Biomedical subjects

A Aliverti

Publications and source records attributed to A Aliverti.

At least 19 recordsLinked to original sources

PubMed2006

Oxygen kinetics and debt during recovery from expiratory flow-limited exercise in healthy humans.

In healthy subjects expiratory flow limitation (EFL) during exercise can lower O(2) delivery to the working muscles. We hypothesized that if this affects exercise performance it should influence O(2) kinetics at the end of exercise when the O(2) debt is repaid. We performed an incremental exercise test on six healthy males with a Starling resistor in the expiratory line limiting expiratory flow to approximately 1 l s(-1) to determine maximal EFL exercise workload (W (max)). In two more square-wave exercise runs subjects exercised with and without EFL at W (max) for 6 min, while measuring arterial O(2) saturation (% SaO(2)), end-tidal pressure of CO(2) (P (ET)CO(2)) and breath-by-breath O(2) consumption VO2 taking into account changes in O(2) stored in the lungs. Over the last minute of EFL exercise, mean P (ET)CO(2) (54.7 +/- 9.9 mmHg) was significantly higher (P < 0.05) compared to control (41.4 +/- 3.9 mmHg). At the end of EFL exercise %SaO(2) fell significantly by 4 +/- 3%. When exercise stopped, EFL was removed, and we continued to measure VO2. During recovery, there was an immediate step increase in [Formula: see text] so that repayment of EFL O(2) debt started at a higher VO2 than control. Recovery VO2 kinetics after EFL exercise was best characterized by a double-exponential function with fundamental and slow time constants of 27 +/- 11 and 1,020 +/- 305 s, compared to control values of 41 +/- 10 and 1,358 +/- 320 s, respectively. EFL O(2) debt was 52 +/- 22% greater than control (2.19 +/- 0.58 vs. 1.49 +/- 0.38 l). We conclude that EFL exercise increases the O(2) debt and leads to hypoxemia in part due to hypercapnia.

Carbon Dioxide↗

PubMed2006

Effects of rehabilitation on chest wall volume regulation during exercise in COPD patients.

In order to investigate underlying mechanisms, the present authors studied the effect of pulmonary rehabilitation on the regulation of total chest wall and compartmental (ribcage, abdominal) volumes during exercise in patients with chronic obstructive pulmonary disease. In total, 20 patients (forced expiratory volume in one second, mean +/- SEM 39 +/- 3% predicted) undertook high-intensity exercise 3 days x week(-1) for 12 weeks. Before and after rehabilitation, the changes in chest wall (cw) volumes at the end of expiration (EEV) and inspiration (EIV) were computed by optoelectronic plethysmography during incremental exercise to the limit of tolerance (W(peak)). Rehabilitation significantly improved W(peak) (57+/-7 versus 47+/-5 W). In the post-rehabilitation period and at identical work rates, significant reductions were observed in minute ventilation (35.1+/-2.7 versus 38.4+/-2.7 L x min(-1)), breathing frequency (26+/-1 versus 29+/-1 breaths x min(-1)) and EEV(cw) and EIV(cw) (by 182+/-79 and 136+/-37 mL, respectively). Inspiratory reserve volume was significantly increased (by 148+/-70 mL). Volume reductions were attributed to significant changes in abdominal EEV and EIV (by 163+/-59 and 125+/-27 mL, respectively). The improvement in W(peak) was similar in patients who progressively hyperinflated during exercise and those who did not (24 and 26%, respectively). In conclusion, pulmonary rehabilitation lowers chest wall volumes during exercise by decreasing the abdominal volumes. The improvement in exercise capacity following rehabilitation is independent of the pattern of exercise-induced dynamic hyperinflation.

Aged↗

PubMed2006

Expiratory flow limitation detected by forced oscillation and negative expiratory pressure.

The within-breath change in reactance (Delta(rs)) measured by forced oscillation technique (FOT) at 5 Hz reliably detects expiratory flow limitation in chronic obstructive pulmonary disease (COPD). The present study compared this approach to the standard negative expiratory pressure (NEP) method. In total, 21 COPD patients were studied by applying both techniques to the same breath and in 15 patients the measurements were repeated after bronchodilator. For each patient and condition five NEP tests were performed and independently scored by three operators unaware of the FOT results. In 180 tests, FOT classified 53.3% as flow limited. On average, the operators scored 27.6% of tests flow limited and 47.6% non-flow limited, but could not score 24.8%. The methods disagreed in 7.9% of cases; in 78% of these the NEP scores differed between operators. Bronchodilation reduced NEP and DeltaX(rs) scores, with only the latter achieving significance. Averaging the operators' NEP scores, a threshold between 24.6-30.8% of tidal volume being flow limited by NEP produced 94% agreement between methods. In conclusion, when negative expiratory pressure and forced oscillation technique were both available they showed good agreement. As forced oscillation technique is automatic and can measure multiple breaths over long periods, it is suitable for monitoring expiratory flow limitation continuously and identifying patients' breathing close to the onset of expiratory flow limitation, where intermittent sampling may be unrepresentative.

Forced Expiratory Flow Rates↗

PubMed2006

Noninvasive detection of expiratory flow limitation in COPD patients during nasal CPAP.

The difference between mean inspiratory and expiratory respiratory reactance (delta(rs)) measured with forced oscillation technique (FOT) at 5 Hz allows the detection of expiratory flow limitation (EFL) in chronic obstructive pulmonary disease (COPD) patients breathing spontaneously. This aim of this study was to evaluate whether this approach can be applied to COPD patients during noninvasive pressure support. Delta(rs) was measured in seven COPD patients subjected to nasal continuous positive airway pressure (CPAP) at 0, 4, 8 and 12 cmH2O in sitting and supine positions. Simultaneous recording of oesophageal pressure and the Mead and Whittenberger (M-W) method provided a reference for scoring each breath as flow-limited (FL), non-flow-limited (NFL) or indeterminate (I). For each patient, six consecutive breaths were analysed for each posture and CPAP level. According to M-W scoring, 47 breaths were FL, 166 NFL and 51 I. EFL scoring using FOT coincided with M-W in 94.8% of the breaths. In the four patients who were FL in at least one condition, delta(rs) was reduced with increasing CPAP. These data suggest that the forced oscillation technique may be useful in chronic obstructive pulmonary disease patients on nasal pressure support by identifying continuous positive airway pressure levels that support breathing without increasing lung volume, which in turn increase the work of breathing and reduce muscle effectiveness and efficiency.

Aged↗

PubMed2005

Influence of expiratory flow-limitation during exercise on systemic oxygen delivery in humans.

To determine the effects of exercise with expiratory flow-limitation (EFL) on systemic O(2) delivery, seven normal subjects performed incremental exercise with and without EFL at approximately 0.8 l s(-1) (imposed by a Starling resistor in the expiratory line) to determine maximal power output under control (W'(max,c)) and EFL (W'(max,e)) conditions. W'(max,e) was 62.5% of W'(max,c), and EFL exercise caused a significant fall in the ventilatory threshold. In a third test, after exercising at W'(max,e) without EFL for 4 min, EFL was imposed; exercise continued for 4 more minutes or until exhaustion. O(2) consumption (V'(O)(2)) was measured breath-by-breath for the last 90 s of control, and for the first 90 s of EFL exercise. Assuming that the arterio-mixed venous O(2) content remained constant immediately after EFL imposition, we used V'(O)(2) as a measure of cardiac output (Q'(c)). Q'(c) was also calculated by the pulse contour method with blood pressure measured continuously by a photo-plethysmographic device. Both sets of data showed a decrease of Q'(c) due to a decrease in stroke volume by 10% (p < 0.001 for V'(O)(2)) with EFL and remained decreased for the full 90 s. Concurrently, arterial O(2) saturation decreased by 5%, abdominal, pleural and alveolar pressures increased, and duty cycle decreased by 43%. We conclude that this combination of events led to a decrease in venous return secondary to high expiratory pressures, and a decreased duty cycle which decreased O(2) delivery to working muscles by approximately 15%.

Adult↗

PubMed2005

Effect of salbutamol on lung function and chest wall volumes at rest and during exercise in COPD.

BACKGROUND: Inhaled bronchodilators can increase exercise capacity in chronic obstructive pulmonary disease (COPD) by reducing dynamic hyperinflation, but treatment is not always effective. This may reflect the degree to which the abdomen allows dynamic hyperinflation to occur. METHOD: A double blind, randomised, crossover trial of the effect of 5 mg nebulised salbutamol or saline on endurance exercise time was conducted in 18 patients with COPD of mean (SD) age 67.1 (6.3) years and mean (SD) forced expiratory volume in 1 second (FEV1) of 40.6 (15.0)% predicted. Breathing pattern, metabolic variables, dyspnoea intensity, and total and regional chest wall volumes were measured non-invasively by optoelectronic plethysmography (OEP) at rest and during exercise. RESULTS: Salbutamol increased FEV1, forced vital capacity (FVC) and inspiratory capacity and reduced functional residual capacity (FRC) and residual volume significantly. OEP showed the change in resting FRC to be mainly in the abdominal compartment. Although the mean (SE) end expiratory chest wall volume was 541 (118) ml lower (p<0.001) at the end of exercise, the endurance time was unchanged by the bronchodilator. Changes in resting lung volumes were smaller when exercise duration did not improve, but FEV1 still rose significantly after active drug. After the bronchodilator these patients tried to reduce the end expiratory lung volume when exercising, while those exercising longer continued to allow end expiratory abdominal wall volume to rise. The change to a more euvolumic breathing pattern was associated with a lower oxygen pulse and a significant fall in endurance time with higher isotime levels of dyspnoea. CONCLUSIONS: Nebulised salbutamol improved forced expiratory flow in most patients with COPD, but less hyper-nflated patients tried to reduce the abdominal compartmental volume after active treatment and this reduced their exercise capacity. Identifying these patients has important therapeutic implications, as does an understanding of the mechanisms that control chest wall muscle recruitment.

Aged↗

PubMed2005

Patterns of dynamic hyperinflation during exercise and recovery in patients with severe chronic obstructive pulmonary disease.

BACKGROUND: Not all patients with severe chronic obstructive pulmonary disease (COPD) progressively hyperinflate during symptom limited exercise. The pattern of change in chest wall volumes (Vcw) was investigated in patients with severe COPD who progressively hyperinflate during exercise and those who do not. METHODS: Twenty patients with forced expiratory volume in 1 second (FEV(1)) 35 (2)% predicted were studied during a ramp incremental cycling test to the limit of tolerance (Wpeak). Changes in Vcw at the end of expiration (EEVcw), end of inspiration (EIVcw), and at total lung capacity (TLCVcw) were computed by optoelectronic plethysmography (OEP) during exercise and recovery. RESULTS: Two significantly different patterns of change in EEVcw were observed during exercise. Twelve patients had a progressive significant increase in EEVcw during exercise (early hyperinflators, EH) amounting to 750 (90) ml at Wpeak. In contrast, in all eight remaining patients EEVcw remained unchanged up to 66% Wpeak but increased significantly by 210 (80) ml at Wpeak (late hyperinflators, LH). Although at the limit of tolerance the increase in EEVcw was significantly greater in EH, both groups reached similar Wpeak and breathed with a tidal EIVcw that closely approached TLCVcw (EIVcw/TLCVcw 93 (1)% and 93 (3)%, respectively). EEVcw was increased by 254 (130) ml above baseline 3 minutes after exercise only in EH. CONCLUSIONS: Patients with severe COPD exhibit two patterns during exercise: early and late hyperinflation. In those who hyperinflate early, it may take several minutes before the hyperinflation is fully reversed after termination of exercise.

Exercise↗

PubMed2004

Regional chest wall volumes during exercise in chronic obstructive pulmonary disease.

BACKGROUND: Dynamic hyperinflation of the lungs impairs exercise performance in chronic obstructive pulmonary disease (COPD). However, it is unclear which patients are affected by dynamic hyperinflation and how the respiratory muscles respond to the change in lung volume. METHODS: Using optoelectronic plethysmography, total and regional chest wall volumes were measured non-invasively in 20 stable patients with COPD (mean (SD) forced expiratory volume in 1 second 43.6 (11.6)% predicted) and dynamic hyperinflation was tracked breath by breath to test if this was the mechanism of exercise limitation. Resting ventilation, breathing pattern, symptoms, rib cage and abdominal volumes were recorded at rest and during symptom limited cycle ergometry. Pleural, abdominal, and transdiaphragmatic pressures were measured in eight patients. RESULTS: End expiratory chest wall volume increased by a mean (SE) of 592 (80) ml in 12 patients (hyperinflators) but decreased by 462 (103) ml in eight (euvolumics). During exercise, tidal volume increased in euvolumic patients by reducing end expiratory abdominal volume while in hyperinflators tidal volume increased by increasing end inspiratory abdominal and rib cage volumes. The maximal abdominal pressure was 22.1 (9.0) cm H(2)O in euvolumic patients and 7.6 (2.6) cm H(2)O in hyperinflators. Euvolumic patients were as breathless as hyperinflators but exercised for less time and reached lower maximum workloads (p<0.05) despite having better spirometric parameters and a greater expiratory flow reserve. CONCLUSIONS: Dynamic hyperinflation is not the only mechanism limiting exercise performance in patients with stable COPD. Accurate measurement of chest wall volume can identify the different patterns of respiratory muscle activation during exercise.

Aged↗

PubMed2004

Detection of expiratory flow limitation in COPD using the forced oscillation technique.

Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present. To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean +/- sD forced expiratory volume in one second was 36.8 +/- 11.5% predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited. Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (deltaXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2.53-3.12 cmH2O x s x L(-1) (deltaXrs) and -7.38- -6.76 cmH2O x s x L(-1) (Xexp,min) representing 6.0% and 3.9% of the total range of values respectively. No flow-limited breaths were seen in the normal subjects by either method. Within-breath respiratory system reactance provides an accurate, reliable and noninvasive technique to detect expiratory flow limitation in patients with chronic obstructive pulmonary disease.

Aged↗

PubMed2003

Breath-by-breath assessment of alveolar gas stores and exchange.

The volume of O(2) exchanged at the mouth during a breath (Vo(2,m)) is equal to that taken up by pulmonary capillaries (Vo(2,A)) only if lung O(2) stores are constant. The latter change if either end-expiratory lung volume (EELV), or alveolar O(2) fraction (Fa(O(2))) change. Measuring this requires breath-by-breath (BbB) measurement of absolute EELV, for which we used optoelectronic plethysmography combined with measurement of O(2) fraction at the mouth to measure Vo(2,A) = Vo(2,m) - (DeltaEELV x Fa(O(2)) + EELV x DeltaFa(O(2))), and divided by respiratory cycle time to obtain BbB O(2) consumption (Vo(2)) in seven healthy men during incremental exercise and recovery. To synchronize O(2) and volume signals, we measured gas transit time from mouthpiece to O(2) meter and compared Vo(2) measured during steady-state exercise by using expired gas collection with the mean BbB measurement over the same time period. In one subject, we adjusted the instrumental response time by 20-ms increments to maximize the agreement between the two Vo(2) measurements. We then applied the same total time delay (transit time plus instrumental delay = 660 ms) to all other subjects. The comparison of pooled data from all subjects revealed r(2) = 0.990, percent error = 0.039 +/- 1.61 SE, and slope = 1.02 +/- 0.015 (SE). During recovery, increases in EELV introduced systematic errors in Vo(2) if measured without taking DeltaEELV x Ca(O(2))+EELV x DeltaFa(O(2)) into account. We conclude that optoelectronic plethysmography can be used to measure BbB Vo(2) accurately when studying BbB gas exchange in conditions when EELV changes, as during on- and off-transients.

Adult↗

PubMed2003

Spatial distribution of human respiratory system transfer impedance.

Transfer impedance (Ztr) of the respiratory system provides specific information on airways and tissues, but little is known about its spatial distribution in the different thoracoabdominal regions. To study Ztr distribution on the chest wall surface we analyzed five healthy subjects in the supine position by applying a sinusoidal forcing pressure (4, 8, and 12 Hz) at the mouth and measuring airway opening pressure and flow. Three-dimensional positions of 68 reflective markers placed on the chest wall over selected reference points were simultaneously measured by an optoelectronic motion analyzer. A subset of ten points placed on the midline were used to measure chest wall movements in the craniocaudal direction. While the motion of rib cage markers was synchronous, the abdominal markers demonstrated surface waves propagating caudally. The amplitude and phase of these waves were strongly dependent on position and frequency. We used a new method to measure total and local chest wall volume variations to compute the distribution of Ztr over the chest wall. Above 4 Hz we found that Ztr was inhomogeneously distributed and strongly dependent on position and frequency, mainly in the abdomen where the phase was often more more than 180 degrees with high values of modulus. For this reason, we conclude that above 8 Hz Ztr represents rib cage mechanics almost exclusively.

Abdomen↗

PubMed2002

Chest wall kinematic determinants of diaphragm length by optoelectronic plethysmography and ultrasonography.

To estimate diaphragm fiber length from thoracoabdominal configuration, we measured axial motion of the right-sided area of apposition by ultrasonography and volumes displaced by chest wall compartments [pulmonary, abdominal rib cage, and abdomen (Vab)] by optoelectronic plethysmography in four normal men during quiet breathing and incremental exercise without and with expiratory flow limitation. Points at the cephalic area of apposition border were digitized from echo images and mapped into three-dimensional space, and the axial distance from the xyphoidal transverse plane (D(ap)) was measured simultaneously with the volumes. Linear regression analysis between changes (Delta) in D(ap) and the measured volume changes under all conditions showed that 1) DeltaD(ap) was linearly related more to DeltaVab than to changes in pulmonary and abdominal rib cage volumes; and 2) this was highly repeatable between measures. Multiple stepwise regression analysis showed that DeltaVab accounted for 89-96% of the variability of DeltaD(ap), whereas the rib cage compartments added <1%. We conclude that, under conditions of quiet breathing and exercise, with and without expiratory flow limitation, instantaneous DeltaD(ap) can be estimated from DeltaVab.

Adult↗

PubMed2001

Biochemical and crystallographic characterization of ferredoxin-NADP(+) reductase from nonphotosynthetic tissues.

Distinct forms of ferredoxin-NADP(+) reductase are expressed in photosynthetic and nonphotosynthetic plant tissues. Both enzymes catalyze electron transfer between NADP(H) and ferredoxin; whereas in leaves the enzyme transfers reducing equivalents from photoreduced ferredoxin to NADP(+) in photosynthesis, in roots it has the opposite physiological role, reducing ferredoxin at the expense of NADPH mainly for use in nitrate assimilation. Here, structural and kinetic properties of a nonphotosynthetic isoform were analyzed to define characteristics that may be related to tissue-specific function. Compared with spinach leaf ferredoxin-NADP(+) reductase, the recombinant corn root isoform showed a slightly altered absorption spectrum, a higher pI, a >30-fold higher affinity for NADP(+), greater susceptibility to limited proteolysis, and an approximately 20 mV more positive redox potential. The 1.7 A resolution crystal structure is very similar to the structures of ferredoxin-NADP(+) reductases from photosynthetic tissues. Four distinct structural features of this root ferredoxin-NADP(+) reductases are an alternate conformation of the bound FAD molecule, an alternate path for the amino-terminal extension, a disulfide bond in the FAD-binding domain, and changes in the surface that binds ferredoxin.

Crystallography, X-Ray↗

PubMed2001

Sulfur K-edge X-ray absorption spectroscopy of 2Fe-2S ferredoxin: covalency of the oxidized and reduced 2Fe forms and comparison to model complexes.

Ligand K-edge X-ray absorption spectroscopy (XAS) provides a direct experimental probe of ligand-metal bonding. In previous studies, this method has been applied to mononuclear Fe-S and binuclear 2Fe-2S model compounds as well as to rubredoxins and the Rieske protein. These studies are now extended to the oxidized and reduced forms of ferredoxin I from spinach. Because of its high instability, the mixed-valence state was generated electrochemically in the protein matrix, and ligand K-edge absorption spectra were recorded using an XAS spectroelectrochemical cell. The experimental setup is described. The XAS edge data are analyzed to independently determine the covalencies of the iron-sulfide and -thiolate bonds. The results are compared with those obtained previously for the Rieske protein and for 2Fe-2S model compounds. It is found that the sulfide covalency is significantly lower in oxidized FdI compared to that of the oxidized model complex. This decrease is interpreted in terms of H bonding present in the protein, and its contribution to the reduction potential E degrees is estimated. Further, a significant increase in covalency for the Fe(III)-sulfide bond and a decrease of the Fe(II)-sulfide bond are observed in the reduced Fe(III)Fe(II) mixed-valence species compared to those of the Fe(III)Fe(III) homovalent site. This demonstrates that, upon reduction, the sulfide interactions with the ferrous site decrease, allowing greater charge donation to the remaining ferric center. That is the dominant change in electronic structure of the Fe(2)S(2)RS(4) center upon reduction and can contribute to the redox properties of this active site.

Electrochemistry↗

PubMed2001

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

OBJECTIVE: 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. DESIGN: Laboratory and clinical investigation. SETTING: Intensive care unit of the Ospedale Maggiore Policlinico di Milano. PATIENTS: A total of eight patients with respiratory failure of various degrees, sedated and paralyzed. INTERVENTIONS: PEEP variations (+/-5 cm H2O) relative to the baseline PEEP of 10 cm H2O. MEASUREMENTS AND MAIN RESULTS: 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. CONCLUSION: OEP measurements of EEVCW accurately reflect the changes of EELV. Furthermore, OEP allows a continuous compartmental analysis, even during unsteady conditions.

Adult↗

PubMed2001

Compartmental analysis of breathing in the supine and prone positions by optoelectronic plethysmography.

Optoelectronic plethysmography (OEP) has been shown to be a reliable method for the analysis of chest wall kinematics partitioned into pulmonary rib cage, abdominal rib cage, abdomen, and right and left side in the seated and erect positions. In this paper, we extended the applicability of this method to the supine and prone positions, typically adopted in critically ill patients. For this purpose we have first developed proper geometrical and mathematical models of the chest wall which are able to provide consistent and reliable estimations of total and compartmental volume variations in these positions suitable for clinical settings. Then we compared chest wall (CW) volume changes computed from OEP(deltaVCW) with lung volume changes measured with a water seal spirometer (SP) (deltaVSP) in 10 normal subjects during quiet (QB) and deep (DB) breathing on rigid and soft supports. We found that on a rigid support the average differences between deltaVSP and deltaVCW were -4.2% +/- 6.2%, -3.0% +/- 6.1%, -1.7% +/- 7.0%, and -4.5% +/- 9.8%, respectively, during supine/QB, supine/DB, prone/QB, and prone/DB. On the soft surface we obtained -0.1% +/- 6.0%, -1.8% +/- 7.8%, 18.0% +/- 11.7%, and 10.2% +/- 9.6%, respectively. On rigid support and QB, the abdominal compartment contributed most of the deltaVCW in the supine (63.1% +/- 11.4%) and prone (53.5% +/- 13.1%) positions. deltaVCW was equally distributed between right and left sides. In the prone position we found a different chest wall volume distribution between pulmonary and abdominal rib cage (22.1% +/- 8.6% and 24.4% +/- 6.8%, respectively) compared with the supine position (23.3% +/- 9.3% and 13.6% +/- 13.0%).

Abdomen↗

PubMed2001

Transfer impedance of the respiratory system by forced oscillation technique and optoelectronic plethysmography.

To estimate the transfer impedance of the respiratory system (Ztr), we applied pressure forcing at the mouth from 1 to 24 Hz in eight healthy subjects and used optoelectronic plethysmography (OEP) to measure volume changes of the chest wall and its different compartments: pulmonary rib cage (RCp), abdominal rib cage (RCa) and abdomen (AB). Spectral analysis allowed assessment of input impedance (Zin) and total (Ztr) and compartmental (ZRCP, ZRCa, and ZAB) transfer impedances. As expected, averaged values of Zin and Ztr were similar at low frequencies (< 8 Hz) while they progressively differed at high frequencies. The percentage contributions of ZRCp, ZRCa , and ZAB to Ztr were, respectively, 35.3 +/- 1.4SD, 13.8 +/- 1.4, and 50.8 +/- 2.8 at low frequencies (< 8 Hz) and 63.1 +/- 5.5, 20.7 +/- 5.2, and 16.2 +/- 2.3 at higher frequencies (> 10 Hz). The validation of our approach was based on the comparison with a physical model comprised of a rubber membrane stretched over and attached to the lip of a bowl. We conclude that the combination of forced oscillations with OEP provides the simultaneous assessment of Zin and Ztr, it does not require the use of a plethysmographic chamber and it allows the separation between the different rib cage-abdominal pathways.

Abdomen↗

PubMed2001

How and why exercise is impaired in COPD.

Published data indicate that exercise in COPD is more often limited by leg effort than breathlessness. This casts some doubt on the classical belief that inability to ventilate limits exercise performance. In fact, symptoms limiting exercise appear to be essentially the same in COPD and in health or congestive heart failure, where exercise is limited by inadequate energy supply to locomotor muscles. In COPD, impaired O2 delivery to locomotor muscles is suggested by: (1) the O2 cost (VO2) of breathing may be approximately 50% of whole body VO2; (2) decreasing the work of breathing improves performance and VO2 of locomotor muscles, and (3) locomotor muscle VO2 is greater when it is the only muscle exercising than during whole body exercise. Excessive expiratory pressures when expiratory flow is limited may lead to decreased venous return and contribute importantly to exercise limitation.

Cardiac Output↗