bluuebunny/crossref_metadata_2025 huggingface dataset:
Insulin and glucose responses during bed rest with isotonic and isometric exercise
Authors: Dolkas C. B. , Greenleaf J. E.
Published: December 2017

The effects of daily intensive isotonic (68% maximum oxygen uptake (VO2 max)) and isometric (21% maximum extension force) leg exercise on plasma insulin and glucose responses to an oral glucose tolerance test (OGTT) during 14-day bed-rest (BR) periods were investigated in seven young healthy men. The OGTT was given during ambulatory control and on day 10 of the no-exercise, isotonic, and isometric exercise BR periods during the 15-wk study. The subjects were placed on a controlled diet (mean +/- SD = 344 +/- 34 g CHO/day and 3,073 +/- 155 (SD) kcal/day) starting 10 days before each BR period. During BR, basal plasma glucose concentration remained unchanged with no exercise, but increased (P less than 0.05) to 87–89 mg/100 ml with both exercise regimens on day 2, and then fell slightly below control levels on day 13. The fall of glucose content (-11 to -15%) during BR was independent of the exercise regimen and was an adjustment for the loss of plasma vol. The intensity of the response of insulin and glucose to the OGTT (integrated area under the curves) was inversely proportional to the total daily energy expenditure during BR; i.e., the largest response with no exercise, then isometric, isotonic, and ambulatory exercise. It was estimated that at least 1,020 kcal/day must be provided by supplemental exercise to restore the hyperinsulinemia to control levels.
Determinants of transmembrane bicarbonate flux during acid-base changes
Authors: Strome D. R. , Clancy R. L. , Gonzalez N. C.
Published: December 2017

Experiments were designed to determine the contribution of increased extracellular HCO3- concentration, [HCO-3e], to the net extracellular-to-intracellular HCO3- flux observed in hearts during hypercapnia. Isolated rabbit hearts were perfused by recirculating for 15-min periods a small volume of Ringer solution in which [HCO-3e] and carbon dioxide tension (PCO2) could be independently altered. A net HCO-3 flux was evidenced by a decrease in [HCO-3e] during recirculation. [HCO-3e] was randomly increased from 19 mM over a range of 19–42 mM at a constant PCO2 of 38.7 Torr. The resulting flux increased linearly with the [HCO-3e] existing at the start of recirculation. The same relationship was observed at 95.8 Torr PCO2. The disappearance of HCO-3 from the perfusate could not be explained by dilution in the interstitium or by lactate accumulation. When PCO2 was increased from 40 Torr over a range of 40–160 Torr at a constant [HCO-3e] of 20 or 30 mM, a small flux was observed only at the highest PCO2 levels. Essentially the same results were obtained when recirculation time was prolonged to 30 min. These results suggest that the major determinant of the HCO-3 flux is a change in extracellular HCO-3 concentration.
Effect of pH on cardiorespiratory and metabolic responses to exercise
Authors: Jones N. L. , Sutton J. R. , Taylor R. , Toews C. J.
Published: December 2017

Five male subjects performed exercise at 33, 66, and 95% of their maximum power output on three occasions in random order. Each study was preceded by a 3-h period in which capsules were taken by mouth, containing either CaCO3 (control, NH4Cl (acidosis), or NaHCO3 (alkalosis) in a dose of 0.3 g/kg body wt; preexercise blood pH was 7.38 +/- 0.015, 7.21 +/- 0.033, and 7.43 +/- 0.029, respectively. Exercise was continuous and maintained for 20 min at the two lower power outputs and for as long as possible at the highest. Compared with control (270 +/- 13 s), endurance time at the highest power output was reduced in acidosis (160 +/- 22 s) and increased in alkalosis (438 +/- 120 s). No differences were observed for central cardiovascular changes in exercise (cardiac output, frequency, or stroke volume). The respiratory changes expected from changes in blood pH were observed, with a higher alveolar ventilation in acidosis. At all power outputs arterialized venous lactate was lowest in acidosis and highest in alkalosis. Plasma glycerol and free fatty acids were lowest in acidosis. Changes in blood [HCO3-] and pH were shown to have major effects on metabolism in exercise which presumably were responsible for impaired endurance.
Contractile function and myofibrillar ATPase activity in the exercise-trained dog heart
Authors: Dowell R. T. , Stone H. L. , Sordahl L. A. , Asimakis G. K.
Published: December 2017

Myocardial contractility and the enzymatic (ATPase) activity of cardiac contractile proteins were examined after exercise training using the chronically instrumented, unanesthetized dog as an experimental model. Before training, heart rate and the maximum rate of left ventricular pressure development (max dP/dt) were measured at rest and during submaximal exercise. Animals were then subjected to an 8- to 10-wk treadmill running program. Training was verified by the establishment of a 10- to 20-beat/min reduction in heart rate during submaximal exercise. After training max dP/dt was within normal limits at rest, but significantly elevated during submaximal exercise. When max dP/dt was plotted as a function of heart rate, either with the animal standing quietly on the treadmill or during submaximal exercise, a marked elevation in max dP/dt at any given heart rate was observed following training. Myofibrillar protein yield and ATPase activity values were nearly identical in left ventricles from exercise-trained and sedentary control dogs. Although exercise training by treadmill running improved contractile function in the unanesthetized dog myocardium, this response does not appear to involve alterations in myofibrillar ATPase activity.
Age and sex difference in response to short exposure to extreme dry heat
Authors: Shoenfeld Y. , Udassin R. , Shapiro Y. , Ohri A. , Sohar E.
Published: December 2017

Sixty volunteers, 33 males and 27 females (18–63 yr), were divided according to age and sex. They were exposed for 10 min to extreme dry heat: 80–90 degrees C dry bulb temperature and 3–4% relative humidity. Their rectal temperature, skin temperature at eight different points, weight, and heart rate were recorded prior to and immediately following the exposure. A mean rise of only 0.5 degrees C in rectal temperature was recorded following exposure as compared to a mean rise of 5.2 degrees C in mean weighted skin temperature (MWST). Female subjects showed a significantly higher rise in MWST than the male subjects. Similarly, a significantly higher rise in MWST was observed in elderly male subjects as compared to the youngest male group (P less than 0.05). The differences in MWST possibly resulted from differences in mean skin blood flow causing differences in skin conductance. Large individual variation in heat response was recorded in rectal temperature, as well as in weighted skin temperatures. The increase in skin temperature during the first 10 min of exposure to extreme dry heat may serve as an indicator for heat tolerance time, and may help predicting heatstroke susceptible individuals.
Intravascular volume and tonicity as factors in the regulation of body temperature
Authors: Harrison M. H. , Edwards R. J. , Fennessy P. A.
Published: December 2017

The effect of alterations in intravascular volume and tonicity on thermoregulatory and cardiovascular responses to heat and exercise have been compared in four subjects. Core temperatures were found to be significantly higher during dehydration, and when dehydration was prevented by administration of 1% saline, than when dehydration was prevented by water administration. These higher temperatures were associated with elevated levels of plasma [Na] and osmolarity, but no consistent relationship between temperature and changes in intravascular volume could be demonstrated. Relationships observed between core temperature and plasma tonicity were consistent with the hypothesis that the adverse effects of dehydration on thermoregulation can be attributed to an inhibition of sweating mediated by an increase in either plasma osmotic pressure or plasma [Na]. In separate experiments the heart rate response to exercise was shown to be reduced by saline, compared with water and dehydration, and this may be explained by the smaller reduction in intravascular volume which occurs during exercise following administration of hypertonic saline. It is concluded that the effects of reduced intravascular volume, and increased intravascular tonicity on physical work capacity may be distinguished by the adverse effect on the cardiovascular system of the former, and on the thermoregulatory system of the latter.
Microvascular responses to norepinephrine in skeletal muscle of cold-acclimated rats
Authors: Koo A. , Liang I. Y.
Published: December 2017

The microcirculation of the spinotrapezius muscle in normal and cold-acclimated (4 degrees C) rats was observed by an in vivo microscopic technique. The responses of the arterioles and venules in the skeletal muscle microcirculation to topical application of norepinephrine (NE) were recorded by a photomicrographic method. Results show that the skeletal muscle microcirculation possesses both alpha- and beta-adrenergic vascular receptors. Stimulation of the alpha-receptor results in vasoconstriction, and of the beta-receptor, vasodilatation. These microvascular responses are antagonized by specific alpha- and beta-adrenergic blockers. Cold-acclimation (4 degrees C) for 3 wk decreases the responses of the skeletal muscle microvessels to NE stimulation. This diminished sensitivity is due to an attenuation of the alpha-adrenergic receptor mechanism.
Regrowth of atrophied skeletal muscle in adult rats after ending immobilization
Authors: Booth F. W.
Published: December 2017

The recovery time course of muscle atrophied by immobilization was followed after removal of hindlimb casts from adult female rats. Increases of only 9% in body weight, 4% in gastrocnemius weight, and 10% in soleus weight occurred in controls during the 78-day duration of the experiment. There were no increases in the amounts of total protein or of citrate synthase activities in gastrocnemius or soleus during the first 3 days after removal of hindlimb casts; thereafter, there were increases in these paramters. Citrate synthase activities per mg of gastrocnemius protein were significantly higher at the 16th and 50th day of recovery. No significant differences for citrate synthase activity per mg of soleus occurred during recovery. Until the 50th day of recovery, no significant differences for total protein in soleus and for total protein and wet weight of gastrocnemius were observed between control and recovery values. However, the wet weight of the soleus returned rapidly during recovery and was not significantly different from control during recovery.
Inert gas a-A differences: a direct reflection of V/Q distribution
Authors: Neufeld G. R. , Williams J. J. , Klineberg P. L. , Marshall B. E.
Published: December 2017

A computer model was developed to study the relationship between ventilation-to-perfusion (V/Q) mismatch and the development of inert gas arterial-to-alveolar partial pressure differences (a-A differences). Increasing inhomogeneity of V/Q ratio is revealed directly as an increase in the a-A difference of each gas. The quantitative relationships between the Q vs. V/Q distribution and the fractional a-A difference solubility plot (a-A difference plot) were studied and described. These studies demonstrated that for log normally distributed V/Q ratios, the area under the a-A difference plot is linearly related to the log variance of the V/Q distribution and can be estimated directly from the values obtained from six gases. The maximum a-A difference occurs for a gas whose solubility is numerically equal to the mean V/Q. The effects of departure from log normality and multimodality are discussed. We conclude from these studies that quantitative information regarding the degree of inhomogeneity of V/Q for log normal distribution is available from direct calculations of inert gas retention and excretion data. Qualitative information is also available indicating the departure from log normality and the region toward which the distribution is skewed.
Functional residual capacity and body position in the dog
Authors: Minh V. D. , Dolan G. F. , Brach B. B. , Moser K. M.
Published: December 2017

Resting lung volumes in the supine position (FRCs) were determined by N2 washout method in 67 dogs under pentobarbital anesthesia and computed in ml/kg body weight (BW). In 21 other dogs, FRCs and the change in FRC from the supine to upright positions (deltaFRC) were determined; these lung volumes were expressed in ml/kg BW and in percentage of TLC40 (lung volume at 40 cmH2O positive-pressure inflation). It was found that a) FRCs averaged 38.6 plus or minus 8.2 and 42 plus or minus 5.9 ml/kg BW in the two groups of dogs; b) deltaFRC averaged 23 plus or minus 4 ml/kg BW resulted in large data dispersion, a large coefficient of variation (CV) and a poor correlation (r) of lung volume to BW; D) on the contrary, marked uniformity of FRCs and FRCu (upright FRC) was obtained by expressing the resting lung volumes in %TLC40, allowing an accurate prediction of FRC from the inspiratory capacity (IC). Relationship of FRCu to TLC was comparable to human data reported in the literature. FRCs (%TLC40) was smaller than values previously reported for awake human subjects, probably due to the FRCs reduction in our dogs by anesthesia.
Effects of arachidonic acid and prostaglandins on lung function in the intact dog
Authors: Spannhake E. W. , Lemen R. J. , Wegmann M. J. , Hyman A. L. , Kadowitz P. J.
Published: December 2017

The effects of the prostaglandin (PG) precursor, arachidonic acid (AA), and the primary PG's, PGF2alpha, and PGD2, on lung function were compared in 39 intact-chest, paralyzed, artificially ventilated dogs. Intravenous AA decreased dynamic compliance (Cdyn) and functional residual capacity and increased airway resistance (Rl) and transpulmonary pressure at end-passive expiration. The decrease in Cdyn correlated closely with a rise in pulmonary arterial pressure (Ppa). Indomethacin abolished airway and vascular responses to AA, but did not attenuate responses to the PG's. The effects of AA, PGD2, and PGF2alpha on lung function and Ppa were similar, whereas PGE2 had little effect. Vagotomy attentuated the RL increase in response to AA, PGE2alpha, and PGD2 and the Cdyn decrease in response to the PG's. The effects of the PG's on compliance were greater than those produced by mechanically increasing pulmonary venous pressure. The present studies suggest that the PG precursor is rapidly converted to agents that have marked effect on both pulmonary vessels and airways, particularly peripheral airways, in the dog.
Continuous measurement of gas partial pressures in intracerebral tissue
Authors: Seylaz J. , Pinard E.
Published: December 2017

A mass spectrograph technique has been developed for measurement of physiological gas partial pressures locally in the brain. The sampling cannula is implanted stereotaxically and remains in situ for several weeks. It is a thin cylinder in shape, and is covered with a thin polyethylene membrane across which gas molecules can be sampled continuously. The conductance of this membrane is well adapted to the limited rate of replacement of gas molecules afforded by the cerebral tissue, hence there is no depletion around the cannula; this depletion has until now been the major problem of this technology. The present technique provides a continuous measurement with fast response time, which is directly proportional to the partial pressures of the gases. The variations can be expressed as a percentage of the base-line value.
Effect of curare on maximum static PV relationships of the respiratory system
Authors: Saunders N. A. , Rigg J. R. , Pengelly L. D. , Campbell E. J.
Published: December 2017

The effect of respiratory muscle weakness on the maximum static pressure-volume (PV) characteristics of the respiratory system was studied in four healthy males infused slowly with d-tubocurarine (dtc). Inspiratory capacity (IC), expiratory reserve volume (ERV), maximum static inspiratory and expiratory mouth pressures at four lung volumes, and handgrip were measured during induction of, and recovery from muscle weakness. The maximum effect of dtc varied among the muscle groups tested; peripheral muscles were most severely affected, expiratory muscles moderately, and inspiratory muscles least affected. At each level of weakness studied, decreases of IC and ERV were proportional to decreases of maximum static mouth pressures. Vital capacity, measured at each level of weakness was much less than values predicted from the static mechanical properties of the respiratory system. Our findings suggest that the marked change in the extremes of lung volume during submaximal neuromuscular blockade (SMNB) is due, in part, to unequal distribution of muscle weakness, reflected by decreased ability to change ribcage dimensions even at modest levels of SMNB.
Mechanics of the human diaphragm during voluntary contraction: statics
Authors: Grassino A. , Goldman M. D. , Mead J. , Sears T. A.
Published: December 2017

We related diaphragm electromyographic activity (Edi) to transdiaphragmatic pressure (Pdi) in man during graded inspiratory efforts. Estimates of rib cage and abdominal volume displacements were based on their anteroposterior (AP) diameter changes. The diaphragm was assumed to contract isometrically when subjects performed inspiratory efforts against a closed airway at specified abdominothoracic configurations, increasing Edi and Pdi while holding lung volume and rib case and abdominal AP diameters constant. The relationship between Pdi and Edi depends primarily on abdominothoracic configuration rather than lung volume. For equal increments in lung volume, the Pdi developed at constant Edi is four to eight times more sensitive to changes in abdominal than in rib cage AP diameter. We demonstrate an isofunctional state of the diaphragm at different lung volumes, when increases in lung volume and rib cage AP diameter are compensated for by slight decreases in abdominal AP diameter, resulting in a constant relationship between Edi and Pdi. We conclude that diaphragm shortening is reflected more directly in abdominal displacement than in lung volume change.
Influence of aspirin and indomethacin on variability of alveolar hypoxic vasoconstriction
Authors: Hales C. A. , Rouse E. T. , Slate J. L.
Published: December 2017

Alveolar hypoxia induces pulmonary vasoconstriction but the strength of alveolar hypoxic vasoconstriction (AHV) is variable even within the same species. The influence of aspirin and indomethacin, cyclo-oxygenase inhibitors, was examined in two groups of dogs, those with weak AHV and those with vigorous AHV. A double-lumen endotracheal tube allowed ventilation of one lung with nitrogen as an alveolar hypoxic stimulus and ventilation of the other lung with O2 to maintain systemic oxygenation. Perfusion to each lung was measured with xenon-133 and external counters. In weak reactors both aspirin and indomethacin induced fourfold enhancement of AHV (P less than 0.01), whereas no significant influence on vigorous reactors was noted. Cyclo-oxygenase inhibitors also produced enhanced reactivity in the isolated lung to alveolar hypoxia and prostaglandin F2alpha but not to angiotensin II and norepinephrine. Aspirin-enhanced AHV in the isolated lung could not be diminished with blockade of angiotensin II receptors or of alpha receptors. In summary, weak AHV in intact or isolated dog lung may be due to an excess of a prostaglandin or prostacyclin vasodilator.
Energy status of the rat lung after exposure to elevated PO2
Authors: Fisher A. B.
Published: December 2017

To study hyperoxic effects on adenine nucleotide content and lactate and pyruvate production by lungs, rats were exposed to oxygen at 1 ATA for 18, 24, or 48 h or to 4 ATA for 1 h. Subsequently, lungs were removed from rats, placed in an isolated-lung apparatus, ventilated with 5% CO2 in O2, and perfused with Krebs-Ringer bicarbonate medium containing 5.5 mM glucose and 4% bovine serum albumin. Uptake of serotonin from the perfusate was depressed 28% in rats exposed to hyperbaric oxygen compared with unexposed controls. Concentrations of adenine nucleotides, the ATP/ADP ratio, and the “energy charge” were similar in control and oxygen-exposed rats. The production of lactate and the ratio of lactate to pyruvate production were significantly higher in rats exposed to oxygen for 48 h compared with other exposure regimens. Comparison of these results with those previously reported for serotonin uptake in lungs after hyperoxic exposure indicates that serotonin clearance is depressed prior to alteration of the energy status of the rat lung.
Metabolic, cardiovascular, and respiratory factors in the development of fatigue in lifting tasks
Authors: Petrofsky J. S. , Lind A. R.
Published: December 2017

Three well-trained male subjects served as volunteers in these experiments to examine the physiological capacity for extended work during lifting tasks. The maximal oxygen uptake (VO2max) during lifting was always lower than work on the bicycle ergometer. However, the work load during lifting which could be maintained for 1--4 h was 50% of the VO2max for lifting each specific weight of box; the limit for lifting light boxes without fatigue was at an oxygen uptake of about 25% of the VO2max obtained from bicycle ergometry. Significant fatigue in the forearm muscles was found during prolonged lifting as assessed from the endurance of isometric contractions and from the surface electromyogram (EMG), and was more pronounced as the weight of the box increased.
Effect of hyperinflation and atelectasis on fluid accumulation in the puppy lung
Authors: Pang L. M. , Rodriguez-Martinez F. , Stalcup S. A. , Mellins R. B.
Published: December 2017

The effects of hyperinflation and of atelectasis on accumulation of fluid in the lung was studied in 12 anesthetized spontaneously breathing puppies. Vascular pressures were raised and the plasma colloid osmotic pressure was reduced by the infusion of 0.9% saline thus promoting the formation of pulmonary edema. A tracheostomy was performed and the left lower lobe catheterized in all puppies. In five puppies hyperinflation of the left lower lobe was achieved by applying a continuous positive airway pressure (CPAP) of 10 Torr. In seven other puppies the left lobe was made atelectatic by occluding its bronchus after ventilating the lungs with 100% oxygen. The right lung was ventilated to ambient pressure in all puppies. The extravascular lung water content was determined by the difference in wet and dry lung weights corrected for residual blood. We found that hyperinflation produced by CPAP enhanced and atelectasis opposed fluid accumulation in the puppy lung.
Role of shell diffusion area in incubating eggs at simulated high altitude
Authors: Weiss H. S.
Published: December 2017

Embryonic development is inhibited when eggs are incubated at 9,100 m (0.3 atm) despite a normoxic environment. The problem apparently relates to respiratory gas exchange occurring by diffusion through gas-filled pores in the shell. Gaseous flux is therefore inversely proportional to ambient pressure and is affected by the physical characteristics of the ambient gas (Chapman-Enskog equation). Excess loss of H2O and CO2 occurs in eggs incubating at altitude and could be detrimental. Such increased loss should be correctable by decreasing diffusion area. This was tested by progressively increasing coverage of the shell with paraffin and incubating at simulated 0.3 ATA (225 Torr) in 100% O2. Uncoated eggs failed to hatch, but numbers of chicks increased with increased coverage. Maximum hatch was an extrapolated 90% of controls at 69% shell coverage. With further coverage, hatch size decreased. Egg weight loss, and estimate of H2O diffusion, was around three times controls in uncoated eggs but decreased linearly with paraffin coverage, reaching near normal at maximum hatch. Reduction of diffusion area to 0.3 normal at maximum hatch generally balanced the increased flux predicted for 0.3 ATA.
Lactate uptake by inactive forearm during progressive leg exercise
Authors: Poortmans J. R. , Delescaille-Vanden Bossche J. , Leclercq R.
Published: December 2017

Eleven male subjects were studied during graded leg exercise from 60 to 270 W. Arterial and venous lactate concentrations were measured from the resting forearm during the exercise and recovery periods. Lactate concentration rose regularly during the work and declined slowly to basal levels after the exercise. The arteriovenous difference rapidly became positive during the exercise, indicating a net uptake of lactate by the nonexercising muscles. The uptake of lactate by the muscle correlated directly with the arterial concentration. After the 5th min of recovery, there was no longer any significant difference between arterial and venous lactate concentrations. It is concluded that 1) nonexercising muscles play a small role in the removal of lactate during exercise and 2) significant removal of lactate from the blood by nonexercising muscles stops soon after the cessation of exercise.
Respiratory mechanics in normal bonnet and rhesus monkeys
Authors: Kosch P. C. , Gillespie J. R. , Berry J. D.
Published: December 2017

We measured lung volumes and quasi-static volume-pressure relationships in 22 normal upright bonnet (Macaca radiata) and 12 rhesus (M. mulatta) monkeys. In comparison with interspecies pulmonary function/body weight regressions our monkeys' lung volumes are larger and their lungs are considerably more compliant, but their chest wall compliance is similar to a wide range of mammalian species. However, chest wall compliance of our monkeys was found to be considerably less than that of other more commonly used experimental mammals such as dogs, cats, and rodents. The monkey chest walls were found to be about four times as stiff (3.3 +/- 0.1 (ml/cmH2O)/kg), whereas their lungs were nearly twice as compliant (9.2 +/- 0.7 (ml/cmH2O)/kg) compared to those of supine beagle dogs. Thus, their stiff chest wall sets their functional residual capacity (64.1 +/- 1.2% TLC30) at a much larger percentage of total lung capacity (TLC30) than that of the supine beagle dog (33.8% TLC30). Residual volume (13.2 +/- 1.9% TLC30) equaled the trapped gas volume after bilateral thoracotomy and was set by airway closure. We found more hysteresis area in the chest wall than in the lungs. Our measurements indicate that the static mechanical behavior of the respiratory system of the monkey compares well to man and that the monkey has considerable merit as an animal model for human respiratory function and disease research.
Susceptibility of different gases to ventilation-perfusion inequality
Authors: Wagner P. D.
Published: December 2017

Calculations of O2 and CO2 transfer in lung models of both series and parallel ventilation-perfusion (VA/Q) inequality have been performed by several investigators. In some cases, O2 uptake was found to be depressed more than CO2 output but in other examples CO2 elimination was interfered with to a greater extent. To understand the fundamental basis of differential susceptibility of various gases to VA/Q inequality, an algebraic analysis of inert gas exchange in two-compartment models of both series and parallel inequality is presented. For both types of inequality, the result is remarkably simple, in that the gas most affected is one whose partition coefficient is the geometric mean of the ventilation-to-perfusion ratios of the two compartments. Transfer of O2 and CO2 in these models was predicted well by the inert gas results not only qualitatively but even quantitatively. Similarly good quantitative predictions were obtained in more complicated multicompartment VA/Q distributions. The results therefore explain and reconcile the findings of various reported studies and in particular account for the observation that CO2 transfer is compromised in many examples of series inequality.
Effects of chronic changes in hemoglobin-O2 affinity in rats
Authors: Teisseire B. P. , Soulard C. D. , Herigault R. A. , Leclerc L. F. , Laver M. B.
Published: December 2017

We have assessed the characteristics of oxygen transport following chronic intraperitoneal administration of sodium cyanate (NaCNO, 90 mg/kg; P50 decreased), o-iodosodium benzoate (OISB, 300 mg/kg; P50 increased), or sodium chloride (NaCl; P50 unchanged) to rats at a rate of 5 times/wk for 16 wk. At the end of this period, the animals were exposed to a low inspired O2 concentration and were subjected to exercise stress. Hill's n50 at pH 6.90–7.60, hematocrit, and the saturation dependency of the Bohr effect (PCO2 constant) were altered by NaCNO only. Cyanate-treated rats gained less weight, probably due to a toxic side effect of the drug. Hypoxemia-induced lactatemia was greatest with a high P50 (OISB). Physical effort (swimming) was tolerated poorly at normal arterial PO2 when P50 was low (NaCNO). Although a left-shifted curve appears beneficial when FIO2 is reduced, reasons for the physiological advantage may be the result of other characteristics of the O2 dissociation curve, not P50 alone.
Decreased exercise hyperpnea in patients with bilateral carotid chemoreceptor resection
Authors: Honda Y. , Myojo S. , Hasegawa S. , Hasegawa T. , Severinghaus J. W.
Published: December 2017

Exercise hyperpnea was compared in 5 asthmatics 25 yr after bilateral carotid body resection (BR), 4 others 19 yr after unilateral resection (UR), and 12 controls (C) matched for age and pulmonary flow limitation. In the BR group, ventilation rose less with exercise, mostly because BR experienced less tachypnea. End-tidal PCO2 rose 5.8 +/- 3.2 (P less than 0.05) to 46 Torr at 50 W. In UR and C the same load did not increase PETCO2 significantly (+2.1 and +1.4 Torr, respectively). Arterial-end-tidal PCO2 differences before and 15--45 s postexercise were insignificant in all three groups. Heart rate and blood pressure rose equally in the three groups, suggesting that the ventilatory effects were not secondary to blood flow differences and disclosing no evidence of baroreceptor denervation during glomectomy.
Circulatory response to arterial hyperoxia
Authors: Cassuto Y. , Farhi L. E.
Published: December 2017

We have studied the circulatory response to 100% O2 at 1 and 3 atm, using unanesthetized rabbits in which a systemic artery and the right heart had been cannulated previously. One group of animals served as controls; the other was infused with a flurocarbon emulsion that boosted blood O2 solubility to approximately 5 ml.100 ml-1.atm-1. Exposure to hyperoxia caused an identical sustained rise in arterial PO2 in both groups. O2 uptake was measured during normobaric exposure to 100% O2 and was found to be the same as in control conditions. There was an immediate rise in right heart PO2, more marked in infused animals, but this increase was only temporary, and PO2 dropped, while the right heart-arterial PCO2 difference rose, indicating a gradual fall in cardiac output. This readjustment occurred at a faster rate in the infused animals, a difference that led us to conclude that the peripheral response to hyperoxia is influenced by factors other than arterial PO2. The pronounced decrease in cardiac output seen in infused rabbits was accompanied by lactic acidosis, implying that some of the animals' tissues were becoming hypoxic in the presence of arterial hyperoxia.
Solubility of inert gases in homogenates of canine lung tissue
Authors: Young I. H. , Wagner P. D.
Published: December 2017

The solubility of sulfur hexafluoride (SF6), ethane, cyclopropane, halothane, diethyl ether, and acetone in homogenates of dog lung tissue were measured and compared with values obtained in dog blood. The measurements were made to provide data for a method for determining distribution of ventilation, blood flow, and tissue volume (Physiologist 20: 95, 1977) and for reasons discussed, the blood was not washed from the tissue prior to homogenization. All gases except SF6 were significantly more soluble in blood than lung tissue, whereas SF6 was 3.7 times more soluble in tissue than blood. It was further found that SF6 is 5 times more soluble, and ethane is twice as soluble in tissue obtained from lungs containing blood than in tissue obtained from rinsed lungs, suggesting that measurements of parenchymal solubility made on tissue from sinsed lungs may be considerably in error for some lipid-soluble gases.
Effect of positive end-expiratory pressure on canine ventricular function curves
Authors: Marini J. J. , Culver B. H. , Butler J.
Published: December 2017

Recent observations have been interpreted to suggest altered ventricular function during ventilation with positive end-expiratory pressure (PEEP), apart from the effect of reduced preload. We constructed ventricular function curves in 14 anesthetized dogs as PEEP was varied under closed- and open-chest conditions. The systemic venous flow of the animal was diverted through an external circuit so that blood return to the right atrium could be varied stepwise from 1--4.5 l/min before and after 15 cmH2O PEEP was applied to the airway. Pressures adjacent to the heart were measured with thin fluid-filled water sensors to enable estimation of transmural pressure. Alterations in ventricular function were assessed by comparing tangential slopes as well as the atrial pressure differences separating the curves at high and low stroke volumes. Sensitivity of this method to cardiac depression was demonstrated by similar comparisons made before and after propranolol. Curves using transmural pressure on and off PEEP were statistically indistinguishable. We conclude that hemodynamic changes resulting from PEEP are attributable to the combined effects of reduced preload and raised juxtacardiac pressure, without ventricular dysfunction.
Effect of an exercise run to exhaustion on cAMP in the rat heart
Authors: Goldfarb A. H. , Kendrick Z. V.
Published: December 2017

The purpose of this investigation was to determine whether adenosine 3′,5′-cyclic monophosphate (cAMP) content is increased in vivo in the heart as a result of exercise at a time when there is rapid cardiac glycogen utilization. Rats were run to exhaustion on a treadmill for a period of 164.5 +/- 9.5 min. Blood norepinephrine and epinephrine were significantly elevated approximately 2.5-fold above resting levels at the end of the treadmill run. Myocardial glycogen was reduced by 54.7% at exhaustion compared with control values. Myocardial cAMP was significantly elevated 88% above control levels as a result of the run. Associated with the depletion of myocardial glycogen and the elevation of cAMP was an activation of phosphorylase to its a form. These data suggest that myocardial glycogen metabolism during exercise is, in part, mediated by hormonal influences that are associated with increases in cAMP.
Noninvasive ventilatory monitoring by respiratory inductive plethysmography in conscious sheep
Authors: Abraham W. M. , Watson H. , Schneider A. , King M. , Yerger L. , Sackner M. A.
Published: December 2017

The respiratory inductive plethysmograph is a noninvasive device that has been used to measure tidal volume (VT) in humans from changes in self-inductance of wire coils excited by an oscillator circuit placed about the rib cage and abdomen. We investigated its accuracy in conscious sheep utilizing a new calibration procedure during quiet breathing and breathing associated with bronchospasm provoked by aerosolized carbachol. Seven sheep were intubated with a nasotracheal tube and an esophageal balloon placed for determination of transpulmonary pressure. Base-line mean pulmonary flow resistance (RL) in the sheep was 1.5 +/- 0.7 (SD) cmH2O X l–1 X s. After carbachol inhalation, mean RL increased to a maximum of 8.8 +/- 2.8 cmH2O X l–1 X s (P less than 0.002). AT base line, mean VT estimated by respiratory inductive plethysmography over a 20-s period fell within +/- 6% of spirometry. After carbachol VT in five of the sheep remained close to the initial validation, but in two, it deviated +/- 11% from spirometry. Analysis of the continuous recording of timing and volume components of the breaths revealed that bronchoprovocation did not significantly alter mean VT or frequency. However, there was a slight increase in both parameters resulting in an increase in minute ventilation from 7.6 +/- 2.4 to 9.6 +/- 2.8 l/min (P less than 0.02). Similarly, a slight decline in inspiratory time coupled with the slight rise in VT produced an increase in mean respiratory flow from a base-line value of 0.35 +/- 0.12 to 0.44 +/- 0.17 l/s (P less than 0.05). These results indicate that the respiratory inductive plethysmography accurately monitors breathing pattern in conscious sheep even during severe bronchospasm.
Bradykinin-induced increase in pulmonary vascular permeability in hypoxic sheep
Authors: Pang L. M. , O'Brodovich H. M. , Mellins R. B. , Stalcup S. A.
Published: December 2017

Bradykinin (BK) is a potent edematogenic agent in systemic tissues. It is degraded by angiotensin-converting enzyme (ACE), which is located on the surface of all vascular endothelia. We hypothesized that since oxygen tension modulates ACE activity, the high pulmonary oxygen tension and hence high ACE activity protects the lung from the edematogenic effects of BK. We therefore studied the effect of exogenous BK in unanesthetized sheep with surgically created lymph fistulas and vascular catheters during normoxia and hypoxia. BK significantly elevated lung lymph flow and protein flux only when the sheep were made hypoxic and the lung's ability to degrade BK was impaired. This increase could not be attributed to recruitment of vascular surface area or to an increase in the driving force for fluid exchange because there were no changes in pulmonary arterial or left atrial pressures, cardiac output, or pulmonary vascular resistance. We conclude that BK increases water and protein movement in the lung by increasing vascular permeability.
Functional significance of compensatory overloaded rat fast muscle
Authors: Roy R. R. , Meadows I. D. , Baldwin K. M. , Edgerton V. R.
Published: December 2017

Chronic overload of a skeletal muscle by removing its synergists produces hypertrophy and marked changes in its metabolic and biochemical properties. In this study alterations in the contractile properties of the plantaris 12–14 wk after bilateral removal of the soleus and gastrocnemius were investigated. In situ isometric and isotonic contractile properties of overloaded plantaris (OP), normal plantaris (NP), and normal soleus (NS) were tested at 33 +/- 1 degree C. Op were 97% heavier than NP and produced 43 and 46% higher twitch (Pt) and tetanic (Po) tensions. However, NP produced more tension per cross-sectional area than OP (mean 26.2 vs. 21.6 N/cm2; P less than 0.001). Isometric twitch time to peak tension (TPT) and half-relaxation time (1/2RT) were significantly longer in OP (mean 36.4 vs. 32.5 ms and 23.9 vs. 18.4 ms). Mean maximum shortening velocity (Vmax, mm/s per 1,000 sarcomeres) were 34.1 for NP and 18.1 for OP (P less than 0.001). The degree of conversion toward the Vmax of NS was 74% compared with only 19 and 14% for TPT and 1/2RT. OP produced a higher proportion of Po at a given stimulation frequency than NP and showed less fatigue than NP after repetitive stimulation. Chronic overload of the fast plantaris modified to varying degrees the contractile properties studied toward that resembling a slow muscle. Although the maximum tension of OP was markedly enhanced it was not in proportion to the increase in muscle mass.
Interactions between placental O2 and CO transfer
Authors: Gurtner G. H. , Traystman R. J. , Burns B.
Published: December 2017

In 14 pregnant ewes the fetal side of the placenta was artificially perfused with adult sheep blood or with an emulsion of the fluorocarbon FC-47 containing varying amounts of CO. We measured diffusing capacities for O2 and Ar and permeability for urea and tritiated water (3H2O). We found that O2 diffusing capacity fell markedly in the presence of low levels of CO but that AR diffusing capacity and the permeability of urea and 3H2O remained constant at different levels of exposure to CO. We interpret the results as being consistent with the hypothesis that placental O2 transport is partially carrier mediated and that O2 and CO compete for the same carrier.
Failure of body plethysmography in bronchial asthma
Authors: Stanescu D. C. , Rodenstein D. , Cauberghs M. , Van de Woestijne K. P.
Published: December 2017

To determine whether acute changes in lung volumes in asthma are accurately measured by body plethysmography, we induced acute changes in lung mechanics with acetylcholine in nine asthmatic patients and with salbutamol in six others. Total lung capacity (TLC) was measured with a body plethysmograph and derived from mouth pressure vs. box volume (Vbox) changes (TLCm) or esophageal pressure vs. Vbox changes (TLCes). In six patients (4 after acetylcholine) TLCm was significantly (P less than 0.05) different from prechallenge values (differences ranged from 0.29 to 1.55 liters), but TLCes did not change. In three additional patients both TLCm (mean difference 0.62 liter) and TLCes (mean difference 0.43 liter) changed (P less than 0.05), but no changes occurred in six others. An electrical analog of the lung demonstrates in the presence of intrathoracic airway obstruction overestimation of thoracic gas volume and TLC. This is due to the presence of a compliant extrathoracic airway that acts as a shunt impedance. The magnitude of the overestimation of TGV appears to depend on the distensibility of the extrathoracic airway and the degree of airway obstruction. We conclude that the plethysmographic method may introduce important errors in lung volume measurements in the obstructive syndrome, especially a severe one. Some of previously reported acute increases in TLC in asthmatics may be artifactual.
A prediction-correction scheme for forcing alveolar gases along certain time courses
Authors: Robbins P. A. , Swanson G. D. , Howson M. G.
Published: December 2017

A computerized prediction-correction scheme has been devised for the control of alveolar gases. First, a model is run off-line to predict the inspiratory gas tensions at each second that should yield the desired alveolar patterns. Second, during the experiment, there is feedback correction based on the deviation of the actual alveolar values from the desired alveolar values. The actual alveolar values are found by a second computer and passed to the controlling computer using interrupts. The controlling computer has four digital-toi-analog outputs for controlling CO2, O2, N2, and air flows so as to achieve the commanded inspiratory PCO2 and PO2 (CO2 and O2 partial pressures, respectively). The scheme is illustrated for the generation of sinusoidal alveolar PCO2 with alveolar PO2 held constant and for steps of alveolar PCO2 at constant alveolar PO2.
A fast gas-mixing system for breath-to-breath respiratory control studies
Authors: Robbins P. A. , Swanson G. D. , Micco A. J. , Schubert W. P.
Published: December 2017

A computer-controlled gas-mixing system that manipulates inspired CO2 and O2 on a breath-to-breath basis has been developed. The system uses pairs of solenoid valves, one pair for each gas. These valves can either be fully shut when a low voltage is applied, or fully open when a high voltage is applied. The valves cycle open and shut every 1/12 s. A circuit converts signals from the computer, which dictates the flows of the gases, into a special form for driving the valve pairs. These signals determine the percentage of time within the 1/12-s cycle each valve spends in a open state and the percentage of time it spends shut, which, in effect, set the average flows of the various gases to the mixing chamber. The delay for response of the system to commanded CO2 or O2 changes is less than 200 ms. The system has application for the manipulation of inspired gas fractions so as to achieve desired end-tidal forcing functions.
Hypoxic suppression of dietary-induced component of resting metabolism in rats
Authors: Hayashi M. , Nagasaka T. , Shibata H.
Published: December 2017

Wistar rats fasted for 48 h were exposed to hypoxia (9.5% O2 in N2) at ambient temperatures (Ta) of 13.5, 24.5, and 32.0 degrees C. In normoxic environment, fasted rats showed significantly lower values of oxygen consumption (VO2), dry heat loss (R + C + K), and colonic temperature (Tcol) than in fed counterparts. The extent of decrease in each parameter was nearly same at any Ta. On exposure to hypoxia, fed rats showed a significant decrease in VO2, (R + C + K), and Tcol at any Ta. The decrease was particularly great at Ta 13.5 degrees C. In contrast to fed rats, fasted rats showed a significant decrease in all of these parameters only at Ta 13.5 degrees C. No such decrease was observed at Ta 24.5 and 32.0 degrees C. However, a significant difference in Tcol was found at Ta 24.5 degrees C in fasted rats between normoxic and hypoxic environments. Moreover, there was no statistically significant difference between fed and fasted rats in each parameter at any Ta in hypoxia. These results suggest that hypoxia suppresses both dietary-induced and cold-induced components of metabolism in rats.
Force-length relationship of the normal human diaphragm
Authors: Braun N. M. , Arora N. S. , Rochester D. F.
Published: December 2017

To characterize the in vivo force-length relation of the human diaphragm, we related pressures during static inspiratory efforts (Pmus and Pdi, respiratory muscle and transdiaphragmatic pressures, respectively) to diaphragm lengths measured on chest X rays from 22 normal subjects. At total lung capacity, the intersection of diaphragm and chest wall contours corresponds to the anatomic junction of diaphragm and chest wall. This point is located by skeletal landmarks to reveal the entire diaphragm contour on films taken at lower lung volumes. To validate the X-ray measurements, corresponding diameters were measured on 32 normal diaphragms at necropsy. After correction for height and diaphragm position, in vivo and necropsy length estimates along the coronal section agreed within 9%. The diaphragm length-lung volume relation is curvilinear, with length increasing primarily in the portion of the diaphragm apposed to the chest wall. As length increases, Pmus and Pdi rise sharply then plateau, generally conforming to force-length behavior of isolated muscle. However, absence of a Pdi peak at presumed diaphragm resting length suggests that Pdi is submaximal during voluntary inspiratory effort.
Effect of exercise conditioning on coronary resistance
Authors: Liang I. Y. , Stone H. L.
Published: December 2017

Diastolic coronary resistance (DCR) was determined in seven conscious dogs in the untrained state and after 4–5 wk of daily exercise conditioning (partial training). The conditioning regime consisted of treadmill running 5 days/wk. The dogs were instrumented to measure aortic pressure and left circumflex coronary flow during atrial pacing with implanted electrodes. Heart rate was varied from the resting value to 240 beats/min before and after adrenergic blockade with propranolol (beta B, 1 mg/kg) or phentolamine (alpha B, 1 mg/kg); myocardial oxygen consumption (MVO2) was measured in three dogs under the same condition in both the untrained (UT) and partially trained (PT) condition. DCR decreased with increasing heart rate [from 4.75 +/- 0.56 (SE) to 2.48 +/- 0.22 Torr . ml-1 . min at 240 beats/min]; alpha B reduced DCR, whereas beta B increased DCR. In the PT condition, DCR decreased to 4.02 +/- 0.40 Torr . ml-1 . min at rest and was decreased to 1.82 +/- 0.16 Torr . ml-1 . min at 240 beats/min (P less than 0.05 compared with UT). alpha-Adrenergic and beta-adrenergic blockade in the PT condition resulted in parallel reduction in DCR compared with the UT condition. MVO2 was unaffected by either PT or adrenergic blockade but increased as heart rate increased with atrial pacing. These data suggest a change in caliber of the coronary resistance vessel because of the parallel shift in the relationship between DCR and heart rate.