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PubMed1996

Effect of surgical lung volume reduction on respiratory muscle function in pulmonary emphysema.

Lung volume reduction surgery (LVRS) in patients with severe lung emphysema restores the thoracic configuration to a more normal functional capacity. The aim of this study was to investigate whether reduction in intrathoracic volume by LVRS improves the inspiratory muscle force generation of the respiratory pump. Pulmonary function tests, maximal inspiratory mouth pressure (MIP), sniff nasal inspiratory pressure (SNIP), sniff transdiaphragmatic pressure (Pdi), and inspiratory mouth occlusion pressure (P0.1) were measured in 17 emphysematous patients (mean (+/- SEM) age 53 +/- 2 yrs) before and 1 month after LVRS. The mean value of forced expiratory volume in one second (FEV1) increased (0.82 +/- 0.07 vs 1.12 +/- 0.08 L; p < 0.0001), whilst there was a decrease (p < 0.0001) in residual volume (RV) (337 +/- 31 vs 250 +/- 21 % of predicted), functional residual capacity (FRC) (210 +/- 9 vs 159 +/- 9% pred), and total lung capacity (TLC) (138 +/- 6 vs 110 +/- 5% pred). The mean value of MIP increased by 52% from 4.8 +/- 0.4 to 7.3 +/- 0.6 kPa (p < 0.001), the mean value of SNIP increased by 66% from 3.9 +/- 0.4 to 6.5 +/- 0.5 kPa (p < 0.001), and the mean value of Pdi increased by 28% from 6.0 +/- 0.6 to 7.7 +/- 0.8 kPa (p < 0.05) after LVRS. P0.1 decreased on average by 24% from 0.46 +/- 0.03 to 0.35 +/- 0.02 kPa after LVRS. No significant correlations were found between inspiratory muscle (MIP, SNIP, Pdi) and respiratory drive (P0.1) indices, lung function data, 6 min walk distance, or dyspnoea score. In conclusion, the observed clinical improvement of patients with severe emphysema after lung volume reduction surgery results, in part, from an increased ability of the inspiratory muscles to generate force, which is paralleled by a significant decrease in central respiratory drive.

Adult↗
PubMed2004

Pressure-volume curve does not predict steady-state lung volume in canine lavage lung injury.

To better understand strategies for recruiting and maintaining lung volume in acute lung injury, we examined relationships between steady-state lung volume and cumulative cyclic recruitment/derecruitment volume history and the quasi-static pressure-volume curve, in an animal saline lavage lung injury model. Small-volume tidal pressure-volume loops performed after inflation from functional residual capacity demonstrated incremental, cyclic recruitment only if the peak pressure achieved exceeded the pressure at which the compliance increased (Pflex) on the pressure-volume curve, whereas loops performed after deflation from total lung capacity remained close to the envelope deflation curve. Recruitment continued to occur up to and beyond a peak inspiratory airway pressure of 40 cm H(2)O, as demonstrated by both the tidal loops and by computed tomography-derived lung volume data. Tidal-specific compliance was relatively constant across positive end-expiratory pressure levels after inflation from functional residual capacity, but peaked at moderate positive end-expiratory pressure after deflation from total lung capacity, further demonstrating the effects of volume history and providing experimental validation of the recruitment models of Hickling (AJRCCM 2001;163:69-78). These results support the interpretation of Pflex as pressure threshold for recruitment, but otherwise do not suggest a role for the pressure-volume curve in predicting steady-state lung volume.

Airway Resistance↗
PubMed1984

Relaxation rate of mouth pressure with sniffs at rest and with inspiratory muscle fatigue.

The relaxation rate of transdiaphragmatic pressure (Pdi) after voluntary contractions of the diaphragm slows with fatigue. We determined a range of values for the relaxation rate of mouth pressure (Pm) after voluntary contractions of the inspiratory muscles in 27 normal men and women at various lung volumes at rest. Values were similar for both sexes. The relaxation rates were similar at functional residual capacity (FRC) and below FRC, but were greater above FRC (p less than 0.05). In addition, we studied the effect of diaphragmatic fatigue induced by inspiratory resistive loading on the relaxation rates of Pdi and Pm with voluntary contractions of the inspiratory muscles in 6 subjects. With fatigue, the relaxation rates of Pdi and Pm both decreased by similar amounts, indicating that a decrease in the relaxation rate of Pm is as useful a predictor of inspiratory muscle fatigue as a decrease in the relaxation rate of Pdi has been shown to be for the diaphragm. The relaxation rate of Pm varies widely in normal subjects at rest, so isolated values do not indicate whether fatigue is present or developing. However, this may be predicted if relaxation rate decreases with serial measurements.

Adult↗
PubMed2001

[Physiopathology of acute respiratory failure in COPD and asthma].

Asthma and chronic obstructive pulmonary diseases (COPD) lead to functional obstruction of airways, identified by increased inspiratory and expiratory resistances. Increased expiratory resistances cause, in turn, a reduction in expiratory flow. The analysis of flow-volume loops shows that, as the disease progresses, the flow generated during expiration of a tidal volume becomes very close to the flow generated during forced maximal expiration. In such condition, where there is little or no reserve of expiratory flow, higher tidal volumes need to be reached in order to increase the expiratory flow, and hyperinflation inevitably occurs. Hyperinflation, a key feature in COPD pathophysiology, is generated by two mechanisms: reduction of elastic recoil of the lung (static hyperinflation) and interruption of expiration at lung volumes still higher than FRC, due to reduction of expiratory flow (dynamic hyperinflation). When dynamic hyperinflation occurs, a residual positive pressure remains in the alveoli, which is defined as intrinsic positive end-expiratory pressure (PEEPi). Hyperinflation carries several consequences: 1) Respiratory mechanics: at lung volumes close to total lung capacity, lung compliance is physiologically reduced, and elastic work required to generate the same inspiratory volume is therefore increased; 2) Respiratory muscles: contractile properties of diaphragm deteriorate when the dome is pushed downward by an increased lung volume, inspiration is mainly performed by inspiratory muscles, and expiration becomes active; 3) Circulation: pulmonary vascular resistances increase due to compression exerted by hyperinflation on alveolar vessels and to hypoxic vasoconstriction; right ventricle afterload increases and right sided hypertrophy and dilation ensue; left ventricular afterload may increase due to increased negative intrapleural pressure which translates into an increased transmural pressure which needs to be overcome by ventricular contraction. Ventilatory support of COPD patients should decrease work of breathing and improve gas exchange without increasing hyperinflation. This target can be achieved during assisted ventilation by applying a positive pressure both during inspiration and expiration; the level of PEEP should equal PEEPi. During mechanical ventilation in sedated paralyzed patients hyperinflation should be limited by decreasing minute volume and by increasing expiratory time, eventually choosing controlled hypercapnia.

Airway Resistance↗
PubMed1993

Respiratory muscle function in trained and untrained adolescents during short-term high intensity exercise.

The breathing pattern and respiratory muscle function were investigated in ten trained and ten untrained adolescents (aged 15-16 years) while undergoing an incremental intensity exercise test on a cycle ergometer up to 80% maximal oxygen consumption (VO2max), maintained to exhaustion. Before and after exercise, maximal inspiratory (PImax) and expiratory (PEmax) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [tidal volume (VT), respiratory frequency (fR), ventilation] and the relative contribution of ribcage and abdomen to VT were assessed using inductance plethysmography. Electromyographic activities of transversus abdominis (EMGtr) and diaphragm (EMGdi) muscles were recorded and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained group; fR increased significantly (P < 0.05) at 40% VO2max for the untrained group. Before exercise there was no difference in the maximal respiratory pressures. Up to 60% and 80% VO2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adolescents. However in this group, no evidence of respiratory muscle fatigue appeared: PImax, PEmax and the frequency spectrum of EMGtr and EMGdi were not altered by exercise up to exhaustion. In the untrained group, who had high ventilatory responses, expiratory muscle function was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that PImax was significantly decreased after exercise.

Adolescent↗
PubMed2005

Which pulmonary volume should be used in physiotherapy to obtain higher maximal inspiratory pressure in COPD patients?

BACKGROUND AND PURPOSE: Patients with chronic obstructive pulmonary disease (COPD) present pulmonary hyperinflation as the main cause of mechanical disadvantages in respiratory muscles. Measurement of the force generated by those muscles is converted into pressure changes. The aim of the present study was to evaluate the maximal inspiratory pressure (MIP) from the residual volume (RV) and from the functional residual capacity (FRC), in patients with COPD, and to determine which pulmonary volume should be used in physiotherapy so as to obtain higher MIP results. METHOD: An investigation of 18 male patients with stable COPD. Patients were examined using a manual vacuometer to measure the MIP of 20 daily manoeuvres. Ten measurements were taken from the RV and 10 from the FRC, taken alternately with an interval of 1 minute between each measurement, for five consecutive days. RESULTS: Increases in MIP were obtained from the RV measurements (mean +/- SE) from 59.7 (+/- 5.2) to 66.6 (+/- 5.3) cm H2O (F(4,64) = 3.34; p < 0.015) and from the FRC measurements, from 55.4 (+/- 4.9) to 64.4 (+/- 4,8) cm H2O (F(4,64) = 6.72; p < 0.001). Post hoc analysis showed an increase, over consecutive days, in both RV and FRC. For FRC, an increase was revealed on the second and third days, a fall was found on the fourth day and a new increase was found on the last day. MIP reached different levels, between RV and FRC, on the first (t = 2.888; p = 0.010) and fourth (t = 2.165; p = 0.045) days. CONCLUSION: In the present study, MIP reached higher levels at FRC during the five days of evaluation, and a learning effect occurred in the patients. Motor units from the respiratory muscles may have been recruited in order to perform the manoeuvres during the days of evaluation. The study suggests that there is good evidence for the use of the FRC as a parameter to find the major MIP value.

Aged↗
PubMed2004

A prospective, blinded evaluation of indexes proposed to predict weaning from mechanical ventilation.

OBJECTIVE: To conduct a blinded evaluation of the predictors of weaning from mechanical ventilation. DESIGN: A prospective clinical study. SETTING: A 23-bed general intensive care unit. PATIENTS: Ninety-three non-selected patients, ventilated for more than 48 h. METHODS: The study had two steps: at first, patients' data were used to select the cut-off value for weaning predictors (the minimal false classification). The cut-off value for each index was prospectively assessed in a group of 52 patients. The predictive performance of these indexes was evaluated by calculating the area under the receiver operating characteristic curve. In the prospective-validation set we used Bayes' theorem to assess the probability of each test in predicting weaning. The physicians making decisions about the weaning process were always unaware of the predictive values. Weaning was considered successful if spontaneous breathing was sustained for more than 48 h after extubation. MEASUREMENTS AND RESULTS: During the first 2 min after discontinuation of mechanical ventilation the following tests were performed: vital capacity, tidal volume, airway occlusion pressure (P(0.1)), minute ventilation, respiratory rate, maximal inspiratory pressure (MIP), respiratory frequency to tidal volume (f/V(T)), P(0.1)/MIP and P(0.1) x f/V(T). The areas under the curve showed that the tests had not the ability to distinguish between successful and unsuccessful weaning. CONCLUSION: Our results show that all the evaluated indexes are poor predictors of weaning outcome in a general intensive care unit population.

Aged↗
PubMed2004

[COPD: an inflammatory disease of the airways?].

COPD is characterized by a not fully reversible airflow limitation which is progressive and associated with an abnormal inflammatory reaction of the lungs. Airflow limitation is most often assessed by FEV (1.0). However, FEV (1.0) does not always reflect the course of the disease and does not appropriately describe the functional effect of a pharmacological or non-pharmacological intervention. Measurement of inspiratory parameters, e.g. IC or FIV (1.0), as well as assessment of exercise capacity should therefore be part of functional tests. The abnormal inflammatory reaction of the lungs can be assessed by a variety of methods. However, the characteristic increase of the number of neutrophils does not indicate a new therapeutic target. The term abnormal inflammation of the airways in bronchial asthma as well as in COPD presumably prompted a number of studies investigating the effects of inhalative corticosteroids in COPD. ICS do not alter the course of the disease, however they may reduce the number and severity of exacerbations. Combination of long-acting beta -agonists and ICS exert a better effect than either compound alone. This beneficial effect is difficult to explain by an anti-inflammatory action, as the long acting anticholinergic tiotropium has a comparable symptomatic and functional effect and reduces exacerbations without any known anti-inflammatory component. Future pharmacological therapies should therefore be based on a better understanding of the functional consequences of the disease and its pathogenesis.

Humans↗
PubMed2006

Function of intracoelomic septa in lung ventilation of amniotes: lessons from lizards.

Aspiration breathing is the dominant mechanism of lung inflation among extant amniotes. However, aspiration has two fundamental problems associated with it: paradoxical visceral translation and partial lung collapse. These can constrain the inspiratory tidal volume, reduce the effective lung ventilation, and ultimately curtail the aerobic capacity of an animal. Separation of the pleural and peritoneal cavities by an intracoelomic septum can restrict the cranial shift of abdominal viscera and provide structural support to the caudal lung surface. A muscular septum, such as the diaphragm of mammals or the diaphragmaticus of crocodilians, can exert active control over visceral translation and the degree of lung inflation. To a lesser degree, a nonmuscular septum can also function as a passive barrier when stretched taut by rib rotation. Studies of the posthepatic septum in teiid lizards and the postpulmonary septum in varanid lizards underscore the importance of nonmuscular septa in aspiration. These septa provide plausible functional models that help us infer the evolution of mammalian and avian lung ventilatory systems, respectively.

Animals↗
PubMed1987

Reduction of tonic ribcage muscle activity by anesthesia with thiopental.

Surface electromyograms were recorded from the scalene, sternomastoid, and parasternal intercostal muscles in 16 supine premedicated adult patients before, during, and after the induction of anesthesia with thiopental and after the administration of succinylcholine. Muscle activity was measured as the rectified, integrated signal, and expressed as a percentage of the activity detected during a maximal inspiration. Activity was found in the scalene and sternomastoid muscles of all patients, and in the intercostal muscles of 13. This activity was more commonly tonic, and, at end-expiration, it was 7%, 6%, and 5% of the activity that could be generated by a maximal inspiration, for the scalene, sternomastoid, and intercostal muscles, respectively. In all subjects, this activity was markedly reduced or abolished by the administration of thiopental, to 0.7%, 0.6%, and 0.6%, respectively. There was no tonic activity in these muscles during spontaneous respiration after induction of anesthesia. It is suggested that the reduction of tonic inspiratory activity in these muscles may contribute to the reduction in functional residual capacity associated with anesthesia.

Anesthesia↗
PubMed1978

Lung volumes and distensibility, and maximum respiratory pressures in thyroid disease before and after treatment.

Lung volumes, static pressure volume curves of the lung, and maximum respiratory pressures were measured in six patients with thyrotoxicosis and three with myxoedema before and after treatment. After treatment three of the thyrotoxic patients had increases in vital capacity of the same order as previously reported, but in contrast to previous reports, the lung volume changes were not associated with, nor due to, concomitant changes in respiratory muscle performance. Static pulmonary compliance increased in four of the six patients. The initial findings were more in keeping with the presence of pulmonary congestion. Only one of the myxoedematous patients had any significant increase in vital capacity after treatment, and in her case this was clearly attributable to increased inspiratory muscle force.

Aged↗
PubMed1985

Ventilatory response to fatiguing and nonfatiguing resistive loads in awake sheep.

To study the changes in ventilation induced by inspiratory flow-resistive (IFR) loads, we applied moderate and severe IFR loads in chronically instrumented and awake sheep. We measured inspired minute ventilation (VI), ventilatory pattern [inspiratory time (TI), expiratory time (TE), respiratory cycle time (TT), tidal volume (VT), mean inspiratory flow (VT/TI), and respiratory duty cycle (TI/TT)], transdiaphragmatic pressure (Pdi), functional residual capacity (FRC), blood gas tensions, and recorded diaphragmatic electromyogram. With both moderate and severe loads, Pdi, TI, and TI/TT increased, TE, TT, VT, VT/TI, and VI decreased, and hypercapnia ensued. FRC did not change significantly with moderate loads but decreased by 30-40% with severe loads. With severe loads, arterial PCO2 (PaCO2) stabilized at approximately 60 Torr within 10-15 min and rose further to levels exceeding 80 Torr when Pdi dropped. This was associated with a lengthening in TE and a decrease in breathing frequency, VI, and TI/TT. We conclude that 1) timing and volume responses to IFR loads are not sufficient to prevent alveolar hypoventilation, 2) with severe loads the considerable increase in Pdi, TI/TT, and PaCO2 may reduce respiratory muscle endurance, and 3) the changes in ventilation associated with neuromuscular fatigue occur after the drop in Pdi. We believe that these ventilatory changes are dictated by the mechanical capability of the respiratory muscles or induced by a decrease in central neural output to these muscles or both.

Airway Resistance↗
PubMed1994

Pulmonary dead space and airway dimensions in dogs at different levels of lung inflation.

The quasi-stationary front that separates inspired gas from mixed alveolar gas is largely determined by the balance between diffusive and convective forces of gas transport. To investigate parameters influencing this balance, a study was performed on eight anesthetized ventilated beagle dogs. Measurements were made of the volume of pulmonary dead space corresponding to four end-inspiratory lung volumes. Aerosol recovery techniques were used to determine airway sizes at lung depths corresponding to those respective dead space volumes as well as at fixed volumetric depths between 70 and 250 ml. Mean dead space volumes as measured by a single inhalation of He (and SF6) were 112 +/- 15 (SD) ml (127 +/- 15 ml), 120 +/- 18 ml (137 +/- 20 ml), 127 +/- 18 ml (145 +/- 20 ml), and 133 +/- 19 ml (155 +/- 21 ml) at end-inspiratory lung volumes of 64, 71, 79, and 86%, respectively, of total lung capacity. At fixed lung depths the airway diameters increased with higher levels of lung inflation. However, airway diameters "at the end of the dead space" did not change significantly. They were approximately 0.5 mm for SF6 dead space and approximately 0.75 mm for He dead space. These findings support the theoretical prediction that the position of the diffusion front during breathing is strongly dependent on airway geometry and much less dependent on parameters of the breathing maneuver.

Animals↗
PubMed1989

Detrimental effects of positive end-expiratory pressure during controlled mechanical ventilation of patients with severe airflow obstruction.

Positive end-expiratory pressure (PEEP) in treatment of asthma may be beneficial by dilating airways or detrimental by increasing hyperinflation. Several studies have reported beneficial results but with conflicting effects on lung volume. We studied the effects of PEEP on pulmonary hyperinflation, gas exchange, and circulation in six patients (59 +/- 19 yr, four men, two women) with severe airflow obstruction requiring mechanical ventilation (four with asthma, two with an exacerbation of chronic airflow obstruction). Three levels of PEEP (5, 10, and 15 cm H2O) were studied. All patients were paralyzed and ventilated with a tidal volume of 1.0 L, and respiratory rates (R) of 10, 16, and 22 breaths per min. End-inspiratory lung volume (VEI) or the degree of pulmonary hyperinflation above functional residual capacity (FRC) was quantified by measuring total exhaled gas volume during a period of apnea following steady-state tidal inspiration (1). Two patients were not studied at 15 cm H2O PEEP because of hypotension. Without PEEP, all patients showed gas trapping above FRC that increased progressively as R was increased (i.e., expiratory time decreased). At each R, increases in PEEP progressively increased FRC up to 1.42 +/- 0.43 L (mean +/- SD) at 15 cm H2O PEEP (n = 4) and progressively reduced the degree of gas trapping above the PEEP FRC.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Obstruction↗
PubMed1987

Effect of salbutamol on respiratory mechanics in bronchiolitis.

The effect of inhaled bronchodilators in bronchiolitis has been difficult to evaluate due to problems with techniques for assessing respiratory function in infants. Two new techniques were used to assess the response to inhaled salbutamol in 17 infants with bronchiolitis. With one technique, expiratory flow, volume, and airway occlusion pressure were measured and used to derive compliance (Crs) and conductance (Grs) of the respiratory system from a passive expiration induced by a brief end-inspiratory airway occlusion. With the other technique, the maximum flow at functional residual capacity (VmaxFRC) was measured from a partial maximum expiratory flow-volume curve generated by external chest compression. For the group, there was no change in compliance or conductance after salbutamol, but salbutamol caused a fall in maximum flow at functional residual capacity (p less than 0.01) and in the time constant of tidal expiration (p less than 0.01). The decrease in maximum flow at functional residual capacity with salbutamol is consistent with increased airway collapse on forced expiration. The decrease in tidal time constant suggests that the drug decreases expiratory braking. Presence of such braking activity may be an important strategy for maintaining lung volume. In summary, salbutamol failed to produce a beneficial effect on airways in bronchiolitis, but did produce changes in expiration which may be harmful in some infants.

Administration, Inhalation↗
PubMed1991

Extrapulmonary thoracic restriction (hidebound chest) complicating eosinophilic fasciitis.

Eosinophilic fasciitis (EF) is an unusual disorder characterized by diffuse skin thickening and induration due to inflammation within the deep fascia; visceral involvement is generally mild or absent. A patient with biopsy-proved EF developed progressive respiratory limitation. Physical examination revealed marked induration of the thoracic integument with a severely limited chest wall excursion. Total lung capacity was 62 percent of predicted with a normal corrected Dco and maximal inspiratory force; a chest computed tomogram with thin sections showed no evidence of parenchymal lung disease. Extrapulmonary thoracic restriction ("hidebound chest") has not been previously reported to complicate EF.

Aged↗
PubMed1994

A functional and morphologic analysis of pressure-controlled inverse ratio ventilation in oleic acid-induced lung injury.

STUDY OBJECTIVE: To compare volume-controlled ventilation (VCV PEEP) with pressure-controlled inverse ratio ventilation (PCIRV) at equal levels of end-expiratory pressure. DESIGN: Animal study using an oleic acid lung injury model with random application of VCV PEEP and PCIRV. SETTING: Experimental laboratory investigation at the Department of Clinical Physiology at Uppsala University. ANIMALS: Twelve pigs. INTERVENTIONS: VCV PEEP and PCIRV at an end-expiratory pressure level of 10 cm H2O. MEASUREMENTS AND RESULTS: Lung mechanics, hemodynamics, and gas exchange. Recruitment of lung tissue, regional lung density, and distribution of inspired gas by computed tomography. Mean and peak airway pressures were 29 and 35 cm H2O with PCIRV and 17 and 45 cm H2O with VCV PEEP. Cardiac output and mean systemic blood pressure were lower with PCIRV (2.5 L/min and 82 mm Hg) than with VCV PEEP (3.1 L/min and 97 mm Hg). Physiologic dead space was 24 percent with VCV PEEP and 20 percent with PCIRV. Static compliance, arterial oxygen tension, and functional residual capacity were equal between the two ventilatory modes. End-expiratory, end-inspiratory, and dynamic computed tomographic densities were equal between VCV PEEP and PCIRV. Nonaerated and poorly aerated lung areas were of equal size with VCV PEEP and PCIRV. CONCLUSIONS: PCIRV was no better than VCV with similar PEEP levels in alveolar recruitment and aeration of the lung tissues or in oxygenating the blood. Cardiac output was lower with PCIRV than with VCV, causing lower oxygen delivery to peripheral tissues. PCIRV does allow for a reduction in minute ventilation and for lowering peak airway pressure.

Analysis of Variance↗
PubMed1982

Increased exercise performance in patients with severe COPD following inspiratory resistive training.

Six patients with severe chronic obstructive pulmonary disease underwent a six-week outpatient program to train their respiratory muscles with an inspiratory resistive device. Exercise performance was measured using a cycle ergometer. Maximum exercise capacity, represented by VO2 max, increased 15 percent. The maximum work rate increased 37 percent, and the minute ventilation attained during exercise increased 17 percent after training. Respiratory muscle endurance increased 56 percent. All patients reported an increased ability to perform the activities of daily living. No changes were reported in three patients who underwent sham training.

Breathing Exercises↗