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1. The pattern of breathing in 12 patients with severe irreversible airflow obstruction has been studied during ventilatory stimulation by rebreathing CO2. Mean maximum tidal volume response was only 1·23 ± 0·30 litres (mean ± sd); this represented 65% of mean measured vital capacity and 82% of mean measured inspiratory capacity. During the course of rebreathing mean total breath duration was reduced from 3·48 ± 0·93 to 2·44 ± 0·48 s. 2. End-expiratory thoracic gas volume (FRC) was elevated at rest in all subjects and increased significantly by a further 0·50–1·90 litres during ventilatory stimulation in 10 of the 12 subjects. The maximum increase in FRC was proportional to the degree of airflow obstruction afforded by the airways in each subject. 3. It is suggested that the increase in FRC during ventilatory stimulation is responsible for the diminished tidal volume response and is an important determinant of breathing pattern and symptomatology in patients with airflow obstruction.

Electrical stimulation of intercostal muscles was employed to measure thoracic gas volume (TGV) during airway occlusion in the absence of respiratory effort at different levels of lung inflation. In 15 tracheostomized and mechanically ventilated CBA/Ca mice, the value of TGV obtained from the spontaneous breathing effort available in the early phase of the experiments (TGVsp) was compared with those resulting from muscle stimulation (TGVst) at transrespiratory pressures of 0, 10, and 20 cmH2O. A very strong correlation ( r2 = 0.97) was found, although with a systematically (∼16%) higher estimation of TGVst relative to TGVsp, attributable to the different durations of the stimulated (∼50 ms) and spontaneous (∼200 ms) contractions. Measurements of TGVst before and after injections of 0.2, 0.4, and 0.6 ml of nitrogen into the lungs in six mice resulted in good agreement between the change in TGVst and the injected volume ( r2 = 0.98). In four mice, TGVsp and TGVst were compared at end expiration with air or a helium-oxygen mixture to confirm the validity of isothermal compression in the alveolar gas. The TGVst values measured at zero transrespiratory pressure in all CBA/Ca mice [0.29 ± 0.05 (SD) ml] and in C57BL/6 ( N = 6; 0.34 ± 0.08 ml) and BALB/c ( N = 6; 0.28 ± 0.06 ml) mice were in agreement with functional residual capacity values from previous studies in which different techniques were used. This method is particularly useful when TGV is to be determined in the absence of breathing activity, when it must be known at any level of lung inflation or under non-steady-state conditions, such as during pharmaceutical interventions.

Thoracic gas volume (Vtg) can be measured with body plethysmography by either repetitive panting or one single inspiratory effort against a shutter occluding the airways. The panting technique is preferred, but may be demanding. We aimed to assess the precision of these two methods and the degree of agreement between them. Vtg and functional residual capacity (FRC) were measured in 155 subjects with a standard, commercially available plethysmograph, acting as a variable-pressure, constant-volume device when Vtg is determined. Total lung capacity (TLC) and residual lung volume (RV) were calculated subsequent to a full vital capacity manoeuvre. For non-asthmatic healthy subjects, the standard deviations (SD) of the differences between two replicate measurements of FRC, TLC and RV were respectively 0.16, 0.13 and 0.14 litres with the panting technique, and 0.18, 0.18 and 0.23 litres with the single inspiratory effort technique. In percentage of the respective lung volumes, the corresponding 1.96 SDs were 20%, 8% and 40% with the panting technique and 23%, 12% and 67% with the single inspiratory effort technique. Between the two techniques, 95% limits of agreement were 21% for FRC, 11% for TLC and 58% for RV. The variability of Vtg and FRC accounted for most of the variability of TLC and RV. In conclusion, the panting and the single inspiratory effort technique produced results that were comparable in magnitude, however with a better precision with the panting technique. The single inspiratory effort technique can be used as an alternative if the panting technique fails.

We have previously measured thoracic gas volume (V-TG) in spontaneously breathing mice using a whole body plethysmograph and have now extended our technique to allow for V-TG measurements during paralysis. BALB/c mice were anesthetized and placed in a body-box and ventilated via a tracheostomy cannula through the box wall. Box pressure (P-b) and tracheal pressure (P-ao) were measured during spontaneous breathing, and again after paralysis while mechanically compressing the chest. V-TG was much larger after paralysis (0.49+/-0.06 ml, positive end-expiratory pressure=2 cmH(2)O) when compared with spontaneous breathing (0.31+/-0.01 ml). External chest compression produced looping in the plots of P-b versus P-ao that was attributable to gradual changes in P-b upon release of the mechanical chest compression and had the character of thermal transients. Under the assumption that the rate of heating of the air in the chamber was proportional to the pressure applied to the animal's chest, and that any increase in air temperature was dissipated by heat absorption by the chamber walls, we developed an algorithm that corrected for the thermal events. This yielded similar results for V-TG (0.30+/-0.02 ml) as obtained during spontaneous efforts. Our method may prove particularly useful when paralysis is required for the precise measurement of lung mechanics. (Less)

The aim of our study was to examine the effect of labor and birth canal compression on the rate of clearance of lung fluid. We recruited 10 babies born by vaginal delivery and 10 born by elective cesarean section (ECS). Thoracic gas volume (TGV) was measured using total body plethysmography, and functional residual capacity (FRC) by argon dilution, at ages 4-6 h and 24 h. Additional measurements were obtained at age 48 h in the infants born by ECS. Our results showed significant increases in mean TGV (from 23.1 mL/kg to 27.4 mL/kg, P = 0.002) and FRC (from 21.2 mL/kg to 24.1 mL/kg, P = 0.04) between 4-6 h and 24 h of age after ECS delivery. Lung volumes did not change significantly over the next 24 h (TGV, 27.4 mL/kg, P = 0.97; FRC, 25.5 mL/kg, P = 0.42). In those infants born by vaginal delivery, the mean TGV at 4-6 h and 24 h were 26.7 and 28.7 mL/kg, respectively (P = 0.09), and the mean FRC results were 23.1 and 24.9 mL/kg, respectively, P = 0.08). The TGV tended to be lower at 4-6 h in those born by ECS than in infants born vaginally (23.1 vs. 26.7 mL/kg, P = 0.05). We conclude that there is a delay of up to 24 h in the establishment of final lung volumes in babies born without exposure to labor or passage through the birth canal, and that this may explain the increased respiratory morbidity associated with delivery by ECS.

In order to determine if inspiratory time in preterm infants was influenced by lung volume, two studies were carried out. In the first investigation, carbon dioxide was used to stimulate tidal volume to a level three to six times normal. The anticipated decrease in inspiratory time at increased tidal volumes was not found. These preterm infants behaved in a similar fashion to vagotomized animals studied in the same way by Clark and von Euler. In the second investigation, Hering-Breuer activity was measured in relation to lung volume changes occurring with growth, measured in a body plethysmograph. Although thoracic gas volume correlated well with age and weight, inspiratory slowing with airway occlusion was found to be independent of both age and lung volume. These investigations suggest that neurologic factors have a significant influence on the inspiratory time in newborn human infants.

Pressure, flow and volume characteristics of the lung were measured using a body plethysmograph. The body plethymograph is a large airtight box used to measure thoracic gas volume and airway resistance. Using a volume displacement body plethysmograph, with rebreathing bag to minimize thermal exchange between lung and plethysmograph air, alveolar pressures were measured over a wide range of airflow rates and lung volumes. To collect isovolume pressure versus flow curves, software was custom designed. The results provide information concerning the mechanics of the respiratory system for use with the airflow perturbation device.

Partial expiratory flow-volume curves are commonly used in infant pulmonary function testing. The flow measurements are volume dependent and thoracic gas volume (TGV) is often measured in conjunction with forced expiratory maneuvers. Since it is not possible to make continuous, simultaneous measurements of TGV during forced expiration, it is assumed that lung volume returns to its original value after forced expiration. To test this assumption we measured TGV using a whole body plethysmograph in 14 wheezy infants before and after a series of forced expirations produced with an inflatable jacket. Forced expiration did not cause a significant change in group mean TGV measurements. Examination of individual data did not show any systematic difference between TGV measured before and after forced expiration. These results suggest that repeated forced expirations do not alter TGV within the time scale of usual pulmonary function testing protocols.

This study was attempted to observe the rate of oxygen desaturation after full oxygenation in six parturients scheduled for Cesarean sections and six patients scheduled for transabdominal hysterectomies. We calculated the mean rate of fall of arterial saturation (slope of desaturation: less than SaO2 (t2)-SaO2(t1) greater than/t2-t1) and changes in arterial blood gases were observed. All subjects were denitrogenated then a single isolated apnea was carried out. The mean time to obtain 90% saturation was longer in the nonpregnant group (7.5 min vs 3.6 min in parturients). The mean slope of desaturation was steeper in the parturients (-3.34) than the nonpregnant group (-1.52). As far as the oxygen reserve is concerned, the parturients had a lesser margin of safety than the nonpregnant women. It was concluded that the lower the thoracic gas volume (parturients), the lower the alveolar O2 stores and, the more rapidly these stores are depleted.

During the measurement of thoracic gas volume, mouth pressure changes were compared to oesophageal pressure changes using an oesophageal balloon system. In individual babies the correlation was high, with r values in excess of 0.98. In other babies the correlation was less satisfactory due to cardiac contractions producing artefacts in the oesophageal pressure trace. The overall correlation obtained from analysing 155 respiratory efforts in a group of 21 babies studied on 23 occasions exceeded an r value of 0.90. We conclude that it is valid to use an oesophageal balloon system to measure changes in intrathoracic pressure.

We examined the possibility that cyclic gas exchange between alveolar space and the surrounding tissue, induced by alveolar pressure variations, could interfere with plethysmographic measurements of thoracic gas volume (TGV). A model study suggested that TGV could be overestimated by up to 100 ml and that the phenomenon could account for some of its previously reported negative frequency dependence (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 739–747, 1982). As the error would be mainly due to CO2 exchange and be proportional to its partial pressure (PCO2), we studied in nine normal subjects the influence of increasing alveolar PCO2 from 30 to 50 Torr on TGV measurements at panting frequencies (f) of 0.5 and 22.5 Hz. Contrary to model predictions, CO2 tended to decrease TGV estimates at low frequency and to increase them at high frequency. As a consequence, frequency dependence of TGV (delta TGV/delta f) was less at high than at low PCO2 (-39 +/- 32 vs. -84 +/- 49 ml x Hz-1, P less than 0.001). The data are not satisfactorily explained but suggest that gas exchange is not an important factor in TGV measurements.

A 521 L, variable pressure, body plethysmograph, connected to preamplifiers and recorder, has been used to study airway resistance and conductance, thoracic gas volume and specific conductance on a group of healthy adolescents, from 12 to 17 years.

In airway obstruction, thoracic gas volume derived from mouth pressure vs. plethysmographic volume changes (TGVm) is overestimated, whereas TGVes, derived from esophageal pressure vs. plethysmographic volume changes, is not (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 939–954, 1982). The reason appears to be that mouth pressure swings are less than alveolar pressure swings. We measured TGVm and TGVes in six normal subjects and in nine asthmatic patients before and during bronchospasm, while panting at the same lung volume at 0.8 Hz (low), 2–2.5 Hz (medium), and 4.5–5 Hz (high). No difference was observed between TGVm and TGVes (P greater than 0.05) at any frequency (f) in normal subjects or asthmatics before bronchospasm. During bronchospasm, TGVm and TGVes were similar at low f. However, TGVm increased from 5.66 +/- 1.16 (SD) liters at low f to 6.50 +/- 1.71 liters at medium f (P less than 0.01), resulting in a TGVm 1.16 +/- 0.95 liters higher than TGVes (P less than 0.01). In three asthmatics during bronchospasm, mean TGVm-TGVes difference was 0.01 liter at low f, 0.26 liter at medium f, and 0.73 liter at high f. Surprisingly TGVes was in average 5% higher at low f than at medium or high f, both in normal subjects and asthmatics. A similar pattern was observed for TGVm, except in asthmatics during bronchospasm. We conclude that in airway obstruction overestimation of TGVm is frequency dependent and can be avoided by panting at low f. However, at this f TGV is 5% larger than at higher f, difference which is not related to airway obstruction.

Thoracic gas volume (TGV) was measured with a whole-body plethysmograph in 20 infants at functional residual capacity (FRC) and at a series of higher lung volumes achieved by artificial inflation of the lungs with known volumes of air after airway occlusion. There was a discrepancy between the corrected values of TGV measured at high and low lung volumes in nine infants; in six cases TGV measured at high lung volumes exceeded that measured at FRC, and in three cases it was reduced when compared with the measurement made at FRC. These changes were not related to age, size, or clinical status and could be explained by airway closure at FRC, combined with an uneven distribution of pleural pressure.

The validity of measuring thoracic gas volume using a single inspiratory effort against an occlusion (Vtginsp) was determined in children and young adults (8 normal control subjects and 17 patients with cystic fibrosis [CF] or asthma). In addition, the validity of the measurement of Vtg at FRC in children at a low panting frequency (Vtgpant) was also determined. During both the panting (encouraged to be about 1 Hz) and inspiratory maneuvers, mouth pressure (Pm) and esophageal pressure (Pes) were measured simultaneously. Hence, Vtgpant and Vtginsp were determined using both delta Pm and delta Pes. Vtginsp using delta Pm was found to be similar to Vtginsp using delta Pes. Values for Vtgpant using either delta Pm or delta Pes were also found to be similar. The percent difference between Vtginsp (using delta Pm) and the average of Vtgpant and Vtginsp (using delta Pes for both) was calculated as an indication of the error of the inspiratory method. The error ranged from -13 to +13% and did not correlate with indices of air-flow limitation or hyperinflation. We have found that Vtginsp can be used to determine FRC in normal children and young adults as well as in those with CF or asthma. In addition, we have also validated the use of Vtgpant at a low panting frequency in these subjects.

We studied the dependence of the Plethysmographic measurement of thoracic gas volume on the frequency of panting during occlusion in 3 normal subjects and in 10 patients with chronic obstructive pulmonary disease (COPD). Total lung capacity was derived using changes in both mouth (ΔPm) and esophageal (ΔPes) pressure to reflect changes in alveolar pressure (TLCm and TLCes, respectively). In the normal subjects, both TLCm and TLCes decreased slightly with increasing frequency of panting; the difference between TLCm and TLCes (TLCm—TLCes) was small and did not vary with frequency. In the patients, TLCes also decreased slightly, but, in contrast to the normal subjects, TLCm increased with increasing frequency. At low frequencies (less than 1 Hz), TLCm—TLCes averaged 0.14 ± 0.09 1 (mean ± SE) and was not significantly different from 0. However, TLCm — TLCes increased with frequency, averaging 1.49 ± 0.40 L at frequencies between 2.5 and 3 Hz. At all frequencies tested, cheek support reduced but did not abolish...

In a body plethysmograph we have demonstrated differences in total lung capacity (TLC) derived from panting maneuvers performed at different levels in the vital capacity. In almost all cases, the discrepancies were due to the magnitude of the abdominal gas volume (AGV) and the relative magnitude of abdominal and thoracic pressure swings during the panting mandeuver. When panting was performed at functional residual capacity (FRC), the effect of AGV compression on the determination of thoracid gas volume (TGV) was small. Of 11 individuals studied 2 were known to have mild asthma. Compression and decompression of AGV appeared to be an insufficient explanation for discrepancies in derived TLC's in these two, suggesting that other as yet unidentified factors may influence the plethysmographic determination of TGV.

A simple noninvasive technique for measuring specific airway resistance (airway resistance X thoracic gas volume) in unanesthetized guinea pigs is described. Specific airway resistances measured by this technique correlated well (r = 0.81) with the resistances obtained using a pleural catheter pressure measurement over a wide range of airway resistances. This range of resistances was generated by exposing the pigs to an aerosolized histamine bronchial challenge. The average specific airways resistance in unchallenged pigs was 1.24 +/- 3.47 cmH2O/s, somewhat lower than found by others, probably reflecting in part our larger pigs and in part some uncertainty in the absolute value of resistance inherent in our measurement technique. This technique is particularly useful in bronchial challenge experiments because of its sensitivity to acute changes in airway resistance.

In 14 normal subjects and in 13 patients with obstructive pulmonary diseases, we studied the variability within an individual of values for the maximal expiratory flow rate ( V ˙ max) recorded simultaneously vs expired pulmonary volume (at the mouth) and vs thoracic volume (measured with a body plethysmograph). We found that the variance of V ˙ max within an individual at 25, 50, and 75 percent of the expired vital capacity did not differ statistically whether pulmonary volume was the expired or the thoracic gas volume. In ten healthy subjects on two occasions (at an interval of 12 days, on the average), we measured the peak expiratory flow rate and V ˙ max at different levels of inflation, with respect to either expired or thoracic volume. There was no statistical difference in V ˙ max between the first and the last day. A larger variability of V ˙ max measured vs expired volume implies a change in the expiratory effort from one forced expiration to another and a different degree of compression of intrathoracic air. Since this was not the case, we conclude that muscular effort during repeated forced expirations is similar. The good reproducibility of effort explains in great measure the good reproducibility of V ˙ max .

The relationship between airway conductance (G A ) and spontaneous thoracic gas volume (V TG ) was examined in a series of studies conducted on 10 asthmatic children. Our results showed no consistency in the degree of correlation of these measurements. Under the conditions in which our studies were performed, no significant changes in V TG occurred after the administration of a Freon-generated bronchodilator aerosol, although there was substantial reduction in airway resistance. Therefore, no benefit was derived from making conductance or resistance measurements specific to thoracic gas volume. Changes in airway resistance in response to a bronchodilator appear to be related to the initial level of resistance.

The changes of ventilatory function during laparoscopy were proved both by spirometry and blood gas measurements. With 32 patients the spirometric data, the thoracic gas volume and the airway resistan

SYNOPSIS Respiratory function studies have been performed on 24 infants with acute viral bronchiolitis. The results of these have demonstrated increased thoracic gas volume and total pulmonary resistance, and decreased dynamic compliance. These changes have reverted to normal within 7 to 10 days of the onset of the illness.

A body plethysmograph may be used for the measurement in man of thoracic gas volume, airway resistance, instantaneous pulmonary capillary flow and abdominal gas volume; if functional residual capacity (dilution method) and pulmonary resistance (esophageal balloon technique) are measured concomitantly, calculations of ‘trapped’ gas (in the lungs or pleural cavity) and of pulmonary tissue resistance may also be made. The design of the plethysmograph, the electrical circuits and recording devices used and the direct reading attachments for the cathode ray oscillograph are presented together with details of operation and some suggestions for modifications of the original design. Submitted on July 14, 1958

Gas trapping has been suggested to be common in healthy newborns in the immediate postnatal period. To determine the veracity of that finding, functional residual capacity (FRC) and thoracic gas volume (TGV) were measured in such a population and the FRC:TGV ratios were related to measurements of airway resistance (Raw). FRC was assessed by a helium gas dilution technique, TGV and Raw by plethysmography. Twenty-four healthy infants born at term were studied at a median age of 2 days (range 1–5 days). None had respiratory problems, nor had their mothers undergone invasive antenatal procedures. Their median FRC, which was 27·1 (range 23·8–32·0) ml kg−1, was significantly lower than their TGV (median 29·8, range 26–33 ml kg−1, P

We made concurrent measurements of the functional residual capacity (FRC) with the body plethysmograph (thoracic gas volume) and by 7-min and prolonged open-circuit nitrogen dilution methods (communicating gas volume). The mean difference between the 7-min communicating gas volume and the thoracic gas volume in 13 healthy subjects was only 0.13 liters. The thoracic gas volume averaged 0.99 liters larger than the communicating gas volume after 7 min of O2 breathing in 13 patients with emphysema. The communicating gas volume at 12–18 min was the same as the thoracic gas volume in 11 of 13 patients but was smaller in the other 2. When the thoracic gas volume was used to measure FRC, the total lung capacity averaged 142% of predicted normal in 13 patients with emphysema. Submitted on January 4, 1962

We measured airway resistance and thoracic gas volume by the body plethysmograph technique, and transpulmonary pressure in seven healthy, adult subjects, before and after induction of bronchoconstriction. A deep inspiration never altered airway resistance, measured at functional residual capacity in the control state, but always reduced it for 1—2 min when bronchoconstriction was present. Discrepancies in data published on airway resistance may be due to use of methods which require a deep inspiration, or to occurrence of a spontaneous deep inspiration shortly before the test. Submitted on January 13, 1961

Using the technique of whole body plethysmography, lung mechanics were measured in a group of infants with wheezy bronchitis. Compared with a group of normal infants previously studied, airway resistance and thoracic gas volume were found to be raised. Nebulized salbutamol was then administered and measurements were repeated when it was found that there was no objective improvement. It is concluded that salbutamol may not be an effective form of treatment of wheezy bronchitis in young infants and the reasons for this are discussed.

1. The pattern of breathing expressed as the relationship between tidal volume and the components of breath interval was studied in normal subjects during CO2 rebreathing, both under unloaded conditions and following the introduction of a non-elastic expiratory resistance. 2. Under unloaded conditions end-expiratory thoracic gas volume (FRC) measured plethysmographically did not alter during the course of the rebreathing experiment. Maximum tidal volume attained (VT, max.) was equal to or just less than the inspiratory capacity of the subject measured at rest. Expiratory reserve volume was not encroached upon even at the highest levels of ventilation. 3. Under loaded conditions the pattern of breathing was altered. VT, max. was diminished in all subjects and FRC showed a progressive rise during rebreathing which was proportional to the resistive load afforded by the artificial resistance. There were no consistent differences in the components of breath duration either at rest or on maximal ventilatory stimulation between the loaded and unloaded states. 4. It is suggested that the pattern of breathing adopted under conditions of expiratory non-elastic loading is influenced more by the secondary effects of breathing at an elevated lung volume, than by the effect of the non-elastic load per se.

Airway resistance and thoracic gas volume were measured in 21 normal infants aged 1 to 10 months using a whole body plethysmograph. Precautions were taken to eliminate temperature changes of inspired and expired gas. The mean value of airway resistance was 22·6 ± 8·9 (SD) cm H2O/l. per sec, and the mean thoracic gas volume in relation to body weight 34·9 ± 5·8 (SD) ml/kg. The reproducibility of the technique was assessed by making repeated measurements in 5 subjects, when the mean coefficient of variation of airway resistance was 11·8% and of thoracic gas volume 10·1%.

Within the first 6 hours of life a consistent difference can be demonstrated between the TGV measured plethysmographically and the FRC measured using a helium dilution technique. This difference persists despite oxygen administration which has little or no effect on the lung volumes in this group of babies.

Specific airway conductance (sGaw) was measured during quiet breathing and during panting in 21 normal subjects and 10 patients with obstructive lung disease. The direct method used does not require measuring thoracic gas volume (TGV). Coefficients of variation were 5.5% for panting and 5.1% for quiet breathing. Interobserver variability was 4.7% in the quiet-breathing method and 6.3% in the panting method. The two methods gave equivalent results for sGaw. A slightly greater sGaw was found by the panting method in normal subjects with the highest sGaw values, probably due to widening of the oropharynx-glottis during panting. In six normal subjects studied for intrasubject variability over time, no significant diurnal or day-to-day variability was seen by either method. We conclude that the quiet-breathing method is a simple valid means of determining sGaw and utilizes a physiological respiratory maneuver. Obviation of the need to measure TGV is advantageous. Results are equivalent to those of the panting method and variability is similar.

Using an integrated flow pressure-corrected body plethysmograph we obtained total lung capacities (TLC) derived from thoracic gas volumes measured at low, medium, and high panting frequencies in 10 healthy men and in 13 patients with chronic airflow obstruction before and after an aerosol of albuterol. Using a gastric balloon we also assessed gastric-to-mouth pressure ratios (delta Pga/delta Pm). In patients before albuterol, estimated TLC remained unchanged from low to medium and increased (not significantly) from medium to high frequency. Healthy subjects and patients after albuterol showed a significant decrease in TLC from low to medium panting frequencies, which persisted after correcting the data for abdominal gas compression using observed delta Pga/delta Pm. In patients after albuterol the results may be explained, at least in part, by intrathoracic airway compliance and mechanical inhomogeneity of the lung. In healthy subjects a remote possibility is the association of mechanical inhomogeneity and nonuniform pleural pressure.

Serial measurements of thoracic gas volume revealed no evidence of air trapping in maintenance of functional residual capacity (FRC) in healthy term babies in the first days of life. Tidal pressure/volume and flow/volume analysis demonstrated intermittent air trapping in only 2 of 19 such babies. Artificial FRC reduction by continuous positive external pressure of 7 cm H 2 O induced grunting in 4 babies, but otherwise had no effect on spontaneous breathing pattern or on dynamic compliance. Group mean total pulmonary resistance rose by 52.9% but only one baby demonstrated evidence of air trapping. Our findings suggest that FRC is maintained in the immediate neonatal period by some means other than air trapping.

Thoracic gas volume (TGV) and specific airway conductance (SGaw) were measured in 6 infants, 21-42 weeks of age, who had been mechanically ventilated during the neonatal period. SGaw was significantly decreased while TGV was normal. Administration of a nebulized beta 2-sympathomimetic stimulant did not improve lung function. It is concluded that inhalation of beta 2 stimulant drugs is not effective in improving airway obstruction in infants with postventilation-elevated airway resistance and that this is likely to be of structural origin.

Twenty-four asthmatic volunteers were exposed to 0, 0.3, and 0.6 ppm sulfur dioxide (SO2) in purified background air at each of three temperatures--21 degrees, 7 degrees, and -6 degrees C--in a controlled-environment chamber. Relative humidity was approximately 80%. Exposures consisted of 5 min heavy exercise periods plus brief warmup and cooldown periods. Airway resistance, thoracic gas volume, and symptoms were measured immediately before and after exposure. For the group, increasing SO2 concentration and decreasing temperature were associated with statistically significant unfavorable effects on airway resistance and respiratory symptoms, as expected from previous findings. Effects of SO2 and cold usually appeared to combine in an additive or less-than-additive fashion; there was little evidence of synergism. Individuals' response patterns were variable: a few suggested synergism, but others suggested a mitigating effect of cold on the bronchoconstrictive response to SO2.

Respiratory function studies were carried out in 22 infants who had successful repair of diaphragmatic herniae of the Bochdalek type. Thoracic gas volume was initially reduced in only 3 of these, but subsequent studies showed that improvement occurred. There were no consistent abnormalities in either dynamic compliance or mean pulmonary conductance. This is evidence that there is rapid adaptation which compensates for any alteration in the parenchymatous tissue in the lungs or abnormalities in the bronchial tree in infants soon after the repair of congenital diaphragmetic herniae. Further studies are necessary to determine the changes in these lungs with growth.

With airways obstruction, panting frequency affects plethysmographically determined thoracic gas volume (Vtg) because the extrathoracic airway acts as a shunt capacitor. Stanescu et al. (19) suggested that in the calculation of Vtg, use of esophageal (delta Pes) rather than mouth pressure (delta Pm) swings might eliminate the problem. We measured total lung capacity (TLC) plethysmographically in 10 subjects with chronic airways obstruction (CAO) and in four normal subjects. TLC (using delta Pm) was derived from Vtg obtained from slow-(approximately 1 Hz) and fast- (approximately 4 Hz) panting frequencies. In the normal subjects and four subjects with CAO, TLC was also obtained using delta Pes. In these subjects abdominal gas compression and decompression did not contribute significantly to the frequency dependence of TLC. In CAO, TLC was frequency dependent in direct proportion to the severity of obstruction. Although the frequency dependence was greater using delta Pm to calculate Vtg, it also occurred using delta Pes. Thus it could not be explained entirely by the shunt capacitor effect of the extrathoracic airways. The residual and significant overestimations of TLC (reflected by frequency dependency of TLC derived from Vtg calculated from delta Pes) may be explained by interregional nonhomogeneities during the panting maneuver.

Long-term effects on lung size and lung mechanics were sought in a 12-month follow-up study of 15 infants of very low birthweight (less than 1500 g), 7 of whom had been exposed to antepartum dexamethasone (mean dose 21 mg). None of the infants had significant neonatal respiratory disease. No differences were found between the dexamethasone-treated and control groups for thoracic gas volume, dynamic pulmonary compliance, or airways resistance during the first year of life. This suggests that the growth and development of the lungs are not adversely affected by antepartum exposure to dexamethasone.

Extract: Thoracic gas volume (TGV), specific compliance (SC), and mean pulmonary resistance were measured in 38 healthy infants between 4 and 46 weeks of age. TGV had a mean value of 30±3.3 ml/kg of body weight or 0.768±0.089 × 10-3 ml/cm body length3. The mean value for SC was 0.056±0.01 cm H2O/l TGV; that for specific pulmonary conductance was 0.298±0.075 1/sec/cm H2O/TGV. Pulmonary conductance related to body length3 had a mean value of 0.221±0.066 × 10-6 1/sec/cm H2O/cm3. The value for the change in intraesophageal pressure between the minimum and maximum values in each respiratory cycle was 8.0±1.47 cm H2O. The results of this study indicate that TGV, SC, and pulmonary resistance, when related to body size, show little difference when comparing newborn infants and adults. Speculation: Measurements of respiratory function in infants are known to be practical. The availability of such measurements in healthy infants should make possible the determination of abnormalities in the respiration of infants with acute viral bronchiolitis and cystic fibrosis of the pancreas, or other respiratory diseases.

This study was performed to find out whether the two common modes of administration of atropine and neostigmine used for reversal of neuromuscular blockade - neostigmine preceded by atropine, or both drugs given simultaneously - differ in their effects on airway resistance. Peak expiratory flow (PEF) and airway resistance (Raw) were measured in eight healthy volunteers after intravenous administration of 1) a placebo, 2) atropine only (0.0075 mg/kg), 3) neostigmine (0.015 mg/kg) preceded by atropine and 4) atropine together with neostigmine. Airway resistance and thoracic gas volume (Vtg) were measured with a volume-constant body plethysmograph. No statistically significant differences were found when the changes in PEF, Raw and Raw x Vts from the basal values were compared between the four experiments. At 30 min Raw was decreased by 28.6% after atropine, but this decrease is not significantly different from that after placebo (21.4%). ZUSAMMENFASSUNG Diese Untersuchung wurde unternommen, um herauszufinden, ob die zwei gebrauchlichen Anwendungsarten von Atropin und Neostigmin zur Aufhebung einer neuromuskularen Blockade - Atropin vor Neostigmin oder beide Mittel gleichzeitig - in ihrer Wirkung auf den Atemwegswiderstand differieren. Bei acht gesunden Probanden wurden PEF (ex-spiratorischer Spitzenstrom) und Raw (Atemwegswiderstand) gemessen und zwar nach i.v. Verabreichung von 1) einem Plazebo, 2) Atropin allein (0,0075 mg/kg), 3) Neostigmin (0,015 mg/kg) im Anschlus an Atropin und 4) Atropin und Neostigmin gleichzeitig. Atemwegswiderstand und thorakales Gasvolumen (Vtg) wurden mittels volumenkonstantem Ganzkorper-Plethysmographen bestimmt. Beim Vergleich der Veranderungen von PEF, Raw und Raw x Vtb gegenuber den Ausgangswerten ergab sich kein signifikanter Unterschied zwischen den vier Versuchsreihen. 30 Minuten nach Atropin war Raw um 28,6% vermindert, doch unterschied sich diese Abnahme nicht signifikant von der nach dem Plazebo gefundenen (21,4%).

The aim was to study thoracic gas volume (TGV) in anesthetized and paralyzed subjects (n = 16) and to analyze any change in TGV in terms of thoraco-abdominal dimensions. TGV was measured by means of a body plethysmograph, using a super syringe for lung inflation during muscle paralysis. The thoraco-abdominal shape at the mamillary and umbilical levels was studied by means of magnetometry for the assessment of antero-posterior diameters (A-P), a strain gauge technique for measuring circumferences and respiratory inductive plethysmography for the recording of cross-sectional areas. TGV was reduced by an average of 28 per cent, from 2.38 1 awake to 1.72 1 during pentothal anesthesia and spontaneous breathing. No change in A-P diameters or cross-sectional areas were noticed. Muscle paralysis and mechanical ventilation caused no further change in TGV, nor were there any changes in A-P diameters, circumferences or cross-sectional areas of the chest or abdomen. The rib cage contribution to the tidal breath was significantly increased, from 41 per cent to 62 per cent to the tidal volume. The result of a lowered TGV during anesthesia concurrently with no measurable change in chest-abdomen dimensions remains a paradox not yet fully understood.

We combined two recently developed methods to assess lung function in 6 healthy infants on 4 occasions between 1 and 12 months and in 14 infants with bronchiolitis during the acute phase and 3 months later. We used a modified rapid chest compression technique to obtain partial expiratory flow-volume (PEFV) curves and VmaxFRC. Passive respiratory mechanics were assessed by brief occlusion at end inspiration and calculation of time constant(Trs), respiratory compliance(Crs) and resistance(Rrs) from the subsequent passive expiration. During the acute phase 13/14 patients had markedly concave PEFV curves and 5 infants showed flow limitation during tidal breathing. VmaxFRC was significantly reduced,Rrs and thoracic gas volume(TGV) were elevated.No difference was found for Crs and Trs. In 3 infants the normally straight passive expiratory flow-volume curve showed curvilinearity approaching end expiration. This curvilinearity was also found in 2 ventilated and paralysed infants with bronchiolitis and explained by increasing Rrs and decreasing Crs. This suggests small airway closure during tidal breathing. Despite some improvement after the acute phase, VmaxFRC was still significantly reduced after 3 months, whereas Rrs was no longer different from the healthy controls. TGV was still elevated and therefore VmaxFRC/TGV and specific conductance reduced. These result suggest that VmaxFRC is a more sensitive parameter for the abnormalities in bronchiolitis than Rrs and should be included in follow up studies. (supported by Deutsche Forschungsgemeinschaft, West Germany)

Trapped gas (TG), defined as the difference between thoracic gas volume at end expiration (TGV) and functional residual capacity (FRC), has been reported to be of considerable magnitude in the neonatal period. In a previous investigation we found TG to average 20 ml in 26 full term infants 2 hours after birth, and 17 ml 24 hours later. The study to be reported was performed to assess how much of the TG that could be mobilized from the lungs by hyperventilation. Fifteen fullterm, healthy newborn infants were studied 1 to 4 days after birth by a modified nitrogen wash-out method. A face mask with its outlet connected to an opening in the side of a wide tube was gently applied to the sleeping baby. Air at high flow rate was continuously flushed through the tube which had a pneumotachygraph mounted at the outlet. The probe of a fast nitrogen analyzer was inserted into the mask. During an expiration the gas flow was instantanously shifted to 100% oxygen. After the expired nitrogen concentration reached below 2% the baby was stimulated to cry with the face mask still in place. Flow and nitrogen concentration signals were sampled at high rate by a computer and the lung nitrogen content before the wash-out was calculated. No rise in nitrogen output was detected during hyperventilation after the wash-out in any infant. We conclude, that the difference between TGV and FRC found by other investigators and ourselves in newborn infants most likely does not represent gas trapped in the lungs but is either an artifact due to methodological inaccuracy, or is due to gas localized in other oroans.

The effects of droperidol, hydroxyzine, and diazepam on airway resistance (AR), functional residual capacity (FRC), and thoracic gas volume (TGV) were compared, using a CPI model-2000 body plethysmograph. Significant decreases in AR were seen following droperidol and hydroxyzine at all time intervals. A significant increase in AR also was noted 90 minutes after diazepam injection. FRC significantly decreased at 60, 90, 120, and 150 minutes following droperidol, and at 90 minutes following hydroxyzine, while no change was seen following diazepam. No significant changes in TGV were seen following administration of any of the drugs.