Effects of physical exercise and anti-G suit inflation on atrial natriuretic factor plasma level

The purpose of this study was to measure the effect of enhanced venous return on atrial natriuretic factor (ANF) secretion during exercise and upright posture and the consequences on renin angiotensin aldosterone system (RAAS) activity. Six healthy male subjects were submitted to four different procedures. All procedures were performed in the same position, i.e. riding on a support with legs hanging. Two procedures were performed at rest: the subjects were studied after a 25-min rest in this position, with and without the lower limb fitted with an anti-G suit inflated to 60 mmHg. Two procedures were carried out with physical exercise; arm-cranking was performed in the same position with and without the anti-G suit inflated to 60 mmHg. Venous blood was collected before and after each procedure in order to measure plasma ANF, plasma aldosterone concentration (PAC), plasma renin activity (PRA), corticotrophin (ACTH) and catecholamine level. The data mean +/- SEM showed that the ANF plasma level decreased significantly (p less than 0.05) from 32.5 +/- 4 to 28 +/- 6 pg.ml-1 after a 20-min rest in the upright posture, whereas this effect was absolished with anti-G suit inflation. Physical exercise with and without the anti-G suit increased the ANF level above control values (60 +/- 13.6 pg.ml-1 and 53 +/- 13 pg.ml-1): anti-G suit inflation had no significant effect. PRA increased after rest in an upright posture and during physical exercise; anti-G suit inflation abolished this increase in both conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of hypergravity on the distributions of lung ventilation and perfusion in sitting humans assessed with a simple two-step maneuver.

Increased gravity impairs pulmonary distributions of ventilation and perfusion. We sought to develop a method for rapid, simultaneous, and noninvasive assessments of ventilation and perfusion distributions during a short-duration hypergravity exposure. Nine sitting subjects were exposed to one, two, and three times normal gravity (1, 2, and 3 G) in the head-to-feet direction and performed a rebreathing and a single-breath washout maneuver with a gas mixture containing C(2)H(2), O(2), and Ar. Expirograms were analyzed for cardiogenic oscillations (COS) and for phase IV amplitude to analyze inhomogeneities in ventilation (Ar) and perfusion [CO(2)-to-Ar ratio (CO(2)/Ar)] distribution, respectively. COS were normalized for changes in stroke volume. COS for Ar increased from 1-G control to 128 +/- 6% (mean +/- SE) at 2 G (P = 0.02 for 1 vs. 2 G) and 165 +/- 13% at 3 G (P = 0.002 for 2 vs. 3 G). Corresponding values for CO(2)/Ar were 135 +/- 12% (P = 0.04) and 146 +/- 13%. Phase IV amplitude for Ar increased to 193 +/- 39% (P = 0.008) at 2 G and 229 +/- 51% at 3 G compared with 1 G. Corresponding values for CO(2)/Ar were 188 +/- 29% (P = 0.02) and 219 +/- 18%. We conclude that not only large-scale ventilation and perfusion inhomogeneities, as reflected by phase IV amplitude, but also smaller-scale inhomogeneities, as reflected by the ratio of COS to stroke volume, increase with hypergravity. Except for small-scale ventilation distribution, most of the impairments observed at 3 G had been attained at 2 G. For some of the parameters and gravity levels, previous comparable data support the present simplified method.     

Hemodynamic effects of anti-G suit inflation in a 1-G environment

This study evaluated effects of various anti-G inflation pressures on cardiac volumes and the relationship of these volume changes to mean arterial pressure changes. Ventricular volumes were calculated using two-dimensional echocardiography. An anti-G suit was inflated to 2, 4, and 6 psi in the standing and supine positions for 10 male subjects. In the supine position, mean arterial pressure increased from base line for all three inflation pressures (P = 0.05). The end-diastolic volume increased after 2-psi inflation (P = 0.03). Cardiac output or stroke volume did not change. After standing, mean arterial pressure (P = 0.002), end-diastolic volume (P = 0.002), and stroke volume (P = 0.05) fell after suit deflation. Peripheral vascular resistance fell in the 2- and 4-psi inflation profiles. In the standing protocol, mean arterial pressure, end-diastolic volume, stroke volume, and cardiac output rose with all three inflation pressures (P less than 0.05). After reclining, heart rate increased (P = 0.02) and mean arterial pressure fell (P less than 0.05) in the 4- and 6-psi inflation profiles after suit deflation. Increases in mean arterial pressure are caused by increases in cardiac preload and cardiac output after inflation of the anti-G suit while subjects were standing. Increased cardiac preload was not consistently seen after inflation while subjects were supine. Changes in end-diastolic volume and mean arterial pressure were dependent on the pressure used to inflate the anti-G suit.     

Effects of inertial load and countermeasures on the distribution of pulmonary blood flow.

We assessed the influence of cranial-to-caudal inertial force (+G(z)) and the countermeasures of anti-G suit and positive pressure breathing during G (PBG), specifically during +G(z), on regional pulmonary blood flow distribution. Unanesthetized swine were exposed randomly to 0 G(z) (resting), +3 G(z), +6 G(z), and +9 G(z), with and without anti-G suit and PBG with the use of the Air Force Research Laboratory centrifuge at Brooks Air Force Base (the gravitational force of the Earth, that is, the dorsal-to-ventral inertial force, was present for all runs). Fluorescent microspheres were injected into the pulmonary vasculature as a marker of regional pulmonary blood flow. Lungs were excised, dried, and diced into approximately 2-cm(3) pieces, and the fluorescence of each piece was measured. As +G(z) was increased from 0 to +3 G(z), blood flow shifted from cranial and hilar regions toward caudal and peripheral regions of the lung. This redistribution shifted back toward cranial and hilar regions as anti-G suit inflation pressure increased at +6 and +9 G(z). Perfusion heterogeneity increased with +G(z) stress and decreased at the higher anti-G suit pressures. The distribution of pulmonary blood flow was not affected by PBG. ANOVA indicated anatomic structure as the major determinant of pulmonary blood flow.     

Effects of hypergravity and anti-G suit pressure on intraregional ventilation distribution during VC breaths.

The effects of increased gravity in the head-to-foot direction (+G(z)) and pressurization of an anti-G suit (AGS) on total and intraregional intra-acinar ventilation inhomogeneity were explored in 10 healthy male subjects. They performed vital capacity (VC) single-breath washin/washouts of SF(6) and He in +1, +2, or +3 G(z) in a human centrifuge, with an AGS pressurized to 0, 6, or 12 kPa. The phase III slopes for SF(6) and He over 25-75% of the expired VC were used as markers of total ventilation inhomogeneity, and the (SF(6) -- He) slopes were used as indicators of intraregional intra-acinar inhomogeneity. SF(6) and He phase III slopes increased proportionally with increasing gravity, but the (SF(6) -- He) slopes remained unchanged. AGS pressurization did not change SF(6) or He slopes significantly but resulted in increased (SF(6) -- He) slope differences at 12 kPa. In conclusion, hypergravity increases overall but not intraregional intra-acinar inhomogeneity during VC breaths. AGS pressurization provokes increased intraregional intra-acinar ventilation inhomogeneity, presumably reflecting the consequences of basilar pulmonary vessel engorgement in combination with compression of the basilar lung regions.     

Inter- and intraregional ventilation inhomogeneity in hypergravity and after pressurization of an anti-G suit.

This study assessed the effects of increased gravity in the head-to-foot direction (+G(z)) and anti-G suit (AGS) pressurization on functional residual capacity (FRC), the volume of trapped gas (V(TG)), and ventilation distribution by using inert- gas washout. Normalized phase III slope (Sn(III)) analysis was used to determine the effects on inter- and intraregional ventilation inhomogeneity. Twelve men performed multiple-breath washouts of SF(6) and He in a human centrifuge at +1 to +3 G(z) wearing an AGS pressurized to 0, 6, or 12 kPa. Hypergravity produced moderately increased FRC, V(TG), and overall and inter- and intraregional inhomogeneities. In normogravity, AGS pressurization resulted in reduced FRC and increased V(TG), overall, and inter- and intraregional inhomogeneities. Inflation of the AGS to 12 kPa at +3 G(z) reduced FRC markedly and caused marked gas trapping and intraregional inhomogeneity, whereas interregional inhomogeneity decreased. In conclusion, increased +G(z) impairs ventilation distribution not only between widely separated lung regions, but also within small lung units. Pressurizing an AGS in hypergravity causes extensive gas trapping accompanied by reduced interregional inhomogeneity and, apparently, results in greater intraregional inhomogeneity.     

Cardiovascular responses to military antishock trouser inflation during standing arm exercise

Military antishock trousers (MAST) inflated to 50 mmHg were used with 12 healthy males (mean age 28 +/- 1 yr) to determine the effects of lower-body positive pressure on cardiac output (Q), stroke volume (SV), heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MABP), total peripheral resistance (TPR), and O2 uptake (VO2) during graded arm-cranking exercise. Subjects were studied while standing at rest and at 25, 50, and 75% of maximal arm-cranking VO2. At each level, rest or work was continued for 6 min with MAST inflated and for 6 min with MAST deflated. Order of inflation and deflation was alternated at each experimental rest or exercise level. Measurements were obtained during the last 2 min at each level. Repeated-measures analysis of variance revealed significant increases (P less than 0.001) in Q, SV, and MABP and a consistent decrease in HR with MAST inflation. There was no apparent change in Q/VO2 between inflated and control conditions. There was no effect of MAST inflation on VO2 or TPR. MAST inflation counteracts the gravitational effect of venous return in upright exercise, restoring central blood volume and thereby increasing Q and MABP from control. HR is decreased consequent to increased MABP through arterial baroreflexes. The associated decrease in TPR is not observed, being offset by the mechanical compression of leg vasculature with MAST inflation.     

Morphological evidence for alveolar recruitment during inflation at high transpulmonary pressure

The effect of continuous inflation of lungs at 30 cmH2O transpulmonary pressure (Ptp) on air-space size was assessed by chord length-frequency distribution analysis. Lungs from gerbils were excised, allowed to collapse freely, and inflated to 30 cmH2O Ptp in a humidified chamber kept at 37 degrees C. When the lungs appeared fully inflated with no observable pleural surface atelectasis, the left lung was occluded while the right was maintained at 30 cmH2O for 10 min longer and then occluded. During this time, the right lung increased its volume from 70 to 100%. Then both lungs were quick frozen, freeze dried, and embedded in glycol methacrylate, and 1- to 2-microns-thick histological sections cut. Lungs from a control group of gerbils were similarly inflated to 30 cmH2O, both left and right were occluded, the left was quick frozen immediately, and the right was frozen 10 min later. Chord lengths of air spaces from cranial and caudal lobes of lungs were acquired using a Dapple Systems image analyzer, and a two-population frequency distribution was generated for analysis with an IBM PC. The results indicate that the volume increase during continuous inflation at 30 cmH2O Ptp was associated with a shift in the chord length distribution toward the smaller chord lengths. A two-population statistical analysis indicated that the inflation resulted in an increase in the relative proportion of smaller chord lengths, with no increase in the mean of this smaller population. We conclude that continuous inflation at 30 cmH2O Ptp results in alveolar recruitment.     

Identification of heterotrimeric G protein α and β subunits in rice

Like those in mammals, heterotrimeric G protein complexes have been implicated in signal transduction pathways in plants; however, the subunits themselves have not been isolated. In this study, the rice heterotrimeric G protein subunits α (Gα) and β (Gβ) were purified by affinity chromatography using anti-Gα and -Gβ antibodies and SDS-PAGE. Six and seven peptides, respectively, were identified by mass spectrometry and identified as the translation products of the Gα gene RGA1 and Gβ gene RGB1. During purification, the subunits dissociated easily from the G protein complex.     

Effect of cardiogenic oscillations on gas mixing during tracheal insufflation of oxygen

In a previous study using tracheal insufflation of O2 (TRIO) at a rate of 2 l/min, we showed that anesthetized paralyzed dogs could be adequately oxygenated for up to 5 h, albeit with hypercapnia (mean arterial PCO2 approximately 160 Torr). To examine the contribution of cardiogenic oscillations in producing this gas exchange, we studied seven anesthetized paralyzed dogs weighing between 19.6 and 25.5 kg and quantified gas transport by analyzing continuous N2-washout curves in vivo and postmortem. We found that cardiogenic oscillations increase gas mixing roughly fourfold and that this value was independent of insufflation flow rate (0.2-10.0 l/min). Our results lend indirect evidence that, with regard to gas exchange, there are two mechanistically different zones in the lung during TRIO. One zone, located in the more peripheral areas of the lung, is dominated by the effects of cardiac oscillations and molecular diffusion and accounts for the increase in gas mixing found in the alive vs. dead dog. A second zone, close to the insufflated jet of O2, uses convective streaming to produce greater gas mixing at higher flows.     

Computer-aided S-phase fraction determination in DNA static cytometry in breast cancer. A preliminary methodologic study on cytologic material.

This methodologic study was performed on a single-cell-cycle breast carcinoma to evaluate the feasibility of computer-aided S-phase fraction determination in DNA static cytometry. The investigation was performed on Feulgen-stained cytologic material in which the total optical density values of 1,000 consecutive, randomly selected nuclei were analyzed (MultiCycle software). A good correlation in the S-phase fraction value with flow cytometry was obtained when the G2/G1 ratio was fixed at 1.95, when the histogram data points were smoothed at least once and the coefficient of variation of the G2 peak was the same as that of G0-G1 or when a first-order S-phase polynomial model was used. The percentages of nuclei in G0-G1 and G2 were somewhat similar to those obtained with flow cytometry. The greatest discrepancy with flow cytometry was observed in the value of the coefficient of variation of the G0-G1 peak of the static cytometric data: it was at least twice as great. It always remained high despite the software options used. As for the influence of the sample size in the S-phase calculation, the software was also run on samples of 600 and 200 nuclei. When the G2/G1 ratio was fixed at 1.95, the data obtained from 600 nuclei did not differ from those obtained with 1,000 nuclei, whereas an analysis on 200 nuclei showed a substantial variation. The software also allowed calculation of the ratio of the G0-G1 peak of the neoplastic population against that of the diploid reference (DNA index), the value of which in flow cytometry was 1.0.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of cardiogenic gas mixing on arterial O2 and CO2 tensions during breath holding

To examine the effect of cardiogenic gas mixing on gas exchange we measured arterial tension of O2 (PaO2) and arterial tension of CO2 (PaCO2) during 3- to 5-min breath holds (BH) before and after infusing 50 ml of saline into the pericardial space (PCF) of seven anesthetized, paralyzed, mechanically ventilated dogs. During BH the ventilator was disconnected and a bias flow of 50% O2 at 4-5 l/min was delivered through the side ports of a small catheter whose tip was positioned 1 cm cephalad of the carina. Paired runs, alternately with and without PCF, were performed in triplicate in each dog. Initial PaO2 was similar for control runs [81 +/- 3 mmHg (SE)] and PCF runs (78 +/- 3 mmHg; P greater than 0.1). After 3-min BH, PaO2 in PCF runs (33 +/- 3 mmHg) was less than that in control runs (58 +/- 4 mmHg) (P less than 0.001). In contrast, the pattern of PaCO2 during BH did not differ with PCF. After 3-min BH, PaCO2 was 49 +/- 3 mmHg with PCF and 49 +/- 2 mmHg in the control runs (P greater than 0.7). In two dogs, repeated 50-ml reductions in lung volume, produced by rib cage compression, did not alter the time course of PaO2 during BH. Although cardiac output decreased slightly with PCF, hemodynamic changes due to PCF were unlikely to account for the observed fall in PaO2. Our results indicate a substantial effect of cardiogenic gas mixing on O2 uptake when tracheal gas is O2 enriched during breath holding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of antigravity suit inflation on cardiovascular, PRA, and PVP responses in humans

Blood pressure, pulse rate (PR), serum osmolality and electrolytes, as well as plasma vasopressin (PVP) and plasma renin activity (PRA), were measured in five men and two women [mean age 38.6 +/- 3.9 (SE) yr] before, during, and after inflation of an antigravity suit that covered the legs and abdomen. After 24 h of fluid deprivation the subjects stood quietly for 3 h: the 1st h without inflation, the 2nd with inflation to 60 Torr, and the 3rd without inflation. A similar control noninflation experiment was conducted 10 mo after the inflation experiment using five of the seven subjects except that the suit was not inflated during the 3-h period. Mean arterial pressure increased by 14 +/- 4 (SE) Torr (P less than 0.05) with inflation and decreased by 15 +/- 5 Torr (P less than 0.05) after deflation. Pulse pressure (PP) increased by 7 +/- 2 Torr (P less than 0.05) with inflation and PR decreased by 11 +/- 5 beats/min (P less than 0.05); PP and PR returned to preinflation levels after deflation. Plasma volume decreased by 6.1 +/- 1.5% and 5.3 +/- 1.6% (P less than 0.05) during hours 1 and 3, respectively, and returned to base line during inflation. Inflation decreased PVP from 6.8 +/- 1.1 to 5.6 +/- 1.4 pg/ml (P less than 0.05) and abolished the significant rise in PRA during hour 1. Both PVP and PRA increased significantly after deflation: delta = 18.0 +/- 5.1 pg/ml and 4.34 +/- 1.71 ng angiotensin I X ml-1 X h-1, respectively. Serum osmolality and Na+ and K+ concentrations were unchanged during the 3 h of standing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiogenic oscillations in He and SF6 expirograms during airway and venous loading

Cardiogenic oscillations in the expired partial pressure profiles of two inert gases (He and SF6) were monitored in seven anesthetized paralyzed mechanically ventilated dogs. He and SF6 were administered either intravenously by a membrane oxygenator and partial arteriovenous bypass [venous loading (VL)] or by washin into lung gas [airway loading (AL)]. The single-breath expirograms obtained during constant-flow expiration after inspiration of test gas-free air displayed distinct and regular cardiogenic oscillations. The relative oscillation amplitude (ROA), calculated as oscillation amplitude divided by mixed expired-inspired partial pressure difference, was in the range of 1-8%. The ROA for both He and SF6 was approximately 4.2 times higher in VL than in AL, which indicated that among lung units that emptied sequentially in the cardiac cycle, the effects of alveolar ventilation-perfusion (VA/Q) inequality were more pronounced than those of alveolar ventilation-alveolar volume (VA/VA) inequality. In AL, He and SF6 oscillations were 180 degrees out of phase compared with CO2 and O2 oscillations and with He and SF6 oscillations in VL, which suggests that regions with low VA/VA had high VA/Q and very low Q/VA. The ROA was practically unaffected by breath holding in both AL and VL, which indicates that there was little diffusive or convective (cardiogenic) mixing between the lung units that were responsible for cardiogenic oscillations. The ROA was consistently higher for He than for SF6, and the He-to-SF6 ratio was independent of route of test gas loading, averaging 1.6 in both AL and VL. This result may be explained by laminar Taylor dispersion, whereby oscillations generated in peripheral lung regions are dissipated in inverse proportion to diffusion coefficient during transit through the proximal (larger) airways.     

Effect of alveolar and pleural pressures on interstitial pressures in isolated dog lungs

We report the first direct measurements of perialveolar interstitial pressures in lungs inflated with negative pleural pressure. In eight experiments, we varied surrounding (pleural) pressure in a dog lung lobe to maintain constant inflation with either positive alveolar and ambient atmospheric pleural pressures (positive inflation) or ambient atmospheric alveolar and negative pleural pressures (negative inflation). Throughout, vascular pressure was approximately 4 cmH2O above pleural pressure. By the micropuncture servo-null technique we recorded interstitial pressures at alveolar junctions (Pjct) and in the perimicrovascular adventitia (Padv). At transpulmonary pressure of 7 cmH2O (n = 4), the difference of Pjct and Pady from pleural pressure of 0.9 +/- 0.4 and -1.1 +/- 0.2 cmH2O, respectively, during positive inflation did not significantly change (P less than 0.05) after negative inflation. After increase of transpulmonary pressure from 7 to 15 cmH2O (n = 4), the decrease of Pjct by 3.3 +/- 0.3 cmH2O and Pady by 2.0 +/- 0.4 cmH2O during positive inflation did not change during negative inflation. The Pjct-Pady gradient was not affected by the mode of inflation. Our measurements indicate that, in lung, when all pressures are referred to pleural or alveolar pressure, the mode of inflation does not affect perialveolar interstitial pressures.     

Pressure-flow behavior of a bronchopleural fistula during mechanical ventilation with positive pressure

We examined the mechanical behavior of a bronchopleural fistula created by sectioning a small subpleural bronchus in seven anesthetized lambs. The pressure across the fistula was measured as the difference between the pressure recorded by a retrograde bronchial catheter inserted in the vicinity of the fistula and the outflow pressure at the fistula exit. The effective resistance of the fistula (Rf) was computed by dividing this pressure difference by the gas flow through the fistula measured at the outlet of an intrapleural tube adjacent to the fistula. Rf increased by 114 +/- 25% (SE) when we inflated the lungs in a stepwise manner from a tracheal pressure of 2-20 cmH2O. Rf also increased when inflation pressure varied continuously; this increase, however, was less evident when we decreased the inflation time from 1.0 to 0.2 s. The relationship between Rf and lung volume was similar during the stepwise inflations and deflations but showed marked hysteresis during the continuous inflation-deflation maneuvers, when Rf was greater during deflation than inflation. Our results suggest that the fistula behaves as a compliant pathway whose relevant transmural pressure is the transmural pressure at or near the fistula's exit. We attribute the increase in Rf during inflation to decreases in transmural pressure caused by convective and dissipative losses inside the fistula and by the stress applied by the chest wall on the outer surface of the fistula.     

G-suit inflation to 50 mmHg alters the cardiovascular transients when entering micro-G in parabolic flight

In the present experiments it was decided to have each test-subject serve as his own control by fitting the test-subjects with a G-suit and comparing the condition of inflated G-suit to the normal situation. G-suit inflation was intended to only displace blood on the venous side of the circulation, not to increase total peripheral resistance. Therefore, a very modest inflation of 50 mmHg was applied. This was considered sufficient to expel most of the blood from the venous pool in abdomen and legs, even under the condition of increased G-loading in the pull-up phase. The parabolas were to be undergone in three body positions: standing upright, sitting and supine. The prediction of the experimental outcome was that we would find no difference between transients with and without G-suit inflation in the supine position, that an initial overshoot in pressure and stroke volume in the upright position would be very much damped by the G-suit, even more in the standing than in the sitting position. Studies were performed in 5 flights of NASA's KC-135, in January 1993. Per flight 40 parabolas were flown in an adapted 'roller coaster profile', i.e. 0-G phases were followed by a 2-G pull-out phase, after a very brief 1-G phase again followed by the next 2-G pull-up phase. This sequence was flown for 10 parabolas, then a 1-G horizontal flight period was inserted. The first 3 parabolas of each set of 10 the subjects were sitting upright, seat belt fastened. The next three they were standing, feet stuck under a load strap on the floor, stabilizing themselves by a grip on the ceiling. Then three parabolas were flown with the test-subject supine, loosely attached to the floor by a load strap and further aided by a grip to another strap on the floor. The last parabola of a set was used as 'spare' to repeat any failed maneuver.     

Pulmonary lymphatic clearance of 99mTc-DTPA from air spaces during lung inflation and lung injury

A total of 22 sheep with lymphatic cannulas were used to determine if 99mTc-labeled diethylenetriaminepentaacetic acid (DTPA) clears directly from the air spaces of the lungs into the lymph vessels. Each sheep was anesthetized and ventilated with an aerosol of the DTPA for 2-5 min, and the DTPA activities in the lymph and plasma were measured every 15 min for 2 h. After the first 45 min, the average ratio of the DTPA in the lymph to that in the plasma (L/P) was 1.03 +/- 0.06 (SD) in the six control experiments and 1.11 +/- 0.05 in the six experiments in which the lungs were inflated with a positive end-expired pressure of 10 cmH2O throughout the study. Direct movement of the DTPA from the air spaces into the lymph was not necessary to account for the DTPA clearance in these experiments because the L/P ratio was not significantly different from 1.0. Eight additional sheep received intravenous infusions of air at 0.2 ml.kg-1.min-1 for 2 h to induce lung injury before depositing the DTPA. In these sheep L/P was 1.53 +/- 0.28, which was significantly higher than the value measured in the control group (P less than 0.01). We considered the possibility that the increased L/P ratio in these sheep could be due to alterations in the distribution of the blood flow to the tissue, but the L/P ratio in four sheep whose distribution of blood flow was altered by inflation of a balloon in the right pulmonary artery was 1.05 +/- 0.10, the same as the control value.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulmonary venous pressure increases during alveolar hypoxia in isolated lungs of newborn pigs.

The purpose of this study was to determine whether pulmonary venous pressure increases during alveolar hypoxia in lungs of newborn pigs. We isolated and perfused with blood the lungs from seven newborn pigs, 6-7 days old. We maintained blood flow constant at 50 ml.min-1.kg-1 and continuously monitored pulmonary arterial and left atrial pressures. Using the micropuncture technique, we measured pressures in 10 to 60-microns-diam venules during inflation with normoxic (21% O2-69-74% N2-5-10% CO2) and hypoxic (90-95% N2-5-10% CO2) gas mixtures. PO2 was 142 +/- 21 Torr during normoxia and 20 +/- 4 Torr during hypoxia. During micropuncture we inflated the lungs to a constant airway pressure of 5 cmH2O and kept left atrial pressure greater than airway pressure (zone 3). During hypoxia, pulmonary arterial pressure increased by 69 +/- 24% and pressure in small venules increased by 40 +/- 23%. These results are similar to those obtained with newborn lambs and ferrets but differ from results with newborn rabbits. The site of hypoxic vasoconstriction in newborn lungs is species dependent.     

Lack of gas bladder inflation by the larvae of zebrafish in the absence of an air-water interface

Compared to a control gas bladder inflation rate of 95·1±1·9%, zebrafish Danio rerio larvae 72 h post-fertilization maintained in closed chambers had an inflation rate of just 19·1±7·7%. Larval survivorship through 10 days in closed chambers (32%) was significantly less than that in open chambers (76%), and the extent of spinal curvature was significantly higher among larvae maintained in closed chambers. Larvae which failed to inflate their gas bladder showed very little change in body length, and had a final dry weight c. 14% of that for control larvae. The small number of larvae with inflated gas bladders found in closed chambers might be attributed to the inadvertent introduction of small bubbles into two replicates. These results indicate that access to an air-water interface is critical for the normal development of zebrafish larvae, but also that a small, submerged, spherical gas volume may to a limited extent be used for initial gas bladder inflation.