Uneven Distribution Of Ventilation Research Articles

Visualizing exertional dyspnea in a post-COVID patient using electrical impedance tomography

Purpose and methodMany post-COVID patients suffer from dyspnea on exertion. To visualize exercise-induced dyspnea, a post-COVID patient and a healthy volunteer underwent an exercise test on a treadmill under stress relevant to everyday life monitored by electrical impedance tomography (EIT).ResultsThe lung-healthy volunteer showed an even ventilation distribution throughout the assessment, a large ventilated area, and a butterfly-like lung shape with a convex lung rim. The post-COVID patient showed clear differences in the ventilated area compared to the control subject. During exercise, a constantly changing picture of differently ventilated areas is shown. However, especially the anterior regions were under-ventilated and larger areas were partially absent from ventilation. Overall, uncoordinated breathing and an uneven distribution of ventilation dominated the findings.ConclusionEIT is suitable for visualizing disturbed ventilation of the lungs, both at rest and under stress. The potential as a diagnostic tool in dyspnea assessment should be investigated.

Effect of late preterm birth on lung clearance index and respiratory physiology in school-age children.

We hypothesized that former late preterm (LP) children have abnormal pulmonary physiology parameters, including uneven ventilation distribution, due to premature disruption of normal lung development. A cross-sectional study evaluating former LP children at the age of 6 to 12 years as compared to term controls. Demographics and child's and family history of asthma/atopy/smoking were recorded. The outcome parameters were spirometry, multiple breath washout (MBW) measurement by lung clearance index (LCI), 6-minute walk test (6MWT), symptoms related to asthma and allergy, and Godin Leisure-Time Exercise Questionnaire. Twenty-nine former LP were compared to 30 term-control children (mean age, 8.2 ± 1.7 and 8.8 ± 1.8 years, respectively). LP had reduced forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) compared to term controls (FEV1 1.59 ± 0.48 vs 1.80 ± 0.39 L, P = 0.005 and FVC 1.73 ± 0.45 vs 1.99 ± 0.49 L, P = 0.009). There were no differences between the two groups regarding FEV1/FVC, forced expiratory flow between 25 and 75 (FEF25-75), LCI (7.10 ± 0.79 vs 6.96 ± 0.75, P = 0.50), 6MW distance, and weekly leisure-activity score. Former LP children had more episodes of wheezing and greater use of asthma medication. This pilot study suggests that LP have lower pulmonary function tests (PFTs) but not ventilation inhomogeneity measured by LCI or functional disturbance. It is unclear if the differences in PFTs are due to late prematurity by itself or are the consequence of maternal and neonatal factors associated with LP. Further larger studies are required to assess the long-term respiratory consequences of LP birth.

Monitoring changes in distribution of pulmonary ventilation by functional electrical impedance tomography in anaesthetized ponies

ObjectiveTo assess changes in the distribution in pulmonary ventilation in anaesthetized ponies using electrical impedance tomography (EIT). Study designProspective experimental study. AnimalsA group of eight adult pony geldings. MethodsGeneral anaesthesia was induced and maintained using isoflurane in oxygen with volume-controlled ventilation [tidal volume (VT) (10 mL kg−1), respiratory rate (8–12 breaths minute−1)] to maintain end-tidal carbon dioxide between 35 and 40 mmHg (4.66–5.32 kPa). Regional distribution of ventilation was assessed with EIT (plane of fifth to sixth intercostal space) at 30, 60 and 90 minutes after intubation. The resulting functional images were divided into four regions of interest (ROI, A–D) to determine: 1) the ratio of VT distribution between dependent to nondependent lung (D/ND) and 2) changes in distribution within the lungs in the latero-lateral direction. The centre of ventilation (COV) was calculated. The dimension of the chest in the latero-lateral (W) and dorso-ventral (H) direction was measured at the height of the withers and the W/H ratio was calculated. The influence of time on the D/ND ratio, COV and ROI A–D were analysed with anova followed by post hoc Bonferroni tests. Pearson correlation coefficient and the coefficient of determination (r2) were calculated to evaluate the relationship between the W/H ratio and D/ND ratio, and COV. Statistical significance was set at p < 0.05. ResultsThe median D/ND ratio (T30–T90) was 0.67 (0.40–1.01) and for COV 31.15% (11.20–45.20), confirming the expected uneven distribution of ventilation. The D/ND ratio had a moderate negative correlation with the W/H ratio (r = −0.68, r2 = 0.46, p < 0.001), while the COV did not correlate with the W/H ratio (r = −0.04). Conclusions and clinical relevanceUneven ventilation in mechanically ventilated right laterally recumbent anaesthetized ponies occurs within 30 minutes and changed little over the following 60 minutes.

Ventilation heterogeneity: small length scales, big challenges

the distribution of regional ventilation is heterogeneous in normal lung and increases dramatically under pathological conditions. This has been demonstrated both in humans and in animal models using a number of different imaging techniques. General anesthesia and mechanical ventilation can

Double-lumen tube for ventilation in severe kyphoscoliosis

The presence of kyphoscoliosis can adversely affect gas exchange because of restriction to gas flow and reduction of lung volume. The effects become more exaggerated during positive-pressure ventilation due to the uneven distribution of ventilation. The use of a double-lumen tube helps to reduce the ventilation perfusion mismatch that occurs because of positive-pressure ventilation. We report a patient with severe kyphoscoliosis who underwent repair of an atrial septal defect, in whom a double-lumen tube was used for ventilation and the conduct of general anesthesia.

Uneven distribution of ventilation in acute respiratory distress syndrome

IntroductionThe aim of this study was to assess the volume of gas being poorly ventilated or non-ventilated within the lungs of patients treated with mechanical ventilation and suffering from acute respiratory distress syndrome (ARDS).MethodsA prospective, descriptive study was performed of 25 sedated and paralysed ARDS patients, mechanically ventilated with a positive end-expiratory pressure (PEEP) of 5 cmH2O in a multidisciplinary intensive care unit of a tertiary university hospital. The volume of poorly ventilated or non-ventilated gas was assumed to correspond to a difference between the ventilated gas volume, determined as the end-expiratory lung volume by rebreathing of sulphur hexafluoride (EELVSF6), and the total gas volume, calculated from computed tomography images in the end-expiratory position (EELVCT). The methods used were validated by similar measurements in 20 healthy subjects in whom no poorly ventilated or non-ventilated gas is expected to be found.ResultsEELVSF6 was 66% of EELVCT, corresponding to a mean difference of 0.71 litre. EELVSF6 and EELVCT were significantly correlated (r2 = 0.72; P < 0.001). In the healthy subjects, the two methods yielded almost identical results.ConclusionAbout one-third of the total pulmonary gas volume seems poorly ventilated or non-ventilated in sedated and paralysed ARDS patients when mechanically ventilated with a PEEP of 5 cmH2O. Uneven distribution of ventilation due to airway closure and/or obstruction is likely to be involved.

Anesthetic Considerations for Bariatric Surgery

According to the National Institutes of Health, obesity is a major health problem with clearly established health implications, including an increased risk for coronary artery disease, hypertension, dyslipidemia, diabetes mellitus, gallbladder disease, degenerative joint disease, obstructive sleep apnea, and socioeconomic and psychosocial impairment (1). The risk of developing one or more of these obesityrelated conditions is based on body mass index (BMI), with 25–30 kg/m 2 being low risk and 40 kg/m 2 being very high risk (2). The prevalence of obesity in the 18- to 29-yr-old group increased from 12% in 1991 to 18.9% in 1999 (3). Bariatric surgery encompasses a variety of surgical weight loss procedures used to treat morbid obesity. Obesity is clinically expressed in terms of BMI or Quetelet’s index (4), which is derived by dividing weight by the square of height to estimate the degree of obesity. Thus, BMI body weight (kg)/height 2 (m 2 ). Morbid obesity is a BMI more than 35 kg/m 2 , and super morbid obesity is BMI more than 55 kg/m 2 . The indications for surgical treatment of severe obesity, as outlined in the 1991 National Institutes of Health Consensus Development Conference Panel, include an absolute BMI more than 40 kg/m 2 or BMI more than 35 kg/m 2 in combination with lifethreatening cardiopulmonary problems or severe diabetes mellitus (1). Patients seeking surgical weight loss must have proven attempts at medically supervised weight loss. Documentation of loss of 5% to 10% excess body weight or weight gain after at least 6 mo of diet modification, exercise, and medical therapy or nonimprovement in comorbid conditions during this period indicates failure. Studies have shown that weight loss of 5%–10% of initial body weight improves glucose intolerance and Type II diabetes, hypertension, and dyslipidemia (5–7). The average expenditure is approximately $7000 per year per patient on weight loss programs and equipment. Unfortunately, long-term weight loss is the exception, and most patients regain weight, sometimes more than they initially lost.

Resolution of Pulmonary Overinflation in an Extremely Low-Birth-Weight Infant Utilizing A ‘Lung Squeezing’ Technique — A Case Report

Abstract Uneven distribution of ventilation in infants ventilated with high-frequency oscillation may be presented as regional overinflation of the lungs. Current evidence supports that inflation pattern aberrations and pseudocyst formation are pathologic lesions associated with ventilator-induced lung injuries. Physiotherapy with a ‘lung squeezing’ technique was utilized to reduce the regional overinflation in a preterm infant of extremely low birth weight. The infant responded with complete resolution of the regional overinflation and improved homogeneous distribution of ventilation. This single case report suggests that the lung squeezing technique may be useful in promoting normal lung inflation in preterm infants receiving high-frequency oscillation.

Evaluation of pulmonary ventilation and diaphragmatic movement in idiopathic scoliosis using radioaerosol ventilation scintigraphy.

Regional distribution of lung ventilation and diaphragmatic movement were evaluated using a non-invasive scintigraphic method in patients with idiopathic scoliosis. Twenty-four non-smoking patients aged 20 +/- 9 years (mean +/- S.D.), all with a right convex dorsal curve (mean Cobb's angle of 65.1 +/- 26.4 degrees), underwent lung ventilation scintigraphy after inhalation of 99Tcm-labelled human albumin microspheres. The distribution of the inhaled aerosol was assessed and scored based on four scintigraphic patterns, ranging from homogeneous distribution (score = 1) to diffuse severe hypoventilation (score = 4). Diaphragmatic movement, evaluated in 11 of the 24 patients, was assessed using an index (DM-Index) computed for each hemi-diaphragm by the normalization and subtraction of two digital scans obtained during maximal inspiration and expiration respectively. The left lung, situated on the concave side of the scoliotic curve, showed a more uneven distribution of ventilation (scintigraphic score: 2.62 +/- 1.17 vs 1.50 +/- 1.02, P < 0.01) and a reduced hemi-diaphragm movement (DM-Index: 29.2 +/- 4.0 vs 35.9 +/- 2.9, P < 0.001). A significant inverse correlation was found between Cobb's angle and both the right and left DM-Index (r = -0.82 and -0.66 respectively). In a stepwise multiple-regression analysis, the scintigraphic score correlated significantly with the functional index of distribution of inspired gas (IDI) derived from the multiple-breath nitrogen washout curve (P = 0.02). We conclude that lung ventilation scintigraphy provides information on the regional distribution of ventilation and on diaphragmatic movement in idiopathic scoliosis. The pulmonary function derangements in scoliotic patients were mainly localized in the lung on the concave side of the scoliotic curve and were related to the severity of the spinal curvature.

Precision and accuracy of a noninvasive inert gas washin method for determination of cardiac output in men

Stout et al. (J. Appl. Physiol. 38:913-918, 1975) suggested an open-circuit multibreath (MB) inert gas method for determining pulmonary capillary blood flow (Qc) in anesthetized dogs receiving artificial ventilation. In the present work we investigated the accuracy and reproducibility of the MB method in nine healthy human subjects at spontaneous ventilation, and we compared the MB method with the inert gas rebreathing (RB) method. Qc was calculated at rest and during exercise at 50 or 100 W, and experimental errors were evaluated in computer simulations of a two-alveoli lung model. The calculated mean Qc values of the MB method were 5.56 +/- 1.23 (SD), 10.02 +/- 0.78, and 13.2 +/- 0.84 l/min, and the mean difference (MB Qc - RB Qc) was not significantly different (P > 0.05). The variation in Qc of the MB method was found to be significantly larger than that in Qc of the RB method (P < 0.01). Random measurement errors and uneven distribution of ventilation contributed to the experimental errors. We conclude that the MB method is inferior to the RB method but that the MB method may be useful under exercise conditions.

Changes in lung function of granite crushers exposed to moderately high silica concentrations: a 12 year follow up.

45 granite crushers and 45 age and smoking matched referents underwent pulmonary function tests in 1976 and 1988. On average, the granite crushers at follow up had worked for 22 years, were 52 (range 36-78) years old, and had inhaled a cumulated amount of 7 mg of silica in the respirable dust fraction. Between 1976 and 1988 the average concentration of respirable quartz in air was 0.16 mg/m3 (threshold limit value (TLV) = 0.10 mg/m3). In 1988 the granite crushers had somewhat lower forced expiratory flows (forced expiratory volume in one second/vital capacity (FEV1/VC) -4.5% and forced midexpiratory flow FEF50 -15%) compared with the referents and a more uneven ventilation distribution (17% higher slope of phase III in the nitrogen single breath curve). Five smoking granite crushers, but none of the referents, had an FEV1 < 80% of the predicted. During the 12 year interval the granite crushers had--compared with the matched referents--a greater decrease in FEV1 (-4.6%), FEV1/VC (-5.4%), maximal expiratory flow, (-8%) and FEF50 (-14%), and a larger increase in phase III and static compliance (p < 0.02 in all variables). The functional changes suggest the presence of airways obstruction and increased compliance of the lungs. Exposure to silica at concentrations of about twice the present TLV was thus associated with airways obstruction and loss of elastic recoil rather than fibrosis and a restrictive function loss as seen in silicosis. The changes were on average small, but in some tobacco smokers more pronounced changes were found.

Effect of methacholine on low-frequency mechanics of canine airways and lung tissue.

We measured tracheal flow, tracheal pressure, and alveolar capsule pressure in four anesthetized paralyzed tracheostomized open-chest dogs. Lung impedance between 0.12 and 4.88 Hz was measured with a forced volume oscillation technique before and after the intravenous administration of methacholine (MCh). Before MCh administration, lung impedance was well described by a model featuring a single airway leading to an alveolar region surrounded by tissue with a continuous distribution of viscoelastic time constants as used by Hantos et al. (J. Appl. Physiol. 68: 849-860, 1990). After MCh, however, this model gave a poor fit to the impedances. The impedances were well accounted for, however, when the model was enhanced to include an extra time constant term, which we suspect is required to account for the uneven ventilation distribution produced by MCh. Airway impedance before MCh administration was well described by a simple resistance-inertance model, but a model incorporating serial inhomogeneity of ventilation was again required after MCh. Our results support those of previous studies indicating that the impedance of the normal dog lung is well described by a homogeneously ventilated viscoelastic tissue model. In contrast, our results after MCh administration show strong evidence of marked regional ventilation inhomogeneity in addition to the rheological properties of the tissues.

A simple method for correcting single breath total lung capacity for underestimation.

The single breath method underestimates total lung capacity by comparison with the multiple breath method (TLCmb) because of inhomogeneity of ventilation distribution. This study proposes a simple correction for the single breath TLC (TLCsb), using inert gas phase III slope to account for the effects of uneven ventilation distribution. A model of a non-uniform lung ventilation was designed, composed of a serial dead space and two alveolar compartments arranged in parallel, whose relative ventilations were determined from the phase III plateau. Before correction TLCsb was 104-44% of TLCmb in 64 subjects (17 with diffuse interstitial disease, 42 with chronic obstructive pulmonary disease, and five healthy subjects). The limit of acceptability for the correction (TLCcorr) was determined from the 95% confidence interval of TLCsb/TLCmb in the healthy subjects. The correction resulted in a significant increase in TLCsb (p less than 0.004). TLCcorr remained under the limit of acceptability for only 12 patients with emphysema, and all 12 showed a large improvement in the TLC estimate. The presence of poorly ventilated zones during a single breath in these patients may explain this partial correction.

Cardiac output by rebreathing in patients with cardiopulmonary diseases.

Noninvasive estimates of cardiac output by rebreathing soluble gases (Qc) can be unreliable in patients with cardiopulmonary diseases because of uneven distribution of ventilation to lung gas volume and pulmonary blood flow. To evaluate this source of error, we compared rebreathing Qc with invasive measurements of cardiac output performed by indicator-dilution methods (COID) in 39 patients with cardiac or pulmonary diseases. In 16 patients with normal lung volumes and 1-s forced expiratory volumes (FEV1), Qc measured with acetylene [Qc(C2H2)] overestimated COID insignificantly by 2 +/- 9% (SD). In subjects with mild to moderate obstructive lung disease, Qc(C2H2) slightly overestimated COID by 6 +/- 15% (P = 0.11). In patients with restrictive disease or combined obstructive and restrictive disease, Qc(C2H2) underestimated COID significantly by 9 +/- 14% (P less than 0.04). The magnitude of the discrepancy between Qc and COID correlated with size of the volume rebreathed and an index of uneven ventilation calculated from helium mixing during rebreathing that determined a dead space to inspired volume ratio (VRD/VI). Rebreathing volumes less than 40% of the predicted FEV or VRD/VI of 0.4 or greater identified all subjects with a discrepancy between Qc(C2H2) and COID of 20% or greater.

Gas transit times in the pig lung.

1. A method of measuring the time taken by a front of gas to pass from the carina to individual small airways in the lung is described. 2. This method has been used to investigate the movement of a gas front through hollow lung casts, excised lungs, and excised lungs subjected to a gradient of pleural pressure. 3. The results obtained support the suggestion of morphometric studies that the asymmetrical anatomy of the bronchial tree plays a part in the uneven distribution of ventilation in the lung. 4. The effect of a gradient of pleural pressure over the surface of the upright lung was to increase the time taken by a gas front to reach dependent regions.

An up-dated method for determining v̇ a/Q̇ inequalities and direct shunt using 0 2, CO 2 and N 2

An attempt was made to determine the contributions of uneven v̇ a/Q̇ distribution and direct shunting to the impairment of gas exchange by alveolar-arterial differences for O 2, CO 2 and N 2 in five surgical patients anesthetized with halothane in 38% O 2 and N 2 (A-a)D0 2 varied from 122 to 146 mm Hg, (a-A)DN 2 from −3 to 55 mm Hg and (a-A)DCO 2 from 1.5 to 9.5 mm Hg. A lung model was constructed for each patient with one low v̇ a/Q̇ compartment, one high v̇ a/Q̇ compartment and a direct right to left shunt. When the low v̇ a/Q̇ compartment had a value less than 0.10, uneven distribution of ventilation and perfusion was the prime cause of the (A-a)DO 2. In two patients whose low v̇ a/Q̇ compartments had values greater than O.20 direct right to left shunting was the predominant cause of impaired gas exchange even though ventilation and perfusion were unevenly distributed. In the fifth patient, direct shunting was the sole cause of the (A-a)DO 2. We suggest the “triple gas difference” as a useful method for separating the effects of v̇ a/Q̇ mismatching from direct shunt.

Expiratory gas concentration curves for examination of uneven distribution of ventilation and perfusion in the lung. Second communication: experiments.

The experiments in this paper pertain to theory developed in a preceding article of Respiration Recording of expiratory gas concentration curves yield parameter values with good reproducibility, e. g. RHe, MHe, He1.5, measures for several aspects of uneven ventilation, and Rco2 a measure for unequal distribution of ventilation-perfusion ratio in the lung. The minimum radius of curvature of He and CO2 curves, RHe and Rco2 resp., is compared with clinical diagnoses and a correlation is shown of RHe, Rco2 and emphysema. The values of RHe and Rco2 correlate significantly with other lung function parameters. The pathological slope (M) of the alveolar plateau is suggested to be caused by a gradual change in ratio between the flows from individual lung regions. This is proved with bronchospirometry. With the parameter He1•5 it might be possible to reveal disturbances in small parts of the lung.

Pulmonary function in status asthmaticus: effect of therapy.

In 11 patients with bronchial asthma, lung volumes, FEV 1·0 , PaO 2 , and lung diffusing capacity (single breath CO method) were measured in status asthmaticus and after recovery. Ventilatory capacity improved following therapy. The improvement was associated with a rise in vital capacity and a fall in residual volume, but the total lung capacity might either decrease, increase or remain unchanged. A decreased value of PaO 2 was found in all patients in status asthmaticus. After treatment PaO 2 increased in all patients. In two of them PaO 2 increased despite the unchanged values of the other parameters of pulmonary function. The improvement of PaO 2 after treatment is considered to be the result of adjustment of perfusion to ventilation. The lung diffusing capacity was below normal values in three patients before treatment. After treatment the diffusing capacity increased in six patients. The diffusion constant, although within the normal range in status asthmaticus, increased after treatment in one and decreased in three other patients. The decreased diffusing capacity in status asthmaticus is the consequence of a reduced effective alveolar volume due to uneven distribution of ventilation. The changes observed in the diffusion constant following corticotherapy are ascribed to a dependence of this constant on the different level of the alveolar volume at which the single breath test is performed.

Expiratory gas concentration curves for examination of uneven distribution of ventilation and perfusion in the lung. First communication: theory.

Expiratory gas concentration curves for examination of uneven distribution of ventilation and perfusion in the lung. First communication: theory.

Changes in alveolar-arterial oxygen tension difference (A-aDO2) during variations in alveolar ventilation.

AbstractThe alveolar‐arterial PO2 difference (A—aDO2) was determined at various levels of alveolar ventilation in anesthetized, tracheotomized dogs, ventilated with room air by means of a volume cycled respirator; the ventilation being changed by varying the tidal volume, keeping the respiratory rate constant.—A decrease in ventilation was accompanied by a marked decrese in A—aDO2, and vice versa: At PaCO2≤30 mm Hg (mean 25.5 mm Hg) A—aDO2 was 28.3 mm Hg (range 18—42 mm Hg), at PaCO2 31–50 mm Hg (mean 41.5 mm Hg) A—aDO2 was 19.3 mm Hg (range 13—30 mm Hg); at PaCO2≥51 mm Hg (mean 60.5 mm Hg).A—aDO2 was 9.7 mm Hg (range 5—14 mm Hg).—Assuming an arterio‐venous difference in hemoglobin O2 saturation of 20% and 40%, respectively, the A—aDO2 for the 3 PCO2 intervals were calculated as venous admixture, being 7.1, 10.4 and 23.0%, and 3.7, 5.5 and 13.0%, respectively.—This indicates that reduction of the alveolar ventilation is accompanied by increasing disturbances of the alveolar‐arterial gas exchange,—of the nature uneven distribution of ventilation and perfusion, and/or venous admixture.The inverse relationship between the extent of the disturbances of alveolar‐arterial gas exchange and A—aDO2 in these studies show that A—aDO2 should only be used for the evaluation of changes in the alveolar‐arterial gas exchange when the alveolar ventilation remains unchanged.