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PubMed1982

Oxygen wash-in method for monitoring functional residual capacity.

Atelectasis, pulmonary edema, fibrosis, pneumothorax, and mucous plug airway obstruction all result in reduced lung volume. The oxygen (O2) wash-in method provides a way to monitor routinely the functional residual capacity (FRC) in the ICU without disconnecting the patient from the ventilator and without additional personnel or instrumentation. This method is a modification of an open-circuit nitrogen (N2) wash-out procedure and requires a computer-based respiratory monitoring system with a fast response O2 analyzer and respiratory flowmeter. FRC is computed after a 20% or greater change in the ventilator FIO2 setting. The accuracy and reproducibility of the method were evaluated using artificial lungs, normal subjects, and postcardiac surgery patients. FRC estimates by O2 wash-in and helium dilution were highly correlated, with r = 0.97 and a regression slope and zero intercept of 1.06 and -0.13, respectively. The FRC difference between 23 repeated trials in 18 postcardiac surgery patients was 70 +/- 160 ml (mean +/- SD).

Cardiac Surgical Procedures↗
PubMed1975

Mechanics of breathing, gas distribution and functional residual capacity at different frequencies of respiration during spontaneous and artificial ventilation.

Nine healthy volunteers were investigated, both while awake and breathing spontaneously, and while anaesthetized with IPPV, in all cases at rates of both 12 and 24 b.p.m. Gas flow and volume were measured with a pneumotachography. The transpulmonary pressure (the pressure difference between the trachea or the buccal cavity and the oesophagus) was also recorded. The distribution of gas was analysed by means of nitrogen washout curves, which also permitted the determination of functional residual capacity (FRC). Lung compliance during IPPV was approximately half that during spontaneous breathing. During IPPV the compliance was dependent on the frequency of ventilation, being lower with the greater frequency. Pulmonary resistance was approximately twice as great with artificial ventilation, but no significant relationship to frequency was demonstrated. Gas distribution was within normal limits and in this respect there was no difference between low and high rates of spontaneous breathing. With IPPV at the higher rate, gas distribution was significantly less even, but still within normal limits. Dfferences in FRC under the different conditions during the experiments were not significant, but the values obtained were lower with artificial ventilation. Neither the reduction in dynamic lung compliance induced by anaesthesia and artificial ventilation, nor its dependence on the frequency of such ventilation, can be explained with certainty by changes in gas distribution.

Adult↗
PubMed2002

The effect of a single remote course versus weekly courses of antenatal corticosteroids on functional residual capacity in preterm infants: a randomized trial.

OBJECTIVE: There are no randomized data on the effect of repeat courses of corticosteroids during pregnancy on newborn pulmonary function. Our objective was to compare the effect of a single remote course of antenatal steroids (AS) with weekly courses of AS on functional residual capacity (FRC) and respiratory compliance in preterm infants. STUDY DESIGN/METHODS: Pregnant women 25 to 33 weeks' gestation, who remained undelivered 1 week after their first course of antenatal corticosteroids (two 12-mg doses of betamethasone) were randomized to weekly courses of corticosteroids versus weekly placebo until delivery or 34 weeks' gestation. FRC was measured with the nitrogen washout technique and respiratory compliance with the single breath occlusion technique within 48 hours of life. RESULTS: Thirty-seven infants (mean gestational age at delivery approximately 32.5 weeks) were studied. Maternal and infant demographics were similar. There was no significant difference in FRC (28.5 vs 27.5 mL/kg) or respiratory compliance between the infants who received a single remote course of antenatal corticosteroids and those who received weekly courses of corticosteroids until delivery. There was no significant difference in admission head circumference or birth weights between the groups. CONCLUSIONS: Our results demonstrate that weekly repetitive courses of AS do not significantly increase FRC or respiratory compliance in preterm infants when compared with a single remote course of steroids given at a mean gestational age of 29 weeks.

Double-Blind Method↗
PubMed2003

Tidal volume, cardiac output and functional residual capacity determine end-tidal CO2 transient during standing up in humans.

In man assuming the upright position, end-tidal P(CO(2)) (P(ETCO(2))) decreases. With the rising interest in cerebral autoregulation during posture change, which is known to be affected by P(ETCO(2)), we sought to determine the factors leading to hypocapnia during standing up from the supine position. To study the contribution of an increase in tidal volume (V(T)) and breathing frequency, a decrease in stroke volume (SV), a ventilation-perfusion (V/Q) gradient and an increase in functional residual capacity (FRC) to hypocapnia in the standing position, we developed a mathematical model of the lung to follow breath-to-breath variations in P(ETCO(2)). A gravity-induced apical-to-basal V/Q gradient in the lung was modelled using nine lung segments. We tested the model using an eight-subject data set with measurements of V(T), pulmonary O(2) uptake and breath-to-breath lumped SV. On average, the P(ETCO(2)) decreased from 40 mmHg to 36 mmHg after 150 s standing. Results show that the model is able to track breath-to-breath P(ETCO(2)) variations (r(2)= 0.74, P P 0.05). Model parameter sensitivity analysis demonstrates that the decrease in P(ETCO(2)) during standing is due primarily to increased V(T), and transiently to decreased SV and increased FRC; a slight gravity-induced V/Q mismatch also contributes to the hypocapnia. The influence of cardiac output on hypocapnia in the standing position was verified in experiments on human subjects, where first breathing alone, and then breathing, FRC and V/Q were controlled.

Adult↗
PubMed1993

Resistive and elastic unloading to assist spontaneous breathing does not change functional residual capacity.

Resistive and/or elastic unloading (a negative ventilator impedance, otherwise termed proportional assist ventilation) may be a useful means to assist spontaneous breathing. This only applies if the ventilator accurately provides pressure changes at the airway opening (P(ao)) proportional to the instantaneous flow and/or volume signal of spontaneous breathing and no significant phase lag. We designed such an infant ventilator, which controls the P(ao) by a negative feedback loop, and superimposes a second positive feedback circuit to generate unloading. To test this mode and the ventilator's accuracy in performing the synchronized pressure changes, we examined the functional residual capacity (FRC). We hypothesized that unloading by itself would not alter FRC because P(ao) should return to a preset baseline at end-expiration, and furthermore, that FRC could be actively altered by changing the baseline. Five anesthetized, tracheotomized, spontaneously breathing rabbits [respiratory system compliance 22.4 +/- 4.6 mL/kPa (mean +/- SEM)] were exposed to end-expiratory P(ao) levels of 0, 0.2, 0.4, and 0.6 kPa. At each of these levels a period of regular continuous positive airway pressure (CPAP) was alternated with a period of unloading (-40 mL/kPa ventilator compliance combined with -3 kPa/L/s ventilator resistance). FRC measured by a sulfur hexafluoride washout technique was virtually identical on CPAP and during unloading at equal end-expiratory P(ao) (difference, 1.41% +/- 0.95%), but FRC increased upon elevation of the end-expiratory P(ao) by 29.4 +/- 3.6 mL/kPa on CPAP and 30.2 +/- 3.2 at unloading (difference NS). We conclude that FRC is not destabilized by unloading, but that during unloading, as during CPAP, it depends on the end-expiratory P(ao).

Animals↗
PubMed1983

Diazepam sedation reduces functional residual capacity and alters the distribution of ventilation in man.

We measured ventilation and static lung volumes in five fit volunteers in the right lateral decubitus position, while they were fully awake and while sedated with diazepam. We also assessed the distributions of ventilation and perfusion in the lungs, using inhalations and intravenous injections of xenon-127. Diazepam, 0.04 mg . kg-1, was administered every three to five minutes as required to induce and maintain a state of sedation which was moderately heavy. Total doses ranged from 0.16 to 0.38 mg . kg-1. Sedation did not alter minute ventilation, but reduced tidal volume, increased breathing frequency and reduced functional residual capacity slightly. Sedation also diminished the normal gradient of ventilation from non-dependent to dependent regions of the lungs. Spontaneous episodes of very small tidal volume breathing during sedation were associated with a marked reduction or cessation of ventilation of the most dependent region of the lungs. There were no sedation-related changes in the distribution of perfusion. These effects of moderately heavy sedation may contribute to the hypoxaemia and impairment of pulmonary gas exchange often present during recovery from general anaesthesia.

Adult↗
PubMed2006

Lung function tests in neonates and infants with chronic lung disease of infancy: functional residual capacity.

This is the second paper in a review series that will summarize available data and discuss the potential role of lung function testing in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses the expansive subject of measurements of lung volume using plethysmography and gas dilution/washout techniques. Following orientation of the reader to the subject area, we focus our comments on areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. Measurements of lung volume are important both for assessing growth and development of lungs in health and disease, and for interpreting volume-dependent lung function parameters such as respiratory compliance, resistance, forced expiratory flows, and indices of gas-mixing efficiency. Acute neonatal lung disease is characterized by severely reduced functional residual capacity (FRC), with treatments aimed at securing optimal lung recruitment. While FRC may remain reduced in established chronic lung disease of infancy, more commonly it becomes normalized or even elevated due to hyperinflation, with or without gas-trapping, secondary to airway obstruction. Ideally, accurate and reliable bedside measurements of FRC would be feasible from birth, throughout all phases of postnatal care (including assisted ventilation), and during subsequent long-term follow-up. Although lung volume measurements in extremely preterm infants were described in a research environment, resolution of several issues is required before such investigations can be translated into routine clinical monitoring.

Airway Resistance↗
PubMed1992

Lung volume measured by functional residual capacity in infants following first trimester amniocentesis or chorion villus sampling.

OBJECTIVE: To determine the incidence of respiratory problems and lung volume abnormalities in babies born after first trimester amniocentesis or chorion villus sampling. DESIGN: A prospective randomized study. SETTING: Harris Birthright Research Centre for Fetal Medicine, Paediatric Respiratory Laboratory, King's College Hospital. SUBJECTS: Babies of mothers who had undergone first trimester amniocentesis (n = 74) or chorion villus sampling (CVS) (n = 86) for fetal karyotyping because of advanced maternal age, parental anxiety or family history of chromosomal abnormality in the absence of parental chromosome re-arrangement. MAIN OUTCOMES: Respiratory distress in the neonatal period and lung volume as assessed by measurement of functional residual capacity (FRC). RESULTS: CVS was associated with a significantly higher incidence of neonatal respiratory distress, six infants in the CVS group but none in the amniocentesis group required admission to the special care baby unit because of respiratory distress (P less than 0.05). Although there was no significant difference in the mean FRC between the two groups (amniocentesis 29.7 ml/kg vs CVS 29.6 ml/kg) the overall incidence of FRC values less than 2.5th centile of the normal range was 9%. CONCLUSION: Both amniocentesis and CVS performed in the first trimester of pregnancy may impair antenatal lung growth.

Amniocentesis↗
PubMed1987

Ventilatory compensation for changes in functional residual capacity during sleep.

The role of conscious factors in the ventilatory compensation for shortened inspiratory muscle length and the potency of this compensatory response were studied in five normal subjects during non-rapid-eye-movement sleep. To shorten inspiratory muscles, functional residual capacity (FRC) was increased and maintained for 2-3 min at a constant level (range of increase 160-1,880 ml) by creating negative pressure within a tank respirator in which the subjects slept. Minute ventilation was maintained in all subjects over the entire range of increased FRC (mean change +/- SE = -3 +/- 1%) through preservation of tidal volume (-2 +/- 2%) despite slightly decreased breathing frequency (-6 +/- 2%). The decrease in frequency (-13 +/- 2%) was due to a prolongation in expiratory time. Inspiratory time shortened (-10 +/- 1%). Mean inspiratory flow increased 15 +/- 3% coincident with an increase in the slope of the moving time average of the integrated surface diaphragmatic electromyogram (67 +/- 21%). End-tidal CO2 did not rise. In two subjects, control tidal volume was increased 35-50% with CO2 breathing. This augmented tidal volume was still preserved when FRC was increased. We concluded that the compensatory response to inspiratory muscle shortening did not require factors associated with the conscious state. In addition, the potency of this response was demonstrated by preservation of tidal volume despite extreme shortening of the inspiratory muscles and increase in control tidal volumes caused by CO2 breathing. Finally, the timing changes we observed may be due to reflexes following shortening of inspiratory muscle length, increase in abdominal muscle length, or cardiovascular changes.

Adult↗
PubMed1969

Changes in blood gas tensions and functional residual capacity chronic asthmatics treated with disodium cromoglycate.

Twenty chronic asthmatic subjects were treated with disodium cromoglycate in open trial. Although in the group as a whole spirometric findings improved, some patients showed a significant increase in arterial oxygen tension or a significant fall in functional residual capacity without any appreciable changes in spirometry. These changes may partly explain the clinical efficacy of this drug.

Adult↗
PubMed1990

[The tidal volume, arterial blood gas and functional residual capacity changes during negative extra-thoracic pressure ventilation and positive airway pressure ventilation].

Eight patients, of ASA physical status I or II soon after total knee replacement under general anesthesia, were studied to compare negative extra-thoracic pressure ventilation (NETPV) with positive airway pressure ventilation (PAPV). The measured parameters during the two ventilatory modes were tidal volume, arterial blood gas and functional residual capacity change (delta FRC). Tidal volume obtained during NETPV was 60 to 80% of that during PAPV at the same absolute values of peak pressure. delta FRC obtained during NETPV was 30 to 40% of that during PAPV at the same absolute values of end-expiratory pressure. A decrease in the esophageal pressure was 4 to 11cmH2O at an end-expiratory negative extra-thoracic pressure of -10 to -20 cmH2O. When the patients were ventilated with the same values of minute ventilation on NETPV and PAPV, there was no significant difference in blood gas values. These findings suggest that efficiency of NETPV is less than that of PAPV at the same absolute working pressure but pulmonary gas exchange of NETPV is almost equal to that of PAPV at the same minute ventilation in the normal lung.

Aged↗