Maximal Expiration Research Articles

T2* and proton density measurement of normal human lung parenchyma using submillisecond echo time gradient echo magnetic resonance imaging

Objective: To obtain T2* and proton density measurements of normal human lung parenchyma in vivo using submillisecond echo time (TE) gradient echo (GRE) magnetic resonance (MR) imaging. Materials and methods: Six normal volunteers were scanned using a 1.5-T system equipped with a prototype enhanced gradient (GE Signa, Waukausha, WI). Images were obtained during breath-holding with acquisition times of 7–16 s. Multiple TEs ranging from 0.7 to 2.5 ms were tested. Linear regression was performed on the logarithmic plots of signal intensity versus TE, yielding measurements of T2* and proton density relative to chest wall muscle. Measurements in supine and prone positions were compared, and effects of the level of lung inflation on lung signal were also evaluated. Results: The signal from the lung parenchyma diminished exponentially with prolongation of TE. The measured T2* in six normal volunteers ranged from 0.89 to 2.18 ms (1.43±0.41 ms, mean±S.D.). The measured relative proton density values ranged between 0.21 and 0.45 (0.29±0.08, mean±S.D.). Calculated T2* values of 1.46±0.50, 1.01±0.29 and 1.52±0.18 ms, and calculated relative proton densities of 0.20±0.03, 0.32±0.13 and 0.35±0.10 were obtained from the anterior, middle and posterior portions of the supine right lung, respectively. The anterior–posterior proton density gradient was reversed in the prone position. There was a pronounced increase in signal from lung parenchyma at maximum expiration compared with maximum inspiration. The ultrashort TE GRE technique yielded images demonstrating signal from lung parenchyma with minimal motion-induced noise. Conclusion: Quantitative in vivo measurements of lung T2* and relative proton density in conjunction with high-signal parenchymal images can be obtained using a set of very rapid breath-hold images with a recently developed ultrashort TE GRE sequence.

Computerised measurements of QT dispersion in healthy subjects

ObjectiveTo assess the stability and reproducibility of computerised QT dispersion (QTd) measurement in healthy subjects, as this is presently being incorporated into commercial electrocardiographic systems.Methods70 healthy volunteers (mean (SD) age...

A forward model for maximum expiration

The maximum expiratory flow–volume (MEFV) curve is a sensitive test of respiratory mechanics. Several mathematical models for forced expiration have been developed, but they suffer from various shortcomings. It is impossible to calculate the parts of the MEFV curve beyond the flow limiting conditions and computational algorithms do not allow a direct calculation of maximal flow. In the present work a complex, nonlinear forward model, including exciting signal and static recoil pressure–lung volume descriptions and 132 parameters, has been constructed. Direct determination of maximum flow is achieved by means of successive approximation algorithm. The model enables prediction of flow during forced expiration in the whole range of forced vital capacity.

A metrological model for maximum expiration

A metrological model for maximum expiration formulated by means of complex model reduction and selection of a parameter set for estimation was the purpose of this investigation. Reduction of the model was based on the forward-inverse method. Carrying out regression analysis showed that the properties of the airways were well approximated by exponential functions. The cross-sectional areas, airway lengths and compliances were replaced by these exponential relationships. Some other dependencies between mechanical quantities were also included. This reduced the number of parameters from 132 to 12. The complex and reduced models for maximal expiration were implemented on a PC and compared. The sensitivity index expressing the effect of parameter reduction was 3.2%. The selection of parameters for estimation was based on sensitivity analysis. This analysis showed that the reduced model was insensitive or weakly sensitive to eight parameters. This allowed for the selection of four parameters that influence the shape of the maximal expiration curve more than the others.

The forced expiratory volume–time curve estimation using the electrocardiogram

The feasibility of estimating the forced expiratory volume–time curve from the amplitude modulation of the electrocardiogram was studied using a numerical torso model and ECG signal processing. A two dimensional numerical model of the torso was solved for the maximum expiration and inspiration to study the changes in the surface potential as a result of changes in the lung volume. The numerical model showed that significant changes in the surface potential amplitude occur between maximum inspiration and maximum expiration and that this amplitude change in the left–right axis of the torso might be three times as large as in the front–back axis. In the experimental setup, ECG waveforms from the surface of the chest and the mouth air flow were simultaneously recorded from four male subjects during several forced vital capacity (FVC) maneuvers. The amplitude of the QRS complex was measured for different expired lung volumes and an estimation of the forced expiratory volume–time curve was obtained. The FVC and the FEV 1 (forced expiratory volume after 1 s) spirometry indices were calculated for the two volume–time curves obtained from the electrocardiogram and from the spirometry measurements. The results differ between 0.1 and 0.8 l. These preliminary results are encouraging and might indicate that a relationship between the volume–time curve during FVC test and the electrocardiogram signals does exist. Further validation in a larger number of subjects and patients is needed before the technique can be applicable for clinical use.

Expiration of ethane in rats under variously elevated inspiratory O 2 -concentrations

Expired ethane is regarded as a noninvasive indicator of lipid peroxidation. As a model of oxidative stress we have investigated in male Wistar rats (body wt. 309 +/- 15 g) the effects of various levels of elevated inspiratory oxygen concentrations on the expiration rate of ethane. After 4 days under 21 vol% O2 (basic condition) the rats were exposed for 6 or 5 days to 40, 60 or 80 vol% O2 over 8 or 23 h/day. The variously O2-enriched air was conducted through the cages and expired ethane adsorbed onto charcoal was thermo-desorbed and measured by gas chromatography. Basic ethane expiration was 3.1 +/- 0.8 pmol/100 g body wt. per min. At 40 vol% O2 over 8 or 23 h/day no increase or a maximum average 47% increase (P < 0.01) in ethane expiration occurred on day 4; 60 vol% O2 over 8 or 23 h/day led to a corresponding increase of 56 or 87% (P < 0.05 or P < 0.01) on day 3; 80 vol% O2 over 8 or 23 h/day led to a corresponding increase of 81 or 66% (P < 0.01) on days 3 or 2. Our results indicate that with up to 60 vol% O2 a temporary increase in lipid peroxidation occurs in a dose dependent manner. However, at 80 vol% O2 no further increase in the maximum ethane expiration occurred. The latter finding and the finding of only transient increase in ethane expiration in probably due to antioxidative counteraction.

Reproducibility of Nasal Peak Inspiratory Flow Among Healthy Adults: Assessment of Epidemiologic Utility

To assess the reproducibility of nasal peak inspiratory flow (PIFn). Twelve healthy nonsmoking volunteers were studied. Repeated measurements of PIFn and oral (PIFm) peak inspiratory flow were performed for 5 consecutive days. Two methods of inhalation were compared. In the residual volume (RV) method, the forced maximal inspiratory maneuver was initiated from the end of a maximal expiration, while in the functional residual capacity (FRC) method, the maneuver was from the end of a tidal breath. Reproducibility was assessed by the intraclass correlation coefficient. Time trend for the 5 days was assessed by random effect models adjusting for different baseline for each subject. The intraclass correlation coefficient (ICC) of PIFn was 0.89 (lower limit of one-sided 95% confidence interval is 0.80) by the RV method and 0.78 (95% lower limit is 0.63) by the FRC method, suggesting that both methods have good reproducibility. These were similar to the ICCs of PIFm by each method. The FRC method did not show a significant time trend for PIFn. The RV method had a small, but significant, decreasing time trend of a magnitude considered inconsequential for the purpose of epidemiologic study. PIFn, measured from either RV or from FRC, showed good reproducibility and can be employed in epidemiologic studies investigating the upper airways' response to air pollutant exposure. Further studies of the relationships between PIFn and signs and symptoms of rhinitis are needed to evaluate the utility of this test for clinical and epidemiologic use.

QT Dispersion Magnitude Is Related to the Respiratory Phase in Healthy Subjects

Twelve-lead electrocardiograms in 20 healthy volunteers during quiet respiration, maximum inspiration, and maximum expiration were recorded. QT dispersion was statistically significantly shorter both at maximum inspiration and maximum expiration than during quiet breathing.

Inspiratory maneuver effects on peak expiratory flow. Role of lung elastic recoil and expiratory pressure.

We investigated the effects of two different inspiratory maneuvers (fast or slow) on the ability of normal subjects to generate peak expiratory flows (PEF) and maximal dynamic expiratory pressures (Pexp) during the performance of a forced vital capacity maneuver. During the fast maneuver (F), the subject inspired rapidly to total lung capacity (TLC) and immediately performed a maximal expiration, whereas in the slow maneuver (S) the subject inspired slowly to TLC, paused for 4-5 s at TLC and then performed a maximal expiration. Ten normal subjects performed a series of such maneuvers. In addition to PEF and Pexp, we measured EMG activity of abdominal (EMGabd) and rib cage muscles, and lung elastic recoil pressure (PesL). Overall, F yielded higher PEF values than S (by approximately 7%); in addition, PesL, Pexp, rate of rise of Pexp (dPexp/dt), and EMGabd were similarly higher with F than with S (p < 0.05 for all). Analysis of individual data showed that the intermaneuver differences in PEF were largely explained by differences in PesL, Pexp or dPexp/dt. Our data suggest that, in comparison with the slow maneuver, the fast maneuver induces a greater change in both the lung elastic recoil and expiratory muscle activation which account for differences in PEF between the two maneuvers. The enhanced expiratory muscle activation with the fast maneuver suggests a specific inspiratory-expiratory muscle interaction analogous to agonist-antagonist interactions described for skeletal muscles.

PATTERN OF EXPIRATORY MUSCLE RECRUITMENT DURING INCREMENTAL EXERCISE1637

The purpose of this project was to examine the pattern of recruitment in external oblique (EO) and rectus abdominis (RA) muscles during incremental bicycle exercise. Nine human subjects (six male, three female) performed an incremental exercise bout to exhaustion. Hypoxia (11% O2) was administered briefly at each workload. Electromyographic (EMG) activity was recorded using surface electrodes, and quantified as a percentage of the activity elicited during maximal expiration from functional residual capacity(max). Peak phasic EO and RA expiratory EMG activities showed a small initial increase followed by a marked rise at 60% of maximal workload. At the end of exercise, EO EMG was 13.0±3.6% and 14.4±4.5% max during normoxia and hypoxia, respectively, while RA activity was 15.2±5.8% and 20.1±6.2% max during normoxia and hypoxia, respectively. There was a trend of greater activity in both muscles during hypoxia; however, activity was similar when corrected for differences in ventilation. This was likely due to disfacilitation of abdominal motoneurons by hypocapnia, which was prevalent in hypoxia (-3.5 mmHg). In light exercise, the EMG burst began ≈400 and≈600 msec after the beginning of expiration for EO and RA, respectively, and in peak exercise activity began 90±60 msec and 10±40 msec before expiration for EO and RA, respectively. The offset time remained constant at ≈80 msec before inspiration for both muscles. These data indicate that: EO and RA activities increase in parallel as a function of exercise intensity; hypoxia does not influence EO and RA recruitment when normalized for ventilation, possibly due to hypocapnia; EO and RA activities begin earlier in expiration as ventilation increases, and may even precede expiration at high exercise intensities, while the offset of activity does not change.

Reduction of the Model for Maximal Expiration

The purpose of this investigation was to reduce a model for maximal expiration and to make it more suitable for parameter estimation. Reduction of the model was based on the forward-inverse method. Carried out regression analysis showed good approximation of airway properties by exponential functions. The cross-sectional areas, airway lengths and compliances were replaced by these exponential relationships. Some other dependencies between mechanical quantities were also included. The complex and reduced models for maximal expiration were implemented on a PC and compared. Sensitivity index expressing the effect of parameter reduction was 1.7%. The study showed possibility to reduce the parameters number of the maximal expiration model to 15.

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.

Respiration-induced motion of the kidneys in whole abdominal radiotherapy: implications for treatment planning and late toxicity

Purpose: Whole abdominal radiotherapy (WAR) has potential utility in the management of several malignancies. The limited radiation tolerance of the kidneys is an important consideration in the design of WAR fields. Although renal blocking is standard for WAR, few guidelines exist in the literature to factor respiration-induced kidney motion into the design of these blocks. Methods: Radiographs were obtained to measure kidney excursion under forced respiratory conditions in eight patients (14 visualized kidneys). Intravenous contrast was administered and AP films were obtained at maximum inspiration and expiration. Renal excursion was measured relative to a horizontal reference line at the bottom of the L3 vertebral body. The kidney position on the actual treatment simulation film was also determined using this technique. Treatment isodose distributions through the kidneys were obtained for a sample patient using phantom measurements and two blocking schemes: AP/PA and PA only. These provided quantification of the actual dose received by the kidney in a typical WAR treatment. Results: In the worst case scenario, the left kidney block required an additional 10 mm above and 15 mm below the renal silhouette on the simulation film in order to account for all phases of respiration. The corresponding values for the right kidney were 2 mm and 19 mm, respectively. The dose received by the kidney under the center of the block was 20% of prescribed using AP/PA blocks and 50% of prescribed using PA blocks only. However, portions of ‘blocked’ kidney received up to 90% of the prescribed dose with either technique. Conclusions: Although kidney motion under forced respiratory conditions is not representative of typical treatment conditions, the data highlight the possibility of renal movement during treatment. This is particularly important in light of the significant dose (20 to 50%) delivered to the kidney under the center of the kidney block in typical treatments. Given the potential for overdosage of this critical organ, careful prospective documentation of renal function is warranted in patients receiving WAR.

Hydrothorax as a Complication of Percutaneous Access to the Renal Pelvis

Hydrothorax as a Complication of Percutaneous Access to the Renal Pelvis

The influence of breathhold on peak expiratory flow in normal and asthmatic children.

We have previously demonstrated a 10% reduction in peak expiratory flow (PEF) in healthy adults following a breathhold at total lung capacity (TLC). This fall was attributed to dissipation of airway wall viscoelasticity, increasing airway wall compliance (Caw). To investigate this phenomenon in children and to determine whether the effect of breathhold would be greater in asthmatics than in normal children, 15 asthmatics and 14 normal children (aged 10-15 yrs) performed maximal post expirations (MFE) with and without a 5 s breathhold at TLC. The entire study was repeated following the inhalation of salbutamol (800 micrograms) to relax the airway smooth muscle (and to increase Caw). Breathhold at TLC resulted in a significant decrease in PEF both in the asthmatics (group mean fall 5.8%; p < 0.01) and normal children (group mean fall 10.3%; p < 0.05). Salbutamol diminished this fall, becoming nonsignificant in the normal children. Similar patterns were also seen in forced expiratory volume in one second (FEV1) and in maximal expiratory flow at 50% vital capacity (V'50). These data are consistent with the proposal that breathhold at total lung capacity dissipated viscoelastic energy (increasing airway compliance) and decreased maximal expiratory flows both in normal and asthmatic children. They also demonstrate the need to standardize the forced vital capacity manoeuvre to decrease the variability in the flows recorded during the subsequent forced expiration.

Right Ventricular Diastolic Dysfunction in Heart Failure

Left ventricular (LV) diastolic dysfunction is common in heart failure and is an important predictor of prognosis and mortality. Less attention has been paid to right ventricular (RV) diastolic function. In this study, we compared RV diastolic function in a large cohort of patients with heart failure (HF) with two groups: patients with pulmonary hypertension and normal LV function (the PHT group) and normal subjects. Transtricuspid and pulmonary artery flow were assessed by two-dimensional Doppler echocardiography at maximum inspiration and expiration in 185 subjects: 114 symptomatic HF patients (ejection fraction < 0.5), 31 PHT patients (pulmonary artery systolic pressure > 40 mm Hg), and 40 normal subjects. A subset was matched for age and heart rate. The results showed a high prevalence of RV diastolic abnormalities: HF patients had lower tricuspid E-A ratios, lower peak E-wave velocity, and prolonged RV isovolumic relaxation time (all P< .0001). Tricuspid E-wave deceleration time was significantly shorter only in those who had an LV restrictive filling pattern. The PHT group had similar findings. Compared with a normal range, more than half of the patients had lower tricuspid E-A ratios (HF, 55%; PHT, 69%), and 61% of HF and 58% of PHT patients had a prolonged RV isovolumic relaxation time. In the PHT group, RV diastolic parameters (E-wave deceleration time, E-A ratio, and isovolumic relaxation time) correlated significantly with pulmonary artery systolic pressure (P< .05). In the HF group, however, only tricuspid E-wave deceleration time correlated significantly with pulmonary artery systolic pressure, and HF patients with normal pulmonary artery systolic pressures had significantly lower tricuspid E-A ratios and prolonged RV isovolumic relaxation times compared with normal subjects. A close correlation existed between individual RV and LV diastolic parameters, suggesting that LV diastolic dysfunction may directly affect RV function, but there was no relation between LV size or systolic function and RV diastolic dysfunction. RV diastolic function is frequently abnormal in HF patients, and this is not related to elevated pulmonary artery systolic pressure alone, although high pulmonary artery pressure by itself also is associated with impaired RV diastolic function. Assessment of the role of right ventricular diastolic function in determining the symptoms and prognosis of heart failure is warranted.

497 Respiration induced motion of the kidneys: Implications for block design in whole abdominal radiotherapy (WAR)

<h3>Purpose</h3> Whole abdominal radiotherapy (WAR) is frequently used in the treatment of tumors of the ovary and endometrium. The limited radiation tolerance of several critical organs, especially the kidneys, is an important consideration in the design of WAR fields. Although renal blocking is standard for WAR, few guidelines exist in the literature to factor respiration-induced kidney motion into the design of these blocks. <h3>Methods</h3> Radiographs were obtained to measure kidney excursion under forced respiratory conditions in 6 patients (10 visualized kidneys). Intravenous contrast was administered and AP films were obtained at maximum inspiration and expiration. A horizontal reference line was drawn at the bottom of the L3 vertebral body and the excursion of each kidney was determined relative to this line. The kidney position on the actual treatment simulation film was also determined using this technique. These excursion movements were incorporated into the design of an idealized block to account for all phases of respiration. <h3>Results</h3> The range of excursion for the left kidney was 1–32mm and for the right kidney was 3–14mm. In a worst case scenario, the left kidney block required an additional 14mm above and 32mm below the renal silhouette on the simulation film. The corresponding values for the right kidney were 17mm and 10mm, respectively. <h3>Conclusions</h3> Although kidney motion under forced respiratory conditions is not representative of typical treatment conditions, the data highlight the possibility of significant renal movement during treatment. These factors must be kept in mind when customizing renal blocks.

Are tidal breathing indices useful in infant bronchial challenge tests?

Tidal breathing indices have been used to assess histamine-induced airway obstruction in adults and children. The aim of this study was to see whether they could be used to assess histamine challenge in infants. Tidal flow during quiet breathing was measured using a face mask and pneumotachograph and maximum flow at functional residual capacity (VmaxFRC) was measured from partial forced expirations in 18 sleeping, sedated infants who responded to histamine challenge and in 18 nonresponders. The tidal indices calculated were inspiratory and expiratory time (ti and te), tidal peak expiratory flow (PEF), mean tidal expiratory flow rate (VT/te) and the expiratory time constant of the respiratory system (trs). The time to maximal expiration divided by expiratory time (tme/te) and 2 revised forms of this index (tme(a)/te and tme(b)/te) were also calculated. Recordings of tme(a) and tme(b) were taken at 95% of peak tidal expiratory flow, before and after the peak, respectively. In nonresponders, there was an insignificant mean rise in VmaxFRC of 11.8% but no change in any tidal index. In responders, the mean percentage fall in VmaxFRC was 43.3% (range, -31 to -81%); trs fell from 0.61 s to 0.51 s (P < 0.05) and breathing frequency and mean tidal expiratory flow rate increased from 34.0 to 37.5 min-1 (P < 0.01) and from 66.6 to 72.6 mL.s-1 (P < 0.05), respectively, suggesting that infants had adopted a strategy of active expiration in response to bronchial challenge. There was no change either in tme/te or in the revised indices after challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantification of the Effects of Respiration and Parallax on Inferior Vena Caval Filter Position

The change in inferior vena caval (IVC) filter position at follow-up relative to the filter position at implantation has been used as a criterion for evaluation and comparison of these devices. Perceived changes in filter position may be due to respiratory movement and/or changes in parallax between the initial and follow-up imaging studies. In this study the authors evaluated and attempted to quantify the effects of respiratory movement and parallax. After placement of an IVC filter, radiographs of the abdomen were taken at maximum inspiration and maximum expiration in 30 patients. The effect of parallax on apparent filter movement was studied by using a phantom. The average filter movement on inspiration/expiration radiographs (corrected for magnification) was 3.6 mm +/- 2.2. An 8.5-mm maximal change secondary to parallax was seen in the phantom study. When follow-up images are obtained, efforts should be made to closely reproduce patient positioning and patient respiration to reduce errors in the interpretation of filter migration.

Lung volumes and forced ventilatory flows

Lung volumes are subdivided into static and dynamic lung volumes. Static lung volumes are measured by methods which are based on the completeness of respiratory manoeuvres, so that the velocity of the manoeuvres should be adjusted accordingly. The measurements taken during fast breathing movements are described as dynamic lung volumes and as forced inspiratory and expiratory flows. ### 1.1 Static lung volumes and capacities The volume of gas in the lung and intrathoracic airways is determined by the properties of lung parenchyma and surrounding organs and tissues, surface tension, the force exerted by respiratory muscles, by lung reflexes and by the properties of airways. The gas volumes of thorax and lung are the same except in the case of a pneumothorax. If two or more subdivisions of the total lung capacity are taken together, the sum of the constituent volumes is described as a lung capacity. Lung volumes and capacities are described in more detail in § 2. #### 1.1.1 Determinants Factors which determine the size of the normal lung include stature, age, sex, body mass, posture, habitus, ethnic group, reflex factors and daily activity pattern. The level of maximal inspiration (total lung capacity, TLC) is influenced by the force developed by the inspiratory muscles (disorders include e.g. muscular dystrophy), the elastic recoil of the lung (disorders include e.g. pulmonary fibrosis and emphysema) and the elastic properties of the thorax and adjacent structures (disorders include e.g. ankylosis of joints). The level of maximal expiration (residual volume, RV) is determined by the force exerted by respiratory muscles (disorders include e.g. muscle paralysis), obstruction, occlusion and compression of small airways (disorders include e.g. emphysema) and by the mechanical properties of lung and thorax (disorders include diffuse fibrosis, kyphoscoliosis). Assessing the total lung capacity is indispensable in establishing a restrictive ventilatory defect or in diagnosing abnormal lung distensibility, as may occur in patients …