Maximum Inspiratory Flow Rate Research Articles

Effects of Inspiratory Muscle Training on Respiration and Balance in Patients with Stroke: A Pilot Randomized Controlled Trial

PURPOSE: Respiratory function can be adversely affected after a cerebrovascular accident. This study aimed to determine whether inspiratory muscle training (IMT) changes the respiration and balance abilities of patients with stroke.METHODS: Twelve patients with stroke were randomly assigned to the study (n=6) and control (n=6) groups. The study and control groups received IMT and general physical therapy, respectively for 6 weeks, five times a week for 30 min/day. Inspiratory and expiratory functions and balance were measured pre- and post-evaluation.RESULTS: After IMT intervention, the weight distribution ratio (WDR) for balance ability measurement was significantly decreased (p<.05), and the maximum inspiratory pressure (MIP), maximum inspiratory flow rate (MIFR), maximum inspiratory capacity (MIC), peak expiratory flow (PEF), forced expiratory volume in 1 second (FEV1), and limits of stability (LOS) were significantly increased in the study group (p<.05). A comparison of the study and control groups revealed statistically significant differences in MIP (p<0.01), MIFR (p<.01), MIC (p<.05), PEF (p<.05), FEV1 (p<.05), WDR (p<.01), and LOS (p<.05).CONCLUSIONS: This study suggests that IMT is a useful and effective exercise intervention for patients with stroke.

Changes and significance of autophagy in rat lung injury induced by gas explosion

Objective: To explore the changes and significance of autophagy in acute lung injury (ALI) induced by gas explosion in rats. Methods: In February 2018, the gas explosion in underground coal mine was simulated by large tunnel explosion experiment system, SD rats were randomly divided into control group and 6 distance groups (40 m, 80 m, 120 m, 160 m, 200 m, 240 m) with 18 rats in each group. The respiratory function of rats 24 h before and after explosion was detected. Post-explosion rats were anesthetized and sacrificed, histopathological changes of lung were observed by HE staining. Immunohistochemistry was performed to detect the in situ expression of autophagy marker protein microtubule-associated protein 1 light chain 3 (LC3B) . The expression levels of autophagy related gene 12 (Atg12) , LC3B, P62, lysosomal associated membrane protein 2 (Lamp2) , B-cell lymphoma/leukemia-2 (Bcl-2) and Bcl2 interaction protein (Beclin-1) were detected by Western blot. Results: After gas explosion, the rats in 80 m distance point group had the hightest mortality (n=13, 72.22%) and the most severe lung injury degree, and the histopathological scores was (4.00±0.00) point. After gas explosion, the minute ventilation volume (MVb) , maximum inspiratory flow rate (PIFb) and maximum expiratory flow rate (PEFb) of rats were lower than before the gas explosion (P<0.05) . The respiratory frequency of rats in 80 m, 200 m, and 240 m distance point groups were significantly higher than that in the control group (P<0.05) . The expression levels of LC3B in 40 m, 80 m, 120 m, 160 m, and 200 m distance point groups were higher than that in the control group (P<0.05) . The relative expression levels of Atg12 and LC3BⅡ/Ⅰ in lung tissues of rats in different distance point groups were higher than those in the control group (P<0.05) . The relative expression levels of Beclin1 in 40 m, 80 m, 120 m, and 160 m distance point groups were significantly higher than that in the control group (P<0.05) . The relative expression levels of P62 in 80 m, 160 m and 200 m distance point groups were lower than that in the control group (P<0.05) . The relative expression levels of Lamp2 and Bcl-2 in lung tissues of rats in all distance groups except 240 m distance group were lower than those in the control group (P<0.05) . Conclusion: Gas explosion could induce increased autophagy in lung tissues of ALI rats. Autophagy-related signaling pathway could be involved in the pathophysiological process of ALI in rats caused by gas explosion, then the autophagy and the severity of the lesion showed a significant positive correlation.

Peak In- and Expiratory Flow Revisited: Reliability and Reference Values in Adults

Background: While peak in- and expiratory flow rates offer valuable information for diagnosis and monitoring in respiratory disease, these indices are usually considered too variable to be routinely used for quantification in clinical practice. Objectives: The aim of the study was to obtain reproducible measurements of maximal inspiratory flow rates and to construct reference equations for peak in- and expiratory flows (PIF and PEF). Method: With coaching for maximal effort, 187 healthy Caucasian subjects (20–80 years) performed at least 3 combined forced inspiratory and expiratory manoeuvres, until at least 2 peak inspiratory flow measurements were within 10% of each other. The effect on PIF preceded by a slow expiration instead of a forced expiration and PIF repeatability over 3 different days was also investigated in subgroups. Reference values and limits of normal for PIF, mid-inspiratory flow, and PEF were obtained according to the Lambda-Mu-Sigma statistical method. Results: A valid PIF could be obtained within 3.3 ± 0.6(SD) attempts, resulting in an overall within-test PIF variability of 4.6 ± 3.2(SD)%. A slow instead of a forced expiration prior to forced inspiration resulted in a significant (p < 0.001) but small PIF increase (2.5% on average). Intraclass correlation coefficient for between-day PIF was 0.981 (95% CI: 0.960–0.992). Over the entire age range, inter-subject PIF variability was smaller than in previous reports, and PIF could be predicted based on its determinants gender, age, and height (r² = 0.53). Conclusions: When adhering to similar criteria for the measurement of effort-dependent portions of inspiratory and expiratory flow-volume curves, performed according to current ATS/ERS standards, it is possible to obtain reproducible PIF and PEF values for use in routine clinical practice.

Nasal Peak Inspiratory Flow in Healthy and Obstructed Patients: Systematic Review and Meta-Analysis.

Nasal peak inspiratory flow (NPIF) is a practical and affordable tool that measures maximum inspiratory flow rate through both nostrils. Although NPIF values for healthy controls and patients appear to differ considerably, a generally expected value for populations with and without nasal obstruction has yet to be established. The aim of this systematic review and meta-analysis was to determine the mean NPIF value in populations with and without nasal obstruction. Medline (1946-) and Embase (1947-) were searched until July 1, 2017. A search strategy was used to identify studies that reported NPIF values for defined healthy or disease states. All studies providing original data were included. The study population was defined as having either normal nasal breathing or nasal obstruction. A meta-analysis of the mean data was presented in forest plots, and data were presented as mean (95% confidence interval [CI]). The search yielded 1,526 studies, of which 29 were included. The included studies involved 1,634 subjects with normal nasal breathing and 817 subjects with nasal obstruction. The mean NPIF value for populations with normal nasal breathing was 138.4 (95% CI: 127.9-148.8) L/min. The mean value for populations with nasal obstruction was 97.5 (95% CI: 86.1-108.8) L/min. Current evidence confirms a difference between mean NPIF values of populations with and without nasal obstruction. The mean value of subjects with no nasal obstruction is 138.4 L/min, and the mean value of nasally obstructed populations is 97.5 L/min. Prospective studies adopting a standardized procedure are required to further assess normative NPIF values. Laryngoscope, 131:260-267, 2021.

Flow-Volume Curve Analysis for Predicting Recurrence After Endoscopic Dilation of Airway Stenosis

The flow-volume curve is a simple test for diagnosing upper airway obstruction. We evaluated its use to predict recurrence in patients undergoing endoscopic dilation for treatment of benign upper airway stenosis. The data of 89 consecutive patients undergoing endoscopic dilation of simple upper airway stenosis were retrospectively reviewed. Morphologic distortion of flow-volume loop (visual analysis) and quantitative criteria, including maximal expiratory flow rate at 50% of the vital capacity (MEF50%)/maximal inspiratory flow rate at 50% of the vital capacity (MIF50%) of less than 0.3 or more than 1.0, forced expiratory volume in 1 second/MEF exceeding 10, and forced expiratory volume in 1 second/forced expiratory volume in .05 second exceeding 1.5, were considered predictive of recurrence. In all cases, the recurrence was confirmed by radiologic or bronchoscopic findings, or both. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of visual, quantitative, and aggregate criteria for detecting recurrence were computed and compared. Of 89 patients treated, 27 (30%) had a recurrence. Visual analysis presented a sensitivity, specificity, PPV, NPV, and accuracy of 63%, 83.9%, 63%, 83.9%, and 77.5%, respectively. Among the quantitative criterion, the MEF50%/MIF50% was the most accurate, having a sensitivity, specificity, PPV, NPV, and accuracy of 77.8%, 79%, 61.8%, and 89.1%, and 78.7%, respectively. Aggregate criterion presented the best yield compared with other criteria in sensitivity (81.5%), specificity (91.9%), PPV (81.5%), NPV (91.9%), and accuracy (88.8%). The flow-volume curve is a simple and noninvasive method to monitor patients undergoing endoscopic dilation of upper airway stenosis. Morphologic changes in the flow-volume loop and in the MEF50%/MIF50% ratio are suggestive of recurrence and guide the physician to implement the follow-up with further diagnostic (non)invasive examinations.

Dry powder inhalers and the right things to remember: a concept review

Dry powder inhalers (DPIs) are widely and increasingly used in clinical practice because they represent a substantial advancement in inhalation technology. The effectiveness of a powdered drug to inhale depends on the inspiratory flow rate generated by the patient and on the turbulence produced by the intrinsic resistance of the DPI. While the inspiratory flow is variable with the patient’s ability and conditions, the turbulence is differently sized within each device because depending of its technical design. There are higher - medium-, and low-resistance devices. With low-resistance DPIs, the disaggregation and the microdispersion of the drug highly depend on the patient’s inhalation airflow rate, because the role of the resistance-induced turbulence is obviously negligible in these cases. This flow-rate dependency is minimized in the presence of a sufficient regimen of turbulence as in the case of medium-resistance DPIs. Both the disaggregation and the micro-dispersion of the powdered drug are optimized in these circumstances even in the absence of a maximal inspiratory flow rate. The low resistance DPIs should not be regarded as the best performer DPIs because their intrinsic low-resistance regimen requires a higher inspiratory airflow rate and effort, which frequently cannot be achieved by subjects suffering from a disease-induced airflow limitation. Only when the ratio between the inhalation flow rate and the DPI intrinsic resistance is balanced, the speed of the particulate, the distribution of the drug within the lung, and the variability of the effective inhaled dose are optimized.

Maximal Inspiratory Flow Rates in Patients with COPD.

Maximal Inspiratory Flow Rates in Patients with COPD.

Maximal Inspiratory Flow Rates in Patients With COPD

To assess the relevance of maximal inspiratory flow rates (MIFR) in the assessment of airway obstruction in COPD. University teaching hospital. Ten consecutive COPD patients (O group; mean [+/- SD] age, 58.5+/-8.3 years) and 10 matched healthy subjects (H group; mean age, 58.7+/-7.4 years). Lung volumes, FEV(1), specific airway conductance, single-breath lung diffusing capacity, MIFR, and maximal expiratory flow rates (MEFR). Mean FEV(1)/vital capacity (VC) was 74.7% in the H group and 37.8% in the O group (p<0.001). Total lung capacity was higher (p<0.001) in the O group compared with the H group. Lung diffusing capacity was less than half in the O group compared with the H group (p<0.001). MEFR at all lung volumes were lower in the O group (p<0.001). MIFR were comparable in the two groups, except at 25% inspired VC, where MIFR were lower in the O group (p< 0.05). MIFR are less sensitive than MEFR to detect airway obstruction in COPD patients. Yet, the interest of MIFR lay in the possibility to separate intrinsic from extrinsic involvement of airways. A normal MIFR associated with low MEFR, as in the present study, suggests either a lack of parenchymal support, an increased collapsibility of the airways, or a reversible peripheral airway narrowing. A fixed, generalized airway narrowing would be associated with a decrease of both MIFR and MEFR.

Pulmonary Function in Obese Subjects With a Normal FEV1/FVC Ratio

To determine pulmonary function test (PFT) profile and respiratory muscle strength (RMS) of a group of obese individuals who did not have evidence of obstructive airway disease or other underlying diseases affecting their respiratory system. Prospective, open. PFT laboratory, VA Medical Center. Sixty-three consecutive obese (body mass index greater than 27.8 kg/m2) male subjects without overt obstructive airway disease (FEV1/FVC ratio greater than 80%). Standard PFTs and maximum static inspiratory (PImax) and expiratory (PEmax) mouth pressures were determined. RMS was calculated from the following formula: (PImax+PEmax):2. Two distinct groups were identified, those with normal maximum voluntary ventilation (MVV) (> 80% predicted) and those with low MVV. Both inspiratory and expiratory flow rates (FVC, FEV1, forced expiratory flow at 50% vital capacity [V50], maximum inspiratory flow rate [MIFR]), lung volumes (vital capacity [VC], inspiratory capacity [IC], expiratory reserve volume), PImax, and RMS were significantly lower, and residual volume/total lung capacity (RV/TLC) ratio was significantly higher in obese subjects with low MVV compared with those in whom MVV was normal. MVV correlated significantly with FVC, FEV1, V50, MIFR, TLC, VC, IC, RV/TLC, and RMS; the strongest correlation was with MIFR (r = 0.76, p < 0.0001). Standard PFTs allow recognition of a subgroup of obese subjects without overt obstructive airway disease who have more severe lung dysfunction, the marker of which is a low MVV. Peripheral airway abnormalities may be responsible for these observations.

Breakthrough time of a respirator cartridge for carbon tetrachloride vapor flow of workers' respiratory patterns.

Breakthrough times of a commercially-available respirator cartridge packed with a small amount of activated carbon were determined by three different flow patterns: workers' respiratory patterns, conventional steady-state flows, and three standard patterns consisting of rectangle, sine, and triangle waves. A mechanical breathing simulator was used to reproduce the three standard wave patterns as well as the workers' respiratory patterns, which had been recorded from three workers of a paint manufacturing plant wearing a gas mask equipped with a respirator cartridge. The breakthrough test was carried out with 300 ppm carbon tetrachloride vapor at average flow rates of the respiratory and standard patterns equivalent to the steady-state flow rates. The breakthrough times determined by the workers' respiratory patterns were found to be shorter than those by a steady-state flow of the equivalent flow rate, and to be as short as those by sine and triangle wave patterns. It was considered that shorter breakthrough times in the workers' respiratory patterns could be attributed to a faster maximum inspiratory flow rate than that in the case of steady-state flow. The present results suggest that the passing time of CCl4 molecules through the thin activated carbon layer of respirator cartridge may be too short to attain an adsorption equilibrium.

Pressure-controlled ventilation versus controlled mechanical ventilation with decelerating inspiratory flow

To ascertain whether pressure-controlled ventilation offers any advantage with respect to conventional controlled mechanical ventilation with decelerating flow. Prospective, comparative study. Intensive care unit. Eleven consecutive critically ill adult patients. Study of respiratory mechanics and arterial blood gases after 30 mins of pressure-controlled ventilation. Repetition of the same measurements after 30 mins of controlled mechanical ventilation with decelerating flow waveform, with equal tidal volumes, using a commercially available mechanical ventilator. Student's t-test for paired comparisons. A lesser maximum inspiratory flow rate was required for pressure-controlled ventilation (55.7 +/- 16 L/sec) than for controlled mechanical ventilation (72 +/- 2 L/sec) (p < .001). Nevertheless, the peak pressures measured in the orotracheal tubes of the patients were higher in pressure-controlled ventilation (20.4 +/- 3.5 cm H2O) than in controlled mechanical ventilation (18.4 +/- 4.8 cm H2O) (p < .05). This model measured pressure in the inspiratory line, providing erroneous information regarding the behavior of pressures in the airway. The peak pressure measured by the ventilator was significantly higher in controlled mechanical ventilation than in pressure-controlled ventilation and was, in addition, reached at initiation of inspiration in ten of 11 patients with controlled mechanical ventilation, while peak pressure measured in the orotracheal tube was invariably reached at the end of the inspiration, both in pressure-controlled ventilation and controlled mechanical ventilation. The rest of the parameters analyzed, including end-inspiratory pressure, mean pressure, intrinsic positive end-expiratory pressure, and arterial blood gases, showed no differences. The difference between quasi-static compliances almost reached statistical significance (72 +/- 25.4 mL/cm H2O in pressure-controlled ventilation vs. 68.8 +/- 24.3 mL/cm H2O in controlled mechanical ventilation; p = .052). Our study failed to demonstrate any important difference between pressure-controlled ventilation and controlled mechanical ventilation with decelerating inspiratory flow waveform. The differences in the airway pressures detected by the ventilator are spurious and are due to the place (inspiratory line) where these pressures were measured. The difference between the peak pressure measured in the orotracheal tube has statistical, but not clinical, value and is lower in controlled mechanical ventilation. Based on the limited number of variables we studied and unless the tendency indicated in the quasi-static compliance is demonstrated in the future, we do not believe that pressure-controlled ventilation contributes any uniqueness to the theory or practice of mechanical ventilation.

Maximum Voluntary Ventilation: Spirometric Determinants in Chronic Obstructive Pulmonary Disease Patients and Normal Subjects

The 12-s maximum voluntary ventilation (MVV) provides an estimate of the ventilatory reserves available to meet the physiologic demands of exercise. Earlier studies established a general relationship between MVV and FEV1. We hypothesized that the resting maximum inspiratory flow rate (MIFR) also serves as a clinically useful predictor of the MVV. A total of 105 subjects, 45 women and 60 men (age 57 +/- 5 yr, mean +/- SD), with expiratory impairment categories of severe (n = 26), moderate (n = 22), mild (n = 18), and normal (n = 39) based on FEV1 (percentage of predicted), comprised the study samples. The ratio MVV/FEV1 averaged 41 +/- 7 overall. The FEV1 correlated with MVV in normal subjects (p < 0.05, r2 = 0.642) and patients (p < 0.05, r2 = 0.787) better than MIFR (p < 0.05, r2 > or = 0.480). MIFR joined with FEV1 in multiple linear regression to significantly improve the description of MVV:MVV L/min = 30.77FEV1 (L) + 5.94MIFR (L/s) - 4.77 (n = 105; p < 0.05, r2 = 0.849). The 95% confidence limits for MVV varied from 90 to 110% of predicted from the equation for this sample. The factors sex and impairment category did not reduce the unexplained variability in MVV after inclusion of FEV1 and MIFR as covariates in ANOVA (p > 0.05). Addition of MIFR to the model with FEV1 produced greater improvement in r2 than PImax. We conclude that MIFR, although secondary in importance to FEV1, is a significant determinant of MVV in patients with COPD and normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow Volume Loops in Patients With Goiters

Plain radiology is the standard means of assessing upper airway obstruction in patients with goiters. Flow volume loop curves will provide additional information, because they allow a quantitative assessment of airflow dynamics in the respiratory cycle. Fifty-one patients had flow volume loops performed before and after thyroidectomy. There was a significant increase in the maximum inspiratory flow rate (3.9 +/- 0.2 versus 4.9 +/- 0.2 L/second, p less than 0.01) after thyroidectomy. Eight of twelve patients with normal tracheal radiology had improved airflow dynamics in the postoperative period. The flow volume loop curve is a simple noninvasive means of assessing airflow dynamics in patients with goiters and may be superior to conventional radiology.

Inspiratory muscle training in patients with chronic obstructive pulmonary disease: Chen H, Dukes R, Martin BJ. Am Rev Respir Dis 131:251, 1985

We analyze the effect of inspiratory muscle training (IMT) in patients with chronic obstructive pulmonary disease (COPD), with special emphasis on its effects on inspiratory muscle function and clinical outcomes. We reviewed only randomized, controlled studies that have either controlled both the load and the breathing pattern when using resistive training or have employed a threshold trainer in which the load is independent of the pattern of breathing, since methodological aspects may explain inconsistent results in the literature. In these circumstances, most of the studies demonstrated positive effects on inspiratory muscle function. Clinical effects were seldom evaluated; limited available data showed a reduction in dyspnea that was related to an increase in maximal inspiratory pressures (PIMax). When exercise capacity was evaluated through the distance the patients were able to walk in 6 or 12 minutes, most studies demonstrated a significant increase. Other reported positive effects were improvement in nocturnal SaO2, inspiratory muscle power output and maximal inspiratory flow rate. Based in this review, a recommended training regime appears to be an intermediate load (30-40% PIMax) using a threshold device for 30 minutes daily for at least 5 weeks. Although in the literature the criteria for selecting patients are not always well defined, we consider IMT as a helpful procedure for pulmonar rehabilitation in those patients with a moderately severe inspiratory muscle dysfunction presenting dyspnea during daily living activities despite optimal therapy.

Pulmonary function in relapsing polychondritis.

The pulmonary mechanics and bronchoscopic findings in 5 patients with relapsing polychondritis were studied to evaluate the mechanism of obstruction. Two of the patients did not have clinical symptoms referable to the respiratory tract: pulmonary function was normal in 1 patient and was suggestive of mild restriction in the other. Three patients had dyspnea; pulmonary function studies revealed expiratory and inspiratory obstruction in all 3. The maximal flow-static recoil curves demonstrated that the expiratory obstruction was due predominantly to airway abnormality and not to loss of elastic recoil forces of the lung. The bronchoscopic appearance of the extrathoracic airway during quiet breathing did not accurately reflect pulmonary function results. One patient had a visually normal upper airway but greatly reduced maximal inspiratory flow rates, whereas another patient had pronounced narrowing of the upper airway but only a modest reduction of maximal inspiratory flow rates. The bronchoscopic appearance of the intrathoracic airway during quiet breathing did relate well to maximal expiratory flow rates. We conclude that in our group of patients the predominant mechanism of expiratory obstruction in relapsing polychondritis is due to airway abnormality. Although the bronchoscopic and radiographic findings are useful, spirometry is more important in determining functional abnormality.

Variable Tracheal Stenosis Related to Body Position

We demonstrated a variable extrathoracic tracheal stenosis which developed after technically adequate tracheostomy and was worsened by changes in body position. When the patient's arms were above his head, minimal airway diameter was reduced 31 percent, and maximal inspiratory flow rate 37 percent below values measured with arms down, but expiratory flow rates were preserved. Tracheostomy may disrupt the integrity of tracheal support and allow airway collapse under circumstances of increased extratracheal or decreased intratracheal pressure.

Adenoid Cystic Carcinoma (Cylindroma) of the Trachea Masquerading as Asthma

A 40-year-old woman was admitted with upper airway obstruction; chest roentgenogram with tomograms, laryngoscopy, and bronchoscopy verified the presence of a subglottic tumor. Spirometry disclosed a maximum inspiratory flow rate more reduced than in the maximum expiratory flow rate, suggestive of upper airway obstruction. The pathologic conditions were consistent with cystic adenoid carcinoma (cylindroma) of the trachea. The patient underwent tracheostomy and total laryngectomy with an uneventful recovery. No evidence of local extension or distant metastases were evident at time of surgery.

Forced inspiratory measurements and the vital and inspiratory capacities

Observations on 27 patients with chronic airways obstruction, 5 other patients and 6 healthy subjects indicate that forced inspiratory tests are of limited value. The one-second forced inspiratory volume (FIV 1 ) was found to be dependent on the vital capacity (VC). Consequently the ratio of the one-second forced expiratory to forced inspiratory volumes (FEV 1 /FIV 1 ) correlated with FEV 1 as a percentage of VC ( r =0·93). The dependence of FIV 1 on VC was found to reside mainly in the inspiratory capacity (IC). The maximal inspiratory flow rate (MIFR) correlated with FIV 1 ( r = 0·87). Forced inspiratory measurements are unlikely to provide information on ventilatory function additional to that given by VC, except in cases of inspiratory obstruction due to a lesion of a main airway. It is possible that a bronchodilator response in forced inspiratory tests may be due to a dynamic improvement in airflow or an increase in ‘static’ volume (VC or IC), or both.

Forced inspiratory measurements and the vital and inspiratory capacities

Observations on 27 patients with chronic airways obstruction, 5 other patients and 6 healthy subjects indicate that forced inspiratory tests are of limited value. The one-second forced inspiratory volume (FIV 1) was found to be dependent on the vital capacity (VC). Consequently the ratio of the one-second forced expiratory to forced inspiratory volumes (FEV 1/FIV 1) correlated with FEV 1 as a percentage of VC ( r=0·93). The dependence of FIV 1 on VC was found to reside mainly in the inspiratory capacity (IC). The maximal inspiratory flow rate (MIFR) correlated with FIV 1 ( r = 0·87). Forced inspiratory measurements are unlikely to provide information on ventilatory function additional to that given by VC, except in cases of inspiratory obstruction due to a lesion of a main airway. It is possible that a bronchodilator response in forced inspiratory tests may be due to a dynamic improvement in airflow or an increase in ‘static’ volume (VC or IC), or both.