bluuebunny/crossref_metadata_2025 huggingface dataset:
Axial forces in the bronchial tree
Authors: Hoppin F. G. , Hughes J. M. , Mead J.
Published: December 2017

Dog airways in situ are longer and extend more with inflation than when dissected out. The associated deformation of the parenchyma, from considerations of elasticity, appears to be small. The associated axial forces, to the extent they are transmitted along the tree, are governed by branching angles. Overall, average angles are such as would maintain constant axial stress along the tree and thus favor symmetrical lengthening. But locally, angles indicate considerable variation of transmitted stresses. Since radiography shows relatively homogeneous lengthening, we infer powerful local axial stabilization. In confirmation, dog airways were much less extended by locally applied forces in situ than excised. Do forced expirations apply substantial axial forces? In one subjects, during forced expiration, airway pressure fell abruptly near the carina but calculations showed relatively small axial forces applied to the airway. However, we speculate that large forces may be applied by airway plugs. We conclude that parenchyma stabilizes airway length against variably transmitted axial forces, and, perhaps, forces on airway plugs.
Effect of pentobarbital sodium on respiratory control in newborn rabbits
Authors: Goldberg M. S. , Milic-Emili J.
Published: December 2017

Using the airway occlusion pressure technique, control of breathing was studied in unanesthetized and anesthetized newborn rabbits breathing various gas mixtures under steady-state conditions. Independent of the gas mixture breathed, barbiturate anesthesia resulted in a reduction of ventilation. This was not due to a change in inspiratory drive since for each gas mixture breathed the pressure generated by the inspiratory muscles 0.3 s after the onset of the occluded inspiration (P0.3) remained virtually unchanged, nor could this be attributed to changes in respiratory mechanics as indicated by the fact that the relation between P0.3 and V0.3 (the volume generated 0.3 s after onset of the immediately preceding unoccluded inspiration) did not change. On the other hand, during anesthesia inspiratory time was slightly shortened as a result of a change in both central (bulbopontine) and peripheral (volume-related vagal reflex) modulation, while expiratory duration was markedly prolonged. This disproportionate increase in expiratory duration with respect to inspiratory duration was responsible for most of the depression of ventilation found in the newborn rabbits during barbiturate anesthesia.
Thermoregulatory responses during competitive marathon running
Authors: Maron M. B. , Wagner J. A. , Horvath S. M.
Published: December 2017

To assess thermoregulatory responses occuring under actual marathon racing conditions, rectal (Tre) and five skin temperatures were measured in two runners approximately every 9 min of a competitive marathon run under cool conditions. Race times and total water losses were: runner 1 = 162.7 min, 3.02 kg; runner 2 = 164.6 min, 2.43 kg. Mean skin temperature was similar throughout the race in the two runners, although they exhibited a marked disparity in temperature at individual skin sites. Tre plateaued after 35--45 min (runner 1 = 40.0--40.1, runner 2 = 38.9--39.2 degrees C). While runner 2 maintained a relatively constant level for the remainder of the race, runner 1 exhibited a secondary increase in Tre. Between 113 and 119 min there was a precipitous rise in Tre from 40.9 to 41.9 degrees C. Partitional calorimetric calculations suggested that a decrease in sweating was responsible for this increment. However, runner 1's ability to maintain his high Tre and running pace for the remaining 44 min of the race and exhibit no signs of heat illness indicated thermoregulation was intact.
Rate of pH changes in blood plasma in vitro and in vivo
Authors: Hill E. P. , Power G. G. , Gilbert R. D.
Published: December 2017

The rate of pH decrease in dog blood after addition of CO2 (dissolved in saline) was measured in vitro with a combination pH electrode and fast-response amplifier. The pH change was found to have an apparent half time of 6.0 +/- 0.5 s at 38 degrees C, similar to that predicted by previous mathematical simulations on the basis of uncatalyzed CO2 hydration kinetics and the buffering characteristics of plasma. Measurements were also made in vivo in dogs by withdrawing blood rapidly from a carotid artery through a temperature-controlled chamber containing a pH electrode. When the flow was stopped, we measured the pH change which occurs in blood (after it leaves the lungs) as the slow dehydration of bicarbonate continues. The measured half time was 7.3 +/- 0.6 s, again agreeing well with predictions. Essentially the same half time was found when the direction of approach to chemical equilibrium was reversed by adding CO2 to the inspired air. The rate of the reactions could be increased markedly by hemolyzing the blood to release carbonic anhydrase into the plasma.
Effect of lung collapse on compensatory lung growth
Authors: Inselman L. S. , Mellins R. B. , Brasel J. A.
Published: December 2017

The effect of unilateral lung collapse on compensatory lung growth was studied in 3-wk-old (young) and 10-wk-old (adult) male Long-Evans rats. Under light halothane anesthesia, left lung collapse was produced by injection of dental plastic through a thracheostomy cannula. The rats were killed either 5 days or 4 wk later. At 5 days postcollapse, the 3-wk-old rats had an increase in DNA over sham controls (21%) (P less than 0.05), with no significant change in the protein/DNA ratio. At 4 wk postcollapse, increases in DNA over shamoperated controls were observed in both the 3-wk-old (58%) and the 10-wk-old (28%) rats, whereas the protein/DNA ratio at both ages was significantly less than that of sham controls (P less than 0.05). Thus, unilateral lung collapse stimulates growth of the contralateral lung by cellular hyperplasia, not hypertrophy, both in the young and adult rat. The hyperplasia begins within 5 days after collapse and is greater by 4 wk. The extent of hyperplasia is greater in the young than in the adult rat.
Effects of exercise and eucapnic hyperventilation on bronchial clearance in man
Authors: Wolff R. K. , Dolovich M. B. , Obminski G. , Newhouse M. T.
Published: December 2017

The effects of exercise and eucapnic hyperventilation on bronchial clearance were assessed in 10 healthy nonsmoking adults. A 99mTc-albumin aerosol was inhaled as a bolus in late inspiration under controlled conditions to produce deposition primarily in large airways. Lung retention of radioactivity was quantified using a gamma camera and subsequent computer analysis. Compared with quiet breathing (control), exercise significantly speeded clearance (P less than 0.05). Resting eucapnic hyperventilation at levels similar to those achieved during exercise produced less speeding. Compared to control conditions these changes may be brought about by a) mechanical effect of increased lung movement, and b) effects on the autonomic nervous system, mediated via the parasympathetic pathway producing stimulation of airway mucus glands and/or sympathetic stimulation of cilia due to exercise-induced catecholamine release.
Effects of water immersion on lung volumes: implications for body composition analysis
Authors: Girandola R. N. , Wiswell R. A. , Mohler J. G. , Romero G. T. , Barnes W. S.
Published: December 2017

Lung volumes of 20 healthy young men were measured before and after water immersion to the neck level. Immersion resulted in significant decreases (P less than 0.01) in forced vital capacity (FVC) (8.9%), expiratory reserve volume (ERV) (61%), total lung capacity (TLC) (5.6%), and functional residual capacity (FRC) (2.9%). Significant increases were observed in inspiratory capacity (IC) (10%) and residual volume (RV) (6.7%). The increase in RV was attributed to a possible “stiffness” of the lung tissue caused by pulmonary vascular engorgement. Densitometric analysis was made on each subject using hydrostatic weighing techniques. Subsequent calculation of body density and per-cent body fat indicated significant (P less than 0.01) differences when using RV measured on land and in water. Body fat was 14.0% using the land RV in the computation of density and decreased to 13.4% using the RV measured in water. It was concluded that when obtaining body density values. RV should be measured concurrently while the subject is in the water.
Influence of temperature on hemoglobin-ligand interaction in whole blood
Authors: Hlastala M. P. , Woodson R. D. , Wranne B.
Published: December 2017

Temperature-dependent change in hemoglobin-oxygen affinity was measured as a function of hemoglobin-oxygen saturation. In addition, the CO2 Bohr factor and fixed acid Bohr factor were measured as a function of saturation of temperatures of 23, 30, 37, and 44 degrees C. Measurements were made on normal blood and blood with reduced 2,3-diphosphoglycerate (DPG). The influence of temperature is greatest at low saturation and is enhanced slightly by DPG depletion. The CO2 Bohr factor is increased at high temperatures; this is primarily due to increased carbamino formation with rising temperature, especially at lower oxygen saturation. The effect of DPG on oxygen affinity is reduced at a high temperature and elevated at low temperature. These diverse effects of temperature on hemoglobin-ligand interaction require consideration in assessing oxygen delivery when temperature is increased or decreased.
beta-Receptor influence on lung vasoconstrictor responses to hypoxia and humoral agents
Authors: Porcelli R. J. , Viau A. T. , Naftchi N. E. , Bergofsky E. H.
Published: December 2017

The role of the adrenergic receptor in mediating pulmonary vascular responses to gaseous and humoral agents was investigated by use of epinephrine injections in the perfused feline pulmonary circulation. Alteration of the balance between alpha- and beta-adrenergic activity was quantified by measurement of decreasing vasoconstrictor activity to epinephrine and rising lobar tissue 3′,5′-adenosine cyclic monophosphate (cAMP) levels. The increased beta-adrenergic activity thus generated was associated with marked reductions in the pulmonary vasoconstrictor responses to hypoxia, hypercapnic acidosis, and histamine, but not to serotonin. Repeated pulmonary vasodilations or increases in blood, but not pulmonary tissue, levels of cAMP induced by theophylline doses, which would not necessarily affect the beta-adrenergic activity, did not alter the pulmonary vasoconstrictor responses to hypoxia, hypercapnia, or histamine. These data support the significant role which the adrenergic system plays in mediating pulmonary vasoconstrictor responses to certain specific gaseous and humoral agents, and the specificity with which this mediation occurs serves to link hypoxia and histamine together so that the latter could serve as a mediator of the former.
Changes induced by exercise in rates of turnover and oxidation of ketone bodies in fasting man
Authors: Balasse E. O. , Fery F. , Neef M. A.
Published: December 2017

Seven normal subjects fasted for 3 days were exercised for 30 min on a bicycle ergometer at 60 +/- 30% (mean +/- SE) of their maximal aerobic capacity. Rates of transport and oxidation of ketone bodies were determined at rest and during exercise using a primed constant infusion of [14C]acetoacetate. During the initial 7.5 min of exercise, ketone concentration abruptly decreased (-19.4 +/- 3.1%; P less than 0.001) as the result of a 22.2 +/- 7.0% reduction (P less than 0.05) in ketone production rate (Ra) and a 30.4 +/- 7.5% increase (P less than 0.01) in the rate of uptake (Rd) of ketones. As work progressed, blood ketones continued to fall slowly until the 15th min of exercise and thereafter plateaued at a level which was 21.9 +/- 4.1% lower (P less than 0.005) than resting values. During this apparent new steady state, both Ra and Rd were below control values but tended to be equal and to return simultaneously to their preexercise level. The metabolic clearance rate was increased throughout the entire period of exercise, the rise being more marked during the initial 7.5 min (+40.7 +/- 7.5%; P less than 0.01) than at later periods (+19.0 +/- 7.4%; P less than 0.05). Exercise greatly enhanced ketone oxidation which became virtually complete; despite this, the %CO2 derived from ketones, which averaged 17.6 +/- 1.6% at rest, decreased to 10.1 +/- 0.6% (P less than 0.01) after 30 min of work. This indicates that even during the hyperketonemia of fasting, the increased energy needs related to exercise are met primarily by fuels other than ketones.
Potentiation of hypoxic pulmonary vasoconstriction by ethyl alcohol in dogs
Authors: Doekel R. C. , Weir E. K. , Looga R. , Grover R. F. , Reeves J. T.
Published: December 2017

Pulmonary and systemic hemodynamics and arterial blood gases were measured in anesthetized and mechanically ventilated dogs before and after oral or intravenous administration of ethanol. Increases in mean pulmonary artery pressure and pulmonary vascular resistance occurred. Platelet antiserum-induced thrombocytopenia inhibition of prostaglandin synthesis with meclofenamate, or alpha-adrenergic blockade did not alter the pulmonary pressor response to ethanol. However, the increase in resistance following ethanol was abolished by hyperoxia and potentiated by hypoxia. Thus, it appears that the effect of ethanol is to augment hypoxic pulmonary vasoconstriction, whereas ethanol per se has no independent pulmonary pressor activity.
Dynamic viscoelastic properties of the canine trachea
Authors: Bobbaers H. , Clement J. , van de Woestijne K. P.
Published: December 2017

The dynamic elastance (E) and viscous resistance (R) of the canine intrathoracic trachea were determined by submitting excised tracheal segments to periodic variations of pressure at frequencies between 0.5 and 9 Hz, and by relating simultaneous transmural pressure and volume variations. Mean values of E and R are, respectively, 17.3 cmH2O.cm-1 and 0.16 cmH2O.cm-1.s, or, expressed in volume changes per cm length of the trachea, 53.5 cmH2O.ml-1 and 0.49 cmH2O.ml-1.s. E and R increase at higher longitudinal tension of the trachea and under the influence of acetylcholine.
Spatial distribution of pulmonary blood flow in dogs in increased force environments
Authors: Greenleaf J. F. , Ritman E. L. , Chevalier P. A. , Sass D. J. , Wood E. H.
Published: December 2017

Spatial distribution of pulmonary blood flow (SDPBF) during 2- to 3-min exposures to 6–8 Gy acceleration was studied, using radioactive microspheres in dogs, and compared to previously reported 1 Gy control distributions. Isotope distributions were measured by scintiscanning individual 1-cm-thick cross sections of excised, fixed lungs. Results indicate: 1) the fraction of cardiac output traversing left and right lungs did not change systematically with the duration and magnitude of acceleration; but 2) the fraction is strongly affected by the occurrence or absence of fast deep breaths, which cause an increase or decrease, respectively, in blood flow through the dependent lung; and 3) Gy acceleration caused a significant increase in relative pulmonary vascular resistance (PVR) in nondependent and dependent regions of the lung concurrent with a decrease in PVR in the midsagittal region of the thorax. Result 3 may be mediated primarily by changes in regional alveolar volume and geometry in the nondependent hemithorax conbined with hydrostatic effects of extravascular fluid and active hypoxic response in the dependent region and is superimposed on, and may override, hydrostatic effects of perfusion pressures on SDPBF during acceleration.
Evolution of intrathoracic airway mechanics during lung growth
Authors: De Troyer A. , Yernault J. C. , Englert M. , Baran D. , Paiva M.
Published: December 2017

Elastic recoil pressure of the lungs (Pst(L)), maximum expiratory flow rates (MEF), critical transmural pressure of the collapsible flow-limiting segment (Ptm'), and S-segment conductance (Gs) have been determined in 40 healthy subjects, 7–18 yr old. Pst(L), measured at different lung volumes (fractional) from the expiratory quasi-static pressure-volume curves, increases progressively with age. MEF's, at different lung volumes, are closely related to total lung capacity (TLC); the ratios MEF/TLC, at all lung volumes, are independent of age. Ptm' is also independence of age and body height, most values lying between 0 and -15 cmH2O; this finding suggests that the locus and the behavior of the collapsible segment do not change during growth. Gs, in absolute value, increases with growth but, when adjusted for lung size, Gs decreases steadily with age and body height. These relations suggest that, from childhood to adolescence, the air spaces grow disproportionately more than the airway system.
Maximal frequency of breathing at various tidal volumes in airways obstruction
Authors: Marazzini L. , Gatti L. , Cavestri R. , Longhini E.
Published: December 2017

To determine the relative importance of control system and of mechanical and metabolic properties of the motor system on the maximal frequency of breathing (1/t) at various tidal volumes (VT), we have studied the relationship between cycle period (t) and tidal volume in 10 normal subjects, in 9 patients with chronic obstructive lung disease, and in a normal subject breathing against different resistive loads. The results, expressed according to the equation t = t0 + b VT (where t0 represents the time required for a breathing cycle at zero VT and b means the additional time required for a breathing cycle with a VT equal to vital capacity), indicate that t0 is independent from the load either in unloaded or loaded normal subjects or in obstructive patients. In fact, although b was found significantly different, t0 remained essentially constant. These findings suggest that the level of maximal voluntary ventilation may be mainly related to metabolic and mechanical properties of the motor system (muscles of breathing and load imposed on them).
Response of the iron-deficient erythrocyte in the rat to hyperoxia
Authors: Larkin E. C. , Kimzey S. L. , Siler K.
Published: December 2017

Normal and iron-deficient rats were exposed to 90% O2 at 760 Torr for 24 or 48 h. Erythrocyte response to hyperoxia was monitored by potassium (rubidium) influx studies, by storage stress, and by ultrastructural studies. Normal rat erythrocytes exhibited morphological changes and decrease of ouabain-sensitive potassium influx compared to unexposed controls. Both components of erythrocyte potassium influx were affected by iron deficiency. Erythrocytes from unexposed iron-deficient rats showed a 50% increase in ouabain-sensitive potassium influx compared to controls. Iron-deficient rats exposed to hyperoxia for 24 or 48 h, had erythrocytes with morphological changes. Erythrocytes of iron-deficient rats exposed for 24 h showed no influx change; those exposed for 48 h showed a decrease of ouabain-sensitive influx compared to erythrocytes of controls.
Estimation of cardiac output by the CO2 rebreathing method during tethered swimming
Authors: Heigenhauser G. J. , Faulkner J. A.
Published: December 2017

The reproducibility of cardiac output (Q) estimated by the CO2 rebreathing method during tethered swimming was studied in five highly trained college swimmers. The reproducibility of the CO2 rebreathing method for estimations of Q during tethered swimming was similar to the reproducibility reported for the CO2 rebreathing method, direct Fick method, or dye-dilution method during either cycling or treadmill walking. All duplicate estimates of Q by the CO2 rebreathing method were within 15% of one another. A comparison was made between the Q's estimated by the CO2 rebreathing method during tethered swimming and previously published data on Q determined by the dye-dilution method during free swimming in a flune. At any given oxygen uptake, Q obtained by the CO2 rebreathing method during tethered swimming was not significantly different from the Q obtained by the dye-dilution method during flume swimming. Estimates of Q by the CO2 rebreathing method made during high intensities of tethered swimming were reproducible and appear to be valid.
In vitro evaluations of monopolar intravascular oxygen sensors
Authors: Beran A. V. , Shigezawa G. Y. , Whiteside D. A. , Yeung H. N. , Huxtable R. J.
Published: December 2017

Intravascular PO2 electrodes of a commercially available design were tested in vitro to establish their characteristics and to further elucidate on their clinical usability. In addition, four different cathode-anode combinations, utilizing the same geometrical design, were evaluated to establich the best combination. Au-Ag/AgCl exhibited the best characteristics as verified by the evaluation of stabilization time, sensitivity and reproducibility of the response, response time, linearity, drift, effects of temperature, flow, and pH, and the useful life of the sensors. Even though the Au-Ag/AgCl combination exhibited the best characteristics, it fell far below clinically recommended criteria for continuous monitoring of less than 10 Torr/24 h.
Peribronchial pressure in excised dog lungs
Authors: Sasaki H. , Hoppin F. G. , Takishima T.
Published: December 2017

To characterize the stresses which determine bronchial diameter in the lung, we estimated peribronchial pressure (Px) relative to intrabronchial pressure (Pbr) and to alveolar pressure (PA) for the main lobar bronchus of excised dog lobes using the technique of Takishima et al. (J. Appl. Physiol. 38: 875--881, 1975). The recoil of the bronchial wall, Pbr---Px, when smooth muscle was relaxed varied primarily with bronchial diameter. The recoil of the parenchyma around the bronchus, Px---Pa, varied with lung volume but was also diameter-dependent and served to double approximately the effective elastance of the bronchus in situ. We estimated recoils during slow deflations from TLC with the bronchus untreated, or pharmacologically contracted or relaxed. In untreated and relaxed states, local parenchymal and bronchial recoils were of similar magnitude to overall lung recoil (i.e., Px congruent to Ppl) except at high inflating pressure (PA -- Ppl = 30 cmH2O) where they were about half as great. With contraction, bronchial and local parenchymal recoils increased to as much as twice overall lung recoil. Contracted smooth muscle exerted a radial stress of 36+/-14 cmH2O at full lung inflation but much less during stepwise deflation.
Oxygen consumption by chick embryos exposed to mechanical (shaking) stress
Authors: Schmidt R. R. , Kaplan S. , Smith J. J.
Published: December 2017

Stage 34 (8-day) and 41 (15-day) chick embryos (Gallus gallus; in ovo) were exposed (3 min) to two separate amounts of mechanical (shaking) stress. Oxygen consumption determinations, following a temperature equilibration period (60 min), were made on entire, intact eggs using a Warburg apparatus equipped with 130-ml flasks modified to hold the egg. Shaking at 300 excursions per minute (epm) resulted in depressed O2 consumption by stages 34 and 41. Only stage 34 embryos had markedly depressed O2 consumption values when shaken at 100 epm. When exposed to 300 epm and reincubated for either 1, 2, or 4 hr prior to O2 consumption determinations stage 34 embryos, following an early return to control levels exhibited a marked fall in O2 consumption by 4 h reincubation. The stage 41 embryos, on the other hand, demonstrated a gradual rise to control O2 consumption levels by 4 h reincubation. Oxygen consumption has now been shown for the first time in an embryonic system (at two distinct developmental stages) to be functionally impaired by mechanically induced stress.
Demonstration of interlobar collateral ventilation
Authors: Scanlon T. S. , Benumof J. L.
Published: December 2017

In an ongoing series of experiments on mongrel dogs, three dogs were observed to have incomplete lobar fissures (interlobar connection present) between the left upper and left lower lobes. With the interlobar connection unclamped, selective hypoxia of the left lower lobe caused the electromagnetically measured blood flow to the left lower lobe to decrease 41 +/- 4%, whereas with the interlobar connection clamped selective hypoxia of the left lower lobe caused a 52 +/- 4% decrease in left lower lobe flow (P less than 0.05). Following 100% O2 ventilation and with the interlobar connection unclamped, complete occlusion of the left lower lobe bronchus caused no atelectasis or decrease in left lower lobe blood flow, whereas with the interlobar connection clamped complete occlusion of the left lower lobe bronchus caused complete left lower lobe atelectasis and a 58 +/- 3% decrease in left lower lobe blood flow. Histological confirmation of interlobar pulmonary parenchymal connection was obtained in each dog. We conclude that a sufficient amount of interlobar collateral ventilation can occur in dogs with incomplete lobar fissures to prevent absorption atelectasis and alter lobar blood flow reduction usually caused by selective lobar hypoxia.
A dryer for rapid response on-line expired gas measurements
Authors: Deno N. S. , Kamon E.
Published: December 2017

A dryer is described for use in on-line breath-by-breath gas analysis systems. The dryer continuously removes water vapor by condensation and controls the sample gas at 2 degrees C dew-point temperature or 5 Torr water vapor partial pressure. It is designed to operate at gas sampling flow rates from 0.5 to 1 1.min-1. The step-response time for the described system including a Beckman LB-2 CO2 analyzer, sampling tubing, and dryer is 120 ms at 1 l.min-1. The time required for gas samples to transport through the dryer is 105 ms at a gas sampling-flow rate of 1 l.min=1.
Enhanced heat production in physically restrained rats in hypoxia
Authors: Hayashi M. , Nagasaka T.
Published: December 2017

Combined effects of restraint and hypoxia (9.5% O2 in N2) on heat production (M), heat loss (HL), colonic temperature (Tcol), and cardiovascular activity were studied in unanesthetized rats. In freely moving (F) rats, hypoxia decreased M, HL, Tcol, and heart rate (HR). In restrained (R) rats, however, hypoxia increased M, HL, Tcol, and HR. The increase in these parameters was greatest within 30 min of hypoxia, and the peak value of M was 10.4 W X m-2 higher than in normoxia. After chemical sympathectomy with 6-hydroxydopamine hydrobromide, no such increase was observed in R rats. l-Norepinephrine bitartrate (0.4 mg X kg-1) increased M and HR in F rats in hypoxia. The increase in M was, however, 9.5 W X m-2 and significantly less than that observed in normoxia. Hypoxia significantly reduced blood flow to the brown adipose tissues (BAT) in R rats. The BAT may not be responsible for the increased metabolism in restrained hypoxia-exposed rats. Hypoxia significantly increased blood flow to the heart and the diaphragm, and to a lesser extent to the limb muscles. The increased metabolism in the cardiac and respiratory muscles may be a cause of hyper-metabolism in restrained rats. The limb muscles may also play some role in increasing metabolism in these rats.
Stapedius reflex in curarized subjects: an index of neuromuscular weakness
Authors: Ruth R. A. , Arora N. S. , Gal T. J.
Published: December 2017

To examine the validity of the acoustical stapedial reflex (AR) as an index of neuromuscular weakness, the AR was measured along with other indices of muscle strength during administration of d-tubocurarine (dTc) to six healthy subjects. AR decreased immediately after each dTc dose and preceded changes in handgrip strength and respiratory muscle strength, but the peak effects of each dose similarly affected AR and other muscle strength. The findings with electrocutaneous stimulation and effects on growth function of the AR indicate that dTc affects primarily stapedius muscle contraction, the efferent portion of the reflex arc, and does not affect afferent or central portions of the reflex. We therefore conclude that the AR is a valid index of the integrity of neuromuscular transmission which promptly reflects early phase weakness. Unlike other measures of muscle strength, AR testing does not depend on subject cooperation, and involves no discomfort. The test therefore provides a useful means of assessing neuromuscular weakness.
Postnatal maturation of the respiratory response to O2 in awake newborn lambs
Authors: Bureau M. A. , Begin R.
Published: December 2017

The present study was designed to analyze maturation of the respiratory response to hypoxia and hyperoxia in 41 newborn lambs aged 2–90 days. The O2 respiratory response was tested by progressive isocarbic hypoxia while minute ventilation (VE), tidal volume (VT), respiratory frequency (f), mean inspiratory flow (VT/TI), were measured. The occlusion pressure (P0.1) was also determined as an index of the neuromuscular output of the drive to breathe. The strength of the peripheral chemoreceptors was evaluated by the transient O2 100% inhalation test and by the early change in VE (delta VE) to cyanide (KCN) infusion. In all of the 2-, 10-, 30-, and 90-day groups of lambs, hypoxia induced a significant increase in P0.1 and in delta VE, delta VT, f, and VT/TI. The 2-day-old lambs showed a significantly lower response to hypoxia than did the older groups. Similarly, during the hyperoxia test and KCN infusion. Delta VE was smaller in the 2-day lambs than in the other lambs. We conclude that the postnatal maturation of the ventilatory response to O2 occurs in the first 10 days of life in newborn lambs and it is largely due to an increase in sensitivity of the O2 chemoreceptors.
Genioglossus muscle responses to upper airway pressure changes: afferent pathways
Authors: Mathew O. P. , Abu-Osba Y. K. , Thach B. T.
Published: December 2017

The afferent pathway of an upper airway reflex in which genioglossus muscle electromyographic (GG EMG) activity is influenced by pharyngeal pressure changes was investigated in 20 anesthetized rabbits. We took advantage of the fact that the upper airway was separated into two compartments by pharyngeal closure occurring when the animals breathe through a tracheostomy. This allowed pressure to be delivered selectively either to the nose and nasopharynx or to the larynx and hypopharynx. Midcervical vagotomy did not eliminate the GG EMG response to pressure stimuli. On the other hand high cervical vagotomy or superior laryngeal nerve section eliminated the response in the laryngeal compartment, but not in the nasopharyngeal compartment. Topical anesthesia of the mucosa of the nose, pharynx, and larynx abolished the response in both compartments. Therefore we conclude that more than one afferent pathway exists for this upper airway pressure reflex; the primary afferent pathway from the laryngeal compartment is the superior laryngeal branch of the vagus nerve, whereas the primary afferent pathway for the nasopharynx is nonvagal. Trigeminal nerve, glossopharyngeal nerve, and/or nervus intermedius carry nonvagal afferents from the nasopharynx and nose. The topical anesthetic and nerve section studies suggest that superficial receptors mediate this response. The occurrence of swallowing in response to upper airway pressure changes and its elimination by topical anesthesia or superior mechanoreceptors may mediate both genioglossus respiratory responses and swallowing responses.
A refrigerated treadmill apparatus for exercising dogs
Authors: Stavert D. M. , Reischl P. , Murdock L. C.
Published: December 2017

To prevent overheating and panting in exercising dogs, a refrigerated enclosure was constructed on a standard laboratory treadmill to regulate skin and body temperature of exercising beagles. The enclosure temperature is controlled by a computer software algorithm that analyzes the exercising dog's skin and rectal temperatures and stabilizes rectal temperature to within +/- 0.1 degree C of a preselected resting level. Refrigeration is activated depending on the skin and rectal temperature dynamics lowering enclosure temperature as skin temperature and rectal temperature increase. The system has been used extensively to inhibit panting in exercising beagles, maintaining a mean and standard deviation respiratory frequency of 32 +/- 5 breaths/min during exercise at 5 km/h, 0% grade. These respiratory rates can be compared with reported respiratory frequencies of 95 +/- 57 breaths/min for beagles exercising at the same work load but at room temperature (Mauderly and Pickrell, Research Animals in Medicine, DHEW Publ. 72–333, 1973). This reduction in respiratory frequency is also accompanied by a reduced and repeatable expired minute ventilation and O2 consumption of 9.40 +/- 1.0 1/min (BTPS) and 0.331 +/- 0.031 1/min (STPD), respectively, and can be compared with 24.84 +/- 6.44 1/min (BTPS) and 0.440 +/- 0.0831 1/min (STPD) reported for beagles exercising at room temperature.
High-frequency oscillation compared with standard ventilation in pulmonary injury model
Authors: Thompson W. K. , Marchak B. E. , Froese A. B. , Bryan A. C.
Published: December 2017

Hemorrhagic pulmonary edema was induced by intra-atrial infusion of 0.04--0.1 ml/kg of oleic acid into six anesthetized dogs. Gas exchange and cardiac outputs were then compared at identical mean airway pressures during randomized ventilation with either a volume-cycled ventilator with positive end-expiratory pressure (conventional positive-pressure ventilation, tidal volume 16--21 ml/kg, frequency 15--20 cycles/min) or a variable volume piston pump operating at 15 Hz (high-frequency oscillation). The fractional inspired oxygen concentration was maintained at 0.5 throughout. During 17 data sets matched for intratracheal mean airway pressures over a range of 7.5--27 cmH2O, measurements of systemic arterial pressure, arterial blood gas tensions, thermodilution cardiac outputs, and pulmonary arterial and capillary wedge pressures were identical (P less than 0.05) during ventilation with conventional positive-pressure ventilation and high-frequency oscillation. With both forms of ventilation, arterial oxygen tension progressively improved as mean airway pressure increased. In a shunt model of acute lung injury we were unable to show significant differences in oxygenation or cardiac output when high-frequency oscillation was compared with conventional positive-pressure ventilation with positive end-expiratory pressure at equivalent mean airway pressures.
Ventilatory responses to mechanical loads in cervical cord-injured humans
Authors: Axen K.
Published: December 2017

Load compensation in 29 cervical cord-injured men was inferred from the difference between actual first-breath responses to graded elastic and resistive loads and those calculated assuming identical respiratory muscle pressure (Pmus) wave forms in the unloaded and loaded states (i.e., the passive prediction). At every load, respiratory frequency (f) and tidal volume (VT) responses from different individuals formed a continuum ranging from a weak VT defense coupled with an increased f to a strong VT defense coupled with a decreased f. Individual VT responses ranged from values smaller than the passive prediction to values exceeding control, suggesting that phrenic motoneuron output was not constant but decreased in some subjects and increased in others. In support of this hypothesis, 1) individual VT responses varied with inspiratory duration (TI; P less than 0.01); 2) TI responses indicated some subjects prematurely terminated their phrenic motoneuron output, whereas others prolonged it; 3) VT/TI responses suggested that some subjects modified the discharge frequency of their phrenic output; and 4) rib cage instability contributed insignificantly to these responses. These findings, which are similar to those reported for normal men, indicate that 1) afferent pathways from the rib cage and intercostal muscles are not required for the initiation of a range of ventilatory responses to loads; and 2) afferent pathways from the mouth, lung, and/or diaphragm are sufficient, by themselves, to modulate the duration, intensity, and timing of the phrenic discharge during the first loaded breath.
Bronchial-arterial interdependence in isolated dog lung
Authors: Lai-Fook S. J. , Kallok M. J.
Published: December 2017

The bronchus and artery, embedded in the lung parenchyma, were modeled as adjoining cylindrical tubes in an elastic continuum. Solutions using finite-element analysis of nonuniform stress and strain occurring from an initial uniform state were computed for a reduction in arterial pressure. Maximal nonuniform principal and shear stresses in the parenchyma, equal to 2.5 times the mean periarterial stresses, occurred in the region adjacent to the bronchial-arterial joint. Bronchial cross section became oval and elongated along the line passing through the centers of the tubes, whereas arterial cross section elongated at right angles to this line. These predicted changes in shape of bronchus and artery were verified by radiographic measurements in isolated lobes, held at constant transpulmonary pressures of 4 and 25 cmH2O while arterial pressure was varied. Results suggest that peribronchovascular interstitial fluid pressure may be nonuniform and that the bronchial-arterial joint may be the preferential site for emphysematous perivascular lesions, which may occur on lung hyperinflation.
Adaptive changes in cats after long-term exposure to various temperatures
Authors: Hensel H. , Banet M.
Published: December 2017

Two groups of cats were exposed to 5 and 30 degrees C, respectively for 24 mo in climatic chambers under artificial illumination. Then the ambient temperatures were reversed for both groups for another 36 mo. The group adapted to cold for 36 mo showed an increase in fur growth (+35%), an increase in resting metabolism (+20%), and a shift in threshold of the cold-induced metabolic response to 8 degrees C lower ambient temperatures. Norepinephrine (0.4 mg . kg-1) elicited nonshivering thermogenesis (+37%) in the cold-adapted animals but was ineffective in the warm-adapted ones. Fur insulation at thermoneutrality was 55% higher in the cold-adapted cats. During acute exposure to -5 degrees C, tissue insulation decreased in both groups; fur insulation increased by 34% in the warm-adapted cats but remained nearly constant in the cold-adapted animals. At all ambient temperatures cold-adapted cats had higher (+0.4 degrees C) rectal temperatures. Body weight was not significantly different in both groups, although the cats living in the cold had a 45% higher metabolism. This was compensated by an increased food consumption.
Body fluid and hematologic adjustments during resting cold acclimation in rhesus monkey
Authors: Oddershede I. R. , Elizondo R. S.
Published: December 2017

The purpose of this study was to examine body fluid adjustments during prolonged cold exposure in primates. Six male rhesus monkeys were acclimated for 35 days and 6 degrees C and 80% rh. Red cell mass, extracellular fluid volume, and total body water (TBW) were determined with 51Cr, 35SO4, and 3H2O, respectively, prior to and at various intervals during the cold stress. TBW was increased throughout the exposure, whereas changes in extravascular compartments had occurred within the 1st wk of cold exposure, after which they returned to control values. An increased concentration of blood constituents on day 1 was not accompanied by a decrease in cardiovascular volume. Blood volume and plasma volume in relation to TBW were significantly increased on day 3 and remained increased during the remainder of the exposure. These cardiovascular volume changes were accompanied by a significant hemodilution on day 3 and a gradual return to control values. An increased plasma osmolality and expansion of the erythrocytes (decrease in mean corpuscular hemoglobin concentration) were observed throughout the cold stress. These data suggest that the rhesus monkey may be an adequate primate model for studies of body fluid adjustments, especially during prolonged cold exposure, in primates in general, including the human.
Hemodynamic responses to methoxamine in exercise-conditioned and aorta-constricted rats
Authors: Hasser E. M. , Dowell R. T. , Haithcoat J. L.
Published: December 2017

Hemodynamic responses to methoxamine hydrochloride (Vasoxyl) were determined in rats conditioned by a moderate treadmill exercise program and in rats subjected to 5 wk of abdominal aortic constriction. Rats of comparable age served as controls. Initial hemodynamic values for control rats were as follows: left ventricular pressure, 124 +/- 4 Torr and cardiac index, 145 +/- 8 ml . min-1 . kg-1. Although minor variations were noted, initial hemodynamic values for exercise-conditioned rats were within the normal range, and no left ventricular hypertrophy was present. Aorta-constricted rats exhibited a 50% increase in left ventricular weight and significant differences in left ventricular pressure (173 +/- 9 Torr) and cardiac index (117 +/- 10 ml . min-1 . kg-1). Sequentially increasing doses of methoxamine were infused to elevate myocardial preload and afterload. When compared with control rats, exercise-conditioned animals were better able to maintain cardiac index at comparable increases in either mean arterial or left ventricular end-diastolic pressures. In contrast, aorta-constricted rats demonstrated profound reductions in hemodynamic functions in response to methoxamine infusion. Directionally divergent hemodynamic results occur in exercise-conditioned and aorta-constricted animals when subjected to identical cardiovascular stresses.
Effect of aerobic conditioning on cardiovascular response to isometric exercise
Authors: Morgan B. J. , Brammell H. L. , Sable D. L. , Morton M. L. , Horwitz L. D.
Published: December 2017

The response to isometric handgrip exercise (IHE) and isometric quadriceps exercise (IQE) (30% maximum voluntary contraction held 3 min) was studied before and after 5 wk of aerobic training. Training exercises involved only the lower extremities. Seventeen healthy unconditioned males aged 21--35 yr were subjects. During training nine subjects received propranolol in doses that provided a high degree of beta-adrenergic blockade; eight received a placebo. All subjects were tested before training or drug and after training, 3--5 days off drug. With IGE after training, the placebo group had lower maximum heart rate (91 +/- 4 to 79 +/- 5 beats/min, P less than 0.05), systolic blood pressure (151 +/- 5 to 139 +/- 4 mmHg, P less than 0.05), and double product (heart rate x systolic blood pressure) (138 +/- 10 x 10(2) to 110 +/- 7 x 10(2), P less than 0.05). The response to IQE in the propranolol group was unchanged after training. Heart rate, systolic blood pressure, and double product with IHE was unchanged in either group after training. Aerobic conditioning can modify the hemodynamic response to isometric exercise. This effect is specific for the trained muscle group and is prevented by beta-adrenergic blockade.
Stimulation of carotid chemoreceptors and ventilation by doxapram in the cat
Authors: Nishino T. , Mokashi A. , Lahiri S.
Published: December 2017

Small doses of doxapram (less than 0.5 mg . kg-1 iv) were used to study its effect on carotid chemoreceptor activity and ventilation in cats anesthesized with alpha-chloralose. The effects were studied at several levels of partial pressures of O2 and CO2 in arterial blood (PaO2 and PaCO2). It was found that doxapram stimulated discharge rate of the carotid chemoreceptor afferents by the same magnitude at all levels of PaO2 and PaCO2 studied. However, the ventilatory effect of doxapram was more than additive to the concomitant stimulation by hypoxia or hypercapnia. This ventilatory effect was eliminated by sectioning the carotid sinus and aortic nerves. These results led to the conclusion that the ventilatory stimulus interaction due to doxapram is dependent on the excitatory input from the peripheral chemoreceptors.
Influence of Bohr-Haldane effect on steady-state gas exchange
Authors: Grant B. J.
Published: December 2017

The influence of the Bohr-Haldane effect (BH) on steady-state gas exchange has previously been described by its effect of gas transfer from the blood when arterial and venous blood gas tensions were held constant. This report quantifies by computer analysis the effects of BH when either or both arterial and venous blood gas tensions are subject to change. When mixed venous blood gas composition is held constant, elimination of BH from a single lung unit typically reduces CO2 output by 6.5% and O2 uptake by 0.5%. Similar effects occur in a two-compartment lung model whether alveolar ventilation-perfusion (VA/Q) mismatch occurs in a parallel or series ventilatory arrangement. When arterial blood gas composition is held constant, elimination of BH increases systemic venous CO2 partial pressure, but O2 partial pressure is hardly affected in the absence of metabolic acidosis. When both mixed venous and arterial blood gas tensions vary and gas exchange is stressed by VA/Q inequality, altitude, anemia, or exercise, elimination of BH predominantly affects mixed venous rather than arterial blood gas tensions. it is concluded that BH may act primarily to reduce tissue acidosis.
Elicitation of supramaximal thermogenesis by aminophylline in the rat
Authors: Wang L. C. , Anholt E. C.
Published: December 2017

Previous studies in rats indicate that maximal thermogenesis during severe cold exposure is suppressed by overnight fasting. Since fasting depresses sympathetic activity and the activity of adrenergic receptors, both of which affect substrate mobilization in cold, the present study attempted to restore maximal thermogenesis in fasted rats by exogenous sympathomimetics and a hypoxanthine (aminophylline). In overnight-fasted rats, exogenous sympathomimetics had no effect in further enhancing maximal thermogenesis induced by exposure to severe cold (in He-O2 at -10 degrees C), indicating maximization of endogenous sympathetic discharge and saturation of adrenergic receptor binding during severe cold exposure. In contrast, aminophylline (1.25–37.5 mg/kg ip) elicited “supramaximal thermogenesis” beyond control maximums in both fasted (+19.4%) and fed +14.4%) conditions in a dose-dependent manner, resulting in improved cold tolerance and prevention of hypothermia. Since aminophylline acts distally to adrenergic receptors to increase intracellular adenosine 3′,5′-cyclic monophosphate concentration, it is possible that such increases could enhance substrate mobilization to support supramaximal thermogenesis in severe cold.
Action of costal and crural parts of the diaphragm on the rib cage in dog
Authors: De Troyer A. , Sampson M. , Sigrist S. , Macklem P. T.
Published: December 2017

We studied the action of the costal and crural (vertebral) parts of the diaphragm on the lower rib cage in normal supine dogs. The two parts of the diaphragm were separately stimulated by electrodes directly implanted in the muscle or via the different phrenic nerve roots in the neck. The results of the experiments indicate the following. 1) The costal and crural parts of the diaphragm have a different segmental innervation and a different mechanical action on the rib cage. 2) The costal diaphragm expands the lower rib cage when it contracts. This rib-cage expansion is due mostly to the fulcrum of the abdominal contents and partly to the rise in abdominal pressure that takes place during diaphragmatic contraction. The pericardial attachments play no role in this action of the diaphragm. 3) The action of the crural diaphragm on the lower rib cage depends only on the balance between the inspiratory force exerted by the rise in abdominal pressure and the expiratory force exerted by the fall in pleural pressure. In the intact animal at functional residual capacity, these two opposite effects cancel each other. 4) The inflationary action of both parts on the rib cage decreases progressively as lung volume increases. The findings also suggest that the rise in abdominal pressure which occurs when the diaphragm contracts expands the lower rib cage by acting through the area of apposition of the diaphragm to the rib cage. These findings also strengthen the idea that the diaphragm actually consists of two muscles.