Assessment of gas compression and lung volume during air stacking maneuver.

PURPOSE: We reasoned that the application of positive pressure through air stacking (AS) technique could cause gas compression and the absolute lung volumes could be estimated. The aim of this study was to estimate the amount of gas compression (ΔV comp) during AS in healthy subjects positioned at 45° trunk inclination and verify if the simultaneous measurements of chest wall volume changes (ΔV CW), by optoelectronic plethysmography, and changes in lung volume (ΔV ao), by pneumotachograph, combined with pressure variation at the airways opening (ΔP ao) during AS are able to provide reliable data on absolute lung volumes. METHODS: Twenty healthy subjects (mean age 23.5 ± 3.8 years) were studied during a protocol that included slow vital capacity and AS maneuvers. V comp was calculated by subtracting ΔV ao and ΔV CW occurring during AS and total lung capacity (TLC) was estimated by applying Boyle-Mariote's law using V comp and ΔP ao. RESULTS: During AS, 0.140 ± 0.050 L of gas was compressed with an average ΔP ao of 21.78 ± 6.18 cmH2O. No significant differences between the estimated TLC (-0.03 ± 3.0% difference, p = 0.6020), estimated FRC (-2.0 ± 12.4% difference, p = 0.5172), measured IC (1.2 ± 11.2% difference, p = 0.7627) and predicted values were found. CONCLUSION: During AS, a significant gas compression occurs and absolute lung volumes can be estimated by simultaneous measurements of ΔV CW, ΔV ao and ΔP ao.

Whole Body Plethysmography: Practical Considerations.

Pediatric pulmonary plethysmography is an important tool used in the diagnosis of lung diseases. Understanding the physiology underlying the functioning of the test can aid the health care provider in its interpretation. The following article reviews the basic science behind whole body plethysmography, and provides an overview of the types of plethysmographs available. Finally, the limitations of the available normative values are discussed.

Detection of mouse cough based on sound monitoring and respiratory airflow waveforms.

Detection for cough in mice has never yielded clearly audible sounds, so there is still a great deal of debates as to whether mice can cough in response to tussive stimuli. Here we introduce an approach for detection of mouse cough based on sound monitoring and airflow signals. 40 Female BALB/c mice were pretreated with normal saline, codeine, capasazepine or desensitized with capsaicin. Single mouse was put in a plethysmograph, exposed to aerosolized 100 µmol/L capsaicin for 3 min, followed by continuous observation for 3 min. Airflow signals of total 6 min were recorded and analyzed to detect coughs. Simultaneously, mouse cough sounds were sensed by a mini-microphone, monitored manually by an operator. When manual and automatic detection coincided, the cough was positively identified. Sound and sound waveforms were also recorded and filtered for further analysis. Body movements were observed by operator. Manual versus automated counts were compared. Seven types of airflow signals were identified by integrating manual and automated monitoring. Observation of mouse movements and analysis of sound waveforms alone did not produce meaningful data. Mouse cough numbers decreased significantly after all above drugs treatment. The Bland-Altman and consistency analysis between automatic and manual counts was 0.968 and 0.956. The study suggests that the mouse is able to present with cough, which could be detected by sound monitoring and respiratory airflow waveform changes.

Body-density measurement in children: the BOD POD versus Hydrodensitometry.

OBJECTIVE: To compare estimates of body density (Db) from air-displacement plethysmography (ADP) with measured and predicted thoracic-gas-volume (TGV) measurements and those from hydrodensitometry (HD) in children. METHODS: Seventeen participants (13 male and 4 female; 10.1 ± 2.20 yr, 42.0 ± 15.03 kg, 145.6 ± 17.41 cm, 30.0 ± 8.66 kg/m²) were tested using ADP and HD, with ADP always preceding HD. Db estimates were compared between ADP with measured TGV, ADP with predicted TGV, and the reference measure, HD. Regression analyses were used to assess the accuracy of the ADP methods, and potential bias between the ADP procedures and HD were evaluated using Bland-Altman analyses. The cross-validation criteria described by Lohman for estimating Db relative to HD were used to interpret the results of the study. RESULTS: A significant difference was found between Db estimates from ADP with measured TGV (1.0453 ± 0.01934 g/cm³) and ADP with predicted TGV (1.0415 ± 0.01858 g/cm³); however, neither was significantly different from Db obtained by the reference HD procedure (1.0417 ± 0.02391 g/cm³). For both ADP procedures, regression analyses produced an r = .737-.738, r² = .543-.544, and SEE = 0.02 g/cm³, and the regression lines deviated significantly from the line of identity; however, no significant biases were indicated. CONCLUSIONS: Despite no significant mean differences between Db estimates from the ADP procedures and HD, more cross-validation research is needed before recommending the BOD POD for routine use with children in clinical and research settings.

Body plethysmography--its principles and clinical use.

Body plethysmography allows to assess functional residual capacity (FRC(pleth)) and specific airway resistance (sRaw) as primary measures. In combination with deep expirations and inspirations, total lung capacity (TLC) and residual volume (RV) can be determined. Airway resistance (Raw) is calculated as the ratio of sRaw to FRC(pleth). Raw is a measure of airway obstruction and indicates the alveolar pressure needed to establish a flow rate of 1 L s(-1). In contrast, sRaw can be interpreted as the work to be performed by volume displacement to establish this flow rate. These measures represent different functional aspects and should both be considered. The measurement relies on the fact that generation of airflow needs generation of pressure. Pressure generation means that a mass of air is compressed or decompressed relative to its equilibrium volume. This difference is called "shift volume". As the body box is sealed and has rigid walls, its free volume experiences the same, mirror image-like shift volume as the lung. This shift volume can be measured via the variation of box pressure. The relationship between shift volume and alveolar pressure is assessed in a shutter maneuver, by identifying mouth and alveolar pressure under zero-flow conditions. These variables are combined to obtain FRC(pleth), sRaw and Raw. This presentation aims at providing the reader with a thorough and precise but non-technical understanding of the working principle of body plethysmography. It also aims at showing that this method yields significant additional information compared to spirometry and even bears a potential for further development.

Measurement of respiratory function using whole-body plethysmography in unanesthetized and unrestrained nonhuman primates.

Extended term, continuous measurement and observation of drug responses were performed to examine the feasibility of a custom-made whole-body plethysmograph for measuring respiratory function in unanesthetized, unrestrained monkeys. Using this apparatus, respiratory function (respiration rate, tidal volume, and minute volume) was observed for 23 hr in unanesthetized, unrestrained cynomolgus monkeys (Macaca fascicularis). The respiration rate, tidal volume, and minute volume in the light period (7:00 to 19:00) reached approximately 30% to 50% higher values than in the dark period (19:00 to 7:00), thus clearly exhibiting circadian variation in the cynomolgus monkey respiratory functions. Administration of morphine (10 mg/kg, s.c.) resulted in sustained reduction in tidal volume and minute volume, and ketamine (30 mg/kg [sub-anesthetic dose], i.m.) also produced sustained reduction in respiration rate, tidal volume, and minute volume. With dimorpholamine (1 mg/kg, i.v.) or caffeine (10 mg/kg, s.c.), respiration rate, tidal volume, and minute volume increased. Physiological saline (1 ml/kg, s.c. and 0.1 ml/kg, i.v.) and chlorpromazine (10 mg/kg, s.c.) produced no clear-cut changes in respiration rate, tidal volume, or minute volume. From the above results, we conclude that our custom-made whole-body plethysmograph is useful for measuring respiratory function in unanesthetized and unrestrained monkeys.

Whole body composition analysis by the BodPod air-displacement plethysmography method in children with phenylketonuria shows a higher body fat percentage.

BACKGROUND: Phenylketonuria (PKU) causes irreversible central nervous system damage unless a phenylalanine (PHE) restricted diet with amino acid supplementation is maintained. To prevent growth retardation, a protein/amino acid intake beyond the recommended dietary protein allowance is mandatory. However, data regarding disease and/or diet related changes in body composition are inconclusive and retarded growth and/or adiposity is still reported. The BodPod whole body air-displacement plethysmography method is a fast, safe and accurate technique to measure body composition. AIM: To gain more insight into the body composition of children with PKU. METHODS: Patients diagnosed with PKU born between 1991 and 2001 were included. Patients were identified by neonatal screening and treated in our centre. Body composition was measured using the BodPod system (Life Measurement Incorporation©). Blood PHE values determined every 1-3 months in the year preceding BodPod analysis were collected. Patients were matched for gender and age with data of healthy control subjects. Independent samples t tests, Mann-Whitney and linear regression were used for statistical analysis. RESULTS: The mean body fat percentage in patients with PKU (n = 20) was significantly higher compared to healthy controls (n = 20) (25.2% vs 18.4%; p = 0.002), especially in girls above 11 years of age (30.1% vs 21.5%; p = 0.027). Body fat percentage increased with rising body weight in patients with PKU only (R = 0.693, p = 0.001), but did not correlate with mean blood PHE level (R = 0.079, p = 0.740). CONCLUSION: Our data show a higher body fat percentage in patients with PKU, especially in girls above 11 years of age.

[Aerodynamics study on pressure changes inside pressure-type whole-body plethysmograph produced by flowing air].

When using pressure-type plethysmography to test lung function of rodents, calculation of lung volume is always based on Boyle's law. The precondition of Boyle's law is that perfect air is static. However, air in the chamber is flowing continuously when a rodent breathes inside the chamber. Therefore, Boyle's law, a principle of air statics, may not be appropriate for measuring pressure changes of flowing air. In this study, we deduced equations for pressure changes inside pressure-type plethysmograph and then designed three experiments to testify the theoretic deduction. The results of theoretic deduction indicated that increased pressure was generated from two sources: one was based on Boyle's law, and the other was based on the law of conservation of momentum. In the first experiment, after injecting 0.1 mL, 0.2 mL, 0.4 mL of air into the plethysmograph, the pressure inside the chamber increased sharply to a peak value, then promptly decreased to horizontal pressure. Peak values were significantly higher than the horizontal values (P<0.001). This observation revealed that flowing air made an extra effect on air pressure in the plethysmograph. In the second experiment, the same volume of air was injected into the plethysmograph at different frequencies (0, 0.5, 1, 2, 3 Hz) and pressure changes inside were measured. The results showed that, with increasing frequencies, the pressure changes in the chamber became significantly higher (P<0.001). In the third experiment, small animal ventilator and pipette were used to make two types of airflow with different functions of time. The pressure changes produced by the ventilator were significantly greater than those produced by the pipette (P<0.001). Based on the data obtained, we draw the conclusion that, the flow of air plays a role in pressure changes inside the plethysmograph, and the faster the airflow is, the higher the pressure changes reach. Furthermore, the type of airflow also influences the pressure changes.

Respiratory monitoring by inductive plethysmography in unrestrained subjects using position sensor-adjusted calibration.

BACKGROUND: Portable respiratory inductive plethysmography (RIP) is promising for noninvasive monitoring of breathing patterns in unrestrained subjects. However, its use has been hampered by requiring recalibration after changes in body position. OBJECTIVES: To facilitate RIP application in unrestrained subjects, we developed a technique for adjustment of RIP calibration using position sensor feedback. METHODS: Five healthy subjects and 12 patients with lung disease were monitored by portable RIP with sensors incorporated within a body garment. Unrestrained individuals were studied during 40-60 min while supine, sitting and upright/walking. Position was changed repeatedly every 5-10 min. Initial qualitative diagnostic calibration followed by volume scaling in absolute units during 20 breaths in different positions by flow meter provided position-specific volume-motion coefficients for RIP. These were applied during subsequent monitoring in corresponding positions according to feedback from 4 accelerometers placed at the chest and thigh. Accuracy of RIP was evaluated by face mask pneumotachography. RESULTS: Position sensor feedback allowed accurate adjustment of RIP calibration during repeated position changes in subjects and patients as reflected in a minor mean difference (bias) in breath-by-breath tidal volumes estimated by RIP and flow meter of 0.02 liters (not significant) and limits of agreement (+/-2 SD) of +/-19% (2,917 comparisons). An average of 10 breaths improved precision of RIP (limits of agreement +/-14%). CONCLUSIONS: RIP calibration incorporating position sensor feedback greatly enhances the application of RIP as a valuable, unobtrusive tool to investigate respiratory physiology and ventilatory limitation in unrestrained healthy subjects and patients with lung disease during everyday activities including position changes.

Effect of bacterial filter on measurement of interrupter resistance in preschool and school-aged children.

BACKGROUND: The interrupter technique is increasingly used in preschool children to assess airway resistance (Rint). Use of a bacterial filter is essential for prevention of cross-infection in a clinical setting. It is not known how large an effect this extra resistance and compliance exert upon interrupter measurements, especially on obstructive airways and in smaller children. We aim to determine the contribution of the filter to Rint, in a sample of children attending lung function testing at an asthma clinic. METHODS: Interrupter measurements were performed according to ATS/ERS guidelines during quiet normal breathing at an expiratory flow trigger of 200 ml s(-1), with the child seated upright with cheeks supported and wearing a nose clip. A minimum of 10 interrupter measurements was made with and without a bacterial filter. Spirometric and plethysmographic tests were also performed. RESULTS: A small but significant difference (0.12 (95% CI 0.06-0.17) kPa s L(-1), P = 0.0002) with 2x SD of 0.34 kPa s L(-1) was observed between Rint with and without filter in 39 children, with a large spread. This difference was not dependent on Rint magnitude, age or height, nor on lung function parameters (effective resistance, forced expiratory volume in 1 sec, and maximal expiratory flow at 50% of expired vital capacity). CONCLUSIONS: A bacterial filter causes a small difference but is not clinically significant, with a wide spread comparable to the variability of the technique and recommended cut-offs for assessing repeatability and bronchodilation. Age, height or severity of obstruction need not be corrected for in general.

Effect of electronic compensation on plethysmographic airway resistance measurements.

OBJECTIVES: To compare the performance of a plethysmograph which incorporated electronic compensation (Jaeger) to one which incorporated a heated humidified breathing system (Hammersmith plethysmograph). WORKING HYPOTHESIS: The performance of a plethysmograph which incorporated electronic compensation would be impaired compared to that which incorporated a heated humidified system. STUDY DESIGN: In vitro and in vivo comparison. PATIENT SELECTION: Eleven children, median postnatal age 13 (range 5-15) months. METHODS: In vitro, the plethysmographs were assessed using known resistances (1.94, 4.85, and 6.80 kPa, equivalent to 20, 50, and 70 cm H(2)O/L/sec, respectively). In vivo, comparison was made of the results of children studied in both plethysmographs. RESULTS: In vitro, the resistance results of the two plethysmographs were similar to each other and to the known resistances. In vivo, the median "effective" airways resistance result of the Jaeger (4.15 kPa/L/sec) was significantly higher than the inspiratory resistance of the Hammersmith plethysmograph (3.0 kPa/L/sec), but the median inspiratory resistances of the Jaeger were significantly lower than those of the Hammersmith plethysmograph (2.8 kPa/L/sec vs. 3.0 kPa/L/sec). The mean within patient coefficient of variability for inspiratory resistance of the Jaeger plethysmograph (16.7%) was significantly higher than that of the Hammersmith plethysmograph (11.6%) (P = 0.014). CONCLUSION: These results suggest plethysmographs which incorporate electronic compensation may be inappropriate for use in infants and very young children.

Unrestrained acoustic plethysmograph for measuring tidal volume in mice.

The traditional method for measurement of tidal volume in unrestrained mice relies on pressure changes induced by a freely respiring animal in a whole body plethysmograph. These changes have been assumed to be the result of thermo-hygrometric differences between respired air and gas within the chamber. It is known, however, that gas compression in the lung can also contribute significantly to changes in plethysmograph pressure. This study describes an acoustic plethysmograph for mice that is capable of measuring the tidal volume time series without the errors associated with the traditional method. The plethysmograph was designed as a resonating cavity at a fixed frequency. It had a sharp resonant peak and was tuned so that changes in body volume produced nearly linear changes in sound amplitude. The plethysmograph was tested with a water filled balloon connected to a syringe pump. The volume of the balloon was varied as a triangle wave with an amplitude of 250 microL. The RMS error between measured and delivered volume was 4.43 microL. A volume step test, performed to assess the response time of the system, showed that the plethysmograph responded in less than one millisecond.

Restrained whole body plethysmography for measure of strain-specific and allergen-induced airway responsiveness in conscious mice.

The mouse is the most extensively studied animal species in respiratory research, yet the technologies available to assess airway function in conscious mice are not universally accepted. We hypothesized that whole body plethysmography employing noninvasive restraint (RWBP) could be used to quantify specific airway resistance (sRaw-RWBP) and airway responsiveness in conscious mice. Methacholine responses were compared using sRaw-RWBP vs. airway resistance by the forced oscillation technique (Raw-FOT) in groups of C57, A/J, and BALB/c mice. sRaw-RWBP was also compared with sRaw derived from double chamber plethysmography (sRaw-DCP) in BALB/c. Finally, airway responsiveness following allergen challenge in BALB/c was measured using RWBP. sRaw-RWBP in C57, A/J, and BALB/c mice was 0.51 +/- 0.03, 0.68 +/- 0.03, and 0.63 +/- 0.05 cm/s, respectively. sRaw derived from Raw-FOT and functional residual capacity (Raw*functional residual capacity) was 0.095 cm/s, approximately one-fifth of sRaw-RWBP in C57 mice. The intra- and interanimal coefficients of variations were similar between sRaw-RWBP (6.8 and 20.1%) and Raw-FOT (3.4 and 20.1%, respectively). The order of airway responsiveness employing sRaw-RWBP was AJ > BALBc > C57 and for Raw-FOT was AJ > BALB/c = C57. There was no difference between the airway responsiveness assessed by RWBP vs. DCP; however, baseline sRaw-RWBP was significantly lower than sRaw-DCP. Allergen challenge caused a progressive decrease in the provocative concentration of methacholine that increased sRaw to 175% postsaline values based on sRaw-RWBP. In conclusion, the technique of RWBP was rapid, reproducible, and easy to perform. Airway responsiveness measured using RWBP, DCP, and FOT was equivalent. Allergen responses could be followed longitudinally, which may provide greater insight into the pathogenesis of chronic airway disease.

Further exploration of the Penh parameter.

Unrestrained plethysmography (UP) has been widely used to measure airway reactivity in conscious mice. It is non-invasive, easy to use, suitable for longitudinal studies, and allows a large throughput of animals for screening purposes. A non-dimensional parameter based on a characteristic change in the expiratory waveshape of the UP box signal, Penh, has been used as an indicator of bronchconstriction. Hamelmann et al. [Non-invasive measurement of airway responsiveness in allergen mice using barometric plethysmography. Am J Respir Crit Care Med 1997;156:766-77] presented experimental data showing a correlation between Penh and intrapleural pressure, as well as lung resistance; and Dohi et al. [Non-invasive system for evaluating the allergen-specific airway response in a murine model of asthma. Lab Invest 1999;79:1559-71] showed that Penh tracked the bronchial response to allergen challenge. More recently, papers and letters to the editor have argued against the use of UP and Penh in resistance applications, presenting mathematical and theoretical arguments that the UP waveform, and parameters derived from it (Penh) are dominated by conditioning, and are essentially unrelated to resistance [Lundblad et al. A reevaluation of the validity of UP in mice. J Appl Physiol 2002;93:1198-207; Mitzner and Tankersley. Interpreting Penh in mice. J Appl Physiol 2003;94:828-32]. This paper discusses the mathematics of UP as applied to two types of whole body plethysmographs (WBPs): a sealed chamber (pressure plethysmograph, PWBP); and a chamber with a pneumotachograph in its wall (flow plethysmograph, FWBP). We show that the PWBP waveform is largely dominated by conditioning, and exhibits little effect due to resistance; thus supporting the claim that UP and Penh are unrelated to resistance, when applied to measurements at typical room temperatures. By contrast, the effects of resistance or specific airway resistance (sRaw) are evident in the FWBP waveform, even at room temperature. Penh is derived from the FWBP waveform. We show that the changes in the FWBP waveform which occur in response to methacholine challenge cannot be due to conditioning, and are not simply due to changes in respiratory timing. Finally, we describe how Penh quantifies those changes.

Application-oriented programming model for sensor networks embedded in the human body.

This work presents a new programming model for sensor networks embedded in the human body which is based on the concept of multi-programming application-oriented software. This model was conceived with a top-down approach of four layers and its main goal is to allow the healthcare professionals to program and to reconfigure the network locally or by the Internet. In order to evaluate this hypothesis, a benchmarking was executed in order to allow the assessment of the mean time spent in the programming of a multi-functional sensor node used for the measurement and transmission of the electrocardiogram.

The birth of clinical body plethysmography: it was a good week.

Nearly fifty years ago, Arthur B. DuBois, Julius H. Comroe Jr., and their colleagues published two papers on the use of body plethysmography to measure lung volume and airway resistance. These two articles in the JCI are almost the most-cited doublet in the Journal's entire archive. Remarkably, the methods described then are still in use today in clinical pulmonary function laboratories. Though body plethysmography had been used before, there were serious technical problems; it was extraordinary that DuBois managed to solve most of these in one week. Times have changed and molecular medicine now dominates the JCI, but these articles remind us that biomedical research goes beyond the molecular.

Comparison of Bod Pod and DXA in female collegiate athletes.

PURPOSE: This study was designed to evaluate the reliability and validity of air displacement plethysmography (ADP) compared with dual energy x-ray absorptiometry (DXA) Hologic QDR 4500A (Waltham, MA) in female collegiate athletes. METHODS: Forty-seven females representing various Division II collegiate sports and 24 controls participated in the current study. All women underwent both methods of testing within a 30-min period. RESULTS: Comparison of means indicated that the ADP and DXA are not different when measuring body fat (BF%) in the athletes (ADP = 22.5 +/- 5.5%, DXA = 22.0 +/- 4.7%P = 1.0). Furthermore, this study determined that ADP is a reliable measure of body fat (BF%; r = 0.96, P < 0.001; 0.97, P < 0.001) in collegiate female athletes and nonathletes, respectively. CONCLUSION: The results from this study indicate that ADP is a valid measure of body composition in female athletes and nonathletes when compared with DXA.