bluuebunny/crossref_metadata_2025 huggingface dataset:
Adenosine and the acid-base state of vascular smooth muscle
Authors: Fenton R. A. , Rubio R. , Berne R. M.
Published: December 2017

Hog carotid artery media was incubated under conditions of normocapnia (95% O2–5% CO2) and hypercapnia (nominally 75% O2–25%CO2). The intracellular pH (pHi) was determined from the distribution of 14C-labeled 5,5-dimethyloxazoladine-2,4-dione, alpha- and beta-receptor antagonists were used to block the effects of endogenous catecholamines. With 5% CO2, adenosine had no effect on the pHi. High K+ (25mM) and dipyridamole (DPM) induced a cellular metabolic acidosis that was reversed by adenosine and not affected by 0.5 mM ca2+ or ouabain. Hypercapnia decreased the resting pHi from 7.30 to 6.79. Adenosine significantly attenuated this decrease. With high K+ or DPM, a similar degree of hypercapnia only depressed the pHi to 6.91 and 6.90, respectively. The alkalinizing effect of high K+ and DPM was not altered by 0.5 mM Ca2+, was partically reversed by ouabain, and was completely reversed by adenosine. These results suggest that, under normocapnic conditions, although adenosine relaxes the contraction associated with K+-depolarization, it does not do so by elevating cellular proton levels. However, adenosine may decrease a tissue's ability to attenuate a local respiratory acidosis characteristic of increased O2 demand, resulting in relaxation under hypercapnic conditions. In any case, this demonstrates an interaction, with respect to the acid-base state of the vascular smooth muscle cells, among adenosine, K+, and H+, all suggested components of the metabolic theory of blood flow autoregulation.
Respiratory timing and depth of breathing in dogs anesthetized with halothane or enflurane
Authors: Marsh H. M. , Rehder K. , Hyatt R. E.
Published: December 2017

Tidal volume (VT) and inspiratory (TI) and expiratory (TE) times were measured during enflurane and halothane anesthesia in 12 prone dogs before and after bilateral vagotomy. "Elastic" loading or airway occlusion was used to obtain a VT-to-TI relationship in each state and to examine the rate of change in airway pressure. VT, TI, and TE were significantly (P less than 0.05) larger during enflurane than during halothane anesthesia, both before and after bilateral vagotomy. Before vagotomy, the rate of change in airway pressure during airway occlusion was similar for the two agents, as was an index of impedance of the respiratory system (Z'rs). Thus the difference in maximal pressure generated and in VT was most likely due to the difference in TI. Before vagotomy, TI increased as VT decreased with loading during enflurane but not halothane anesthesia, demonstrating a different effect of the two agents on the phasic vagal inspiratory inhibitory mechanism. After bilateral vagotomy, TI was unaltered during elastic loading with both agents but was still significantly longer during enflurane than halothane anesthesia. Thus it was concluded that TI was longer in the enfluraneanesthetized dogs than in the halothane-anesthetized dogs because of a different effect of these two agents on the bulbopontine "pacemaker" mechanism and not because of different effects on the phasic vagal inspiratory inhibitory mechanism.
Fluid dynamic factors in tracheal pressure measurement
Authors: Chang H. K. , Mortola J. P.
Published: December 2017

Because tracheal pressure measurement generally involves the use of a cannula or an endotracheal tube, fluid dynamic factors may cause a considerable artifact. We present a theoretical explanation of the observed apparent paradox in which the resistance of a tracheal cannula or an endotracheal tube is isolation was found to exceed the resistance of the airways plus the cannula or the tube in situ. By estimating the viscous dissipation and the kinetic energy change in a conduit with sudden variation of cross-sectional area, a predictive model is derived. The predictions are verified by a series of in vitro experiments with both steady and oscillatory flows. The experiments showed that the pressure recorded from the sidearm of a tracheal cannula or endotracheal tube contains an error which, in general, increased with the mean Reynolds' number of the through flow and also depends on the diameter ratio between the trachea and the tube or cannula, the position of the pressure tap, and the frequency of ventilation. When feasible, direct measurement with a needle in the trachea is suggested as a way to avoid the possible artifacts arising from the use fo a side tap of the cannula. Theoretical considerations, as well as in vitro and animal experiments, indicate that adding a properly chosen expansion to the tracheal cannula makes it possible to alter inspiratory and expiratory pressures selectively. This device may prove useful in control of breathing studies.
Modified chronic lung lymph fistula in goats via thoracic duct
Authors: Stothert J. C. , Winn R. , Nadir B. , Weaver L. J. , Carrico C. J. , Hildebrandt J.
Published: December 2017

Pure lung lymph has previously been obtained in awake sheep and goats via a cannula placed in an efferent duct of the caudal mediastinal lymph node (CMN). We describe a modification in goats wherein a segment of the thoracic duct collecting pulmonary efferents is isolated and cannulated. Lymph purity and responses to elevation of pulmonary microvascular pressure are illustrated and are found to be comparable to data obtained from a series of animals prepared by standard CMN cannulation. We have adopted the alternative procedure whenever, at cannulation may be complicated. When used in combination with the CMN approach, the overall rate of successful cannulation has increased from 50% to about 80%.
Comparison of aortic and carotid chemoreceptor responses to hypercapnia and hypoxia
Authors: Lahiri S. , Mokashi A. , Mulligan E. , Nishino T.
Published: December 2017

A quantitative comparison of the responses between aortic and carotid chemoreceptors to steady-state levels of arterial CO2 and O2 partial pressure was made in 35 cats anesthetized, paralyzed, and artificially ventilated. The measurements on the two receptors were made simultaneously in 6 cats and separately in 29 cats. The response of aortic chemoreceptors to a CO2 stimulus was a fraction of that of carotid chemoreceptors, and the response to hypoxia was relatively blunted. The differences between the two chemoreceptors are quantitative rather than qualitative. Since a low arterial CO2 partial pressure stimulus is known to attenuate the hypoxic response of carotid chemoreceptors, it is suggested that the low CO2 response of aortic body chemoreceptors is responsible for their blunted hypoxic response.
Absolute intraesophageal pressure at functional residual capacity in frequency
Authors: Helms P. , Beardsmore C. S. , Stocks J.
Published: December 2017

Absolute intraesophageal pressure at functional residual capacity (FRC) has been estimated in 15 infants (age 1-30 wk) by the extrapolation of the esophageal pressure-volume relationships to zero balloon volume by use of air-filled balloons in their ranges of infinite compliance. The pressure-volume relationships of the esophageal balloons (length 3.5-5.0 cm, perimeter 1.7-2.5 cm, wall thickness 0.045-0.075 mm) were determined in air and in erect and horizontal positions under water, the behavior of the balloons placed horizontally under water closely approximated that of the balloons in vivo. The mean absolute intraesophageal pressure at FRC was -1.44 cmH2O in eight normal infants and -1.56 cmH2O in seven convalescent infants with a variety of cardiorespiratory disorders. The less negative absolute end-expiratory esophageal pressure in infants when compared with that in adults can be explained by changes in lung elastic recoil, chest wall recoil, or a combination of these factors during the development and growth of the respiratory system from birth to adulthood.
Effect of sodium nitroprusside on hypoxic pulmonary vasoconstriction in the dog
Authors: Parsons G. H. , Leventhal J. P. , Hansen M. M. , Goldstein J. D.
Published: December 2017

The objective of the study was to determine the direct actions of sodium nitroprusside (SNP) on the pulmonary vasculature actively constricted by hypoxic ventilation in the closed-chest dog. In 21 supine anesthetized (pentobarbital sodium, 25 mg/kg) dogs the left lower lobe was catheterized with a 20 F wedged-flow catheter. With constant flow to this lung lobe, lobar pulmonary artery pressure (PAP), left ventricular end-diastolic pressure (LVEDP), and lobar pulmonary vascular resistance (PVR) were studied during room air and 10% O2 mechanical ventilation. With lobar flow and LVEDP constant, observed changes of lobar PAP and PVR represent direct effects on vascular tone unaffected by passive factors. Ventilation with 10% O2 resulted in a significant increase in lobar PAP [12.2 +/- 1.6 to 17.2 +/- 1.2 (SE) Torr] and PVR [42.2 +/- 13.3 to 61.2 +/- 15.0 (SE) Torr X 1(-1) X min]. Then during continued hypoxia in 12 animals, femoral vein infusion of SNP at doses of 1, 2, and 5 microgram X kg-1 X min-1 resulted in significant decreases in lobar PAP to 14.8 +/- 1.5, 14.8 +/- 1.5, and 13.4 +/- 1.6 Torr, respectively, and in PVR to 56.7 +/- 14.1, 54.0 +/- 13.9, and 47.8 %/- 13.2 Torr X 1(-1) X min, respectively. In six animals the sequence of drug infusion was then reversed with similar results. It is concluded that the actively constricted pulmonary vascular bed is directly dilated by SNP infusion.
Previous volume history of the lung and regional distribution of residual volume
Authors: Ruff F. , Martin R. R. , Milic-Emili J.
Published: December 2017

By use of 133Xe, the regional distribution of residual volume (RV) was measured in six seated healthy men, following a fast vital capacity (VC) expiration a) without and b) with a breath hold at residual volume of approximately 30 s and c) following a slow (greater than 30 s) VC expiration from total lung capacity (TLC) without a breath hold at RV. After the breath hold at RV, regional RV/TLC in the lower lung zones decreased significantly compared wih results obtained with fast expiratory VC and no breath hold at RV. At lung top the opposite was true. The distribution of regional RV/TLC was the same following the slow VC expiration with no breath hold at RV as with the fast expiration with the breath hold at RV. The different regional distribution of RV in b and c relative to a was probably due mainly to collateral ventilation, i.e., during the breath hold at RV and the slow expiration some of the gas that was trapped in the dependent lung zones behind closed airways escaped into the upper regions of the lung where the small airways had remained patent, leading to increased expansion of upper alveoli.
Correlation between lung structure and function in a canine model of emphysema
Authors: Klassen T. , Thurlbeck W. M. , Berend N.
Published: December 2017

To correlate lung structure and function in an animal model of emphysema, 17 dog lungs were treated with intrabronchial instillation of papain (range of concentration 0.5-5%); the contralateral lungs served as controls. The lungs were inflated to the volume at a transpulmonary pressure (PL) of 25 cmH2O (V25), and static pressure-volume and maximal expiratory flow-volume curves were obtained. Eight pairs of lungs were processed for histology at a PL of 5 cmH2O, and eight pairs of lungs were processed at a PL of 25 cmH2O. Significant loss of elastic recoil was found in the papain-treated lungs, between 30 and 90% predicted V25 (P less than 0.02). However, there was no correlation between the mean linear intercept corrected to predicted lung volume (indicative of alveolar destruction) and loss of elastic recoil. There was a significant reduction of maximal flow (Vmax) between 20 and 90% predicted V25. However, the reduction in Vmax was commensurate with the reduction of elastic recoil, since there was no significant change in resistance of the upstream segment between 30 and 70% predicted V25. Airway morphometry demonstrated no significant differences in small airway dimensions between control and emphysema-treated lungs. In both control and papain-treated lungs, small airway dimensions changed relatively more than lung volume a PL of 25 and 5 cmH2O.
Human lung pressure-volume relationships: alveolar collapse and airway closure
Authors: Salmon R. B. , Primiano F. P. , Saidel G. M. , Niewoehner D. E.
Published: December 2017

We investigated the effect of airway closure and alveolar collapse on the large-volume deflation and inflation transpulmonary pressure-volume (Ptp-V) curves of five postmortem excised human lungs. For stepwise static cycles, no inflection occurred on the deflation curve, while either one or two inflections occurred on the inflation curve. These relations were stimulated by a multicompartment model, which assumed a bimodal distribution of compartmental collapse-pressure differences. The simulations indicate that alveolar collapse can occur without causing an inflection on the deflation curve and that hysteresis in reopening of collapsed alveoli on inflation can account for a major portion of Ptp-V hysteresis. In contrast, for slow dynamic cycles, an inflection occurred on the experimental deflation Ptp-V curve, and when inflations were begun at sufficiently low volumes, volume did not change until a threshold pressure difference was reached about which PtP began to oscillate as lung volume increased. These differences in the stepwise static and dynamic Ptp-V curves can result from sustained airway closure on deflation and popping-opening on inflation.
Evidence of active regulation of cerebrospinal fluid acid-base balance
Authors: Bledsoe S. W. , Eng D. Y. , Hornbein T. F.
Published: December 2017

To test the passive transport hypothesis of cerebrospinal fluid (CSF) [H+] regulation, we altered the relationship between plasma [H+] and the electrical potential difference between CSF and blood (PD) by elevating plasma [K+] during 6-h systemic acid-base disturbances. In five groups of pentobarbital-anesthetized dogs, we increased plasma [K+] from 3.5 to an average of 7.8 meq/l. Hyperkalemia produced an increase in the PD of 6.3 mV by 6 h with normal plasma acid-base status (pHa 7.4), of 8.3 mV with isocapnic metabolic acidosis (pHa 7.2), of 5.3 mV with isocapnic metabolic alkalosis (pHa 7.6), of 9.2 mV with isobicarbonate respiratory acidosis (PaCO2 61 Torr) and of 5.7 mV with isobicarbonate respiratory alkalosis (PaCO2 25 Torr). The change in CSF [H+] at 6 h in each group was the same as that observed in normokalemic animals (Am. J. Physiol. 228: 1134-1154, 1975). This result is not consistent with the passive transport hypothesis. The CSF-blood PD is therefore not an important determinant of CSF [H+] CSF [H+] homeostasis must result from some form of active transport control.
Detection of ozone toxicity during continuous exercise via the effective dose concept
Authors: Adams W. C. , Savin W. M. , Christo A. E.
Published: December 2017

In evaluating O3 toxicity in humans, the effective dose, expressed as the simple product of concentration, exposure duration and ventilation volume (VE), has been applied only to resting or intermittent exercise (IE) exposures. In the present study, we examined the validity of effective dose in predicting pulmonary function impairment when effective dose was determined both as a simple product and as a weighted function via multiple regression. Eight trained male subjects (ages 22-46) completed 18 protocols, including exposures (via mouthpiece) to filtered air and three levels of O3 concentration (0.20, 0.30, and 0.40 ppm), while exercising continuously for durations ranging from 30 to 80 min. The O3 effective dose was significantly related to pulmonary function impairment and exercise ventilatory pattern alteration. Multiple regression analysis, however, substantiated the predominant importance of O3 concentration, with the threshold for O3 toxicity during exercise at a moderately heavy work load [approximately 65% maximum O2 uptake (VO2 max)] shown to be between 0.20 and 0.30 ppm. Although considerable individual variability in O3 toxicity response was noted, group mean responses in our continuous exercise mouthpiece exposures were similar to those previously observed with IE chamber exposures. Thus while the effective dose concept has notable deficiencies in predicting the individual degree of O3 toxicity, it remains a useful approach and warrants further investigation.
Effects of temperature on acid-base balance and ventilation in desert iguanas
Authors: Bickler P. E.
Published: December 2017

The effects of constant and changing temperatures on blood acid-base status and pulmonary ventilation were studied in the eurythermal lizard Dipsosaurus dorsalis. Constant temperatures between 18 and 42 degrees C maintained for 24 h or more produced arterial pH changes of -0.0145 U X degrees C-1. Arterial CO2 tension (PCO2) increased from 9.9 to 32 Torr plasma [HCO-3] and total CO2 contents remained constant at near 19 and 22 mM, respectively. Under constant temperature conditions, ventilation-gas exchange ratios (VE/MCO2 and VE/MO2) were inversely related to temperature and can adequately explain the changes in arterial PCO2 and pH. During warming and cooling between 25 and 42 degrees C arterial pH, PCO2 [HCO-3], and respiratory exchange ratios (MCO2/MO2) were similar to steady-state values. Warming and cooling each took about 2 h. During the temperature changes, rapid changes in lung ventilation following steady-state patterns were seen. Blood relative alkalinity changed slightly with steady-state or changing body temperatures, whereas calculated charge on protein histidine imidazole was closely conserved. Cooling to 17-18 degrees C resulted in a transient respiratory acidosis correlated with a decline in the ratio VE/MCO2. After 12-24 h at 17-18 degrees C, pH, PCO2, and VE returned to steady-state values. The importance of thermal history of patterns of acid-base regulation in reptiles is discussed.
Vagal stimulation and aerosol histamine increase hysteresis of lung recoil
Authors: Loring S. H. , Drazen J. M. , Smith J. C. , Hoppin F. G.
Published: December 2017

Bronchoconstriction changes pulmonary resistance and dynamic compliance by altering both airway properties and dynamic lung tissue recoil. To assess the contribution of recoil, we measured transpulmonary pressure in anesthetized open-chest dogs during sinusoidal ventilation with gas flow and during sinusoidal compression of intrapulmonary gas without flow. Measurements with gas flow characterized total pulmonary behavior, including the contribution of gas flow in airways, whereas measurements during gas compression characterized lung tissue recoil alone. Histamine aerosol produced a 54% decrease in dynamic compliance, a 465% increase in total pulmonary resistance, and a 153% increase in pressure-volume hysteresis of dynamic recoil. Vagal stimulation produced a 31% decrease in dynamic compliance, a 135% increase in total pulmonary resistance, an 82% increase in the hysteresis of recoil, and a 15% increase in mean recoil pressure. At slow oscillation frequencies (0.2 Hz) and high transpulmonary pressures (10 cmH2O), hysteresis of lung recoil contributes substantially to total pulmonary resistance, and changes in dynamic lung recoil can account for much (35%) of the increase in pulmonary resistance seen with bronchoconstriction.
Reflex tracheal contraction induced by stimulation of bronchial C-fibers in dogs
Authors: Roberts A. M. , Kaufman M. P. , Baker D. G. , Brown J. K. , Coleridge H. M. , Coleridge J. C.
Published: December 2017

Bradykinin stimulates the afferent vagal endings of bronchial C-fibers but has little effect on other pulmonary vagal afferents. In anesthetized dogs with open chest, we recorded transverse tension in the posterior wall (trachealis muscle) of an upper cervical tracheal segment and stimulated bronchial C-fibers selectively by injecting bradykinin (19 ng-3 microgram) into a bronchial artery. The recurrent and pararecurrent laryngeal nerves were cut so that the superior laryngeal nerves provided the motor supply to the segment. Bradykinin caused a dose-dependent increase in tracheal muscle tension and often a conspicuous decrease in heart rate, which were abolished by vagotomy or administration of atropine. Injection of bradykinin still evoked tracheal contraction when myelinated lung afferents were blocked by cooling the midcervical vagi to 7 degrees C, but contraction was abolished when unmyelinated lung afferents were blocked by cooling to 0-1 degrees C, the effects of cooling being reversible. Our results indicate that stimulation of bronchial C-fibers, like that of pulmonary C-fibers, evokes reflux contraction of airway smooth muscle and reflex cardiac slowing.
Comparison of heart rate measurement protocols used during autonomic function tests
Authors: Baun W. B. , Jackson A. , Patton R. W. , Raven P. B.
Published: December 2017

The five most used cold pressor test heart rate protocols were compared to the true R-R interval responses recorded during a cold hand test. Forty-one nonsmoking male volunteers between 18 and 55 yr were given a cold hand pressor test. Heart rate was evaluated by averaging the R-R interval within 2-, 5-, 6-, 10-, and 30-s time intervals and by the true R-R interval measurement. No significant physiological differences existed at rest; however, during stress the maximum values obtained were successively diminished the greater the time utilized to average the heart rate pressure (P less than 0.05). During recovery an underestimation of the true response was observed that increased as the averaging time increased (P less than 0.05). Comparison between the R-R interval measure and the 6-s average data indicated a 18% decrease in the time of peak response. Therefore, the responses recorded with the 6-s averaged data were less sensitive and obscured the rapidity of autonomic changes. Hence, when sensitivity and absolute response are a primary concern in determining autonomic function, measurements should include R-R interval measures of heart rate or the average of the number of R-R intervals in 2-s time blocks.
Patterns of glycogen loss in muscle fibers: response to arterial occlusion during exercise
Authors: Armstrong R. B. , Peterson D. F.
Published: December 2017

This experiment was designed to determine if glycogen loss in active rat skeletal muscle fibers could be accentuated by periodic occlusion of blood to the muscles without significantly altering the numbers of types of fibers that lose glycogen. We attempted to augment glycogen loss by periodically occluding blood flow to the muscles while the animals ran on a treadmill. An occluder cuff was placed on the right common iliac artery of 10 rats. While the rats ran for 5 min at 26 m . min-1, blood flow to the right hindlimb was completely occluded for 16 +/- 5 (SD) s during every 30 s of the run. Glycogen loss in soleus (S), plantaris (P), and gastrocnemius (G) muscles was determined biochemically and histochemically. Muscles from both the occluded limb (S, P, and the deep red portion of G) and the nonoccluded limb (S and red G) of the runners showed significant glycogen loss compared with the controls. Furthermore, glycogen concentration was significantly lower in S, P, and red G of the occluded limb than in the same muscles of the nonoccluded limb. Significantly greater numbers of fibers within fiber type populations of P and G showed glycogen loss in the occluded limb, indicating that more motor units were recruited during the exercise bout in these muscles. The data suggest a sensitive link between motor unit recruitment and the metabolic condition of the contracting fibers, as the increased number of fibers showing glycogen loss presumably, resulted from fatigue of active units. We conclude that occlusion of blood flow to active muscles is not a feasible means of accentuating glycogen loss in active fibers while maintaining normal patterns of recruitment.
Thermodilution technique for measurement of cardiac output during artificial ventilation
Authors: Jansen J. R. , Schreuder J. J. , Bogaard J. M. , van Rooyen W. , Versprille A.
Published: December 2017

The feasibility of using the thermodilution method to monitor cardiac output during artificial ventilation was studied in anesthetized pigs. Normal saline (0.5 ml) at room temperature was injected into the left ventricle or the right atrium. The dilution curves were detected in the aortic arch and the pulmonary artery, respectively. The ventilation rate was 10 cycles/min at end-expiratory pressures of 0, 5, 10, and 15 cmH2O. For each level, 50 measurements of cardiac output were performed at regular intervals over the ventilatory cycle. The order of measurements were randomly selected. The average of each series of 50 measurements showed excellent correlation with the estimates of cardiac output based on the direct Fick method for oxygen. The maximum difference between the values of cardiac output randomly measured by the thermodilution method was 40% for the left side of the heart and 70% for the right side. However, when the values of cardiac output were sorted according to the specific phases of the respiratory cycle, there was a systematic variation with a small random error. For the left side of the heart, a satisfactory moment of injection for estimation of mean cardiac output appeared to be at the end of the spontaneous expiration. On the other hand, the analysis of cardiac output values at the right side did not reveal any satisfactory moment for injectate administration under changing circumstances, e.g., positive end-expiratory pressure.
Norepinephrine turnover in lung: effect of cold exposure and chronic hypoxia
Authors: Johnson T. S. , Young J. B. , Landsberg L.
Published: December 2017

The lung contains sympathetic efferent nerves, but their participation in conditions associated with sympathetic nervous system activation is unknown. To assess sympathetic activity in lung during cold exposure and hypoxia, the measurement of radiolabeled norepinephrine (NE) turnover was carried out in this organ. In preliminary studies this technique, which measures in vivo the activity of sympathetic nerves in an individually innervated organ, was validated for use as a measure of sympathetic activity in rat lung. NE turnover was then measured in unanesthetized rats during cold (4 degrees C, 24 h) and hypobaric hypoxic (PB = 380 Torr, 7 days) exposure. Cold exposure increased calculated NE turnover rate in lung by 63% from 4.2 +/- 1.4 to 6.8 +/- 1.6 ng NE.organ-1.h-1 (95% confidence limits). Chronic hypobaric hypoxia increased NE turnover rate in lung by 114% from 4.0 +/- 1.8 to 8.6 +/- 2.4 NE.organ-1.h-1. Thus NE turnover techniques are applicable to rat lung and demonstrate increased sympathetic activity during cold exposure and chronic hypoxia.
A physiological comparison of young and older endurance athletes
Authors: Heath G. W. , Hagberg J. M. , Ehsani A. A. , Holloszy J. O.
Published: December 2017

Sixteen highly trained masters endurance athletes, 59 +/- 6 yr, were compared with 16 young athletes, with whom they were matched on the basis of their training regimens, and with 18 untrained middle-aged men. On echocardiographic evaluation, both groups of athletes had a significantly greater left ventricular volume and mass than the untrained men; their were no significant differences in percent fiber shortening or velocity of fiber shortening among the three groups. Maximum O2 uptake (VO2max) averaged 15% less in the masters than in the young athletes (58.7 vs. 69 ml.kg-1.min-1). When expressed in terms of lean body mass to correct for differences in body fat content, VO2max of the masters athletes was about 60% higher than that of the middle-aged untrained men. Maximum heart rate was 14% lower in the masters athletes than in the young athletes (169 vs. 197 beats/min). The O2 pulse during maximum exercise (i.e., VO2max/heart rate at VO2max) was identical in the masters and young athletes. This finding suggests that the major factor responsible for the lower VO2max of the masters athletes, compared with the young athletes, is their slower heart rate.
Mouth and nose resistance in newborn kittens and puppies
Authors: Mortola J. P. , Fisher J. T.
Published: December 2017

Newborn mammals, including infants, have difficulties in mouth breathing when the nasal passages are occluded. In this study we examined the possibility that differences in the passive mechanical properties of the upper airways could fully explain this behavior. Steady inspiratory flows through the upper airways in anesthetized supine newborn kittens and puppies resulted in upper airway obstruction, even at flows less than those occurring during resting breathing, suggesting that in the unanesthetized condition muscle tone plays an important role in maintaining upper airway patency. Mouth (Rm) and nose (Rn) resistances have been measured during steady expiratory flows with nostrils closed and mouth passively open or nostrils open and mouth closed. In all the newborns, Rn was substantially smaller than Rm. In contrast, the Rn/Rm in adult dogs is greater than unity. In adult cats Rn/Rm is above or below unity depending upon the flow rate, but the ratio is always larger than in newborn kittens. The difference between newborns and adults is entirely due to the small Rn of the newborn, as Rm is not greater in the newborn than in the adult. We conclude that the obligatory nose breathing behavior of newborns is not fully explained by the passive mechanical properties of the upper airways.
Effect of transrespiratory pressure on PETCO2-PaCO2 and ventilatory reflexes in humans
Authors: Banzett R. , Strohl K. , Geffroy B. , Mead J.
Published: December 2017

Inspiratory muscle activity increases when lung volume is increased by continuous positive-pressure breathing in conscious human subjects (Green et al., Respir. Physiol. 35: 283–300, 1978). Because end-tidal CO2 pressure (PETCO2) does not change, these increases have not been attributed to chemoreflexes. However, continuous positive-pressure breathing at 20 cmH2O influences the end-tidal to arterial CO2 pressure differences (Folkow and Pappenheimer, J. Appl. Physiol. 8: 102–110, 1955). We have compared PETCO2 with arterial CO2 pressure (PaCO2). We have compared PETCO2 with arterial CO2 pressure (PaCO2) in healthy human subjects exposed to continuous positive airway pressure (10 cmH2O) or continuous negative pressure around the torso (-15 cmH2O) sufficient to increase mean lung volume by about 650 ml. The difference between PETCO2 and PaCO2 was not decreased, and we conclude that PETCO2 is a valid measure of chemical drive to ventilation in such circumstances. We observed substantial increases in respiratory muscle electromyograms during pressure breathing as seen previously and conclude this response must originate by proprioception. On average, the compensation of tidal volume thus afforded was complete, but the wide variability of individual responses suggests that there was a large cerebral cortical component in the responses seen here.
Effect of ventilatory frequency on regional transpulmonary pressure in normal adults
Authors: Hida W. , Suzuki S. , Sasaki H. , Fujii Y. , Sasaki T. , Takishima T.
Published: December 2017

The relation between the ventilatory frequency and the elastic (delta Pel) or resistive (delta Prs) components of changes of the regional pleural pressure (delta PL) was studied at functional residual capacity (FRC) in six normal adults. The regional delta PL was measured simultaneously at three levels in the esophagus using a three-balloon-catheter system. Elastic components of regional delta PL normalized by overall tidal volume (delta Pel/delta V) increased with frequency at all three balloon positions; the percentages of delta Pel/delta V at 60 breaths/min to those at zero frequency were 107, 119, and 157% in the upper, middle, and lower balloon, respectively. The resistive component of regional delta PL normalized by overall air flow (delta Prs/delta V) did not show significant dependence on frequency at any of the three positions and was almost the same everywhere. It is suggested that the increase of local delta Pel with frequency might reflect mainly the frequency dependence of local dynamic compliance (Cdyn) and that the change of the local Cdyn with frequency might be larger in dependent than in upper lung.
Osmoregulation and interstitial fluid pressure changes in humans during water immersion
Authors: Khosla S. S. , DuBois A. B.
Published: December 2017

The aim of the present study was to determine the magnitude and direction of the shift of body fluids during water immersion of humans to the neck. Five healthy male subjects were studied lying in air for 1.5 h, sitting in 34 degrees C water to the neck for 1 h, and again lying in air for 1.5 h in two sets of experiments. For the first set, vasopressin (0.75 IU, sc) was injected before immersion. Blood and urine samples were drawn every 30 min in air and every 20 min in water. Urinary sodium, potassium, and osmolal clearances were significantly increased during immersion. When the mean maximum change during immersion was calculated for five subjects hematocrit fell by 1.1 U, plasma concentrations of sodium by 3.9 meq/l, chloride by 3.5 meq/l, potassium by 0.2 meq/l, osmolality by 7.9 mosmol/kg H2O, and proteins by 0.25 g/100 ml, whereas total plasma CO2 content increased by 1.33 mmol/l, threonine by 11.6%, proline by 9.0%, methionine by 14.0%, and alanine by 29%. Plasma volume increased 6.1%, and red blood cell volume calculated from hematocrit and hemoglobin increased 3.5%. In the second set of immersion experiments, without vasopressin injection, interstitial fluid pressures were measured with a cotton wick in PE-50 tubing inserted subcutaneously. A mean interstitial fluid pressure of -0.5 cmH2O was observed when the subjects were lying in air. Interstitial fluid pressure had started to decrease by 20 min of immersion, with a maximum decrease during immersion averaging 2.10 cmH2O. We conclude that hyposmotic fluid is mobilized into the blood from interstitial and other extravascular spaces during immersion.
Catheterization of the pulmonary artery in the closed-chest rat
Authors: Stinger R. B. , Iacopino V. J. , Alter I. , Fitzpatrick T. M. , Rose J. C. , Kot P. A.
Published: December 2017

A simple technique has been devised to catheterize the pulmonary artery in rats for measurement of pulmonary artery pressure. A no. 3 1/2 French umbilical vessel catheter (Argyle), angled to 90 degrees over the distal 1 cm, was introduced into the right external jugular vein of the anesthetized (50 mg/kg pentobarbital sodium, ip) rat (male Wistar, 250–350 g). With the angle directed anteriorly, the catheter was inserted 2.5 cm proximally, which placed the catheter in the right atrium. The catheter was rotated 90 degrees counterclockwise and inserted 1.0 cm further, which placed the catheter in the right ventricle. Advancement of the catheter an additional 1.5 cm allowed placement in the pulmonary artery. Placement at each stage was confirmed by the respective pressure contours. This technique is easily and rapidly performed and has many potential applications in measuring parameters of the pulmonary circulation in a variety of small laboratory animals.
Surfactant release in excised rat lung is stimulated by air inflation
Authors: Hildebran J. N. , Goerke J. , Clements J. A.
Published: December 2017

Because increased ventilation has been associated with an acceleration of lung surfactant turnover, we investigated the effect of fluid and air inflations on the release of surfactant into the air spaces. We found that excised rat lungs, initially lavaged three times at 23 degrees C, release approximately 40–90 micrograms of phospholipid/g wet lung wt into the air spaces in response to a further infusion of fluid into the airway equal to total lung capacity. A single air inflation to the same volume, followed by degassing and lavage, contributes approximately 230 micrograms to the yield of phospholipid. We estimated basal release of phospholipid as 112 micrograms wet lung wt-1 . h-1, which is far less than the 2,050 micrograms -1 . h-1 retrieved during a series of air and fluid inflations. The above findings are consistent with the hypothesis that air inflation to total lung capacity is a major physiological stimulus to release of lung surfactant into the alveolar space. The lung lavage process itself also causes the release of surfactant.
A model for the relation between respiratory neural and mechanical outputs. III. Validation
Authors: Younes M. , Riddle W. , Polacheck J.
Published: December 2017

In the preceding two communications we described a model for the relation between respiratory neural and mechanical outputs. In the present report we test the accuracy of the model in predicting volume and flow from occlusion pressure wave forms, and vice versa. We performed single-breath airway occlusions in 21 unconscious subjects and determined the time course of occlusion pressure. We also measured the passive properties of the respiratory system. The time course of volume and flow was predicted from the occlusion pressure wave forms, and the results were compared with the spontaneous breaths immediately preceding occlusion. Inspiratory duration, shape and amplitude of occlusion-pressure wave forms, and the passive properties of the respiratory system varied widely among subjects. There was good agreement between predicted and observed values in all cases. Except for some prolongation of inspiration (Hering-Breuer reflex), diaphragmatic activity did not change during occlusion. Since occlusion pressure is proportional to inspiratory activity, we conclude that the model described provides a good approximation of the relation between inspiratory activity and spirometric output.
Coordination of mucociliary transport in human trachea and intrapulmonary airways
Authors: Yeates D. B. , Pitt B. R. , Spektor D. M. , Karron G. A. , Albert R. E.
Published: December 2017

A wide range of both mucus velocities in the trachea and rates of bronchial mucociliary clearance have been measured in humans. To investigate the coordination of mucociliary transport in the intrapulmonary and extrapulmonary airways, simultaneous measurements of tracheal mucus velocity and lung clearance were made in 22 healthy nonsmoking adults. Each subject inhaled several breaths of an iron oxide aerosol tagged with 99mTc. Measurements of retained activity in the right lung were made for 2.25 h with a pair of 5 x 2 in. NaI (T1) detectors. Tracheal mucociliary transport rates (TMTR) were measured with a probe containing six vertically aligned rectangular NaI (T1) detectors. The mean TMTR was 5.1 +/- 2.9 mm/min. The mean time for the first bolus to be detected on the multidetector probe (large airway transit time, LATT) was 52 +/- 24 min. At this time the percent cleared (Bi) was 24 +/- 15% and the rate of clearance (Bi) was 0.64 +/- 0.35%/min. The mean percent cleared within a 2-h interval (B120) was 51 +/- 22%. The TMTR was closely correlated with Bi and Bi with B120. The TMTR was also correlated to B120, but not closely correlated with LATT. It is suggesting that coordination of mucus transport throughout the airways of the lung represents the nonchallenged state and is responsible for the maintenance of normal bronchial toilet.
Steady pressure-flow relationship of a model of the canine bronchial tree
Authors: Reynolds D. B. , Lee J. S.
Published: December 2017

Static pressure differences (deltaP) across the entire length and portions of a latex reproduction of a canine bronchial tree were measured during steady inspiratory or expiratory flow (V). The reproduction consists of a 10-cm length of trachea through bronchi of about 2 mm in diameter. The airflow was simulated by a water flow with tracheal Renolds number (Re0) in the range from 1,500 to 10,000. Loss in total pressure (deltaPt) was computed by summing deltaPt and V were well described (r greater than 0.98) by a dimensionless Rohrer equation deltaPt/deltaPd0 = A + B Re0 applicable to gas flow, in which deltaPd0 is a Poiseuille pressure drop. For expiratory deltaPt, A was about twice that for inspiration, while the values for B were nearly equal. Differences in kinetic energy between sites of static pressure measurement are important in determining loss in total pressure. Rohrer's equation is a good approximation to the phenomenological laws of steady inspiratory and expiratory flow-pressure relations in the canine bronchial tree for the range of Reynolds number investigated.
Efficient computer subroutines for interconversion of oxygen tension and saturation
Authors: Nordby G. L. , Ellis J. H.
Published: December 2017

Two digital computer subroutines are described. NORSAT computes human hemoglobin saturation from oxygen tension data; NORINV performs the inverse computation. Each subroutine is based on an algorithm that is a direct mathematical inverse of the other. The effects of nonstandard conditions of temperature, pH, and CO2 tension on the saturation curve can be computed. The relative efficiency of these subroutines is compared to that of published subroutines having similar function. The new subroutines use computer time more efficiently with no loss of accuracy. The subroutines are provided in FORTRAN in a form suitable for direct inclusion in a number of user-specified programs.
Helium and sulfur hexafluoride washout in asymmetric lung models
Authors: de Vries W. R. , Luijendijk S. C. , Zwart A.
Published: December 2017

Model calculations were carried out on extensible lung models that are characterized by asymmetries in branching pattern or cross section within the acinus. The calculations contribute to a better understanding of the intrapulmonary mixing of gases poorly soluble in blood. For single-breath washout stimulations of helium (He) and sulfur hexafluoride (SF6), only small differences were found between the results obtained from a lung model with an asymmetric branching pattern using either a local homogeneous or inhomogeneous delta V/V distribution. This indicates that the geometry of this model is the most important factor for generating realistic values for the slope of the alveolar plateau, the Bohr dead space and the end-tidal concentration ratio for SF6 and He. The calculated relation between the decrease in the slope of the alveolar plateau and postinspiratory breath-holding times showed good agreement with experimental findings in healthy adult subjects. Multiple-breath washout simulations enabled us to explain the experimentally observed high dilution of poorly soluble tracer gases in the end-tidal gas for the first few breaths during the washout procedure. Simulations of simultaneous multiple-breath washout experiments of He and SF6 showed that a shift in the crossover point of the normalized end-tidal washout curves is related in particular to cross-section asymmetry of the lung model. These asymmetric lung models are the only ones described up to now that explain many of the features of single- and multiple-breath washout experiments for gases poorly soluble in blood.
Role of perfusion and diffusion in 14CO2 exchange in the rabbit lung
Authors: Effros R. M. , Mason G. , Silverman P.
Published: December 2017

The rate of transfer of H14CO-3 and 14CO2 from the alveoli to the capillaries was studied in rabbit lungs perfused without erythrocytes. Aliquots of 0.5 ml of buffered solutions containing these 14C indicators and 3H2) were injected into the distal airways, and the recoveries of 14C and 3H were compared in the left atrial outflow. It was assumed that 3H2O had equilibrated between the alveoli and fluid leaving the pulmonary capillaries, and a decline in the initial 14C recovery relative to that of 3H was attributed to incomplete equilibration of 14C between these compartments. No disequilibrium of 14C could be detected at pH 7.4 when excess carbonic anhydrase was present. When the pH was increased to 8.4, 14C equilibration was only 69% complete at 36 ml/min and 41% complete at 160 ml/min. Confirmatory evidence was obtained that carbonic anhydrase is associated with the endothelial side of the alveolar-capillary barrier but is absent on the epithelial surface. The data suggest that the barrier is at least 600 times more permeable to 14CO2 than to H14CO-3, and diffusion of 14CO2 would not limit exchange at normal pH unless pulmonary flow reached extremely high values.
Proposed mechanism for increased thyroxine deiodination in cold-acclimated rats
Authors: Scammell J. G. , Barney C. C. , Fregly M. J.
Published: December 2017

Groups of male rats were administered isoproterenol (ISO), thyroxine (T4), or both (ISO + T4) daily for 20 days in an attempt to mimic the effect of cold acclimation on the rate of outer-ring deiodination of T4 to triiodothyronine (T3) by 2,000-g supernatants of homogenates of liver and kidney. The rates of hepatic and renal deiodination of T4 to T3 in an additional group of rats exposed to 4 +/- 1 degree C for 20 days were 53 and 71% higher, respectively, than control. Administration of ISO (100 micrograms . kg-1 . day-1) did not affect the rate of deiodination of T4 to T3 by either hepatic or renal tissue. Administration of T4 (50 micrograms . kg-1 . day-1) resulted in rates of hepatic and renal deiodination of T4 that were 297 and 222% higher, respectively, than control. Administration of ISO + T4 resulted in a rate of conversion of T4 to T3 not significantly different from that observed when T4 was administered alone. Serum concentration of T4 was elevated after administration of both T4 and ISO + T4, whereas serum concentration of T3 was elevated significantly above that of control only in the cold-acclimated group. These results suggest that the increased rate of 5′-monodeiodination of T4 by hepatic and renal homogenates from cold-acclimated rats is not a result of increased beta-adrenergic activity but can be accounted for by the increase in thyroid activity observed in these animals.
Breuer-Hering inflation reflex and breathing pattern in anesthetized humans and cats
Authors: Gautier H. , Bonora M. , Gaudy J. H.
Published: December 2017

In nine cats and nine human subjects anesthetized with alfaxalone, respiratory activity and tracheal pressure were recorded prior to and during occlusion of the airway at end inspiration or end expiration. Lung inflations at the end of expiration were also performed. In addition, the ventilatory pattern was analyzed during hypercapnia. The results show that occlusions at the end of inspiration or inflations provoked an apnea in both cats and humans. However, concomitant with increases in tidal volume during hypercapnia, inspiratory duration decreased in cats and did not change in human subjects. These results indicate that the Breuer-Hering reflex, which delays the onset of inspiration during inflation was equally operative in cats and humans. In contrast, the “Breuer-Hering threshold curve,” which accounts for the off-switch“ of inspiration was different in cats and humans. Thus, in summary, the Breuer-Hering inflation reflex is operative in human subjects, but it does not seem to be involved in the control of the inspiratory off-switch mechanism during increases respiratory activity resulting from hypercapnia.