bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in collateral ventilation with increased vascular pressure and edema formation
Authors: Emery D. L. , Shown B. , Batra G. , Gee M. H.
Published: December 2017

To test the hypothesis that development of hemodynamic edema results in decreased collateral ventilation, we rapidly volume-expanded anesthetized dogs with volumes equivalent to 10 (n = 5) and 15% (n = 5) of body weight. We measured collateral resistance (Rcoll), pulmonary arterial pressure, and left ventricular end-diastolic pressure before, during, and for 1–2 h after the infusion. Lungs were subsequently processed for microscopic examination and measurement of extravascular lung water content. During the infusion, Rcoll increased modestly independent of the fluid-infusion rate or the rate of increase in vascular pressures. After the infusion, Rcoll continued to increase to maximum levels 2–33 times base line even though pressures decreased dramatically. At the end of the experiment, Rcoll returned to base line in one dog and was 3–15 times base line in the other dogs. These changes bore no relationship to the severity of edema formation. Until alveolar flooding occurs, accumulation of lung interstitial fluid and changes in collateral ventilation appear to be coincident events rather than causally related variables.
Effect of different levels of positive end-expiratory pressure on lung water content
Authors: Russell J. A. , Hoeffel J. , Murray J. F.
Published: December 2017

To compare the effects of 2-, 5-, and 10-cmH2O positive end-expiratory pressure (PEEP) on pulmonary extravascular water volume (PEWV), pulmonary blood volume (PBV), pulmonary dry weight (PDW), and distensibility, we separately ventilated perfused dogs' lungs in situ and produced pulmonary edema with oleic acid (0.06 ml/kg). Three groups were studied: I, PEEP, 5 cmH2O in both lung; II, PEEP, 2 cmH2O in one lung and 10 cmH2O in the other; and III, PEEP, same as II, but the chest was rotated to compensate for differences in heights. The PEWV and distensibility were less (P less than 0.05) in lungs exposed to 10-cmH2O than to either 2- or 5-cmH2O PEEP. After chest rotation, the difference between 10- and 2-cmH2O PEEP on PEWV was eliminated but that on distensibility was not. We conclude that 10-cmH2O PEEP 1) decreased water content because of lung volume-induced effects on intravascular hydrostatic pressure and 2) improved distensibility by recruitment of alveoli, irrespective of PEWV.
Ventilatory and heart rate responses to hypoxia and hypercapnia during sleep in adults
Authors: Hedemark L. L. , Kronenberg R. S.
Published: December 2017

Ventilatory and heart rate responses to hypoxia and hypercapnia were measured in eight normal subjects (5 women, 3 men, ages 2213;27 yr) during wakefulness (W), slow-wave sleep (SWS), and rapid-eye-movement sleep (REM). Ventilatory responses to progressive isocapnic hypoxia were measured as k, the slope of the line relating the logarithm of incremental ventilation to alveolar O2 partial pressure (PAO2) and as the incremental ventilation at PAO2 = 40 Torr delta V 40. Values for k (mean +/- SE) were 40.5 +/- 2.4 Torr during W, 42.1 +/- 2.5 during SWS, and 29.9 +/- 2.3 (5 subj) during REM (P less than 0.02 vs. W). Comparable values for delta V 40 were 5.4 +/- 0.3, 6.3 +/- 1.0, and 5.4 +/- 0.31/min. Hypoxia increased heart rate 19 +/- 1.3% during W, 18 +/- 1.8% during SWS, and 15 +/- 2.2% during REM. Ventilatory responses to rebreathing CO2 (6 subj) were 1.7 +/- 0.3 1 X min-1 X Torr-1 during W and 1.3 +/- 0.2 during SWS. Hypercapnia consistently produced arousal from sleep in all eight subjects at levels between 6 and 15 Torr (11.2 +/- 1.1) above resting alveolar CO2 partial pressure. No consistent arousal was noted during hypoxia. Arousal occurred in 87% of the CO2-rebreathing tests compared with only 28% of the progressive isocapnic hypoxia tests (P less than 0.001). We conclude that ventilatory and heart rate responses to hypoxia and ventilatory responses to hypercapnia are not significantly altered by SWS. Arousal from sleep during hypercapnia is reproducible and predictable, but there is no consistent arousal during hypoxia.
Metabolic and cardiovascular adaptations in trained hypophysectomized rats
Authors: Edwards J. G. , Lund D. D. , Bedford T. G. , Tipton C. M. , Matthes R. D. , Schmid P. G.
Published: December 2017

Metabolic and cardiovascular changes resulting from acute and chronic exercise were examined in male Sprague-Dawley rats assigned to sham-control or hypophysectomized groups. Two weeks after surgery, the hypophysectomized rats had decreased their maximum oxygen consumption (VO2 max) and heart rate values by 4 ml X min-1 X kg-1 and 142 beats X min-1, respectively. Twenty weeks later, hypophysectomy was associated with a 22 ml X min-1 X kg-1 decrease in VO2 max and a 215 beat X min-1 decline in their maximal heart rates when compared with sham-control means. Endurance training was responsible for the significantly higher O2 consumption values. Additionally, trained animals exhibited longer run times, higher muscle cytochrome oxidase activity, and reduced food consumption. Measurements of right atrial choline acetyltransferase (CAT) activity and [3H]quinuclidinyl benzilate (QNB) binding revealed significantly higher CAT values and fewer muscarinic receptors. However, training had no significant effect on resting blood pressure, blood pressure changes with conditions of lower body negative pressure, muscle glycogen concentrations, CAT levels and QNB binding of the left atrium and ventricular regions, or receptor density. These results indicated that many of the adaptations that are characteristic of normal populations can occur in the absence of the hormones from the pituitary gland.
Relationship between muscle QO2 and fatigue during repeated isokinetic contractions
Authors: Ivy J. L. , Sherman W. M. , Miller J. M. , Maxwell B. D. , Costill D. L.
Published: December 2017

The percent slow-twitch fibers (%ST) of the vastus lateralis muscle and selected indicators of maximum aerobic power (QO2, VO2 max, and leg extensor VO2 max) were compared with the rate of fatigue development during 45 s of repeated maximum isokinetic leg extension-flexion contractions (180 degrees/s) on 13 males. Subjects with muscle respiratory capacities (QO2) above the mean (2,472 microliter O2 X h-1 X g-1) displayed a significantly slower rate of fatigue development than those subjects with QO2 values below the mean. In addition, indicators of maximum aerobic power were correlated with the percent of maximum power and power/ml fat-free thigh volume at 5, 15, 30, and 45 s during the fatigue test. The correlations increased progressively during the fatigue test and became significant at 45 s. This trend was not observed when the %ST fibers were compared with the percent of maximum power and power/ml fat-free thigh volume at these time intervals. These data suggest that 1) the muscle tissue's capacity for aerobic metabolism influences the rate of fatigue development even during a strenuous short-term isokinetic exercise task, and 2) factors other than fiber type may interact to confound the prediction of fiber type by noninvasive means.
Pulmonary microcirculation: tubules rather than sheet and post
Authors: Guntheroth W. G. , Luchtel D. L. , Kawabori I.
Published: December 2017

We examined latex casts of the pulmonary microcirculation with the scanning electron microscope (SEM). Mature rats were anesthetized and ventilated; the pulmonary vasculature was washed out with lactated Ringer solution and then filled with a mixture of Geon latexes. The airways were filled with glutaraldehyde with resulting transmural vascular pressures of 10 cmH2O. After critical-point drying and corrosive removal of the lung tissue, SEM studies of the vascular replicas revealed two distinct patterns of pulmonary microcirculation: 1) sparse, long, tubular capillaries that comprise the thin subpleural layer and appear as “filler” in the peribronchial spaces; and 2) alveolar microcirculation that is composed of tightly matted, intersecting tubules, shorter but of the same diameter as type 1, in spherical array in two layers. The alveolar capillaries at low magnification appear superficially as sheets; however, the detailed morphology is not consistent with the sheet-and-post model. We conclude that the basic component of the pulmonary microcirculation is tubular and not different from other capillary beds except in density.
Electron microscopy of rapidly frozen lungs: evaluation on the basis of standard criteria
Authors: Weibel E. R. , Limacher W. , Bachofen H.
Published: December 2017

In recent years there has been a debate about the validity of the various methods for fixing lung tissue for electron microscopy in a state that faithfully reflects the physiological conditions prevailing at the time of fixation. Mazzone et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45: 32513;333, 1978) introduced a method of rapid freezing followed by freeze-substitution fixation and found good preservation of fine structure; they claimed this method to be superior to others because it allowed careful control of physiological conditions. We have tested the suitability of this method for morphometric studies, where random sampling requires homogeneity of tissue preservation. The results are discussed on the basis of some standard criteria for the faithfulness of structural preservation. In terms of external standards, it was confirmed that one can find parts of the lung tissue samples to show a picture that is compatible with the established equivalent image of eucaryotic cells and tissues; however, the structure of blood was poorly preserved. In terms of the internal standards the method was found to yield inconsistent results; the specimens showed a wide spectrum of images of alveolar septa and capillaries, with “good preservation” limited to a very narrow area; furthermore, the method has a low level of reproducibility. We conclude that for the lung the method of freeze-substitution fixation is not suitable for morphometric work.
A critical value for O2 transport in the rat
Authors: Adams R. P. , Dieleman L. A. , Cain S. M.
Published: December 2017

Rat skeletal muscle O2 uptake (VO2) has been reported to be supply dependent even at normal blood flow rates. To find the point at which whole-animal VO2 became dependent on total O2 transport (TOT), intact anesthetized rats were ventilated under hypoxic, normoxic, and hyperoxic conditions while either normovolemic or hypovolemic. In this manner, TOT (cardiac output X arterial O2 content) was varied over a range of 513;80 ml . kg-1 . min-1 . VO2 was measured in a closed-circuit, double servospirometer system. O2 contents were measured in carotid artery and right heart blood. Arterial PCO2, pH, and rectal temperature were kept within normal limits. Above a TOT of 23 ml . kg-1 . min-1, reciprocal changes in O2 extraction and cardiac output maintained VO2 independently of TOT (VO2 = 17.9 +/- 1.3 ml . kg-1 . min-1). Below a TOT of 23 ml . kg-1 . min-1, Vo2 became linearly dependent upon TOT. For TOT between 5 and 16 ml . kg-1 . min-1, VO2 = 0.89 + 0.78 TOT (r = 0.98). These data indicate that above a critical TOT of approximately 23 ml . kg-1 . min-1, VO2 in anesthetized rats does not depend on TOT.
Hyperoxia inhibits stimulated superoxide release by rat alveolar macrophages
Authors: Forman H. J. , Williams J. J. , Nelson J. , Daniele R. P. , Fisher A. B.
Published: December 2017

Factors responsible for the loss of respiratory burst capacity (stimulated extracellular O2-. release) of alveolar macrophages (AM) exposed to prolonged hyperoxia were assessed. Specific pathogen-free rats were exposed to 1 ATA O2 for 24–72 h, and lungs of survivors lavaged. Release of O2-. by cells after addition of concanavalin A, which stimulated AM but not polymorphonuclear leukocytes (PMN), or digitonin, which stimulated both cell types, was measured using cytochrome c reduction +/- superoxide dismutase. O2-. release by AM declined 47.2% (P less than 0.05) after 24 h of hyperoxia and 100% after 60 h. Percent PMN in the lavage was less than 3% at 0–36 h but increased to 16% at 48 h and to 44% at 72 h. Although addition of PMN to AM in vitro caused inhibition of AM O2-. release, the percent PMN required for inhibition was not reached in vivo until after a significant decline in AM O2-.-releasing capacity had already occurred. Cell-free lavage fluid from either control or hyperoxic rats did not affect AM O2-. release. AM in culture for 24 h in hyperoxia lost 76.7% (P less than 0.005) of O2-.-releasing capacity vs. cells incubated in 20% O2, although dye exclusion was unaffected. The results indicate that the major cause of loss of AM O2-. release by hyperoxia is a direct effect of O2 on the cells.
Pulmonary vascular reactivity is blunted in pregnant rats
Authors: Fuchs K. I. , Moore L. G. , Rounds S.
Published: December 2017

Pulmonary arterial pressure is decreased in pregnant women despite increased cardiac output, suggesting that pulmonary vascular resistance is decreased in pregnancy. To determine if pulmonary vascular reactivity is decreased in pregnant rats, lungs isolated from pregnant rats were perfused with blood from other pregnant rats at constant flow rate, and pressor responses to airway hypoxia and to angiotensin II were measured. Compared with responses obtained in lungs from nonpregnant female rats, hypoxic and angiotensin II pressor responses were blunted in pregnancy. To separate possible effects of pregnancy on the lung from those of substance(s) circulating in the blood in pregnancy, we perfused lungs from nonpregnant rats with blood from pregnant rats. Both the hypoxic and angiotensin II pressor responses were blunted by blood from pregnant rats. The angiotensin II pressor response was blunted also in lungs from pregnant rats perfused with blood from nonpregnant rats. These results suggest that a circulating substance is responsible for blunting of pulmonary vascular reactivity in pregnancy and that changes in the lung induced by pregnancy also depress angiotensin II responses. It is unlikely that estrogen and progesterone were responsible for these effects, since lungs and blood obtained from animals treated with these hormones did not have blunted pulmonary vascular reactivity.
Alveolar liquid pressure measured by micropipettes in isolated dog lung
Authors: Lai-Fook S. J. , Beck K. C.
Published: December 2017

Micropipettes (2–5 microns), in conjunction with a servo-nulling system, were used to measure liquid pressure (Pliq) in subpleural alveoli of lobes of dog lungs made edematous by perfusing with plasma to a constant extravascular weight gain (W). Pliq was measured at fixed transpulmonary pressure (Ptp) in lungs whose W was more than 0.5 that of the initial weight (Wi). In six lobes at W/Wi = 0.6, Pliq, relative to alveolar pressure (Palv), was -2.6 +/- 0.4 cmH2O (mean +/- SE), -11.8 +/- 0.6, and -17.5 +/- 1.7 at deflation Ptp values of 5, 15, and 25 cmH2O, respectively. The Pliq increased to -2, -7, and -13.7, respectively, at W/Wi = 2.8. Based on a mean alveolar radius of 50 micron at Ptp at 25 cmH2O and values of Palv - Pliq, values for alveolar surface tension (tau) at W/Wi = 0.6 were 6, 30, and 44 dyn/cm at Ptp of 5, 15, and 25 cmH2O, respectively. In five other lobes at W/Wi = 0.5 and at 65 and 84% total lung capacity, tau was much higher on lung inflation than on deflation. If pericapillary interstitial fluid pressure (Pi) and Pliq were identical under edematous conditions, tau would be the main determinant of Pi.
Effects of arachidonic acid, PGF2 alpha, and a PGH2 analogue on airway diameters in dogs
Authors: Quan S. F. , Moon M. A. , Lemen R. J.
Published: December 2017

The effects of intravenous arachidonic acid, a prostaglandin H2 analogue [(15S)-hydroxyl-11 alpha, 9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (PGH2-A)], and prostaglandin F2 alpha (PGF2 alpha) on lung mechanics and airway diameters were compared using tantalum bronchography in 20 paralyzed, artificially ventilated, pentobarbital-anesthetized dogs. These agents produced dose-related increases in lung resistance (RL) and decreases in dynamic compliance (Cdyn). Both RL and Cdyn changed maximally within 25 s after injection. RL, however, returned to base line within 2 min, whereas the decrease in Cdyn persisted much longer. Changes in the diameter of airways less than 2 mm produced small changes in RL and Cdyn. Larger changes in RL corresponded with changes in airways as large as 4 mm. Vagal reflexes or pulmonary edema were not important contributors to these effects. These data suggest that the changes in RL and Cdyn produced by intravascular injections of arachidonic acid, PGH2-A, and PGF2 alpha result from their direct effects on smooth muscle in airways as large as 4 mm.
Heart rate response to cough
Authors: Wei J. Y. , Harris W. S.
Published: December 2017

It was hypothesized that the chronotropic response to intrathoracic pressure changes generated by cough may provide a reliable and rapid index of the cardioacceleratory capacity, a complex reflex response important for survival. In 27 adults in the supine position we measured the heart rate response following three forceful coughs performed over a 3-s period. At approximately four beats after the last cough, the mean instantaneous heart rate rose from 72 +/- 3 (SE) (range 5413;91) to 94 +/- 5 beats/min (range 71–115), resulting in a maximal rate change of 31 +/- 3% (P less than 0.001). The time course and magnitude of response were reproducible within and similar among the subjects. Thus the heart rate response to large intrathoracic pressure transients generated by cough provides a quantitative and noninvasive estimate of integrity of the capacity for cardiac acceleration.
Measurement of regional bronchial arterial blood flow and bronchovascular resistance in dogs
Authors: Baile E. M. , Nelems J. M. , Schulzer M. , Pare P. D.
Published: December 2017

Little is known about normal variations and control of bronchial blood flow and bronchovascular resistance. We have used the reference-flow technique and 15-microns-diameter microspheres to measure bronchial blood flow under physiological conditions. Dogs (n = 13) were anesthetized and ventilated, and their chests were opened. A ligature was placed loosely around the left main pulmonary artery, and the left atrium was cannulated. In six dogs three sets of microspheres were injected simultaneously into the left atrium, and in another seven dogs the three sets of microspheres were injected sequentially at 0.5-h intervals. Prior to each injection measurements of pulmonary arterial, left atrial, and aortic pressures, cardiac output, and blood gases were made. Five seconds after injection the left main pulmonary artery was transiently occluded to prevent recirculation. After the final injection, dogs were killed, the lungs were removed, and the parenchyma was stripped off the large and small airways of the left lung. Knowing the radioactivity in the trachea, bronchi, parenchyma, and in the reference flow blood and also the aortic and left atrial pressures, we calculated bronchial blood flow (ml X min-1 X g dry lung-1) and bronchovascular resistance (cmH2O X ml-1 X min X 100 g dry lung). Results showed that there were no significant differences between the three measurements of bronchial blood flow when microspheres were injected simultaneously or sequentially. Bronchial blood flow to the left lung was 0.4% of cardiac output; 55% of the total flow went to lung parenchyma and 45% to trachea and bronchi. Expressed as flow/g dry lung the greatest flow was to the airways.
Surfaces and volumes of alveolar tissue under zone II and zone III conditions
Authors: Bachofen H. , Wangensteen D. , Weibel E. R.
Published: December 2017

The functional anatomy of alveolar septa has been studied in rabbit lungs fixed by vascular perfusion under middle zone II and zone III conditions at a constant lung inflation level of 60% of total lung capacity. Capillary volume increases down the vertical axis of the lungs in both conditions and is larger by about 30% in zone III than in zone II lungs. The concomitant changes of free alveolar, epithelial, and capillary surface areas are small. Capillary volume increases within the observed range of pressures neither by recruitment of collapsed capillaries nor by unfolding of pleats of alveolar septa and capillary walls, but rather by deformation and distension of tissue: scanning electron micrographs reveal a more conspicuous bulging of capillaries in zone III than in zone II lungs. Accordingly, the mechanical structure of alveolar septa appears to be largely consistent with a sheet-flow model.
Effect of ventilatory drive on the perceived magnitude of added loads to breathing
Authors: Burdon J. G. , Killian K. J. , Campbell E. J.
Published: December 2017

Using open-magnitude scaling we studied the importance of ventilatory drive on the perceived magnitude of respiratory loads by applying a range of externally added resistances (2.1–77.1 cmH2O X l-1 X s) to normal subjects at rest and at three increasing levels of ventilatory drive induced by exercise, CO2-stimulated breathing, and hypoxia. Under all conditions studied the perceived magnitude of the added loads increased with the magnitude of the resistive load and as the underlying level of ventilatory drive increased. When the results were expressed in terms of peak inspiratory pressure, the perceived magnitude was related to the magnitude of the peak inspiratory pressure by a power function (mean r = 0.97). These results suggest that the perceived magnitude of added resistive loads increased with increasing ventilatory drive, in such a manner that the increase in sensory magnitude is proportional to the increase in the inspiratory muscle force developed and suggests that something dependent on this force mediates the sensation.
Cutaneous vascular response to exercise and acute hypoxia
Authors: Rowell L. B. , Freund P. R. , Brengelmann G. L.
Published: December 2017

Six normal young men were studied during 50 min of moderate exercise (100–137 W) that included one 15-min (protocol 1) or two 10-min periods of breathing 11–12% O2 (in N2) (protocol 2). Absolute work intensity was kept constant for each subject, but relative severity increased during hypoxia owing to reduction in maximum O2 uptake. Our question was whether hypoxia causes cutaneous vasoconstriction; this in turn should cause a rise in esophageal temperature (Tes) and a shift in the forearm skin blood flow (SkBF)-Tes relationship. In all subjects forearm blood flow (FBF) (venous occlusion plethysmography) rose throughout exercise and Tes tended to stabilize. Neither 10- nor 15-min periods of hypoxia caused systematic changes in FBF or Tes or their relationship to each other. We conclude that hypoxia equivalent to that incurred at 4,500–5,000 m does not significantly alter the short-term regulation of SkBF and body temperature during moderate exercise. Net cutaneous vasoconstriction is not elicited by arterial chemoreflexes under these conditions.
Supraglottic airway resistance in normal subjects and patients with occlusive sleep apnea
Authors: Anch A. M. , Remmers J. E. , Bunce H.
Published: December 2017

We assessed the flow-impeding properties of nose and pharynx combined in four normals and five patients with occlusive sleep apnea (OSA) while awake by measuring supraglottic pressure and airflow at the nose. We calculated two indices of impedance presented by the supraglottic airway: the second coefficient (K2) of Rohrer's equation and supraglottic resistance (Rsg) at 0.4 l/s. The influence of posture and nasal mucosal circulation was evaluated by measuring these indices in sitting and supine position before and after administration of a nasal decongestant. The effects of changes in posture were similar in both normals and patients: K2 and Rsg values were significantly larger in supine than in sitting position. The nasal decongestant significantly decreased both values in sitting and supine positions for normals and patients but did not eliminate the posturally induced changes. Patients had significantly greater K2 and Rsg values than normals in all conditions. These results indicate supraglottic airway narrowing in OSA patients. This narrowing probably results from structural encroachment on the pharyngeal airway.
Effect of pressure and timing of contraction on human diaphragm fatigue
Authors: Bellemare F. , Grassino A.
Published: December 2017

The relationship between the mean transdiaphragmatic pressure swing developed with each inspiration (Pdi) and the fraction of the breathing cycle time spent in inspiration (TI/Ttot) (Pdi X TI/Ttot) was related to the maximal time that such a run could be sustained (Tlim). Four normal subjects breathed with a constant breathing pattern for 45 min or until Pdi could no longer be sustained, whichever came first. The breathing patterns included Pdi of 0.15–0.90 of Pdimax and TI/Ttot of 0.15–1.0. Pdi was obtained by adjusting an inspiratory resistance, and the timing by monitoring tidal volume with time base from an oscilloscope. The Tlim of a run was found to be inversely related to both Pdi and TI/Ttot and hence inversely related to their product, following a quadratic hyperbole function. Pdi X TI/Ttot represents an index of the tension time of the diaphragm (TTdi). The breathing pattern that could be sustained more than 45 min was found to have a TTdi of about 0.15, which was termed critical TTdi. Above that value Tlim decreased as a function of TTdi. The results are consistent with Tlim being related to diaphragmatic blood flow limitation.
Evaluation of human diaphragm fatigue
Authors: Bellemare F. , Grassino A.
Published: December 2017

The time course of the frequency content of the electromyogram (EMG) was studied in the diaphragm of five normal subjects breathing through high inspiratory resistance. The ratio between the power content of a high-frequency band (150– Hz) (H) and a low-frequency band (20http://hwmaint.jap.physiology.org/cgi/content/abstract/53/4/99240 Hz) (L) was calculated for each breath and expressed as a fraction of the initial breath. The rate of decay (when existent) was exponential and was quantified by measuring the time constant of decay of H/L (TF). Runs were held sustaining the ratio of inspiratory time to total breath cycle duration (TI/Ttot) from 0.2 to 1 and transdiaphragmatic pressure (Pdi) of 0.1http://hwmaint.jap.physiology.org/cgi/content/abstract/53/4/992 0.8 of Pdimax. It was found that TF was monotonically related to Pdi X TI/Ttot, following a hyperbolic relationship. TF was compared with velocity of conduction of the myopotentials and with center frequency of the EMG power spectrum and found to follow similar trends showing, however, different absolute rate of change. The values of TF were found to be directly related to the time a given pattern could be sustained (Tlim). It is concluded that EMG changes and Tlim are related and are expressions of the metabolic changes induced by the contraction pattern.
Models for a comparative functional analysis of gas exchange organs in vertebrates
Authors: Piiper J. , Scheid P.
Published: December 2017

The analysis of external gas exchange in the various respiratory organs of vertebrates is based on models with gas transport properties determined by ventilatory, diffusive, and perfusive conductances and by the geometric arrangement of medium and blood flows. The following factors are examined: water vs. air as external medium; gas transport properties of blood; diffusive gas transfer between medium and blood; problems in assessing diffusion limitation in fish gills, amphibian skin, avian lungs, and mammalian lungs. Finally the limitations to the analysis imposed by various physiological and anatomical complexities are discussed.
Nervous control of heart rate: activity in the cardiac vagus of the dogfish
Authors: Taylor E. W. , Butler P. J.
Published: December 2017

In the absence of any sympathetic innervation to the heart, nervous control of heart rate in the dogfish is solely attributable to inhibitory parasympathetic input from the vagus nerve. Action potentials can be recorded from the cardiac vagus of the dogfish following its exposure in the anterior cardinal sinus. The rates of heartbeat and ventilation, blood pressure, hematocrit, and responses to external stimuli such as hypoxia, which include a bradycardia, remained typical of fish with their nervous and circulatory systems virtually intact. The recordings included sporadically active units that accelerated during hypoxia, possibly inducing the bradycardia, and regular bursts of action potentials synchronous with ventilatory movements that appeared to arise reflexly from stimulation of pharyngeal proprioceptors. These bursts may loosely couple the respiratory and cardiac pumps, increasing the probability of concurrence between periods of maximum water and blood flow. The preparation enables detailed study of the temporal relationships between the pumps and its neurophysiological basis.
Effects of hypoxia on blood gas and acid-base parameters of sea bass
Authors: Thomas S. , Hughes G. M.
Published: December 2017

Continuous recordings have been made of pH, PO2, and PCO2 of arterial blood (pHa, PaO2, PaCO2) in an extracorporeal circulation during periods of hypoxia (inspired PO2 45–10 Torr) in sea bass, Morone labrax. During moderate hypoxia hyperventilation was accompanied by an increase in pHa. Continuation of moderate hypoxia for periods up to 24 h produces an increase in lactate and a consequent decrease in pHa. During deep hypoxia there is a very brief alkalosis as ventilation increases but a marked decrease in pHa as lactate levels rise. Recovery from hypoxia is associated with an increase in lactate concentration reaching values of more than 6 meq X l-1 following deep hypoxia, and pHa falls to 7.73. PaO2 recovers rapidly, but recovery of PaCO2 is not so rapid and together with the residual hyperventilation indicates that the fish is paying off an O2 debt.
Rapid ventilatory responses to changes in insufflated CO2 in awake roosters
Authors: Clanton T. L. , Ballam G. O. , Moore R. K. , Kunz A. L.
Published: December 2017

The ventilatory responses to pulses or steps in the fraction of CO2 in the insufflated gas stream (FICO2) in awake, unidirectionally ventilated White Leghorn roosters (Gallus domesticus) were studied. Within 0.2–.5 s of the change in FICO2 at the syrinx, a change in inspiratory or expiratory flow occurred. Increases in FICO2 increased flow and tidal volume (VT), whereas decreases in FICO2 decreased flow and VT. Expiratory duration (TE) was markedly prolonged by decreases in FICO2 and shortened by increases. Inspiratory duration was affected little by FICO2 changes. The TE response to pulses of FICO2 (0.2–0.4 s duration) revealed a time dependency such that a maximum effect occurred when the pulses arrived at the syrinx at approximately midexpiration. The magnitudes of the responses were approximately proportional to the amplitude and duration of the FICO2 changes, but decreases in FICO2 had greater effects than increases. A likely receptor site for these responses is the intrapulmonary chemoreceptors, which appear to function in a reflex controlling airflow and timing of the ongoing breath.
Control of heart rate by carotid body chemoreceptors during diving in tufted ducks
Authors: Butler P. J. , Woakes A. J.
Published: December 2017

Previous work has shown that during forcible submersion of domestic ducks there is a gradual reduction in heart rate to 10–20% of its predive value after 45–60 s. Bilateral denervation of the carotid body chemoreceptors abolishes most of this bradycardia. By use of implanted radio transmitters it has been shown that in free-swimming tufted ducks, Aythya fuligula, there is an immediate reduction in heart rate, on spontaneous diving, from an elevated predive level. It then increases for a few seconds before it stabilizes at a level similar to that recorded when the duck is swimming fairly vigorously. The present study has shown that, following bilateral denervation of the carotid bodies, there is a significant increase in mean dive duration but no effect on the immediate reduction in heart rate on submersion. Heart rate is, however, significantly higher toward the end of spontaneous dives after carotid body denervation. Unlike the situation in mallards and their domesticated varieties, carotid body denervation has no effect on heart rate in tufted ducks during the first 40 s of forced dives. The carotid bodies therefore do not play the dominant role in cardiac control during submersion of diving ducks that has been suggested by work involving the forcible submersion of the mallard duck and its domesticated varieties.
Intracellular pH in lizard Dipsosaurus dorsalis in relation to changing body temperatures
Authors: Bickler P. E.
Published: December 2017

Mean whole-body and tissue-specific intracellular pH values (pHi) were measured in Dipsosaurus dorsalis by the dimethyloxazolidinedione technique. pHi was measured in lizards at constant body temperatures (Tb) (18, 25, 35, and 42 degrees C) and in lizards undergoing changes in Tb between 18 and 42 degrees C. Constant Tb between 18 and 42 degrees C maintained for 24 h or more produced a delta pH/delta Tb of -0.015 for the mean whole-body, -0.012 for venous blood, -0.0104 for cardiac muscle, and -0.0098 for skeletal muscle. Within the preferred range of Tb values (35–42 degrees C), the delta pH/delta Tb patterns were closer to that expected to achieve constant dissociation of protein imidazole (approximately -0.017): mean whole-body -0.020, cardiac muscle -0.016, and skeletal muscle -0.018. Tissue water contents were independent of Tb. Whole-body pHi during gradual warming and cooling (approximately 2 h elapsed time for each direction) closely corresponded to steady-state values. Upon cooling to 18 degrees C, tissue-specific and whole-body pHi often fell 0.1–0.2 unit below that expected; in each case this was correlated with an extracellular acidosis. A gradual recovery of pHi occurred with the recovery of the extracellular acidosis. Over the normally experienced Tb range, adjustments in pHi apparently rapidly achieve steady-state values and are in accord with the imidazole alphastat hypothesis. These patterns are discussed in terms of the thermal ecology of Dipsosaurus.
Sensation of inspired volume in normal subjects and quadriplegic patients
Authors: DiMarco A. F. , Wolfson D. A. , Gottfried S. B. , Altose M. D.
Published: December 2017

To investigate the influence of respiratory muscle tension and feedback from rib cage receptors, the sensation of inspired volume was compared in normal subjects and quadriplegic patients during active breathing, with and without the addition of an inspiratory resistive load, and during passive ventilation produced by a tank respirator. In separate trials, volume sensation was assessed using tests of magnitude estimation and volume reproduction. The mean exponents and standard errors for the magnitude estimation of inspired volume in normal subjects were 1.32 +/- 0.08, 1.24 +/- 0.06, and 1.23 +/- 0.09 during passive, active, and loaded breathing, respectively. These values were not significantly different from one another, nor were there any differences between normal subjects and quadriplegics. During volume reproduction trials where the mechanical conditions were different between control and test breaths, the inspired volumes during active unloaded breathing were significantly smaller than during passive ventilation but greater than the inspired volumes during loaded breathing. Errors in volume reproduction were no different in normal subjects and quadriplegics, suggesting that inputs from rib cage receptors are not essential for the sensation of inspired volume. The sensation of inspired volume in both normal subjects and quadriplegics was found to be unaffected by inhalation of a 2% lidocaine solution. This suggests that upper airway receptors are also not essential for volume sensation. The intensity of the sensation of a given inspired volume may depend on the level of the central nervous system motor command and/or on the tension developed by the diaphragm.
Surface tension-surface area curves calculated from pressure-volume loops
Authors: Wilson T. A.
Published: December 2017

An energy analysis and data from the literature on the relation among surface area, recoil pressure, and lung volume are used to calculate the surface tension-surface area curves corresponding to pressure-volume loops. The energy analysis has been described earlier (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 50: 921–926, 1981). It is based on the assumption that the tissue structure of the lung constitutes a conservative mechanical system and hence that pressure-volume hysteresis is primarily a result of surface tension-surface area hysteresis. Unlike previous methods of calculating surface tension from recoil pressure, this method does not rely on the assumption that the tissue component of recoil in the air-filled lung is the same as recoil pressure of the saline-filled lung at the same lung volume. The calculated values of surface tension decrease to less than 2 dyn/cm as surface area decreases along the deflation limb of the pressure-volume curve. Surface tension increases very steeply with surface area on the inflation limbs, reaching a limiting value of just under 30 dyn/cm. The shape of the surface tension-surface area curves, unlike the shape of the curves calculated by previous methods, is similar to the shape obtained on surface tension balances for fluid extracted from lungs.
Plasma electrolyte content and concentration during treadmill exercise in humans
Authors: Wilkerson J. E. , Horvath S. M. , Gutin B. , Molnar S. , Diaz F. J.
Published: December 2017

Five healthy males volunteered to exercise for 20 min on a motor-driven treadmill at five submaximal intensities (30, 45, 60, 75, and 90% of VO2 max). Peripheral venous blood samples were drawn from an indwelling catheter prior to and at 9, 14, and 19 min of each exercise bout. Blood samples were assayed for whole-blood hemoglobin, total plasma protein concentrations, and hematocrit, with plasma water concentration calculated from these values. The plasma concentration of the electrolytes sodium (Na+), potassium (K+), total calcium (Catot), ionized calcium (Ca2+), chloride (Cl-), and inorganic phosphorus (Pi) were also determined. With plasma and blood volumes the total plasma contents of each of the measured constituents and the concentration of each electrolyte per liter of water were calculated. Statistically significant linear increases in plasma concentrations of Na+, K+, and Cl- relative to exercise intensity were observed, with linear decreases in plasma contents of Na+ and Cl- and linear increases in K+ content. Plasma Pi concentration decreased with a Pi increased content, with plasma Catot concentration elevated at the highest two work loads. Plasma Catot content increased linearly with exercise intensity and duration. Plasma water concentration and content decreased with exercise intensity, resulting in no change in electrolyte concentration per liter of water except at the highest two exercise intensities. These data suggest that extrapolation from plasma electrolyte concentration to muscle concentration and/or content is not supported. Changes in plasma volume and plasma water must be considered when postulating a role for electrolytes in the physiological responses of the human to exercise.
Sweat composition in exercise and in heat
Authors: Verde T. , Shephard R. J. , Corey P. , Moore R.
Published: December 2017

Sweat samples were collected from the forearms of eight male volunteers using light gauze pads applied for 20-min periods. Preliminary trials indicated that this technique yielded realistic figures for both sweat volume and sweat composition. Tests were conducted under three conditions: a) outdoor exercise, cool environment; b) indoor exercise, normal room temperatures; and c) sauna exposure. In all environments, proximal forearm samples indicated a larger sweat secretion than distal forearm or hand samples. [Mg2+] decreased as sweat flow increased, but after allowance for interindividual differences of sweat volume, [Na+], [K+], [Ca2+], and [Cl-] were independent of sweat flow rates. The differential effect of sweat flow suggests active regulation rather than contamination. Interindividual differences of sweat composition could not be explained in terms of differences in personal fitness. Sauna bathing yielded sweat with a higher [Mg2+] and [Ca2+] content than did exercise; however, [Na+], [K+], and [Cl-] were similar for the three experimental conditions. Again, the data are best explained in terms of an active regulation of sweat composition. Total ionic losses do not seem sufficient to deplete body mineral reserves unless many days of training are undertaken in a hot climate.
Effect of heart rate and stroke volume on gas mixing in dog lung
Authors: Horsfield K. , Gabe I. , Mills C. , Buckman M. , Cumming G.
Published: December 2017

In nine anesthetized and ventilated dogs heart block was induced at thoracotomy, a pacemaker was inserted, and an electromagnetic flow transducer was placed round the main pulmonary artery. The chest was then closed. Stroke volume (SV) was varied by changing central blood volume. Ventilatory dead space (VDS) and alveolar nitrogen mixing efficiency (ANME) were measured at three levels of heart rate (HR) and three levels of SV independently varied during life and also after cessation of heartbeat. Neither VDS nor ANME showed a significant change with HR or SV during life, but mean VDS increased by 43 ml (22%) and mean ANME decreased by 4.4% postmortem. We conclude that cardiac action increases gas mixing at the interface between inspired and resident gas but has only a small effect on gas mixing distal to the interface during respiration without breath holding.
Canine thoracic electrical impedance with changes in pulmonary gas and blood volumes
Authors: Smith R. M. , Gray B. A.
Published: December 2017

The purpose of this study was to evaluate transthoracic impedance (Z) as an index of total lung liquid content at constant lung gas volume (LGV). To this end we produced rapid changes in pulmonary blood volume (PBV) in anesthetized, paralyzed, closed-chest dogs with the airway occluded at functional residual capacity. Changes in PBV produced by inflation of balloons on catheters positioned in the left atrium (LA) or inferior vena cava (IVC) were estimated from the changes in chest wall recoil pressure, using the chest wall as a plethysmograph after calibration with changes in LGV. Whereas Z increased linearly with decreases in PBV (1–6 ml/kg) produced by the IVC balloon (% delta Z/delta PBV = -0.43 ml/kg, r = -0.81), Z did not change significantly with increases in PBV (1–6 ml/kg) produced by the LA balloon. These observations indicate that changes in PBV are not the primary determinant of changes in Z and raise the possibility that other hemodynamic events are more important. Whereas aortic pressure decreased with both IVC and LA balloon inflations, right atrial pressure (Pra) increased with mitral valve obstruction and decreased with IVC obstruction. Changes in chest wall blood volume in response to changes in Pra could explain the changes in thoracic impedance. Thus, even at constant LGV, events in the systemic circulation appear to invalidate Z as an indicator of lung liquid content.
Regional circulatory responses to head-out water immersion in anesthetized dog
Authors: Krasney J. A. , Pendergast D. R. , Powell E. , McDonald B. W. , Plewes J. R.
Published: December 2017

Thermoneutral head-out water immersion (WI) of humans leads to a sustained elevation of cardiac output (QCO), while systemic VO2 is unchanged. However, the regional blood flow responses (Qr) to WI are largely unknown. In eight dogs anesthetized with pentobarbital sodium, relative to the control vertical position in air with the chest and abdomen upright (Erect1), after 30 min of WI at 38 degrees C the QCO (thermodilution), stroke volume, and aortic pressure were elevated (P less than 0.01) by 88.5 +/- 6.4% (SE), 55 +/- 9%, and 29 +/- 4% from levels of 2.24 +/- 0.01 1 X min-1, 18.4 ml +/- 1.7, and 109 +/- 7.9 mmHg, respectively. Qr (ml X min-1 X 100 g-1), measured by 15 microns-radiolabeled microspheres at WI30 min relative to the Erect1 levels, increased (P less than 0.01) in the stomach (104 +/- 27%), jejunum (78 +/- 19%), ileum (102 +/- 23%), liver (hepatic artery) (485 +/- 46%), pancreas (200 +/- 44%), spleen (88.7 +/- 33%), renal cortex (88 +/- 30%), left ventricle (157 +/- 15%), skin (726 +/- 30%), fat (680 +/- 43%), gastrocnemius (200 +/- 36%), triceps (414 +/- 61%), intercostals (317 +/- 44%), and diaphragm (477 +/- 24%). Qr responses at WI10 min were largely similar. Rectal temperature and VO2 were unchanged during WI. In the lateral recumbent position in air, QCO rose by 44.3% (P less than 0.01), but only hepatic arterial Q rose significantly (89 +/- 29%). Therefore, there may be a partial uncoupling of the normal Q/VO2 relationship in WI.
A new system for ventilating with high-frequency oscillation
Authors: Ngeow Y. K. , Mitzner W.
Published: December 2017

We describe simple high-frequency oscillation systems that incorporate a CO2 absorber and supply O2 on a need basis. These systems have the advantage of easy control of mean airway pressure and airway hydration and negligible loss of oscillatory tidal volume. Experiments done at constant tidal volume showed that as frequency (and hence total ventilation) increased, arterial CO2 tension (PaCO2) decreased. The fall in PaCO2 occurred until frequency reached approximately 20 Hz; above 20 Hz further increases in frequency had little or no effect on PaCO2. Because of their practical advantages the techniques described here may be quite useful in a clinical setting where an oscillator, rather than jet-type high-frequency, ventilation system is desired.
Determination of maximal aerobic power during upper-body exercise
Authors: Sawka M. N. , Foley M. E. , Pimental N. A. , Toner M. M. , Pandolf K. B.
Published: December 2017

The purpose of this investigation was to evaluate four protocols for their effectiveness in eliciting maximal aerobic power (peak VO2) during arm-crank exercise. Comparisons were made 1) between a continuous (CON) and an intermittent (INT) protocol (both employed a crank rate of 50 rpm) and 2) among the CON protocols employing crank rates of 30, 50, or 70 rpm. For the first group of experiments no significant (P greater than 0.05) differences were found between the CON and INT protocols for peak VO2, maximal pulmonary ventilation (VEmax), maximal heart rate (HRmax), or maximal blood lactate (LAmax) responses. For the second group of experiments, the CON-50 was compared with the CON-30 and CON-70 protocols. In comparison to the CON-50, significantly higher peak VO2 (+10%) and VEmax (+14%) responses were elicited by the CON-70 protocol, whereas significantly lower peak VO2 (-11%), VEmax (-23%), HRmax (-8%), and LAmax (-29%) responses were elicited by the CON-30 protocol. Of the arm-crank protocols examined the combination of a continuous design and a crank rate of 70 rpm provided the most effective protocol to elicit peak VO2 values.