Human lung volumes and the mechanisms that set them.
Definitions of human lung volumes and the mechanisms that set them are reviewed in the context of pulmonary function testing, with attention to the distinction between functional residual capacity (FRC) and the static relaxation volume of the respiratory system, and to the circumstances in which FRC and residual volume are set by dynamic rather than by static mechanisms. Related terms, conventions, and issues are addressed, including some common semantic and conceptual difficulties, with attention to "gas trapping", "hyperinflation", and "restriction". (+info)
Decrease in lung volume depends on end-expiratory pressure in a rabbit model of airway lavage.
BACKGROUND: In the past, the rabbit model of repeated airway lavage has been extensively used to induce a decrease in lung volume accompanied by impairment in lung mechanics and gas exchange. OBJECTIVES: The rationale of our study was to investigate the influence of different end-expiratory pressure (EEP) levels (0.4-4.2 cm H2O) on changes in functional residual capacity (FRC) and the efficacy of lavages administered. METHODS: Forty-five rabbits were subjected to 2-8 lavages with 20 ml/kg warm normal saline until arterial/alveolar oxygen tension (a/A ratio) had decreased to +info)
Distribution of lung density after strenuous, prolonged exercise.
The postexercise alteration in pulmonary gas exchange in high-aerobically trained subjects depends on both the intensity and the duration of exercise (G. Manier, J. Moinard, and H. Stoicheff. J. Appl. Physiol. 75: 2580-2585, 1993; G. Manier, J. Moinard, P. Techoueyres, N. Varene, and H. Guenard. Respir. Physiol. 83: 143-154, 1991). In a recent study that used lung computerized tomography (CT), evidence was found for accumulation of water within the lungs after exercise (C. Caillaud, O. Serre-Cousine, F. Anselme, X. Capdevilla, and C. Prefaut. J. Appl. Physiol. 79: 1226-1232, 1995). On representative slices of the lungs, mean lung density increased by 0.040 +/- 0.007 g/cm(3) (19%, P < 0.001) in athletes after a triathlon. To verify and quantify the mechanism, we determined the change in pulmonary density and mass after strenuous and prolonged exercise using another exercise protocol and methodology for CT scanning. Nine trained runners (age 30-46 yr) volunteered to participate in the study. Each subject ran for 2 h on a treadmill at a rate corresponding to 75% of maximum O(2) consumption. CT measurements were made before and immediately after the exercise test with the subject supine and holding his breath at a point close to functional residual capacity. The lungs were scanned from the apex to the diaphragm and reconstructed in 8-mm-thick slices. Attenuation values of X-rays in each part of the lung were expressed in Hounsfield units (HU), which are related to density (D): D = 1 + HU/1,000. No significant alteration in pulmonary density (0.37 +/- 0.04 vs. 0.35 +/- 0.03, not significant) was observed after the 2-h run test. Although lung volume slightly increased (change of 166 +/- 205 ml, P < 0.05), lung mass remained stable because of a change in density distribution. We failed to detect any changes in postexercise lung mass, suggesting that other mechanisms need to be considered to explain the observed alterations in pulmonary gas exchange after prolonged strenuous exercise. (+info)
In normal subjects bracing impairs the function of the inspiratory muscles.
Normal subjects can increase their capacity to sustain hyperpnoea by bracing their arms on fixed objects, a procedure which is also known to reduce dyspnoea in patients with chronic obstructive pulmonary disease (COPD). In the present study, it was tested whether bracing per se could improve the function of the diaphragm. The effect of bracing on diaphragm function was studied in six normal subjects by recording changes in oesophageal (delta Poes) and transdiaphragmatic (delta Pdi) pressure during inspiratory capacity (IC) manoeuvres in the seated and upright postures, and in the seated posture, also during bilateral phrenic nerve stimulation (BPNS) at functional residual capacity (FRC). The pattern of ribcage motion and deformation associated with bracing and with diaphragm contraction was also evaluated using inductance plethysmography and magnetometers. Bracing increased FRC by >300 mL and reduced IC by approximately 200 mL, in both postures. Delta Pdi during BPNS decreased on average by 15% indicating an impaired diaphragmatic function. The ribcage was deformed with bracing and was more distortable during BPNS. In conclusion, in normal subjects, bracing impairs the function of the inspiratory muscles and reduces ribcage stability. These negative effects cannot explain the improved capacity to sustain hyperpnoea when the arms are braced. (+info)
The open circuit nitrogen washout technique for measuring the lung volume in infants: methodological aspects.
BACKGROUND: Lung volume measurement by nitrogen washout is widely used in infants, though a lack of accuracy and changes of calibration over time have been reported. The potential sources of error were explored in order to increase the accuracy and reliability of the technique. METHODS: A commercial system for nitrogen washout and a 0.5 litre calibrating syringe as a lung model were used to perform over 2000 in vitro washouts, including simulated rapid breathing, shallow breathing, periodic breathing, sighs, and brief apnoeas. A constant 10 l/min bias flow of oxygen and extended equipment warming times were employed. A collapsible breathing bag was incorporated into the washout circuit. Following a single two point calibration, known air volumes from 42 ml to 492 ml were measured by nitrogen washout over a 14 hour period. The flow waveform in the nitrogen mixing chamber during a washout in vitro, with and without the breathing bag in the circuit, was also studied. RESULTS: The mean coefficient of variation of all volumes was 0.66%. The mean difference between measured and known volumes was 0.30 ml (95% confidence interval (CI) -0.18 to 0.79). This difference was not statistically significant (p = 0.22). The mean percentage error was -0.1% (range -0.47% to 0.46%). Nitrogen calibration remained stable for 14 hours. Without the breathing bag flow transients were frequent in the mixing chamber during in vitro washout. CONCLUSIONS: This technique increases the accuracy in vitro and the precision in vivo of volume measurement by nitrogen washout. Sources of potential errors including baseline drifting and inadequate equipment warming times were identified. The breathing bag acted as a buffer reservoir, preventing large swings in flows within the nitrogen mixing chamber during washouts, and should be an integral component of the nitrogen washout circuit. (+info)
Effect of negative expiratory pressure on respiratory system flow resistance in awake snorers and nonsnorers.
In spontaneously breathing subjects, intrathoracic expiratory flow limitation can be detected by applying a negative expiratory pressure (NEP) at the mouth during tidal expiration. To assess whether NEP might increase upper airway resistance per se, the interrupter resistance of the respiratory system (Rint,rs) was computed with and without NEP by using the flow interruption technique in 12 awake healthy subjects, 6 nonsnorers (NS), and 6 nonapneic snorers (S). Expiratory flow (V) and Rint,rs were measured under control conditions with V increased voluntarily and during random application of brief (0.2-s) NEP pulses from -1 to -7 cmH(2)O, in both the seated and supine position. In NS, Rint,rs with spontaneous increase in V and with NEP was similar [3.10 +/- 0.19 and 3.30 +/- 0.18 cmH(2)O x l(-1) x s at spontaneous V of 1.0 +/- 0.01 l/s and at V of 1.1 +/- 0.07 l/s with NEP (-5 cmH(2)O), respectively]. In S, a marked increase in Rint,rs was found at all levels of NEP (P < 0.05). Rint,rs was 3.50 +/- 0.44 and 8.97 +/- 3.16 cmH(2)O x l(-1) x s at spontaneous V of 0.81 +/- 0.02 l/s and at V of 0.80 +/- 0.17 l/s with NEP (-5 cmH(2)O), respectively (P < 0.05). With NEP, Rint,rs was markedly higher in S than in NS both seated (F = 8.77; P < 0.01) and supine (F = 9.43; P < 0.01). In S, V increased much less with NEP than in NS and was sometimes lower than without NEP, especially in the supine position. This study indicates that during wakefulness nonapneic S have more collapsible upper airways than do NS, as reflected by the marked increase in Rint,rs with NEP. The latter leads occasionally to an actual decrease in V such as to invalidate the NEP method for detection of intrathoracic expiratory flow limitation. (+info)
A novel non-invasive technique for measuring the residual lung volume by nitrogen washout with rapid thoracoabdominal compression in infants.
BACKGROUND: The functional residual capacity (FRC), the only lung volume to be routinely measured in infants, is an unreliable volume landmark. In addition to FRC, the residual volume (RV) was measured by nitrogen washout using rapid thoracoabdominal compression (RTC) in nine infants with cystic fibrosis aged 5-31 months. METHODS: A commercial system for nitrogen washout to measure lung volumes and a custom made system to perform RTC were used. Lung volume was raised to an airway opening pressure of 30 cm H(2)O (V(30)). RTC was performed from V(30). The jacket pressure (Pj; 65-92 cm H(2)O) which generated the highest forced expiratory volume (mean 40.2 ml/kg; 95% confidence interval (CI) 33.03 to 47.33) was used during the RV manoeuvre. The infants were manually hyperventilated to inhibit the respiratory drive briefly. RTC was initiated during the last passive expiration. RV was estimated by measuring the volume of nitrogen expired after end forced expiratory switching of the inspired gas from room air to 100% oxygen while jacket inflation was maintained at the time of switching into oxygen during the post-expiratory pause. RESULTS: In each infant RV and FRC measurements were reproducible and did not overlap; the difference between mean values, which is the expiratory reserve volume, was statistically significant (p<0.05). Mean RV was 21.3 (95% CI 18.7 to 24.0), FRC was 25.5 (95% CI 22.8 to 28.1), and TLC(30) (total lung capacity at V(30)) was 61.5 (95% CI 54.4 to 68.7) ml/kg. These values were dependent on body length, weight and age. When measuring RV the period between switching to oxygen and the end of the Pj plateau was 0.301 (95% CI 0.211 to 0.391) s. The washout duration was longer for RV than for FRC measurement (80.9 s (95% CI 71.3 to 90.4) versus 72. 4 s (95% CI 64.9 to 79.8)) (p<0.001). CONCLUSIONS: A new non-invasive and reliable technique for routine measurement of RV in infants is presented. (+info)
Exhaled nitric oxide increases during high frequency oscillatory ventilation in rabbits.
This study compared the effects of high frequency oscillatory ventilation (HFOV) and intermittent mandatory ventilation (IMV) on the homeostasis of nitric oxide (NO) in the lower respiratory tract of healthy rabbits. The mechanisms underlying a putative stretch response of NO formation in the airways were further elucidated. Male New Zealand White rabbits were anaesthetized, tracheotomized and ventilated with IMV or HFOV in random order. Total NO excretion increased from 9.6 +/- 0.8 nl min-1 (mean +/- S.E.M.) during IMV to 22.6 +/- 2.7 nl min-1 during HFOV (P < 0.001). This increase was not explained by changes of functional residual capacity ([Delta]FRC). A similar increase in NO excretion during HFOV was seen in isolated buffer-perfused lungs under constant circulatory conditions (P < 0. 05, n = 4). Intratracheal mean CO2 and NO concentrations, measured at 2.5, 5, 7.5 and 10 cm below tracheostomy, increased significantly with increasing distance into the lung during both IMV and HFOV (P < 0.001 for each comparison). At every intratracheal location of the sampling catheter, particularly low in the airways, both CO2 and NO concentrations were significantly higher during HFOV than during IMV (P < 0.01 for each comparison). We conclude that HFOV increases pulmonary NO production in healthy rabbits. Increased stretch activation of the respiratory system during HFOV is suggested as a possible underlying mechanism. The increase in mean airway NO concentrations may have biological effects in the respiratory tract. Whether it can account for some of the benefits of HFOV treatment needs to be considered. (+info)