Minute Ventilation Research Articles

Association of dead space fraction to mortality in patients with COVID-19-related ARDS: A historical cohort observational study

ObjectiveTo assess the correlation of dead space fraction (VD/VT) measured through time capnography, corrected minute volume (CMV) and ventilation ratio (VR) with clinical outcomes in COVID-19 patients requiring invasive mechanical ventilation. DesignObservational study of a historical cohort. SettingUniversity hospital in Medellin, Colombia. ParticipantsPatients aged 15 and above with a confirmed COVID-19 diagnosis admitted to the ICU and requiring mechanical ventilation. InterventionsMeasurement of VD/VT, CMV, and VR in COVID-19 patients. Main variables of interestVD/VT, CMV, VR, demographic data, oxygenation indices and ventilatory parameters. ResultsDuring the study period, 1047 COVID-19 patients on mechanical ventilation were analyzed, of whom 446 (42%) died. Deceased patients exhibited a higher prevalence of advanced age and obesity, elevated Charlson index, higher APACHE II and SOFA scores, as well as an increase in VD/VT ratio (0.27 in survivors and 0.31 in deceased) and minute ventilation volume on the first day of mechanical ventilation. The multivariate analysis revealed independent associations to in-hospital mortality, higher VD/VT (HR 1.24; 95%CI 1.003–1.525; p = 0.046), age (HR 1.024; 95%CI 1.014–1.034; p < 0.001), and SOFA score at onset (HR: 1.036; 95%CI: 1.001–1.07; p = 0.017). ConclusionsVD/VT demonstrated an association with mortality in COVID-19 patients with ARDS on mechanical ventilation. These findings suggest that VD/VT measurement may serve as a severity marker for the disease.

Diamedica Draw-over Vaporiser: bench testing the UK Defence Anaesthesia System in the deployed environment

IntroductionThe Diamedica Draw-over Vaporiser 2 (DDV2) is the sevoflurane vaporiser used by the UK Defence Medical Services to provide deployed volatile general anaesthesia. The Defence Anaesthesia System employs the DDV2...

Prognostic utility of cardiopulmonary exercise testing with simultaneous exercise echocardiography in heart failure with preserved ejection fraction.

Cardiopulmonary exercise testing (CPET) combined with exercise echocardiography (CPETecho) allows simultaneous assessments of cardiac, pulmonary, and ventilation in heart failure (HF) with preserved ejection fraction (HFpEF). This study sought to determine whether simultaneous assessment of CPET variables could provide additive predictive value over exercise stress echocardiography in patients with dyspnoea. CPETecho was performed in 443 patients with suspected HFpEF (240 HFpEF and 203 controls without HF). Patients with HFpEF were divided based on peak oxygen consumption (VO2, ≥10 or <10 ml/min/kg) or the slope of minute ventilation to carbon dioxide production (VE vs. VCO2 slope ≥45.0 or <45.0). The primary endpoint was defined as a composite of all-cause mortality, HF hospitalization, unplanned hospital visits requiring intravenous diuretics, or intensification of oral diuretics. During a median follow-up of 399 days, the composite outcome occurred in 57 patients. E/e' ratio during peak exercise was associated with adverse outcomes. Patients with HFpEF and lower peak VO2 had increased risks of the composite event (hazard ratio [HR] 5.05, 95% confidence interval [CI] 2.65-9.62, p < 0.0001 vs. controls; HR 3.14, 95% CI 1.69-5.84, p = 0.0003 vs. HFpEF with higher peak VO2). Elevated VE versus VCO2 slope was also associated with adverse events in HFpEF. The addition of either the presence of abnormal peak VO2 or VE versus VCO2 slope increased the predictive ability over the model based on age, sex, atrial fibrillation, left atrial volume index, and exercise E/e' (p < 0.05). These data provide new insights into the role of CPETecho in patients with HFpEF.

Time-restricted feeding reveals a role for neural respiratory clocks in optimizing daily ventilatory-metabolic coupling in mice.

The master circadian clock, located in the suprachiasmatic nuclei (SCN), organizes the daily rhythm in minute ventilation (VE). However, the extent that the daily rhythm in VE is secondary to SCN-imposed O2 and CO2 cycles (i.e., metabolic rate), or driven by other clock mechanisms, remains unknown. Here, we experimentally shifted metabolic rate using time-restricted feeding (without affecting light-induced synchronization of the SCN) to determine the influence of metabolic rate in orchestrating the daily VE rhythm. Mice eating predominantly at night exhibited robust daily rhythms in O2 consumption (VO2), CO2 production (VCO2), and VE with similar peak times (~ZT18) that were consistent with SCN organization. However, feeding mice exclusively during the day separated the relative timing of metabolic and ventilatory rhythms, resulting in a ~8.5-hr advance in VCO2, and a disruption of the VE rhythm, suggesting opposing circadian and metabolic influences on VE. To determine if the molecular clock of cells involved in the neural control of breathing contribute to the daily VE rhythm, we examined VE in mice lacking BMAL1 in Phox2b-expressing respiratory cells (i.e., BKOP mice). The ventilatory and metabolic rhythms of predominantly night-fed BKOP mice did not differ from wild-type mice. However, in contrast to wild-type mice, exclusive day feeding of BKOP mice led to an unfettered daily VE rhythm with a peak time aligning closely with the daily VCO2 rhythm. Taken together, these results indicate that both daily VCO2 changes and intrinsic circadian time-keeping within Phox2b respiratory cells are predominant orchestrators of the daily rhythm in ventilation.

A novel, cassette-based nitric oxide delivery system with an advanced feedback control algorithm accurately delivers nitric oxide via the anesthesia machine independent of fresh gas flow rate and volatile anesthetic agent.

Nitric oxide (NO), a selective pulmonary vasodilator, can be delivered via conventional ICU and anesthesia machine ventilators. Anesthesia machines are designed for rebreathing of circulating gases, reducing volatile anesthetic agent quantity used. Current cylinder- and ionizing-based NO delivery technologies use breathing circuit flow to determine NO delivery and do not account for recirculated gases; therefore, they cannot accurately dose NO at FGF below patient minute ventilation (MV). A novel, cassette-based NO delivery system (GENOSYL® DS, Vero Biotech Inc.) uses measured NO concentration in the breathing circuit as an input to an advanced feedback control algorithm, providing accurate NO delivery regardless of FGF and recirculation of gases. This study evaluated GENOSYL® DS accuracy with different anesthesia machines, ventilation parameters, FGFs, and volatile anesthetics. GENOSYL® DS was tested with GE Aisys and Dräger Fabius anesthesia machines to determine NO dose accuracy with FGF < patient MV, and with a Getinge Flow-i anesthesia machine to determine NO dose accuracy when delivering various volatile anesthetic agents. Neonatal and adult mechanical ventilation parameters and circuits were used. GENOSYL® DS maintained accurate NO delivery with all three anesthesia machines, at low FGF with recirculation of gases, and with all volatile anesthetic agents at different concentrations. Measured NO2 levels remained acceptable at ≤ 1ppm with set NO dose ≤ 40ppm. GENOSYL® DS, with its advanced feedback control algorithm, is the only NO delivery system capable of accurately dosing NO with anesthesia machines with rebreathing ventilation parameters (FGF < MV) regardless of anesthetic agent.

Dead space volumes in cats and dogs with small body mass ventilated with a fixed tidal volume

ObjectiveTo compare the portion of tidal volume (VT) ventilating dead space volumes in nonbrachycephalic cats and dogs with small body mass receiving volume-controlled ventilation (VCV) with a fixed VT. Study designProspective, experimental study. Animal populationEight healthy adult cats and dogs [ideal body weight (IBW): 3.0 ± 0.5 and 3.8 ± 1.1 kg, respectively]. MethodsAnesthetized cats and dogs received VCV with a 12 mL kg-1 VT (inspiratory pause ≥ 0.5 seconds). Respiratory rate (fR) was adjusted to maintain normocapnia. Airway dead space (VDaw) and alveolar tidal volume (VTalv) were measured by volumetric capnography. Physiological dead space (VDphys) and VDphys/VT ratio were calculated using the Bohr-Enghoff method. Data recorded before surgery were compared by an unpaired t test or Mann-Whitney U test (p < 0.05 considered significant). ResultsThe IBW (p = 0.07), PaCO2 (p = 0.40), and expired VT (VT(exp)) did not differ significantly (p = 0.77) between species. The VDaw (mL kg-1) was lower in cats (3.7 ± 0.4) than in dogs (7.7 ± 0.9) (p < 0.0001). The VTalv (mL kg-1) was larger in cats (8.3 ± 0.7) than in dogs (4.3 ± 0.7) (p < 0.0001). Cats presented a smaller VDphys/VT ratio (0.33 ± 0.03) and VDphys (4.0 ± 0.3 mL kg-1) than dogs (VDphys/VT: 0.60 ± 0.09; VDphys: 7.2 ± 1.4 mL kg-1) (p < 0.0001). The fR and minute ventilation (VT(exp) × fR) were lower in cats than in dogs (p = 0.048 and p = 0.038, respectively). Conclusions and clinical relevanceA fixed VT results in more effective ventilation in cats than in dogs with small body mass because of species-specific differences in and VDaw and VDphys. Because of the smaller VDaw and VDphys in cats than in dogs, a lower fR is required to maintain normocapnia in the former species.

Effects of running with surgical masks on cardiopulmonary function in healthy male university students.

[Purpose] In Japan, one measure against the novel coronavirus disease-2019 infection involves the public use of surgical masks. Research indicates that exercising while wearing a mask increases the physical burden, particularly affecting young people during high-intensity exercise. This study examined the effects of wearing masks while running in male university students. [Participants and Methods] The participants were 20 healthy male university students (21.6 ± 1.6 years). The participants underwent cardiopulmonary exercise tests with the masks on and off on different days until exhaustion. The following parameters were measured: exercise duration, Borg Scale rating (respiratory or lower extremities), surface temperature around the mouth, time to sweat onset, metabolic reaction, pulmonary ventilation, and cardiovascular reaction parameters. [Results] The results showed that VO2 max remained consistent between the mask-on and mask-off conditions. However, minute ventilation, respiratory rate, and heart rate decreased in the mask-on condition, which correlated with a reduction in exercise duration. Furthermore, running with the mask significantly decreased the VE/VO2, VE/ VO2, Borg Scale rating of the lower extremities, and the time to sweat onset. [Conclusion] Running with a surgical mask affected respiratory function and decreased exercise duration in healthy male university students. However, it did not induce any changes in VO2 max.

Test-Retest Reliability of Running Economy and Metabolic and Cardiorespiratory Parameters During a Multistage Incremental Treadmill Test in Male Middle- and Long-Distance Runners.

This study investigated the test-retest reliability of running economy (RE) and metabolic and cardiorespiratory parameters related to endurance running performance using a multistage incremental treadmill test. On two occasions separated by 21-28days, 12 male middle- and long-distance runners ran at 10, 11, 12, 13, and 14km/hr for 8min each stage, immediately followed by a ramp test to volitional exhaustion. Carbohydrate (10% maltodextrin solution) was consumed before and during the test to provide ∼1g/min of exercise. RE, minute ventilation (V˙E), oxygen consumption (V˙O2), carbon dioxide production (V˙CO2), respiratory exchange ratio(RER), heart rate(HR), ratings of perceived exertion(RPE), and blood glucose and lactate concentrations were recorded for each stage and at volitional exhaustion. Time-to-exhaustion (TTE) and peak oxygen consumption (V˙O2peak) during the ramp test were also recorded. Absolute reliability, calculated as the coefficient of variation (CV) between repeated measures, ranged from 2.3% to 3.1% for RE, whereas relative reliability, calculated as the intraclass correlation coefficient(ICC), ranged from .42 to .79. V˙E, V˙O2, V˙O2peak, V˙CO2, RER, and HR had a CV of 1.1%-4.3% across all stages. TTE and RPE had a CV of 7.2% and 2.3%-10.8%, respectively, while glucose and lactate had a CV of 4.0%-17.8%. All otherparameters, except for blood glucose, were demonstrated to have good-to-excellent relative reliability assessed by ICC. Measures of RE, V˙O2peak, and TTE were reliable during this two-phase multistage incremental treadmill test in a cohort of trained and highly trained male middle- and long-distance runners.

Elevated muscle pain induced by a hypertonic saline injection reduces power output independent of physiological changes during fixed perceived effort cycling.

Pain is a naturally occurring phenomenon that consistently inhibits exercise performance by imposing unconscious, neurophysiological alterations (e.g., corticospinal changes) as well as conscious, psychophysiological pressures (e.g., shared effort demands). Although, several studies indicate that pain would elicit lower task outputs for a set intensity of perceived effort, no study has tested this. Therefore, this study investigated the impact of elevated muscle pain through a hypertonic saline injection on the power output, psychophysiological, cerebral oxygenation, and perceptual changes during fixed perceived effort exercise. Ten participants completed three visits (one familiarisation + two fixed perceived effort trials). Fixed perceived effort cycling corresponded to 15% above gas exchange threshold (mean RPE = 15; hard). Before the 30-minute fixed perceived effort exercise, participants received a randomised, bilateral hypertonic or isotonic saline injection in the vastus lateralis. Power output, cardiorespiratory, cerebral oxygenation, and perceptual markers (e.g., affective valence) were recorded during exercise. Linear mixed model regression assessed the condition and time effects and condition × time interactions. Significant condition effects showed that power output was significantly lower during hypertonic conditions (t_107= 2.08,p=.040,β=4.77 Watts,95%CI [0.27 to 9.26 Watts]). Meanwhile all physiological variables (e.g., heart rate, oxygen uptake, minute ventilation) demonstrated no significant condition effects. Condition effects were observed for deoxyhaemoglobin changes from baseline (t_107= -3.29,p=.001,β=-1.50 ΔµM,95%CI [-2.40 to-0.61 ΔµM]) and affective valence (t_127= 6.12,p=.001,β=0.93,95%CI [0.63,1.23]). Results infer that pain impacts the self-regulation of fixed perceived effort exercise, as differences in power output mainly occurred when pain ratings were higher after hypertonic versus isotonic saline administration.

Noninvasive Surrogate for Physiologic Dead Space Using the Carbon Dioxide Ventilatory Equivalent: Testing in a Single-Center Cohort, 2017-2023.

We sought to evaluate the association between the carbon dioxide (co2) ventilatory equivalent (VEqco2 = minute ventilation/volume of co2 produced per min), a marker of dead space that does not require a blood gas measurement, and mortality risk. We compared the strength of this association to that of physiologic dead space fraction (VD/Vt = [Paco2-mixed-expired Pco2]/Paco2) as well as to other commonly used markers of dead space (i.e., the end-tidal alveolar dead space fraction [AVDSf = (Paco2-end-tidal Pco2)/Paco2], and ventilatory ratio [VR = (minute ventilation × Paco2)/(age-adjusted predicted minute ventilation × 37.5)]). Retrospective cohort data, 2017-2023. Quaternary PICU. One hundred thirty-one children with acute respiratory distress syndrome. None. All dead space markers were calculated at the same 1-minute timepoint for each patient within the first 72 hours of using invasive mechanical ventilation. The 131 children had a median (interquartile range, IQR) age of 5.8 (IQR 1.4, 12.6) years, oxygenation index (OI) of 7.5 (IQR 4.6, 14.3), VD/Vt of 0.47 (IQR 0.38, 0.61), and mortality was 17.6% (23/131). Higher VEqco2 (p = 0.003), VD/Vt (p = 0.002), and VR (p = 0.013) were all associated with greater odds of mortality in multivariable models adjusting for OI, immunosuppressive comorbidity, and overall severity of illness. We failed to identify an association between AVDSf and mortality in the multivariable modeling. Similarly, we also failed to identify an association between OI and mortality after controlling for any dead space marker in the modeling. For the 28-day ventilator-free days outcome, we failed to identify an association between VD/Vt and the dead space markers in multivariable modeling, although OI was significant. VEqco2 performs similarly to VD/Vt and other surrogate dead space markers, is independently associated with mortality risk, and may be a reasonable noninvasive surrogate for VD/Vt.

Rosmarinic acid alleviates septic acute respiratory distress syndrome in mice by suppressing the bronchial epithelial RAS-mediated ferroptosis

Activating angiotensin-converting enzyme 2 (ACE2) is an important player in the pathogenesis of septic-related acute respiratory distress syndrome (ARDS). Rosmarinic acid (RA) as a prominent polyphenolic secondary metabolite derived from Rosmarinus officinalis modulates ACE2 in sepsis remains unclear, although its impact on ACE inhibition and septic-associated lung injury has been explored. The study investigated the ACE2 expression in lipopolysaccharide (LPS)-induced lungs in mice and BEAS2B cells. Additionally, molecular docking, protein–protein interaction (PPI) network analysis, and western blotting were employed to predict and evaluate the molecular mechanism of RA on LPS-induced ferroptosis in vivo and in vitro. LPS-induced glutathione peroxidase 4 (GPX4) downregulation, ACE/ACE2 imbalance, and alteration of frequency of breathing (BPM), minute volume (MV), and the expiratory flow at 50% expired volume (EF50) were reversed by captopril pretreatment in vitro and in vivo. RA notably inhibited the infiltration into the lungs of neutrophils and monocytes with increased amounts of GPX4 and ACE2 proteins, lung function improvement, and decreased inflammatory cytokines levels and ER stress in LPS-induced ARDS in mice. Molecular docking showed RA was able to interact with ACE and ACE2. Moreover, combined with different pharmacological inhibitors to block ACE and ferroptosis, RA still significantly inhibited inflammatory cytokines Interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), and C-X-C motif chemokine 2 (CXCL2) levels, as well as improved lung function, and enhanced GPX4 expression. Particularly, the anti-ferroptosis effect of RA in LPS-induced septic ARDS is RAS-dependent.

INDICATORS OF CENTRAL HEMODYNAMICS IN ACQUIRED MYOPIA

Introduction. The presented study focuses on investigating the impact of acquired myopia on human central hemodynamics. Myopia, or nearsightedness, ranks as one of the most common ophthalmological disorders globally and in Ukraine, manifesting either congenitally or acquired over a lifetime. Ophthalmology specialists note a rapid increase in myopia cases across all age groups, with its prevalence posing a significant threat to vision and overall health. Viewing myopia as an adaptive response to a substantial visual strain one can presume that this adaptation might not be localized but generalized. The objective of the study is to examine the characteristics of central hemodynamics in individuals with acquired myopia. Materials and methods. The research was conducted on volunteers, 81 individuals aged 18 – 35, who were divided into a control group of 40 persons and a study group of 41 individuals diagnosed as having myopia. The diagnosis was established by specialists in Dnipro. The study was carried out at the General Practice Family Medicine Clinic No. 7 in Dnipro during 2022-2023. Central hemodynamic status was characterized by the following indicators: heart rate, systolic and diastolic blood pressure, pulse pressure, systolic blood volume, and minute blood volume. The Kerdo’s vegetative index was also calculated. Results. The study revealed that acquired myopia was accompanied by an increase in the absolute values of heart rate, systolic blood pressure, diastolic blood pressure, pulse pressure, and minute blood volume compared to the control group of volunteers. It is noteworthy that the systolic blood volume in the context of acquired myopia was lower than in the control group. The Kerdo’s index was higher in the group with acquired myopia compared to the control group. The obtained results indicate a certain dependency between central hemodynamics indicators, the Kerdo’s index value, and acquired myopia, which is an adaptive reaction of the visual system to significant loads in the modern information-cybernetic society. Changes in central hemodynamics indicators in individuals with myopia may reflect certain adaptive reactions of the cardiovascular system to this eye refraction disorder.

Expiratory braking defines the breathing patterns of asphyxiated neonates during therapeutic hypothermia.

Although neonatal breathing patterns vary after perinatal asphyxia, whether they change during therapeutic hypothermia (TH) remains unclear. We characterized breathing patterns in infants during TH for hypoxic-ischemic encephalopathy (HIE) and normothermia after rewarming. In seventeen spontaneously breathing infants receiving TH for HIE and in three who did not receive TH, we analyzed respiratory flow and esophageal pressure tracings for respiratory timing variables, pulmonary mechanics and respiratory effort. Breaths were classified as braked (inspiratory:expiratory ratio ≥1.5) and unbraked (<1.5). According to the expiratory flow shape braked breaths were chategorized into early peak expiratory flow, late peak expiratory flow, slow flow, and post-inspiratory hold flow (PiHF). The most braked breaths had lower rates, larger tidal volume but lower minute ventilation, inspiratory airway resistance and respiratory effort, except for the PiHF, which had higher resistance and respiratory effort. The braked pattern predominated during TH, but not during normothermia or in the uncooled infants. We speculate that during TH for HIE low respiratory rates favor neonatal braked breathing to preserve lung volume. Given the generally low respiratory effort, it seems reasonable to leave spontaneous breathing unassisted. However, if the PiHF pattern predominates, ventilatory support may be required.

Возрастные особенности аэробных возможностей организма у спортсменов с разной направленностью физических нагрузок

The purpose of this study was to identify age-related features of aerobic capacity in athletes working on their endurance or speed-strength qualities. Materials and methods. The research involved 103 male athletes, who were divided into groups according to the type of physical activity (endurance (n = 58) and strength-speed (n = 45)) and age (12–15, 16–18 and 19–26 years). Their aerobic capacity was determined using cardiorespiratory exercise testing. Results. It was shown that the increase in relative peak oxygen consumption (VO2peak) was influenced not so much by age as by the type of physical activity (ANOVA: F = 18.1, p = 0.00004). At the same time, respiratory coefficient (F = 5.6, p = 0.007), heart rate at anaerobic threshold (F = 4.9, p = 0.009), tidal volume (F = 7.5, p = 0.01) and minute ventilation (F = 6.6, p = 0.002) were influenced mainly by age. In athletes aged 12–15 years, factor analysis established a negative correlation of type of physical activity with oxygen pulse, while physical working capacity was positively correlated with breathing parameters. Subjects aged 16–18 years showed no significant correlations between the variables and type of physical activity; at the same time, the number of correlations between ergometry parameters and physical working capacity factor increased with age. In athletes aged 19–26, the variables correlated strongly with the type of physical activity; the contribution of VO2peak to the physical working capacity factor is clearly demonstrated. The development of aerobic capacity is mainly influenced by the type of physical activity. However, in athletes aged 12–15 years, aerobic loads do not lead to a significant increase in VO2peak. The greatest increase in VO2peak is observed in 16–18-year-olds, while after 18 years of age, its growth halts.

Impact of MCT Oil and Caffeine on Substrate Metabolism during Submaximal Exercise

Introduction: Recent research has suggested that medium-chain triglyceride (MCT) supplementation may increase fat oxidation (FatOx) during aerobic exercise, sparing muscle glycogen and, perhaps, enhancing performance. As both MCT and caffeine (CAF) are theorized to elicit these effects, this pilot study’s purpose was to compare the physiological responses of their combined supplementation during submaximal cycling exercise. Methods: Eight aerobically trained males (mean±SD; age 23.6±4.4 years; body mass 82.3±15.8 kg; height 180.9±8.7 cm) completed one aerobic capacity (VO2peak) test and three 45-min exercise trials at 60% VO2peak. Blinded and counterbalanced, one-hour prior to each trial, participants consumed: MCT+CAF (20 mL + 100 mg), long-chain triglycerides (LCT)+CAF (40 mL + 100 mg), or CAF (100 mg). Oxygen consumption (VO2), carbon dioxide output (VCO2), and minute ventilation (VE) were measured, subsequently calculating respiratory exchange ratio (RER), energy expenditure (EE), carbohydrate oxidation (CarbOx), and FatOx. Results: No significant differences between conditions were observed for average VO2 (p=0.474; η2=0.101), VE (p=0.323; η2=0.149), (RER (p=0.323; η2=0.149), EE (p=0.474; η2=0.101), CarbOx (p=0.274; η2=0.169), or FatOx (p=0.478; η2=0.100) or for total EE (p=0.474; η2=0.101), CarbOx (p=0.274; η2=0.169), or FatOx (p=0.478; η2=0.100). Conclusions: Co-ingestion of MCT+CAF didn’t produce any significantly different physiological responses compared to co-ingestion of LCT+CAF or the CAF control.

Effects of Obesity and Sex on Ventilatory Constraints during a Cardiopulmonary Exercise Test in Children.

Ventilatory constraints are common during exercise in children, but the effects of obesity and sex are unclear. The purpose of this study was to investigate the effects of obesity and sex on ventilatory constraints (i.e., expiratory flow limitation (EFL) and dynamic hyperinflation) during a maximal exercise test in children. Thirty-four 8-12-year-old children without obesity (18 females) and 54 with obesity (23 females) completed pulmonary function testing and maximal cardiopulmonary exercise tests. EFL was calculated as the overlap between tidal flow-volume loops during exercise and maximal expiratory flow-volume loops. Dynamic hyperinflation was calculated as the change in inspiratory capacity from rest to exercise. Maximal minute ventilation was not different between children with and without obesity. Average end-inspiratory lung volumes (EILV) and end-expiratory lung volumes (EELV) were significantly lower during exercise in children with obesity (EILV: 68.8 ± 0.7%TLC; EELV: 41.2 ± 0.5%TLC) compared with children without obesity (EILV: 73.7 ± 0.8%TLC; EELV: 44.8 ± 0.6%TLC; P < 0.001). Throughout exercise, children with obesity experienced more EFL and dynamic hyperinflation compared with those without obesity (P < 0.001). Also, males experienced more EFL and dynamic hyperinflation throughout exercise compared with females (P < 0.001). At maximal exercise, the prevalence of EFL was similar in males with and without obesity, however the prevalence of EFL in females was significantly different with 57% of females with obesity experiencing EFL compared with 17% of females without obesity (P < 0.05). At maximal exercise, 44% of children with obesity experienced dynamic hyperinflation compared with 12% of children without obesity (P = 0.002). Obesity in children increases the risk of developing mechanical ventilatory constraints such as dynamic hyperinflation and EFL. Sex differences were apparent with males experiencing more ventilatory constraints compared with females.

Study of gas exchange under different modes of ventilation in yoga breathing exercises

Yoga breathing exercises that develop the ability to voluntarily regulate the minute volume of respiration (MV) and maintain the state of hypoventilation, hypoxia and hypercapnia, can be considered as a way of hypoxic-hypercapnic training, potentially capable of influencing cerebral circulation and neuroprotective factors. However, at the moment, individual anthropometric features that affect the ability to develop a hypoventilation mode of breathing have not been studied, and methodological criteria for training have not been developed.Methods: The study involved 44 people (32 men and 12 women) who regularly practice yoga breathing techniques with a voluntary decrease in respiratory rate using maximum tidal volume (TV). Free breathing was recorded for 2 minutes, then each subject performed the respiratory hypoventilation pattern available to him or her (minimum RR values with maximum TV, inhalation and exhalation were of equal duration). The following parameters of external respiration were determined: respiratory rate (RR), minute ventilation (MV), tidal volume (TV), partial pressure of CO2 in the exhaled air at the end of exhalation (PetCO2 ), percentage of O2 in the exhaled air (FeO2) and hemoglobin saturation (SpO2 ).Results: Compared to breathing at rest (MV = M±SD 8.51 ± 2.57 (95% CI 7.72–9.29) l/min; PetCO2 = M±SD 36.98 ± 3.71 (95% CI 35.85–38.11) mm Hg), the mode with RR = 3 times/min (inspiration and expiration for 10 s), n = 44, leads to an increase in MV up to M±SD 12.02 ± 3.42 (95% CI 10.98–13.06) l/min (p &lt; 0.001) and a decrease of CO2 : PetCO2 = M±SD 33.99 ± 3.59 (95% CI 32.90–35.08) mm Hg (p &lt; 0.001) — that is, to development of alveolar hypocapnia. The mode with RR = 1.5 times/min (inhalation and exhalation for 20 s), n = 44, demonstrates a decrease in MV to M±SD 5.95 ± 1.59 (95% CI 5.46–6.43) l/min (p &lt; 0.001) and growth of PetCO2 up to M±SD 41.19 ± 3.71 (95% CI 40.06–42.32) mm Hg (p &lt; 0.001). The mode with RR = 1 time/min (inspiration and exhalation for 30 s), n = 24: with a decrease in RR to 1 time/min, a decrease in MV was observed to M±SD 4.22 ± 0.92 (95% CI 3.83–4.61) l / min (p &lt; 0.001) and an increase in PetCO2 up to M±SD 44.05 ± 3.05 (95% CI 42.76–45.33) mm Hg (p &lt; 0.001). The breathing pattern with RR = 1 r/min is accompanied by a statistically significant decrease in MV compared to rest, as well as an increase in PetCO2 and a decrease in FeO2 , that is, it is hypoventilation. We have proposed a ventilation coefficient (Qvent), which is the ratio MV/VC, which allows us to judge at what values of MV an individual reaches a state of hypoventilation. It was previously shown in this sample that the breathing exercise becomes hypoventilation when Qvent values are equal to or less than 1. With Qvent in the range from 1 to 2, the ventilation mode is within normal values, and when Qvent is more than 2, hyperventilation occurs.Conclusion: when performing yoga breathing exercises, variations in MV are observed both in the direction of hyperventilation and in the direction of hypoventilation with corresponding shifts in gas exchange (hypocapnia with hyperventilation, hypercapnia with hypoventilation). The MV values at which an individual reaches hypoventilation vary from person to person and can be predicted using the ventilation coefficient (Qvent).

Ethanol pre-exposure attenuates the hypoxic ventilatory response and may attenuate expression of long term facilitation following intermittent hypoxia treatment in adult rats

Obstructive sleep apnea (OSA) is a highly prevalent breathing disorder in which airway collapse or obstruction during sleep leads to periodic bouts of inadequate (hypopneic) or absent (apneic) ventilation despite neurorespiratory effort. Repetitive apneic and hypopneic exposures during sleep can induce intermittent hypoxemia, sympathetic activation, and sleep fragmentation which can lead to a host of maladaptive behavioral and physiological outcomes. Intermittent hypoxia, which consists of alternating exposure to hypoxia and normal oxygen levels (normoxia), can induce a long-lasting increase in breathing motor output called long term facilitation (LTF) and is currently being investigated as a therapeutic treatment. Interestingly, experts in the field of LTF have noted how IH models some key aspects of OSA. It has been well established through clinical studies that ethanol consumption prior to sleep exacerbates existing OSA, increasing the apnea/hypopnea index and worsening arterial blood oxygen desaturations during the night. However, it is unknown whether ethanol affects expression of LTF following IH treatment. If LTF might serve as a means of increasing ventilatory output to compensate for periods of apnea and hypopnea during OSA, ethanol might not only worsen the severity of OSA, but impede individuals’ compensatory response. Thus, for this study we hypothesized that ethanol treatment would attenuate LTF expression and the magnitude of the hypoxic ventilatory response during IH treatment. Using adult female Sprague-Dawley rats, we administered either low-dose (0.8 g/kg) or high-dose (3 g/kg) ethanol through intraperitoneal injection to model a 2-drink nightcap or binge drinking-type ethanol exposure, respectively. Immediately afterwards, we measured subjects’ ventilatory output during baseline, then during a 5 by 3-minute moderate IH protocol, and for one hour following the end of IH using whole-body plethysmography. Finally, we took venous blood samples to assay serum ethanol concentration at the end of the approximately 2.5 hour plethysmography measurement. Results from the high-dose ethanol group indicate that ethanol pre-exposure might attenuate respiratory rate and minute volume LTF in comparison to saline-treated control. Furthermore, high-dose ethanol attenuated the hypoxic ventilatory response with respect to respiratory rate and minute volume. Low dosage of ethanol attenuated subjects’ HVR of respiratory rate and minute volume, but conflictingly trends towards increasing LTF of tidal volume while diminishing LTF of respiratory rate when compared to saline control. Overall, our findings indicate that high levels of ethanol exposure dramatically diminish the acute ventilatory response to hypoxic exposure and may impede long-term increases in ventilatory output following IH treatment. On the other hand, lower doses of ethanol have a subtler effect on the ventilatory response to hypoxia. Future directions will include analysis of additional parameters of ventilatory function to gain a more detailed understanding of how ethanol effects respiratory plasticity in the context of intermittent hypoxic exposure. NIH 5T32 AA027488 to ALSUniversity of Kentucky Endowment to WJA. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Surgeons Experience Greater Physiologic Stress and Strain in the Direct Anterior Approach Than the Posterior Approach for Total Hip Arthroplasty

BackgroundThe direct anterior approach (DAA) and posterior approach (PA) for total hip arthroplasty (THA) have advantages and disadvantages, but their physiologic burden to the surgeon has not been quantified. This study was conducted to determine whether differences exist in surgeon physiological stress and strain during DAA in comparison to PA. MethodsWe evaluated a prospective cohort of 144 consecutive cases (67 DAA and 77 PA). There were 5, high-volume, fellowship-trained arthroplasty surgeons who wore a smart-vest that recorded cardiorespiratory data while performing primary THA DAA or PA. Heart rate (beats/minute), stress index (correlates with sympathetic activations), respiratory rate (respirations/minute), minute ventilation (L/min), and energy expenditure (calories) were recorded, along with patient body mass index and operative time. Continuous data was compared using t-tests or Mann Whitney U tests, and categorical data was compared with Chi-square or Fischer’s exact tests. ResultsThere were no differences in patient characteristics. Compared to PA, performing THA via DAA had a significantly higher surgeon stress index (17.4 versus 12.4; P < .001), heart rate (101 versus 98.3; P = .007), minute ventilation (21.7 versus 18.7; P < .001), and energy expenditure per hour (349 versus 295; P < .001). However, DAA had a significantly shorter operative time (71.4 versus 82.1; P = .001). ConclusionsSurgeons experience significantly higher physiological stress and strain when performing DAA compared to PA for primary THA. This study provides objective data on energy expenditure that can be factored into choice of approach, case order, and scheduling preferences, and provides insight into the work done by the surgeon.

Changes in preBötzinger Complex neuron discharge associated with changes in PCO2 in decerebrate rabbits

Background: Maskrey and Nicol reported a strong increase in minute ventilation with increase in PCO2 (J Physiol 1980, 301: 49-58). We investigated a) whether there was a ceiling to this effect at high CO2 levels and b) whether the change in ventilation was associated with specific changes in respiratory neurons in the preBötzinger complex (preBC). Methods: The study was approved by the local Animal Care Committee and conformed to NIH standards. Adult New Zealand White rabbits (3-4 kg) were anesthetized, tracheotomized, ventilated, decerebrated and vagotomized. Phrenic nerve activity was recorded from the C5 rootlet, time averaged and used to calculate inspiratory (TI) and expiratory durations (TE) and peak phrenic activity (PPA). PPA was normalized to the value at PCO2 50mmHg. Individual neurons were recorded in the functionally identified preBC using multichannel electrodes at increasing CO2 levels. Statistical analysis used the Wilcoxon signed-rank test to determine changes in respiratory parameters between CO2 levels and Friedman RM-ANOVA to determine changes in neuronal discharge frequency (Fn). A generalized linear mixed model was used to determine associations between CO2-dependent changes in TI, TE, PPA, and changes in Fn for different neuron types. p&lt;0.05 indicated a significant difference. Results: In 34 animals, the increase in minute ventilation with increasing PCO2 was due mostly to the change in PPA. The increase in respiratory rate was due mostly to a decrease in TE. There was little increase in respiratory output at PCO2 &gt; 50 mmHg. In 209 neurons, increasing PCO2 increased Fn in inspiratory augmenting (I aug, n= 70, p&lt;0.0001 for CO2 30 vs 40 and 40 vs 50mmHg), I parabolic (I para, n=43, p&lt;0.0001 for CO2 40 vs 50 mmHg), pre-inspiratory (pre-I, n=35, p&lt;0.01 for CO2 30 vs 40 mmHg), and expiratory decrementing (E dec, n=44, p&lt;0.01 for CO2 40 vs 50 mmHg) neurons, but not in I dec (n=8) and non-respiratory modulated (NRM, n=9) neurons. The strongest correlation was found between the changes in phase timing and PPA and Fn in I aug and pre-I neurons. Conclusion: We found a ceiling effect to the increase in respiratory output at PCO2 levels &gt; 50 mmHg. Inspiratory preBC neuron subtypes were more affected by the changes in PCO2. NIH R01HL159546. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.