Simple parametrizations of maximum expiratory flow-volume curves

Summary Four elementary mono-compartmental lung models yield parametrizations of Maximal Expiratory Flow-Volume curves of normal subjects. The respective analytical functions are fitted to the measured curves and the mathematically derived ventilation indices are compared with standard measured data. While individual values of resistance and compliance seem devoid of a simple physical interpretation, their product indeed matches the models.     

Partial expiratory flow-volume curves in infancy: technical aspects

We have constructed a simple pressure-jacket with which to produce passive forced expiration in sleeping, supine infants by thoraco-abdominal compression. During expiration, flow and volume were measured at the airway opening with a face-mask and pneumotachograph. From partial expiratory flow-volume (PEFV) curves, peak expiratory flow rate (PEFR) and maximum expiratory flow at a lung volume equal to the functional residual capacity (VmaxFRC) were obtained. Using the jacket in groups of normal and wheezy infants, we have assessed the effects on PEFR and VmaxFRC of variable inflation pressure, rate and duration of jacket inflation, timing of chest compression in relation to the breathing cycle and subject interaction with the compression manoeuvre. The within-subject reproducibility of PEFR and VmaxFRC was measured. Consistent values were produced by inflating the jacket within 100 ms at end inspiration to a pressure of 3-4 kPa and maintaining the inflation (in wheezy infants) for at least 1 s. The median within-subject coefficients of variation of PEFR and VmaxFRC for both normal infants and wheezy infants were 9 and 12% respectively. The technique is clearly reproducible and can provide information about intrathoracic airway function in infancy.     

Forced expiratory flow-volume curves during the application of lower-body negative pressure

Ten normal subjects were studied during supine rest and quiet standing, and when exposed, supine, to lower-body negative pressure (LBNP) of 30, 40 and 50 mmHg, each for a period of 7 min, in random order. Their partial and complete flow-volume curves, heart rate and blood pressure were recorded during the last 3 min in each condition. The expected reflex cardiovascular responses to the decrease in central blood volume during standing and during LBNP were seen. The forced vital capacity was somewhat greater during standing and during LBNP than while supine. The airflow variables measured from the flow-volume curve-except MEF25% (partial)--were significantly increased during progressive LBNP but did not reach the raised values found when the posture changed from supine to standing. The observations suggest that besides the redistribution of the central blood volume to the periphery, other factors must contribute to the increase in airflows during standing.     

Classification of maximal expiratory flow-volume types observed in non-smoking healthy young subjects

Pulmonary function tests were performed on 234 healthy non-smoking young subjects (189 males and 45 females free from respiratory and allergic symptoms). Maximal expiratory flow-volume (MEFV) curves were visually classified into five MEFV types: Type A, convex or straight flow changes; types B, C, and D, concave-convex-concave flow changes; and type E, sudden flow-fall and accompanying decreased flow rates at lower lung volumes. The reproducibility of MEFV patterns were shown by one way analysis of variance (ANOVA) of MEFV data obtained from 4 groups each consisting of 3-4 males and representing different MEFV types. Distribution of MEFV types was different between males and females; the rate of type A was higher in females than in males and those of types B and E were higher in males than in females. When analyzed in terms of three fractional flow rates, Fr-75, Fr-50, and Fr-25, these values could also be classified into 5 types similarly to the visual MEFV type analysis. It is concluded that MEFV type analysis is useful in assessing health conditions.     

Non-invasive forced expiratory flow-volume curves to measure lung function in cats

Forced expiratory flow-volume curves were performed in 15 cats using the non-invasive thoracic compression techniques developed for use in human infants. Cats breathed through a face mask and pneumotachygraph from which flow and volume were obtained. Thoracic compression was applied from an inflatable bag in a non-expandable jacket surrounding the animal. Bag inflation at end inspiration was initiated by a computer pulse to a pressurized chamber. Processed signals from the pneumotachygraph determined maximum-forced expiratory flow at lung volume equivalent to functional residual capacity (FRC), termed V'maxFRC. Different compression pressures were used, and the highest value from a technically satisfactory flow-volume loop was taken as the result. Mean (+/- 95% CI) V'maxFRC was 422 (369-475) ml/s. Compared with infants of similar weight (V'maxFRC approximately 180 ml/s), cats had a much higher V'maxFRC. Tests repeated another day showed a mean (+/-95% CI) percentage difference between paired tests to be 2.8 (-12.6, +18.3)%. Non-invasive forced expiratory flow-volume measurements can be reliably obtained in sedated cats.     

Effect of intensive swimming training on lung volumes, airway resistances and on the maximal expiratory flow-volume relationship in prepubertal girls

The aim of the present study was to analyse the effect of 1 year of intensive swimming training on lung volumes, airway resistance and on the flow-volume relationship in prepubertal girls. Five girls [9.3 (0.5) years old] performing vigorous swimming training for 12?h a week were compared with a control group of 11 girls [9.3 (0.5) years old] who participated in various sport activities for 2 h per week. Static lung volumes, maximal expiratory flows (MEF) at 75, 50 and 25% of vital capacity, 1-s forced expiratory volume (FEV_1.0) and airway resistance (R _aw) were measured by means of conventional body plethysmograph techniques. Prior to the training period there were no significant differences between the two groups for any of the parameters studied. Moreover, for both groups, all parameters were within the normal range for children of the corresponding age. After 1 year of training, vital capacity (VC), total lung capacity (TLC) and functional residual capacity (FRC) were larger (P<0.05) in the girl swimmers than in the control group, while physical development in terms of height and weight was similar. FEV_1.0 (P<0.01), MEF₂₅, MEF₅₀ (P<0.05) and MEF₇₅ as well as the ratio MEF₅₀ / TLC (P<0.05) had increased in the girl swimmers but were unchanged in the control group. R _aw tended to be lower in the girl swimmers and higher in the control group. The results indicate that intensive swimming training prepuberty enhances static and dynamic lung volumes and improves the conductive properties of both the large and the small airways. As to the causative mechanism, it can be speculated that at prepuberty intensive swimming training promotes isotropic lung growth by harmonizing the development of the airways and of alveolar lung spaces.     

Maximal expiratory flow-volume patterns in allergic rhinitis. Characteristic flow-volume patterns of the lower airways

On 37 patients with nasal allergy and 37 non-smoking healthy volunteers, maximal expiratory flow-volume curve and volume-time curve were obtained. To find the characteristic flow changes, the flow curves were classified into five patterns from type A to type E. The results showed that the incidence of type A was significantly lower in patients with nasal allergy than in the control group, while the rate of type E was significantly higher at 46% and the rate of type B was particularly high (32.4%) in the patient group. It was demonstrated that 77% of the subjects provided B or C flow-volume curves, while those with pale nasal mucous membranes developed D and E formats. In patients with nasal allergy, these patterns are useful in diagnosing remarkable differences in the lower airways.     

Effect of bronchodilators on density dependence of expiratory flow-volume curves. An attempt to localize bronchodilators site of activity (author transl)

In order to localize bronchodilators site of activity we studied the maximal expiratory flow-volume curves breathing air and 80 percent-20 percent helium-oxygen mixture in 11 normal and 23 asthmatic children. We measured delta Vmax. 60 percent TLC. delta Vmax. 45 percent TLC and VisoV. Half of the subjects received 400 gamma of fenoterol (beta2-sympathicomimetic), the other ones 200 gamma of SCH 1000 (synthetic atropine). Whatever the bronchodilator used, we found different types of response: 1 degree No modification in comparison with control period; 2 degree Increase of deltaVmax. with decrease of VisoV; 3 degree decrease of delta Vmax. with rise of VisoV. Thus we were unable to show a specific bronchodilator site of activity. However, in a few subjects, SCH 1000 principally acted on large airways whereas in some others fenoterol essentially acted on small airways.     

Microprocessor-based system for the measurement and analysis of an expiratory flow-volume curve

Analogue recording and plotting on an xy plotter of flow-time signals to produce inaccurate analysis of respiratory data. To improve on the accuracy of the measurement and reduce the time required for such an analysis a microprocessor-based system has been developed. The system is designed to be easily operated and requires minimum time from the user. It give the operator an indication of the drift in the transducer based on calibration at a standard flow rate. The system is interactive with the user via a visual display terminal. It offers the user full freedom in selecting the parameters to be measured. The displayed results are calculated from the measured signal and compared with predicted values. Hard copy of the displayed information can be produced upon user command. The software is flexibly designed to allow for any modification or future expansion.     

Maximal expiratory flow-volume types in young subjects with past history of nasal allergy and bronchial asthma

Pulmonary function tests were performed on 252 healthy young subjects free from respiratory and allergic symptoms, and 80 young subjects with past history of nasal allergy (PNA) and 10 subjects with past history of bronchial asthma (PBA). All the subjects were non-smokers. Maximal expiratory flow-volume (MEFV) curves were visually classified into five types (A-E). The percent distribution of type A in healthy subjects was significantly higher than in the PNA group, while the total sum of percentage of types B, C, and D in the PNA group was significantly higher than in the healthy subjects. The percent distribution of type E in the PNA group was similar to that in the healthy subjects. The percent distribution of MEFV types were significantly different between healthy males and healthy females. The percent distribution of types A, B and E were the highest in healthy subjects, PNA and PBA groups, respectively. Conclusively, the difference in the percent distributions of MEFV types was recognized among healthy subjects, PNA and PBA groups.     

Influence of L-carnitine administration on maximal physical exercise

Summary The effects of L-carnitine administration on maximal exercise capacity were studied in a double-blind, cross-over trial on ten moderately trained young men. A quantity of 2 g of L-carnitine or a placebo were administered orally in random order to these subjects 1 h before they began exercise on a cycle ergometer. Exercise intensity was increased by 50-W increments every 3 min until they became exhausted. After 72-h recovery, the same exercise regime was repeated but this time the subjects, who had previously received L-carnitine, were now given the placebo and vice versa. The results showed that at the maximal exercise intensity, treatment with L-carnitine significantly increased both maximal oxygen uptake, and power output. Moreover, at similar exercise intensities in the L-carnitine trial oxygen uptake, carbon dioxide production, pulmonary ventilation and plasma lactate were reduced. It is concluded that under these experimental conditions pretreatment with L-carnitine favoured aerobic processes resulting in a more efficient performance. Possible mechanisms producing this effect are discussed.     

Influence of vibration on endurance of maximal isometric contraction

In order to investigate how vibration affects endurance during muscular contraction, knee-joint extension efforts were performed with and without superimposed vibrations. Fourteen healthy non-smoking 20-year-old males performed maximal isometric and sustained knee-joint extension efforts (angle 90 degrees) in sitting posture three times with each leg, with or without vibration. The tests were done once with each leg in a randomly chosen order. The frequency of the vibration was 20 Hz and the acceleration 20 m/s2 RMS, applied in a horizontal sagittal direction to the ankle. The endurance was defined as the time in seconds that it took for the exerted force to decrease by 10% of the initial value. The endurance time averages 22.5 s without vibration and 15.8 s with vibration. The vibratory stress reduced endurance by 6.7 +/- 1.84 s (mean +/- SEM) (P less than 0.005). The difference in maximal force recorded initially was 34 +/- 1.9 N (P less than 0.1). Our conclusion is that vibration may decrease the endurance of maximal och sustained isometric muscular contraction.     

Influence of isocapnic hyperpnoea on maximal arm cranking performance

Isocapnic hyperpnoea has been shown to reliably produce fatigue of the diaphragm. The aim of the present study was to investigate whether incremental isocapnic hyperpnoea (IH_incr) impairs the arm exercise performance and alters the breathing pattern during subsequent maximal incremental arm cranking. Nine healthy volunteers performed an arm cranking test with prior IH_incr (AC_IH) and without prior IH_incr (AC_control). Minute ventilation (V_̇E), tidal volume (V_T), breathing frequency (f_b), O₂ uptake (O₂), CO₂ elimination (CO₂), respiratory exchange ratio (RER) and end-tidal partial pressure of CO₂ (P_ETCO₂) were measured at three different time intervals (t₁: the average of the 3.30th min to the 6.30th min, t₂: 1 min before the end, t₃: peak value) and expressed as mean (SD). V_T at t₁ and at t₃ was significantly (P<0.05) lower during AC_IH [AC_control: t₁: 1.3 (0.5) l, t_p: 1.9 (0.3) l; AC_IH: t₁: 1.1 (0.3) l, t_p: 1.6 (0.3) l]. f_b at t₁ and t₂ was significantly (P<0.05) higher during AC_IH [AC_control: t₁: 23 (4) breaths min^–1, t₂: 42 (14) breaths min^–1; AC_IH: t₁: 27 (5) breaths min^–1, t₂: 48 (14) breaths min^–1]. The maximal voluntary ventilation (MVV), measured before and immediately after the IH_incr, demonstrated a small but significant decrease from 157 (15) l min^–1 to 150 (14) l min^–1 (P<0.05) after the IH_incr. In conclusion, rapid shallow breathing occurred during maximal arm cranking exercise after IH_incr. The alteration was irrespective of the workload and had already occurred at the start of exercise.     

Assessing effects of PEEP and global expiratory lung volume on regional electrical impedance tomography

Objective: This study was performed to assess the value of electrical impedance tomography (EIT) as an indicator of tidal (V_T) and end expiratory lung volume (EELV).

Methods: EIT measurements were performed in seven healthy piglets during constant tidal volume ventilation at incremental and decremental positive end-expiratory pressure (PEEP) levels. Tidal impedance changes were calibrated to volume using V_T calculated from flow at the airway opening. Simultaneously, calibrated respiratory inductive plethysmography was used to measure EELV changes, and used as a reference standard.

Results: EIT systematically underestimated both V_T and EELV changes when EELV deviated from the level at which it was calibrated. Calculated over the entire pressure–volume curve, EIT systematically underestimated V_T by 28 ml, with a precision from ?16 to 72 ml. EELV was systemically underestimated by 406 ml, with a precision of ?38 to 849 ml. Nonlinear recruitment in the ventral regions of the lungs was the main cause of this underestimation.

Conclusions: Tidal and end-expiratory changes in pulmonary impedance reflect corresponding changes in lung volume, but the increasing underestimation with increasing lung volume should be taken into account in the analysis of EIT data.