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 883 records · Page 49Linked to original sources
PubMed2001

Significance of the changes in the respiratory system pressure-volume curve during acute lung injury in rats.

UNLABELLED: The hypothesis that the changes in the respiratory system pressure- volume (PV) curve during pulmonary edema mainly reflect distal airway obstruction was investigated in rats. Normal rats had a well-defined upper inflection point (UIP) at low airway pressure. Airway occlusion by liquid instillation decreased compliance (Crs) and the volume (Vuip) of the UIP, and increased end-inspiratory pressure. The same changes were observed during the progression of edema produced by high volume ventilation (HV). Changes in Vuip and in Crs produced by HV were correlated with edema severity in normal rats or rats with lungs preinjured with alpha-naphthylthiourea. Vuip and Crs changes were proportional, reflecting compression of the PV curve on the volume axis and suggesting reduction of the amount of ventilatable lung at low airway pressure. In keeping with this explanation, the lower Vuip and Crs were before HV, the more severe HV-induced edema was in alpha-naphthylthiourea-injected rats. When edema was profuse, PV curves displayed a marked lower inflection point (LIP), the UIP at low pressure disappeared but another was seen at high volume above the LIP, and the correlation between Vuip changes and edema severity was lost. These observations may have clinical relevance in the context of the "open lung" strategy. KEYWORDS: ventilator-induced lung injury; respiratory mechanics; acute respiratory distress syndrome

Airway Resistance↗
PubMed2001

Helium-oxygen in the postextubation period decreases inspiratory effort.

After tracheal extubation, upper and total airway resistances may frequently be increased resulting in an increase in inspiratory effort to breathe. We tested whether breathing a helium-oxygen mixture (HeO(2)) would reduce inspiratory effort in the period after extubation. Eighteen consecutive patients with no chronic obstructive pulmonary disease who had received mechanical ventilation (> 48 h) were successively studied immediately after extubation (N(2)O(2)), 15 min after breathing HeO(2), and after return to N(2)O(2). Effort to breathe, assessed by the transdiaphragmatic pressure swings (DeltaPdi) and the pressure-time index of the diaphragm (PTI), comfort, and gas exchange, were the main end points. The mean reduction of the transdiaphragmatic pressure under HeO(2) was 19 +/- 5%. All but three patients presented a decrease in transdiaphragmatic pressure under HeO(2), ranging from - 4 to - 55%, and a significant reduction in DeltaPdi was observed between HeO(2) and N(2)O(2) (10.2 +/- 0.7 versus 8.6 +/- 1.1 versus 10.0 +/- 0.8 cm H(2)O for the three consecutive periods; p < 0.05). PTI also differed significantly between HeO(2) and N(2)O(2) (197 +/- 19 versus 166 +/- 22 versus 201 +/- 23 cm H(2)O/s/min for the three periods; p < 0.05). Breathing HeO(2) significantly improved comfort, whereas gas exchange was not modified. We conclude that the use of HeO(2) in the immediate postextubation period decreases inspiratory effort and improves comfort.

Administration, Inhalation↗
PubMed1987

The relationship of nonspecific bronchial responsiveness to respiratory symptoms in a random population sample.

The relationship of airway responsiveness to respiratory symptom prevalence has been studied in a cross-sectional analysis of a random subpopulation from a large-scale population study on chronic obstructive pulmonary disease (COPD) being conducted in the Netherlands. In 1,905 subjects with complete data on age, sex, area of residence, smoking habits, and respiratory symptom prevalence, airway responsiveness was assessed by a histamine challenge test. Subjects with a decrease in FEV1 of greater than or equal to 10% at a histamine concentration of less than or equal to 16 mg/ml were considered to be responders. Bronchial hyperresponsiveness appeared to be age dependent, with the proportion of responders increasing from 13% in those 14 to 24 yr of age to 40% in those 55 to 64 yr of age (p less than 0.001). Respiratory symptom outcomes included chronic cough, chronic phlegm, dyspnea, bronchitic episodes, persistent wheeze, and asthmatic attacks. Respiratory symptom prevalence rates were significantly higher in responders (p less than 0.001 for all symptoms). Cigarette smoking is known to be related to respiratory symptom prevalence and possibly to bronchial responsiveness. Because of these associations, we examined the relationship of bronchial responsiveness to respiratory symptoms within cigarette smoking categories. For all respiratory symptoms, it was found that, regardless of smoking category, responders were more likely to be symptomatic than were nonresponders. Odds ratios ranged from 1.7 for chronic cough to 4.4 for asthmatic attacks.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Inspiratory muscle training with a pressure threshold breathing device in patients with chronic obstructive pulmonary disease.

The inspiratory pressure load is an important variable in inspiratory muscle training (IMT), but previous studies with chronic obstructive pulmonary disease (COPD) patients have not controlled for this variable. We compared the effects of two months of IMT with a pressure threshold breathing device at inspiratory pressure loads equal to either 15 or 30% of each patient's maximal inspiratory pressure (Plmax). This study was double blind and patients were randomly assigned to the treatment groups, 12 in the 15% group and ten in the 30% group. Dependent variables were measured at baseline, and after one and two months of IMT. Patients who exercised with the 30% load improved the following: Plmax by a mean of -12 +/- 9 cm H2O (p less than 0.01), endurance time while breathing against an inspiratory pressure load equal to 66% of Plmax by 5 +/- 9 min (p less than 0.01), and 12-min distance walk (12MD) by 199 +/- 90 feet (p less than 0.01). Patients who exercised with the 15% load demonstrated no improvements in Plmax, endurance time, and 12MD. There were no changes in patients' report of functional impairment (Sickness Impact Profile), mood (Profile of Mood States), health status (Health Perceptions Questionnaire), and pulmonary symptoms (respiratory symptom log). We conclude that the 30% load was more effective than the 15% load in this sample.

Affect↗
PubMed1988

Improvement in exercise endurance in patients with chronic airflow limitation using continuous positive airway pressure.

To cope with the increased ventilatory demands of exercise, patients with severe expiratory flow limitation adopt strategies that ultimately place greater demands on their inspiratory muscles. Increased inspiratory muscle work may contribute to dyspnea causation and exercise limitation in such patients even before their ventilatory ceiling is attained. In this setting, continuous positive airway pressure (CPAP) should, by favorably affecting inspiratory muscle function and respiratory sensation, improve exercise performance. Six patients with chronic airflow limitation (CAL) (FEV1 +/- SD = 35 +/- 12% predicted) undertook constant-load, submaximal, cycle exercise at 50% of their predetermined maximal oxygen consumption: CPAP of 4 to 5 cm H2O was delivered during one exercise session and bracketed by one or two unassisted control sessions. In four patients, CPAP-assisted (4 to 5 cm H2O) exercise was bracketed by two unassisted control exercise sessions; two remaining patients undertook CPAP-assisted exercise and one unassisted control session. CPAP resulted in a significant increase in exercise endurance time (TLIM) (by 48%: CPAP TLIM (mean +/- SE) = 8.82 +/- 1.90 min; averaged control TLIM = 5.98 +/- 1.23 min (p less than 0.01). CPAP effectively ameliorated exertional dyspnea in the majority of patients; selected dyspnea ratings (Borg scale) during control (final minute) and CPAP at isotime, at comparable levels of ventilation, were (mean +/- SD) 7.83 +/- 2.25 and 5.5 +/- 2.2, respectively (p less than 0.025). Breathing frequency fell significantly during CPAP application (at isotime) by 17% (p less than 0.02); other steady-state ventilatory variables and end-expiratory lung volumes were not significantly different during CPAP and control.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Intraindividual variability in serial measurements of DLCO and alveolar volume over one year in eight healthy subjects using three independent measuring systems.

To evaluate intraindividual and between-machine variability in DLCO, one technician performed triplicate measurement of DLCO in eight healthy subjects on three consecutive days using three different systems (Collins [C], Gould [G], SRL [S]) on five separate occasions over the course of 1 yr. For each subject and machine, we calculated the coefficient of variation (CV) of the DLCO and its associated alveolar volume (VA) and inspiratory vital capacity (IVC) over the five different measurement periods using the mean value for each period. CV (in %) for DLCO in each of the eight subjects for each machine varied from 2.4 to 7.1% for machine C, 4.1 to 10.5% for machine G, and 2.5 to 8.7% for machine S. Two-way ANOVA showed significant differences in CV for DLCO and IVC but not for VA across subjects (p less than 0.01) and for DLCO, VA, and IVC across machines (p less than 0.03): CV for DLCO was higher for G than for C or S; CV for VA and IVC was lower for C than for G or S. Multiple regression did not show a significant relationship between within-individual CV for DLCO and that for VA or IVC. We conclude that variability in DLCO measurements is affected by both subject and machine, but, at least in healthy cooperative subjects, it does not appear to be affected by variability in VA or IVC. For the average subject and the two less variable machines we tested, DLCO measurements could vary within the same subject as much as +/- 9.6% (two-tailed 95% confidence interval) with repeated measurements over 1 yr.

Adult↗
PubMed1990

The mechanism of respiratory arrest in inspiratory loading and hypoxemia.

Respiratory arrests occur in the clinical setting of respiratory failure, but the mechanism is unclear. We used a dog model with increased inspiratory resistance and hypoxemia to explore the cause. We hypothesized that respiratory muscle fatigue (RMF) played a role in these respiratory arrests, and that the combination of hypoxia and resistive loading would produce respiratory arrest by the mechanism of RMF. Our preparation had transdiaphragmatic pressures that were 40% of maximum (Pdimax = 46.3 +/- 10.0 cm H2O) and progressive hypoxia resulting in a final arterial PO2 of 38 +/- 9 mm Hg and a phrenic vein O2 content of 1.8 +/- 1.1 mg/dl. Instead of failure associated with carbon dioxide retention and RMF, we saw a rapid decrease in tidal volume and respiratory rate, leading to apnea over 30 to 60 s while the diaphragm still responded with significant pressure generation when externally stimulated. These results suggest that respiratory muscle fatigue may not be a major factor in respiratory arrests associated with inspiratory loading and hypoxia, but that suppression of central drive, induced by the combination of inspiratory loading and hypoxemia, may be important.

Acid-Base Equilibrium↗
PubMed1992

Effect of inspiratory flow rate on respiratory output in normal subjects.

We wished to determine the independent effect of inspiratory flow rate (VI) on respiratory output in the awake state. Seven normal subjects were connected to a volume-cycled ventilator in the assist/control mode. While the tidal volume setting remained constant, inspiratory flow rate was increased in steps (3 to 4 min each) from 30 to 90 L/min and then back to 30 L/min. Flow pattern was square, and all breaths were subject-triggered. Spontaneous respiratory rate (f) increased in all subjects as VI increased. Mean (+/- SD) f at 30 and 90 L/min were 8.8 (+/- 1.7) and 14.1 (+/- 4.4) min-1, respectively (p less than 0.01). VE increased (10.1 +/- 1.9 at 30 L/min to 16.3 +/- 5.6 at 90 L/min p less than 0.01) and the percentage of end-tidal CO2 decreased (4.7 (+/- 0.5) at 30 L/min to 3.3 (+/- 0.7) at 90 L/min (p less than 0.01)). The response was graded and reversible. The change in f was nearly complete within the first two breaths after transition, and there was no systematic tendency for f to change beyond this early response. The rate of change in airway pressure prior to triggering (dp/dt) increased as VI increased (5.3 +/- 2.0 cm H2O/s at 30 L/min to 10.8 +/- 2.6 cm H2O/s at 90 L/min; p less than 0.01). We conclude that inspiratory flow rate exerts an excitatory effect on respiratory frequency and on the rate of rise of inspiratory activity in conscious humans. This may be relevant to the mechanism of ventilatory response to various respiratory stimuli and to the management of patients receiving mechanical ventilation.

Adult↗
PubMed1992

Evidence of acute diaphragmatic fatigue in a "natural" condition. The diaphragm during labor.

Acute diaphragmatic fatigue has been experimentally shown to occur in normal healthy subjects and in patients with chronic obstructive pulmonary disease by asking them to modify their pattern of breathing or to breathe against high inspiratory resistances. During the expulsive period of labor women are asked periodically to make strong expulsive efforts and to sustain them isometrically for many seconds; this is likely to produce "natural" diaphragmatic fatigue. To investigate whether this was the case, six women were studied in the delivery room from the moment of the rupture of the amnion until delivery of the infant occurred. The development of diaphragmatic fatigue was assessed both by measuring the static maximal inspiratory pressure (MIP) and by analyzing the electromyographic power spectrum of the diaphragm (H/L ratio). The majority of contractions were concentrated in the expulsive period of labor. MIP, recorded in the supine position, significantly decreased from 103.2 +/- 17.2 cm H2O (at the beginning of the expulsive period) to 73.8 +/- 10.1 cm H2O (after the delivery). The H/L ratio fell progressively during the expulsive period; after the delivery, it was 59.2 +/- 15.7% of the value recorded at the beginning of the expulsive period. This study demonstrates that (1) the diaphragm is active in the expulsive efforts during labor and (2) the tension developed and the time each contraction is maintained may lead to the development of diaphragmatic fatigue. Therefore, we provide evidence of acute diaphragmatic fatigue in a natural condition.

Acute Disease↗
PubMed1993

Long-term variability of bronchial responsiveness to histamine in a random population sample of adults.

Long-term variability of bronchial responsiveness has been studied in a random population sample of adults. During a follow-up period of 18 yr, 2,216 subjects contributed 5,012 observations to the analyses. Each subject could have as many as seven observations. Bronchial responsiveness was assessed with a histamine challenge test. The threshold value was defined as the concentration of histamine that caused a decrease in FEV1 of 10% of more (PC10). After a 3-yr interval, a change of the threshold value with two or more doubling concentrations occurred in 21% of the subjects. This proportion increased to 43% if the time between two measurements increased to 18 yr. Of all subjects with multiple observations, 41% were always nonresponders (PC10 > or = 32 mg/ml), 11% were always responders (PC10 < or = 16 mg/ml), and 48% changed responder status. Of the subjects with greater than three observations, 65% changed responder status. Regression analyses, stratified by symptom status, sex, and smoking habit, were used to estimate intraclass correlation coefficients (ICC) as a measure of variability of responsiveness. On average, ICC values were low (0.40), also indicating considerable variability. With adjustment for FEV1, age, area of residence, and eosinophil count, the ICC values decreased slightly. This indicated that with adjustment, the total variability decreased more than the within-subject variability. ICC values did not differ significantly between asymptomatic and symptomatic subjects. Analyses of responsiveness as a binary variable revealed similar results.

Adolescent↗
PubMed1976

Effects of shape changes of the chest wall on distribution of inspired gas.

The configuration of the chest wall was measured with magnetometers applied at various levels of the rib cage and abdomen. Distribution of ventilation was measured in the supine position using a bolus of xenon-133 inspired at a flow rate of 0.1 liter per sec. Measurements were made during spontaneous breathing, during augmented abdominal breathing, after manual lateral compression of the lower part of the rib cage followed by a predominantly abdominal motion, and after similar compression followed only by increase of the lateral basal rib cage diameter. Basal compression gave a decrease in lateral diameter of 5 to 7 per cent. During spontaneous breathing, apical ventilation exceeded basal ventilation. During an inspiration with an increase of the lateral basal rib cage diameter after compression, the ventilation of basal peripheral regions increased somewhat. No other systematic effects of the changes in either chest wall diameter at the start of inspiration or the type of inspiration were found on distribution of inspired boli.

Humans↗