Low Respiratory System Research Articles

Impact of extended lung protection during mechanical ventilation on lung recovery in patients with COVID-19 ARDS: a phase II randomized controlled trial

BackgroundProtective ventilation seems crucial during early Acute Respiratory Distress Syndrome (ARDS), but the optimal duration of lung protection remains undefined. High driving pressures (ΔP) and excessive patient ventilatory drive may hinder lung recovery, resulting in self-inflicted lung injury. The hidden nature of the ΔP generated by patient effort complicates the situation further. Our study aimed to assess the feasibility of an extended lung protection strategy that includes a stepwise protocol to control the patient ventilatory drive, assessing its impact on lung recovery.MethodsWe conducted a single-center randomized study on patients with moderate/severe COVID-19-ARDS with low respiratory system compliance (CRS < 0.6 (mL/Kg)/cmH2O). The intervention group received a ventilation strategy guided by Electrical Impedance Tomography aimed at minimizing ΔP and patient ventilatory drive. The control group received the ARDSNet low-PEEP strategy. The primary outcome was the modified lung injury score (mLIS), a composite measure that integrated daily measurements of CRS, along with oxygen requirements, oxygenation, and X-rays up to day 28. The mLIS score was also hierarchically adjusted for survival and extubation rates.ResultsThe study ended prematurely after three consecutive months without patient enrollment, attributed to the pandemic subsiding. The intention-to-treat analysis included 76 patients, with 37 randomized to the intervention group. The average mLIS score up to 28 days was not different between groups (P = 0.95, primary outcome). However, the intervention group showed a faster improvement in the mLIS (1.4 vs. 7.2 days to reach 63% of maximum improvement; P < 0.001), driven by oxygenation and sustained improvement of X-ray (P = 0.001). The intervention group demonstrated a sustained increase in CRS up to day 28 (P = 0.009) and also experienced a shorter time from randomization to room-air breathing (P = 0.02). Survival at 28 days and time until liberation from the ventilator were not different between groups.ConclusionsThe implementation of an individualized PEEP strategy alongside extended lung protection appears viable. Promising secondary outcomes suggested a faster lung recovery, endorsing further examination of this strategy in a larger trial.Clinical trial registration This trial was registered with ClinicalTrials.gov (number NCT04497454) on August 04, 2020.

Rapidly and slowly progressive neuromuscular disease: differences in pulmonary function, respiratory tract infections and response to lung volume recruitment therapy (LVR)

IntroductionReduced lung volumes are a hallmark of respiratory muscle weakness in neuromuscular disease (NMD). Low respiratory system compliance (Crs) may contribute to restriction and be amenable to lung volume recruitment...

Chest wall loading during supine and prone position in patients with COVID-19 ARDS: effects on respiratory mechanics and gas exchange

BackgroundRecent reports of patients with severe, late-stage COVID-19 ARDS with reduced respiratory system compliance described paradoxical decreases in plateau pressure and increases in respiratory system compliance in response to anterior chest wall loading. We aimed to assess the effect of chest wall loading during supine and prone position in ill patients with COVID-19-related ARDS and to investigate the effect of a low or normal baseline respiratory system compliance on the findings.MethodsThis is a single-center, prospective, cohort study in the intensive care unit of a COVID-19 referral center. Consecutive mechanically ventilated, critically ill patients with COVID-19-related ARDS were enrolled and classified as higher (≥ 40 ml/cmH2O) or lower respiratory system compliance (< 40 ml/cmH2O). The study included four steps, each lasting 6 h: Step 1, supine position, Step 2, 10-kg continuous chest wall compression (supine + weight), Step 3, prone position, Step 4, 10-kg continuous chest wall compression (prone + weight). The mechanical properties of the respiratory system, gas exchange and alveolar dead space were measured at the end of each step.ResultsTotally, 40 patients were enrolled. In the whole cohort, neither oxygenation nor respiratory system compliance changed between supine and supine + weight; both increased during prone positioning and were unaffected by chest wall loading in the prone position. Alveolar dead space was unchanged during all the steps. In 16 patients with reduced compliance, PaO2/FiO2 significantly increased from supine to supine + weight and further with prone and prone + weight (107 ± 15.4 vs. 120 ± 18.5 vs. 146 ± 27.0 vs. 159 ± 30.4, respectively; p < 0.001); alveolar dead space decreased from both supine and prone position after chest wall loading, and respiratory system compliance significantly increased from supine to supine + weight and from prone to prone + weight (23.9 ± 3.5 vs. 30.9 ± 5.7 and 31.1 ± 5.7 vs. 37.8 ± 8.7 ml/cmH2O, p < 0.001). The improvement was higher the lower the baseline compliance.ConclusionsUnlike prone positioning, chest wall loading had no effects on respiratory system compliance, gas exchange or alveolar dead space in an unselected cohort of critically ill patients with C-ARDS. Only patients with a low respiratory system compliance experienced an improvement, with a higher response the lower the baseline compliance.

Respiratory Mechanics in a Cohort of Critically Ill Subjects With COVID-19 Infection.

Patients with coronavirus disease 2019 (COVID-19) often develop acute hypoxemic respiratory failure and receive invasive mechanical ventilation. Much remains unknown about their respiratory mechanics, including the trajectories of pulmonary compliance and [Formula: see text]/[Formula: see text], the prognostic value of these parameters, and the effects of prone positioning. We described respiratory mechanics among subjects with COVID-19 who were intubated during the first month of hospitalization. We included patients with COVID-19 who were mechanically ventilated between February and May 2020. Daily values of pulmonary compliance, [Formula: see text], [Formula: see text], and the use of prone positioning were abstracted from electronic medical records. The trends were analyzed separately over days 1-10 and days 1-35 of intubation, stratified by prone positioning use, survival, and initial [Formula: see text]/[Formula: see text]. Among 49 subjects on mechanical ventilation day 1, the mean compliance was 41 mL/cm H2O, decreasing to 25 mL/cm H2O by day 14, the median duration of mechanical ventilation. In contrast, the [Formula: see text]/[Formula: see text] on day 1 was similar to day 14. The overall mean compliance was greater among the non-survivors versus the survivors (27 mL/cm H2O vs 24 mL/cm H2O; P = .005), whereas [Formula: see text]/[Formula: see text] was higher among the survivors versus the non-survivors over days 1-10 (159 mm Hg vs 138 mm Hg; P = .002) and days 1-35 (175 mm Hg vs 153 mm Hg; P < .001). The subjects who underwent early prone positioning had lower compliance during days 1-10 (27 mL/cm H2O vs 33 mL/cm H2O; P < .001) and lower [Formula: see text]/[Formula: see text] values over days 1-10 (139.9 mm Hg vs 167.4 mm Hg; P < .001) versus those who did not undergo prone positioning. After day 21 of hospitalization, the average compliance of the subjects who had early prone positioning surpassed that of the subjects who did not have prone positioning. Respiratory mechanics of the subjects with COVID-19 who were on mechanical ventilation were characterized by persistently low respiratory system compliance and [Formula: see text]/[Formula: see text], similar to ARDS due to other etiologies. The [Formula: see text]/[Formula: see text] was more tightly associated with mortality than with compliance.

Ventilation management and clinical outcomes in invasively ventilated patients with COVID-19 (PRoVENT-COVID): a national, multicentre, observational cohort study

BackgroundLittle is known about the practice of ventilation management in patients with COVID-19. We aimed to describe the practice of ventilation management and to establish outcomes in invasively ventilated patients with COVID-19 in a single country during the first month of the outbreak.MethodsPRoVENT-COVID is a national, multicentre, retrospective observational study done at 18 intensive care units (ICUs) in the Netherlands. Consecutive patients aged at least 18 years were eligible for participation if they had received invasive ventilation for COVID-19 at a participating ICU during the first month of the national outbreak in the Netherlands. The primary outcome was a combination of ventilator variables and parameters over the first 4 calendar days of ventilation: tidal volume, positive end-expiratory pressure (PEEP), respiratory system compliance, and driving pressure. Secondary outcomes included the use of adjunctive treatments for refractory hypoxaemia and ICU complications. Patient-centred outcomes were ventilator-free days at day 28, duration of ventilation, duration of ICU and hospital stay, and mortality. PRoVENT-COVID is registered at ClinicalTrials.gov (NCT04346342).FindingsBetween March 1 and April 1, 2020, 553 patients were included in the study. Median tidal volume was 6·3 mL/kg predicted bodyweight (IQR 5·7–7·1), PEEP was 14·0 cm H2O (IQR 11·0–15·0), and driving pressure was 14·0 cm H2O (11·2–16·0). Median respiratory system compliance was 31·9 mL/cm H2O (26·0–39·9). Of the adjunctive treatments for refractory hypoxaemia, prone positioning was most often used in the first 4 days of ventilation (283 [53%] of 530 patients). The median number of ventilator-free days at day 28 was 0 (IQR 0–15); 186 (35%) of 530 patients had died by day 28. Predictors of 28-day mortality were gender, age, tidal volume, respiratory system compliance, arterial pH, and heart rate on the first day of invasive ventilation.InterpretationIn patients with COVID-19 who were invasively ventilated during the first month of the outbreak in the Netherlands, lung-protective ventilation with low tidal volume and low driving pressure was broadly applied and prone positioning was often used. The applied PEEP varied widely, despite an invariably low respiratory system compliance. The findings of this national study provide a basis for new hypotheses and sample size calculations for future trials of invasive ventilation for COVID-19. These data could also help in the interpretation of findings from other studies of ventilation practice and outcomes in invasively ventilated patients with COVID-19.FundingAmsterdam University Medical Centers, location Academic Medical Center.

Influence of tidal volume and positive end-expiratory pressure on ventilation distribution and oxygenation during one-lung ventilation

Objective: The aim of the study was to explore the feasibility of titrating tidal volume (VT) and positive end-expiratory pressure (PEEP) during one-lung ventilation (OLV) based on ventilation distribution and oxygenation. Approach: Twenty-four consecutive patients requiring intubation with a double-lumen tube and subsequent OLV for thoracic surgical procedures were examined prospectively in lateral posture. Electrical impedance tomography (EIT), blood gases, respiratory mechanics were successfully measured in 21 patients at various combinations of VT (4 ml kg−1, 6 ml kg−1, 8 ml kg−1 body weight) and PEEP (0 cm H2O, 4 cm H2O, 8 cm H2O) during OLV. Main results: Low VT and low PEEP resulted in low global respiratory system compliance (Crs). Arterial partial pressure of O2 (PaO2) decreased with falling VT. Regional Crs measured with EIT showed high values at high VT and high PEEP in all but two patients. Regional Crs in mid and most dependent regions indicated tidal recruitment/derecruitment in eight patients at 8 ml kg−1 of VT and 4 cm H2O of PEEP; in four patients at 8 ml kg−1 and 0 cm H2O; in one patient at 6 ml kg−1 and 8 cm H2O. The changes in regional Crs induced by decreasing PEEP from 8 to 4 cm H2O were much smaller than those from 4 to 0 cm H2O. Ventilation distribution was most inhomogeneous with VT of 8 ml kg−1. All measures differed significantly among various VT and PEEP steps (p < 0.05). Significance: By using EIT in combination with PaO2, it is feasible to titrate VT and PEEP at the bedside during OLV.

The effects of low tidal ventilation on lung strain correlate with respiratory system compliance

BackgroundThe effect of alterations in tidal volume on mortality of acute respiratory distress syndrome (ARDS) is determined by respiratory system compliance. We aimed to investigate the effects of different tidal volumes on lung strain in ARDS patients who had various levels of respiratory system compliance.MethodsNineteen patients were divided into high (Chigh group) and low (Clow group) respiratory system compliance groups based on their respiratory system compliance values. We defined compliance ≥0.6 ml/(cmH2O/kg) as Chigh and compliance <0.6 ml/(cmH2O/kg) as Clow. End-expiratory lung volumes (EELV) at various tidal volumes were measured by nitrogen wash-in/washout. Lung strain was calculated as the ratio between tidal volume and EELV. The primary outcome was that lung strain is a function of tidal volume in patients with various levels of respiratory system compliance.ResultsThe mean baseline EELV, strain and respiratory system compliance values were 1873 ml, 0.31 and 0.65 ml/(cmH2O/kg), respectively; differences in all of these parameters were statistically significant between the two groups. For all participants, a positive correlation was found between the respiratory system compliance and EELV (R = 0.488, p = 0.034). Driving pressure and strain increased together as the tidal volume increased from 6 ml/kg predicted body weight (PBW) to 12 ml/kg PBW. Compared to the Chigh ARDS patients, the driving pressure was significantly higher in the Clow patients at each tidal volume. Similar effects of lung strain were found for tidal volumes of 6 and 8 ml/kg PBW. The “lung injury” limits for driving pressure and lung strain were much easier to exceed with increases in the tidal volume in Clow patients.ConclusionsRespiratory system compliance affected the relationships between tidal volume and driving pressure and lung strain in ARDS patients. These results showed that increasing tidal volume induced lung injury more easily in patients with low respiratory system compliance.Trial registrationClinicaltrials.gov identifier NCT01864668, Registered 21 May 2013.

Macroscopic Anatomy of the Lower Respiratory System in Mole rats (Spalax leucodon)

The morphologic and morphometric features of the lower respiratory system in mole rats were examined. It was seen that the low respiratory system of this species leading a special life under highly hypoxic/hypercapnic conditions underground is structurally similar to other mammals living on land in terms of the parts examined; trachea was formed by 29.5 ± 4 oval-formed cartilaginous tracheals arranged backwards and became gradually more stenotic diameter from cranial to the caudal of the neck. The trachea was separated in two principal bronchus at the fourth thoracal intercostal spatium level. The angle between the two main principal bronchi was 60.5 ± 2.35°. The lung constituted 1.29 ± 0.03% of the body weight and the right lung was heavier than the left lung. Fissura inter-lobaris was deep and separated the lung lobes wholly, and the right lung was separated in four lobes, whereas the left lung was not separated into the lobes. Also, the medial lobe of the left lung was the lightest lobe.

Patient–ventilator interaction in ARDS patients with extremely low compliance undergoing ECMO: a novel approach based on diaphragm electrical activity

Patients with acute respiratory distress syndrome (ARDS) requiring extracorporeal membrane oxygenation (ECMO) usually present very low respiratory system compliance (Cst(rs)) values (i.e., severe restrictive respiratory syndrome patients). As a consequence, they are at high risk of experiencing poor patient-ventilator interaction during assisted breathing. We hypothesized that monitoring of diaphragm electrical activity (EAdi) may enhance asynchrony assessment and that neurally adjusted ventilatory assist (NAVA) may reduce asynchrony, especially in more severely restricted patients. We enrolled ten consecutive ARDS patients with very low Cst(rs) values undergoing ECMO after switching from controlled to pressure support ventilation (PSV). We randomly tested (30 min) while recording EAdi: (1) PSV30 (PSV with an expiratory trigger at 30 % of flow peak value); (2) PSV1 (PSV with expiratory trigger at 1 %); (3) NAVA. During each step, we measured the EAdi-based asynchrony index (AI(EAdi)) = flow-, pressure- and EAdi-based asynchrony events/EAdi-based respiratory rate × 100. AI(EAdi) was high during all ventilation modes, and the most represented asynchrony pattern was specific for this population (i.e., premature cycling). NAVA was associated with significantly decreased, although suboptimal, AI(EAdi) values in comparison to PSV30 and PSV1 (p < 0.01 for both). The PSV30-NAVA and PSV1-NAVA differences in AI(EAdi) values were inversely correlated with patients' Cst(rs) (R (2) = 0.545, p = 0.01 and R (2) = 0.425, p < 0.05; respectively). EAdi allows accurate analysis of asynchrony patterns and magnitude in ARDS patients with very low Cst(rs) undergoing ECMO. In these patients, NAVA is associated with reduced asynchrony.

Locally measured shear moduli of pulmonary tissue and global lung mechanics in mechanically ventilated rats

This study was aimed at measuring shear moduli in vivo in mechanically ventilated rats and comparing them to global lung mechanics. Wistar rats (n = 28) were anesthetized, tracheally intubated, and mechanically ventilated in supine position. The animals were randomly assigned to the healthy control or the lung injury group where lung injury was induced by bronchoalveolar lavage. The respiratory system elastance E(rs) was analyzed based on the single compartment resistance/elastance lung model using multiple linear regression analysis. The shear modulus (G) of alveolar parenchyma was studied using a newly developed endoscopic system with adjustable pressure at the tip that was designed to induce local mechanostimulation. The data analysis was then carried out with an inverse finite element method. G was determined at continuous positive airway pressure (CPAP) levels of 15, 17, 20, and 30 mbar. The resulting shear moduli of lungs in healthy animals increased from 3.3 ± 1.4 kPa at 15 mbar CPAP to 5.8 ± 2.4 kPa at 30 mbar CPAP (P = 0.012), whereas G was ~2.5 kPa at all CPAP levels for the lung-injured animals. Regression analysis showed a negative correlation between G and relative E(rs) in the control group (r = -0.73, P = 0.008 at CPAP = 20 mbar) and no significant correlation in the lung injury group. These results suggest that the locally measured G were inversely associated with the elastance of the respiratory system. Rejecting the study hypothesis the researchers concluded that low global respiratory system elastance is related to high local resistance against tissue deformation.

Passive leg-raising and end-expiratory occlusion tests perform better than pulse pressure variation in patients with low respiratory system compliance*

We tested whether the poor ability of pulse pressure variation to predict fluid responsiveness in cases of acute respiratory distress syndrome was related to low lung compliance. We also tested whether the changes in cardiac index induced by passive leg-raising and by an end-expiratory occlusion test were better than pulse pressure variation at predicting fluid responsiveness in acute respiratory distress syndrome patients. Prospective study. Medical intensive care unit. We included 54 patients with circulatory shock (63 ± 13 yrs; Simplified Acute Physiology Score II, 63 ± 24). Twenty-seven patients had acute respiratory distress syndrome (compliance of the respiratory system, 22 ± 3 mL/cm H2O). In nonacute respiratory distress syndrome patients, the compliance of the respiratory system was 45 ± 9 mL/cm H2O. We measured the response of cardiac index (transpulmonary thermodilution) to fluid administration (500 mL saline). Before fluid administration, we recorded pulse pressure variation and the changes in pulse contour analysis-derived cardiac index induced by passive leg-raising and end-expiratory occlusion. Fluid increased cardiac index ≥ 15% (44% ± 39%) in 30 "responders." Pulse pressure variation was significantly correlated with compliance of the respiratory system (r = .58), but not with tidal volume. The higher the compliance of the respiratory system, the better the prediction of fluid responsiveness by pulse pressure variation. A compliance of the respiratory system of 30 mL/cm H2O was the best cut-off for discriminating patients regarding the ability of pulse pressure variation to predict fluid responsiveness. If compliance of the respiratory system was >30 mL/cm H2O, then the area under the receiver-operating characteristics curve for predicting fluid responsiveness was not different for pulse pressure variation and the passive leg-raising and end-expiratory occlusion tests (0.98 ± 0.03, 0.91 ± 0.06, and 0.97 ± 0.03, respectively). By contrast, if compliance of the respiratory system was ≤ 30 mL/cm H2O, then the area under the receiver-operating characteristics curve was significantly lower for pulse pressure variation than for the passive leg-raising and end-expiratory occlusion tests (0.69 ± 0.10, 0.94 ± 0.05, and 0.93 ± 0.05, respectively). The ability of pulse pressure variation to predict fluid responsiveness was inversely related to compliance of the respiratory system. If compliance of the respiratory system was ≤ 30 mL/cm H2O, then pulse pressure variation became less accurate for predicting fluid responsiveness. However, the passive leg-raising and end-expiratory occlusion tests remained valuable in such cases.

Decreased respiratory system compliance on the sixth day of mechanical ventilation is a predictor of death in patients with established acute lung injury

BackgroundMultiple studies have identified single variables or composite scores that help risk stratify patients at the time of acute lung injury (ALI) diagnosis. However, few studies have addressed the important question of how changes in pulmonary physiologic variables might predict mortality in patients during the subacute or chronic phases of ALI. We studied pulmonary physiologic variables, including respiratory system compliance, P/F ratio and oxygenation index, in a cohort of patients with ALI who survived more than 6 days of mechanical ventilation to see if changes in these variables were predictive of death and whether they are informative about the pathophysiology of subacute ALI.MethodsNinety-three patients with ALI who were mechanically ventilated for more than 6 days were enrolled in this prospective cohort study. Patients were enrolled at two medical centers in the US, a county hospital and a large academic center. Bivariate analyses were used to identify pulmonary physiologic predictors of death during the first 6 days of mechanical ventilation. Predictors on day 1, day 6 and the changes between day 1 and day 6 were compared in a multivariate logistic regression model.ResultsThe overall mortality was 35%. In multivariate analysis, the PaO2/FiO2 (OR 2.09, p < 0.04) and respiratory system compliance (OR 3.61, p < 0.01) were predictive of death on the 6th day of acute lung injury. In addition, a decrease in respiratory system compliance between days 1 and days 6 (OR 2.14, p < 0.01) was independently associated with mortality.ConclusionsA low respiratory system compliance on day 6 or a decrease in the respiratory system compliance between the 1st and 6th day of mechanical ventilation were associated with increased mortality in multivariate analysis of this cohort of patients with ALI. We suggest that decreased respiratory system compliance may identify a subset of patients who have persistent pulmonary edema, atelectasis or the fibroproliferative sequelae of ALI and thus are less likely to survive their hospitalization.

Successful use of neurally adjusted ventilatory assist in a patient with extremely low respiratory system compliance undergoing ECMO

Successful use of neurally adjusted ventilatory assist in a patient with extremely low respiratory system compliance undergoing ECMO

Respiratory failure due to morbid obesity in a patient with Prader-Willi syndrome: an experience of long-term mechanical ventilation

Prader-Willi syndrome (PWS) is characterized by obesity, mild mental retardation or learning disability, and behavior problems, especially in association with food and eating. A 19 year-old man, 150 cm, 140 kg (body mass index [BMI], 62.2 kg.m(-2)), whose condition had been diagnosed as PWS, received 41-day mechanical ventilation because of respiratory failure, chiefly due to morbid obesity. Because the patient frequently developed bronchoconstriction, metered-dose inhalers of a corticosteroid (beclomethasone dipropionate) and a beta2 agonist (salbutamol) were needed. To achieve adequate sedation, which was also crucial to control the bronchoconstriction, the concurrent use of midazolam, fentanyl, ketamine, and propofol was required. Pressure-control ventilation was useful to avoid high airway pressure due to low respiratory system compliance associated with the morbid obesity. Because it appeared that the basic problem leading to respiratory failure in this patient was morbid obesity, body weight reduction was considered to be mandatory. Thus, caloric intake was limited to 1000 kcal.day(-1), resulting in body weight reduction by 50 kg during the patient's stay in the intensive care unit (ICU). The patient was successfully extubated on ICU day 35.

Lung-protective ventilation in neurosurgical patients

Concepts of ventilator-induced lung injury have revolutionized our approach to the ventilatory management of patients with acute lung injury and acute respiratory distress syndrome over the past 10 years. The extension of these principles to patients with brain injuries is challenging, as many of them are out of keeping with usual brain-protective management. Many patients with acute lung injury or acute respiratory distress syndrome and an acute brain injury may in fact be managed safely within the confines of a lung-protective strategy. Elevated levels of positive end-expiratory pressure in head-injured patients with acute lung injury or acute respiratory distress syndrome also appear to be safe, particularly when the level is set below that of the intracranial pressure, when patients have a low respiratory system compliance, or when positive end-expiratory pressure results in significant lung volume recruitment. Several novel therapies to minimize ventilator-induced lung injury are currently in the early stages of investigation in neurosurgical patients. In many patients with brain injuries and acute lung injury the goals of lung protection can be achieved without threatening cerebral perfusion. In patients with more refractory raised intracranial pressure the optimal balance between brain and lung is not well established. Further research is needed on lung-protective strategies in this vulnerable population.

Interrupter airway and tissue resistance: errors caused by valve properties and respiratory system compliance.

The interrupter technique is used to determine airway and tissue resistance. Their accuracy is influenced by the technical properties of the interrupter device and the compliance of the respiratory system. We investigated the influence of valve characteristics and respiratory system compliance on the accuracy of determining airway and tissue resistance by means of a computer simulation. With decreasing compliance we found increasing errors in both airway and tissue resistance determination of up to 34 and 71%, respectively. On this basis we developed a new occlusion valve, with special emphasis on rapid closing time and tightness in the closed state to improve the accuracy of resistance determination. The newly developed occlusion device greatly improves the accuracy of airway and tissue resistance determination. We conclude that respiratory system compliance is a limiting factor for the accuracy of the interrupter technique. To apply the interrupter technique in patients with extremely low respiratory system compliances, we need sophisticated technical devices.

Ventilatory, cardiovascular and metabolic responses to hypoxia and hypercapnia in the armadillo

Armadillos have a low resting metabolic rate and high hemoglobin affinity for their size, a rigid carapace and a semi-fossorial life style. These characteristics could contribute to unusual respiratory responses to hypoxia and hypercapnia which were investigated in this study. Ventilatory and oxygen consumption responses of six adult unanesthetized armadillos to 15, 12, 10 and 8% O 2 and 1.5, 3, 5 and 7% CO 2 were measured by barometric plethysmography and flow-through respirometry. A significant increase in ventilation occurred in response to 10 and 8% O 2 but a decline in oxygen consumption only occurred at 8% inspired O 2. The convection requirement response has a threshold at a Pa O 2 of ≈28 Torr which corresponds to a Hb saturation of ∼70%. Ventilation increased in response to 3% and higher levels of CO 2, with no change in oxygen consumption. The magnitude of the ventilatory response to CO 2 was similar to other semi-fossorial mammals and less than that of nonburrowing species. However, the pattern of the response was unique in being largely a frequency response with little change in tidal volume, contrary to the tidal volume dominated response to hypercapnia typical of mammals. This feature, not shared by another Xenarthran, the sloth, who lacks a carapace, is likely attributable to the low respiratory system compliance and increased airway resistance resulting from the rigid carapace and small lungs of armadillos and emphasizes the importance of respiratory mechanics in determining breathing pattern.

180 LUNG VOLUMES AND LUNG MECHANICS IN NEONATES AND INFANTS WITH CONGENITAL DIAPHRAGMATIC HERNIA (CDH)

Neonates with CDH are exceptionally vulnerable to complications of artificial ventilation such as pneumothorax and bronchopulmonary dysplasia (BPD) because of their reduced lung volumes, demonstrable by measurement of functional residual capacity (FRC) and thoracic gas volume (TGV). Methods: Serial lung function tests were performed in three infants with CDH, including single occlusion tests, nitrogen washout measurement of FRC (SensorMedics 2600, USA), and determination of TGV (Jaeger Baby-Bodyplethysmograph). Results: Two neonates with right-sided CDH showed appropriate increase of initially low respiratory system compliance, FRC, and TGV shortly after operation. The remaining infant had left-sided CDH and developed severe BPD accompanied by extremely low compliance and FRC, and elevated resistance and TGV values. Conclusions: Serial measurement of both FRC and TGV permits early detection of lung overinflation in infants with CDH threatened by BPD. Our results are consistent with reports indicating a better prognosis for right-sided CDH in regard of lung function. *) supported by BMFT-project “Risikoneugeborenes”

An on-line microcomputer-based respiratory monitor for manual materials handling

The main objective of the present study is to develop a low cost microcomputer-based respiratory system that is capable of computing the oxygen consumption and minute ventilation of individuals engaged in manual materials handling on an on-line basis. The design, specifications, and merits of the system are given. The software package developed was written in assembly language for the IBM AT personal computer.