Maximal Inspiratory Maneuvers Research Articles

Breathing a low-density gas reduces respiratory muscle force development and marginally improves exercise performance in master athletes.

We tested the hypothesis that breathing heliox, to attenuate the mechanical constraints accompanying the decline in pulmonary function with aging, improves exercise performance. Fourteen endurance-trained older men (67.9 ± 5.9 year, [Formula: see text]O2max: 50.8 ± 5.8ml/kg/min; 151% predicted) completed two cycling 5-km time trials while breathing room air (i.e., 21% O2-79% N2) or heliox (i.e., 21% O2-79% He). Maximal flow-volume curves (MFVC) were determined pre-exercise to characterize expiratory flow limitation (EFL, % tidal volume intersecting the MFVC). Respiratory muscle force development was indirectly determined as the product of the time integral of inspiratory and expiratory mouth pressure (∫Pmouth) and breathing frequency. Maximal inspiratory and expiratory pressure maneuvers were performed pre-exercise and post-exercise to estimate respiratory muscle fatigue. Exercise performance time improved (527.6 ± 38 vs. 531.3 ± 36.9s; P = 0.017), and respiratory muscle force development decreased during inspiration (-22.8 ± 11.6%, P < 0.001) and expiration (-10.8 ± 11.4%, P = 0.003) with heliox compared with room air. EFL tended to be lower with heliox (22 ± 23 vs. 30 ± 23% tidal volume; P = 0.054). Minute ventilation normalized to CO2 production ([Formula: see text]E/[Formula: see text]CO2) increased with heliox (28.6 ± 2.7 vs. 25.1 ± 1.8; P < 0.001). A reduction in MIP and MEP was observed post-exercise vs. pre-exercise but was not different between conditions. Breathing heliox has a limited effect on performance during a 5-km time trial in master athletes despite a reduction in respiratory muscle force development.

Voluntary activation of the diaphragm after inspiratory pressure threshold loading.

After a bout of isolated inspiratory work, such as inspiratory pressure threshold loading (IPTL), the human diaphragm can exhibit a reversible loss in contractile function, as evidenced by a decrease in transdiaphragmatic twitch pressure (PDI,TW ). Whether or not diaphragm fatigability after IPTL is affected by neural mechanisms, measured through voluntary activation of the diaphragm (D-VA) in addition to contractile mechanisms, is unknown. It is also unknown if changes in D-VA are similar between sexes given observed differences in diaphragm fatigability between males and females. We sought to determine whether D-VA decreases after IPTL and whether this was different between sexes. Healthy females (n=11) and males (n=10) completed an IPTL task with an inspired duty cycle of 0.7 and targeting an intensity of 60% maximal transdiaphragmatic pressure until task failure. PDI,TW and D-VA were measured using cervical magnetic stimulation of the phrenic nerves in combination with maximal inspiratory pressure maneuvers. At task failure, PDI,TW decreased to a lesser degree in females vs. males (87 ± 15 vs. 73 ± 12% baseline, respectively, p=0.016). D-VA decreased after IPTL but was not different between females and males (91 ± 8 vs. 88 ± 10% baseline, respectively, p=0.432). When all participants were pooled together, the decrease in PDI,TW correlated with both the total cumulative diaphragm pressure generation (R2 =0.43; p=0.021) and the time to task failure (TTF, R2 = 0.40; p = 0.30) whereas the decrease in D-VA correlated only with TTF (R2 =0.24; p=0.041). Our results suggest that neural mechanisms can contribute to diaphragm fatigability, and this contribution is similar between females and males following IPTL.

Single-breath oxygen dilution for the measurement of total lung capacity: technical description and preliminary results in healthy subjects

Objective. Total lung capacity (TLC) assessment outside of a research laboratory is challenging. We describe a novel method for measuring TLC that is both simple and based only on portable equipment, and report preliminary data in healthy subjects. Approach. We developed an open circuit system to administer a known amount of oxygen to a subject in a single maximal inspiratory maneuver. Oxygen fraction, expired and inspired flows were continuously monitored to allow a precise computation of the mass balance. Values of TLC and functional residual capacity (FRC) were compared with standard methods (body plethysmography and multiple-breath helium dilution). Twenty healthy subjects participated to the study, eleven of which performed the maneuver twice to assess test-retest reliability. Main results. There was high agreement in TLC between the proposed method and the two standard methods (R 2 > 0.98, bias not different from 0, and 95% limits of agreements <± 0.4 l for both). Test-retest reliability was high (intraclass correlation coefficient >0.99 and no bias). Results were similar for FRC, with a slightly higher variability due its sensitivity to changes in posture or breathing pattern. Significance. Single-breath oxygen dilution is accurate and reliable in assessing TLC and FRC in healthy subjects. The technique is appealing for time- or resource-limited settings, such as field physiological research expeditions or mass screenings.

Expiratory Pressure Generation In Adult Survivors Of Preterm Birth

Adult survivors of preterm birth (PRE) have arrested lung development resulting in lower pulmonary function compared to their counterparts born at full term (CON). PRE have normal lung volumes, but lower expiratory airflow, which could be caused, in part, by a lesser driving (alveolar) pressure. During forced expiration alveolar pressure is the sum of pleural pressure, a function of respiratory muscle effort/strength, and lung recoil pressure. Whether or not PRE have normal respiratory muscle strength and/or lung compliance (CL) has not yet been explored. PURPOSE: The purpose of this study was to quantify respiratory muscle strength and CL in PRE and CON. Based upon the existing literature, we hypothesized that PRE and CON will have equivalent respiratory muscle strength and CL. METHODS: To date, n = 8 PRE and n = 5 CON, visited the lab on two occasions. First, subjects performed standard spirometry (e.g. fast and slow vital capacity maneuvers). Next, to assess respiratory muscle strength, subjects performed maximal inspiratory and maximal expiratory pressure maneuvers (MIP and MEP, respectively). For MIP, subjects inhaled maximally against an occluded mouthpiece at residual volume. For MEP, subjects exhaled exhale maximally against an occluded mouthpiece at total lung capacity. Each maneuver was performed 3-5 times. On the second visit, CL was measured. To do so, subjects were instrumented with an esophageal balloon catheter and performed quasi-static expiratory deflation curves (i.e., very slow exhalations from total lung capacity to residual volume). To test for differences in MIP, MEP, and CL between groups we computed multiple independent samples t-tests with significance set to p<0.05. RESULTS: We found no difference in MIP (-130.6 ± 29.3 vs. -106.5 ± 36.1 cm H2O; p = 0.24) or MEP (165.7 ± 42.9 vs.121.0 ± 51.6 cm H2O; p = 0.14) between CON and PRE, respectively. Likewise, CL was comparable between CON (0.29 ± 0.11 L/cm H2O) and PRE (0.33 ± 0.10 L/cm H2O; p = 0.53). CONCLUSION: Our data suggests no effect of birth status on the ability to generate expiratory pressure during forced expiration. Likewise, results suggest that the lower pulmonary function in PRE is not the result of a lesser driving pressure, but instead may be the result of excessive airflow resistance. Support: Hooper Undergraduate Research Award from NAU.

Indices of acceleration atelectasis and the effect of hypergravity duration on its development.

What is the central question of the study? The aim was to determine the effects of duration of acceleration in the cranial-caudal direction (+Gz) on acceleration atelectasis and identify measurement techniques that can be used to assess it. What is the main finding and its importance? Non-invasive measurement of acceleration atelectasis using electrical impedance tomography and estimates of pulmonary shunt provide more detailed assessment of acceleration atelectasis than traditional forced vital capacity measures. Using these techniques, it was found that as little as 30s of exposure to +Gz acceleration can cause acceleration atelectasis. The results of the present study will allow a more accurate and detailed assessment of acceleration atelectasis in the future. Recently, there have been reports of acceleration atelectasis during fast jet flight despite the use of systems designed to minimize this. Before further investigation of this, indices suitable for use in applied settings and identification of acceleration durations that elicit it are required. Fifteen non-aircrew subjects underwented five centrifuge exposures lasting 15, 30, 60 and 2×90s with a plateau of +5 Gz (acceleration in the cranial-caudal direction) while breathing 94% O2 during all but one control exposure (21% O2 ). Lung volumes and gas exchange limitation were assessed after each exposure. Regional lung impedance and compliance were measured after Gz exposure using electrical impedance tomography and the forced oscillatory technique, respectively. The presence of acceleration atelectasis was confirmed by reductions of 10-17% in vital and inspiratory capacity after 60 and 90s Gz exposures (P<0.05) and resulted in reduced regional lung impedance and a gas exchange limitation of 8.1 and 12.5%, respectively (P<0.05). There was also a small but significant decrease in regional lung impedance after 30s exposures. Functional residual capacity and lung compliance were unchanged in atelectatic lungs (P>0.05). In the majority of individuals,>60 s of Gz exposure while breathing 94% O2 causes acceleration atelectasis. Electrical impedance tomography and the measurement of gas exchange limitation provide useful indicators of acceleration atelectasis. Acceleration atelectasis exerts its effects primarily through basal lung closure and reflex inspiratory limitation, both of which can be reversed by performing three maximal inspiratory breathing manoeuvres.

Effect of inspiratory resistive training on diaphragm shear modulus and accessory inspiratory muscle activation.

This study aimed to elucidate changes in diaphragm and accessory inspiratory muscle (sternocleidomastoid (SCM) muscle and intercostal muscle (IC)) function after a 6-week training program. Nineteen male elite collegiate swimmers were assigned to either a control group (n = 9) or training group (n = 10). The subjects in the training group performed 30 maximum inspirations at a load resistance of 50% of maximum inspiratory mouth pressure (PImax) using an inspiratory muscle training device. These were conducted twice per day and 6 days per week. At baseline and after 6 weeks, PImax, shear modulus of the diaphragm, and electromyograms (EMG) of the SCM and IC during a maximal inspiratory maneuver were evaluated. Relative change in PImax was greater in the training group than in controls. The shear modulus during a PImax maneuver had increased significantly in both groups after 6 weeks. EMG amplitudes of the SCM increased in the training group after 6 weeks, but not in the control group. EMG amplitudes of the IC did not change after 6 weeks in either group. These results suggest that 6-week inspiratory resistive training significantly improves the activation of the SCM, which could be one of the major mechanisms behind increases in inspiratory muscle strength after resistive training. Novelty Six-week inspiratory resistive training increased diaphragm stiffness during maximal inspiration maneuver. Six-week inspiratory resistive training increased electromyogram amplitudes of the sternocleidomastoid during maximal inspiration maneuver.

Effects of caffeine on inspiratory muscle function

Research suggests that caffeine can enhance measures of muscular strength in the upper and lower extremities, although the literature is somewhat equivocal. Little is known on whether or not caffeine will improve maximal inspiratory pressure (MIP), a surrogate measure of inspiratory muscle strength. The purpose of the study was to determine the effects of a moderate dose of caffeine on inspiratory muscle function. Fifteen (8 male, 7 female) healthy adults (mean ± SD: age = 24.3 ± 6.4 years; height = 1.75 ± 0.11 m; body mass = 78.8 ± 16.5 kg) volunteered to participate in the study which used a double-blind, placebo-controlled, cross-over design. During the initial visit, baseline data was collected and participants were familiarized with inspiratory muscle measurements. For the second and third visits, participants ingested either a 5 mg kg−1 dose of caffeine (CAF) or placebo capsule (PL). After one hour, they completed at least 12 maximal inspiratory manoeuvres with 1 min rest between each attempt. MIP, maximal inspiratory peak pressure (PP), and maximal rate of pressure development (MRPD) were recorded. The CAF trial resulted in significantly higher MIP (154.7 ± 35.8 vs. 146.6 ± 37.6 cmH2O; p = 0.02) and PP (165.8 ± 36.8 vs. 158.3 cmH2O; p = 0.01) compared to the PL condition. No significant difference was observed in MRPD (p = 0.18). MIP and PP improved after ingestion of caffeine compared to the placebo condition. The findings from the study further establish caffeine’s potential ergogenic benefit on measures of muscular strength.

Correlations between change in neural respiratory drive and heart rate variability in patients submitted to open-heart surgery.

Respiratory muscle dysfunction after open-heart surgery may influence the cardiopulmonary interactions. The purpose of this study was to examine the correlation between change in the neural respiratory drive (NRD) and change in heart rate variability (HRV) in patients submitted to open-heart surgery. An observational cross-sectional study was conducted among 32 participants. NRD was assessed via a surface electromyogram of the parasternal intercostal muscle (sEMGpara). Polar heart rate monitor was used to measure HRV during the deep breathing maneuver. Evaluations were performed on the day of admission and discharge. There were statistically significant differences in NRD and HRV indices between admission and discharge periods (P<0.05). The difference in peak root mean square of sEMGpara recorded during resting (ΔRMS sEMGpara tidal), during maximal inspiratory maneuver (ΔsEMGpara max), and its normalized values (ΔRMS sEMGpara%max) were significantly correlated with the difference in total power (ΔTotal power), mean of heart rate (ΔMeanHR), and mean of R to R intervals (ΔMeanRR) (r=−0.844, P=0.004, r=−0.835, P=0.005, and r=0.643, P=0.043, respectively). It can be concluded that NRD correlated well with HRV in patients who had undergone open-heart surgery.

Diaphragm Stimulation Enhances Respiratory Function After Cervical Spinal Cord Injury

Purpose/HypothesisCervical spinal cord injury (CSCI) causes severe respiratory impairment and respiratory complications are a leading cause of illness and death. Although mechanical ventilation (MV) is lifesaving, MV use is associated with diaphragm atrophy and high respiratory infection rates. Intramuscular diaphragm stimulation, or diaphragm pacing (DP), is now used acutely to promote MV weaning. Preliminary reports suggest that DP may improve diaphragm activation, respiratory function, and promote recovery of independent respiration. The effects of DP, however, have not been systematically evaluated. Our purpose was to test the hypothesis that DP leads to an increase in voluntary diaphragm activation and improvements in respiratory function.SubjectsEleven adults with acute, traumatic CSCIs (6 males, mean age 40.8±12 years) who underwent implantation of DP wires due to failure to wean from MV participated (mean time on MV until DP wire implantation 16±10 days). Injuries were classified as C1 to C4 based on the ASIA Impairment Scale A or B (motor complete, n=10) and C (motor incomplete, n=1).Materials/MethodsRespiratory function and diaphragm activation were assessed within 3 days post implantation of the DP wires and assessments were repeated at regular intervals up to four months post DP implantation. Respiratory function was assessed using standard measures of tidal volume (Vt), forced vital capacity (FVC), and maximal inspiratory and expiratory pressures (MIP, MEP). Diaphragm activation was assessed by recording electromyograms (EMGs) from the intramuscular DP wires during maximal inspiratory maneuvers. All tests were conducted without assistance from DP and with the lowest ventilator setting tolerated.ResultsFollowing onset of DP, 9 of 11 individuals weaned from MV (mean time 35±24 days) and 6 individuals resumed independent respiration without use of DP. All measures of respiratory function increased over time (p&lt;0.05). Average gains in respiratory function were: Vt, +24±31% (range −31 – 77%); FVC, +37±16% (range 17 – 63%); MIP, +43±56% (range −45 – 124%); MEP +67±64% (range −31 – 176%). Mean peak EMG burst amplitude during maximal inspiratory maneuvers increased 20% (range 0 – 92%).ConclusionsDuring an extended period of DP, adults with severe CSCIs demonstrated gains in respiratory function and volitional diaphragm activation. Nearly all individuals weaned from MV and over half progressed to independent respiration following onset of DP. Stimulation of the diaphragm is likely to promote muscle health which would contribute to weaning. In addition, the increased diaphragm muscle activation in many subject raises the possibility that DP and associated activation of sensory afferents evokes beneficial plasticity in the respiratory neural control system.Support or Funding InformationCraig H. Neilsen Foundation (EJF); NIH/NICHD K12 HD055929 (EJF); T32‐HD043730 (MDS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Genioglossus activation during maximal sniff manoeuvres: Is upper airway function relevant in the clinical assessment of inspiratory and expiratory muscle strength?

Genioglossus activation during maximal sniff manoeuvres: Is upper airway function relevant in the clinical assessment of inspiratory and expiratory muscle strength?

Assessment of diaphragmatic thickness by ultrasonography in Duchenne muscular dystrophy (DMD) patients.

IntroductionIn Duchenne muscular dystrophy (DMD) the assessment of diaphragmatic function is crucial because respiratory muscle weakness can cause respiratory failure. We aimed to noninvasively assess diaphragmatic function in DMD by measuring diaphragmatic thickness by ultrasonography, under the hypothesis that the progressive decrease of lung function is related to alterations of diaphragmatic thickness.MethodsForty-four DMD patients and thirteen healthy controls were enrolled and subdivided into three age groups. Diaphragmatic thickness was measured during quiet breathing, inspiratory capacity, maximal inspiratory pressure and expiratory pressure maneuvers.ResultsIn DMD, absolute values of diaphragmatic thickness were significantly lower than in controls in the majority of the manoeuvers and diaphragmatic thickness significantly decreased with age at end-expiration, remaining constant at end-inspiration and during maximal inspiratory pressure maneuvers. Comparing to controls, absolute values of diaphragmatic thickness and diaphragmatic thickness variations were significantly lower (p<0.001), with the exception of quiet breathing and maximal expiratory pressure maneuvers in the youngest DMD. During maximal inspiratory pressure maneuver, variation of diaphragmatic thickness was not significantly different in the all groups, nevertheless maximal inspiratory pressure decreases with age.ConclusionsThe diaphragm is prone to pseudo-hypertrophy in the youngest DMD, and to progressive atrophy in middle-age and oldest DMD. Diaphragm impairment could be expressed as a dissociation between muscle drive and muscle developed force. Ultrasonography could be used as a noninvasive method to assess progressive diaphragmatic weakness.

Acute effects of different inspiratory efforts on ventilatory pattern and chest wall compartmental distribution in elderly women

It is not completely described how aging affect ventilatory kinematics and what are the mechanisms adopted by the elderly population to overcome these structural modifications. Given this, the aim was to evaluate the acute effects of different inspiratory efforts on ventilatory pattern and chest wall compartmental distribution in elderly women. Variables assessed included: tidal volume (Vt), total chest wall volume (Vcw), pulmonary rib cage (Vrcp%), abdominal rib cage (Vrca%) and abdominal compartment (Vab%) relative contributions to tidal volume. These variables were assessed during quiet breathing, maximal inspiratory pressure maneuver (MIP), and moderate inspiratory resistance (MIR; i.e., 40% of MIP). 22 young women (age: 23.9±2.5 years) and 22 elderly women (age: 68.2±5.0 years) participated to this study. It was possible to show that during quiet breathing, Vab% was predominant in elderly (p<0.001), in young, however, Vab% was similar to Vrcp% (p=0.095). During MIR, Vrcp% was predominant in young (p<0.001) and comparable to Vab% in elderly (p=0.249). When MIP was imposed, both groups presented a predominance of Vrcp%. In conclusion, there are differences in abdominal kinematics between young and elderly women during different inspiratory efforts. In elderly, during moderate inspiratory resistance, the pattern is beneficial, deep, and slow. Although, during maximal inspiratory resistance, the ventilatory pattern seems to predict imminent muscle fatigue.

Respiratory motor output during an inspiratory capacity maneuver is preserved despite submaximal exercise

It is unknown whether respiratory motor output is constrained during exhaustive exercise in healthy adults. We hypothesised that neural inhibition did occur; to test this hypothesis we measured diaphragm EMG from a maximal inspiratory capacity maneuver (EMGdi-IC) at rest and during exercise. EMGdi-IC was measured before and after the amplitude of the diaphragm EMG entered a plateau phase in eleven healthy adults undertaking exercise at 60% and 80% of maximal workload achieved from incremental exercise. The mean EMGdi-IC at rest was 65±16% of the maximum that could be obtained from a battery of inspiratory tasks. Before and after the plateau phase of diaphragm EMG, EMGdi-IC was 68±13% and 72±12% (p>0.05) during 60% of the maximum workload, and was 70±13% and 78±13% (p>0.05) during 80% of the maximum workload achieved on an incremental test. A further sub-study in which 5 participants exercised at 90% of the maximum workload also showed that EMGdi-IC was not diminished during exercise. Our data show that exercise condition does not reduce the magnitude of EMGdi-IC. This argues against neural inhibition as feature of submaximal exercise in healthy adults.

Expiratory muscle fatigue does not regulate operating lung volumes during high-intensity exercise in healthy humans

To determine whether expiratory muscle fatigue (EMF) is involved in regulating operating lung volumes during exercise, nine recreationally active subjects cycled at 90% of peak work rate to the limit of tolerance with prior induction of EMF (EMF-ex) and for a time equal to that achieved in EMF-ex without prior induction of EMF (ISO-ex). EMF was assessed by measuring changes in magnetically evoked gastric twitch pressure. Changes in end-expiratory and end-inspiratory lung volume (EELV and EILV) and the degree of expiratory flow limitation (EFL) were quantified using maximal expiratory flow-volume curves and inspiratory capacity maneuvers. Resistive breathing reduced gastric twitch pressure (-24 ± 14%, P = 0.004). During EMF-ex, EELV decreased from rest to the 3rd min of exercise [39 ± 8 vs. 27 ± 7% of forced vital capacity (FVC), P = 0.001] before increasing toward baseline (34 ± 8% of FVC end exercise, P = 0.073 vs. rest). EILV increased from rest to the 3rd min of exercise (54 ± 8 vs. 84 ± 9% of FVC, P = 0.006) and remained elevated to end exercise (88 ± 9% of FVC). Neither EELV (P = 0.18) nor EILV (P = 0.26) was different at any time point during EMF-ex vs. ISO-ex. Four subjects became expiratory flow limited during the final minute of EMF-ex and ISO-ex; the degree of EFL was not different between trials (37 ± 18 vs. 35 ± 16% of tidal volume, P = 0.38). At end exercise in both trials, EELV was greater in subjects without vs. subjects with EFL. These findings suggest that 1) contractile fatigue of the expiratory muscles in healthy humans does not regulate operating lung volumes during high-intensity sustained cycle exercise; and 2) factors other than "frank" EFL cause the terminal increase in EELV.

The influence of rowing-related postures upon respiratory muscle pressure and flow generating capacity

During the rowing stroke, the respiratory muscles are responsible for postural control, trunk stabilisation, generation/transmission of propulsive forces and ventilation (Bierstacker et al. in Int J Sports Med 7:73-79, 1986; Mahler et al. in Med Sci Sports Exerc 23:186-193, 1991). The challenge of these potentially competing requirements is exacerbated in certain parts of the rowing stroke due to flexed (stroke 'catch') and extended postures (stroke 'finish'). The purpose of this study was to assess the influence of the postural role of the trunk muscles upon pressure and flow generating capacity, by measuring maximal respiratory pressures, flows, and volumes in various seated postures relevant to rowing. Eleven male and five female participants took part in the study. Participants performed two separate testing sessions using two different testing protocols. Participants performed either maximal inspiratory or expiratory mouth pressure manoeuvres (Protocol 1), or maximal flow volume loops (MFVLs) (Protocol 2), whilst maintaining a variety of specified supported or unsupported static rowing-related postures. Starting lung volume was controlled by initiating the test breath in the upright position. Respiratory mouth pressures tended to be lower with recumbency, with a significant decrease in P (Emax) in unsupported recumbent postures (3-9% compared to upright seated; P=0.036). There was a significant decrease in function during dynamic manoeuvres, including PIF (5-9%), FVC (4-7%) and FEV(1) (4-6%), in unsupported recumbent postures (p<0.0125; Bonferroni corrected). Thus, respiratory pressure and flow generating capacity tended to decrease with recumbency; since lung volumes were standardised, this may have been, at least in part, influenced by the postural co-contraction of the trunk muscles.

S115 The effect of posture on the 2nd intercostal space surface parasternal electromyogram (EMGpara): validating a novel clinical tool to measure neural respiratory drive

IntroductionAlthough neural respiratory drive (NRD), as measured by diaphragm EMG, has been shown to reflect the balance between the respiratory muscle load and capacity providing a marker of disease severity,...

Regional chest wall volume changes during various breathing maneuvers in normal men.

The purpose of this study is to investigate the regional chest wall volume changes during various breathing maneuvers in normal men with an optical reflectance system (OR), which tracks reflective markers in three dimensions. Chest wall volume was measured by the OR system [VL(CW)], and lung volume was measured by hot wire spirometry [VL(SP)] in 15 healthy men during quiet breathing (QB), during breathing at a rate of 50 tidal breaths/min paced using a metronome (MT: metronome-paced tachypnea), and during a maximal forced inspiratory and expiratory maneuver (MFIE maneuver). There were few discrepancies between VL(CW) and VL(SP) for QB and MT. In the MFIE maneuver, however VL(CW) was often underestimated compared with VL(SP), particularly during forced maximal expiration, because of pulmonary rib cage volume changes. Furthermore, the regional chest wall volume changes were affected by breathing maneuver alternation. In the pulmonary and abdominal rib cage, inspiratory reserve volume was larger than expiratory reserve volume, respectively, and in the abdomen, expiratory reserve volume was larger than inspiratory reserve volume. Alternation of breathing maneuvers affects regional chest wall volume changes.

P124 Neuroventilatory uncoupling during cycle and treadmill exercise in COPD

BackgroundIt is widely accepted that neuroventilatory uncoupling drives breathlessness in COPD. COPD patients are more likely to stop exercising because of breathlessness during treadmill exercise than whilst cycling.AimTo test the...

Change in the zone of apposition of the human diaphragm associated with ventilatory movement

The movement of the cephalic margin of the zone of apposition (ZOA) of the diaphragm associated with ventilatory movement was measured using ultrasonography in 24 healthy subjects and 45 patients with various pulmonary diseases. A transducer was placed on the lower chest wall, and movement of the cephalic margin of ZOA was measured during maximal inspiratory maneuver and expiratory maneuver from end expiratory position in supine and sitting positions in healthy subjects, and in the supine position in patients. In healthy subjects, there was a linear relationship between inspiratory or expiratory volumes and movement of the cephalic margin of ZOA. Movement in the supine position during vital capacity maneuver was 103.0 +/- 15.6 (mean +/- SD), 106.6 +/- 17.2, 108.5 +/- 18.2, and 114.8 +/- 16.3 mm on the left anterior, right anterior, left posterior, and right posterior axillary lines, respectively. In the supine position, movement on the right posterior axillary line was significantly larger than that measured on other axillary lines (p less than 0.05). Movement during maximal inspiratory maneuver in the supine position was significantly larger than that in the sitting position (p less than 0.01). Movement during maximal expiratory maneuver in the supine position was significantly smaller than that in the sitting position (p less than 0.01). Patients showed decreased movement and great differences in movement between the left and right anterior axillary lines. Seven patients out of 28 with normal spirograms showed decreased movement on either or both sides. These data suggest that: 1) the movement of the cephalic margin of ZOA reflects diaphragm displacement; and 2) difference in ventilatory function of right and left hemithorax can be detected by movement of the cephalic margin of ZOA.

Inspiratory Muscle Unloading by Neurally Adjusted Ventilatory Assist During Maximal Inspiratory Efforts in Healthy Subjects

Background:Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation in which the ventilator is controlled by the electrical activity of the diaphragm (EAdi). During maximal inspirations, the pressure delivered can theoretically reach extreme levels that may cause harm to the lungs. The aims of this study were to evaluate whether NAVA could efficiently unload the respiratory muscles during maximal inspiratory efforts, and if a high level of NAVA would suppress EAdi without increasing lung-distending pressures.Method:In awake healthy subjects (n = 9), NAVA was applied at increasing levels in a stepwise fashion during quiet breathing and maximal inspirations. EAdi and airway pressure (Paw), esophageal pressure (Pes), and gastric pressure, flow, and volume were measured.Results:During maximal inspirations with a high NAVA level, peak Paw was 37.1 ± 11.0 cm H2O (mean ± SD). This reduced Pes deflections from − 14.2 ± 2.7 to 2.3 ± 2.3 cm H2O (p < 0.001) and EAdi to 43 ± 7% (p < 0.001), compared to maximal inspirations with no assist. At high NAVA levels, inspiratory capacity showed a modest increase of 11 ± 11% (p = 0.024).Conclusion:In healthy subjects, NAVA can safely and efficiently unload the respiratory muscles during maximal inspiratory maneuvers, without failing to cycle-off ventilatory assist and without causing excessive lung distention. Despite maximal unloading of the diaphragm at high levels of NAVA, EAdi is still present and able to control the ventilator.