Comparison of two new methods for the measurement of lung volumes with two standard methods

BACKGROUND: The two most commonly used methods for the measurement of lung volumes are helium dilution and body plethysmography. Two methods have been developed which are both easier and less time consuming to perform. Mathematical modelling uses complex calculations from the flow-volume loop to derive total lung capacity (TLC), and the nitrogen balance technique uses nitrogen from the atmosphere to calculate lung volume in a similar way to helium dilution. This study was designed to compare the two new methods with the two standard methods. METHODS: Sixty one subjects were studied, 23 with normal lung function, 17 with restrictive airway disease, and 21 with obstructive ventilatory defects. Each subject underwent repeated measurements of TLC by each of the four methods in random order. Reproducible values were obtained for each method according to BTS/ARTP guidelines. Bland-Altman plots were constructed for comparisons between the methods and paired t tests were used to assess differences in means. RESULTS: Bland-Altman plots showed that the differences between body plethysmography and helium dilution fell into clinically acceptable ranges (agreement limits +/-0.9 l). The agreement between mathematical modelling or the nitrogen balance technique and helium dilution or body plethysmography was poor (+/-1.8-3.4 l), especially for subjects with airflow obstruction. CONCLUSIONS: Neither of the new methods agrees sufficiently with standard methods to be useful in a clinical setting.     

Pattern of lung volumes in patients with sighing breathing.

BACKGROUND--Sighing breathing is observed in subjects suffering from anxiety with no apparent organic disease. METHODS--Lung volumes and expiratory flow rates were measured in 12 patients with a sighing pattern of breathing and in 10 normal subjects matched for age, gender, and anthropometric data. In both groups the measurements were made by spirographic and plethysmographic techniques. In normal subjects functional residual capacity (FRC) and residual volume (RV) were measured during normal breathing and again during simulated sighing breathing to exclude technical artifacts resulting from hyperventilation during measurement by the helium closed circuit method. RESULTS--Patients with a sighing pattern of breathing had a normal total lung capacity (TLC) but significantly different partitioning of lung compartments compared with normal subjects. The vital capacity (VC) was lower when measured by both spirographic and plethysmographic methods and RV was higher. The forced expiratory volume in one second (FEV1) was also lower in patients with sighing breathing. The FEV1/VC and the maximal expiratory flow rates at 50% and at 25% of the forced vital capacity (V50 and V25) were normal and similar in both groups. In normal subjects there were no differences in RV when measured during quiet or simulated sighing breathing. CONCLUSIONS--Subjects with sighing breathing have a normal TLC with a higher RV and lower VC than normal subjects. There was no obvious physiological or anatomical explanation for this pattern.     

Static lung volumes in healthy subjects assessed by helium dilution during occlusion of one mainstem bronchus.

BACKGROUND--Single lung function is usually assessed by radioisotopes or, more rarely, by bronchospirometry in which a double lumen catheter is used to separate ventilation of the two lungs. The latter is more precise but less comfortable. An alternative bronchoscopic method is described for determining the volume of a single lung. METHODS--One mainstem bronchus was temporarily occluded with an inflatable balloon during fibreoptic bronchoscopy in 12 healthy volunteers aged 18-29 years. The functional residual capacities (FRC) of the right, left, and both lungs were measured in duplicate by closed circuit helium dilution. Supplementary vital capacity (VC) manoeuvres permitted calculation of single lung capacities (TLC) and residual volumes (RV). RESULTS--The standard deviation of a single determination of capacities of the right, left, and both lungs were: TLC, 80, 96, and 308 ml; VC, 56, 139, 171 ml; FRC, 131, 74, and 287 ml; RV, 112, 185, and 303 ml, respectively. The sum of the right and left unilateral TLC was not different from bilateral TLC (6.12 v 5.95 l) and the sum of the unilateral FRC was not different from the bilateral FRC (2.60 v 2.78 l). The sum of the unilateral VC was lower than bilateral VC (4.52 v 4.80 l), that of the unilateral RV was higher than bilateral RV (1.60 v 1.16 l). For all subdivisions of lung volume, the right lung was larger than the left. The most common complaint was substernal discomfort during complete exhalation. Oxygen saturation rarely fell below 90%. CONCLUSIONS--Temporary occlusion of a mainstem bronchus in normal subjects is safe, relatively simple, and allows fairly precise and accurate measurements of unilateral static lung volumes. Occlusion at TLC, however, probably prevents proper emptying of the non-occluded lung.     

The lung volume at which shunting occurs with inhalation anesthesia

The relationship between functional residual capacity (FRC) and shunt development with halothane anesthesia in 18 nonobese surgical patients (age, 21-34 yr) was studied. FRC was measured by helium dilution, and intrapulmonary shunt was distinguished from ventilation-perfusion inequality by multiple tracer inert gas elimination analysis. Awake supine FRC was 34.6 +/- 6.6% (mean +/- SD) of total lung capacity (TLC), and closing capacity (CC) was 29.8 +/- 5.3% of TLC. Anesthesia, muscle paralysis, tracheal intubation, and mechanical ventilation produced an average 14.6 +/- 13.3% FRC reduction to an average anesthesia FRC 29.8% of TLC (P = 0.002). Shunt increased from 1.2% +/- 1.5% awake to 8.6 +/- 8.3% during anesthesia (P = 0.005). A nonlinear relationship was found between shunt and FRC/TLC so that anesthetized subjects with an FRC less than awake CC had an average 11.4 +/- 8.3% shunt, whereas subjects with an FRC greater than CC had a 2.4 +/- 2.8% shunt (P = 0.025). Nonsmokers developed shunt only if FRC was less than CC. Smokers showed a significantly higher shunt for a given (FRC-CC)/TLC compared to nonsmokers (P less than 0.001). The slope of the regression of shunt on BMI (body mass index = weight/height2) showed a significant increase during anesthesia (P = 0.005), and smokers had a significantly higher slope compared to nonsmokers (P = 0.001). These findings suggest a gravity-dependent mechanism for intrapulmonary shunting during anesthesia. Therefore, shunting was due to dependent regional lung volume reduction associated with an FRC decrease to less than closing capacity. The enhanced intrapulmonary shunting in smokers may have been related to the increased dependent regional residual volume associated with smoking.     

The diaphragmatic compound muscle action potentials (DCMAPs) at different lung volumes--a prospective electrophysiological study of the respiratory system

Phrenic nerve conduction study and measurements of static lung volumes such as functional residual capacity (FRC), total lung capacity (TLC) and residual volumes (RV) using body plethysmography were carried out in 31 normal healthy male subjects (31 +/- 8 years). The objective was to correlate changes in latency, amplitude, duration and area of diaphragmatic compound muscle action potential (DCMAPs) with lung volumes and changes in them with changes in postures. The mean phrenic nerve latency did not show any significant change with lung volumes or postures, but the latency and height of the subject had a significant correlationship (r = 0.68). The peak to peak amplitude of DCMAP showed a significant relationship with the quantitative lung volumes (r = 0.65). The amplitude was significantly higher and duration reduced (p < 0.001) at TLC as compared with those at measured FRC and RV in both sitting and supine postures. The area under the curve did not change significantly. Similarly, amplitudes and latency did not show any significant relation with other anthropometric parameters. The study evaluates a new quantitative relationship between DCMAPs amplitude and lung volumes. This may be carefully used along with other clinical parameters in critically ill patients for an early weaning from ventilator. Posture exerts minimal influence on DCMAPs amplitude; since DCMAPs amplitudes depends on the position of the diaphragm which in turn depends on dipolic potential, its electromagnetic fields and its moving angle subtends at the recording electrode, one can confidently use it to predict lung volume in respiratory failure due to neuromuscular diseases where subjective lung function assessment is impossible. However, a further study is in process in the critical care unit to confirm its utility.     

Difference between functional residual capacity and elastic equilibrium volume in patients with chronic obstructive pulmonary disease.

BACKGROUND: A study was performed to determine the elastic equilibrium volume (Vr) of the respiratory system in patients with chronic obstructive pulmonary disease (COPD). METHODS: Voluntary relaxed expiration from total lung capacity (TLC) was studied in three groups of subjects: seven patients with severe chronic airways obstruction (COPD), 10 normal subjects, and 15 subjects with restrictive disease. RESULTS: In the normal subjects and the patients with restrictive disease voluntary relaxed expiration from TLC stopped close to end tidal volume (FRC) and the volume expired in this manoeuvre was less than that expired in a slow vital capacity manoeuvre (SVC). In the patients with COPD the voluntary relaxed expiration continued beyond the end tidal volume (FRC) and the volume expired was not different from the SVC. Oesophageal (pleural) pressures and surface diaphragmatic EMG recordings in the patients with COPD supported the premise that relaxation was achieved. CONCLUSIONS: In patients with COPD, end tidal volume (FRC) is higher than the elastic equilibrium volume, Vr, of the respiratory system. This is in contrast to patients with restrictive disease and normal subjects in whom end tidal volume (FRC) is close to Vr. This study shows that, in patients with severe chronic obstructive pulmonary disease, Vr is at least as small as residual volume (RV).     

Effects of pneumothorax or pleural effusion on pulmonary function.

The effects of pneumothorax or pleural effusion on respiratory function as measured by the commonly applied tests were investigated by studying 13 patients (six with pneumothorax, seven with effusion) with and, as far as possible, without air or fluid in the pleural cavity. Measurements included spirometric volumes, carbon monoxide transfer factor (TLCO), and KCO by the single breath method, maximum expiratory flow-volume curves, and subdivisions of lung volume estimated by both inert gas dilution and body plethysmography. In patients with pneumothorax "pleural volume" was estimated as the difference between lung volumes measured by dilution and thoracic gas volume measured by plethysmography. In patients with effusion the change in "pleural volume" was equated with the volume of fluid subsequently aspirated. "Total thoracic capacity" (TTC) was estimated by adding total lung capacity (TLC) measured by dilution and "pleural volume." Both effusion and pneumothorax produced a restrictive ventilatory defect with reductions of vital capacity, functional residual capacity, and TLC. In the patients with effusion TTC fell after aspiration, suggesting that the pleural fluid produced relative expansion of the chest wall as well as compression of the lung. In patients with pneumothorax, however, there was no difference in TTC with and without air in the pleural space. In the presence of pleural air or fluid there was a slight decrease in TLCO and increase in KCO, with a small but significant increase in the rate of lung emptying during forced expiration.     

Estimation of lung volumes from chest radiographs using shape information.

The cross-sectional shapes of the chest and its contained structures have been assessed in post-mortem anatomical sections and from computerised tomographic scans in living subjects. These shapes are described by simple equations that can be used to increase the accuracy of measuring lung volumes from chest radiographs. Radiographic estimates of total lung capacity, using the equations, were compared with plethysmographic and single-breath helium dilution measurements in 35 normal subjects. The postures commonly used for taking chest radiographs were found, on average, to decrease total lung capacity (TLC) and to increase residual volume by about 200 ml when compared with the sitting positions used for the other two measurements (studies made in 18 of the subjects). After correction for this effect, the radiographic estimates of TLC, which measure the displacement volume of the lung, exceeded the plethysmographic estimates of contained gas volume by a mean of 720 ml, which was taken as the volume of tissue, blood, and water in the lungs. The single-breath dilution estimates of TLC fell short of the plethysmographic values by a mean of 480 ml, taken as the volume of contained gas that was inaccessible to helium in 10 seconds. The tomographic studies suggested that the radiographic technique of measuring lung displacement volumes has an accuracy of +/- 210 ml. The method is rapid and simple to use and has intra- and inter-observer variabilities of less than 1% and less than 5% respectively.     

Lung volumes in normal Cantonese subjects: preliminary studies.

Measurements of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC ratio, functional residual capacity (FRC), total lung capacity (TLC), residual volume (RV), and RV/TLC ratio have been made in 331 normal Cantonese subjects (134 male and 197 female). The results have been expressed in multiple regression equations relating the volumes to age, height, and weight and have been compared with those of other workers. Lung volumes obtained in this study are in general lower for Chinese subjects than those reported for Caucasians. Similar findings for FVC were reported by Chuan and Chia (1969) in Singapore and by Wu and Yang (1962) in Taiwan. Significant differences, however, are noted for FRC, TLC, RV, and RV/TLC between our findings and those of Chuan and Chia. Our series is unbalanced because of an uneven distribution of age groups. In fact in none of the reported studies on Chinese subjects, including that of da Costa (1971), is the series large or balanced. Clearly, further research is required in this ethnic group to get more reliable predictive formulae for lung volumes.     

Lung mechanics after cardiac valve replacement.

Fourteen patients undergoing single aortic or mitral valve replacement had measurements made of lung volumes, static pressure-volume (P-V) relationships, and conductance-pressure relationships during deflation before operation and again between one and two years later. At follow-up, total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), and static tidal compliance (slope of static P-V deflation line for one litre above FRC) had increased significantly, in association with a decrease in heart size. There was a change in the shape and position of some P-V curves both in the aortic and mitral patients. In the patients with aortic disease P-V deflation curves shifted to the left after operation. In the patients with mitral disease the P-V deflation curves before operation crossed those measured after operation, so that at high lung volumes recoil became less after operation, but at low lung volumes recoil increased. Conductance had increased at high lung volumes. The data suggest that in longstanding pulmonary congestion, airways are more rigid making them less distensible at high and less compressible at low transpulmonary pressures than after operation when congestion has been at least partly relieved.     

Lung mechanics in subjects showing increased residual volume without bronchial obstruction.

Fourteen subjects showing an increase of residual volume (RV) without any clinical or functional signs of bronchial obstruction were studied. Maximum expiratory flow volume (MEFV) curves were obtained with a pressure-corrected volume plethysmograph. Static pressure-volume curves were obtained by stepwise interruption of a slow expiration from total lung capacity (TLC) to RV. Static compliance was measured by the slope of pressure-volume curve between functional residual capacity (FRC) and FRC+20% of TLC. Maximum flow static recoil (MFSR) curves were constructed by plotting MEF obtained from MEFV curves against elastic pressure (Pst) obtained from pressure-volume curves at the same lung volumes. Most patients demonstrated a decrease of MEF 50% and 25% of VC. From the MFSR curves it was clear that this reduction was not the result of increased airways resistance, but rather of loss of elastic recoil. Most patients showed a significant decrease of Pst at different volumes and changes seem likely to be evidence of emphysema.     

Effect of salbutamol on lung function and chest wall volumes at rest and during exercise in COPD

BACKGROUND: Inhaled bronchodilators can increase exercise capacity in chronic obstructive pulmonary disease (COPD) by reducing dynamic hyperinflation, but treatment is not always effective. This may reflect the degree to which the abdomen allows dynamic hyperinflation to occur.Method: A double blind, randomised, crossover trial of the effect of 5 mg nebulised salbutamol or saline on endurance exercise time was conducted in 18 patients with COPD of mean (SD) age 67.1 (6.3) years and mean (SD) forced expiratory volume in 1 second (FEV1) of 40.6 (15.0)% predicted. Breathing pattern, metabolic variables, dyspnoea intensity, and total and regional chest wall volumes were measured non-invasively by optoelectronic plethysmography (OEP) at rest and during exercise. RESULTS: Salbutamol increased FEV1, forced vital capacity (FVC) and inspiratory capacity and reduced functional residual capacity (FRC) and residual volume significantly. OEP showed the change in resting FRC to be mainly in the abdominal compartment. Although the mean (SE) end expiratory chest wall volume was 541 (118) ml lower (p<0.001) at the end of exercise, the endurance time was unchanged by the bronchodilator. Changes in resting lung volumes were smaller when exercise duration did not improve, but FEV1 still rose significantly after active drug. After the bronchodilator these patients tried to reduce the end expiratory lung volume when exercising, while those exercising longer continued to allow end expiratory abdominal wall volume to rise. The change to a more euvolumic breathing pattern was associated with a lower oxygen pulse and a significant fall in endurance time with higher isotime levels of dyspnoea. CONCLUSIONS: Nebulised salbutamol improved forced expiratory flow in most patients with COPD, but less hyper-nflated patients tried to reduce the abdominal compartmental volume after active treatment and this reduced their exercise capacity. Identifying these patients has important therapeutic implications, as does an understanding of the mechanisms that control chest wall muscle recruitment.     

Comparison of lung volume measurements in individuals with spinal cord injury by two different methods

BACKGROUND/OBJECTIVE: Few detailed studies have been performed among subjects with spinal cord injury (SCI) using whole body plethysmography for measurement of static lung volumes. Because abdominal gas volumes and respiratory patterns among subjects with varying levels of SCI may differ significantly from able-bodied individuals, methodological concerns related to this technique could conceivably lead to inaccuracies in lung volume measurements. The purpose of this study was to compare lung volume parameters obtained by whole body plethysmography with those determined by the commonly used nitrogen washout technique among individuals with SCI. PARTICIPANTS: Twenty-nine clinically stable men, 14 with chronic tetraplegia (injury C4-C7) and 15 with paraplegia (injury below T5) participated in the study. METHODS: Lung volumes were obtained using whole body plethysmography and the open-circuit nitrogen washout technique. Within both study groups, data were evaluated by the paired Student's t test and by determination of correlation coefficients. RESULTS: No statistically significant differences for any lung volume parameter were found within either group. In subjects with tetraplegia on paraplegia, respectively, strong correlation coefficients were found for measurements of total lung capacity (.86 and .97), functional residual capacity (.87 and .96), and residual volume (.77 and .85). CONCLUSION: These findings indicate that body plethysmography is a valid technique for determining lung volumes among subjects with SCI. Because airway resistance measurements can also be obtained during same study sessions for assessment of airway caliber and bronchial responsiveness, body plethysmography is a useful tool for examining multiple aspects of pulmonary physiology in this population.     

The effect of ketamine on the functional residual capacity in young children

The effect of ketamine on the functional residual capacity (FRC) was measured in nine ASA class I children prior to elective surgery. FRC was determined by the closed-circuit helium dilution method on the day prior to surgery in the awake state and also following induction of anesthesia on the day of the operation. Anesthesia consisted of ketamine by continuous intravenous infusion following preanesthetic sedation with atropine and triclofos or flunitrazepam. There were no significant differences in FRC between the measurements in the awake state and anesthetized (392 +/- 43 SEM ml, and 411 +/- 53 SEM ml, respectively), and the authors conclude that ketamine does not affect resting lung volume in young children.     

Errors in the measurement of total lung capacity in chronic obstructive lung disease.

The standard plethysmographic method of measuring total lung capacity (TLC) has been reported to result in spuriously high estimates in patients with severe airway obstruction. The helium-dilution method is known to underestimate TLC in the same patients. To determine the magnitude of these possible errors we measured TLC by four methods in 20 patients with varying degrees of chronic obstructive lung disease and in 11 normal subjects. TLC was measured by (1) helium dilution (TLCHe); (2) a volume-displacement body plethysmograph, box volume being plotted against mouth pressure (TLCm); (3) the same body plethysmograph with volume plotted against pressure measured with an oesophageal balloon (TLCes); and (4) a radiological technique (TLCxr). In normal subjects there was no difference between TCLm (6.57 +/- 1.20) and TLCes (6.51 +/- 1.24). In the patients with chronic obstructive lung disease TLCm gave results significantly higher than those of any other method. If TLCes is taken as the closest estimate of true TLC, TLCm consistently overestimates and TLCHe underestimates TLC. There was no relationship between the degree of airway obstruction and (TLCm - TLCes) but there was between (TLCes - TLCHe) and severity of airway obstruction. We conclude that using mouth pressure in the plethysmographic measurement of TLC in patients with chronic obstructive lung disease results in consistent but slight overestimation of TLC.     

Radiographic measurement of total lung capacity in acute asthma.

The thoracic cage appears to be large during attacks of asthma. Lung volume measurements by body plethysmography and helium dilution have suggested that total lung capacity may be increased during an acute attack of asthma, but doubt has been cast on the accuracy of these measurements in the presence of airflow obstruction. The change in total lung capacity has therefore been investigated during and after an acute attack of severe asthma in 32 patients by a radiographic technique. There was a small decrease (0.29 l) in mean total lung capacity between admission and follow up, though a quarter of the subjects showed a slight increase. There was no correlation between change in total lung capacity and change in expiratory flow rates, arterial carbon dioxide tension on admission, body mass index, and length of stay in hospital. Our findings agree with previous reports of a decrease in total lung capacity with improving airway obstruction, but the changes were small and inconsistent.     

Evaluating the Use of CT-Derived Lung Volumes in Donor-Recipient Lung Size Matching for Lung Transplantation in Patients With Interstitial Lung Disease and/or Idiopathic Pulmonary Fibrosis

PurposeThis study aims to assess the efficacy of current measurement strategies for lung sizing and the feasibility of future use of computed tomography (CT)-derived lung volumes to predict a donor-recipient lung size match during bilateral lung transplants.MethodsWe reviewed the data of 62 patients who underwent bilateral lung transplantation for interstitial lung disease and/or idiopathic pulmonary fibrosis from 2018 to 2019. Data for recipients was retrieved from the department's transplant database and medical records, and the donor's data was retrieved from the DonorNet. The data included demographic data, lung heights, measured total lung capacity (TLC) from plethysmography for recipients and estimated TLC for donors, clinical data, and CT-derived lung volumes in both pre- and post-transplant recipients. The post-transplant CT-derived lung volume in recipients was used as a surrogate for donor lung CT volumes due to inadequate or poor donor CT data. Computed tomography–derived lung volumes were calculated using thresholding, region growing, and cutting techniques on Computer-Aided Design and Mimics (Materialise NV, Leuven, Belgium) programs. Preoperative CT-derived lung volumes in recipients were compared with the plethysmography TLC, Frustum Model, and donor-predicted TLC. The ratio of the recipient's pre-and postoperative CT-derived volumes, the ratio of preoperative CT-derived lung volume, and donor-estimated TLC were studied to detect a correlation with 1-year outcomes.ResultsThe recipient preoperative CT-derived volume correlated with the recipient preoperative plethysmography TLC (Pearson correlation coefficient [PCC] of 0.688) and with the recipient Frustum model volume (PCC of 0.593). The recipient postoperative CT-derived volume correlated with the recipient's postoperative plethysmography TLC (PCC of 0.651). There was no statistically significant correlation between recipients' CT-derived pre- or postoperative volume with donor-estimated TLC. The ratio of preoperative CT-derived volume to donor-estimated TLC correlated inversely with the length of ventilation (P value = .0031). The ratio of postoperative CT-derived volume to preoperative CT-derived volume correlated inversely with delayed sternal closure (P = .0039). No statistically significant correlations were found in evaluating outcomes related to lung oversizing in the recipient (defined as a postoperative to preoperative CT-derived lung volume ratio of >1.2).ConclusionsGenerating CT-derived lung volumes is a valid and convenient method for evaluating lung volumes for transplantation in patients with ILD and/or IPF. Donor-estimated TLC should be interpreted carefully. Further studies should derive donor lung volumes from CT scans for a more accurate evaluation of lung size matching.     

Effects of barbiturate anesthesia on functional residual capacity and ribcage/diaphragm contributions to ventilation

The effect of iv methohexital infusion anesthesia on functional residual capacity (FRC) (helium dilution) in 14 surgical patients (age 23 to 59 years) was determined. Eight subjects were studied wearing an inflatable mask, sealed with surgical lubricant. They showed a mean +/- SD 3.5 +/- 6.4% FRC decrease (no significance). Six subjects studied via mouthpiece awake and via endotracheal tube during anesthesia showed a mean 22 +/- 19% reduction in FRC, significantly greater than face mask studies (P less than 0.05). The greatest FRC decrease occurred in subjects with repetitive or protracted coughing after intubation. The serum methohexital level was 6.6 +/- 3.6 micrograms/ml for intubated patients, and 6.0 +/- 1.1 micrograms/ml in those with face mask (no significance). The depth of anesthesia was sufficient to produce a 50% reduction in ventilatory response to CO2 rebreathing, from 15.8 to 8.7 l/min/% CO2. Respitrace plethysmography indicated a 38 +/- 12% ribcage contribution to tidal volume during quiet breathing, which increased to 47 +/- 14% with CO2 breathing (end-tidal FCO2 9-10%). There was no dimunition of ribcage contribution during anesthesia in either group, irrespective of CO2 concentration. The authors interpret their findings to indicate that iv methohexital anesthesia does not produce FRC reduction, in contrast to an inhaled anesthetic such as halothane. It is proposed that this difference may be related to maintenance of coordinated ribcage/diaphragm muscle activity, because ribcage activity is markedly suppressed by halothane. In addition, it is proposed that FRC reduction in intubated subjects was the result of a confounding variable, namely coughing in response to the endotracheal tube.     

Pulmonary function abnormalities in children with sickle cell disease

BACKGROUND: Adults with sickle cell disease (SCD) have restrictive lung function abnormalities which are thought to result from repeated lung damage caused by episodes of pulmonary vaso-occlusion; such episodes start in childhood. A study was therefore undertaken to determine whether children with SCD have restrictive lung function abnormalities and whether the severity of such abnormalities increases with age. METHODS: Sixty four children with SCD aged 5-16 years and 64 ethnic matched controls were recruited. Weight and sitting and standing height were measured, and lung function was assessed by measurement of lung volumes and forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEF) before and after bronchodilator. RESULTS: Compared with the control subjects, the children with SCD had lower mean (SD) sitting height (69 (6.3) cm v 73 (7.7) cm; p=0.004), sitting:standing height ratio (0.50 (0.02) v 0.51 (0.01); p<0.0001), weight (33 (10.9) kg v 41 (14.9) kg; p=0.001), functional residual capacity measured by a helium gas dilution technique (1.2 (0.3) l v 1.3 (0.4) l; p=0.04), FEV1 (1.5 (0.5) l v 1.9 (0.7) l; p=0.0008), FVC (1.7 (0.6) l v 2.1 (0.8) l; p=0.001), and PEF (3.9 (1.3) l/s v 4.8 (1.5) l/s; p=0.0004). The effect of age on lung function differed significantly between the children with SCD and the controls for total lung capacity and vital capacity measured by plethysmography and functional residual capacity measured by helium gas dilution. CONCLUSION: Lung function differs significantly in children with SCD compared with ethnic matched controls of a similar age. Our results suggest that restrictive abnormalities may become more prominent with increasing age.     

Relation between nocturnal symptoms and changes in lung function on lying down in asthmatic children.

Nocturnal symptoms are common in young asthmatic children. Such symptoms may be caused by increased impairment of lung function when they adopt the supine posture. Thirty one children aged 2.8-8.3 years were studied, of whom 20 had asthma (10 with frequent nocturnal symptoms) and 11 had no respiratory problems (control subjects). Peak expiratory flow (PEF) was measured with a Wright's peak flow meter and functional residual capacity (FRC) by a helium gas dilution technique after 30 minutes of lying supine; the values were compared with FRC measured sitting and PEF standing. Peak flow fell significantly on adoption of the supine posture in the asthmatic children, but there was no difference in this fall between the asthmatic children with and without nocturnal symptoms. FRC also fell on adoption of the supine posture, but the decrease in FRC was significant only in the control children and the asthmatic children without nocturnal symptoms. The failure to find a greater fall in PEF or a greater change in FRC on adoption of the supine posture among asthmatic children with nocturnal symptoms suggests that mechanisms other than increased impairment of lung function are responsible for nocturnal asthma.