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PubMed1985

Inspiratory muscle training in patients with chronic obstructive pulmonary disease.

To investigate the effects of inspiratory muscle resistive loading training (IMT) on exercise performance in chronic obstructive pulmonary disease (COPD), 13 patients undergoing standard pulmonary rehabilitation were divided into control (n = 6) and experimental (n = 7) groups. Prior to training, we measured inspiratory muscle strength and endurance, resting pulmonary function, and exercise performance on a bicycle ergometer (a progressive test and an endurance test at two thirds of maximal work load). We then determined their resistive loads for training by measuring their 10-min maximal sustainable resistance. Training by patients in the experimental group involved inspiring against a predetermined resistive load. The control subjects breathed through a sham training tube, so that studies were performed in double-blind fashion. The training consisted of 15-min sessions twice daily for 4 wk. The IMT dramatically improved inspiratory muscle endurance--represented as either sustainable inspiratory pressure (SIP) or endurance time at 60% of maximal inspiratory mouth pressure (Pimmax) at functional residual capacity. The SIP of the trained group increased from 29 +/- 11 to 46 +/- 11% of Pimmax (p less than 0.005). Training slightly increased inspiratory muscle strength (p less than 0.05), as determined by Pimmax. In contrast, resting pulmonary function and performance of both progressive and constant-load exercise remained unchanged. We conclude that 4-wk IMT in a pulmonary rehabilitation setting improves inspiratory muscle endurance in patients with COPD without changing pulmonary function or exercise performance.

Aged↗
PubMed2006

Training with inspiratory pressure support in patients with severe COPD.

This study evaluates the effects of training with noninvasive ventilatory support in patients with chronic obstructive pulmonary disease in a randomised, controlled, observer-blinded trial. Twenty-nine patients with chronic obstructive pulmonary disease and with a ventilatory limited exercise capacity (forced expiratory volume in one second < 60% predicted, breathing reserve at maximal exercise < 20% of maximally voluntary ventilation, resting arterial oxygen tension > or = 8 kPa (60 mmHg), end-exercise arterial oxygen saturation measured by pulse oximetry > or = 85%) completed an 8-week supervised outpatient cycle exercise programme. Fourteen patients were randomised to training with inspiratory pressure support of 10 cmH2O and 15 patients to training with control (sham) inspiratory pressure support of 5 cmH2O. Outcome measures were the incremental shuttle walking test and a constant-load cycle endurance test at 75% of peak work rate including the measurement of physiological responses, and health status measured using the St. George's Respiratory Questionnaire. Statistically significant between-group differences were found in favour of the inspiratory pressure support of 10 cmH2O group for improvement in shuttle walking distance (16+/-17 versus 3+/-13%), cycle endurance (164+/-124 versus 88+/-128%), and the reduction in minute ventilation during exercise (-11+/-10 versus -2+/-9%). It was concluded that exercise training with inspiratory pressure support of 10 cmH2O resulted in statistically significantly larger improvements in exercise performance than training with inspiratory pressure support of 5 cmH2O in patients with chronic obstructive pulmonary disease suffering from a ventilatory limited exercise capacity. Inspiratory pressure support of 10 cmH2O may be considered as adjunct during high-intensity exercise training.

Aged↗
PubMed2007

Perflubron dosing affects ventilator-induced lung injury in rats with previous lung injury.

OBJECTIVES: Randomized controlled trials of partial liquid ventilation in acute respiratory distress syndrome have been negative. Reasons for this failure may reside in the use of too large doses of perfluorocarbon. The objective was to evaluate whether various doses of perflubron affect ventilation-induced injury in edematous lungs in different ways. DESIGN: Prospective, controlled animal study. SETTING: Research laboratory of a university. SUBJECTS: Male Wistar rats weighing 300+/-20 g. INTERVENTIONS: Separate groups of rats were injected with alpha-naphtylthiourea to produce mild permeability pulmonary edema. They were then given 0, 7 (low), 13 (moderate), or 20 mL/kg (near functional residual capacity) perflubron doses and mechanically ventilated with a large (33 mL/kg) tidal volume for 15 mins. MEASUREMENTS AND MAIN RESULTS: 125I-albumin distribution space was used to assess lung microvascular permeability. Quasi-static respiratory system pressure-volume curves were analyzed. Administration of low and moderate perflubron doses significantly improved respiratory mechanics and reduced the ventilator-induced permeability alterations to the level observed in rats that were not ventilated. By contrast, a perflubron dose that was near functional residual capacity increased end-inspiratory plateau pressure and aggravated the permeability alterations due to high tidal volume ventilation. CONCLUSIONS: Near functional residual capacity but not low perflubron dose worsens ventilation-induced lung injury of preinjured lungs. This may provide some explanation for the negative results of the recent clinical trials, and it stresses the importance of the amount of perflubron used for partial liquid ventilation.

Animals↗
PubMed2005

Long-term reduction of hyperinflation in stable COPD by non-invasive nocturnal home ventilation.

OBJECTIVE: The role of non-invasive positive pressure ventilation (NPPV) in stable COPD with chronic ventilatory failure remains controversial. The impact of long-term home nocturnal NPPV treatment on deflation has not yet been evaluated in detail. METHODS: Retrospective explorative study of 46 patients with stable COPD undergoing NPPV treatment. Effects of NPPV on body plethysmographic parameters, blood gas tensions and inspiratory muscle function after 6.2 (+/-1.7) and 12.7 (+/-2.1) months of treatment. Further, evaluation of 1-year survival, compliance and ventilation parameters. RESULTS: One-year survival was 89.1%. The effectiveness of ventilation was proven by a significant reduction in nocturnal and daytime PaCO2. We observed a decrease in the ratio of residual volume (RV) to total lung capacity (TLC) on the average of 5.2+/-9.8% (or 15.2+/-29.7% pred.; P<0.01) at six and 3.9+/-9.0% (or 12.9+/-18.6% pred.; P<0.001) at 12 months. As a consequence, we found significant improvements in inspiratory capacity (IC), vital capacity (VC) and forced expiratory volume in one second (FEV1). For patients with the most severe hyperinflation (RV/TLC>75%), we found a significant positive correlation between inspiratory positive airway pressure (IPAP) and reductions in PaCO2 (r=0.56; P<0.05) and RV/TLC (r=0.50; P<0.05). CONCLUSIONS: In severe hypercapnic stable COPD long-term nocturnal NPPV can reduce hyperinflation with sustained improved daytime blood gas parameters.

Aged↗
PubMed1994

Indices of upper airway obstruction in patients with simultaneous chronic airflow limitation.

In patients with chronic airflow limitation (CAL), the detection of upper airway obstruction (UAO) by analysis of forced flows can be difficult due to the masking of conventional UAO indices. We analyzed five indices: maximum inspiratory flow at 50% of forced vital capacity (FIF50), the ratio of maximum expiratory to inspiratory flow at 50% of forced vital capacity (FEF50/FIF50), the ratio FEV1/PEFR, the ratio FEV1 to forced expiratory volume in 0.5 s (FEV1/FEV0.5), and the ratio maximum voluntary ventilation (MVV)/FEV1, to determine their usefulness in evaluating patients with simultaneous UAO and CAL. One hundred and thirty-seven patients participated: 54 had UAO alone, 23 presented simultaneous UAO and CAL and 60 suffered from CAL with no evidence of UAO. The patients with UAO and CAL on the average presented fewer abnormal indices and these were less severely altered. Twenty-seven of the 60 with CAL alone presented at least one abnormal index, but in no case were more than two present. FEF50/FIF50 and FEV1/PEFR were significantly less sensitive in patients with both UAO and CAL than in those with UAO alone (35 vs. 85% and 52 vs. 72%, respectively). In all patients the most specific indices (100%) were FEF50/FIF50 and MVV/FEV1. The index MVV/FEV1 was the most accurate in patients with UAO and CAL. We conclude that when patients with CAL present 3 or more abnormal UAO indices, or have FEF50/FIF50 > or = 1 or MVV/FEV1 < or = 25, the possibility of simultaneous UAO must be strongly considered.

Adult↗
PubMed1997

Inspiratory muscle training in chronic airflow limitation: effect on exercise performance.

The effect of inspiratory muscle training (IMT) on exercise capacity in patients with chronic airflow limitation (CAL) has been debated. The present study was planned to further investigate the effects of IMT on exercise performance. Twenty patients (aged 62+/-1 yrs; forced expiratory volume in one second/forced vital capacity (FEV1/FVC) 36+/-2%) were trained 30 min daily for 6 days a week during 10 weeks, with either 30% (Group 1) or 10% (Group 2) of peak maximal inspiratory pressure (PI,max) as a training load. Exercise performance was evaluated by the distance walked in 6 min (6MWD) and by changes in oxygen consumption (V'O2) and minute ventilation (V'E) during a progressive exercise test. Changes in PI,max and dyspnoea were also measured. Results showed a significant increment in peak PI,max in both groups, whereas dyspnoea and 6MWD improved only in Group 1 (p<0.05 and p<0.01, respectively). No increment in maximal workload or in peak V'O2 was observed in either group. Patients in Group 1, however, showed a reduction in V'E and V'O2 for the same exercise. A correlation between changes in V'E and V'O2 during a workload of 75 kpm x min(-1) was observed in Group 1 (r=0.92; p<0.001). We conclude that inspiratory muscle training using a load of 30% peak maximal inspiratory pressure, improves dyspnoea, increases walking capacity and reduces the metabolic cost of exercise.

Breathing Exercises↗
PubMed2004

Use of Sniff nasal-inspiratory force to predict survival in amyotrophic lateral sclerosis.

Respiratory muscle weakness is the usual cause of death in amyotrophic lateral sclerosis. The prognostic value of the forced vital capacity (FVC), mouth-inspiratory force, and sniff nasal-inspiratory force were established in a group of 98 patients with amyotrophic lateral sclerosis who were followed trimonthly for 3 years. Sniff nasal-inspiratory force correlated with the transdiaphragmatic pressure (r = 0.9, p < 0.01). Sniff nasal-inspiratory force was most likely to be recorded at the last visit (96% of cases), compared with either the FVC or mouth-inspiratory force (86% and 81%, respectively, p < 0.01). A sniff nasal-inspiratory force less than 40 cm H(2)O was significantly related with nocturnal hypoxemia. When sniff nasal-inspiratory force was less than 40 cm H(2)O, the hazard ratio for death was 9.1 (p = 0.001), and the median survival was 6 +/- 0.3 months. The sensitivity of FVC < 50% for predicting 6-month mortality was 58% with a specificity of 96%, whereas sniff nasal-inspiratory force less than 40 H(2)O had a sensitivity of 97% and a specificity of 79% for death within 6 months. Thus the sniff nasal-inspiratory force test is a good measure of respiratory muscle strength in amyotrophic lateral sclerosis, it can be performed by patients with advanced disease, and it gives prognostic information.

Adult↗
PubMed1976

Effect of inspired volume on closing volume.

Closing volume (CV) was ?EASURED WITH THE RESIDENT GAS TECHNIQUE IN 12 HEALTHY SEATED SUBJECTS AGE 22-70 YR, AND IN 8 SUBJECTS WITH THE BOLUS TECHNIQUE. Various volumes were inspired (Vi range: 20-100% vital capacity) from residual volume and CV was assessed on the subsequent recording of expired volume versus gas concentration. The results indicate that the resident gas technique may erroneously underestimate CV at reduced Vi in conformity with calculations which predict that during expiration, after a certain reduced VI, the nitrogen concentration is identical in the most basal lung region and at the mouth. CV obtained with the bolus technique decreased linearly with reduced Vi and the effect appeared to be age dependent according to the equation CV50/CV100=0.0078 X age +1.18, where CV50 and CV100 denote the bolus CV corresponding to Vi=50% and 100% of vital capacity. Therefore, in older subjects, during tidal breathing, airways appear to close at substantially lower lung volume than previously considered.

Adult↗
PubMed2003

Respiratory pressures in boys from 11-17 years old: a semilongitudinal study.

We hypothesized that in children, maximal respiratory pressures increase with age and more during the pubertal growth spurt. The aim of this work was to follow maximal respiratory pressures, with a semilongitudinal study, in three groups of prepubertal, peripubertal, and postpubertal children in order to specify pressure changes with age and determine the contributions of growth and puberty. A semilongitudinal study was conducted in 44 boys assigned to three overlapping age groups: from 11-13 (prepubertal stage), from 13-15 (pubertal stage), and from 15-17 years (postpubertal stage). The children underwent annual testing for maximal respiratory pressures and spirometric values. Body mass, height, lean body mass assessed from four skinfold thicknesses, and stage of development were also evaluated. Maximal respiratory pressure increased significantly with growth from 11-17 years for maximal inspiratory pressure, and from 11-15 years for maximal expiratory pressure. We observed an increase in the slope of the regression lines between age and lean body mass during the pubertal growth spurt, without an increase in the slopes of the regression lines between age and respiratory pressures. In conclusion, the relationships between age and respiratory pressures are not modified by the growth spurt, indicating that anthropometric characteristics have little role in determining respiratory pressures.

Adolescent↗
PubMed1992

Effects of posture on flow-volume curves during normocapnia and hypercapnia in patients with obstructive sleep apnoea.

BACKGROUND: A high ratio of forced expiratory to forced inspiratory maximal flow at 50% of vital capacity (FEF50/FIF50) may identify upper airway dysfunction. Since hypercapnia increases the motor activity of airway dilating muscles its effects on the maximum expiratory and inspiratory flow-volume curves (MEIFV) in patients with obstructive sleep apnoea and in normal subjects in different postures was studied. METHODS: The effects of posture on the maximum expiratory and inspiratory flow-volume curves during the breathing of air and 7% carbon dioxide in 11 patients with obstructive sleep apnoea were compared with those in nine normal subjects. Measurements were made in the sitting, supine, and right lateral recumbent positions. Forced expiratory flow at 50% vital capacity (FEF50), forced inspiratory flow at 50% vital capacity (FIF50) and FEF50/FIF50 were determined. RESULTS: In the normal subjects FEF50, FIF50, and FEF50/FIF50 were not affected by change in posture or by breathing carbon dioxide. In the patients there was a fall in FIF50 and an increase in FEF50/FIF50 when breathing air in the supine position compared with values in the seated and lateral position. While they were breathing carbon dioxide there was a slight increase in FEF50 when patients were seated or in the lateral position compared with values during air breathing. Hypercapnia abolished the effects of posture on FEF50/FIF50. Values for FEF50/FIF50 in the supine position while they were breathing air correlated with the apnoeic index but not with other polysomnographic data. CONCLUSION: In patients with obstructive sleep apnoea the upper airway is prone to collapse during inspiration when the patient is supine, even when awake; this tendency can be reversed by breathing carbon dioxide.

Adult↗
PubMed1986

Maximum flow ratios at mid-vital capacity in young healthy adults.

Upper airway obstruction is usually diagnosed by visual examination of maximum expiratory and inspiratory flow-volume curves and by calculating a ratio of expiratory to inspiratory flow at 50 percent of vital capacity (mid-vital capacity flow ratio); however, reference values of this ratio have not been well established, and considerable variability exists. The purpose of this study was to examine the range of mid-vital capacity flow ratios in a group of healthy subjects and to determine if some of the variability is accounted for by different maximum inspiratory pressures. We measured maximum expiratory and inspiratory flows at 50 percent of vital capacity from the flow-volume curves, and maximum inspiratory pressures in a group of 60 healthy nonsmokers (30 men and 30 women) whose ages ranged from 21 to 40 years. We found that mid-vital capacity flow ratio (mean +/- SD) was 0.72 +/- 0.19 in men and 0.77 +/- 0.18 in women. The coefficient of variation of the mid-vital capacity flow ratio was 28 percent for men and 23 percent for women. The 95 percent confidence limits for the mid-vital capacity flow ratio were 0.65 to 0.79 for men and 0.70 to 0.84 for women. Maximum inspiratory pressures (mean +/- SD) were 129 +/- 30 cm H2O in men and 91 +/- 16 cm H2O in women, not significantly different from previous studies. Normalizing maximum inspiratory flow for maximum inspiratory pressure did not reduce the coefficient of variation, which became 29 percent in men and 30 percent in women. We conclude that the range of mid-vital capacity flow ratios is wide, and it cannot be reduced by standardizing it for maximum inspiratory pressures.

Adult↗
PubMed2001

[Relation between neck accessory inspiratory muscle electromyographic activity and lung volume].

Years ago it was reported that, as lung volume increased, there was a corresponding increase in scalene EMG activity (Raper et al. J Appl Physiol 21: 497-502, 1966). Otherwise, the relationship between changing lung volume and the EMG of the respiratory muscles has not been defined. We therefore inserted fine wire electrodes into the scalene (SCLN), sternocleidomastoid (STERNO), and trapezius (TRAPEZ) muscles in 6 healthy subjects under direct vision using high-resolution ultrasound. Maximum EMG activity (EMGmax) was obtained for each muscle by a variety of respiratory and postural maneuvers. Then, in the standing posture, air flow, raw and moving average EMG signals were sampled and input to a computer during quasi-static inspiration from functional residual capacity (FRC) to total lung capacity (TLC). We found that the relationship between EMG and lung volume for SCLN, but not for STERNO or TRAPEZ, was expressed by exponential curves. The onset of SCLN, STERNO and TRAPEZ EMG occurred at 13.3 +/- 7.4 (mean +/- SE), 67.8 +/- 14.6, and 89.2 +/- 3.9% of inspiratory capacity. The EMG of SCLN, STERNO, TRAPEZ, reached 85.7 +/- 2.6, 60.7 +/- 8.6, and 11.8 +/- 5.2% of EMGmax, respectively, at TLC. We conclude that: 1) SCLN is the most, and TRAPEZ the least, active neck accessory inspiratory muscle, while STERNO is intermediate, and 2) there is a lung volume dependency of the neck accessory muscle EMG activity.

Adult↗
PubMed2004

Maintenance of inspiratory muscle training in COPD patients: one year follow-up.

In most chronic obstructive pulmonary disease (COPD) patients, dyspnoea and functional exercise capacity may improve as a result of inspiratory muscle training (IMT). However, the long-term benefits of IMT have been investigated to a much lesser extent. The present study investigated the short-term and long-term benefits of IMT on inspiratory muscle performance (strength and endurance), exercise capacity and the perception of dyspnoea. Thirty-eight patients with significant COPD had 3 months of basic IMT and were then randomised into a group that received maintenance IMT for the next year, and a group that got training with very low load. Following the basic training there was a statistically significant increase in inspiratory muscle performance, 6-min walk test (6MWT), and a decrease in the dyspnoea. During the second stage of the study, the training group continued to maintain the improvement in all parameters, while there was already deterioration in the inspiratory muscle performance, exercise capacity and dyspnoea in the low intensity group during the 6-12 month period. The present study concludes that, in patients with significant chronic obstructive pulmonary disease, inspiratory muscle training results in improvement in performance, exercise capacity and in the sensation of dyspnoea. The benefits of 12-weeks of inspiratory muscle training decline gradually over 1 yr of follow-up if maintenance training is not performed.

Aged↗
PubMed1996

Microcirculatory vasoconstrictor response: relationship with vital capacity and smoking.

Vasoconstrictor response (VR) induced by inspiratory gasp exhibited a strong positive correlation with vital capacity (VC) which reflects the magnitude of the input stimulus for VR (Lau et al., Clin. Sci. 89:233-237, 1995). Whether a stoichiometric relationship existed between VC and VR is not known. We examined this question in two studies by determining VC and microcirculatory blood flow with laser Doppler flowmetry in healthy subjects. We first studied 40 non-smokers of different gender and age and found that the variation in VR cannot be eliminated by normalization with VC. In the second study we examined 10 young male smokers as well as matched non-smokers of identical VC, we found that smokers had reduced VR. Taking together, the present studies demonstrated that vasoconstrictor response (VR) was not determined by vital capacity alone and that smoking adversely affected VR in the absence of altered VC.

Adult↗
PubMed2001

Inspiratory flow reserve in boys with Duchenne muscular dystrophy.

Patients with advanced muscular dystrophy frequently develop ventilatory failure. Currently respiratory impairment usually is assessed by measuring vital capacity and the mouth pressure generated during a maximal inspiratory maneuver (PI,max), neither of which directly measures ventilatory capacity. We assessed inspiratory flow reserve in 26 boys [mean (SD) age 12.8 (3.8) years] with Duchenne muscular dystrophy (DMD) without ventilatory failure and in 28 normal boys [mean (SD) age 12.6 (1.9) years] by analyzing the ratio between the largest inspiratory flow during tidal breathing (V'I,max(t)) and during a forced vital capacity maneuver (V'I,max(FVC), (V'I,max(t)/V'I,maxFVC). We have compared this ratio with the forced vital capacity FVC and PI,max measured at functional residual capacity. Mean PI,max was -90(30)cmH2O, average 112% (range 57-179%) of predicted values in control boys and -31(11)cmH2O, average 40% predicted values in DMD boys (control vs DMD, P < 0.001). FVC was reduced in DMD boys [59(20)% predicted values vs 86(10)% predicted values in controls, P < 0.01]. Absolute V'I,max(FVC) was strongly related to FVC in both control and DMD boys; V'I,max(FVC) (expressed as FVC. s(-1)) was not related to PI,max in either group. The mean V'I,max(t)/V'I,max(FVC); ratio was higher in DMD 0.22 (0.08) than in controls 0.12 (0.03) (P < 0.001) indicating a reduction in inspiratory flow reserve in DMD. Inspiratory flow reserve was within the normal range in 8 of 19 DMD patients with PI,max less than 50% of predicted values. We conclude that measurement of inspiratory flow reserve (V'I,max(t)/V'I,maxFVC ratio) provides a simple and direct assessment of dynamic inspiratory muscle function which is not replicated by static measurement of PI,max or vital capacity and might be useful in assessment of respiratory impairment in boys with Duchenne muscular dystrophy. Follow-up studies are required to establish whether measures of inspiratory flow reserve are of clinical value in predicting subsequent ventilatory failure.

Adolescent↗
PubMed2005

Inspiratory muscle training and the perception of dyspnea in Parkinson's disease.

BACKGROUND: Pulmonary and respiratory muscle function impairment are common in patients with Parkinson's disease (PD). Inspiratory muscle training may improve strength, dyspnea and functional capacity in healthy subjects and in those with chronic obstructive pulmonary disease. This study investigated the effect of specific inspiratory muscle training (SIMT) on pulmonary functions, inspiratory muscle performance, dyspnea and quality of life, in patients with PD. PATIENTS AND METHODS: Twenty patients with PD (stage II and III Hoehn and Yahr scale) were recruited for the study and were divided into two groups: (a) ten patients who received SIMT and (b) ten patients who received sham training, for three months. Pulmonary functions, the respiratory muscle strength and endurance, the perception of dyspnea (POD) and the quality of life were studied before and within one week after the training period. All subjects trained daily, six times a week, each session consisting of 1/2 hour, for 12 weeks. RESULTS: Following the training period, there was a significant improvement, in the training group but not in the control group, in the following parameters: inspiratory muscle strength, (PImax, increased from 62.0 +/- 8.2 to 78.0 +/- 7.5 cm of H2O (p < 0.05), inspiratory muscle endurance (increased from 20.0 +/- 2.8 to 29.0 +/- 3.0 cm of H2O (p < 0.05), and the POD (decreased from 17.9 +/- 3.2 to 14.0 +/- 2.4 units (p < 0.05). There was a close correlation between the increase in the inspiratory muscle performance and the decrease in the POD. CONCLUSIONS: The inspiratory muscle performance may be improved by SIMT in patients with PD. This improvement is associated with a significant decrease in their POD.

Aged↗
PubMed1989

Determinants of maximum exercise capacity in patients with chronic airflow obstruction.

Patients with chronic airflow obstruction (CAO) often develop impairment of respiratory muscle function. We hypothesized that inspiratory muscle strength, as assessed by resting, peak inspiratory pressure (PIP) may be an important determinant of maximum exercise capacity in patients with CAO. Twenty ambulatory male patients (mean age, 56 +/- 3 years [+/- SE]) with CAO (FEV1, 1.72 +/- 0.21 L) comprised the studied population. Oxygen consumption at incremental cycle ergometry to tolerance (VO2max, 1.80 +/- 0.20 L/min) served as the dependent variable for regression vs measures of resting pulmonary function. Significant correlations with VO2max included power output in watts (r = 0.951), VEmax (r = 0.858), Dsb (r = 0.841), PIP (r = 0.816), age (r = -0.809), FEV1 (r = 0.763), and FVC (r = 0.663). The FEV1, Dsb, and PIP each entered into a multiple linear regression relationship describing VO2max. Also, when paired with VEmax as independent variables in multiple regression, PIP and Dsb each improved description of VO2max over VEmax alone (p less than 0.05), whereas FEV1 and FVC did not (p greater than 0.05). We conclude that factors other than ventilatory capacity also have a quantitative effect on VO2max and that PIP constitutes a determinant of maximum exercise capacity in patients with CAO.

Exercise Test↗
PubMed1989

Effect of airway closure on ventilation distribution.

We examined the effect of airway closure on ventilation distribution during tidal breathing in six normal subjects. Each subject performed multiple-breath N2 washouts (MBNW) at tidal volumes of 1 liter over a range of preinspiratory lung volumes (PILV) from functional residual capacity (FRC) to just above residual volume. All subjects performed washouts at PILV below their measured closing capacity. In addition five of the subjects performed MBNW at PILV below closing capacity with end-inspiratory breath holds of 2 or 5 s. We measured the following two independent indexes of ventilation maldistribution: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency of those breaths of the washout where 80-90% of the initial N2 had been cleared. Between a mean PILV of 0.28 liter above closing capacity and that 0.31 liter below closing capacity, mean Snf increased by 132% (P less than 0.005). Over the same volume range, mean alveolar mixing efficiency decreased by 3.3% (P less than 0.05). Breath holding at PILV below closing capacity resulted in marked and consistent decreases in Snf and increases in alveolar mixing efficiency. Whereas inhomogeneity of ventilation decreases with lung volume when all airways are patent (J. Appl. Physiol. 66: 2502-2510, 1989), airway closure increases ventilation inequality, and this is substantially reduced by short end-inspiratory breath holds. These findings suggest that the predominant determinant of ventilation distribution below closing capacity is the inhomogeneous closure of airways subtending regions in the lung periphery that are close together.

Adult↗