions.In healthy subjects at rest, an increase in respiratory rate during a simulated obstruction with an expiratory threshold load resulted in paradoxical response with DH emergence while intercostal muscle oxygenation was preserved.

Basal and Hypoxic Respiratory Behaviors in Aged 6‐OHDA‐Induced SN Lesion PD Rat Model: Effects of the 5‐HT1A Receptor Agonist Buspirone

Parkinson’s disease (PD) is progressive neurodegenerative disease, with the diagnosis of idiopathic PD occurring in humans at ~60 years of age. Most studies, however, use young adult (≤3 month old) rats to investigate PD‐related abnormalities in various physiological systems, with the most commonly used experimental rat PD model being generated by unilateral injection of the neurotoxin 6‐hydroxydopamine (6‐OHDA) into specific regions of the nigrostriatal pathway. While this model results in the loss of dopaminergic neurons and the subsequent changes in downstream neurotransmitter signaling that are characteristic of PD, it does not consider potential contributions of physical changes to the brain and neurotransmitter signaling that are part of normal aging on the progression of PD. To better understand age‐related influences and potential contributions of PD‐related abnormalities in serotonergic (5‐HT) neurotransmission on respiratory dysfunction (which is a common non‐motor symptom) in PD, we investigated basal and hypoxic (12% O2; 90s) respiratory behaviors before and after acute administration of the frequently prescribed anxiolytic 5‐HT1A receptor agonist buspirone (BUS; 0.5 mg/kg, iv) in an aged (~9 month old) female Sprague‐Dawley PD rat model produced by unilateral 6‐OHDA injection into the substantia nigra (SN). For these experiments, diaphragm EMG activity was recorded and quantified from spontaneously breathing urethane‐anesthetized rats at 2‐weeks after SN 6‐OHDA or vehicle (control) injections. We found that 6‐OHDA‐injected rats have a lower basal breathing frequency (P&lt;0.05) due to shorter expiratory duration (TE; P&lt;0.05) than vehicle‐injected rats, but both 6‐OHDA‐ and vehicle‐injected rats exhibit significant increases in breathing frequency (P≤0.001) and EMG amplitude (P≤0.023) during hypoxia; the magnitude of the peak frequency increase in 6‐OHDA‐injected rats was slightly greater (P=0.083). Both 6‐OHDA‐ and vehicle‐injected rats also showed similar post‐hypoxic frequency decline (P≤0.003), but only vehicle‐injected rats displayed a slight and sustained post‐hypoxic amplitude depression (P&lt;0.1). In vehicle‐injected rats, acute BUS injection produced a progressive decrease in basal EMG amplitude (P=0.066) and a persistent increase in breathing frequency (P=0.064) by decreasing inspiratory duration (TI; P&lt;0.001) while in 6‐OHDA‐injected rats, a transient initial increase in EMG amplitude (P=0.043) and a persistent decrease in TI (P=0.005) and TE (P=0.089) were noted. In both 6‐OHDA‐ and vehicle‐injected rats, BUS injection also slightly exaggerated the initial hypoxic frequency increase, but blunted the amplitude increase with amplitude progressively declining to near pre‐hypoxic levels before the end of the hypoxic exposure. BUS injection also shortened the duration of post‐hypoxic EMG amplitude depression in vehicle‐injected rats. These data demonstrate that some differences in basal and hypoxic respiratory behaviors exist between older 6‐OHDA‐ and vehicle‐injected rats, and that some respiratory behaviors of these rat models are differentially impacted by BUS‐induced effects on respiratory control. We suggest that this older PD rat model be further evaluated.

Mild‐to‐Moderate Chronic Hypercapnia Impairs Adaptation of Acute CO2/H+ Chemosensitivity but Not Steady‐State Ventilation

CO2 retention (hypercapnia, CH) presents in a number of etiologies including sedative use, chronic lung disease, and central/peripheral neuromuscular disorders. Acute‐on‐chronic hypercapnia can develop in these disorders during times of acute stress (i.e., infection and postoperative states). Recurrent acute‐on‐chronic CH may lead to respiratory failure and transient, life‐threatening worsening of the hypercapnia. We previously established in awake goats that exposure to mild CH (PaCO2 ~55mmHg) elicits changes across multiple physiologic systems but does not impair the response to acute increases in inspired CO2(InCO2).Herein, we test the hypothesis that progressive exposure from mild‐to‐moderate CH (~55‐to‐65mmHg CO2) results in secondary adaptations across several physiologic systems but increases the risk of pathological responses during acute‐on‐chronic exacerbations. Utilizing our established large animal model of CH, female goats (n=7) were exposed to 7 days (d) of 6% InCO2 followed by 7d of 8% InCO2. Throughout the protocol, we regularly assessed steady‐state cardiorespiratory function (i.e., VI, f, VT, HR, and BP) and acute CO2/H+ chemosensitivity. During 6% InCO2, the temporal pattern of physiologic adaptations was consistent with that previously reported (J. Physiol. 2018). As expected, increasing steady‐state (SS) InCO2 resulted in a sustained 10 mmHg increase in PaCO2 and an increase in arterial [H+] that decreased over the 7d at 6%. During 6% InCO2 there was a transient decrease (6%‐Day 2) in acute chemosensitivity (DVI/DCO2) that returned to control values by Day 5 at 6%. Upon increasing SS InCO2from 6% to 8%, minute ventilation (VI) increased from 23±3.4L/min on Day 7 at 6% InCO2 to 34±2.2L/min on Day 1 at 8% InCO2,which was primarily driven by an increase in breathing frequency. By 24h at 8% InCO2, VIhad declined from the 8%‐Day 1 values and remained at or near that level thereafter. This temporal pattern of adaptation is comparable to that observed during 6% CO2. A similar pattern of adaptation in [H+] occurred during 8% as occurred at 6%, while [HCO3‐] continually increased. PaCO2remained elevated throughout the 8% InCO2 exposure, compared to 6% InCO2. Finally, when SS InCO2 was increased to 8% the acute chemoreflex remained suppressed throughout the 7d. Our results suggest that progressive worsening of chronic hypercapnia results in similar SS adaptations compared to initial hypercapnic exposure. However, more severe levels of CH, such as 8% InCO2, perturb the acute chemoreflex, creating a risk for consequences such as CO2 narcosis and cardiorespiratory failure in patients with pre‐existing CH.

Abnormal hypoxic and hypercapnic ventilatory responses in 5XFAD Alzheimer’s disease mice

Alzheimer’s disease (AD) is a neurodegenerative disease commonly associated with aging. Along with regression in cognition and memory, AD patients often have respiratory disturbances such as sleep apnea, insufficient ventilation during sleep, and shortness of breath. Further, at least one chemosensitive region located in the pons, the locus coeruleus, undergoes dramatic degeneration during AD progression. These observations suggest chemoreception may be altered during the progression of AD. To begin testing this hypothesis, we examined the hypoxic (HVR) and hypercapnic (HCVR) ventilatory responses on 5XFAD mice (&gt;6months) using whole body plethysmography. Preliminary data showed a reduced capacity to lower metabolic rate and body temperature during hypoxia (5.5% inspired O2) in 5XFAD mice, such that average oxygen consumption was reduced by 34.8 ± 2.8% (S.E.M) and body temperature fell to 33.5 ± 0.4°C. In wild type (WT) mice oxygen consumption was reduced by 53% and body temperature fell to 32.8°C. Further, 5XFAD mice sustained a slight ventilatory increase (1.3 ± 3.6% increase from baseline) during hypoxia while WT mice reduced ventilation by 5%. 5XFAD mice also displayed a reduced hypercapnic ventilatory response, showing little increase in tidal volume in response to hypercapnia; but they appeared to augment this with a greater increase in breathing frequency compared to WT mice. The net result, however, was an increase in ventilation by 122 ± 22% from baseline in response to 5% CO2 while WT mice had a 181 ± 26% increase from baseline to the same challenge. Our data suggest that ventilatory chemoresponses are altered by disease progression in the 5XFAD mouse model. These alterations may contribute to the respiratory disturbances observed in AD patients.

Metabolic trade-offs favor regulated hypothermia and inhibit fever in immune-challenged chicks.

The febrile response to resist a pathogen is energetically expensive, while regulated hypothermia seems to preserve energy for vital functions. We hypothesized here that immune-challenged birds facing metabolic trade-offs (reduced energy supply/increased energy demand) favor a regulated hypothermic response at the expense of fever. To test this hypothesis, we compared 5day old broiler chicks exposed to fasting, cold (25°C), and fasting combined with cold with a control group fed under thermoneutral conditions (30°C). The chicks were injected with saline or with a high dose of endotoxin known to induce a biphasic thermal response composed of a drop in body temperature (Tb) followed by fever. Then Tb, oxygen consumption (metabolic rate), peripheral vasomotion (cutaneous heat exchange), breathing frequency (respiratory heat exchange) and huddling behavior (heat conservation indicator) were analyzed. Irrespective of metabolic trade-offs, chicks presented a transient regulated hypothermia in the first hour, which relied on a suppressed metabolic rate for all groups, increased breathing frequency for chicks fed/fasted at 30°C, and peripheral vasodilation in chicks fed/fasted at 25°C. Fever was observed only in chicks kept at thermoneutrality and was supported by peripheral vasoconstriction and huddling behavior. Fed and fasted chicks at 25°C completely eliminated fever despite the ability to increase metabolic rate for thermogenesis in the phase correspondent to fever when it was pharmacologically induced by 2,4-dinitrophenol. Our data suggest that increased competing demands affect chicks' response to an immune challenge, favoring regulated hypothermia to preserve energy while the high costs of fever to resist a pathogen are avoided.

Effect of respiratory rate and size of cannula on pressure and dead-space clearance during nasal high flow in patients with COPD and acute respiratory failure

Nasal high flow (NHF) is an efficient oxygenation tool for the treatment of respiratory failure. The study investigated the effect of breathing pattern on positive airway pressure and dead-space clearance by NHF. The breathing cycle during NHF was characterized in 26 patients with acute respiratory failure (ARF) and stable COPD and after mechanical ventilation (post-MV) via tracheostomy where also pressure was measured in the trachea. Dead-space clearance was measured in airway models during different breathing patterns. NHF reduced the respiratory rate (RR) and TI/TE through prolonging the TE; the TI/TE ranged between ≤0.5 observed in the COPD patients and ∼1.0 in the ARF patients. NHF via a standard medium-sized cannula interface generated a low-level expiratory pressure proportional to NHF rate and breathing flow; the median generated positive end-expiratory pressure was only 1.71 cmH2O at NHF 45 L/min. The dilution and purging of expired gas from a nasal cavity model were observed to occur at the end of expiration as expiratory flow slowed and the dynamic pressure decreased. The higher RR with shorter end-expiratory period resulted in reduced dead-space clearance by NHF; 20 L/min cleared 43 ± 2 mL at RR 15 min-1 vs. 9 ± 5 mL at RR 45 min-1, P < 0.001, which was increased at higher NHF rate. At lower RR, the clearance was similar between NHF rates 20 and 60 L/min. Higher NHF rates elevate positive airway pressure, and at the increased RR can improve the clearance. This may enhance gas exchange and lead to a reduction in the work of breathing.NEW & NOTEWORTHY During nasal high flow (NHF) an increased breathing frequency, which is commonly observed in acute respiratory failure, can lead to decreased dead-space clearance. Higher NHF rates increase the clearance and reduce the rebreathing which may eventually lower the respiratory rate and the work of breathing. Monitoring of the respiratory rate could be an important indicator of not only the respiratory function but also the NHF rate selection and the therapy efficacy.

Physical Activity in Polluted Air-Net Benefit or Harm to Cardiovascular Health? A Comprehensive Review.

Both exposure to higher levels of polluted air and physical inactivity are crucial risk factors for the development and progression of major noncommunicable diseases and, in particular, of cardiovascular disease. In this context, the World Health Organization estimated 4.2 and 3.2 million global deaths per year in response to ambient air pollution and insufficient physical activity, respectively. While regular physical activity is well known to improve general health, it may also increase the uptake and deposit of air pollutants in the lungs/airways and circulation, due to increased breathing frequency and minute ventilation, thus increasing the risk of cardiovascular disease. Thus, determining the tradeoff between the health benefits of physical activity and the potential harmful effects of increased exposure to air pollution during physical activity has important public health consequences. In the present comprehensive review, we analyzed evidence from human and animal studies on the combined effects of physical activity and air pollution on cardiovascular and other health outcomes. We further report on pathophysiological mechanisms underlying air pollution exposure, as well as the protective effects of physical activity with a focus on oxidative stress and inflammation. Lastly, we provide mitigation strategies and practical recommendations for physical activity in areas with polluted air.

The association of breathing pattern with exercise tolerance and perceived fatigue in women with systemic lupus erythematosus: an exploratory case-control study.

The aims of the study were to (1) to characterize the breathing pattern and work of breathing during peak exercise in patients with SLE; (2) to examine the extent to which the breathing pattern and work of breathing impact the exercise capacity and fatigue. Forty-one women participated in the study (SLE: n = 23, median = 35, range = 21-57years, control: n = 18, median = 38, range = 22-45years). Each subject performed a treadmill cardiopulmonary exercise test (a modified Bruce treadmill protocol) ending with volitional exhaustion. Breathing mechanic was characterized by measures of expired minute volume (VE), tidal volume (Vt), respiratory rate (f), work of breathing, and cardiorespiratory fitness was quantified by measures of peak oxygen consumption (VO2) and time to exhaustion. Data presented as median and interquartile range (IQR). Women with SLE had lower Vt {1221 [488.8] mL/min vs. 1716 [453.1] mL; p = .006}, VE {58.9 [18.9] L/min vs 70 [28.1] L/min, p = 0.04} and increased breathing frequency {51.5 [10.8] vs 43.6 [37.8] bpm, p = 0.01} compared to the control group. The time to exhaustion and peak VO2 during the CPET were significantly reduced in those with SLE compared to controls {13.3 [10.2] vs 16.1 [2.2] min; p = 0.004}, {20 [6.1] mL/kg/min vs 26.6 [7] mL/kg/min p < 0.001}, respectively. Differences remained when the analyses were controlled for the observed differences in peak VO2. When the regression model adjusted for the peak VO2, it had been shown that Vt, WOB and f were explained variances in the fatigue severity by 64% [p < 0.001]. The decline in VE and Vt coupled with a decreased peak VO2, and work of breathing may have contributed to low cardiorespiratory fitness and fatigue in patients with systemic lupus erythematosus.

Ventilatory responses during and following hypercapnic gas challenge are impaired in male but not female endothelial NOS knock-out mice

The roles of endothelial nitric oxide synthase (eNOS) in the ventilatory responses during and after a hypercapnic gas challenge (HCC, 5% CO2, 21% O2, 74% N2) were assessed in freely-moving female and male wild-type (WT) C57BL6 mice and eNOS knock-out (eNOS-/-) mice of C57BL6 background using whole body plethysmography. HCC elicited an array of ventilatory responses that were similar in male and female WT mice, such as increases in breathing frequency (with falls in inspiratory and expiratory times), and increases in tidal volume, minute ventilation, peak inspiratory and expiratory flows, and inspiratory and expiratory drives. eNOS-/- male mice had smaller increases in minute ventilation, peak inspiratory flow and inspiratory drive, and smaller decreases in inspiratory time than WT males. Ventilatory responses in female eNOS-/- mice were similar to those in female WT mice. The ventilatory excitatory phase upon return to room-air was similar in both male and female WT mice. However, the post-HCC increases in frequency of breathing (with decreases in inspiratory times), and increases in tidal volume, minute ventilation, inspiratory drive (i.e., tidal volume/inspiratory time) and expiratory drive (i.e., tidal volume/expiratory time), and peak inspiratory and expiratory flows in male eNOS-/- mice were smaller than in male WT mice. In contrast, the post-HCC responses in female eNOS-/- mice were equal to those of the female WT mice. These findings provide the first evidence that the loss of eNOS affects the ventilatory responses during and after HCC in male C57BL6 mice, whereas female C57BL6 mice can compensate for the loss of eNOS, at least in respect to triggering ventilatory responses to HCC.

Neuronal Mediators of the Frequency Increase Evoked by Activation of P2Y 1 Receptors in the preBötzinger Complex Inspiratory Rhythm Generating Network in Vitro

The ventilatory response to acute hypoxia (HVR) comprises an initial, carotid body-mediated increase in breathing followed by a centrally-mediated secondary respiratory depression when ventilation falls to a new steady state. Recent evidence suggests that ATP is released from astrocytes in the preBötzinger Complex (preBötC; site of inspiratory rhythm generation) during the secondary phase where it acts via P2Y1 receptors (Rs) to excite preBötC neurons, increase breathing frequency and attenuate the secondary respiratory depression. The preBötC network comprises a heterogenous population of excitatory and inhibitory inspiratory neurons that can be further classified based on expression of transcription factors, receptors and transmitters, discharge pattern and membrane properties. An important goal is to establish the neuronal phenotype(s) that underlie the P2Y1R frequency increase. Perhaps surprisingly, preBötC frequency increases in response to optogenetic stimulation of excitatory OR inhibitory preBötC neurons. Thus, the objective of this study was to determine if the P2Y1R-mediated frequency increase results from activation of excitatory (glutamatergic) or inhibitory (GABA/glycinergic) preBötC inspiratory neurons. Analysis of P2Y1R and somatostatin (SST) immunolabeling in the medulla of neonatal vGLUT2TdTomato and GLYT2EGFP reporter mice showed that P2Y1R immunolabeled neurons are concentrated in a discrete region of the ventral respiratory column (VRC) that features strong SST immunolabeling (a preBötC marker). P2Y1R+ neurons were sparse in all other regions of the VRC. In addition, 95% of P2Y1R+ neurons were glutamatergic (VGLUT2+), but <10% of glutamatergic neurons were P2Y1R+. None of the GLYT2+ (glycinergic) preBötC neurons were P2Y1R+. Whole-cell analyses of neurons in rhythmic slices from vGLUT2 mice showed that all VGLUT2+ inspiratory preBötC neurons excited by the P2Y1R agonist MRS2365 (100 µM) were glutamatergic, but only1/3 of VGLUT2+ neurons were P2Y1R sensitive. In contrast, calcium imaging of rhythmic slices identified subpopulations (4/16) of glutamatergic and non glutamatergic inspiratory neurons that in TTX were P2Y1R sensitive. Finally, we demonstrated that the frequency increase evoked by MRS2365 (100 µM) in the preBötC was unaffected by block of inhibitory synaptic transmission via GABAA (bicuculline, 20 µM) and glycine (strychnine, 20 µM) receptor antagonists. In summary, we found that P2Y1R-expressing neurons are concentrated in the preBötC and are primarily glutamatergic. P2Y1R-sensitive neurons are primarily glutamatergic, but a subpopulation is nonglutamatergic. These data, combined with the observation that the P2Y1R-evoked excitation of the preBötC does not depend on synaptic inhibition, suggest that the P2Y1R-mediated excitation of the preBötC is primarily achieved through activation of excitatory, glutamatergic neurons.

Dose‐dependent multiple physiologic effects of systemic fentanyl in awake adult goats

It is well known that opioid analgesics induce life-threatening respiratory depression. A few studies have also documented additional deleterious effects of opioids on multiple physiologic functions. Moreover, there are reports of interindividual variation in susceptibility, magnitude, and duration of physiologic effects of opioids such as fentanyl. Here we tested the dose-dependent effects of intravenous injected fentanyl on physiologic functions in 7 awake, adult goats. Goats were instrumented for recording of multiple cardiorespiratory variables including respiratory pump and airway muscle activity. After a 30-minute control period, 0, 10, 20, or 50 µg/kg fentanyl was infused intravenously. We found that rapid IV infusion of fentanyl over 2 min caused a dose-dependent decrease in minute ventilation due to dramatic suppression of breathing frequency within 5 min after IV injection. These effects were coupled with dose-dependent increases in VT, which represents a more human like ventilatory response to opioids. The major suppression of ventilation occurred in 5 of the 7 goats, whereas in 2 of the goats IV fentanyl injections increased breathing frequency in a dose-dependent manner. This variation in ventilatory response to opioids agrees with findings that in a subset of humans, opioids have an excitatory effect on physiologic functions (Br. J. Anaesth 81, 1998). The suppression of ventilation seen in the majority of goats is transient, lasting for 3-10 minutes post-injection and is accompanied by an increased or normal VT up to 30-90 minutes. Over the initial 10 minutes after injection, there were obstructive and central apneas often exceeding one minute resulting in arterial hypoxemia (PaO2<50 mmHg) and hypercapnia (PaCO2>50mmHg). Heart rate was decreased for up to 15 minutes following 50µg/kg injection, whereas arterial blood pressure was increased for at least 90 minutes post-injection. Particularly over the initial minutes after 50µg/kg, fentanyl infusion decreased the duration but increased the intensity of diaphragm and intercostal muscle activity while increasing tonic activity of abdominal and airway muscles. Infusion of naloxone before or after infusion of fentanyl prevented or reversed the acute and delayed physiologic effects induced by fentanyl. Injection of Naloxone alone had no effect on physiological measures of goats. We conclude that goats have multiple dose- and individual-dependent physiologic responses to systemic infusion of fentanyl. Furthermore, our reversal data suggests the effects of fentanyl in goats are likely mediated by activation of µ-opioid receptors.

Hyperexcitability of Nucleus Tractus Solitarii Neurons in the Streptozotocin‐Induced Model of Alzheimer's Disease

Besides the stereotypical problems of memory and cognition in patients with Alzheimer's Disease (AD), another highly prevalent symptom is of respiratory origin. We have repeatedly shown blunted respiratory responses to hypoxia in the streptozotocin (STZ) -induced AD model, which is similar to sleep disordered breathing found in nearly 80% of AD patients. Our current study focuses on the electrophysiological changes within the nucleus tractus solitarii (nTS), a brainstem area known to control respiratory function. Using male Sprague-Dawley rats (n = 15 rats, 240±8 g), we induced AD symptoms with microinjections of 2 mg/kg Streptozotocin (STZ) into the lateral cerebral ventricles. Control animals received 0.9 mM citrate buffer as vehicle control (CTL). The disease model was verified using the Morris water maze to test for memory dysfunction. We recorded nTS neuronal responses via whole cell patch clamp. Action potential (AP) discharge upon current-stimulation was higher in STZ-AD when compared to control. Also, spontaneous spike activity (no stimulation) was elevated. These data corroborate earlier results using a higher (2x1.5 mg) STZ dosage. Spontaneous post-synaptic currents in the absence of stimulation resemble nTS network activity. The number of spontaneous events in nTS neurons of the STZ-AD group was surprisingly similar to CTL in the current study. On the other hand, network activity mirrors the hyperexcitability seen from our current injection when using the higher STZ dosage. While there was no appreciable change in resting membrane potential, AP threshold of STZ-AD nTS cells shifted towards a more negative membrane potential, overall contributing to increased excitability in these cells. AP phase plane plots in STZ-AD had a significantly smaller overshoot with a reduced velocity of up and down stroke, possibly indicating altered function of voltage-gated sodium channels. Analysis of transient K+ currents (A-type) revealed a slight shift to higher activation voltages (from -20 mV [CTL] to 0 mV [STZ-AD]) in STZ-AD. This shift favors AP generation and may contribute to a lower spike threshold in STZ-AD. There were no changes in the steady state K+ currents between groups. In summary, nTS cells of the STZ-AD group showed increased excitability that may involve gating properties of voltage-gated sodium channels and A-type potassium channels. The observed neurophysiological changes in the nTS may be part of the neuronal correlate for increased breathing frequency and blunted (ceiling effect) respiratory responses to hypoxia in the STZ-AD model.

Role of Medulary Raphe in the Control of Thermoeffectors of Precocious Birds

In mammals, caudal brain regions, such as raphe nuclei, are involved in the modulation of thermoeffectors such as peripheral vasodilation/vasoconstriction and nonshivering and shivering thermogenesis. In birds, it is still completely unknown if the same scenario occurs. The aim of the present study was to verify the effect of GABAA and GLU inhibition in the medullary raphe on body temperature (Tb), oxygen consumption, ventilation and heat loss index (HLI) of precocious birds under neutral (31ºC) and cold (26ºC), using of one-week-old chicks as animal models. To this end, the Tb, oxygen consumption (index of thermogenesis), ventilation and heat loss index were measured before and after intra-raphe microinjections of the GABAA receptor antagonist, bicuculline (0.05 mM and 0.5 mM), and the NMDA receptor antagonist, AP5 (0.5mM and 5mM), or vehicle. Protocols were approved by the local Animal Care Committee (CEUA of FCAV/Unesp, nº 013907/17). Bicuculline (0.5 mM) at 31°C significantly decreased (P<0.05) Tb (vehicle: 41.2±0.1°C; Bicuculline 0.05mM: 40.9±0.1°C; Bicuculline 0.5mM: 40.6±0.2°C) and oxygen consumption (13.9±0.7% decrease) of the animals when compared to the vehicle group. Bicuculline (0.05 mM) at 26°C significantly reduced (P<0.05) Tb (vehicle: 41.4±0.1°C; Bicuculline 0.05mM: 40.6±0.1°C) and oxygen consumption (12.6±1.4% of decrease) of the animals when compared to the vehicle group. AP5 (5 mM) at 31°C significantly decreased (P<0.05) Tb (vehicle: 41.3±0.1°C; AP5 0.5mM: 40.9±0.1°C; AP5 5mM: 40.3±0.2°C) and oxygen consumption (14.7±0.6% decrease) of the animals when compared to the vehicle group. AP5 (0.5 mM) at 26°C significantly reduced (P<0.05) Tb (vehicle: 41.2±0.2°C; AP5 0.5mM: 40.7±0.1°C) and oxygen consumption (17.4±3.1% of decrease) of the animals when compared to the vehicle group. Regarding ventilation, only treatment with AP5 transiently increased breathing frequency during cold exposure (30.6±9.8% increase; P <0.05). At 31ºC, the highest doses of bicuculline and AP5 increased HLI at the beginning of the Tb reduction (P<0.05) and at 26°C there was no difference on HLI. Our results suggest that GABAA and NMDA receptors inhibition in raphe neurons show an inhibitory effect on Tb of chicks affecting thermogenesis under neutral (31ºC) and cold (25ºC) conditions.

A thermoregulatory role of the medullary raphe in birds.

The brainstem region medullary raphe modulates non-shivering and shivering thermogenesis and cutaneous vasomotion in rodents. Whether the same scenario occurs in the other endothermic group, i.e. birds, is still unknown. Therefore, we hypothesised that the medullary raphe modulates heat gain and loss thermoeffectors in birds. We investigated the effect of glutamatergic and GABAergic inhibitions in this specific region on body temperature (Tb), oxygen consumption (thermogenesis), ventilation (O2 supply in cold, thermal tachypnea in heat) and heat loss index (cutaneous vasomotion) in one-week-old chicken exposed to neutral (31°C), cold (26°C) and heat (36°C) conditions. Intra-medullary raphe antagonism of NMDA glutamate (AP5; 0.5, 5 mM) and GABAA (bicuculline; 0.05, 0.5 mM) receptors reduced Tb of chicks at 31°C and 26oC, due mainly to an O2 consumption decrease. AP5 transiently increased breathing frequency during cold exposure. At 31°C, heat loss index was higher in the bicuculline and AP5 groups (higher doses) than vehicle at the beginning of the Tb reduction. No treatment affected any variable tested at 36oC. The results suggest that glutamatergic and GABAergic excitatory influences on the medullary raphe of chicks modulate thermogenesis and glutamatergic stimulation prevents tachypnea, without having any role in warmth-defence responses. A double excitation influence on the medullary raphe may provide a protective neural mechanism for supporting thermogenesis during early life, when energy expenditure to support growth and homeothermy is high. This novel demonstration of a thermoregulatory role for the raphe in birds suggests a convergent brainstem neurochemical regulation of body temperature in endotherms.

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague–Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO2 and sO2 and increases in pCO2 (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.