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PubMed1998

Measuring tidal volume and functional residual capacity change in sleeping infants using a volume displacement plethysmograph.

The noninvasive measurement of infant lung function during unsedated sleep in infants has been a long-standing objective in paediatric respiratory medicine. This note reports on the design and performance of a head-out volume-displacement plethysmograph (VDP) that overcomes some of the limitations of traditional lung function apparatus. The VDP comprises a rigid acrylic box with an integral water-sealed spirometer and a novel neck seal. The bilayer neck seal is of variable compliance and is comfortable and simple to use. The spirometer permits volume resolution of 1.5 mL and a dynamic range in excess of 100 mL. The frequency response extends from 0-7 Hz. Spirometer inertance was measured as 0.0015 kPa.L(-1).s(-2), resistance 0.021 kPa.L(-1).s(-1) and box capacitance 0.18L.kPa(-1). Tidal volume, respiratory rate and changes in functional residual capacity can be recorded during unsedated rapid eye movement and nonrapid eye movement whilst monitoring with conventional polysomnographic methods. The head-out configuration allows additional instrumentation to be implemented with ease, avoids facial stimulation and allows unimpeded access to the upper airway. A polysomnograph illustrating the limitations of respiratory inductance plethysmography signals and typical changes in functional residual capacity are shown.

Functional Residual Capacity↗

PubMed1985

A simple method for measuring functional residual capacity by N2 washout in small animals and newborn infants.

An open circuit N2 washout technique is described for the determination of functional residual capacity in infants. Either 100% O2 or any oxygen/helium mixture can be used as the washing gas. The subject breathes the washing gas through a T-tube and the washed out nitrogen is mixed with this gas in a mixing chamber, placed into the exhalation part of the circuit. The N2 concentration of the mixed gas is analyzed continuously, and the concentration signal is electronically integrated over time. Calibration of the system is accomplished by injecting known amounts of nitrogen or room air into the circuit. The gas flow through the system must remain constant and is adjusted to approximate peak inspiratory flow of the infant. In vitro testing of the system showed that the technique gives reproducible values (coefficient of variance less than 1.0%) and that the integrated signal output has a close linear correlation with the amount of N2 washed out (r = 0.99). In vivo measurements in 10 cats confirmed the accuracy and reproducibility of the method when compared with N2 collection. The technical advantages of the system are simplicity of components, absence of valves, easy calibration, low dead space, and no need to collect or measure expired gases. For the infant this means no added resistance during washout and no risk of hypoxia, hyperoxia, or hypercapnea. In the presence of pulmonary disease and poor gas mixing the washout period can be prolonged as needed. There is no lower limit of weight or size for functional residual capacity measurements in small infants or animals.

Animals↗

PubMed1980

Functional residual capacity and ventilatory pressures during positive-pressure ventilation at high frequencies.

The functional residual capacity (FRC) was measured in cats by the nitrogen washout technique during positive-pressure ventilation. Frequencies of 60 and 100 b.p.m. were used with insufflation periods of 20% and 35% of the ventilatory cycle, without and with a positive end-expiratory pressure. The higher frequency combined with the shorter insufflation period gave FRC close to that obtained during spontaneous breathing. The lower frequency and the longer insufflation period always gave greater FRC values. A further increase in FRC of about 23-27% was obtained after application of a positive end-expiratory pressure of 0.5 kPa. Adequate ventilation was achieved with small intratracheal and intrapleural pressures at all settings used.

Animals↗

PubMed1986

Changes in functional residual capacity during cardiac surgery.

A gas washout technique was used to measure the functional residual capacity (FRC) in eight patients during anaesthesia for cardiac surgery. The patients were anaesthetized with droperidol, fentanyl and nitrous oxide, alcuronium was given and the lungs were ventilated with a volume controlled ventilator. FRC was measured at three stages before skin incision, after sternotomy but before cardiopulmonary bypass, and after closure of the sternum. The pleural cavities were intact in all patients during the operation. FRC before skin incision was 1.7 +/- 0.5 litre (mean +/- 1 SD). A 55% mean increase in volume was noted after sternotomy and placement of the sternal retractor (P less than 0.001). Mean FRC after sternal closure was 16% lower than the preincision value (P less than 0.05). Arterial Po2 was measured in 22 other patients who underwent coronary artery bypass surgery and in whom F/o2 was 0.5. Pao2 increased significantly when the sternum was opened, but decreased after cardiopulmonary bypass. There was a further significant decrease on closure of the sternum.

Aged↗

PubMed1992

Comparison of helium dilution and nitrogen washout measurements of functional residual capacity in infants and very young children.

In infants and very young children, functional residual capacity (FRC) is the lung volume most frequently measured and gas dilution techniques are most frequently used to measure FRC. We compared measurements of FRC by helium dilution (FRCHe) and nitrogen washout (FRCN2) in a lung model of known volumes (20, 40, 60, 80 mL) in 8 normal infants (NL), 8 infants with acute respiratory illness (ARI), and 7 infants with chronic lung disease (CLD). In the model lung, measurements of FRCHe had a significantly greater coefficient of variation compared to FRCN2 (6.5 vs 1.5%, P less than 0.02), but there was no such difference in the results from all infants combined (6.5 vs 6.2%). In the model lung, the difference between known volumes and the measured values was significantly different from zero only for FRCHe at 20 mL (-4.4 mL, P less than 0.02). For both FRCHe and FRCN2, the slopes of the regression equations were 0.99 and the intercepts not significantly different from zero. We conclude that techniques for measuring FRCHe and FRCN2 yield accurate, reproducible, and comparable results in normal, healthy infants and very young children, and in those with respiratory disease.

Child, Preschool↗

PubMed1997

Modification of the open circuit N2 washout technique for measurement of functional residual capacity in premature infants.

We compared the standard nitrogen (N2) washout technique for measuring functional residual capacity (FRC) with a modified technique that uses a helium/oxygen mixture (heliox) at different ratio instead of pure oxygen. The tests were made with a standard lung function system equipped with an ultraviolet (UV) analyzer for measurement of N2 concentrations in the expired gas. We examined models of "spontaneous breathing" and "mechanical ventilation," each with volumes of FRC in the range of a premature and a newborn lung (20-80 ml), using both techniques at different baseline inspired oxygen concentrations (FIO2). Correlations between known and measured volumes were high and identical for the two techniques (r = 0.996), and the mean error was not significantly different from zero (P = 0.111). Measurements of FRC in 6 infants gave a correlation coefficient of r = 0.989 between the two techniques; reproducibility, as measured by the coefficient of variation, was high, showing no significant differences between both techniques (P = 0.792). However, values of individual infants were different (P = 0.011), and the slope of the regression line relating measurements by the 2 techniques was 1.04, with an intercept on the y-axis at 1.46. We conclude that FRC can be measured with the modified N2 washout technique, using heliox as a washout gas. Volumes can be measured with high precision and reproducibility, even in premature infants with low lung volumes and/or high baseline FIO2. A correction factor may be necessary to equate FRC measurements made by oxygen-N2 vs. heliox-N2 washouts. Hyperoxemia and hypoxemia can be avoided by admixing different flows of oxygen to a standard heliox mixture.

Calibration↗

PubMed1995

Functional residual capacity (FRC) measurements by plethysmography and helium dilution in normal infants.

Comparative measurements of functional residual capacity (FRC) made by plethysmography (FRCpleth) and by helium dilution (FRCHe) were obtained on 27 infants and young children without known pulmonary disease (14 males, 13 females; 4 weeks-26 months; mean age 32.2 weeks) while under chloral hydrate sedation. Clinical histories, clinical examinations, and pulmonary functions were normal for all members of the group. FRCpleth, whether measured near end expiration (EE) or near end inspiration (EI), and corrected to mean expiratory levels of at least 3 breathing cycles, was consistently and significantly greater than FRCHe. Comparative values for mean (+/- standard deviation) were FRCpleth EE, 182.0 (+/- 79.7) mL and FRCpleth El, 171.8 (+/- 77.4) mL vs. FRCHe, 154 (+/- 72.2) mL, P < 0.0001 and P < 0.005, respectively. Normalizing values by weight, FRCpleth EE was 23.8 mL/kg (+/- 5.3) vs. FRCHe, 20.2 (+/- 4.7) mL/kg, mean (+/- standard deviation). The difference between FRCpleth and FRCHe, expressed as FRCpleth - FRCHe/FRCpleth x 100, was 9% for occlusions at end inspiration and 16% for occlusions at end expiration. The following equations describe our FRC results in relation to length: In (FRCHe) = 2.74 x ln (length) - 6.53 r2 = 0.781 slope = 2.74 +/- 0.29 SE Y intercept = 6.53 +/- 1.12 SE ln (FRCPleth EI) = 2.69 x ln (length) - 6.21 r2 = 0.752 slope = 2.69 +/- 0.31 SE Y intercept = 6.21 +/- 1.29 SE The difference between FRCpleth and FRCHe was more marked when occlusions were performed at end expiration than at end inspiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1985

Comparison of the effect of continuous positive airway pressure and blowing bottles on functional residual capacity after abdominal surgery.

In two groups of comparable patients undergoing elective abdominal surgery, functional residual capacity (FRC) was measured preoperatively and on the first 2 days after surgery. One group was treated by regular application of continuous positive airway pressure (CPAP), the other group by bottle blowing (BB). In both groups there was a significant reduction of FRC on the first postoperative day. BB and CPAP increased FRC preoperatively by approximately 50%. Postoperative CPAP or BB increased FRC towards the preoperative value. However, 10 min after the treatment was stopped, FRC was not different from the pretreatment level. In 4 healthy subjects the resistive work of breathing produced by CPAP or BB was measured. Both treatments increased mainly expiratory and total resistive work of breathing. BB resulted in especially high expiratory and total resistive work. It is concluded that CPAP and BB increase temporarily the reduced FRC after abdominal surgery. CPAP was much better tolerated by the patients due to the lower resistive work of breathing.

Abdomen↗

PubMed1981

[A simple method for determination of the functional residual capacity during artificial ventilation (author's transl)].

A simple method for determination of the functional residual capacity (FRC) during artificial ventilation by inert gas dilution using a rebreathing technique is described. The measurements can be made during various techniques of mechanical ventilation (eg. PEEP, IMV etc.). Myorelaxation is not required. This technique was used to assess the volume of a lung model (actual volume: 3670 ml) with the result of repeated measures being 3686 +/- 29 ml. Duplicate measurements in artificially ventilated pigs showed a coefficient of variation of +/- 3.2%. In artificially ventilated patients FRC was determined both with this technique and with a reference method, giving a difference of 111 +/- 55 ml (p less than 0.001). The errors in measurements of FRC by this method are small, and as the measurement requires a minimum of time and the apparatus is simple, the method is accurate and yet simple enough to be used on a routine basis in the intensive care unit. Even high risk patients are not disturbed by this technique. The method has the advantage that it can easily be learned by nurses and paramedical personal.

Animals↗

PubMed1983

Response of pulmonary stretch receptors to shifts of functional residual capacity.

The response of slowly adapting pulmonary stretch receptors (PSRs) to sustained elevations of functional residual capacity (FRC) was investigated in spontaneous breathing anesthetized cats. A subatmospheric pressure was produced around the thorax and abdomen to increase FRC by approximately one tidal volume (VT) for up to 60 min. During eupneic breathing the PSR frequency (fPSR) was closely related to changes in transpulmonary pressure (PTP), but occasionally hysteresis was observed in the FPSR - PTP relationship. Elevation of FRC caused most phasic PSRs to discharge continuously for a few breaths before returning to a phasic discharge pattern. During the shift in FRC there were increases in mean fPSR, peak fPSR firing threshold which were sustained throughout the period of elevated FRC. PSRs that normally showed discharges at FRC similarly increased their mean and peak firing rates. For all PSRs the y-intercept (fPSR at PTP = 0) of the fPSR - PTP relationship was decreased but the sensitivity of the PSR as defined by delta fPSR/delta PTP was not changed until the period of elevated FRC exceeded 30 min. Thereafter, PSR sensitivity tended to decline. These results suggest that PSRs undergo some modification of their discharge parameters during prolonged elevation of FRC.

Action Potentials↗

PubMed1992

[Clinical use of the measurement of functional residual capacity during non-panting breathing--study on healthy subjects and respiratory patients].

The functional residual capacity (FRC) has been measured by gas dilution technique (GA) and body plethysmographic technique (BP) using the panting maneuver (PA). However, this maneuver is difficult to perform for patients who experience discomfort in breathing, and in cases of chronic obstructive pulmonary diseases, the FRC value measured by panting maneuver overestimates the true FRC value. Thus, in order to minimize these factors, we measured FRC during non-panting breathing (NP) using a BP device (BX-82, Minato Co., Osaka) and compared the results with the usual two methods. One hundred healthy subjects (Group I), 72 patients with restrictive ventilatory disorder (Group II, %VC = 62.7%) and 66 patients with pulmonary emphysema (Group III, FEV1.0% = 44.9%) were studied. All measurements were performed under 0.5 Hz respiratory frequency. The non-panting FRC measurement was performed by closing the mouth shutter of the BP for about 500 msec at the end of both the expiratory and inspiratory phase. From the box volume change and mouth pressure change, lisajous curves were formed and fitted by linear regression method. From this regression line, the volume of FRC was calculated. The obtained data had no significant differences among them, and there was a significant relationship between each technique. The correlation coefficient of non-panting breathing technique in Group III was slightly poor compared with the other techniques, and we therefore tried to re-classify Group III into small groups according to the severity of obstruction. It was subsequently found that this technique did not have the tendency to give a higher FRC value with increase in obstructive disorder.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Measurement of functional residual capacity during high-frequency oscillatory ventilation (HFOV) by argon washout method without interruption of HFOV.

A modified indicator gas washout method was developed to measure functional residual capacity (FRC) during high-frequency oscillatory ventilation (HFOV) without interruption of HFOV. A hot-wire flowmeter and medical gas analyzer measured the flow rate and argon concentration, respectively, at the expiratory end of the respiratory circuit. Upstream of the hot-wire flowmeter, two heat-and-moisture exchangers for resistance and a rubber balloon for capacitance were placed to convert the oscillating expiratory flow to an almost continuous flow. This made it possible to measure FRC during HFOV without interrupting HFOV. To measure the volume of the entire respiratory circuit, a 10 percent argon in 90 percent oxygen gas mixture was initially used as a bias flow, and after equilibration, the test gas was switched to 100 percent oxygen. By electrical integration of the product of the expiratory flow rate and argon concentration, the total amount of argon equilibrated in the entire respiratory circuit was calculated. The volume of the circuit was calculated by dividing the total amount of argon by the initial argon concentration. Functional residual capacity plus the volume of the respiratory circuit was similarly calculated and the difference was estimated as FRC. The accuracy and reproducibility of our method were evaluated by using a one-compartment lung model. There was a high correlation between the volume setting of the model lung and the estimated FRC. This method can be used to estimate FRC in a one-compartment lung model during HFOV, and it is potentially useful in clinical situations.

Argon↗

PubMed1987

Automated measurement of functional residual capacity by sulfur hexafluoride washout.

We have constructed a computerized, totally automated system for measuring functional residual capacity (FRC) during mechanical ventilation, at any positive end-expiratory pressure (PEEP) and fraction of inspired oxygen. This system uses washout of a small amount (0.5 to 1.0%) of an insoluble, nontoxic tracer gas, sulfur hexafluoride, to measure FRC. It requires no modification of the ventilator and only minimal changes in the breathing circuit; it can be programmed to make measurements routinely without manual intervention. The system was evaluated with three tests. The prototype sulfur hexafluoride analyzer characteristic curve was determined, and the analyzer was evaluated to determine carbon dioxide interference. A comparison with nitrogen washout FRC measurements was made in an extensive bench test with a Plexiglas lung model. The bench test was designed to determine the effects of changing gas composition and minute volume. A study was done in six healthy dogs to determine reproducibility of the FRC measurements at four PEEP levels (0, 5, 10, and 15 cm H2O: two repetitions in each animal). The sulfur hexafluoride analyzer was well characterized by an exponential equation with a multiple r2 = 0.996. The analyzer was not affected by the presence of carbon dioxide (paired t test, t19 = 1.23, P greater than 0.10). The bench test indicated that FRC (measured) = 0.969 X FRC (true) - 5.3 ml. (Multiple r2 = 0.979.) This was significantly better than the nitrogen washout system, whose regression equation was also a function of minute volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

[Measurement of functional residual capacity by sulfur hexafluoride washout].

An open circuit tracer gas washout method for measurement of functional residual capacity (FRC) during mechanical ventilation is described and tested. The system employed a piezo-valve for dispensing sulfur hexafluoride (SF6) gas, a fast response infrared SF6 analyzer, Servo 900-C ventilator and a computer. The piezo-valve unit delivers SF6 into the airway in proportion to instantaneous inspiratory flow so that inspiratory SF6 concentration was held constant regardless of the inspiratory flow pattern. The washin concentration was approximately 0.6% which was so low that the supply of other gases was hardly influenced. The amount of SF6 at the end of a washin was calculated during washout by signals of expired SF6 concentration and expired flow. The results obtained in model lungs were accurate and reproducible; mean difference (limits of agreements) was 14 +/- 48ml (M +/- 2SD) in the range between 0.5 and 3.0 liters. Comparison with helium dilution methods in 24 healthy subjects gave a regression equation: y = 0.98x + 56, r = 0.98. The mean difference of the values between the two methods was 21 +/- 142 ml (M +/- 2SD). The authors conclude that the system is quite useful in determining FRC of the patients under mechanical ventilation.

Functional Residual Capacity↗

PubMed2001

Physical effects of heliox versus oxygen on measurements of functional residual capacity by the nitrogen washout technique in small lung volumes: a model study.

Measurements of functional residual capacity (FRC) by the nitrogen (N(2)) washout technique yield low N(2) signals in neonates and preterm infants, especially when they are on high fractions of inspired oxygen (FiO(2)). Thus, recorded values often lie in the low range of detectability. We hypothesized that using heliox instead of oxygen as a washout gas would affect the electric discharge conditions of N(2) molecules in a standard UV analyzer and thus yield higher N(2) signals. We performed three laboratory experiments using conditions similar to those in neonates with pulmonary disease, reproducing different initial FiO(2) values and very small lung volumes. Standard calibration procedures with physical models between 13.5-87 mL using a calibration syringe and purpose-built small calibration cylinders were carried out, and washout gas was either pure oxygen (as is general practice) or heliox at different ratios. We observed that the calibration line with heliox was shifted upwards and the slope was increased, depending on helium concentration and initial FiO(2). Since this effect was dose-dependent with respect to the proportion of helium in the washout gas, this strongly suggests a physical process elicited by the noble gas helium. We conclude that the heliox wash-out modification may help to increase the accuracy of FRC measurements and thus may enable studies of smaller patients or patients on high inspired FiO(2).

Functional Residual Capacity↗

PubMed1988

Functional residual capacity as a noninvasive indicator of optimal positive end-expiratory pressure.

We hypothesized that functional residual capacity (FRC) could be used as a noninvasive indicator of "optimal" positive end-expiratory pressure (PEEP), the level of PEEP that results in venous admixture below 15% with an inspired oxygen fraction less than 0.5. We compared several variables for PEEP optimization--oxygen transport, total respiratory system compliance, FRC-based compliance, mixed venous oxygen saturation, end-tidal to arterial carbon dioxide tension difference, and arterial oxygen saturation--by producing four different PEEP levels, 0, 5, 10 and 15 cm H2O, in 24 mongrel dogs in which pulmonary injury was produced. The data were regressed versus PEEP by using analysis of variance for regression. Venous admixture (F1,23 = 149.3; P less than 0.0001), end-tidal to arterial carbon dioxide tension difference (F1,23 = 64.9; P less than 0.0001), and oxygen transport (F1,23 = 95.1; P less than 0.0001) decreased linearly with PEEP. FRC (F1,23 = 248.1; P less than 0.0001) and arterial oxygen saturation (F1,23 = 66.9; P less than 0.0001) increased linearly with PEEP. Total respiratory system compliance (F1,23 = 66.6; P less than 0.0001) and mixed venous oxygen saturation (F1,23 = 12.2; P less than 0.002) had a quadratic relationship with respect to PEEP with a peak at 5 cm H2O. FRC-based compliance did not have a significant relationship to PEEP. The maximum values of total respiratory system compliance, FRC-based compliance, mixed venous oxygen saturation, and oxygen transport did not occur at PEEP levels that corresponded to a venous admixture below 15% ("optimal" PEEP).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1982

A simple method for measuring the effect of PEEP on functional residual capacity during mechanical ventilation.

An indirect method for measuring the increment of functional residual capacity (FRC) produced by positive end-expiratory pressure (PEEP) during controlled mechanical ventilation was evaluated in 13 patients with acute respiratory failure. The actual FRC with and without PEEP was measured with a computerized nitrogen washout method. The results obtained did not show significant differences between the measured and the calculated increment of FRC. This indirect method accurately measures how much alveolar recruitment (estimated as increment of FRC) is produced by PEEP.

Female↗

PubMed1985

Functional residual capacity, thoracoabdominal dimensions, and central blood volume during general anesthesia with muscle paralysis and mechanical ventilation.

Functional residual capacity (FRC), rib cage and abdominal dimensions (rc-ab), central blood volume (CBV), and extra vascular lung water (EVLW) were measured in six lung-healthy subjects awake and during halothane anesthesia, muscle paralysis, and mechanical ventilation. FRC was assessed by multiple breath nitrogen washout, rc-ab dimensions by computerized tomography, and CBV and EVLW by a double-indicator dilution technique (thermo-dye). During anesthesia, FRC decreased by 0.5 1 (17%). The cross-sectional chest area was reduced by 12-20 cm2, causing an approximate reduction in thoracic volume by 0.3 1. Concomitantly, the diaphragm was moved cranially by an average of 1.9 cm, diminishing the thoracic volume a further 0.5 1. The abdominal cross-sectional area did not alter significantly, despite the shift of the diaphragm. CBV decreased by 0.3 1. EVLW did not change significantly. It is concluded that the thoracic volume is reduced during halothane anesthesia, muscle paralysis, and mechanical ventilation as a result of cranial shift of the diaphragm and reduction in transverse area. The decrease in thoracic volume is accompanied by a reduction in FRC and a displacement of blood from the thorax to the abdomen, the transverse area of the latter thus being maintained despite the shift of the diaphragm.

Abdomen↗