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PubMed1976

Occlusion pressure responses in asthma and chronic obstructive pulmonary disease.

During CO2 rebreathing we measured ventilation and the pressure generated during the first 0.1 sec of inspiratory effort against a closed airway (P 0.1) in 12 asthmatics during acute exacerbation, 10 normal subjects, and 10 patients with chronic obstructive pulmonary disease. In normal subjects, the ventilatory responst to CO2 correlated with the P 0.1 response measured as delta In P 0.1. Patients with chronic obstructive pulmonary disease showed depressed responses to CO2 in terms of both ventilation and deltaIn P0.1. However, P 0.1 values in the patients with chronic obstructive pulmonary disease were greater than those of the normal subjects when they were compared at an alveolar PCO2 of 60 mm Hg. Asthmatics' responses to CO2 were similar to those of patients with chronic obstructive pulmonary disease. When measured at an alveolar PCO2 of 60 mm Hg, asthmatics' P 0.1 values were greater than those of both normal subjects and patients with chronic obstructive pulmonary disease. As the asthmatics' airway obstruction decreased so did their P 0.1. The asthmatics, and to a lesser extent the patients with chronic obstructive pulmonary disease, demonstrated increased inspiratory muscle activity that could not be explained on the basis of chemical drive or alterations in functional residual capacity. In the case of the asthmatics it was possible that the increased inspiratory muscle activity was a response to airway obstruction.

Adult↗
PubMed1992

Use of a measurement of pulmonary hyperinflation to control the level of mechanical ventilation in patients with acute severe asthma.

Mechanical ventilation causes significant morbidity and mortality in patients with severe asthma. Hypoventilation may reduce this morbidity and mortality, but indicators to guide the degree of hypoventilation are unclear. We used a measure of pulmonary hyperinflation to assess the degree of airflow obstruction and to guide the extent and duration of hypoventilation. Ten patients who required mechanical ventilation for acute severe asthma were studied. All were sedated, paralyzed, and given an initial minute ventilation (VE) of 200 ml/kg/min. End-inspiratory lung volume (VEI) above FRC was measured from the total exhaled gas volume during 40 to 60 s of apnea. VEI was used to regulate VE to a safe level (VEsafe), irrespective of PaCO2, by reducing the rate when VEI was > 20 ml/kg and increasing it when VEI was < 20 ml/kg. Each patient was weaned when VEsafe resulted in PaCO2 < or = 40 mm Hg (the weaning point). FRC was measured computer analysis of anterior and lateral chest radiographs taken at the end of apnea. Using the weaning point criterion, 2 patients (PaCO2 < 40 mm Hg) were weaned shortly after arrival. The remaining eight (initial PaCO2, 63 +/- 17 mm Hg) continued hypoventilation until the weaning point was reached (30 +/- 29 h). The weaning point was reached by the VE required for PaCO2 40 mm Hg decreasing concurrent with the VEsafe increasing. All but 1 patient were successfully weaned within 24 h of the weaning point.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1995

Analysis of tidal expiratory flow pattern in the assessment of histamine-induced bronchoconstriction.

BACKGROUND: There are times in clinical practice when it would be useful to be able to assess the severity of airways obstruction from tidal breathing. Three indices of airways obstruction derived from analysis of resting tidal expiratory flow have previously been described: (1) Tme/TE = time to reach maximum expiratory flow/expiratory time; (2) Krs = decay constant of exponential fitted to tidal expiratory flow versus time curve; and (3) EV = extrapolated volume--that is, area under the curve when the fitted exponential is extrapolated to zero flow. In this paper a further index--dtr/TE, time from the beginning of expiration till the rapid decay of flow begins/expiratory time--is evaluated. The aim of this study was to assess the ability of these indices to detect mild airways obstruction. METHODS: A histamine bronchial provocation test was performed in 20 adult patients with a diagnosis of asthma or symptoms of cough and/or shortness of breath. Baseline forced expiratory volume in one second (FEV1), functional residual capacity (FRC), and specific inspiratory conductance (sGaw) were measured and the measurements repeated after the final inhalation of histamine. Expiratory flow patterns during quiet breathing over five consecutive representative breaths were analysed before and after histamine. The test was concluded in 12 subjects when FEV1 had decreased by 20% of the post saline value, and in the remaining eight after inhalation of 16 or 32 mg/ml histamine. RESULTS: FEV1, sGaw, FRC, Krs, EV, and dtr/TE were all different after histamine (paired t test). For Tme/TE no difference was shown. Change in EV detected change in end tidal volume but underestimated it compared with the change measured by body plethysmography. Percentage fall in Krs after histamine correlated with percentage fall in FEV1 (r = 0.527, Pearson correlation coefficient). This was of a similar order to the correlation between the percentage fall in sGaw and in FEV1 (r = 0.543). CONCLUSIONS: Analysis of expiratory tidal flow-time patterns predicted a decrease in FEV1 following histamine challenge as did measurement of sGaw. This analysis of tidal breathing would be useful in circumstances where forced expiratory manoeuvres are unreliable or inapplicable.

Adult↗
PubMed1999

Weaning from mechanical ventilation: a model for extubation.

OBJECTIVE: To develop a model able to determine the right time for extubation and to validate its performance. paragraph sign DESIGN: A prospective clinical study. SETTING: 14-bed medical intensive care unit in a university hospital. PATIENTS: 101 patients (37 women/64 men) ventilated over more than 48 h (mean 10.4 +/- 10.3 days) and considered ready to be weaned by the medical team (February 1996-February 1998). METHODS: This study included two series: a development series with 53 patients and a validation series with 48 patients. Before extubation, a weaning test was performed measuring tidal volume (V(T)), respiratory rate (f), f/V(T) ratio, minute ventilation, vital capacity (VC) and maximum inspiratory and expiratory pressures (MIP and MEP). The success of extubation was assessed after 48 h. Receiver operating characteristic (ROC) curves allowed the analysis of the discriminating power of each parameter. Threshold values were determined using the Youden's index. To create the best predictive model, we performed a multiple logistic regression analysis. To assess the calibration and the discrimination of the model, the Hosmer- Lemeshow goodness-of-fit test and area under ROC curves (AUC) were adopted. MEASUREMENTS AND RESULTS: In a development series, 60 tests were carried out with 38 successful extubations and 22 extubation failures. The multivariate analysis found three significant variables: VC (threshold value = 635 ml), f/V(T) ratio (threshold value = 88 breaths/min.l) and MEP (threshold value = 28 cmH(2)O). The validation cohort included 59 tests (38 successes and 21 failures). The validation series shows a good discrimination (AUC = 0.855 +/- 0.059) and calibration (goodness-of-fit test C: p = 0.224) of the model. CONCLUSION: VC together with the f/V(T) ratio and MEP offer accurate prediction of early extubation.

Adolescent↗
PubMed1999

Noninvasive measurement of respiratory muscle performance after exhaustive endurance exercise.

The use of noninvasive techniques to measure respiratory muscle performance after different types of endurance exercise has not been entirely successful, as the results have not consistently indicated diminished performance for similar types of exercise. The aim of the present study was 1) to compare different, noninvasive methods to assess respiratory muscle performance before and after an exhaustive cycling endurance test (which has previously been shown to induce diaphragmatic fatigue) and 2) to determine which of the tests best reflect published results of measurements of diaphragmatic fatigue. Twelve healthy subjects participated in the study and performed three different test series in a random order on three different days. These tests were performed before, and 5, 40 and 75 min after an exhausting task (a cycling endurance run at 85% of maximal oxygen uptake (V'O2,max)). The tests of the three test series were 1) breathing against a constant inspiratory resistance to task failure, 2) determination of 12-min sustained ventilatory capacity, and 3) spirometric and maximal inspiratory and expiratory mouth pressure measurements. The only measurement that was affected by exhaustive cycling was the time to task failure breathing against inspiratory resistance. It was significantly reduced from (mean+/-sD) 364+/-88 s before exercise to 219+/-122 s at 5 min after cessation of exercise. It is concluded that the constant-load resistive breathing test to task failure is the only noninvasive respiratory muscle performance test evaluated in this study which shows a decrease in respiratory muscle performance after exhaustive endurance exercise.

Adult↗
PubMed1975

Treatment of flail chest. Use of intermittent mandatory ventilation and positive end-expiratory pressure.

For the past two years we have treated patients with flail chest injuries and concomitant respiratory failure with intermittent mandatory ventilation (IMV) and positive end-expiratory pressure (PEEP). Prior to 1972 these patients were treated with controlled mechanical ventilation (CMV) until gross flailing ceased and inspiratory force and vital capacity measurements were adequate. We retrospectively studied the charts of 37 consecutive patients to compare the length of mechanical ventilatory support of patients managed by conventional CMV with those ventilated with IMV and PEEP. The mean ventilation time of patients treated with IMV and PEEP (5.1 +/- 4.7 days) was significantly less than that of the patients treated with CMV (18.8 +/- 14.4 days) (P less than .001).

Accidents, Traffic↗
PubMed2005

Slow moderate pressure recruitment maneuver minimizes negative circulatory and lung mechanic side effects: evaluation of recruitment maneuvers using electric impedance tomography.

OBJECTIVE: To evaluate the efficacy of different lung recruitment maneuvers using electric impedance tomography. DESIGN AND SETTING: Experimental study in animal model of acute lung injury in an animal research laboratory. SUBJECTS: Fourteen pigs with saline lavage induced lung injury. INTERVENTIONS: Lung volume, regional ventilation distribution, gas exchange, and hemodynamics were monitored during three different recruitment procedures: (a) vital capacity maneuver to an inspiratory pressure of 40 cmH2O (ViCM), (b) pressure-controlled recruitment maneuver with peak pressure 40 and PEEP 20 cmH2O, both maneuvers repeated three times for 30 s (PCRM), and (c) a slow recruitment with PEEP elevation to 15 cmH2O with end inspiratory pauses for 7 s twice per minute over 15 min (SLRM). MEASUREMENTS AND RESULTS: Improvement in lung volume, compliance, and gas exchange were similar in all three procedures 15 min after recruitment. Ventilation in dorsal regions of the lungs increased by 60% as a result of increased regional compliance. During PCRM compliance decreased by 50% in the ventral region. Cardiac output decreased by 63+/-4% during ViCM, 44+/-2% during PCRM, and 21+/-3% during SLRM. CONCLUSIONS: In a lavage model of acute lung injury alveolar recruitment can be achieved with a slow lower pressure recruitment maneuver with less circulatory depression and negative lung mechanic side effects than with higher pressure recruitment maneuvers. With electric impedance tomography it was possible to monitor lung volume changes continuously.

Analysis of Variance↗
PubMed1980

The effect of training on strength and endurance of the diaphragm in quadriplegia.

The diaphragmatic electromyogram was used to detect fatigue of the diaphragm in six chronic quadriplegics while they breathed for 10 minutes against a variety of inspiratory resistances. The maximum static inspiratory mouth pressure was measured at functional residual capacity (Pmmax) and from the electromyogram the critical inspiratory mouth pressure that developed in each inspiration (Pmcrit) below which electromyographic changes of diaphragmatic fatigue do not develop was estimated. The measurements were repeated after 8, 12 and 16 weeks of inspiratory muscle training consisting of inspiring for a period of 30 minutes daily, six days a week, against a resistance just sufficient to produce the electromyographic changes of fatigue. A significant and progressive increase in Pmmax and Pmcrit was found during the training. It was concluded that (1) quadriplegics are predisposed to the development of inspiratory muscle fatigue due to reduced muscle strength and reduction in endurance, and (2) in these patients inspiratory muscle training increases both strength and endurance, and protects against fatigue.

Adolescent↗
PubMed2007

Air trapping in mild and moderate asthma: effect of inhaled corticosteroids.

BACKGROUND: Air trapping reflects small airway obstruction in asthma and can be assessed quantitatively by high-resolution computed tomography (HRCT). Hydrofluoroalkane-beclomethasone dipropionate (HFA-BDP) is deposited across all sizes of airways, including the small ones. However, its long-term effect on air trapping remains unknown in uncontrolled asthma. OBJECTIVES: To compare the effect of inhaled corticosteroids of different particle size - HFA-BDP and fluticasone propionate (FP) - on lung attenuation in mild-to-moderate uncontrolled asthma. METHODS: A randomized study was performed to analyze the effect of HFA-BDP (400 microg/d) or FP (500 microg/d) given over a period of 3 months to patients with uncontrolled mild-to-moderate asthma. HRCT was performed with spirometric gating, and lung attenuation was measured at residual volume and at pulmonary total capacity. The difference between inspiratory and expiratory attenuation was calculated as an air trapping index. RESULTS: Twenty-five out of 58 patients had abnormal air trapping and could be included in the study. Lung attenuation significantly diminished in the posterior zones of the lung after a 3-month treatment with HFA-BDP or FP, but the difference between the groups was not significant. Adjusted mean variations of the air trapping index from baseline to treatment completion were 34.3 (11.2, 57.3) and 27.3 (6.4, 48.2) for the HFA-BDP and FP groups, respectively. However, the reduction of air trapping area was more pronounced in the group treated with HFA-BDP. CONCLUSION: Inhaled corticosteroids decrease air trapping in uncontrolled asthma regardless of their particle size. CLINICAL IMPLICATIONS: In mild-to-moderate asthma, air trapping assessed by HRCT may be a new outcome related to the control of the disease.

Administration, Inhalation↗
PubMed2006

Respiratory muscle energetics during exercise in healthy subjects and patients with COPD.

The energy expenditure required by the respiratory muscles during exercise is a function of their work rate, cost of breathing, and efficiency. During exercise, ventilatory requirements increase further exacerbating the potential imbalance between inspiratory muscle load and capacity. High level of exercise intensity in conjunction with contracting respiratory muscles is the reason for respiratory muscle fatigue in healthy subjects. Available evidence would suggest that fatigue of the diaphragm and other respiratory muscles is an important mechanism involved in redistribution of blood flow. Reflex mechanisms of sympathoexcitation are triggered in fatigued diaphragm during heavy exercise when cardiac output is not sufficient to adequately meet the high metabolic requirements of both respiratory and limb musculature. It is very likely that local changes in locomotor muscle blood flow may occur during exhaustive endurance exercise and that changes may have important effect on O2 transport to the working locomotor muscles and, therefore, on their fatigability. In a condition when the respiratory muscles receive their share of blood flow at the expense of limb locomotor muscles, minimizing mechanical work of breathing and therefore its metabolic cost allows a greater amount of cardiac output to be available to be delivered to working limb muscles. Malfunction in any of the multiple components responsible for circulatory flow and O2 delivery will limit the blood supply therefore inhibiting the supply of O2 and the energy substrate to the contracting muscles. Studies are needed to overcome these limitations.

Energy Metabolism↗
PubMed1998

Quality of life in severe chronic obstructive pulmonary disease: correlation with lung and muscle function.

UNLABELLED: Chronic obstructive pulmonary disease (COPD) patients suffer from significant impairment in quality of life (QL), but the variables related to this impairment are not well known. The aim of this study has been to identify physiological parameters related to QL in severe COPD patients undergoing long-term oxygen therapy. MATERIALS AND METHODS: We studied 47 COPD patients using long-term oxygen therapy (43 men/four women, 65.17 SD 8.21 years, 3.17 SD 2.61 years on oxygen). The Nottingham Health Profile (NHP) and activities of daily living (ADL) questionnaire were used to measure QL. Subjective assessment of dyspnoea was performed using a visual analogue scale. The physiological parameters determined were lung function (spirometry, arterial blood gases, lung volumes and carbon monoxide diffusing capacity), muscle function (maximum inspiratory and expiratory pressures, deltoid muscle and handgrip strength), and nutrition status (tricipital skin fold and mid-arm muscle circumference). RESULTS: High ADL (8.32 SD 6.97) and NHP scores (energy 63.3 SD 40.43, pain 35.11 SD 31.56, emotional reactions 43.03 SD 25.13, sleep 51.91 SD 32.75, social isolation 30.64 SD 26.98, physical mobility 49.73 SD 24.93) demonstrated clinically significant QL impairment in the severe COPD patients studied. Stepwise multiple regression analysis found a correlation between lung function and QL. Low FEV1% was associated with impairment in energy, physical mobility and social isolation NHP scores and ADL score (r = -0.3, P < 0.05). RV/TLC also correlated with ADL and social isolation scores (r = 0.3, P < 0.05). Lung function explained 39-45% of the variation in these QL dimensions. QL did not correlate with other lung function parameters, muscle function or nutrition status. CONCLUSION: COPD patients using long-term oxygen suffer from severe QL impairment affecting not only energy and mobility but also emotional reactions, social isolation and sleep. Lung function is related to energy, mobility and social isolation dimensions, but muscle function is unrelated to QL in these patients.

Aged↗
PubMed1984

Effects of theophylline on diaphragmatic strength and fatigue in patients with chronic obstructive pulmonary disease.

We studied the effects of theophylline on diaphragmatic strength and fatigue in 15 patients with severe chronic obstructive pulmonary disease. Diaphragmatic strength was assessed by measurement of the transdiaphragmatic pressure generated at functional residual capacity during a maximal inspiratory effort against closed airways. Diaphragmatic fatigue was induced by resistive loaded breathing. The electrical activity of the diaphragm was recorded with an esophageal electrode during the fatigue runs, and the high-low ratio of the electrical signal was analyzed to assess diaphragmatic fatigue. Studies were performed before and after 7 and 30 days of theophylline administration (mean plasma level, 13 +/- 2 mg per liter). A control group received a placebo instead of theophylline. Theophylline increased maximal transdiaphragmatic pressure by 16 per cent after 7 days of administration (P less than 0.01), and this increase persisted after 30 days. No significant change in maximal transdiaphragmatic pressure was observed in the group given the placebo. Theophylline also suppressed diaphragmatic fatigue in all patients who received it. We conclude that theophylline has a potent and long-lasting effect on diaphragmatic strength and fatigue in patients with fixed airway obstruction.

Diaphragm↗
PubMed1986

Positive response to edrophonium in patients with neurotoxic envenoming by cobras (Naja naja philippinensis). A placebo-controlled study.

To study the ability of anticholinesterase drugs to reverse the potentially fatal paralytic effects of cobra venom, we conducted a placebo-controlled, double-blind crossover trial of intravenous edrophonium (Tensilon) in 10 adults with neurotoxic envenoming caused by bites of the Philippine cobra (Naja naja philippinensis). There was significantly more improvement in ptosis and endurance of upward gaze after edrophonium than after placebo. Five minutes after injection, the mean difference (+/- SD) in the percentage of the iris that was uncovered was 39 +/- 5.47 (70 vs. 31 percent; P less than 0.01), and the mean difference in the number of seconds of upward gaze was 33.1 +/- 9.29 (39.7 vs. 6.6 seconds; P less than 0.01). The expiratory and inspiratory pressures, forced vital capacity, and ability to cough, speak, and swallow also improved after edrophonium. In both the patients who were studied electromyographically, pretreatment and postplacebo responses were typical of myasthenia gravis and became normal after edrophonium. We conclude that anticholinesterases are beneficial in the management of neurotoxic envenoming by Asian cobras (Naja naja), and we recommended a test of edrophonium in any patient with signs of neurotoxic envenoming after snakebite.

Adolescent↗
PubMed1981

Mechanical inefficiency of the thoracic cage in scoliosis.

The mechanism of impairment of ventilatory function in idiopathic scoliosis has been studied in 23 children, all girls, and compared with 27 normal children and 24 normal young adult females. The vital capacity, FEV 1, gas transfer factor, and the maximum static expiratory airway pressure were all significantly reduced. total lung capacity and the maximum inspiratory pressure were lower than in the normal subjects, but the difference was not significant. Restriction of thoracic cage movement by a belt showed that the thorax in the children with scoliosis was as mobile as in the normal subjects. The results are explained in terms of the characteristic deformity in scoliosis which causes one hemi-thorax to become relatively smaller than the other. It is concluded that this causes an inherent mechanical inefficiency of ventilation which is likely to contribute to respiratory failure in these subjects.

Adolescent↗
PubMed1979

Electromyogram pattern of diaphragmatic fatigue.

We studied the effect of breathing at various levels of transdiaphragmatic pressure (Pdi) on the EMG power spectrum of the diaphragm. The diaphragmatic EMG was measured simultaneously with a bipolar esophageal electrode (EE) and surface electrode (SE) placed on the ventral portion of the sixth and seventh intercostal spaces in five normal subjects breathing at functional residual capacity (FRC) against an inspiratory resistance. During each fatigue run the subjects generated a Pdi, with each inspiration, that was 25, 50, or 75% of maximum Pdi (Pdimax) for a period up to 15 min. During runs at 50 and 75% of the Pdimax, which are known to produce fatigue, we found for both EE and SE a progressive increase in the amplitude of the low-frequency (L = 20-46.7 Hz) and a decrease in the high-frequency (H = 150-350 Hz) component of the EMG. These changes were not seen at 25% of Pdimax. The diaphragmatic H/L ratio was independent of Pdi when the diaphragm was not fatigued. H/L fell while the diaphragm performed fatiguing work and this was more rapid at higher Pdi's. It was thus concluded that frequency spectrum analysis of the EMG can detect diaphragmatic fatigue reliably, prior to the time when the diaphragm fails as a pressure generator.

Diaphragm↗
PubMed1985

Human esophageal pressures and chest wall configuration in upright and head-down posture.

Pressures were measured at two levels in the esophagus in 14 young healthy subjects performing slow inspiratory and expiratory vital capacity (VC) maneuvers in upright and head-down posture (180 degrees body tilt). In both postures, a gravitational pressure gradient was found, which increased very slightly with decreasing lung volumes (0.006 cmH2O X % VC-1 X cm descent-1) except for upright expiratory curves above 60% VC. The expiratory pressure gradient tended to be larger in head-down than in upright posture; however, during inspiration the opposite was true. In both postures the pressure change between 100 and 20% VC was smaller in the uppermost zone, which is consistent with the smaller changes in alveolar expansion in this zone. Also, in seven of the subjects, changes in cross-sectional area of the middle and lower part of the rib cage (HRC and LRC) and of the abdomen (ABD) were measured by respiratory inductive plethysmography in upright and head-down posture. The ratio of HRC motion to LRC motion was constant throughout the VC and did not change with posture, yet the ratio of ABD motion to mean RC motion changed with overall volume and was also larger in head-down than in upright posture. In conclusion, the changes in esophageal pressure gradient during slow VC maneuvers in head-down vs. upright posture were not related to (and thus not caused by) changes in chest wall configuration.

Adult↗
PubMed1992

Relationship between axial motion and volume displacement of the diaphragm during VC maneuvers.

During semistatic inspiratory and expiratory vital capacity (VC) maneuvers, axial motion of the diaphragm was measured by lateral fluoroscopy and was compared with diaphragmatic volume displacement. Axial motion was measured at the anterior, middle, and posterior parts of the diaphragm, and the mean of these measurements was used. The volume displacement was calculated in two ways: first, from respiratory inductive plethysmograph-(Respitrace) derived cross-sectional area changes of rib cage and abdomen (Vdi,RIP) by means of a theoretical analysis described by Mead and Loring (J. Appl. Physiol. 53: 750-755, 1982) and, second, from fluoroscopically measured changes in position and anteroposterior surface of the diaphragm (Vdi,F). A very good linear relationship was found between Vdi,RIP and Vdi,F during inspiration as well as expiration (r greater than 0.95), indicating that the analysis of Mead and Loring was valid in the conditions of the present study. The diaphragmatic volume displacement (active or passive) accounted for 50-60% of VC. A very good linear relationship was also found between mean axial motion and volume displacement of the diaphragm measured with both methods during inspiration and expiration (r greater than 0.98). Our data suggest that, over the VC range, diaphragmatic displacement functionally can be represented by a pistonlike model, although topographically and anatomically it does not behave as a piston.

Adult↗