Respiratory mechanical effects of abdominal distension

Lung function responses to cold water ingestion: A randomised controlled crossover trial

This study tested the hypothesis that cold water ingestion would reduce lung function and thereby confound its measurement in a way that is mediated by both temperature and volume. In a randomised crossover trial, 10 healthy adults performed spirometry before and 5, 10, 15, and 30-minutes after consuming one-of-four drinks: 500 mL or 1000 mL refrigerated water (∼2 °C); identical water volumes at ambient temperature (∼18 °C). Ingesting 1000 mL cold water significantly reduced forced vital capacity (FVC) for at least 10 min (mean difference =0.28 L, p < 0.05, d=1.19) and forced expiratory volume in 1 s (FEV1) for at least 15 min (0.20-0.30 L, p < 0.05, d=1.01). Ingesting 500 mL cold water reduced FEV1 for 5 min (0.09 L, p < 0.05, d=1.05). Room-temperature water had no influence on lung function. To avoid confounding the measurement of lung function, we conclude that individuals should avoid drinking cold water, especially in large volumes, immediately prior to a given test.

A concise overview of non-invasive intra-abdominal pressure measurement techniques: from bench to bedside

This review presents an overview of previously reported non-invasive intra-abdominal pressure (IAP) measurement techniques. Each section covers the basic physical principles and methodology of the various measurement techniques, the experimental results, and the advantages and disadvantages of each method. The most promising non-invasive methods for IAP measurement are microwave reflectometry and ultrasound assessment, in combination with an applied external force.

Ontogenetic changes to bone microstructure in an archaeologically derived sample of human ribs

There is considerable variation in the gross morphology and tissue properties among the bones of human infants, children, adolescents, and adults. Using 18 known-age individuals (n_female  = 8, n_male  = 9, n_unknown  = 1; birth to 21 years old), from a well-documented cemetery collection, Spitalfields Christ Church, London, UK, this study explores growth-related changes in cortical and trabecular bone microstructure. Micro-CT scans of mid-shaft middle thoracic ribs are used for quantitative analysis. Results are then compared to previously quantified conventional histomorphometry of the same sample. Total area (Tt.Ar), cortical area (Ct.Ar), cortical thickness (Ct.Th), and the major (Maj.Dm) and minor (Min.Dm) diameters of the rib demonstrate positive correlations with age. Pore density (Po.Dn) increases, but age-related changes to cortical porosity (Ct.Po) appear to be non-linear. Trabecular thickness (Tb.th) and trabecular separation (Tb.Sp) increase with age, whereas trabecular bone pattern factor (Tb.Pf), structural model index (SMI), and connectivity density (Conn.D) decrease with age. Sex-based differences were not identified for any of the variables included in this study. Some samples display clear evidence of diagenetic alteration without corresponding changes in radiopacity, which compromises the reliability of bone mineral density (BMD) data in the study of past populations. Cortical porosity data are not correlated with two-dimensional measures of osteon population density (OPD). This suggests that unfilled resorption spaces contribute more significantly to cortical porosity than do the Haversian canals of secondary osteons. Continued research using complementary imaging techniques and a wide array of histological variables will increase our understanding of age- and sex-specific ontogenetic patterns within and among human populations.

The neglected role of abdominal compliance in organ-organ interactions

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2016. Other selected articles can be found online at http://www.biomedcentral.com/collections/annualupdate2016. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Respiratory mechanical effects of surgical pneumoperitoneum in humans

Pneumoperitoneum for laparoscopic surgery is known to stiffen the chest wall and respiratory system, but its effects on resting pleural pressure in humans are unknown. We hypothesized that pneumoperitoneum would raise abdominal pressure, push the diaphragm into the thorax, raise pleural pressure, and squeeze the lung, which would become stiffer at low volumes as in severe obesity. Nineteen predominantly obese laparoscopic patients without pulmonary disease were studied supine (level), under neuromuscular blockade, before and after insufflation of CO2 to a gas pressure of 20 cmH2O. Esophageal pressure (Pes) and airway pressure (Pao) were measured to estimate pleural pressure and transpulmonary pressure (Pl = Pao - Pes). Changes in relaxation volume (Vrel, at Pao = 0) were estimated from changes in expiratory reserve volume, the volume extracted between Vrel, and the volume at Pao = -25 cmH2O. Inflation pressure-volume (Pao-Vl) curves from Vrel were assessed for evidence of lung compression due to high Pl. Respiratory mechanics were measured during ventilation with a positive end-expiratory pressure of 0 and 7 cmH2O. Pneumoperitoneum stiffened the chest wall and the respiratory system (increased elastance), but did not stiffen the lung, and positive end-expiratory pressure reduced Ecw during pneumoperitoneum. Contrary to our expectations, pneumoperitoneum at Vrel did not significantly change Pes [8.7 (3.4) to 7.6 (3.2) cmH2O; means (SD)] or expiratory reserve volume [183 (142) to 155 (114) ml]. The inflation Pao-Vl curve above Vrel did not show evidence of increased lung compression with pneumoperitoneum. These results in predominantly obese subjects can be explained by the inspiratory effects of abdominal pressure on the rib cage.

A joint computational respiratory neural network-biomechanical model for breathing and airway defensive behaviors

Data-driven computational neural network models have been used to study mechanisms for generating the motor patterns for breathing and breathing related behaviors such as coughing. These models have commonly been evaluated in open loop conditions or with feedback of lung volume simply represented as a filtered version of phrenic motor output. Limitations of these approaches preclude assessment of the influence of mechanical properties of the musculoskeletal system and motivated development of a biomechanical model of the respiratory muscles, airway, and lungs using published measures from human subjects. Here we describe the model and some aspects of its behavior when linked to a computational brainstem respiratory network model for breathing and airway defensive behavior composed of discrete "integrate and fire" populations. The network incorporated multiple circuit paths and operations for tuning inspiratory drive suggested by prior work. Results from neuromechanical system simulations included generation of a eupneic-like breathing pattern and the observation that increased respiratory drive and operating volume result in higher peak flow rates during cough, even when the expiratory drive is unchanged, or when the expiratory abdominal pressure is unchanged. Sequential elimination of the model's sources of inspiratory drive during cough also suggested a role for disinhibitory regulation via tonic expiratory neurons, a result that was subsequently supported by an analysis of in vivo data. Comparisons with antecedent models, discrepancies with experimental results, and some model limitations are noted.

Causes of respiratory ailments in pregnancy

Objective

During pregnancy, especially during its third trimester, most pregnant women reported respiratory discomfort (dyspnea), despite the absence of previously coexisting respiratory illnesses. The aim of this study was to determine the reason for this discomfort.

Materials and methods

The study included 24 women examined before and after childbirth. Evaluation of respiratory complains was made on the basis of the respiratory questionnaire of St. George's Hospital. The data were correlated with the results of static and dynamic spirometric tests performed before and after childbirth.

Results

Pregnancy did not affect vital capacity (VC). Frequency of perceived symptoms correlated positively with IRV and the ratio IC/VC. A negative correlation was found between ERV and its derivative ERV/VC. There was no relationship between perceived discomfort and parameters of the flow-volume loop.

Conclusions

The extent of perceived respiratory discomfort (dyspnea) during pregnancy was primarily associated with a reduction in expiratory reserve (ERV).

[Influence of volume increase on intra-abdominal pressure]

The aim of this review is to summarize the physiological and pathological aspects of the relationship between volume and intra-abdominal pressure (IAP). A capillary leak following trauma or inflammation can induce a volume shift into the abdomen. An increase of the IAP depends on the abdominal compliance, which is reduced by increases in intra-abdominal volume and pressure as well as by an upright body position and obesity. A pathological increase of IAP (>12 mmHg) depends on the amount and type of resuscitation volume and is known to cause increased morbidity und mortality. Colloids or hypertensive solutions can reduce IAP however, current data are still insufficient. Therapeutic options are IAP monitoring and decompression.

Effects of Eating on Professional and Amateur Singers for Select Pulmonary and Vocal Tasks

Singers will often refrain from eating a meal before a performance because they believe it will interfere with breath support. As there are no objective data to support or refute this belief, the purpose of this study was to obtain pre- and postmeal data from professional and amateur singers to investigate whether increased stomach contents from eating a meal adversely affected performance on specific maximal vocal/respiratory gestures. This was a prospective, repeated measures study. Forced vital capacity, maximum phonation times, and pitch range were obtained from professional and amateur singers before, immediately after, and 1 hour after eating a meal. There were no changes in measures across conditions for either group, indicating that eating does not interfere with maximal vocal and pulmonary measures.

Fentanyl decreases end-expiratory lung volume in patients anaesthetized with sevoflurane

BACKGROUND

In patients breathing spontaneously during anaesthesia, expiratory muscle activity can be a prominent feature. This activity is triggered or exaggerated by opioid administration, which causes a prompt increase in intra-abdominal pressure. The effect of this increased expiratory activity on end-expiratory lung volume is not described.

METHODS

Nine patients having minor gynaecological procedures were studied during stable anaesthetic conditions, breathing sevoflurane (end tidal 2.6%) through a laryngeal mask airway, in a circle system. The spill valve was closed and the fresh gas flow was temporarily reduced to approximate the oxygen uptake. The volume of the reservoir bag was then measured by placing it in a hinged, wedge-shaped container. Fentanyl (0.5 microg kg(-1) ideal body weight) was given after 1 min of stable recording, and the change in end-expiratory volume measured after 3 min.

RESULTS

End-expiratory lung volume decreased in all patients by 160 (111) ml (mean, SD) (P<0.01). The decrease did not relate to obesity.

CONCLUSIONS

During sevoflurane anaesthesia, fentanyl causes a rapid reduction in functional residual capacity. This is caused by increased activity of expiratory muscles and an increase in intra-abdominal pressure.

Sexual dimorphism of human ribs

The volume of the rib cage is about 10% smaller in females than in males having the same height although the reason for this is presently unclear. The cranio-caudal inclination of ribs is greater in females than males but the length of ribs has not previously been compared between the sexes. In 23 males and 23 females studied at necropsy, body length, the length of the upper and lower limbs and the length of the thoracic spine were all smaller in females but the ratios of upper and lower limb lengths to body length and of thoracic spine length to body length were not different. By contrast, the lengths of the third, sixth and ninth ribs were not significantly different between males and females and the ratios of rib length to body length were all significantly greater in females. We conclude that in females the ribs grow longer in relation to the axial skeleton than in males.

Respiratory muscle activity and respiratory obstruction after abdominal surgery

BACKGROUND

Respiratory movements in patients after abdominal surgery are frequently abnormal, with associated disturbances in the pattern of inspiratory pressure generation. The reasons for these abnormalities are not clear and have been attributed to impaired action of the diaphragm. However, an alternative is that partial airway obstruction could trigger reflex activation of the inspiratory ribcage muscles, which would cause a similar pattern of inspiratory pressure change. Direct measurement of electrical activity can indicate if reflex activation of inspiratory muscles occurs when partial airway obstruction is present.

METHODS

In an open study, we implanted electrodes to measure the EMG of scalene, intercostal and external oblique abdominal muscles in patients after lower abdominal surgery. Analgesia was with morphine i.v. by patient control. We used nasal cannulae to measure nasal airflow and compared EMG activity when airway obstruction was present with activity when breathing was not obstructed.

RESULTS

The pattern of activity of the different muscles was distinct. Intercostal activity reached a maximum during inspiration, before the scalene muscles, whereas scalene activity increased in phase with increasing lung volume. Abdominal muscle activity commenced when expiratory flow had ceased and continued until the next inspiration. In all three muscle groups, partial airway obstruction did not alter muscle activity.

CONCLUSIONS

Partial airway obstruction does not activate inspiratory ribcage muscles, in patients receiving morphine for postoperative analgesia after lower abdominal surgery. Changes in respiratory pressures and abnormalities of chest wall movement described in previous studies cannot be attributed to reflex responses and probably result from increased airway resistance and abdominal muscle action.

Postural changes in lung volumes and respiratory resistance in subjects with obesity

Reduced functional residual capacity (FRC) is consistently found in obese subjects. In 10 obese subjects (mean +/- SE age 49.0 +/- 6 yr, weight 128.4 +/- 8 kg, body mass index 44 +/- 3 kg/m2) without respiratory disease, we examined 1) supine changes in total lung capacity (TLC) and subdivisions, 2) whether values of total respiratory resistance (Rrs) are appropriate for mid-tidal lung volume (MTLV), and 3) estimated resistance of the nasopharyngeal airway (Rnp) in both sitting and supine postures. The results were compared with those of 13 control subjects with body mass indexes of <27 kg/m2. Rrs at 6 Hz was measured by applying forced oscillation at the mouth (Rrs,mo) or the nose (Rrs,na); Rnp was estimated from the difference between sequential measurements of Rrs,mo and Rrs,na. All measurements were made when subjects were seated and when supine. Obese subjects when seated had a restrictive defect with low TLC and FRC-to-TLC ratio; when supine, TLC fell 80 ml and FRC fell only 70 ml compared with a mean supine fall of FRC of 730 ml in control subjects. Values of Rrs,mo and Rrs,na at resting MTLV in obese subjects were about twice those in control subjects in both postures. Relating total respiratory conductance (1/Rrs) to MTLV, the increase in Rrs,mo in obese subjects was only partly explained by their reduced MTLV. Rnp was increased in some obese subjects in both postures. Despite the increased extrapulmonary mass load in obese subjects, further falls in TLC and FRC when supine were negligible. Rrs,mo at isovolume was increased. Further studies are needed to examine the causes of reduced TLC and increases in Rrs,mo and sometimes in Rnp in obese subjects.

Effect of rectal distension on abdominal girth

It has been postulated that a viscerosomatic reflex activated by gut distension and inhibiting abdominal wall muscle tone may be one of the mechanisms underlying functional abdominal distension. Any demonstration of such a reflex has to take into account the fact that gut distension may increase abdominal girth as a result of volume displacement. As biomechanical and sensory rectal responses vary at different rates of rectal distension, we hypothesized that different rates of rectal distension might reveal different changes in abdominal girth. Abdominal girth was continuously recorded in 14 healthy subjects using a previously validated extensometer. The rectal distensions were made in a randomized order at rates of 100 mL min(-1) or 10 mL min(-1) up to 150 mL, and sham distensions were used as controls. An increase in abdominal girth was observed at the end of both distensions (P </= 0.008): it was greater after the fast (1.1 +/- 0.5 mm) than after the slow distension (0.8 +/- 0.7 mm), but this difference was not statistically significant (P = 0.2). In conclusion, we were unable to demonstrate the existence of a viscerosomatic reflex activated by gut distension under our experimental conditions.

Bronchospasm and its biophysical basis in airway smooth muscle

Airways hyperresponsiveness is a cardinal feature of asthma but remains unexplained. In asthma, the airway smooth muscle cell is the key end-effector of bronchospasm and acute airway narrowing, but in just the past five years our understanding of the relationship of responsiveness to muscle biophysics has dramatically changed. It has become well established, for example, that muscle length is equilibrated dynamically rather than statically, and that non-classical features of muscle biophysics come to the forefront, including unanticipated interactions between the muscle and its time-varying load, as well as the ability of the muscle cell to adapt rapidly to changes in its dynamic microenvironment. These newly discovered phenomena have been described empirically, but a mechanistic basis to explain them is only beginning to emerge.

Sex differences in thoracic dimensions and configuration

The volume of adult female lungs is typically 10-12% smaller than that of males who have the same height and age. In this study, we investigated how this volume difference is distributed between the rib cage and the diaphragm abdomen compartments. Internal rib cage dimensions, diaphragm position relative to spine, and diaphragm length were compared in 21 normal male and 19 normal female subjects at three different lung volumes using anterior-posterior and lateral chest radiographs. At all lung volumes examined, females had smaller radial rib cage dimensions in relationship to height than males, a greater inclination of ribs, a comparable diaphragm dome position relative to the spine, and a shorter diaphragm length. Female subjects exhibited a greater inspiratory rib cage muscle contribution during resting breathing than males, presumably reflecting an improved mechanical advantage conferred to these muscles by the greater inclination of ribs. Because of a greater inclination of ribs, female rib cages could accommodate a greater volume expansion. The results suggest a disproportionate growth of the rib cage in females relative to the lung, which would be well suited to accommodate large abdominal volume displacements as in pregnancy.

Effects of abdominal distension on breathing pattern and respiratory mechanics in rabbits

The effects of acute abdominal distension (AD) on the electromechanical efficiency (Eff) of the inspiratory muscles were investigated in anesthetized rabbits by recording the electrical activity (A), pressure (P) exerted by the diaphragm (di) and parasternal intercostal muscles (ic), and lung volume changes when an abdominal balloon was inflated to various degrees. Eff,ic increased with increasing AD both in supine and upright postures. In upright rabbits Eff,di increased for intermediate but decreased at higher levels of AD, whilst it decreased at all levels of AD in supine rabbits. Tidal volume (VT) response followed that of Eff,di. Tonic Aic and Adi and inspiratory prolongation were elicited by AD. The effects of these neural mechanisms, acting to limit end-expiratory lung volume and VT changes, were however small since vagotomy prevented tonic Adi and inspiratory prolongation and reduced tonic Aic, but changed lung volume responses to AD only little. Hence, reduced respiratory system compliance and changes in inspiratory muscle electromechanical efficiency dominate lung volume responses to acute AD.

Serial changes in spirometry during an ascent to 5,300 m in the Nepalese Himalayas

The aims of the present study were to determine the changes in forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and peak expiratory flow (PEF), during an ascent to 5,300 m in the Nepalese Himalayas, and to correlate the changes with arterial oxygen saturation measured by pulse oximetry (SpO2) and symptoms of acute mountain sickness (AMS). Forty-six subjects were studied twice daily during an ascent from 2,800 m (mean barometric pressure 550.6 mmHg) to 5,300 m (mean barometric pressure 404.3 mmHg) during a period of between 10 and 16 days. Measurements of FVC, FEV1, PEF, SpO2, and AMS were recorded. AMS was assessed using a standardized scoring system. FVC fell with altitude, by a mean of 4% from sea level values [95% confidence intervals (CI) 0.9% to 7.4%] at 2,800 m, and 8.6% (95% CI 5.8 to 11.4%) at 5,300 m. FEV1 did not change with increasing altitude. PEF increased with altitude by a mean of 8.9% (95% CI 2.7 to 15.1%) at 2,800 m, and 16% (95% CI 9 to 23%) at 5,300 m. These changes were not significantly related to SpO2 or AMS scores. These results confirm a progressive fall in FVC and increase in PEF with increasing hypobaric hypoxia while FEV1 remains unchanged. The increase in PEF is less than would be predicted from the change in gas density. The fall in FVC may be due to reduced inspiratory force producing a reduction in total lung capacity; subclinical pulmonary edema; an increase in pulmonary blood volume, or changes in airway closure. The absence of a correlation between the spirometric changes and SpO2 or AMS may simply reflect that these measurements of pulmonary function are not sufficiently sensitive indicators of altitude-related disease. Further studies are required to clarify the effects of hypobaric hypoxia on lung volumes and flows in an attempt to obtain a unifying explanation for these changes.

Treatment of intracranial hypertension using nonsurgical abdominal decompression

BACKGROUND

Elevated intra-abdominal pressure (IAP) increases intracranial pressure (ICP) and reduces cerebral perfusion pressure (CPP). We evaluated a nonsurgical means of reducing IAP to reverse this process.

METHODS

Swine with a baseline ICP of 25 mm Hg produced by an intracranial balloon catheter were studied. In group 1 (n = 5), IAP was increased by 25 mm Hg. Continuous negative abdominal pressure (CNAP) was then applied. Group 2 (n = 4) had neither IAP elevation nor CNAP. Group 3 (n = 4) had CNAP without IAP elevation.

RESULTS

Elevation of IAP by 25 mm Hg above baseline led to deleterious changes in ICP (25.8+/-0.8 to 39.0+/-2.8; p < 0.05) and CPP (85.2+/-2.0 to 64.8+/-2.6; p < 0.05). CNAP led to a reduction in IAP (30.2+/-1.2 to 20.4+/-1.3; p < 0.05) and improvements in cerebral perfusion (ICP, 33+/-2.7; CPP, 74.4+/-1.2; both p < 0.05). Group 2 had stable ICP (25.8+/-0.25 to 28.7+/-1.7; p > 0.05) and CPP (80.8+/-1.4 to 80.5+/-1.8; p > 0.05). In group 3, CNAP decreased cardiac index (2.9+/-0.2 to 1.1+/-0.4; p < 0.05), mean arterial pressure (105.2+/-4.0 to 38.2+/-12.0; p < 0.05), and CPP (74.2+/-4.7 to 14.5+/-12.2; p < 0.05).

CONCLUSION

Elevations in IAP led to increased ICP and decreased CPP. CNAP ameliorated these intracranial disturbances. With normal IAP, CNAP impaired cerebral perfusion.

Stomach distension increases efferent muscle sympathetic nerve activity and blood pressure in healthy humans

Although the enteric nervous system is usually described as a separate and independent entity, animal studies show that gastric distension causes a reflex increase in arterial pressure and a sympathetically mediated increase in heart rate and peripheral vascular resistance. To assess the influence of gastric distension on sympathetic outflow and blood pressure, we recorded muscle sympathetic nerve activity (MSNA) from the peroneal nerve by microneurography in eight healthy volunteers. The stomach was distended by means of a barostat, using a single staircase protocol by which pressure was increased by 2 mmHg every 3 min. Gastric sensory function was assessed at each distension step by using a visual analog scale (VAS) for sensations of fullness, nausea and pain. For comparison, we also performed a cold pressor test. The MSNA increased on barostat-induced gastric distension with an almost concomitant elevation of blood pressure. The increase in both was proportional to the intragastric pressure and both decreased towards initial values after the end of distension. Heart rate increased inconsistently and only at higher distension pressures that were associated with high VAS scores. The opposite was found for the cold pressor test. The results of this study confirm the existence of a functional relationship between gastrointestinal distension and cardiovascular function. Decrease in this gastrovascular response may play a role in postprandial hypotension in the elderly, since the MSNA responses to simulated microgravity decrease with age.

Hypoxia and chest pain due to acute constipation: an underdiagnosed condition?

An obese, previously healthy, 10-year-old boy presented with acute respiratory distress, chest, and abdominal pain. He was hypoxic and dyspneic in the emergency room. The abdomen was distended and tender, and the rectum was full of hard stool. Following catharsis, he made a complete recovery with resolution of all clinical signs. A review of the literature reveals that acute constipation as a cause of hypoxia and respiratory distress has been recognized, but has rarely been reported. We believe that this is a common phenomenon but probably infrequently recognized.

Pulmonary gas exchange improves in the prone position with abdominal distension

Arterial blood oxygenation in patients with adult respiratory distress syndrome is often improved in the prone position. Critically ill patients often have abdominal distension and whether similar improvements in gas exchange occur with the prone position is not known. We therefore studied the effect of posture on gas exchange in eight ketamine-anesthetized pigs with abdominal distension. A rubber balloon, placed in the abdominal cavity, was filled with water to increase intra-abdominal pressure. The animals were mechanically ventilated with FIO2 = 0.4, and PaCO2 was kept constant. Gas exchange was measured in the supine and prone positions, with and without abdominal distension, in random order, using the multiple inert gas elimination technique (MIGET). When the abdomen was normal, the prone position increased PaO2 by 16 +/- 21 mm Hg (p < 0.05), accompanied by a small, but statistically insignificant, decrease in AaPO2 (p = 0.08) and no change in ventilation/perfusion (V A/Q) heterogeneity measured by MIGET. In the presence of abdominal distension, the prone position increased Pa O2 by 26 +/- 18 mm Hg (p < 0.01) and decreased AaPO2 (p < 0.05) and V A/Q heterogeneity as measured by the log standard deviation of the perfusion distribution (p < 0.01) and the arterial-alveolar difference area (p < 0.05). In addition, intragastric pressure was lower in the prone position (p < 0.01). We conclude that in anesthetized, mechanically ventilated pigs, the prone position improves pulmonary gas exchange to a greater degree in the presence of abdominal distension than when the abdomen is normal.

Impairment of lung and chest wall mechanics in patients with acute respiratory distress syndrome: role of abdominal distension

Recent data have suggested that the elastic properties of the chest wall (CW) may be compromised in patients with ARDS because of abdominal distension (4). We partitioned CW and lung (L) mechanics, assessed the role of abdominal distension, and verified whether the underlying disease responsible for ARDS affects the impairment of respiratory mechanics. Volume-pressure (V-P) curves (interrupter technique) were assessed in nine patients with surgical ARDS and nine patients with medical ARDS. Relative to nine patients undergoing heart surgery, V-P curves of the respiratory system (rs) and L of patients with surgical or medical ARDS showed a rightward displacement. V-P curves of the CW and the L showed an upward concavity in patients with medical ARDS and a downward concavity in patients with surgical ARDS. Although the CW and the abdomen (abd) V-P curves in patients with medical ARDS were similar to those obtained in patients undergoing heart surgery, they showed a rightward shift and a downward flattening in patients with surgical ARDS. In five of these patients, a reduction in static end-inspiratory pressure of the abd (69+/-4%), rs (30+/-3%), CW (41+/-2%), and L (27+/-3%) was observed after abdominal decompression for acute bleeding. Abdominal decompression therefore caused an upward and leftward shift of the V-P curves of the respiratory system, chest wall, lung, and abdomen. In conclusion we showed that impairment of the elastic properties of the respiratory system may vary with the underlying disease responsible for ARDS. The flattening of the V-P curve at high pressures observed in some patients with ARDS may be due to an increase in chest wall elastance related to abdominal distension. These observations have implications for the assessment and ventilatory management of patients with ARDS.

Association of chest wall motion and tidal volume responses during CO2 rebreathing

The purpose of this study is to investigate the effect of chest wall configuration at end expiration on tidal volume (VT) response during CO2 rebreathing. In a group of 11 healthy male subjects, the changes in end-expiratory and end-inspiratory volume of the rib cage (delta Vrc,E and delta Vrc,I, respectively) and abdomen (delta Vab,E and delta Vab,I, respectively) measured by linearized magnetometers were expressed as a function of end-tidal PCO2 (PETCO2. The changes in end-expiratory and end-inspiratory volumes of the chest wall (delta Vcw,E and delta Vcw,I, respectively) were calculated as the sum of the respective rib cage and abdominal volumes. The magnetometer coils were placed at the level of the nipples and 1-2 cm above the umbilicus and calibrated during quiet breathing against the VT measured from a pneumotachograph. The delta Vrc,E/delta PETCO2 slope was quite variable among subjects. It was significantly positive (P < 0.05) in five subjects, significantly negative in four subjects (P < 0.05), and not different from zero in the remaining two subjects. The delta Vab,E/delta PETCO2 slope was significantly negative in all subjects (P < 0.05) with a much smaller intersubject variation, probably suggesting a relatively more uniform recruitment of abdominal expiratory muscles and a variable recruitment of rib cage muscles during CO2 rebreathing in different subjects. As a group, the mean delta Vrc,E/delta PETCO2, delta Vab,E/delta PETCO2, and delta Vcw,E/delta PETCO2, slopes were 0.010 +/- 0.034, -0.030 +/- 0.007, and -0.020 +/- 0.032 1/Torr, respectively; only the delta Vab,E/delta PETCO2, slope was significantly different from zero. More interestingly, the individual delta VT/delta PETCO2 slope was negatively associated with the delta Vcr,E/delta PETCO2 (r = 0.68, P = 0.021) and delta Vcw,E/delta PETCO2 slopes (r = 0.63, P = 0.037) but was not associated with the delta Vab,E/delta PETCO2 slope (r = 0.40, P = 0.223). There was no correlation of the delta Vrc,E/delta PETCO2 and delta Vcw,E/delta PETCO2 slopes with age, body size, forced expiratory volume in 1 s, or expiratory time. The group delta Vab,I/delta PETCO2 slope (0.004 +/- 0.014 1/Torr) was not significantly different from zero despite the VT nearly being tripled at the end of CO2 rebreathing. In conclusion, the individual VT response to CO2, although independent of delta Vab,E, is a function of delta Vrc,E to the extent that as the delta Vrc,E/delta PETCO2 slope increases (more positive) among subjects, the VT response to CO2 decreases. These results may be explained on the basis of the respiratory muscle actions and interactions on the rib cage.

Effects of carbon dioxide insufflation for laparoscopic cholecystectomy on the respiratory system

The changes occurring in total respiratory system, lung and chest wall mechanics, lung volume and gas-exchange during abdominal insufflation with carbon dioxide for laparoscopic cholecystectomy were studied. Using the technique of rapid airway occlusion during constant flow inflation together with an oesophageal balloon, we computed compliance and maximum resistance of the respiratory system, subsequently apportioning it into its lung and chest wall components. Maximum resistance of the respiratory system was further divided into airway resistance and the viscoelastic properties of the lung and the chest wall. In 10 patients (group 1), we measured respiratory system, lung and chest wall mechanics (compliance and resistance), functional residual capacity, end-tidal carbon dioxide tension and oxygen saturation. In addition, arterial blood gas analysis and end-tidal carbon dioxide tension were measured in a second group of 10 patients (group 2). Measurements, in both groups, were obtained in the reverse Trendelenburg position, at 15 min after the induction of anaesthesia, 5 min and 45 min after abdominal insufflation and at 15 min after abdominal deflation. Tidal volume, respiratory rate, inspiratory flow and the fraction of inspired oxygen were similar in both groups and maintained constant during the procedure. We found that abdominal carbon dioxide insufflation caused: a reduction in compliance of the respiratory system (both lung and chest wall components) and of functional residual capacity; a marked increase in the maximum resistance of the respiratory system (mainly due to increases in the viscoelastic properties of the lung and chest wall); no change in oxygenation, but an increase in the end-tidal carbon dioxide tension (which was correlated closely with the arterial carbon dioxide tension). These changes were not affected by the duration of anaesthesia.

Pulmonary consequences of carbon dioxide insufflation for laparoscopic cholecystectomies

Twenty patients having laparoscopic cholecystectomies were studied for changes in thoracic and lung compliance at 5, 10 and 15 mmHg of intra-abdominal pressure. Fifteen mmHg of intra-abdominal pressure decreased the thoracic and the lung static compliance by 49 and 39% respectively. This was unaffected by the degree of head elevation. During the procedure the end-tidal carbon dioxide increased by a mean of 1.6 kPa at 1 h and 2.0 kPa at 2 h. This did not appear to be related to either the mean intra-abdominal pressure or the total volume of carbon dioxide insufflated. The physiological changes and implications for anaesthetic practice are considered.

[Intra-abdominal pressure]

The abdominal pressure is a hydrostatic one, which can be measured in the bladder, the rectum and the stomach. In physiologic conditions, the abdominal pressure is variable, with peaks as high as 100 to 200 mmHg at the time of defecation, cough. The increase in abdominal pressure elicited by abdominal distension or compression acts directly on the abdominal compartment, indirectly on the thoracic compartment, and modifies the circulation and the ventilation. Venous return is decreased as the inferior vena cava is compressed. The systemic resistances are also increased as the abdominal vessels are compressed. Therefore the circulation is mainly distributed to the superior part of the body. Although the cardiac output is decreased, the usual haemodynamic parameters remain in the normal range: arterial pressure is increased, heart rate is unchanged, central venous pressure is increased, cardiac failure is unusual. The abdominal distension is also responsible for a restrictive respiratory syndrome, mainly due to the ascension of the diaphragm. The compression of the abdominal content explains renal effects and the decreased diuresis. A sustained increase in abdominal pressure occurs in several clinical conditions. During coelioscopy, abdominal pressure is a under control and the cardiovascular effects are minor. Insufflation with CO2 carries the risk of hypercapnia, gas embolism and pneumothorax. During abdominal tamponade, anuria is directly related to the level of pressures. At an abdominal pressure over 25 mmHg, anuria is common and decompression becomes essential. The G suit increases arterial pressure either by elevating vascular resistances or increasing blood content in the upper part of the body. Therefore cardiac tolerance can be decreased especially in cardiac patients. The adverse effects of abdominal pressure can also be observed in case of peritoneal dialysis and ascites. The risk of regurgitation associated with an increased abdominal pressure must also be kept in mind. The abdominal pressure plays an important role in anaesthesia as well as in surgery. Therefore its measurement, which is easy, should become a routine.

Ascites: its effect upon static inflation of the respiratory system

This report presents a simple clinical method to quantify the pressure generated within ascites fluid and thus to examine the effect of that fluid upon lung volume. The intra-abdominal hydrostatic pressure (Pih) given in cm H2O is the height of the meniscus of a column of water above the anterior abdominal wall measured with the patient supine. Pih thus may be thought of as a pressure in excess of the height of the anterior abdominal wall. In 23 study subjects, Pih measured 7.0 +/- 4.8 cm H2O; Pih correlated inversely with all static volumes. Furthermore, abdominal compliance (measured as the ratio of 100 ml ascites fluid removed divided by the difference between Pih before and after fluid removal) correlated directly with functional residual capacity. We conclude that the effect of ascites upon respiratory function varies among patients; the variation may be explained in part by Pih.

Coordination of eating, drinking and breathing in adults

The coordination of breathing and swallowing was studied in seven normal males at rest, as well as during eating and drinking. Ventilation was monitored using respiratory inductive plethysmography and swallowing was recorded by submental electromyogram. Swallowing occurred almost exclusively in expiration. Two hundred and seventy-one swallows were seen and only two occurred in inspiration. The mean expiratory duration (Te) of breaths containing a swallow was significantly greater than the mean Te of all breaths during the same period. There was no change in mean tidal volume (VT), inspiratory duration (Ti), expiratory duration (Te), mean inspiratory flow (VT/Ti) or minute ventilation (VE) between the periods of normal breathing, eating and drinking. However, breathing became more irregular during eating and drinking. The mean coefficient of variation of VT, Te, and VT/Ti was significantly greater during eating and drinking than at rest. The coefficient of variation for VT was 22 + 3 percent, 36 +/- 5 percent, and 41 +/- 5 percent during the initial period of resting breathing, eating and drinking. For VT/Ti it was 24 +/- 6 percent, 43 +/- 14 percent and 44 +/- 8 percent during resting breathing, eating and drinking. We conclude that swallowing is almost exclusively an expiratory activity. This may play a protective role in preventing aspiration. Although the level of ventilation is maintained constant during eating and drinking, the pattern of breathing becomes increasingly irregular. This may contribute to dyspnea during meals in some patients with lung disease.