bluuebunny/crossref_metadata_2025 huggingface dataset:
Buffering capacity of deproteinized human vastus lateralis muscle
Authors: Parkhouse W. S. , McKenzie D. C. , Hochachka P. W. , Ovalle W. K.
Published: December 2017

The in vitro deproteinized vastus lateralis muscle buffer capacity, carnosine, and histidine levels were examined in 20 men from 4 distinct populations (5 sprinters, 800-m runners; 5 rowers; 5 marathoners; 5 untrained). Needle biopsies were obtained at rest from the vastus lateralis muscle. The buffer capacity was determined in deproteinized homogenates by repeatedly titrating supernatant extracts over the pH range of 7.0–6.0 with 0.01 N HCl. Carnosine and histidine levels were determined on an amino acid AutoAnalyzer. Fast-twitch fiber percentage was determined by staining intensity of myosin adenosinetriphosphatase. High-intensity running performance was assessed on an inclined treadmill run to fatigue (20% incline; 3.5 m X s-1). Significantly (P less than 0.01) elevated buffer capacities, carnosine levels, and high-intensity running performances were demonstrated by the sprinters and rowers, but no significant differences existed between these variables for the marathoners vs. untrained subjects. Low but significant (P less than 0.05) interrelationships were demonstrated between buffer capacity, carnosine levels, and fast-twitch fiber composition. These findings indicate that the sprinters and rowers possess elevated buffering capabilities and carnosine levels compared with marathon runners and untrained subjects.
Effects of arachidonate on permeability and resistance distribution in canine lungs
Authors: Townsley M. I. , Korthuis R. J. , Taylor A. E.
Published: December 2017

In this study, 14 canine lung lobes were isolated and perfused with autologous blood at constant pressure (CP) or constant flow (CF). Pulmonary capillary pressure (Pc) was measured via venous occlusion or simultaneous arterial and venous occlusions. Arterial and venous pressures and blood flow were measured concurrently so that total pulmonary vascular resistance (RT) as well as pre- (Ra) and post- (Rv) capillary resistances could be calculated. In both CP and CF perfused lobes, 5-min arachidonic acid (AA) infusions (0.085 +/- 0.005 to 2.80 +/- 0.16 mg X min-1 X 100 g lung-1) increased RT, Rv, and Pc (P less than 0.05 at the highest dose), while Ra was not significantly altered and Ra/Rv fell (P less than 0.05 at the highest AA dose). In five CP-perfused lobes, the effect of AA infusion on the pulmonary capillary filtration coefficient (Kf,C) was also determined. Neither low-dose AA (0.167 +/- 0.033 mg X min-1 X 100 g-1) nor high-dose AA (1.35 +/- 0.39 mg X min-1 X 100 g-1) altered Kf,C from control values (0.19 +/- 0.02 ml X min-1 X cmH2O-1 X 100 g-1). The hemodynamic response to AA was attenuated by prior administration of indomethacin (n = 2). We conclude that AA infusion in blood-perfused canine lung lobes increased RT and Pc by increasing Rv and that microvascular permeability is unaltered by AA infusion.
Effect of outflow pressure on lung lymph flow in unanesthetized sheep
Authors: Drake R. , Giesler M. , Laine G. , Gabel J. , Hansen T.
Published: December 2017

Studies in anesthetized animals have shown that the flow rate from lung lymphatics (QL) depends on the pressure at the outflow end of the vessels (Po). We tested this in unanesthetized sheep prepared with chronic lung lymph cannula. We measured QL with the lymph cannula held at various heights above the olecranon and calculated Po as the height + QL X cannula resistance. QL decreased with increases in Po (delta QL/delta Po = -8.2 +/- 6.4 microliter X min-1 X cmH2O-1, mean +/- SD). We increased QL by raising left atrial pressure or infusing Ringer solution or Escherichia coli endotoxin and found that QL was even more sensitive to Po (delta QL/delta Po = -32 +/- 22). Cannula resistance caused a 9–70% reduction in QL. Changes in QL caused by increasing Po were not associated with changes in lymph protein concentration for up to 330 min. This indicates that increases in Po shunt lymph away from cannulated vessels but do not substantially effect microvascular filtration rate. The shunted lymph may flow into other vessels or collect in the lung. We conclude that QL does not accurately represent microvascular filtration rate because it depends on the cannula resistance and position at which the investigator chooses to place the cannula.
Alteration of surfactant function due to protein leakage: special interaction with fibrin monomer
Authors: Seeger W. , Stohr G. , Wolf H. R. , Neuhof H.
Published: December 2017

In isolated rabbit lungs standardized amounts of edema were induced. Stimulation with the Ca ionophore A23187, leukotriene C4, Pseudomonas aeruginosa cytotoxin and human serum (activated complement) all resulted in protein leakage into the alveolar space with no change in the total phospholipid content. The pressure-volume characteristics of the lungs and the characteristics of the lavage surfactant (Wilhelmy balance) were markedly altered, correlating to the lavage protein content. The surfactant alterations were reproduced by addition of perfusion fluid protein to control surfactant in vitro. All changes were far less expressed or even missing in isolated lungs developing the same amount of edema due to omittance of proteins from the perfusion liquid. Different proteins added to control surfactant in the Wilhelmy balance showed a marked rank order of potency in interfering with surfactant function: immunoglobulins G and M and elastin less than albumin less than fibrinogen less than fibrin monomers. The fibrin monomer effect was reproduced by addition of thrombin to a surfactant fibrinogen mixture and was partly reversed by subsequent incubation with plasmin. In conclusion, high-permeability edema induced by different means results in alterations of lung mechanics and surface activity of lavaged surfactant, presumably due to protein surfactant interaction. Among different proteins, fibrin monomers are especially effective in interfering with surfactant function.
Gas exchange and hatchability of chicken eggs incubated at simulated high altitude
Authors: Visschedijk A. H.
Published: December 2017

Chicken eggs laid at sea level were incubated at sea level (control conditions), at a simulated altitude of 5.5 km without any further measures (natural conditions), and at a simulated altitude of 5.7 km at optimal incubator gas composition (optimal conditions). Under optimal conditions the incubator relative humidity was 70% throughout incubation, the gas mixture supplied to the incubator contained 45% O2–55% N2, and the ventilation rate was reduced to 6% of control in order to maintain the normal air-space gas tensions and to compensate for the increased eggshell conductance at altitude. The embryos that developed under control conditions showed a normal CO2 production with 94% hatchability of fertile eggs. Under natural conditions at altitude all embryos died within a few days. Optimal conditions resulted in an almost normal gas exchange and in an improvement of hatchability from 0 to 81% of fertile eggs.
Effect of exercise duration on feed intake and body composition of Swiss albino mice
Authors: Bulbulian R. , Grunewald K. K. , Haack R. R.
Published: December 2017

The purpose of this study was to examine the effects of daily exercise of varying duration on the body composition, weight, and feed intake of mature Swiss albino mice. Fifty-four male mice were equally divided into a control group and five exercise groups (n = 9) performing 20, 40, 60, 120, and 240 min of daily exercise on a treadmill (7.2 m/min). Feed intake and body weight were measured weekly for 10 wk. At the completion of the study the mice were killed and the animal carcasses were chemically analyzed for fat, dry matter, and protein content. The results of this study demonstrate no differences in the body weight among groups (P less than 0.97) with all groups gaining 4.5–5.8 g during the 10-wk period. However, fat content decreased significantly from 15.7% in the control to 12.0% in the 120- and 240-min exercise groups (P less than 0.05). In contrast, protein content showed an insignificant rising trend from 13.0 to 14.6% with increasing duration of exercise. Feed intake showed a nonsignificant drop during the 20-min exercise treatment and remained unchanged among groups. These data show a slight but variable appetite-suppressing effect of light exercise in mice accompanied by favorable body composition changes even in the absence of differences in body weight. These findings suggest the mouse to be an acceptable experimental model for body composition and exercise studies.
In vitro responses of cat skeletal muscle to halothane and caffeine
Authors: Deuster P. A. , Bockman E. L. , Muldoon S. M.
Published: December 2017

Strips of soleus (100% type I) and gracilis (90% type II) muscle were obtained from anesthetized cats and mounted in organ baths filled with aerated Krebs-Ringer solution (37 degrees C). The contractile patterns in response to electrical stimulation (0.1 Hz, 25 V, 5 ms), caffeine, halothane, and caffeine in the presence of halothane were examined in the two fiber types. The ability of 25 microM dantrolene to alter the contractile patterns was also evaluated. In vitro contractile properties in response to electrical stimulation were similar to properties observed in situ, except that twitch tension in soleus muscle was significantly less in vitro than in situ. In the presence of halothane, type I soleus muscle developed a rapid contracture. The contracture was blocked by pretreatment with dantrolene and was reversed by addition of dantrolene at the peak of the response. Halothane-induced contractures were not observed at any time in type II gracilis. Type I soleus was also significantly more sensitive both to caffeine alone and to caffeine in the presence of halothane than was type II gracilis. In both fiber types, halothane increased the sensitivity of the muscles to caffeine. Dantrolene attenuated caffeine-induced contractures in both fiber types, but the attenuating effect was less in the presence of halothane. The findings of a halothane-induced contracture in the cat soleus and differential sensitivities of the two muscle fiber types to caffeine indicate that further studies in these two muscles may be useful for delineating the mechanisms inducing contracture in muscle from individuals susceptible to malignant hyperthermia.
Angiotensin II-induced hypothermia in rats
Authors: Wilson K. M. , Fregly M. J.
Published: December 2017

Systemic administration of angiotensin II (ANG II) (200 micrograms/kg sc) to the rat induced a hypothermic response that was characterized within 12 min by a reduction in the rate of O2 consumption, vasodilation of the tail, and a 1.3 degrees C fall in colonic temperature. Administration of ANG II in doses ranging from 10 to 200 micrograms/kg resulted in a decrease in colonic and an increase in tail skin temperature. Angiotensin I (ANG I) (200 micrograms/kg sc) induced a similar hypothermic response which was abolished by pretreatment with the ANG I-converting enzyme inhibitor, captopril (35 mg/kg ip). The interaction of ANG II with cholinergic and adrenergic pathways was evaluated to determine possible mechanisms. Treatment with ANG II (200 micrograms/kg sc) and propranolol, a beta-adrenoceptor antagonist (6 mg/kg ip), resulted in a greater depression of colonic temperature (Tco) than was observed with ANG II alone but did not affect the increase in tail skin temperature (Tsk) accompanying administration of ANG II. When ANG II was administered in combination with the beta-adrenergic agonist, isoproterenol (50 micrograms/kg ip), Tco remained at control levels, whereas an enhancement of the ANG II-induced increase in Tsk occurred. Administration of ANG II in combination with atropine sulfate (6 mg/kg ip), a muscarinic receptor antagonist which crosses the blood-brain barrier, significantly reduced the extent of the fall in Tco without affecting the increase in Tsk. The combined treatment of ANG II and the quaternary analogue, atropine methyl nitrate (3.25 mg/kg ip), which does not cross the blood-brain barrier, failed to affect the hypothermic responses to ANG II. These results suggest that the hypothermic responses to ANG II may be mediated through a central cholinergic pathway and possibly influenced by an adrenergic component. The inability of both adrenergic and cholinergic blockers to affect the vasodilatory response of the tail of the rat to administration of ANG II suggests that the mechanisms subserving heat production can be blocked independently of those subserving heat loss.
Epinephrine is unessential for stimulation of liver glycogenolysis during exercise
Authors: Carlson K. I. , Marker J. C. , Arnall D. A. , Terry M. L. , Yang H. T. , Lindsay L. G. , Bracken M. E. , Winder W. W.
Published: December 2017

To determine the role of adrenal medullary hormones in controlling the rate of liver glycogenolysis during exercise, adrenodemedullated (ADM) and sham-operated (SO) rats were run on a rodent treadmill at 21 m/min up a 15% grade for 0, 30, or 60 min. Rats were anesthetized by intravenous injection of pentobarbital sodium, and liver, muscle, and blood were collected and frozen. Liver glycogen decreased at similar rates in ADM and SO rats. Hepatic adenosine 3′,5′-cyclic monophosphate (cAMP), plasma glucagon, and plasma free fatty acids increased to the same extent in both ADM and SO rats. The adrenodemedullation caused a reduction in glycogenolysis in the fast-twitch white region of the quadriceps, soleus, and lateral gastrocnemius during exercise. The normal exercise-induced increase in blood glucose and lactate and the decline in plasma insulin were not observed in the demedullated rats. During submaximal exercise the principal targets for epinephrine released from the adrenal medulla appear to be pancreatic beta-cells and skeletal muscle and not the liver.
Airway reactivity in ponies with recurrent airway obstruction (heaves)
Authors: Derksen F. J. , Robinson N. E. , Armstrong P. J. , Stick J. A. , Slocombe R. F.
Published: December 2017

We measured lung function and airway reactivity to histamine administered by aerosol in two groups of ponies. Principal ponies had a history of heaves, a disease characterized by recurrent airway obstruction when ponies are housed in a barn and fed hay; control ponies had no history of airway obstruction. Ponies were paired (principal and control) and measurements were made when principal ponies were at pasture and in clinical remission (period A), following barn housing when principal ponies had acute airway obstruction (period B), and after a further 1 and 2 wk at pasture (periods C and D). At periods A, C, and D dynamic compliance (Cdyn), pulmonary resistance (RL), arterial O2 tension (PaO2), and CO2 tension (PaCO2) of principals and controls did not differ. Barn housing (period B) decreased Cdyn and PaO2 and increased RL in principals but not controls. The ED65Cdyn (the dose of histamine to reduce Cdyn to 65% of base line) did not differ in principals and controls at periods A, C, and D. At period B, ED65Cdyn decreased by 2.5-log doses of histamine in principals while ED65Cdyn was not affected in controls. There was no correlation between changes in airway reactivity and changes in RL and Cdyn. We conclude that ponies in clinical remission from heaves are not hyperreactive to histamine aerosol. This model of lung disease is similar to some forms of industrial asthma in which hyperreactivity occurs only during acute airway obstruction. The lack of correlation between ED65Cdyn and the degree of airway obstruction suggests that the hyperreactivity of principal ponies to histamine aerosol cannot be explained solely by alterations in baseline airway caliber.
Potentiation of lung vascular response to endotoxin by superoxide dismutase
Authors: Traber D. L. , Adams T. , Sziebert L. , Stein M. , Traber L.
Published: December 2017

We studied the effects of superoxide dismutase (SOD), an enzyme that converts superoxide into peroxide, on the cardiopulmonary response to endotoxin in sheep. Sheep (n = 18) were prepared for chronic measurement of cardiopulmonary variables, including lung lymph flow, by surgically implanting catheters under halothane anesthesia. Nine of the animals were studied before and after the administration of endotoxin (0.75 microgram/kg) with and without SOD. An additional nine animals received SOD without the lipopolysaccharide. Endotoxin produced an increase in lung lymph flow that was initially associated with a marked pulmonary arterial (PA) hypertension and reduced lymph-to-plasma protein ratio (L/P). The lymph flow remained elevated later in the response, but there was only a mild increase in PA pressure, and the L/P was normal. There was also a fall in blood neutrophils and in cardiac index. SOD increased this secondary elevation in lung lymph flow, and the corresponding L/P was greater than the preendotoxin value. The fall in neutrophil count, cardiac output, and the elevation in PA pressure seen with endotoxin were not affected by SOD. When administered in the absence of endotoxin, SOD produced no perceptible change in the cardiopulmonary and lymph values. We conclude that peroxide, hydroxyl ion, and/or other free radicals formed by the action of SOD must be responsible for a portion of the endotoxin response rather than superoxide itself.
Muscle blood flow patterns during exercise in partially curarized rats
Authors: Armstrong R. B. , Vandenakker C. B. , Laughlin M. H.
Published: December 2017

We studied the distribution of blood flow within and among muscles of partially curarized (40–100 micrograms/kg body wt) rats during preexercise and at 1 min of low-speed treadmill exercise (15 m/min). Glycogen loss in the deep red muscles and parts of muscles was significantly reduced in the curarized animals during exercise, indicating the fibers in these muscles were recruited to a lesser extent and/or had lower metabolisms than fibers in the same muscles of control rats. However, elevations in blood flow in the red muscles of the curarized rats were as great or greater than those in the control rats. Thus reduced recruitment and/or metabolism of the deep red muscle fibers of the curarized animals was not accompanied by reduced blood flow. These findings suggest a dissociation between red fiber metabolism and blood flow in the curarized rats during the 1st min of slow treadmill exercise and indicate that release of vasodilator substances or local physical factors associated with muscle fiber activity are not solely responsible for the initial hyperemia during exercise.
Model simulation of single-breath washout of insoluble gases from dog lungs
Authors: Hook C. , Meyer M. , Piiper J.
Published: December 2017

Intrapulmonary gas mixing by convection and diffusion is analyzed on the basis of various analog lung models incorporating singly or in combination series inhomogeneity, parallel inhomogeneity, intercompartmental diffusion, sequential inspiration, and sequential expiration. The slope of the alveolar plateau of insoluble gases is used as an indicator for incomplete gas mixing. By use of the models, we have attempted to simulate experimental results obtained in artificially ventilated dog lungs with simultaneous single-breath washout of He and SF6 (Meyer et al., J. Appl. Physiol. 55: 1795–1802, 1983). Sufficient agreement with experimental data is obtained only when diffusion between serial-parallel compartments and sequential expiration are incorporated, the first being mainly responsible for separation of He and SF6, the latter for the slope of the alveolar plateau of these gases. A combined operational model comprising two parallel compartments connected to a mixing compartment, with both convective and diffusive gas transport between the compartments, could account for most of the experimental observations.
Effects of prolonged elevated microvascular pressure on lung fluid balance in sheep
Authors: Parker R. E. , Roselli R. J. , Brigham K. L.
Published: December 2017

Experiments were conducted in seven chronically instrumented unanesthetized sheep to estimate the osmotic reflection coefficient (sigma d) for total proteins and the solvent-drag reflection coefficients (sigma f) for six endogenous protein fractions. We measured the lymph-to-plasma ratio of total proteins (CL/CP) and six protein fractions during base-line conditions and after left atrial pressure elevations of 24–26 h per elevation. We also monitored pulmonary arterial pressure, left atrial pressure, systemic arterial pressure, and lung lymph flow at the various levels of pulmonary microvascular pressure. Our results indicate the CL/CP may require up to 24 h to reach a true steady state. It was found that sigma d is at least 0.89 for total proteins and sigma f is at least 0.84, 0.87, 0.86, 0.92, 0.95, and 0.96 for protein fractions with effective molecular radii of 36, 39.5, 44, 66, 105, and 123 A, respectively. In addition, the sigma f values for various protein fractions obtained from this investigation are compared with the predicted values of various mathematical models of the lung microcirculation.
Peripheral mucociliary clearance with high-frequency chest wall compression
Authors: Gross D. , Zidulka A. , O'Brien C. , Wight D. , Fraser R. , Rosenthal L. , King M.
Published: December 2017

We investigated the effects of high-frequency chest wall compression (HFCWC) on peripheral and tracheal mucus clearance in anesthetized spontaneously breathing dogs. HFCWC was achieved by oscillating the pressure in a thoracic cuff with a piston pump. Regional lung retention of a technetium-99m sulfur colloid aerosol was monitored with a gamma camera. A peripheral mucus clearance index (PMCI) was defined for each region of interest. The tracheal mucus clearance rate (TMCR) was determined by bronchoscopic visualization of marker particle transport. Phase I: In seven dogs, 30 min of HFCWC at 13 Hz with peak cuff pressure (Pcuff) 100–120 cmH2O was found to significantly enhance PMCI in regions immediately under the cuff. (delta PMCI = 24.4 +/- 4.6 in the basal peripheral region.) Phase II: Because of subpleural hemorrhage in phase I, the effect of HFCWC on TMCR at various Pcuff levels was studied in five dogs. The enhancement of TMCR by HFCWC reached a plateau level at Pcuff = 50 cmH2O. Phase III: HFCWC at 13 Hz with Pcuff = 50–60 cmH2O was found to significantly enhance PMCI in five dogs without the consequence of hemorrhage. Correlations were found between the enhancement of PMCI and TMCR by HFCWC. These results demonstrate that HFCWC is effective in enhancing both peripheral and central mucus clearance in dogs and safe when moderate pressures are applied.
Influence of chronic respiratory acid-base disorders on acute CO2 titration curve
Authors: Adrogue H. J. , Madias N. E.
Published: December 2017

We have recently shown that background presence of chronic metabolic acid-base disorder markedly alters in vivo acute CO2 titration curve. These studies were carried out to assess the influence of chronic respiratory acid-base disorders on response to acute hypercapnia and to explore whether the chronic level of plasma pH is the factor responsible for alterations in the CO2 titration curve. We compared whole-body responses to acute hypercapnia of dogs with preexisting chronic respiratory alkalosis (n = 8) with that of normal animals (n = 4) and animals with chronic respiratory acidosis (n = 13). Chronic respiratory alkalosis and acidosis, as well as the acute CO2 titrations, were produced in unanesthetized dogs within a large environmental chamber. For comparison with our data on chronic metabolic acidosis and alkalosis, plasma bicarbonate levels, which are secondarily altered in chronic respiratory acid-base disorders, were used as an index of chronic acid-base status of the animals. Results indicate that, as with chronic metabolic acid-base disorders, a larger increment in plasma bicarbonate occurs during acute hypercapnia when steady-state plasma bicarbonate is low (respiratory alkalosis) than when it is high (respiratory acidosis). Yet, in further analogy with the metabolic studies, plasma hydrogen ion concentration is better defended at higher plasma bicarbonate levels in accordance with mathematical relationships defined by the Henderson-Hasselbalch equation. Combined results demonstrate that the influence of chronic acid-base status on whole-body response to acute hypercapnia is independent of initial plasma pH.
Lactate threshold and distance-running performance in young and older endurance athletes
Authors: Allen W. K. , Seals D. R. , Hurley B. F. , Ehsani A. A. , Hagberg J. M.
Published: December 2017

Many well-trained elite older runners have performances comparable to those of much younger nonelite runners. We sought to determine whether the physiological determinants of endurance performance in two groups of such athletes were the same. Eight master athletes (age 56 +/- 5 yr) were matched on the basis of 10-km performance and training to younger runners (age 25 +/- 3 yr). The master athletes had a 9% lower maximum O2 uptake (VO2max) (P less than 0.05) than the matched young runners, despite the similarity in their performance. Running economy was not different between these groups. However, the master athletes attained a 2.5-mM blood lactate level during steady-state exercise at a higher percentage of their VO2max (P less than 0.05), although both groups attained this lactate level at the same running speed and VO2. Thus, despite having significantly lower VO2max values, the older athletes were able to perform as well as the younger runners because they were able to work closer to their VO2max for the duration of the race.
Laryngeal influences on breathing pattern and posterior cricoarytenoid muscle activity
Authors: Sant'Ambrogio F. B. , Mathew O. P. , Clark W. D. , Sant'Ambrogio G.
Published: December 2017

Receptors responding to transmural pressure, airflow, and contraction of laryngeal muscles have been previously identified in the larynx. To assess the relative contribution of these three types of receptors to the reflex changes in breathing pattern and upper airway patency, we studied diaphragmatic (DIA) and posterior cricoarytenoid muscle (PCA) activity in anesthetized dogs during spontaneous breathing and occluded efforts with and without bypassing the larynx. Inspiratory duration (TI) was longer, mean inspiratory slope (peak DIA/TI) was lower, and PCA activity was greater with upper airway occlusion than with tracheal occlusion (larynx bypassed). Bilateral section of the superior laryngeal nerves eliminated these differences. When respiratory airflow was diverted from the tracheostomy to the upper airway the only change attributable to laryngeal afferents was an increase in PCA activity. These results confirm the importance of the superior laryngeal nerves in the regulation of breathing pattern and upper airway patency and suggest a prevalent role for laryngeal negative pressure receptors.
Effects of prolonged undernutrition on structure and function of the diaphragm
Authors: Kelsen S. G. , Ference M. , Kapoor S.
Published: December 2017

The present study examined the effect of prolonged undernutrition on diaphragmatic structure and force-generating ability. Studies were performed on 58 Syrian hamsters in which the feed was reduced by 33% for a 4-wk period. Sixty animals fed a similar diet ad libitum served as controls. Diaphragm muscle structure was assessed from its mass (wet and dry weight), thickness, fiber composition, and fiber size. Isometric force produced in vitro by isolated muscle strips in response to electrical stimulation of the phrenic nerve was examined over a range of muscle lengths (length-tension relationship). In undernourished animals, body weight decreased 25 +/- 5%. Diaphragm wet and dry weight, muscle thickness, and the cross-sectional area of fast-glycolytic (FG) and fast-oxidative (FO) fibers were significantly less in undernourished than control animals and correlated with reductions in body weight. The cross-sectional area of slow-oxidative (SO) fibers was the same in the two groups. The percentage of FG fibers in undernourished animals was decreased slightly and the percentage of SO fibers increased. Maximum isometric tension was reduced in undernourished animals as compared with controls, but the position and shape of the length-tension relationship was the same in the two groups. Reductions in muscle force appeared to be explained by decreases in muscle mass, since tension corrected for cross-sectional area or tissue weight was the same in the two groups. Therefore muscle mechanical efficiency appeared to be unaffected by undernutrition. These data indicate that prolonged undernutrition causes deleterious changes in diaphragm muscle structure that impair its ability to generate force.
Adaptation to reflex effects of prolonged lung inflation
Authors: Grippi M. A. , Pack A. I. , Davies R. O. , Fishman A. P.
Published: December 2017

Adaptation to the reflex effects of sustained changes in lung volume on inspiratory duration (TI), expiratory duration (TE), and the phrenic neurogram was examined. Test inflations in gallamine-paralyzed dogs anesthetized with pentobarbital sodium were made during a 6-min trial while the animal was not ventilated: 2 min at functional residual capacity (FRC), 2 min at elevated airway pressure, and 2 min back at FRC. The dogs were hyperoxygenated and arterial PCO2 was kept constant by an infusion of tris (hydroxymethyl) aminomethane. The maintained inflations produced minimal changes in TI. On return to FRC, TI was prolonged in proportion to the magnitude of the prior inflation. In contrast, inflation produced marked prolongation of TE, which then adapted back toward preinflation values. On return to FRC, TE shortened initially to values below control. This shortening increased with greater prior lung inflations. The times to reestablish steady-state values upon return to FRC differed for TI (14.8 +/- 4.6 s) and TE (33.8 +/- 12.7 s). The magnitude of the phrenic neurogram at a fixed time from onset of inspiration and its slope were unchanged with inflation. These results indicate that respiratory phase durations are influenced not only by pulmonary afferent input within each respiratory cycle but also by prior vagal afferent activity that engages central processes with long, although different, time constants. Afferent input to the slow central process controlling TI is not gated to only one phase of the respiratory cycle.
Endogenous opioids and ventilatory responses to hypercapnia in normal humans
Authors: Weinberger S. E. , Steinbrook R. A. , Carr D. B. , von Gal E. R. , Fisher J. E. , Leith D. E. , Fencl V. , Rosenblatt M.
Published: December 2017

Though administration of opioid peptides depresses ventilation and ventilatory responsiveness, the role of endogenous opioid peptides in modulating ventilatory responsiveness is not clear. We studied the interaction of endogenous opioids and ventilatory responses in 12 adult male volunteers by relating hypercapnic responsiveness to plasma levels of immunoactive beta-endorphin and by administering the opiate antagonist naloxone. Ventilatory responsiveness to hypercapnia was not altered by pretreatment with naloxone, and this by itself suggests that endogenous opioids have no role in modulating this response. However, there was an inverse relationship between basal levels of immunoactive beta-endorphin in plasma and ventilatory responsiveness to CO2. Furthermore, plasma beta-endorphin levels rose after short-term hypercapnia but only when subjects had been pretreated with naloxone. We conclude that measurement of plasma endorphin levels suggests relationships between endogenous opioid peptides and ventilatory responses to CO2 that are not apparent in studies limited to assessing the effect of naloxone.
Spontaneous running activity in male rats: effect of age
Authors: Mondon C. E. , Dolkas C. B. , Sims C. , Reaven G. M.
Published: December 2017

Alterations in the intensity and pattern of spontaneous running activity as rats increase in age from 7 wk to 1 yr was studied in male rats placed in exercise wheel cages. Daily running records were obtained on 27 rats for periods up to 12 mo, and 24-h activity recordings were made of selected runners to study the variation in activity during the day. The data indicate that for rats running over 2,940 revolutions (or 2 miles/day), the maximum intensity of running attained can be divided into a group of high achievers (approximately 8 miles/day) and moderate achievers (averaging 4.5 miles/day). For both groups, spontaneous running activity reached maximal rates after 4–5 wk. This maximal rate was sustained for 7–8 wk, then fell to levels approximately 60% of maximum for 4–5 mo, and then fell again to levels approximately 25% of maximum from 8 to 12 mo of age. The hourly pattern of running activity during the day was defined in rats of increasing age, who averaged 13,280, 6,662, 3,874, and 1,755 rev/day, corresponding to 9.0, 4.5, 2.6, and 1.2 miles/day, respectively. The overall patterns at each level indicated that the major running period occurred between 6:00 P.M. and 6:00 A.M., the greater activity of younger rats was paralleled by faster speeds and longer duration at each hour of the day, and the peak running activity for each group generally occurred between 7:00 and 9:00 P.M. In summary, there is a progressive loss in speed and duration of spontaneous running activity as male rats increase in age, with intensity of exercise falling below 2 miles/day after 7–8 mo of age.
Effect of frequency on perceived magnitude of added loads to breathing
Authors: Killian K. J. , Summers E. , Basalygo M. , Campbell E. J.
Published: December 2017

Using open-magnitude scaling, six normal subjects estimated the perceived magnitude of a range of added elastic loads (20–76 cmH2O/l), applied for a sequence of five breaths, at frequencies varying from 5 to 26.4 breaths/min. Two experiments were performed. In the first, frequency was increased by a reduction in expiratory duration (TE), and the duty cycle (ratio of inspiratory duration to total breath duration, TI/TT) ranged between 0.10 and 0.52. The perceived magnitude psi increased significantly with the peak airway pressure (Pm) (P less than 0.0001) but did not reach conventional significance with frequency (fb) (P = 0.15): psi = K0Pm1.23fb0.07 (r = 0.911). However, the sensory magnitude increased significantly as the duty cycle increased (P less than 0.01), but when it was included, the magnitude decreased minimally with frequency (P less than 0.01): psi = K0Pm1.3fb-0.97 TI/TT1.14 (r = 0.92). In the second experiment the duty cycle (TI/TT) was kept constant [(0.43 +/- 0.008 (SE)] and frequency (5–26.4 breaths/min) increased at the expense of shortening both TI and TE. The perceived magnitude of the added elastances decreased with the increase in frequency. However, when the perceived magnitude was corrected for the duration of inspiration, which is known to increase the sensory magnitude, psi = K0Pm1.3TI0.56, the sensory magnitude increased significantly with frequency (P less than 0.001): psi/TI0.56 = K0Pm1.21fb0.28 (r = 0.773). The decrease in inspiratory duration had a greater quantitative effect decreasing sensory magnitude than frequency had on increasing the magnitude. The effect of increasing frequency is complex and depends on the simultaneous intensity, duration of inspiratory pressure, and the duty cycle.
Peripheral factors influencing expression of pressor reflex evoked by muscular contraction
Authors: Iwamoto G. A. , Botterman B. R.
Published: December 2017

The effect of evoked muscle tension, active muscle mass, and fiber-type composition on the pressor reflex evoked by muscular contraction was examined in decerebrate and anesthetized cats. Muscular contraction was induced by stimulating the L7 and S1 ventral roots with 0.1-ms duration pulses three times motor threshold at various frequencies. The experiments were designed to isolate the variable under study as much as possible and included the use of selectively denervated preparations to limit contractions to specific muscles. It was found that altering the evoked tension by varying the resting muscle length had commensurate effects on the pressor reflex (greater evoked tension caused a larger reflex). In addition it was found that changing the amount of active muscle mass caused similar changes in the reflex (the smaller the muscle mass, the smaller the reflex). Finally, it was found that contrary to other accounts, pressor reflexes could be evoked by activation of the slow-twitch muscle soleus, composed exclusively of red (type I) fibers.
Metabolic response of equine muscle to intermittent maximal exercise
Authors: Snow D. H. , Harris R. C. , Gash S. P.
Published: December 2017

Four thoroughbred horses performed 4 gallops (G1-G4) with intervals of 5 min. With one exception, gallops were sustained at maximal speed over 620 m. Muscle biopsy samples of the middle gluteal and brachiocephalicus were taken before, during, and after exercise and assayed for ATP and intermediary metabolites. The results showed a major involvement of the brachiocephalicus, in addition to the middle gluteal, during galloping. In three horses, who were clearly fatigued, muscle ATP decreased by up to 50% by the end of G4. This was matched by an equal rise in inosine 5′-monophosphate. Pronounced accumulations of glycerol 3-phosphate, glycerol, and lactate (up to 204 mmol X kg dry muscle-1) occurred with exercise. In the fourth horse, which was less fatigued, a decrease in ATP and increases in intermediary metabolites were much less. Postexercise there was little or no recovery in muscle ATP or lactate during 30 min. The decreases in ATP are consistent with a high activity of adenosine 5′-monophosphate deaminase in horse muscle and indicative also of the high level of anaerobic stress of the exercise program. There was evidence to suggest that the increase in muscle glycerol resulted from hydrolysis of glycerol 3-phosphate and not from the utilization of triglyceride.
Human maternal and fetal response to graded exercise
Authors: Jovanovic L. , Kessler A. , Peterson C. M.
Published: December 2017

Six healthy active women in the third trimester of pregnancy participated in a graded exercise protocol to levels of exertion perceived to be equivalent to that of their usual exercise regimen. Fetal heart rate response (FHR) was documented by ultrasound transducer and confirmed (n = 1) by ultrasonic visualization. Resting maternal O2 consumption was 277 +/- 50 (SD) ml/min and rose to 1,132 +/- 202 ml/min at a mean final exercise intensity of 79 +/- 9 W after 12.8 +/- 1.7 min on a cycle ergometer. There was no significant change in maternal serum insulin, growth hormone, glucose, or pH values. Maternal leukocyte count, hemoglobin, and venous lactate levels rose significantly during the exercise (P less than 0.05). FHR prior to exercise was 142 +/- 4 beats/min and decreased to 84 +/- 34 beats/min during exercise. The decrease in FHR was documented within 1 min of initiating exercise in all cases. During exercise, fetal movements were not accompanied by FHR accelerations. Within 1 min following the cessation of exercise, FHR rose to 143 +/- 8 beats/min and fetal movements were accompanied by FHR accelerations. Since the recovery of FHR occurred immediately after cessation of maternal exercise, this level of maternal exercise does not appear to be harmful to the fetus.
Brain amino acid concentrations during diving and acid-base stress in turtles
Authors: Hitzig B. M. , Kneussl M. P. , Shih V. , Brandstetter R. D. , Kazemi H.
Published: December 2017

To assess the role of brain amino acid neurotransmitters in the breath hold of diving animals, concentrations of free amino acids present in the brains of turtles immediately after 2 h of apneic diving (at 20 degrees C) were measured. Additionally, the same measurements were performed on four other groups of animals subjected to 2 h of hypercapnia (8% CO2 in air), anoxia (N2 breathing), anoxia plus hypercapnia (8% CO2–92% N2), or air breathing (control). Significant changes in the concentrations of the inhibitory amino acid neurotransmitters known to affect respiration [gamma-aminobutyric acid (GABA) and taurine] were seen. GABA increased significantly in those animals subjected to anoxia, whereas taurine decreased significantly in the diving animals and increased significantly in those subjected to anoxia plus hypercapnia. These results suggest that the attenuated central ventilatory drive during diving in these animals may be related to alterations in brain concentrations of GABA and taurine.
Differential costal and crural diaphragm compensation for posture changes
Authors: van Lunteren E. , Haxhiu M. A. , Cherniack N. S. , Goldman M. D.
Published: December 2017

The electromyographic (EMG) activities of the costal and crural diaphragm were recorded from bipolar fine-wire electrodes placed in the costal fibers adjacent to the central tendon and in the anterior portions of the crural fibers in 12 anesthetized cats. The EMG activities of costal and crural recordings were compared during posture changes from supine to head up and during progressive hyperoxic hypercapnia in both positions. The activity of both portions of the diaphragm was greater in the head up compared with supine posture at all levels of CO2; and increases in crural activity were greater than those in costal activity both as a result of changes in posture and with increasing CO2 stimuli. These results are consistent with the concept that diaphragm activation is modulated in response to changes in resting muscle length, and further, that neural control mechanisms allow separate regulation of costal and crural diaphragm activation.
Effects of exhaustive submaximal exercise on cardiovascular function during sleep
Authors: Bunnell D. E. , Bevier W. C. , Horvath S. M.
Published: December 2017

The influence of an afternoon bout of exhaustive submaximal exercise on cardiovascular function and catecholamine excretion during sleep was examined in five female and four male subjects. Subjects walked on a treadmill for successive 50-min periods at 50, 60, and 70% maximal O2 consumption, separated by 10-min rest periods. Exercise terminated with volitional exhaustion. Following an adaptation night, electroencephalographic and impedance cardiographic measures were obtained during three successive nights of sleep, with exercise preceding night 3. Relative to the base-line night (night 2), exhaustive exercise resulted in a sustained elevation of heart rate and cardiac output throughout the entire night's sleep. The magnitude of these elevations was unaffected by sleep stage but decreased over the night. The typical pattern of circadian decline in cardiac output was unaltered. However, the decline in heart rate with sleep onset was greater on the exercise night. Changes in impedance dZ/dt and R-Z interval suggested an enhanced myocardial contractility during the first 3 h of sleep postexercise. Analysis of morning urine samples revealed that in seven of nine subjects norepinephrine excretion increased, epinephrine excretion decreased, and dopamine excretion was unchanged during sleep on the exercise night. It is suggested that these cardiac changes reflect a sustained increase in myocardial beta-receptor activity.
Nonhomogeneity of lung response to inhaled histamine assessed with alveolar capsules
Authors: Fredberg J. J. , Ingram R. H. , Castile R. G. , Glass G. M. , Drazen J. M.
Published: December 2017

To assess the homogeneity of airway responses to inhaled histamine we examined regional alveolar pressure excursions (PA) arising from small-amplitude oscillations applied at the airway opening (Pao). In five anesthetized and vagotomized dogs the sternum was split and the anterior right lung field exposed. PA was sampled using four capsules affixed to the right apical and middle lobes while lung impedance (ZL) and airway impedances (Zaw) were measured during conventional tidal breathing and during forced oscillations (2–60 HZ at 10 cmH2O distending pressure). During tidal breathing after exposure to aerosol histamine regional PA's could be separated into three groups by plotting Lissajous figures of PA vs. Pao: PA in phase with Pao (no looping), PA lagging Pao (moderate looping), and PA decreasing while Pao was increasing and vice versa (paradoxical looping), suggesting unresponsive, responsive, and closed pathways, respectively, between the airway opening and specific alveolar zones. During high-frequency oscillation the corresponding PA spectra were markedly different from control spectra and revealed resonant amplification, overdamped resonance, and marked attenuation, respectively. With induced bronchospasm resonant amplification of PA was damped on average. However, the more obstructed and closed pathways were protected from resonant amplification, and the more open (nonlooping) pathways were subjected to resonant amplification greater than in the control state. In spite of this markedly nonhomogeneous behavior, frequency dependence of ZL was consistent with the model by Mead (J. Appl. Physiol. 26: 670–673, 1969), which ignores nonhomogeneity of peripheral compartments. These data demonstrate that the response of airways to inhaled histamine is nonhomogeneous but that frequency dependence of ZL above 2 Hz is not sufficient to characterize this nonhomogeneity.
Immediate effects of cigarette smoking on cardiorespiratory responses to exercise
Authors: Hirsch G. L. , Sue D. Y. , Wasserman K. , Robinson T. E. , Hansen J. E.
Published: December 2017

To determine the acute action of cigarette smoking on cardiorespiratory function under stress, the immediate effects of cigarette smoking on the ventilatory, gas exchange, and cardiovascular responses to exercise were studied in nine healthy male subjects. Each subject performed an incremental exercise test to exhaustion on two separate days, one without smoking (control) and one after smoking 3 cigarettes/h for 5 h. The order of the two tests was randomized. Arterial blood gases and pH were measured during rest and all levels of exercise; CO blood levels confirmed the absorption of cigarette smoke. In addition, minute ventilation (VE), end-tidal PCO2 and PO2, O2 uptake (VO2), CO2 production, directly measured blood pressure, electrocardiogram, and heart rate (HR) were recorded every 30 s. The dead space-to-tidal volume ratio (VD/VT), maximal aerobic capacity (VO2max), and anaerobic threshold (AT) were determined from the gas exchange data. Cigarette smoking resulted in a significantly lower VO2max, AT, and VO2/HR (O2 pulse) and a significantly higher HR, pulse-pressure product, and pulse pressure (P less than 0.05) compared with the control. Additionally, a trend toward a higher VD/VT and arterial-end-tidal PCO2 difference was found during exercise after smoking. We conclude that cigarette smoking causes immediate detrimental effects on cardiovascular function during exercise, including tachycardia, increased pulse-pressure product, and impaired O2 delivery. The acute effects on respiratory function were less striking and primarily limited to abnormalities reflecting ventilation-perfusion mismatching.