FRC Measurements Research Articles

Study of the functional residual capacity of the lungs caused by nitrogen leaching during multiple respirations and the diffusion capacity of the lungs in patients with bronchial asthma and chronic obstructive pulmonary disease

Relevance. This article discusses the use of nitrogen depletion and lung diffusivity measurements to assess functional lung capacity (FLC) in patients with bronchial asthma (BA) and chronic obstructive pulmonary disease (COPD).Relevance. This article discusses the use of nitrogen depletion and lung diffusivity measurements to assess functional lung capacity (FLC) in patients with bronchial asthma (BA) and chronic obstructive pulmonary disease (COPD).The purpose. Comparative assessment of FRC values measured using diffusion tests and nitrogen-leaching methods during multiple respirations.Material and methods. An observational cross-sectional study was conducted. The examination results of the two groups were compared. Group 1: included 30 patients with BA of 3–4 severity — 13 men (43.4 %) and 17 women (56.6 %); the average age was 50.6±4.3 years at the stage of subsiding exacerbation. Group 2: included 30 patients with moderate COPD — 13 men (43.4 %) and 17 women (56.6 %), average age was 50.6±4.3 years. The functional residual capacity of the lungs was determined using the multiple-breath nitrogen washout method, whereas the diffusion capacity of the lungs. The statistical analysis and visualization of the obtained data were performed using the statistical computing environment R 4.3.0 (R Foundation for Statistical Computing, Vienna, Austria). Differences were considered statistically significant at a p<0.05. The Bland — Altman method was used to assess the consistency of the FRC measurements obtained from the two methods.Results. Two groups of patients were examined: first group — 30 patients with BA of 3–4 severity; second group — 30 patients with COPD. When statistically analyzed between the two methods, no significant differences were observed in the FRC values using the nitrogen washout method and lung diffusivity. The Bland-Altman method produced similar statistical results.Conclusion. Measurement of FRC in patients with asthma and COPD can be performed using both lung diffusivity and multibreath nitrogen washout methods.

The effect of sex and body weight on lung volumes during sleep.

Low lung volumes are thought to contribute to obstructive sleep apnea (OSA). OSA is worse in the supine versus lateral body position, men versus women, obese versus normal-weight (NW) individuals and REM versus NREM sleep. All of these conditions may be associated with low lung volumes. The aim was to measure FRC during wake, NREM, and REM in NW and overweight (OW) men and women while in the supine and lateral body positions. Eighty-one healthy adults were instrumented for polysomnography, but with nasal pressure replaced with a sealed, non-vented mask connected to an N2 washout system. During wakefulness and sleep, repeated measurements of FRC were made in both supine and right lateral positions. Two hundred eighty-five FRC measures were obtained during sleep in 29 NW (body mass index [BMI] = 22 ± 0.3 kg/m2) and 29 OW (BMI = 29 ± 0.7 kg/m2) individuals. During wakefulness, FRC differed between BMI groups and positions (supine: OW = 58 ± 3 and NW = 68 ± 3% predicted; lateral OW = 71 ± 3, NW = 81 ± 3% predicted). FRC fell from wake to NREM sleep in all participants and in both positions by a similar amount. As a result, during NREM sleep FRC was lower in OW than NW individuals (supine 46 ± 3 and 56 ± 3% predicted, respectively). FRC during REM was similar to NREM and no sex differences were observed in any position or sleep stage. Reductions in FRC while supine and with increased body weight may contribute to worsened OSA in these conditions, but low lung volumes appear unlikely to explain the worsening of OSA in REM and in men versus women.

Abnormal infant pulmonary function in young children with neuroendocrine cell hyperplasia of infancy

Lung function in children with neuroendocrine cell hyperplasia of infancy (NEHI) and correlations with future clinical outcomes are needed to guide clinical management. To compare results of infant pulmonary function tests (IPFTs) in children with NEHI to disease control (DC) subjects and to correlate NEHI IPFTs with future outcomes. We performed a retrospective, single center study of IPFT in subjects diagnosed by lung biopsy (NEHI) or clinically (NEHI syndrome) and in DC subjects evaluated for cancer or pre-hematopoietic stem cell transplantation (HSCT). Raised volume rapid thoracoabdominal compression (RVRTC) and plethysmography were performed on all infants and evaluated for quality. Standard spirometry measures, room air oxygen saturations (RA O2 sat), and weight percentiles were collected during follow up. Fifty-seven IPFTs were performed in 15 NEHI, 22 NEHI syndrome, and 20 DC subjects. RVRTC and FRC measurements were obtained in 85% or more of subjects in all groups. Significant airflow limitation (FEV0.5 P-value ≤ 0.01) and air trapping (FRC P-value ≤ 0.01) were seen in NEHI and NEHI syndrome subjects compared to DCs. No significant correlations were found between IPFT, oxygen use, RA O2 sat, and weight at the time of the IPFTs. Initial FEV0.5 and FRC z-scores correlated with RA O2 sat (r = 0.60 and -0.49) at short-term follow up (6-12 months). Most measurements of RVRTC correlated with FEV1 (n = 5) measured 4-5 years later (r > 0.50). IPFTs in NEHI subjects are feasible, demonstrate significant obstruction and air trapping, and correlate with future RA O2 sat and FEV1 . IPFTs may provide valuable clinical information when caring for NEHI patients. Pediatr Pulmonol. 2013; 48:1008-1015. © 2012 Wiley Periodicals, Inc.

Multicenter Evaluation of Infant Lung Function Tests as Cystic Fibrosis Clinical Trial Endpoints

The conducting of clinical trials in infants with cystic fibrosis (CF) has been hindered by lack of sensitive outcome measures. To evaluate safety, feasibility, and ability to detect abnormalities in lung function of serial pulmonary function tests (PFTs) in infants with CF. Multicenter observational study using a commercial device, rigorous training, ongoing quality control, and over-reading of data by an independent panel. Raised volume rapid thoracoabdominal compression technique and plethysmography were performed at enrollment and at 6 and 12 months, with an additional 1-month reproducibility visit. A total of 342 procedures were performed in 100 infants with CF at 10 centers. FRC measurements were acceptable at a higher proportion of study visits (89%) than raised volume (72%) or fractional lung volume (68%) measurements. Average Z scores for many parameters differed significantly from historical control values. Mean (95% confidence interval) Z scores were: -0.52 (-0.78 to -0.25) for forced expiratory flow at 75% (FEF₇₅) for FVC; 1.92 (1.39-2.45) for FRC; 1.22 (0.68-1.76) for residual volume; 0.87 (0.60-1.13) for FRC/total lung capacity; and 0.66 (0.27-1.06) for residual volume/total lung capacity. For future multicenter clinical trials using infant PFTs as primary endpoints, minimum detectable treatment effects are presented for several sample sizes. In this 10-center study, key PFT measures were significantly different in infants with CF than in historical control subjects. However, infant PFTs do not yet appear ready as primary efficacy endpoints for multicenter clinical trials, particularly at inexperienced sites, based on acceptability rates, variability, and potentially large sample sizes required to detect reasonable treatment effects.

Serial Measurements of Lung Function in a Cohort of Young Children With Bronchopulmonary Dysplasia

We aimed to prospectively and longitudinally measure lung function in a cohort of children with bronchopulmonary dysplasia (BPD) during their first 3 years of life. Forty-four children with BPD with a mean (+ or - SD) gestational age of 25.6 (+ or - 1.7) weeks and birth weight of 0.767 (+ or - 0.2) kg underwent serial measurements of lung function (maximum flow at functional residual capacity [V(max)FRC] and functional residual capacity [FRC]) at 6, 12, and 24 months after initial discharge from the neonatal care unit. Compared with normative data, children with BPD had low partial expiratory airflow, measured by V(max)FRC, with mean z score (+ or - SD) of -1.92 (+ or - 1.04), -1.79 (+ or - 1.5), and -1.67 (+ or - 1.5) at 6, 12, and 24 months, respectively. Over time there was no significant improvement in z scores (P = .66), and 45% of the patients had a z score value of less than -2 (2 SDs below the mean) at the end of the study. FRC measurements steadily and significantly increased over time. Partial expiratory flow showed no correlation with gestational age, birth weight, or length of mechanical ventilation. Mean FRC was significantly higher in children who were using bronchodilators and inhaled steroids but showed no correlation with clinical symptoms. Bronchodilator response was initially present in 30% of the patients and declined to 20% at the end of the study. During the first 3 years of life, children with mostly moderate-to-severe BPD continue to show significant abnormalities with airflow limitation according to lung-function testing.

Comprehensive integrated spirometry using raised volume passive and forced expirations and multiple-breath nitrogen washout in infants.

With the rapid somatic growth and development in infants, simultaneous accurate measurements of lung volume and airway function are essential. Raised volume rapid thoracoabdominal compression (RTC) is widely used to generate forced expiration from an airway opening pressure of 30 cmH(2)O (V(30)). The (dynamic) functional residual capacity (FRC(dyn)) remains the lung volume most routinely measured. The aim of this study was to develop comprehensive integrated spirometry that included all subdivisions of lung volume at V(30) or total lung capacity (TLC(30)). Measurements were performed on 17 healthy infants aged 8.6-119.7 weeks. A commercial system for multiple-breath nitrogen washout (MBNW) to measure lung volumes and a custom made system to perform RTC were used in unison. A refined automated raised volume RTC and the following two novel single maneuvers with dual volume measurements were performed from V(30) during a brief post-hyperventilation apneic pause: (1) the passive expiratory flow was integrated to produce the inspiratory capacity (IC) and the static (passive) FRC (FRC(st)) was estimated by initiating MBNW after end-passive expiration; (2) RTC was initiated late during passive expiration, flow was integrated to produce the slow vital capacity ((j)SVC) and the residual volume (RV) was measured by initiating MBNW after end-expiration while the jacket (j) was inflated. Intrasubject FRC(dyn) and FRC(st) measurements overlapped (p=0.6420) but neither did with the RV (p<0.0001). Means (95% confidence interval) of FRC(dyn), IC, FRC(st), (j)SVC, RV, forced vital capacity and tidal volume were 21.2 (19.7-22.7), 36.7 (33.0-40.4), 21.2 (19.6-22.8), 40.7 (37.2-44.2), 18.1 (16.6-19.7), 40.7 (37.1-44.2) and 10.2 (9.6-10.7)ml/kg, respectively. Static lung volumes and capacities at V(30) and variables from the best forced expiratory flow-volume curve were dependent on age, body length and weight. In conclusion, we developed a comprehensive physiologically integrated approach for in-depth investigation of lung function at V(30) in infants.

FRC measurements using body plethysmography in young children

Measurement of FRC in whole body plethysmography (FRCpleth) is not performed in young children (aged 3-5 years) because it involves sitting alone in a closed box and breathing attempts against occlusion. To assess the feasibility of measuring FRCpleth in young children. Seventy-one of 102 children (age range 3.3-6.9 years) performed spirometry and FRCpleth measurements. Twenty-six children had controlled asthma (Group-A); 26 children were tested during asthma exacerbation had uncontrolled asthma (Group-UA), and 19 children were tested after receiving chemotherapy treatment (Group-C). Tests according to adult recommendations were first taught outside the plethysmograph and then performed with minor technical adaptations. Each test included two consecutive FRC measurements obtained during 2-3 sec of occlusion. Total lung capacity (TLC) and residual volume (RV) were calculated. Values were compared to FRC measured by Helium-dilution (FRC-He) in healthy preschool children and to extrapolated FRCpleth values of school children, and between the groups. Group-A showed normal spirometry and normal TLC values, with mildly elevated FRCpleth and RV values (125 +/- 20 and 153 +/- 33 %predicted, respectively; P < 0.0001 for both values). Group-UA showed obstructed flows combined with high FRCpleth and RV (146 +/- 26 and 189 +/- 38 %predicted; P < 0.0001) and normal TLC. Group-C showed a restrictive spirometry pattern combined with lower than normal TLC (86 +/- 15 %predicted; P < 0.0251). Measuring absolute lung volumes by plethysmography in young children is feasible and can detect abnormal lung volumes. It is essential to study a larger group of healthy children for reference values and to allow for standardization of the procedure.

A novel physiological investigation of the functional residual capacity by the bias flow nitrogen washout technique in infants

The dynamic functional residual capacity (FRC(dyn)), the lung volume most routinely measured in infants, is an unreliable volume landmark. In addition to the FRC(dyn), we measured the (passive) static FRC (FRC(st)) by inducing a brief post-hyperventilation apnea (PHA) in 33 healthy infants aged 7.4-127.2 weeks. A commercial system for nitrogen (N2) washout to measure FRC, and a custom made system to monitor and record flow and airway opening pressure signals in real-time were used in unison. Infants were manually hyperventilated to induce a PHA. After the last passive expiration, FRC(st) was estimated by measuring the volume of N2 expired after end-passive expiratory switching of the inspired gas from room air to 100% oxygen during the post-expiratory apneic pause. Repeatable intrasubject FRC(st) and FRC(dyn) measurements overlapped in most infants including the younger ones (P = 0.2839). Mean (95% confidence interval [CI]) FRC(st) was 21.1 (20.0-22.3), and error-corrected FRC(dyn) was 21.4 (20.4-22.4) ml/kg. Mean (washout time [t]) tFRC(st) was longer than tFRC(dyn) 60 sec (95% CI 55-65) versus 47 sec (95% CI 43-51) (P < 0.0001). The FRC and washout time were dependent on body length, weight and age. We conclude that the FRC(st) is not different from the FRC(dyn) in infants. The FRC(st) is a reliable volume landmark because the PHA stabilizes the end-expiratory level by potentially abolishing the sedated infant's breathing strategies. The FRC(st) lacks potential sources of errors and disadvantages associated with measuring the FRC(dyn). The findings cast significant doubt on the traditional physiology of air trapping in healthy infants' lungs.

Longitudinal assessment of lung function from infancy to childhood in patients with cystic fibrosis

Infant pulmonary function testing (IPFT) has become an important clinical tool for the evaluation of lung function in infants with Cystic Fibrosis (CF); however, it is still unclear whether lung function in infancy is predictive of lung function later in life. We hypothesized that measures of airflow obstruction by IPFT would correlate strongly with lung function by conventional spirometry later in childhood. A retrospective analysis was performed of all CF infants studied with IPFT at the University of Minnesota Children's Hospital between September 1994 and March 2003. A total of 41 patients underwent IPFT and had valid spirometry results available at age 6 or later. IPFT values, such as I:E ratio, respiratory rate, tidal volume, and T(ptef)/T(e), were calculated from tidal breathing loops. Passive respiratory system mechanics, which included C(rs), R(rs), and tau(rs), were measured by the single breath end-inspiratory occlusion technique. Forced expiratory flows, including V(max)FRC, FVC, FEF(50), and FEF(75), were obtained by rapid thoracic compression and included a full vital capacity maneuver by the multiple inflation method. FRC measurements were calculated from data obtained via nitrogen washout in a subset of patients. In addition, information on age at diagnosis and results of oropharyngeal (OP) cultures at diagnosis and on subsequent visits was recorded. Standard spirometry was performed in all patients starting at age 5. The first valid flow-volume loop after age six was selected for analysis. Significant correlations were observed for the R(rs) and the FEF(50) by IPFT and the FEV(1) and the FEF(25-75) by standard spirometry (r > 0.4 and P < 0.03 for all correlations). These correlations were the strongest for those IPFT measurements obtained within 1 month of diagnosis and when R(rs) was expressed as sG(rs). The correlations observed were independent of the effects of age at diagnosis, gender and presence of Pseudomonas in oropharyngeal cultures at the time of diagnosis. Mean R(rs) declined from 0.050 to 0.027 cm H(2)O/ml/sec with treatment (P < 0.0001). There were no other significant associations found between other IPFT values measured and FEV(1) by spirometry. Measures of airflow obstruction on IPFT, specifically R(rs), sG(rs), and FEF(50), were strongly correlated with future lung function. IPFT measurement of R(rs) in addition to forced expiratory flows may help select patients at the greatest risk of early lung function decline. This study supports the use of R(rs) as a surrogate variable to help assess the impact of early therapies in CF.

Deadspace estimation from CO2 versus molar mass measurements in infants

Estimation of respiratory deadspace is often based on the CO2 expirogram, however presence of the CO2 sensor increases equipment deadspace, which in turn influences breathing pattern and calculation of lung volume. In addition, it is necessary to correct for the delay between the sensor and flow signals. We propose a new method for estimation of effective deadspace using the molar mass (MM) signal from an ultrasonic flowmeter device, which does not require delay correction. We hypothesize that this estimation is correlated with that calculated from the CO2 signal using the Fowler method. Breath-by-breath CO2, MM and flow measurements were made in a group of 77 term-born healthy infants. Fowler deadspace (Vd,Fowler) was calculated after correcting for the flow-dependent delay in the CO2 signal. Deadspace estimated from the MM signal (Vd,MM) was defined as the volume passing through the flowhead between start of expiration and the 10% rise point in MM. Correlation (r = 0.456, P < 0.0001) was found between Vd,MM and Vd,Fowler averaged over all measurements, with a mean difference of -1.4% (95% CI -4.1 to 1.3%). Vd,MM ranged from 6.6 to 11.4 ml between subjects, while Vd,Fowler ranged from 5.9 to 12.0 ml. Mean intra-measurement CV over 5-10 breaths was 7.8 +/- 5.6% for Vd,MM and 7.8 +/- 3.7% for Vd,Fowler. Mean intra-subject CV was 6.0 +/- 4.5% for Vd,MM and 8.3 +/- 5.9% for Vd,Fowler. Correcting for the CO2 signal delay resulted in a 12% difference (P = 0.022) in Vd,Fowler. Vd,MM could be obtained more frequently than Vd,Fowler in infants with CLD, with a high variability. Use of the MM signal provides a feasible estimate of Fowler deadspace without introducing additional equipment deadspace. The simple calculation without need for delay correction makes individual adjustment for deadspace in FRC measurements possible. This is especially important given the relative large range of deadspace seen in this homogeneous group of infants.

Bleomycin-induced chronic lung damage does not resemble human idiopathic pulmonary fibrosis.

Administration of bleomycin into the lungs of experimental animals has been utilized as a model to understand human pulmonary fibrosis. Most of the studies, however, have focused on early stages of the lung reaction. We hypothesized that chronic stages of the model may not mimic idiopathic pulmonary fibrosis, since in preliminary studies, lung volume and compliance were not decreased. Eight male Sprague-Dawley rats receiving intratracheal bleomycin (0.5 U/100 g body weight) underwent measurement of FRC, inspiratory capacity, and lung compliance 120 d later. Lung histologic changes were evaluated using light microscopy. Eight rats without intervention served as controls. Results show that our model, in early stages, has histologic changes no different from those previously described elsewhere. In chronic stages, however, the model does not behave as a restrictive syndrome: FRC is normal or increased, whereas lung compliance is normal. Focal peribronchiolar inflammation and fibrosis associated with paracicatricial emphysematous changes are the main histologic features of long-term lung remodeling after bleomycin. We conclude that while the chronic stages of the model may be informative in understanding mechanisms of fibrosis, care should be taken not to extrapolate to human idiopathic pulmonary fibrosis. We speculate that the model might resemble a particular subgroup of human interstitial lung disease, namely, those involving peribronchiolar structures.

Total lung capacity by N2 washout from high and low lung volumes in ventilated infants and children.

Although there is a strong rationale for the assessment of the subdivisions of lung volume, lung function testing has focused on the measurement of FRC alone in ventilated infants and children. To assess the feasibility, reproducibility, and accuracy of measurements of total lung capacity (TLC), FRC, and their ratio, we determined both lung volumes in 50 critically ill, intubated, and paralyzed infants (mean age [SEM]), 19.9 [4.6] mo) with a variety of lung diseases, by a modified N2 washout technique from end-exhalation and from +40 cm H2O inspiratory pressure, respectively. In the same infants, we also defined TLC by adding inspiratory capacity, measured by pneumotachograph during a passive exhalation from +40 cm H2O to FRC measured by N2 washout. Respiratory mechanics were measured by single-breath occlusion, and the patients were classified according to clinical picture and lung function into groups without lung disease or with restrictive or obstructive disease. The TLC data obtained by both methods showed good agreement for the infants without lung disease or restrictive disease (limits of agreement [LOA]: -3.8/4.6 and -2.9/3.2 ml/kg, respectively). The agreement was less in the infants with airflow obstruction where the N2 washout gave slightly higher values (LOA: -7.1/11.3 ml/kg). Mean FRC/TLC was significantly elevated in the obstructive group, whereas mean FRC alone did not differ from the group without lung disease. Our results suggest that TLC can be measured by both methods in intubated infants, but with limited agreement in obstructive disease. FRC/TLC ratios allow an estimation of the degree of pulmonary hyperinflation.

Functional residual capacity measurement during tracheal gas insufflation.

Tracheal gas insufflation (TGI) is considered an adjunctive method to enhance carbon dioxide elimination during permissive hypercapnia in patients with acute respiratory distress syndrome. Due to increasing tidal volume and/or expiratory resistance, TGI may cause intrinsic PEEP (PEEPi), and may lessen the advantages of permissive hypercapnia. There is no reliable method to measure PEEPi during TGI. Using an argon washout method to evaluate dynamic hyperinflation, we developed a method to measure FRC with TGI flow. We measured FRC during TGI by washing out both the ventilator and TGI circuit with 100% oxygen (O2) previously equilibrated with 10% argon and 90% O2. To test the accuracy of our system, we measured the volume in a model lung composed of two flasks. The FRC of the model lung was changed by varying its volume of water, to active 500, 1000, and 1500 mL. The change of FRC (deltaFRC) of the model lung was measured at a flow of 0, 4, 8, and 12 L/min. Then the FRC of a bellows-type model lung was measured at the same TGI flow. PEEPi of the model lung was also recorded as the pressure inside the bellows at end-expiration. Our FRC measurements were accurate within 10% except for that of 500 mL without TGI (12.7%+/-1.1%). As inspiratory time (TI) and/or TGI flow increased, the FRC of the bellows-type model lung increased. PEEPi and deltaFRC showed a positive correlation (r = 0.843, p < 0.001). The higher the TGI flow, the greater was the deltaFRC with both continuous and expiratory-phase TGI. FRC during continuous TGI was higher than during expiratory-phase TGI especially during long TI and high TGI flow. The system developed in this study can be used as a method to detect air-trapping during TGI.

Alveolar and dead space volume measured by oscillations of inspired oxygen in awake adults.

Forced sinusoidal oscillations in the inspired concentration of a low-solubility inert gas can be used to measure airways dead space and alveolar volume. When inspired oxygen is oscillated about its mean value in the same way, the ratio between the amplitudes of the resulting end-expired and inspired oxygen oscillations is the same as that of an inert gas such as argon. Thus, oxygen forcing oscillations can be used to measure lung volume. In nine healthy spontaneously breathing adults, the FIO2 (mean FIO2 = 0.26, mean minute volume = 8.5 L/min) was forced to sinusoidally oscillate with an amplitude of +/- 0.04. The mean airways dead space measured using FIO2 oscillations with a forcing period of 3 min was 0.17 +/- 0.04 L, and the airways dead space measured by a single-breath C02 technique was no different at 0.19 +/- 0.03 L. An oxygen oscillation of the same period measured the mean end-expired alveolar volume at 3.1 +/- 0.7 L. Adding together the airways dead space and end-expired alveolar volume, obtained by the oxygen oscillation technique, provided a measure of FRC that at 3.3 +/- 0.7 L matched the FRC of 3.3 +/- 0.8 L measured by whole-body plethysmography. A third measure of FRC using a multiple-breath nitrogen washout technique gave a smaller volume of 3.00 +/- 0.85 L. The advantage of using FIO2 oscillations is that accurate FRC measurements can be made continuously, without interfering with the subject's natural breathing rhythm.

Peripheral Chemoreceptor Response To Hyperoxia In Term And Preterm Infants. 1540

There is very few data in the literature comparing term and preterm infants regarding the response to 100% oxygen. It is well known that newborn infants and adults have a similar peripheral chemoreceptor response to hyperoxia. It is also known that preterm infants also decrease ventilation after administration of high oxygen concentrations and the response is similar in quiet and rem sleep. In this study, we report marked differences in the ventilatory response of term and preterm infants to 100% oxygem observed during measurements of FRC with the N2 washout technique. We analysed the ventilatory response to 100% oxygen in 10 fullterm (39 ± 1.2 weeks) and 10 preterm infants (35 ± 1.5 weeks). All infants were breathing room air and none of the preterm infants had been previously exposed to more than 24 hs of oxygen. Studies were performed with the infants in quiet sleep and no sedation. Air flow was measured with a face mask and a pneumotach before and during exposure to 100% oxygen during a 2 minute nitrogen washout. Data was digitized in computer and stored for further analysis. We analysed changes in ventilatory parameters (Vt, Ti, Ve and f) before and during the oxygen exposure. Mean birth weight was 2970 ± 150 g for the term and 1570± 210 g for the preterm infants. We measured ventilation second by second and report here the mean data for the first 10 seconds after oxygen exposure. Our data is shown on the table below: All infants showed an imediate decrease in tidal volume and frequency. The response was much more marked in the preterm infants. Mean% change in VE was 18% for the term and 37% for the preterm. Our data show that peripheral chemoreceptor response is exarcerbated in healthy preterms compared to fullterms infants. It implies that a maturation in the respiratory control of breathing must occur until term.(CNPq)

The Effect of Maternal Smoking during Pregnancy on Early Infant Lung Function

We studied the effect of prenatal maternal cigarette smoking on the pulmonary function (PF) of 80 healthy infants tested shortly after birth (mean, 4.2 +/- 1.9 wk). Mothers' prenatal smoking was measured by: (1) questionnaire reports at each prenatal visit of the number of cigarettes smoked per day, and (2) urine cotinine concentrations (corrected for creatinine) obtained at each visit. Infant PF was assessed by partial expiratory flow-volume curves and helium-dilution measurement of FRC. Forced expiratory flow rates were significantly lower in infants born to smoking mothers, both when unadjusted and after controlling for infant size, age, sex, and passive exposure to environmental tobacco smoke (ETS) between birth and the time of PF testing. Flow at functional residual capacity (VFRC) in infants born to smoking mothers was lower than that found in infants whose mothers did not smoke during pregnancy (74.3 +/- 15.9 versus 150.4 +/- 8.9 ml/s; p = 0.0007). Differences remained significant when flow was corrected for lung size (VFRC/FRC: 0.87 +/- 0.26 versus 1.77 +/- 0.12 s-1; p = 0.013). No differences in pulmonary function were evident among infants exposed and unexposed to ETS in the home after stratifying by prenatal exposure status. We conclude that maternal smoking during pregnancy is associated with significant reductions in forced expiratory flow rates in young infants. The results suggest that maternal smoking during pregnancy may impair in utero airway development and/or alter lung elastic properties. We speculate that these effects of maternal prenatal smoking on early levels of forced expiratory flow may be an important factor predisposing infants to the occurrence of wheezing illness later in childhood.

Inductance plethysmography measurement of CPAP-induced changes in end-expiratory lung volume

The respiratory inductance plethysmograph (RIP) has recently gained popularity in both the research and clinical arenas for measuring tidal volume (VT) and changes in functional residual capacity (delta FRC). It is important however, to define the likelihood that individual RIP measurements of VT and delta FRC would be acceptably accurate (+/- 10%) for clinical and investigational purposes in spontaneously breathing individuals on continuous positive airway pressure (CPAP). Additionally, RIP accuracy has not been compared in these regards after calibration by two commonly employed techniques, the least squares (LSQ) and the quantitative diagnostic calibration (QDC) methods. We compared RIP with pneumotachographic (PTH) measurements of delta FRC and VT during spontaneous mouth breathing on 0-10 cmH2O CPAP. Comparisons were made after RIP calibration with both the LSQ (6 subjects) and QDC (7 subjects) methods. Measurements of delta FRC by RIPLSQ and RIPQDC were highly correlated with PTH measurements (r = 0.94 +/- 0.04 and r = 0.98 +/- 0.01 (SE), respectively). However, only an average of 30% of RIPQDC determinations per subject and 31.4% of RIPLSQ determinations per subject were accurate to +/- 10% of PTH values. An average of 55.2% (QDC) and 68.8% (LSQ) of VT determinations per subject were accurate to +/- 10% of PTH values. We conclude that in normal subjects, over a large number of determinations, RIP values for delta FRC and VT at elevated end-expiratory lung volume correlate well with PTH values. However, regardless of whether QDC or LSQ calibration is used, only about one-third of individual RIP determinations of delta FRC and one-half of two-thirds of VT measurements will be sufficiently accurate for clinical and investigational use.

1737 FUNCTIONAL RESIDUAL CAPACITY (FRC) CHANGES IN PRETERM BABOONS WITH HYALINE MEMBRANE DISEASE (HMD)

FRC, related to alveolar stability at end expiration, would be expected to improve with recovery from HMD. Intubated, paralyzed preterm (140±2 days) baboons with HMD were evaluated with serial FRC measurements by the He dilution method on Day 0, 3, 7 and 9. Values on Day 0 were obtained within 4 hrs. of birth when all animals were ventilated by conventional ventilation (CV). Animals were then randomized to CV or high frequency ventilation (HFV). Mean values (±SD) obtained were: On Day 0, FRC was not significantly different (ANOVA for repeated measures) between ventilator groups indicating groups of equivalent initial disease severity. Analysis of differences due to ventilator type and interaction between ventilator type and time proved nonsignificant. FRCs on Day 3, 7 and 9 were significantly improved (P< 0.01) over Day 0 values. Changes in FRC appear to reflect recovery in surviving preterm baboons with HMD treated with CV or HFV.

Clinical significance of pulmonary function tests: horacic Gas Volume Measurement: Increased Variability in Patients With Obstructive Ventilatory Defects

We measured the thoracic gas volume (FRC) in normal subjects and patients by body plethysmography to determine the within-subject variability and to identify factors which might influence the variability. The coefficient of variation (CV), a measure of variability, was significantly greater in patients with obstructive ventilatory defects than in patients with restrictive ventilatory defects and normal subjects, and there was a direct correlation between the CV and the FRC and an inverse correlation between the CV, the FEV1/FVC, and the FEV1. These results suggest that the disease state and its severity influence the variability in FRC measurements and that both factors should be considered in the interpretation of serial pulmonary function studies measuring lung volumes.

Pressure-Volume Relationships in the Lung during Laparoscopy

Pressure-volume relationships for the total respiratory system and for the lung were recorded in anaesthetized and paralysed patients, during deflation from an airway pressure of 3 kPa to FRC at a rate of 2 litre min-1. Pleural pressure was estimated by means of an oesophageal balloon. A group of nine female patients (mean age 32.7 yr) about to undergo laparoscopy were each studied in four successive states: supine, 15° head down tilt, tilt and lithotomy position, and again in this position after abdominal inflation with nitrous oxide to a pressure of 0.8–1 kPa. Compliance values were calculated from the curves. Mean total compliance was increased significantly by moving to the lithotomy position, and reduced markedly after inflation of the abdomen, because of a large reduction in thoracic compliance. Mean lung compliance was unaltered, except for a slight but statistically significant increase on moving from the supine to the Trendelenburg position. Measurement of FRC by helium dilution in a group of seven patients showed that abdominal inflation caused a mean decrease of 19%. Airway closure manoeuvres were carried out using a helium bolus technique from FRC in five patients, but closing volume could be measured in only one patient, in the supine position. The absence of an inflexion in the slope of the pressure-volume curves for the other patients supported this negative finding.