Total Respiratory System Compliance Research Articles

Impact of obesity on pulmonary function: current understanding and knowledge gaps.

Obesity is an increasing world-wide public health concern. Obesity both causes respiratory symptoms and contributes to many cardiorespiratory diseases. The effects of obesity on commonly used lung function tests are reviewed. The effects of obesity on lung function are attributed both to mechanical factors and to complex metabolic effects that contribute to a pro-inflammatory state. The effects of obesity on lung function correlate with BMI and correlate even better when the distribution of excess adipose tissue is taken into account, with central obesity associated with more prominent abnormalities. Obesity is associated with marked decreases in expiratory reserve volume and functional residual capacity. Total lung capacity, residual volume, and spirometry are less affected by obesity and are generally within the normal range except with severe obesity. Obesity decreases total respiratory system compliance primarily because of decreased lung compliance, with only mild effects on chest wall compliance. Obesity is associated with impaired gas transfer with decreases in oxygenation and varied but usually mild effects on diffusing capacity for carbon monoxide, while the carbon monoxide transfer coefficient is often increased. Obesity has significant effects on lung function. The relative contribution of the mechanical effects of obesity and the production of inflammatory cytokines by adipose tissue on lung function needs further study.

Evaluation of pulse pressure variation validity criteria in critically ill patients: a prospective observational multicentre point-prevalence study

Respiratory variation in pulse pressure (ΔPP) is commonly used to predict the fluid responsiveness of critically ill patients. However, some researchers have demonstrated that this measurement has several limitations. The present study was designed to evaluate the proportion of patients satisfying criteria for valid application of ΔPP at a given time-point. A 1 day, prospective, observational, point-prevalence study was performed in 26 French intensive care units (ICUs). All patients hospitalized in the ICUs on the day of the study were included. The ΔPP validity criteria were recorded prospectively and defined as follows: (i) mechanical ventilation in the absence of spontaneous respiration; (ii) regular cardiac rhythm; (iii) tidal volume ≥8 ml kg(-1) of ideal body weight; (iv) a heart rate/respiratory rate ratio >3.6; (v) total respiratory system compliance ≥30 ml cm H2O(-1); and (vi) tricuspid annular peak systolic velocity ≥0.15 m s(-1). The study included 311 patients with a Simplified Acute Physiology Score II of 41 (39-43). Overall, only six (2%) patients satisfied all validity criteria. Of the 170 patients with an arterial line in place, only five (3%) satisfied the validity criteria. During the 24 h preceding the study time-point, fluid responsiveness was assessed for 79 patients. ΔPP had been used to assess fluid responsiveness in 15 of these cases (19%). A very low percentage of patients satisfied all criteria for valid use of ΔPP in the evaluation of fluid responsiveness. Physicians must consider limitations to the validity of ΔPP before using this variable.

Expiratory Resistance Increases End-Expiratory Lung Volume during Sleep

A 37-year-old man with severe obstructive sleep apnea presented to our sleep disorders research laboratory and was instrumented with an epiglottic catheter, pneumotachograph, and magnetometers (to measure relative changes in lung volume) as part of an ongoing study. During the night there were periods of spontaneous, sustained increases in upper airway resistance during expiration (Figure 1A). During these periods, expiratory positive airway pressure developed at the level of the epiglottis (epiglottic pressure channel). Note that although epiglottic pressure increases during expiration, there is no corresponding increase in flow or mask pressure, suggesting a choke point between the epiglottis and airway opening. Expiratory positive airway pressure was associated with an increase in end-expiratory lung volume (rib cage, abdomen, and change in lung volume channels) according to the total respiratory system compliance (Figure 1B). Although other factors may be important, such as upper airway muscle activation, the increase in end-expiratory lung volume was generally associated with a decrease in upper airway resistance (increased flow despite less negative epiglottic pressure) (Figure 1C). Figure 1. Nasal expiratory resistance valves may improve obstructive sleep apnea in a subset of patients, but the mechanism of action is not known (1, 2). Expiratory resistance valves increase end-expiratory lung volume during wakefulness, which might stabilize the upper airway, but this phenomenon has not been clearly demonstrated during sleep. This spontaneously occurring example provides proof of concept that expiratory resistance acts to increase end-expiratory lung volume during sleep via generation of expiratory positive airway pressure. Furthermore, it suggests that such increased end-expiratory lung volume can stabilize the upper airway during inspiration. This image has not been previously published in any form.

Does Decline of Lung Function in Wheezy Infants Justify the Early Start of Controller Medications?

To compare lung function in wheezy infants, with risk factors of asthma and with some immunological parameters which may be useful as predictors of subsequent asthma. The data of 241 infants aged 5–36 mo, with recurrent wheeze (≥3 episodes of physician confirmed wheeze) prior to receiving inhaled corticosteroids or anti-leukotrine agents was retrospectively analyzed. They were subdivided into 2 subgroups; those with asthma risk factors (132 patients) and those without (109 patients) Also, 67 healthy, age and sex matched children without recurrent wheezes were taken as control group. Total serum IgE, eosinophilic percentage, tPTEF/tE (time to peak expiratory flow to total expiratory time), total respiratory system compliance (Crs) and resistance of the respiratory system (Rrs) was done for patients and control groups. Wheezy infants had a significantly higher eosinophilic percentage and total serum IgE as well as a significantly lower pulmonary function parameters when compared to healthy controls. Wheezy infants with positive family history of asthma and those who had not been breast fed showed significant reduction in the mean values of tPTEF/tE and increased both eosinophilic percentage and total serum IgE. Crs was significantly decreased in wheezy infants with positive seasonal variations and those who had increased both eosinophilic percentage and total serum IgE. Rrs showed significant increase in wheezy infants with positive family history of atopy and those who had increased eosinophilic percentage and increased total serum IgE. Lung function, eosinophilic percentage, total serum IgE and asthma risk factors could be used as predictors for ongoing wheeze in this subset of children.

Impact of obesity on respiratory function

Obesity has long been recognized as having significant effects on respiratory function. The topic has been studied for at least the last half century, and some clear patterns have emerged. Obese patients tend to have higher respiratory rates and lower tidal volumes. Total respiratory system compliance is reduced for a variety of reasons, which will be discussed. Lung volumes tend to be decreased, especially expiratory reserve volume. Spirometry, gas exchange and airway resistance all tend to be relatively well preserved when adjusted for lung volumes. Patients may be mildly hypoxaemic, possibly due to ventilation-perfusion mismatching at the base of the lungs, where microatelectasis is likely to occur. Weight loss leads to a reversal of these changes. For all of these changes, the distribution of fat, that is, upper versus lower body, may be more important than body mass index.

Which OSA Patients Might Respond to Nasal Valves?

Which OSA Patients Might Respond to Nasal Valves?

Impact of airway obstruction on lung function in very preterm infants at term*

Morbidity and mortality in preterm infants is significantly determined by the development of pulmonary complications. We thus investigated the impact of obstructive ventilatory disorders on lung function in very preterm infants with a history of respiratory distress syndrome and/or bronchopulmonary dysplasia using repeated body plethysmographic measurements before and after bronchodilation. Lung function, including effective airway resistance (Raw), specific conductance (SGaw), functional residual capacity (FRCbox), and total respiratory system compliance (Crs, multiple occlusion technique) was assessed in 27 preterm infants pound31 wks gestational age at a median postmenstrual age of 38 wks after mild oral sedation before and after inhalation of nebulized salbutamol (1.25 mg/2.5 mL; PARI JuniorBOY N) using the MasterScreen Baby Body (Jaeger, Hoechberg, Germany). In preterm infants median Raw was initially found to be within the normal range as determined for healthy term newborns, but decreased significantly after administration of salbutamol; SGaw changed accordingly. FRCbox was significantly reduced compared with healthy term newborns (16.6 vs. 19.6 mL/kg, mean) and decreased further after bronchodilation, whereas Crs was not significantly altered. This is the first report quantifying the important impact of obstructive ventilatory disorders on lung function in very preterm infants at term. Besides its important role in preterm lung function consecutive overinflation could furthermore be shown to mask reduction of lung volume in these infants. Thus, body plethysmographic measurements seem to be an important diagnostic tool in preterm infants at term before hospital discharge in order to quantify ventilation disorders and to define therapeutic strategies.

Decreased Respiratory Compliance in Infants Less Than or Equal to 32 Weeks' Gestation, Delivered More Than 7 Days After Antenatal Steroid Therapy

Our objective was to compare the pulmonary function (respiratory compliance) of infants who were < or = 32 weeks' gestation and delivered > 7 days after a single course of antenatal steroids versus infants who were delivered 1 to 7 days after a single course of antenatal steroids. A prospective cohort study of respiratory system compliance was conducted of infants < or = 32 weeks' gestation within 72 hours of life and before surfactant therapy if needed. The study (remote) group was composed of infants who were treated with antenatal steroids > 7 days before delivery and the comparison group (ideal group) of matched infants who were treated with antenatal steroids 1 to 7 days before delivery. Respiratory system compliance was measured with the single-breath occlusion technique. Twenty-eight remotely treated infants and 28 ideally treated infants were studied. The remote group had a significantly lower respiratory system compliance per kilogram and total respiratory system compliance when compared with the ideal antenatal steroids group. Within the remote group, infants who received antenatal steroids 8 to 14 days (n = 10) before delivery had a significantly higher respiratory system compliance and a trend to less surfactant need (10% vs 33%) as compared with infants who received antenatal steroids > 14 days (n = 18) before delivery. Infants who were < or = 32 weeks' gestation and remotely treated with antenatal steroids (average 21 days) had a significantly lower respiratory compliance compared with matched infants who were ideally treated with antenatal steroids. We speculate that the lower respiratory system compliance may reflect the dissipation of beneficial effects of antenatal steroids on pulmonary function when delivery occurs > 7 days after therapy and particularly when therapy is > 14 days before delivery.

Non-invasive measurement of total respiratory compliance and resistance in cats

We adapted non-invasive techniques developed for human infants to measure total respiratory system compliance (Crs) and resistance (Rrs) in 21 healthy cats. The animals breathed through a face mask attached to a respiratory circuit and measurements were taken of changes in lung volume and airway pressure during brief occlusions of the airway at different lung volumes. The slope of the plot of change in volume against airway pressure yielded the multiple occlusion Crs with a mean (+/-95%CI) value of 6.8 (6.3-7.3) ml/cm H2O. In 12 animals measurements were made by the single breath technique in which occlusion was made early in expiration and on release, a plot of the subsequent relaxed expiratory flow and volume yielded the time constant (taurs), Crs and Rrs with mean (+/-95%CI) values of 0.27 (0.22-0.31) s, 7.0 (6.1-7.8) ml/cm H2O, and 38.7 (33.7-43.6) cm H2O/l/s, respectively. Rrs was significantly correlated inversely with forced expiratory flow at resting lung volume (V'maxFRC).

Effect of aging on respiratory system physiology and immunology

With the looming expansion of the elderly population of the US, a thorough understanding of "normal" aging-related changes on the respiratory system is paramount. The respiratory system undergoes various anatomical, physiological and immunological changes with age. The structural changes include chest wall and thoracic spine deformities which impairs the total respiratory system compliance leading to increase work of breathing. The lung parenchyma loses its supporting structure causing dilation of air spaces: "senile emphysema". Respiratory muscle strength decreases with age and can impair effective cough, which is important for airway clearance. The lung matures by age 20-25 years, and thereafter aging is associated with progressive decline in lung function. The alveolar dead space increases with age, affecting arterial oxygen without impairing the carbon dioxide elimination. The airways receptors undergo functional changes with age and are less likely to respond to drugs used in younger counterparts to treat the same disorders. Older adults have decreased sensation of dyspnea and diminished ventilatory response to hypoxia and hypercapnia, making them more vulnerable to ventilatory failure during high demand states (ie, heart failure, pneumonia, etc) and possible poor outcomes.

Effects of Lung Squeezing Technique on Lung Mechanics in Mechanically-Ventilated Preterm Infants with Respiratory Distress Syndrome

Effects of conventional chest physiotherapy on preterm infants may be compromised due to the maturation difference in immature lungs. The lung squeezing technique (LST) has been shown to be beneficial in correcting atelectasis in preterm infants. The purpose of this study was to investigate the effects of LST on the parameters of lung mechanics in preterm infants on mechanical ventilation. LST was used as an intervention to improve the distribution of ventilation in infants with respiratory distress syndrome. Eleven preterm infants on mechanical ventilation were enrolled. Serial measurements on static respiratory system compliance (Crs) and resistance (Rrs) by an airway occlusion technique with passive flow-volume analysis were performed before and immediately after LST, and repeated 4 hours later to assess the carryover effect. Crs improved by 21% (0.92 ± 0.37 mL/cmH 2 O/kg vs. baseline 0.76 ± 0.33 mL/cmH 2 O/kg, p = 0.023) immediately after LST. Split group analysis showed that only the lower Crs group had a significant carryover effect at 4 hours post-LST (p = 0.046). LST increases total respiratory system compliance, possibly through decompression of the overdistended lung units and recruitment of atelectatic alveoli. Rrs showed no significant change after LST. Individual trends of decreased Rrs were observed in infants with obvious secretion. The effect of LST on respiratory system resistance needs to be further explored by recruiting other disease conditions that present with pulmonary secretions.

Small size at birth and greater postnatal weight gain: relationships to diminished infant lung function.

Recent evidence suggests that impaired lung development is linked with diminished lung function and an increased risk of chronic obstructive airway disease in adulthood. To examine environmental influences on early lung development, we measured lung function in 131 normal-term infants aged 5-14 weeks. Adjusting for age at measurement, FEV at 0.4 seconds fell by 4.4% for each standard deviation decrease in birth weight (p = 0.047); when adjusted for FVC, FEV at 0.4 seconds was not related to birth weight but fell by 3.2% per standard deviation increase in infant weight gain (p = 0.001). Age- and sex-adjusted total respiratory system compliance fell by 7.0% per standard deviation decrease in birth weight (p < 0.001) but was not related to infant weight gain. In univariate analyses, age-adjusted forced expiratory flow at functional residual capacity was not related to birth weight, but decreased by 11.0% per standard deviation increase in infant weight gain (p = 0.007). The respiratory rate rose by 5.1% per standard deviation increase in infant weight gain (p = 0.001). Lung function measurements were not related to infant feeding. The observations suggest that lower rates of fetal growth and higher rates of early infancy weight gain are associated with impaired lung development.

Respiratory physiopathology in surgical repair for large incisional hernias of the abdominal wall

Background: The computerized noninvasive measurement of respiratory mechanics enables new prospects in the study of respiratory physiopathology in surgical repair of large incisional hernias. Study design: We studied 10 patients with COPD ventilated with a Servo Ventilator 900C. We measured inspiratory flow by means of a pneumotacograph, the volume by integrating the flow signal, and esophageal and airway opening pressure by means of two differential pressure transducers (an esophageal balloon measures, separately, chest wall and lung mechanical properties). The signals were sent by an analogic-digital converter to a personal portable computer to be analyzed. We calculated compliance of total respiratory system (Crs), chest wall (Ccw), and lung (Cl); maximum resistance of the total respiratory system (Rmax, Rs), chest wall (Rmax, w), and lung (Rmax, L); and work of breathing (Wob). Statistics were performed using one-way analysis of variance and p = 0.05 was considered significant. Results: At the closure of the peritoneum a reduction of Crs and Wob was recorded in seven patients in whom a PTFE prosthesis widening the abdominal cavity was used to restore the baseline value. Variations in respiratory compliance are from variations in Ccw with unaffected Cl (Ccw varied from 0.180 to 0.130 L/cmH 2O at peritoneal closure and from 0.130 to 0.170 L/cmH 2O by prosthetic peritoneal widening). Respiratory resistances remained unchanged (11.3 cmH 2O/L/s) at any time of measurement. Conclusions: The intraoperative assessment of respiratory mechanics is useful to evaluate and eventually to decrease the mechanical workload (prosthesis widening peritoneum or fascia incisions). The passive mechanical work performed by the ventilator needs to be kept constant or no higher than 10% basic data: if these conditions are maintained, mostly in patients with COPD, there is no risk of respiratory muscular fatigue during the postoperative period.

Total and prolonged filling of the lungs with Ringer's solution under extracorporeal lung assist (ECLA) in dogs.

Massive alveolar lavage has been used clinically to remove materials accumulated in the alveoli. Recently, filling the lungs with oxygenated perfluorochemical (total liquid ventilation) has been investigated. However, effects of complete and prolonged filling of bilateral lungs with aqueous fluid, such as saline or Ringer's solution, has not been evaluated, although it is possible to sustain gas exchange without the natural lung by using extracorporeal circulation and an artificial lung (extracorporeal lung assist: ECLA). It is also not known whether the lung can recover gas exchange ability after prolonged fluid filling. Normal mongrel dogs were endotracheally intubated under general anesthesia and mechanically ventilated. After initiation of venoarterial ECLA, warmed lactated Ringer's solution was instilled into the lungs through the endotracheal tube, and the lungs were completely filled at a hydrostatic pressure of 15 cmH2O (fluid-filled group: group F). After the lungs were filled for 4 h, the fluid was drained and ventilation was re-instituted. ECLA, then mechanical ventilation was gradually weaned within 24 h after fluid drainage. In control group (group C), dogs were kept apneic for 4 h with their lungs inflated at an airway pressure of 15 cmH2O with air. Transient hypoxemia occurred during fluid filling but every dog could be weaned from ECLA and mechanical ventilation to spontaneous respiration. The average rate of fluid absorption from the lung during fluid filling was 4.2+/-1.8 ml kg(-1) h(-1). After fluid drainage and restart of mechanical ventilation, bilateral lungs were expanded and well aerated. Total static respiratory system compliance (static compliance) remained unchanged even after fluid filling, and the weight of the lung water did not increase significantly compared to that in group C. Total urine volume was significantly increased in group E Histologically, alveolar structures were preserved and no interstitial edema or bleeding was seen in either group. Complete filling of the bilateral lungs for 4 h with lactated Ringer's solution under ECLA causes no deterioration in gas exchange or static compliance in normal dogs, although transient hypoxemia occurs during fluid filling.

Comparison of Lung Function in Infants Exposed to Maternal Smoking and in Infants With a Family History of Asthma

To compare lung function in infants exposed to maternal smoking with lung function in infants with a family history of asthma. There are no published studies comparing lung function in both groups. Cross-sectional study. A tertiary pulmonary care center at a children's hospital. One hundred five infants with daily wheezing. Thirty-five infants had persistent exposure to maternal smoking, and 70 had a family history of asthma in parents or siblings. Infant pulmonary function tests were compared between the two groups. The ratio of terminal to peak expiratory flow at tidal breathing at 25% of the previous expiration remaining and the ratio of terminal to peak expiratory flow with forced expiration at 25% of the previous expiration remaining (FEF25/PFEF) were used to evaluate peripheral airflow. A > 25% improvement in FEF25/PFEF after a bronchodilator challenge test was considered a positive response. Most infants in both groups had evidence of peripheral airflow obstruction with forced expiration. In infants exposed to maternal smoking, only 4 of 35 (11.4%) responded to a bronchodilator, compared to 51 of 70 (72.9%) in the group with a family history of asthma (p < 0.0005). There was no statistically significant difference in total respiratory system compliance, total respiratory system resistance, tidal volume, and degree of peripheral airflow obstruction at tidal breathing or after forced expiration in both groups. Infants with exposure to maternal smoking and infants with a family history of asthma have altered lung function, and a positive response to a bronchodilator is one variable that seems to differentiate the two groups.

Changes in respiratory mechanics during abdominal laparoscopic surgery in children.

We designed this study in order to measure the changes in respiratory mechanics during laparoscopic surgery in children. Ventilation parameters (Flow (Ví) and Peak Pressure (Pmax)) were measured and total respiratory system mechanics (resistance (Rrs) and compliance (Crs)) were derived using multiple linear regression analysis in 11 children aged 8 months to 11 years. The Pmax increased by 26.6% and the Rrs increased by 20.2% whilst the Crs decreased by 38.9% after pneumoperitoneum. These findings suggest that clinically important changes in respiratory mechanics occur as a result of the pneumoperitoneum produced during abdominal laparoscopic surgery.

Assisted mechanical ventilation using combined elastic and resistive unloading in cats with severe respiratory failure: effects on gas exchange and phrenic nerve activity

Schulze A, Jonzon A, Sindelar R, Schaller P, Dammann V, Sedin G. Assisted mechanical ventilation using combined elastic and resistive unloading in cats with severe respiratory failure: effects on gas exchange and phrenic nerve activity. Acta Pædiatr 1999; 88: 636‐41. Stockholm. ISSN 0803‐5253This study tests the efficacy of respiratory mechanical unloading as a mode of assisted mechanical ventilation in cats with an intact breathing‐control system but severe pulmonary parenchymal injury. Twelve anaesthetized, intubated cats received multiple saline lung lavages so that their total respiratory system compliance decreased from 56.1 ± 10.4 to 26.8 ± 6.8 ml/kPa (p &lt; 0.001) and their PaO2 fell to 12.38 ± 4.71 kPa when 100% O2 was used as inspired gas. They were then exposed to three consecutive 15‐min periods of CPAP of 0.5 kPa, respiratory unloading and again CPAP of 0.5 kPa. Unloading was applied with end‐expiratory pressure of 0.5 kPa, elastic assistance of 0.03 kPa/ml and resistance compensation of 2.0 kPa/l/s. Arterial blood gases for the CPAP baselines did not differ significantly before and after unloading: pH 7.14 ± 0.04 vs. 7.16 ± 0.06; PaCO2 8.99 ± 2.07 vs. 8.33 ± 2.01 kPa; PaO2 12.4 ± 4.7 vs. 13.3 ± 7.6 kPa. Nor did the baselines differ in terms of tidal volume, respiratory rate and phrenic nerve activity. Unloading increased tidal volume substantially by about 50% and increased respiratory rate slightly, while inspiratory time remained unchanged. PaCO2 fell to 6.63 ± 1.57 kPa and pH rose to 7.25 ± 0.06. Phrenic nerve activity was significantly down‐regulated in terms of total number of impulses and mean impulse frequency in the phrenic nerve burst. These results suggest that combined elastic and resistive unloading may be an effective means of assisted mechanical ventilation in severe respiratory failure of pulmonary parenchymal origin. □Control of breathing, phrenic nerve activity, proportional assist ventilation, respiratory failure, respiratory mechanical unloading

Factors predisposing infants to lower respiratory infection with wheezing in the first two years of life.

Acute lower respiratory illness (LRI) early in life has been implicated as a factor for adverse respiratory outcomes later in life. Factors that predispose infants to LRI with wheezing have not been conclusively defined. This prospective study assessed factors that might contribute to LRI with wheezing in the first 2 years of life. Seventy-one healthy full-term infants (44 boys, 27 girls) completed the 2-year follow-up. Demographic and environmental factors were evaluated by questionnaire. Respiratory function was assessed by single occlusion technique and rapid thoracic compression technique. Both techniques were performed successfully in 40 infants at 2.6 (+/- 1.4) months old before they developed any episode of LRI. Eighteen infants (25%) developed LRI with wheezing. The first episode of LRI with wheezing occurred in the first year of life in 8 infants, and in the second year of life in 10 infants. There were no significant differences in the demographic or environmental features between infants with or without wheezing LRI, or between infants who acquired LRI with wheezing in the second year of life and those who did not acquire or acquired in the first year of life. Infants from different groups did not differ in airway resistance or maximal flow at functional residual capacity. Infants who developed LRI with wheezing had higher incidence of low values for total respiratory system compliance corrected for body weight compared with those who did not (5/30 versus 6/10, odds ratio = 7.5, 95% confidence interval: 1.53 to 36.7, P = .013). None of the variables of the pulmonary function test could differentiate infants who subsequently developed LRI with wheezing in the first year of life or did not develop any episode of LRI with wheezing from those who developed LRI with wheezing in the second year of life. Differences in lung function in early life may predispose infants to LRI with wheezing in the first 2 years of life.

Assisted mechanical ventilation using combined elastic and resistive unloading in cats with severe respiratory failure: effects on gas exchange and phrenic nerve activity.

This study tests the efficacy of respiratory mechanical unloading as a mode of assisted mechanical ventilation in cats with an intact breathing-control system but severe pulmonary parenchymal injury. Twelve anaesthetized, intubated cats received multiple saline lung lavages so that their total respiratory system compliance decreased from 56.1+/-10.4 to 26.8+/-6.8 ml/kPa (p < 0.001) and their PaO2 fell to 12.38+/-4.71 kPa when 100% O2 was used as inspired gas. They were then exposed to three consecutive 15-min periods of CPAP of 0.5 kPa, respiratory unloading and again CPAP of 0.5 kPa. Unloading was applied with end-expiratory pressure of 0.5 kPa, elastic assistance of 0.03 kPa/ml and resistance compensation of 2.0 kPa/l/s. Arterial blood gases for the CPAP baselines did not differ significantly before and after unloading: pH 7.14+/-0.04 vs. 7.16+/-0.06; PaCO2 8.99+/-2.07 vs. 8.33+/-2.01 kPa; PaO2 12.4+/-4.7 vs. 13.3+/-7.6 kPa. Nor did the baselines differ in terms of tidal volume, respiratory rate and phrenic nerve activity. Unloading increased tidal volume substantially by about 50% and increased respiratory rate slightly, while inspiratory time remained unchanged. PaCO2 fell to 6.63+/-1.57 kPa and pH rose to 7.25+/-0.06. Phrenic nerve activity was significantly down-regulated in terms of total number of impulses and mean impulse frequency in the phrenic nerve burst. These results suggest that combined elastic and resistive unloading may be an effective means of assisted mechanical ventilation in severe respiratory failure of pulmonary parenchymal origin.

Total respiratory system compliance after thoracoplasty

Recent attention has been directed towards the deleterious effects of the sequelae of pulmonary tuberculosis on respiratory function. Thus, a study was undertaken to find out to what extent the deformity of thorax after thoracoplasty increases the mechanical work of breathing. Compliance of the total respiratory system (Crs) was measured with a pressure-type body plethysmograph in nine post-thoracoplasty tuberculosis patients, 15 patients with pulmonary tuberculosis and three patients with pleural diseases. Mean Crs in nine post-thoracoplasty tuberculosis patients was 0·086 l cmH 2O −1, and that in six patients with moderately advanced pulmonary tuberculosis was 0·084 l cmH 2O −1. Mean Crs (0·130 l cmH 2O −1) in nine patients with a minimum lesion of tuberculosis was not different from the reference Crs values reported to date by several authors. Crs was significantly correlated with vital capacity, but not with functional residual capacity. There was no difference in specific Crs between post-thoracoplasty tuberculosis patients and patients with moderately advanced pulmonary tuberculosis. Crs of patients with a pleural disease was smaller than Crs of patients with a minimal lesion of pulmonary tuberculosis. The deformity of thorax after thoracoplasty caused a decrease of Crs. However, ventilation is not as severely impaired as anticipated from the degree of thorax deformity on chest X-ray film, providing that movement of the diaphragm is unrestricted.