Reference value for expiratory time constant calculated from the maximal expiratory flow-volume curve.

BACKGROUND: The expiratory time constant (RCEXP), which is defined as the product of airway resistance and lung compliance, enable us to assess the mechanical properties of the respiratory system in mechanically ventilated patients. Although RCEXP could also be applied to spontaneously breathing patients, little is known about RCEXP calculated from the maximal expiratory flow-volume (MEFV) curve. The aim of our study was to determine the reference value for RCEXP, as well as to investigate the association between RCEXP and other respiratory function parameters, including the forced expiratory volume in 1 s (FEV1)/ forced vital capacity (FVC) ratio, maximal mid-expiratory flow rate (MMF), maximal expiratory flow at 50 and 25% of FVC (MEF50 and MEF25, respectively), ratio of MEF50 to MEF25 (MEF50/MEF25). METHODS: Spirometric parameters were extracted from the records of patients aged 15 years or older who underwent pulmonary function testing as a routine preoperative examination before non-cardiac surgery at the University of Tokyo Hospital. RCEXP was calculated in each patient from the slope of the descending limb of the MEFV curve using two points corresponding to MEF50 and MEF25. Airway obstruction was defined as an FEV1/FVC and FEV1 below the statistically lower limit of normal. RESULTS: We retrospectively analyzed 777 spirometry records, and 62 patients were deemed to have airway obstruction according to Japanese spirometric reference values. The cut-off value for RCEXP was 0.601 s with an area under the receiver operating characteristic curve of 0.934 (95% confidence interval = 0.898-0.970). RCEXP was strongly associated with FEV1/FVC, and was moderately associated with MMF and MEF50. However, RCEXP was less associated with MEF25 and MEF50/MEF25. CONCLUSIONS: Our findings suggest that an RCEXP of longer than approximately 0.6 s can be linked to the presence of airway obstruction. Application of the concept of RCEXP to spontaneously breathing subjects was feasible, using our simple calculation method.

Evaluación de flujos y volúmenes dinámicos en pacientes con compromiso muscular respiratorio / Dynamic flows and volumes evaluation in patients with respiratory muscle impairment

Spirometry measures the forced expiratory volumes and flows. In patients with neuromuscular disease, these are altered since there is some respiratory muscle involvement. The usefulness of this test is based on the interpretation of the shape of the flow / volume loop and values of spirometric variables. In patients with neuromuscular disease, Forced Vital Capacity is the most used especially for its prognosis value.

La espirometría mide volúmenes y flujos espiratorios forzados. En los pacientes con enfermedad neuromuscular (ENM) estos se ven alterados debido al compromiso muscular respiratorio. La utilidad de este examen se basa en la interpretación de la forma de la curva flujo/volumen y los valores de las variables espirométricas. En los pacientes con ENM la Capacidad Vital Forzada es la más utilizada ya que otorga valor pronóstico.

Fisiología de la curva flujo/volumen espirométrica / Flow-volume curve: its physiological basis

We describe physiological basis to explain flow/volume curve obtained by forced spirometry. The main factors involved are alveolar and intraluminal airway pressure and transthoracic pressure, whose interrelationship determines dynamic airway compression. Lung and thoracic elastic recoil pressure and lung volumes also participate.

Se describen las bases fisiológicas de la curva flujo/volumen obtenida mediante espirometría forzada. Los principales factores involucrados son la presión alveolar y de la vía aérea y la presión transtorácica, cuyo balance determina la compresión dinámica de la vía aérea. Además intervienen la presión de retracción elástica pulmonar y de la caja torácica y los volúmenes pulmonares.

Mid-term survival after abdominal aortic aneurysm surgery predicted by cardiopulmonary exercise testing.

BACKGROUND: Cardiopulmonary exercise (CPX) testing measures how efficiently subjects meet increased metabolic demand. This study aimed to determine whether preoperative CPX testing predicted postoperative survival following elective abdominal aortic aneurysm (AAA) repair. METHODS: Some 130 patients had CPX testing before elective open AAA repair. Additional preoperative, operative and postoperative variables were recorded prospectively. Median follow-up was 35 months. The correlation of variables with survival was assessed by single and multiple regression analyses. RESULTS: CPX testing identified 30 of 130 patients who had been unfit before surgery. Two years after surgery the Kaplan-Meier survival estimate was 55 per cent for the 30 unfit patients, compared with 97 per cent for the 100 fit patients. The absolute difference in survival between these two groups at 2 years was 42 (95 per cent confidence interval 18 to 65) per cent (P < 0.001). CONCLUSION: Preoperative CPX testing, combined with simple co-morbidity scoring, identified patients unlikely to survive in the mid-term, even after successful AAA repair.

Maximal expiratory flow volume curve in quarry workers.

Maximal Expiratory Flow Volume (MEFV) curves were recorded with a computerized Spirometer (Med Spiror). Forced Vital Capacity (FVC), Forced Expiratory Volumes (FEV), mean and maximal flow rates were obtained in 25 quarry workers who were free from respiratory disorders and 20 healthy control subjects. All the functional values are lower in quarry workers than in the control subject, the largest reduction in quarry workers with a work duration of over 15 years, especially for FEF75. The effects are probably due to smoking rather than dust exposure.

Comparison of normal infants and infants with cystic fibrosis using forced expiratory flows breathing air and heliox.

SUMMARY. The detection of early airway disease in infants with cystic fibrosis (CF) may lead to earlier intervention and an improved prognosis. We hypothesized that the ratio of maximal expiratory flows while breathing a mixture of helium and oxygen (heliox) and air, referred to as density dependence (DD), would identify early airway disease in infants with CF who have normal lung function. We also hypothesized that these infants with CF might be better differentiated from normal infants when the flows breathing heliox are compared instead of room air flows. We evaluated 10 infants with CF and 21 infants without CF and with normal lung function, defined as a forced vital capacity (FVC) and forced expiratory flows between 25-75% of expired volume (FEF(25-75)) of greater than 70% predicted (z-score > -2.0). Full forced expiratory maneuvers by the rapid thoracic compression technique were obtained while breathing room air and then heliox. Flow at 50% and 75% of expired volume (FEF(50), FEF(75)), FEF(25-75), and FVC were calculated from the flow volume curve with patients and control subjects breathing each gas mixture. The ratio of heliox to air flow at FEF(50) and FEF(75) was calculated (DD(50), DD(75)), and the point where the two flow-volume curves crossed (V(iso) V') was also measured. DD parameters did not distinguish the infants with CF from the infants without CF; length-adjusted FEF(50) breathing air was significantly lower in the infants with CF compared to the infants without CF (P < 0.05). Length-adjusted flows breathing heliox did not distinguish the two groups. We conclude that the lower FEF(50) value may reflect early airway obstruction in healthy infants with CF, and that measurements obtained with the less dense gas mixture did not improve detection of airway disease in this age group.

Application of chest high-resolution computer tomography in young children with cystic fibrosis.

SUMMARY. High-resolution computed tomography (HRCT) of the chest permits early detection of lung disease; two relevant scoring systems (Bhalla and Nathanson) have been developed to describe CF lung disease. Comparisons between the two scoring systems have not been made, and it is not known which system is more appropriate for young children, i.e., the age group where other objective markers are scarce. We reviewed the clinical findings, pulmonary function data, and HRCT of 16 children aged less than 12 years. The Bhalla scoring system had a better correlation with FEV(1) (r = -0.65, P = 0.012) than the Nathanson score (r = 0.53, P = 0.05). All children had bronchiectasis, including 5 with normal pulmonary function tests. The lower lobes were universally involved, and 5 children did not have any upper lobe disease. Four of these 5 children were aged less than 7 years. We conclude that the Bhalla scoring system is more applicable to young children than is the Nathanson system. Also, in this group of young children with CF, lower lobes are more commonly involved than upper lobes, which is in contrast to the classical teaching that CF lung disease begins in the upper lobes.

Relief of central airways obstruction following spinal release in a patient with idiopathic scoliosis.

SUMMARY. Patients with idiopathic scoliosis are reported to have a restrictive pattern on pulmonary function tests. A case is presented of a teenage girl with juvenile idiopathic scoliosis who had evidence of airways obstruction in addition to restriction on pulmonary function tests (PFT). Examination of flow-volume loops suggested central airways obstruction. At the time of induction of anesthesia for the initial spinal release surgery, a double-lumen endotracheal tube could not be passed, despite fiberoptic visualization, because of extreme deviation of the left main-stem bronchus. Postoperatively, PFT demonstrated improved flows at high lung volumes and normalization of the shape of the flow volume loop. We suggest that preoperative PFT may be used to predict which patients have central airways obstruction. This may lessen unanticipated problems with intubation at the time of surgery and may identify patients who may expect immediate improvement in lung function after scoliosis repair.

[Configurations of F-V curve and their transformation rule in COPD patients analysed with wave-speed theory].

This study sought to analyse the mechanism on the formation of configurations of F-V curve and their transformation rule in COPD and cor pulmonale patients with wave-speed theory. The F-V curves were measured in 90 COPD patients (43 with chronic bronchitis, 47 with emphysema) and 31 complicated with cor pulmonale, all of them were in the ameliorated period. The indices selected were FVC, V75, V50, V25. Both the measured value and the measured value/predicted value (%) of all indices showed chronic bronchitis > emphysema > cor pulmonale. Never was there the concave type of normal humans in the F-V curves of COPD and cor pulmonale patients; however, the convex type was much increased in the curves and the hyperbolic type specific to COPD and cor pulmonale appeared. The mechanisms of formation for plateau, convex and hyperbolic types were analysed with the wave-speed theory. In summary, the unifying rule for the transformation of F-V curve configuration from normal adolescents to old persons, smokers, COPD and cor pulmonale patients in various degrees can be outlined as, concave type normality convex type abnormality hyperbolic type. This implicates a unifying process of pulmonary functions from healthy state to weakness and from slight to serious abnormality.

[Tangent time constant and wave-speed mechanism of F-V curve configuration in smokers and clinical significance].

This study was conducted to explore the mechanical mechanism of the formation of F-V curve configuration with tangent time constant (tau 1) and wave-speed theory for smokers. F-V curves were measured on 22 passive smokers and 94 active ones. FVC, V75, V50 and V25 were obtained, and tangent time constants at high, mid, low lung volumes, tau t75, tau t50 and tau t25 were calculated, and analysed with wave-speed theory. The results showed that the chief changes taking place only in heavy smokers and convex type of F-V curve were: decreased V50 and V25; tau t25 > or = 1s; tau t75-tau t50 < tau t25 in "trumpet fashion" change; and tau t75 < tau t50 < tau t25 in "tower fashion" change. Then, tau t25 > or = 1s, tau t75-tau t50 < tau t25 and tau t75 < tau t50 < tau t25 were assigned as three tau t characters of smoking effect. They led to an increased convexity of the convex type of F-V curve, and reflected the decrease of small airway functions. Similar to the decrease of V50 and V25, they have important significance in assessing small airway functions and thus merit clinical use.

[A study on the changes of blood levels of type III procollagen and type IV collagen in relation to artery blood gas and lung function in patients with cor pulmonale].

This study was conducted to explore the changes of PC III (type III procollagen) and C IV (type IV collagen) in the serum in patients with chronic pulmonary heart diseases. The blood levels of PC III and C IV in 25 patients with chronic pulmonary heart diseases and 20 normal subjects were measured by radioimmunoassay and were analysed in relation with the artery blood gas and pulmonary function parameters. The results revealed that the blood levels of PC III and C IV in the patients were significantly higher than those in normal subjects, and were negatively correlated with PaO2, FEV1%, MBC and MMEF (P < 0.05, P < 0.01). The results suggest that the blood levels of PC III and C IV of patients with chronic pulmonary heart diseases are significantly increased and significantly correlated with pulmonary function damage and hypoxia.

Causes of allograft dysfunction after single lung transplantation for emphysema: extrinsic restriction versus intrinsic obstruction. Brigham and Women's Hospital Lung Transplantation Group.

BACKGROUND: A subset of patients with emphysema who have undergone single lung transplantation (SLT) may subsequently present with dyspnea, worsening airways obstruction, hypoxemia, and progressive chronic native lung hyperinflation. The leading cause of late allograft dysfunction is bronchiolitis obliterans syndrome (BOS). However, extrinsic restriction manifests with a similar clinical presentation and is an additional mechanism to consider. We describe the use of the inspiratory lung resistance (RLi) to distinguish a decline in respiratory status due predominantly to either extrinsic restriction or BOS. METHODS: We studied five patients who underwent SLT for emphysema between 1992 and 1995, in whom the diagnoses of BOS and extrinsic restriction were subsequently entertained. Forced expiratory volume in 1 second (FEV1), RLi, static lung compliance, elastic recoil pressure at total lung capacity (TLC), and the slope of the maximum flow static recoil (MFSR) plot were measured. RESULTS: All patients had severe airflow obstruction, with mean FEV1 0.98 +/- 0.24 liter (26 +/- 5% predicted), elevated static lung compliance, reduced elastic recoil pressure at TLC, and reduced slope of the MFSR plot. Three patients had "low" RLi (9.3-12.8 cm H20/L/sec). Obstruction was attributed predominantly to extrinsic restriction. These patients underwent lung volume reduction surgery (LVRS) on the native lung; improvements in pulmonary mechanics were observed at 6 months. In contrast, two patients had markedly elevated RLi (17.3 and 17.4 cm H2O/L/sec). Obstruction was attributed predominantly to intrinsic airway disease from BOS that was subsequently documented at autopsy. CONCLUSIONS: The RLi appears to be a useful adjunct to the clinical history in distinguishing a decline in respiratory status due predominantly to either BOS or extrinsic restriction in patients who have undergone SLT for emphysema. Determination of the mechanism of allograft dysfunction may allow the selection of an appropriate subset of patients who would benefit from LVRS.

[Significance of maximal midexpiratory time and F-V curve configuration in testing small airway function for smokers].

To evaluate the clinical significance of maximal midexpiratory time (MET) in testing small airway functions for smokers, the routine ventilatory functions, MET and F-V curve configurations were studied in 116 passive and light, heavy active smokers. Routine ventilatory functions and F-V curve configuration were determined with LR80 flow volume recorder. The MET was measured with FJD80 spirometer. The results showed that the distribution of convex type rose with the degree of smoking. In heavy smokers, the MET elongated to 127% of the predicted value and in the convex type F-V curve, it elongated to 120% of the predicted value; both were consistent with the decrease of corresponding V50, V25. This implied when MET elongated to 120%-130% of the predicted value in smokers, there had been slight disturbances in small airway functions. It is therefore suggested that MET and convex type F-V curve both are sensitive indices for testing small airway functions, thus it should be of clinical significance and be appropriate for general application.

[Comparative study of ventilatory functions of smokers with MTTp and F-V curve configuration].

To assess the clinical significance of partial mean transit time(MTTp) and F-V curve configuration for testing small airway functions in smokers, routine ventilatory functions, MTTp and F-V curve configuration were studied in 116 passive and active light, heavy smokers. Routine ventilatory functions and F-V curve configuration were determined with routine methods. MTTp were calculated with "convenient calculation". The results showed that the distribution of convex type of F-V curve rose with the degree of smoking. The decrease of V50, V25 and prologation of MTT45%-55%, MTT70%-80% in convex type were just correspondent with heavy smokers. The range of prolongation of MTT45%-55% and MTT70%-80% was 110%-120% of predicted value both in heavy smokers and convex type. These showed there were light disturbances in small airways. Therefore, the convex type, the prolongation of MTT45%-55% and MTT70%-80%, and the decrease of V50 and V25 should all be used as sensitive indices for testing small airway functions. The value of MTTp calculated with "convenient calculation" is accurate and easy-to-do so the method is appropriate for clinical application.

[Significance of specific time constant and F-V curve configuration in evaluating small airway function for smokers].

To evaluate the clinical significance of the specific time constant (S tau) and F-V curve configuration in testing small airway functions for smokers, routine ventilatory functions, S tau and F-V curve configuration were studied in 116 passive and light, heavy active smokers. Routine ventilatory functions and F-V curve configuration were determined with routine method. S tau were calculated from S tau = 1/V. The results showed that the distribution of convex type rose with the degree of smoking, and the decrease of V50, V25 and elongation of S tau 50, S tau 25 in convex type were just consistent with heavy smokers. The range of elongation of S tau 50 and S tau 25 was 120%-130% of predicted value in both heavy smokers and convex type. These showed there were slight disturbances in functions of small airways. Compared with COPD patients previously measured, their S tau 75, S tau 50, S tau 25 all prolongated to higher degree and meant both large and small airways were affected. Therefore, the convex type, elongation of S tau 50 and S tau 25, and decrease of V50 and V25 were sensitive indices for detecting small airway functions. They can be recommended for clinical application.

[Characteristics of chord time constant and F-V curve configuration in testing small airway functions for smokers].

UNLABELLED: To study the significance of chord time constant (tau ch) and F-V curve configuration in testing small airway function for smokers, the routine ventilatory functions, chord time constant (tau ch) and F-V curve configurations were studied in 116 passive and active (light, heavy) smokers. The tau ch was calculated with Knudson's method, tau ch = V/V. RESULTS: The distribution of convex type rose with the degree of smoking. The tau ch50 in heavy smokers and convex F-V curve prolongated to 130% of predicted value; tau ch50 in light smokers prolongated to 120%. These reflected that there were different degrees of disturbance in small airway functions of smokers and suggested that tau ch50 should be a sensitive and specific index for testing small airway functions. On the other hand, the tau ch75, tau ch50 and tau ch25 by the present authors previously measured in patients with chronic obstructive pulmonary diseases (COPD) all prolongated with the severity of the disease, which reflected that both large and small airways were affected. Therefore it is concluded that in terms of clinical implications the specificity of tau ch50 for small airway functions and the prolongation of tau ch with the severity of COPD are useful indexes.

Lung volume reduction surgery and airflow limitation.

Interest has recently been renewed in lung volume reduction surgery (LVRS) for end-stage emphysema. However, numerous questions about its role in the treatment of emphysema remain, including the clinical characteristics of optimal candidates and its mechanism of improvement in pulmonary function. In this report, we develop a mathematical analysis and graphic depiction of the mechanism of improvement in expiratory airflow and vital capacity. This analysis is based on consideration of the interaction between lung function and respiratory muscle function. We also reexamine previously published pulmonary mechanics in patients with alpha1-antitrypsin deficiency, chronic obstructive pulmonary disease, and asthma. We find a major determinant of airflow limitation common to these diseases is the ratio of residual volume to total lung capacity (RV/TLC). Moreover, RV/TLC is found to be the single most important determinant of the improvement in pulmonary function after LVRS. Regardless of the specific underlying lung disease, the impairment of airflow is due primarily to mismatch between the sizes of the lung and the chest wall, and the effects of LVRS are almost exclusively due to improvement of that match. This analysis can be used to develop testable hypotheses to guide patient selection for this procedure.

[Respiratory function and surgical reduction of lung volume]. / Fonction respiratoire et réduction chirurgicale du volume pulmonaire.

Emphysema is characterised by an enlargement of the terminal air spaces. Destructions of alveolar walls lead to a loss of the lung elastic recoil. The driving pressure for expiration is decreased and the outward forces acting on the bronchioles are lost, leading to bronchiolar collapse and airflow limitation. Hyperinflation of the lungs and overdistension of the chest wall cause the respiratory muscles to operate in unfavourable conditions. Patients with advanced emphysema have decreased quality of live: they are dyspneic at rest and are unable to perform exercise. Surgical excision of parts of diffusely emphysematous lungs (Lung Volume Reduction Surgery, LVRS) has been proposed since many years. Expansion of the remaining lung should increase lung elastic recoil and restore the outward forces on the bronchioles. It has been demonstrated that LVRS reduces dyspnea symptoms, improves exercise tolerance and enhances the quality of live. LVRS increases lung elastic recoil, airway conductance and maximal expiratory flow, reduces dynamic hyperinflation and improves the efficiency of the respiratory muscles. These improvements are maintained for at least 12 to 18 months. Preoperative evaluation, surgical-induced modifications of pulmonary functions and postoperative exercise training are exposed.

The use of the flow-volume loop in assessing the results of laryngotracheal reconstruction.

The difficult problem of assessing pre- and postoperative airway function in patients with laryngotracheal upper airway obstruction is discussed. A series of 26 patients with various forms of this problem is presented. The method of performing the flow-volume loop (FVL) is described and the theory behind the investigation is reviewed. Five of the series of 26 patients are described in detail as examples, and the advantages and disadvantages of this investigation are discussed fully. The FVL appears to be the only really objective test to assist the laryngotracheal reconstructive surgeon. It is easily performed in most cases and should form part of the diagnostic and postoperative workup.