Vascular segmental permeabilities at high peak inflation pressure in isolated rat lungs

The response of segmental filtration coefficients (Kf) to high peak inflation pressure (PIP) injury was determined in isolated perfused rat lungs. Total (K f,t ), arterial (K f,a ), and venous (K f,v ) filtration coefficients were measured under baseline conditions and after ventilation with 40-45 cmH(2)O PIP. K f,a and K f,v were measured under zone I conditions by increasing airway pressure to 25-27 cmH(2)O. The microvascular segment K f (K f,mv ) was then calculated by: K f,mv = K f,t - K f,a - K f,v. The baseline K f,t was 0.090 +/- 0.022 ml. min(-1). cm H2O(-1). 100 g(-1) and segmentally distributed 18% arterial, 41% venous, and 41% microvascular. After high PIP injury, K f,t increased by 680%, whereas K f,a, K f,v, and K f,mv increased by 398, 589, and 975%, respectively. Pretreatment with 50 microM gadolinium chloride prevented the high PIP-induced increase in K f in all vascular segments. These data imply a lower hydraulic conductance for microvascular endothelium due to its large surface area and a gadolinium-sensitive high-PIP injury, produced in both alveolar and extra-alveolar vessel segments.     

Morphological evidence for calcium stores at Sertoli-Sertoli and Sertoli-spermatid interrelations

Potassium pyroantimonate technique has been employed to localize calcium ultrastructurally at Sertoli-Sertoli and Sertoli-spermatid junctional specializations. Identification of Ca++ as the major cation precipitated was performed by EGTA sensitivity and X-ray microprobe analysis. Ca++ deposits have been demonstrated in the endoplasmic reticulum cisternae underlying junctional complexes and along the plasma membranes of both Sertoli and germ cells.     

Heterogeneity of mean alveolar pressure during high-frequency oscillations

Mean alveolar pressure may exceed mean airway pressure during high-frequency oscillations (HFO). To assess the magnitude of this effect and its regional heterogeneity, we studied six excised dog lungs during HFO [frequency (f) 2-32 Hz; tidal volume (VT) 5-80 ml] at transpulmonary pressures (PL) of 6, 10, and 25 cmH2O. We measured mean pressure at the airway opening (Pao), trachea (Ptr), and four alveolar locations (PA) using alveolar capsules. Pao was measured at the oscillator pump, wherein the peak dynamic head was less than 0.2 cmH2O. Since the dynamic head was negligible here, and since these were excised lungs, Pao thus represented true applied transpulmonary pressure. Ptr increasingly underestimated Pao as f and VT increased, with Pao - Ptr approaching 8 cmH2O. PA (averaged over all locations) and Pao were nearly equal at all PL's, f's, and VT's, except at PL of 6, f 32 Hz, and VT 80 ml, where (PA - Pao) was 3 cmH2O. Remarkably, mean pressure in the base exceeded that in the apex increasingly as f and VT increased, the difference approaching 3 cmH2O at high f and VT. We conclude that, although global alveolar overdistension assessed by PA - Pao is small during HFO under these conditions, larger regional heterogeneity in PA's exists that may be a consequence of airway branching angle asymmetry and/or regional flow distribution.     

Quantitative imaging of alveolar recruitment with hyperpolarized gas MRI during mechanical ventilation

The aim of this study was to assess the utility of (3)He MRI to noninvasively probe the effects of positive end-expiratory pressure (PEEP) maneuvers on alveolar recruitment and atelectasis buildup in mechanically ventilated animals. Sprague-Dawley rats (n = 13) were anesthetized, intubated, and ventilated in the supine position ((4)He-to-O(2) ratio: 4:1; tidal volume: 10 ml/kg, 60 breaths/min, and inspiration-to-expiration ratio: 1:2). Recruitment maneuvers consisted of either a stepwise increase of PEEP to 9 cmH(2)O and back to zero end-expiratory pressure or alternating between these two PEEP levels. Diffusion MRI was performed to image (3)He apparent diffusion coefficient (ADC) maps in the middle coronal slices of lungs (n = 10). ADC was measured immediately before and after two recruitment maneuvers, which were separated from each other with a wait period (8-44 min). We detected a statistically significant decrease in mean ADC after each recruitment maneuver. The relative ADC change was -21.2 ± 4.1 % after the first maneuver and -9.7 ± 5.8 % after the second maneuver. A significant relative increase in mean ADC was observed over the wait period between the two recruitment maneuvers. The extent of this ADC buildup was time dependent, as it was significantly related to the duration of the wait period. The two postrecruitment ADC measurements were similar, suggesting that the lungs returned to the same state after the recruitment maneuvers were applied. No significant intrasubject differences in ADC were observed between the corresponding PEEP levels in two rats that underwent three repeat maneuvers. Airway pressure tracings were recorded in separate rats undergoing one PEEP maneuver (n = 3) and showed a significant relative difference in peak inspiratory pressure between pre- and poststates. These observations support the hypothesis of redistribution of alveolar gas due to recruitment of collapsed alveoli in presence of atelectasis, which was also supported by the decrease in peak inspiratory pressure after recruitment maneuvers.     

Filtration profile in isolated zone 1 and zone 3 dog lungs at constant high alveolar pressure

We measured the rate of liquid filtration in isolated dog lung lobes inflated to a constant alveolar pressure of 25 cmH2O and with all open vessels filled with plasma. We measured lung weight gain at vascular pressures ranging from 5 to 40 cmH2O relative to pleural pressure. We confirmed that under zone 1 conditions the "arterial" and "venous" extra-alveolar segments have essentially the same filtration characteristics. Using the combined extra-alveolar vascular system, we determined when recruitment of filtration surface area occurred as we increased vascular pressure from 0 to 40 cmH2O. Based on an abrupt increase in filtration rate as vascular pressure approached the zone 1/3 boundary, we infer that a sudden recruitment of exchange surface area occurred at that point. Based on the slopes of the zone 1 and zone 3 filtration profiles, we conclude that extra-alveolar vascular segments contribute approximately 25% of total to filtration in the lung under zone 3 conditions, although the exact vessels filtering under zone 1 conditions have yet to be determined. Our analysis of the data supports the concept that there is a difference in the perimicrovascular pressure around alveolar and extra-alveolar vessels, which in part may account for the apparent high filtration fraction apportioned to extra-alveolar vessels.     

Mean airway pressure and mean alveolar pressure during high-frequency jet ventilation in rabbits

Mean airway pressure underestimates mean alveolar pressure during high-frequency oscillatory ventilation. We hypothesized that high inspiratory flows characteristic of high-frequency jet ventilation may generate greater inspiratory than expiratory pressure losses in the airways, thereby causing mean airway pressure to overestimate, rather than underestimate, mean alveolar pressure. To test this hypothesis, we ventilated anesthetized paralyzed rabbits with a jet ventilator at frequencies of 5, 10, and 15 Hz, constant inspiratory-to-expiratory time ratio of 0.5 and mean airway pressures of 5 and 10 cmH2O. We measured mean total airway pressure in the trachea with a modified Pitot probe, and we estimated mean alveolar pressure as the mean pressure corresponding in the static pressure-volume relationship to the mean volume of the respiratory system measured with a jacket plethysmograph. We found that mean airway pressure was similar to mean alveolar pressure at frequencies of 5 and 10 Hz but overestimated it by 1.1 and 1.4 cmH2O at mean airway pressures of 5 and 10 cmH2O, respectively, when frequency was increased to 15 Hz. We attribute this finding primarily to the combined effect of nonlinear pressure frictional losses in the airways and higher inspiratory than expiratory flows. Despite the nonlinearity of the pressure-flow relationship, inspiratory and expiratory net pressure losses decreased with respect to mean inspiratory and expiratory flows at the higher rates, suggesting rate dependence of flow distribution. Redistribution of tidal volume to a shunt airway compliance is thought to occur at high frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of alveolar pressure in closed-chest dogs during flow interruption

We have developed a technique for installing alveolar capsules in dogs with intact chest wall, by exposing a region of parietal pleura between a pair of ribs and gluing the parietal and visceral pleura together around a small region of lung. This allows the direct measurement of alveolar pressure during spontaneous breathing. We measured alveolar pressure in normal dogs using this technique while suddenly interrupting flow at the trachea during passive expiration. Tracheal pressure exhibited a very rapid rise immediately on interruption that we showed to be composed of two distinct and roughly equal parts: one was the resistive pressure drop across the airways, and the other was a resistive pressure drop across tissues. By simultaneously measuring pleural pressure we showed that the tissues responsible were only in the chest wall and not in the lungs.     

Morphological evidence of basal keratinocyte migration during the re-epithelialization process

The regeneration of wounded stratified epithelium is accomplished via the migration of keratinocytes from the margins of the wound. However, the process of keratinocyte migration on the wound surface and the role of epithelial stem cells during re-epithelialization remain to be elucidated. Therefore, we administered BrdU to embryonic mice and generated epithelial defects on the buccal mucosa of these mice at two weeks after birth, using CO₂ laser irradiation, with which we removed the entire thickness of the epithelium. In the unwounded epithelium, cytokeratin 14, p63, and BrdU were localized within the basal layer of the epithelium, but the majority of cells within the regenerated epithelium were immunopositive for these proteins. PCNA-negative and BrdU-positive basal keratinocytes, which evidence a slow cell cycle, were localized solely within the basal layer of the unwound epithelium facing the tips of dermal papillae. After laser irradiation, these basal keratinocytes facing the tips of the papillae evidenced positive immunoreactivity for PCNA, in addition to BrdU. These results indicate that epithelial stem cells of oral mucosa may be localized in the basal layer of the epithelium facing the tips of dermal papillae, and may migrate laterally with other basal keratinocytes in response to external stimuli. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Airflow and pressure during canary song: direct evidence for mini-breaths

Summary Male canaries (Serinus canaria) produce songs of long duration compared to the normal respiratory cycle. Each phrase in a song contains repetitions of a particular song syllable, with repetition rates for different syllables ranging from 3 to 35 notes/s. We measured tracheal airflow and air sac pressure in order to investigate respiratory dynamics during song.Song syllables (11–280 ms) are always accompanied by expiratory tracheal airflow. The silent intervals (15–90 ms) between successive syllables are accompanied by inspiration, except for a few phrases where airflow ceases instead of reversing. Thus, the mini-breath respiratory pattern is used most often by the five birds studied and pulsatile expiration is used only occasionally.Songs and phrases accompanied by minibreaths were of longer duration than those accompanied by pulsatile expiration, presumably because the animal's finite vital capacity is not a limiting factor when the volume of air expired for one note is replaced by inspiration prior to the next. Pulsatile expiration was used for only a few syllable types from one bird that were produced at higher repetition rates than syllables accompanied by mini-breaths. We suggest that male canaries switch to pulsatile expiration only when the syllable repetition rate is too high (greater than about 30 Hz) for them to achieve mini-breaths.Changes in syringeal configuration that may accompany song are discussed, based on the assumption that changes in the ratio of subsyringeal (air sac) pressure to tracheal flow rate reflect changes in syringeal resistance.     

Acoustic evidence of airway opening during recruitment in excised dog lungs.

The aim of this study was to test the hypothesis that the mechanism of recruitment and the lower knee of the pressure-volume curve in the normal lung are primarily determined by airway reopenings via avalanches rather than simple alveolar recruitments. In isolated dog lung lobes, the pressure-volume loops were measured, and crackle sounds were recorded intrabronchially during both the first inflation from the collapsed state to total lobe capacity and a second inflation without prior degassing. The inflation flow contained transients that were accompanied by a series of crackles. Discrete volume increments were estimated from the flow transients, and the energy levels of the corresponding crackles were calculated from the sound recordings. Crackles were concentrated in the early phase of inflation, with the cumulative energy exceeding 90% of its final value by the lower knee of the pressure-volume curve. The values of volume increments were correlated with crackle energy during the flow transient for both the first and the second inflations (r(2) = 0.29-0.73 and 0.68-0.82, respectively). Because the distribution of volume increments followed a power law, the correlation between crackle energy and discrete volume increments suggests that an avalanche-like airway opening process governs the recruitment of collapsed normal lungs.