Pulmonary densities during anesthesia with muscular relaxation--a proposal of atelectasis

Twenty patients (23-76 yr) were studied with regard to lung tissue changes prior to and following induction of general anesthesia with muscular relaxation, and another four subjects were studied for a longer period awake. The transverse thoracic area and the structure of the lung tissue were determined by computerized tomography. No abnormalities in the lung tissue were noted before anesthesia. Within 5 min after induction, including muscular relaxation, all subjects had developed crest-shaped changes of increased density in the dependent regions of both lungs. They were largest in the most caudal segment (4.8 +/- 0.8% of the transverse lung area, mean +/- SE) and smaller in the cephalad exposures (3.4 +/- 0.7% of the transverse area). The size of the densities showed no correlation to age. The densities did not increase after a further 20 min of anesthesia and were not affected by the inspiratory oxygen fraction. When the subjects were moved from the supine to the lateral position, the crest-shaped densities disappeared in the nondependent lung and remained in the dorsal part of the dependent lung. The application of positive end-expiratory pressure of 10 cmH2O eliminated or reduced the densities. The four awake subjects showed no lung densities after 90 min in the supine position. It is suggested that these crest-shaped densities represent atelectases, which develop by compression of lung tissue rather than by resorption of gas.

Distribution of pulmonary ventilation and perfusion during short periods of weightlessness

Information on the distributions of pulmonary ventilation and perfusion was obtained from four subjects on board a Learjet during 112 weightless periods lasting up to 27 s each. Zero gravity (G) was obtained during all or part of each test by varying the aircraft flight profile. Single-breath N2 washouts were performed with the test inspiration containing an initial bolus of argon at residual volume (RV). When the test inspiration was at 0 G, and the washout at 0 G or greater, the terminal rises and the cardiogenic oscillations in both N2 and argon were small and often absent. If instead the test inspiration was at 1 G with the washout at 0 G, the terminal rises were again small or absent but the cardiogenic oscillations remained. The terminal rise and the cardiogenic oscillations for N2, but not argon, were also nearly eliminated by performing just the preliminary exhalation to RV at 0 G with the test inspiration and washout following at 1 G. Aleveolar plateaus for N2 sloped upward at 0 G apparently due to nontopographical inequalities of ventilation. In further tests during air breathing, recordings were made of expired partial pressure of oxygen PO2) and carbon dioxide (POO2) following a brief hyperventilation and a 15-s breath hold. These recordings revealed marked cardiogenic oscillations in PO2 and PCO2 at 1 G that were enhanced at 2 G but almost eliminated at 0 G. The results suggest that virtually all the topographical inequality of ventilation, blood flow, and lung volume seen under 1-G conditions are abolished during short periods of 0 G.

Respiratory status of seventy-four habitual marijuana smokers

Previous studies of the long-term effects of habitual marijuana smoking on respiratory status and lung function have yielded conflicting results. In the present study, lung function tests obtained in 74 regular marijuana smokers (duration of smoking > two-five years; frequency of smoking three days/week to several times/day) who denied intravenous narcotic drug abuse were compared with similar tests performed in two groups of control subjects. One group consisted of individuals tested in a mobile laboratory who were computer-matched to the marijuana smokers for anthropometric characteristics and quantity and duration of tobacco smoking; the other group was comprised of 41 nonsmokers of marijuana who were tested in the same laboratory as the marijuana smokers. Paired and unpaired t analyses revealed lower values for specific airway conductance (-0.07 to -0.08 +/- 0.02; P < 0.001) in the marijuana smokers compared with either group of control subjects, but no differences in spirometric indices, closing volume or delta N2 750-1250. When non-tobacco smoking marijuana users (n = 50) were matched with either non-tobacco smoking or tobacco smoking control subjects, significant differences were again noted in specific airway conductance (P < 0.001) but not in spirometric tests, closing volume or delta N2 750-1250. These results suggest that habitual smoking of marijuana may cause mild, but significant, functional impairment predominantly involving large airways which is not detectable in individuals of the same age who regularly smoke tobacco. The clinical implications of these findings await further study.

Closing capacity in awake and anesthetized-paralyzed man

Functional residual capacity (FRC), closing capacity (CC), and (FRC--CC) were determined in 61 supine patients using the 133Xe bolus test. In 28 of the 61 patients measurements were made both while the patients were awake and during anesthesia-paralysis. Both FRC and CC decreased significantly after induction of anesthesia-paralysis. The magnitude of the reduction in CC, but not of FRC, was dependent on the relationship between FRC and CC in the awake state. Patients whose FRC was larger than their CC while awake (group I) showed less decrease in CC than FRC, i.e., (FRC--CC) decreased. By contrast, those patients whose CC was larger than their FRC while awake (group II) showed a greater decrease in CC than in FRC, i.e., (FRC--CC) became less negative. The reduction in CC after induction of anesthesia-paralysis may result from an increased elastic recoil of the lung. The larger reduction in CC in group II patients may have been due to a larger increase in elastic recoil, possibly due to the development of atelactasis.

Postural effects on lung volumes and asynchronous ventilation in anesthetized horses

Quasi-static pressure-volume curves and single-breath nitrogen washouts were performed simultaneously on eight anesthetized horses (average body wt = 485 kg) in left lateral, right lateral, prone, and supine postures (sequence randomized). The shift from prone to lateral or supine posture decreased expiratory reserve volume (ERV), vital capacity (VC), residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC); RV and FRC expressed as %TLC were unchanged, suggesting that in the lateral and supine postures a significant portion of the lung volume was not recruited by VC maneuvers. Phase III slope increased from 0.13 %N2/l in prone horses to 0.34 %N2/l in the lateral and supine positions. The onset of phase IV was not significantly different from FRC in the prone or laterally recombent animal, but exceeded FRC in the supine horse. The sequence of body positions had no effect on any of our results indicating that all changes in lung volumes and regional asynchronous ventilation c;n be reversed by placing the horse in the prone posture. The reduction in lung volume and increased asynchronous ventilation in the lateral and supine horse suggests that impaired gas exchange in anesthetized horses is predominantly related to posture, and not general anesthesia.

Changes in pulmonary diffusing capacity and closing volume after running a marathon

The purpose of this study was to evaluate changes in lung function after running a marathon. Pulmonary function tests were administered to 8 men before, immediately after, and the day following competition (mean run time = 3 hr 30 min). Subjects completed maximum expiratory flow volume maneuvers breathing air and 80% He/20% O2. Lung volumes were determined by N2 washout and single breath He dilution. Closing volumes (CV) were determined using a single breath O2 test. Pulmonary diffusing capacity (DLCO), pulmonary capillary blood volume (Vc), and membrane diffusing capacity (DM) were measured with the single breath technique. There were no changes in lung volumes or flow rates, except for an increase in FEV1, after the marathon. The He/O2 delta Vmax50, delta Vmax25, and isoflow values were similar pre- compared to post-race. There were significant decreases, however, in DLCO, DM and increases in CV post-race. Vc remained similar to pre-race values. These results suggest that small airways obstruction does not occur after a marathon. The significant increase in alveolar-capillary membrane resistance, however, may reflect the occurrence of subclinical edema. Such a change would decrease lung elastic recoil and could explain the increase in CV.

Regional intrapulmonary gas distribution in awake and anesthetized-paralyzed prone man

The intrapulmonary distribution of inspired gas (ventilation/unit lung volume, VI), functional residual capacity (FRC), closing capacity (CC), and the slope of phase III were determined in five awake and five anesthetized-paralyzed volunteers who were in the prone position with the abdomen unsupported. After induction of anesthesia-paralysis, FRC was less in four of five subjects and CC was consistently less. At FRC there was no difference in the vertical gradient of regional lung volumes between the awake and anesthetized-paralyzed prone subjects. Also, there was no difference in VI between the two states. The normalized slope of phase III decreased consistently with induction of anesthesia-paralysis, but the vertical distribution of a 133Xe bolus inhaled from residual volume was not different between the two states. The data of the study are compatible with 1) a pattern of expansion of the respiratory system during anesthesia-paralysis and mechanical ventilation different than that during spontaneous breathing and 2) a more uniform intraregional distribution of inspired gas and/or a different sequence of emptying during anesthesia-paralysis.

Effects of electric arc welding on ventilatory lung function

Respiratory symptoms, spirometry, forced expiratory flows, and the nitrogen closing volume test were studied in 119 welders and 90 controls, matched with respect to age, height, and smoking habits. Respiratory symptoms according to a questionnaire were more prevalent in the welders. No short-term changes of the measured variables during the day or week attributable to welding were found in twenty-one nonsmoking welders. Compared to the controls, closing volume and closing capacity (i. e., closing volume + residual volume) were significantly higher, and total lung capacity and the amplitude of the cardiogenic oscillations in the nitrogen curve were significantly lower in the welders who were nonsmokers or exsmokers, whereas there were no differences among smokers. These findings in welders may be attributable to deposition of welding fume particles in peripheral small airways or alveoli.

The mechanics of airway closure

We describe how surface-tension-driven instabilities of the lung's liquid lining may lead to pulmonary airway closure via the formation of liquid bridges that occlude the airway lumen. Using simple theoretical models, we demonstrate that this process may occur via a purely fluid-mechanical "film collapse" or through a coupled, fluid-elastic "compliant collapse" mechanism. Both mechanisms can lead to airway closure in times comparable with the breathing cycle, suggesting that surface tension is the primary mechanical effect responsible for the closure observed in peripheral regions of the human lungs. We conclude by discussing the influence of additional effects not included in the simple models, such as gravity, the presence of pulmonary surfactant, respiratory flow and wall motion, the airways' geometry, and the mechanical structure of the airway walls.

Bronchial obstruction after oesophageal acid perfusion in asthmatics

Fifteen patients with the combination of bronchial asthma and symptoms of gastro-esophageal reflux reproduced at endo-oesophageal acid perfusion (group 1) were investigated to detect bronchial obstruction, reflexly elicited from the distal oesophagus. Five patients with bronchial asthma but without symptoms of gastro-oesophageal reflux (group 2) and five patients with symptoms of gastro-oesophageal reflux but without respiratory symptoms (group 3) served as controls. The vital capacity (VC), the slope of the alveolar plateau (delta N2) and the closing volume (CV) were measured with the single breath nitrogen test before and after acid perfusion of the oesophagus, and again after antacid and glucose perfusion of the oesophagus. In group 1 a significant decrease of VC by 0.21 (P less than 0.001) and a significant increase of delta N2 by 0.9% (P less than 0.05) was seen while no change in CV was found. There was no change after acid perfusion in groups 2 or 3. After glucose and antacid the VC increased significantly in group 1 while no significant change was seen in delta N2 or CV. These findings were taken as indirect evidence of bronchial obstruction induced by the acid infusion. Since the changes were provoked in the sitting position and only in asthmatics with a positive acid perfusion test and since no patient complained of acid taste in the mouth it is unlikely that the bronchial obstruction was due to aspiration. A neural oesophago-bronchial reflex mechanism is suggested.

Closing volume in normal pregnancy

Closing volume and other principal lung volumes were measured during and after pregnancy in 10 healthy non-smoking women aged 18--25 yr. There were no significant changes on closing volume or closing capacity. A decrease in functional residual capacity as pregnancy progressed resulted in airway closure during tidal breathing in more than 50% of subjects at term when in a supine position, but this did not occur when they were seated.

The lung volume at which shunting occurs with inhalation anesthesia

The relationship between functional residual capacity (FRC) and shunt development with halothane anesthesia in 18 nonobese surgical patients (age, 21-34 yr) was studied. FRC was measured by helium dilution, and intrapulmonary shunt was distinguished from ventilation-perfusion inequality by multiple tracer inert gas elimination analysis. Awake supine FRC was 34.6 +/- 6.6% (mean +/- SD) of total lung capacity (TLC), and closing capacity (CC) was 29.8 +/- 5.3% of TLC. Anesthesia, muscle paralysis, tracheal intubation, and mechanical ventilation produced an average 14.6 +/- 13.3% FRC reduction to an average anesthesia FRC 29.8% of TLC (P = 0.002). Shunt increased from 1.2% +/- 1.5% awake to 8.6 +/- 8.3% during anesthesia (P = 0.005). A nonlinear relationship was found between shunt and FRC/TLC so that anesthetized subjects with an FRC less than awake CC had an average 11.4 +/- 8.3% shunt, whereas subjects with an FRC greater than CC had a 2.4 +/- 2.8% shunt (P = 0.025). Nonsmokers developed shunt only if FRC was less than CC. Smokers showed a significantly higher shunt for a given (FRC-CC)/TLC compared to nonsmokers (P less than 0.001). The slope of the regression of shunt on BMI (body mass index = weight/height2) showed a significant increase during anesthesia (P = 0.005), and smokers had a significantly higher slope compared to nonsmokers (P = 0.001). These findings suggest a gravity-dependent mechanism for intrapulmonary shunting during anesthesia. Therefore, shunting was due to dependent regional lung volume reduction associated with an FRC decrease to less than closing capacity. The enhanced intrapulmonary shunting in smokers may have been related to the increased dependent regional residual volume associated with smoking.

Pressure-volume relationships in the lung during laparoscopy

Pressure-volume relationships for the total respiratory system and for the lung were recorded in anaesthetized and paralysed patients, during deflation from an airway pressure of 3 kPa to FRC at a rate of 2 litre min-1. Pleural pressure was estimated by means of an oesophageal balloon. A group of nine female patients (mean age 32.7 yr) about to undergo laparoscopy were each studied in four successive states: supine, 15 degrees head down tilt, tilt and lithotomy position, and again in this position after abdominal inflation with nitrous oxide to a pressure of 0.8(-1) kPa. Compliance values were calculated from the curves. Mean total compliance was increased significantly by moving to the lithotomy position, and reduced markedly after inflation of the abdomen, because of a large reduction in thoracic compliance. Mean lung compliance was unaltered, except for a slight but statistically significant increase on moving from the supine to the Trendelenburg position. Measurement of FRC by helium dilution in a group of seven patients showed that abdominal inflation caused a mean decrease of 19%. Airway closure manoeuvres were carried out using a helium bolus technique from FRC in five patients, but closing volume could be measured in only one patient, in the supine position. The absence of an inflexion in the slope of the pressure-volume curves for the other patients supported this negative finding.

Contribution of the closure of pulmonary units to impaired oxygenation during anesthesia

Associations between airway closure, alveolar-arterial oxygen tension difference (A-aDO2), and positive end-expiratory pressure (PEEP) were investigated in anesthetized, paralyzed, artifically ventilated patients. The difference between closing capacity (CC) and functional residual capacity (FRC) was measured with a modified standard technique using a bolus of N2 to detect airway closure in denitrogenated patients. At FIO2 = 0.4 during anesthesia before application of PEEP, A-aDO2 was larger than expected in comparable conscious subjects and increased at about 1 mmHg/yr of age. CC was below FRC in young subjects but above FRC in older subjects, the two coinciding at about age 43 yr. Thus, during anesthesia both A-aDO2 and CC-FRC increased with age. The proximity and point of coincidence of CC and FRC suggested that CC is reduced during anesthesia. In patients whose CC exceeded FRC, imposition of PEEP estimated to be sufficient to elevate FRC above CC decreased A-aDO2 to a level comparable to that in patients exhibiting airway closure below FRC without PEEP. Patients in whom CC was initially below FRC failed to improve oxygenation with PEEP. At least half of the decrease in A-aDO2 associated with application of PEEP persisted for 20-30 min after the withdrawal of PEEP, although the withdrawal resulted in an immediate recurrence of airway closure above FRC. The authors conclude that closure of pulmonary units operates in some circumstances to contribute to pulmonary dysfunction in anesthetized patients but is neither the only nor necessarily the most important such mechanism.

Training and oxygen conductance in the elderly. I. The respiratory system

Static lung volumes, closing volumes and pulmonary diffusing capacity have been measured in a group of 19 subjects (9 M, 10 F) 60 - 76 years old, all volunteers for an exercise training program (nominal 4 hours per week for 11 weeks). Initial static lung volumes were larger than in some previous series, perhaps because our sample was health-conscious and mainly nonsmokers. Training produced no significant changes in any of the pulmonary variables tested, despite a 10% increase of maximum oxygen intake seen in those members of the group who progressed to intensive training (heart rate 145 - 155/min). This reflects the fact that oxygen transport depends more on blood transport than on the respiratory system.

Effect of airway closure on ventilation distribution

We examined the effect of airway closure on ventilation distribution during tidal breathing in six normal subjects. Each subject performed multiple-breath N2 washouts (MBNW) at tidal volumes of 1 liter over a range of preinspiratory lung volumes (PILV) from functional residual capacity (FRC) to just above residual volume. All subjects performed washouts at PILV below their measured closing capacity. In addition five of the subjects performed MBNW at PILV below closing capacity with end-inspiratory breath holds of 2 or 5 s. We measured the following two independent indexes of ventilation maldistribution: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency of those breaths of the washout where 80-90% of the initial N2 had been cleared. Between a mean PILV of 0.28 liter above closing capacity and that 0.31 liter below closing capacity, mean Snf increased by 132% (P less than 0.005). Over the same volume range, mean alveolar mixing efficiency decreased by 3.3% (P less than 0.05). Breath holding at PILV below closing capacity resulted in marked and consistent decreases in Snf and increases in alveolar mixing efficiency. Whereas inhomogeneity of ventilation decreases with lung volume when all airways are patent (J. Appl. Physiol. 66: 2502-2510, 1989), airway closure increases ventilation inequality, and this is substantially reduced by short end-inspiratory breath holds. These findings suggest that the predominant determinant of ventilation distribution below closing capacity is the inhomogeneous closure of airways subtending regions in the lung periphery that are close together.

Volume of trapped gas in lungs of healthy humans

The volume of trapped gas (Vtg) that could be mobilized by maximal breaths at the end of a nitrogen washout to 2% N2 was measured in 70 healthy women and 62 healthy men while seated. The average Vtg was found to be 102 +/- 21 (SD) ml in men and 73 +/- 18 ml in women. The Vtg was positively related to total lung capacity (TLC) (r = 0.67; P less than 0.001). An average percent Vtg/TLC of 1.4 +/- 0.31 (DS) % was applicable to both sexes. Vtg/TLC (%) was positively related to age (4 = 0.45; P less than 0.001). The error of a single determination was 8 ml, i.e., the reproducibility was very high. The existence of lung compartments that are unventilated or extremely underventilated may explain part of the physiological alveolararterial O2 difference. An increase in Vt has been found to be a very sensitive sign of subclinical bronchospasm.

Closing volume during normal pregnancy

Serial lung function studies were performed in ten healthy, primiparous women aged 21--28. Measurements were made at two-monthly intervals during pregnancy and included functional residual capacity (FRC), total lung capacity (TLC), vital capacity (VC), specific conductance (SGaw) and closing volume (CV) on each occasion. Closing volume expressed as formular: (see text), showed a progressive rise during pregnancy in all subjects with a linear relationship to time (P less than 0.001, P greater than 0.01, respectively). No consistent changes in lung volume could be shown during pregnancy over the study period. It is suggested that the increase in closing volume during pregnancy might result in abnormalities of distribution of ventilation sufficient to explain the maternal blood gas disturbances of pregnancy.

Mechanisms of reduced pulmonary function after a saturation dive

Deep saturation diving has been shown to have prolonged effects on pulmonary function. We wanted to assess the relative contribution of various factors that could contribute to these effects. Pulmonary function was, therefore, measured before and after 17 different saturation diving operations to depths of 5-450 m of sea water, corresponding to absolute pressures of 0.15-4.6 MPa. Four to fifteen divers participated in each operation. The measurements included static and dynamic lung volumes and flows, transfer factor of the lungs for carbon monoxide (TLCO), and closing volume. The dives were characterized by the cumulative hyperoxic and hyperbaric exposures, and the load of venous gas microemboli encountered during decompression was measured in 41 divers in three dives to 0.25, 1.2 and 3.7 MPa. TLCO was reduced by 8.3 +/- 7.0% mean +/- SD after the dives, this correlated with cumulative hyperoxic exposure and load of venous gas microembolism, independently of each other. Closing volume was increased and forced mid-expiratory flow rate reduced, in correlation with cumulative hyperoxic exposure. An increase in total lung capacity correlated with cumulative hyperbaric exposure. We conclude that hyperoxia, hyperbaria, and venous gas microembolism all contribute to the changes in pulmonary function after a single saturation dive, and all may explain some of the long-term effects of diving on pulmonary function.

Effect of elastase or histamine on single-breath N2 washouts in the rat

A method for performing single-breath N2 washouts (SBNW) in rats was developed and the test's usefulness was studied using two experimentally induced models of lung disease. Rats were anesthetized, intubated with oral tracheal and esophageal catheters, and tested by plethysmography. The SBNW expirogram was recorded during exhalation after inhaling 100% O2 from residual volume. The slope of phase III (slope III), closing volume (CV), and closing capacity (CC) were calculated. Changes in the SBNW expirogram were compared with changes in breathing pattern, dynamic and quasistatic lung mechanics, lung volumes, and forced expiratory indices. Pre- and postinstillation tests were performed on rats treated with elastase or histamine and on untreated controls. The SBNW indices were altered at significant levels equal to those of other indices of lung function, and different patterns of change were induced by the two disease models. Elastase increased CV and CC, but slope III was unchanged. Other tests suggested loss of elastic recoil and expiratory flow limitation. Histamine increased slope III, but CV and CC were unchanged. Other tests suggested large airway constriction. These results suggested the usefulness of the SBNW in rats, but the relationships between SBNW changes and underlying physiological phenomena remain to be defined.