Role of nitric oxide, adenosine,N-methyl-d-aspartate receptors, and neuronal activation in hypoxia-induced pial arteriolar dilation in rats

In this study, we tested the hypothesis that nitric oxide (NO) and adenosine (ADO) are the principal mediators of severe hypoxia-induced vasodilation. In addition, we examined whether activation ofN-methyl-d-aspartate (NMDA) receptors and/or perivascular nerves plays a role. A closed cranial window and intravital microscopy system was used to monitor diameter changes in pial arterioles (∼ 40 μm) in anesthetized rats. The relative contributions of ADO, NMDA, NO, and neuronal activation to hypoxic cerebrovasodilation were assessed using the blockers 8-sulfophenyltheophylline (8-SPT), MK-801, nitro-l-arginine methylester (LNAME), and tetrodotoxin (TTX). Two experimental series were studied. In the first, we tested the effects of NOS inhibition, via topical L-NAME (1 mM), on moderate (PaO₂ ≈ 46 mmHg)then severe (PaO₂ ≈ 34 mmHg) hypoxia-induced dilation. To confirm that L-NAME was affecting specifically NO-dependent responses, we also examined, in each experiment, the vasodilatory responses to topical applications of NOS-dependent (adenosine diphosphate (ADP); acetylcholine (ACh)(and -independent (sodium nitroprusside (SNP)) agents, in the presence of L-NAME or, in controls, the presence of D-NAME or no added analogue. In the second series, topical suffusions of ADP, ADO, and NMDA were sequentially applied, followed by 5 min exposure to severe hypoxia (PaO, ≈ 32 mmHg). Following return to normoxia, a suffusion of either 8-SPT (10 μM), MK-801 (10 μM), TTX (1 μM), or 8-SPT + MK-801 was initiated (or, in controls, application of a drug-free suffusate was maintained), and the above sequence repeated. In control, TTX, and 8-SPT + MK-801 experiments, baseline conditions were then restored and hypercapnia (PaCO₂ = 70–85 mmHg) was imposed. In the series 1 control groups, moderate and severe hypoxia elicited ≈ 20% and 35–40% increases in diameter, respectively. L-NAME attenuated ADP- and ACh-induced dilations, did not alter the arteriolar responses to SNP or moderate hypoxia, but prevented further dilation upon imposition of severe hypoxia. This suggested that 45–50% of the severe hypoxia response was NO-dependent. In series 2, 8-SPT blocked the adenosine response and reduced severe hypoxia-induced dilation by 46%. MK-801 predictably blocked NMDA-induced relaxation and reduced the hypoxic response by 42%. When combined, 8-SPT and MK-801 affected hypoxic vasodilation additively. After TTX, the ADP and ADO responses were normal, but NMDA and hypoxia responses were completely blocked. Hypercapnia-induced dilation was unaffected by TTX or 8-SPT + MK-801. The results imply that severe hypoxia-induced release of NO and ADO, and the accompanying pial arteriolar dilation, are wholly dependent on the capacity to generate action potentials in perivascular nerves. The similarity of the L-NAME and MK-801 effects on hypoxic cerebrovasodilation suggests that the NO-dependency, to a large degree, derives from NMDA receptor activation.     

Cerebral hemodynamics measured with simultaneous PET and near-infrared spectroscopy in humans

Near-infrared spectroscopy (NIRS) enables continuous non-invasive quantification of blood and tissue oxygenation, and may be useful for quantification of cerebral blood volume (CBV) changes. In this study, changes in cerebral oxy- and deoxyhemoglobin were compared to corresponding changes in CBF and CBV as measured by positron emission tomography (PET). Furthermore, the results were compared using a physiological model of cerebral oxygenation. In five healthy volunteers changes in CBF were induced in a randomized order by hyperventilation or inhalation of 6% CO(2). Arterial content of O(2) and CO(2) was measured several times during each scanning. Changes in deoxyhemoglobin (deltaHb), oxyhemoglobin (deltaHbO(2)) and total hemoglobin (deltaHb(tot)) were continuously recorded with NIRS equipment. CBF and CBV was also determined in MRI-coregistered PET-slices in regions determined by the placement of the two optodes, as localized from the transmission scan. The PET-measurements showed an average CBV of 5.5+/-0.74 ml 100 g(-1) in normoventilation, with an increase of 29% during hypercapnia, whereas no significant changes were seen during hyperventilation. CBF was 51+/-10 in normoventilation, increased by 37% during 6% CO(2) and decreased by 25% during hyperventilation. NIRS showed significant increases in oxygenation during hypercapnia, and a trend towards decreases during hyperventilation. Changes in CBV measured with both techniques were significantly correlated to CO(2) levels. However, deltaCBV(NIRS) was much smaller than deltaCBV(PET), and measured NIRS parameters smaller than those predicted from the model. It is concluded that while qualitatively correct, NIRS measurements of CBV should be used with caution when quantitative results are needed.     

The cerebellar fastigial nucleus contributes to CO2-H+ ventilatory sensitivity in awake goats

The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is an important determinant of CO(2)-H(+) sensitivity during wakefulness. Bilateral, stainless steel microtubules were implanted into the CFN (N=9) for injection (0.5-10 microl) of the neurotoxin ibotenic acid. Two or more weeks after implantation of the microtubules, eupneic breathing and CO(2)-H(+) sensitivity did not differ significantly (P>0.10) from pre-implantation conditions. Injection of ibotenic acid (50 mM) did not significantly alter eupneic Pa(CO2) (P>0.10). The coefficient of variation of eupneic Pa(CO2) was 4.0+/-0.6 and 3.7+/-0.4% over the 2 weeks before and after the lesion, respectively. CO(2)-H(+) sensitivity expressed as inspired ventilation/Pa(CO2) decreased from 2.15+/-0.17 pre-lesion to 1.58+/-0.26 l/(min mmHg) 3-6 days post-lesion (P<0.02, -27%). There was no significant (P>0.10) recovery of sensitivity between 7 and 10 days post-lesion. The lesion also increased (P<0.05) the day-to-day variability of this index by nearly 100%. When CO(2) sensitivity was expressed as elevated inspired CO(2)/room air V (I), values at 7%, but not 3 and 5% inspired CO(2), were reduced and more variable (P<0.05) after the ibotenic acid injections. We conclude that during wakefulness, the CFN contributes relatively more to overall ventilatory drive at high relative to low levels of hypercapnia.     

Influence of hypercapnic acidosis and hypoxia on abdominal expiratory nerve activity in the rat

We studied the influence of hypercapnic acidosis and hypoxia on the neural drive to abdominal muscles in anesthetized and decerebrate rats; this information is unavailable despite widespread use of the rat as an experimental model in respiratory physiology and neurobiology. To minimize confounding influences from receptors in the lungs and chest wall, the animals were vagotomized, paralyzed and mechanically ventilated, and electrical activity was recorded from abdominal muscle nerves. In anesthetized and decerebrate rats, both stimuli evoked steady, low amplitude expiratory discharge that persisted throughout the expiratory phase (E-all activity), but was inhibited during inspiration. We also observed late expiratory, high-amplitude bursts (E2 activity) superimposed on this steady activity, but only at the highest levels of respiratory drive. Hypoxia enhanced abdominal motor activity transiently, whereas hypercapnic acidosis caused a sustained increase in activity. Thus, both hypercapnic acidosis and hypoxia activate abdominal muscle motoneurons in the absence of phasic afferent inputs.     

Effects of air constituents on thermosensitivities of preoptic neurons: hypoxia versus hypercapnia

The effects of hypoxia (10% O₂) on the thermosensitivities of preoptic neurons were studied in urethanized rats and compared to the effects of hypercapnia (10% CO₂). This was examined by regression of neuronal activity on preoptic temperature. During hypoxia, the slope of the regression line increased significantly in 8 (23%) of 35 warmsensitive neurons and decreased in eight other neurons (P<0.05). During hypercapnia, the slope of the regression line decreased significantly in 7 (30%) of the 23 warmsensitive neurons (P<0.05). No neuron was found that significantly increased the slope of the regression line. The effects of hypoxia on thermosensitivities (i.e. the slope of the regression line) of PO neurons differed from those of hypercapnia in chi-square analysis (P<0.05). Responses of the cold-sensitive neurons to hypoxia or hypercapnia did not generally differ from those of the warm-sensitive neurons. During hypoxia and hypercapnia, arterial blood pressure, respiratory frequency, heart rate, and EEG were recorded to examine their relations to neuronal activity. The present results indicate that the thermosensitivities of preoptic neurons are modified by both hypoxia and hypercapnia, but that hypoxic differ from hypercapnic effects.     

硫氮卓酮对慢性低O2高CO2大鼠肺动脉压力和结构型一氧化氮合酶及其基因表达的影响

目的：探讨硫氮卓酮对慢性低O₂高CO₂大鼠肺动脉压力的影响及其作用机制。方法：将Sprague-Dawley大鼠分为正常对照组（A组）、四周低O₂高CO₂组（B组）和四周低O₂高CO₂+硫氮卓酮组（C组），采用透射电镜、图像分析、免疫组化、原位杂交等方法，研究硫氮卓酮对慢性低O₂高CO₂大鼠肺动脉平均压（mPAP）、颈动脉平均压（mCAP）及肺动脉显微和超微结构、肺动脉结构型一氧化氮合酶（ceNOS）及其基因表达的影响。结果：①B组mPAP明显高于A组（P<0.01），C组mPAP明显低于B组（P<0.01），A组和B组mCAP无明显差异（P>0.05），C组mCAP低于B组（P<0.01）；②光镜下，肺细小动脉管壁面积/管总面积比值（WA/TA）C组明显低于B组（P<0.01）；电镜下，C组大鼠肺细小动脉内皮损伤、中膜平滑肌细胞和胶原纤维增生明显轻于B组；③免疫组化见C组肺细小动脉ceNOS的平均吸光度值明显高于B组（P<0.01）；原位杂交发现C组肺细小动脉ceNOS mRNA平均吸光度值明显高于B组（P<0.01）。结论：硫氮卓酮可抑制慢性低O₂高CO₂性肺动脉高压形成和肺血管结构重建，肺动脉ceNOS及其基因表达的增加为其重要作用机制，硫氮卓酮可能为治疗COPD、肺动脉高压伴高血压或室上性心律失常患者较为理想的药物。     

老年妇科腹腔镜手术气腹、体位及高碳酸血症对循环功能的影响

目的探讨老年妇科腹腔镜手术术中气腹、体位改变及高碳酸血症对患者循环功能的影响。方法选取80例老年妇科腹腔镜手术患者为研究对象,均给予气管插管全麻及术中机械通气,分别在麻醉后15 min、T位后15 min、平卧气腹后15min、过度通气后15 min、过度通气后30 min检测患者的MAP、HR、pH、PETCO2、PaCO2、Pa-ETCO2。结果MAP、HR与PaCO2在平卧气腹后15 min时较麻醉后15 min提高,过度通气后15 min与30 min较平卧气腹后15 min降低(P<0.05);pH在T位后15 min与平卧气腹后15 min较麻醉后15 min降低,在过度通气后15 min、30 min较平卧气腹后15 min提高(P<0.05);PETCO2、Pa-ETCO2在平卧气腹后15 min较麻醉后15 min提高,过度通气后15 min、30 min较平卧气腹后15 min降低(P<0.05)。结论腹腔镜手术术中构建气腹、体位改变及高碳酸血症均会对循环功能产生一定影响,需加强术中监测并科学调整呼吸机参数,以改善患者循环功能,促进患者康复。     

葛根素对慢性低氧高二氧化碳大鼠肺动脉高压形成的预防作用

目的探讨葛根素对慢性低氧（O2）高二氧化碳（CO2）大鼠肺高压形成的预防作用。方法图像分析、氯胺T法、免疫组化、组织原位杂交技术等方法观察葛根素对慢性低O2高CO2大鼠肺组织羟脯氨酸含量、肺小血管显微结构、肺动脉管壁MMP-2、MMP-9、TIMP-2及其基因的影响。结果①光镜下葛根素组内弹力板扭曲、中膜平滑肌细胞增生及管腔狭窄程度均明显轻于低O2高CO2组。②血浆NO含量低O2高CO2组低于正常对照组（P〈0．01），葛根素组高于低O2高CO2组（P〈0．01）。③氯胺T法发现肺组织羟脯氨酸含量低O2高CO2组高于正常对照组（P〈0．01），葛根素组低于低O2高CO2组（P〈0．01）。④肺组织匀浆MMP-2、MMP-9H和TIMP-2含量低O2高CO2组高于正常对照组（P〈0．01）。葛根素组肺组织匀浆MMP-2、MMP-9和TIMP-2含量皆低于低O2高CO2组（P〈0．01）。⑤免疫组化、原位杂交法发现肺细小动脉MMP-2、MMP-9、TIMP-2和MMP-2mRNA、MMP-9mRNA、TIMP-2mRNA平均吸光度值（A）低O2高CO2组均高于正常对照组（P〈0．01），葛根素组均低于低O2高c0I组（P〈0．01）。结论葛根素预防慢性低氧高二氧化碳大鼠肺血管重建，降低肺动脉高压与其调节MMPs／TIMPs体系表达、抑制肺动脉管壁胶原的沉积有关。     

无创正压通气治疗拒绝插管的COPD急性加重并重度高碳酸血症呼吸衰竭患者的临床观察

目的探讨应用无创正压通气(NiPPV)治疗慢性阻塞性肺疾病急性加重(AECOPD)并重度高碳酸血症呼吸衰竭(HRF)的可行性。方法选取AECOPD并重度HRF患者12例,常规治疗时选其中6例(通气组)应用中等吸氧浓度(FiO2)与NiPPV治疗,注意管理气道(引流排痰、扩张气道)、管理面罩(防漏气)、防治通气并发症,另外6例为对照组。结果通气组6例患者中3例在通气治疗2h后动脉血气好转,3例于12h后好转,神志转清,36h后血气稳定,48～72h后,5例逐渐成功脱机最后好转出院,1例在第7天死亡。对照组中2例于治疗36h后血气好转,第5天出院,4例死亡。结论应用NiPPV可以成功抢救AECOPD并重度HRF患者,其难点在于排痰通畅气道,同时应用中等FiO2改善缺氧意义重大,其成功率取决于包括NiPPV在内的综合疗效。     

幼儿腹腔镜手术时预防高碳酸血症的临床研究

目的探讨幼儿腹腔镜手术时预防高碳酸血症的方案。方法选择接受腹腔镜手术,体征约10k左右患儿40例,随机将其分为A、B两组,设定使用相同的9mmHg气腹压力,A组改变呼吸通气参数提前进行麻醉干预,B组选择通常呼吸通气参数进行麻醉,观察末梢二氧化碳分压及心率改变,同时对比两组发生二氧化碳潴留的机率并记录两组相关数据。结果提前麻醉干预组术中血气二氧化碳分压、心率和呼末二氧化碳大致正常,而进行正常呼吸通气参数麻醉麻醉组血气二氧化碳分压、心率和呼末二氧化碳高于干预组（P〈0．05）。结论腹腔镜手术对小儿的呼吸、循环及血气虽有较大影响,但通过改变呼吸通气参数提前进行麻醉干预,对预防高碳酸血症有积极意义。