Abdominal muscle recruitment and PEEPi during bronchoconstriction in chronic obstructive pulmonary disease

Combination of inspiratory and expiratory muscle training in same respiratory cycle versus different cycles in COPD patients: a randomized trial

Background

Difference between combined inspiratory and expiratory muscle training in same respiratory cycle or different cycles remained unclarified. We explored the difference between both patterns of combined trainings in patients with COPD.

Methods

In this randomized, open-label, controlled trial, stable COPD subjects trained for 48 minutes daily, for 8 weeks, using a monitoring device for quality control. Ninety-two subjects were randomly and equally assigned for sham training, inspiratory muscle training(IMT), combined inspiratory and expiratory muscle training in same cycle(CTSC) or combined inspiratory and expiratory muscle training in different cycles(CTDC). Respiratory muscle strength, as the primary endpoint, was measured before and after training. Registry: ClinicalTrials.gov (identifier: NCT02326181).

Results

Respiratory muscle training improved maximal inspiratory pressure(PImax), while no significant difference was found in PImax among IMT, CTSC and CTDC. Maximal expiratory pressure(PEmax) in CTSC and CTDC was greater than IMT(P = 0.026, and P=0.04, respectively) and sham training (P = 0.001). IMT, CTSC, and CTDC shortened inhalation and prolonged exhalation(P < 0.01). Subjects with respiratory muscle weakness in IMT and CTDC exhibited greater increase in PImax than those without. IMT, CTSC and CTDC showed no difference in symptoms and quality of life scales among themselves(P > 0.05).

Conclusion

Both patterns of CTSC and CTDC improved inspiratory and expiratory muscle strength, while IMT alone only raised PImax. Respiratory muscle training might change the respiratory cycles, and be more beneficial for COPD patients with inspiratory muscle weakness.

Respiratory Muscle Strength in Patients With Chronic Obstructive Pulmonary Disease

OBJECTIVE

To compare the respiratory muscle strength between patients with stable and acutely exacerbated (AE) chronic obstructive pulmonary disease (COPD) at various stages.

METHODS

A retrospective medical record review was conducted on patients with COPD from March 2014 to May 2016. Patients were subdivided into COPD stages 1-4 according to the Global Initiative for Chronic Obstructive Lung Disease guidelines: mild, moderate, severe, and very severe. A rehabilitation physician reviewed their medical records and initial assessment, including spirometry, maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), COPD Assessment Test, and modified Medical Research Council scale. We then compared the initial parameters in patients with a stable condition and those at AE status.

RESULTS

The AE group (n=94) had significantly lower MIP (AE, 55.93±20.57; stable, 67.88±24.96; p=0.006) and MIP% (AE, 82.82±27.92; stable, 96.64±30.46; p=0.015) than the stable patient group (n=36). MIP, but not MEP, was proportional to disease severity in patients with AE and stable COPD.

CONCLUSION

The strength of the inspiratory muscles may better reflect severity of disease when compared to that of expiratory muscles.

Breathing techniques in patients with chronic obstructive pulmonary disease (COPD)

Background:Breathing techniques are included in the rehabilitation program of patients with chronic obstructive pulmonary disease (COPD). The efficacy of breathing techniques aiming at improving symptoms of dyspnea and eliciting physiological effects is discussed in this paper. In patients with COPD, breathing techniques aim to relieve symptoms and ameliorate adverse physiological effects by: 1) increasing strength and endurance of the respiratory muscles; 2) optimizing the pattern of thoracoabdominal motion; and 3) reducing dynamic hyperinflation of the rib cage and improving gas exchange. Evidence exists to support the effectiveness of pursed lips breathing, forward leaning position, active expiration and inspiratory muscle training, but not for diaphragmatic breathing. Careful patient selection, proper and repeated instruction and control of the techniques, and assessment of the effects are necessary. Despite the evidence that breathing techniques are effective, several problems need to be resolved. The limited evidence for the transfer of the effects of breathing techniques during resting conditions to exercise conditions raises several questions. Do breathing techniques have to be practiced during activities of daily living?

Dysfunctional breathing: a review of the literature and proposal for classification

Dysfunctional breathing is a term describing breathing disorders where chronic changes in breathing pattern result in dyspnoea and other symptoms in the absence or in excess of the magnitude of physiological respiratory or cardiac disease. We reviewed the literature and propose a classification system for the common dysfunctional breathing patterns described. The literature was searched using the terms: dysfunctional breathing, hyperventilation, Nijmegen questionnaire and thoraco-abdominal asynchrony. We have summarised the presentation, assessment and treatment of dysfunctional breathing, and propose that the following system be used for classification. 1) Hyperventilation syndrome: associated with symptoms both related to respiratory alkalosis and independent of hypocapnia. 2) Periodic deep sighing: frequent sighing with an irregular breathing pattern. 3) Thoracic dominant breathing: can often manifest in somatic disease, if occurring without disease it may be considered dysfunctional and results in dyspnoea. 4) Forced abdominal expiration: these patients utilise inappropriate and excessive abdominal muscle contraction to aid expiration. 5) Thoraco-abdominal asynchrony: where there is delay between rib cage and abdominal contraction resulting in ineffective breathing mechanics.

This review highlights the common abnormalities, current diagnostic methods and therapeutic implications in dysfunctional breathing. Future work should aim to further investigate the prevalence, clinical associations and treatment of these presentations.

Muscle dysfunction in chronic obstructive pulmonary disease: update on causes and biological findings

Respiratory and/or limb muscle dysfunction, which are frequently observed in chronic obstructive pulmonary disease (COPD) patients, contribute to their disease prognosis irrespective of the lung function. Muscle dysfunction is caused by the interaction of local and systemic factors. The key deleterious etiologic factors are pulmonary hyperinflation for the respiratory muscles and deconditioning secondary to reduced physical activity for limb muscles. Nonetheless, cigarette smoke, systemic inflammation, nutritional abnormalities, exercise, exacerbations, anabolic insufficiency, drugs and comorbidities also seem to play a relevant role. All these factors modify the phenotype of the muscles, through the induction of several biological phenomena in patients with COPD. While respiratory muscles improve their aerobic phenotype (percentage of oxidative fibers, capillarization, mitochondrial density, enzyme activity in the aerobic pathways, etc.), limb muscles exhibit the opposite phenotype. In addition, both muscle groups show oxidative stress, signs of damage and epigenetic changes. However, fiber atrophy, increased number of inflammatory cells, altered regenerative capacity; signs of apoptosis and autophagy, and an imbalance between protein synthesis and breakdown are rather characteristic features of the limb muscles, mostly in patients with reduced body weight. Despite that significant progress has been achieved in the last decades, full elucidation of the specific roles of the target biological mechanisms involved in COPD muscle dysfunction is still required. Such an achievement will be crucial to adequately tackle with this relevant clinical problem of COPD patients in the near-future.

Diaphragm efficiency estimated as power output relative to activation in chronic obstructive pulmonary disease

Muscle efficiency increases with fiber length and decreases with load. Diaphragm efficiency (Eff(di)) in healthy humans, measured as power output (Wdi) relative to the root mean square of diaphragm electromyogram (RMS(di)), increases with hyperpnea due to phasic activity of abdominal muscles acting to increase diaphragm length at end expiration (L(di ee)) and decrease inspiratory load. In chronic obstructive pulmonary disease (COPD), hyperpnea may decrease Eff(di) if L(di ee) decreases and load increases due to airflow obstruction and dynamic hyperinflation. To examine this hypothesis, we measured Eff(di) in six COPD subjects (mean forced expiratory volume in 1 s: 54% predicted) when breathing air and at intervals during progressive hypercapnic hyperpnea. Wdi was measured as the product of mean inspiratory transdiaphragmatic pressure (ΔPdi(mean)), diaphragm tidal volume measured fluoroscopically, and 1/inspiratory duration. Results were compared with those of six healthy subjects reported previously. In COPD, L(di ee) was normal when breathing air. ΔPdi(mean) and Wdi increased normally, and RMS(di) increased disproportionately (P = 0.01) with hyperpnea, and, unlike health, inspiratory capacity (IC), L(di ee), and Eff(di) did not increase. IC and L(di ee) were constant with hyperpnea because mean expiratory flow increased as expiratory duration decreased (r(2) = 0.65), and because expiratory flow was terminated actively by the balance between expiratory and inspiratory muscle forces near end expiration, and these forces increased proportionately with hyperpnea (r(2) = 0.49). At maximum ventilation, diaphragm radius of curvature at end inspiration increased in COPD (P = 0.04) but not controls; diaphragm radius of curvature at end inspiration and ln(Eff(di)) were negatively correlated (P = 0.01). Thus in COPD with modest airflow obstruction, Eff(di) did not increase normally with hyperpnea due to a constant L(di ee) and inspiratory flattening of the diaphragm.

Use of bladder pressure to correct for the effect of expiratory muscle activity on central venous pressure

OBJECTIVE

To assess whether subtracting the expiratory change in intra-abdominal (bladder) pressure (Delta IAP) from central venous pressure (CVP) provides a reliable estimate of transmural CVP in spontaneously breathing patients with expiratory muscle activity.

DESIGN AND SETTING

Prospective observational study in a medical ICU.

PATIENTS

Twenty-four spontaneously breathing patients with central venous and bladder catheters: 18 with no clinical evidence of active expiration (group 1) and 6 with active expiration (group 2).

INTERVENTIONS

Patients in group 1 were coached to change their breathing pattern to one of active expiration for several breaths; those in group 2 were asked to sip water through a straw to briefly interrupt active expiration.

MEASUREMENTS AND RESULTS

During active expiration end-expiratory CVP (uncorrected CVP) and Delta IAP were measured; Delta IAP was subtracted from uncorrected CVP to obtain corrected CVP. End-expiratory CVP during relaxed breathing (best CVP) was assumed to represent the best estimate of transmural CVP. The absolute difference between corrected CVP and best CVP was much less than the difference between uncorrected CVP and best CVP (2.3+/-2.0 vs. 12.5+/-4.7 mmHg).

CONCLUSIONS

In patients with active expiration, subtracting Delta IAP from end-expiratory CVP yields a more reliable (and lower) estimate of transmural CVP than does the uncorrected CVP value.

Diagnostic and prognostic utility of brain natriuretic Peptide in subjects admitted to the ICU with hypoxic respiratory failure due to noncardiogenic and cardiogenic pulmonary edema

BACKGROUND

Brain natriuretic peptide (BNP) is useful in diagnosing congestive heart failure (CHF) in patients presenting in the emergency department with acute dyspnea. We prospectively tested the utility of BNP for discriminating ARDS vs cardiogenic pulmonary edema (CPE).

METHODS

We enrolled ICU patients with acute hypoxemic respiratory failure and bilateral pulmonary infiltrates who were undergoing right-heart catheterization (RHC) to aid in diagnosis. Patients with acute coronary syndrome, end-stage renal disease, recent coronary artery bypass graft surgery, or preexisting left ventricular ejection fraction </= 30% were excluded. BNP was measured at RHC. Two intensivists independently reviewed the records to determine the final diagnosis.

RESULTS

Eighty patients were enrolled. Median BNP was 325 pg/mL (interquartile range [IQR], 82 to 767 pg/mL) in acute lung injury/ARDS patients, vs 1,260 pg/mL (IQR, 541 to 2,020 pg/mL) in CPE patients (p = 0.0001). The correlation between BNP and pulmonary capillary wedge pressure was modest (r = 0.27, p = 0.02). BNP offered good discriminatory performance for the final diagnosis (C-statistic, 0.80). At a cut point </= 200 pg/mL, BNP provided specificity of 91% for ARDS. At a cut point >/= 1,200 pg/mL, BNP had a specificity of 92% for CPE. Higher levels of BNP were associated with a decreased odds for ARDS (odds ratio, 0.4 per log increase; p = 0.007) after adjustment for age, history of CHF, and right atrial pressure. BNP was associated with in-hospital mortality (p = 0.03) irrespective of the final diagnosis and independent of APACHE (acute physiology and chronic health evaluation) II score.

CONCLUSION

In ICU patients with hypoxemic respiratory failure, BNP appears useful in excluding CPE and identifying patients with a high probability of ARDS, and was associated with mortality in patients with both ARDS and CPE. Larger studies are necessary to validate these findings.

Clinical outcomes of expiratory muscle training in severe COPD patients

The most common symptoms in chronic obstructive pulmonary disease (COPD) patients are breathlessness and exercise limitation. Although both general and inspiratory muscle training have shown clinical benefits, the effects of specific expiratory muscle training remain controversial.

OBJECTIVE

To investigate the effects of expiratory training on lung function, exercise tolerance, symptoms and health-related quality of life in severe COPD patients.

METHODS

Sixteen patients (FEV(1), 28+/-8% pred.) were randomised to either expiratory muscle or sham training groups, both completing a 5-week programme (30 min sessions breathing through an expiratory threshold valve 3 times per week) (50% of their maximal expiratory pressure (MEP) vs. placebo, respectively). Lung function, exercise capacity (bicycle ergometry and walking test), and clinical outcomes (dyspnoea and quality of life (St. George Respiratory Questionnaire (SGRQ)) were evaluated both at baseline and following the training period.

RESULTS

Although lung function remained roughly unchanged after training, exercise capacity, symptoms and quality of life significantly improved. The improvement in both walking distance and the SGRQ score significantly correlated with changes in MEP.

CONCLUSION

Our results confirm that a short outpatient programme of expiratory training can improve symptoms and quality of life in severe COPD patients. These effects could be partially explained by changes in expiratory muscle strength.

Chest wall motion after thixotropy conditioning of inspiratory muscles in healthy humans

Inspiratory muscle conditioning at a lower or higher lung volume based on the principles of muscle thixotropy causes acute changes in end-expiratory chest wall and lung volumes. The present study aimed to demonstrate the time course of effects of this conditioning on both end-expiratory chest wall volume and thoracoabdominal synchrony. We measured chest wall motion with respiratory induction plethysmography at 0.5, 1, 2, 3, and 6 min after conditioning at three different lung volumes in 15 healthy men. After conditioning at total lung capacity - 20% inspiratory capacity, increases in end-expiratory chest wall volume were significant at 0.5, 1, and 2 min (P < 0.05), being most obvious at 0.5 min (Delta 0.24 +/- 0.20 liter). After conditioning at residual volume, reductions in end-expiratory chest wall volume were significant at any time point (P < 0.05), being most obvious at 0.5 min (Delta 0.16 +/- 0.08 liter). Conditioning at functional residual capacity had little effect on the volume. Spirometric inspiratory capacity at 6 min after conditioning at residual volume (2.68 +/- 0.35 liter) was higher than the baseline value (2.53 +/- 0.31 liter, P < 0.05). Reductions in the phase angle, quantified by the Konno-Mead diagram, occurred after conditioning at residual volume at any time point (P < 0.05), being most obvious at 2 min (Delta 3.47 +/- 3.02 degrees). In conclusion, there is a 6-min time course of changes in end-expiratory chest wall volume after conditioning. More synchronous motion between the rib cage and abdomen occurs after conditioning at residual volume.

Respiratory muscle training in chronic obstructive pulmonary disease: inspiratory, expiratory, or both?

PURPOSE OF REVIEW

Most patients with significant chronic obstructive pulmonary disease (COPD) have inspiratory and expiratory muscle weakness. In addition, hyperinflation induces functional weakening of the inspiratory muscles, increased elastic load to breathing, and intrinsic positive end expiratory pressure (PEEPi). Therefore, it was rational to expect that patients with COPD would benefit from specific inspiratory or expiratory muscle training (SIMT, SEMT respectively). However, the functional benefits of SIMT have remained equivocal. In recent years, a number of studies have demonstrated that, when training loads are controlled, SIMT results in important functional benefits. The role of SEMT is still unclear.

RECENT FINDINGS

Well-controlled SIMT in patients with COPD leads to relief of dyspnea, during both daily activities and during physical activity. This yields increased exercise tolerance, and thus the capacity to walk, improving health related quality of life. We argue that there is now evidence that SIMT is an important addition to pulmonary rehabilitation programs for patients with COPD. Although two recent studies have shown that SEMT also provides a beneficial effect in patients with COPD, this does not appear to be supplementary to the effect to SIMT.

SUMMARY

Inspiratory and expiratory muscles can be specifically trained yielding improvements in both strength and endurance. The improvement in inspiratory muscle performance is associated with an improvement in the sensation of dyspnea, exercise tolerance, and quality of life. When the expiratory muscles are specifically trained, a significant increase in exercise performance has also been shown. However, there is probably no additional benefit in combining SEMT with SIMT.

Comparison of Specific Expiratory, Inspiratory, and Combined Muscle Training Programs in COPD

BACKGROUND

Respiratory muscle weakness may contribute to dyspnea and exercise limitation in patients with significant COPD. In an attempt to reduce the severity of breathlessness and to improve exercise tolerance, inspiratory muscle training has been applied in many COPD patients. On the other hand, there is a paucity of data related to expiratory muscle performance and training in COPD.

METHODS

Thirty-two patients with significant COPD (ie, mean FEV(1), 37% of predicted) were recruited for the study. The patients were randomized into four groups: eight patients were assigned to receive specific expiratory muscle training (SEMT); eight patients received specific inspiratory muscle training (SIMT); eight patients received SEMT and SIMT (ie, the SEMT + SIMT group); and eight patients who were assigned to a control group received training with very low load. All patients trained daily, six times a week, with each session consisting of one half hour of training, for 3 months. Spirometry, respiratory muscle strength and endurance, 6-min walk test distance, the perception of dyspnea, and the Mahler baseline dyspnea index (BDI) were measured before and following training.

RESULTS

Training caused a statistically significant specific increase in the expiratory muscle strength and endurance (in the SEMT and SEMT + SIMT groups) and in the inspiratory muscle strength and endurance (in the SIMT and SEMT + SIMT groups). There was significant increase in the distance walked in 6 min in the SEMT, SIMT, and SEMT + SIMT groups. However, the increase in the SIMT and SEMT + SIMT groups was significantly greater than that in the SEMT group. There was a statistically significant increase in the BDI, and a decrease in the mean Borg score during breathing against resistance in the SIMT and SEMT + SIMT groups, with no changes in the SEMT and control groups.

CONCLUSIONS

The inspiratory and expiratory muscles can be specifically trained with improvement of both muscle strength and endurance. The improvement in the inspiratory muscle performance is associated with an increase in the 6-min walk test distance and the sensation of dyspnea. There is no additional benefit gained by combining SIMT with SEMT, compared to using SIMT alone.

Specific expiratory muscle training in COPD

BACKGROUND

There are several reports showing that expiratory muscle strength and endurance can be impaired in patients with COPD. This muscle weakness may have clinically relevant implications. Expiratory muscle training tended to improve cough and to reduce the sensation of respiratory effort during exercise in patients other than those with COPD.

METHODS

Twenty-six patients with COPD (FEV(1) 38% predicted) were recruited for the study. The patients were randomized into two groups: group 1, 13 patients were assigned to receive specific expiratory muscle training (SEMT) daily, six times a week, each session consisting of 1/2 h of training, for 3 months; and group 2, 13 patients were assigned to be a control group and received training with very low load. Spirometry, respiratory muscle strength and endurance, 6-min walk test, Mahler baseline dyspnea index (before), and the transitional dyspnea index (after) were measured before and after training.

RESULTS

The training-induced changes were significantly greater in the SEMT group than in the control group for the following variables: expiratory muscle strength (from 86 +/- 4.1 to 104 +/- 4.9 cm H(2)O, p < 0.005; mean difference from the control group, 24%; 95% confidence interval, 18 to 32%), expiratory muscle endurance (from 57 +/- 2.9% to 76 +/- 4.0%, p < 0.001; mean difference from the control group, 29%; 95% confidence interval, 21 to 39%), and in the distance walked in 6 min (from 262 +/- 38 to 312 +/- 47 m, p < 0.05; mean difference from the control group, 14%; 95% confidence interval, 9 to 20%). There was also a small but not significant increase (from 5.1 +/- 0.9 to 5.6 +/- 0.7, p = 0.14) in the dyspnea index.

CONCLUSIONS

The expiratory muscles can be specifically trained with improvement of both strength and endurance in patients with COPD. This improvement is associated with increase in exercise performance and no significant change in the sensation of dyspnea in daily activities.

Breathing frequency and use of expiratory muscles do influence the dynamic positive end-expiratory pressure

End-expiratory air trapping due to obstructive airway disease can be estimated through the measurement of intrinsic positive end-expiratory pressure PEEPi. The influence of breathing-frequency and use of expiratory muscles on PEEPi were measured in 10 normal and 10 chronic bronchitic patients (COPD). Insignificant control values of PEEPi increased to measurable values at high breathing rate in normal subjects. Control values were higher in COPD patients and increased at fast breathing rate. When corrected for the use of expiratory muscles according to simultaneous gastric pressure drop, PEEPi decreased in COPD, but still increased at high rate. We conclude that modifying the respiratory rate can increase PEEPi values independently of the severity of airway obstruction and the use of expiratory muscles. Before estimating the pathological value of a PEEPi measurement or evaluating the effects of a treatment, we always need to know the simultaneous breathing frequency.

Dyspnea, respiratory function and sputum profile in asthmatic patients during exacerbations

Dyspnea is often used as a marker of asthma severity although a wide variation in dyspnea perception associated with bronchoconstriction (PB) has been described in asthmatic patients. Our hypothesis is that changes of airway inflammation, airway narrowing and hyperinflation may account for a part of the variability of breathlessness in spontaneous asthma attack. In asthmatic patients with exacerbation of the disease, we evaluated respiratory function, dyspnea (using visual Analogue Scale--VAS) and peak expiratory flow (PEF) values and variability (amplitude % mean), and sputum cellular and biochemical profile before (day I) and after (day II) therapy with i.v. corticosteroids and inhaled beta2-agonists, as appropriate. By day II, forced expiratory volume in 1 s (FEV1), inspiratory capacity (IC), PEF or VAS values and variability, sputum eosinophils and eosinophilic cationic protein (ECP) had improved. Improvement of dyspnea expressed as a decrease in VAS and reduction in variability of dyspnea sensation significantly correlated with increase in FEV1 %predicted value (%pv) (P=0.03; p=0.72 and P=0.02; p=0.74, respectively). No significant correlation was found between IC and VAS either in absolute values or as changes from days I and II, nor between sputum outcomes and PEF or VAS, regardless of how they were measured. We conclude that in acute asthmatic patients, dyspnea measurement, functional measurements and sputum analysis may be useful in monitoring disease activity, response to therapy and can provide different information on the state of the disease.

Expiratory muscle endurance in chronic obstructive pulmonary disease

BACKGROUND

A reduction in expiratory muscle (ExM) endurance in patients with chronic obstructive pulmonary disease (COPD) may have clinically relevant implications. This study was carried out to evaluate ExM endurance in patients with COPD.

METHODS

Twenty three patients with COPD (FEV(1) 35 (14)% predicted) and 14 matched controls were studied. ExM endurance was assessed using a method based on the use of an expiratory threshold valve which includes two steps. In step 1 the load is progressively increased (50 g every 2 minutes) until task failure is reached, and the pressure generated against the highest tolerated load is defined as the maximal expiratory sustainable pressure (Pthmax). In step 2 subjects breathe against a submaximal constant load (80% of Pthmax) and the time elapsed until task failure is termed the expiratory endurance time (Tth(80)). In addition, the strength of peripheral muscles (handgrip, HGS) and respiratory muscles (maximal inspiratory and expiratory pressures, PImax and PEmax, respectively) was evaluated.

RESULTS

Patients with COPD had lower ExM strength and endurance than controls: PEmax 64 (19)% predicted v 84 (14)% predicted (mean difference 20%; 95% confidence intervals (CI) 14 to 39); Pthmax 52 (27) v 151 (46) cm H(2)O (mean difference 99, 95% CI 74 to 123); and Tth(80) 9.4 (6.3) v 14.2 (7.4) min (mean difference 4.8, 95% CI 1.0 to 10.4; p<0.01 for all). Interestingly, ExM endurance directly correlated with both the severity of airways obstruction (Pthmax with FEV(1), r=0.794, p<0.01) and the reduction in strength observed in different muscle groups (Pthmax with HG, PImax or PEmax, r=0.550, p<0.05; r=0.583, p<0.001; and r=0.584, p<0.001, respectively).

CONCLUSIONS

ExM endurance is decreased in patients with COPD. This impairment is proportional to the severity of the disease and is associated with lower strength in different muscle groups. This suggests that systemic effects are implicated in the impairment observed in ExM function.

Amplitude variation in static-charge-sensitive bed signal increased in obstructive airways disease

The relationship between oesophageal pressure variation and amplitude variation in the static-charge-sensitive bed (SCSB) ballistocardiogram suggests that changes in intrathoracic pressure can be detected using the SCSB method. We investigated whether amplitude variation in the static-charge-sensitive bed ballistocardiogram (SAV) is related to severity of airway obstruction in patients with asthma and chronic obstructive pulmonary disease. The ability of SAV to detect an increase in airway obstruction induced by histamine challenge was also tested. Twenty-six patients suffering from asthma and 12 patients with chronic obstructive pulmonary disease (COPD) were enrolled in the study. SAV, amplitude from the SCSB ballistocardiogram, respiratory amplitude from the SCSB respiratory wave form and heart rate from the electrocardiogram (ECG) were computed using analysing software (Biorec, Helsinki, Finland) during a 7-min supine rest. SAV was related to forced expiratory volume in one second (FEV1) immediately after signal recording. Asthma patients participated in a standardized histamine challenge test to reveal the effect of acute bronchoconstriction on SAV. An inverse relationship existed between baseline FEV1 and SAV in asthma and COPD. In the histamine inhalation test, FEV1 fell by 0.7 +/- 0.3 l or 26% +/- 11% (P < 0.0001) and SAV increased by 12% +/- 5% (P < 0.0001) in 12 asthma patients. The fall in FEV1 induced by histamine followed regularly and correlated significantly with the rise in SAV (n = 24, r = -0.58, P = 0.002). Changes in respiratory amplitude or heart rate did not explain changes in SAV. SAV may not separate the upper airway obstruction from the bronchial obstruction but it is related to severity of airway obstruction. The clinically significant increase in airway obstruction induced by histamine inhalation increases amplitude variation in SCSB.

Interpretation of the pulmonary artery occlusion pressure in mechanically ventilated patients with large respiratory excursions in intrathoracic pressure

OBJECTIVE

To assess the reliability of the pulmonary artery occlusion pressure (Ppao) when respiratory excursions in intrathoracic pressure are prominent.

DESIGN

We studied 24 critically ill patients who had 15 mm Hg or more of respiratory excursion in their Ppao tracing. Large respiratory excursions resulted from respiratory muscle activity that persisted despite sedation and mechanical ventilation in the assist-control mode. From the Ppao tracing, the end-expiratory and mid-point values were recorded; the latter was measured halfway between end-expiration and the nadir due to inspiratory triggering. The Ppao was then re-measured after administration of a non-depolarizing muscle relaxant.

SETTING

Medical intensive care unit of a university-affiliated teaching hospital.

MEASUREMENTS AND RESULTS

The difference between the pre-relaxation end-expiratory Ppao and the relaxed Ppao was larger than the difference between the pre-relaxation mid-point Ppao and the relaxed Ppao (11 +/- 5 vs 3 +/- 3 mm Hg, p < 0.01). In 21 of 24 (88%) cases, the relaxed Ppao was more closely approximated by the mid-point Ppao than by the end-expiratory Ppao. The difference between the end-expiratory Ppao and the relaxed Ppao increased as the amount of respiratory excursion increased (r = 0.51; p < 0.01).

CONCLUSIONS

In mechanically ventilated patients whose respiratory muscles produce large excursions in the Ppao, the end-expiratory Ppao is often much higher than the Ppao measured after muscle relaxation. The pre-relaxation mid-point Ppao and the relaxed Ppao are usually similar, but this may not be true in individual patients. In this setting, the Ppao measured after muscle relaxation probably provides the most clinically reliable estimate of left heart filling pressure.