bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of red blood cell HCO3(-)/Cl- exchange kinetics on lung CO2 transfer: theory
Authors: Crandall E. D. , Bidani A.
Published: December 2017

A mathematical model has been used to study the influences of the kinetics of erythrocyte HCO3(-)/Cl-- exchange on CO2 elimination in the lung. In addition to the chloride shift, the model includes 1) CO2-H2CO3 hydration-dehydration reactions in plasma and erythrocytes; 2) CO2 reactions with hemoglobin; 3) O2 binding to hemoglobin; 4)buffering of H+ intra- and extracellularly; 5) red cell volume changes; and 6) diffusion of gases between alveoli and blood. Carbonic anhydrase activity was assumed to be available to plasma as it passes through the lung capillaries. The results show that a reduction of PHCO3(-) leads to a reduction in pulmonary CO2 elimination of up to 30%, whether or not carbonic anhydrase activity is available to plasma. Characteristic slow downstream pH and PCO2 changes predicted for each case may represent an explanation for the apparent discrepancy between in vivo and in vitro slow downstream pH changes reported previously. We conclude that red cell HCO3(-)/Cl- exchange partially limits CO2 elimination from blood in the lung and may have a major influence on capillary gas transfer when its speed is abnormally slow.
Series distribution of airway collapsibility in dogs
Authors: Nakamura M. , Sasaki H. , Sekizawa K. , Ishii M. , Takishima T. , Hoppin F. G.
Published: December 2017

We studied the series distribution of collapsibility in four different-sized airways in dogs. The trachea and the extrapulmonary main bronchi in situ were isolated from the rest of the lungs by glued beads of 6-12 mm OD. In excised dog lungs, the intrapulmonary large and small bronchi were isolated from the rest of the lung by glued beads of 1-9 mm OD. Pressure-volume relationships were measured directly in the trachea and in the extrapulmonary bronchi; those of the intrapulmonary bronchi were derived from orthogonal bronchograms. Airway collapsibility, defined as the slope of the pressure-volume curve, was found to increase in all airways as transpulmonary pressure (PL) decreased. At PL 30 cmH2O there was little difference of airway collapsibility among the different sized airways; but, as PL decreased, the peripheral airways became more collapsible than the central airways. It is concluded that the tissues surrounding the trachea provided as much or more stiffness than did the lung tissues that surrounded the intrapulmonary airways. The larger collapsibility in the peripheral airways. The larger collapsibility in the peripheral airways relative to that of the central airways at lower PL may account for the peripheral migration of the flow-limiting segment during forced expiration.
Kinetics of sulfated mucous glycoprotein secretion in dog trachea in vitro
Authors: Estep J. A. , Zorn J. P. , Marin M. G.
Published: December 2017

Previous studies on mucous glycoprotein secretion in respiratory epithelium most often provided qualitative, rather than quantitative, data. This study describes a new technique to measure the secretion rate, pool size, and turnover time of the pool of sulfated mucous glycoproteins of dog tracheal epithelium. The technique involved interposing dissected tracheal epithelium between the halves of an Ussing-type chamber, incubating the submucosal side of the tissue with 35SO4, and measuring the rate of appearance of nondialyzable 35SO4 on the luminal side of the chamber of both during the labeling and "washout" of the mucous pool. By analyzing the pattern of elimination, we showed that 1) a steady secretion rate of labeled mucous glycoprotein occurs within 3-4 h when free 35 SO4 is present on te submucosal side of the tissue, 2) secretion is consistent with first-order kinetics from a single pool, 3) puromycin decreases the rate of secretion of labeled mucous glycoprotein, 4) secretion rate is greater in medium 199 than in modified Krebs-Henseleit solution, and 5) 1.2 mM SO4 supports maximal baseline secretion. In six tracheas, bathed in Krebs-Henseleit solution, the secretion rate was (mean +/- SE) 467 +/- 74 pmol SO4 x cm-2 x h-1, pool size, 964 +/- 144 pmol SO4/cm2, and turnover time, 2.12 +/- 0.16 h. This technique provides a quantitative method to characterize kinetics of sulfated mucous glycoprotein secretion.
Conditioning versus exercise in heat as methods for acclimatizing 8- to 10-yr-old boys to dry heat
Authors: Inbar O. , Bar-Or O. , Dotan R. , Gutin B.
Published: December 2017

Two heat-acclimatization protocols were studied in 8- to 10-yr-old boys: exercise in dry heat (WH, n = 9) and exercise in neutral climate (W, n = 9). Five 90-min acclimatization sessions were conducted within a 12-day period. Base-line (BL) and criterion (CT) tests sessions were held at 43 degrees C db and 24 degrees C wb, with three 20-min exercise bouts at approximately 40 Ws. With acclimatization, the WH group showed a significant reduction in heart rate (HR) (11.4 beat x min-1), mean skin temperature (0.64 degrees C), and an increase in the population density of heat-activated sweat glands (HASG) (25.2 glands x cm-2). The W group showed a significant reduction in HR (13.4 beat x min-1) and rectal temperature (0.24 C). Total sweat rate per body surface area did not increase significantly in either group. However, the sweat rate relative to rise in core temperature increased in both groups. No significant differences were found between the two acclimatization procedures in any of the variables studies except for the HASG, which showed a greater increase in the WH group. It is suggested that in 8- to 10-yr-old boys physiological changes compatible with heat acclimatization could be achieved either by exercise in heat or by mere physical conditioning (approximately 65% of VO2max), in neutral climate. It is postulated that age-related factors associated with the thermoregulatory system prevent children from deriving full effectiveness of exercise-in-heat acclimatization protocol as used in this study.
Respiratory reflexes evoked by tracheal distension
Authors: Rao S. V. , Sant'Ambrogio F. B. , Sant'Ambrogio G.
Published: December 2017

In 13 dogs that were anesthetized and ventilated through an endotracheal tube, segments of either the intrathoracic (ITT) or extrathoracic trachea (ETT) were distended by over-inflating the sealing cuff within the first half of an inspiration and maintaining this overinflation for two breathing cycles. ITT distension caused a significant prolongation of the expiratory duration (TE) of the first challenged breath in 12 of the 13 dogs. ETT distension prolonged the TE in only 5 of the 13 dogs. An inhibition of inspiration resulting in shortened inspiratory time and reduced peak phrenic amplitude (PPA) was measured in three experiments. In six other experiments, there was only a transient decrease in phrenic discharge, which immediately resumed. In the remaining four experiments, the inspiratory burst was unaffected. After vagotomy, ITT distension shortened TE in 8 of the 13 dogs. ETT distension was ineffective in 10 out of 11 experiments; in the remaining experiment TE was significantly lengthened. No significant effects were elicited on TI and PPA by either ITT or ETT distension. These results could be explained by the known behavior of tracheal receptors and could indicate the presence of extravagal influences.
Exchanges of oxygen and carbon dioxide alter inert gas pattern in single-breath tests
Authors: Van Liew H. D. , Arieli R.
Published: December 2017

Concentration of inert gas in the lung is lowered when CO2 entrance exceeds O2 exit and is raised when O2 exit predominates. In air-breathing subjects who expire to residual volume, this "metabolic gas effect" often causes a rising N2 concentration when in fact there should be a terminal fall because of low N2 in apical regions. In single-breath tests, we compared the dilution of resident N2 with dilution of an inspired gas, Ne, to find the "ideal" inert gas concentration (due only to mixing of resident gas with inspired gas). The displacement from the ideal concentration vs. volume pattern depends on the timing of the breath, because early CO2 entrance gives way later to O2 exit. Sometimes observed patterns are above or below but parallel to the ideal, and sometimes the observed slope of phase III is steeper than ideal for N2 and flatter than ideal for Ne. In addition to phase III distortions, the metabolic gas effect sometimes also distorts phase IV height and the intersection between phases III and IV. The distortions depend strongly on absolute concentration of the indicator gas in the lung, so they are very small when "closing volume" maneuvers are done in the conventional manner. However, distortions can be large and misleading when single-breath maneuvers are done in unconventional ways.
Effect of PEEP on gas exchange and pulmonary perfusion in canine lobar pneumonia
Authors: Mink S. N. , Light R. B. , Cooligan T. , Wood L. D.
Published: December 2017

We investigated the effects of positive end-expiratory pressure (PEEP) on respiratory gas exchange and pulmonary perfusion in 10 dogs with left lower lobe (LLL) pneumonia. In 6 dogs, measurements were made with the chest closed and 12 cmH2O were applied; in 4 other open-chest dogs (group O), 6 cmH2O were used. Both groups showed similar changes, and the individual results for all dogs were averaged. With the animals breathing 100% oxygen, total pulmonary shunt (Qs/Qt), arterial oxygen tension (PaO2), and the relative distribution of pulmonary blood flow were measured before, during, and after PEEP. During the control periods, QLLL when expressed as a percent cardiac output averaged 24 +/- 7%. With PEEP, QLLL increased by more than 50% to a mean value of 37 +/- 5%. Despite this increase, the respective values of Qs/Qt and PaO2 improved slightly from 28% and 288 Torr to 25% and 370 Torr. This result suggested that PEEP also improved regional gas exchange, and this finding was subsequently confirmed in Group O where the shunt fractions of the lower lobes were additionally measured. Accordingly, our results show that PEEP altered regional perfusion and shunt so that, on the mean, there was little change in total pulmonary shunt. Whether PEEP worsened or improved gas exchange in any individual experiment was dependent on the relative magnitude of the changes in each of these regional parameters.
Volume, flow, and timing of each breath during negative airway pressure in humans
Authors: Hirsch J. A. , Bishop B.
Published: December 2017

We have analyzed the effects of 4-6 min of 5, 10 and 15 cmH2O continuous negative airway pressure breathing (NPB) on steady-state end-expiratory lung volume (delta VR) and breathing pattern. Fourteen healthy adults, seated in a full body box, breathed via a mouthpiece on a bag-in-box. Pressure in the body box was elevated to the desired pressure level. Inspiratory (TI) and expiratory (TE) durations, tidal volume (VT), minute ventilation (VI), mean inspiratory flow (VT/TI), and mean expiratory flow (VT/TE) were calculated from pneumotachometer recordings. The effects of NPB are decreases in delta VR, VT, and VT/TI and increases in VT/TE. The responses to NPB are an increase in breathing frequency, due to a shortened TE, and an increase in inspiratory activity. The decrease in delta VR and the increase in VT/TE are limited by an active retardation of expiratory flow. End-tidal CO2 and VI were not altered significantly during NPB, suggesting no alveolar hyperventilation. Thus multiple components of the human response to NPB are not all engaged at the same levels of NPB. The changes in the timing of respiratory events occur at -5 cmH2O, whereas VT compensation is not seen until -15 cmH2O.
Inhalation patterns and predominant site of bronchoconstriction in healthy subjects
Authors: Strohl K. P. , O'Cain C. F. , Ingram R. H. , Yanta M. A. , Kaplan W. D. , McFadden E. R.
Published: December 2017

To determine the relationship between changes in density dependence of maximal expiratory flow and changes in the predominant site of bronchoconstriction, we altered the pattern of inhalation of a methacholine aerosol to achieve deposition either centrally (by short choppy breaths) or peripherally (by slow deep breaths). Partial expiratory flow volume curves on air and on 80% helium-20% oxygen (HeO2) were recorded in six healthy subjects before and after each pattern of methacholine inhalation. We varied concentrations of methacholine and number of inhalations to achieve equivalent degrees of bronchoconstriction as assessed by decreases in maximal flow (Vmax) on air, which fell 27% from control values. Vmax on HeO2 also fell after both inhalation patterns. Density dependence (Vmax on HeO2 divided by Vmax on air) decreased following slow deep breaths of bronchoconstrictor aerosol, and increased following short choppy breaths. In three subjects, inhalation of radiolabeled methacholine aerosol confirmed that the slow deep pattern was associated with a diffuse, more peripheral deposition, whereas the short choppy pattern led to central deposition. We conclude that changes in density dependence reflect the predominant site of obstruction after acute methacholine aerosol challenge in healthy subjects.
Comparison of airway closure measured in vivo and from single-breath washout curve
Authors: Susskind H. , Atkins H. L. , Klopper J. F. , Ansari A. N. , Richards P.
Published: December 2017

The volume of air trapped (Vat) in alveoli subtended by airways closed at residual volume (RV) was correlated with the volume of air left in the lungs at the start of airway closure (CC) in a clinical study of 13 patients with a variety of pulmonary disorders and 5 normal subjects. Vat was quantitated at RV from the in vivo distribution differences between 127Xe inspired as a bolus and again after equilibrium; CC was measured from the inflection point on the single-breath washout curve at the onset of phase IV. 127Xe activity was measured with a scintillation camera, and activity profiles were obtained for 28-45 consecutive 6.5-mm horizontal lung slices between base and apex. Three well-defined regions were found: A, in the upper lung, all of whose airways remained completely open; B, located above the base and containing both open and closed airways; and C, above the base, all of whose airways were closed. Of the Vat of 0.43 liter for the normals, 41% was located in region C. For the patients, the values were 59% of 0.59 liter. The relationship between the onset of phase IV and regional airway closure was confirmed for normals as well as patients. A statistically significant increase in closure was found for the patients over the normals. Excellent agreement was obtained between Vat/TLC (total lung capacity) and CC/TLC (r = 0.79, P less than 0.001) for normals as well as patients, and CC appears to reflect regional airway closure in both health and disease. Similar excellent agreement was obtained for the normals between lung height with closed airways and CC/TLC (r = 0.88, P less than 0.001). Vat appears to be the most important physiological determinant of phase IV, the value at RV representing the limiting case.
Mechanisms of renal dysfunction during positive end-expiratory pressure ventilation
Authors: Priebe H. J. , Heimann J. C. , Hedley-Whyte J.
Published: December 2017

Twenty-seven anesthetized dogs were studied to determine the effects of intrarenal blood flow distribution, hepatic congestion, and cardiac output (Q) and/or intravascular volume on renal function during ventilation with positive end-expiratory pressure (PEEP) of 10 cmH2O. In 10 dogs intrarenal blood flow distribution, as determined by the radioactive-microsphere technique, remained unchanged although PEEP caused a significant antidiuresis and antinatriuresis. The selective release of hepatic congestion during PEEP in eight animals by means of a vena cava to jugular venous shunt circuit did not restore renal function. Nine dogs were transfused with 25 ml/kg of autologous blood during PEEP. Although Q remained at only 70% of control, renal blood flow and renal function (glomerular filtration rate, urinary sodium excretion, urine output, osmolar clearance, and free water clearance) were restored to control values. Our results suggest that the impairment in renal function during PEEP is not caused by changes in intrarenal blood flow distribution, Q, or hepatic congestion, but rather by a decrease in intravascular volume.
Correction for nonlinearity of body flow plethysmograph
Authors: Harf A. , Atlan G. , Lorino H. , Deshayes S. , Morin C. , Laurent D.
Published: December 2017

A modification of conventional signal processing for the pressure-compensated flow plethysmograph is proposed to correct the nonlinearity of the flow element that appears for high flows as encountered during forced expiration. Woven screens behave as porous media with a viscous and an inertial component in the resistance; this explains the nonlinearity (23% at 15.1.s-1 with a 400-mesh wire screen area = 50 cm2). It was shown that the pressure drop-flow relationship can be described by a second-degree equation, which can be included in the computation of the thoracic signal from the box pressure. The need for such a correction is evidenced by testing the plethysmograph with a flow step input (0-15 l.s-1) equivalent both in amplitude and in frequency to the thoracic flow during a forced expiration. Such correction for nonlinearity avoids an overestimation of the thoracic forced vital capacity of up to 0.5 liter in normal subjects.
Hypercapnic stimulation of respiratory activity in unanesthetized fetal sheep in utero
Authors: Bowes G. , Wilkinson M. H. , Dowling M. , Ritchie B. C. , Brodecky V. , Maloney J. E.
Published: December 2017

Respiratory responses to hypercapnia were studied in seven chronic in utero fetal lambs between 105 and 138 days' gestation (16 expts). Fetal arterial CO2 tension was raised (mean increase 9.9 Torr) by altering maternal inspired gas concentrations. Diaphragmatic electromyogram (EMG) was recorded as the index of respiratory activity. Electrocortical and electroocular activity (3 fetuses) were monitored in an attempt to define sleep state. Average respiratory rate increased (90%) and fetal apnea decreased (60%) during hypercapnia. Mean respiratory rate during "on" periods (greater than 6 EMG bursts/min) increased significantly during hypercapnia throughout the gestational epoch studied. Mean duration of the inspiratory time (TI) showed no significant change. Variability in both rate and TI decreased in response to CO2 at all gestations. Integrated EMG activity per burst divided by TI increased significantly at all gestations; however, no gestational increase in responsiveness to CO2 was seen. Sleep states were not able to be consistently identified, and a quantifiable electrocortical response to CO2 was not observed. These results indicate a relatively early functional maturation of fetal respiratory responses to CO2.
Effect of quiet sleep on resting and CO2-stimulated breathing in humans
Authors: Gothe B. , Altose M. D. , Goldman M. D. , Cherniack N. S.
Published: December 2017

We examined the effects of different levels of inspired CO2 on ventilation and the pattern of breathing in healthy adults during the awake and the stage II quiet-sleep states. During both states, subjects were studied supine with their heads enclosed in a canopy. Tidal volume (VT) was determined from quantitative measurements of abdominal and rib cage excursions with magnetometers. Inspired CO2 was raised by blending CO2-enriched gas into the airflow, which continuously flushed the canopy. During sleep, while room air was breathed, VT decreased significantly from 410 to 360 ml, and respiratory rate also fell from 17 to 16 breaths/min. As a consequence, ventilation was significantly reduced from 6.5 to 5.8 l/min, and end-tidal CO2 partial pressure (PCO2) rose from 39.1 to 42.5 Torr. Ventilatory responses to CO2 were reduced, on the average, during sleep to 79% of waking levels. The change in average inspiratory flow produced by CO2 was also less during sleep. Waking and sleeping ventilatory responses to CO2 correlated inversely with the rise in end-tidal PCO2 when room air was breathed during sleep. At all levels of VT, the rib cage contribution to VT was greater during quiet sleep than during wakefulness. These findings suggest that quiet sleep, in addition to depressing ventilation and the response to CO2 alters the manner in which VT is attained by rib cage and abdominal displacements.
Contribution of environmental factors in development of hyperbaric bradycardia
Authors: Shida K. K. , Lin Y. C.
Published: December 2017

Bradycardia has been observed in animals and humans upon exposure to various hyperbaric environments. However, the relative contribution of ambient pressure, gas density, inert gas species, and inspired O2 tension has not been defined. By means of cutaneous ECG leads, the heart rates of unanesthetized rats were recorded and compared in 11 separate thermo-neutral environments. Ambient pressures applied were 1, 3, and 10 ATA, O2 partial pressure PO2 ranged from 140 to 1,590 Torr, and gas densities were varied from 0.40 to 11.45 g/l, utilizing either N2-O2 or He-O2 mixtures. The exposure heart rates were averaged over a 30-min period and compared with a preceding control value obtained in 1 ATA normoxic He or N2. Significant bradycardia was associated with hyperoxia in environments containing either He or N2, with a magnitude proportional to log PO2. On the other hand, under normoxic conditions bradycardia was not observed despite the similar density, pressure, and inert gas components. It is concluded that hyperoxia is the most important variable of those considered in the development of hyperbaric bradycardia.
Release of oxygen products from lung macrophages by N-formyl peptides
Authors: Holian A. , Daniele R. P.
Published: December 2017

Incubation of guinea pig pulmonary macrophages with N-formylmethionylphenylalanine (FMP) resulted in 1) a rapid increase in O2 consumption and 2) an accumulation of superoxide anion and hydrogen peroxide in the extracellular medium. The accumulation of superoxide anion and hydrogen peroxide was completely prevented in the presence of superoxide dismutase and catalase, respectively. FMP-stimulated O2 consumption and superoxide anion and hydrogen peroxide accumulation were proportional to the macrophage concentration, showed similar dependence on FMP concentration, had nearly identical kinetics, and were partially abolished by antimycin A, an inhibitor of mitochondrial respiration. FMP also stimulated a three- to fourfold increase in hexose monophosphate shunt (HMS) activity. Catalase had no effect on the amount of glucose oxidized by the HMS, indicating that removal of hydrogen peroxide was without effect on the observed HMS activity. Since FMP is similar in structure to the oligopeptides of bacterial metabolism, its ability to stimulate the release of these microbiocidal products of oxygen metabolism may be important in vivo.
Pulmonary mechanisms and work of breathing at maximal ventilation and raised air pressure
Authors: Hesser C. M. , Linnarsson D. , Fagraeus L.
Published: December 2017

Pulmonary ventilation (V) and the interrelationships of airflow, transpulmonary pressure, and lung volume during inspiration and expiration were studied in eight healthy subjects who performed maximal exercise (MEx; 140% VO2 max), 15-s maximal voluntary ventilation (MVV), and forced inspiratory and expiratory vital capacity (FVC) maneuvers at 1, 3, and 6 ATA. Maximal exercise ventilation and MVV amounted to 149 +/- 7 (mean +/- SE) and 193 +/- 9 l . min-1, respectively, at 1 ATA and were both reduced by approximately 37% at 3 ATA and by 50% at 6 ATA. Expiratory peak flows during MEx and MVV were equal to the maximal flows obtained during FVC at comparable lung volumes, whereas inspiratory peak flows during MEx were 20% less than the FVC flows. Despite a sixfold increase in gas density, the rate of mechanical work of breathing decreased when the pressure was raised to 6 ATA, during MEx from 8 +/- 1 to 6 +/- 1 W, and during MVV from 28 +/- 5 to 18 +/- 3 W. With increasing gas density there was a shift of lung volumes in the inspiratory direction with consequent reductions of inspiratory-to-expiratory flow ratios. We conclude that depletion of energy stores in the inspiratory muscles contributed to limiting V during MEx at raised air pressure.
Bronchial reactivity to inhaled methacholine in cigarette-smoking baboons
Authors: Roehrs J. D. , Rogers W. R. , Johanson W. G.
Published: December 2017

We expected that cigarette smoking would increase airway reactivity to inhaled methacholine. To remove the self-selection bias inherent among humans, we randomly assigned young male baboons (Papio cynocephalus) to cigarette-smoking or sham-smoking groups. The animals were taught to puff on lit cigarettes (smokers) or on a similar resistance (shams). After 6 pack-yr of smoking (40 cigarettes/day for 3 yr), we studied airway reactivity. The animals were anesthetized and intubated for measurement of lung volumes, compliance, and expiratory flow with air and with 80% helium-20% oxygen using both partial expiratory flow-volume and maximal expiratory flow-volume maneuvers. Baseline lung function was similar in smokers and shams. Following methacholine, residual volume increased significantly (P less than 0.05) in shams but not in smokers. Smokers showed significantly (P less than 0.04) greater postchallenge flow rates than did shams, and the dose of methacholine required to produce a 20% decrement in flow was significantly (P less than 0.05) greater in smokers. Chronic cigarette smoking in a nonhuman primate model decreases airway reactivity to inhaled methacholine even when base-line lung function is normal.
Basenji-Greyhound dog model of asthma: influence of atropine on antigen-induced bronchoconstriction
Authors: Hirshman C. A. , Downes H.
Published: December 2017

To test the relative importance of cholinergic effects on the Basenji-Greyhound (BG) model of asthma, we administered Ascaris antigen to Ascaris-sensitive BG dogs without other treatment, and following intravenous atropine. Pulmonary resistance (RL) increased from 1.4 +/- 0.43 cmH2O . l-1 . s (mean + SE) to 26.0 +/- 5.21 after Ascaris antigen exposure in seven untreated dogs. In the same dogs pretreated with 0.2 mg/kg atropine, RL increased from 1.5 +/- 0.31 to 18 +/- 5.00. Atropine 0.4 and 1.0 mg/kg did not result in increased protection. Although 0.2 mg/kg atropine markedly inhibited the airway responses to both inhaled citric acid and methacholine, it only slightly prevented antigen-induced airway constriction. We conclude that in BG dogs, cholinergic pathways elicit bronchomotor responses to irritants but that the major component of antigen-induced bronchoconstriction is not cholinergically mediated.
Glucose ingestion before and during intense exercise
Authors: Bonen A. , Malcolm S. A. , Kilgour R. D. , MacIntyre K. P. , Belcastro A. N.
Published: December 2017

Glucose and insulin responses were compared in glycogen depleted subjects when glucose (1.5 g/kg) was ingested 15 min before (n = 7) or during (min 3-5) intense exercise (80% VO2 max; n = 8). A nonexercise group (n = 8) and a no-glucose group (n = 8) were also included for comparisons. A 36- to 44-h fast, combined with exhaustive exercise to deplete muscle glycogen, (congruent to 80% in pilot studies) suggested that the subjects initiated exercise with substantially depleted hepatic and muscle glycogen reserves. With no glucose ingestion, blood glucose decreased during exercise (P less than 0.05) and blood lactate (HLa congruent to 3.8 mM) and the respiratory exchange ratio (R) remained low (0.83); with glucose ingestion before or during exercise, HLa concentrations were doubled (7.3 mM) and R was greater (0.90-0.92; P less than 0.05). Although insulin concentrations decreased rapidly to basal levels within 10 min after the onset of exercise in the preexercise glucose group (P less than 0.05), blood glucose continued to decrease throughout exercise. No such decrease occurred in the subjects who ingested glucose during exercise, nor did insulin concentrations change markedly in this group (P greater than 0.05). The HLa and R data indicated that a considerable portion of glucose was metabolized during exercise. Differences in the preexercise insulin environment appear to exert a persistent effect on glucose uptake throughout exercise.
Physiological and hematologic responses to summer and winter dry-heat acclimation
Authors: Shapiro Y. , Hubbard R. W. , Kimbrough C. M. , Pandolf K. B.
Published: December 2017

Differences between acclimation to heat at the end of winter (W) and at the end of summer (S) were studied on the same eight male volunteers. Subjects were exposed to 40 degrees C, 30% rh for 10 consecutive days on two separate occasions approximately 5 mo apart (S and W). Daily exposures lasted 120 min: 10 min rest, 50 min walking 1.34 m . s-1 on the level, 10 min rest, 50 min walking. During W acclimation, rectal temperature (Tre) and heart rate (HR) decreased, sweat rate (msw) remained unchanged, and plasma and red cell volume of the blood expanded. During S acclimation, HR decreased while Tre and msw remained unchanged, and plasma volume increased. The Tre of the acclimated subjects remained higher in W, and the msw lower, than in S. It was concluded that acclimation does not totally eliminate the seasonal differences in thermoregulatory set point and sweating sensitivity. Further, acclimation to a more severe heat did not lower the thermoregulatory set point that was achieved by natural acclimatization to a milder heat but affected the cardiovascular adjustment and caused greater plasma volume expansion. W acclimation caused both plasma and blood cell volume expansion, whereas S acclimation affected only plasma volume.
Pulmonary mechanisms of the normal ferret
Authors: Boyd R. L. , Mangos J. A.
Published: December 2017

Pulmonary mechanics were measured in normal anesthetized male Fitch ferrets (200-360 g). In eight transorally intubated ferrets, pressure-volume (PV) curves for the lung and chest wall were obtained with an esophageal balloon and body plethysmograph. The lung volumes and capacities expressed as a percentage of the total lung capacity (mean, 49.8 ml) were: vital capacity, 84.7%; inspiratory capacity, 63.7%; inspiratory reserve volume, 58.2%; functional residual capacity, 33.8%; expiratory reserve volume, 16.8%; residual volume, 15.3%; and tidal volume, 8.0%. The compliance of the lung (2.93 ml . cmH2O-1), chest wall (22.42 ml . cmH2O-1) and respiratory system (2.55 ml . cmH2O-1) were determined from the PV curves. The dynamic compliance (1.6 ml . cmH2O-1), pulmonary resistance (0.024 cmH2O . ml-1 . s), frequency of breathing (43.5 breaths . min-1), and minute ventilation (195 ml . min-1) were measured during spontaneous breathing. In a second group of 10 ferrets the total airway resistance (0.116 cmH2O . ml-1 . s) and specific conductance (0.915 ml . s-1 . cmH2O . ml-1) were measured during spontaneous nasal breathing. In general the pulmonary mechanics of the ferret were similar to those of the rabbit and dog, when the data were normalized for lung volume.
Effect of upright exercise on threshold for cutaneous vasodilation and sweating
Authors: Johnson J. M. , Park M. K.
Published: December 2017

To find whether exercise or upright posture affected the internal temperature threshold for cutaneous vasodilation or the relationship between skin blood flow (SkBF) and sweat rate (SR), the relationship of esophageal temperature (Tes) to forearm SkBF and SR was measured in four settings: supine rest, upright rest, supine exercise, and upright exercise. All studies were performed at an elevated skin temperature (38-38.5 degrees C). Compared with values from supine rest, upright exercise was associated with an increase in the internal temperature threshold for vasodilation of 0.39 +/- 0.07 degrees C (P less than 0.01), whereas there was no significant alteration in the threshold for the onset of sweating. Neither the ultimate slope of the SkBF-Tes relationship nor that of the SR-Tes relationship was altered by upright exercise. The upright posture and exercise each contributed to the elevation in the threshold for cutaneous vasodilation, with the average shifts being 0.11 +/- 0.05 degrees C (P less than 0.05) and 0.28 +/- 0.08 degrees C (P less than 0.01), respectively. The net effect of this shift in threshold was to reduce the level of SkBF at any level of Tes during exercise and to increase the difference in threshold between vasomotor and sudomotor responses.
Computer simulation of experiments in responses to intravenous and inhaled CO2
Authors: Yamamoto W. S.
Published: December 2017

A simulation of ventilatory responses to infused and inhaled CO2 at controlled cardiac output and high and low levels of neural excitation mimics comparable experiments in animals. The model suggests that at low levels of endogenous and exogenous CO2 load the alert quiescent animal will show hyperpnea to both test states associated with hypercapnia. The nonalert quiescent animal simulated will show an isocapnic response to endogenous load and hypercapnic response to exogenous load. The explanation of this behavior lies in the model formulation, which allows the neural signal from metabolically active sources to drive the proportional component of the controller below an operating level established by its set point. By this reasoning the excited but metabolically inactive animal should be paradoxically less sensitive to small changes in CO2, whether exogenous or endogenous, than the quiescent animal. The model demonstrates further that a neural "exercise" signal in proportion to venous return better simulates observations in which CO2 load and venous return are dissociated than one in which the neural signal is computed from metabolism. The use of delta V/delta P slopes as estimates of sensitivity go awry in experiment and simulation when blood flow, CO2 level, and neural excitatory state are dissociated. This is particularly true when the organism is operating at and below the hypothesized set point.
Cardiorespiratory and metabolic responses to treadmill exercise in the horse
Authors: Thomas D. P. , Fregin G. F.
Published: December 2017

The purpose of this study was to measure cardiovascular, respiratory, and metabolic responses to graded treadmill exercise in the horse. A five-stage treadmill test up to 90% of predicted maximal heart rate was administered to five sedentary horses. The highest measured level of exercise produced a sixfold increase in cardiac output and a 41% elevation of stroke volume over standing values. Left ventricular, arterial, and right atrial pressures as well as the maximal time derivative of left ventricular pressure were all elevated during exercise. Under the same two conditions hematocrit (Hct) increased from 33 +/- 2 to 47 +/- 1%, oxygen uptake (VO2) from 1.1 +/- 0.1 to 32.7 +/0 2.1 1.min-1, and respiratory exchange ratio (RQ) increased from 0.83 +/- 0.02 to 0.96 +/- 0.01. In addition, three of the horses were willing to trot at a sixth stage (14 km.h-1, 11.5% grade), which elicited a VO2 of 39.8 +/- 0.31.min-1 and an RQ of 0.98 +/- 0.01. In response to the sympathetic stimulation of exercise, the horse is able to elevate Hct, hemoglobin, and oxygen-carrying capacity by emptying the spleen, thus increasing total circulating red blood cells by as much as 50%. This enabled three of the five horses used in the present study to increase aerobic metabolism almost 40-fold above resting or twice that seen in humans. Therefore, in the horse "blood-boosting" is an efficient mechanism for increasing aerobic metabolism. This finding lends further support to the view that the oxygen transport system limits maximal aerobic capacity in humans.
beta-Endorphin central depression of respiration and circulation
Authors: Moss I. R. , Scarpelli E. M.
Published: December 2017

Beta-Endorphin was injected into cerebrospinal fluid of lightly anesthetized dogs. Its effects on ventilation (V), tidal volume (VT), respiratory frequency (f), preinspiratory occlusion pressure (P500), and respiratory timing of unoccluded and occluded breaths were studied during CO2 rebreathing. Blood pressure and heart rate (HR) were monitored throughout the study. beta-Endorphin produced 1) early (approximately 15 min) but temporary depression of VT-PCO2 and P500-PCO2 responses; 2) progressive hypoventilation during spontaneous breathing and progressive depression of V-PCO2 and f-PCO2 responses, which were maximal at about 75 min, followed by gradual recovery; 3) progressive hypotension and bradycardia starting at about 15 min and reaching maximal effect at about 105 min. Increased expiratory time (TE) accounted for the changes in f. TE increased in unoccluded breaths and during both preinspiratory and inflation occlusion. After vagotomy, beta-endorphin produced insignificant effect on f, TE, and HR. Naloxone itself increased P500-PCO2 response; when given during beta-endorphin effect, it reversed the hypotension, bradycardia, V-PCO2, and f-PCO2 responses and facilitated the P500-PCO2 and VT-PCO2 responses. We conclude that beta-endorphin effect is produced by both depression of specific central cardiovascular and respiratory control units and facilitation of central vagal projections.
Functional aspects of canine bronchial-pulmonary vascular communications
Authors: Modell H. I. , Beck K. , Butler J.
Published: December 2017

Experiments in anesthetized open-chest dogs indicated that blood from the canine bronchial circulation may drain into both the arterial and venous sides of the alveolar drain into both the arterial and venous sides of the alveolar vessel bed. Evan's blue dye injected into the systemic circulation appeared in the effluent from a left lower lobe pulmonary arterial segment in which inflow was stopped with a snare and outflow through the alveolar vessel bed was stopped by maintaining zone 1 conditions. To determine the influence of mean systemic arterial pressure on lobar bronchial flow, flows from arterial and venous cannulas were measured at different mean systemic arterial pressures (lung volume history constant). Influence of lung volume and transpulmonary pressure (Ptp) change were each examined utilizing the hysteresis characteristics of the lung pressure-volume curve. Mean total flows ranged from 2.26 to 5.26 ml/min with 43.61% draining through the arterial side. Flow decreased with lower systemic arterial pressure, high Ptp, and higher lung volume. Distribution of flow was influenced only by lung volume changes. Results indicate that the communication sites contributing to the arterial drainage are located within the alveolar vessel bed. Since bronchial flow drains to both sides of the alveolar vessel bed, it must be considered when interpreting results from "isolated" pulmonary circulation preparations.
Evaluation of alveolar amplitude response technique for determination of lung perfusion in exercise
Authors: Luijendijk S. C. , Zwart A. , van der Kooij A. M. , de Vries W. R.
Published: December 2017

We investigated the influence of tracer gas venous return on the determination of pulmonary perfusion (Qp) using the alveolar amplitude response technique (AART) to evaluate the applicability of this technique at rest and during exercise. The venous return influence was calculated by a computer simulation applied to a simplified body compartment model. Using the AART method, which neglects the influence of venous return, a simulation based on acetylene as a tracer gas predicted an overestimation of the actual value of Qp ranging from 0 to 10% for all work loads investigated. These theoretical results were compared with experimental results. Experiments with human subjects with acetylene as the tracer gas yielded an underestimation of Qp of about 20% at rest and an overestimation of about 7% under different exercise conditions. Experiments with anesthetized dogs showed an underestimation of Qp of about 12% for acetylene and about 6% for halothane. The theoretical and experimental results related to exercise conditions are thus in good quantitative agreement. The experimental data obtained for acetylene with human subjects at rest and with anesthetized dogs are also in good quantitative agreement. However, they deviate considerably from theoretical predictions. This discrepancy may be due to the simplified body compartment model used in the calculations, which can considerably influence the calculated results, especially for conditions at rest. The main conclusion of this paper is that recirculating tracer gas does not unduly influence results for Qp obtained with the AART method when halothane is used as the tracer gas.
Work of breathing in dog during exercise
Authors: Saibene F. , Mognoni P. , Aguggini G. , Clement M. G.
Published: December 2017

In six dogs trained to wear a mask and to swallow an esophageal balloon, the dynamic work of breathing (Wdyn) was measured while the animals ran on a treadmill at different intensities (7-13 km.h-1,+10%). Wydn (kg.m.min-1) increased with ventilation (VE, 1.min-1) according to Wdyn = 0.308.10(-2) VE2 + 0.0098.10(-2).VE3. However, if the exercise was prolonged so that the body temperature rose above approximately 39 degrees C, Wdyn, for a given ventilation, decreased; and hence Wdyn = 0.253.10(-2).VE2 -- 0.0011.10(-2).VE3. Similar observations have been made on another dog heated from an external source. From this finding it seems that during exercise, when the temperature rises and the ventilation increases to dissipate heat, the airway size, at least in some portion of the respiratory tract, increases markedly and therefore the cost of breathing is greatly diminished.This mechanism would save oxygen for the exercising limb muscles when exercise has to be continued for an extended time.
Influence of acute microwave radiation on cardiac function in normal and myocardial ischemic cats
Authors: Galvin M. J. , McRee D. I.
Published: December 2017

Exposure of biological specimens to microwave radiation in vivo and in vitro has been reported to cause alterations to the cardiovascular system. In addition, microwave radiation may cause effects in damaged cardiac tissue that are not observed in normal tissue. In this study, we examined the influence of direct microwave irradiation (2.45 GHz, continuous wave) of the intact exposed heart on cardiac function in cats with and without myocardial ischemia. Myocardial ischemia was induced by occlusion of the left anterior descending coronary artery. In the sham-nonexposed and sham-plus-microwave exposed animals the coronary artery was isolated but not occluded. The exposed hearts were either irradiated at a specific absorption rate (SAR) of 30 mW/g or not irradiated, and were monitored for 5 h. At a SAR of 30 mW/g, the temperature of the exposed tissue increased at an initial rate of 0.43 degrees C/min in dead cats. However, in live animals, no increases in aortic blood temperatures occurred during irradiation. Mean arterial blood pressure, cardiac output, heart rate, plasma and myocardial creatine phosphokinase, and S-T segment were not influenced by 5 h of microwave irradiation of the myocardium in cats with or without myocardial ischemia.
Muscular enlargement and number of fibers in skeletal muscles of rats
Authors: Gollnick P. D. , Timson B. F. , Moore R. L. , Riedy M.
Published: December 2017

The effect of muscular enlargement produced by surgical ablation of a synergist and the combination of synergist ablation and exercise on the number of fibers in the soleus (S), plantaris (P), and extensor digitorum longus (EDL) muscles of the rat was studied. The number of fibers per muscle was determined by direct counts of individual fibers dissected from HNO3-treated muscles. Ablation of a synergist produced average enlargements of about 25, 45, and 29% for the S, P, and EDL muscles, respectively. Exercise and synergist ablation produced increases in wet weight to about 44 and 88% for the S and P muscles, respectively, whereas no further increases were observed in the EDL muscles. Intra-animal comparisons revealed that no differences existed for total fiber number or the incidence of fibers with bifurcations between the enlarged and contralateral control muscles. The difference in dry weight of fibers from the enlarged as compared with control muscles was closely correlated to differences in total muscle wet weight. These data demonstrate that hypertrophy rather than hyperplasia was responsible for increases from 10 to over 100% in the weight of skeletal muscles.
Effect of prolonged recombency on pulmonary blood volume in normal humans
Authors: Hirasuna J. D. , Gorin A. B.
Published: December 2017

We have observed a progressive decrease in pulmonary blood volume during sustained recumbency measured using two independent methods. Pulmonary capillary blood volume (Vc) was estimated by the method of Roughton and Forster (J. Appl. Physiol. 11: 290, 1957). We measured regional pulmonary blood volume (PBVR) using 99mTc-labeled erythrocytes (Gorin et al., J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45: 225, 1978). In 21 studies in 19 normal subjects, we measured pulmonary CO diffusing capacity by the single-breath technique and calculated Vc with the subjects seated and at fixed times after lying down. After 5 min in the recumbent position, there was a mean 49% increase in Vc over the value in the seated position. With sustained recumbency Vc decreased 18.3%/h over 90 min. In 12 studies in 8 normal subjects, PBVR declined 16.7%/h with prolonged recumbency in studies lasting 60-90 min. The initial increase in Vc after subjects assumed a supine position has been well described. The subsequent fall in pulmonary blood volume to levels equal to or below that measured with the subject seated has not previously been reported.
Influence of joint position on ankle dorsiflexion in humans
Authors: Marsh E. , Sale D. , McComas A. J. , Quinlan J.
Published: December 2017

A method is described for investigating the contractile properties of the dorsiflexor muscles of the ankle. With the joint in the midposition the tibialis anterior was found to contribute less than half of the maximum voluntary torque, the remainder presumably being provided by the long extensors of the toes. The mean contraction and half-relaxation times of tibialis anterior muscles in healthy young men were 81.2 +/- 7.4 (SD) ms and 83.6 +/- 17.2 ms, respectively. When the tibialis anterior was stretched, the twitch became slower and more complete fusion of the contractions occurred during tetanic stimulation at low frequencies. Stimulation of tibialis anterior at 30 and 40 Hz disclosed that the optimum length of the muscle corresponded to about 10 degrees of plantarflexion. Maximum voluntary torque was also developed at 10 degrees of plantarflexion and decreased sharply as the ankle was dorsiflex beyond 5 degrees. The position assumed by the ankle joint at rest depended on whether the subject was sitting, standing, or lying, but was always greater, in the plantarflexed direction, than the "optimum" position for torque development. At low rates of stimulation the torque continued to increase throughout the full range of plantarflexion, probably because of the elasticity of the tendon. During maximum effort motoneuronal excitability did not appear to be influenced significantly by changes in joint angle.