This study compared metabolic and cardiopulmonary responses to incremental supine and upright sitting arm crank ergometry (ACE) in nine men with spinal cord injured paraplegia ranging from T1-T5. Both tests consisted of continuous graded ACE from rest to volitional fatigue on a modified electronically braked cycle ergometer with the work ...

This investigation was designed to describe alterations in O2 uptake (VO2) and tension development in a contracting in situ gastrocnemious-plantaris muscle preparation during three conditions of reduced O2 delivery [arterial O2 concentration X blood flow (Q)]. The three conditions, hypoxemia (H), ischemia (I), and anemia (A), were matched for O2 ...

The purpose of the present study was to investigate the contribution of ventilation to arterial O2 desaturation during maximal exercise. Nine untrained subjects and 22 trained long-distance runners [age 18-36 yr, maximal O2 uptake (VO2max) 48-74 ml.min-1 x kg-1] volunteered to participate in the study. The subjects performed an incremental ...

We have shown previously that continuous fetal breathing can be induced by 100% O2 alone or combined with umbilical cord occlusion (Baier, Hasan, Cates, Hooper, Nowaczyk & Rigatto, 1990). To know whether it could also be induced by lower O2 concentrations plus cord occlusion, we studied 9 chronically instrumented fetal ...

To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg ...

1. Recently it was suggested that submaximal cardiac output (Q) could vary in response to changes in arterial O2 concentration (Ca,O2), so that arterial O2 delivery (Qa,O2 = Q x Ca,O2, in ml min-1) is kept constant. 2. This hypothesis was tested on eight healthy male subjects, at rest and ...

We compared face immersion and exercise stress testing by diving and swimming as screening methods for arrhythmias induced by immersion in water. The subjects were 64 children with various arrhythmias who were tested using 5 methods: diving, swimming, face immersion in 25 degrees C water, face immersion in 6 degrees ...

Low-flow continuous oxygen can lead to significant improvement in exercise capacity in selected patients with stable hypoxemic pulmonary disease. Although the mechanisms of improvement are incompletely understood, two tenable hypotheses are (1) the relief of hypoxic pulmonary vasoconstriction and (2) improved peripheral oxygen delivery. This prospective study was performed to ...

To measure the response time of the peripheral chemoreceptors, we studied 13 preterm infants [birth weight 1602 +/- 230 g (mean +/- SEM); gestational age 31 +/- 1 wk; postnatal age 15 +/- 1 d] during inhalation of 21% O2 (15 +/- 5 s) followed by 100% O2 (1 min). ...

Fetal peripheral chemoreceptor responses to arterial O2 saturation and changes in PCO2 have not yet been quantitated. In 24 late-term chronically instrumented fetal sheep, we measured the heart rate response to acute hypoxemia induced by uterine arterial occlusion at various resting O2 saturations (25-86%) and at induced reductions and increases ...

In order to evaluate the value of the inspiratory to end-tidal oxygen concentration difference (Io2-E'o2) as a monitor during general anaesthesia, we studied 40 orthopaedic patients allocated randomly to four groups: anaesthesia with enflurane or isoflurane in nitrous oxide with either spontaneous or controlled ventilation. (Io2-E'o2) followed an asymptotically increasing ...

In normal subjects, exercise widens the alveolar-arterial PO2 difference (P[A-a]O2) despite a more uniform topographic distribution of ventilation-perfusion (VA/Q) ratios. While part of the increase in P(A-a)O2 (especially during heavy exercise) is due to diffusion limitation, a considerable amount is caused by an increase in VA/Q mismatch as detected by ...

Superoxide anion release (O2-) after stimulation with phorbol myristate acetate was measured in alveolar macrophages (AM) obtained by bronchoalveolar lavage and in blood monocytes from 47 patients with diffuse interstitial lung disease: idiopathic pulmonary fibrosis (N = 15), hypersensitivity pneumonitis (N = 7), pneumoconiosis (N = 6) and sarcoidosis (N ...

We have studied the conditions under which a perfluorocarbon emulsion of perfluorooctyl bromide (PFOB; Alliance Pharmaceutical, San Diego, CA) enhances tissue O2 delivery. Measurements of retinal tissue O2 tension (PO2) were made in anesthetized, artificially respirated, dark-adapted, normovolemic cats before, during, and after the infusion of three successive doses of ...

To quantitate the O2 cost of maximal exercise hyperpnea, we required eight healthy adult subjects to mimic, at rest, the important mechanical components of submaximal and maximal exercise hyperpnea. Expired minute ventilation (VE), transpulmonary and transdiaphragmatic (Pdi) pressures, and end-expiratory lung volume (EELV) were measured during exercise at 70 and ...

The factors limiting maximal oxygen consumption (VO2max) in humans are analyzed according to a multifactorial model derived from the O2 conductance equation. The alveolar ventilation (VA) and lung O2 transfer (GL) are not considered to be limiting, at least at sea level in healthy subjects, because changes in VA and/or ...

The standard treatment for cerebral arterial gas embolism (CAGE) is an initial recompression to 6 atm abs on air for 30 min followed by oxygen breathing at 2.8 and 1.9 atm abs. It has been suggested that initial recompression to 2.8 atm abs on O2 may be as beneficial, thus ...

We addressed two questions concerned with the metabolic cost and performance of respiratory muscles in healthy young subjects during exercise: 1) does exercise hyperpnea ever attain a "critical useful level"? and 2) is the work of breathing (WV) at maximum O2 uptake (VO2max) fatiguing to the respiratory muscles? During progressive ...

The VO2 response to a step change in work rate resembles a first order exponential function. This suggests that a single site of the many which link ATP demand to VO2 is limiting. The location of this site is controversial. Some authors suggest that O2 delivery regulates the VO2 response. ...

STUDY SETTINGS AND INTERVENTIONS: Sixty individuals complaining of dyspnea on exertion, but with normal spirometry and lung volumes and normal chest roentgenograms were reviewed for this study. These individuals were selected from a large group of outpatients (552 individuals over a seven-year period) who were referred to our laboratory for ...

It is known that the O2 COV in COLD is high; O2 administration to these patients lowers airway resistance, a major determinant of the COV. Thus, O2 should lower the COV. We measured the COV in ten stable COLD patients and five normal control subjects breathing room air and 30 ...

The metabolic rates of freely diving Weddell seals were measured using modern methods of on-line computer analysis coupled to oxygen consumption instrumentation. Oxygen consumption values were collected during sleep, resting periods while awake and during diving periods with the seals breathing at the surface of the water in an experimental ...

1. The forced oscillation technique is an effort-independent method used to characterize the mechanical impedance of the respiratory system. To support the hypothesis that non-invasive partitioning of total pulmonary resistance is possible by this technique, impedance was measured during air breathing and after equilibration with a mixture of 80% helium ...

This study was undertaken to determine the effect of high intensity exercise on the time course and magnitude of excess postexercise O2 consumption (EPOC). Six healthy male subjects performed three intermittent 2-min exercise bouts on a cycle ergometer at 108% of VO2max with 3-min rest periods (3 x 2 min). ...

This commentary demonstrates that VO2max depends, in part, on diffusive O2 transport; exercise hyperemia is necessary but not sufficient. Experiments and new mathematical models place the principal site of resistance to O2 diffusion between the surface of a red cell and the sarcolemma. The large drop in PO2 over this ...

Just what determines maximum O2 uptake (VO2max) has been the subject of much study and discussion over the years, with agreement among investigators still beyond reach. However, the evidence that in normal man VO2max is limited generally by the supply of O2 is substantial. Turning to the well-known steps of ...

Patients with cystic fibrosis (CF) and advanced pulmonary disease have pulmonary limitation of exercise, often associated with arterial oxygen desaturation. Improving oxygenation during exercise by providing supplemental oxygen may improve exercise performance in these patients. To test this, we performed graded exercise stress tests in 22 CF patients with severe ...

Brain tissue O2 tension (pO2) was measured in brainstem slices of adult and neonatal rats using carbon fiber polarographic microelectrodes. These studies were performed in order to examine the relation between pO2 and a variety of experimental conditions including temperature, distance from slice surface, brain region, animal age, tissue thickness ...

1. In response to an acute exercise-induced metabolic acidosis, the fall of arterial pH is constrained by the magnitude of the compensatory hyperventilation. To determine the role of the carotid bodies in this regulatory process, subjects performed prolonged (24 min) square-wave cycle ergometry from a background of unloaded cycling at ...

We have developed an exercise designed to give students practice calculating arterial O2 content, O2 delivery, physiological dead space, dead space and alveolar ventilation, and alveolar partial pressure of O2 and CO2. The exercise is in the form of a "murder mystery" in which students are required to make these ...

This study was undertaken to determine the effect of fasting on the magnitude and time course of the excess postexercise O2 consumption (EPOC). Six lean untrained subjects were studied in the fasted state for 7 h after a previous strenuous exercise bout (80 min at 75% of maximal O2 uptake) ...

The authors' aim was to examine direct cardiac responses to isoflurane, enflurane and halothane, as altered during mild hypoxia by the substitution of nitrogen (N2) for oxygen (O2), and additionally by the substitution of nitrous oxide (N2O) for N2. Heart rate, atrioventricular conduction time, left ventricular pressure (LVP), peak positive ...

Our objective was to determine whether the chemoreflex from human muscle is elicited by small graded reductions in muscle blood flow (MBF) during mild exercise or whether this reflex has an obvious threshold associated with large changes in femoral venous lactate and H+ levels (i.e., as in dogs with high ...

Cerebral blood flow and O2 delivery during exercise are important for well-being at altitude but have not been studied. We expected flow to increase on arrival at altitude and then to fall as O2 saturation and hemoglobin increased, thereby maintaining cerebral O2 delivery. We used Doppler ultrasound to measure internal ...

The effect of brain transection at two levels on cardiovascular responses to forced submergence has been investigated in ducks. Compared with intact ducks, neither decerebration nor brain stem transection at the rostral mesencephalic (RM) level had any effect on development of diving bradycardia, or heart rate at the end of ...

The objectives of these experiments were 1) to describe the effect of maximum treadmill exercise on gas exchange, arterial blood gases, and arterial blood oxygenation in rats acclimated for 3 wk to simulated altitude (SA, barometric pressure 370-380 Torr) and 2) to determine the contribution of acid-base changes to the ...

The objective of the present experiments was to determine whether prevention or moderation of exercise acidosis would influence arterial blood oxygenation and exercise capacity in hypoxia. The effect of administration of 0.3 M NaHCO3 (3 ml/100 g) on maximum O2 uptake (VO2max) and arterial blood oxygenation was determined in rats ...

After exercise, there is an increase in O2 consumption termed the excess postexercise O2 consumption (EPOC). In this study, we have examined the effect of exercise intensity on the time course and magnitude of EPOC. Six healthy male subjects exercised on separate days for 80 minutes at 29%, 50%, and ...

The present study was carried out to examine diaphragmatic O2 extraction and lactate and ammonia production during prolonged exhaustive exercise. Experiments were performed on nine healthy exercise-conditioned ponies in which catheters had been implanted in the phrenic vein previously. Blood-gas variables and lactate and ammonia concentrations were determined on simultaneously ...

We have shown that in patients with COPD, myocardial efficiency during exercise is enhanced following acute elevations of plasma phosphate (Pi). A decrease in Hb-O2 affinity (increase in P50) was not responsible for the improvement. We postulated that the physiologic benefit was due to the acute reversal of a subclinical ...

We have previously reported that O2 in the breathing gas mixture contributed significantly to the risk of decompression sickness (DCS) in rats after rapid (less than 10 s) decompression to the surface from depth. The rate of O2 uptake was extremely fast (less than 1 min estimated for equilibrium after ...

Examination of the alveolar-to-arterial O2 tension (A-a PO2 difference) provides a method of examining the efficiency of pulmonary gas exchange during exercise. At present, considerable confusion exists as to the exact pattern of the A-a PO2 difference during incremental exercise. We tested the hypothesis that the A-a PO2 difference during ...

The mechanisms leading to rapid changes in arterial blood gas values soon after exercise ends have not been well established. To further study these phenomena, we exercised seven normal male volunteers to exhaustion on a cycle ergometer with a 25-W/min ramped protocol measuring arterial blood gas values, and breath-by-breath gas ...

Resting O2 consumption, net mechanical efficiency during cycling exercise and excess postexercise O2 consumption (EPOC) was measured in 15 army cadets after 3 or 4 days of continuous simulated combat exercises (estimated energy demand: 40 MJ day-1), no organized sleep and virtually no food intake (stress experiment). They exercised for ...

Each of three monkeys was trained to slow its heart, to exercise (lift weights), and to attenuate the tachycardia of exercise by combining these two skills. During all experiments, heart rate, stroke volume, intra-arterial blood pressure, O2 consumption, and CO2 production were recorded on a beat-to-beat basis. All animals reliably ...

The effect of the curvature of the O2 equilibrium curve (OEC), in the range between mixed venous and alveolar PO2, on alveolar O2 uptake was quantitatively investigated in a simple homogeneous lung model. The O2 uptake achieved with a linear OEC (Mlin) was subtracted from the O2 uptake (M) attained ...

We evaluated the combined effects of reduced O2 (12%) and graded ergometer exercise (10, 70, and 140 W) on the performance of a psychomotor task. Six men participated in two test sessions each. Each session began with the baseline data (air) and finished with exposure data (12% or 21%, random, ...

Arterial O2 delivery during short-term submaximal exercise falls on arrival at high altitude but thereafter remains constant. As arterial O2 content increases with acclimatization, blood flow falls. We evaluated several factors that could influence O2 delivery during more prolonged submaximal exercise after acclimatization at 4,300 m. Seven men (23 +/- ...

The effects of sustained mesenteric nerve stimulation on intestinal oxygenation were determined in 3- and 35-day-old swine. Studies were conducted in pentobarbital-anesthetized animals during free-flow or constant-flow perfusion. Square-wave stimuli sufficient to induce maximal resistance vessel constriction were applied to postganglionic periarterial mesenteric nerves and each stimulation was sustained until ...

Myoglobin (Mb) saturation in individual subepicardial myocytes was determined by cryospectroscopy in dogs, cats, ferrets, rabbits, and rats. Mb saturation within 800 microns of the epicardium is not affected by quick freezing or absorption of light by cytochromes. The PO2 in equilibrium with Mb (PMbO2) was calculated from the Mb ...