Stochastic Modeling Predictions for the Clearance of Insoluble Particles from the Tracheobronchial Tree of the Human Lung

Bronchial clearance of deposited particles was simulated using a stochastic model of the tracheobronchial tree. The clearance model introduced in this study considers (1) a continuous decrease of the mucus thickness from the trachea to the terminal bronchioles according to a linear or an exponential function, (2) the possibility of mucus discontinuities, which are mainly found in intermediate and distal airways of the tracheobronchial compartment, (3) mucus production in proximal airways, (4) a slow bronchial clearance phase due to the capture of a defined particle fraction f _s in the periciliary sol phase, and (5) an eventual delay of the mucociliary transport at carinal ridges of airway bifurcations. Based on the concept of mucus volume conservation in single bifurcations, a reduction of the thickness of the mucus blanket from proximal to distal airways causes a significant increase of the mucus velocities in small ciliated airways compared to other stochastic modeling predictions assuming a constant thickness of the mucus layer throughout the conducting airways. This effect is further enhanced by the consideration of mucus discontinuities. In contrast, the ability of bronchial airways to produce a certain volume of mucus has a decreasing effect on the mucus velocities. In all generated clearance velocity models, mucociliary clearance is completely terminated within 24 h after exposure, consistent with the experimental evidence. Implementation of a slow bronchial clearance phase predicts a long-term retention fraction, which is fully cleared from the lung after several weeks. For 1-μm MMAD particles, 24-h retention varies between 0.42 and 0.52, in line with the suggestions of the ICRP. Mucus delay at carinal ridges only affects short-term clearance by increasing the retained particle fraction at a given time, while long-term retention is not influenced.     

Prolonged plasma half-life of insulin in patients with a genetic defect of high affinity binding sites

Plasma clearance of endogenous and intravenously administered insulin was studied in three sibs with severe insulin resistance secondary to an affinity defect of their insulin receptors, and in five healthy controls. Intravenous infusion of somatostatin was used to inhibit the insulin secretion. 0.3 U of insulin/kg body weight was administered as an intravenous bolus. Plasma glucose, immunoreactive insulin and C-peptide were determined subsequently at constant intervals. We found a prolonged plasma half-life of insulin in the three patients, being 33.5 +/- 11.8 min vs 8.2 +/- 2.2 min in controls, P less than 0.002, but a normal half-life of C-peptide. The result indicates, that the plasma insulin clearance is predominantly mediated by intact insulin receptors. We conclude, that insulin has a prolonged half-life in all patients with insulin resistance secondary to an impaired receptor function.     

Clearance, metabolic fate and tissue distribution of an injected bolus of photoaffinity-labeled rat androgen binding protein

An injected bolus of tritiated photolabeled rat androgen binding protein (ABP) is cleared from the circulation in a biphasic manner. The rapid component of the clearance curve indicates a clearance half time (t1/2) of 4.24 +/- 0.20 h and the slow component indicates a t1/2 of 13.27 +/- 2.92 h. After injection, photolabeled ABP is rapidly degraded as determined by electrophoresis on polyacrylamide gels containing sodium dodecyl sulfate. This method dissociates ABP into subunits of approximately 48,000 daltons. One-half hour after injection of photolabeled ABP, 90% of the radioactivity migrates as a 20,000- rather than as a 48,000-dalton moiety; at the 24-h point only 20,000- and 16,000-dalton species were detectable. Chromatography of plasma on Sephadex G-150 indicated that, under nondenaturing conditions, radioactivity was still associated with proteins having a molecular weight similar to the native ABP dimer. These results suggest that the dimer is substrate for the proteolytic processes affecting ABP. Small (congruent to 7000 dalton) fragments of ABP could be detected in urine by G-150 chromatography 2 h after injection. The control protein [3H] bovine serum albumin (BSA) was cleared from the blood with a time course identical to that of photolabeled ABP (t1/2's 4.69 +/- 0.09 h and 13.56 +/- 1.03 h). [3H] BSA was degraded to peptides that were similar in size to those formed from photolabeled ABP. The uptake of photolabeled ABP and [3H] BSA by potential target tissues (testis, epididymis and ventral prostate) was equivalent, suggesting that the uptake of ABP was a nonspecific phenomenon rather than a receptor-mediated event. The liver and kidneys contained more radioactivity that did the other tissues and there was a differential uptake and clearance of photolabeled ABP and [3H] BSA by these organs. Whether this difference is related to specific uptake processes or to differences in the size and/or structure of the proteins or other factors remains to be determined.     

Bronchial edema alters (99m)Tc-DTPA clearance from the airway surface in sheep.

Airway wall edema, prominent in inflammatory airways disease, may alter barrier properties at the airway air-liquid interface such that normal absorption of soluble substances into the airway circulation is altered. We studied the effects of bradykinin-induced airway wall edema on the clearance of the soluble tracer technetium-99m-labeled diethylenetriamine pentaacetic acid ((99m)Tc-DTPA) from subcarinal airways in sheep (n = 8). (99m)Tc-DTPA (6-10 microl) was delivered by a microspray nozzle inserted through a bronchoscope to a fourth-generation bronchus both before and 1 h after bradykinin (20 ml; 10(-6) M) had been infused through a cannulated and perfused bronchial artery. Airway retention (by scintigraphy) and blood levels of radiolabel were monitored for 30 min after the local deposition of (99m)Tc-DTPA. During control conditions, 85-90% of the tracer cleared from the deposition site within 30 min. The maximum blood level during that time was 17% of the total delivered tracer. However, 1 h after bradykinin infusion, there was significant retention of the marker at the deposition site with clearance within 30 min reduced to 63-70% and decreased blood levels of radiolabel (8%; both P < 0.05). These results demonstrate that moderate airway wall edema alters blood uptake and removal of soluble substances delivered to the subcarinal airways. We suggest that the interplay between vascular and mucociliary clearance routes will impact the resident time for clearance of soluble air toxins and/or therapeutic agents from the epithelial surface.     

Multiple gas washout during jet ventilation

Simultaneous washouts of He, N2, and SF6 were monitored during jet ventilation with tidal volumes of 50-200 ml and rates of 1-2 Hz. Gas concentrations were measured from the trachea and from a lower lobe bronchus in six baboons by mass spectrometry. Washouts using large tidal volumes approximated single exponential decays with the relative exponential rates of decay being He fastest, SF4 slowest, and N2 intermediate. Washouts using smaller tidal volumes demonstrated a two-phase exponential decay pattern. During the fast phase, the relative exponential rates of decay were He slowest, SF6 fastest, and N2 intermediate, the reverse order seen during large-volume washouts. During the slow phase, the relative exponential rates of decay were He fastest, SF4 slowest, and N2 intermediate, the same order seen during large-volume washouts. The magnitude of the first phase observed from the lower lobe bronchus was less than that observed from the trachea. These data are consistent with a serial two-compartment transport model incorporating a limitation of molecular diffusion between the peripheral and proximal compartments. The more rapid clearance of less diffusible gases from the central airways during the first phase of washout was due to slower transport from the alveoli to the central airways rather than faster transport from the central airways to the airway opening.     

Effect of resting smooth muscle length on contractile response in resistance airways

We studied the effect of resting smooth muscle length on the contractile response of the major resistance airways (generations 0-5) in 18 mongrel dogs in vivo using tantalum bronchography. Dose-response curves to 10(-10) to 10(-7) mol/kg methacholine (MCh) were generated [at functional residual capacity (FRC)] by repeated intravenous bolus administration using tantalum bronchography after each dose. Airway constriction varied substantially with dose-equivalent stimulation and varied sequentially from trachea (8.8 +/- 2.2% change in airway diam) to fifth-generation bronchus (49.8 +/- 3.0%; P less than 0.001). Length-tension curves were generated for each airway to determine the airway diameter (i.e., resting in situ smooth muscle length) at which maximal constriction was elicited using bolus intravenous injection of 10(-8) mol/kg MCh. A Frank-Starling relationship was obtained for each airway; the transpulmonary pressure at which maximal constriction was elicited increased progressively from 2.50 +/- 1.12 cmH2O for trachea (approximately FRC) to 18.3 +/- 1.05 cmH2O for fifth-generation airways (approximately 50% TLC) (P less than 0.001). A similar relationship was obtained when change in airway diameter was plotted as a function of airway radius. We demonstrate substantial heterogeneity in the lung volumes at which maximal constriction is elicited and in distribution of parasympathomimetic constriction within the first few generations of resistance bronchi. Our data also suggest that lung hyperinflation may lead to augmented airway contractile responses by shifting resting smooth muscle length toward optimum resting smooth muscle length.     

The elimination rates of intact GIP as well as its primary metabolite, GIP 3-42, are similar in type 2 diabetic patients and healthy subjects

The incretin hormone, glucose-dependent insulinotropic polypeptide (GIP, previously known as gastric inhibitory polypeptide), is rapidly degraded to the biologically inactive metabolite GIP (3-42) in the circulation, but little is known about the kinetics of the intact hormone and the metabolite and whether differences exist between patients with type 2 diabetes mellitus and healthy subjects. We examined eight type 2 diabetic patients (six men, two women); mean (range) age: 59 (48-69) years; BMI: 31.6 (26.0-37.7) kg/m2; HbA1C: 9.0 (8.2-13.2) %; fasting plasma glucose (FPG): 10.0 (8.3-13.2) mmol/l and 8 healthy subjects matched for age, gender and BMI. An intravenous bolus injection of GIP (7.5 nmol) was given and venous blood samples were drawn the following 45 minutes. Peak concentrations of total GIP (intact+metabolite, mean+/-SEM) and intact GIP (in brackets) were 920+/-91 (442+/-52) pmol/l in the type 2 diabetic patients and 775+/-68 (424+/-30) pmol/l in the healthy subjects (NS). GIP was eliminated rapidly with the clearance rate for intact GIP being 2.3+/-0.2 l/min in the type 2 diabetic patients and 2.4+/-0.2 l/min in the healthy subjects (NS). The volumes of distributions were similar in the two groups and ranged from 8 to 21 l per subject. The primary metabolite, GIP 3-42, generated through the action of dipeptidyl peptidase IV (DPP-IV), was eliminated with a mean half-life of 17.5 and 20.5 min in patients and healthy subjects (NS). CONCLUSION: Elimination of GIP is similar in obese type 2 diabetic patients and matched healthy subjects. Differences in elimination of GIP and its primary metabolite, therefore, do not seem to contribute to the defective insulinotropic effect of GIP in type 2 diabetes.     

Measuring airway exchange of endogenous acetone using a single-exhalation breathing maneuver.

Exhaled acetone is measured to estimate exposure or monitor diabetes and congestive heart failure. Interpreting this measurement depends critically on where acetone exchanges in the lung. Health professionals assume exhaled acetone originates from alveolar gas exchange, but experimental data and theoretical predictions suggest that acetone comes predominantly from airway gas exchange. We measured endogenous acetone in the exhaled breath to evaluate acetone exchange in the lung. The acetone concentration in the exhalate of healthy human subjects was measured dynamically with a quadrupole mass spectrometer and was plotted against exhaled volume. Each subject performed a series of breathing maneuvers in which the steady exhaled flow rate was the only variable. Acetone phase III had a positive slope (0.054+/-0.016 liter-1) that was statistically independent of flow rate. Exhaled acetone concentration was normalized by acetone concentration in the alveolar air, as estimated by isothermal rebreathing. Acetone concentration in the rebreathed breath ranged from 0.8 to 2.0 parts per million. Normalized end-exhaled acetone concentration was dependent on flow and was 0.79+/-0.04 and 0.85+/-0.04 for the slow and fast exhalation rates, respectively. A mathematical model of airway and alveolar gas exchange was used to evaluate acetone transport in the lung. By doubling the connective tissue (epithelium+mucosal tissue) thickness, this model predicted accurately (R2=0.94+/-0.05) the experimentally measured expirograms and demonstrated that most acetone exchange occurred in the airways of the lung. Therefore, assays using exhaled acetone measurements need to be reevaluated because they may underestimate blood levels.     

Interdependence of bronchial circulation and clearance of 99mTc-DTPA from the airway surface.

The extent to which the systemic vasculature is involved in soluble-particle uptake in the conducting airways has not been studied extensively. In anesthetized, ventilated sheep, 6-10 microl of technetium-99m-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) was delivered through a microspray nozzle to a fourth-generation airway. Perfusion of the cannulated bronchial artery was varied between control flow (0.6 ml x min(-1) x kg(-1)), high flow (1.8 ml x min(-1) x kg(-1)) or no flow (the infusion pump was stopped). Airway retention of the radioactive tracer was monitored using gamma camera imaging, and venous blood was sampled. During control perfusion, tracer retention at the site of deposition at 30 min averaged 20 +/- 6% (n = 7). With no flow, retention was significantly elevated to 32 +/- 8% (P = 0.03). In another group of sheep (n = 5) with a control retention of 13 +/- 4%, high flow resulted in an increase in tracer (25 +/- 4%; P = 0.04). Maximum blood uptake of tracer was calculated by estimating circulating blood volume and averaged 16% of total activity during control flow. Only during high-flow conditions was 99mTc-DTPA in the blood decreased (10%; P = 0.04). Most of the tracer was cleared by mucociliary clearance as visualized by imaging. This component was substantially decreased during no flow. The results demonstrate that both decreased and increased airway perfusion limit removal of soluble tracer applied to the conducting airways.     

Differential inflammatory response to inhaled lipopolysaccharide targeted either to the airways or the alveoli in man

Endotoxin (Lipopolysaccharide, LPS) is a potent inducer of inflammation and there is various LPS contamination in the environment, being a trigger of lung diseases and exacerbation. The objective of this study was to assess the time course of inflammation and the sensitivities of the airways and alveoli to targeted LPS inhalation in order to understand the role of LPS challenge in airway disease.In healthy volunteers without any bronchial hyperresponsiveness we targeted sequentially 1, 5 and 20 μg LPS to the airways and 5 μg LPS to the alveoli using controlled aerosol bolus inhalation. Inflammatory parameters were assessed during a 72 h time period. LPS deposited in the airways induced dose dependent systemic responses with increases of blood neutrophils (peaking at 6 h), Interleukin-6 (peaking at 6 h), body temperature (peaking at 12 h), and CRP (peaking at 24 h). 5 μg LPS targeted to the alveoli caused significantly stronger effects compared to 5 μg airway LPS deposition. Local responses were studied by measuring lung function (FEV(1)) and reactive oxygen production, assessed by hydrogen peroxide (H(2)O(2)) in fractionated exhaled breath condensate (EBC). FEV(1) showed a dose dependent decline, with lowest values at 12 h post LPS challenge. There was a significant 2-fold H(2)O(2) induction in airway-EBC at 2 h post LPS inhalation. Alveolar LPS targeting resulted in the induction of very low levels of EBC-H(2)O(2).Targeting LPS to the alveoli leads to stronger systemic responses compared to airway LPS targeting. Targeted LPS inhalation may provide a novel model of airway inflammation for studying the role of LPS contamination of air pollution in lung diseases, exacerbation and anti-inflammatory drugs.     

Anatomic localization of 24- and 96-h particle retention in canine airways.

Long-term retention of particles in airways is controversial. However, precise anatomic localization of the particles is not possible in people. In this study the anatomic location of retained particles after shallow bolus inhalation was determined in anesthetized, ventilated beagle dogs. Fifty 30-cm(3) boluses containing monodisperse 2.5-micron polystyrene particles (PSL) were delivered to a shallow lung depth of 81-129 cm(3). At 96 h before euthanasia, red fluorescent PSL were used; at 24 h, green fluorescent PSL and (99m)Tc-labeled PSL were used. Clearance of (99m)Tc-PSL was measured during the next 24 h. Sites of particle retention were determined in systematic, volume-weighted random samples of microwave-fixed lung tissue. Precise particle localization and distribution was analyzed by using gamma counting, conventional fluorescence microscopy, and confocal microscopy. Within 24 h after shallow bolus inhalation, 50-95% of the deposited (99m)Tc-PSL were cleared, but the remaining fraction was cleared slowly in all dogs, similar to previous human results. The three-dimensional deposition patterns showed particles across the entire cross-sectional plane of the lungs at the level of the carina. In these locations, 33 +/- 9.9% of the retained particles were found in small, nonrespiratory airways (0.3- to 1-mm diameter) and 49 +/- 10% of the particles in alveoli; the remaining fraction was found in larger airways. After 96 h, a similar pattern was found. These findings suggest that long-term retention in airways is at the bronchiolar level.     

Effect of raised thoracic pressure and volume on 99mTc-DTPA clearance in humans

Although positive airway pressure is often used to treat acute pulmonary edema, the effects on epithelial solute flux are not well known. We measured independently the effect of 1) positive pressure and 2) voluntary hyperinflation on the clearance of inhaled technetium-99m-labeled diethylenetriaminepentaacetic acid (99mTc-DTPA) in six nonsmokers and six smokers. Lung volumes were monitored by inductance plethysmography. Each subject was studied in four situations: 1) low end-expiratory volume (LO-), 2) low volume plus 9 cmH2O continuous positive airway pressure (LO+), 3) high end-expiratory volume (HI-), and 4) high volume plus continuous positive airway pressure (HI+). The clearance half time of 99mTc-DTPA for the nonsmokers decreased from 64.8 +/- 7.0 min (mean +/- SE) at LO- to 23.2 +/- 5.3 min at HI- (P less than 0.05). Positive pressure had no synergistic effect. The mean clearance half time for the smokers was faster than nonsmokers at base line but unaffected by similar changes in thoracic volume and pressure. We conclude that, in nonsmokers, positive airway pressure increases 99mTc-DTPA clearance primarily through an increase in lung volume and that smokers are immune to these effects.     

Alveolar and lung liquid clearance in anesthetized rabbits

Alveolar and lung liquid clearance were studied over 8 h in intact anesthetized ventilated rabbits by instillation of either isosmolar Ringer lactate (2 ml/kg) or autologous plasma (2 or 3 ml/kg) into one lower lobe. The half time for lung liquid clearance of the isosmolar Ringer lactate was 3.3 h and that for plasma clearance was 6 h. In the plasma experiments, the alveolar protein concentration after 1 h was 5.2 +/- 0.8 g/dl, which was significantly greater than the initial instilled protein concentration of 4.3 +/- 0.7 g/dl (P less than 0.05). Thus alveolar protein concentration increased by 21 +/- 12% over 1 h, which matched clearance from the entire lung of 19 +/- 11% of the instilled volume. Overall the rate of alveolar and lung liquid clearance in rabbits was significantly faster than in prior studies in dogs and sheep. The fast alveolar liquid clearance rate in rabbits was not due to higher endogenous catecholamine release, because intravenous and alveolar (5 x 10(-5) M) propranolol did not slow the clearance. Also, beta-adrenergic therapy with alveolar terbutaline (10(-5) or 10(-4) M) did not increase the alveolar or lung liquid clearance rates. Phloridzin (10(-3) M) did not slow alveolar liquid clearance. However, amiloride (10(-4) M) inhibited 75% of the basal alveolar liquid clearance in rabbits, thus providing evidence that alveolar liquid clearance in rabbits depends primarily on sodium-dependent transport. This rabbit study provides further evidence for important species differences in the basal rates of alveolar liquid and solute clearance as well as the response to beta-adrenergic agonists and ion transport inhibitors.     

Cardioacceleration produced by close intra-arterial injection of neurotensin into the stellate ganglion of the cat

The effect on heart rate of close i.a. injection of neurotensin (NT), substance P (SP), and vasoactive intestinal peptide (VIP) into the decentralized right stellate ganglion was tested in anaesthetized spinal cats. These peptides are present in the stellate ganglion and may mediate the stellate ganglion cell excitation underlying a previously described slow cardioacceleration evoked by preganglionic stimulation during block of cholinergic transmission. NT (Tyr11-NT) at doses of 25-200 micrograms produced increases in heart rate of 10-125 beats/min (bpm) and of slow time course. At the dose of 100 micrograms, NT produced a cardioacceleration of 56 +/- 8.4 bpm (mean +/- SEM, n = 13) with an onset latency of 23 +/- 4 s, a slow rise to peak (rise time 62 +/- 4.5 s), and a half decay of 167 +/- 14 s. A cardioacceleration of comparable magnitude (78 +/- 3.8 bpm) caused by close i.a. administration of acetylcholine (100 micrograms, n = 13) had an onset latency of 2 +/- 1 s, a fast rise to a sharp peak (rise time 3 +/- 1 s), and a half decay of 23 +/- 4 s. The analogues, Phe11-NT and Trp11-NT, as well as the stereoisomer, D-Tyr11-NT, had no effect on heart rate when injected at doses up to 400 micrograms. The NT-evoked cardioacceleration was blocked by propranolol or by section of the inferior cardiac nerve and may therefore be attributed to prolonged excitation of stellate ganglion cells. Administration of hexamethonium and atropine was without effect on the NT response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of upper and lower airway responses of two sensitized rat strains to inhaled antigen.

The purpose of the study was to investigate the relationships between upper airways responses and pulmonary responses of two strains of highly inbred rats to inhaled antigen. To do this we measured the upper and lower airways resistance for 60 min after challenge of Brown-Norway rats (BN; n = 13) and an inbred rat strain (MF; n = 11), derived from Sprague-Dawley, with aerosolized ovalbumin (OA). Rats were actively sensitized with OA (1 mg sc) using Bordetella pertussis as an adjuvant. Two weeks later the animals were anesthetized and challenged. Tracheal pressure, esophageal pressure, and airflow were measured, from which total pulmonary resistance was partitioned into upper airway and lower pulmonary resistance (RL). The peak upper airway response to inhaled OA was similar in BN (1.89 +/- 0.66 cmH2O.ml-1.s; n = 7) and MF (2.85 +/- 0.68 cmH2O.ml-1.s; n = 6). The lower airway response to OA challenge was substantially greater in BN, and RL changed from 0.07 +/- 0.01 to 0.34 +/- 0.13 (n = 6; P < 0.05). The MF did not have any significant increase in RL after challenge; the baseline RL was 0.12 +/- 0.02 and only reached a peak value of 0.15 +/- 0.05 (n = 5; P = NS). Lower airway responsiveness of BN (n = 10) to serotonin, an important mediator early allergic airway responses, was similar to MF (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ventilatory and gas exchange kinetics during exercise in chronic airways obstruction

The influence of chronic obstructive pulmonary disease (COPD) on exercise ventilatory and gas exchange kinetics was assessed in nine patients with stable airway obstruction (forced expired volume at 1 s = 1.1 +/- 0.33 liters) and compared with that in six normal men. Minute ventilation (VE), CO2 output (VCO2), and O2 uptake (VO2) were determined breath-by-breath at rest and after the onset of constant-load subanaerobic threshold exercise. The initial increase in VE, VCO2, and VO2 from rest (phase I), the subsequent slow exponential rise (phase II), and the steady-state (phase III) responses were analyzed. The COPD group had a significantly smaller phase I increase in VE (3.4 +/- 0.89 vs. 6.8 +/- 1.05 liters/min), VCO2 (0.10 +/- 0.03 vs. 0.22 +/- 0.03 liters/min), VO2 (0.10 +/- 0.03 vs. 0.24 +/- 0.04 liters/min), heart rate (HR) (6 +/- 0.9 vs. 16 +/- 1.4 beats/min), and O2 pulse (0.93 +/- 0.21 vs. 2.2 +/- 0.45 ml/beat) than the controls. Phase I increase in VE was significantly correlated with phase I increase in VO2 (r = 0.88) and HR (r = 0.78) in the COPD group. Most patients also had markedly slower phase II kinetics, i.e., longer time constants (tau) for VE (87 +/- 7 vs. 65 +/- 2 s), VCO2 (79 +/- 6 vs. 63 +/- 3 s), and VO2 (56 +/- 5 vs. 39 +/- 2 s) and longer half times for HR (68 +/- 9 vs. 32 +/- 2 s) and O2 pulse (42 +/- 3 vs. 31 +/- 2 s) compared with controls. However, tau VO2/tau VE and tau VCO2/tau VE were similar in both groups. The significant correlations of the phase I VE increase with HR and VO2 are consistent with the concept that the immediate exercise hyperpnea has a cardiodynamic basis. The slow ventilatory kinetics during phase II in the COPD group appeared to be more closely related to a slowed cardiovascular response rather than to any index of respiratory function. O2 breathing did not affect the phase I increase in VE but did slow phase II kinetics in most subjects. This confirms that the role attributed to the carotid bodies in ventilatory control during exercise in normal subjects also operates in patients with COPD.     

Simultaneous measurement of nitric oxide production by conducting and alveolar airways of humans.

Human airways produce nitric oxide (NO), and exhaled NO increases as expiratory flow rates fall. We show that mixing during exhalation between the NO produced by the lower, alveolar airways (VL(NO)) and the upper conducting airways (VU(NO)) explains this phenomenon and permits measurement of VL(NO), VU(NO), and the NO diffusing capacity of the conducting airways (DU(NO)). After breath holding for 10-15 s the partial pressure of alveolar NO (PA) becomes constant, and during a subsequent exhalation at a constant expiratory flow rate the alveoli will deliver a stable amount of NO to the conducting airways. The conducting airways secrete NO into the lumen (VU(NO)), which mixes with PA during exhalation, resulting in the observed expiratory concentration of NO (PE). At fast exhalations, PA makes a large contribution to PE, and, at slow exhalations, NO from the conducting airways predominates. Simple equations describing this mixing, combined with measurements of PE at several different expiratory flow rates, permit calculation of PA, VU(NO), and DU(NO). VL(NO) is the product of PA and the alveolar airway diffusion capacity for NO. In seven normal subjects, PA = 1.6 +/- 0.7 x 10(-6) (SD) Torr, VL(NO) = 0.19 +/- 0.07 microl/min, VU(NO) = 0.08 +/- 0.05 microl/min, and DU(NO) = 0.4 +/- 0.4 ml. min(-1). Torr(-1). These quantitative measurements of VL(NO) and VU(NO) are suitable for exploring alterations in NO production at these sites by diseases and physiological stresses.     

A new and more accurate technique to characterize airway nitric oxide using different breath-hold times.

Exhaled nitric oxide (NO) arises from both airway and alveolar regions of the lungs, which provides an opportunity to characterize region-specific inflammation. Current methodologies rely on vital capacity breathing maneuvers and controlled exhalation flow rates, which can be difficult to perform, especially for young children and individuals with compromised lung function. In addition, recent theoretical and experimental studies demonstrate that gas-phase axial diffusion of NO has a significant impact on the exhaled NO signal. We have developed a new technique to characterize airway NO, which requires a series of progressively increasing breath-hold times followed by exhalation of only the airway compartment. Using our new technique, we determined values (means +/- SE) in healthy adults (20-38 yr, n = 8) for the airway diffusing capacity [4.5 +/- 1.6 pl.s(-1).parts per billion (ppb)(-1)], the airway wall concentration (1,340 +/- 213 ppb), and the maximum airway wall flux (4,350 +/- 811 pl/s). The new technique is simple to perform, and application of this data to simpler models with cylindrical airways and no axial diffusion yields parameters consistent with previous methods. Inclusion of axial diffusion as well as an anatomically correct trumpet-shaped airway geometry results in significant loss of NO from the airways to the alveolar region, profoundly impacting airway NO characterization. In particular, the airway wall concentration is more than an order of magnitude larger than previous estimates in healthy adults and may approach concentrations (approximately 5 nM) that can influence physiological processes such as smooth muscle tone in disease states such as asthma.     

Methodology for the measurement of mucociliary function in the mouse by scintigraphy.

The objective of the study was to develop a scintigraphic method for measurement of airway mucociliary clearance in small laboratory rodents such as the mouse. Previous investigations have characterized the secretory cell types present in the mouse airway, but analysis of the mucus transport system has been limited to in vitro examination of tissue explants or invasive in vivo measures of a single airway, the trachea. Three methods were used to deposit insoluble, radioisotopic colloidal particles: oropharyngeal aspiration, intratracheal instillation, and nose-only aerosol inhalation. The initial distribution of particles within the lower respiratory tract was visualized by gamma-camera, and clearance of particles was followed intermittently over 6 h and at the conclusion, 24 h postdelivery. Subsets of mice underwent lavage for evidence of tissue inflammation, and others were restudied for reproducibility of the methods. The aspiration and instillation methods of delivery led to greater distributions of deposited activity within the lungs, i.e., approximately 60--80% of the total respiratory tract radioactivity, whereas the nose-only aerosol technique attained a distribution of 32% to the lungs. However, the aerosol technique maximized the fraction of particles that cleared the airway over a 24-h period, i.e, deposited onto airway epithelial surfaces and cleared by mucociliary function such that lung retention at 24 h averaged 57% for delivery by aerosol inhalation and > or =80% for the aspiration or intratracheal instillation techniques. Particle delivery methods did not cause lung inflammation/injury with use of inflammatory cells and chemoattractant cytokines as criteria. Scintigraphy can discern particle deposition and clearance from the lower respiratory tract in the mouse, is noninvasive and reproducible, and includes the capability for restudy and lung lavage when time course or chronic treatments are being considered.     

Reassessment of the interruption technique for measuring flow resistance in humans

We have previously produced evidence that, in patients with obstructive lung disease, compliance of extrathoracic airways is responsible for lack of mouth-to-alveolar pressure equilibration during respiratory efforts against a closed airway. The flow interruption method for measuring respiratory resistance (Rint) is potentially faced with the same problems. We reassessed the merits of the interruption technique by rendering the extrathoracic airways more rigid and by using a rapid shutter. We measured airway resistance (Raw) with whole body plethysmography during panting (at 2 Hz) and Rint during quiet breathing. Rint and Raw were expressed as specific airway (sGaw) and interruptive conductance (sGint), respectively. In nine healthy subjects (cheeks supported), sGint (0.140 +/- 0.050 s-1.cmH2O-1) was lower (P less than 0.02) than sGaw (0.182 +/- 0.043 s-1.cmH2O-1). By contrast, in 12 patients with severe obstructive lung disease (forced expiratory volume in 1 s/vital capacity = 41.0 +/- 19.8%), sGint (0.058 +/- 0.012 s-1.cmH2O-1) was higher (P less than 0.05) than sGaw (0.047 +/- 0.007 s-1.cmH2O-1), when the cheeks were supported. When the mouth floor was also supported, average values of sGaw (0.048 +/- 0.008 s-1.cmH2O-1) and sGint (0.049 +/- 0.014 s-1.cmH2O-1) became similar. In conclusion, we confirm previous findings in healthy subjects of higher values of Rint, with respect to Raw, probably because of differences in glottis opening between quiet breathing and panting. In airflow obstruction, supporting both the cheeks and the mouth floor decreased sGint, which became similar to sGaw.