Changes In End-expiratory Lung Volume Research Articles

Mild obesity does not limit change in end-expiratory lung volume during cycling in young women.

To investigate the effects of obesity on the regulation of end-expiratory lung volume (EELV) during exercise we studied nine obese (41 +/- 6% body fat and 35 +/- 7 yr, mean +/- SD) and eight lean (18 +/- 3% body fat and 34 +/- 4 yr) women. We hypothesized that the simple mass loading of obesity would constrain the decrease in EELV in the supine position and during exercise. All subjects underwent respiratory mechanics measurements in the supine and seated positions, and during graded cycle ergometry to exhaustion. Data were analyzed between groups by independent t-test in the supine and seated postures, and during exercise at ventilatory threshold and peak. Total lung capacity (TLC) was reduced in the obese women (P < 0.05). EELV was significantly lower in the obese subjects in the supine (37 +/- 6 vs. 45 +/- 5% TLC) and seated (45 +/- 6 vs. 53 +/- 5% TLC) positions and at ventilatory threshold (41 +/- 4 vs. 49 +/- 5% TLC) (P < 0.01). In conclusion, despite reduced resting lung volumes and alterations in respiratory mechanics during exercise, mild obesity in women does not appear to constrain EELV during cycling nor does it limit exercise capacity. Also, these data suggest that other nonmechanical factors also regulate the level of EELV during exercise.

EFFECTS OF FAT DISTRIBUTION ON LUNG VOLUME IN OBESE MEN

Obesity decreases lung volume subdivisions, particularly end-expiratory lung volume (EELV). The effect of abdominal fat distribution (i.e., visceral and subcutaneous) on EELV has not been studied. PURPOSE: To investigate the effects of fat distribution on EELV, we studied body composition and EELV in 9 lean (18 ± 4% body fat) and 10 obese (38 ± 4% body fat) men. We hypothesized that abdominal fat distribution would better predict the change in EELV with mild-to-moderate obesity than overall percent body fat. METHODS: All subjects underwent spirometry and lung volume measurements, hydrostatic weighing, and abdominal fat distribution estimates based on MRI scans. Data were analyzed between groups by independent t-test and the relationship between variables was determined by regression analysis. RESULTS: Age and height were not different between groups. All body composition measurements were significantly different between the lean and obese men (p < 0.001). However, fat distribution was similar between the two groups. Spirometry data were not significantly different, nor was total lung capacity (TLC). On the other hand, EELV was significantly lower in the obese men (39 ± 6 vs. 46 ± 4%TLC, p < 0.01). While the correlation coefficient between percent body fat and EELV was significant (p < 0.05) at −0.56, the correlation between visceral fat (kg) and EELV was 00.70 (p < 0.001). CONCLUSION: It appears that visceral fat is a large contributor to low lung volume breathing in otherwise healthy mild-to-moderately obese men. Supported by the American Lung Association.

Expiratory flow limitation during exercise in COPD: detection by manual compression of the abdominal wall.

Manual compression of the abdomen (MCA) during spontaneous expiration is a simple method for the detection of flow limitation in the chronic obstructive pulmonary disease (COPD) patients during resting breathing, based on comparison of flow/volume curves obtained during MCA with that of the preceding control breath. It was assessed whether this nonstandardized technique is also feasible during exercise. MCA was performed during resting breathing and constant-exercise work at one- and two-thirds maximal mechanical power output (W'max) in six normal subjects and 12 COPD patients. Changes in end-expiratory lung volume (EELV) were also studied. With the aid of inspection, abdominal palpation and lung auscultation, MCA could always be applied during expiration. Flow limitation was never detected in the six normal subjects, whereas four of the COPD patients were flow limited at rest, seven during exercise at one-third W'max and nine during exercise at two-thirds W'max. Expiratory flow limitation detected by MCA was always associated with an increase in EELV during exercise, indicating dynamic hyperinflation occurrence or increase. It is concluded that manual compression of the abdomen is a very simple and reliable method for the detection of flow limitation during exercise.

Ventilation, EELV and diaphragmatic activity in rats during chronic normobaric hypoxia

We determined the effects of chronic hypoxia on end-expiratory lung volume (EELV), end-expiratory diaphragmatic activity (DE) and ventilation ( V ̇ E) in 27 intact (awake and anesthetized) and six carotid body-denervated (CBD; anesthetized) rats. Twenty-nine control animals were also studied. Recordings were made during hypoxia and normoxia before and after 2 or 3 weeks of hypoxia (+3 days of recovery from chronic hypoxia). In awake rats, 2 weeks of chronic hypoxia increased only normoxic V ̇ E, while 3 weeks of chronic hypoxia did not change V ̇ E or DE. In anesthetized intact rats, after both exposures, hypoxic and normoxic V ̇ E tended to decrease, DE did not change and hypoxic and normoxic EELV were enlarged. In CBD animals, 2 weeks of chronic hypoxia did not affect hypoxic V ̇ E but decreased normoxic ventilation and enlarged EELV similar to the intact animals. After 3 days of recovery in normoxia, all parameters except EELV were restored to prehypoxic values. Also, transition from hypoxia to normoxia induced parallel changes in EELV and DE while chronic hypoxia increased only EELV. Therefore, chronic normobaric hypoxia induced, (1) an increase in normoxic ventilation reflecting a process of acclimatization; (2) an enlargement of EELV that did not depend on changes in DE and carotid chemoreceptors.

Estimation of end-expiratory lung volume variations by optoelectronic plethysmography.

To test the capability of optoelectronic plethysmography (OEP) to monitor positive end-expiratory pressure (PEEP)-induced changes of end-expiratory lung volume (EELV) changes in mechanically ventilated paralyzed patients. Laboratory and clinical investigation. Intensive care unit of the Ospedale Maggiore Policlinico di Milano. A total of eight patients with respiratory failure of various degrees, sedated and paralyzed. PEEP variations (+/-5 cm H2O) relative to the baseline PEEP of 10 cm H2O. In the model protocol, we tested the reproducibility of the OEP by repeating volume measurements of a plastic torso model over a 21-hr period, every 30 mins. The variations of OEP measurements of the torso model (9337 mL value) were encountered in a range of 16 mL (sd = 4 mL). In the patient protocol, we measured the end-expiratory volume of the chest wall (EEVCW) breath-by-breath by OEP before, during, and after the PEEP increase/decrease and we compared its variations with the corresponding variations of EELV measured by helium dilution technique. The regression line between EELV changes measured by helium and EEVCW changes measured by OEP resulted very close to the identity line (slope 1.06, intercept -0.02 L, r(2) = 0.89) and their difference was not related to their absolute magnitude. After PEEP increase, the new steady state of EEVCW was reached approximately in 15 breaths; and, after PEEP decrease, in 3-4 breaths. The slow increase in EEVCW was mainly because of the abdominal compartment. OEP measurements of EEVCW accurately reflect the changes of EELV. Furthermore, OEP allows a continuous compartmental analysis, even during unsteady conditions.

Effects of PEEP on inspiratory resistance in mechanically ventilated COPD patients.

This study aimed to investigate the effect of increased lung volume with positive end-expiratory pressure (PEEP) on respiratory resistance in patients with chronic obstructive pulmonary disease (COPD). Ten patients with COPD were mechanically ventilated for acute respiratory failure. PEEP was set at 0, 5, 10 and 15 cm H2O. Using the rapid airway occlusion technique, the total inspiratory resistance of the respiratory system was partitioned into interrupter (Rint,rs) and additional effective (deltaRrs) resistances. At each level of PEEP, at constant inflation flow, the inflation volume (deltaV) was varied from 0.2-1 L, and, at constant deltaV, the inflation flow was varied from 0.2-1.2 L x s(-1). The changes in end-expiratory lung volume (deltaEELV) induced by PEEP were also measured. The difference between the EELV and the relaxation volume of the respiratory system (deltaFRC) increased significantly with PEEP of 10 and 15 cm H2O as compared to a PEEP of 0, the increase being associated with a significant reduction of Rint,rs. By contrast, deltaRrs was independent of deltaFRC. At constant deltaV, Rint,rs fitted Rohrer's equation (Rint,rs = K1 + K2 x flow). While K2 significantly declined with AFRC, K1 did not change. At all levels of PEEP, deltaRrs was not influenced by deltaFRC. With increasing lung volume induced by positive end-expiratory pressure, the inspiratory airway resistance decreased, whereas the viscoelastic behaviour of the respiratory system, as reflected by additional effective resistance, did not change.

Validation of a new respiratory inductive plethysmograph

The respiratory inductive plethysmograph (RIP) can be used to monitor changes in end-expiratory lung volume (deltaEELV), and thus, used in intensive care when evaluating positive end-expiratory pressure (PEEP)-induced changes in lung volumes in order to optimise the ventilator settings. We validated the newest model of RIP (Respitrace Plus), both under laboratory and clinical conditions, and made a comparison with a previously validated RIP (Respigraph) in the measurement of tidal volume (V(T)), long-term EELV and PEEP-induced acute deltaEELV. The in vitro validation was performed using a lung model and the in vivo evaluation in five spontaneously breathing normal subjects, four patients with acute lung injury (ALI) and eight anaesthetised patients. The difference in V(T) values during PEEP manipulations between pneumotachometer (PNT) and RIP in spontaneously breathing volunteers and mechanically ventilated ALI patients was 0.1-0.9% (mean+/-SEM) and -5.2+/-0.6, respectively (effect of device NS). In anaesthetised patients, the difference between the new RIP and spirometer in the measurement of PEEP-induced acute deltaEELV was -2.6+/-1.5% (PEEP-device interaction, P<0.05). In ALI patients, the difference between PNT and RIP in the measurement of PEEP-induced acute deltaEELV was 1.0+/-9.7% (NS). The new RIP had a baseline drift over 50-fold when cold and over 10-fold when warm compared to the old RIP in vitro. The new RIP is accurate enough for clinical and research purposes in the measurement of V(T). Semiquantitative measurements of acute deltaEELV can be done with accuracy sufficient for clinical use, but long-term deltaEELV monitoring is not possible. The new RIP should be kept on for several hours before measurements to minimise the drift.

Recruitment maneuvers in three experimental models of acute lung injury. Effect on lung volume and gas exchange.

Recruitment maneuvers (RM), consisting of sustained inflations at high airway pressures, have been advocated as an adjunct to mechanical ventilation in acute respiratory distress syndrome (ARDS). We studied the effect of baseline ventilatory strategy and RM on end-expiratory lung volume (EELV) and oxygenation in 18 dogs, using three models of acute lung injury (ALI; n = 6 in each group): saline lavage (LAV), oleic acid injury (OAI), and intratracheal instillation of Escherichia coli (pneumonia; PNM). All three models exhibited similar degrees of lung injury. The PNM model was less responsive to positive end-expiratory pressure (PEEP) than was the LAV or OAI model. Only the LAV model showed an oxygenation response to increasing tidal volume (VT). After RM, there were transient increases in Pa(O(2)) and EELV when ventilating with PEEP = 10 cm H(2)O. At PEEP = 20 cm H(2)O the lungs were probably fully recruited, since the plateau airway pressures were relatively high ( approximately 45 cm H(2)O) and the oxygenation was similar to preinjury values, thus making the system unresponsive to RM. Sustained improvement in oxygenation after RM was seen in the LAV model when ventilating with PEEP = 10 cm H(2)O and VT = 15 ml/kg. Changes in EELV correlated with changes in Pa(O(2)) only in the OAI model with PEEP = 10 cm H(2)O. We conclude that responses to PEEP, VT, and RM differ among these models of ALI. RM may have a role in some patients with ARDS who are ventilated with low PEEP and low VT.

Ventilatory Constraints During Exercise in Patients With Chronic Heart Failure

We examined the degree of ventilatory constraint in patients with a history of chronic heart failure (CHF; n = 11; mean +/- SE age, 62 +/- 4 years; cardiac index [CI], 2.0 +/- 0.1; and ejection fraction [EF], 24 +/- 2%) and in control subjects (CTLS; n = 8; age, 61 +/- 5 years; CI, 2.6 +/- 0.3) by plotting the tidal flow-volume responses to graded exercise in relationship to the maximal flow-volume envelope (MFVL). Inspiratory capacity (IC) maneuvers were performed to follow changes in end-expiratory lung volume (EELV) during exercise, and the degree of expiratory flow limitation was assessed as the percent of the tidal volume (VT) that met or exceeded the expiratory boundary of the MFVL. CHF patients had significantly (p < 0.05) reduced baseline pulmonary function (FVC, 76 +/- 4%; FEV(1), 78 +/- 4% predicted) relative to CTLS (FVC, 99 +/- 4%; FEV(1), 102 +/- 4% predicted). At peak exercise, oxygen consumption (VO(2)) and minute ventilation (V(E)) were lower in CHF patients than in CTLS (VO(2), 17 +/- 2 vs 32 +/- 2 mL/kg/min; VE, 56 +/- 4 vs 82 +/- 6 L/min, respectively), whereas VE/carbon dioxide output was higher (42 +/- 4 vs 29 +/- 5). In CTLS, EELV initially decreased with light exercise, but increased as VE and expiratory flow limitation increased. In contrast, the EELV in patients with CHF remained near residual volume (RV) throughout exercise, despite increasing flow limitation. At peak exercise, IC averaged 91 +/- 3% and 79 +/- 4% (p < 0.05) of the FVC in CHF patients and CTLS, respectively, and flow limitation was present over > 45% of the VT in CHF patients vs < 25% in CTLS (despite the higher VE in CTLS). The least fit and most symptomatic CHF patients demonstrated the lowest EELV, the greatest degree of flow limitation, and a limited response to increased inspired carbon dioxide during exercise, all consistent with VE constraint. We conclude that patients with CHF commonly breathe near RV during exertion and experience expiratory flow limitation. This results in VE constraint and may contribute to exertional intolerance.

Variations in End-Expiratory Pressure During Partial Liquid Ventilation: Impact on Gas Exchange, Lung Compliance, and End-Expiratory Lung Volume

To determine the effects of different levels of positive end-expiratory pressure (PEEP) during partial liquid ventilation (PLV) on gas exchange, lung compliance, and end-expiratory lung volume (EELV). Prospective animal study. Animal physiology research laboratory. Nine piglets. Animals underwent saline solution lavage to produce lung injury. Perflubron was instilled via the endotracheal tube in a volume estimated to represent functional residual capacity. The initial PEEP setting was 4 cm H(2)O, and stepwise changes in PEEP were made. At 30-min intervals, the PEEP was increased to 8, then 12, then decreased back down to 8, then 4 cm H(2)O. After 30 min at each level of PEEP, arterial blood gases, aortic and central venous pressures, heart rates, dynamic lung compliance, and changes in EELV were recorded. Paired t tests with Bonferroni correction were used to evaluate the data. There were no differences in heart rate or mean BP at the different PEEP levels. CO(2) elimination and oxygenation improved directly with the PEEP level and mean airway pressure (Paw). Compliance did not change with increasing PEEP, but did increase when PEEP was lowered. EELV changes correlated directly with the level of PEEP. As previously reported during gas ventilation, oxygenation and CO(2) elimination vary directly with PEEP and proximal Paw during PLV. EELV also varies directly with PEEP. Dynamic lung compliance, however, improved only when PEEP was lowered, suggesting an alteration in the distribution of perflubron due to changes in pressure-volume relationships.

Sensation of inspiratory difficulty during inspiratory threshold and hyperinflationary loadings. Effect of inspiratory muscle strength.

Dynamic hyperinflation loads the inspiratory muscles by increasing end-expiratory lung volume (EELV) and imposing intrinsic positive end-expiratory pressure (PEEPi), the latter behaving as an inspiratory threshold load (ITL). The aim of the current study was to examine how induced-inspiratory muscle fatigue affects the independent effects of the imposed ITL and increasing operating lung volume on the perceived inspiratory difficulty. Dynamic hyperinflation in healthy subjects was induced by positive end-expiratory pressure (PEEP). Increasing operating lung volume alone (without PEEPi) and increasing ITL alone (without change in EELV) were induced by continuous positive airway pressure (CPAP) and external ITL, respectively. Inspiratory difficulty was quantified by the modified Borg scale and analyzed by step forward multiple regression, using the imposed ITL, EELV, and end-inspiratory lung volume (EILV) as independent variables. When fresh, the first entered variable was the imposed ITL (r(2), 0.38). Adding EILV into the model increased r(2) to 0.67. After fatigue, the first entered variable became EILV (r(2), 0.50) and the second selected variable was the imposed ITL, which increased r(2) to 0.66. EELV was insignificant under both conditions. The coefficient of EILV increased significantly from 0.039 +/- 0.005 to 0.092 +/- 0.012 (% inspiratory capacity(-)(1)) after fatigue run (p < 0.001), whereas that of the imposed ITL did not change. It is concluded that in the experimental conditions studied, inspiratory muscle fatigue increased the importance of lung volume over that of inspiratory threshold load in determining the perceived inspiratory difficulty.

Hospitalization trends for paediatric asthma in eastern Finland: a 10-yr survey

Although persistent activation of the inspiratory muscles and narrowing of the glottic aperture during expiration have been indicated as relevant mechanisms leading to dynamic hyperinflation in acute asthma, expiratory flow limitation (EFL) has recently been proposed as a possible triggering factor for increasing endexpiratory lung volume (EELV). To establish whether the attainment of maximal flow rate during tidal expiration could elicit dynamic elevation of EELV, breathing pattern, change in EELV by measuring inspiratory capacity (IC) and occurrence of EFL by the negative expiratory pressure (NEP) method were monitored in 10 stable asthmatic subjects during methacholine-induced, progressive bronchoconstriction in seated position. Change in dyspnoea was scored using the Borg scale. At maximum response forced expiratory volume in one second (FEV1) fell on average by 45+/-2% (p&lt;0.001 versus control), while IC decreased 29+/-2%, (by 0.89+/-0.07 L, (p&lt;0.01 versus control)). Only 2 subjects exhibited EFL at the end of methacholine challenge. In 7 subjects EELV started to increase before the occurrence of EFL. Dyspnoea, which increased from 0.2+/-0.1 to 5.5+/-1.0 (Borg scale) at maximum response (p&lt;0.001), was significantly related to the level of bronchoconstriction as assessed by change in (delta)FEV1 (r=0.72; p&lt;0.001) and to dynamic hyperinflation as measured by deltaIC (r=0.50; p&lt;0.001). However, for both deltaFEV1 and deltaIC the slope of the relationship with increasing dyspnoea was highly variable among the subjects. It is concluded that in acute methacholine-induced bronchoconstriction, dynamic hyperinflation may occur in the absence of expiratory flow limitation and that expiratory flow limitation does not represent the triggering factor to generate dynamic hyperinflation. In these circumstances, dyspnoea appears to be related to the increase in end-expiratory lung volume and not to the onset of expiratory flow limitation.

Dynamic hyperinflation and flow limitation during methacholine-induced bronchoconstriction in asthma.

Although persistent activation of the inspiratory muscles and narrowing of the glottic aperture during expiration have been indicated as relevant mechanisms leading to dynamic hyperinflation in acute asthma, expiratory flow limitation (EFL) has recently been proposed as a possible triggering factor for increasing endexpiratory lung volume (EELV). To establish whether the attainment of maximal flow rate during tidal expiration could elicit dynamic elevation of EELV, breathing pattern, change in EELV by measuring inspiratory capacity (IC) and occurrence of EFL by the negative expiratory pressure (NEP) method were monitored in 10 stable asthmatic subjects during methacholine-induced, progressive bronchoconstriction in seated position. Change in dyspnoea was scored using the Borg scale. At maximum response forced expiratory volume in one second (FEV1) fell on average by 45+/-2% (p<0.001 versus control), while IC decreased 29+/-2%, (by 0.89+/-0.07 L, (p<0.01 versus control)). Only 2 subjects exhibited EFL at the end of methacholine challenge. In 7 subjects EELV started to increase before the occurrence of EFL. Dyspnoea, which increased from 0.2+/-0.1 to 5.5+/-1.0 (Borg scale) at maximum response (p<0.001), was significantly related to the level of bronchoconstriction as assessed by change in (delta)FEV1 (r=0.72; p<0.001) and to dynamic hyperinflation as measured by deltaIC (r=0.50; p<0.001). However, for both deltaFEV1 and deltaIC the slope of the relationship with increasing dyspnoea was highly variable among the subjects. It is concluded that in acute methacholine-induced bronchoconstriction, dynamic hyperinflation may occur in the absence of expiratory flow limitation and that expiratory flow limitation does not represent the triggering factor to generate dynamic hyperinflation. In these circumstances, dyspnoea appears to be related to the increase in end-expiratory lung volume and not to the onset of expiratory flow limitation.

End-expiratory lung volume during arm and leg exercise in normal subjects and patients with cystic fibrosis.

There are no reports concerning the regulation of end-expiratory lung volume (EELV) and flow-volume relationships during upper limb exercise in health and disease. We studied EELV during such exercise in 22 adults with cystic fibrosis (CF) and nine age-matched healthy control subjects. Subjects with CF were grouped according to the severity of their lung disease, as follows: mild = FEV1 > 80% predicted; moderate = FEV1 40 to 80% predicted, and severe = FEV1 < 40% predicted. EELV was calculated from measurements of inspiratory capacity (IC) made at each workload during an incremental arm and leg ergometer test to peak work capacity. In the control group, the decrease in EELV was significantly smaller for arm than for leg exercise at peak work (-0.13 L versus -0.53 L, p < 0.001) and for arm than for leg exercise at an equivalent submaximal ventilation (-0.13 L versus -0.46 L, p < 0.01). In the groups with moderate and severe CF, arm exercise resulted in an increase in EELV from resting levels (dynamic hyperinflation) that was not significantly different from the increase observed for leg exercise. For CF subjects there was a significant inverse relationship between FEV1 and changes in EELV from rest to peak arm exercise (r = -0.46, p < 0.05). In normal subjects, there was a difference in the EELV response for arm versus leg exercise. In CF subjects with airflow limitation, dynamic hyperinflation occurred with both forms of exercise.

Control of ventilation during lung volume changes and permissive hypercapnia in dogs.

We investigated the effect changes in end-expiratory lung volume (EEVL) had on the response to progressive hypercapnia (CO2-response curve) in eight open-chest, anesthetized dogs, in order to clarify the role that vagal lung mechanoreceptors have in altered respiratory drive during permissive hypercapnia. The dogs were ventilated using a positive-pressure ventilator driven by phrenic neural activity. Systemic arterial CO2 tension (PaCO2) was elevated by increasing the fraction of CO2 delivered to the ventilator. EEVL was altered from approximated functional residual capacity ("FRC") to 1.5 and 0.5 "FRC" by changing positive end-expiratory pressure. Although the tidal volume (VT)-PaCO2 and inspiratory time (TI)-PaCO2 relationships were not affected, decreasing EEVL from 1.5 "FRC" to "FRC" and then to 0.5 "FRC" caused a significant (p < 0.01) upward shift in the CO2-response curves for minute ventilation (V I) and frequency (f ), and a significant (p < 0.01) downward shift in the CO2- response curve for expiratory time (TE). We conclude that these shifts were explained by a decrease in the inhibitory activity of slowly adapting pulmonary stretch receptors (PSRs) as EEVL was lowered. In addition, increases in EEVL from 0.5 "FRC" to 1.5 "FRC" caused a significant (p < 0.05) increase in the apneic threshold, which we attribute to an inhibitory effect on central drive caused by increased PSR activity.

Effects of Positive End-Expiratory Pressure on Oscillated Flow Rate During High-Frequency Chest Compression

To investigate the effects of positive end-expiratory pressure (PEEP) on end-expiratory lung volume (EELV) and mean oscillated flow rate (VOSC) during high-frequency chest compression (HFCC) in normal subjects and patients with severe COPD. Comparative study. Pulmonary function and lung mechanics laboratory, University of Alberta Hospitals. Six normal subjects (five male; one female) and six patients with clinically stable COPD (five male; one female) with hypercapnia. A pneumatic vest system was operated at 10 Hz with a mean chest wall pressure of 16 cm H2O to provide the HFCC. A closed-circuit spirometer system permitted measurement of HFCC- and PEEP-induced changes in EELV that were expressed as per cent baseline functional residual capacity (FRC). An isothermic chamber connected near the mouthpiece permitted measurement of VOSC. For the normal subjects, HFCC caused a significant decrease in EELV to 82.0% of FRC (p < or = 0.01) and the addition of 4.8+/-0.5 cm H2O of PEEP during HFCC increased EELV to 97.5% FRC. In the COPD patients, HFCC decreased EELV to 92.3% of FRC (p < or = 0.01), and the addition of 3.7+/-1.0 cm H2O of PEEP increased EELV to 98.4% FRC. For the normal subjects, increasing EELV to near FRC caused VOSC during expiration to increase 14.6% (p < or = 0.01), but there was no significant effect on VOSC during inspiration (5.1% increase). In the COPD patients, PEEP increased VOSC during both inspiration (30.5%) and expiration (57.0%) (both, p < or = 0.01). Addition of a modest amount of PEEP during HFCC prevents the decrease in EELV and increases VOSC during both phases of spontaneous breathing in COPD patients. This higher VOSC during HFCC+PEEP may improve the effectiveness of HFCC in clearing mucus from the lungs of patients with airway disease.

Evaluation of Respiratory Inductive Plethysmography in Controlled Ventilation: Measurement of Tidal Volume and PEEP-Induced Changes of End-Expiratory Lung Volume

To determine the accuracy of respiratory inductive plethysmography (RIP) with a respiratory monitor (Respitrace Plus; NIMS Inc., Miami) operating in the DC-mode for the measurement of tidal volumes (VT) and positive end-expiratory pressure (PEEP)-induced changes of end-expiratory lung volume (deltaEELV) in patients with normal pulmonary function, acute lung injury (ALI), and COPD during volume-controlled ventilation. Prospective comparison of RIP with pneumotachography (PT) for assessment of VT and with multibreath nitrogen washout procedure (N2WO) for determination of deltaEELV as reference methods. Mixed ICU at a university hospital. Thirty-one sedated and paralyzed patients: 12 patients with normal pulmonary function mechanically ventilated after major surgery, 10 patients with respiratory failure due to ALI, and 9 patients with a known history of COPD ventilated after surgery or because of respiratory failure due to bronchopulmonary infection. Stepwise increase of PEEP from 0 to 5 to 10 cm H2O and reduction to 0 cm H2O again. On each PEEP level, N2WO was performed. The baseline drift of RIP averaged 25.4+/-29.1 mL/min but changed over a wide range even in single patient measurements. Determination of VT for single minutes revealed that 66.5% and 90.0% of all values were accurate within a range of +/-10% and +/-20%, respectively. The deviation for VT measurements between RIP and PT in patients with COPD was significantly (p<0.05) higher compared to patients with ALI or normal pulmonary function. The difference of deltaEELV between RIP and N2WO was 11.6+/-174.1 mL with correlation coefficients of 0.77 (postoperative and COPD patients) and 0.86 (ALI patients). However, just 25.8% and 46.2% were precise within +/-10% and +/-20%, respectively. deltaEELV determination in COPD patients differed more between RIP and N2WO than in the other groups, but this was not significant. In a mixed group of patients undergoing controlled ventilation, RIP using the Respitrace Plus monitor was not consistently precise enough for quantitative evaluation of VT and EELV when compared to our reference methods. This was most evident in patients with COPD. For long-term volume measurements, a better control of the baseline drift of RIP should be achieved.

Measurements of PEEP-Induced Changes in Lung Volume: Evaluation of a Laser Monitor

To evaluate a newly developed laser monitor in the measurement of positive end-expiratory pressure (PEEP)-induced changes in end-expiratory lung volume (EELV) in spontaneously breathing subjects. An open comparison between two different methods to assess breathing parameters. A respiratory research unit. Six spontaneously breathing, healthy volunteers. Stepwise increases of PEEP from 0 to 0.8 to 1.6 kPa during spontaneous breathing; repeated validation of the laser monitor in each subject. Pressure and flow were recorded at the airway opening. Abdominal wall displacement (AWD) measured by the laser sensor was recorded simultaneously. The time lag between the volume and the laser signals during baseline was 0.068+/-0.052 s and during maximal PEEP, 0.108+/-0.093 s. There was no baseline drift in either the PEEP or the AWD signals. Mean EELV decreased by 290 mL to 1,157 mL after the PEEP valve was removed. Within each individual, the ratio between EELV and AWD showed only small variations. Measurements of tidal volume (VT) and AWD showed good agreement at all PEEP levels. Mean VT decreased in all but one subject during PEEP. With the increase in PEEP, the end-expiratory abdominal baseline increased linearly over a large range of end-expiratory pressures with a flattening of the curve at high PEEP levels in all subjects. The laser monitor is sufficiently accurate for measuring PEEP-induced changes in EELV during spontaneous breathing in healthy adult subjects. Monitors incorporating multiple laser sensors may have considerable clinical promise.

Reliability of inspiratory capacity for estimating end-expiratory lung volume changes during exercise in patients with chronic obstructive pulmonary disease.

The inspiratory capacity (IC) maneuver is increasingly used to monitor exercise-induced dynamic hyperinflation in patients with COPD. However, the reliability of this method in patients with COPD exercising to symptom limitation has not been systematically studied and presented. The purpose of the present study was therefore to evaluate the reliability of the IC maneuver in assessing changes in end-expiratory lung volume (EELV) by assessing the pressure developed during IC maneuvers, in patients with COPD during incremental bicycle exercise to exhaustion. Fifteen patients with stable COPD performed bicycle exercise to symptom limitation. During the experiment, the patients performed IC efforts during resting breathing and at the end of each exercise work load. Esophageal pressure (Pes) measured at peak inspired volume plateau (zero flow) was -13.5 +/- 1.9 and -13.4 +/- 1.9 cm H2O (p = 0.79) during IC maneuvers at resting breathing and during the final exercise work load, respectively. When the Pes values at the peak inspired volume plateau during IC efforts at each exercise level were expressed as a percentage of those during resting breathing, the great majority of the ratios were above 90% with the lowest at 84%, and these ratios were independent of exercise intensity. Despite a constant Pes during IC, there was a progressive decrease in IC with increasing exercise work load in most patients, suggesting an increase in EELV. At the highest exercise work load achieved, delta EELV calculated as the decrease in IC was 0.26 +/- 0.06 L (p < 0.001). We conclude that repeated IC maneuver is a simple and reliable method for estimating EELV changes during exercise to exhaustion in patients with COPD.

Effects of positive end-expiratory pressure on right ventricular function in COPD patients during acute ventilatory failure.

To examine the effects of external positive end-expiratory pressure (PEEP) on right ventricular function in chronic obstructive pulmonary disease (COPD) patients with intrinsic PEEP (PEEPi). Prospective study. General intensive care unit in a university teaching hospital. Seven mechanically ventilated flow-limited COPD patients (PEEPi = 9.7 +/- 1.3 cmH2O, mean +/- SD) with acute respiratory failure. Hemodynamic and respiratory mechanic data were collected at four different levels of PEEP (0-5-10-15 cmH2O). Hemodynamic parameters were obtained by a Swan-Ganz catheter with a fast response thermistor. Cardiac index (CI) and end-expiratory lung volume (EELV) reductions started simultaneously when the applied PEEP was approximately 90% of PEEPi measured on 0 cmH2O (ZEEP). Changes in transmural intrathoracic pressure (PEEPi,cw) started only at a PEEP value much higher (120%) than PEEPi. The reduction in CI was related to a decrease in the right end-diastolic ventricular volume index (RVEDVI) (r = 0.61; p < 0.001). No correlation between CI and transmural right atrial pressure was observed. The RVEDVI was inversely correlated with PEEP-induced changes in EELV (r = -55; p < 0.001), but no with PEEPi,cw (r = -0.08; NS). The relationship between RVEDVI and right ventricular stroke work index, considered an index of contractility, was significant in three patients, i.e., PEEP did not change contractility. In the other patients, an increase in contractility seemed to occur. In COPD patients an external PEEP exceeding 90% of PEEPi causes lung hyperinflation and reduces the CI due to a preload effect. The reduction in RVEDVI seems related to changes in EELV, rather than to changes in transmural pressures, suggesting a lung/heart volume interaction in the cardiac fossa. Thus, in COPD patients, application of an external PEEP level lower than PEEPi may affect right ventricular function.