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Biomedical subjects

C J Lanteri

Publications and source records attributed to C J Lanteri.

At least 19 recordsLinked to original sources
PubMed1999

Influence of inertance on respiratory mechanics measurements in mechanically ventilated puppies.

The complete equation of motion for a single compartment model (SCM) includes an inertance term to describe pressure changes in phase with acceleration, as well as terms for resistance and elastance. Inertance has traditionally been excluded from the model when measuring respiratory mechanics at conventional ventilatory frequencies in mature respiratory systems. However, this omission has been questioned recently for measurements of respiratory mechanics in intubated infants where higher ventilation frequencies and smaller tracheal tubes are the norm. We investigated 1) the significance of inertance in an immature respiratory system during mechanical ventilation, and 2) the effect of omitting it from the model on estimates of respiratory mechanics. Six anesthetised, paralysed and mechanically ventilated puppies (2.6-3.9 kg) were studied. A SCM, including an inertance term was fitted to measurements of flow and airway opening (P(AO)) or transpulmonary (P(TP)) pressure using multiple linear regression to estimate respiratory system and lung resistance (R(RS), R(L)), elastance (E(RS), E(L)) and inertance (I(RS), I(L)) respectively, at various ventilation frequencies (0.2-2 Hz). Data obtained at each ventilation frequency were also fitted with a similar model without the inertance term. Inertance contributed significantly to the model at frequencies greater than approximately 0.3-0.5 Hz (20-30 breaths per minute), with I(RS) dominated by the lung. The importance of including the inertance term in the model increased as ventilation frequency increased. Exclusion of inertance from the model led to underestimation of E(RS) and E(L), but no errors in estimates of R(RS) or R(L). The errors increased with ventilation frequency to approximately 10-20% for E(RS) and approximately 10-40% for E(L) at 2 Hz. While inertance contributed significantly to the SCM at ventilation frequencies typically required to maintain normal gas exchange in puppies, the errors from excluding this term were small: <3% for E(RS) and <9% for E(L).

Airway Resistance↗
PubMed1997

Respiratory mechanics during mechanical ventilation: a model study on the effects of leak around a tracheal tube.

Air leak around a tracheal tube (TT) during mechanical ventilation is likely to occur during the inspiratory phase because airway pressure is high for a prolonged period. The presence of a leak may introduce errors in measurements of respiratory mechanics made at the airway opening. If so, respiratory mechanics can be measured more accurately when data are collected during the expiratory phase of ventilation. We examined this phenomenon in a lung model. When a leak was introduced into the model, simulating a leak around the TT, the leak occurred predominantly during the inspiratory phase of respiration. As the magnitude of the leak increased, the overestimation of resistance progressively increased, when calculated from pressure and flow measured at the airway opening. A large leak (38%) resulted in an overestimation of respiratory system resistance by 51% and an underestimation of elastance (Ers) by 23% when calculated from the entire ventilatory cycle. However, there was no under- or overestimation in Rrs when calculated from the expiratory phase only, and ERS was overestimated by only 6.1%. Varying peak inspiratory pressure, end-expiratory pressure, and expiratory time did influence the effect of leak, however, respiratory mechanics could still be calculated accurately from the expiratory phase under these conditions. We conclude that measurements of lung mechanics from the expiratory phase is a promising approach to dealing with the problem of measuring respiratory mechanics in mechanically ventilated infants with leaks around the tracheal tube.

Airway Resistance↗
PubMed1996

Differing patterns of mechanical response to direct fetal hormone treatment.

A single combined intramuscular dose of betamethasone and l-thyroxine (T4) or placebo was injected into the shoulder of fetal lambs 48 hours prior to delivery at days 121 (n = 14), 128 (n = 25) or 135 (n = 20) of gestation. Respiratory mechanics were calculated using multiple linear regression analysis. Both respiratory system resistance (RRS) and elastance (ERS) decreased approximately 4 fold between gestational days 121 (D121) and 135 (D135). Both variables were also reduced by hormone treatment. Reduction in ERS was due to a reduction in both lung (EL) and chest wall (EW) components. In absolute terms EW decreased with gestational age; however, EW as a proportion of total elastance (% EW) increased. Inclusion of a volume-dependent elastance term in the multiple linear regression model enabled us to separate total elastance into volume-independent (E1) and volume-dependent (E2V) components. E1 decreased almost 8-fold compared with only a 2.5-fold fall in E2V between D121 and D135. %E2, the proportion of ERS which is volume-dependent and which provides an index of overventilation, doubled over this time period. Hormone treatment affected E1 and E2V components equally hence %E2 was not altered. Both excised lung volume and end expiratory alveolar volume increased with gestational age and with treatment. The response to treatment was qualitatively similar at each of the gestational ages examined, however, for all mechanics variables, except resistance and E1, the magnitude of response to treatment was significantly smaller in D135 animals compared with other age groups.

Airway Resistance↗
PubMed1995

Changes in respiratory mechanics in children undergoing cardiopulmonary bypass.

Congenital heart malformations are often associated with altered pulmonary hemodynamics. Lesions associated with increased pulmonary blood flow (PBF) or increased mean pulmonary artery pressure (MPAP) may in turn alter respiratory mechanics. Surgical correction of these cardiac defects frequently involves the use of cardiopulmonary bypass (CPB), during which the lung may be partially or completely atelectatic for lengthy periods, further compromising lung mechanics. The aims of this study were to document the effect of PBF on respiratory mechanics in children and to determine whether the detrimental effects of CPB were outweighed by the potentially positive effects of the corrective surgery. Twenty-three children (2-120 mo) undergoing surgery were studied while anesthetized, paralyzed, and mechanically ventilated. Pulmonary to systemic blood flow ratio was used as an index of PBF. Seventeen children had lesions associated with increased PBF (group 1), while six had decreased or normal PBF (group 2). Respiratory mechanics were measured just before the commencement of CPB and within approximately 2 h after the cessation of CPB, with the chest closed. Dynamic elastance (Ers,dyn) and resistance (RRS) were calculated from flow, volume (V), and pressure (Pao) measurements, using multiple linear regression with a volume-dependent single compartment model. Static elastance (ERS,st) was calculated from Pao and V measurements obtained when deflating the lung in steps from a maximal Pao of 30 cm H2O. ERS,dyn, ERS,st, and RRS increased significantly with increasing PBF to 220-330% predicted. There was no correlation between MPAP and respiratory mechanics. After CPB, ERS, dyn and RRS fell to normal levels in group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Validation of esophageal pressure occlusion test after paralysis.

Measurements of respiratory mechanics are frequently made in ventilated infants and children. Esophageal pressure measurements (Pes) using a balloon on a catheter have been used to partition the respiratory mechanics into lung and chest wall components. Appropriate positioning of this balloon is crucial to obtain accurate estimates of pleural pressure. Traditionally, in spontaneously breathing subjects the balloon position is assessed with an occlusion test. In ventilated subjects, it is not always possible to perform an occlusion test prior to paralysis, and even if such a test is performed it may be relevant under conditions of positive pressure ventilation. By occluding the airway opening and applying gentle pressure to the abdomen or rib cage, positive swings in pressure can be measured by both Pes and airway opening pressure (Pao). We compared traditional occlusion tests measured in 16 spontaneously breathing puppies to the positive pressure occlusion test performed after paralysis. In 2 pups we were unable to obtain a reasonable traditional occlusion test (> 15% difference between Pes and Pao) but we obtained 10 traditional occlusion tests in each of the remaining 14 pups (2.1-14 kg). In 11 of these animals delta Pes was within 10% of delta Pao. This compared well to positive pressure occlusion test using abdominal pressure performed after analysis, where delta Pes was within 10% of delta Pao in 10 animals. In 9 of these pups occlusion tests were also performed by applying pressure on the rib cage, where delta Pes was within 10% of delta Pao in 6 animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Pressure transmission across the respiratory system at raised lung volumes in infants.

Forced expiratory flow-volume (FEFV) curves can be generated from end-tidal inspiration in infants with use of an inflatable jacket. We have developed a technique to raise lung volume in the infant before generation of FEFV curves. Measurements of pressure transmission to the airway opening by use of static maneuvers have shown no change with increasing lung volume above end-tidal inspiration. The aim of this study was to determine, under dynamic conditions (i.e., during rapid thoracic compression), whether the efficiency of pressure transmission across the chest wall is altered by raising lung volume above the tidal range. Dynamic pressure transmission (Ptx,dyn) was measured in five infants (age 6-17 mo). Jacket pressure (Pj), esophageal pressure, and volume were measured throughout passive and FEFV curves at lung volumes set by 10, 15, and 20 cmH2O preset pressure. The group mean Ptx,dyn was 37 +/- 6% (SE) of Pj at end-tidal inspiration, and no change was seen with further increases in lung volume. However, a mean decrease in Ptx,dyn of 42% was evident throughout the tidal volume range (i.e., from end-tidal inspiration to end expiration). Isovolume static pressure transmission (Ptx,st) was measured in three of the five infants by inflation of the jacket in a stepwise manner with the airway closed. Measurements were made at end-tidal inspiration and lung volumes at 10, 15, and 20 cmH2O preset pressure. Resulting changes in Pj, esophageal pressure, and airway opening pressure were compared using linear regressions to determine Ptx,st.(ABSTRACT TRUNCATED AT 250 WORDS)

Cystic Fibrosis↗
PubMed1994

Influence of nonlinearities on estimates of respiratory mechanics using multilinear regression analysis.

To investigate the influence of nonlinearities on estimates of respiratory mechanics, differing patterns of mechanical ventilation patterns were analyzed from 8 puppies and 14 children. Respiratory mechanics were calculated using multiple linear regression to fit a linear single-compartment model, a volume-dependent single-compartment model (VDSCM), and a flow-dependent single-compartment model. The ratio of the compliance of the last 20% of the dynamic volume-pressure (V-P) curve to the total compliance (C20/C) and the contribution of a volume-dependent elastance to total elastance [%E2 = E2 (VT)/[(E1 + E2)VT], where E1 + E2 is total elastance, E2 is the volume-dependent component, and VT is tidal volume] were used as the indexes of over-distension. By positioning the dynamic loops on the static V-P curves, ventilation patterns were classified as overdistended or nonoverdistended. In the overdistended group, the C20/C was significantly lower (0.71 +/- 0.10 vs. 0.92 +/- 0.16; P < 0.0001) and %E2 was significantly higher (43.4 +/- 15.0 vs. 0.51 +/- 18.02%, P < 0.0001) than in the nonoverdistended group. The mode of ventilation (pressure controlled vs. volume controlled) and the resistive pressures that resulted in widening of the dynamic V-P loop were found to alter C20/C but not %E2. When the respiratory system was overdistended, i.e., ventilated up to the flattened portion of the V-P curve, the VDSCM gave more accurate estimates of respiratory mechanisms. Furthermore, %E2 calculated from VDSCM is a useful parameter for estimating respiratory system overdistension that is not affected by resistive pressures.

Animals↗
PubMed1994

Time course of changes in lung mechanics following fetal steroid treatment.

We studied the effect of a single-dose, corticosteroid treatment on preterm lambs (gestational age: 128 d). A low, medium, or high betamethasone dose (0.1, 0.5, and 2.0 mg/kg) or saline control was administered directly to the fetus by ultrasound-guided intramuscular injection 48 h before delivery. A second group received either the high dose of betamethasome or saline 24 h before delivery. The lambs were delivered at 128 d gestation, anesthetized with ketamine, and ventilated for 50 min. Respiratory system elastance and resistance were measured at 10-min intervals using multiple linear regression analysis of pressure, flow, and volume. Similarly, estimates of lung mechanics were calculated from transpulmonary pressure. The viscoelastic time constant (tau) was calculated by fitting an exponential to the pressure changes occurring after occluding the airway during expiration. Excised lung volume at 40 cm H2O and lung weight were used to calculate specific elastance and resistance correcting for lung size using volume or weight, respectively. Of the 13 lambs in the 48-h high-dose betamethasone group, five developed pulmonary interstitial emphysema (PIE) as did 3 of 11 animals in the high-dose group treated 24 h before delivery. These animals were analyzed separately. The lambs receiving medium- or high-dose (24 and 48 h predelivery) betamethasone had significantly lower elastance and a trend toward lower resistance when compared with the control groups. Ten minutes after delivery, the animals that developed PIE all had elastance values comparable to that of the control animals despite corticosteroid treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1994

Improved detection of abnormal respiratory function using forced expiration from raised lung volume in infants with cystic fibrosis.

The raised volume rapid thoracic compression (RVRTC) technique is a recently developed method of measuring lung function in infants. The measurements of forced expiratory volume-time (FEVt) parameters from raised lung volumes have been shown to be less variable than maximal flow at functional residual capacity (VmaxFRC), obtained from the conventional rapid thoracic compression (RTC) technique. Measurements of VmaxFRC are highly variable, and may not be sensitive enough to detect a difference between normal infants and infants with cystic fibrosis (CF). The aim of this study was to determine whether the raised volume rapid thoracic compression technique could detect abnormal lung function in a group of CF infants with no current respiratory symptoms. Twelve CF infants were studied (median age 10.5 months, range 3-18 months), and compared to normative data collected previously on 26 healthy infants (median age 14 months, range 3-23 months). We found that VmaxFRC failed to detect any difference between the two groups. CF infants had significantly smaller FEV0.5 and FEV0.75 measurements at a lung volume set by 17.5 cmH2O predetermined inflation pressure (PP) both as raw values and when expressed as percentage predicted. We conclude that the raised volume rapid thoracic compression technique is a sensitive tool, able to detect abnormal lung function in infants with cystic fibrosis. This abnormality was not demonstrated by measurements derived from the conventional rapid thoracic compression technique in the tidal volume range.

Cystic Fibrosis↗
PubMed1993

Changes in respiratory mechanics with age.

A cross-sectional survey involving 51 children, ranging in age from 3 wk to 15 yr, was performed to examine the changes in respiratory mechanics with age in mechanically ventilated children, using both a single-compartment model of the respiratory system and a more sophisticated two-compartment model. Children were studied while under anesthesia for urological surgery and were considered to have normal lungs. They were paralyzed and mechanically ventilated throughout measurements. Respiratory mechanics were measured during ventilation by applying a single-compartment model and by using multilinear regression to calculate dynamic compliance and respiratory system resistance (Rrs). We then used the interrupter technique, which allowed us to partition Rrs into airway resistance and a tissue viscoelastic component known as Pdif. A static volume-pressure curve was constructed from multiple occlusions made at different lung volumes throughout expiration, and static compliance was determined. Rrs and airway resistance decreased as height increased. There was a progressive increase in respiratory system compliance with height. Pdif fell in the first 2 yr of life and then subsequently increased after the age of approximately 5 yr.

Adolescent↗
PubMed1993

Effect of pulmonary blood flow on measurements of respiratory mechanics using the interrupter technique.

The relationship between respiratory mechanics, changes in pulmonary blood flow (PBF), pulmonary arterial pressure, and left atrial pressure is unclear. Conventional methods for the measurement of respiratory mechanics model the respiratory system as a single compartment, which may not adequately represent the respiratory system in a diseased state. The interrupter technique models the respiratory system as two compartments, with the "flow resistance" of the conducting airways and chest wall (Raw) considered separately from Pdif, a measure of the viscoelastic properties of the lung and chest wall, together with any pendelluft present. The respiratory mechanics of 15 infants in the first year of life were studied during cardiac catheterization with the use of conventional methods and the interrupter technique. The infants had a PBF-to-systemic blood flow ratio ranging from 0.6 to 4.0:1. The specific dynamic compliance of the respiratory system was not related to the PBF; however, there was a significant relationship between PBF and the total resistance of the respiratory system (Rrs) [analysis of variance (ANOVA) F = 5.69, P < 0.05], Raw (ANOVA, F = 12.30, P < 0.01), and Pdif (ANOVA, F = 3.79, P < 0.05). Rrs increased significantly with an increase in mean left atrial pressure (ANOVA, F = 6.92, P < 0.05); however, dynamic compliance, Raw, and Pdif did not. These results suggest that the relationship between Rrs and PBF is due an increase in the resistive properties of the conducting airways and tissue components.

Airway Resistance↗
PubMed1993

Inherent coupling of elastic and dissipative behavior of the lung through a viscoelastic time constant.

The simple model best able to describe the viscoelastic behavior of lung tissues contains a Kelvin body. Some facets of the viscoelastic behavior of the model can be characterized by a time constant. We have performed a series of experiments to demonstrate this viscoelastic time constant in open-chest mechanically ventilated puppies by recording the stress recovery after midexpiratory flow interruption. In 19 8- to 10-wk-old puppies, the mean time constant was 0.64 +/- 0.01 (SE) s. This time constant remained unchanged after inhalation challenge with histamine, methacholine, or hypertonic saline, despite marked changes in tissue mechanics (resistance and elastance) and in hysteresivity. The constancy of the viscoelastic time constant demonstrates a tight coupling of the parameters of the Kelvin body model, effectively reducing the viscoelastic parameters to a single degree of freedom, and may explain the coupling between the dynamic elastic and resistive properties of the lung tissues previously demonstrated.

Administration, Inhalation↗
PubMed1993

Fast versus slow ventilation for neonates.

To investigate the effect of ventilation rate on respiratory mechanics, 21 neonates ventilated in the neonatal period for various reasons were studied while being ventilated at 30 and 80 breaths/min. Dynamic respiratory system elasticity (ERS), dynamic respiratory system resistance (RRS), and alveolar pressure at end expiration (EEP) were calculated by using multilinear regression to fit the equation of motion of a linear single-compartment model. Technically satisfactory data were obtained from 13 neonates. With the fast ventilation rate, tidal volume and RRS decreased by a mean of 41.3% (p < 0.01) and 17.5% (p < 0.01), respectively, ERS and EEP increased by a mean of 8.3% (p < 0.05) and 22.2% (p < 0.01), respectively. Fast ventilation produced a shorter effective time constant during expiration, limiting the changes in EEP and, hence, in end-expiratory lung volume. The same changes in respiratory mechanics were also observed in neonates who did not show an increase in EEP even at high frequency. These neonates had a high elastance and time constant short enough to ensure adequate lung emptying. These results suggest that the respiratory mechanics of ventilated neonates are frequency dependent and that neonates with higher ERS, such as those with hyaline membrane disease, can cope with fast rate ventilation without developing dynamic hyperinflation.

Anthropometry↗
PubMed1993

The effect of nedocromil sodium on histamine responsiveness in clinically stable asthmatic children.

A double-blind, randomized, placebo-controlled, parallel-group study was undertaken in 120 clinically stable asthmatic children (aged 6-19 years) to determine the ability of 8 weeks of treatment with nedocromil sodium (4 mg, three times a day) to reduce the level of histamine responsiveness. Despite the subjects being clinically stable and reporting few asthma symptoms, approximately one-third had abnormal pulmonary function on enrollment into the study. Statistically significant increases in pulmonary function were seen in the group treated with nedocromil sodium but not in the control group (p = 0.01). Furthermore, 52% of the individuals with abnormal pulmonary function returned to normal following treatment with nedocromil sodium compared to 11% of those with abnormal pulmonary function who received placebo. However, there were no differences in the level of histamine responsiveness between the two treatment groups at baseline or after 4 or 8 weeks of treatment with nedocromil sodium or placebo. These data suggest that the level of histamine responsiveness is not intimately related to the level of asthma control in children.

Adolescent↗
PubMed1993

Frequency dependence of elastance and resistance in ventilated children with and without the chest opened.

Measurements of respiratory mechanics in mechanically-ventilated children are potentially useful for understanding the pathogenesis and progress of diseases resulting in respiratory failure. Measurement techniques that can be simply and noninvasively employed model the respiratory system as a single compartment. The frequency dependence of elastance and resistance, both of the total respiratory system and of the lungs, was investigated in eight children (aged 2-56 months) undergoing open-heart surgery. The children were studied whilst anaesthetized, paralysed and mechanically-ventilated. Dynamic elastance (Ers) and resistance (Rrs) of the respiratory system and of the lung (EL, RL) were calculated using a multilinear regression technique, with the chest wall intact, prior to the commencement of surgery, and with the chest wall opened via a mid-line sternotomy. Measurements were repeated after brief (60 s) changes in ventilation frequency. The total respiratory system and the lungs demonstrated frequency-dependent behaviour, with elastance increasing and resistance decreasing with frequency. The pattern of the frequency-dependent behaviour was essentially the same, whether the chest wall was intact or opened, suggesting that the chest wall was not solely responsible for this behaviour in these children. These data are consistent with a linear viscoelastic model containing a Kelvin body. When using measurements of respiratory mechanics to follow the progress of respiratory disease in mechanically-ventilated children, this frequency-dependent behaviour must be taken into account.

Airway Resistance↗
PubMed1993

Determination of peak expiratory flow.

It is still unknown whether peak expiratory flow (PEF) is determined by "wave speed" flow limitation in the airways. To investigate the influences of airway mechanical properties on PEF, five healthy adults performed maximal forced expiratory effort (MFEE) manoeuvres, in the standard manner and following breathholds at total lung capacity (TLC) of 2 s and 10 s. Oesophageal pressure (Poes) was measured as an index of respiratory effort. Subjects also performed a MFEE following a 10 s breathhold during which intrathoracic pressure was voluntarily raised by a Valsalva manoeuvre, which would increase transmural pressure and cross-sectional area of the extrathoracic airway. Additional MFEEs were performed with the neck fully flexed and extended, to change longitudinal tracheal tension. In separate studies, PEF was measured with a spirometer and with a pneumotachograph. Breathholds at TLC (2 s and 10 s), and neck flexion reduced PEF by a mean of 9.8% (SD 2.9%), 9.6% (SD 1.6%), and 8.7% (SD 2.8%), respectively, when measured with the spirometer. The same pattern of results was seen when measured with the pneumotachograph. These reductions occurred despite similar respiratory effort. Voluntarily raising intrathoracic pressure during a 10 s breathhold did not reverse a fall in PEF. MFEE manoeuvre with neck extension did not result in an increase in PEF, the group mean % changes being -3.0% (SD 5.0%). We conclude that these results do not allow the hypothesis that "wave-speed" (Vws) is reached at PEF to be rejected. A breathhold at TLC could increase airway wall compliance by allowing stress-relaxation of the airway, thus reducing the "Vws" achievable.

Adult↗
PubMed1991

Do wheezy infants recovering from bronchiolitis respond to inhaled salbutamol?

Wheezy infants, less than 6 months of age, were given either inhaled salbutamol or saline in a double-blind study. A significant change in maximal flow at functional residual capacity (VmaxFRC) was defined as being greater than twice the coefficient of variation of the baseline measurements. There was no difference in the infants' response to saline or salbutamol. Wheezy infants, less than 6 months of age, do not have an increase in VmaxFRC following a single dose of inhaled salbutamol.

Acute Disease↗