bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of acute and chronic hypercapnia on oxygen tolerance in rats
Authors: Clark J. M.
Published: December 2017

Groups of 16-52 normal or CO2-adapted rats were exposed top 100% O2 or to O2 with 60 Torr PICO2 (O2-CO2) at pressures of 1.0, 1.5, 2.0, 3.0, and 4.0 ATA. Exposure durations for 50% mortality (LD50) in normal rats at 4.0, 3.0, 2.0, 1.5, and 1.0 ATA O2 were 6.3, 9.3, 17.2, 27.4, and 76.1 h, respectively. Corresponding LD50 values for normal rats exposed to O2-CO2 were 2.0, 2.9, 16.3, 24.8, and 74.8 h. Survival times of CO2-adapted rats exposed to O2 were nearly identical to those of normal rats. LD50 values for CO2-adapted rat exposed to O2-CO2 were 4.1, 7.5, 17.9, 23.6, and 65.4 h, respectively. These data confirm acceleration of O2 intoxication by acute hypercapnia at 4.0 and 3.0 ATA, but they show less prominent effects at 2.0, 1.5, and 1.0 ATA. Hypercapnia adaptation clearly has a protective effect in rats exposed to O2-CO2 at 4.0 and 3.0 ATA. At 2.0, 1.5, and 1.0 ATA, where acute hypercapnia has less effect, the effects of CO2 adaptation are also less prominent. The observed changes in oxygen tolerance can be explained by cerebral vasodilation with increased brain oxygenation in acute hypercapnia and by significant amelioration of this response during chronic hypercapnia.
Ventilation by high-frequency oscillation in rabbits with oleic acid lung disease
Authors: Wright K. , Lyrene R. K. , Truog W. E. , Standaert T. A. , Murphy J. , Woodrum D. E.
Published: December 2017

The feasibility and efficiency of ventilation by high-frequency oscillation (HFO) were examined in animals with diffuse hemorrhagic lung disease. Twenty-four hours after injection with 0.12 ml/kg oleic acid, 11 spontaneously breathing rabbits had a mean (+/- SD) arterial O2 partial pressure (PaO2) of 65 +/- 16 Torr and arterial CO2 partial pressure (PaCO2) of 38 +/- 7 Torr [inspired fractional O2 concentration (FIO2) of 0.21]. Following paralysis animals were ventilated using a high-frequency oscillator for periods of 20 min followed by three successive hyperinflations to prevent atelectasis. Maintaining a constant mean airway pressure (MAP) of 6 cmH2O and fresh gas flow (FGF) of 2 1/min (FIO2 = 0.21), all combinations of frequency (5, 10, 20, and 30 Hz) and stroke volume (Vs) 2.6, 5.0, and 8.9 ml) were tested. At each frequency, an increase in Vs tended to lower mean PaCO2. At each Vs, CO2 elimination appeared maximal at 20 Hz, an effect attributable to decreasing effective Vs with increasing frequency. With constant Vs, MAP, and frequency, increasing FGF from 1 to 2 or 61/min decreased mean PaCO2 (P less than 0.05). With constant Vs, frequency, and FGF, increases in MAP from 2 to 10 cmH2O increased mean PaO2 (P less than 0.05). HFO, coupled with periodic hyperinflation, supports satisfactory gas exchange in rabbits with oleic acid lung injury. The efficiency of gas exchange is improved by independent increases in Vs, FGF, MAP, or frequency.
Competitive inhibition of carbon monoxide transport: evidence against a carrier
Authors: Rubin D. Z. , Fujino D. , Mittman C. , Lewis S. M.
Published: December 2017

The existence of a saturable carbon monoxide (CO) carrier in the lung remains controversial. The carrier hypothesis was invoked to explain data that indicated that pulmonary diffusing capacity for CO (DLCO) decreases with increasing CO concentration. To test this hypothesis, we measured DLCO in 14 normal adult subjects at three alveolar CO concentrations (60, 660, and 2,060 ppm). Each mixture contained a constant amount of labeled C18O (60 ppm) and a balance of unlabeled C16O. If a saturable carrier exists at increasing CO concentrations, the unlabeled CO would compete for most of the sites on the carrier molecule, effectively inhibiting the uptake of the labeled C18O. C18O diffusing capacities (mean +/- SD) for the three levels of CO were 34.9 +/- 5.6, 33.0 +/- 6.0, and 34.7 +/- 7.8. There were no significant differences (P greater than 0.2) among the three levels. In another group of subjects we repeated the study using a gas mixture containing 130 ppm C18O. No significant differences were found. As a result, we find no evidence to support a CO carrier hypothesis.
Phrenic activity, respiratory pressures, and volume changes in cats
Authors: Siafakas N. M. , Peslin R. , Bonora M. , Gautier H. , Duron B. , Milic-Emili J.
Published: December 2017

In eight anesthetized cats we measured the integrated ("moving time average") phrenic activity [using phrenic electroneurogram (EPHR)] and the active transdiaphragmatic pressure [Pdi(mus)] during room air breathing, hypoxia, and hypercapnia. The relationship between Pdi(mus) and EPHR was unaffected by either hypoxic or hypercapnic stimulation of breathing, suggesting that in spontaneously breathing cats the pressure losses are negligible. In all cats, however, there was a substantial volume-related decrease in Pdi(mus), indicating that with increasing lung volume the effectiveness of the diaphragm as a pressure generator decreases. In addition, we have developed a model that allows prediction of the time course changes in lung volume for different morphology of inspiratory driving pressure. This model explains many of the features of control of breathing found experimentally in our cats.
Hyperthermia in running sled dogs
Authors: Phillips C. J. , Coppinger R. P. , Schimel D. S.
Published: December 2017

Hyperthermia, as measured by increase in rectal temperature, was studied in a group of 22 adult mongrel sled dogs that had been selectively bred for high-speed (up to 33 km/h) races 16–50 km in distance. Under normal working conditions, rectal temperature in the sled dogs increased significantly during initial 15–20 min of run (gathered gallop) after which temperature usually stabilized or decreased slightly. Amount of increase in rectal temperature was correlated directly with ambient temperature but not with speed or distance. Significant differences in degree of hyperthermia were found among dogs but these differences were not correlated with such factors as sex, size, coat color, weight, or genetic history. Training was found to significantly diminish amount of increase in rectal temperature during work. Data from the present study were compared to those of other laboratory investigations and relationships of heat storage and radiative surface area to body weight are discussed.
Volume of trapped gas in lungs of healthy humans
Authors: Christensson P. , Arborelius M. , Kautto R.
Published: December 2017

The volume of trapped gas (Vtg) that could be mobilized by maximal breaths at the end of a nitrogen washout to 2% N2 was measured in 70 healthy women and 62 healthy men while seated. The average Vtg was found to be 102 +/- 21 (SD) ml in men and 73 +/- 18 ml in women. The Vtg was positively related to total lung capacity (TLC) (r = 0.67; P less than 0.001). An average percent Vtg/TLC of 1.4 +/- 0.31 (DS) % was applicable to both sexes. Vtg/TLC (%) was positively related to age (4 = 0.45; P less than 0.001). The error of a single determination was 8 ml, i.e., the reproducibility was very high. The existence of lung compartments that are unventilated or extremely underventilated may explain part of the physiological alveolararterial O2 difference. An increase in Vt has been found to be a very sensitive sign of subclinical bronchospasm.
Asymmetric distribution of carbonic anhydrase in the alveolar-capillary barrier
Authors: Effros R. M. , Mason G. , Silverman P.
Published: December 2017

Pulmonary carbonic anhydrase (CA) activity was studied by injecting 0.5 ml of a buffered solution of NaH14CO3 and 3H2O into the distal airways of perfused rabbit lungs. The early recovery of 14C in the pulmonary venous outflow averaged 0.28 +/- 0.02 (SE) that of 3H under control circumstances. Incorporation of a CA inhibitor (20 mg/l acetazolamide) in the perfusate reduced 14C recovery relative to 3H by two-thirds, whereas this inhibitor had no effect when placed in the airway injection fluid. Addition of 100 mg/l Ca to the perfusate did not increase 14C recovery, but addition of the enzyme to the bronchial fluid increased 14C recovery relative to 3H by a factor of more than 5. It is concluded that CA is associated with the endothelial side of the alveolar-capillary barrier but is absent on the airway surfaces.
Correlation of airway resistance with forced random noise resistance parameters
Authors: Pimmel R. L. , Fullton J. M. , Ginsberg J. F. , Hazucha M. J. , Haak E. D. , McDonnell W. F. , Bromberg P. A.
Published: December 2017

The correlation between airway resistance (Raw) measured in a plethysmograph and three respiratory resistance parameters measured by forced random noise was evaluated. Forced random noise resistance parameters were the average resistance between 5 and 9 hz (R5–9), the average resistance between 20 and 24 Hz (R20–24), and the extrapolated resistance at 1 Hz (R1). We studied 22 healthy, nonsmoking subjects, 10 of whom had a history suggesting childhood asthma. Serial measurements were made after inhalation of aerosols containing increasing concentrations of methacholine of aerosols containing increasing concentrations of methacholine to obtain data in various stages of bronchoconstriction. There was a broad range of responsiveness to methacholine; the ratio of the peak to base-line values of Raw ranged from 1.1 to 6.3. R1, R5–9, and R20–24 were related to Raw by linear regression analysis. R1 and R5–9 showed excellent correlation with Raw (r = 093 and 4=0.91, respectively); R20–24 showed much poorer correlation (r = 0.62). The slopes of the regression equations for R1 and R5–9 were 1.56 and 0.51, respectively; thus neither provided an exact measure of Raw. The data appear to be consistent with a model in which most of the methacholine-induced increase in resistance occurred in the peripheral airways and only a small fraction in the central airway.
Effect of carotid body denervation on arousal response to hypoxia in sleeping dogs
Authors: Bowes G. , Townsend E. R. , Kozar L. F. , Bromley S. M. , Phillipson E. A.
Published: December 2017

We studied the arousal and ventilatory responses to hypoxia during sleep in three trained dogs, before and 1–4 wk after carotid body denervation (CBD). During the studies the dogs breathed through a cuffed endotracheal tube inserted via a chronic tracheostomy. Eucapnic progressive hypoxia was induced by a rebreathing technique, and arterial O2 saturation (Sao2) was measured with an ear oximeter. Sleep stage was determined by electroencephalographic and behavioral criteria. Following CBD, all dogs exhibited hypoventilation under resting conditions; hypoxic ventilatory responses during wakefulness, slow-wave sleep (SWS), and rapid-eye-movement (REM) sleep were less than 10% of control. Prior to CBD, hypoxic arousal occurred at Sao2 of 83.2 +/- 4.6% (mean +/- Se) during SWS and 70.6 +/-2.2% in REM sleep. Following CBD, arousal failed to occur during progressive desaturation to 60% in SWS and 50% in REM sleep, at which levels hypoxia was arbitrarily terminated. In a few studies following CBD where rebreathing was allowed to continue, the dogs occasionally failed to arouse at all and require active resuscitation. The results indicate a critical role for the carotid chemoreceptors in mediating the arousal response to hypoxia.
Effects of dehydration on thermoregulation in cats exposed to high ambient temperatures
Authors: Doris P. A. , Baker M. A.
Published: December 2017

Measurements of evaporative water loss (EWL), metabolic rate (MR), body core temperature (Tc), and respiratory rate (RR) were made in nine hydrated cats exposed to several high ambient temperatures. Measurements were made in animals hydrated ad libitum and during progressive dehydration. At 43 and 40 degrees C, no significant change in EWL occurred during dehydration. At 38 and 35 degrees C, EWL in animals dehydrated for 4 days was reduced to about 50% of hydrated levels. Reductions in RR correlated highly with reduced EWL, suggesting that control of evaporation in dehydrated cats is dependent largely on control of RR. Significant elevations in Tc occurred in dehydrated animals at 43, 40, and 38 degrees C, and an insignificant upward trend was observed at 35 degrees C. Multiple linear regression analysis of data for EWL, Tc, and level of dehydration indicates that dehydration reduces the evaporative response to elevations in Tc and suggests that a change in the sensitivity of the thermoregulatory system is occurring. A similar analysis for MR, Tc, and level of dehydration shows that dehydration results in a lower MR at a given Tc. Changes in MR, corrected for body temperature, during dehydration are principally related at altered ventilatory energy expenditure. A model has been formed for estimating the metabolic cost of ventilation in the cat.
Hindrance to diffusive gas mixing in the lung in hyperbaric environments
Authors: Van Liew H. D. , Thalmann E. D. , Sponholtz D. K.
Published: December 2017

Diffusivity of a gas is inversely proportional to atmospheric pressure. We studied pulmonary gas mixing in hyperbaric environments (5.5 and 9.5 ATA) as a means of understanding the role played by diffusion in normal situations and also as a means of determining whether persons in hyperbaric environments will be handicapped by poor diffusive mixing. Our subjects took single breaths of a mixture of indicator gases (5% each of SF6, Ar, Ne, and He; 20% O2, balance N2). Recordings of expired volumes and concentrations showed that heavier indicators were less well mixed than lighter ones, as evidenced by a slower fall during the transition between dead space and "alveolar" gas and a steeper slope of the alveolar plateau. Differences between light and heavy gases increased as pressure increased. Amounts of the indicators retained in the functional residual capacity (FRC) or residual volume after a single breath had a weak positive relation to diffusivity; the amounts (A) in the FRC (as fraction of inspired amounts) were well fitted by a simple equation. ARFC/AI = 0.55 - (0.0010/D), where D is molecular diffusivity. We conclude that the changes of distribution of inspired gas that occur with large changes of diffusivity have only a minor effect on the amount of gas exchanged between the inspirate and residual gas in the FRC.
Ventilatory responses to muscular vibrations in healthy humans
Authors: Jammes Y. , Mathiot M. J. , Roll J. P. , Prefaut C. , Berthelin F. , Grimaud C. , Milic-Emili J.
Published: December 2017

In healthy humans, we studied the effect of high-frequency mechanical vibrations applied unilaterally to the tendon of the biceps or triceps brachialis on ventilation and the breathing pattern. This stimulus preferentially activates the muscle spindle afferents. Increase of respiratory frequency and changes in the ventilatory timing started at the first or second inspiration during tendon stimulation, and no adaptation occurred as long as the vibrations continued. The tidal volume and mean inspiratory flow rate were only enhanced in individuals having high-frequency breathing during eupnea. The changes in ventilatory variables were observed when the motor response to vibrations was tested under isometric or isotonic conditions. Various experimental procedures enabled us to induce a tonic reflex contraction in either the vibrated muscle or the antagonist of no reflex contraction in either group of muscles. In all cases the increase in minute ventilation was identical. These changes in breathing pattern was not associated with a significant decrease in alveolar CO2 pressure and did not seem to be responsible for important variations in respiratory gas exchanges. The response to high-frequency vibrations was also studied after ventilation was increased with added dead space. The magnitude of hyperventilation an the pattern of ventilatory response produced by tendon stimulation did not change with increased ventilation. In conclusion, the stimulation of muscle spindles in human induces changes in ventilation and pattern of breathing , and the occurrence of a reflex muscular contraction does not seem necessary in order to obtain such effects.
Adrenergic neurotransmission in airways: inhibition by acetylcholine
Authors: Russell J. A. , Bartlett S.
Published: December 2017

Superfusion techniques were used to examine the effect of acetylcholine (ACh) on the release of norepinephrine (NE) from isolated canine airways. Trachealis strips and helical strips of intrapulmonary airways were incubated with 3H-labeled NE, rinsed, and mounted in superfusion chambers. The superfusate was collected at timed intervals for estimation of total radioactivity and for column chromatographic separation of NE and its metabolites. Field electrical stimulation (2 Hz) and tyramine perfusion (3 X 10(-5) M) increased the total radioactivity of the perfusate by increasing the amount of intact 3H-labeled NE as well as the amounts of all metabolic fractions. Both extraneuronal and neuronal uptake mechanisms were important in inactivating the NE released by either stimulus. Exogenously administered ACh (10(-6)-10(-5) M) inhibited the release of NE that was caused by nerve stimulation but not that caused by tyramine perfusion. The inhibitory effect of ACh was antagonized by atropine (10(-6) M) but not by hexamethonium (5 X 10(-6) M). We conclude that ACh inhibits the exocytotic nerve-stimulated NE release by activating muscarinic receptors on adrenergic nerve varicosities.
Prepartum maturation of the lung in fetal sheep: relation to cortisol
Authors: Kitterman J. A. , Liggins G. C. , Campos G. A. , Clements J. A. , Forster C. S. , Lee C. H. , Creasy R. K.
Published: December 2017

We studied the relationship of certain fetal and maternal hormones to indicators of lung maturation in 12 fetal lambs delivered at gestational ages (GA) of 123-149 days. Maternal estrogen, maternal progesterone, and fetal prolactin did not correlate with GA or the indicators of fetal lung maturation. Fetal cortisol (range 4-165 ng X ml-1) increased with advancing GA (r = 0.747, P less than 0.01). All of the following showed a wide range of late gestation and showed a significant positive correlation with fetal cortisol: lung volumes at 40 cmH2O and 10 cmH2O on the deflation during air pressure-volume studies; saturated phosphatidylcholine (SPC) in lung tissue and in lavage fluid expressed both as mg X g-1 of wet lung and as percent of total phospholipids (%PL); total SPC (lung tissue plus lavage fluid): and SPC in lavage fluid as percent of total SPC. Lung DNA correlated inversely with GA and cortisol. All variables (except lavage fluid SPC as %PL) correlated more closely with cortisol than GA. Morphological development of lung was also related more closely to cortisol than GA. These results suggest that functional lung maturity is attained late in gestation and that endogenous cortisol is an important physiological factor in control of fetal lung maturation.
Interactions between fatiguing and nonfatiguing isometric contractions
Authors: Stafford D. E. , Petrofsky J. S.
Published: December 2017

Isometric contractions of the handgrip muscles were exerted by eight male subjects (age range 19-24 yr) to determine the relationship between fatiguing and nonfatiguing isometric contractions. In a first series of experiments, subjects exerted fatiguing isometric contractions at tensions of 25, 40, or 70% of the maximum strength of the subjects (MVC) following a contraction at a nonfatiguing tension of 5 or 10% MVC for 3, 7, or 20 min. In a second series of experiments, subjects exerted pairs of fatiguing isometric contractions at the same tensions; however, during the 3-, 7-, or 20-min interval between the contractions the subjects either rested or exerted a contraction at 5 or 10% MVC. Nonfatiguing isometric contractions exerted prior to fatiguing contractions had little influence on the endurance for the fatiguing static effort. In contrast, when contractions at nonfatiguing tensions were exerted in the recovery interval following an isometric contraction at a fatiguing tension, the recovery of endurance was dramatically reduced.
Kinetics of serotonin uptake in the dog lung
Authors: Rickaby D. A. , Linehan J. H. , Bronikowski T. A. , Dawson C. A.
Published: December 2017

A bolous containing [3H]serotonin and indocyanine green dye was rapidly introduced into the pulmonary artery on an isolated blood-perfused left lower dog lung lobe. Sequential samples of the venous effluent were collected for approximately 25 s following the injections. The lung intake of the injected [3H]serotonin was inversely proportional to the injected dose, ranging from about 70% for a 10-nmol injection to about 38% for a 100-nmol injection. Less than 2% of the injected 3H, which appeared in the venous effluent over the sampling interval, was in the form of [3H]5-hydroxyindoleacetic acid; and during the bolous transit through the lung lobe, uptake of serotonin by platelets was negligible. The serotonin extraction ratio curves exhibited dose-dependent characteristic shapes that we have interpreted using a model in which it is assumed that serotonin uptake follows Michaelis-Menten kinetics and flow through the capillary bed is heterogeneous. Using this model and a multiple regression analysis, the outflow dye and 3H concentration vs. time curves were used to estimate Km and Vmax for serotonin uptake by the lungs.
Selective autonomic stimulation of canine trachealis with dimethylphenylpiperazinium
Authors: Leff A. R. , Munoz N. M.
Published: December 2017

The response of canine tracheal muscle to autonomic stimulation with 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) was studied isometrically in 39 dogs in vivo. Intra-arterial (ia) DMPP (2.5 X 10(-4) to 2.5 X 10(-2) mg/kg) caused selective dose related contraction [maximum 30.1 +/- 6.5 gram-force (gf)/cm] due to regional stimulation of parasympathetic ganglia. This contraction was blocked by regional administration of atropine 10(-3) mg/kg ia and hexamethonium 5 X 10(-2) mg/kg ia. Nonselective intravenous (iv) administration of DMPP 2.5 X 10(-2) mg/kg caused parasympathetic tracheal contraction [+13.4 +/- 1.64 gf/cm] followed by later sympathetic relaxation [-11.8 +/- 2.3 gf/cm]; 0.5 mg/kg iv atropine abolished contraction but did not affect relaxation. The role of the adrenal gland vs. direct sympathetic innervation in producing tracheal relaxation after sympathetic stimulation was also studied. Tracheal relaxation to 2.5 X 10(-2) mg/kg iv DMPP was -18.2 +/- 4.0 gf/cm before adrenalectomy (ADX) and -4.3 +/- 0.9 gf/cm afterward (P less than 0.001). In contrast, tracheal contraction resulting from alpha-adrenergic stimulation after 2.5 X 10(-2) mg/kg iv DMPP in beta-blocked (BB) dogs was not significantly altered by ADX. At 2.5 X 10(-1) mg/kg iv DMPP, the alpha-adrenergic contractile response was still 70% of the response prior to ADX. We conclude that sympathetic tracheal relaxation in dogs is predominantly mediated by circulating catecholamine from the adrenal gland, but that alpha-adrenergic contraction after BB results predominantly from direct sympathetic innervation and is not greatly augmented by adrenal secretion. We also report a new method for selective stimulation of airway cholinergic nerves in vivo without systemic effects.
Cough dynamics during progressive expiratory muscle weakness in healthy curarized subjects
Authors: Arora N. S. , Gal T. J.
Published: December 2017

The dynamics of voluntary cough were studied in healthy supine subjects during four successive infusions of d-tubocurarine (dTc) (0.05 mg/kg) to assess the effects of progressive expiratory muscle weakness on cough performance. Curarization produced a progressive decline in maximal static expiratory muscle strength (PEmax) measured at the mouth and in pleural pressures (Ppl) generated during coughing. Expiratory flow rates during coughing did not decrease except during the initial cough from total lung capacity with the last dTc dose (18% below control). This was associated with a decrease in end-inspiratory volume prior to coughing and with a marked decrease in Ppl to 30% of control. Although the decrease in flow rates was minimal compared with Ppl, flow patterns suggest that dynamic airway compression was reduced during these coughs. We conclude that the principal effect of the expiratory muscle weakness in curarized subjects is to reduce the cough-induced dynamic compression and linear velocity of airflow though the major intrathoracic airways.
Pulmonary diffusing capacity for CO independent of alveolar CO concentration
Authors: Meyer M. , Lessner W. , Scheid P. , Piiper J.
Published: December 2017

Pulmonary diffusing capacity for CO (DCO) was measured in human subjects at various CO concentrations using a rebreathing procedure. Two stable CO isotopes, 12C18O and 13C18O, were used. These isotopes could be simultaneously and continuously recorded by a respiratory mass spectrometer. For 13C18O the initial concentration in the rebreathing bag was constant at 0.00016, whereas it was varied for 12C18O from 0 to 0.00224. DCO was calculated for both isotopes. In five normal subjects, both D12C18O and D13C18O were independent of the rebreathing CO concentration, with mean values of 31.0 and 30.2 ml . min-1 . Torr-1, respectively. These results, which are at variance with those of Mendoza et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 43: 880–884, 1977), are compatible with the assumption that diffusion is the sole mechanism of alveolocapillary CO transport; in particular, there is no evidence for facilitated transport.
Flow partitioning in symmetric cascades of branches
Authors: Snyder B. , Dantzker D. R. , Jaeger M. J.
Published: December 2017

We have found markedly nonuniform partitioning of flow in idealized models of physiological cascades of branches. Liquids having viscosities of 0.8–7.0 cP were used to investigate this effect systematically in a regime characterizing a limited range of pulmonary flows, comprising inlet flow rates of 500–3,000 ml/min and branch diameters of 1.0 cm ID. Factors that affect the nonuniformity of inspiratory flow include inlet velocity profile and flow rate, cascade aspect (L/D) ratio, exit pressure distribution, and, to a lesser extent, kinematic viscosity (mu/rho). More qualitative observations using sinusoidally oscillating airflow revealed inspiratory and expiratory flow patterns to be quite dissimilar, emphasizing the inadequacy of a resistance model of flow partitioning based on Kirchhoff's law. These results might suggest, in part, why regional ventilation in man is flow or frequency dependent and how bronchial smooth muscle could fine tune regional ventilation.
Effect of carotid chemoreceptor denervation on breathing in utero and after birth
Authors: Jansen A. H. , Ioffe S. , Russell B. J. , Chernick V.
Published: December 2017

The influence of the carotid bodies on fetal breathing activity in utero and on the establishment of postnatal breathing was studied. The electrocorticogram, the electromyogram of the lateral rectus and postural muscles, and tracheal and arterial pressures were monitored on chronically prepared intact and carotid sinus-denervated fetal lambs. The denervated fetuses required a longer time for recovery from the operation, but thereafter the sleeping and breathing behavior was similar to that of the control group. Four of the carotid sinus-denervated fetuses were allowed to be delivered spontaneously, and all established regular postnatal respiration despite conclusive evidence of nonfunctional carotid bodies. These experiments indicate that the fetal carotid chemoreceptors are not essential for the spontaneous intrauterine breathing activity during rapid-eye-movement sleep nor for the establishment of effective breathing at birth.
Surfactant aggregation in rat lungs: influence of temperature and ventilation
Authors: Massaro D. , Clerch L. , Massaro G. D.
Published: December 2017

We examined the effect of the ventilatory rate and the temperature of excised lungs and of increased body temperature of anesthetized spontaneously breathing rats on the centrifugal sedimentation of disaturated phosphatidylcholine (DSPC) present in lung lavage returns. More DSPC sedimented from lungs ventilated at low than at high rates, and sedimentation of DSPC and lung volume loss were temperature dependent, 41 greater than 37 greater than 4 degrees C. Most of the noncellular sedimented material was tubular and common myelin; these had diminished ability to lower surface tension rapidly compared with less-aggregated surfactant. More aggregated DSPC accumulated and lung volume decreased more in spontaneously breathing rats anesthetized for 30 min than in rats killed immediately after being anesthetized; these changes were greater after 30 min of anesthesia in hyperthermic rats (40.4 +/- 0.3 degrees C) than in normothermic rats (37.4 +/- 0.1 degrees C). These studies have shown a correlation between the increased accumulation of surfactant as large aggregates and the loss of alveolar stability; however, a cause and effect between these events has not yet been shown.
Changes in distribution of ventilation with lung growth
Authors: Cooper D. M. , Mellins R. B. , Mansell A. L.
Published: December 2017

We systematically studied the effects of varying preinspiratory lung volumes and expiratory flow rates on the alveolar plateau of the single-breath oxygen test in children and adults. With inhalations of oxygen beginning at functional residual capacity (FRC) compared with residual volume (RV), the slope of phase III increased in 52 of 54 children and 6 of 6 adults (mean increase 29.2%, P less than 0.001) but then decreased at preinspiratory volumes greater than FRC. With maximal expiratory flows, the slopes were smaller than slopes from conventional maneuvers in 14 of 15 children by a mean 24.1%, P less than 0.001. These data suggest that apex-to-base differences in regional lung volume are a major determinant of the slope. Slopes (FRC maneuver) decreased as a function of the height of the children (r = -0.73, P less than 0.001), but differences in nitrogen concentration over the alveolar plateau increased with height (r = 0.70, P less than 0.001). This indicates that the apex-to-base differences in regional lung volume increase with lung size. An estimate of mixing efficiency between resident and inspired gas derived from the alveolar plateau increased with height for both RV (r = 0.40, P less than 0.005) and FRC maneuvers (r = 0.45, p less than 0.005) and was greater for FRC than RV (P less than 0.001). These increases in mixing efficiency are consistent with previously demonstrated decreases in closing volume with growth.
Size of pores of Kohn: influence of transpulmonary and vascular pressures
Authors: Mazzone R. W. , Kornblau S.
Published: December 2017

We investigated the influence of transpulmonary (Ptp) and vascular pressures on the size of the pores of Kohn in primary alveolar septa. Dogs lungs, perfused and ventilated in situ, were rapidly frozen with Freon 22 in zone II or III conditions following deflation to Ptp of 5, 15, or 25 cmH2O. Frozen samples were freeze-substituted for transmission electron microscopy. Five fields containing at least one pore each were selected randomly from each section of tissue, and the minimum diameter visible in the cut section was measured. For both zone II and III conditions, as Ptp increased, mean pore size increased. The mean pore size under zone III conditions was 1.2015, 1.788, and 2.249 micrometer for Ptp of 5, 15, and 25 cmH2O, respectively. For zone 2 conditions, the corresponding values were 1.1438, 1,8757, and 2.08 micrometer. For both zones II and III, increasing capillary hydrostatic pressure had no significant effect on pore size. The results support the notion that alveolar pores can increase collateral ventilation by dynamically stretching as Ptp increases. Capillary pressure does not influence pore size probably because of collagen fibers, which surround the pore lumen. Presumably, these fibers resist encroachment of capillaries on the pore lumen as vascular pressures increase.
Skeletal muscle cytochrome c and myoglobin, endurance, and frequency of training
Authors: Hickson R. C.
Published: December 2017

This study was undertaken to evaluate the effects of various training frequencies on performance capacity, the mitochondrial marker cytochrome c, and myoglobin, which is responsible for storage and transport of O2, in the three types of skeletal muscle. Female rats were trained by treadmill running up to 120 min/day, either 2, 4, or 6 days/wk for 14 wk. As a result of training, exercise time to exhaustion was increased in proportion to the number of training sessions per week. Cytochrome c concentration increased (range 20–90%) as a linear function of the number of exercises per week in the fast-twitch red vastus lateralis (FTR), the slow-twitch soleus (STR), and the mixed plantaris muscles. However, the concentration of cytochrome c in fast-twitch white vastus lateralis (FTW) muscles increased to approximately the same extent (40–50%) in all training groups. The increases in myoglobin concentration (13–45%) with training were significantly related to frequency in FTR muscle but not in STR muscle. Myoglobin levels in FTW muscle remained unchanged, regardless of training group. These results provide evidence that the capacity to perform endurance exercise and the mitochondrial content of the red skeletal muscle types are directly affected by training frequency.
Training-induced alterations of the in vivo force-velocity relationship of human muscle
Authors: Caiozzo V. J. , Perrine J. J. , Edgerton V. R.
Published: December 2017

Seventeen male and female subjects (ages 20–38 yr) were tested pre- and posttraining for maximal knee extension torque at seven specific velocities (0, 0.84, 1.68, 2.51, 3.35, 4.19, and 5.03 rad . s-1) with an isokinetic dynamometer. Maximal knee extension torques were recorded at a specific joint angle (0.52 rad below the horizontal plane) for all test speeds. Subjects were randomly assigned to one of three experimental groups: group A, control, n = 7; group B, training at 1.68 rad . s-1, n = 5; or group C, training at 4.19 rad . s-1, n = 5. Subjects trained the knee extensors by performing two sets of 10 single maximal voluntary efforts three times a week for 4 wk. Before training, each training group exhibited a leveling-off of muscular tension in the slow velocity-high force region of the in vivo force-velocity relationship. Training at 1.68 rad . s-1 resulted in significant (P less than 0.05) improvements at all velocities except for 5.03 rad . s-1 and markedly affected the leveling-off in the slow velocity-high force region. Training at 4.19 rad . s-1 did not affect the leveling-off phenomenon but brought about significant improvements (P less than 0.05) at velocities of 2.51, 3.35, and 4.19 rad . s-1. The changes seen in the leveling-off phenomenon suggest that training at 1.68 rad . s-1 might have brought about an enhancement of motoneuron activation.
Pulmonary hypertension induced by repeated pulmonary inflammation in the rat
Authors: Herget J. , Palecek F. , Preclik P. , Cermakova M. , Vizek M. , Petrovicka M.
Published: December 2017

The effect of repeated lung inflammation on the pulmonary vascular bed was studied in rats. Nonbacterial lung inflammation was induced by repeated carrageenan instillations into the lungs. Three days after the single carrageenan injection, the mean pulmonary arterial blood pressure was only slightly raised [16.3 +/- 0.6 (mean +/- SE) Torr in controls and 19.5 +/- 0.5 Torr in rats with lung inflammation, P less than 0.001]. A substantial pulmonary hypertension was found in rats 3 days after the sixth lung inflammation (24.6 +/- 1 Torr). In this group, arterial hypoxemia, hypercapnia, and right-heart hypertrophy were found. In the 14th day of recovery after the last injection of carrageenan, the mean pulmonary artery blood pressure decreased (18.5 +/- 0.9 Torr) but remained higher than in the control group. There was no difference in cardiac output measured by dye-dilution technique between the experimental and control groups. After repeated inflammation, the media of distal pulmonary vessels thickened and the number of pulmonary arterioles with distinct media increased.
Total plasma creatinine: an accurate measure of total striated muscle mass
Authors: Schutte J. E. , Longhurst J. C. , Gaffney F. A. , Bastian B. C. , Blomqvist C. G.
Published: December 2017

Creatinine is a metabolite unique to striated muscle. Measurement of 24-h urinary creatinine excretion is an established method for estimating striated muscle mass. However, accurate assessment of urinary creatinine excretion is often impractical. We investigated the hypothesis that total plasma creatinine could be used instead of urinary creatinine excretion to estimate body composition. In 24 men, plasma volume and plasma creatinine concentration were measured, and total plasma creatinine was calculated as the product of these two measurements. Other measurements included urinary creatinine excretion, total body water, and anthropometry. Total plasma creatinine correlated strongly with urinary creatinine excretion (r = 0.82) and with weight, total body water, and anthropometrically estimated lean body mass. Muscle mass could be predicted by the equation: 0.88 x total plasma creatinine (mg). To verify this relationship, total plasma creatinine was prospectively measured in four dogs, then their total striated muscle was removed and weighed. Predicted muscle mass was within +/- 3.9% (range = 0.5–10.8%) of observed muscle mass. The ability to estimate muscle mass conveniently and accurately from total plasma creatinine should prove valuable for future studies in physiology and body composition.
Direct dynamic measurements of tracheal diameter
Authors: Fouke J. M. , Pimmel R. L. , Bromberg P. A.
Published: December 2017

Methods of monitoring airway caliber as an indicator of bronchomuscular tone have been indirect, static, and invasive. A diameter transducer has been developed the static and dynamic characteristics of which indicate that it should overcome some methodological problems. The catheter-mounted spring-loaded braces of the transducer track the motion of the airway wall, which is reflected in the output changes of a linear-variable transformer. The range of the transducer was 5.3–24.3 mm. The amplitude response was flat up to 8 Hz, and the phase difference between the forcing signal and the response of the gauge was 0 degrees up to 8 Hz. The minimum specific compliance was 0.15 cmH2O–1, an order of magnitude larger than the specific compliance of isolated trachea, indicating that the airway was not significantly loaded by the transducer. In vivo studies in ventilated dogs revealed tidal changes in tracheal diameter and marked constriction during apnea. Bilateral vagotomy increased diameter up to 20%, and vagal stimulation decreased diameter as much as 30% below postvagotomy levels. It appears that this transducer is suitable for measuring resting diameter, tidal changes in diameter, and changes in diameter induced by alteration in bronchomotor tone.
Hydrodynamic features of pulmonary air embolism: a model study
Authors: Chang H. K. , Weber M. E. , Thomson J. , Martin R. R.
Published: December 2017

To elucidate the hydrodynamic events during pulmonary air embolism, experiments were conducted in a branching-tube apparatus and in small vessels. It was found that, as long as there existed an elevation differential between the two branches of a bifurcation, the vast majority of air bubbles always entered the higher branch. This finding is explained in terms of buoyancy, shear forces, and liquid flow velocity and is consistent with the in vivo finding of increased blood perfusion in the dependent lung regions during air embolization (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 211–217, 1981). The pressures required to drive air bubbles through various small vessels were determined using three aqueous solutions of different surface tensions. Based on these measurements and a theoretical analysis, the diameter of air bubbles that could not pass through the pulmonary vessels was calculated to be 20–30 micrometers, agreeing well with a recent in vivo measurement (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 537–543, 1979).
Effect of O2 and CO2 in N2, He, and SF6 on chick embryo blood pressure and heart rate
Authors: Tazawa H.
Published: December 2017

Arterial pressure of chick embryos was measured electromanometrically to investigate the effect of altered gaseous environments on blood pressure (BP) and heart rate (HR). The experiments were made in eggs incubated for 14–16 days at 38 degrees C without impeding the diffusive respiratory gas exchange through the shell and chorioallantois. In air, the HR was counted 260–270 beats/min and the BP increased from 14/7 Torr at day 14 to 21/12 Torr at day 16. Both the BP and HR decreased with hypoxia, whereas hyperoxia affected a slight increase in BP and little change in HR. Hypercapnia decreased the HR and tended to enhance a systolic maximum pressure. The effect of hypoxia was augmented markedly in the presence of hypercapnia and vice versa. When N2 was replaced with helium (He), the effect of hypoxia was mitigated significantly. On the contrary, replacement of N2 with sulfur hexafluoride (SF6) augmented the effect of hypoxia. Because the respiratory gas exchange of the egg takes place by diffusion through the shell and chorioallantoic capillaries, the effect of He and SF6 atmospheres on BP and HR is attributed to an altered diffusivity of O2 and CO2 in these inert gases.
Measurement of blood pressure of chick embryo with an implanted needle catheter
Authors: Tazawa H.
Published: December 2017

A catheter, consisting of a hypodermic needle and polyethylene tube, was implanted in the allantoic artery and/or vein of chick embryos ranging in incubation ages from 13 to 17 days. The procedure was performed through a small hole opened in the shell (less than 1 cm2). The hole was covered after implantation of the catheter, ensuring the adequate gas exchange by the chorioallantois and physiological values of blood gases. Blood pressure was measured with an electromanometric transducer. The arterial pressure lacked a dicrotic elevation. Both the systolic and diastolic pressures increased markedly with days of incubation, but the heart rate showed no significant change. The venous pressure was pulsatile in some eggs, and the pulsations became prominent after administration of epinephrine.
A combined transcutaneous PO2-PCO2 electrode with electrochemical HCO3- stabilization
Authors: Severinghaus J. W.
Published: December 2017

Combined transcutaneous PO2-PCO2 electrodes are described in which the interaction between the two electrodes due to OH- production at the O2 cathode has been eliminated. An anode of either anodized aluminum or platinum has been driven at a current equal to cathode current to force stoichiometric consumption of OH- at its rate of production. The AgCl reference electrode operates at zero current. O2 sensitivity was not significantly altered by electrolyte pH variation from 6.7 to 9.0 with variations by PCO2. These electrodes have been found stable both with and without spacers, and with electrolytes dissolved in 50–100% ethylene glycol. In 22 anesthetized patients, with electrode temperature of 43 degrees C (s refers to skin surface, a to arterial blood); PsO2 = 0.52PaO2 + 15 (range 54–300) (r = 0.66; Sy . x = 29.6; n = 46); and PsCO2 = 1.39PaCO2 + 2.1 (range 24–98) (r = 0.99; Sy . x = 2.28; n = 48).
Plasma norepinephrine response to exercise before and after training in humans
Authors: Peronnet F. , Cleroux J. , Perrault H. , Cousineau D. , de Champlain J. , Nadeau R.
Published: December 2017

Plasma norepinephrine (NE) concentration was measured by means of a sensitive radioenzymatic assay in blood collected from an antecubital vein in 10 healthy male subjects (37 +/- 2 yr, mean +/- SE). The subjects were evaluated at rest and during exercise before and after a 20-wk training program on bicycle ergometer (three 30-min sessions per week at 80% of maximal heart rate). Following the training program, maximal oxygen uptake increased significantly from 33 +/- 2 to 42 +/- 1 ml . kg-1 . min-1. Resting plasma NE remained unchanged after training (167 +/- 38 before and 185 +/- 29 pg . ml-1 after training). For a given absolute work load (735 +/- 51 kg . m. min-1) the sympathetic nervous response was lower after training as reflected by the decrease in NE concentration (1,371 +/- 286 vs. 687 +/- 64 pg . ml-1). At the same relative work load (heart rate: 158 +/- 5 before and 157 +/- 5 beats . min-1 after training) plasma NE concentration was unchanged after training (1,371 +/- 286 vs. 1,729 +/0 371 pg . ml-1). Results from the present study show that the sympathetic nervous activity is closely linked to the exercise demands and confirm earlier suggestions that it remains constant in relation to the relative work load.
Respiratory neuron responses to hypercapnia and carotid chemoreceptor stimulation
Authors: St John W. M.
Published: December 2017

In decerebrate, vagotomized, paralyzed, and ventilated cats, activities were recorded from the phrenic nerve and from respiratory units within the dorsal and ventral medullary respiratory nuclei and the pontile reticular formation. These unit activities were monitored during equivalent augmentations in peak integrated phrenic nerve activity induced by stimuli acting primarily on the peripheral or central chemoreceptors. These stimuli were intracarotid infusions of sodium cyanide or nicotine and exposure to hyperoxic hypercapnia, respectively. Both stimuli caused similar increases in activities for most dorsal nucleus inspiratory units. For units of the ventral medullary nucleus, augmentations in activity were only significant (inspiratory neurons) or were of greater magnitude (expiratory neurons) during hypercapnia. As opposed to medullary units, the discharge frequencies of many pontile units were unaltered or declined during both peripheral and central chemoreceptor stimulations. These results support the concept that excitatory influences from the peripheral and central chemoreceptors are not equally distributed among all groups of brain stem respiratory neurons.
Temperature and surface forces in excised rabbit lungs
Authors: Inoue H. , Inoue C. , Hildebrandt J.
Published: December 2017

This study was designed to determine whether the effects of temperature on lung pressure-volume (PV) curves were influenced by the state of the surface lining at the time of warming or cooling. In successive runs, temperature was varied (21, 37, or 5 degrees C) with lung gas volume fixed at either 55% total lung capacity (TLC) or 0% TLC (degassed), followed by PV curves to TLC. Peak inflation volume in a given lung was made identical at all temperatures. The starting pressure at 55% TLC remained fixed during temperature changes, whereas peak pressure ranged from 24 cmH2O at 37 degrees C to 40 cmH2O at 5 degrees C. However, below 75% TLC all deflation curves differed by less than 1 cmH2O, and the lowest recoil occurred at 5 degrees C. At 0% TLC, a similar dispersion in pressures appeared at TLC. However, on deflation, recoil at 37 degrees C was always less than at 21 degrees C, whereas at 5 degrees C a drastic shift to the right occurred. First-cycle hysteresis and midinflation pressure also increased with cooling. Thus, with cooling, the spreading and adsorption of surfactant during lung expansion are inhibited, and during deflation aggregation is greatly facilitated, accounting for the above results. When an already spread surface is cooled, then expanded, as at 55% TLC, the more rigid lining causes some rise in peak pressure at TLC but little change elsewhere. However, when lungs are degassed and then cooled, the aggregated surfactant spreads extremely poorly, leading to greatly increased recoil throughout the cycle. Changes in pressure at TLC may depend considerably on tissue effects.