Air Perfusion Research Articles

Infection Using ERCP Endoscopes

© 2016 by the AGA Institute 0016-5085/$36.00 http://dx.doi.org/10.1053/j.gastro.2016.05.040 Ttion during endoscopic retrograde cholangiopancreatography (ERCP) continues to evolve. The occurrence of carbapenem-resistant Enterobacteriaceae infections after ERCP reached the awareness of the medical community in 2014 when the Centers for Disease Control and Prevention (CDC) published the findings of their investigation of a suburban Chicago case cluster. In early 2015, reports of similar outbreaks at several major medical centers across the United States prompted the US Food and Drug Administration (FDA) to issue safety alerts and convene an FDA expert panel; there was intense media attention and both the CDC and industry provided guidance regarding steps for ensuring safe clinical care in the absence of definitive solutions. In 2016, the release of a US Senate committee investigative report culminated in a closely coordinated FDA and industry recall of duodenoscopes for refurbishment and replacement of suspect parts, among other related actions. Despite progress in our awareness and understanding of the problem, the currently proposed solutions remain cumbersome and unproven. Endoscope cleaning and reprocessing technologies and practices progressed greatly in the latter part of the 20th century, culminating in enduring standards for high-level disinfection (HLD). In the Spaulding classification for reprocessing of durable medical devices, endoscopes are designated as “semicritical” devices that make contact with mucous membranes and thus are suitable for HLD. Transmission of infection by flexible endoscopes has historically been ascribed to inconsistent practice of manual cleaning and HLD. Outbreaks of Pseudomonas aeruginosa after ERCP using side-viewing duodenoscopes dating to the 1980s were noted to occur particularly in the first patient of the day after overnight storage and shortly after reprocessing. This problem was largely eliminated with adoption of complete channel drying by alcohol flushing and forced air perfusion after HLD. Clinical infections occasionally follow the use of ERCP in patients with preexisting chronic colonization of bacteria (owing to obstructing pathology, abnormal anatomy, indwelling prostheses, or prior interventions). The recent occurrences of interpatient transmission via the duodenoscope only became evident when infections with newly recognized, highly resistant species prompted point source investigations using sophisticated bacterial typing to determine their origin. A recent single-center study using universal culturing of reprocessed endoscopes demonstrated that 2% of patient-ready instruments harbored persistent enteric pathogens. Thus, we now realize that contaminated endoscopes can transmit some antibioticsensitive, as well as highly resistant cases, of post-ERCP cholangitis. Furthermore, the unusual resistant cases can result in chronic colonization of the gastrointestinal tract, with delayed infectious complications weeks to months later in unrelated organ systems. Infectious cross-contamination also occurs from other hospital or institutional sources, as demonstrated in outbreaks of carbapenem-resistant Enterobacteriaceae in intensive care units and chronic nursing facilities. The frequency of transmission through the environment, however, is generally far lower than for iatrogenic exposure and investigations strongly suggest that the endoscope is the transmission source in most outbreaks of post-ERCP multidrug-resistant infections. The recent report of the Senate’s Health, Education, Labor, and Pensions Committee thoroughly outlines the breadth of the problem and potential regulatory and industry factors contributing to the delay in response to the risk of duodenoscope transmission of infection (Table 1).

Development of approaches for deuterium incorporation in plants.

Soon after the discovery of deuterium, efforts to utilize this stable isotope of hydrogen for labeling of plants began and have proven successful for natural abundance to 20% enrichment. However, isotopic labeling with deuterium ((2)H) in higher plants at the level of 40% and higher is complicated by both physiological responses, particularly water exchange through transpiration, and inhibitory effects of D2O on germination, rooting, and growth. The highest incorporation of 40-50% had been reported for photoheterotrophic cultivation of the duckweed Lemna. Higher substitution is desirable for certain applications using neutron scattering and nuclear magnetic resonance (NMR) techniques. (1)H(2)H NMR and mass spectroscopy are standard methods frequently used for determination of location and amount of deuterium substitution. The changes in infrared (IR) absorption observed for H to D substitution in hydroxyl and alkyl groups provide rapid initial evaluation of incorporation. Short-term experiments with cold-tolerant annual grasses can be carried out in enclosed growth containers to evaluate incorporation. Growth in individual chambers under continuous air perfusion with dried sterile-filtered air enables long-term cultivation of multiple plants at different D2O concentrations. Vegetative propagation from cuttings extends capabilities to species with low germination rates. Cultivation in 50% D2O of annual ryegrass and switchgrass following establishment of roots by growth in H2O produces samples with normal morphology and 30-40% deuterium incorporation in the biomass. Winter grain rye (Secale cereale) was found to efficiently incorporate deuterium by photosynthetic fixation from 50% D2O but did not incorporate deuterated phenylalanine-d8 from the growth medium.

Unexplained postoperative retinal hemorrhage after 23-gauge sutureless vitrectomy

We report five cases of unexplained retinal hemorrhage after 23-gauge sutureless vitrectomy. A 23-gauge sutureless vitrectomy was performed for four cases of macular holes (MH) and one case of macular hole retinal detachment (MHRD). Retinal hemorrhages were observed on the first day after surgery and disappeared within several months without leaving any recognizable damage. We speculate that the retinal hemorrhages might have resulted from repeated collapse of the globe through a cannula under air perfusion, but other causes such as retinal vein congestion by face-down positioning are also possible.

Surfactant reduction in embolism bubble adhesion and endothelial damage.

Surfactants may reduce the adhesion force holding bubbles to the vessel wall in gas embolism. The authors measured bubble adhesion force using excised microvessels. They assessed endothelial damage by measuring vessel reactivity and with microscopy. Microbubbles injected into arterioles resided for 5, 10, or 30 min, with intact or damaged endothelium. Perfusion was with rat serum alone (control) or with 1% Perftoran (OJSC SPC Perftoran, Moscow, Russia) or 1% Pluronic F-127 (Molecular Probes, Eugene, OR) added. Pressure across the bubble, bubble length, and bubble diameter were measured, and adhesion force per unit surface area, K = deltaPD/4 l, was calculated. Vessel reactivity was assessed using topical application of phenylephrine and acetylcholine. With the endothelium intact, K was higher in controls than with Perftoran at 10 and 30 min or Pluronic F-127 at 10 min (P < 0.05). With surfactant added after air perfusion to damage the endothelium, K was lower (P < 0.05) at all times for both Perftoran and Pluronic F-127. With surfactant in the perfusate before air perfusion, K was lower at 10 and 30 min for Perftoran and at 10 min for Pluronic F-127 than for controls (P < 0.05). Phenylephrine-induced vasoconstriction was identical among groups. Acetylcholine-induced vasodilatation was the same among groups with an intact endothelium but was found to be lower in controls after air perfusion that followed surfactant exposure than in either surfactant group (P < 0.05). Surfactants reduced bubble adhesion force and preserved basic endothelial structure and vasodilatory function despite attempts to damage the endothelium. Surfactants seem to protect the endothelium from mechanically induced injury in addition to decreasing bubble adhesion forces.

Cytochrome P-450 metabolites but not NO, PGI2, and H2O2 contribute to ACh-induced hyperpolarization of pressurized canine coronary microvessels.

The endothelium-dependent hyperpolarization of cells has a crucial role in regulating vascular tone, especially in microvessels. Nitric oxide (NO) and prostacyclin (PGI2), in addition to endothelium-derived hyperpolarizing factor (EDHF), have been reported to hyperpolarize vascular smooth muscle in several organs. Studies have reported the hyperpolarizing effects of these factors are increased by a stretch in large coronary arteries. EDHF has not yet been identified and cytochrome P-450 metabolites and H2O2 are candidates for EDHF. With the use of the membrane potential-sensitive fluorescent dye bis-(1,3-dibutylbarbituric acid)trimethione oxonol [DiBAC4(3)], we examined whether NO, PGI2, cytochrome P-450 metabolites, and H2O2 contribute to ACh-induced hyperpolarization in pressurized coronary microvessels. Canine coronary arterial microvessels (60-356 mum internal diameter) were cannulated and pressurized at 60 cmH2O in a vessel chamber perfused with physiological salt solution containing DiBAC4(3). Fluorescence intensity and diameter were measured on a computer. There was a linear correlation between changes in the fluorescence intensity and membrane potential. ACh significantly decreased the fluorescence intensity (hyperpolarization) of the microvessels without any inhibitors. Endothelial damage caused by air perfusion abolished the ACh-induced decrease in fluorescence intensity. The inhibitors of NO synthase and cyclooxygenase did not affect the ACh-induced decreases in the fluorescence intensity. The addition of 17-octadecynoic acid, a cytochrome P-450 monooxygenase inhibitor, to those inhibitors significantly attenuated the ACh-induced decreases in fluorescence intensity, whereas catalase, an enzyme that dismutates H2O2 to form water and oxygen, did not. Furthermore, catalase did not affect the vasodilation produced by ACh. These results indicate that NO and PGI2 do not contribute to the ACh-induced hyperpolarization and that the cytochrome P-450 metabolites but not H2O2 are involved in EDHF-mediated hyperpolarization in canine coronary arterial microvessels.

Organ Sites of Lipopolysaccharide-Induced Nitric Oxide Production in the Anesthetized Rat

The objective of this research was to determine the amount and timing of nitric oxide (NO, nitrogen monoxide) gas produced by the lungs, intestinal mucosa, and organ surfaces facing the peritoneal cavity after iv injection of a bacterial toxin, lipopolysaccharide (LPS). Some of the deleterious effects of LPS on organ function have been attributed to NO or strong oxidants formed locally from NO. Medical-grade air was used as an inspiratory air source (50 strokes/min × 3 ml/stroke) or was pumped through the ileal lumen or peritoneal cavity (20 strokes/min × 3 ml/stroke). The air was collected at intervals of 15–30 min for 3 h after LPS and analyzed for authentic NO gas by chemiluminescence. LPS (5 mg/kg) or saline was injected iv. Sodium nitroprusside (SNP) was injected to determine the appearance of its NO released into the perfused compartments. Blood pressure, plasma nitrate plus nitrite (NOx), and total plasma leukocytes were measured as other manifestations of LPS effects. NO began to increase in the pulmonary expired air 90 min after LPS and continued to increase for the remainder of the experiment. The final pulmonary post-LPS [NO] was about 20-fold greater than the [NO] before LPS. LPS had no effect on intraluminal or intraperitoneal [NO]. The saline injection had no effect on [NO] in any compartment. SNP injection increased NO entry into all three air-perfused compartments. Thus, NO from an exogenous tissue source was not prevented from being detected. Blood pressure was decreased by LPS only during the pulmonary perfusion. There were no significant effects of LPS on leukocytes or plasma NOx. LPS decreased blood pressure and leukocytes and increased plasma NOx when air perfusion was not done. It was concluded that different organs can produce LPS-induced NO at markedly different rates and times. However, some aspect of the experimental technique of air perfusion could alter the effects of LPS.

Flow modulation of pressure-sensitive tone in rat pial arterioles: role of the endothelium.

Cerebral arteriolar tone is modulated in response to changes in transmural pressure and luminal flow. The effect of flow on the relation between pressure and diameter has not been fully evaluated in these vessels. This study was conducted to investigate this interaction and to determine the role of the endothelium in mediating it. Rat pial arterioles from the territory of the posterior cerebral artery were mounted in a perfusion myograph. In some arterioles, the endothelium was removed by air perfusion. Diameters were recorded at pressures from 20 to 200 mmHg in the presence and absence of flow (10 microl/min). The response to flow (0-30 microl/min) was recorded at 60 and 120 mmHg. In the absence of flow, endothelium-intact arterioles demonstrated tone at distending pressures between 40 and 140 mmHg. In the presence of flow, tone did not develop until pressure exceeded 100 mmHg, and the vessels remained active at pressures up to 200 mmHg. Endothelium-denuded arterioles developed tone at the same pressure when perfused as when unperfused, but perfused vessels were able to maintain active tone at higher pressures. At 60 mmHg, flow caused dilation if the endothelium was intact and constriction if it had been removed. At 120 mmHg, flow caused constriction. Endothelium-dependent flow-relaxation was inhibited by N(G)-nitro-L-arginine methyl ester (10(-5) M) and abolished by indomethacin (10(-5) M). Flow inhibits the development of pial arteriolar tone at low intraluminal pressures through endothelium-dependent mechanisms. Conversely, perfusion extends the upper limit of the myogenically regulated pressure range through endothelium-independent activation of arteriolar smooth muscle contraction.

Dilation of rat diaphragmatic arterioles by flow and hypoxia: roles of nitric oxide and prostaglandins.

The in vitro responses to ACh, flow, and hypoxia were studied in arterioles isolated from the diaphragms of rats. The endothelium was removed in some vessels by low-pressure air perfusion. In endothelium-intact arterioles, pressurized to 70 mmHg in the absence of luminal flow, ACh (10(-5) M) elicited dilation (from 103 +/- 10 to 156 +/- 13 microm). The response to ACh was eliminated by endothelial ablation and by the nitric oxide synthase antagonists NG-nitro-L-arginine (L-NNA; 10(-5) M) and NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) but not by indomethacin (10(-5) M). Increases in luminal flow (5-35 microl/min in 5 microl/min steps) at constant distending pressure (70 mmHg) elicited dilation (from 98 +/- 8 to 159 +/- 12 microm) in endothelium-intact arterioles. The response to flow was partially inhibited by L-NNA, L-NAME, and indomethacin and eliminated by endothelial ablation and by concurrent treatment with L-NAME and indomethacin. The response to hypoxia was determined by reducing the periarteriolar PO2 from 100 to 25-30 Torr by changing the composition of the gas used to bubble the superfusing solution. Hypoxia elicited dilation (from 110 +/- 9 to 165 +/- 12 microm) in endothelium-intact arterioles but not in arterioles from which the endothelium had been removed. Hypoxic vasodilation was eliminated by treatment with indomethacin and was not affected by L-NAME or L-NNA. In rat diaphragmatic arterioles, the response to ACh is dependent on endothelial nitric oxide release, whereas the response to hypoxia is mediated by endothelium-derived prostaglandins. Flow-dilation requires that both nitric oxide and cyclooxygenase pathways be intact.

Nitric oxide lowers the calcium sensitivity of tension in the rat tail artery.

1. Controversy exists as to whether a fall in the intracellular Ca2+ concentration ([Ca2+]i) is a requisite element of the vasodilatory response to nitric oxide (NO). 2. We studied the effect of NO on the coupling between [Ca2+]i and vasoconstriction in arterial segments loaded with the [Ca2+]i-sensitive, intracellular dye fura-2. As data interpretation is equivocal when fura-2 is loaded into both endothelial and smooth muscle cells, we compared results from in vitro experiments on segments of the rat tail artery in which fura-2 and noradrenaline were applied on the luminal or adventitial side, and endothelium was removed 'physically' (rubbing or air) or 'functionally' (Nomega-nitro-L-arginine methyl ester). The use of air perfusion to remove endothelium is of considerable benefit since it allows paired observations in a single tissue. 3. Fura-2 loaded into endothelial cells but endothelial 'contamination' of the smooth muscle cell [Ca2+]i signal was minimal. 4. Endogenous NO decreased vasoconstrictor responses to noradrenaline but had no effect on [Ca2+]i. 5. Nitroglycerine decreased vasoconstrictor responses in a concentration-dependent fashion but had no effect on [Ca2+]i. 6. In conclusion, NO causes vasodilatation via a mechanism which is downstream of [Ca2+]i mobilization.

Disruption of the rat mesenteric arterial bed endothelial function by air perfusion

The impact of air perfusion on the endothelial function of the rat mesenteric arterial bed (MAB; perfused with Krebs' bicarbonate plus indomethacin) was compared to that of the NO synthase inhibitor, N ω-nitro-L-arginine methyl ester (L-NAME). Air shifted the dose-response curve for the alpha-adrenoceptor agonist, norepinephrine (NE) to the left (ED 50%: 2.9 ± 0.7 to 0.9 ± 0.7 μg, P < 0.05); maximal vasoconstriction did not change. L-NAME produced a similar increase in midrange sensitivity (ED 50% 1.4 ± 0.7 μg, P < 0.05) and a 20% increase in maximum (152 ± 6 to 183 ± 7 mmHg, P < 0.05). Electromechanical stimulation with potassium chloride (KCL) was not modified by reserpine. Neither air nor L-NAME modified midrange sensitivity to KCL. L-NAME produced a 17% increase in maximum (91 ± 4 to 107 ± 5 mmHg, P < 0.05); reserpine abolished the latter effect. Air and L-NAME diminished endothelium-dependent vasodilation elicited by carbachol. Air did not modify endothelium-dependent vasodilation elicited by sodium nitroprusside; this response was potentiated by L-NAME. In summary, air and L-NAME produced similar effects on receptor-dependent activation of the endothelial L-arginine nitric oxide (NO) pathway. Potentiation by L-NAME of the maximal electromechanical response suggests the existence of a tone-dependent NO system. Abolition of the latter response by reserpine suggests that this system is of sympathetic origin.

Modulation of myogenic responsiveness by CO2 in rat diaphragmatic arterioles: role of the endothelium

The effect of hypercapnia on the myogenic response was determined in arterioles (80- to 100-microm internal diameter) isolated from the diaphragms of rats killed by decapitation. All arterioles were exposed to step changes in intraluminal pressure over a range of 10-200 mmHg and had no flow through their lumen. In five separate groups of vessels (n = 7 per group), PCO2 of the superfusing buffer was adjusted to 40, 60, 80, 90, or 100 mmHg. In three further groups of vessels (n = 7 per group), the endothelium was removed by low-pressure air perfusion (2 ml at 20 mmHg) and PCO2 of the superfusing buffer was adjusted to 40, 80, or 100 mmHg. In endothelium-intact vessels, increasing PCO2 to 80 mmHg enhanced the myogenic response, as reflected by a negative slope of the pressure-diameter relationship (slope = -0.164 +/- 0.03 vs. 0.004 +/- 0.02 for vessels at PCO2 = 40 mmHg, P < 0.05). With a PCO2 of 100 mmHg, dilation accompanied increasing intraluminal pressure and the slope of the pressure-diameter curve was positive (0.154 +/- 0.03, P < 0.05 for difference from vessels at PCO2 = 40 mmHg). In deendothelialized vessels, the curve was shifted upward in a parallel manner during exposure to increased PCO2 levels. Moderate hypercapnia (PCO2 < 80 mmHg) elicits endothelium-dependent enhancement of myogenic tone. Severe hypercapnia (PCO2 > 80 mmHg) inhibits myogenic tone through a direct effect on vascular smooth muscle and through endothelium-dependent inhibitory mechanisms.

Role of venular endothelium in control of arteriolar diameter during functional hyperemia

This study was designed to determine the importance of the venular endothelium in the vasodilation of adjacent arterioles during functional hyperemia. The hamster cremaster muscle was prepared for in vivo microscopy. Two silver-silver chloride electrodes were placed across the pedicle of the cremaster muscle, and a square-wave pulse (10 V amplitude, 1 ms duration, and 1 Hz frequency) was used to elicit muscle contraction. Muscle stimulation for 1 min resulted in a vasodilation of the first-order arterioles from 74 +/- 2 to 91 +/- 2 microns (n = 9, P < 0.05). After perfusion of the venule with air to disrupt the venular endothelium, there was no significant effect on the resting diameter, 73 +/- 3 microns, but the vasodilation associated with the muscle stimulation was significantly attenuated to 82 +/- 3 microns (P < 0.01). After completion of these experiments, the disruption of venular endothelium was confirmed by electron microscopy. The functional vasodilation of arterioles adjacent to venules with an intact endothelium (venules in which air did not enter) was retained after air perfusion (n = 6). These results suggest that the presence of the venular endothelium is important for the arteriolar vasodilation during functional hyperemia. We propose that the venular endothelium releases a relaxing factor responsible for a portion of the functional arteriolar vasodilation.

Myogenic activation of canine small renal arteries after nonchemical removal of the endothelium

Myogenic activation of isolated small arteries (200-500 microns) of the dog kidney was evaluated by measuring vessel diameters during stepwise elevations of transmural pressure before and after removal of the endothelium by mechanical rubbing or air perfusion. Myogenic activation was unaffected by mechanical rubbing, but air perfusion caused the arteries to constrict and attenuated the myogenic response; i.e., vessel diameters increased as transmural pressure was elevated. However, air-perfused arteries still constricted in response to norepinephrine and dilated during superfusion with Ca(2+)-free solution, demonstrating that loss of the myogenic response did not result from an inability of the vessel to contract. Intact arteries contracted with 1 microM norepinephrine exhibited normal myogenic responses, demonstrating that loss of myogenic activation in the air-perfused vessels was not a nonspecific effect secondary to constriction of the artery. These results suggest that myogenic activation of small renal arteries is independent of the endothelium and that the method of endothelial removal may affect conclusions regarding the role of the endothelium in mediating the myogenic response.

Inner ear injury caused by air intrusion to the scala vestibuli of the cochlea.

In a previous communication, we demonstrated that the introduction of air into the scala tympani of the cochlea causes a decrease of cochlear potentials; however, the change in endocochlear dc potential (EP) was mild and the decreased cochlear microphonics (CM) and compound action potentials (CAP) were, at least partially, reversible. In contrast, we have now found that air perfusion (3-60 microliters/min) in the scala vestibuli decreased cochlear potentials more drastically than that in the scala tympani. The change in the EP after air perfusion in the scala vestibuli was characterized by a decrease of the negative EP in response to anoxia. The CM drastically decreased upon the initiation of air perfusion and no recovery was observed after refilling of the perilymph. Histological examination showed collapse of Reissner's membrane in 12 out of 17 cochleas examined. The extent and frequency of the collapse increased with an increase in the amount of air perfused in the scala vestibuli. As the minimal amount of air needed to cause inner ear damage by air perfusion in the scala vestibuli is as small as 3 microliters, it is possible that the prognosis is worse in cases with fistula of the oval window compared to that of the round window area, if the pneumolabyrinth is involved in the pathophysiology of perilymphatic fistula. It is also indicated that air inflation of the middle ear is dangerous in cases with fistula in the oval window.

The Effects of Heparin and Annexin V on Fibrin Accretion after Injury in the Jugular Veins of Rabbits

We compared the relative abilities of unfractionated heparin and annexin V to prevent fibrin accretion onto injured jugular veins in vivo. Heparin was used to accelerate the inhibition of thrombin by antithrombin III, and annexin V was used to inhibit the assembly of the prothrombinase complex on phospholipid surfaces, thereby blocking thrombin generation. Rabbit jugular veins were isolated in situ, a 2 cm segment was injured by perfusing it with air, and then blood flow was re-established. Five minutes later, each rabbit was injected with heparin (20 U/kg) or annexin V (0.3 mg/kg) and then with 125I-fibrinogen. The amount of 125I-fibrin accumulation onto each injured vessel wall segment was measured 4 h later. Each injured vessel was completely de-endothelialized as a result of the air perfusion as demonstrated by electron microscopy. 125I-fibrin accretion onto the injured jugular veins was enhanced 2.4-fold as compared to the uninjured veins in sham-operated animals. Heparin treatment did not reduce fibrin accretion, whereas, annexin V treatment decreased fibrin accretion by 60%, p < 0.05. This latter effect was achieved without sustained circulating anticoagulation. Additional experiments confirmed that the inhibitory effect of annexin V on fibrin accretion was associated with a surface specific effect, since more annexin V bound to the injured jugular vein segments as compared to the non-injured jugular veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the vascular endothelium in regulating the response of small arteries of the dog kidney to transmural pressure elevation and reduced PO2.

The goal of this study was to determine the role of the vascular endothelium in regulating the response of small renal arteries to increased transmural pressure and reduced PO2. Canine small renal arteries (496 +/- 32 microns) were isolated, cannulated with micropipettes, and mounted in an in vitro chamber that allowed transmural pressure, tissue bath PO2, and vessel lumen PO2 to be controlled. In intact arteries, elevation of transmural pressure caused contractile activation and a progressive depolarization (0.17 +/- 0.09 mV/mm Hg pressure increase) of the vascular smooth muscle cells. Endothelial damage by air perfusion caused a 13-14% reduction in resting diameter and an 18 +/- 3 mV depolarization of the vascular smooth muscle, but eliminated the progressive contraction and depolarization that occurred in intact vessels in response to transmural pressure elevation. Reduction of either tissue bath O2 concentration or vessel lumen PO2 significantly enhanced norepinephrine-induced contractions of the arteries. Endothelial damage prevented the enhancement of norepinephrine-induced contractions by reduced PO2 in the vessels. The results of this study suggest that the vascular endothelium regulates both myogenic contraction and the enhancement of norepinephrine-induced contractions by reduced PO2 in small arteries of the dog kidney.

Effect of Perilymphatic Air Perfusion on Cochlear Potentials

Perilymphatic fistula is now widely recognized to cause acute profound hearing loss. It is still controversial, however, which mechanism it is that causes the reversible hearing loss. Recently, it has been suggested by two groups of researchers that the intrusion of air bubbles into the perilymphatic space (a condition called pneumolabyrinth or aerolabyrinth) through the ruptured labyrinthine window(s) may be one of the causes. In order to examine the mechanism underlying the hearing loss associated with pneumolabyrinth, the perilymphatic space of the guinea pig cochlea was perfused with air and cochlear potentials were recorded. Although perfusion of the scala tympani with air at a rate as high as 200 microliter/min caused an immediate and drastic decrease of the cochlear microphonics (CM) and the compound action potential (AP), it had little effect on the endocochlear dc potential (EP) during perfusion for 20 min. A decline in EP was seen in half the ears, but only when the duration of perfusion exceeded 30 min. These results show that the EP has an amazing resistance to air trapped in the scala tympani of the cochlea and that the initial decrease of hearing acuity after the elimination of perilymph from the scala tympani (or introduction of air into the scala tympani) is probably due to interference in CM and AP generation mechanisms rather than to strial dysfunction.

Induction of alveolar epithelial injury by phospholipase A2.

Severe damage to the alveolar type I epithelial cell is a characteristic morphological feature of lung injury due to numerous cases. It is postulated that excess phospholipase A2 (PLA2) activity might be responsible for these changes, as one of the naturally occurring products of this enzyme, lysophosphatidylcholine (lysoPC) has been shown to cause selective injury to the type I pneumonocyte when it is instilled into the lower air spaces of the lung. To further investigate this potential mechanism of type I epithelial cell toxicity, we have measured the epithelial permeability-surface area product (PS) for [14C]sucrose as well as whole-lung lysoPC content at several times after instilling PLA2 (Naja naja venom) into either the air spaces or the perfusate of an isolated hamster lung preparation. As a molar percentage of total phospholipids, the normal hamster lung contains approximately 1.5% lysoPC, and this value is not affected by fluid filling of the air spaces or perfusion of the excised lung for periods up to 90 min. When 0.15 U/ml PLA2 is instilled into the air spaces, lung lysoPC content increases to approximately 2.5% and there are barely detectable increases in [14C]sucrose PS. With air space PLA2 concentrations of 0.30 U/ml, lysoPC content increases to between 4 and 5%, [14C]sucrose PS increases by greater than a factor of 10, and flooding of the alveolar spaces occur. Ultrastructural studies of similarly treated lungs show widespread but selective damage to the type I epithelial cells. These same biochemical and functional changes are not seen when the same concentrations of PLA2 are added to the lung perfusate.(ABSTRACT TRUNCATED AT 250 WORDS)

The Basement Membrane Underlying the Vascular Endothelium Is Not Thrombogenic: In Vivo and In Vitro Studies with Rabbit and Human Tissue

Studies examining the interaction of platelets with exposed subendothelium in vivo have reported conflicting results. To examine possible explanations for the apparently discrepant findings, we measured the platelet reactivity of subendothelium prepared by a number of methods both in vivo and in vitro. In addition, we examined the possibility that 13-hydroxyoctadecadinoic acid (13-HODE), an endothelial cell-derived chemorepellant, modulates the reactivity of the subendothelium to platelets. In vivo, the subendothelium of segments of rabbit carotid arteries was exposed by removing the endothelial cells by air perfusion or by balloon catheter stripping. Platelet accumulation onto the de-endothelialized segments was assessed by 3H-radioactivity uptake, using 3H-adenine-labelled platelets, and by scanning electron microscopy. In vitro, 3H-adenine-labelled platelet adhesion was measured onto plain plastic discs and onto plastic discs coated with the following purified basement membrane components: collagens type I, III, IV, V, laminin, or fibronectin. In addition, 3H-adenine-labelled platelet adhesion was measured onto plastic discs covered with human endothelial cells or onto the basement membrane underlying the endothelial cells. In vivo, there was marked 3H-platelet accumulation onto the balloon catheter carotid arteries one hour after injury. In contrast, there was no platelet accumulation onto the subendothelium of carotid arteries de-endothelialized by air perfusion. These differences were confirmed by scanning electron microscopy. Transmission electron microscopic examination demonstrated that the extracellular matrix was intact following the air perfusion injury whereas the majority of it was removed by the balloon catheter injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of formaldehyde and ozone on the trigeminal nasal sensory system.

The effects of formaldehyde and ozone on the electrical activity of the nasopalatine nerve were studied in anesthetized rats. The response (increase in action potential frequency) of nasopalatine and ethmoidal nerves to brief presentations of formaldehyde, ozone, or amyl alcohol was a power function of stimulus concentration. When formaldehyde was presented continuously for one hour, it produced a decrease in nasopalatine nerve response to amyl alcohol that varied directly with the formaldehyde concentrations employed. Perfusion of the nasal cavities with air for one hour following the formaldehyde exposure resulted in a partial recovery of the neural response to amyl alcohol. Ozone exposures of 5 ppm lasting one hour produced an increase in nasopalatine nerve response to amyl alcohol. Air perfusion following the ozone exposure reduced the neural response to amyl alcohol, but not to preexposure levels.