bluuebunny/crossref_metadata_2025 huggingface dataset:
Continuous measurement of minute ventilation and gaseous metabolism of newborn infants
Authors: Schulze K. , Kairam R. , Stefanski M. , Sciacca R. , James L. S.
Published: December 2017

A system of instrumentation for continuous measurement of gaseous metabolism and minute volume (VI) in the human newborn is described. O2 uptake and CO2 production are measured by open-circuit techniques utilizing a Servomex OA184 differential paramagnetic O2 analyzer and a BEckman LB-2 infrared CO2 analyzer. VI is measured with bias-flow pneumotachometry. Bench performance is described, methodological errors are defined, and clinical data are presented. The instrumentation is capable of safe, accurate, and continuous measurement of respiratory and metabolic variables in low-birth-weight infants.
Relations among recoil pressure, surface area, and surface tension in the lung
Authors: Wilson T. A.
Published: December 2017

The difference between energy stored in air- and saline-filled lungs is the sum of surface energy and the energy of tissue distortion caused by surface tension. The surface energy is zeta gamma dS, where gamma is surface tension and S is surface area. There is no corresponding relation between tissue energy and measurable variables. However, two equations can be obtained from the expression for the total energy difference. One is the statement that the total energy of the lung is minimum at equilibrium, and the other is the statement of conservation of mechanical energy as lung volume changes. The expression for tissue energy is eliminated between the two equations to obtain a single relation among the variables of interest: recoil pressure, surface area, and surface tension. Published data on recoil pressure and surface area of saline-filled, air-filled, and detergent-washed rabbit lungs are used in these equations to determine surface tension as a function of lung volume. The values of surface tension deduced from this analysis are lower than the values that would be obtained if the additional tissue forces in the air-filled lung were neglected. The contribution of tissue forces to the added recoil of the air-filled lung increases with increasing lung volume and accounts for approximately half the additional recoil at high lung volume.
Blood and blood vessel wall changes induced by decompression sickness in dogs
Authors: Levin L. L. , Stewart G. J. , Lynch P. R. , Bove A. A.
Published: December 2017

Healthy female dogs of mixed breed were anesthetized with pentobarbital sodium and given 51Cr-labeled autologous red blood cells and 125I-labeled anticanine vessel wall fiber (collagen and elastin) antibody. The anesthetized dogs were exposed to the equivalent of a 220-ft dive on air for 40-45 min (descent rate 75 ft/min, ascent rate 60 ft/min). The animal's condition was adjusted by additional shorter and/or shallower dives. Four dogs had mild decompression sickness (DCS), and seven had severe DCS judged by electrocardiogram. Three of the seven died before completion of the experiment. Permeability of the endothelial sheet of jugular veins and carotid arteries to the tracer (125I-gamma-globulin) was significantly increased in animals with severe but not mild DCS. There was slight hemoconcentration (increased capillary and venular permeability). Scanning electron microscopy showed that the endothelium was grossly intact with no evidence of mechanical damage, but giant cells (derived from monocytes) frequently adhered to the endothelium. Leukocytes and platelets adhered occasionally. Fibrin monomer was found in the plasma. Thus DCS is accompanied by endothelial cell alteration and limited blood cell adhesion to vessel walls in addition to activation od the clotting mechanism. s
Increasing intracranial pressure with air causes air embolism, not neurogenic pulmonary edema
Authors: Luce J. M. , Huseby J. S. , Robertson H. T.
Published: December 2017

In an effort to duplicate a previous model of neurogenic pulmonary edema (NPE), we maintained intracranial pressure (PIC) at 20 Torr below mean arterial pressure in six closed-chested dogs anesthetized with alpha-chloralose and urethan. This was accomplished by infusing 1) isotonic saline (NS), 2) a gas mixture of 80% helium and 20% oxygen (HeO2), or 3) 100% carbon dioxide (CO2) through a trephined hole into the subdural space. Three more animals were studied with the same protocol after thoracotomy to permit Doppler examination for bubbles in the left pulmonary artery. Significant increases in pulmonary artery pressure, pulmonary vascular resistance, physiological shunt, dead space fraction, and hypoxemia were recorded when Pic was elevated by HeO2 infusion but not during infusion of NS or CO2. Pulmonary gas-bubble embolism was suggested by an increase in the fraction of helium in expired gas during HeO2 infusion and confirmed by Doppler recordings. We conclude that increasing Pic with air produces the physiological changes of air embolism; this is not a satisfactory model for investigating NPE.
An invertible simple equation for computation of blood O2 dissociation relations
Authors: Lobdell D. D.
Published: December 2017

An equation that will represent blood O2 dissociation relations over the saturation range of 0-100% and be invertible is presented. The Hill equation is contained as a special case of this form. Determination of the four parameters of the equations by standard dissociation curves presented by Severinghaus gives an equation of improved accuracy when contrasted to previous treatments. A program for use of this equation with certain hand-held calculators is available.
Influence of skin temperature on central thermoregulatory control of leg blood flow
Authors: Proppe D. W.
Published: December 2017

This study examined the influence of elevated skin temperature (Tsk) on the central thermoregulatory control of leg blood flow in five unanesthetized, chronically instrumented, resting baboons (Papio anubis and P. cynocephalus). In each experiment, mean iliac blood flow (MIBF), mean arterial blood pressure, arterial blood temperature (Tbl), and Tsk were measured, and iliac vascular conductance (IVC) was calculated. A heat exchanger was incorporated into a chronic arteriovenous femoral shunt to control Tbl. The protocol consisted of raising Tbl approximately 2.6 degrees C in thermoneutral environment (cool Tsk) an then again after Tsk had been elevated by environmental heating. A major influence of raising Tsk was the lowering of threshold Tbl at which the rise in MIBF and IVC commenced. This threshold Tbl was lowered at least 0.8 degrees C on the average. Also, over the whole range of Tbl studied (37.0-39.6 degrees C), MIBF and IVC were higher at high Tsk than at cool Tsk. Thus an elevation of Tsk significantly influences the control of skin blood flow by central thermoreceptors.
Pulmonary defense mechanisms in Boa constrictor
Authors: Grant M. M. , Brain J. D. , Vinegar A.
Published: December 2017

We studied aerosol deposition and the response to inhaled particles and irritants in lungs of Boa constrictor. Snakes which breathed submicrometric particles radiolabeled with 99mTc retained 41.4 +/- 9.9% of the aerosol in the trachea, 42.5 +/- 8.8% in the anterior faveolar regions, and 8.7 +/- 4.1% in the posterior saccular regions of the lungs. Low activity recovered in the gastrointestinal tract over a 5-h period following aerosol exposure indicated slow clearance of inhaled particles. In contrast to mammalian lungs, there are no macrophages resident on the surface of boa lungs, and uningested particles persist for up to 4 days without being phagocytized. Particles and irritant stimuli (Fe2O3, endotoxin, and N-formylmethionylphenylalanine) elicited only eosinophilic granulocytes that were not phagocytic. The numbers of these cells peaked at 24 h following exposure and declined gradually over the next 7 days. Lavage fluid from stimulated snake lungs contained many large lamellar figures continuous with tubular myelin, a form of surfactant. Very little of this material was recovered from control lungs. Response to inhaled particles and lung injury in boas increased surfactant release, elicited eosinophilic granulocytes, but did not recruit phagocytic mononuclear cells.
Comparison of phrenic motoneuron activity during eupnea and gasping
Authors: St John W. M. , Bartlett D.
Published: December 2017

Single-fiber phrenic nerve action potentials were recorded together with activity of contralateral whole phrenic nerve rootlets during eupnea and gasping in decerebrate, cerebellectomized, vagotomized, paralyzed, and ventilated cats. Gasping was reversibly produced by cooling a fork thermode positioned through the pontomedullary junction. In eupnea, phrenic motoneurons were distributed into "early" and "late" populations relative to their onset of activity during inspiration. During gasping, however, both fiber types typically commenced activity at the beginning of the phrenic nerve burst. Moreover, late fibers, but not early units, exhibited an augmentation of discharge frequency with the onset of gasping. The concentration of activity of all phrenic motoneurons at the beginning of inspiration and the increase in late-unit discharge frequency account for the faster rise of the gasp as compared with the eupneic breath. It is concluded that the pattern of phrenic nerve activation during gasping differs fundamentally from that during eupnea. These results support the concept that mechanisms underlying the neurogenesis of gasping and eupnea may not be identical.
Respiratory control during hypoxia in newborn rabbits: implied action of endorphins
Authors: Grunstein M. M. , Hazinski T. A. , Schlueter M. A.
Published: December 2017

The mechanism of ventilatory depression during hypoxia in the neonate is unknown. Since endorphins depress ventilation and their actions are antagonized by naloxone, we tested the effect of naloxone on respiration during acute hypoxia in newborn rabbits. In 27 tracheotomized unanesthetized pups, ranging in age from 1 to 15 days, ventilation (VE) was measured in a body plethysmograph. At all ages, inhalation of 5% O2 initially increased VE; thereafter VE became depressed in association with a decrease in CO2 elimination (VCO2). The time constant of VE depression increased with age. During ventilatory and VCO2 depression, saline infusion had no effect. Infusion of naloxone (4 micrograms/g body wt), however, abruptly stimulated both VE and VCO2. Since naloxone acts by competitive blockade of opiate (endorphin) receptors, these data provide evidence that 1) depression in respiration and metabolism during hypoxia is related to the action of endorphins, 2) the degree of endorphin influence decreases with age, and 3) naloxone is effective in reversing hypoxic respiratory depression provided apnea is not established.
Erythrocyte alterations endurance exercise in horses
Authors: Boucher J. H. , Ferguson E. W. , Wilhelmsen C. L. , Statham N. , McMeekin R. R.
Published: December 2017

The erythrocytes of 14 conditioned horses participating in a 157-km endurance ride (requiring 14–21 h) were examined before the ride, immediately upon entering the 44–91-, and 130-km rest stops, and at the finish. At the first rest stop (44 km), the mean erythrocyte count increased 41% (P less than 0.001), the mean hematocrit (Hct) increased 30% (P less than 0.001) and the mean hemoglobin (Hb) increased 33% ( P less than 0.001). Although subsequent mean erythrocyte counts, Hct, and Hb values remained significantly elevated above controls, the values decreased 9–9% from the 4-km values later in the ride. These changes suggest a lost of red cells mass during the prolonged exercise. Spiculated red blood cells that increased markedly in number during exercise were also observed in these conditioned horses. The appearance of an increased number of spiculated red cells with exercise was associated with corresponding changes in red cell indices.
Energy expenditure during load carriage at high altitude
Authors: Cymerman A. , Pandolf K. B. , Young A. J. , Maher J. T.
Published: December 2017

To determine the applicability of a prediction equation for energy expenditure during load carriage at high altitude that was previously validated at sea level, oxygen uptake (Vo2) was determined in five young men at 4,300 m while they walked with backpack loads of 0, 15, and 30 kg at treadmill grades of 0,8, and 16% at 1.12 m.s-1 for 10 min. Mean +/- SE maximal Vo2, determined on the cycle ergometer, was 42.2 +/- 2.3 at sea level and 35.6 +/- 1.7 ml.kg-1 .min-1 at altitude. There were no significant differences in daily Vo2 at any specific exercise intensity on days 1, 5, and 9 of exposure, nor were there any differences in endurance times at the two most difficult exercise intensities. Endurance times for 15- and 30-kg loads at 16% grade were 7.3 and 4.2 min, respectively. Measured energy expenditure was compared with that predicted by the formula of Pandolf et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 43: 577–581, 1977) and found to be significantly different. The differences could be attributed to measurements at metabolic rates exceeding 730 W or 2.1 1.min-1 Vo2. These data indicate that the prediction equation can be used at altitude for exercise intensities not exceeding this upper limit. The observed deviations from predicted values at the high exercise intensities could possibly be attributed to the occurrence of appreciable oxygen deficits and the inability to achieve steady-state conditions.
Vasomotor control in healed grafted skin in humans
Authors: Freund P. R. , Brengelmann G. L. , Rowell L. B. , Engrav L. , Heimbach D. M.
Published: December 2017

Do the vasomotor functions unique to skin recover in a skin graft? To determine whether locally mediated vasodilation and active reflex vasodilation recovery, we applied direct heating and whole-body heating, respectively. Also, presence of sympathetic cutaneous vasoconstriction was tested with application of lower body negative pressure (LBNP) during local heating. Subjects were six men who had been severely burned. Forearm blood flow (FBF) was recorded (venous occlusion plethysmography) in regions with healed split-thickness circumferential grafts. All subjects responded normally to local heating of the forearm (irrigation with 42 degrees C water). All but one showed cutaneous vasoconstriction in response to LBNP. Three subjects responded normally to whole-body heating with water-perfused suits (oral temperature elevation approximately 1.5 degrees C); two subjects had attenuated responses. No active vasodilation was normal cutaneous vasomotor functions return in (or under) split-thickness skin grafts, recovery and associated thermoregulatory function may be attenuated or absent, perhaps in relation to the survival of dermis.
Effect of CO2 set point on ventilatory response to exercise
Authors: Oren A. , Wasserman K. , Davis J. A. , Whipp B. J.
Published: December 2017

The ventilatory response to exercise was determined in seven normal adults during induced chronic metabolic acidosis, chronic metabolic alkalosis, and a control state. Incremental and constant-load exercise tests were performed in each condition on a cycle ergometer. Ventilation and gas exchange variables were determined breath by breath, and CO2 partial pressure (PCO2), pH, and HCO3 were determined from arterialized venous blood (Pa-VCO2). During chronic metabolic acidosis PaVCO2 was lower than control (36.3 +/- 2.1 and 43.7 +/- 2.9 Torr, respectively) and during alkalosis it was elevated to 47.1 +/- 1.3 Torr.The new PCO2 levels caused by chronic acid-base alterations were unchanged during moderate exercise. The ventilatory response (VE) to the same metabolic rate increment was therefore larger (delta VE = 20.6 +/- 2.91/min) when PCO2 was lower than the control level (delta VE = 14.5 +/- 2.01/min. VE also increased more steeply in response to incremental exercise tests when PCO2 was reduced. Thus the hyperpnea of moderate exercise reflects the level at which arterial PCO2 is regulated at rest, as well as the metabolic load (VCO2).
Dynamics of ventilatory response to exercise in humans
Authors: Bennett F. M. , Reischl P. , Grodins F. S. , Yamashiro S. M. , Fordyce W. E.
Published: December 2017

The dynamics of the ventilatory response to moderate exercise on a bicycle ergometer have been studied in humans. The work load was varied between 25 and 100 W as a pseudorandom binary sequence (PRBS) that enabled the impulse responses to be calculated by cross-correlation techniques. The response of all five subjects exhibited a bimodal response, i.e., a fast component that was followed after a delay by a slow component. The fast component accounted for a relatively small proportion of the total response. Also, it was demonstrated that to identify the rapid component it was necessary to excite the respiratory system with an input containing highfrequency components; this result was used to reconcile the findings from this study with those of previous investigation.
Brain stem genesis of automatic ventilatory patterns independent of spinal mechanisms
Authors: St John W. M. , Bartlett D. , Knuth K. V. , Hwang J. C.
Published: December 2017

Efferent activities on the phrenic and recurrent laryngeal (RLN) nerves were monitored during eupnea, apneusis, and gasping in decerebrate, paralyzed, and ventilated cats before and after spinal cord transection at the first cervical level. The vagi were sectioned caudal to the RLN being studied and at the midcervical level contralaterally. Before spinal transection, the onset of RLN inspiratory activity preceded that of the phrenic nerve during eupnea and apneusis; in gasping, phrenic activity began before the RLN. These results were the same in normocapnia, hypercapnia, and hypoxia. After spinal transection, no phasic phrenic activity was observed at normoxia or hyperoxia, whereas the RLN exhibited discharge patterns similar to those before transection. Upon end-tidal O2 partial pressure diminutions below 50 Torr, one or more "burst" of phrenic activity were recorded. These bursts were not synchronized with the phasic RLN discharge. It is concluded that automatic ventilatory activity may be generated by inherent brain stem mechanisms. These results further imply the processes underlying gasping neurogenesis may differ fundamentally from those of eupnea or apneusis.
Redistribution of pulmonary blood flow during experimental air embolism
Authors: Chang H. K. , Delaunois L. , Boileau R. , Martin R. R.
Published: December 2017

The effect of experimental pulmonary air embolism on pulmonary perfusion was studied in 14 closed-chest, anesthetized, paralyzed dogs. During constant-rate air infusion through a femoral vein, regional distribution of lung perfusion was measured with radioactive xenon boluses injected via a catheter positioned distally to the pulmonary valve. The results obtained from nine prone dogs indicate a large shift of blood perfusion toward the dependent areas of the lung during air embolism; the results obtained in five supine dogs were similar but statistically less significant. Concomitant with the perfusion shift, pulmonary arterial pressure increased, more acutely during the first 30 min. Switching from air to N2O-O2 ventilation accentuated the perfusion shift, which may be reverted towards control values by intravenous administration of 0.4 mg of isoproterenol. Other alterations observed included moderate increase of pulmonary resistance and decrease of cardiac output. It is concluded, based on these results and an adjunct model study, that the observed changes were predominantly due to aggregation of air bubbles in the upper part of the pulmonary vasculature.
Boundary-layer oxygen depletion in blood gas analysis
Authors: Venkatesh S. , Cumming G.
Published: December 2017

When O2 is withdrawn from blood by diffusion through a membrane and an O2-depleted boundary layer is formed, it is suggested that the depletion can cause significant dissociation of oxyhemoglobin (HbO2) in this layer. The resulting nonlinear relation between net diffusive flux of O2 through the membrane and the blood PO2 should be observable with membrane systems having a sufficiently high permeability to O2. Evidence for this suggestion is presented from in vitro experiments using a mass spectrometer to analyze the O2 flux through membrane systems. A theoretical model of HbO2 dissociation in the depleted boundary layer of blood that explains these results qualitatively is developed to yield quantitative predictions found to be in reasonable agreement with the experimental observations. The effect was seen to be of significance for membrane systems with O2-sampling rates of about 2 X 10(-9) ml. s-1. Torr-1 and over; so if such systems are to be used for the analysis of blood PO2, the phenomenon must be taken into account.
Prostaglandin E1 hyperthermia: effects on ability to work in the heat
Authors: Francesconi R. , Mager M.
Published: December 2017

To assess the effects of preinduced hyperthermia on the ability to exercise in the heat, prostaglandin E1 (PGE1) was administered intracerebroventricularly to male rats weighing 275–350 g. Following injection of PGE1, a fever of 2 degrees developed within 20–30 min, at which time a 1-ml blood sample was taken. When these animals exercised in the heat (37 degrees C) to hyperthermic exhaustion (42.5–43 degrees C), their endurance capacity was significantly reduced (P less than 0.001) when compared with controls. Exercise to hyperthermic exhaustion resulted in significantly (P less than 0.05, minimal) increased plasma levels of lactate, potassium, and urea nitrogen in both control animals and those receiving PGE1. However, PGE1 pretreatment did not exacerbate these increments. Plasma glucose and sodium levels were significantly (P less than 0.05) increased in PGE1-treated animals, whereas glucose levels were reduced significantly (P less than 0.05) in both groups postrun. We concluded that preinduced hyperthermia severely reduces the ability to work in the heat. Although the clinical chemical indices of heat injury are unaffected by PGE1 pretreatment, the effects of PGE1 administration on circulating levels of glucose and sodium require further study.
Protein synthesis rates in atrophied gastrocnemius muscles after limb immobilization
Authors: Tucker K. R. , Seider M. J. , Booth F. W.
Published: December 2017

Fractional rates of protein synthesis in rats were determined by the constant-infusion technique. Rates of protein synthesis in the gastrocnemius muscle were significantly reduced from control values throughout a 7-day period of hindlimb immobilization and 1) significantly increased to control values during the first 6 h following the 7-day period of hindlimb immobilization; 2) remained at control values for the next 2 days; and 3) then significantly increased to about twice control values on the 4th day following immobilization. Exercise of sufficient duration and/or intensity affected a further increase in the protein synthesis rate during recovery from atrophy. For example, running on a motor-driven treadmill 1 h daily for 3 days after ending limb immobilization resulted in a significant increase in the fractional rate of protein synthesis in the gastrocnemius muscle on the 2nd day following immobilization. Also, weight lifting for 200 s on the 2nd day of protein synthesis in the gastrocnemius muscle. Thus increased usage of atrophied muscle was followed by an increased rate of protein synthesis.
Effect of low-potassium diet on rat exercise hyperthermia and heatstroke mortality
Authors: Hubbard R. W. , Mager M. , Bowers W. D. , Leav I. , Angoff G. , Matthew W. T. , Sils I. V.
Published: December 2017

A total of 182 male Sprague-Dawley rats weighing 250–300 g were fed either a control (n = 122) diet for 32 days. The diets contained either 125 or 8 meq potassium/kg, respectively. Rats fed the low-K diet gained weight at only one-third the rate of controls (1.7 vs. 5.2 g/day), and their skeletal muscle and plasma potassium levels were reduced by 28 and 47%, respectively. When run to exhaustion at either 15 or 20 degrees C, low K+-fed rats accomplished less than one-half of the work done by the controls (26 vs. 53 kg. m) but exhibited a markedly greater rate of heat gain per kilogram-meter of work than controls (0.12 vs. 0.05 degrees C)ambient temperature of 20 degrees C, the rats of the low-K+ group despite large differences in body weight (-25%), run time temperature and twice (33 vs 17%) the mortality rate of the controls. Postexercise increases in circulating potassium (less than 90%) of heat-injured rats raised the plasma levels of low K+-fed rats to normal (5.9 +/- 2.2 meq/l). These results appear to characterize the existence of an insidious and, therefore, undocumented form of fatal exertion-induced heat illness.
Control of release of surfactant phospholipids in the isolated perfused rat lung
Authors: Nicholas T. E. , Barr H. A.
Published: December 2017

We used the isolated rat lung to investigate surfactant release. The lung was ventilated at 60.min-1 with 5% CO2–95% O2 and perfused at 10 ml.min-1 with Krebs-bicarbonate (4.5% albumin). After 20 min during which antagonist drugs were present, the lungs were either hyperventilated or agonist drugs were added. After another 15 min lungs were lavaged. Peak inspired pressures (PIP) in excess of 12 cmH2O produced progressively greater phospholipid (PL) yields. Whereas ventilating with PIP of 9 cmH2O and end-expired pressure(EEP) of 5 cmH2O produced 5.9 +/- 0.8 (mean +/-SD) (n = 17) mg PL. g dry lung-1, ventilating with PIP of 20 cmH2O and EEP of 0 cmH2O produced 10.1 +/- 1.3 (n = 26). PL release was unaffected by tetrodotoxin, propranolol, atropine, cyproheptadine, or indomethacin. PL was increased by salbutamol and dibutyryl adenosine 3',5'-cyclic monophosphate but not by pilocarpine or dibutyryl guanosine 3',5'-cyclic monophosphate. We conclude, that increasing tidal volume immediately releases surfactant, probably by distorting the type II cell and elevating cAMP. An intrapulmonary neural reflex is not involved in this response of the isolated rat lung, nor is histamine, 5-hydroxytryptamine, or a prostaglandin.
Time course of phrenic activity and respiratory pressures during airway occlusion in cats
Authors: Siafakas N. M. , Chang H. K. , Bonora M. , Gautier H. , Milic-Emili J. , Duron B.
Published: December 2017

The morphology of integrated ("moving time average") phrenic electroneurograms (EPHR) and of tracheal (Ptr) and transdiaphragmatic (Pdi) pressure waves during occluded inspirations was studied in eight anesthetized cats breathing air and various hypercapnic and hypoxic mixtures. The shape of the rising part of EPR-, Ptr-, and Pdi-time profiles varied between animals (from convex to concave), but in each animal it remained virtually unchanged by hypoxia and hypercapnia. The shape of the Ptr and Pdi occlusion waves reflected the shape of EPHR. The relationship of EPHR to Pdi and Ptr did not change with chemical drive. It is concluded that central inspiratory activity (CIA) (as reflected by EPHR and its mechanical transforms Pdi and Ptr) increases in amplitude with stimulation of breathing but that the profile of CIA remains essentially unchanged. However, substantial differences in the time course development of phrenic activity, Pdi, and Ptr exist between cats. The fixed interrelationships among EPHR, Pdi, and Ptr indicate a proportional increase in activity among all inspiratory muscles with increased chemical drive.
Decreased vascular sensitivity to norepinephrine following exercise training
Authors: Wiegman D. L. , Harris P. D. , Joshua I. G. , Miller F. N.
Published: December 2017

Twenty Sprague-Dawley rats (230 +/- 9 g; mean +/- SE) were exercised daily for 6 wk by swimming 1 h/day with weights (5% of body wt) attached to their tails. Nineteen additional rats (237 +/- 8 g) remained sedentary in their cages. All animals were anesthetized with urethan (800 mg/kg) and alpha-chloralose (60 mg/kg). In the first series of experiments, increasing doses of norepinephrine were injected into the jugular vein and the responses in mean arterial blood pressure was recorded from a cannulated femoral artery. Exercise training had no effect on the maximal increase in blood pressure, but significantly decreased blood pressure sensitivity to norepinephrine, expressed as a pD2 value (=-log ED 50), from 5.64 +/- 0.07 to 5.20 +/- 0.06. In the second series, the cremaster muscle with intact circulation and innervation was suspended in a tissue bath and norepinephrine in increasing concentrations was added to the cremaster bath. The responses of the main arteriole (approximately 110 micron) and venule (approximately 170 micron) were recorded by television microscopy. Exercise training had no effect on vessel diameters of resting muscle or on the maximal vessel constrictions obtained in response to high concentrations of norepinephrine. Arteriole sensitivity to norepinephrine was significantly decreased (pD2 of 6.69 +/- 0.24 vs. 5.96 +/- 0.18) and there was some tendency for reduced venule sensitivity. These data suggest that exercise training in rats produces a decrease in alpha- or an increase in beta-adrenergic receptor sensitivity.
Effects of phrenic nerve section on the respiratory system of fetal lambs
Authors: Fewell J. E. , Lee C. C. , Kitterman J. A.
Published: December 2017

We investigated the effects of phrenic nerve section (PNS) on the respiratory system of fetal lambs. Seven ewes, three of which had twin fetuses, were given a general anesthetic. The thoracic phrenic nerves were cut in two singleton fetuses and in one fetus in each set of twins (116-121 days); two singleton fetuses and one fetus in each set of twins underwent the same procedure except for PNS. Fetal arterial blood pressure, heart rate, and arterial pH and blood gas tensions were the same in both groups. Phrenic nerve section eliminated fetal breathing movements and decreased airway fluid volume, lung weight, and total lung DNA (P less than 0.05). However, PNS did not affect production of tracheal fluid or percent dry weight of the lungs. Furthermore, PNS did not affect the concentration of saturated phosphatidylcholine in the lung or its flux in tracheal fluid. We conclude that PNS in fetal lambs retards lung growth but does not affect tracheal fluid production or formation and release of surfactant.
Exercise training hypotension: implications for plasma volume, renin, and vasopressin
Authors: Greenleaf J. E. , Sciaraffa D. , Shvartz E. , Keil L. C. , Brock P. J.
Published: December 2017

To determine the function of changes in plasma volume (PV), plasma renin activity (PRA), and arginine vasopressin (AVP) in the mechanism of the reduction of resting blood pressure during exercise training, resting supine, sitting, and standing systolic (SBP) and 5th-phase diastolic (DBP) blood pressures were measured in 10 men (19-24 yr) before and after an 8-day (2 h/day) training period on a cycle ergometer. The control group (5 men) exercised at 1.4 1/min [44% peak O2 uptake (VO2 max)] at 23.8 degrees C Tdb and 50% rh, and the acclimation group at 1.5 1/min (46% VO2 max) at 39.8 degrees C Tdb and 50% rh. After acclimation, resting supine and sitting DPB decreased (P less than 0.05) by 6 and 9 mmHg, respectively. There were no significant changes in DBP in the controls or in SBP in either group. After training, PV increased by 12.2% in controls and by 17.6% after acclimation. The resting hypotension could not be attributed to changes in resting levels of PV, AVP, or PRA. However, large decreases in PV and large increases in AVP and especially PRA during acclimation exposures suggest these responses may play a role in the chronic hypotensive response.
Surface activity following natural surfactant treatment in premature lambs
Authors: Ikegami M. , Jobe A. , Glatz T.
Published: December 2017

Premature lambs with respiratory failure [CO2 partial pressure (PCO2) greater than 70 Torr] were treated with 50 mg/kg 3H-labeled natural surfactant by tracheal instillation. Minimum surface tensions of sequential samples suctioned from the airways fell from 25 +/- 3 dyn/cm before treatment to 8 +/- 5 dyn/cm after treatment and again rose to 32 +/- 2 dyn/cm at death. Minimum surface tensions of alveolar wash samples taken at death were 27 +/- 4 dyn/cm, whereas surfactant fractions reisolated from the alveolar washes lowered surface tension to under 10 dyn/cm. The alveolar washes, surfactant reisolated from the alveolar washes, and natural surfactant had similar phospholipid compositions; however, the alveolar washes contained about 40 times more protein per micromole phosphatidylcholine. The natural surfactant used for treatment apparently was inactivated by an inhibitor of surfactant function. After intravenous injections of [14C]palmitic acid, labeled saturated phosphatidylcholine appeared on the airways, indicating endogenous synthesis and secretion. However, the specific activity of the 3H-labeled saturated phosphatidylcholine in the natural surfactant used for treatment decreased by only 30 +/- 4% in the alveolar wash; thus the treatment dose was not diluted to a large extent by endogenous pools.
Cold-specific feeding response of rats to cold exposure and energy density of body weight change
Authors: Morrison S. D.
Published: December 2017

The increased food intake of rats exposed to cold is the result of increased intake due to cold (cold-specific compartment; A) and decreased intake due to simultaneously decreased body weight (weight-specific compartment; B). The two compartments are evaluated at 5, 13, and 17 degrees C. B is evaluated as the food intake of theoretical, isogravimetric control (identical to cold-exposed rats with respect to body weight and rate of change of body weight and identical to nonexposed rats in all other respects) that takes into account both the change in energy expenditure due to decreased body weight and the energy yield from tissue catabolism represented by change of body weight. A is the observed food intake minus B. A theoretical heat-flow model, in which expected changes in heat flow during cold exposure drive food intake to maintain or restore preexposure body weight status, corroborated the partition derived from experimental data. However, both the experimental results and the heat-flow model imply that the energy density of body weight change is negatively correlated with rate of body weight change. The energy density of weight change is high with high rates of weight loss and low with high rats of weight gain.
Mechanical properties of mouse lungs: effects of degassing on normal, hyperoxic, and irradiated lungs
Authors: Gross N. J.
Published: December 2017

We critically examined conventional techniques for studying static mechanical properties of the lungs using normal mice, mice exposed to high O2 concentrations, and mice with radiation pneumonitis and radiation fibrosis. Successive pressure-volume (PV) curves were performed in situ both before and after degassing the lungs in vacuo. In both hyperoxia and radiation pneumonitis the deflation limbs of the curves were shifted to the right compared with their corresponding controls. However, the curves were further shifted rightward and downward after degassing the lung, as compared with the curve obtained before degassing. This effect of degassing was most marked in abnormal lungs and was not corrected by repeating inflation-deflation cycles nor by inflating to higher pressures and allowing time for units to open. Histology showed that abnormal lungs fixed in inflation after degassing were unevenly reinflated. It is speculated that, in conditions such as hyperoxia and radiation pneumonitis, altered surface tension properties may result in uneven reinflation of the lungs after degassing and that nonuniform reinflation may produce spurious shifts in the shape as well as the amplitude of PV curves. Thus PV curves performed with air after degassing the lung may not correctly represent the mechanical properties of abnormal lungs.
Carotid body O2 chemoreception and mitochondrial oxidative phosphorylation
Authors: Mulligan E. , Lahiri S. , Storey B. T.
Published: December 2017

The effect on carotid chemoreceptor afferents of oligomycin, an inhibitor of mitochondrial oxidative phosphorylation that does not affect energy conservation, was studied in 20 cats that were anesthetized, paralyzed, and artificially ventilated. Responses of single or a few chemoreceptor afferents to changes in arterial O2 tension (PaO2) at constant arterial CO2 tension were recorded. In addition, responses to nicotine, cyanide, and antimycin A or carbonyl cyanide p-tri-fluoromethoxyphenylhydrazone (FCCP) were tested in normoxia. Oligomycin (50-500 microgram) was administered by close intra-arterial injection, and the same tests were repeated at timed intervals. Initially, oligomycin caused vigorous stimulation of carotid chemoreceptor activity. Subsequently, although the afferent fibers were still active and could be vigorously stimulated by nicotine, they no longer responded to changes in PaO2 or to doses of cyanide, antimycin A, or FCCP. These results separate stimulation of chemoreceptor afferents by hypoxia and metabolic inhibitors and uncouplers from that by nicotine and suggest that intact oxidative phosphorylation, required for maintenance of the intracellular high-energy phosphate levels, forms the basis of O2 chemoreception in the carotid body.
Effect of pedaling rate on submaximal exercise responses of competitive cyclists
Authors: Hagberg J. M. , Mullin J. P. , Giese M. D. , Spitznagel E.
Published: December 2017

This investigation was undertaken to determine the effect of pedal frequency on submaximal exercise responses. Seven well-trained competitive cyclists were studied riding their road-racing bicycles on a motor-driven treadmill at 80% of maximum O2 consumption (VO2 max) using different gear ratios. Cyclists were also studied during a series of unloaded trials to assess the effects of varying rates of limb movements independent of external work load. Heart rate (HR) increased, whereas net HR (after subtracting the HR during unloaded cycling) decreased with increasing pedal frequency during loaded cycling. Expiratory flow (VE), O2 consumption (VO2), blood lactate, net VO2 (after subtracting the VO2 of unloaded cycling), and net VE (after subtracting the VE during unloaded cycling) were quadratically related to pedal frequency. The quadratic relationships evident after corrections were made for the additional work needed to move the legs more frequently may be explained at the lower pedaling rates by a less uniform pattern of blood flow caused by increasing the force requirement per pedal stroke and, at the higher pedal frequencies, by the recruitment of additional musculature to stabilize the trunk. The average of preferred frequency for the group, which was also the most economical pedaling rate judged by most of the variables was 91 rpm, although the preferred pedaling rate for each subject ranged from 72 to 102 rpm.
Use of aerosols to estimate pulmonary air-space dimensions
Authors: Gebhart J. , Heyder J. , Stahlhofen W.
Published: December 2017

Single-breath inhalations of monodisperse aerosols were performed with a group of normal subjects to determine aerosol recovery from the human lung after periods of breath holding. Aerosols of monodisperse nonhygroscopic droplets of bis(2-ethylhexyl) sebacate of between 0.5 and about 2.5 micron diam were used for the inhalation. The inhalation apparatus allows continuous monitoring of particle number concentration and flow rate close to the mouth. Experiments were designed to find the optimum experimental conditions for the principal concept of Palmes et al (In: Inhaled Particles and Vapours. London: Pergamon, 1976, vol. II. p. 339-347) to evaluate pulmonary air-space dimensions by means of aerosols. The experimental results obtained for various respiratory flow rates (125, 250, and 500 cm3 X s-1), settling velocities of the particles (10(-3) to 1.5 X 10(-2) cm X s-1) and volumes of inspired aerosols (500, 1,000, and 2,000 cm3) are compared with the results derived from a mathematical model for the particle deposition during respiratory pauses. Monodisperse aerosols with particles between 1 and about 1.5 micron diam. inspired for breath holding into the lung region of interest, may provide optimum conditions for the sizing of air spaces by means of aerosols.
A method of producing calibrated microtubules for air embolism studies
Authors: Hills B. A. , Butler B. D.
Published: December 2017

Utilizing the differential absorption techniques in conjunction with gas injection methods has enabled the production of calibrated microtubules with diameters ranging from 14 to 300 micron. Nitrogen was blended with CO2, the "diluent" gas, to produce the initial bubbles, while tris(hydroxymethyl)-aminomethane hydrochloride (THAM) was used as an absorbent to remove the diluent gas from the bubbles. Hence, the diameters of the initial bubbles were significantly reduced with only the inert gas remaining. The Coulter counter was used for immediate size monitoring of the microtubules. To verify the inertness of the absorbent medium, nine anesthetized dogs were infused with increasing amounts of the solution. In five of the animals plasma surface tension and pH (arterial) were measured, while in the remaining four arterial blood pressure, heart rate, breathing frequency, and pulmonary artery pressure was measured before, during, and after the injections. Changes in plasma surface tension and pH were minimal while acceptable physiological values were recorded, all of which were in agreement with previous investigations. Differential absorption techniques provided a reliable means for producing calibrated micro-bubbles for air embolism studies.
Synergistic behavior of inspiratory muscles after diaphragmatic fatigue in the newborn
Authors: Lopes J. M. , Muller N. L. , Bryan M. H. , Bryan A. C.
Published: December 2017

We studied diaphragmatic and intercostal muscle activity and the pattern of motion of rib cage and abdomen after diaphragmatic muscle fatigue in 15 newborn infants (birth wt 1,251 +/- 424 g, mean +/- SD). Rib cage and abdominal motion were monitored with magnetometers and intercostal and diaphragmatic electromyograms (EMG's) with surface electrodes. Twelve infants showed a total of 66 episodes of muscle fatigue identified by EMG frequency spectrum analysis. Two patterns of responses to fatigue were observed. In the first case, five infants consistently recruited their intercostal muscles; this was followed by a normalization of the diaphragmatic frequency spectrum. In these infants, recruitment of intercostal muscles successfully prevented any clinical deterioration. In the second, seven infants showed no change in their intercostal muscle activity, and diaphragmatic fatigue was followed by apnea. We conclude that in newborn infants the synergistic behavior of the diaphragm and intercostal muscles can maximize the performance of these muscles and, in some infants, seems to prevent development of apnea.
Blood flow and O2 uptake in dog hindlimb with anemia, norepinephrine, and propranolol
Authors: Chapler C. K. , Cain S. M.
Published: December 2017

To examine the relative importance of 1) reduced blood viscosity, 2) vasodilation mediated through beta-adrenergic receptors, and 3) sympathetic nerve activity on the regulation of limb blood flow during anemia, norepinephrine (NE) was infused in 10 anesthetized-paralyzed dogs at normal and reduced hematocrit (Hct). Cardiac output (QT), limb and total oxygen uptake (VO2)n and limb venous flow (QL) were determined. After a control period, NE (2 micrograms . kg-1 . min-1) was infused followed by another control period. The Hct was then reduced to 9% by isovolemic hemodilution with dextran, and data were obtained during anemia, anemia plus NE, and after isovolemic reinfusion of red blood cells (Hct 25%) during NE. Another 10 dogs were treated identically after propranolol (1.0 mg/kg) administration. At normal Hct, NE increased limb resistance (RL) (P less than 0.01) in the beta-block group; a decrease in RL (P less than 0.05) and a rise in QL (P less than 0.01) occurred in the no block group. QL and VO2 (limb and total) were not changed by NE. During anemia, RL was not altered in either group by NE; QT fell (P less than 0.05) in both, and QL decreased in the no block group. After reinfusion of cells, NE produced an increase in RL and total peripheral resistance (P less than 0.01) and a fall in QL (P less than 0.01) and QT (P less than 0.01) in both groups; limb and total VO2 rose in the no block group. We conclude that the reduction in viscosity prevented an increase in both RL and redistribution of QL during severe anemia (Hct 9%).
Effect of systemic venous hypertension on pulmonary function and lung water
Authors: Pare P. D. , Brooks L. A. , Baile E. M.
Published: December 2017

We studied the effects of systemic venous hypertension (SVH) of 25 cmH2O, with and without fluid overload (100 ml.kg-1.h-1 x 4 h), on the lung water content and pulmonary function of anesthetized dogs. SVH was produced by inflating a balloon in the right atrium. Pulmonary extravascular water (PEW) was measured by gravimetric techniques taking the water content of trapped blood into consideration. Subdivisions of lung volume, pulmonary resistance, dynamic compliance, and the single-breath nitrogen washout curve were performed in a body plethysmograph. Vascular pressures, serum oncotic pressure, and arterial blood gases were also measured. Systemic venous hypertension alone produced no change in lung water content (control PEW = 3.46 +/- 0.16; SVH PEW = 3.44 +/- 0.18 g H2O/g dry tissue, mean +/- SD) or alterations in pulmonary function. Fluid overload alone produced an insignificant increase in PEW (4.24 +/- 0.72 g H2O/g dry tissue) and decreases in vital capacity and functional residual capacity. SVH in combination with fluid overload resulted in a significant increase in lung water (4.78 +/- 1.03 g H2O/g dry tissue) and decreases in functional residual capacity, vital capacity, dynamic compliance, and arterial blood oxygen tension as well as increased pulmonary resistance. We conclude that SVH favors the formation of pulmonary edema under conditions of increased pulmonary transcapillary fluid exchange and may particularly augment airway edema.
Frequency dependence and partitioning of respiratory impedance in dogs
Authors: Kappos A. D. , Rodarte J. R. , Lai-Fook S. J.
Published: December 2017

Total pulmonary resistance (Rt) and reactance (Xt) from 1 to 30 Hz were determined by time series analysis in open-chest vagotomized dogs. Rt and Xt were partitioned by retrograde catheter into central airway resistance (Rc) and reactance (Xc) and peripheral resistance (Rp) and reactance (Xp). Rt, Rc, or Rp did not change with transpulmonary pressure (Pst) from 5 to 15 cmH2O, although Rc tended to decrease and Rp to increase. Vagal stimulation (Vs) and intravenous histamine (H) increased all resistances (R) at all lung volumes (V) and produced an inverse relationship between R and V. The increases in Rt produced by H and Vs were not significantly different at any volume, but H predominantly increased Rp and Vs predominantly increased Rc. In the control (vagotomized) dogs at Pst of 5 cmH2O, Rp/Rt was 0.41 +/- 0.03 (SE). Rp/Rt was significantly increased by H but not by Vs. Control Rt decreased slightly from 5 to 10 Hz and increased from 15 to 30 Hz. The increase of Rt at higher frequencies caused by the frequency dependence of Rc was not changed by H but was augmented by Vs. The slope of Xt and Xc vs. frequency was increased by Vs but not by H. The frequency dependence of Rt and Xt above 10 Hz appears to be caused by inertial losses proximal to the 2-mm airways. Thus central and peripheral bronchoconstriction caused by Vs and H, respectively, could be differentiated by increased frequency dependence of Rt and Xt above 15 Hz.