Total Work Of Breathing Research Articles

Acute Effects of a Respiratory Sprint-Interval Session on Muscle Contractility.

Respiratory muscle training has been shown to improve physical performance in healthy individuals and patients. One training modality for both inspiratory and expiratory muscles is respiratory muscle endurance training (RMET), which consists of normocapnic hyperpnea at constant ventilation for 30 min. Here, a new training regimen, respiratory muscle sprint-interval training (RMSIT), is introduced and tested for its potential to fatigue respiratory muscles. In addition, effects of both modalities on airway properties are investigated. In 12 healthy subjects (six men and six women; 24 ± 3 yr; forced expiratory volume in 1 s, 115% ± 10%), changes in inspiratory transdiaphragmatic twitch pressure (Pdi,tw) and expiratory gastric twitch pressure (Pga,tw) were assessed during cervical magnetic stimulation or thoracic magnetic stimulation before and after a single bout of RMET and RMSIT. At similar time points, mechanical airway properties were assessed by impulse oscillometry. RMET was performed for 30 min at 60% of maximal voluntary ventilation, with constant tidal volume and breathing frequency. RMSIT consisted of six 30-s respiratory sprints (with 2-min breaks in between) at constant tidal volume, with the greatest possible breathing frequency and added resistance. Pdi,tw and Pga,tw decreased significantly after RMET (-17.7% ± 9.0% and -22.4% ± 18.5%; P < 0.01) and RMSIT (-18.1% ± 12.8% and -21.2% ± 13.1%; P < 0.01), and changes did not differ between training modalities (P = 0.50 and P = 0.12), suggesting similar levels of fatigue. Work of breathing per minute was 2.4 ± 0.8-fold greater in RMSIT than in RMET, whereas total work of breathing was substantially smaller in RMSIT (3.4 ± 0.8 kJ) than in RMET (15.0 ± 0.42 kJ). No subject showed clinically relevant changes in mechanical airway properties. Despite different work history, RMSIT appears to place a metabolic load on respiratory muscles similarly to RMET and could therefore be considered a time-saving and safe training alternative.

Mechanisms of exercise intolerance in global initiative for chronic obstructive lung disease grade 1 COPD.

The purpose of this study was to determine if a dissociation existed between respiratory drive, as estimated by diaphragmatic electromyography (EMGdi), and its pressure-generating capacity during exercise in mild chronic obstructive pulmonary disease (COPD) and whether this, if present, had negative sensory consequences. Subjects meeting spirometric criteria for mild COPD (n=16) and age and sex-matched controls (n=16) underwent detailed pulmonary function testing and a symptom limited cycle test while detailed ventilatory, sensory and respiratory mechanical responses were measured. Compared with controls, subjects with mild COPD had greater ventilatory requirements throughout submaximal exercise. At the highest equivalent work rate of 60 W, they had a significantly higher: total work of breathing (32±17 versus 16±7 J·min(-1); p<0.01); EMGdi (37.3±17.3 versus 17.9±11.7% of maximum; p<0.001); and EMGdi to transdiaphragmatic pressure ratio (0.87±0.38 versus 0.52±0.27; p<0.01). Dyspnoea-ventilation slopes were significantly higher in mild COPD than controls (0.17±0.12 versus 0.10±0.05; p<0.05). However, absolute dyspnoea ratings reached significant levels only at high levels of ventilation. Increased respiratory effort and work of breathing, and a wider dissociation between diaphragmatic activation and pressure-generating capacity were found at standardised work rates in subjects with mild COPD compared with controls. Despite these mechanical and neuromuscular abnormalities, significant dyspnoea was only experienced at higher work rates.

Respiratory mechanics during NCPAP and HHHFNC at equal distending pressures

ObjectiveTo compare the effect of heated, humidified, high-flow nasal cannula (HHHFNC) and nasal continuous positive airways pressure (NCPAP) on lung function and mechanics in preterm infants with respiratory distress syndrome...

Clinical factors associated with success of proportional assist ventilation in the acute phase of critical illness: Pilot study

Abstract Reason Proportional assist ventilation plus (PAV+) applies pressure depending on the patient's inspiratory effort, automatically adjusting flow and volume assist to changes in respiratory mechanics. We aimed to assess the clinical factors associated with the success of PAV+ as first-line support in the acute phase of critical illness. Methods A prospective cohort study was carried out. Mechanically ventilated patients >24 h were switched from assist-control ventilation to PAV+ as soon as they regained spontaneous breathing activity. PAV+ was set to deliver the highest assistance. We compared patients in whom PAV+ succeeded vs those in whom it failed. Results PAV+ succeeded in 12 (63%) patients, but failed in 7 (37%) due to tachypnea (n = 4), hypercapnia (n = 2), and metabolic acidosis (n = 1), but without statistical significance. Both groups had similar clinical parameters. On the day of inclusion, total work of breathing per breath was lower in the successful PAV+ group (WOBTOT: 0.95 [0.8–1.35] vs 1.6 [1.4–1.8] J/l; P Conclusion PAV+ proved feasible as first-line ventilatory support in 63% of the patients, mostly in individuals without extreme derangements in WOBTOT. Tachypnea and hypercapnia were the clinical factors associated with failure, though statistical significance was not reached.

INDICATION OF PULMONARY MECHANICAL ENERGY DURING SPONTANEOUS BREATHING

Registered spirogram and transpulmonary pressure in spontaneous breathing in 10 healthy volunteers and in 10 patients with community-acquired pneumonia. For the first time the work inside the lung-a source of mechanical energy (RVI) was measured by the method of interruption of the air on 0.2 with inhalation and exhalation in the middle of the respiratory cycle. Alveolar pressure exceeding the total nonelastic pressure on the inhale and exhale through self-mechanical activity of the lungs. RVI was determined by the area of a triangle, where one cathetus were breathing capacity and the amount of excess air pressure. The total work of breathing (TWB) was measured by the square of the chart pressure-volume. Total breathing (Рt) was determined by adding TWB and RVI. RVI average was 29.6 (25.0–43.3)% to Рt in healthy individuals and to 19.4 (0–55.1) % of patients with community-acquired pneumonia. In 2 patients, RVI has not been determined, and 2 were increased significantly. The nature of variations RVI in healthy people and change its degree of severity of community-acquired pneumonia remain unknown.

Factores clínicos asociados al éxito de la ventilación asistida proporcional en la fase aguda del paciente crítico: estudio piloto

ReasonProportional assist ventilation plus (PAV+) applies pressure depending on the patient's inspiratory effort, automatically adjusting flow and volume assist to changes in respiratory mechanics. We aimed to assess the clinical factors associated with the success of PAV+ as first-line support in the acute phase of critical illness. MethodsA prospective cohort study was carried out. Mechanically ventilated patients>24h were switched from assist-control ventilation to PAV+ as soon as they regained spontaneous breathing activity. PAV+ was set to deliver the highest assistance. We compared patients in whom PAV+ succeeded versus those in whom it failed. ResultsPAV+ succeeded in 12 (63%) patients, but failed in 7 (37%) due to tachypnea (n=4), hypercapnia (n=2), and metabolic acidosis (n=1), but without statistical significance. Both groups had similar clinical parameters. On the day of inclusion, total work of breathing per breath was lower in the successful PAV+ group (WOBTOT: 0.95 [0.8-1.35] vs. 1.6 [1.4-1.8] J/L; P<.007). The area under the ROC curve was 0.89±0.08 for WOBTOT. The best cut-off for predicting PAV+ success was WOBTOT<1.4J/L (sensitivity: 1 [0.7-1], specificity: 0.6 [0.4-0.6], PPV: 0.7 [0.5-0.7], and NPV: 1 [0.6-1]). ConclusionPAV+ proved feasible as first-line ventilatory support in 63% of the patients, mostly in individuals without extreme derangements in WOBTOT. Tachypnea and hypercapnia were the clinical factors associated with failure, though statistical significance was not reached.

A new endotracheal tube for infants – laboratory and clinical assessment: a preliminary study

Conventional endotracheal pediatric tubes offer high resistance due to their small diameters and relatively high flow during ventilation. Any increase of the diameter of the tube lumen decreases the airway resistance and subsequently, the work of breathing (WOB). We compared ventilation mechanics using a new, cone-shaped endotracheal tube of our design to the Cole and standard tubes. The study has been divided into three parts: (i) preliminary laboratory tests, (ii) in vitro study with infant lung model, and (iii) clinical study in infants. Flow resistance and WOB were compared, using standard, Cole (in experimental phase only) and cone tubes. We proved that inspiratory (Ri ) and expiratory (Re ) resistance, and WOB, were significantly lower in patients ventilated via a cone tube. Mean Ri decreased by 37%, compared with the baseline values, Re - by 35%, and total WOB - by 12%. The cone tube offers lower resistance to gas flow than the standard, used nowadays in clinical practice. It can be especially beneficial to spontaneously breathing patients reducing WOB and improving gas exchange.

The effect of angiotensin-converting enzyme inhibition by captopril on respiratory mechanics in healthy rats

Context: Angiotensin stimulates smooth-muscle contraction. Accordingly, angiotensin-converting enzyme (ACE) inhibition is expected to decrease airway resistance.Objectives: To measure the effects of ACE inhibition on respiratory mechanics in healthy mammals.Materials and methods: We measured respiratory mechanics before and after i.p. ACE inhibitor captopril (100 mg/kg) in normal anaesthetised rats. The end-inflation occlusion method allowed the measurements of respiratory system elastance and ohmic and viscoelastic pressure dissipations. Respiratory system hysteresis and the elastic and resistive work of breathing were calculated.Results: Captopril induced a reduction of the ohmic and the total respiratory system resistances, while respiratory system hysteresis and elastance did not change. Accordingly, a reduction of the resistive and of the total work of breathing was observed.Conclusions: The captopril-induced reduction of airway resistance indicates that angiotensin modulates bronchomotor tone in basal conditions. ACE inhibition may positively affect respiratory system mechanics and work of breathing.

Sex differences in the resistive and elastic work of breathing during exercise in endurance-trained athletes

It is not known whether the high total work of breathing (WOB) in exercising women is higher due to differences in the resistive or elastic WOB. Accordingly, the purpose of this study was to determine which factors contribute to the higher total WOB during exercise in women. We performed a comprehensive analysis of previous data from 16 endurance-trained subjects (8 men and 8 women) that underwent a progressive cycle exercise test to exhaustion. Esophageal pressure, lung volumes, and ventilatory parameters were continuously monitored throughout exercise. Modified Campbell diagrams were used to partition the esophageal-pressure volume data into inspiratory and expiratory resistive and elastic components at 50, 75, 100 l/min and maximal ventilations and also at three standardized submaximal work rates (3.0, 3.5, and 4.0 W/kg). The total WOB was also compared between sexes at relative submaximal ventilations (25, 50, and 75% of maximal ventilation). The inspiratory resistive WOB at 50, 75, and 100 l/min was 67, 89, and 109% higher in women, respectively (P < 0.05). The expiratory resistive WOB was 131% higher in women at 75 l/min (P < 0.05) with no differences at 50 or 100 l/min. There were no significant sex differences in the inspiratory or expiratory elastic WOB across any absolute minute ventilation. However, the total WOB was 120, 60, 50, and 45% higher in men at 25, 50, 75, and 100% of maximal exercise ventilation, respectively (P < 0.05). This was due in large part to their much higher tidal volumes and thus higher inspiratory elastic WOB. When standardized for a given work rate to body mass ratio, the total WOB was significantly higher in women at 3.5 W/kg (239 +/- 31 vs. 173 +/- 12 J/min, P < 0.05) and 4 W/kg (387 +/- 53 vs. 243 +/- 36 J/min, P < 0.05), and this was due exclusively to a significantly higher inspiratory and expiratory resistive WOB rather than differences in the elastic WOB. The higher total WOB in women at absolute ventilations and for a given work rate to body mass ratio is due to a substantially higher resistive WOB, and this is likely due to smaller female airways relative to males and a breathing pattern that favors a higher breathing frequency.

Modulation of ventilatory mechanics during exercise in ventilation-limited populations

The aim of this thesis was to examine the impact of modifications to ventilatory constraint in populations who have reductions in expiratory flow and ventilatory limitations during exercise. The first study examined the effect of the self-contained breathing apparatus (SCBA) regulator on work of breathing (WOB) and lung volume changes in healthy subjects. The second study further examined the effect of the SCBA on the above outcomes, as well as on pulmonary function and respiratory muscle fatigue during stair-stepping (in healthy subjects). In addition, the effect of breathing heliox on the aforementioned variables was studied. The third thesis study examined the effect of heliox on ventilatory constraint, exercise tolerance, and leg muscle fatigue in patients with chronic obstructive pulmonary disease (COPD). The main results of the first study were that, compared with a low-resistance breathing valve (RV), the SCBA regulator increased inspiratory elastic (32%), expiratory resistive (59%), and total WOB (13%), and increased end-expiratory lung volume creating a plateau in end-inspiratory lung volume at approximately 90% of vital capacity. When these variables were examined with the full SCBA and compared with the RV in the second study, similar results were found. In addition, resting pulmonary function was reduced with the SCBA. Exercise with the SCBA induced reductions in both inspiratory and expiratory maximal pressures indicating the presence of respiratory muscle fatigue. When compressed air was replaced with heliox in the SCBA, end-expiratory lung volume, total WOB, and respiratory muscle fatigue were reduced. These observations regarding the effect of heliox on ventilatory function led to the third study, which found that heliox increased exercise tolerance (53%) and leg muscle fatigue (15%) in patients with COPD, but only in those limited by ventilatory constraints and who did not have a significant level of leg fatigue while breathing room air. Those patients who did have leg fatigue on room air did not increase exercise tolerance despite reduced ventilatory constraint. Together, these findings indicate that reducing ventilatory constraint during exercise can have specific positive effects on exercise performance in populations who are ventilatory limited and have implications for occupational or rehabilitation exercise training.

Evaluation of pressure support ventilation with seven different ventilators using Active Servo Lung 5000.

In modern emergency and critical care, physicians tend to choose the mode of mechanical ventilation based on spontaneous breathing for the purpose of promoting discharge of pulmonary secretion and preventing atelectasis in patients with acute respiratory insufficiency. However, we often observe "differences in recovery" among patients treated using the same PSV settings beyond "differences in individual characteristics." We evaluated the Pressure Support Ventilation (PSV) mode aiming to certify the difference among 7 representative mechanical ventilators using the Active Servo Lung 5000 (ASL5000) respiratory simulation system. The following parameters were measured: The time delay that resulted in the lowest inspiratory pressure from the point at which the ventilator recognized spontaneous breathing (TD), the lowest inspiratory airway pressure (cmH2O) generated prior to the initiation of PSV (DeltaPaw), the work of breathing while triggering required to achieve the lowest inspiratory negative pressure from the beginning of inspiratory support (WOBtrig), and the inspiratory work of breathing (WOBi). The mean TD of the Puritan-Bennett type 840 (PB840) was signifi cantly shorter than those of other ventilators (p0.01). The WOBtrig of the PB840 was significantly lower than those of others (p0.01). However, the WOBi values of the Servo-I and T-Bird were greater than the others, with the Evita series showing the smallest WOBi of the 7 ventilators tested. According to this simulation study using ASL 5000, we concluded that PB840 was the most rapid response ventilator, but the Evita series was the gentlest mechanical ventilator among 7 ventilators from the standpoint of the total work of breathing during the inspiration phase in the setting of PSV.

Work of breathing is increased during exercise with the self-contained breathing apparatus regulator

The self-contained breathing apparatus (SCBA) increases the expiratory pressure required to maintain high rates of ventilation, suggesting that the expiratory work of breathing (WOB) is increased; however, this has never been reported. The objective of this study, therefore, was to determine if the WOB is increased with the SCBA regulator (BA condition) compared with a low-resistance breathing valve (RV condition) during exercise. Twelve healthy male subjects underwent two randomized exercise trials, consisting of cycling at 150, 180, 210, and 240 W. Inspired and expired tidal volumes were measured using a body plethysmograph, whereas esophageal pressures were measured with an esophageal balloon. Modified Campbell diagrams were created to calculate the resistive and elastic components of WOB during inspiration and expiration. There were no differences in WOB between BA and RV conditions at 150 W. End-inspiratory and -expiratory lung volumes were elevated (p < 0.05) in the BA condition at higher ventilation rates, which increased inspiratory elastic work and decreased expiratory elastic work at 180 and 210 W (p < 0.05). At 240 W (VE=112 +/- 17 L.min-1 in the BA condition), active expiratory resistive work increased by 59% +/- 51%, inspiratory elastic work increased by 26% +/- 24%, and total WOB increased by 13% +/- 12% in the BA condition (p < 0.05). The SCBA regulator causes an increase in the active expiratory resistive work to maintain high ventilatory rates and an increase inspiratory elastic work through an elevation in lung volumes.

Imposed work of breathing during high-frequency oscillatory ventilation: a bench study

IntroductionThe ventilator and the endotracheal tube impose additional workload in mechanically ventilated patients breathing spontaneously. The total work of breathing (WOB) includes elastic and resistive work. In a bench test we assessed the imposed WOB using 3100 A/3100 B SensorMedics high-frequency oscillatory ventilators.MethodsA computer-controlled piston-driven test lung was used to simulate a spontaneously breathing patient. The test lung was connected to a high-frequency oscillatory ventilation (HFOV) ventilator by an endotracheal tube. The inspiratory and expiratory airway flows and pressures at various places were sampled. The spontaneous breath rate and volume, tube size and ventilator settings were simulated as representative of the newborn to adult range. The fresh gas flow rate was set at a low and a high level. The imposed WOB was calculated using the Campbell diagram.ResultsIn the simulations for newborns (assumed body weight 3.5 kg) and infants (assumed body weight 10 kg) the imposed WOB (mean ± standard deviation) was 0.22 ± 0.07 and 0.87 ± 0.25 J/l, respectively. Comparison of the imposed WOB in low and high fresh gas flow rate measurements yielded values of 1.63 ± 0.32 and 0.96 ± 0.24 J/l (P = 0.01) in small children (assumed body weight 25 kg), of 1.81 ± 0.30 and 1.10 ± 0.27 J/l (P < 0.001) in large children (assumed body weight 40 kg), and of 1.95 ± 0.31 and 1.12 ± 0.34 J/l (P < 0.01) in adults (assumed body weight 70 kg). High peak inspiratory flow and low fresh gas flow rate significantly increased the imposed WOB. Mean airway pressure in the breathing circuit decreased dramatically during spontaneous breathing, most markedly at the low fresh gas flow rate. This led to ventilator shut-off when the inspiratory flow exceeded the fresh gas flow.ConclusionSpontaneous breathing during HFOV resulted in considerable imposed WOB in pediatric and adult simulations, explaining the discomfort seen in those patients breathing spontaneously during HFOV. The level of imposed WOB was lower in the newborn and infant simulations, explaining why these patients tolerate spontaneous breathing during HFOV well. A high fresh gas flow rate reduced the imposed WOB. These findings suggest the need for a demand flow system based on patient need allowing spontaneous breathing during HFOV.

Helium-oxygen decreases inspiratory effort and work of breathing during pressure support in intubated patients with chronic obstructive pulmonary disease

To evaluate the impact of helium-oxygen (He/O2) on inspiratory effort and work of breathing (WOB) in intubated COPD patients ventilated with pressure support. Prospective crossover interventional study in the medical ICU of a university hospital. Ten patients. Sequential inhalation (30 min each) of three gas mixtures: (a) air/O2, (b) He/O2 (c) air/O2, at constant FIO2 and level of pressure support. Inspiratory effort and WOB were determined by esophageal and gastric pressure. Throughout the study pressure support and FIO2 were 14+/-3 cmH2O and 0.33+/-0.07 respectively. Compared to Air/O2, He/O2 reduced the number of ineffective breaths (4+/-5 vs. 9+/-5 breaths/min), intrinsic PEEP (3.1+/-2 vs. 4.8+/-2 cmH2O), the magnitude of negative esophageal pressure swings (6.7+/-2 vs. 9.1+/-4.9 cmH2O), pressure-time product (42+/-37 vs. 67+/-65 cmH2O s(-1) min(-1)), and total WOB (11+/-3 vs. 18+/-10 J/min). Elastic (6+/-1 vs. 10+/-6 J/min) and resistive (5+/-1 vs. 9+/-4 J/min) components of the WOB were decreased by He/O2. In intubated COPD patients ventilated with pressure support He/O2 reduces intrinsic PEEP, the number of ineffective breaths, and the magnitude of inspiratory effort and WOB. He/O2 could prove useful in patients with high levels of PEEPi and WOB ventilated in pressure support, for example, during weaning.

Comparison of the work of breathing imposed by three anaesthetic breathing systems in children

Introduction There is concern that the resistance of the valves in circle systems may impose an unacceptable respiratory load in children (1). In this study we compared the work of breathing imposed by the Bain, Jackson Rees and the circle systems in anaesthetised spontaneously breathing children.Methods Following local ethics committee approval and the written informed consent of a parent, 12 children, aged 2–6 years, ASA grades I–II scheduled for routine genital surgery (e.g. circumcision) were recruited [Weight 14.4 ± 2.9 kg and age 3.02 ± 1.3 years (meant SD)]. Patients were premedicated with midazolam 0.5 mg·kg−1. Anaesthesia was induced by inhalation of 66% N2O in O2 and sevoflurane 8%, and the trachea was intubated. Caudal analgesia was provided using bupivacaine 0.25% in a dose of 0.5 mg·kg−1. Anaesthesia with spontaneous ventilation was maintained with 66% N2O in O2, and sevoflurane 2–4%. Routine monitoring consisted of ECG, pulse oximetry, capnography and non‐invasive blood pressure.When anaesthesia had been stable for at least 15 min, the patients were attached to three different breathing systems in random succession for 10 min: 1, a Circle (Draeger Julian); 2, a Bain; 3, a Jackson Rees system. At the end of these 10 min periods, work of breathing was measured using a computerised, portable respiratory monitor (CP‐100 Pulmonary Monitor, Bear Medical). Work of breathing (W) was calculated by measuring the area enclosed in the oesophageal pressure‐volume loop (2). Oesophageal pressure was measured using a disposable balloon catheter (Smartcath, Bear Medical) and flow was measured using a disposable flow transducer (Varflex, Bear Medical). All equipment was calibrated in accordance with the manufacturers instructions prior to use.The total work of breathing (W) was expressed as Joules per litre of ventilation (J·l−1). This was compared between breathing systems using anova. P &lt; 0.05 was considered statistically significant.Results The results are presented in Table 1. Direct measurements and calculated variables (mean ± SD) Circle Bain Jackson – Rees Work of breathing (J·l−1) 0.34 ± 0.1 0.36 ± 0.07 0.34 ± 0.09 Peak inspiratory flow rate (l·s−1) 0.19 ± 0.03 0.20 ± 0.04 0.20 ± 0.04 Peak expiratory flow rate (l·s−1) 0.16 ± 0.03 0.14 ± 0.03 0.16 ± 0.03 Δ Poes(cmH2O) 5.5 ± 2.71 6.3 ± 1.49 5.9 ± 1.83 Minute ventilation (l·min−1) 2.9 ± 0.6 2.8 ± 0.7 2.9 ± 0.6 End‐tidal CO2 (kPa) 7.8 ± 0.9 7.7 ± 0.9 7.0 ± 2.4 Δ Poes = difference between end‐expiratory oesophageal pressure and lowest oesophageal pressure. Conclusions Our results indicate that there was no difference in the total work of breathing in children attached to a circle system compared to a Bain or Jackson Rees systems.Acknowledgements This work was supported by a grant from Draeger UK Ltd.

Changes in Pulmonary Mechanics with Increasing Disease Severity in Children and Young Adults with Cystic Fibrosis

As forced expiratory volume in 1 second (FEV(1)) is a major predictor of outcome in patients with cystic fibrosis (CF), we investigated the effect of FEV(1) on pulmonary mechanics in children and young adults with CF. We measured respiratory rate; tidal volume; minute ventilation; arterial blood gases; sniff esophageal pressure; dynamic lung compliance; total pulmonary resistance; intrinsic positive end expiratory pressure; and total, elastic, and resistive work of breathing in 32 patients (FEV(1) range: 12-49% predicted). We observed correlations between FEV(1) and Pa(O(2)) (r = 0.76, p < 0.0001) and Pa(CO(2)) (r = -0.70, p < 0.0001), FEV(1) and respiratory rate/tidal volume (r = -0.41, p = 0.02), FEV(1) and dynamic lung compliance (r = 0.64, p < 0.0001), and FEV(1) and total work of breathing (r = -0.52, p = 0.002) and elastic work of breathing (r = -0.60. p = 0.0003). No correlations were observed between FEV(1) and sniff esophageal pressure (p = 0.5), minute ventilation (p = 0.9), total pulmonary resistance (p = 0.3), intrinsic positive end expiratory pressure (p = 0.3), or resistive work of breathing (p = 0.1). As FEV(1) declines in children and young adults with CF, there is an increase in the elastic load and work of breathing, resulting in a rapid shallow breathing pattern, that is associated with further impairment of gas exchange.

Breathing He-O2 Increases Ventilation but Does Not Decrease the Work of Breathing during Exercise

We previously observed an increase in minute ventilation (V E) with resistive unloading (He-O2 breathing) in healthy elderly subjects with normal pulmonary function. To investigate the effects of resistive unloading in elderly subjects with mild chronic airflow limitation (FEV(1)/FVC: 61 +/- 4%), we studied 10 elderly men and women 70 +/- 3 yr of age. These subjects performed graded cycle ergometry to exhaustion, once breathing room air and once breathing a He-O2 gas mixture (79% He, 21% O2). V E, pulmonary mechanics, and PET(CO2) were measured during each 1-min increment in work rate. Data were analyzed by paired t test at rest, at ventilatory threshold (VTh), and during maximal exercise. V E was significantly (p < 0.05) increased at VTh (3.4 +/- 4.0 L/min or 12 +/- 15% increase) and maximal exercise (15.2 +/- 9.7 L/min or 22 +/- 13% increase) while breathing He-O2. Concomitant to the increase in V E, PET(CO2) was decreased at all levels (p < 0.01), whereas total work of breathing against the lung was not different. We concluded that V E is increased during He-O2 breathing because of resistive unloading of the airways and the maintenance of the relationship between the work of breathing and exercise work rate.

RESISTIVE UNLOADING IN OLDER MEN AND WOMEN WITH MILD CHRONIC AIRFLOW LIMITATION

1031 We had previously observed an increase in maximal ventilation (VE) with resistive unloading (HeO2 breathing) in healthy elderly subjects. To investigate the effects of resistive unloading in elderly individuals with mild chronic airflow limitation (CAL, FEV1/FVC: 61 ± 4%), we studied ten Elderly (70 ± 3 yr) men and women. These subjects performed graded cycle ergometry to exhaustion, once breathing room air and once breathing a HeO2 gas mixture (79% He, 21% O2). Pulmonary mechanics and PetCO2 were measured during each 1 min increment in work rate. Data were analyzed by paired T-test at rest, ventilatory threshold (VTh), and maximal exercise. VE was significantly (p<0.05) increased at VTh (3.4 ± 4.0 L/min, 12 ± 15%) and maximal exercise (15.2 ± 9.7 L/min, 22 ± 13%) while breathing HeO2. Concomitant to the increase in VE, PetCO2 was decreased at all levels (p<0.01), while total work of breathing against the lung (WOBT) was not different. End expiratory lung volume was decreased at rest, VTh, and maximal exercise (p<0.05), although tidal volume was only increased (p<0.01) during maximal exercise. Despite the significant increase in maximal VE while breathing HeO2, there were no significant differences in maximal work rate, or exercise time between the room air and HeO2 tests. We conclude that VE is increased during HeO2 breathing due to resistive unloading of the airways and the maintenance of the relationship between WOBT and exercise level. Supported by NIA AG-11805

Respiratory work in elastase treated hamsters

Biomechanical adaptations of the diaphragm in the hamster model of emphysema are similar to those observed in skeletal muscle with exercise training. The aim of this study was to evaluate whether the dynamic pressure-volume (PV) work of breathing in hamsters with elastase-induced emphysema may contribute to these adaptations. PV work in elastase treated animals was compared to healthy controls. The studies were performed in adult hamsters 14–16 months following intratracheal administration of elastase (elastase treated group, ET) or saline (control group, CTL). Airway and esophageal pressures and air flows were measured during spontaneous breathing in anesthetized, supine animals. Pulmonary work (W l) was computed from transpulmonary pressures and airflows. Functional residual capacity (FRC) and total lung capacity (TLC; defined as volume at 25 cmH 2O) in ET were increased 2 and 1.8 times, respectively, compared with CTL. Averaged tidal volume (V t) and inspiratory flows were comparable between groups. Total work of breathing (W t) normalized per ml V t was not significantly affected with elastase treatment but the pulmonary elastance work (W e) was significantly less in ET animals than controls (0.88±0.61 g cm −2 vs. 1.63±0.32). Pulmonary resistive work was not significantly different between ET and CTL animals. These results suggest that biomechanical adaptations of the diaphragm observed in ET hamsters are caused by mechanisms other than the changes in dynamic mechanical properties of the lung following elastase treatment.

Tracheal pressure triggering a demand-flow continuous positive airway pressure system decreases patient work of breathing

Triggering a ventilator "ON" at the carinal end of the endotracheal tube decreases imposed work of breathing by bypassing the resistance imposed by the breathing circuit and the endotracheal tube. We compared work of breathing during spontaneous ventilation between three methods of triggering the ventilator "ON": a) conventional pressure triggering from inside the ventilator; b) flow-by triggering; or c) tracheal pressure triggering at the carinal end of the endotracheal tube. We hypothesized that the work of breathing would be substantially decreased with tracheal pressure triggering compared with conventional pressure and flow-by methods in patients receiving continuous positive airway pressure. Clinical, prospective study. University teaching hospital. Fourteen adults diagnosed with acute respiratory failure. All patients were breathing spontaneously at an FIO2 of 0.30 to 0.40 and received 5 cm H2O of continuous positive airway pressure. Three different methods of triggering the ventilator while set in the continuous positive airway pressure mode were administered in random order. Real-time measurements of esophageal pressure and tidal volume were integrated with a respiratory monitor (CP-100, Bicore, Riverside, CA) that uses the Campbell diagram to calculate total work of breathing. Imposed work of breathing was calculated by integrating tidal volume with the pressure at the carinal end of the endotracheal tube. Physiologic work of breathing was calculated by subtracting imposed work of breathing from the total work of breathing. Breathing frequency, the index of rapid shallow breathing (breathing frequency/tidal volume), peak inspiratory flow rate demand, exhaled minute ventilation, and the duration of respiratory muscle contraction assessed by the ratio of inspiratory time to total cycle time were also measured. Data were analyzed by Friedman's repeated-measures analysis of variance on ranks. Alpha was set at .05 for statistical significance. Imposed work of breathing decreased to approximately zero during tracheal pressure triggering. As a result, total work of breathing decreased by approximately 40% compared with the flow-by and conventional methods. During tracheal pressure triggering only, airway pressure increased above baseline pressure to approximately 11 cm H2O, which resembled pressure-support ventilation. Also, during tracheal pressure triggering, tidal volume and peak inspiratory flow rate were significantly increased, while the pressure-time product and the index of rapid shallow breathing were significantly decreased. Hemodynamic status and oxygen saturation were not clinically affected. The tracheal pressure triggering of a demand-flow continuous positive airway pressure system creates an effect similar to pressure-support ventilation that significantly decreases imposed work of breathing and, thus, total work of breathing. We recommend moving the triggering site of the ventilator to the carinal end of the endotracheal tube.