Influence of an inspiratory muscle fatigue protocol on healthy youths on respiratory muscle strength, vertical jump performance and muscle oxygen saturation: a randomized controlled trial.

BACKGROUND: Inspiratory muscle fatigue has been shown to have effects on limbs blood flow and physical performance. This study aimed to evaluate the influence of an inspiratory muscle fatigue protocol on respiratory muscle strength, vertical jump performance and muscle oxygen saturation in healthy youths. METHODS: A randomized and double-blinded controlled clinical trial, was conducted. Twenty-four participants aged 18-45 years, non-smokers and engaged in sports activity at least three times a week for a minimum of one year were enrolled in this investigation. Participants were randomly assigned to three groups: Inspiratory Muscle Fatigue (IMFG), Activation, and Control. Measurements of vertical jump, diaphragmatic ultrasound, muscle oxygen saturation, and maximum inspiratory pressure were taken at two stages: before the intervention (T1) and immediately after treatment (T2). RESULTS: The IMFG showed lower scores in muscle oxygen saturation and cardiorespiratory variables after undergoing the diaphragmatic fatigue intervention compared to the activation and control groups (p < 0.05). For the vertical jump variables, intragroup differences were found (p < 0.01), but no differences were shown between the three groups (p > 0.05). CONCLUSIONS: Inspiratory muscle fatigue appears to negatively impact vertical jump performance, muscle oxygen saturation and inspiratory muscle strength in healthy youths. TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT06271876. Date of registration 02/21/2024. https://clinicaltrials.gov/study/NCT06271876 .

Area under the inspiratory flow-volume curve (AIN): Proposed normative values.

RATIONALE: Area under expiratory flow-volume curve (AEX) has been shown to be a valuable functional measurement in respiratory physiology. Area under inspiratory flow-volume loop (AIN) also shows promise in characterizing upper and/or lower airflow obstruction. OBJECTIVES: we aimed here to develop normative reference values for AIN, able to ascertain deviations from normal. METHODS: We analyzed AIN in 4,980 spirometry tests recorded in non-smoking, healthy individuals in the Pulmonary Function Testing Laboratory. RESULTS: The mean (95% confidence interval, CI), standard deviation and median (25th-75th interquartile range) AIN were 16.05 (15.79-16.31), 9.08 and 14.72 (9.12-21.42) L2·sec-1, respectively. The mean (95% CI) and standard deviation of the best-trial measurements for square root of AIN (Sqrt AIN) were 3.84 (3.81-3.87) and 1.14; 4.15 (4.12-4.18) and 1.03 in men, and 2.68 (2.63-2.72) and 0.72 L·sec-1/2 in women. The mean (standard deviation) of pre- and post-bronchodilator Sqrt AIN were 3.71 (1.17) and 3.81 (1.19) L·sec-1/2, respectively. The mean (95% CI), standard deviation and lowest 5th percentile (lower limit of normal, LLN) of Sqrt AIN/Sqrt AEX (%) were 101.3 (100.82-101.88), 18.7, and 71.8%; stratified by gender, it was 102.2 (101.6-102.8), 18.6, and 72.8% in men, and 98 (96.9-99.2), 18.8, and 68.6% in women, respectively. CONCLUSIONS: The availability of area under the inspiratory flow-volume curve (AIN) and the derived indices offers a promising opportunity to assess upper airway disease (e.g., involvement of larynx, trachea or major bronchi), especially because some of these measurements appear to be independent of age, race, height, and weight.

Clinical characteristics of chronic obstructive pulmonary disease patients with superoptimal peak inspiratory flow rate.

Characteristics of chronic obstructive pulmonary disease (COPD) patients with superoptimal peak inspiratory flow rates (PIFR) has not been thoroughly investigated. This study aimed to compare the characteristics between COPD patients with superoptimal PIFR and those with optimal and sub-optimal PIFR. PIFR was measured using In-Check DIAL G16 and categorized into sub-optimal (PIFR lower than that required by the patient's device), optimal, and superoptimal (peak PIFR ≥ 90 L/min). Considering COPD patients with sub-optimal PIFR as the reference group, analyses were performed to identify PIFR-related factors. Subgroup analysis was performed according to the forced expiratory volume in 1 s (FEV1) % of the predicted value (%pred). Among 444 post-bronchodilator-confirmed COPD patients from seven tertiary hospitals in South Korea, 98, 223, and 123 were classified into the sub-optimal, optimal, and superoptimal PIFR groups, respectively. The superoptimal PIFR group were younger, had an increased proportion of males, a higher body mass index, lowest number of comorbidities and less frequent exacerbation in the previous year, as well as the highest forced vital capacity %pred. The adjusted odds ratio for frequent exacerbation in the previous year was lower in the superoptimal PIFR group than in the sub-optimal PIFR group and was more pronounced in patients with an FEV1%pred of < 70%. COPD patients with superoptimal PIFR have clinical characteristics different from those patients with the sub-optimal and optimal PIFR. Having a high inspiratory flow may be a favorable trait in COPD.

Effect of inspiratory muscle training in esophageal cancer patients receiving esophagectomy: A meta-analysis of randomized controlled trials.

PURPOSE: To identify the clinical effect of inspiratory muscle training (IMT) among esophageal cancer patients undergoing esophagectomy based on randomized controlled trials (RCTs). METHODS: Several databases were searched for relevant RCTs up to August 23, 2023. Primary outcomes were respiratory muscle function, including the maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP), and pulmonary function, including the forced expiratory volume in one second % (FEV1%), forced vital capacity% (FVC%), maximal ventilator volume (MVV), FEV1/FVC% and FVC. The secondary outcomes were exercise performance, including the six-minute walk distance test (6MWT) and Borg index; mental function and quality of life, as evaluated by the Hospital Anxiety Depression Scale (HADS) and Nottingham Health Profile (NHP) score; and postoperative complications. All the statistical analyses were performed with REVMAN 5.3 software. RESULTS: Eight RCTs were included in this meta-analysis, with 368 patients receiving IMT and 371 control subjects. The pooled results demonstrated that IMT could significantly enhance respiratory muscle function (MIP: MD = 7.14 cmH2O, P = 0.006; MEP: MD = 8.15 cmH2O, P<0.001) and pulmonary function (FEV1%: MD = 6.15%, P<0.001; FVC%: MD = 4.65%, P<0.001; MVV: MD = 8.66 L, P<0.001; FEV1/FVC%: MD = 5.27%, P = 0.03; FVC: MD = 0.50 L, P<0.001). Furthermore, IMT improved exercise performance (6MWT: MD = 66.99 m, P = 0.02; Borg index: MD = -1.09, P<0.001), mental function and quality of life (HADS anxiety score: MD = -2.26, P<0.001; HADS depression score: MD = -1.34, P<0.001; NHP total score: MD = -48.76, P<0.001). However, IMT did not significantly decrease the incidence of postoperative complications. CONCLUSION: IMT improves clinical outcomes, such as respiratory muscle function and pulmonary function, in esophageal cancer patients receiving esophagectomy and has potential for broad applications in the clinic.

Influence of Sensory Monitoring on Speech Breathing Planning Processes: An Exploratory Study in Aging Speakers Reporting Dyspnea.

PURPOSE: Previous studies have suggested that inspirations during speech pauses are influenced by the length of adjacent utterances, owing to respiratory motor planning and physiological recovery processes. The goal of this study was to examine how attention to respiratory sensations may influence these processes in aging speakers with dyspnea, by measuring the effect of sensory monitoring on the relationship between utterance length and the occurrence of inspirations, as well as on functional voice and respiratory measures. METHOD: Seventeen adults aged 50 years and older with complaints of voicing-related dyspnea completed a repeated-measures protocol consisting of a 2-week baseline phase and a 4-week sensory monitoring phase. Audiovisual recordings of semistructured speech and self-report questionnaires were collected at study onset, after the baseline phase, and after the sensory monitoring phase. Repeated-measures logistic regressions were conducted to examine changes in the relationship between utterance length and the occurrence of inspirations in adjacent pauses, and repeated-measures analyses of variance were used to investigate any changes in functional voice and respiratory measures. RESULTS: Planning and recovery processes appeared to remain constant across the baseline phase. From postbaseline to postsensory monitoring timepoints, a strengthening of the relationship between the presence of an inspiration during a speech pause and the length of the subsequent-but not preceding-utterance was noted. Significant improvements were noted in voice-related handicap from study onset to postsensory monitoring, but no changes were reported in respiratory comfort during speech. CONCLUSIONS: Results suggest that respiratory planning processes, that is, the ability to plan breath intakes based on the length of upcoming utterances, may be modifiable behaviorally through targeted sensory monitoring. Further studies are warranted to validate the proposed role of respiratory sensation awareness in achieving skilled temporal coordination between voicing and breathing.

Orexin receptor 2 agonist activates diaphragm and genioglossus muscle through stimulating inspiratory neurons in the pre-Bötzinger complex, and phrenic and hypoglossal motoneurons in rodents.

Orexin-mediated stimulation of orexin receptors 1/2 (OX[1/2]R) may stimulate the diaphragm and genioglossus muscle via activation of inspiratory neurons in the pre-Bötzinger complex, which are critical for the generation of inspiratory rhythm, and phrenic and hypoglossal motoneurons. Herein, we assessed the effects of OX2R-selective agonists TAK-925 (danavorexton) and OX-201 on respiratory function. In in vitro electrophysiologic analyses using rat medullary slices, danavorexton and OX-201 showed tendency and significant effect, respectively, in increasing the frequency of inspiratory synaptic currents of inspiratory neurons in the pre-Bötzinger complex. In rat medullary slices, both danavorexton and OX-201 significantly increased the frequency of inspiratory synaptic currents of hypoglossal motoneurons. Danavorexton and OX-201 also showed significant effect and tendency, respectively, in increasing the frequency of burst activity recorded from the cervical (C3-C5) ventral root, which contains axons of phrenic motoneurons, in in vitro electrophysiologic analyses from rat isolated brainstem-spinal cord preparations. Electromyogram recordings revealed that intravenous administration of OX-201 increased burst frequency of the diaphragm and burst amplitude of the genioglossus muscle in isoflurane- and urethane-anesthetized rats, respectively. In whole-body plethysmography analyses, oral administration of OX-201 increased respiratory activity in free-moving mice. Overall, these results suggest that OX2R-selective agonists enhance respiratory function via activation of the diaphragm and genioglossus muscle through stimulation of inspiratory neurons in the pre-Bötzinger complex, and phrenic and hypoglossal motoneurons. OX2R-selective agonists could be promising drugs for various conditions with respiratory dysfunction.

The impact of deep-inspiration breath-hold total-body PET/CT imaging on thoracic 18F-FDG avid lesions compared with free-breathing.

OBJECTIVES: To investigate PET/CT registration and quantification accuracy of thoracic lesions of a single 30-second deep-inspiration breath-hold (DIBH) technique with a total-body PET (TB-PET) scanner, and compared with free-breathing (FB) PET/CT. METHODS: 137 of the 145 prospectively enrolled patients finished a routine FB-300 s PET/CT exam and a 30-second DIBH TB-PET with chest to pelvis low dose CT. The total-body FB-300 s, FB-30 s, and DIBH-30 s PET images were reconstructed. Quantitative assessment (SUVmax and SUVmean of lung and other organs), PET/CT registration assessment and lesion analysis (SUVmax, SUVpeak, SUVmean and tumor-background ratio) were compared with Wilcoxon signed-rank tests. RESULTS: The SUVmax and SUVmean of the lung with DIBH-30 s were significantly lower than those with FB. The distances of the liver dome between PET and CT were significantly smaller with DIBH-30 s than with FB. 195 assessable lesions in 106 patients were included, and the detection sensitivity was 97.9 % and 99.0 % in FB-300 s, and DIBH-30 s, respectively. For both small co-identified lesions (n = 86) and larger co-identified lesions with a diameter ≥ 1 cm (n = 91), the lesion SUVs were significantly greater with DIBH-30 s than with FB-300 s. Regarding lesion location, the differences of the SUVs for the lesions in the lower thorax area (n = 97, p < 0.001) were significant between DIBH-30 s and FB-300 s, while these differences were not statistically significant in the upper thorax (n = 80, p > 0.05). The lesion tumor-to-surrounding-background ratio (TsBR) was significantly increased, both in the upper and lower thorax. CONCLUSION: The TB DIBH PET/CT technique is feasible in clinical practice. It reduces the background lung uptake and achieves better registration and lesion quantification, especially in the lower thorax.

Is There a Direct Effect Between the Plication of the Myoaponeurotic Layer and the Force of Inspiratory and Expiratory Muscles After Abdominoplasty?

OBJECTIVE: Abdominoplasty may generate an increase in the intra-abdominal pressure (IAP) and consequently an alteration in the pulmonary ventilation. The purpose of this study was to evaluate the potential alterations in the maximal static inspiratory pressure (MIP) and maximal static expiratory pressure (MEP) after abdominoplasty. METHODS: Thirty-three female patients, aged between 18 and 60, with type III/B Nahas abdominal deformity that underwent abdominoplasty with plication of the anterior rectus and external oblique aponeurosis were selected. The MIP and MEP were measured using a mouthpiece. This is a simple way to indirectly gauge inspiratory and expiratory muscle strength. Measurements were performed before surgery and on the 2nd, 7th, 15th, and 180th postoperative day. In addition, IAP was measured before abdominoplasty and after the placement of compression garment. The MIP and MEP were compared using analysis of variance, followed by the Bonferroni multiple comparison test pairing the different points in time. Paired Student's t test was used for comparing IAP measurements. Pearson's correlation test was used to compare MIP and MEP variations with IAP variation. Results were considered statistically significant when P ≤ 0.05. RESULTS: A decrease was observed in MEP on the 2nd day, with a return close to normal values on the 15th day. In opposition MIP had a surprisingly increase on the 15th postoperative day (129 cmH2O), normalizing 180 days after the operation. A leap in IAP values was revealed at the end of the surgical procedure. It was not possible to establish a positive correlation between the increase of IAP and the alterations of MIP and MEP. CONCLUSIONS: There is a decrease in maximum expiratory pressure on the very early postoperative day (2nd postoperative day) and an increase in maximum inspiratory pressure on the 15th postoperative day in patients who underwent abdominoplasty. There was no correlation between the IAP and maximum respiratory pressure variations, both inspiratory and expiratory.

Sex- and age-adjusted reference values for dynamic inspiratory constraints during incremental cycle ergometry.

Activity-related dyspnea in chronic lung disease is centrally related to dynamic (dyn) inspiratory constraints to tidal volume expansion. Lack of reference values for exertional inspiratory reserve (IR) has limited the yield of cardiopulmonary exercise testing in exposing the underpinnings of this disabling symptom. One hundred fifty apparently healthy subjects (82 males) aged 40-85 underwent incremental cycle ergometry. Based on exercise inspiratory capacity (ICdyn), we generated centile-based reference values for the following metrics of IR as a function of absolute ventilation: IRdyn1 ([1-(tidal volume/ICdyn)] x 100) and IRdyn2 ([1-(end-inspiratory lung volume/total lung capacity] x 100). IRdyn1 and IRdyn2 standards were typically lower in females and older subjects (p<0.05 for sex and age versus ventilation interactions). Low IRdyn1 and IRdyn2 significantly predicted the burden of exertional dyspnea in both sexes (p<0.01). Using these sex and age-adjusted limits of reference, the clinician can adequately judge the presence and severity of abnormally low inspiratory reserves in dyspneic subjects undergoing cardiopulmonary exercise testing.

Oscillations of Hemodynamic Parameters Induced by Negative Pressure Breathing in Healthy Humans.

INTRODUCTION: Negative pressure breathing is breathing with decreased pressure in the respiratory tract without lowering pressure acting on the torso. We lowered air pressure only during inspiration (NPBin). NPBin, used to increase venous return to the heart, is considered a countermeasure against redistribution of body fluids toward the head during spaceflight. We studied NPBin effects on circulation in healthy humans with an emphasis on NPBin-induced oscillations of hemodynamic parameters synchronous with breathing. We propose an approach to analyze the oscillations based on coherent averaging.METHODS: Eight men ages 24-42 yr participated in the NPBin and control series. During the series, to reproduce fluids shift observed under microgravity, subjects were supine and head down (-8°). Duration of NPBin was 20 min, rarefaction -20 cm H2O. Hemodynamic parameters were measured by Finometer. Electrical impedance measurements were used to estimate changes in blood filling of cerebral vessels.RESULTS: Mean values of hemodynamic parameters virtually did not change under NPBin, but NPBin induced oscillations of the parameters synchronous with respiration. Peak-to-peak amplitude under NPBin were: mean arterial pressure, 4 ± 1 (mmHg); stroke volume, 7 ± 3 (mL); and heart rate, 4 ± 1 (bpm). Electrical impedance of the head increased during inspiration. The increase under NPBin was three times greater than under normal breathing.DISCUSSION: Analysis of oscillations gives more information than analysis of mean values. NPBin induces short-term decrease in left ventricle stroke volume and arterial blood pressure during each inspiration; the decrease is compensated by increase after inspiration. NPBin facilitates redistribution of body fluids away from the head.Semenov YS, Melnikov IS, Luzhnov PV, Dyachenko AI. Oscillations of hemodynamic parameters induced by negative pressure breathing in healthy humans. Aerosp Med Hum Perform. 2024; 95(6):297-304.

Diaphragm thickness and mobility elicited by two different modalities of inspiratory muscle loading in heart failure participants: A randomized crossover study.

OBJECTIVES: To analyze diaphragmatic thickness, at end-inspiration and end-expiration, diaphragmatic thickening index and mobility via US under two different modalities of inspiratory muscle loading, in two different modalities of inspiratory muscle loading and different load intensities at full-vital capacity maneuvers and the relationship between diaphragmatic thickness with pulmonary function tests in participants with HF. METHODS: This randomized crossover trial, enrolled with 17 HF subjects, evaluated diaphragm thickness (Tdi, mm), fractional thickness (TFdi, %), and mobility (mm) US during low and high intensities (30% and 60% of maximal inspiratory pressure-MIP) with two modalities of inspiratory muscle loading mechanical threshold loading (MTL) and tapered flow-resistive loading (TFRL). RESULTS: Both MTL and TFRL produced a increase in Tdi, but only with high intensity loading compared to baseline-2.21 (0.26) vs. 2.68 (0.33) and 2.73 (0.44) mm; p = .01. TFdi was greater than baseline under all conditions, except during low intensity of TFRL. Diaphragm mobility was greater than baseline under all conditions, and high intensity of TFRL elicited greater mobility compared to all other conditions. Additionally, baseline Tdi was moderately correlated with pulmonary function tests. CONCLUSIONS: MTL and TFRL modalities elicit similar increases in diaphragm thickness at loads, but only during high intensity loading it was greater than baseline. Diaphragm mobility was significantly greater than baseline under both loads and devices, and at high intensity compared to low intensity, although TFRL produced greater mobility compared to modalities of inspiratory muscle loading. There is an association between diaphragm thickness and pulmonary function tests.

Reflex sympathetic activation to inspiratory muscle loading is attenuated in females relative to males.

Intense inspiratory muscle work can evoke a metabolite-stimulated pressor reflex, commonly referred to as the respiratory muscle metaboreflex. When completing similar relative and absolute levels of inspiratory work, females have an attenuated blood pressure response. We sought to test the hypothesis that the lower blood pressure response to the respiratory muscle metaboreflex in females is associated with a reduced sympathetic response. Healthy young (26 ± 4 yr) males (n = 9) and females (n = 7) completed two experimental days. On day 1, participants completed pulmonary function testing and became familiarized with an inspiratory pressure-threshold loading (PTL) task. On the second day, balloon-tipped catheters were placed in the esophagus and stomach to measure pleural and gastric pressures, and transdiaphragmatic pressure was calculated. A microelectrode was inserted into the fibular nerve to quantify muscle sympathetic nerve activity (MSNA), and participants then completed isocapnic PTL to task failure. There was a significant sex-by-time interaction in the mean arterial pressure (MAP, P = 0.015) and burst frequency (P = 0.039) response to PTL. Males had a greater rise in MAP (Δ21 ± 9 mmHg) than females (Δ13 ± 5 mmHg, P = 0.026). Males also demonstrated a greater rise in MSNA burst frequency (Δ18 ± 7 bursts/min) than females (Δ10 ± 5 bursts/min, P = 0.015). The effect of sex was observed despite females and males completing the same magnitude of diaphragm work throughout the task (P = 0.755). Our findings provide novel evidence that the lower blood pressure response to similar relative and absolute inspiratory muscle work in females is associated with lower sympathetic activation.NEW & NOTEWORTHY The blood pressure response to high levels of inspiratory muscle work is lower in females and occurs alongside a reduced sympathetic response. The reduced blood pressure and sympathetic response occur despite males and females performing similar levels of absolute inspiratory work. Our findings provide evidence that sex differences in the respiratory muscle metaboreflex are, in part, sympathetically mediated.

Effects of inspiratory muscle training on thoracoabdominal volume regulation in older adults: A randomised controlled trial.

OBJECTIVES: We investigated the effect of inspiratory muscle training (IMT) on inspiratory muscle strength, functional capacity and respiratory muscle kinematics during exercise in healthy older adults. METHODS: 24 adults were randomised into an IMT or SHAM-IMT group. Both groups performed 30 breaths, twice daily, for 8 weeks, at intensities of ∼50 % maximal inspiratory pressure (PImax; IMT) or <15 % PImax (SHAM-IMT). Measurements of PImax, breathing discomfort during a bout of IMT, six-minute walk distance, physical activity levels, and balance were assessed pre- and post-intervention. Respiratory muscle kinematics were assessed via optoelectronic plethysmography (OEP) during constant work rate cycling. RESULTS: PImax was significantly improved (by 20.0±11.9 cmH2O; p=0.001) in the IMT group only. Breathing discomfort ratings during IMT significantly decreased (from 3.5±0.9-1.7±0.8). Daily sedentary time was decreased (by 28.0±39.8 min; p=0.042), and reactive balance significantly improved (by 1.2±0.8; p<0.001) in the IMT group only. OEP measures showed a significantly greater contribution of the pulmonary and abdominal rib cage compartments to total tidal volume expansion post-IMT. CONCLUSIONS: IMT significantly improves inspiratory muscle strength and breathing discomfort in this population. IMT induces greater rib cage expansion and diaphragm descent during exercise, thereby suggesting a less restrictive effect on thoracic expansion and increased diaphragmatic power generation.

Inhibitory Subpopulations in preBötzinger Complex Play Distinct Roles in Modulating Inspiratory Rhythm and Pattern.

Inhibitory neurons embedded within mammalian neural circuits shape breathing, walking, and other rhythmic motor behaviors. At the core of the neural circuit controlling breathing is the preBötzinger Complex (preBötC), where GABAergic (GAD1/2+) and glycinergic (GlyT2+) neurons are functionally and anatomically intercalated among glutamatergic Dbx1-derived (Dbx1+) neurons that generate rhythmic inspiratory drive. The roles of these preBötC inhibitory neurons in breathing remain unclear. We first characterized the spatial distribution of molecularly defined preBötC inhibitory subpopulations in male and female neonatal double reporter mice expressing either tdTomato or EGFP in GlyT2+, GAD1+, or GAD2+ neurons. We found that the majority of preBötC inhibitory neurons expressed both GlyT2 and GAD2 while a much smaller subpopulation also expressed GAD1. To determine the functional role of these subpopulations, we used holographic photostimulation, a patterned illumination technique, in rhythmically active medullary slices from neonatal Dbx1tdTomato;GlyT2EGFP and Dbx1tdTomato;GAD1EGFP double reporter mice of either sex. Stimulation of 4 or 8 preBötC GlyT2+ neurons during endogenous rhythm prolonged the interburst interval in a phase-dependent manner and increased the latency to burst initiation when bursts were evoked by stimulation of Dbx1+ neurons. In contrast, stimulation of 4 or 8 preBötC GAD1+ neurons did not affect interburst interval or latency to burst initiation. Instead, photoactivation of GAD1+ neurons during the inspiratory burst prolonged endogenous and evoked burst duration and decreased evoked burst amplitude. We conclude that GlyT2+/GAD2+ neurons modulate breathing rhythm by delaying burst initiation while a smaller GAD1+ subpopulation shapes inspiratory patterning by altering burst duration and amplitude.

Percent duration of heart rate acceleration within the respiratory cycle: a novel approach to assess heart rate asymmetry.

Accelerations and decelerations of heart rate are nonsymmetrical in the magnitude and number of beat-to-beat changes. The asymmetric features of heart rate variability are related to respiratory durations. To explore the link between respiration and heart rate asymmetry (HRA), we evaluated 14 seated, healthy young adults who breathed with nine combinations of inspiration duration (TI) and expiration duration (TE), chosen respectively from 2, 4, and 6 s. A 5-min R-R interval (RRI) time series was obtained from each study period to construct an averaged pattern waveform relative to the respiratory cycle. We observed that the time interval between inspiration onset and RRI minimum progressively lengthened as TI and TE increased. The time interval between expiration onset and RRI maximum also lengthened when TE increased but shortened when TI increased. Consequently, TI and TE had different effects on the acceleration time (AT; from RRI maximum to RRI minimum) and deceleration time (DT; from RRI minimum to RRI maximum). The percentage of AT within the respiratory cycle showed a strong correlation with traditional Guzik's (r = 0.862, P < 0.001) and Porta's (r = 0.878, P < 0.001) indexes of HRA assessed in a Poincaré plot analysis. These findings suggest that, in addition to considering the magnitude and number of beat-to-beat changes, HRA can also be assessed based on another aspect: the duration of consecutive changes. The stepwise link between the duration of heart rate change and respiratory duration provides insight into the mechanisms connecting respiration to HRA.NEW & NOTEWORTHY In healthy adults who regulated their breathing across nine combinations of inspiration and expiration durations, we used averaged pattern waveform technique to quantify the durations of heart rate acceleration and deceleration within the respiratory cycle. The percent duration of acceleration showed a strong correlation with traditional heart rate asymmetry indexes, which evaluate the magnitude and number of beat-to-beat changes. This new approach opens a window to explore the asymmetric features of heart rate variability.

Evaluating intra-fractional tumor motion in lung stereotactic radiotherapy with deep inspiration breath-hold.

PURPOSE: To evaluate the intra-fractional tumor motion in lung stereotactic body radiotherapy (SBRT) with deep inspiration breath-hold (DIBH), and to investigate the adequacy of the current planning target volume (PTV) margins. METHODS: Twenty-eight lung SBRT patients with DIBH were selected in this study. Among the lesions, twenty-three were at right or left lower lobe, two at right middle lobe, and three at right or left upper lobe. Post-treatment gated cone-beam computed tomography (CBCT) was acquired to quantify the intra-fractional tumor shift at each treatment. These obtained shifts were then used to calculate the required PTV margin, which was compared with the current applied margin of 5 mm margin in anterior-posterior (AP) and right-left (RL) directions and 8 mm in superior-inferior (SI) direction. The beam delivery time was prolonged with DIBH. The actual beam delivery time with DIBH (Tbeam_DIBH) was compared with the beam delivery time without DIBH (Tbeam_wo_DIBH) for the corresponding SBRT plan. RESULTS: A total of 113 treatments were analyzed. At six treatments (5.3%), the shifts exceeded the tolerance defined by the current PTV margin. The average shifts were 0.0 ± 1.9 mm, 0.1±1.5 mm, and -0.5 ± 3.7 mm in AP, RL, and SI directions, respectively. The required PTV margins were determined to be 4.5, 3.9, and 7.4 mm in AP, RL, and SI directions, respectively. The average Tbeam_wo_DIBH and Tbeam_DIBH were 2.4 ± 0.4 min and 3.6 ± 1.5 min, respectively. The average treatment slot for lung SBRT with DIBH was 25.3 ± 7.9 min. CONCLUSION: Intra-fractional tumor motion is the predominant source of treatment uncertainties in CBCT-guided lung SBRT with DIBH. The required PTV margin should be determined based on data specific to each institute, considering different techniques and populations. Our data indicate that our current applied PTV margin is adequate, and it is possible to reduce further in the RL direction. The time increase of Tbeam_DIBH, relative to the treatment slot, is not clinically significant.

High-intensity intermittent inspiratory and abdominal muscle combined training in respiratory, swallowing and systemic muscles of healthy adults.

BACKGROUND: Low-intensity continuous inspiratory muscle training improves its strength. The abdominal muscles are the main expiratory muscles, and their training may improve expiratory muscle strength. Respiratory muscle strength regulates coughing effectiveness, which is critical for pneumonia management. In older people, risk factors for the development of pneumonia were respiratory muscle weakness and swallowing impairment. Currently, the impact of high-intensity intermittent inspiratory and abdominal muscle combined training on the respiratory, swallowing, and systemic muscles is unclear. OBJECTIVE: We aimed to explore the effects of high-intensity inspiratory muscle training combined with or without abdominal muscle training on respiratory muscle strength as well as the strength, mass, and performance of swallowing and systemic muscles. METHODS: Twenty-eight healthy adults were divided into two groups. Participants performed high-intensity intermittent inspiratory muscle single or its combination with abdominal muscle training for 4 weeks. Respiratory muscle strength, swallowing muscle strength and mass, systemic muscle strength, mass and performance were measured at baseline, Week 2 and Week 4. RESULTS: Both groups showed greater maximal respiratory pressures at Week 2 and Week 4 than baseline. Both groups showed improved tongue pressure and geniohyoid muscle thickness at Week 4. In addition, the combined training group improved body trunk muscle mass, handgrip strength and five-time chair stand test, whereas the single training group did not. CONCLUSION: This study revealed that high-intensity inspiratory muscle training improved inspiratory muscle strength and swallowing muscle strength and mass. Moreover, inspiratory and abdominal muscle combined training showed an additional benefit of improving systemic muscle strength, mass and performance. CLINICAL TRIAL REGISTRATION NUMBER: UMIN000046724; https://upload.umin.ac.jp/cgi-open-bin/ctr/index.cgi?ctrno=UMIN000046724.

The Effects of Inspiratory Flows, Inspiratory Pause, and Suction Catheter on Aerosol Drug Delivery with Vibrating Mesh Nebulizers During Mechanical Ventilation.

Background: Some experts recommend specific ventilator settings during nebulization for mechanically ventilated patients, such as inspiratory pause, high inspiratory to expiratory ratio, and so on. However, it is unclear whether those settings improve aerosol delivery. Thus, we aimed to evaluate the impact of ventilator settings on aerosol delivery during mechanical ventilation (MV). Methods: Salbutamol (5.0 mg/2.5 mL) was nebulized by a vibrating mesh nebulizer (VMN) in an adult MV model. VMN was placed at the inlet of humidifier and 15 cm away from the Y-piece of the inspiratory limb. Eight scenarios with different ventilator settings were compared with endotracheal tube (ETT) connecting 15 cm from the Y-piece, including tidal volumes of 6-8 mL/kg, respiratory rates of 12-20 breaths/min, inspiratory time of 1.0-2.5 seconds, inspiratory pause of 0-0.3 seconds, and bias flow of 3.5 L/min. In-line suction catheter was utilized in two scenarios. Delivered drug distal to the ETT was collected by a filter, and drug was assayed by an ultraviolet spectrophotometry (276 nm). Results: Compared to the use of inspiratory pause, the inhaled dose without inspiratory pause was either higher or similar across all ventilation settings. Inhaled dose was negatively correlated with inspiratory flow with VMN placed at 15 cm away from the Y-piece (rs = -0.68, p < 0.001) and at the inlet of humidifier (rs = -0.83, p < 0.001). The utilization of in-line suction catheter reduced inhaled dose, regardless of the ventilator settings and nebulizer placements. Conclusions: When VMN was placed at the inlet of humidifier, directly connecting the Y-piece to ETT without a suction catheter improved aerosol delivery. In this configuration, the inhaled dose increased as the inspiratory flow decreased, inspiratory pause had either no or a negative impact on aerosol delivery. The inhaled dose was greater with VMN placed at the inlet of humidifier than 15 cm away the Y-piece.

Transient interruption of contrast on CT pulmonary angiography: effect of mid-inspiratory vs. end-inspiratory respiration command.

PURPOSE: To investigate the effects of mid-inspiratory respiration commands and other factors on transient interruption of contrast (TIC) incidence on CT pulmonary angiography. METHODS: In this retrospective study, 824 patients (mean age, 66.1 ± 15.3 years; 342 males) who had undergone CT pulmonary angiography between January 2021 and February 2023 were included. Among them, 545 and 279 patients were scanned at end- and mid-inspiratory levels, respectively. By placing a circular region of interest, CT attenuation of the main pulmonary artery (CTMPA) was recorded. Associations between several factors, including patient age, body weight, sex, respiratory command vs. TIC and severe TIC incidence (defined as CTMPA < 200 and 150 HU, respectively), were assessed using logistic regression analyses with stepwise regression selection based on Akaike's information criterion. RESULTS: Mid-inspiratory respiration command, in addition to patient age and lighter body weight, had negative association with the incidence of TIC. Only patient age, lighter body weight, female sex, and larger cardiothoracic ratio were negatively associated with severe TIC incidence. Mid-inspiratory respiration commands helped reduce TIC incidence among patients aged < 65 years (p = 0.039) and those with body weight ≥ 75 kg (p = 0.005) who were at high TIC risk. CONCLUSION: Changing the respiratory command from end- to mid-inspiratory levels, as well as patient age and body weight, was significantly associated with TIC incidence.