Effect of Small Doses of Azithromycin on Pulmonary Ventilation Function and Inflammatory Factors IL-6, IL-13 in Children with Bronchial Asthma.

OBJECTIVE: To observe the effect of low-dose azithromycin on pulmonary ventilation function and inflammatory factors IL-6, IL-13 in children with bronchial asthma. METHODS: A total of 80 children with asthma in Pediatric Medicine affiliated to Taizhou Women and Children's Hospital of Wenzhou Medical University from January 2019 to December 2022 were selected and divided into control group (42 cases) and study group (38 cases). The control group regularly inhaled Salmeterol Xinafoate and Fluticasone Propionate inhalation, while the study group was additionally given low-dose azithromycin. After four weeks of treatment, pulmonary function tests including FEV1, FVC were performed and inflammatory indicators including CRP, FeNO, IL-6, IL-13 were measured. The occurrence of adverse reactions during treatment was recorded. RESULTS: Pulmonary function tests including FEV1%, FEV1/FVC% were improved in all subjects, and the improvement of pulmonary function was more significant in the study group (P<0.05). The levels of CRP, FeNO, IL-6 and IL-13 were decreased in the two groups, especially in the study group (P<0.05). There was no significant difference in the incidence of adverse drug reactions between the two groups (P>0.05). CONCLUSION: Low-dose azithromycin can significantly improve the pulmonary function in children with bronchial asthma, reduce the levels of inflammatory factors, control airway mucus secretion and inflammation, and can be used to treat chronic lung diseases such as bronchial asthma.

Effects of sodium bicarbonate ingestion on ventilatory and cerebrovascular responses in resting heated humans.

Hyperthermia stimulates ventilation in humans. This hyperthermia-induced hyperventilation may be mediated by the activation of peripheral chemoreceptors implicated in the regulation of respiration in reaction to various chemical stimuli, including reductions in arterial pH. Here, we investigated the hypothesis that during passive heating at rest, the increases in arterial pH achieved with sodium bicarbonate ingestion, which could attenuate peripheral chemoreceptor activity, mitigate hyperthermia-induced hyperventilation. We also assessed the effect of sodium bicarbonate ingestion on cerebral blood flow responses, which are associated with hyperthermia-induced hyperventilation. Twelve healthy men ingested sodium bicarbonate (0.3 g/kg body weight) or sodium chloride (0.208 g/kg). One hundred minutes after the ingestion, the participants were passively heated using hot-water immersion (42°C) combined with a water-perfused suit. Increases in esophageal temperature (an index of core temperature) and minute ventilation (V̇E) during the heating were similar in the two trials. Moreover, when V̇E is expressed as a function of esophageal temperature, there were no between-trial differences in the core temperature threshold for hyperventilation (38.0 ± 0.3 vs. 38.0 ± 0.4°C, P = 0.469) and sensitivity of hyperthermia-induced hyperventilation as assessed by the slope of the core temperature-V̇E relation (13.5 ± 14.2 vs. 15.8 ± 15.5 L/min/°C, P = 0.831). Furthermore, middle cerebral artery mean blood velocity (an index of cerebral blood flow) decreased similarly with heating duration in both trials. These results suggest that sodium bicarbonate ingestion does not mitigate hyperthermia-induced hyperventilation and the reductions in cerebral blood flow index in resting heated humans.NEW & NOTEWORTHY Hyperthermia leads to hyperventilation and associated cerebral hypoperfusion, both of which may impair heat tolerance. This hyperthermia-induced hyperventilation may be mediated by peripheral chemoreceptors, which can be activated by reductions in arterial pH. However, our results suggest that sodium bicarbonate ingestion, which can increase arterial pH, is not an effective intervention in alleviating hyperthermia-induced hyperventilation and cerebral hypoperfusion in resting heated humans.

Dexamethasone weakens the respiratory effects of pro-inflammatory cytokine TNF-α in rat.

The goal of the current study was to identify the role of the glucocorticoids in the respiratory effects of proinflammatory cytokines. For this purpose intravenous injections of TNF-α were used in anesthetized spontaneously breathing rats before and after pretreatment of dexamethasone, a synthetic steroid with predominant glucocorticoid activity. Dexamethasone was injected intraperitoneally at a dose of 1 mg/kg. TNF-α was administrated into the tail vein at a dose of 40 mg/kg. We found that dexamethasone pretreatment eliminated the cytokine-induced increase in pulmonary ventilation and decrease in the hypoxic ventilatory response. Dexamethasone had a pronounced rapid effect on the respiratory activity of TNF-α as early as 30 minutes after administration. Therefore, we assume that this mechanism of action of dexamethasone was non-genomic, associated with the blocking of secondary mediators of the cytokine response.

Using modified Fenn diagrams to assess ventilatory acclimatization during ascent to high altitude: Effect of acetazolamide.

High altitude (HA) ascent imposes systemic hypoxia and associated risk of acute mountain sickness. Acute hypoxia elicits a hypoxic ventilatory response (HVR), which is augmented with chronic HA exposure (i.e., ventilatory acclimatization; VA). However, laboratory-based HVR tests lack portability and feasibility in field studies. As an alternative, we aimed to characterize area under the curve (AUC) calculations on Fenn diagrams, modified by plotting portable measurements of end-tidal carbon dioxide ( P ETC O 2 ${P_{{\mathrm{ETC}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ) against peripheral oxygen saturation ( S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ) to characterize and quantify VA during incremental ascent to HA (n = 46). Secondarily, these participants were compared with a separate group following the identical ascent profile whilst self-administering a prophylactic oral dose of acetazolamide (Az; 125 mg BID; n = 20) during ascent. First, morning P ETC O 2 ${P_{{\mathrm{ETC}}{{\mathrm{O}}_{\mathrm{2}}}}}$ and S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ measurements were collected on 46 acetazolamide-free (NAz) lowland participants during an incremental ascent over 10 days to 5160 m in the Nepal Himalaya. AUC was calculated from individually constructed Fenn diagrams, with a trichotomized split on ranked values characterizing the smallest, medium, and largest magnitudes of AUC, representing high (n = 15), moderate (n = 16), and low (n = 15) degrees of acclimatization. After characterizing the range of response magnitudes, we further demonstrated that AUC magnitudes were significantly smaller in the Az group compared to the NAz group (P = 0.0021), suggesting improved VA. These results suggest that calculating AUC on modified Fenn diagrams has utility in assessing VA in large groups of trekkers during incremental ascent to HA, due to the associated portability and congruency with known physiology, although this novel analytical method requires further validation in controlled experiments. HIGHLIGHTS: What is the central question of this study? What are the characteristics of a novel methodological approach to assess ventilatory acclimatization (VA) with incremental ascent to high altitude (HA)? What is the main finding and its importance? Area under the curve (AUC) magnitudes calculated from modified Fenn diagrams were significantly smaller in trekkers taking an oral prophylactic dose of acetazolamide compared to an acetazolamide-free group, suggesting improved VA. During incremental HA ascent, quantifying AUC using modified Fenn diagrams is feasible to assess VA in large groups of trekkers with ascent, although this novel analytical method requires further validation in controlled experiments.

Acute sodium bicarbonate administration improves ventilatory efficiency in experimental respiratory acidosis: clinical implications.

Administering sodium bicarbonate (NaHCO3) to patients with respiratory acidosis breathing spontaneously is contraindicated because it increases carbon dioxide load and depresses pulmonary ventilation. Nonetheless, several studies have reported salutary effects of NaHCO3 in patients with respiratory acidosis but the underlying mechanism remains uncertain. Considering that such reports have been ignored, we examined the ventilatory response of unanesthetized dogs with respiratory acidosis to hypertonic NaHCO3 infusion (1 N, 5 mmol/kg) and compared it with that of animals with normal acid-base status or one of the remaining acid-base disorders. Ventilatory response to NaHCO3 infusion was evaluated by examining the ensuing change in PaCO2 and the linear regression of the PaCO2 vs. pH relationship. Strikingly, PaCO2 failed to increase and the ΔPaCO2 vs. ΔpH slope was negative in respiratory acidosis, whereas PaCO2 increased consistently and the ΔPaCO2 vs. ΔpH slope was positive in the remaining study groups. These results cannot be explained by differences in buffering-induced decomposition of infused bicarbonate or baseline levels of blood pH, PaCO2, and pulmonary ventilation. We propose that NaHCO3 infusion improved the ventilatory efficiency of animals with respiratory acidosis, i.e., it decreased their ratio of total pulmonary ventilation to carbon dioxide excretion (VE/VCO2). Such exclusive effect of NaHCO3 infusion in animals with respiratory acidosis might emanate from baseline increased VD/VT (dead space/tidal volume) caused by bronchoconstriction and likely reduced pulmonary blood flow, defects that are reversed by alkali infusion. Our observations might explain the beneficial effects of NaHCO3 reported in patients with acute respiratory acidosis.

Role of raphe magnus 5-HT1A receptor in increased ventilatory responses induced by intermittent hypoxia in rats.

BACKGROUND: Intermittent hypoxia induces increased ventilatory responses in a 5-HT-dependent manner. This study aimed to explore that effect of raphe magnus serotonin 1A receptor (5-HT1A) receptor on the increased ventilatory responses induced by intermittent hypoxia. METHODS: Stereotaxic surgery was performed in adult male rats, and acute and chronic intermittent hypoxia models were established after recovery from surgery. The experimental group received microinjections of 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) into the raphe magnus nucleus (RMg). Meanwhile, the control group received microinjections of artificial cerebrospinal fluid instead of 8-OH-DPAT. Ventilatory responses were compared among the different groups of oxygen status. 5-HT expressions in the RMg region were assessed by immunohistochemistry after chronic intermittent hypoxia. RESULTS: Compared with the normoxia group, the acute intermittent hypoxia group exhibited higher ventilatory responses (e.g., shorter inspiratory time and higher tidal volume, frequency of breathing, minute ventilation, and mean inspiratory flow) (P < 0.05). 8-OH-DPAT microinjection partly weakened these changes in the acute intermittent hypoxia group. Further, compared with the acute intermittent hypoxia group, rats in chronic intermittent hypoxia group exhibited higher measures of ventilatory responses after 1 day of intermittent hypoxia (P < 0.05). These effects peaked after 3 days of intermittent hypoxia treatment and then decreased gradually. Moreover, these changes were diminished in the experimental group. 5-HT expression in the RMg region increased after chronic intermittent hypoxia, which was consistent with the changing trend of ventilatory responses. While activation of the 5-HT1A receptor in the RMg region alleviated this phenomenon. CONCLUSIONS: The results indicate that RMg 5-HT1A receptor, via changing the expression level of 5-HT in the RMg region, is involved in the modulation of the increased ventilatory responses induced by intermittent hypoxia.

Rationale and Clinical Use of Bronchodilators in Adults with Bronchiectasis.

Currently, there is much controversy surrounding the therapeutic approach to pulmonary function abnormalities in patients with bronchiectasis and, consequently, whether and when to use bronchodilators in these patients. National and international guidelines on the treatment of bronchiectasis in adults do not recommend the routine use of bronchodilators because there is no evidence that a significant response to a bronchodilator or the presence or hyperresponsiveness of the airway are good predictors of future effective clinical response. However, some guidelines recommend them in the presence of airway obstruction and/or special conditions, which vary according to the guideline in question, although there are no recommendations on optimal dosing and bronchodilator treatment combined with or without inhaled corticosteroids. Nonetheless, in contrast with guideline recommendations, bronchodilators are overused in real-world patients with bronchiectasis even in the absence of airway obstruction, as demonstrated by analysis of national and international registries. This overuse can be explained by the awareness of the existence of a solid pharmacological rationale that supports the use of bronchodilators in the presence of chronic airway obstruction independent of its aetiology. We performed a systematic review of the literature and were able to verify that there are no randomised controlled trials (apart from a small study with methodological limitations and a very recent trial involving a not-very-large number of patients), or any long-term observational studies on the short- or long-term effect of bronchodilators in patients with bronchiectasis. Therefore, we believe that it is essential and even urgent to evaluate the effects of bronchodilators in these patients with appropriately designed studies.

Buprenorphine differentially alters breathing among four congenic mouse lines as a function of dose, sex, and leptin status.

The opioid buprenorphine alters breathing and the cytokine leptin stimulates breathing. Obesity increases the risk for respiratory disorders and can lead to leptin resistance. This study tested the hypothesis that buprenorphine causes dose-dependent changes in breathing that vary as a function of obesity, leptin status, and sex. Breathing measures were acquired from four congenic mouse lines: female and male wild type C57BL/6J (B6) mice, obese db/db and ob/ob mice with leptin dysfunction, and male B6 mice with diet-induced obesity. Mice were injected intraperitoneally with saline (control) and five doses of buprenorphine (0.1, 0.3, 1.0, 3.0, 10 mg/kg). Buprenorphine caused dose-dependent decreases in respiratory frequency while increasing tidal volume, minute ventilation, and respiratory duty cycle. The effects of buprenorphine varied significantly with leptin status and sex. Buprenorphine decreased minute ventilation variability in all mice. The present findings highlight leptin status as an important modulator of respiration and encourage future studies aiming to elucidate the mechanisms through which leptin status alters breathing.

Effect of Global Ventilation to Perfusion Ratio, for Normal Lungs, on Desflurane and Sevoflurane Elimination Kinetics.

BACKGROUND: Kinetics of the uptake of inhaled anesthetics have been well studied, but the kinetics of elimination might be of more practical importance. The objective of the authors' study was to assess the effect of the overall ventilation/perfusion ratio (VA/Q), for normal lungs, on elimination kinetics of desflurane and sevoflurane. METHODS: The authors developed a mathematical model of inhaled anesthetic elimination that explicitly relates the terminal washout time constant to the global lung VA/Q ratio. Assumptions and results of the model were tested with experimental data from a recent study, where desflurane and sevoflurane elimination were observed for three different VA/Q conditions: normal, low, and high. RESULTS: The mathematical model predicts that the global VA/Q ratio, for normal lungs, modifies the time constant for tissue anesthetic washout throughout the entire elimination. For all three VA/Q conditions, the ratio of arterial to mixed venous anesthetic partial pressure Part/Pmv reached a constant value after 5 min of elimination, as predicted by the retention equation. The time constant corrected for incomplete lung clearance was a better predictor of late-stage kinetics than the intrinsic tissue time constant. CONCLUSIONS: In addition to the well-known role of the lungs in the early phases of inhaled anesthetic washout, the lungs play a long-overlooked role in modulating the kinetics of tissue washout during the later stages of inhaled anesthetic elimination. The VA/Q ratio influences the kinetics of desflurane and sevoflurane elimination throughout the entire elimination, with more pronounced slowing of tissue washout at lower VA/Q ratios.

Tiotropium Bromide Attenuates Mucus Hypersecretion in Patients with Stable Chronic Obstructive Pulmonary Disease.

BACKGROUND: Patients with stable chronic obstructive pulmonary disease (COPD) have been observed to benefit from tiotropium bromide. However, there are few studies of tiotropium bromide on sputum and sputum viscosity. To evaluate the effect of tiotropium bromide on mucus hypersecretion, a randomized, double-blind controlled trial was performed. METHODS: 120 cases of patients with pulmonary function grade II were divided into two groups, which include the treatment group given tiotropium bromide powder inhalation (18 µg, inhalation, QD) and the control group given formoterol fumarate powder inhalation (12 µg, inhalation, BID) plus ambroxol hydrochloride tablets (60 mg, oral, TID). After 3 months of treatment, the pulmonary function and α 1-acid glycoprotein (α 1-AGP) in sputum were detected, and the changes of glycoprotein and Ca2+ content were evaluated by Miller classification. RESULTS: Three patients (2 cases in the treatment group and 1 case in the control group) were dropped due to loss of follow-up, and 117 cases of patients were enrolled in this study. After 3 months of treatment, the sputum character score, α1-acid glycoprotein, Ca2+ content, and lung function of the two groups were significantly improved; group comparison analyses revealed that there was no significant difference in the content of α 1-AGP, Ca2+ in sputum, and lung function between the two groups (P > 0.05), but the improvement of sputum properties was significant (P < 0.05), and the treatment group was better than the control group (t = -2.77; P = 0.007). CONCLUSIONS: Inhaled tiotropium bromide can effectively inhibit the mucus hypersecretion in stable COPD patients, improve the sputum properties and lung function of patients, and improve the quality of life of patients.

In-vitro and in-vivo comparisons of high versus low concentrations of inhaled epoprostenol to adult intubated patients.

BACKGROUND: Inhaled epoprostenol (iEPO) has been shown to reduce pulmonary artery pressure and improve oxygenation. iEPO is mainly delivered via a syringe pump with feed tubing connected to a vibrating mesh nebulizer with high or low formulation concentration delivery. METHODS: An in vitro study and a two-period retrospective case-control study were implemented. The in vitro study compared iEPO delivery via invasive ventilation at low concentrations of 7.5, and 15 mcg/mL and high concentration at 30 mcg/mL, to deliver the ordered dose of 30 and 50 ng/kg/min for three clinical scenarios with predicted body weight of 50, 70 and 90 kg. While in the clinical study, adult patients receiving iEPO via invasive ventilation to treat refractory hypoxemia, pulmonary hypertension, or right ventricular failure were included. 80 patients received low concentration iEPO at multiple concentrations (2.5, 7.5, and 15 mcg/mL, depending on the ordered dose) from 2015 to 2017, while 84 patients received high concentration iEPO at 30 mcg/mL from 2018 to 2019. RESULTS: In the in vitro study, there were no significant differences in aerosol deposition between high vs low concentrations of iEPO at a dose of 50 ng/kg/min. In the clinical study, age, gender, ethnicity, and indications for iEPO were similar between high and low concentration groups. After 30-120 min of iEPO administration, both delivery strategies significantly improved oxygenation in hypoxemic patients and reduced mean pulmonary arterial pressure (mPAP) for patients with pulmonary hypertension. However, no significant differences of the incremental changes were found between two delivery groups. Compared to low concentration, high concentration delivery group had better adherence to the iEPO weaning protocol (96% vs 71%, p < 0.001), fewer iEPO syringes utilized per patient (5 [3, 10] vs 12 [6, 22], p = 0.001), and shorter duration of invasive ventilation (6 [3, 12] vs 9 [5, 18] days, p = 0.028). Intensive care unit length of stay and mortality were similar between two groups. CONCLUSION: Compared to low concentration delivery of iEPO, high concentration iEPO via a vibrating mesh nebulizer maintained clinical benefits and increased clinician compliance with an iEPO weaning protocol, required less medication preparation time, and shortened duration of invasive ventilation.

Acute intermittent hypoxia evokes ventilatory long-term facilitation and active expiration in unanesthetized rats.

Acute intermittent hypoxia (AIH) modifies the functioning of the respiratory network, causing respiratory motor facilitation in anesthetized animals and a compensatory increase in pulmonary ventilation in freely behaving animals. However, it is still unclear whether the ventilatory facilitation induced by AIH in unanesthetized animals is associated with changes in the respiratory pattern. We found that Holtzman male rats (80-150 g) exposed to AIH (10 × 6% O2 for 30-40 s every 5 min, n = 9) exhibited a prolonged (30 min) increase in baseline minute ventilation (P < 0.05) compared to control animals (n = 13), combined with the occurrence of late expiratory peak flow events, suggesting the presence of active expiration. The increase in ventilation after AIH was also accompanied by reductions in arterial CO2 and body temperature (n = 5-6, P < 0.05). The systemic treatment with ketanserin (a 5-HT2 receptor antagonist) before AIH prevented the changes in ventilation and active expiration (n = 11) but potentiated the hypothermic response (n = 5, P < 0.05) when compared to appropriate control rats (n = 13). Our findings indicate that the ventilatory long-term facilitation elicited by AIH exposure in unanesthetized rats is linked to the generation of active expiration by mechanisms that may depend on the activation of serotonin receptors. In contrast, the decrease in body temperature induced by AIH may not require 5-HT2 receptor activation.

Orexin contributes to eupnea within a critical period of postnatal development.

Orexin neurons are active in wakefulness and mostly silent in sleep. In adult rats and humans, orexin facilitates the hypercapnic ventilatory response but has little effect on resting ventilation. The influence of orexin on breathing in the early postnatal period, and across states of vigilance, have not been investigated. This is relevant as the orexin system may be impaired in Sudden Infant Death Syndrome (SIDS) cases. We addressed three hypotheses: 1) orexin provides a drive to breathe in infancy; 2) the effect of orexin depends on stage of postnatal development; and 3) orexin has a greater influence on breathing in wakefulness compared with sleep. Whole body plethysmography was used to monitor breathing of infant rats at three ages: postnatal days (P) 7-8, 12-14, and 17-19. Respiratory variables were analyzed in wakefulness (W), quiet sleep (QS), and active sleep (AS), following suvorexant (5 mg/kg ip), a dual orexin receptor antagonist, or vehicle (DMSO). Effects of suvorexant on ventilatory responses to graded hypercapnia ([Formula: see text] = 0.02, 0.04, 0.06), hypoxia ([Formula: see text] = 0.10), and hyperoxia ([Formula: see text] = 1.0) at P12-14 were also tested. At P12-14, but not at other ages, suvorexant significantly reduced respiratory frequency in all states, reduced the ventilatory equivalent in QW and QS, and increased [Formula: see text] to ∼5 mmHg. Suvorexant had no effect on ventilatory responses to graded hypercapnia or hypoxia. Hyperoxia eliminated the effects of suvorexant on respiratory frequency at P12-14. Our data suggest that orexin preserves eupneic frequency and ventilation in rats, specifically at ∼2 wk of age, perhaps by facilitating tonic peripheral chemoreflex activity.

Mangiferin attenuates cigarette smoke-induced chronic obstructive pulmonary disease in male albino rats.

We analyzed the ability of mangiferin to suppress cigarette smoke-induced chronic obstructive pulmonary disease. Control rats showed a marked decrease in the ratio of the forced expiratory volume at 0.1 s to forced vital capacity. The decreases in the peak expiratory flow and maximal mid-expiratory flow indicated airway remodeling and enlargement. The expression levels of superoxide dismutase (SOD), heme oxygenase-1 (HO-1), γ-glutamylcysteine synthetase, nuclear factor erythroid 2-related factor 2, and activating transcription factor 4 were increased in the control rats. The levels of oxidative stress, malondialdehyde, and reactive oxygen species peaked after 24 weeks, whereas the SOD and HO-1 levels and the total antioxidant capacity were reduced in control rats. Mangiferin restored the levels of reactive oxygen species, malondialdehyde, SOD, HO-1, and T-AOC to near normal. Increased numbers of infiltrating inflammatory cells were observed in control rats but were significantly reduced by mangiferin. In addition, edema and airway inflammation were reduced by mangiferin.

D-Cystine di(m)ethyl ester reverses the deleterious effects of morphine on ventilation and arterial blood gas chemistry while promoting antinociception.

We have identified thiolesters that reverse the negative effects of opioids on breathing without compromising antinociception. Here we report the effects of D-cystine diethyl ester (D-cystine diEE) or D-cystine dimethyl ester (D-cystine diME) on morphine-induced changes in ventilation, arterial-blood gas chemistry, A-a gradient (index of gas-exchange in the lungs) and antinociception in freely moving rats. Injection of morphine (10 mg/kg, IV) elicited negative effects on breathing (e.g., depression of tidal volume, minute ventilation, peak inspiratory flow, and inspiratory drive). Subsequent injection of D-cystine diEE (500 µmol/kg, IV) elicited an immediate and sustained reversal of these effects of morphine. Injection of morphine (10 mg/kg, IV) also elicited pronounced decreases in arterial blood pH, pO2 and sO2 accompanied by pronounced increases in pCO2 (all indicative of a decrease in ventilatory drive) and A-a gradient (mismatch in ventilation-perfusion in the lungs). These effects of morphine were reversed in an immediate and sustained fashion by D-cystine diME (500 µmol/kg, IV). Finally, the duration of morphine (5 and 10 mg/kg, IV) antinociception was augmented by D-cystine diEE. D-cystine diEE and D-cystine diME may be clinically useful agents that can effectively reverse the negative effects of morphine on breathing and gas-exchange in the lungs while promoting antinociception. Our study suggests that the D-cystine thiolesters are able to differentially modulate the intracellular signaling cascades that mediate morphine-induced ventilatory depression as opposed to those that mediate morphine-induced antinociception and sedation.

Caffeine Increases Exercise Performance, Maximal Oxygen Uptake, and Oxygen Deficit in Elite Male Endurance Athletes.

PURPOSE: The aims of the present study were to test the hypothesis that caffeine increases maximal oxygen uptake (V˙O2max) and to characterize the physiological mechanisms underpinning improved high-intensity endurance capacity. METHODS: Twenty-three elite endurance-trained male athletes were tested twice with and twice without caffeine (four tests) in a randomized, double-blinded, and placebo-controlled study with crossover design. Caffeine (4.5 mg·kg-1) or placebo was consumed 45 min before standardized warm-up. Time to exhaustion during an incremental test (running 10.5° incline, start speed 10.0 km·h-1, and 0.5 km·h-1 increase in speed every 30 s) determined performance. Oxygen uptake was measured continuously to determine V˙O2max and O2 deficit was calculated. RESULTS: Caffeine increased time to exhaustion from 355 ± 41 to 375 ± 41 s (Δ19.4 ± 16.5 s; P < 0.001). Importantly, caffeine increased V˙O2max from 75.8 ± 5.6 to 76.7 ± 6.0 mL·kg-1·min-1 (Δ 0.9 ± 1.7 mL·kg-1·min-1; P < 0.003). Caffeine increased maximal heart rate (HRpeak) and ventilation (VEpeak). Caffeine increased O2 deficit from 63.1 ± 18.2 to 69.5 ± 17.5 mL·kg-1 (P < 0.02) and blood lactate compared with placebo. The increase in time to exhaustion after caffeine ingestion was reduced to 11.7 s after adjustment for the increase in V˙O2max. Caffeine did not significantly increase V˙O2max after adjustment for VEpeak and HRpeak. Adjustment for O2 deficit and lactate explained 6.2 s of the caffeine-induced increase in time to exhaustion. The increase in V˙O2max, VE, HR, O2 deficit, and lactate explained 63% of the increased performance after caffeine intake. CONCLUSION: Caffeine increased V˙O2max in elite athletes, which contributed to improvement in high-intensity endurance performance. Increases in O2 deficit and lactate also contributed to the caffeine-induced improvement in endurance performance.

Pharmacologically Induced Ventilatory Depression in the Postoperative Patient: A Sleep-Wake State-Dependent Perspective.

Pharmacologically induced ventilatory depression (PIVD) is a common postoperative complication with a spectrum of severity ranging from mild hypoventilation to severe ventilatory depression, potentially leading to anoxic brain injury and death. Recent studies, using continuous monitoring technologies, have revealed alarming rates of previously undetected severe episodes of postoperative ventilatory depression, rendering the recognition of such episodes by the standard intermittent assessment practice, quite problematic. This imprecise description of the epidemiologic landscape of PIVD has thus stymied efforts to understand better its pathophysiology and quantify relevant risk factors for this postoperative complication. The residual effects of various perianesthetic agents on ventilatory control, as well as the multiple interactions of these drugs with patient-related factors and phenotypes, make postoperative recovery of ventilation after surgery and anesthesia a highly complex physiological event. The sleep-wake, state-dependent variation in the control of ventilation seems to play a central role in the mechanisms potentially enhancing the risk for PIVD. Herein, we discuss emerging evidence regarding the epidemiology, risk factors, and potential mechanisms of PIVD.

Cross-effect of TRPV1 and EP3 receptor on coughs and bronchopulmonary C-neural activities.

Prostaglandin E2 (PGE2)-induced coughs in vivo and vagal nerve depolarization in vitro are inhibited by systemic and local administration of prostaglandin EP3 receptor (L-798106) and TRPV1 antagonists (JNJ 17203212). These results indicate a modulating effect of TRPV1 on the EP3 receptor-mediated cough responses to PGE2 likely through the vagal sensory nerve. This study aimed to determine whether 1) inhalation of aerosolized JNJ 17203212 and L-798106 affected cough responses to citric acid (CA, mainly stimulating TRPV1) and PGE2; 2) TRPV1 and EP3 receptor morphologically are co-expressed and electrophysiologically functioned in the individual of vagal pulmonary C-neurons (cell bodies of bronchopulmonary C-fibers in the nodose/jugular ganglia); and 3) there was a cross-effect of TRPV1 and EP3 receptor on these neural excitations. To this end, aerosolized CA or PGE2 was inhaled by unanesthetized guinea pigs pretreated without or with each antagonist given in aerosol form. Immunofluorescence was applied to identify the co-expression of TRPV1 and EP3 receptor in vagal pulmonary C-neurons (retrogradely traced by DiI). Whole-cell voltage patch clamp approach was used to detect capsaicin (CAP)- and PGE2-induced currents in individual vagal pulmonary C-neurons and determine the effects of the TRPV1 and EP3 receptor antagonists on the evoked currents. We found that PGE2-induced cough was attenuated by JNJ 17203212 or L-798106 and CA-evoked cough greatly suppressed only by JNJ 17203212. Approximately 1/4 of vagal pulmonary C-neurons co-expressed EP3 with a cell size < 20 µm. Both CAP- and PGE2-induced currents could be recorded in the individuals of some vagal pulmonary C-neurons. The former was largely inhibited only by JNJ 17203212, while the latter was suppressed by JNJ 17203212 or L-798106. The similarity of the cross-effect of both antagonists on cough and vagal pulmonary C-neural activity suggests that a subgroup of vagal pulmonary C-neurons co-expressing TRPV1 and EP3 receptor is, at least in part, responsible for the cough response to PGE2.

Paraquat herbicide diminishes chemoreflex sensitivity, induces cardiac autonomic imbalance and impair cardiac function in rats.

Paraquat (PQT) herbicide is widely used in agricultural practices despite being highly toxic to humans. It has been proposed that PQT exposure may promote cardiorespiratory impairment. However, the physiological mechanisms involved in cardiorespiratory dysfunction following PQT exposure are poorly known. We aimed to determine the effects of PQT on ventilatory chemoreflex control, cardiac autonomic control, and cardiac function in rats. Male Sprague-Dawley rats received two injections/week of PQT (5 mg·kg-1 ip) for 4 wk. Cardiac function was assessed through echocardiography and pressure-volume loops. Ventilatory function was evaluated using whole body plethysmography. Autonomic control was indirectly evaluated by heart rate variability (HRV). Cardiac electrophysiology (EKG) and exercise capacity were also measured. Four weeks of PQT administration markedly enlarged the heart as evidenced by increases in ventricular volumes and induced cardiac diastolic dysfunction. Indeed, end-diastolic pressure was significantly higher in PQT rats compared with control (2.42 ± 0.90 vs. 4.01 ± 0.92 mmHg, PQT vs. control, P < 0.05). In addition, PQT significantly reduced both the hypercapnic and hypoxic ventilatory chemoreflex response and induced irregular breathing. Also, PQT induced autonomic imbalance and reductions in the amplitude of EKG waves. Finally, PQT administration impaired exercise capacity in rats as evidenced by a ∼2-fold decrease in times-to-fatigue compared with control rats. Our results showed that 4 wk of PQT treatment induces cardiorespiratory dysfunction in rats and suggests that repetitive exposure to PQT may induce harmful mid/long-term cardiovascular, respiratory, and cardiac consequences.NEW & NOREWORTHY Paraquat herbicide is still employed in agricultural practices in several countries. Here, we showed for the first time that 1 mo paraquat administration results in cardiac adverse remodeling, blunts ventilatory chemoreflex drive, and promotes irregular breathing at rest in previously healthy rats. In addition, paraquat exposure induced cardiac autonomic imbalance and cardiac electrophysiology alterations. Lastly, cardiac diastolic dysfunction was overt in rats following 1 mo of paraquat treatment.

Functional role of carbon dioxide on intermittent hypoxia induced respiratory response following mid-cervical contusion in the rat.

Intermittent hypoxia induces respiratory neuroplasticity to enhance respiratory motor outputs and is a potential rehabilitative strategy to improve respiratory function following cervical spinal injury. The present study was designed to evaluate the functional role of intermittent and sustained carbon dioxide (CO2) on intermittent hypoxia-induced ventilatory responses in rats with mid-cervical spinal contusion. The breathing pattern of unanesthetized rats at the subchronic and chronic injured stages was measured in response to one of the following treatments: (1) Intermittent hypercapnic-hypoxia (10 × 5 min 10%O2 + 4%CO2 with 5 min normoxia interval); (2) Intermittent hypoxia with sustained hypercapnia (10 × 5 min 10%O2 + 4%CO2 with 5 min 21%O2 + 4%CO2 interval); (3) Intermittent hypoxia (10 × 5 min 10%O2 with 5 min normoxia interval); (4) Intermittent hypercapnia (10 × 5 min 21%O2 + 4%CO2 with 5 min normoxia interval); (5) Sustained hypercapnia (100 min, 21% O2 + 4% CO2); (6) Sustained normoxia (100 min, 21% O2). The results demonstrated that intermittent hypoxia associated with intermittent hypercapnia or sustained hypercapnia induced a greater ventilatory response than sustained hypercapnia during stimulus exposure. The tidal volume was significantly enhanced to a similar magnitude following intermittent hypercapnic-hypoxia, intermittent hypoxia with sustained hypercapnia, and intermittent hypoxia in subchronically injured animals; however, only intermittent hypercapnic-hypoxia and intermittent hypoxia were able to evoke long-term facilitation of the tidal volume at the chronic injured stage. These results suggest that mild intermittent hypercapnia did not further enhance the therapeutic effectiveness of intermittent hypoxia-induced respiratory recovery in mid-cervical contused animals. However, sustained hypercapnia associated with intermittent hypoxia may blunt ventilatory responses following intermittent hypoxia at the chronic injured stage.