Selected contribution: redistribution of pulmonary perfusion during weightlessness and increased gravity.

To compare the relative contributions of gravity and vascular structure to the distribution of pulmonary blood flow, we flew with pigs on the National Aeronautics and Space Administration KC-135 aircraft. A series of parabolas created alternating weightlessness and 1.8-G conditions. Fluorescent microspheres of varying colors were injected into the pulmonary circulation to mark regional blood flow during different postural and gravitational conditions. The lungs were subsequently removed, air dried, and sectioned into approximately 2 cm(3) pieces. Flow to each piece was determined for the different conditions. Perfusion heterogeneity did not change significantly during weightlessness compared with normal and increased gravitational forces. Regional blood flow to each lung piece changed little despite alterations in posture and gravitational forces. With the use of multiple stepwise linear regression, the contributions of gravity and vascular structure to regional perfusion were separated. We conclude that both gravity and the geometry of the pulmonary vascular tree influence regional pulmonary blood flow. However, the structure of the vascular tree is the primary determinant of regional perfusion in these animals.     

Selected contribution: Variation and heritability for the adaptational response to exercise in genetically heterogeneous rats.

Adaptational response to aerobic exercise was artificially selected for across one generation in a founder population of 20 female and 20 male genetically heterogeneous rats (N:NIH). Selection for low and high response was based on the change in treadmill running capacity, assessed by meters (m) run to exhaustion before and after 24 days of modest treadmill running. The training response of the founder population averaged +222 m, with wide variation from a negative gain (-) of -110 m to a positive gain (+) of +430 m. Six pairs of the lowest (+13 m) and highest (+327 m) responders were mated. Mean response to training of the low-line (+242 m) offspring did not differ from the founder. The high-selected line gained 383 m from training, +161 m above the founder population. Narrow sense heritability estimated from regression of offspring on midparent values for response to training was 0.43 (P < 0.007). One generation of selection resulted in a 58% divide between the low and high lines. Selectively bred models of both intrinsic (untrained) and adaptation response can be useful in resolving the genetic basis of variation in aerobic capacity.     

Selected contribution: variation in acute hypoxic ventilatory response is linked to mouse chromosome 9.

Genetic determinants confer variation among inbred mouse strains with respect to the magnitude and pattern of breathing during acute hypoxic challenge. Specifically, inheritance patterns derived from C3H/HeJ (C3) and C57BL/6J (B6) parental strains suggest that differences in hypoxic ventilatory response (HVR) are controlled by as few as two genes. The present study demonstrates that at least one genetic determinant is located on mouse chromosome 9. This genotype-phenotype association was established by phenotyping 52 B6C3F2 (F2) offspring for HVR characteristics. A genome-wide screen was performed using microsatellite DNA markers (n = 176) polymorphic between C3 and B6 mice. By computing log-likelihood values (LOD scores), linkage analysis compared marker genotypes with minute ventilation (&Vdot;E), tidal volume (VT), and mean inspiratory flow (VT/TI, where TI is inspiratory time) during acute hypoxic challenge (inspired O2 fraction = 0.10, inspired CO2 fraction = 0.03 in N2). A putative quantitative trait locus (QTL) positioned in the vicinity of D9Mit207 was significantly associated with hypoxic VE (LOD = 4.5), VT (LOD = 4.0), and VT/TI (LOD = 5.1). For each of the three HVR characteristics, the putative QTL explained more than 30% of the phenotypic variation among F(2) offspring. In conclusion, this genetic model of differential HVR characteristics demonstrates that a locus approximately 33 centimorgans from the centromere on mouse chromosome 9 confers a substantial proportion of the variance in VE, VT, and VT/TI during acute hypoxic challenge.     

Cerebral blood flow velocity response to induced and spontaneous sudden changes in arterial blood pressure

The influence of different types of maneuvers that can induce sudden changes of arterial blood pressure (ABP) on the cerebral blood flow velocity (CBFV) response was studied in 56 normal subjects (mean age 62 yr, range 23-80). ABP was recorded in the finger with a Finapres device, and bilateral recordings of CBFV were performed with Doppler ultrasound of the middle cerebral arteries. Recordings were performed at rest (baseline) and during the thigh cuff test, lower body negative pressure, cold pressor test, hand grip, and Valsalva maneuver. From baseline recordings, positive and negative spontaneous transients were also selected. Stability of PCO2 was monitored with transcutaneous measurements. Dynamic autoregulatory index (ARI), impulse, and step responses were obtained for 1-min segments of data for the eight conditions by fitting a mathematical model to the ABP-CBFV baseline and transient data (Aaslid's model) and by the Wiener-Laguerre moving-average method. Impulse responses were similar for the right- and left-side recordings, and their temporal pattern was not influenced by type of maneuver. Step responses showed a sudden rise at time 0 and then started to fall back to their original level, indicating an active autoregulation. ARI was also independent of the type of maneuver, giving an overall mean of 4.7 +/- 2.9 (n = 602 recordings). Amplitudes of the impulse and step responses, however, were significantly influenced by type of maneuver and were highly correlated with the resistance-area product before the sudden change in ABP (r = -0.93, P < 0.0004). These results suggest that amplitude of the CBFV step response is sensitive to the point of operation of the instantaneous ABP-CBFV relationship, which can be shifted by different maneuvers. Various degrees of sympathetic nervous system activation resulting from different ABP-stimulating maneuvers were not reflected by CBFV dynamic autoregulatory responses within the physiological range of ABP.     

Theoretical analysis of occlusion techniques for measuring pulmonary capillary pressure.

We have developed a model including three serial compliant compartments (arterial, capillary, and venous) separated by two resistances (arterial and venous) for interpreting in vivo single pulmonary arterial or venous occlusion pressure profiles and double occlusion. We formalized and solved the corresponding system of equations. We showed that in this model 1) pulmonary capillary pressure (Pc) profile after arterial or venous occlusion has an S shape, 2) the estimation of Pc by zero time extrapolation of the slow component of the arterial occlusion profile (Pcao) always overestimates Pc, 3) symmetrically such an estimation on the venous occlusion profile (Pcvo) always underestimates Pc, 4) double occlusion pressure (Pcdo) differs from Pc. We evaluated the impact of varying parameter values in the model with parameter sets drawn either from the literature or from arbitrary arterial and venous pressures, being respectively 20 and 5 mmHg. Resulting Pcao-Pc differences ranged from 0.4 to 5.4 mmHg and resulting Pcvo-Pc differences ranged from -0.3 to -5.0 mmHg. Pcdo-Pc was positive or negative, its absolute value in general being negligible (< 1.1 mmHg).     

Hfe deficiency impairs pulmonary neutrophil recruitment in response to inflammation

Regulation of iron homeostasis and the inflammatory response are tightly linked to protect the host from infection. Here we investigate how imbalanced systemic iron homeostasis in a murine disease model of hereditary hemochromatosis (Hfe(-/-) mice) affects the inflammatory responses of the lung. We induced acute pulmonary inflammation in Hfe(-/-) and wild-type mice by intratracheal instillation of 20 μg of lipopolysaccharide (LPS) and analyzed local and systemic inflammatory responses and iron-related parameters. We show that in Hfe(-/-) mice neutrophil recruitment to the bronchoalveolar space is attenuated compared to wild-type mice although circulating neutrophil numbers in the bloodstream were elevated to similar levels in Hfe(-/-) and wild-type mice. The underlying molecular mechanisms are likely multifactorial and include elevated systemic iron levels, alveolar macrophage iron deficiency and/or hitherto unexplored functions of Hfe in resident pulmonary cell types. As a consequence, pulmonary cytokine expression is out of balance and neutrophils fail to be recruited efficiently to the bronchoalveolar compartment, a process required to protect the host from infections. In conclusion, our findings suggest a novel role for Hfe and/or imbalanced iron homeostasis in the regulation of the inflammatory response in the lung and hereditary hemochromatosis.     

Selected contribution: Ventilatory response to CO2 in high-altitude natives and patients with chronic mountain sickness.

The ventilatory responses to CO(2) of high-altitude (HA) natives and patients with chronic mountain sickness (CMS) were studied and compared with sea-level (SL) natives living at SL. A multifrequency binary sequence (MFBS) in end-tidal Pco(2) was employed to separate the fast (peripheral) and slow (central) components of the chemoreflex response. MFBS was imposed against a background of both euoxia (end-tidal Po(2) of 100 Torr) and hypoxia (52.5 Torr). Both total and central chemoreflex sensitivity to CO(2) in euoxia were higher in HA and CMS subjects compared with SL subjects. Peripheral chemoreflex sensitivity to CO(2) in euoxia was higher in HA subjects than in SL subjects. Hypoxia induced a greater increase in total chemoreflex sensitivity to CO(2) in SL subjects than in HA and CMS subjects, but peripheral chemoreflex sensitivity to CO(2) in hypoxia was no greater in SL subjects than in HA and CMS subjects. Values for the slow (central) time constant were significantly greater for HA and CMS subjects than for SL subjects.     

Selected contribution: Gender differences in the endothelin-B receptor contribution to basal cutaneous vascular tone in humans.

To test whether the contribution of endothelin-B (ET-B) receptors to resting vascular tone differs between genders, we administered the ET-B receptor antagonist BQ-788 into the forearm skin of 11 male and 11 female subjects by intradermal microdialysis. Skin blood flow was measured using laser-Doppler flowmetry at the microdialysis site. The probe was perfused with Ringer solution alone, followed by BQ-788 (150 nM) and finally sodium nitroprusside (28 mM) to effect maximal cutaneous vasodilation. Cutaneous vascular conductance (CVC) was calculated (laser-Doppler flowmetry/mean arterial pressure) and normalized to maximal levels (%max). In male subjects, baseline CVC was (mean +/- SE) 19 +/- 3%max and increased to 26 +/- 5%max with BQ-788 (P < 0.05 vs. baseline). In female subjects, baseline CVC was 13 +/- 1%max and decreased to 10 +/- 1%max in response to BQ-788. CVC responses to BQ-788 differed with gender (P < 0.05); thus the contribution of ET-B receptors to resting cutaneous vascular tone differs between men and women. In men, ET-B receptors mediate tonic vasoconstriction, whereas, in women, ET-B receptors mediate tonic vasodilation.     

Selected contribution: acute cellular and molecular responses to resistance exercise.

Training protocols apply sequential bouts of resistance exercise (RE) to induce the cellular and molecular responses necessary to produce compensatory hypertrophy. This study was designed to 1) define the time course of selected cellular and molecular responses to a single bout of RE and 2) examine the effects of interbout rest intervals on the summation of these responses. Rat muscles were exposed to RE via stimulation of the sciatic nerve in vivo. Stimulated and control muscles were obtained at various time points post-RE and analyzed via Western blot and RT-PCR. A single bout of RE increased intracellular signaling (i.e., phosphorylations) and expression of mRNAs for insulin-like growth factor-I system components and myogenic markers (e.g., cyclin D1, myogenin). A rest interval of 48 h between RE bouts resulted in much greater summation of myogenic responses than 24- or 8-h rest intervals. This experimental approach should be useful for studying the regulatory mechanisms that control the hypertrophy response. These methods could also be used to compare and contrast different exercise parameters (e.g., concentric vs. eccentric, etc.).     

Effect of vasopressin on myocardial capillary recruitment and coronary blood flow in the anesthetized rabbit.

The effects of infusion of arginine vasopressin (20 mU.kg-1.min-1) on coronary blood flow and the proportion of the coronary microvasculature perfused was studied in rabbit myocardium. Fluorescein isothiocyanate--dextran was injected into anesthetized open-chest rabbits to identify the perfused vessels and an alkaline phosphatase stain was employed to locate the total microvasculature. Coronary blood flow (radioactive microspheres) was studied in separate groups of rabbits. Vasopressin infusion caused bradycardia (243 +/- 19 to 165 +/- 22 beats/min, mean +/- SD) and an increase in mean blood pressure (92 +/- 18 to 104 +/- 12 mmHg) (1 mmHg = 133.32 Pa). Coronary blood flow decreased significantly with vasopressin from 209 +/- 68 to 97 +/- 36 mL.min-1.100 g-1. The proportion of the arteriolar bed per millimeter squared perfused decreased significantly after vasopressin from 54 +/- 13 to 44 +/- 21%, while the percentage of capillaries per millimeter squared increased significantly from 57 +/- 6 to 67 +/- 11%. There were no subepicardial versus subendocardial differences in any measured parameter. Thus, both coronary blood flow and the proportion of the arteriolar bed perfused decreased with vasopressin. However, compensation occurred in that the proportion of capillaries perfused increased. This indicated an independent level of control of the coronary arteriolar and capillary beds. These microvascular changes may help to maintain oxygen supply-demand balance with vasopressin in the heart.     

The response of subpleural pulmonary capillary endothelium to hydrothorax in rats

The principal focus of this study was to evaluate the hypothesis that increased interstitial fluid pressures served to stimulate de novo vesicle formation in pulmonary capillary endothelium. Direct measurements of interstitial fluid pressures within the alveolar septa pose great technical difficulty. The pleural space and subpleural capillaries are easily accessible, and thus, provide a more feasible model to test this hypothesis. After hydrostatic pressure of pleural space fluid was increased by periodic saline infusions into the pleural cavity, vesicle numerical densities were significantly increased in portions of the subpleural capillary endothelium. Those segments of the endothelium that directly apposed the interstitium of the visceral pleura displayed de novo vesicle formation. The endothelial segments located immediately adjacent to the alveolar epithelium were not affected by the elevated interstitial fluid pressures. In addition to the increased vesiculation, those same segments of the endothelium were characterized by increased attenuation of their cytoplasmic compartments. These conformational changes in the plasmalemma of portions of the subpleural capillary endothelium provide support to the tentative hypothesis, however, whether the increased numbers of vesicles contribute to a potential transendothelial transport system or expand a possible static network of membrane invaginations remains uncertain.     

Selected contribution: time course and heterogeneity of contractile responses in cultured human airway smooth muscle cells.

We measured the time course and heterogeneity of responses to contractile and relaxing agonists in individual human airway smooth muscle (HASM) cells in culture. To this end, we developed a microrheometer based on magnetic twisting cytometry adapted with a novel optical detection system. Ferromagnetic beads (4.5 microm) coated with Arg-Gly-Asp peptide were bound to integrins on the cell surface. The beads were twisted in a sinusoidally varying magnetic field at 0.75 Hz. Oscillatory bead displacements were recorded using a phase-synchronized video camera. The storage modulus (cell stiffness; G'), loss modulus (friction; G"), and hysteresivity (eta; ratio of G" to G') could be determined with a time resolution of 1.3 s. Within 5 s after addition of histamine (100 microM), G' increased by 2.2-fold, G" increased by 3.0-fold, and eta increased transiently from 0.27 to 0.34. By 20 s, eta decreased to 0.25, whereas G' and G" remained above baseline. Comparable results were obtained with bradykinin (1 microM). These changes in G', G", and eta measured in cells were similar to but smaller than those reported for intact muscle strips. When we ablated baseline tone by adding the relaxing agonist dibutyryl cAMP (1 mM), G' decreased within 5 min by 3.3-fold. With relaxing and contracting agonists, G' could be manipulated through a contractile range of 7.3-fold. Cell populations exhibited a log-normal distribution of baseline stiffness (geometric SD = 2.8) and a heterogeneous response to both contractile and relaxing agonists, partly attributable to variability of baseline tone between cells. The total contractile range of the cells (from maximally relaxed to maximally stimulated), however, was independent of baseline stiffness. We conclude that HASM cells in culture exhibit a clear, although heterogeneous, response to contractile and relaxing agonists and express the essential mechanical features characteristic of the contractile response observed at the tissue level.     

Relative contribution of gravity to pulmonary perfusion heterogeneity.

We designed a series of experiments and analyses to quantify the contribution of gravity to pulmonary perfusion heterogeneity. Regional pulmonary perfusion was measured in five anesthetized and ventilated dogs in both supine and prone positions by use of radiolabeled microspheres injected during apnea at functional residual capacity. Measurements of flow were repeated in each position, and the sequence of positions was prospectively designed to nullify any effect of order. The lungs of each animal were excised, perfused with saline until clear, dried at an inflation pressure of 25 cmH2O, and cut into 1.9-cm3 pieces. Each piece was weighed and the radioactivity determined in a scintillation counter. Measurement errors were minimized by excluding lung pieces that had greater than 25% airway and weighed less than 10 mg or greater than 60 mg. Weight-normalized flows in each position and repetition were determined for each lung piece. An analysis of variance model was used to identify the percentage of variation in regional flow that was due to position (supine vs. prone), to random error and time (measurement and repetition), and to structure, where structure was defined as the component of flow that remained constant across position and replication. The contributions of position, error/time, and structure to the total variability of flow across the five dogs were 7.8 +/- 0.6, 8.4 +/- 8.3, and 83.8 +/- 8.4%, (SD), respectively. Because the contribution of position represents the additive effect of gravity between two opposite positions, the contribution of gravity to perfusion heterogeneity in one position may be as little as 4%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulmonary capillary recruitment during airway hypoxia in the dog.

To study the effect of hypoxia on the pulmonary capillaries, windows were inserted in the chest wall of 9 pentobarbital-anesthetized dogs. A microscope with an image-superimposing device was used to make drawings of the perfused capillaries. Summed lengths of individual perfused capillaries in the drawing were determined with a map-measuring tool. Total capillary length was constant between PaO2 of 160 and 70 Torr. As PaO2 fell below 70 Torr, recruitment of previously unperfused capillaries occurred in every case; at PaO2 of 40 Torr, the total length of perfused capillaries was about 4 times greater than during normoxia. There was no correlation between the recruitment of capillaries and alterations in left atrial pressure, only a weak correlation with cardiac output changes, but a very strong correlation with increased pulmonary artery pressure. This implies that recruitment was probably caused by vasoconstriction within the lung.     

Dynamic response of local pulmonary blood flow to alveolar gas tensions: experiment

The purpose of this study was to investigate the mechanism that causes a damped oscillatory response of local pulmonary blood flow to local hypoxia. The left lower lobe (LLL) of 10 anesthetized dogs was ventilated independently but synchronously with the rest of the lungs. Blood flow to the LLL as a proportion of total flow (QLLL/QT) was measured during the on-transient of the hypoxic response when LLL inspirate was changed from O2 to N2. There was a damped oscillatory response of QLLL/QT to hypoxia (34 of 40 trials). In contrast, the off-transient was always monotonic. There was no enhancement of the steady state or dynamic hypoxic response with repeated challenges. Local alveolar hypercapnia caused a damped oscillatory response in the presence of local hypoxia (15 of 20 trials), but there was no response in the presence of local hyperoxia. We conclude that 1) the dynamic pulmonary vascular response to O2 and CO2 are not additive because the response to CO2 is attenuated by hyperoxia and 2) the damped oscillatory response that occurs during hypoxia is the result of changes of local alveolar CO2 per se.