Changes in blood volume and extravascular water content in isolated perfused rat lungs during ventilation hypoxia

Interstitial lung fluid balance in healthy lowlanders exposed to high-altitude

We aimed to assess lung fluid balance before and after gradual ascent to 5150m. Lung diffusion capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (Dm_CO) and ultrasound lung comets (ULCs) were assessed in 12 healthy lowlanders at sea-level, and on Day 1, Day 5 and Day 9 after arrival at Mount Everest Base Camp (EBC). EBC was reached following an 8-day hike at progressively increasing altitudes starting at 2860m. DLCO was unchanged from sea-level to Day 1 at EBC, but increased on Day 5 (11±10%) and Day 9 (10±9%) vs. sea-level (P≤0.047). Dm_CO increased from sea-level to Day 1 (9±6%), Day 5 (12±8%), and Day 9 (17±11%) (all P≤0.001) at EBC. There was no change in ULCs from sea-level to Day 1, Day 5 and Day 9 at EBC. These data provide evidence that interstitial lung fluid remains stable or may even decrease relative to at sea-level following 8days of gradual exposure to high-altitude in healthy humans.

The effect of exogenous substrate concentrations on true and apparent metabolism of hyperpolarized pyruvate in the isolated perfused lung

Although relatively metabolically inactive, the lung has an important role in maintaining systemic glycolytic intermediate and cytosolic redox balance. Failure to perform this function appropriately may lead to lung disease progression, including systemic aspects of these disorders. In this study, we experimentally probe the response of the isolated, perfused organ to varying glycolytic intermediate (pyruvate and lactate) concentrations, and the effect on the apparent metabolism of hyperpolarized 1-(13)C pyruvate. Twenty-four separate conditions were studied, from sub-physiological to super-physiological concentrations of each metabolite. A three-compartment model is developed, which accurately matches the full range of experiments and includes a full account of evolution of agent concentration and polarization. The model is then refined using a series of approximations which are shown to be applicable to cases of physiological relevance, and which facilitate an intuitive understanding of the saturation and scaling behavior. Perturbations of the model assumptions are used to determine the sensitivity to input parameter estimates, and finally the model is used to examine the relationship between measurements accessible by NMR and the underlying physiological parameters of interest. Based on the observed scaling of lactate labeling with lactate and pyruvate concentrations, we conclude that the level of hyperpolarized lactate signal in the lung is primarily determined by the rate at which NAD(+) is reduced to NADH. Further, although weak dependences on other factors are predicted, the modeled NAD(+) reduction rate is largely governed by the intracellular lactate pool size. Conditions affecting the lactate pool can therefore be expected to display the highest contrast in hyperpolarized (13)C-pyruvate imaging. The work is intended to serve as a basis both to interpret the signal dynamics of hyperpolarized measurements in the normal lung and to understand the cause of alterations seen in a variety of disease and exposure models.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Effects of hypoxia on pulmonary microvascular volume

To determine the effects of alveolar hypoxia on pulmonary microvascular volume, X-ray microfocal angiographic images of isolated perfused dog lung lobes were obtained during passage of a bolus of radiopaque contrast medium during both normoxic (alveolar gas, 15% O(2), 6% CO(2), and 79% N(2)) and hypoxic (3% O(2), 6% CO(2), and 91% N(2)) conditions. Regions of interest (ROIs) over the lobar artery and vein at low magnification and a feeding artery ( approximately 500 microm diameter) and the nearby microvasculature (vessels smaller than approximately 50 microm) at high magnification were identified, and X-ray absorbance vs. time curves were acquired under both conditions from the same ROIs. The total pulmonary vascular volume was calculated from the flow and the mean transit time for the contrast medium passage from the lobar artery to lobar vein. The fractional changes in microvascular volume were determined from the areas under the high-magnification X-ray absorbance curves. Hypoxia decreased lobar volume by 13 +/- 3% (SE) and regional microvascular volume by 26 +/- 4% (SE). Given the morphometry of the lung vasculature, these results suggest that capillary volume was decreased by hypoxia.

Relation between peripheral chemoreceptors stimulation and pulmonary arterial blood pressure in rats

As interactions between peripheral chemoreceptors stimulation (PCS) and pulmonary vasomotor tone remain controversial, experiments were made in rats in order to clear up the effects of PCS on pulmonary arterial pressure (PAP). Different stimulations varying in intensities were used, in rats nervously intact (IR-rats), after vagotomy (XT-rats), after chemodenervation obtained without vagotomy (CDN not XT-rats) or with XT (CDN + XT) and finally after alpha 1-receptors blockade (P-rats = pretreated rats). The observed variations were analysed in view of disentangling reflex part of PCS from a direct activity on the pulmonary vascular bed. Ventilation, PAP and systemic blood pressure (BP) were studied in anaesthetized rats. N2 test, NaCN test, 20 s of 5% O2 inhalation and almitrine bismesylate (ALM) were used as PCS, ranged in the order of their relative intensities, from the ventilatory responses observed in IR-rats. In IR-rats, N2-and CN test produced a similar transient increase of PAP, slightly more extended than the hyperventilation. After XT, the responses were prolonged, but amplified only in CN test. Ventilatory responses disappear after CDN, but as far as pulmonary hypertension is concerned, CDN + XT is more potent than CDN without XT to reduce or even suppress them. This fact is particularly evident with ALM who is the strongest PCS used. Similar reduction of PAP rise was also produced in P-rats in which ventilatory responses remain unchanged. Prolonged hypoxic inhalation induced a progressive fall of systolic BP and of PAP. The return to normal air breathing is followed by BP restoration and a long-lasting PAP increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute alveolar hypoxia increases bronchopulmonary shunt flow in the dog

To study the effects of alveolar hypoxia on canine bronchopulmonary shunt flow, a biventricular bypass preparation was employed. The preparation allowed a constant and sensitive measure of changes in pulmonary venous blood flow. In 16 of 18 dogs with intact bronchial arteries, alveolar hypoxia caused an increase in pulmonary venous return both under conditions of constant pulmonary arterial inflow and under conditions of no pulmonary arterial inflow, suggesting bronchopulmonary shunting. This effect was accompanied by systemic vasodilation despite vagotomy and ganglionic blockade, and was abolished by division of all bronchial vessels. Ibuprofen, 3 mg/kg, and indomethacin, 15 mg/kg, in dogs with intact bronchial vessels, abolished both the increase in pulmonary venous return and the systemic vasodilatation caused by hypoxia. Thus, alveolar hypoxia directly augments bronchopulmonary flow, most likely through release of one or more vasodilating prostaglandins.

The pulmonary vasoconstrictor response to hypoxia. The hypoxia-sensitive site studied with a volatile inhibitor

Recent investigations have revealed that a number of inhalation anesthetics, including halothane, inhibit the pulmonary vasoconstrictor response to hypoxia without affecting other vasoconstrictor stimuli. Various injectable anesthetics do not show this effect. This discrepancy could be due either to different pharmacological properties or to the different routes of administration. There is no general agreement on whether the response to hypoxia is elicited mainly by airway hypoxia or by blood hypoxemia, i.e. where within the lungs hypoxia acts. This work is an attempt to localize the hypoxia-sensitive site employing halothane. We have studied the reduction of standardized vasoconstrictor responses to hypoxia during administration of halothane via: (1) the airways, (2) the pulmonary artery and (3) the pulmonary veins (backward perfusion). Our experimental model has been two pairs of series-perfused hyperventilated isolated rat lungs. An equimolar concentration of halothane most effectively inhibits the response when presented to the alveoli, less when presented to the arterial- and least when presented to the venous segments of the pulmonary vasculature. We suggest that the response to hypoxia is inhibited by halothane at some extravascular site on the arterial side of the pulmonary vasculature, functionally closer to the alveoli than to the responding vessels. A model which combines all the data into an unifying concept has been presented.