Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Inspiratory Capacity”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78Linked to original sources
PubMed1986

Breathlessness and exercise in patients with cardiorespiratory disease.

Previous studies have led to the revival of the hypothesis that breathlessness is the perception of respiratory muscle effort and is present when the tension developed by muscles increases, when the muscles are weak, or when both conditions are present simultaneously. Using a category scale, the intensity of breathlessness was measured in 20 subjects (2 normal subjects and 18 patients) undergoing an incremental exercise test (50 to 100 kpm/min) to maximal capacity. The patients were selected to provide a heterogeneous group of pulmonary diseases, obesity, muscular weakness, and cardiac disease, with a wide variability in exercise capacity (250 to 1,900 kpm/min) and severity of dyspnea. Maximal inspiratory pressure (MIP), pleural pressure (Ppl), the extent of shortening of the inspiratory muscles as indicated by the tidal volume expressed as a percent of vital capacity (VT/VC), the rate of shortening as indicated by flow rate, the frequency of contraction as indicated by breathing frequency (fb), and the duty cycle (TI/Ttot) were measured throughout exercise to assess their relative contribution to the intensity of breathlessness. Using multifactorial analysis, the perception of breathlessness was significantly (p less than 0.01) related to the Ppl, inspiratory flow rate (VI), VT/VC, TI/Ttot, and fb. A multiple linear regression equation that included all these variables explained 69% of the variance, with no single factor being identified as uniquely predominant: Breathlessness = 3.0 (Ppl/MIP) + 1.2 (VI) + 4.5 (VT/VC) + 0.13 (fb) + 5.6 TI/Ttot) - 6.2 (R = 0.83). The intensity of effort required to produce a given pressure increases when the muscle is weak, when the velocity of contraction increases, or when the muscle shortens.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Awake inspiratory airway occlusion in normal humans is followed by hyperpnea and hypocapnia.

The ventilatory response following 15 seconds of inspiratory airway occlusion at functional residual capacity (FRC) was studied in nine normal supine awake subjects. Expired minute ventilation (VE), CO2 output (VCO2), tidal volume (VT), and end-tidal PCO2 (PETCO2) were measured on a breath-by-breath basis. Alveolar PCO2 rose 5.6 mm Hg during the apnea (P less than 0.001). Ventilation rose 10.8 L/min on the first breath following apnea and remained elevated above control measurements for five breaths (P less than 0.05). The persistent hyperpnea was due to an increase in tidal volume and was associated with alveolar hypocapnia for 6 breaths or 30 sec (P less than 0.05) and an increase in CO2 output for 4 breaths (P less than 0.05). Changes in end-tidal PCO2 correlated with excess CO2 output relative to control measurements immediately prior to airway occlusion (P less than 0.03). After 15 sec airway occlusion at FRC, there is alveolar hypercapnia with a 2.6-fold first breath rise in ventilation. Persistent alveolar hyperventilation lasting 30 sec following airway occlusion may be due to delays in central chemoreceptor response or an afterdischarge phenomenon. This overshoot hypercapnia following airway occlusion may have some relevance to the development of central apneas following obstructive apnea episodes.

Adolescent↗
PubMed2000

Asthma: pathophysiology of the bronchial obstruction.

From a pathophysiologic perspective, the changes that occur in asthma are multiple, diverse, and complex. Assessment of the mechanical properties of the ventilatory apparatus provides several different types of information, depending on the gravity of the bronchial obstruction. During asthma, or induced bronchial obstruction, the function of the muscles is altered, causing changes in respiratory timing. Expiratory duration decreases more than inspiratory duration, and the functional residual capacity (FRC) increases, due to mechanical changes within the airways that lead to air trapping. The related hypoventilation is responsible for hypoxemia and hypercapnia, but it does not severely affect the diffusion capacity of the alveolocapillary membrane. We describe the pathophysiology of the bronchial obstruction in asthmatic patients, underlining the critical function of the respiratory muscles. Moreover, we clarify the relations between the ventilatory changes and gas-exchange alteration.

Airway Obstruction↗
PubMed2002

Patient selection for lung volume reduction surgery: is outcome predictable?

Patient selection for lung volume reduction surgery (LVRS) relies on sound physiologic concepts and experience from large case series. LVRS should be considered in severely symptomatic emphysema with marked airflow obstruction and hyperinflation despite optimal medical management, and in the absence of major comorbidities associated with excessive perioperative risks. Qualitative estimation of functional benefit from LVRS in suitable candidates has been based on functional criteria (e.g., high inspiratory conductance, high residual volume/total lung capacity ratio), on heterogeneity of emphysema assessed by computed tomography (CT) or perfusion scans, and on severity of emphysema assessed by CT or impaired diffusing capacity. Selection strategies relying on such criteria have provided favorable functional results at a low mortality, but further validation of potential outcome predictors in prospective trials is needed.

Adult↗
PubMed1996

Transdiaphragmatic pressure in young adult Singaporean subjects--normal values and a comparison between different respiratory manoeuvres.

BACKGROUND: Most published normal values for transdiaphragmatic pressure (Pdi) have been from Caucasian subjects and there is no universal agreement regarding the most appropriate manoeuvre for assessing Pdi. AIMS: The aims of our study were to obtain normal values and to compare the different manoeuvres used to assess Pdi in normal young Singaporean adults. METHODS: Twenty-four normal subjects (23 Chinese, one Indian) were studied by measuring Pdi during maximal sniffs from functional residual capacity (sniff Pdi), maximal inspiration to total lung capacity (Pdi TLC) and maximal static inspiratory efforts from residual volume (Pdi PImax). RESULTS: Mean values +/- SD for sniff Pdi, Pdi TLC and Pdi PImax were 101.8 +/- 31.7, 46.8 +/- 26.4 and 83.5 +/- 35.5 cm H2O respectively. Sniff Pdi was significantly higher than Pdi TLC (p < 0.001) and Pdi PImax (p = 0.005). Pdi PImax was significantly higher than Pdi TLC (p < 0.001). Males had significantly higher values for sniff Pdi (p = 0.026) and Pdi PImax (p = 0.022) than females. There was a significant correlation between the different methods of recording Pdi. Sniff Pdi had the highest values, least between- and within-subject variation and most consistent pattern of respiratory muscle recruitment with the lowest proportion of negative gastric pressure (Pg) values (p < 0.001). CONCLUSIONS: Therefore, sniff Pdi may be better than Pdi TLC and Pdi PImax in assessing diaphragm function. Also, our subjects seemed to have lower sniff Pdi and Pdi PImax, and higher Pdi TLC compared with Caucasian subjects.

Adult↗
PubMed1989

Effects of an external resistance on maximum flow in chronic obstructive lung disease: implications for recognition of coincident upper airway obstruction.

To determine how the presence of generalised airflow limitation due to chronic obstructive lung disease affects the recognition of simulated upper airway obstruction, a study was carried out in 12 patients (mean (SD) age 57 (7) years) with chronic obstructive lung disease (FEV1% predicted 53 (22), range 21-70) and 12 matched control subjects. Patients and control subjects performed maximal inspiratory and expiratory flow-volume curves in a variable volume plethysmograph with and without upper airway obstruction simulated at the mouth with a series of polythene washers of internal diameter 4, 6, 8, 10, and 12 mm. In patients, as in normal subjects, peak expiratory flow (PEF) and maximum inspiratory flow at 50% of vital capacity (Vmax50) were more sensitive to upper airway obstruction than were FEV1 or maximum expiratory flow at 50% VC (VEmax50); but the reductions in all indices caused by simulated upper airway obstruction were smaller in the patients than in the controls. The fall in PEF (whether expressed in absolute units or as a percentages) consequent on severe (4 mm) upper airway obstruction became smaller with increasing severity of chronic obstructive lung disease. The subjects also produced flow-volume curves with and without 6 mm upper airway obstruction while breathing helium and oxygen (heliox). In both groups the effects of heliox on PEF and Vmax50 were increased when upper airway obstruction was simulated. It was confirmed that the functional recognition of upper airway obstruction is more difficult in patients with chronic obstructive lung disease than in normal subjects and this difficulty increases with severity of disease; an unusually large increase in PEF or Vmax50 while the patient is breathing heliox should raise the suspicion of coexisting upper airway obstruction, but such a pattern is not specific.

Aged↗
PubMed1987

Effect of inspiratory resistive loading on control of ventilation during progressive exercise.

Eight healthy volunteers performed gradational tests to exhaustion on a mechanically braked cycle ergometer, with and without the addition of an inspiratory resistive load. Mean slopes for linear ventilatory responses during loaded and unloaded exercise [change in minute ventilation per change in CO2 output (delta VE/delta VCO2)] measured below the anaerobic threshold were 24.1 +/- 1.3 (SE) = l/l of CO2 and 26.2 +/- 1.0 l/l of CO2, respectively (P greater than 0.10). During loaded exercise, decrements in VE, tidal volume, respiratory frequency, arterial O2 saturation, and increases in end-tidal CO2 tension were observed only when work loads exceeded 65% of the unloaded maximum. There was a significant correlation between the resting ventilatory response to hypercapnia delta VE/delta PCO2 and the ventilatory response to VCO2 during exercise (delta VE/delta VCO2; r = 0.88; P less than 0.05). The maximal inspiratory pressure generated during loading correlated with CO2 sensitivity at rest (r = 0.91; P less than 0.05) and with exercise ventilation (delta VE/delta VCO2; r = 0.83; P less than 0.05). Although resistive loading did not alter O2 uptake (VO2) or heart rate (HR) as a function of work load, maximal VO2, HR, and exercise tolerance were decreased to 90% of control values. We conclude that a modest inspiratory resistive load reduces maximum exercise capacity and that CO2 responsiveness may play a role in the control of breathing during exercise when airway resistance is artificially increased.

Adult↗
PubMed1988

Influence of inspiratory flow rate and frequency on O2 cost of resistive breathing in humans.

We examined the combined effect of an increase in inspiratory flow rate and frequency on the O2 cost of inspiratory resistive breathing (VO2 resp). In each of three to six pairs of runs we measured VO2 resp in six normal subjects breathing through an inspiratory resistance with a constant tidal volume (VT). One of each pair of runs was performed at an inspiratory muscle contraction frequency of approximately 10/min and the other at approximately 30/min. Inspiratory mouth pressure was 45 +/- 2% (SE) of maximum at the lower contraction frequency and 43 +/- 2% at the higher frequency. Duty cycle (the ratio of contraction time to total cycle time) was constant at 0.51 +/- 0.01. However, during the higher frequency runs, two of every three contractions were against an occluded airway. Because VT and duty cycle were kept constant, mean inspiratory flow rate increased with frequency. Careful selection of appropriate parameters allowed the pairs of runs to be matched both for work rate and pressure-time product. The VO2 resp did not increase, despite approximately threefold increases in both inspiratory flow rate and contraction frequency. On the contrary, there was a trend toward lower values for VO2 resp during the higher frequency runs. Because these were performed at a slightly lower mean lung volume, a second study was designed to measure the VO2 resp of generating the same inspiratory pressure (45% maximum static inspiratory mouth pressure at functional residual capacity) at the same frequency but at two different lung volumes. This was achieved with a negligibly small work rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1997

Respiratory-related neurons of the fastigial nucleus in response to chemical and mechanical challenges.

Responses of cerebellar respiratory-related neurons (CRRNs) within the rostral fastigial nucleus and the phrenic neurogram to activation of respiratory mechano- and chemoreceptors were recorded in anesthetized, paralyzed, and ventilated cats. Respiratory challenges included the following: 1 ) cessation of the ventilator for a single breath at the end of inspiration (lung inflation) or at functional residual capacity, 2) cessation of the ventilator for multiple breaths, and 3) exposure to hypercapnia. Nineteen CRRNs having spontaneous activity during control conditions were characterized as either independent (basic, n = 14) or dependent (pump, n = 5) on the ventilator movement. Thirteen recruited CRRNs showed no respiratory-related activity until breathing was stressed. Burst durations of expiratory CRRNs were prolonged by sustained lung inflation but were inhibited when the volume was sustained at functional residual capacity; it was vice versa for inspiratory CRRNs. Multiple-breath cessation of the ventilator and hypercapnia significantly increased the firing rate and/or burst duration concomitant with changes noted in the phrenic neurogram. We conclude that CRRNs respond to respiratory inputs from CO2 chemo- and pulmonary mechanoreceptors in the absence of skeletal muscle contraction.

Animals↗
PubMed1995

Airway obstruction during exercise in asthma.

Airway obstruction (AO) in exercise-induced asthma (EIA) is considered a postexercise phenomenon. However, many with EIA complain of respiratory distress during exercise. We evaluated AO in six asthmatic subjects during a short (SX = 6 min) and a long (LX = 20 min) exercise session. We measured peak expiratory flow (PEF) rate, forced expiratory volume in one second (FEV1), and forced expiratory flow at 50% of vital capacity (Vmax50) and calculated expiratory and inspiratory pulmonary resistance (RLe and RLi). Rated perceived exertion (RPE) was evaluated as a measure of dyspnea. All three indices of airflow significantly decreased following SX and LX, but RLi and RLe increased. During SX, PEF, FEV1, and Vmax50 did not decrease, but RLi decreased. During LX, PEF, FEV1, and Vmax50 decreased (20.0, 26.0, and 17.7%, respectively), whereas RLi and RLe significantly increased (74.0 and 53.0%). Rated perceived exertion correlated highly with RLi during exercise (r = 0.95). In summary, there was little or no AO during SX but a frank AO during LX in asthmatic subjects. We conclude that AO occurs during LX and that the manifestation of dyspnea is associated with AO during exercise, as well as in recovery.

Adult↗
PubMed2007

Use of flow-volume curves to predict oral appliance treatment outcome in obstructive sleep apnea.

BACKGROUND: It has been recognized that mandibular advancement splint (MAS) treatment is effective in some, but not all, patients with obstructive sleep apnea (OSA). Hence there is a need for a simple and reliable clinical tool to assist in the differentiation of treatment responses. We hypothesized that abnormalities of flow-volume curves, together with other clinical variables, may have clinical utility in the prediction of MAS treatment outcome. METHODS: Fifty-four patients with known OSA underwent MAS treatment. Expiratory and inspiratory flow-volume curves were measured in the erect and supine positions to derive midinspiratory flow (MIF(50)) and the ratio of expiratory to inspiratory flow at 50% of vital capacity (MEF(50):MIF(50)). Multivariable logistic regression was performed to identify additional significant clinical variables in the prediction of treatment outcome. RESULTS: The mean (+/- SD) apnea-hypopnea index (AHI) in 35 responders was significantly reduced from 28.9 +/- 13.7 to 6.7 +/- 5.8/hour (p<0.001). In 19 nonresponders there was no significant change in AHI. MIF(50) was lower (6.04 +/- 1.80 vs. 6.88 +/- 1.08 L/second; p=0.035) and the MEF(50):MIF(50) ratio was higher (0.82 +/- 0.23 vs. 0.61 +/- 0.15; p=0.001) in responders than nonresponders. Logistic regression analysis revealed that the MEF(50):MIF(50) ratio was the most important predictive factor for MAS treatment outcome, but that body mass index, age, and baseline AHI were also contributory. CONCLUSIONS: These data suggest that flow-volume curves, in combination with other factors such as body mass index, age, and baseline AHI, may have a useful clinical role in the prediction of treatment outcome with MAS.

Adult↗
PubMed2002

Effects of mechanical ventilation on diaphragm function and biology.

The pathophysiological mechanisms of weaning from mechanical ventilation are not fully known, but there is accumulating evidence that mechanical ventilation induces inspiratory muscle dysfunction. Recently, several animal models have provided potential mechanisms for mechanical ventilation-induced effects on muscle function. In patients, weaning difficulties are associated with inspiratory muscle weakness and reduced endurance capacity. Animal studies demonstrated that diaphragm force was already decreased after 12 h of controlled mechanical ventilation and this worsened with time spent on the ventilator. Diaphragmatic myofibril damage observed after 3-days controlled mechanical ventilation was inversely correlated with maximal diaphragmatic force. Downregulation of the diaphragm insulin-like growth factor-I and MyoD/myogenin messenger ribonucleic acid occurred after 24 h and diaphragmatic oxidative stress and increased protease activity after 18 h. In keeping with these findings, diaphragm fibre atrophy was shown after 12 h and reduced diaphragm mass was reported after 48 h of controlled mechanical ventilation. These animal studies show that early alterations in diaphragm function develop after short-term mechanical ventilation. These alterations may contribute to the difficulties in weaning from mechanical ventilation seen in patients. Strategies to preserve respiratory muscle mass and function during mechanical ventilation should be developed. These may include: adaptation of medication, training of the diaphragm, stabilisation of the catabolic state and pharmacotherapy.

Animals↗
PubMed1995

Does phase 2 of the expiratory PCO2 versus volume curve have diagnostic value in emphysema patients?

It has been postulated that serial inhomogeneity of ventilation in the peripheral airways in emphysema is represented by the shape of expiratory carbon dioxide tension versus volume curve. We examined the diagnostic value of this test in patients with various degrees of emphysema. The volumes between 25-50% (V25-50) and 25-75% (V25-75) of the expiratory carbon dioxide tension versus volume curve were determined in 29 emphysematous patients (20 severely obstructed and 9 moderately obstructed), 12 asthma patients in exacerbation of symptoms, and 28 healthy controls. Discriminant analysis was used to examine whether these diagnostic groups could be separated. With regard to phase 2 of the expiratory CO2 versus volume curve (mixture of anatomic deadspace and alveolar air), a plot of intercept versus slope of the relationships of (V25-50) and (V25-75) versus inspiratory volume (VI) from functional residual capacity (FRC), obtained during natural breathing frequency, proved to be most discriminating in the separation between healthy controls and severely obstructed emphysema patients. Separating healthy controls and severely obstructed emphysema patients on the basis of the discriminant line for V25-50, 9 of the 12 asthma patients in exacerbation were classified as normal, and only 5 of the 9 moderately obstructed emphysema patients as emphysematous. For V25-75 involvement of phase 3 of the curve (alveolar plateau) in asthma patients in exacerbation caused a marked overlap with the severely obstructed emphysema patients. In the healthy controls, a fixed breathing frequency of 20 breaths.min-1 led to an increase of both volumes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1997

Long-term outcome of pulmonary rehabilitation in patients with COPD.

BACKGROUND: This study investigates the long-term benefits of pulmonary rehabilitation in terms of health-related quality of life (HRQL). Such information is of particular importance in developing strategies for aftercare at home which aim to maintain the initial improvements seen after rehabilitation. METHODS: Criteria for inclusion were diagnosis of COPD, age 40 to 80 years, and completion of an inpatient pulmonary rehabilitation program. HRQL was assessed by the St. George Respiratory Questionnaire, and the component "well-being" from the Medical Psychological Questionnaire for Lung Diseases. Patient characteristics included lung function parameters such as FEV1, the diffusion capacity for carbon monoxide and maximal inspiratory mouth pressure, age, socio-economic variables, and exercise tolerance evaluated by a 12-min walking test. To define patients in whom long-term benefits were sustained 9 months postdischarge, cases were clustered using hierarchical cluster analysis, based on the HRQL scores at discharge. RESULTS: Complete data sets were obtained from 77 patients. Two groups of cases were clustered. Patient characteristics were essentially the same in both groups. HRQL differed significantly between groups on admission, at discharge, and at follow-up. Within-group analysis revealed that patients in group 1 (n=44) had "moderate" scores on HRQL on admission, a significant improvement between admission and discharge, followed by a significant deterioration of HRQL at follow-up. Group 2 (n=33) had "severely" impaired HRQL on admission, little improvement after rehabilitation, and remained in fairly stable condition 9 months postdischarge. CONCLUSIONS: Results suggest that patients with COPD require a differentiated aftercare program of postdischarge pulmonary rehabilitation.

Adult↗
PubMed2005

Manual hyperinflation improves alveolar recruitment in difficult-to-wean patients.

STUDY OBJECTIVES: To investigate the effect of manual hyperinflation (MH) in patients with atelectasis associated with ventilation support. DESIGN: Patients were randomized to either an experimental group or a control group. SETTING: Pulmonary ICUs from two hospitals. PATIENTS: Twenty-three patients with atelectasis associated with ventilation support. INTERVENTIONS: The MH technique was at a rate of 8 to 13 breaths/min for a period of 20 min each session, three times per day for 5 days. The control group received their standard prescribed mechanical ventilation without supplemental MH. Sputum contents (wet/dry weight ratio, viscosity), respiratory system capacity (spontaneous tidal volume [Vt], maximal inspiratory pressure, rapid shallow breathing index [f/Vt], chest radiograph signs, and Pa(O2)/fraction of inspired oxygen [Fi(O2)]) were measured just prior to the MH at day 0 as baseline, and at day 3 and day 6 of the study. MEASUREMENTS AND RESULTS: There were significant improvements in scores over the 6-day study in the experimental group compared to the control group in spontaneous Vt (p = 0.035) and chest radiograph signs (p = 0.040), and a trend toward improvement of f/Vt (p = 0.066) and Pa(O2)/Fi(O2) (p = 0.061) after adjustment for covariates. Other outcome variables did not differ significantly between the experimental and control groups. CONCLUSIONS: MH performed on patients with atelectasis from ventilation support significantly improved alveolar recruitment.

Aged↗
PubMed2000

The sensitivity of tussiphonography for assessing the effectiveness of treatment.

Our previous studies have demonstrated that tussiphonogram is suitable not only for the detection of pathological condition in the respiratory tract but also for treatment effectiveness assessment. The purpose of this study was to evaluate the possibilities of tussiphonography in detection of already little pathological changes in the airways and lungs. Therefore the changes of voluntary cough sound indexes were compared with pulmonary function tests in selected group of asthmatics before and after a pulsatile electromagnetic therapy in which the effect of therapy on pulmonary function tests was minimal. After magnetotherapy in 18 patients with increased expiratory forced lung capacity by 7.3% and increased peak inspiratory flow by 31.7% in average the voluntary cough sound intensity decreased by 37.8%, the sound duration shortened by 11% and the sound pattern showed the tendency to normalization. The improvement of mentioned cough indexes was absent in 17 patients who were treated by magnetotherapy too, but at the same time suffered from respiratory viral infection and in 22 patients treated only with climatotherapy and antiasthmatics. Changes of flow-volume loops in patients were not in the close relation to other followed indices. The correlation analysis showed a functional connection in relative differences of cough sound indices and some pulmonary function tests. The results confirmed the suitability of tussiphonography to indicate even mild pathological changes in respiratory tract. (Fig. 4, Ref. 21.)

Adult↗
PubMed2002

[Ministernotomy improves the postoperative course in aortic valve replacement].

BACKGROUND: The advantages and the safety aspects of ministernotomy, in aortic valve replacement, are presently under investigation. The aim of this study was to compare the postoperative results between ministernotomy access and standard total sternotomy access. METHODS: Between January 1997 and July 2002, 98 patients underwent elective aortic valve replacement. They were divided into two groups: group Gm (49 patients) undergoing a ministernotomy approach ("reversed C" or "reversed L") and group Gs (49 patients) undergoing conventional total sternotomy. RESULTS: The length of the skin incision was significantly shorter in group Gm (p < 0.001). The total operative time was significantly longer in group Gm (p = 0.02), but no significant differences were found in the cardiopulmonary bypass and aortic cross-clamping times. Mean mediastinal drainage, incidence of bleeding > 800 ml, mechanical ventilation time, intensive care unit stay and hospital stay were significantly greater in group Gs. Five days after the surgical procedure, spirometric analysis demonstrated a significant reduction in total lung capacity, and in maximum expiratory and inspiratory pressures in group Gs compared with group Gm (p = 0.003, p = 0.001, p = 0.01, respectively). CONCLUSIONS: Our results showed that in addition to cosmetic advantages, ministernotomy is also associated with a better outcome in terms of sternal stability, blood loss and transfusions, and postoperative pain. Ministernotomy also improved the recovery of respiratory function, with a shorter mechanical ventilation time and allowed an earlier hospital discharge.

Aortic Valve↗
PubMed1992

[Short-term effects of respiration with external negative ventilation --shield-type respirator-- on the pulmonary function in COPD].

With the objective to test the effect of intermittent and short term rest in respiratory muscles in patients with COPD and maintained hypercapnia we have studied 34 patients in a stable condition: 23 were part of the study group (Group I) and 11 were the control group (Group II). After a complete functional basal study, patients in Group I were treated with intermittent rest of their respiratory muscles, through a negative pressure external respirator--shield type--during three consecutive days. We got, in this study group, a significative improvement in the maximum inspiratory pressure measured at residual volume (PI max RV), which went from 66.6 +/- 15.9 to 71.2 +/- 15.2 (p < 0.005), as well as a lowering, also significative, of partial pressure of CO2 in arterial blood (PaCO2) and in expired air (EFCO2), which went from 55.2 +/- 7.2 to 52.3 +/- 3 (p < 0.0002) and 3.3 +/- 0.5 to 3.1 +/- 0.5 (p < 0.01), respectively. Maximum inspiratory pressure measured to functional residual capacity (PI max FRC) experienced an increase in the limit of statistical signification. Rest of the parameters did not significantly change. These results back the hypothesis that in stabilized COPD with CO2 retention, a chronic fatigue of respiratory muscles could exist, and that intermittent rest of these muscles could mean an hypercapnia diminution, due to the improvement in the function of respiratory muscles.

Adult↗