bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy expenditure during oxygen deficit of submaximal concentric and eccentric exercise
Authors: Pahud P. , Ravussin E. , Acheson K. J. , Jequier E.
Published: December 2017

Aerobic (MR) and anaerobic (Man) energy production was determined in five subjects during the 1st min of concentric and eccentric exercise (steady-state energy expenditure approximately 415 W in both situations). Man was obtained by solving the heat balance equation, MR + Man - S = (R + C + E) ± parallel to W parallel to, all other variables of which could be measured [S is heat storage; (R + C + E) are the radiative, convective, and evaporative heat losses; and W is work output]. The size of the O2 deficit was similar whatever the type of exercise (99 ± 19 W concentric and 102 ± 19 W eccentric). MR + Man was lower than the steady-state MR in both types of exercise (concentric; 364 ± 19 and 407 ± 24 W, respectively, and eccentric; 346 ± 25 and 430 ± 21 W, respectively). The size of the O2 deficit during the 1st min of muscular exercise is imposed by the steady-state energy requirement whatever the type of exercise. The smaller energy expenditure during this phase is probably due to less energy being released when creatinge phosphate is split without resynthesis (O2 deficit) than during splitting and resynthesis of high-energy phosphate bonds (steady state).
Interaction of dopamine and haloperidol with O2 and CO2 chemoreception in carotid body
Authors: Lahiri S. , Nishino T. , Mokashi A. , Mulligan E.
Published: December 2017

Effects of dopamine and of a dopaminergic blocker, haloperidol, on the responses of carotid body chemoreceptors to hypoxia and hypercapnia were investigated in 16 anesthetized cats. Intravenous infusion of dopamine (10-20 micrograms.min-1) decreased carotid body chemoreceptor responses to hypoxia and hypercapnia. The effect was greater at higher levels of arterial oxygen and carbon dioxide tension (PaO2 and PaCO2) stimulus. Thus, the magnitude of the dopamine effect depended on the degree of both PO2- and PCO2-mediated excitation of the receptors. Haloperidol potentiated responses to both hypoxia and hypercapnia but apparently did not stimulate the receptors in the absence of these stimuli. Potentiation by haloperidol and inhibition by dopamine of excitatory effects due to PaO2 decrease and PaCO2 increase are complementary. The data suggest that chemoreception of dopamine, O2, and CO2 converge at some site in the carotid body. Persistence of hypoxic and hypercapnic responses, following dopamine-blocking doses of haloperidol, does not support the theory that regulation of dopamine release is responsible for O2 and CO2 chemoreception in carotid body of the cat.
Ventilatory response to transient hyperoxia in head injury hyperventilation
Authors: Leitch A. G. , McLennan J. E. , Balkenhol S. , McLaurin R. L. , Loudon R. G.
Published: December 2017

We have measured breath-by-breath instantaneous minute ventilation (VIinst) before, during, and after the administration of 10 breaths of 100% oxygen to seven male patients with head injury hyperventilation. The patients were hypoxemic (PaO2 61.2 ± 6.3) and hypocapnic (PaCO2 26.6 ± 5.9) with a respiratory alkalosis (pH 7.53 ± 0.06) while breathing air. Following the oxygen VIinst fell on the average by 40 ± 12.7% from 16.06 ± 3.75 1.min-1 to a minimum of 9.73 ± 3.20 1.min-1 at 20.4 ± 2.9 s after the first breath of oxygen. In the majority of our hyperventilating patients, almost all of the resting hyperventilation could be abolished transiently by 100% oxygen. This fall in ventilation represents the peripheral chemoreceptor contribution to resting ventilation and is increased in the head injury patients in comparison with normal subjects breathing air or hypoxic gas mixtures, altitude-acclimatized subjects and patients who are hypoxic because of chronic bronchitis or interstitial lung disease. We suggest that the increased reflex hypoxic drive to ventilation found in our patients is secondary to their cerebral injury, resulting in a reduction of descending cortical inhibitory influences on the medullary respiratory control centers.
Physiological and pharmacological properties of canine trachealis muscle in vivo
Authors: Brown J. K. , Leff A. R. , Frey M. J. , Reed B. R. , Gold W. M.
Published: December 2017

In 23 dogs anesthetized with chloralose and urethan, we developed a preparation that premitted measurement of isometric tension in segments of the tracheal posterior membrane in situ. Length-tension studies showed an optimal length for contraction in each of 5 segments; in all 5 segments, length was optimal when resting tension was 22-35 g/cm. In 8 other segments, stimuli were delivered by systemic intravenous injections, by electrical stimulation of nerves, or by selective injections into the tracheal circulation; the time between delivery of repeated stimuli required for reproducible responses differed for each form of stimulation. Hypoxemia increased tension by 23.1 ± 5.5 (SE) g/cm in 10 out of 10 other segments; these increases were the results of reflexes, not direct effects. Because the innervation and vascular supply of these segments were largely intact, we concluded that this preparation permits the study of neurohumoral mechanisms which modulate smooth muscle contraction in a prototypic central airway in vivo.
Effect of lung volume on collateral ventilation in the dog
Authors: Kaplan J. , Koehler R. C. , Terry P. B. , Menkes H. A. , Traystman R. J.
Published: December 2017

We studied the effect of lung volume on resistance through collateral pathways (Rcoll) and small airways (Rsaw) before and after the injection of methacholine into obstructed segments of intact dogs. Before methacholine, Rcoll decreased 15.0 ± 4.9 (SE)% per cmH2O increase in transpulmonary pressure (Ptp) and Rsaw decreased 5.1 ± 7.0 (SE)% per cmH2O increase in Ptp. Following methacholine, lung inflation resulted in similar decreases in Rcoll and Rsaw. The fall in Rcoll was significantly greater than the fall in Rsaw. When pressure in an obstructed segment (Ps) was increased with constant Ptp (nonhomogeneous inflation), Rcoll fell approximately half as much for each cmH2O increase in pressure compared to when Ptp was increased (homogeneous inflation). We conclude 1) that increases in lung volume have small effects on Rsaw so that there is a relative increase in flow through collateral channels serving obstructed poritons of lung and 2) that Rcoll is a function of the size of the obstructed segment that increases more under homogeneous than nonhomogeneous conditions.
Clearance of liquid from lungs of newborn rabbits
Authors: Bland R. D. , McMillan D. D. , Bressack M. A. , Dong L.
Published: December 2017

Apparent inconsistencies in the results of previous studies led us to reexamine the process by which fluid leaves the lungs of newborn rabbits after birth. We measured pulmonary blood volume, extravascular lung water, and the size of perivascular cuffs of fluid in frozen sections of lung obtained from 166 full-term rabbits (31 days gestation) born vaginally or by cesarean section. We killed the rabbits by giving them barbiturate intraperitoneally and immersing them in liquid nitrogen before they breathed or at randomly predetermined intervals from 5 min to 24 h after birth. We found that a) pulmonary blood volume of both groups of rabbits increased soon after birth, b) extravascular lung water per gram of dry lung tissue was greater at birth in rabbits born by cesarean section than in those born vaginally, c) extravascular lung water did not begin to decrease in either group of animals until 30-60 min postnatally, after which it decreased progressively for 24 h, and d) the rate of fluid clearance and pattern of puddling around pulmonary vessels was similar in both groups of rabbits, with maximal perivascular cuffs 30 min after birth, followed by diminution of cuff size as the lungs shed water.
Chest wall motion and distribution of inspired gas in anesthetized supine dogs
Authors: Schmid E. R. , Rehder K. , Knopp T. J. , Hyatt R. E.
Published: December 2017

Changes in the anterior-posterior (AP) and lateral diameters of the rib cage and abdomen were assessed by magnetometry in seven anesthetized supine dogs during spontaneous respiration (SR) and mechanical ventilation after muscle paralysis (MV). Regional distribution of inspired gas was measured for both modes of ventilation by determining regional 133Xe clearances. Marked differences in chest wall motion were observed between SR and MV: during MV, the changes in lateral rib cage diameter from FRC to end inspiration were larger, and the changes in both abdominal diameters smaller than during SR. AP rib cage diameter changes were similar for both modes of ventilation. Inward motion of the lateral rib cage during initial inspiration was observed in four dogs during SR; it disappeared consistently with MV. Regional 133Xe clearances were not significantly different: there was no cephalocaudal gradient, and the vertical gradient in regional ventilation was similar with MV and SR. We conclude that significant changes in chest wall motion and shape are not necessarily associated with detectable differences in the distribution of regional ventilation.
Peribronchial electrical admittance measures lung edema and congestion in the dog
Authors: McNamee J. E. , Brodman M. L.
Published: December 2017

A new method has been developed to detect interstitial pulmonary edema. This method utilizes the unique arrangement of air and interstitial fluid within the lung. A 1.3-mm-diam twin catheter electrode was wedged in a peripheral airway of the lung. The electrical impedance measured at 35 kHz between these catheter-tip electrodes was 1,540 ± 240 omega (mean ± SD; n = 10) in the anesthetized closed-chest dog. Intravenous infusion of 1-3 liters 0.154 M NaCl increased extravascular water per gram of dry lung from a control value of 3.54 ± 0.27 to 4.1-5.14. Peribronchial electrical impedance decreased in proportion to the amount of saline infused reaching a minimum of 550 omega. No signs of alveolar flooding were present during the experiments. Linear regression performed on peribronchial electrical admittance (PEA) as a function of extravascular water per gram of dry lung (ELW) resulted in the following relationship: PEA = 0.72 ELW - 1.81; r = 0.95. It is concluded that this method is a sensitive quantitative measure of lung interstitial fluid and can detect pulmonary edema and congestion in the dog lung before alveolar flooding occurs.
Steady flow in a model of human central airways
Authors: Slutsky A. S. , Berdine G. G. , Drazen J. M.
Published: December 2017

We studied the pressure-flow relationships and flow distribution under steady conditions in a model of human central airways, over a range of tracheal Reynolds' numbers (350-30,000) by using air or helium. We found that the Moody diagram [log coefficient of friction CF = delta P/[1/2 rho (V2/A2)] vs. log Reynolds' number (Re)] had a slope of -1 for Re less than 500, a slope 0 for Re greater than 10,000, and slopes between -1 and 0 for 500 less than or equal to Re less than or equal to 10,000. The distribution of flow among branches was dependent on tracheal Reynolds' number so that, as tracheal Reynolds' number increased, the upper lobes received proportionally less of the total flow than the lower lobes. Because the airways in the upper lobes generally had greater branching angles than those in the lower lobes, this result was consistent with the hypothesis that the effective resistances introduced by branching angles was flow dependent, increasing proportionally more the greater the angle.
Fetal cardiovascular and metabolic responses to simulated diving in the Weddell seal
Authors: Liggins G. C. , Qvist J. , Hochachka P. W. , Murphy B. J. , Creasy R. K. , Schneider R. C. , Snider M. T. , Zapol W. M.
Published: December 2017

Fetal responses to normobaric diving simulated by submersion of the maternal head for 20 min were studied in four conscious Weddell seals near term. Microspheres injected into the maternal aorta were distributed to the placenta and kidneys in the ratio of 0.4 in the control period and 19.3 during diving, suggesting minimal placental vasoconstriction. Fetal heart rate fell during diving from a mean control value of 90 to 34 beats/min after 4 min. The onset of fetal bradycardia was not consistently associated with changes in blood gas tensions. Diving was associated with a fall in fetal arterial O2 tension from 24 to 9 Torr, arterial CO2 tension rose from 47 to 85 Torr, and arterial pH fell from 7.35 to 7.24. Fetal-maternal gradients for CO2 and H+ transport remained constant, whereas the gradient for O2 transport fell from 47 Torr before diving to 14 Torr at the end of diving. Blood lactate concentrations increased three- to fourfold during diving and reached peak values 10-15 min after diving ended. The similarity of the fetal and maternal heart rate responses to diving is consistent with the presence of physiological oxygen-conserving reflexes akin to the adult's.
Transfer of oxygen, nitrogen, and carbon dioxide through normal adult human skin
Authors: Hansen T. N. , Sonoda Y. , McIlroy M. B.
Published: December 2017

The resistance to the flow of oxygen, nitrogen, and carbon dioxide through the skin ws measured in three normal adult human subjects. A sampling chamber 2.5 cm in diameter, heated to 43-44 degrees C, was applied to the skin of the forearm and gas sampled with a mass spectrometer at a rate of about 10(-5) ml . s-1 through membranes of different resistance. Skin resistance was calculated from the results of sequential studies with different membranes of known resistance on the sampling chamber. The resistance to oxygen flow (1.79 +/- 0.92 X 10(3) atm . ml-1 . min . cm2) was 1/5 of that for nitrogen and 28.5 times that for carbon dioxide. The response time of the skin to a sudden change in arterial gas tension was investigated by having the subjects rebreathe 5% carbon dioxide in oxygen and then breathe air. The mean transit times though the skin for oxygen and carbon dioxide were similar (approx 30 s) and about twice those for nitrogen. The finding of similar response times for oxygen and carbon dioxide transfer in the face of large differences in resistance suggests that there is a high capacitance for carbon dioxide in the skin, presumably due to its high solubility and the effects of buffering.
Effects of intensive exercise training on myocardial performance and coronary blood flow
Authors: Barnard R. J. , Duncan H. W. , Baldwin K. M. , Grimditch G. , Buckberg G. D.
Published: December 2017

Five instrumented and eight noninstrumented dogs were progressively trained for 12-18 wk on a motor-driven treadmill. Data were compared with 14 instrumented and 8 noninstrumented control dogs. Gastrocnemius malate dehydrogenase activity was significantly increased in the trained dogs (887 +/- 75 vs. 667 +/- 68 mumol . g-1 . min-1). The trained dogs also showed significant increases in maximum work capacity, cardiac output (7.1 +/- 0.5 vs. 9.1 +/- 0.7 1/min), stroke volume (25.9 +/- 2.0 vs. 32.0 +/- 2.0 ml/beat), and left ventricular (LV) positive dP/dtmax (9,242 +/- 405 vs. 11,125 +/- 550 Torr/s). Negative dP/dtmax was not significantly different. Peak LV systolic pressure increased with exercise, but there was no significant difference between the trained and control dogs. LV end-diastolic pressure did not change with exercise and was the same in both groups. Tension-time index was lower in the trained dogs at rest and submaximum exercise (9.7 km/h, 10%) but was not different at maximum exercise. Diastolic pressure-time index was significantly higher in the trained dogs at rest and during submaximum exercise but was not different at maximum exercise. LV coronary blood flow was significantly reduced at rest (84 +/- 4 vs. 67 +/- 6 mo . min-1 . 100 g-1) and during submaximum exercise (288 +/- 24 vs. 252 +/- 8 ml . min-1 . 100 g-1). During maximum exercise flow was not significantly different (401 +/- 22 vs. 432 +/- 11 ml . min-1 . 100 g-1) between the control and trained groups. The maximum potential for subendocardial flow was unchanged with training despite the development of mild hypertrophy.
Reversal of 5HT-induced bronchoconstriction by PGI2: distribution of central and peripheral actions
Authors: Spannhake E. W. , Levin J. L. , Mellion B. T. , Gruetter C. A. , Hyman A. L. , Kadowitz P. J.
Published: December 2017

In anesthetized, mechanically ventilated, and vagotomized cats, we studied the distribution of the bronchodilatory effects of prostaglandin I2 (PGI2) in central and peripheral airways. In the intact-chest cat, bolus intravenous injection of PGI2 in a range of doses from 3 to 100 micrograms produced dose-dependent reversal of 5-hydroxytryptamine- (5HT) induced bronchoconstriction. Bronchodilatory effects were manifested by a pronounced decrease in central airways flow resistance, as estimated by measurement of lung resistance and by an increase in dynamic lung compliance (Cdyn). A similar distribution and magnitude of airway effects were produced by intravenous administration of PGE1 in a range of doses from 0.3 to 10 micrograms. PGI2 significantly reversed the frequency dependence of compliance induced by infusion of 5HT. The PGI2 metabolite, 6-keto-PGF1 alpha, was without effect on pulmonary mechanics. Comparison of right- versus left-heart administration of PGI2 did not point to a significant role of the bronchial circulation in the airway effects of PGI2. Comparison of the effects of PGI2 and PGE1 on cat bronchial and parenchymal strips contracted by 5HT showed both prostaglandins to have predominant action on bronchial smooth muscle with PGI2 being 3-10 times less active than PGE1. These data suggest that PGI2 has central airway bronchodilator activity, similar to, but less potent than PGE1. In addition, they suggest that PGI2 has significant dilator activity in certain peripheral areas of the lung, as well.
Shrinkage of dog lobes during air-drying fixation
Authors: Murphy B. G. , Engel L. A.
Published: December 2017

Air-drying of canine lung lobes, distended at a constant pressure corresponding to 50% of lobar total lung capacity, resulted in a volume shrinkage of 35.8%. To examine associated changes in shape of the lobes, the shrinkage of three orthogonal directions (x, y, and z) was quantitated by measuring the change in length per unit length (strain; epsilon) of straight lines between pleural markers. Epsilon x = 0.14, epsilon y = 0.22, and epsilon z = 0.12. This inequality of strains indicated that moderate shape changes occurred. The direction of the largest strain component (epsilon y) corresponded to a direction normal to the largest projected surface area of the lobe.
Regional extravascular and interstitial lung water in normal dogs
Authors: Snashall P. D. , Keyes S. J. , Morgan B. , Jones B. , Murphy K.
Published: December 2017

We measured the regional distribution of pulmonary extravascular and interstitial water to examine the possibility that regional differences in microvascular pressure or tissue stress may cause regional differences in lung water. We placed chloralose-anesthetized dogs in an upright (n = 6) or supine (n = 7) position for 180 min. We injected 51Cr-labeled EDTA to equilibrate to the extracellular space and 125I-labeled albumin to equilibrate with plasma. At the end of the experiment, the lungs were removed, passively drained of blood, and inflated before rapid freezing. Lungs were divided into horizontal slices, and extravascular, interstitial, and plasma water, red cell volume, and dry lung weight were determined for each slice. We found that regional extravascular and interstitial water were constant throughout the lungs in both groups and that there were no significant differences between upright and supine dogs. There were no significant differences in hematocrit between slices. We conclude that gravity and body position have no measurable effect on either the total size of the extravascular and interstitial compartments or their regional distribution.
Oxidative capacity, blood flow, and capillarity of skeletal muscles
Authors: Maxwell L. C. , White T. P. , Faulkner J. A.
Published: December 2017

Our purpose was to test the hypothesis that the capillarity of mammalian skeletal muscles is correlated with the oxidate capacity of muscle fibers, or with the capacity for maximum blood flow. Capillarity of skeletal muscles from several species was determined using histochemical demonstration of phosphatase activity of capillary endothelium. Serial sections were incubated for succinate dehydrogenase activity as an indicator of muscle fiber oxidative capacity, and for myofibrillar ATPase activity. three types of muscle fibers were identified. Fiber area was determined by planimetry of projected cross sections. Succinate oxidase activity of whole homogenates was determined by differential respirometry. Muscle blood flow was determined experimentally or data were obtained from the literature. No consistent relation was observed for the different fiber types in the number of adjacent capillaries. Capillary density was negatively correlated with mean fiber area. Among adult animals of several species, skeletal muscles representing a 17-fold range of oxidative capacity demonstrated no relation between capillarity and oxidative capacity or muscle blood flow at maximum oxygen uptake. We find no support for relations between oxidative capacity of muscle blood flow and the capillarity of whole muscle or individual fibers and reject the hypothesis.
Activation of upper airway muscles before onset of inspiration in normal humans
Authors: Strohl K. P. , Hensley M. J. , Hallett M. , Saunders N. A. , Ingram R. H.
Published: December 2017

Animal studies have shown activation of upper airway muscles prior to inspiratory efforts of the diaphragm. To investigate this sequence of activation in humans, we measured the electromyogram (EMG) of the alae nasi (AN) and compared the time of onset of EMG to the onset of inspiratory airflow, during wakefulness, stage II or III sleep (3 subj), and CO2-induced hyperpnea (6 subj). During wakefulness, the interval between AN EMG and airflow was 92 +/- 34 ms (mean +/- SE). At a CO2 level of greater than or equal to 43 Torr, the AN EMG to airflow was 316 +/- 38 ms (P < 0.001). During CO2-induced hyperpnea, the AN EMG to airflow interval and AN EMG magnitude increased in direct proportion to CO2 levels and minute ventilation. During stages II and III of sleep, the interval between AN EMG and airflow increased when compared to wakefulness (P < 0.005). We conclude that a sequence of inspiratory muscle activation is present in humans and is more apparent during sleep and during CO2-induced hyperpnea than during wakefulness.
Effect of regional chest wall restriction on regional lung function
Authors: Forkert L.
Published: December 2017

The effect of impeding regional chest wall excursion on regional lung function was assessed. Fourteen subjects were studied while seated in a volume-displacement plethysmography. The lower rib cage and epigastrium were restricted with an inextensible binder. Because such restriction increases lung recoil and diminishes functional residual capacity (FRC), all measurements were made at the unstrapped FRC (FRCus). Regional excursion of the chest wall was measured with magnetometers placed anteroposteriorly at the sternomanubrial angle, the xyphoid, and umbilicus and transversely at the level of the xyphoid at the midaxillary line. Regional lung function was assessed by measuring the distribution of inspired boluses and washout of 133Xe with scintillation detectors positioned against the subject's back at the apical, middle, and basal regions. Restriction of the lower chest wall impeded expansion of the lower rib cage and diminished the distribution of inspired gas to and washout of the lung bases. The upper rib cage expanded normally and was associated with an increased distribution of inspired gas and normal distribution of washout to the apices. These results suggest that regional lung function was dependent on regional rib cage excursion.
Effects of gravitational profiles on the rat's thermoregulatory response to cold
Authors: Schertel E. R. , Horowitz J. M. , Horwitz B. A.
Published: December 2017

Unrestrained rats were subjected to a 1-h period of cold exposure during centrifugation to characterize their ability to regulate core temperature (Tc) and to determine if this regulation was dependent on the amplitude of the hypergravic field before the cold exposure. Tc was measured in unrestrained rats by the use of a thermistor implanted adjacent to the carotid artery. One hour of cold exposure applied over the last hour of either a 1-, 4-, 7-, 13-, 19-. 25-, or 37-h period at 3 G evoked a decrease in Tc of about 3 degrees C. This fall in Tc was significantly greater than changes in Tc in cold-exposed rats at 1 G. No significant differences were found between the measured decreases in Tc observed for the 1-h cold exposures during the first 37 h at 3 G. However, when rats were subjected concurrently to cold and acceleration after 8 days at 3 G, they exhibited a smaller fall in Tc, suggesting a partial recovery of the acceleration-induced impairment of temperature regulation. In another series of experiments, the gravitational field profile was changed in amplitude in three different ways during the 3-h period preceding the 1-h cold exposure at 3 G. Despite the different gravitation field profiles before cold, the magnitude of the fall in Tc over the 1-h period of cold exposure was the same of all cases. These results suggest that the thermoregulatory impairment has a rapid onset, it a manifestation of an ongoing effect of hypergravity, and is not dependent on the prior G profile. The inability of rats to maintain Tc when cold exposed may be transient as indicated by the partial recovery of regulation by the 8th day.
Diaphragmatic EMG and occlusion pressure response to elastic loading during CO2 rebreathing in humans
Authors: Lopata M. , Pearle J. L.
Published: December 2017

The effects of external elastic loading (EL) (19 cmH2O/l), applied continuously (C) and intermittently (I) during CO2 rebreathing, on diaphragmatic electromyogram (EMGdi), mouth occlusion pressure (P0.15), and ventilation (VI) were studied in normal subjects. EMGdi was analyzed as moving time average and quantitated in terms of peak (mean p) and average rate of rise of inspiratory activity (mean p/TI). CEL resulted in an increased mean p/TI response to CO2 in all subjects with P0.15 increasing in proportion to EMGdi. Tidal volume (VT) during rebreathing was decreased in all cases with VI being preserved in four of six runs due to increased breathing frequency (f). Although mean p was increased for a given end-tidal CO2 (PACO2) level during CEL, for a given rate of rise of inspiratory activity mean p was decreased in three of five subjects, indicating a diminished threshold for inspiratory "off-switch." CEL results in an augmented inspiratory drive that serves to increase muscle output and stabilize VT; the increased drive and decrease inspiratory off-switch threshold shorten TI mediating the compensatory increase in f. The first breath IEL resulted in decreased VT and mean p without change in mean p/TI, and all increased with subsequent loaded breaths independent of changes in PCO2. Load compensation for externally applied EL is mediated by neural mechanisms independent of chemical drive.
A comparison of continuous and discrete foreign gas VA/Q distributions
Authors: Teplick R. , Snider M. T. , Gilbert J. P.
Published: December 2017

Estimates of ventilation-perfusion ratio (VA/Q) distributions from foreign gas infusions have utilized a discrete lung model that constrains all alveoli to have 1 of 50 specified VA/Q. In contrast, distribution estimates based on a continuous model allow alveoli to have any VA/Q and can be derived directly from foreign gas data or by transforming distributions derived using the discrete model. We have compared analytically and empirically the properties of distributions based on these two models. Unlike the discrete model, the shape of distributions obtained from the continuous model are insensitive to changes in the VA/Q used in their calculation. Perfusion distributions found from the discrete model using VA/Q values evenly spaced on a logarithmic scale resemble ventilation distributions derived from the continuous model. In contrast, by use of VA/Q evenly spaced on a linear scale, perfusion distributions derived from either model have a similar shape. We concluded that physiological inferences derived from distribution shapes may vary according to the model employed. However, those based upon cumulative perfusion or distribution moments are invariant.
Reactivity of trachea, bronchi, and lung strips to histamine and carbachol in rhesus monkeys
Authors: Chand N. , Dhawan B. N. , Srimal R. C. , Rahmani N. H. , Shukla R. K. , Altura B. M.
Published: December 2017

Responses of isolated airway smooth muscles of a subhuman primate to carbachol and histamine were investigated. Isolated lung parenchymal strips of rhesus monkeys (RM) exhibited approximately equal sensitivity (i.e., ED50) and contractility (i.e., maximum tension) to carbachol and histamine. Tracheal chains and bronchial strips responded with concentration-dependent contractions to carbachol. Trachea did not exhibit any contractile responses to histamine. Bronchial strips responded with weak contractile responses to histamine when compared with those elicited ay carbachol. Histamine-induced contractions on bronchi and lung strips were easily antagonized by pyrilamine (H1-receptor antagonist) (10(-6) to 5 X 10(-6) M). Carbachol-contracted trachea and bronchi responded with relaxations to histamine and dimaprit (H2-receptor agonist) that were antagonized by metiamide (H2-receptor antagonist) (5 X 10(-5) M). The present findings indicate 1) a differential reactivity of central and peripheral airway smooth muscles of RM to histamine and carbachol; 2) lung strips of RM appear to possess only H1 types of histamine receptors; 3) bronchial smooth muscles of RM have a small population of H1-receptors mediating bronchoconstriction; and 4) a preponderance of inhibitory H2-receptors in the tracheobronchial smooth muscles of rhesus monkeys. If these subhuman primate findings apply to the airways of man, they could aid considerably in furthering our understanding of the pathophysiology of the respiratory tract.
Coronary flow, myocardial oxygen consumption, and exercise training in dogs
Authors: Stone H. L.
Published: December 2017

Changes in coronary blood flow (CBF) and myocardial oxygen consumption (MVO2) were measured in 17 conscious dogs during submaximal exercise and before and after exercise training. The CBF responses to atrial pacing and a 10-s occlusion were measured in the resting animals. With atrial pacing at 240 beats/min, the change in CBF from resting values increased significantly (12.8 +/- 1 to 15.2 +/- 3 cm/s), reactive hyperemia response was decreased (463 +/- 55 to 328 +/- 52%), and CBF during submaximal exercise was reduced by the end of the 4th or 5th wk of training. These changes persisted for the duration of the training program. When the animals were trained, the CBF response to submaximal exercise was the same as in the untrained condition. Exercise MVO2 did not change with training, but oxygen extraction increased (80 +/- 1 to 83 +/- 1%). These results indicate that changes in the coronary vascular bed occurred very early in the training program and may be explained by either an autonomic nervous system change in control of coronary flow or a change in the anatomic architecture of the bed.
Cost of locomotion and heat balance during rest and running from 0 to 55 degrees C in a patas monkey
Authors: Mahoney S. A.
Published: December 2017

A young patas monkey was run on a treadmill for 15-20 min at speeds in excess of 15 km times h-1 over a range of laboratory air temperatures from 0 to 55 degrees C. Cost of locomotion for the monkey was 83% that predicted for a running mammal of similar weight, 4 kg. At the highest steady-state running of speeds, the patas monkey's energy expenditure was 11 times the resting rate. Heat storage and respiratory evaporation during running each accounted for less than 16% of the heat production. Cutaneous evaporation, mainly sweating, was the major means of heat loss at high ambient temperatures and during heavy exercise. Maximum sweat rates of 0.5 mg times cm-2 times min-1 found in these experiments approach the sweat rates of humans. Whole-body dry thermal conductance increased 2-3 times the rest value at a given temperature. Environmentally gained heat contributed about two-thirds of the total heat load on the patas monkey at rest at 53 degrees C. At these same temperatures, environmental and metabolic heat loads were about equal when the animal ran at moderately high speeds (11-13.4 km times h-1).
Control of genioglossus muscle inspiratory activity
Authors: Brouillette R. T. , Thach B. T.
Published: December 2017

Tonic and phasic inspiratory genioglossus (GG) electromyographic activity (EMG) was recorded from 13 anesthetized rabbits during unstimulated breathing. Integrated GG EMG peaked earlier in inspiration and presented a more rounded contour than integrated diaphragmatic (DIA) EMG. Spontaneous augmented deep inspirations (sighs) showed a biphasic pattern in both GG and DIA EMGs. Hyperventilation abolished phasic inspiratory activity in the GG before the DIA, suggesting that the GG has a higher CO2 apneic point. Hypercapnia increased both EMGs; however, GG EMG increased more, as a percent of base line, than did DIA EMG. Oxygen breathing decreased GG more than DIA EMG; sodium cyanide injection and brief nitrogen breathing increased GG more than DIA EMG; carotid body denervation abolished these responses. Vagotomy abolished the Hering-Breuer inflation-inhibition reflex in both muscles, and tactile, visual, and auditory stimulation increased GG more than DIA EMG. Thus, the GG responses to chemoreceptor input and to nonspecific respiratory stimuli are qualitatively similar but quantitatively different from DIA responses. The relevance to mixed and obstructive apnea is discussed.
Vasodilator and constrictor responses to hypoxia in isolated pig lungs
Authors: Sylvester J. T. , Harabin A. L. , Peake M. D. , Frank R. S.
Published: December 2017

We examined transient and steady-state responses of the pulmonary circulation to hypoxia in isolated pig lungs perfused with autologous blood. Responses were quantified by the pulmonary artery pressure at a flow of 1 l/min (Ppa1) read directly from pressure-flow recordings. Alveolar carbon dioxide tension was constant at 38 Torr and alveolar oxygen pressure (PAO2) was varied between 670 and 0 Torr. When PAO2 was lowered progressively every 10 min, the relation between PAO2 and Ppa1 was sigmoidal, with maximum constriction occurring at a PAO2 of 0 Torr; however, if Ppa1 was allowed to reach a steady state at each level of PAO2, the relation was reproducibly and reversibly biphasic. Ppa1 increased as PAO2 decreased from 670 to 60 Torr, was maximum and stable at PAO2 between 60 and 30 Torr, and decreased as PAO2 was lowered from 30 to 0 Torr. As a result, steady-state Ppa1 at PAO2 greater than or equal to 200 Torr was similar to that at PAO2 = 0 Torr. When PAO2 was changed from 200 Torr to a constant lower level, Ppa1 required 20-30 min to achieve a steady state at PAO2 greater than or equal to 25 Torr and 40-50 min at PAO2 of 10 and 0 Torr. With the latter, the responses consisted of vasoconstriction followed by marked vasodilation. Thus pulmonary vasomotor tone was a complex function of both PAO2 and time. Attempts to explain the pulmonary vascular response to hypoxia must take these complexities into account.
Role of H1- and H2-receptors in airway reactions to histamine in conscious sheep
Authors: Ahmed T. , Eyre P. , Januszkiewicz A. J. , Wanner A.
Published: December 2017

We investigated the role of histamine H1- and H2-receptors in the control of airway function in six conscious sheep. In five of these, inhalation of histamine (combined H1- and H2-receptor stimulation) caused an increase in pulmonary resistance (RL) and functional residual capacity and had a variable effect on distribution of ventilation as measured by N2-clearance delay. Pretreatment with the H1-antagonist, chlorpheniramine, prevented these functional effects of histamine challenge, whereas pretreatment with the H2-antagonist, metiamide, potentiated the effects of histamine on RL and caused a uniform increase in N2-clearance delay. Pretreatment with both chlorpheniramine and metiamide prevented the effects of histamine on all parameters indicating effective blockade of H1- and H2-receptors at the dosages used. In one sheep, an increase in RL and N2-clearance delay in response to histamine was only observed after metiamide pretreatment. With or without pretreatment, histamine failed to alter the static pressure-volume curve of the lung. We conclude that in conscious sheep a) inhalation of histamine produces bronchoconstriction and pulmonary hyperinflation without changing lung elastic recoil, b) the observed effects of histamine are mediated by H1-receptors, and H2-receptors have a modulating role, and c) variable effects of histamine on RL and distribution of ventilation may be related to differences in the distribution of H1- and H2-receptors in central and peripheral airways.
Effect of defibrinogenation on lung water accumulation after pulmonary microembolism in dogs
Authors: Johnson A. , Malik A. B.
Published: December 2017

We determined the effects of chronic fibrinogen depletion on the development of pulmonary edema after pulmonary microembolization. Dogs were defibrinogenated with a purified fraction of Malayan pitviper venom (ancrod). Studies were made in four groups: control untreated (group I); emboli untreated (group II); control defibrinogenated (group III); and emboli defibrinogenated (group IV). Fibrinogen decreased (P < 0.05) from 570.6 +/- 100.9 to 5.3 +/- 3.1 mg/100 ml in the ancrod-treated groups. Pulmonary arterial pressure was increased to similar levels in both embolized groups after infusion of 100-mug-diam nonsiliconized glass beads into the right atrium. Pulmonary vascular resistance and pulmonary perfusion pressure were initially increased to similar levels in both embolized groups, but by 75 min postembolization (PE) both parameters were higher (P < 0.05) in the defibrinogenated group. The extravascular lung water-to-bloodless dry lung ratio at 75 min PE of 4.53 +/- 0.24 in group II was greater than the control value of 2.84 +/- 0.22 in group I (P < 0.05). In contrast, the extravascular lung water-to-bloodless dry lung ratio of 3.64 +/- 0.09 in group IV was not different from the control value of 3.38 +/- 0.04 in group III, but was less than 4.53 +/- 0.24 in group II (P < 0.05). Therefore, chronic defibrinogenation in dogs prevented the development of pulmonary edema after pulmonary microembolization. The protective effect may be due to inhibition of the increase in lung vascular permeability and to a time-dependent reduction in pulmonary microvascular pressure.
Physiological effects of controlled concussive brain trauma
Authors: Millen J. E. , Glauser F. L. , Zimmerman M.
Published: December 2017

Utilizing a fluid percussion device, we measured the physiological effects of brain trauma in cats exposed to controlled levels of injury. Concussive brain injury at 3-4 atm of intensity led to profound elevations of the mean systemic arterial blood pressure from 128 +/- 26 to 229 +/- 33 mmHg, left ventricular end-diastolic pressure from 4 +/- 2 to 24 +/- 15 mmHg, and pulmonary wedge pressures (PWP) from 5 +/- 3 to 27 +/- 17 mmHg and a relatively moderate increase in intracranial pressure (ICP) from 6 +/- 3 to 38 +/- 31 mmHg (all P < 0.001). Pulmonary edema was evidenced by a significant increase in lung tissue wet-to-dry weight ratios to 3.74 +/- 0.81 as compared with a control group of 2.29 +/- 0.23 (P < 0.001). There was poor correlation between wet-to-dry weight ratios and PWP. Approximately 60% of all spontaneously breathing animals become permanently apneic within 6 min after injury, while the remaining 40% developed transient apnea. Arterial O2 or CO2 pressure alterations, in contrast to pretreatment with phentolamine did not affect the hemodynamic or edemogenic response to trauma. Phentolamine did not block the apneic response or increase in ICP. Comparative studies using intravenous levarterenol without trauma produced responses similar to trauma. Concussive brain injury of 3-4 atm results in pulmonary edema, apnea, sympathetically mediated peripheral vasoconstriction and left ventricular failure effect.
Oxygen uptake, acid-base status, and performance with varied inspired oxygen fractions
Authors: Adams R. P. , Welch H. G.
Published: December 2017

Six subjects rode a bicycle ergometer on three occasions breathing 17, 21, or 60% oxygen. In addition to rest and recovery periods, each subject worked for 10 min at 55% of maximal oxygen uptake (VO2 max) and then to exhaustion at approximately 90% VO2 max. Performance time, inspired and expired gas fractions, ventilation, and arterialized venous oxygen tension (PO2), carbon dioxide tension (PCO2), lactate, and pH were measured. VO2, carbon dioxide output, [H+]a, and [HCO3-]a were calculated. Performance times were longer in hyperoxia than in normoxia or hypoxia. However, VO2 was not different at exhaustion in normoxia compared with hypoxia or hyperoxia. During exercise, hypoxia was associated with increased lactate levels and decreased [H+]a, PCO2, and [HCO3-]a. The opposite trends were generally associated with hyperoxia. At exhaustion, [H+]a was not different under any inspired oxygen fraction. These results support the contention that oxygen is not limiting for exercise of this intensity and duration. The results also suggest that [H+] is a possible limiting factor and that the effect of oxygen on performance is perhaps related to control of [H+].
Rebreathing techniques for pulmonary capillary blood flow and tissue volume
Authors: Sackner M. A. , Markwell G. , Atkins N. , Birch S. J. , Fernandez R. J.
Published: December 2017

The variability of three methods of calculating pulmonary capillary blood flow (Qc) and pulmonary tissue plus capillary blood volume (Vt) during rebreathing was assessed in normal humans by using as markers acetylene, ethyl iodide, and dimethyl ether. The methods of analysis were as follows. Method I, the timing of the disappearance curves of the soluble gases was corrected by assuming that the C18O-disappearance curve intercepted at unity at time O. Method II, it was assumed that the acetylene Qc calculated by method I was correct; ethyl iodide and dimethyl ether Vt were solved by an equation using the disappearance slopes of these gases and the acetylene Qc value, thereby avoiding dependence on extrapolated intercept values. Method III, Vt was calculated by solving for a unique value of Qc between pairs of disappearance slopes of acetylene and dimethyl ether, acetylene and ethyl iodide, and ethyl iodide and dimethyl ether. Among the three methods, method I gave the most reproducible values for Vt as determined with acetylene or dimethyl ether. Using method I, both acetylene and dimethyl ether were equally acceptable gases for measurement of Vt; acetylene was a better marker for Qc measurements.
Ammonia and IMP in different skeletal muscle fibers after exercise in rats
Authors: Meyer R. A. , Dudley G. A. , Terjung R. L.
Published: December 2017

Adenosine 5'-monophosphate (AMP) deamination, estimated from inosine 5'-monophosphate (IMP) accumulation, was studied in the different skeletal muscle fiber types of untrained rats anesthetized with ether immediately after 4 min of treadmill running at 45 or 60 m/min. The adenylosuccinate synthetase-inhibitor hadacidin was administered (200 mg/kg ip) before exercise to block IMP reamination and, therefore, to provide a better assessment of IMP formation. The increases in blood ammonia after exercise (2.5- and 5-fold, respectively) were highly correlated (r = 0.93) with the increases in blood lactate levels (6- and 11-fold). At both speeds, IMP increased in fast-twitch but not in slow-twitch (soleus) muscle. Of the fast muscles, the increase in IMP was greatest (up to 4 mumol/g wet wt) in the white vastus lateralis (fast twitch, glycolytic), intermediate in the plantaris (mixed fibers), and lowest in the red vastus lateralis (fast twitch, oxidative glycolytic). The increases in IMP were coincident with nearly equivalent decreases in ATP. Hadacidin treatment resulted in a greater IMP accumulation after exercise in both fast-twitch types but not in the soleus. The results indicate that fast-twitch muscle fibers, particularly the fast-twitch glycolytic fibers, are the source of the ammonia produced during strenuous exercise.
Platelet count in temporary residents of high altitude
Authors: Sharma S. C.
Published: December 2017

Platelet count was estimated in 65 lowlanders temporarily staying at altitudes above 3,000 m. They were divided in subgroups according to the length of their continuous stay. For comparison, 51 highlanders who were born and reared at high altitude and 48 lowlanders who had never been to an altitude of more than 1,000 m were also studied. Gradually rising counts becoming highly significant (P < 0.001) as compared to the lowlanders after 31 days of stay and stabilizing close to the values in highlanders after 181 days were noted. The significance of these findings in the light of existing knowledge is discussed
End points of lactate and glucose metabolism after exhausting exercise
Authors: Brooks G. A. , Gaesser G. A.
Published: December 2017

To determine the extent of metabolite oxidation, rats were injected with [U-14C]lactate, -glucose, or -bicarbonate (n = 5, each) during rest or after continuous (CE) and intermittent (IE) exercises to exhaustion. Tissue analyses of resting rats, or rats killed following CE and IE and pulse injection with [14C]lactate or -glucose (n = 72, each), were used to determine the metabolic pathways of these two substrates. Oxygen consumption (VO2) declined rapidly for the first 15 min after exercise; thereafter, VO2 declined slowly and remained elevated above resting levels for 120 min. The slow phase of decline in VO2 during recovery did not coincide with lactate removal, which occurred within 15 min. Two-dimensional radiochromatograms produced from blood, kidney, liver, skeletal muscle, and heart indicated a rapid incorporation of 14C into several amino acid pools, including alanine, glutamine, glutamate, and aspartate. Four-hour postexercise recoveries (means of CE and IE) of injected [14C]lactate were lactate (0.75%), glucose (0.52%), protein (8.57%), glycogen (18.30%), CO2 (45.18%), and HCO3- (17.72%). Greater (P < 0.05) incorporation of 14C into protein and glycogen constituents after exercise, compared with rest, was demonstrated. Incorporation of [14C]lactate into glycogen represented a significant but only minor fraction of the metabolism of lactate after exhausting exercise. It is suggested that classical explanations of excess postexercise O2 consumption (i.e., "O2 debt") are too simplistic.
Thermal responses in humans exposed to cold hyperbaric helium-oxygen
Authors: Piantadosi C. A. , Thalmann E. D.
Published: December 2017

The relationship of metabolic heat production to skin and core temperatures, cutaneous heat flow, and respiratory heat loss was measured in 10 male subjects cooled in hyperbaric helium at 20.7 ATA and 15 or 20 degrees C for 60-120 min. Under these conditions, metabolic heat production tended to compensate for the sum of convective and radiant heat losses from the skin but did not increase sufficiently to compensate for additional respiratory heat losses. There was a positive correlation between respiratory heat loss and fall in rectal temperature. Individual variability in ventilatory response to cold hyperbaric helium exposure as shown by a wide range of minute ventilation-to-oxygen consumption ratios (VE/VO2) was similar to that reported during cold water immersion. Subjects with high VE/VO2 had low mean physiological shell insulation values and lost more heat through the skin as well as through the respiratory tract than subjects with low VE/VO2.