bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer measurement of dynamic compliance: technique and reproducibility in man
Authors: Douglas N. J. , Wraith P. K. , Brash H. M. , Millar J. , Sudlow M. F. , Flenley D. C.
Published: December 2017

A computer program was developed to calculate the frequency dependence of dynamic compliance (Cdyn) using continuous data analysis. Cdyn was measured repeatedly in eight normal human subjects over a 2-yr period. Comparison with Cdyn results measured manually showed that the computer program improved 10-fold the ratio of variance within subjects to between subjects of the compliance at specific frequencies, but there was only slight improvement in indices of the slope of the frequency dependence of compliance. We suggest that the absolute compliance at specific frequencies merits further consideration as a pathophysiological measurement and that, if the frequency dependence of compliance continues to be used, standardization of its calculation should be applied and the wide normal range should be more widely appreciated. Measurements of Cdyn in subjects breathing 80% helium-20% oxygen confirm that inertia is insignificant when breathing with tidal volumes of less than 500 ml and frequency of less than 1.5 Hz.
Muscular work as thermal behavior in humans
Authors: Caputa M. , Cabanac M.
Published: December 2017

Human subjects were placed on a bicycle ergometer and left to pedal ad lib. for 43 min to warm themselves and thereby attain thermal comfort at an ambient temperature of 10 degrees C. Esophageal (Tes), tympanic (Tty), forehead, and hand skin temperatures were recorded. In addition, the work of pedaling was noted for each 2-min period. In some experiments sweating rate was also recorded. Two series of experiments were performed, the first with face fanning and the second with thermal insulation of the head. Face fanning resulted in decreased Tty, but in substantially increased Tes, which was 1.5 degrees C higher than Tty after an intense pedaling effort of 46-50 W. In experiments with head covering, a mild increase of both Tes and Tty was observed toward a position halfway between the extreme values obtained during face fanning. Simultaneously, pedaling intensity decreased to 16.7 W and the rate of sweating increased. In general, pedaling work was inversely proportional to intracranial temperature (Tty) and independent of trunk temperature (Tes). Therefore, motivation for muscular activity in humans exposed to cold appears to be goverened chiefly by the brain temperature.
Lung tissue volume during development of edema in isolated canine lungs
Authors: Felton C. R. , Johanson W. G.
Published: December 2017

The technique of estimating pulmonary tissue volume (Vt) by rebreathing a tissue-soluble gas is rapid and noninvasive. We examined the sensitivity of this technique for the estimation of Vt in isolated, perfused canine lungs during the development of pulmonary edema. Vt was 84 ± 15% (mean ± SD) of the associated lung weight for lung weights of up to 240% of base line but decreased to 70 ± 2% when lung weight exceeded 310% of base line. Small rebreathing tidal volumes resulted in significantly smaller values for Vt in edematous lungs. An abrupt increase in pulmonary venous pressure increased lung weight due to vascular distension; Vt measurements detected less than half of this increase, implying that certain portions of the intravascular blood volume are not measured by this technique.
Chemical and nonchemical components of ventilation during hypercapnic exercise in man
Authors: Clark J. M. , Sinclair R. D. , Lenox J. B.
Published: December 2017

Nine young athletes performed treadmill exercise at average VO2 levels of 1.08, 1.78, 3.00, and 3.57 l/min while exposed to inspired PCO2 levels of 0, 10, 20, 30, and 40 Torr. The average slope of the VE-PACO2 relationship increased significantly from 3.59 to 4.70 l.min-1.Torr-1 in the transition from rest to light exercise and then decreased progressively and significantly to 1.34 l.min-1.Torr-1 at the highest work load. A similar pattern of initial increased steepness followed by progressive flattening was found in the VT-PACO2, curves, whereas slopes of the f-PACO2 relationships continuously decreased in the transition from rest through light to heavy exercise. These data are consistent both with an increased ventilatory response to PACO2--[H+]a increments during light exercise and with progressive reduction of that response during the transition from light to heavy exercise in parallel with increasingly severe mechanical influences on VE as maximal limits are approached. They are not consistent with simple addition of chemical and nonchemical components of exercise hyperpnea at all levels of exercise.
Response of pulmonary veins to increased intracranial pressure and pulmonary air embolization
Authors: Peterson B. T. , Grauer S. E. , Hyde R. W. , Ortiz C. , Moosavi H. , Utell M. J.
Published: December 2017

Brain compression with subdural air causes pulmonary hypertension and noncardiogenic pulmonary edema (A. B. Malik, J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42: 335-343, 1977). To see whether air emboli to the lungs rather than brain compression caused these findings, anesthetized dogs received intravenous air infusions, subdural air infusions, or brain compression from balloons inflated in the subdural space. Subdural air and intravenous air resulted in similar vascular responses. Pulmonary artery pressure (Ppa) increased 160% (P less than 0.01) and pulmonary venous pressure transiently rose 13 +/- 5 Torr (P less than 0.05) without an increase in left atrial pressure or cardiac output (Q). The end-tidal PCO2 fell 55% (P less than 0.01) and the postmortem weight of the lungs increased 55% (P less than 0.05). Brain compression with a subdural balloon instead of air only caused a 20% rise in Ppa and Q without pulmonary edema. Thus, pulmonary air emboli rather than brain compression accounts for the edema and pulmonary hypertension caused by subdural air. Catheters in pulmonary veins and the left atrium showed that air emboli cause transient pulmonary venous hypertension as well as a reproducible form of noncardiogenic pulmonary endema.
Collateral resistance at alveolar level in excised dog lungs
Authors: Sasaki H. , Takishima T. , Nakamura M.
Published: December 2017

In excised dog lungs, collateral resistance was measured among separate groups of alveoli. Alveoli beneath the pleural surface were multipunctured by a small needle, and alveolar pressure and flow were measured in capsules glued onto the punctured pleural surface. When the airway opening was closed, collateral ventilation appeared to occur mainly through the regular airway system, but not through the collateral channels. When the airway opening and the segmental bronchus were occluded, collateral airflow appeared to occur first, within the segment through its airway system; second, through the intersegmental collateral channels to other segments; and third, to output alveoli through the airway system. When the airway was obstructed down to the bronchilar level with silicone rubber, collateral resistance became extremely high. It was concluded that collateral resistantce at the alveolar level was considerably higher than the resistance in the regular airway system.
Respiratory capacity and glycogen depletion in thyroid-deficient muscle
Authors: Baldwin K. M. , Hooker A. M. , Herrick R. E. , Schrader L. F.
Published: December 2017

This study was undertaken to determine the effects of propylthiouracil-induced thyroid deficiency on a) the capacity of muscle homogenates to oxidize [2-14C]pyruvate and [U-14C]palmitate and b) glycogen depletion during exercise in liver and in fast-oxidative-glycogenolytic (FOG), fast-glycogenolytic (FG), and slow-oxidative (SO) muscle. Relative to the rates for normal rats, oxidation with pyruvate was reduced by 53, 68, and 58%, and palmitate by 40, 50, and 48% in FOG, FG, and SO muscle, respectively (P less than 0.05). Normal rats ran longer than thyroid-deficient rats at 26.7 m/min (87 ± 8 vs. 37 ± 5 min). After 40 min of running (22 m/min), the amount of glycogen consumed in normal FOG, FG, and SO muscle and in liver amounted to only 23, 12, 66, and 52%, respectively, of that for their thyroid-deficient counterparts. Also, normal rats maintained higher plasma free fatty acid levels than thyroid-deficient rats during both rest and exercise (P less than 0.05). These findings suggest that thyroid deficiency causes a reduced potential for FFA utilization in skeletal muscle that enhances its consumption of glycogen, thereby limiting endurance capacity.
Identification of functional lung unit in the dog by graded vascular embolization
Authors: Young I. , Mazzone R. W. , Wagner P. D.
Published: December 2017

To study the dimensions of the functional gas exchange unit, spherical polystyrene beads (diam 50-500 micrometers) were injected intravenously into 12 normal anesthetized paralyzed dogs (15-24 kg wt). We argued that beads small enough to lodge within gas exchange units would not give rise to a population of high ventilation-perfusion ratio (VA/Q) areas, whereas embolization of larger vessels supplying these units would. Each dog received only one bead size in cumulative 0.25-g doses up to a maximum of 2.25 g. Multiple inert gas elimination data were obtained after each dose to monitor the development of high VA/Q regions. Injection of 50- and 100-micrometers beads never gave rise to high VA/Q regions, whereas 150-, 250-, and 500-micrometers beads consistently induced a high VA/Q mode comprising up to 45% of the ventilation. Histological examination of lungs from five additional dogs injected with small (approximately 0.5 g) doses revealed that beads rarely formed clusters and appeared in vessels of their own diameter in over 90% of instances. By the above criterion, the functional gas exchange unit in these lungs is that volume of tissue subtended by 150- micrometers-diam arteries (vessels associated with respiratory bronchioles).
Lung recoil during rapid vital capacity expirations simulated by gas compression
Authors: Webster P. M. , Loring S. H. , Butler J. P. , Hoppin F. G.
Published: December 2017

Excised dog lobes were inflated to a transpulmonary pressure (PL) of about 30 cmH2O, and their airways were occluded. Then they were rapidly compressed to a volume where PL was about zero, simulating forced expiratory maneuvers. Since there was no airflow during the compression, PL was a direct measure of lung recoil. Lung volume (VL) was calculated from absolute airway pressure using Boyle's law. At ambient temperature, lung recoil pressure during compressive maneuvers simulating forced vital capacity expirations (Pdyn) was less than that during quasi-static (30 s) compressions (Pst). Typically the dynamic component (i.e., Pst--Pdyn) decreased from about 2 cmH2O near total lung capacity to no difference at the end of the compression. Cooling the lobes to 15 degrees C increased Pst-Pdyn, and warming the lobes to 37 degrees C reduced Pst-Pdyn almost to zero. We suggest that the driving force of lung recoil during expirations is adequately modeled by the quasi-static VL/PL relationship, though a small correction should be made for excised lungs at room temperature.
Pulmonary venoconstriction caused by elevated cerebrospinal fluid pressure in the dog
Authors: Maron M. B. , Dawson C. A.
Published: December 2017

Previously we found that raising cerebrospinal fluid pressure (PCSF) caused pulmonary vasoconstriction mediated by adrenal catecholamines. To localize the site of this vasoconstriction we used the outflow occlusion technique to divide changes in the pulmonary arteriovenous pressure gradient (Pa-v) into upstream and downstream pressure drops. Experiments were conducted in 10 dogs in which the animal's left lower lung lobe was denervated and perfused at constant flow and outflow pressure with blood pumped from the dog's pulmonary artery. Raising PCSF to 218 Torr caused Pa-v to rise from 9.0 to 12.5 Torr. Most (83%) of this increase resulted from an increase in the downstream pressure drop. Previous studies have indicated that changes in the upstream and downstream pressure drops, as measured by this technique, are highly correlated with changes in the resistance of the arterial and venous sides of the vascular bed. Thus, it appears that elevated PCSF caused primarily pulmonary venoconstriction. Similar results were obtained with norepinephrine and epinephrine infusion. This is consistent with previous studies, indicating that adrenal catecholamines are responsible for the increase in Pa-v in response to PCSF in this preparation.
Augmented diffusion in the airways can support pulmonary gas exchange
Authors: Fredberg J. J.
Published: December 2017

Bohn et al. (J Appl. Physiol.: Respirat. Environ. Exercise Physiol, 48: 710-716, 1980) reported that paralyzed beagle dogs maintained normal gas exchange for 6 h or more when small tidal volumes at high breathing rates were maintained at the airway opening (15 ml tidal volume at 15 breaths/s). These tidal volumes were 25% of dead space and thereby were too small to permit convective gas exchange with pulmonary air spaces. I have used a semiempirical analysis to show that augmented diffusion in the central airways, akin to Taylor's turbulent dispersion (Proc. R. Soc. Ser. A 223: 446-468, 1954) combined with molecular diffusion in the periphery of the lung, can account for most if not all of the observed gas transport during small tidal volume, high-frequency ventilation. Ventilation efficiency (alveolar ventilation/minute ventilation) is approximately 2-5% and is insensitive to the combination of frequency and tidal volume giving rise to the minute ventilation.
Role of neural afferents from working limbs in exercise hyperpnea
Authors: Weissman M. L. , Whipp B. J. , Huntsman D. J. , Wasserman K.
Published: December 2017

To determine the role of reflex discharge of afferent nerves from the working limbs in the exercise hyperpnea, 1.5- to 2.5-min periods of phasic hindlimb muscle contraction were induced in anesthetized cats by bilateral electrical stimulation of ventral roots L7, S1, and S2. Expired minute ventilation (VE) and end-tidal PCO2 (PETCO2) were computed breath by breath, and mean arterial PCO2 (PaCO2) was determined from discrete blood samples and, also in most animals, by continuous measurement with an indwelling PCO2 electrode. During exercise VE rose progressively with a half time averaging approximately 30 s, but a large abrupt increase in breathing at exercise onset typically did not occur. Mean PaCO2 and PETCO2 remained within approximately 1 Torr of control levels across the work-exercise transition, and PaCO2 was regulated at an isocapnic level after VE had achieved its peak value. Sectioning the spinal cord at L1-L2 did not alter these response characteristics. Thus, reflex discharge of afferent nerves from the exercising limbs was not requisite for the matching of ventilation to metabolic demand during exercise.
Plasma testosterone during treadmill exercise
Authors: Wilkerson J. E. , Horvath S. M. , Gutin B.
Published: December 2017

Five male volunteers performed 20 min of steady-state submaximal exercise on a motor-driven treadmill at five intensities (30, 45, 60, 75, and 90% VO2 max) as well as several maximal aerobic capacity tests. Peripheral venous plasma testosterone concentrations increased above resting values in proportion to exercise intensity. However, this increase in plasma testosterone concentration was virtually equal in magnitude to the decrease in plasma volume observed consequent to the exercise bouts, resulting in no change in total testosterone contents. There was an unexpected anticipatory elevation in resting preexercise control testosterone concentration and content with increasing work intensity. The possibility that testosterone has a direct role in the organism's response to whole-body exercise is questioned.
Ventilation-perfusion lines and gas exchange in liquid breathing: theory
Authors: Matalon S. V. , Farhi L. E.
Published: December 2017

Alveolar exchange of a gas is governed by the ventilation-perfusion ratio (VA/Q) and the Ostwald partition coefficient for that species. We altered the Ostwald coefficients for O2 and CO2 by considering an animal breathing water or a fluorocarbon (FC-80) and studied the effects on gas exchange. Among our conclusions are the following. 1) When the ratio of the CO2 to O2 solubility in the inspirate exceeds the ratio of the O2 to the CO2 slope of the blood dissociation curve, as in water breathing, the VA/Q line becomes concave upward, and elements having a low VA/Q differ from each other more in terms of CO2 than of O2. 2) As the ratio of the CO2 to O2 solubility in the inspired medium increases, CO2 elimination becomes more dependent on perfusion. 3) At times, the same R will prevail in areas having different VA/Q values. 4) The alveolar-to-arterial O2 and CO2 differences resulting from a given VA/Q distribution do not depend on the O2 and CO2 solubility coefficients of the inspired medium, but on the inspired and mixed venous concentrations necessary to maintain adequate arterial gas levels in the presence of different inspired media.
Effect of vagal stimulation on collateral flow resistance in dog lungs
Authors: Olson L. E. , Robinson N. E.
Published: December 2017

Vagal effects on steady-state resistance of pathways within a segment of lung (Rss) were studied in open-chest dogs using a wedged catheter technique. To prevent adrenergic bronchodilation, dogs were pretreated with propranolol. Rss was determined with vagi intact or sectioned and during electrical stimulation of right and left vagi. Following determination of Rss, gas flow into the segment was arrested, segmental pressure decay recorded, and the time for 90% decay (T90) measured. Stimulation of the vagus supplying the lung with the wedged catheter (ipsilateral) increased Rss and T90 at low (2-4 cmH2O) transpulmonary pressures (Pao) and T90 at high (5-9 cmH2O) Pao. Vagal sectioning and contralateral stimulation had minimal effects. Atropine abolished vagal effects. We modeled the segment as two series compartments, one with a rapid time constant and one with a longer time constant. At both low and high Pao, vagal stimulation prolonged the slow time constant. If the fast compartment represents small airways and the slow compartment collateral pathways, collaterals may not be effective in maintaining ventilation to lung segments distal to a vagally constricted bronchus.
Resistance of red blood cell membrane to oxygen uptake
Authors: Rotman H. , Ikeda I. , Chiu C. S. , Kramer E. , Aminoff D.
Published: December 2017

The apparent association velocity constant (k'c) was determined before and after disruption of the red blood cell membrane in one of several ways: 1) radiation of the cells using a 137Cs source did not significantly alter k'c (95 +/- 39.3 and 118 +/- 35.5 mM-1.s-1), 2) incubation of the cells with sialidase produced no change in k'c (112 +/- 42.6 and 123 +/- 46.8 mM-1.s-1), 3) using papain for the incubation similarly produced no significant alteration in k'c (94 +/- 21.2 and 113 +/- 51.8 mM-1.s-1), 4) a radiomimetic agent p-chloromercuribenzene sulfonate likewise produced no significant alteration in k'c (128 +/- 16.3 and 122 +/- 3.5 mM-1.s-1), and 5) employing phospholipase C to disrupt the membrane k'c did not significantly change (115 +/- 15.3 and 112 +/- 8.7 mM-1.s-1). We conclude that either O2 traverses the membrane in a manner uninfluenced by the manipulations here employed, or that the membrane offers no significant resistance to the speed of O2 uptake.
Barometric measurement of tidal volume: effects of pattern and nasal temperature
Authors: Jacky J. P.
Published: December 2017

The accuracy of the formula derived by Drorbaugh and Fenn (Pediatrics 16: 81-86, 1955) for calculating tidal volume (VT) from the phasic pressure change measured when an animal breathes in a closed chamber has recently been challenged. Epstein and Epstein (Respir. Physiol. 32: 105-120, 1978) argue that the formula may underestimate VT by up to 30% and predict that the error increases as the ratio of inspiratory duration (TI) to total breath duration (Ttot) increases, and as the expired temperature at the nares (TN) increases. To test their theory, I measured VT in anesthetized rats by the barometric technique and by conventional pneumotachography simultaneously. TN was varied from ambient to body temperature by passing a variable current through the pneumotachograph heater; TI/Ttot was varied by changing FICO2 and by selecting different rats. The predictions were confirmed. A factor is derived for retrospectively correcting VT estimated by the Drorbaugh-Fenn formula. It requires knowledge of TN and TI/Ttot and reduces the error between experiments to under 20% and within each experiment to about 5%. To facilitate its use, TN was measured in rat, rabbit, cat, man, and infant pigtail monkey.
Sound speed in the upper airways
Authors: Rice D. A.
Published: December 2017

We measured the velocity of audible sound at frequencies above 10 kHz to be 349 m.s-1 (±1%, 95% confidence interval) in the upper airways of eupneic anesthetized dogs. It appears that the velocity of sound propagation is dependent on lumen gas composition, temperature, and mean flow speed. These three variables are sufficient to explain the velocity variations measured during tidal breathing. Lung volume, transpulmonary pressure, and bronchoactive drugs were not shown to have an appreciable effect on sound velocity. Model studies indicate that sound velocity is little affected by flow profile, lumen cross-sectional shape, or changes in lumen area with position. Flow speed proportionally changes the velocity of sound relative to the airway and therefore can be determined from sound propagation measurements. Dividing volume flow by flow speed gives airway cross-sectional area. Tracheal areas after normalization by the cube root of body weight were about half those previously reported. Acoustically inferred areas were confirmed by mechanical measurement.
Pulmonary vascular histamine receptors in newborn and young lambs
Authors: Goetzman B. W. , Milstein J. M.
Published: December 2017

Histamine H1- and H2-receptor-mediated pulmonary vascular responses were evaluated in six newborn and three 4-wk-old lambs. Base-line pulmonary vascular resistance (PVR) was elevated via alveolar hypoxia. Changes in PVR were then determined over a range of 0.001-1.0 microgram/kg of histamine. Multiple phases of relaxation of PVR were observed in all lambs. Two distinct plateaus of relaxation occurred between 0.001 and 0.075 micrograms/kg of histamine. The response at the first and major plateau was abolished by the H1-receptor antagonist, diphenhydramine. The second and smaller relaxation appeared to be attenuated by the H2-receptor antagonist, metiamide. Qualitatively similar results were obtained in the older lambs. Larger doses of histamine, 0.1-1.0 microgram/kg, produced further, but variable decreases in PVR as well as changes in systemic blood pressure. Our findings in newborn lambs are in contrast to those in adults where less sensitive H1-receptors mediate pulmonary vasoconstriction.
In vitro hepatic deiodination of L-thyroxine to 3,5,3'-triiodothyronine in cold-acclimated rats
Authors: Scammell J. G. , Shiverick K. T. , Fregly M. J.
Published: December 2017

An in vitro model has been employed to evaluate the effect of cold acclimation on peripheral outer ring deiodination of thyroxine (T4) to triiodothyronine (T3) by 9,000 g supernatants of fresh liver homogenates. Hepatic T3 generation from T4 in male rats exposed to 4 +/- 1 degree C for 12 wk was 41 and 24% higher than control after 30- and 60-min incubation periods, respectively. This was associated with a 49% increase in serum T3 concentration in the cold-acclimated rats, whereas serum T4 concentration did not differ from the control. Thus, hepatic deiodination of T4 appears to serve as an important source for production of T3 during cold acclimation. It is suggested that the increased beta-adrenergic activity observed previously in cold-acclimated rats stimulates this change.
Changes in CNS responses to high pressure during maturation of newborn mice
Authors: Mansfield W. , Brauer R. W. , Gillen H. W. , Nash K.
Published: December 2017

From birth to maturity CD-2 mice were exposed to progressively increasing pressures of helium-oxygen. In all age groups a regular progression of changes in locomotor behavior was observed including, in sequence, increased locomotor activity and two types of convulsions designated as types I and II. The effects of altering compression rate and of reserpine pretreatment were recorded for all age groups. Maturation in these mice is associated with increased resistance to high-pressure neurological syndrome convulsions of either type, in contrast to what might have been expected from previous phylogenetic studies. The patterns in development of the two seizure types differ greatly in detail, further supporting the previously advanced inference that they represent neurological events that differ in kind rather than merely quantitatively. The effect of the results on theories that concern the mechanism of action of pressure on the vertebrate central nervous system is discussed.
Narrowing of glottis opening in humans associated with experimentally induced bronchoconstriction
Authors: Higenbottam T.
Published: December 2017

An index of the separation of the vocal cords during tidal breathing was obtained in humans; the area of the glottis opening was assessed from photographs of the vocal cord taken on inspiration and expiration via a fiber-optic bronchoscope. The index of glottis width was calculated from the area by dividing it with, as reference, the anteroposterior diameter of the glottis, a relatively invariant measurement of the glottis during breathing. Both inspiratory and expiratory glottis width decreased after histamine had been inhaled (dose range 2.4-9.6 mg) or injected intravenously (dose of 4 micrograms/kg), being associated with a reduction in forced expired volume in 1.0 s. Histamine, which acts directly on smooth muscle or bronchial irritant receptors, is unlikely to have directly caused contraction of the striated laryngeal musculature or to have stimulated receptors above the vocal cords. The narrowing of the glottis opening observed in humans may represent a reflex narrowing of the glottis in association with a reduction of intrapulmonary airway caliber.
Mechanical properties of lungs and chest wall during spontaneous breathing
Authors: Nagels J. , Landser F. J. , van der Linden L. , Clement J. , Van de Woestijne K. P.
Published: December 2017

Using a forced oscillation technique, we measured the resistance (Rrs) and reactance (Xrs) of the respiratory system between 2 and 32 Hz at three different lung volumes in 15 healthy subjects and 7 patients with chronic obstructive pulmonary disease. Rrs and Xrs were partitioned, by means of a pressure recording in the esophagus, into the resistance and reactance of lung and airways (L) and the chest wall. The measurements were validated by checking the adequacy of the frequency response of the esophagus, by the lack of difference between thoracic and mouth flow, by an estimation of the error introduced by the shunt impedance of the cheeks, and by comparisons with the values of pulmonary compliance and resistance determined in the same subjects with classical techniques. In both healthy subjects and patients, the chest wall has a low resistance that increases somewhat at low lung volumes and behaves functionally as a two-compartment system, with low capacitance at frequencies exceeding 4 Hz. Rrs varies with lung volume and is markedly frequency dependent in patients; both phenomena are due primarily to corresponding variations of RL. In healthy subjects, at and above functional residual capacity (FRC) level, the lungs behave as a one-compartment system, the reactance of which is mainly determined by the gaseous inertance, at least beyond 2 Hz. In patients and in healthy subjects breathing below FRC, the observed frequency dependence of resistance and the simultaneous increase in resonant frequency can be simulated satisfactorily by Mead's two-compartment model, assuming a large increase in peripheral airways resistance.
Measurement and analysis of gas exchange during exercise using a programmable calculator
Authors: Sue D. Y. , Hansen J. E. , Blais M. , Wasserman K.
Published: December 2017

Although exercise testing is useful in the diagnosis and management of cardiovascular and pulmonary diseases, a rapid comprehensive method for measurement of ventilation and gas exchange has been limited to expensive complex computer-based systems. We devised a relatively inexpensive, technically simple, and clinically oriented exercise system built around a desktop calculator. This system automatically collects and analyzes data on a breath-by-breath basis. Our calculator system overcomes the potential inaccuracies of gas exchange measurement due to water vapor dilution and mismatching of expired flow and gas concentrations. We found no difference between the calculator-derived minute ventilation, CO2 production, O2 consumption, and respiratory exchange ratio and the values determined from simultaneous mixed expired gas collections in 30 constant-work-rate exercise studies. Both tabular and graphic displays of minute ventilation, CO2 production, O2 consumption, respiratory exchange ratio, heart rate, end-tidal O2 tension, end-tidal CO2 tension, and arterial blood gas value are included for aid in the interpretation of clinical exercise tests.
Coronary blood flow in conscious miniature swine during +GZ acceleration stress
Authors: Laughlin M. H. , Witt W. M. , Whittaker R. N. , Jones E. F.
Published: December 2017

One of the factors determining tolerance to +GZ acceleration may be the ability to maintain adequate coronary blood flow. Consequently, the purpose of these studies was to determine the effect of acute exposure (60 s) to several levels of positive acceleration (+GZ) on total and regional coronary blood flow in conscious adult miniature swine. Blood flow was measured with the radiolabeled microsphere technique in chronically instrumented miniature swine during 60-s exposures to accelerations of +3 GZ, +5 GZ, or +7 GZ with anti-G suit support. All levels of acceleration stress caused two- to threefold increases in coronary blood flow. The regional distribution of coronary blood flow during +GZ was similar to that under resting control conditions as long as aortic diastolic pressure was maintained. All left ventricular endocardial/epicardial flow ratios were significantly greater than one, except in two animals, during exposure to +7 GZ. These were the only animals to have aortic diastolic pressures less than 100 Torr during +GZ stress. These studies indicate that, if an animal is able to compensate and maintain a cardiovascular steady State, coronary blood flow will remain adequate for myocardial needs. However, if decompensation occurs and aortic diastolic pressure falls below a critical value, subendocardial blood flow may become inadequate.
Renal blood flow in miniature swine during +GZ stress and anti-G suit inflation
Authors: Laughlin M. H. , Witt W. M. , Whittaker R. N.
Published: December 2017

The effects of +GZ acceleration stress on renal blood flow were studied in chronically instrumented, conscious miniature swine. Renal blood flow was determined using the radiolabeled (46Sc, 85Sr, 141Ce, and 125I) microsphere technique (29 animals) and Doppler-principle flow probes (1 animal). The results obtained with the microsphere technique indicate that +GZ exposure with anti-G suit support caused decreases in renal blood flow throughout the kidney, and that renal blood flow remains decreased for 1-10 min after +GZ stress. Medullary blood flow appeared to recover after +GZ exposure more rapidly than cortical blood flow. The flow probe data also indicate that +GZ stress with or without anti-G suit support results in decreases in renal blood flow, and that anti-G suit inflation in the absence of +GZ can also cause significant decreases. We conclude that the reductions in renal blood flow observed in miniature swine, during +GZ stress with anti-G suit support, may be due to a combination of direct anti-G suit interference and +GZ-induced reflex increases in alpha-constrictor sympathetic tone to the renal vascular bed.
Bronchovascular adjustments after pulmonary embolism
Authors: Malik A. B. , Tracy S. E.
Published: December 2017

We determined the time course of bronchial blood flow alterations after pulmonary microembolization. Embolization was induced by injecting 100-micrometers-diam glass beads into the right atrium so as to increase pulmonary arterial pressure from 13.8 +/- 1.8 to 35.7 +/- 2.6 Torr in 14 dogs. The increase in pulmonary vascular resistance averaged threefold after embolization (PE). The bronchial blood flow (Qb) was measured using the reference sample method with the 15 +/- 5-micrometers-diam labeled microspheres injected into the left atrium. Simultaneous blood reference samples were collected at constant rates from a femoral artery and the pulmonary artery. The pulmonary arterial reference sample was used to quantify the contribution of peripheral arteriovenous shunts to the total pulmonary activity, and the femoral arterial reference blood was used to quantify Qb. The Qb was decreased to one-third of its base-line value at 60-min PE (P less than 0.05) but not at 5 min PE. Qb was increased 300% at 2 wk PE. The decrease in flow was associated with an increased bronchovascular resistance, whereas the increase in flow was associated with a decreased resistance. The decrease in Qb at 60 min PE may be due to release of peripheral vasoconstrictor substances associated with pulmonary embolism. The finding that bronchial perfusion increased gradually after pulmonary vascular obstruction suggests that increased flow is due to neovascularization.
Energy metabolism and heart rate during treadmill exercise in the Marabou stork
Authors: Bamford O. S. , Maloiy G. M.
Published: December 2017

Oxygen consumption (VO2), heart rate, body temperature, and stride frequency were measured in Marabou storks walking on a treadmill at a range of speeds and gradients. VO2 was linearly related to speed at gradients up to 11 degrees and speeds up to 1.4 m . s-1, and the slope of the VO2/speed regression increased with the treadmill angle up to 9 degrees. At 11 degrees there was a fall in the slope. Analysis indicates the cost of horizontal movement of about 1.1 ml O2 . m-1 (mean wt 4.5 kg). The cost of vertical movement is 7.13 ml O2 . m-1 and the efficiency about 30%. Maximum recorded VO2 was about five times resting, and there was no indication of an oxygen debt at any value for VO2. Heart rate was directly proportional to vO2 over the range studied, and at high heart rates successive cardiac cycles overlapped. Body temperature did not change significantly during exercise. Stride frequency was linearly related to walking speed but with a nonzero intercept so that stride length changed with speed, but there was no observed change in gait with speed. These data are discussed in comparison with published scaling equations and with data from mammals.
Pulmonary mechanics during exercise in normal males
Authors: Stubbing D. G. , Pengelly L. D. , Morse J. L. , Jones N. L.
Published: December 2017

A body plethysmograph adapted to contain the pedals of an electrically braked cycle ergometer was used to measure pulmonary mechanics during steady-state exercise in 12 normal male subjects aged 22-65 yr. During exercise there was a progressive increase in residual volume to 119% of the value at rest (P less than 0.01), but functional residual capacity and total lung capacity did not change. The maximum expiratory flow-volume (MEFV) curves did not change and flow rates during tidal breathing did not exceed the MEFV curve. Dynamic pulmonary compliance fell to 91.3% of the control value and static expiratory pulmonary compliance fell to 76.9% of the control value (P less than 0.05). Pulmonary resistance did not change during exercise. Transpulmonary pressure during tidal breathing was negative even at the highest power outputs. The fall in compliance may be due to an increase in pulmonary capillary blood volume. These results demonstrate the importance of measuring absolute thoracic gas volume and the elastic properties of the lung when comparing pulmonary mechanics at rest and during exercise.
Diphenhydramine reduces endotoxin effects on lung vascular permeability in sheep
Authors: Brigham K. L. , Padove S. J. , Bryant D. , McKeen C. R. , Bowers R. E.
Published: December 2017

Because, in sheep, histamine-induced increased lung vascular permeability is prevented by diphenhydramine, we tested the effects of diphenhydramine on the sheep lung vascular response to endotoxin. We infused E. coli endotoxin (0.40-1.00 micrograms/kg) with and without diphenhydramine (3.0 mg/kg bolus + 1.5 mg . kg-1 . h-1) in the same unanesthetized sheep while measuring pulmonary arterial (Ppa) and left atrial (Pla) pressures, lung lymph flow (Qlym) and lymph (L) and plasma (P) protein concentrations. Endotoxin caused pulmonary hypertension soon after infusion (base-line Ppa = 22 +/- 3 (SE) cmH2O; after endotoxin Ppa = 40 +/- 2; P less than 0.05, n = 6) and after several hours an increase in permeability reflected in high flow of protein-rich lymph (base-line; Qlym = 7.5 +/- 1.4 (SE) ml/h, L/P protein concentration = 0.60 +/- 0.02: after endotoxin; Qlym = 21.4 +/- 3.1, P less than 0.05; L/P = 0.66 +/- 0.03, P less than 0.05). In the presence of diphenhydramine, endotoxin caused identical pressure changes but Qlym was lower during the period of increased permeability (16.7 +/- 3.0 (SE) ml/h, P less than 0.05 compared to endotoxin alone) and L/P protein concentration was similar (0.68 +/- 0.04, P = NS). We conclude that endogenous histamine may be partly responsible for the increase in lung vascular permeability after endotoxemia, but that histamine probably is not the sole mediator of the permeability change.
Carbonic anhydrase activity of rabbit lungs
Authors: Effros R. M. , Shapiro L. , Silverman P.
Published: December 2017

Pulmonary carbonic anhydrase (CA) activity was studied in rabbit lungs perfused with solutions containing no CA. Measurements were made of the amount of 14CO2 appearing in the expired gas following injections of H14CO3(-), 14CO2, or a 20:1 mixture of each into the pulmonary artery. The fraction of the injected label in the expired gas was only 17% greater for 14CO2 than for the mixture, suggesting that equilibration between H14CO3(-) and 14CO2 was nearly complete during the capillary transit time. Inhibition of pulmonary CA decreased excretion of H14CO3(-) and the mixture by 40 and 49% and increased the excretion of 14CO2 by 96%. Addition of CA to the perfusate had no effect. Thus, CO2 exchange is not significantly limited by pulmonary CA if inhibitors are absent. Tissue binding of [3H]acetazolamide injected into the pulmonary artery was diminished by 50% when acetazolamide concentrations reached 0.13 x 10(-6) M. Each liter of extravascular lung water contained 1.25 x 10(-6) mol of receptors for acetazolamide that were accessible to plasma during a single circulation. Binding of [3H]acetazolamide was also observed in lungs of anesthetized rabbits, suggesting that pulmonary CA is accessible to plasma in vivo as well as in situ.
Effects of expiratory loading on respiration in humans
Authors: Gothe B. , Cherniack N. S.
Published: December 2017

We examined the effects of expiratory resistive loads of 10 and 18 cmH2O.l-1.s in healthy subjects on ventilation and occlusion pressure responses to CO2, respiratory muscle electromyogram, pattern of breathing, and thoracoabdominal movements. In addition, we compared ventilation and occlusion pressure responses to CO2 breathing elicited by breathing through an inspiratory resistive load of 10 cmH2O.l-1.s to those produced by an expiratory load of similar magnitude. Both inspiratory and expiratory loads decreased ventilatory responses to CO2 and increased the tidal volume achieved at any given level of ventilation. Depression of ventilatory responses to Co2 was greater with the larger than with the smaller expiratory load, but the decrease was in proportion to the difference in the severity of the loads. Occlusion pressure responses were increased significantly by the inspiratory resistive load but not by the smaller expiratory load. However, occlusion pressure responses to CO2 were significantly larger with the greater expiratory load than control. Increase in occlusion pressure observed could not be explained by changes in functional residual capacity or chemical drive. The larger expiratory load also produced significant increases in electrical activity measured during both inspiration and expiration. These results suggest that sufficiently severe impediments to breathing, even when they are exclusively expiratory, can enhance inspiratory muscle activity in conscious humans.
Effects of contraction force and frequency on postexercise hyperemia in human calf muscles
Authors: Richardson D. , Shewchuk R.
Published: December 2017

The purpose of this study was to examine the separate effects of contraction force and frequency on postexercise hyperemia in the human calf muscle. Nine male subjects were used. Each was seated in a chair with the right foot on a pedal coupled to a load cell and the knee secured. Calf muscle blood flow, measured by a Whitney gauge, was determined before and periodically after 3-pmin bouts of rhythmic isometric plantar-flexor exercise. The contraction frequency was graded from 20 to 50 to 80 contractions/min. The force per contraction was graded from 7.5 to 15 to 30% of maximum voluntary contraction (MVC) of the calf muscle. The average MCV was 502 lb. Peak postexercise blood flow (PBF) increased with either increasing frequency at a given force or increasing force at a given frequency. However, at the higher levels of exercise, PBF tended to plateau at a value of about 50 ml.min-1.100 ml-1. The plateau phase of PBF was associated with a substantial increase in the total volume of postexercise hyperemia. This appeared to be well above any repayment of a blood flow deficit. However, it is not certain that the extra volume represented the repayment of a true blood flow debt.
Cardiovascular responses to static exercise in distance runners and weight lifters
Authors: Longhurst J. C. , Kelly A. R. , Gonyea W. J. , Mitchell J. H.
Published: December 2017

Sixty individuals including 17 competitive weight lifters (CWL), 12 competitive long-distance runners (LDR), 7 amateur (noncompetitive) weight lifters (AWL), 14 heavy controls (HC), and 10 light controls (LC) were studied at supine rest and during static exercise at 40% of maximal voluntary contraction. Blood pressures were similar in all groups at rest (R) and exercise (EX), but the heart rate (HR) and calculated double product (DP) of the LDR were lower at rest (HR: 53 +/- 2.9 beats/min, DP: 6,346 +/- 402) and at fatigue (HR: 78 +/- 5.4 beats/min. DP: 12,739 +/- 1,011) compared to the control group (R-HR: 69 +/- 2.2 beats/min, DP: 8,553 +/- 372; EX-HR: 97 +/- 3.5 beats/min, DP: 16,345 +/- 836). The LDR demonstrated higher end-diastolic volume index (EDVI) and higher end-systolic volume index (ESVI) at rest (EDVI: 84 +/- 3.7, ESVI: 31 +/- 2.7 ml/m2) and at the time of fatigue (EDVI: 90 +/- 5, ESVI: 37 +/- 2.7 ml/m2) compared to the LC group (R-EDVI: 61 +/- 4.4, ESVI: 22 +/- 2.2; EX-EDVI: 75 +/- 3.4, ESVI: 27 +/- 3.2 ml/m2). The CWL, AWL, and control groups had similar HR, DP, and cardiac volumes at rest and during exercise. These data suggest that competitive endurance (dynamic exercise) training alters the cardiovascular response to static exercise. On the other hand, weight lifting (static exercise) training does not alter the cardiovascular response to static exercise.
Factors affecting the development of hyperbaric oxygen toxicity in the awake rat brain
Authors: Mayevsky A. , Shaya B.
Published: December 2017

Hyperbaric oxygen toxicity (HPO), under various environmental and physiological conditions, was identified by measuring the electrical, hemodynamic, and metabolic activity of the awake brain in rats. The electrical activity was evaluated by the electrocorticogram; the hemodynamic and metabolic activity were measured by use of the surface fluorometry/reflectometry technique. The oxidation-reduction state of NADH (metabolic activity) was measured by using the quartz fiber-optic system to excite the tissue and transmit the fluorescence-emitted light from the brain. The hemodynamic responses were evaluated from the reflectance signal. In three sets of experiments we tested the effects of pressure level, age, and protection agents (pentobarbital and diazepam) on the various parameters measured from the brain. The results can be summarized as follows. 1) The effect of the pressure level of the toxicity process is significant; the higher the pressure, the greater the toxicity. 2) The 60-psi level of pressure is a turning point in the toxicity process, and the kinetic of the process is different below and above this point. 3) The 14-day-old rats showed resistance to the HPO exposure as compared to the older aged rats. 4) The pentobarbital and diazepam protect against the toxicity at 60 and 90 psi, as evaluated by various parameters measured.
Glycogen repletion following continuous and intermittent exercise to exhaustion
Authors: Gaesser G. A. , Brooks G. A.
Published: December 2017

Patterns of postexercise glycogen repletion in heart, skeletal muscle, and liver in the absence of exogenously supplied substrates during the first 4 h of recovery were assessed. Female Wistar rats were run to exhaustion using continuous (1.0 mph, 15% grade) and intermittent (alternate 1-min intervals at 0.5 and 1.5 mph, 15% grade) exercise protocols. Rats at exhaustion were characterized by marked depletion of glycogen in heart (55%), skeletal muscle (94%), and liver (97%). Blood glucose levels at exhaustion (1.33 mumol/g) were only 37% of preexercise levels. There were no significant differences between continuous and intermittent exercise groups for any of the tissue glycogen or blood glucose values. Cardiac muscle was the only tissue capable of complete restoration of glycogen levels while relying exclusively upon endogenous substrates. Concentrations of endogenous substrates present at the end of exercise were insufficient to support restoration of blood glucose levels to preexercise values nor support glycogen repletion in skeletal muscle and liver during the initial 4-h food-restricted postexercise period. With subsequent feeding, skeletal muscle demonstrated a glycogen supercompensation effect at 24 h (181.1 and 191.8% of preexercise levels for continuous and intermittent exercise, respectively). Lactate concentration in all tissues at the point exhaustion (1.5--2.5 times resting levels) were only moderately elevated and returned to preexercise levels within 15 min. It was concluded that lactate removal after exercise contributed only minimally to the repletion of muscle glycogen.