Inspiratory Resistive Breathing Research Articles

Acute cardiac autonomic and hemodynamic responses to resistive breathing: Effect of loading type and intensity.

This study aimed to assess the acute impact of distinct loading breathing types and intensities on cardiac autonomic function and hemodynamic responses in healthy young adults. A randomized, crossover trial involved 28 participants who underwent inspiratory resistive breathing, expiratory resistive breathing (ERB) and combined resistive breathing, each at 30% and 60% of maximal respiratory pressures. Data on heart rate variability (HRV) and hemodynamic parameters were collected during each trial. The study revealed significant main and interaction effects for both the performed task and the intensity across all measured variables (all p < 0.001). ERB at 60% load demonstrated significantly higher HRV values in the standard deviation of normal-to-normal RR intervals, the square root of the mean squared difference of successive normal-to-normal RR intervals and high-frequency power, as well as significantly lower values in heart rate, stroke volume, stroke volume index, cardiac output, cardiac index, end-diastolic volume and end-diastolic volume index, compared to other loaded protocols (all p < 0.001). These findings highlight the acute effect of type-specific and load-dependent resistive breathing on cardiac autonomic and hemodynamic functions, where ERB at 60% intensity showed the most significant cardiovagal modulation while causing the least hemodynamic alterations.

Sex differences in blood pressure and inactive limb blood flow responses during dynamic leg exercise with increased inspiratory muscle work.

We hypothesized that, compared with young males, young females have a smaller decrease in blood flow to the inactive limb, accompanied by a smaller increase in arterial blood pressure, during dynamic exercise with increased inspiratory muscle work. Young males and females performed dynamic knee-extension and -flexion exercises for 10 min (spontaneous breathing for 5 min and voluntary hyperpnoea with or without inspiratory resistance for 5 min). Mean arterial blood pressure (MAP) and mean blood flow (MBF) in the brachial artery were continuously measured by means of finger photoplethysmography and Doppler ultrasound, respectively. No sex differences were found in the ΔMAP and ΔMBF (Δ: from baseline) during exercise without inspiratory resistance. In contrast, the ΔMAP during exercise with inspiratory resistive breathing was greater (P < 0.05) in males (+31.3 ± 2.1 mmHg, mean ± SE) than females (+18.9 ± 3.2 mmHg). The MBF during exercise with inspiratory resistance did not change in males (-4.4 ± 10.6 mL/min), whereas it significantly increased in females (+25.2 ± 15.4 mL/min). These results suggest that an attenuated inspiratory muscle-induced metaboreflex in young females affects blood flow distribution during submaximal dynamic leg exercise.

Inspiratory and leg muscle blood flows during inspiratory muscle metaboreflex activation in heart failure with preserved ejection fraction.

The purpose of this study was to determine the cardiovascular consequences elicited by activation of the inspiratory muscle metaboreflex in patients with heart failure with preserved ejection fraction (HFpEF) and controls. Patients with HFpEF (n = 15; 69 ± 10 yr; 33 ± 4 kg/m2) and controls (n = 14; 70 ± 8 yr; 28 ± 4 kg/m2) performed an inspiratory loading trial at 60% maximal inspiratory pressure (PIMAX) until task failure. Mean arterial pressure (MAP) was measured continuously. Near-infrared spectroscopy and bolus injections of indocyanine green dye were used to determine the percent change in blood flow index (%ΔBFI) from baseline to the final minute of inspiratory loading in the vastus lateralis and sternocleidomastoid muscles. Vascular resistance index (VRI) was calculated. Time to task failure was shorter in HFpEF than in controls (339 ± 197 s vs. 626 ± 403 s; P = 0.02). Compared with controls, patients with HFpEF had a greater increase from baseline in MAP (16 ± 7 vs. 10 ± 6 mmHg) and vastus lateralis VRI (76 ± 45 vs. 32 ± 19%) as well as a greater decrease in vastus lateralis %ΔBFI (-32 ± 14 vs. -17 ± 9%) (all, P < 0.05). Sternocleidomastoid %ΔBFI normalized to absolute inspiratory pressure was higher in HFpEF compared with controls (8.0 ± 5.0 vs. 4.0 ± 1.9% per cmH2O·s; P = 0.03). These data indicate that patients with HFpEF exhibit exaggerated cardiovascular responses with inspiratory muscle metaboreflex activation compared with controls.NEW & NOTEWORTHY Respiratory muscle dysfunction is thought to contribute to exercise intolerance in heart failure with preserved ejection fraction (HFpEF); however, the underlying mechanisms are unknown. In the present study, patients with HFpEF had greater increases in leg muscle vascular resistance index and greater decreases in leg muscle blood flow index compared with controls during inspiratory resistive breathing (to activate the metaboreflex). Furthermore, respiratory muscle blood flow index responses normalized to pressure generation during inspiratory resistive breathing were exaggerated in HFpEF compared with controls.

Changes In Splanchnic Blood Flow And Blood Pressure During Inspiratory Resistive Breathing

PURPOSE: The hyperpnea during whole-body heavy exercise leads to an increase in respiratory muscle work, which is associated with cardiovascular regulations during exercise (i.e., respiratory muscle metaboreflex). In resting condition, blood flow to inactive limbs is reduced with inspiratory resistive breathing. Furthermore, increasing the work of breathing during dynamic exercise influences inactive limb blood flow. Therefore, it is conceivable that the respiratory muscle-induced metaboreflex is associated with blood flow redistribution during exercise. Redistribution of blood flow is also associated with splanchnic blood flow as well as inactive blood flow. However, influence of respiratory muscle metaboreflex on splanchnic blood flow in humans remains unknown. We hypothesized that blood flow to splanchnic organs would reduce via respiratory muscle-induced metaboreflex. METHODS: Ten healthy young men (20.2 ± 0.4 yrs, mean ± SE) performed two voluntary hyperventilation tests (tidal volume of 40% of vital capacity, a breathing frequency of 40 breaths/min and inspiratory duty cycle of 50%). One trial was voluntary hyperventilation with inspiratory resistance (about 40% of maximal inspiratory pressure), and the trial was terminated when the subject could not maintain the target ventilation (the resistance trial), and the other one was voluntary hyperventilation without inspiratory resistance until the same time as the resistance trial (the non-resistance trial). During trials, mean arterial blood pressure (MAP) was measured using finger photoplethysmography, and celiac artery blood flow was recorded by Doppler ultrasonography. RESULTS: MAP increased progressively and was higher (P < 0.05) in the resistance trial (100.5 ± 4.4 mmHg) than in the non-resistance trial (92.8 ± 2.0 mmHg) at the end of trial. Celiac artery blood flow decreased gradually from baseline value in the resistance trial (469.3 ± 47.6 mL/min), whereas did not change in the non-resistance trial (605.7 ± 56.2 mL/min). Celiac artery vascular conductance was lower in the resistance trial (4.8 ± 0.6 mL/min/mmHg) than in the non-resistance trial (6.6 ± 0.6 mL/min/mmHg, P < 0.05). CONCLUSIONS: These results suggest that increasing work of breathing affects the splanchnic circulation, via respiratory muscle-induced metaboreflex.

Influence of continuous inspiratory resistive breathing trials on corticospinal excitability of lower limb muscles during isometric contraction

ABSTRACT BACKGROUND Increased work of breathing or fatigue of respiratory muscles has been suggested to reduce exercise performance. PURPOSE The present study investigated the effects of continuous inspiratory resistive breathing (IRB) on the responsiveness of corticospinal pathway innervating the vastus lateralis (VL) to determine whether respiratory muscle fatigue affects the central motor output to exercising limb muscles. METHODS Eight subjects underwent a 6-min IRB trial three times (IRB1–3) in two experiments. During each IRB trial, the subjects performed voluntary hyperventilation through a mask attached with an inspiratory resistive load (approximately 30% of maximal inspiratory pressure (PImax)). In Experiment 1, PImax was measured at baseline and after each IRB trial. In Experiment 2, VL responses to transcranial magnetic stimulation (motor evoked potentials (MEPs) and cortical silent periods were assessed during 5 s isometric knee extension at an intensity of 15% of the maximal voluntary contraction over the same time course as in Experiment 1. RESULTS PImax decreased from baseline after IRB2 and IRB3 (P < 0.05). MEPs increased from baseline after IRB1 and IRB2 (P < 0.05), whereas MEPs after IRB3 were not significantly different from baseline. Cortical silent periods did not change from baseline after IRB1 and IRB2, whereas cortical silent periods after IRB3 increased from baseline (P < 0.05). CONCLUSION These results suggest that as inspiratory muscle fatigue progresses, the corticospinal tract controlling the lower limb muscles can shift from excitatory dominance to inhibitory dominance as a whole, affecting the central motor output to working limb muscles.

Abstract 10528: Exaggerated Inspiratory Muscle Metaboreflex in Heart Failure with Preserved Ejection Fraction

Introduction: Heart failure patients with preserved ejection fraction (HFpEF) may exhibit inspiratory muscle dysfunction potentially contributing to exercise intolerance. Activation of neural afferents in response to inspiratory muscle contraction (metaboreflex) elicits increases in mean arterial pressure (MAP) and leg vascular resistance (LVR) through enhanced sympathetic outflow leading to decreases in leg blood flow (LBF) in healthy humans. It is unknown if HFpEF patients exhibit exaggerated cardiovascular responses to inspiratory muscle metaboreflex activation. Hypothesis: We hypothesize that patients with HFpEF will exhibit a greater increase in MAP and LVR with a decrease in LBF during inspiratory muscle metaboreflex activation than controls. Methods: HFpEF patients (n=15, 10M/5W, 69±10 yrs; 33±4 kg/m2) and controls (n=14; 10M/4W; 70±8 yrs; 28±4 kg/m2) performed inspiratory resistive breathing tasks (IRBT) at 2% and 60% of their maximal inspiratory pressure. During the IRBTs, the breathing frequency was 20 breaths/min with a 50% duty cycle. At rest and during the IRBTs, MAP was measured by photoplethysmography, venous norepinephrine was measured, LBF was measured by near-infrared spectroscopy and indocyanine green dye injections, and LVR was calculated. Results: During the 2% IRBT, there were no differences between groups in the changes from rest in MAP (HFpEF: 2±4 vs. CTL: 3±4 mmHg) or LBF (HFpEF: 1±14 vs. CTL: 1±12%) (both, p&gt;0.05). During the 60% IRBT, venous norepinephrine increased from rest in HFpEF and controls (p&lt;0.05), while no differences existed between groups (p&gt;0.05). During the 60% IRBT, HFpEF patients, compared to controls, exhibited a greater increase from rest in MAP (HFpEF: 16±7 vs. CTL: 10±6 mmHg) and LVR (HFpEF: 76±45 vs. CTL: 32±19%) coupled with a greater decrease in LBF (HFpEF: -32±14 vs. CTL: -17±9%) (all, p&lt;0.05). Conclusions: These data indicate that patients with HFpEF exhibit exaggerated cardiovascular responses with inspiratory muscle metaboreflex activation compared to healthy individuals. These findings have important implications for the integrative physiology of exercise in HFpEF patients.

TGFβ1 Mediates Airway Remodeling Caused by Mechanical Stress during Inspiratory Resistive Breathing

Mechanical stress emerging in the airways during acute or persistent bronchoconstriction is considered to be one of the key mechanisms that may foster airway inflammation and remodeling. TGFβ1is a potent mediator of airway remodeling exerting its pro-fibrotic effect by stimulation of fibroblasts proliferation and enhanced deposition of extracellular matrix. The aim of this study was to investigate the association between airway response to inspiratory resistive breathing, TGFβ1production and severity of airway remodeling. A total of 212 subjects (mean age 47.4±1.10 years, 57% males) including 123 patients with asthma (mostly mild-to moderate) and 89 patients with COPD (GOLD stage II – 53%) were enrolled in the study. All the patients underwent a challenge test with 5-min isocapnic (5% CO2) inspiratory resistive breathing with load at 45% of maximum inspiratory pressure to induce mechanical stress in the airways. Lung function parameters including specific airway conductance (sGaw) were measured before and after the test by body plethysmography. Total TGFβ1was assayed by ELISA in exhaled breath condensate collected before and after the inspiratory resistive breathing. Wall thickness (WT) and area (WA) of the apical (b1) and posterior basal (b10) segmental bronchi were calculated automatically based on CT scans data. We found that 24% of patients responded to experimental mechanical stress by ≥20% reduction in sGaw (group I). At the same time, 18.4% of patients demonstrated ≥20% increase in sGaw after the test (group II). There was no difference in the ratio of high amplitude (≥20%) changes of sGaw between asthma and COPD. However, COPD patients more commonly had low amplitude (<20%) response as compared to asthma (66.3% vs. 51.2%, p=0.03). ΔsGaw negatively correlated with WTb1 (R=-0.16, p=0.04), WAb1 (R=-0.17, p=0.03) and WAb10 (R=-0.17, p=0.03). Group I patients had higher degree of airway remodeling than the patients in group II (WTb1 2.4 (2.1-3.1) mm vs. 2.1 (2.0-2.4) mm, p=0.02; WAb1 69.4 (63.7-75.6)% vs. 63.1 (60.4-67.7)%, p=0.01; WAb10 67.0 (56.0-71.8)% vs. 57.5 (54.9-63.6)%, p=0.03). The changes of TGFβ1level in response to mechanical stress (ΔTGFβ1) significantly correlated with ΔsGaw (R=-0.15, p=0.04). The patients from group I were predominantly characterized by increase in TGFβ1concentration after the test (ΔTGFβ1 8.6 (-13.2-29.8)%) while in group II the level of TGFβ1declined (-12.1 (-30.8-14.3)%, p=0.02). Moreover, the patients with ≥20% increase in TGFβ1after the resistive breathing had more pronounced signs of airway remodeling when compared to those with <20% TGFβ1dynamics (WTb10 2.5 (2.3-2.9) mm vs. 2.3 (2.1-2.7) mm, p=0.04; WAb10 65.7 (58.5-70.8)% vs. 60.2 (54.8-80.5)%, p=0.01). Thus, asthma and COPD patients with ≥20% drop in sGaw in response to 5-min test with inspiratory resistive breathing are more predisposed to airway remodeling. As suggested by the obtained results, this phenomenon is likely mediated by TGFβ1which production is associated both with the decrease in airway conductivity and development of the remodeling.

Effect of TRPV4 Polymorphisms on the Development of Airway Response to Increased Inspiratory Load

Alongside with inflammation, increased airway resistance is a key feature of obstructive lung diseases. The data accumulated up to date suggest that bronchoconstriction commonly observed in asthma or COPD is not only a symptom but serves as an important factor of the diseases’ pathogenesis. Mechanical deformation of the airways occurring during the episodes of bronchoconstriction or accompanying chronic airflow limitation may per se promote respiratory inflammation and remodeling, thus, forming a vicious cycle. The precise molecular mechanisms triggering the response to mechanical stress in the airways have not been established so far. In this regard, a particular attention is drawn to TRP channels – polymodal receptors sensitive to many physical and chemical stimuli including stretching and compression at cellular level. TRPV4 is a mechanosensitive channel abundantly expressed in the airway epithelium that was previously proved to participate in stretch-induced respiratory responses during mechanical ventilation. The aim of this study was to establish the effects of SNPs located in TRPV4 region on the airway response induced by inspiratory resistive breathing. The study enrolled 122 patients with asthma, 82 patients with COPD and 54 healthy subjects. All the participants underwent 5-min isocapnic (5% CO2) inspiratory resistive breathing with load at 45% of maximum inspiratory pressure. Specific airway conductance (sGaw) was measured by body plethysmography before and after the inspiratory load. Relative change (Δ) in sGaw by ≥20% was considered as a significant response. Six SNPs (rs7139451, rs11068434, rs3825394, rs3825396, rs6606743, rs3742034) were genotyped by LATE-PCR with melting analysis of molecular beacon probes. All the studied SNPs were in Hardy-Weinberg equilibrium. SNP rs3825396 located in intronic region of TRPV4 exerted significant effect on the airway response to mechanical stress. In general sample, carriers of the AG genotype had higher ΔsGaw (9.0 (-8.5-30.6)%) in comparison with the GG homozygotes (-6.4 (-20.0-11.9)%, p=0.01). This trend was evident in the subgroups of healthy subjects, asthma and COPD patients, although the difference was not significant due to reduced number of observations. Carriers of the AA genotype were absent both in our sample and in reference HapMap population. The AG genotype was found in 5.4%, 13.3% and 25.0% of subjects with ΔsGaw ≤-20%, -20%<ΔsGaw<20% and ΔsGaw ≥20%, respectively (p=0.01). The difference was even more significant when comparing only between cases with ΔsGaw ≥20% and ΔsGaw ≤-20% (p=0.007). This association retained after adjustment for sex, age and diagnosis in logistic regression model (adjusted OR 5.2 95%CI (1.3-20.6), p=0.02). We did not found significant associations with the airway response to mechanical stress for the other studied SNPs. In conclusion, we established that TRPV4 rs3825396 SNP may influence reaction of the respiratory tract to increased inspiratory load. This association seems to be independent of the presence of the obstructive airway pathology, although further verification on larger sample is required.

Mechanical Stretching of the Airways Provokes Respiratory Oxidative Stress in a Subset of Asthma and COPD Patients

Respiration is normally accompanied by repetitive stretching and relaxation of the bronchial walls. However, bronchial obstruction typically emerging in asthma and COPD significantly increases the effect of mechanical deformation on the airway epithelial lining causing mechanical stress. Obstructive lung pathology is also usually characterized by chronic airway inflammation and ROS production. Oxidative stress arising during the natural course of asthma and COPD has multiple effects on the progression of these diseases due to aggravated synthesis of pro-inflammatory mediators, mucus hypersecretion, increased permeability of the epithelial barrier and fibrosis. The aim of this study was to investigate the effect of experimentally induced mechanical stress in the airways on the production of 8-isoprostane, a marker of oxidative stress, in asthma and COPD patients. The study included 75 asthma patients and 42 COPD patients with mean age of 47.0±1.47 years. Mechanical stress was induced during the test with 5-min isocapnic (5% CO2) inspiratory resistive breathing with load at 45% of maximum inspiratory pressure. Lung function was measured by standard spirometry and body plethysmography just before and after the test. We accepted the changes (Δ) of FEV1 ≥ 10% and sGaw ≥ 20% as indicative for significant airway response. 8-isoprostane level was quantified by ELISA in exhaled breath condensate collected during 15 min before and after the experimental mechanical stress. The airway responses measured by spirometry and body plethysmography were not concordant: 14% were considered significant only by ΔFEV1 while 36% were significant solely according to ΔsGaw. Besides, there was no correlation between ΔFEV1 and ΔsGaw. The studied patients with ΔsGaw ≥20% or ≤-20% did not differ in baseline (18.0 (13.2-26.4) pg/ml vs. 18.8 (11.9-24.2) pg/ml, respectively, p=0.87) and post-test (18.2 (11.4-22.4) pg/ml vs. 19.6 (15.1-26.7) pg/ml, respectively, p=0.31) concentrations of 8-isoprostane. However, the difference in the relative change of 8-isoprostane level (Δ8-iso) was significant between the groups (-18.7 (-31.7-3.64)% vs. 8.5 (-11.6-30.0)%, p=0.02). In general, the patients with increase in sGaw ≥20% had decrease in 8-isoprostane level. On the contrary, in the patients with significant reduction of sGaw the production of 8-isoprostane was rather elevated in response to the mechanical stress. Increase in 8-isoprostane by ≥20% was observed in 45.5% of patients with ΔsGaw ≤-20%, in 32.8% of patients with low amplitude response (-20%≤ΔsGaw≤20%) and only in 13.8% of patients with ΔsGaw ≥20% (p=0.04). In addition, Δ8-iso was negatively correlated with ΔsGaw (R=-0.18, p=0.05). No significant associations were observed between 8-isoprostane levels and ΔFEV1. In summary, we established that about 30% of asthma and COPD patients respond to inspiratory resisting breathing with significant increase of 8-isoprostane level. This reaction is most common in patients with reduction of airway conductance (sGaw) after the test but not dependent on ΔFEV1.

Methodology and reliability of respiratory muscle assessment

The optimal method for respiratory muscle endurance (RME) assessment remains unclear. This study assessed the test-retest reliability of two RME-test methodologies. Fifteen healthy adults attended the laboratory on four occasions, separated by 5 ± 2 days, and completed each test in a random, “one on two” order. They performed spirometry testing, maximal respiratory pressure assessment and two different RME tests: an inspiratory resistive breathing (IRB) and an isocapnic hyperpnea endurance (IHE) test. Typical error, expressed as coefficient of variation, for IRB maximal inspiratory pressure (MIP) and IHE maximal ventilation were 12.21 (8.85–19.67) % and 10.73 (7.78–17.29) %, respectively. Intraclass correlation coefficients for the same parameters were 0.83 (0.46-0.94) and 0.80 (0.41-0.93), respectively. No correlations were found between RME parameters derived from the IHE and IRB tests (all p > 0.05). Significant positive correlations were found between both IRB and IHE outcomes and spirometry parameters, MIP and maximal expiratory pressure (p < 0.05).Given these results, IRB and IHE appear to be suitable for RME testing in healthy people, although they may reflect different physiological mechanisms (respiratory mechanics and respiratory muscle capacity for IHE test vs. inspiratory muscle capacity for IRB test). Future studies are therefore warranted that compare IRB and IHE tests in clinical settings.

P38 Inhibition Ameliorates Inspiratory Resistive Breathing-Induced Pulmonary Inflammation.

Inspiratory resistive breathing (IRB), a hallmark of obstructive airway diseases, is associated with strenuous contractions of the inspiratory muscles and increased negative intrathoracic pressures that act as an injurious stimulus to the lung. We have shown that IRB induces pulmonary inflammation in healthy animals. p38 kinase is activated in the lung under stress. We hypothesized that p38 is activated during IRB and contributes to IRB-induced pulmonary inflammation. Anesthetized, tracheostomized rats breathed spontaneously through a two-way valve. Resistance was connected to the inspiratory port to provoke a peak tidal inspiratory pressure 50% of maximum. Following 3 and 6h of IRB, respiratory system mechanics were measured and bronchoalveolar lavage (BAL) was performed. Phosphorylated p38, TNF-α, and MIP-2α were detected in lung tissue. Lung injury was estimated histologically. SB203580 (p38 inhibitor) was administered prior to IRB (1mgkg-1). Six hours of IRB increased phosphorylated p38 in the lung, compared with quietly breathing controls (p = 0.001). Six hours of IRB increased the numbers of macrophages and neutrophils (p = 0.01 and p = 0.005) in BAL fluid. BAL protein levels and lung elasticity increased after both 3 and 6h IRB. TNF-α and MIP-2α increased after 6h of IRB (p = 0.01 and p < 0.001, respectively). Increased lung injury score was detected at 6h IRB. SB203580 administration blocked the increase of neutrophils and macrophages at 6h IRB (p = 0.01 and p = 0.005 to 6h IRB) but not the increase in BAL protein and elasticity. TNF-α, MIP-2α, and injury score at 6h IRB returned to control. p38 activation contributes to IRB-induced pulmonary inflammation.

Blunted Sympathetic Vasomotor Outflow To Inspiratory Resistive Breathing During Exercise In Women Compared to Men

It has been reported that in young men high inspiratory muscle work at rest and during exercise reflexively increases muscle sympathetic nerve activity (MSNA), with corresponding increases in arterial blood pressure (ABP). This sympathoexcitation occurs through an inspiratory muscle-induced metaboreflex. Young women have attenuated inspiratory muscle metaboreflex-induced increases in ABP compared to age-matched men. One potential mechanism is less sympathetic vasomotor output in women compared to men. PURPOSE: We compared changes in MSNA and cardiovascular variables during leg cycle exercise with increased inspiratory muscle resistance in men and women. METHODS: Eight young women (19.5±0.2) and seven men (20.3±0.3) completed the study. The subjects performed two 10-min submaximal cycle ergometer exercises in a semirecumbent position. The first 5-min was spontaneous breathing, and latter 5-min half was voluntary hyperventilation with or without inspiratory resistive breathing. Mean arterial blood pressure (MAP) was measured using finger photoplethysmography and MSNA was recorded via microneurography of the arm at the elbow. RESULTS: During exercise with inspiratory resistive breathing, MSNA burst frequency was significantly increased accompanied by an increase (p<0.05) in MAP in both men and women. Women had significantly less of an increase in MSNA (Women: +9.6±1.0 vs. Men: +14.6±2.4 bursts/min) and MAP (Women: +22.8±5.7 vs. Men: +32.2±2.0 mmHg) as compared to men. CONCLUSION: These results suggest that lesser sympathetic vasomotor outflow partially contributes the attenuated inspiratory muscle-induced metaboreflex during exercise in young women. Supported by JSPS KAKENHI Grant Number 15H3079.

Elevated sympathetic vasomotor outflow in response to increased inspiratory muscle activity during exercise is less in young women compared with men.

What is the central question of this study? Premenopausal women have an attenuated inspiratory muscle metaboreflex-induced increase in arterial blood pressure compared with men. It is unclear whether sympathetic vasomotor outflow during dynamic exercise with increased inspiratory muscle activation is less in young women than in men. What is the main finding and its importance? The magnitude of increased sympathetic vasomotor outflow during leg cycling with inspiratory resistance was smaller in women than in men. Less sympathetic vasomotor outflow with inspiratory muscle metaboreflex activation could be one of the mechanisms for the attenuated inspiratory muscle-induced metaboreflex during exercise in young women. We compared changes in muscle sympathetic nerve activity (MSNA) and cardiovascular variables during leg cycle exercise with increased inspiratory muscle resistance in men and women. We hypothesized that sympathetic vasomotor outflow during exercise with increased inspiratory resistance would be attenuated in young women compared with age-matched men. Eight women and seven men completed the study. The subjects performed two 10min exercise bouts at 40% peak oxygen uptake using a cycle ergometer in a semirecumbent position [spontaneous breathing for 5min and voluntary hyperventilation with or without inspiratory resistive breathing for 5min (breathing frequency 50breathsmin-1 with a 50% duty cycle; inspiratory resistance 30% of maximal inspiratory pressure)]. Mean arterial blood pressure (MAP) was acquired using finger photoplethysmography. The MSNA was recorded via microneurography of the right median nerve at the cubital fossa. During leg cycle exercise with inspiratory resistive breathing, MSNA burst frequency was increased, accompanied by an increase in MAP in both men and women. Women, compared with men, had less of an increase in MAP (women +22.8±12.3mmHg versus men +32.2±5.4mmHg; P<0.05) and MSNA burst frequency (women +9.6±2.9burstsmin-1 versus men +14.6±6.4burstsmin-1 ; P<0.05). These results suggest that the attenuated inspiratory muscle-induced metaboreflex during exercise in young women is attributable, in part, to a lesser sympathetic vasomotor outflow compared with men.

The role of Src & ERK1/2 kinases in inspiratory resistive breathing induced acute lung injury and inflammation

BackgroundInspiratory resistive breathing (IRB), a hallmark of obstructive airway diseases, is associated with large negative intrathoracic pressures, due to strenuous contractions of the inspiratory muscles. IRB is shown to induce lung injury in previously healthy animals. Src is a multifunctional kinase that is activated in the lung by mechanical stress. ERK1/2 kinase is a downstream target of Src. We hypothesized that Src is activated in the lung during IRB, mediates ERK1/2 activation and IRB-induced lung injury.MethodsAnaesthetized, tracheostomized adult rats breathed spontaneously through a 2-way non-rebreathing valve. Resistance was added to the inspiratory port to provide a peak tidal inspiratory pressure of 50% of maximum (inspiratory resistive breathing). Activation of Src and ERK1/2 in the lung was estimated during IRB. Following 6 h of IRB, respiratory system mechanics were measured by the forced oscillation technique and bronchoalveolar lavage (BAL) was performed to measure total and differential cell count and total protein levels. IL-1b and MIP-2a protein levels were measured in lung tissue samples. Wet lung weight to total body weight was measured and Evans blue dye extravasation was estimated to measure lung permeability. Lung injury was evaluated by histology. The Src inhibitor, PP-2 or the inhibitor of ERK1/2 activation, PD98059 was administrated 30 min prior to IRB.ResultsSrc kinase was activated 30 min after the initiation of IRB. Src inhibition ameliorated the increase in BAL cellularity after 6 h IRB, but not the increase of IL-1β and MIP-2a in the lung. The increase in BAL total protein and lung injury score were not affected. The increase in tissue elasticity was partly inhibited. Src inhibition blocked ERK1/2 activation at 3 but not at 6 h of IRB. ERK1/2 inhibition ameliorated the increase in BAL cellularity after 6 h of IRB, blocked the increase of IL-1β and returned Evans blue extravasation and wet lung weight to control values. BAL total protein and the increase in elasticity were partially affected. ERK1/2 inhibition did not significantly change total lung injury score compared to 6 h IRB.ConclusionsSrc and ERK1/2 are activated in the lung following IRB and participate in IRB-induced lung injury.

Tiotropium bromide exerts anti-inflammatory effects during resistive breathing, an experimental model of severe airway obstruction.

IntroductionResistive breathing (RB), a hallmark of obstructive airway diseases, is characterized by strenuous contractions of the inspiratory muscles that impose increased mechanical stress on the lung. RB is shown to induce pulmonary inflammation in previous healthy animals. Tiotropium bromide, an anticholinergic bronchodilator, is also shown to exert anti-inflammatory effects. The effect of tiotropium on RB-induced pulmonary inflammation is unknown.MethodsAdult rats were anesthetized, tracheostomized and breathed spontaneously through a two-way non-rebreathing valve. Resistances were connected to the inspiratory and/or expiratory port, to produce inspiratory resistive breathing (IRB) of 40% or 50% Pi/Pi,max (40% and 50% IRB), expiratory resistive breathing (ERB) of 60% Pe/Pe,max (60% ERB) or combined resistive breathing (CRB) of both 40% Pi/Pi,max and 60% Pe/Pe,max (40%/60% CRB). Tiotropium aerosol was inhaled prior to RB. After 6 h of RB, mechanical parameters of the respiratory system were measured and bronchoalveolar lavage (BAL) was performed. IL-1β and IL-6 protein levels were measured in lung tissue. Lung injury was estimated histologically.ResultsIn all, 40% and 50% IRB increased macrophage and neutrophil counts in BAL and raised IL-1β and IL-6 lung levels, tissue elasticity, BAL total protein levels and lung injury score. Tiotropium attenuated BAL neutrophil number, IL-1β, IL-6 levels and lung injury score increase at both 40% and 50% IRB. The increase in macrophage count and protein in BAL was only reversed at 40% IRB, while tissue elasticity was not affected. In all, 60% ERB raised BAL neutrophil count and total protein and reduced macrophage count. IL-1β and IL-6 levels and lung injury score were increased. Tiotropium attenuated these alterations, except for the decrease in macrophage count and the increase in total protein level. In all, 40%/60% CRB increased macrophage and neutrophil count in BAL, IL-1β and IL-6 levels, tissue elasticity, total protein in BAL and histological injury score. Tiotropium attenuated the aforementioned alterations.ConclusionTiotropium inhalation attenuates RB-induced pulmonary inflammation.

Effect of cyclooxygenase inhibition on the inspiratory muscle metaboreflex-induced cardiovascular consequences in men.

Inspiratory muscle metaboreflex activation increases mean arterial pressure (MAP) and limb vascular resistance (LVR) and decreases limb blood flow (Q̇L). Cyclooxygenase (COX) inhibition has been found to attenuate limb skeletal muscle metaboreflex-induced increases in muscle sympathetic nerve activity. We hypothesized that compared with placebo (PLA), COX inhibition would attenuate inspiratory muscle metaboreflex-induced 1) increases in MAP and LVR and 2) decreases in Q̇L Seven men (22 ± 1 yr) were recruited and orally consumed ibuprofen (IB; 10 mg/kg) or PLA 90 min before performing the cold pressor test (CPT) for 2 min and inspiratory resistive breathing task (IRBT) for 14.9 ± 2.0 min at 65% of maximal inspiratory pressure. Breathing frequency was 20 breaths/min with a 50% duty cycle during the IRBTs. MAP was measured via automated oscillometry, Q̇L was determined via Doppler ultrasound, and LVR was calculated as MAP divided by Q̇L Electromyography was recorded on the leg to ensure no muscle contraction occurred. The 65% IRBT led to greater increases (P = 0.02) in 6-keto-prostaglandin-F1α with PLA compared with IB. IB, compared with PLA, led to greater (P < 0.01) increases in MAP (IB: 17 ± 7 mmHg vs. PLA: 8 ± 5 mmHg) and LVR (IB: 69 ± 28% vs. PLA: 52 ± 22%) at the final minute of the 65% IRBT. The decrease in Q̇L was not different (P = 0.72) between IB (-28 ± 11%) and PLA (-27 ± 9%) at the final minute. The increase in MAP during the CPT was not different (P = 0.87) between IB (25 ± 11 mmHg) and PLA (24 ± 6 mmHg). Contrary to our hypotheses, COX inhibition led to greater inspiratory muscle metaboreflex-induced increases in MAP and LVR.NEW & NOTEWORTHY Cyclooxygenase (COX) products play a role in activating the muscle metaboreflex. It is not known whether COX products contribute to the inspiratory muscle metaboreflex. Herein, we demonstrate that COX inhibition led to greater increases in blood pressure and limb vascular resistance compared with placebo during inspiratory muscle metaboreflex activation.

Effect of Age on Sex Differences in the Inspiratory Muscle Metaboreflex

Sex differences exist in the cardiovascular consequences of the inspiratory muscle metaboreflex in young adults. However, it is unknown if these sex differences are present in older adults. PURPOSE: To determine the effect of age on sex differences in the cardiovascular consequences of the inspiratory muscle metaboreflex. We hypothesized that, compared to their younger counterparts, older men and women would exhibit greater 1) increases in mean arterial pressure (MAP) and limb vascular resistance (LVR) and 2) decreases in limb blood flow (QL). We also hypothesized that the inspiratory muscle metaboreflex-induced cardiovascular responses would not be different between older men and women. METHODS: Sixteen young (8 men, 8 women; 18-24 yr) and older (8 men, 8 women; 60-73 yr) adults were recruited for this study. Subjects performed inspiratory resistive breathing tasks (IRBTs) at 2% and 65% of their maximal inspiratory pressure. During the IRBTs, breathing frequency was 20 breaths min-1 with a 50% duty cycle. At rest and during the IRBTs, MAP was measured via automated oscillometry, QL was measured via Doppler ultrasound, and LVR was calculated. End tidal CO2 remained at baseline levels during the IRBTs. EMG was recorded on the leg to ensure no muscle contraction occurred. RESULTS: The 65% IRBT led to significantly greater increases in MAP from baseline in OW (15.9±8.1 mmHg) compared to YW (6.9±1.4 mmHg), but not (p>0.05) between OM (12.3±5.7 mmHg) and YM (10.8±5.7 mmHg). OW (-20.2±7.2 %) had greater (p<0.05) decreases in QL from baseline compared to YW (-9.4±10.2 %), but no differences (p>0.05) were present between OM (-22.8±9.7 %) and YM (-22.7±11.3 %) during the 65% IRBT. The 65% IRBT led to greater (p<0.05) increases in LVR in OW (48.2±25.5 %) compared to YW (19.7±15.0 %), but no differences (p>0.05) existed among OM (54.4±17.8 %) and YM (47.1±23.3 %). No differences (p>0.05) were present in MAP, QL, or LVR between OM and OW. The 2% IRBT resulted in no changes (p>0.05) in MAP, QL, or LVR across time or among groups. CONCLUSIONS: These data suggest older women compared to younger women exhibit greater inspiratory muscle metaboreflex-induced cardiovascular consequences, while there were no differences between older and younger men. Lastly, sex differences in the inspiratory muscle metaboreflex are not present in older adults.

Cardiovascular consequences of the inspiratory muscle metaboreflex: effects of age and sex.

With inspiratory muscle metaboreflex activation, we hypothesized that, compared with their younger counterparts, older men and women would exhibit greater 1) increases in mean arterial pressure (MAP) and limb vascular resistance (LVR) and 2) decreases in limb blood flow (Q̇L) but 3) no sex differences would be present in older adults. Sixteen young adults [8 young men (YM) and 8 young women (YW), 18-24 yr] and 16 older adults [8 older men (OM) and 8 older women (OW), 60-73 yr] performed inspiratory resistive breathing tasks (IRBTs) at 2% and 65% of their maximal inspiratory pressure. During the IRBTs, breathing frequency was 20 breaths/min with a 50% duty cycle. At baseline and during the IRBTs, MAP was measured via automated oscillometry, Q̇L was determined via Doppler ultrasound, and LVR was calculated. The 65% IRBT led to significantly greater increases in MAP in OW (15.9 ± 8.1 mmHg) compared with YW (6.9 ± 1.4 mmHg) but not (P > 0.05) between OM (12.3 ± 5.7 mmHg) and YM (10.8 ± 5.7 mmHg). OW (-20.2 ± 7.2%) had greater (P < 0.05) decreases in Q̇L compared with YW (-9.4 ± 10.2%), but no significant differences were present between OM (-22.8 ± 9.7%) and YM (-22.7 ± 11.3%) during the 65% IRBT. The 65% IRBT led to greater (P < 0.05) increases in LVR in OW (48.2 ± 25.5%) compared with YW (19.7 ± 15.0%), but no differences (P > 0.05) existed among OM (54.4 ± 17.8%) and YM (47.1 ± 23.3%). No significant differences were present in MAP, Q̇L, or LVR between OM and OW. These data suggest that OW exhibit a greater inspiratory muscle metaboreflex compared with YW, whereas no differences between OM and YM existed. Finally, sex differences in the inspiratory muscle metaboreflex are not present in older adults.NEW & NOTEWORTHY Premenopausal women exhibit an attenuated inspiratory muscle metaboreflex compared with young men; however, it is unknown whether these sex differences are present in older adults. Older women exhibited a greater inspiratory muscle metaboreflex compared with premenopausal women, whereas no differences were present between older and younger men.

Sex differences in the cardiovascular consequences of the inspiratory muscle metaboreflex.

It is currently unknown whether sex differences exist in the cardiovascular consequences of the inspiratory muscle metaboreflex. We hypothesized that the activation of the inspiratory muscle metaboreflex will lead to less of an increase in mean arterial pressure (MAP) and limb vascular resistance (LVR) and less of a decrease in limb blood flow (Q̇L) in women compared with men. Twenty healthy men (n = 10, 23 ± 2 yr) and women (n = 10, 22 ± 3 yr) were recruited for this study. Subjects performed inspiratory resistive breathing tasks (IRBTs) at 2% or 65% of their maximal inspiratory mouth pressure (PIMAX). During the IRBTs, the breathing frequency was 20 breaths/min with a 50% duty cycle. At rest and during the IRBTs, MAP was measured via automated oscillometry, Q̇L was measured via Doppler ultrasound, and LVR was calculated. EMG was recorded on the leg to ensure no muscle contraction occurred. The 65% IRBT led to attenuated increases (P < 0.01) from baseline in women compared with men for MAP (W: 7.3 ± 2.0 mmHg; M: 11.1 ± 5.0 mmHg) and LVR (W: 17.7% ± 14.0%; M: 47.9 ± 21.0%), as well as less of a decrease (P < 0.01) in Q̇L (W: -7.5 ± 9.9%; M: -23.3 ± 10.2%). These sex differences in MAP, Q̇L, and LVR were still present in a subset of subjects matched for PIMAX The 2% IRBT resulted in no significant changes in MAP, Q̇L, or LVR across time or between men and women. These data indicate premenopausal women exhibit an attenuated inspiratory muscle metaboreflex compared with age-matched men.

The differential effects of inspiratory, expiratory, and combined resistive breathing on healthy lung.

Combined resistive breathing (CRB) is the hallmark of obstructive airway disease pathophysiology. We have previously shown that severe inspiratory resistive breathing (IRB) induces acute lung injury in healthy rats. The role of expiratory resistance is unknown. The possibility of a load-dependent type of resistive breathing-induced lung injury also remains elusive. Our aim was to investigate the differential effects of IRB, expiratory resistive breathing (ERB), and CRB on healthy rat lung and establish the lowest loads required to induce injury. Anesthetized tracheostomized rats breathed through a two-way valve. Varying resistances were connected to the inspiratory, expiratory, or both ports, so that the peak inspiratory pressure (IRB) was 20%–40% or peak expiratory (ERB) was 40%–70% of maximum. CRB was assessed in inspiratory/expiratory pressures of 30%/50%, 40%/50%, and 40%/60% of maximum. Quietly breathing animals served as controls. At 6 hours, respiratory system mechanics were measured, and bronchoalveolar lavage was performed for measurement of cell and protein concentration. Lung tissue interleukin-6 and interleukin-1β levels were estimated, and a lung injury histological score was determined. ERB produced significant, load-independent neutrophilia, without mechanical or permeability derangements. IRB 30% was the lowest inspiratory load that provoked lung injury. CRB increased tissue elasticity, bronchoalveolar lavage total cell, macrophage and neutrophil counts, protein and cytokine levels, and lung injury score in a dose-dependent manner. In conclusion, CRB load dependently deranges mechanics, increases permeability, and induces inflammation in healthy rats. ERB is a putative inflammatory stimulus for the lung.