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Publisher Summary This chapter discusses ventilation–perfusion inhomogeneity and efficiency of alveolar gas exchange. Methods have been developed for deriving a great deal of information about the distributions of ventilation–perfusion ratios, which must be present in life in both the normal and diseased lung. One way of approaching a distribution of ventilation–perfusion ratios is to build it up from separate distributions of ventilation and blood flow. Various indices such as the alveolar–arterial PO2 difference, physiologic dead space, and physiologic shunt have been used very successfully to assess the impairment of gas exchange caused by ventilation–perfusion inequality in normal and diseased lungs. The effect of this pure ventilation–perfusion inequality is to decrease both the oxygen uptake and carbon dioxide output of the lung. Analysis of the behavior of gases of different solubilities in lung models with ventilation–perfusion inequality indicates that gases of moderate solubility always have their transfer impaired most by ventilation–perfusion inequality and that gases of very low or very high solubility are less affected.

Seven normal subjects each performed three transitions to a subanaerobic threshold work rate on a cycle ergometer: 1) from rest, 2) from a low work rate (both at 60 rpm), and 3) from a low work rate at 40 rpm to the high work rate at 80 rpm. Oxygen uptake (VO2), carbon dioxide output (VCO2), and ventilation (VE) were computed breath-by-breath and response kinetics extracted. The mean half-times of VO2, VCO2, and VE were 32, 44, and 49 s, respectively, and were not appreciably affected by the prior exercise or by variation of pedal rate. The kinetics of VE was highly correlated with VCO2 (r = 0.94), with VCO2 leading VE, providing further description of the relation of the exercise hyperpnea to CO2 flow to the lungs.

SUMMARY Equations have been derived to determine the alveolar gas concentrations which occur when the Magill (Mapleson A) circuit is used with a low fresh gas flow. Alveolar oxygen and carbon dioxide concentrations are determined by the fresh gas flow and composition, carbon dioxide output and oxygen uptake. Gas mixing within the circuit and alterations in the inspired gas concentrations do not affect the final equilibrium. If oxygen uptake and carbon dioxide output are constant, the alveolar gas concentrations are unaffected by alterations in ventilation.

A system is described for measuring carbon dioxide output and alveolar carbon dioxide concentration in the neonate and for deriving the volume of alveolar ventilation. Air is drawn through a soft rubber face mask applied loosely to the face so that all expired gas is entrained. A fraction of the flow is sampled by an infra-red analyser, the signal from which is integrated to provide a measure of carbon dioxide output. Alveolar carbon dioxide concentration is measured by continuous sampling of expired gas through a nasal catheter. The response time of the catheter-analyser system is 140 ms. In 20 healthy 1-day-old neonates the mean carbon dioxide excretion was 5.86 ml/min. kg-1 (STPD) and the mean alveolar PCO2 was 4.85 kPa. From these measurements mean alveolar ventilation 147 ml/min. kg-1 (BTPS) was calculated. These results are similar to those obtained by other methods.

A continuous, non-invasive system is described for measuring oxygen uptake ( V • O 2 ) and carbon dioxide output ( V • C O 2 ) in mechanically ventilated patients. Inspiratory and mixed expiratory gas samples were pumped through fine-bore tubing to a remote mass spectrometer for analysis. The expiratory flow transducer of a Siemens Servo 900B ventilator was used for expiratory flow measurement and inspiratory flow was calculated from this using the Haldane transformation. A desk-top computer calculated V • O 2 , V • C O 2 and respiratory quotient. The system has been validated against standard methods of gas analysis and flow measurement ( V • O 2 mean difference −lOml min−1: SD9.13; V • C O 2 mean difference 8.12ml min−1: SD4.66). Comparison with Douglas bag measurements in patients has been made ( V • O 2 mean difference 10.7ml min−1: SD9.8; V • C O 2 mean difference −1.07ml min−1: SD4.7).

This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( $$R = \dot V_{{\text{CO}}_{\text{2}} } /\dot V_{{\text{O}}_{\text{2}} } $$ ) as a predictor of maximum oxygen uptake ( $$\dot V_{{\text{O}}_{{\text{2}} {\text{max}}} } $$ ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( $$\dot V_{{\text{O}}_{\text{2}} } $$ ), $$\dot V_{{\text{O}}_{{\text{2}} {\text{max}}} } $$ or maximum functional heart rate (FHRmax) were found between tests. Mean exercise carbon dioxide output ( $$\dot V_{{\text{CO}}_{\text{2}} } $$ ) and R were significantly lower than normal after the low CHO diet (bothp

A new method is described for measuring the rate of carbon dioxide production, and hence for estimating energy expenditure, in preterm infants receiving assisted ventilation. In a validation study, the mean error in carbon dioxide measurement was 1.9%. Measurements were made, over a 45-min period, on 11 sick, ventilated subjects and carbon dioxide production rate was 5.2 ± 0.7 (SD) ml/min·kg body weight. We suggest that continuous monitoring of carbon dioxide output will contribute to the clinical assessment of the effects of different ventilator settings on pulmonary gas exchange and that estimated values for energy expenditure will be of value in nutritional studies on sick ventilated infants.

1. The effect of mental arithmetic tasks on ventilation, breathing pattern, oxygen intake and carbon dioxide output was studied during air breathing and carbon dioxide rebreathing in healthy subjects. 2. Ventilation and breathing frequency increased significantly on performance of the task during 4 min air breathing and 4 min rebreathing; tidal volume was unchanged. The slopes of the ventilatory, frequency and tidal volume responses to carbon dioxide changed little during task performance. 3. During 15 min air breathing, oxygen intake was unchanged with task performance. Carbon dioxide output increased significantly with task performance, as a result of wash-out of carbon dioxide from body stores by the increased ventilation. 4. Mental arithmetic had no effect on the coefficients of variation of the slope and position variables of the ventilatory, frequency and tidal volume responses to carbon dioxide. It is concluded that task performance does not improve the reproducibility of these responses.

Immediate effects of inhalation of 100% oxygen at one atmosphere on respiration in man were studied. Average increases of 6.4, 6.5 and 11.5%, respectively, were obtained in ventilation volume, carb...

The effect of the mono- and di-nitrophenols and certain related compounds has been determined on the rate of oxygen consumption, the rate of carbon dioxide output and the rectal temperature of the Wistar albino rat. Of the compounds examined, only 2:4-dinitrophenol and its derivative, 3:5-dinitro-o-cresol, stimulated metabolic rate. 2-Nitrophenol and 2:3-, 2:6-, and 3:5-dinitrophenol produced no change in metabolic rate; 3-nitrophenol and 2:5-dinitrophenol had no action on carbon dioxide production although they caused a decrease in oxygen consumption. 4-Nitrophenol and 3:4-dinitrophenol increased only the rate of carbon dioxide output; 2-amino-4-nitrophenol increased the rate of carbon dioxide output and decreased the rate of oxygen consumption; 4-amino-2-nitrophenol caused depression of metabolic rate. It was confirmed that neither rectal temperature nor carbon dioxide output could replace rate of oxygen consumption as a reliable index of metabolic stimulant action. An apparatus is described which facilitates measurement of the oxygen consumption of small mammals.

Publisher Summary This chapter discusses the electrode measurements of carbon dioxide. The major applications of carbon dioxide electrodes have been in the field of clinical biochemistry and physiology, but they can also be successfully used for many microbiological purposes. The in situ use of the electrode to measure carbon dioxide concentrations in growing batch cultures would present two difficulties; first, that of sterilization and, secondly, that arising from the dependence of the partial pressure of CO 2 on the pH of the medium. The carbon dioxide electrode can be more readily applied in controlled pH cultures. The partial pressure of carbon dioxide in the effluent gas phase is equal to that within the culture vessel, and the electrode can be used in the gas phase in a non-sterile position downstream from the culture itself. Measurements of the rates of carbon dioxide output also require accurate measurement and control of the rate of gas flow into the apparatus.

Summary. Spirometric investigations of the respiratory gaseous exchange during resting, not basal, conditions and the recovery after a 70 yard sprint are reported. It is shown that around 10 minutes after connection with the spirometer fairly constant values for oxygen uptake and carbon dioxide output were obtained. These resting values were regained shortly after the exercise. The time used for elimination of excess carbon dioxide was longer and more constant, and showed greater interindividual differences than the time required for covering the oxygen debt. Well trained subjects with good results in track competitions showed the shortest recovery times. Trained subjects with fair to poor results had recovery times overlapping the recovery times of untrained subjects in good physical condition.

Crystal violet, when incorporated in culture media of mycelial felts of Fusarium culmorum, reduced, or in certain cases stopped, the uptake of nitrate-nitrogen, protein and peptide synthesis, and carbon dioxide output by the mycelial mats.

An apparatus is described in which the air exhaled by experimental animals is continuously extracted, permitting the collection of successive samples for the determination of volatile substances excreted by this route. Carbon dioxide output may be determined simultaneously by using a second extractor. The efficiency of the method has been checked with known concentrations of trichloroethylene and carbon dioxide in air.

IN assessing changes of vital function during electronarcosis, we measured oxygen consumption and carbon dioxide output in an experiment in rabbits. The measured values were considered an important index for the evaluation of metabolic changes during electronarcosis.

Blood flow, oxygen consumption, and carbon dioxide output were studied in the slow (latissimus dorsi anterior-ALD) and fast (latissimus dorsi posterior-PLD) muscles in young chicks and adult leghorns and in slow (soleus) and fast (gastrocnemius) muscles in cats at rest and after tetanic contraction. Resting blood flow, measured by a drop counter applied to the venous outflow, was in adult leghorns three times higher in slow muscles as compared with fast muscles. Similar changes were also found in oxygen consumption and CO 2 output. In the cat soleus, blood flow at rest was up to ten times higher than in the gastrocnemius, and the same difference was observed in oxygen consumption and CO 2 output. The respective A-V differences were not significantly different. The differences in blood flow are established during development and appear considerably later than the differences in the speed of contraction and enzyme activity. In 8-day-old chicks (in which the enzyme pattern already resembles that in adult birds; i.e., oxidative enzymes have high activities in slow, glycolytic in fast muscles) blood flow measured by 133 Xe clearance did not differ in the two types of muscle. In 10-day-old chicks a slightly higher blood flow was observed in the slow as compared with the fast muscles. In 28-day-old chicks, flow in slow muscles was 60% higher, and this pattern is also seen in adult leghorns. During the postcontraction period (after 20–30 sec tetanic contraction) blood flow was always increased in fast muscles. In slow muscles the increase in flow measured by 133 Xe clearance was similar to that in fast muscles only in 10-day-old chicks. The increase was much smaller in 28-day-old chicks, and altogether absent in adults. The flow measured by drop counter was slightly increased in the postcontraction period even in slow muscles; however, this increase was significantly smaller than in fast muscles.

Carbon dioxide retention in chronic lung disease is often attributed to "alveolar hypoventilation." This designation is misleading because the patients are usually moving abnormally large amounts of air into their alveoli, and it diverts attention from the real cause: ventilation-perfusion inequality. Recent work using lung models shows that this mechanism can interfere dramatically with carbon dioxide elimination. Indeed, pure uncompensated ventilation-perfusion inequality often impairs carbon dioxide output almost as much as oxygen uptake. Carbon dioxide retention is particularly likely to occur when one lung region inspires gas from another, as in centrilobular emphysema. Treatment should be directed at the cause of the ventilation-perfusion inequality as well as at increasing the amount of air moving into the alveoli.

CARBONIC anhydrase which catalyses the reversible reaction H2CO3 ⇄ CO2 + H2O is present in large concentrations in the red blood corpuscles and some cells of gastric mucosa of mammals. This enzyme plays an important part in accelerating the carbon dioxide output in the lungs; it appears also to promote the formation of hydrochloric acid by the parietal cells of gastric mucosa1.

These experiments were undertaken at suggestion of Prof. Sherrington, to attempt a determination of the amount of energy necessary for maintaining tonus is skeletal muscle. The carbon dioxide output has been measured in decerebrate cats, and its amount compared with the amount given off by the same animal after procedures that abolish the tonus of the decerebrate preparation. These procedures have consisted of decapitation and intravenous injection of curare. The pulmonary ventilation was uniform throughout, as artificial respiration was carried out by means of a pump.

The author, while conducting experiments on insect metabolism, measured the metabolic rate of two species of insects under the influence of thyroid and thyroxin feeding. The forms used were the wasp, Polistes pallipes, and the roach, Periplaneta australasiae. Armour's desiccated thyroid was fed mixed with honey. Squibb's thyroxin crystals were also given in a honey mixture. Carbon dioxide output was measured per hour before and after feeding. In most cases of thyroid feeding results were not pronounced enough to be considered of consequence. In one case in which one wasp fed for approximately 4 minutes (a comparatively long time) the basal metabolic rate increased to more than twice normal for the first 2 hours following feeding. After the 4th hour the rate had again returned to normal. The very slight increases and decreases obtained with feeding desiccated thyroid to roaches were not consequential. It was assumed that proportionately a very great amount of desiccated thyroid gland was necessary to produ...

RECENT work in this Laboratory1 has shown that succinic acid may not only inhibit oxidative processes, as shown by earlier workers2, but also it may be actually toxic to plant material. Succinate supplied to respiring disks of apple peel (in a suitable buffer system at pH 4.1) at concentrations greater than about 0.025 M reduces oxygen uptake and carbon dioxide output, and in a comparatively short time the respiration falls practically to zero and the tissue becomes brown and ‘dead’. At this external concentration of succinate the internal concentration is less than 0.001 M.

THE phenomenon of climacteric rise in respiration of ripening fruits is not fully understood. Blackman and Parija1 explained the rise in respiratory activity in apples on the assumption that in the senescent stage a lowering of ” hydrolysis-resistance” occurs leading to a greater production of effective substrate for respiration. Kidd and West2 have attributed the initial increase in carbon dioxide output during senescence to the action of some ” protoplasmic factor”. Gustafson3 has demonstrated that the rate of respiration is very greatly influenced by the pH of the cell-sap, lower values of pH being usually associated with higher rates of respiration, and in a later communication4 suggests that the climacteric rise is probably due to a lowering of pH, of the cell-sap.

Ball, Dyke and Wilkins1 and Wilkins2 developed an apparatus, incorporating an infra-red gas analyser (Grubb-Parsons, S.B.1), for continuously estimating the rate of carbon dioxide metabolism of plant tissue maintained under constant external conditions for 5–10 days. Using this apparatus the rate of carbon dioxide output of individual adult cockroaches was determined. The insects were kept in 12 : 12 hr. alternations of light and darkness and, at the commencement of an experiment., were transferred to a small flask which was placed in darkness and at a constant temperature at the end of a light period. The records presented here were derived from one insect, but five other cockroaches gave closely similar results.

Experiments designed to compare the energy metabolism of mother and child just previous to and immediately following parturition were carried out with the bed calorimeter. Three subjects were secured through the out-patient department of the McLean Lying-in Hospital. They were cared for in the New England Deaconess Hospital near the laboratory and were kept on a carefully regulated diet, which, except for the day of parturition and one or two days thereafter, was essentially the same throughout for each case. Early in the morning before breakfast was taken, the subjects were brought to the laboratory (in an ambulance when necessary) and were placed in the calorimeter for periods of two or three hours during which hourly determinations of the carbon dioxide output, the oxygen absorption, the heat elimination and the heat production were made.The heat production was calculated also by the Zuntz method from the amount of nitrogen in the urine, the carbon in the expired air and the oxygen absorbed. A very sat...

A thermometer reaching the center of an experimental thermally-insulated lime container, placed in the exhalation limb of a Foregger circle system, was used to measure the carbon dioxide (C02) output of a paralyzed anesthetized patient. Fresh gas inflow, ventilatory rate, and tidal volume were standard. Temperature rise in the canister was found closely related to CO2 output, which was calculated, after a period of stabilization, with the help of a nomogram. The results with this simple instrument coincided with those of more complex procedures.

Carbon dioxide output from lichen-heath, low shrub tundra, and Eriophorum vaginatum tussock tundra was measured several times in July and August at five locations in northcentral Alaska. Carbon dioxide evolution was lowest in the shrub tundra, intermediate in the lichen-heath, and highest in tussock and intertussock areas. Seasonal averages were 2.3 g CO2 * m-2 ? d-' from tussock tundra, 1.4 g CO2 * m-2 * d-' from shrub tundra, and 1.7 g C02 m-2 * d-' from lichen-heath. The sites differed in carbon dioxide output in complex ways. The carbon dioxide output declined from late July through August. Rough carbon budgets indicate that lichen-heath is accumulating carbon slowly and tussock tundra rapidly. Shrub tundra should also be accumulating carbon rapidly, but the current standing crops of carbon do not support this conclusion.

Measurements of minute and alveolar ventilation (VE and VA), respiratory frequency, end-tidal carbon dioxide concentration (E'CO2), deadspace (VD) and carbon dioxide output (VCO2) were made in 22 anaesthetized infants and young children during spontaneous (SV) and intermittent positive pressure ventilation (IPPV). In the children who had been given an opioid premedication, E'CO2 concentrations were significantly greater during SV than the predetermined value set for IPPV. In infants premedicated with atropine alone, E'CO2 during SV was only slightly greater than during IPPV, and VA was not changed. A mean tidal volume (VT) of 9.8 +/- 2.5 ml kg-1, and a mean VE of between 225 and 250 ml min-1 kg-1, were required to produce E'CO2 4.5% during IPPV. Despite a decrease in respiratory frequency, VD/VT and VD per minute were both decreased by IPPV in infants. VCO2 was unchanged in both groups. The decrease in wasted ventilation seen during IPPV in infants supports its use in clinical practice.

The purpose of these experiments was to determine the effects of oral caffeine ingestion on the kinetics of oxygen uptake (VO2), expired carbon dioxide output (VCO2), and expired ventilation (VE) in the transition from rest to exercise. Nine male subjects underwent three repetitions of constant load cycle ergometer exercise (approximately 80% ventilatory threshold) on two occasions. A single blind experimental procedure was followed, with one trial being performed 60 min after the subject ingested caffeine (7 mg X kg-1), while the second trial required the subject to ingest a placebo with the treatment order being counterbalanced. Ventilation and gas exchange were monitored by open circuit techniques. The data from three repetitions of the same protocol were pooled and modeled with a single-component exponential function incorporating a time delay: (formula; see text) Kinetic analysis of VO2 revealed no significant difference (P greater than 0.05) in the mean response time between treatments. In contrast, the mean response time for VCO2 and VE were longer (P less than 0.05) for the caffeine trial when compared to the control experiment. These data suggest that caffeine will influence both VCO2 and VE kinetics in the transition from rest to work and should be considered by investigators when planning experiments to study ventilatory and gas exchange kinetics during exercise.