The relationship between the level (rate) of stimulus and the characteristics of the cough response was studied on 15 spontaneously breathing anesthetized cats. Three modes of stimulation were used to elicit cough. 'High' vs. 'low' level of stimulation was accomplished: 1st mode by 1 vs. 4 penetrations of the soft catheter through the trachea (approximately 10 cm), 2nd mode by 2 penetrations with the soft catheter equipped with 4 fine cross nylon fibers vs. 4 penetrations by the stimulator with 8 fibers, and 3rd mode by a similar stimulator with 4 cross fibers probing 4 cm of the trachea either right below the larynx or deeper under the upper part of the sternum (data were pooled) vs. stimulating both areas at the same time. 'High' stimulation rate in each stimulation mode resulted in a higher number of coughs, increased cough efforts, and shortened several temporal cough features. Mechanical stimulation resulting in higher cough afferent drive induces more vigorous coughing with shorter temporal cough characteristics. Modulation of cough afferent input affects both spatial and temporal components of the cough motor pattern, representing a crucial point in cough management.

Dyspnoea perception is influenced by a complex interplay of physiological, psychological, and environmental factors. Recently, we showed that males with high trait self-control experience less dyspnoea and persist for longer in a carbon dioxide (CO) rebreathing challenge than males with low trait self-control. As self-control can also vary within individuals (state self-control), the primary aim of the present study was to investigate whether prior self-control exertion influenced perceptions of dyspnoea and tolerance of a CO rebreathing challenge in healthy young males. We also used functional near-infrared spectroscopy (fNIRS) to assess haemodynamic activity of the pre-frontal cortex (PFC) which is a region of interest (ROI) in dyspnoea research, and the primary brain region associated with exertion of self-control.

Inspiratory muscle training (IMT) is often employed to enhance improvement in inspiratory muscle strength. However, the relationship between inspiratory muscle recruitment patterns and increasing inspiratory load remains unclear. Furthermore, the effect of breathing instructions on diaphragm activity at various inspiratory loads is unknown.

In addition to its hematopoietic function, erythropoietin (EPO) has demonstrated neuroprotective properties in preclinical studies, particularly in cases of reduced oxygenation or ischemia in the neonatal brain. While these findings have sparked optimism for its potential clinical application, the efficacy of EPO remains contentious in translational assays. Notably, while repeated administration of low doses of EPO has correlated with a decrease in adverse outcomes, the use of high EPO doses has shown either negligible or potentially detrimental effects on the incidence of brain injury. In this pilot study, we explored the effects of low and sustained doses of EPO (400 IU/kg) on the incidence of intraventricular hemorrhage (IVH) in premature infants. EPO was administered intravenously three times a week until the infants reached 32 weeks corrected gestational age. Our results indicate a significant decrease in the incidence of IVH with EPO treatment. Although, this study does not provide conclusive evidence on EPO's ability to reverse established IVH, these results strongly support the need for larger-scale clinical trials to further assess EPO's therapeutic potential.

Acute intermittent hypoxia (AIH) elicits spinal neuroplasticity and is emerging as a potential therapeutic modality to improve respiratory and non-respiratory motor function in people with chronic incomplete spinal cord injury (SCI). Brain-derived neurotrophic factor (BDNF) is necessary and sufficient for moderate AIH-induced phrenic long-term facilitation, a well-studied form of respiratory motor plasticity. Repetitive daily AIH (dAIH) enhances BDNF expression within the phrenic motor neurons of normal rats, but its effects on BDNF after chronic cervical spinal cord injury (cSCI) are unknown. In contrast to AIH, chronic intermittent hypoxia (CIH), simulating that experienced during sleep apnea, elicits neuropathology and undermines plasticity. Here, we tested the hypothesis that daily AIH vs CIH differentially regulate phrenic motor neuron BDNF expression in spinally intact and injured rats. Rats with and without C2 hemisection (C2Hx; 8 weeks post-injury) were exposed to 28 days of: 1) sham normoxia (Nx, 21 % O); 2) daily AIH (dAIH: 10, 5 min episodes of 10.5 % O per day; 5 min normoxic intervals); 3) mild CIH (CIH5/5: 5 min of 10.5 % O, 5 min intervals, 8 hrs/day); or 4) moderate CIH (CIH2/2: 2 min of 10.5 % O, 2 min intervals, 8 hrs/day). After 28 days of daily exposure (i.e., 12 weeks post-injury), BDNF immunoreactivity was assessed within phrenic motor neurons identified via retrograde cholera toxin B fragment labeling. In intact rats, daily AIH increased BDNF protein levels in phrenic motor neurons (∼31 %) but not in rats with C2Hx. CIH had no effects on phrenic motor neuron BDNF levels in intact rats, although there was a trend towards increased phrenic motor neuron BDNF after C2Hx, suggesting the need for further study. Since dAIH effects on phrenic motor neuron BDNF are not observed in rats with chronic cervical SCI, the potential of dAIH to enhance BDNF-dependent phrenic motor plasticity may be suppressed by conditions prevailing with chronic cSCI.

Asthma is a common chronic inflammatory airway disease, imposing a substantial health and economic burden on society and individuals. Current treatments primarily focus on symptom relief and lung function improvement, often failing to address the underlying pathology. Thus, exploring new therapeutic approaches is crucial. Airway smooth muscle cells (ASMCs) play a key role in regulating airway tone and airflow, while abnormal ASMCs proliferation contributes to airway remodeling in asthma. Airway epithelial cells (AECs), serving as the first barrier against pathogens and allergens, also have critical immune functions. This study focuses on the interaction between AECs and ASMCs, as AECs are more accessible for drug delivery due to their location at the airway surface. Investigating this relationship could facilitate novel interventions targeting AECs to inhibit pathological ASMCs activity. In our experiment, we isolated ASMCs and AECs from healthy mice and found that AECs significantly promoted ASMCs proliferation in co-culture. RNA sequencing revealed that this process might be linked to the activation of the canonical Wnt signaling pathway in ASMCs. By using Wnt pathway inhibitors (endo-IWR1) and siRNA to disrupt Wnt receptors, we reversed this phenotype. This finding suggests that AECs may promote ASMCs proliferation by activating the Wnt pathway in ASMCs. The Wnt/β-catenin pathway appears to play an important role in ASMCs proliferation, indicating that future pathological studies should consider the potential involvement of the Wnt pathway in airway remodeling.

Obesity increases the risk of respiratory diseases that reduce respiratory chemosensitivity, such as Obesity Hypoventilation Syndrome and sleep apnea. Recent evidence suggests that obesity-related changes in the brain, including alterations in melanocortin signaling via the melanocortin-4 receptor (MC4R), may underly altered chemosensitivity. Setmelanotide, an MC4R agonist, causes weight loss in both humans and animal models. However, it is unknown the extent to which setmelanotide affects respiratory chemosensitivity independent of body weight loss. The present study uses diet-induced obese, male C57bl/6 J mice to determine the extent to which acute setmelanotide treatment affects the hypercapnic ventilatory response (HCVR). We find that ten days of daily setmelanotide treatment at 1 mg/kg, but not 0.2 mg/kg, is sufficient to cause weight loss and increase HCVR. In a separate group of animals, we find that we can emulate setmelanotide's effect on weight loss by restricting daily calories to match the hypophagia triggered by setmelanotide. These pair-fed animals exhibit improvements in HCVR similar to those who receive setmelanotide. We conclude that acute treatment with setmelanotide is as effective as weight loss at improving respiratory hypercapnic chemosensitivity.

Obstructive sleep apnea, characterized by airway exposure to intermittent hypoxia (IH), is associated with laryngeal airway hyperreactivity (LAH) and laryngeal inflammation. The sensitization of capsaicin-sensitive superior laryngeal afferents (CSSLAs) by inflammatory mediators has been implicated in the pathogenesis of LAH. Nerve growth factor (NGF) is an inflammatory mediator that acts on tropomyosin receptor kinase A (TrkA) and the p75 neurotrophin receptor (p75) to induce lower airway hyperresponsiveness. In this study, we investigated the role of NGF in the development of LAH and laryngeal inflammation induced by IH in anesthetized rats. Compared with rats subjected to room air exposure for 14 days, rats with 14-day IH exposure exhibited augmented reflex apneic responses to the laryngeal provocation of three different chemical stimulants of CSSLAs, resulting in LAH. The apneic responses to laryngeal stimulants were abolished by either perineural capsaicin treatment (a procedure that selectively blocks the conduction of CSSLAs) or denervation of the superior laryngeal nerves, suggesting that the reflex was mediated through CSSLAs. The IH-induced LAH was significantly attenuated by daily treatment with anti-NGF antibody, but was unaffected by daily treatment with immunoglobulin G. IH exposure also induced laryngeal inflammation as evidenced by increases in laryngeal levels of NGF, lipid peroxidation, tumor necrosis factor-α, interleukin-1β, TrkA, and p75. Similarly, IH-induced laryngeal inflammation was significantly reduced by daily treatment with anti-NGF antibody. We concluded that NGF contributes to the development of LAH and laryngeal inflammation induced by IH in rats. The LAH may result from the sensitizing effect of NGF on CSSLAs.

Sevoflurane-induced gasping in mice involves an enormous increase in inspiratory effort, mandibular movement, and a marked decrease in respiratory frequency (fR). We examined differences in breathing patterns and electromyogram activity (EMG) of the suprahyoid muscles (SHMs) during eupnea under 3.2 % (1 MAC: minimum alveolar concentration) sevoflurane inhalation and sevoflurane-induced gasping under 6.5 % (2 MAC) sevoflurane inhalation in eight spontaneously breathing, tracheally intubated, adult mice. We found that the phasic EMG is obtained only during inspiration in eupnea and gasping and that integrated EMG increases more, as a percent of baseline (% baseline) than tidal volume (V) during gasping (median [interquartile range]; integrated EMG: 720 [425-1965] vs. V: 300 [238-373], P < 0.05). We also found that the onset of EMG precedes the start of airflow while maintaining a bell-shaped EMG contour, which characterizes the EMG of upper airway dilator (UAD) muscles during eupnea and gasping. Vigorous respiratory-related mandibular movements were never observed during eupnea but were observed in seven of 8 mice during sevoflurane-induced gasping. Our observations indicate that SHMs act as a preferentially activating UAD muscle, contributing to the development of mandibular respiratory movements.

Post-acute sequelae of SARS-CoV-2 (PASC), or Long COVID, and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are debilitating post-viral conditions with many symptomatic overlaps, including exercise intolerance and autonomic dysfunction. Both conditions are growing in prevalence, and effective safe treatment strategies must be investigated. We hypothesized that inspiratory muscle training (IMT) could be used in PASC and mild to moderate ME/CFS to mitigate symptoms, improve exercise capacity, and improve autonomic function. We recruited healthy controls (n=12; 10 women), people with PASC (n=9; 8 women), and people with mild to moderate ME/CFS (n=12; 10 women) to complete 8 weeks of IMT. This project was registered as a clinical trial (NCT05196529) with clinicaltrials.gov. After completion of IMT, all groups experienced improvements in inspiratory muscle pressure (p<0.001), 6-minute walk distance (p=0.002), resting heart rate (p=0.037), heart rate variability (p<0.05), and symptoms related to sleep (p=0.009). In the ME/CFS group only, after completion of IMT, there were additional improvements with regard to vascular function (p=0.001), secretomotor function (p=0.023), the total weighted score (p=0.005) of the COMPASS 31 autonomic questionnaire, and symptoms related to pain (p=0.016). We found that after 8 weeks of IMT, people with PASC and/or ME/CFS could see some overall improvements in their autonomic function and symptomology.

Excess exercise ventilation (high ventilation (V̇)/carbon dioxide output (V̇CO)) contributes significantly to dyspnea and exercise intolerance since the earlier stages of chronic obstructive pulmonary disease (COPD). A selective pulmonary vasodilator (inhaled nitric oxide) has shown to increase exercise tolerance secondary to lower V̇/V̇CO and dyspnea in this patient population. We aimed to assess whether a clinically more practical option - oral sildenafil - would be associated with similar beneficial effects. In a randomized, placebo-controlled study, twenty-four patients with mild-to-moderate COPD completed, on different days, two incremental cardiopulmonary exercise tests (CPET) one hour after sildenafil or placebo. Eleven healthy participants performed a CPET in a non-interventional visit for comparative purposes with patients when receiving placebo. Patients (FEV= 69.4 ± 13.5 % predicted) showed higher ventilatory demands (V̇/V̇CO), worse pulmonary gas exchange, and higher dyspnea during exercise compared to controls (FEV= 98.3 ±11.6 % predicted). Contrary to our expectations, however, sildenafil (50 mg; N= 15) did not change exertional V̇/V̇CO, dead space/tidal volume ratio, operating lung volumes, dyspnea, or exercise tolerance compared to placebo (P>0.05). Due to the lack of significant beneficial effects, nine additional patients were trialed with a higher dose (100 mg). Similarly, active intervention was not associated with positive physiological or sensory effects. In conclusion, acute oral sildenafil (50 or 100 mg) failed to improve gas exchange efficiency or excess exercise ventilation in patients with predominantly moderate COPD. The current study does not endorse a therapeutic role for sildenafil to mitigate exertional dyspnea in this specific patient subpopulation. Clinical trial registry: https://ensaiosclinicos.gov.br/rg/RBR-4qhkf4 Web of Science Researcher ID: O-7665-2019.

The genioglossus (GG) is known to be the main tongue protrusor, and therefore plays a major role in breathing. However, due to the fan shape of the GG fibers, it could be assumed that contraction of the anterior fibers of the GG do not cause tongue protrusion. In this study, we examined the effect of contraction of the anterior-vertical fibers of the GG (GG) on the tongue and their EMG activity during wakefulness and sleep. The findings were compared to those of the longitudinal fibers (GG), which, based on their orientation, are responsible for tongue protrusion.

Cerebral blood flow is influenced by respiration, primarily through changes in the CO concentration of arterial blood.

Long COVID patients present with a myriad of symptoms that can include fatigue, exercise intolerance and post exertional malaise (PEM). Long COVID has been compared to other post viral syndromes, including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), where a reduction in day 2 cardiopulmonary exercise test (CPET) performance of a two-day CPET protocol is suggested to be a result of PEM. We investigated cardiopulmonary and perceptual responses to a two-day CPET protocol in Long COVID patients.

Respiratory patterns were investigated in male Sprague-Dawley rats throughout their lifespan, from weanling (1 month) to old age (24 months), under natural conditions. Both inter-breath interval (IBI) and respiratory volume (RV) were examined. Sample entropy suggested increasing irregularity in IBI but decreasing irregularity in RV until 12 months. According to detrended fluctuation analysis, alpha exponent of the IBI showed a bimodal pattern around the value 0.7. From 1-15 months, the alpha exponent for RV generally decreased to the value 0.5, but it increased again as the animals neared the end of their lifespan. Cross-sample entropy revealed increasing synchronization between IBI and RV until 12 months, then plateauing. Many measures demonstrated a transition around 12 months, potentially reflecting maturation of respiratory control mechanisms. The findings characterize complex dynamics of respiratory patterns across the rat lifespan, providing a normative foundation to identify deviations indicative of dysfunction or disease.

Mechanical ventilation (MV) is a life support method used to treat patients with respiratory failure. High tidal volumes during MV can cause ventilator-induced lung injury (VILI), but also affect other organs, such as the diaphragm (Dia) causing ventilator-induced diaphragmatic dysfunction (VIDD). VIDD is often associated with a complicated course on MV. Sepsis can induce inflammation and oxidative stress, contributing to the impairment of the Dia and worsening of the prognosis. This study evaluated the additive or synergistic effects of a short course of mechanical ventilation on Dia in healthy and septic adult mice.

Brainstem astrocytes are important for COH chemoreception. Lateral Hypothalamus/Perifornicial Area (LH/PFA) neurons have an excitatory effect on the ventilatory response to CO, however the role of the astrocytes is unknown. We hypothesized that LH/PFA astrocytes play an excitatory role in the hypercapnic ventilatory response in a sleep-wake and light-dark cycles-dependent manner. We manipulated the activity of astrocytes in the LH/PFA of male Wistar rats through microinjection of Fluorocitrate (Fct), which selectively affects astrocytes, inducing the exocytosis of gliotransmitters. We investigated the effects of intra-LH/PFA Fct microinjection on resting breathing and ventilatory responses to hypercapnia and hypoxia during wakefulness and NREM sleep, in the light and dark phases. Fct increased ventilation during hypercapnia but not during room air or hypoxia. The hypercapnic chemoreflex was increased exclusively during the dark-active phase during both, wakefulness and NREM sleep, indicating that LH/PFA astrocytes play an excitatory role in hypercapnic ventilatory response in a light-dark cycle-dependent manner.

The study investigated acute changes in cortisol (C) and testosterone (T) associated with a popular RMT method, voluntary isocapnic hyperpnoea (VIH), in well-trained triathletes. 19 athletes (7 females, 12 males) performed a VIH training session with pre- and post- serum C and T measurements. Repeated measures ANOVA was employed to analyze hormone changes during VIH, with additional time-sex interaction. Pearson correlation coefficient has been computed to identify the relationship between hormonal changes and age, anthropometric indices, respiratory muscle strength, and training experience. There was a statistically significant effect for C changes (F = 13.101, p = 0.002, η = 0.421, ω = 0.08). The C concentration was significantly lower after VIH (Mean Difference = -32.49 ± 39.13 nmol*L). No significant effects for T, T/C ratio, and time-sex interactions were observed (p > 0.05). Amongst many, significant correlations between the percentage of body fat and changes in C (r=-0.464, p=0.045), body mass and changes in T (r=0.516, p=0.024), height and changes in T (r=0.509, p=0.026) were found. VIH significantly lowered C concentration. No significant effects for T, T/C ratio, and no between-sex differences were observed. Noteworthy individual variability was observed in all the monitored indices. Significant correlations were found between acute hormone changes associated with VIH and selected anthropometric indices. The study provides initial insight into VIH's role in athletes' hormonal balance to possibly guide exercise prescription, autoregulation, arousal state management, and recovery practices in athletes.

Expiratory muscle strength training (EMST) is a resistance exercise used to improve maximal expiratory pressure and airway protective functions (cough and swallow) in clinical populations. Although ratings of perceived exertion/effort (RPE) are commonly used in exercise prescription and monitoring, they have been underutilized in EMST and require investigation. Our study aims were to: (1) examine how healthy adults rate their effort using the EMST-150 device and MicroRPM respiratory manometer; (2) assess variability in RPE; and (3) compare RPE and relative expiratory pressures obtained from the two devices.

Substance P (SubP) and endomorphin-2 (Endo2) are co-localized presynaptically in vesicles of neurons adjacent to inspiratory rhythm-generating pre-Botzinger Complex (preBotC) neurons but the effects of co-released SubP and Endo2 on respiratory motor control are not known. To address this question, SubP alone or a combination of SubP and Endo2 (SubP/Endo2) were bath-applied in a sustained (15-min) or intermittent (5-min application, 5-min washout, x3) pattern at 10-100 nM to neonatal rat brainstem-spinal cord preparations. During neuropeptide application, SubP/Endo2 co-applications generally attenuated SubP-induced increases in burst frequency and decreases in burst amplitude. With respect to frequency plasticity (long-lasting increase in burst frequency 60 min post-neuropeptide application), SubP-induced frequency plasticity was increased with sustained SubP/Endo2 co-applications at 20 and 100 nM. Intermittent SubP/Endo2 co-applications tended to decrease the level of frequency plasticity induced by intermittent SubP alone applications. SubP/Endo2 co-applications revealed potentially new functions for neurokinin-1 (NK1R) and mu-opioid (MOR) receptors on respiratory rhythm-generating medullary neurons.

Examine the cardiovascular, muscular function, cognitive, and neural plastic responses to determine the safety and effectiveness of acute Intermittent hypoxia (AIH) at a low, high, and control fractional inspired oxygen (FiO) dosage METHODS: Thirteen human participants performed 30-min of AIH in 60-s intervals at FiO2's of 0.21 (AIH), 0.15 (AIH), and 0.09 (AIH). Heart rate variability (root mean squared of successive differences; RMSSD), heart rate, oxygen saturation (SpO2), blood pressure, muscular strength, neuromuscular activation, cerebral hemodynamic responses, cognition, symptomology, and brain-derived neurotrophic factor (BDNF) responses were measured before (Pre-AIH), after (post-AIH), and at 20-min of recovery (Recovery-AIH) RESULTS: There were no differences between AIH protocols for heart rate, RMSSD, blood pressure, or SpO2. Muscular strength improved Post-AIH for AIH (10 %) and AIH (14 %) and remained elevated (6 %) at Recovery-AIH. Neuromuscular activation increased Pre-AIH to Post-AIH for AIH15 (10 %) and AIH (11 %). Cerebral hemodynamic responses were not impacted between conditions. Both AIH and AIH9 increased BDNF Post-AIH (62 %) and Recovery-AIH (63 %) CONCLUSION: Acute intermittent hypoxia is generally safe and effective at producing neural plastic responses, but further examination of co-occurring cardiovascular diseases is needed. This study provides safety focused findings which will widen the adoption and refinement of AIH protocols.