Respiratory Gas Exchange Measurements Research Articles

Indications and limits of the exercise test in chronic heart failure.

Assessment of exercise capacity has been widely used in the evaluation of chronic heart failure (CHF), both to define the severity of the syndrome and to assess the changes induced by therapy. Various exercise tests and protocols can be used. The simple stress test using the exercise bicycle or the treadmill can give useful indications only in patients with severe or lower functional reductions. Maximum exercise duration usually depends on the patient's and the physician's motivation. The addition of respiratory gas exchange measurements, maximum oxygen consumption (VO(2)) or anaerobic threshold, increases the exactness of the assessment of the exercise limitation in CHF. VO(2) maximum provides an objective marker of aerobic capacity and it is biased by neither the patient nor the physician. This technique, however, requires the patient to exercise to exhaustion, and it is somewhat subjective and not indicative of normal daily exercise routine. The anaerobic threshold is a useful way of evaluating adaptability to submaximal efforts and the impact of the therapy on the daily performance. Nevertheless, it is significantly influenced by the fitness level and it has a reduced prognostic capability compared to VO(2) maximum. Submaximal exercise tests discriminate particularly between patients with severe CHF. The major limits are the influence of the patient's motivation and its limited validation in terms of reproducibility and prediction in controlled surveys.

Dopexamine Hydrochloride in Septic Shock

To test whether dopexamine hydrochloride, by its beta 2-adrenoreceptor and dopaminergic 1 (DA1) and dopaminergic 2 (DA2) agonistic properties, can improve oxygen consumption (VO2) in hyperdynamic patients with septic shock. Prospective, single-cohort study. ICU, university hospital. Twenty-nine postoperative, hemodynamically stabilized, hyperdynamic patients with septic shock. Short-term application (30 min) of dopexamine hydrochloride at a dose of 2 microgram/kg/min. Complete hemodynamic profile with O2 transport-related variables at baseline, 30 min after starting the dopexamine infusion, and 30 min after stopping the infusion. The dopexamine infusion resulted in significant increases in cardiac index (17%) (p<0.001) and O2 delivery (DO2) (16%) (p<0.001). VO2 increased slightly but significantly about 4% (p<0.001) by respiratory gas exchange measurements and 9% (p<0.001) by cardiovascular Fick calculations. The O2 extraction ratio decreased about 8% (0.001). The addition of dopexamine hydrochloride at a dose of 2 microgram/kg/min resulted in significant increases of DO2 and to a lesser extent VO2. Much of the global DO2 increase was not utilized, because O2 extraction ratio decreased. Direct calorigenic effects of dopexamine and an increase in myocardial VO2 likely account for a large portion of the increase in global VO2. Whether any of the VO2 increase reflects improvement in regions of jeopardized tissue oxygenation remains to be clarified before the definite value of this drug in septic shock can be established.

Method of expired gas collection during cardiopulmonary exercise testing does not affect respiratory gas exchange measurements in patients with heart failure

Cardiopulmonary exercise testing is commonly used to assess patients with heart failure. Analysis of expired gases during exercise requires the use of either a facemask or mouthpiece with nose clip. The authors sought to determine if the method of expired gas collection during exercise testing (facemask or mouthpiece) influences gas exchange measurements in patients with heart failure. Nine patients with heart failure performed two maximal treadmill tests. Expired gases were collected with a facemask in one exercise test and a mouthpiece in the other. There were no significant differences in exercise test duration, peak oxygen uptake, heart rate, respiratory exchange ratio, or perceived exertion during maximal exercise performed with the facemask when compared to the mouthpiece. Test subjects reported that the overall comfort of the facemask was significantly greater than that of the mouthpiece ( P < .02). The method of expired gas collection during cardiopulmonary exercise testing does not significantly affect measures of gas exchange or exercise performance in patients with heart failure. Heart failure patients find the overall comfort of the facemask superior to that of the mouthpiece, but this comfort preference does not affect exercise performance.

Increased leucine flux and leucine oxidation during the luteal phase of the menstrual cycle in women

Possible changes in protein metabolism during the menstrual cycle were examined in eight healthy women who received an intravenous infusion of L-[1-13C]leucine on time during the follicular phase of the menstrual cycle and one time during the luteal phase. Enrichment of plasma [13C]ketoisocaproate and expired 13CO2 were measured to determine leucine flux and oxidation. Continuous respiratory gas exchange measurements were made for the determination of CO2 production, O2 uptake, and energy expenditure. The day of the tests, plasma thyroid hormone concentrations were measured as well as plasma and urinary cortisol. Leucine flux was higher during the luteal than during the follicular phase (2.25 +/- 0.39 vs 2.01 +/- 0.42 mumol.kg-1.min-1; P < 0.01), and leucine oxidation was also increased during the luteal phase [0.52 +/- 0.14 vs. 0.44 +/- 0.05 mumol.kg-1.min-1 (P < 0.05) for luteal and follicular phases, respectively]. Resting energy expenditure was increased during the luteal phase compared with the follicular phase (218 +/- 22 and 199 +/- 12 kJ/h, respectively). Plasma free triiodothyronine (T3) and the ratio triiodothyronine/reverse triiodothyronine (T3/rT3) were both significantly higher during the luteal phase [7.7 +/- 0.6 vs. 7.1 +/- 0.8 and 4.65 +/- 0.80 vs. 3.93 +/- 0.70 for T3 and T3/rT3, respectively (P < 0.05 for both comparisons)]. This study shows small changes in protein metabolism during the menstrual cycle in women, with an increase in oxidative leucine metabolism during the luteal phase. The concomitant increase observed in circulating free T3 raises the possibility that fluctuations in protein metabolism and thyroid hormones throughout the menstrual cycle are causally related.

Acute changes in oxygen consumption and body temperature after burn injury.

This study describes the pattern of oxygen consumption (VO2), rectal temperature (Tr), and acral skin temperature (Tac) in sleeping and resting (awake) burned children nursed in a thermoneutral environment. Measurements of respiratory gas exchange (VO2 and carbon dioxide production (VCO2)) were made using an open circuit, flow through system of indirect calorimetry. Tr and Tac were monitored continuously. Sixteen patients were studied during the first 18 hours after being burned. Three phases of change in VO2, Tr, and Tac are described. The first was a stable period and there was little change from admission values. The second (7-10 hours after burn) was a phase of rapid heat storage. It started with a fall in Tac. Peak values of Tr (38.8-41.1, median 40.0 degrees C) and VO2 (8.5-11.8 ml/min/kg) occurred either in phase 2 or in the later phase 3. At its peak VO2 was 12-61% above values in phase 1. In phase 3, Tac returned towards admission values but Tr and VO2 were variable. These changes suggest that both an increase in metabolic heat production as well as heat conservation at the extremities may be involved in the generation of early fever after a burn.

Metabolic rate at rest and during sleep in a thermoneutral environment.

This study characterised the pattern of oxygen consumption (VO2) in healthy infants and children asleep and awake (at rest) in a thermoneutral environment. Measurement of respiratory gas exchange (VO2 and VCO2) was made using an open circuit flow through system of indirect calorimetry with a specially designed facemask for the collection of exhaled breath. Fifty two healthy subjects aged 4.5 months to 12.8 years were studied for 15-20 minutes; 18 during sleep and 34 at rest (awake). There was a curvilinear relation between VO2 and age in the two groups and children aged 2 years or less had the highest values. The value of VO2 was significantly higher in the awake subjects (12.5-15.0 ml/min/kg compared with 7.5-9.0 ml/min/kg in sleeping children). Comparison of the regression lines after log transformation of these data showed a significant difference in VO2 of resting and sleeping subjects up to the age of 9.5 years.

Influence of Epidural Analgesia upon Postoperative Fatigue

This study examined the effect of epidural analgesia on the development of postoperative fatigue and the ability to ambulate after surgery. Seventeen patients admitted for elective abdominal surgery were randomized to receive postoperative analgesia with a continuous infusion of epidural fentanyl (epidural group) or intermittent intramuscular morphine (non-epidural group). Fatigue was assessed on an analogue scale of 1 (fit) to 10 (fatigued). Steady state measurements of respiratory gas exchange, respiratory rate, tidal volume and heart rate were made before operation and repeated on the third postoperative day. Energy expenditure was calculated from Weir's formula. Ambulatory measurements were made during treadmill walking at a work rate of 20 kpm min-1 (3.3 W). At rest, patients in both groups had a similar cardiorespiratory response to surgery irrespective of the method of analgesia. Subjective feelings of fatigue were significantly greater in those patients who had received epidural analgesia (P less than 0.01) and patients in this group expended significantly more energy in performing the postoperative exercise test than did those in the non-epidural group (P less than 0.05). The use of epidural opiate analgesia does not limit postoperative fatigue in patients undergoing upper abdominal surgery.

Evaluation of Breath-by-Breath Measurement of Respiratory Gas Exchange in Pediatric Exercise Testing

In adults, breath-by-breath analysis has been used for measuring respiratory gas exchange during exercise. The present study evaluates the validity and reproducibility of this method in children. In 21 patients with various types of congenital heart disease, steady state exercise testing was performed on a motor-driven treadmill. Based on simultaneous measurements of VO2, VCO2, VE and R, comparisons were made between the breath-by-breath and Douglas bag methods. No significant differences were found between both methods for any of the variables. In seven other patients the reproducibility of cardiorespiratory variables during exercise was assessed. No significant difference was found for the cardiorespiratory variables during any of the tests and the coefficients of variation were comparable to data obtained in adults. It is concluded that the breath-by-breath method for measuring respiratory values can be applied in children with an acceptable degree of validity and reproducibility.

Oxidation of carbohydrate ingested during prolonged endurance exercise.

Classic studies conducted in the 1920s and 1930s established that the consumption of a high carbohydrate (CHO) diet before exercise and the ingestion of glucose during exercise delayed the onset of fatigue, in part by preventing the development of hypoglycaemia. For the next 30 to 40 years, however, interest in CHO ingestion during exercise waned. Indeed, it was not until the reintroduction of the muscle biopsy technique into exercise physiology in the 1960s that a series of studies on CHO utilisation during exercise appeared. Investigations by Scandinavian physiologists showed that muscle glycogen depletion during prolonged exercise coincided with the development of fatigue. Despite this finding, attempts to delay fatigue during prolonged exercise focused principally on techniques that would increase muscle glycogen storage before exercise. The possibility that CHO ingestion during exercise might also delay the development of muscle glycogen depletion and hence, at least potentially, fatigue, was not extensively investigated. This, in part, can be explained by the popular belief that water replacement to prevent dehydration and hyperthermia was of greater importance than CHO replacement during prolonged exercise. This position was strengthened by studies in the early 1970s which showed that the ingestion of CHO solutions delayed gastric emptying compared with water, and might therefore exacerbate dehydration. As a result, athletes were actively discouraged from ingesting even mildly concentrated (greater than 5 g/100ml) CHO solutions during exercise. Only in the early 1980s, when commercial interest in the sale of CHO products to athletes was aroused, did exercise physiologists again begin to study the effects of CHO ingestion during exercise. These studies soon established that CHO ingestion during prolonged exercise could delay fatigue; this finding added urgency to the search for the optimum CHO type for ingestion during exercise. Whereas in the earlier studies, estimates of CHO oxidation were made using respiratory gas exchange measurements, investigations since the early 1970s have employed stable 13C and radioactive 14C isotope techniques to determine the amount of ingested CHO that is oxidised during exercise. Most of the early interest was in glucose ingestion during exercise. These studies showed that significant quantities of ingested glucose can be oxidised during exercise. Peak rates of glucose oxidation occur approximately 75 to 90 minutes after ingestion and are unaffected by the time of glucose ingestion during exercise. Rates of oxidation also appear not to be influenced to a major extent by the use of different feeding schedules.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxygen uptake kinetics in response to exercise in patients with pulmonary vascular disease.

The increase in muscular oxygen consumption that accompanies the onset of exercise is accomplished by increases in blood flow and arterial-venous O2 difference. These processes are reflected in a similar increase in pulmonary oxygen uptake (VO2), which rises in a dynamic pattern having two components and with an overall time course that may be characterized as an exponential. Because the immediate determinants of VO2 are the blood flow and respiratory gas composition in the pulmonary circulation, it was hypothesized that VO2 kinetics at exercise onset would be abnormal in patients with pulmonary vascular disease. To test this, 10 patients with pulmonary hypertension and two with pulmonary hypoperfusion caused by congenital heart disease performed constant work rate (15 +/- 16 SD watt) exercise on an upright cycle ergometer, with breath-by-breath measurement of respiratory gas exchange for determination of VO2 kinetics. The phase I increase in VO2, comprising approximately the first 30 s of exercise, was small (18 +/- 15 SD % above resting VO2). The time constant for the phase II increase in VO2 averaged 74 +/- 16 s, and the mean response time for attainment of the exercise steady state (75 +/- 17 SD s) was prolonged compared with normal values for the same work rate exercise (approximately 100 to 130% increase in phase I, and mean response time less than 25 s). In two patients who underwent surgical procedures substantially improving pulmonary hemodynamics, VO2 kinetics also improved. These findings are consistent with the concept that VO2 kinetics may be limited by pulmonary hemodynamics in the presence of disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary fat polyunsaturated to saturated ratio on energy substrate utilization in obesity

The effect of the polyunsaturated to saturated (P:S) ratio of dietary fat on preprandial and postprandial macronutrient oxidation was studied in normal-weight and obese individuals. Total thermogenic response and fat and carbohydrate oxidation rates were determined by duplicate respiratory gas exchange measurements after test breakfasts, in seven normal and eight overweight subjects who consumed self-selected diets containing fat of high or low P:S ratio. Dietary intake records and erythrocyte linoleic to oleic (L:O) acid ratio changes were used as indicators of compliance. No diet- or weight-related differences were observed in resting fat or carbohydrate oxidation rates, or in protein-free basal energy expenditure. Obese subjects consuming low P:S ratio diets exhibited reduced ( P < .05) contribution of fat oxidation to the thermogenic response, compared with lean individuals consuming high or low P:S ratio diets. However, total calories associated with the thermogenic response, and total fat and carbohydrate oxidation after the test breakfasts, did not differ significantly across groups. These findings suggest that, in obesity, whole-body postprandial disposal of dietary fat is influenced by the long-chain fatty acid composition.

Calibration of respiratory gas exchange measurements in inhalation toxicology studies

The use of simplifying assumptions for determining respiratory gas exchange is associated with substantial errors in the estimates of oxygen consumption (V̇ O2) and carbon dioxide production (V̇ CO2). Studies were done to estimate the magnitude of these errors under common exposure conditions, and a simple procedure that reveals these errors is described for calibrating an open flow respirometer. The errors associated with various simplifying assumptions ranged from −1 to −21% for V̇ O2, 0.1 to 15% for V̇ CO2, and 4 to 45% for the respiratory exchange ratio ( R). The calibration was performed with a standard calibration gas elevated in CO 2 and depressed in O 2 relative to air and bled into the respirometer at a measured flow rate. Dilution of the gas into the respirometer airstream simulates the effect of respiratory gas exchange, and expected values of V̇ O2, V̇ CO2, and R compared to measured values provide a check of accuracy of flow and gas fraction measurements, a test for system leaks, and a test for the effects of any simplifying assumptions on the calculation of respiratory gas exchange.

A Method for Increasing Confidence in Respiratory Gas Exchange Measurements in Mechanically Ventilated Patients

Measurement of O2 uptake (VO2) and CO2 output (VCO2) with automated instruments can be used to optimize nutritional management of critically ill patients. However, these measurements may be made infrequently because of calibration problems or suspected inaccuracies, especially when the patient is given supplemental oxygen. A simple method is described for periodic testing of automated gas exchange measurements. While a test lung is mechanically ventilated an accurately known mixture of CO2 and nitrogen is introduced into the inspired gas, simulating VO2 by dilution and VCO2 by addition of CO2. The ratio of VCO2:VO2 (respiratory gas exchange ratio, R) in the "expired gas" should be [FGCO2/(1-FGCO2)] x [(1-FIO2)/FIO2], where FGCO2 is the fraction of CO2 in the diluting gas and FIO2 is the fraction of O2 in the inspired gas. R is independent of the flow rate of the diluting gas or the rate of ventilation of the test lung. Using a mixing chamber-mass spectrometer, we found that R calculated from measurement of CO2 and O2 concentrations in the simulated mixed expired gas closely matched the predicted R for FIO2 = 0.21-0.50. On the other hand, when an automated gas exchange measurement device was tested, R was sometimes excessively high, especially for FIO2 greater than 0.35. This method, using a single diluting gas and without precision flowmeters, may be useful for periodic testing of respiratory gas exchange instruments in the intensive care unit. If a discrepancy is found between measured and predicted R, measurements should not be relied upon until further calibration or repairs can be effected.

Maximal oxygen uptake in severe aortic regurgitation: A different view of left ventricular function

Respiratory gas exchange was used to assess left ventricular (LV) function in 22 patients with severe aortic regurgitation (19 men and three women, aged 18 and 70 years, mean 49 years). Anaerobic threshold and symptom-limited maximal oxygen consumption (VO 2 max) were measured during treadmill exercise, and the results were compared with conventional echocardiographic and radionuclide indices of LV systolic function. The results were considered with respect to the patients' New York Heart Assoclation functional class. Both rest and exercise LV ejection fractions were variable, but the mean results were similar in all classes. The echocardiographic indices of LV cavity dimensions, fractional shortening, radius/thickness ratio, and systolic wall stress also showed a wide range but with similar mean results in each class. In contrast, VO 2 max and anaerobic threshold showed a relationship to functional class. VO 2 max was 32.4 ± 3.4 ml/kg/min in age-matched control subjects; in the patients it was 27.9 ± 4.7 in class I, 24.7 ± 5.7 in class II, and 14.2 ± 2 in the combined class III/IV. Results in patients in classes I and II were similar, but both groups were significantly different from control subjects ( p < 0.05) and from patients in class III/IV ( p < 0.01). About half of the patients with moderate LV dysfunction (judged by reduced VO 2 max) were asymptomatic, and LV function was imparired in 4 of 10 patients in class I. Thus, unlike conventional indices of LV function, VO 2 max appeared capable of distinguishing patients with moderate-to-severe LV dysfunction from those with little or no LV dysfunction. Measurement of respiratory gas exchange appears to be a valid and useful supplementary means of assessing LV function in severe aortic regurgitation. Further long-term evaluation is required.

Energy exchange in downhill and uphill walking

Energy balance can be written as 1) M = sigma Q +/- W +/- S, expressed as power (W), where M is the rate of metabolic energy transformation, sigma Q the rate of heat loss, W the work rate, and S the rate of body heat storage. When submaximal treadmill exercise continues long enough, body temperature stops changing, S becomes zero, and the heat storage term is dropped from equation 1. For uphill walking the equation becomes 2) M = sigma Q + Wvert, and for downhill walking it becomes 3) M = sigma Q - Wvert. This study tested the energy balance equations with direct measurements of heat exchange using a suit calorimeter and M from standard measurements of respiratory gas exchange. Ten healthy men walked on a motor driven treadmill at 1.5 m.s-1 at grades of 0, 5, 10, -5, and -10% for 70-90 min to ensure a thermal steady state. As expected, +Wvert was identified as a power output, whereas -Wvert was accounted for as a power input, totally transformed to heat in the downhill walking subject. There also appeared to be a quantity of non-thermal energy, Wwalk, needed to satisfy the energy balance equation. This was significant at 0, 5, and 10% grades (P less than 0.01) but not significant at -5 and -10% grades (P greater than 0.05). The data confirm previous results for level walking and extend them to include uphill walking. While it had been suggested that Wwalk represents an externalization of energy at the foot, the present data suggest an alternative explanation.(ABSTRACT TRUNCATED AT 250 WORDS)

Reappraisal of the Weir equation for calculation of metabolic rate

In 1949 Weir (3) demonstrated that the metabolic rate calculated from respiratory gas exchange measurements is to a close approximation proportional to the difference in percentage oxygen content between inspired and expired air. Although values for the energy equivalent of oxygen consumed and for the respiratory quotient for the oxidation of various nutrients have been revised since 1949, we show that the error in the calculation remains generally below 0.5% for the oxidation of dietary carbohydrate, fat, and protein. Where the original equation is uncritically applied to situations in which other nutrients are being oxidized, the error may reach 3%, although alternative methods for calculating the metabolic rate may be similarly in error. We give the derivation from first principles of the general mathematical solution to the calculation of the metabolic rate following Weir's method. Examples are provided of the subsequent derivation of specific equations for the more precise calculation of the metabolic rate where different combinations of nutrients are being oxidized.

The effect of starvation on insulin-induced glucose disposal and thermogenesis in humans

The effect of 48-hour starvation on glucose metabolism was studied in six non-diabetic, normal weight men using a hyperinsulinemic (100 mU/min/m 2) glucose clamp (3.5 mmol/L). The rate of glucose oxidation was calculated from measurements of respiratory gas exchange, after allowing for the oxidation of ketones and of protein. During the glucose clamp, the whole body glucose disposal rate decreased from 39.8 (SEM 4.6) μmol/kg/min in the fed state to 24.1 (2.1) μmol/kg/min in the starved state ( P < .01), consistent with insulin “resistance.” The glucose oxidation rate decreased from 21.8 (1.3) to 3.9 (1.4) μmol/kg/min with starvation ( P < .001), but the nonoxidative glucose disposal rate was unchanged (18.0[3.9] μmol/kg/min normally fed, and 20.2[1.2] μmol/kg/min starved). With starvation, the rate of glucose uptake in the forearm during the glucose clamp was reduced from 59.4 to 15.4 μmol/min/L forearm (SE 5.6, P < .01, ANOVA). There was a significant net increase in thermogenesis during the glucose clamp in the normally fed state (0.27 [0.08] kJ/min, P < .01, ANOVA), but not following starvation (0.11 [0.09] kJ/min, NS, ANOVA). Therefore, starvation caused decreases in oxidative glucose disposal and in forearm glucose uptake; despite the whole body nonoxidative disposal rate of glucose being unchanged, the associated net thermogenic response was diminished.

Long-term Reproducibility of Respiratory Gas Exchange Measurements during Exercise in Patients with Stable Cardiac Failure

Present-day technology has greatly facilitated the monitoring of respiratory gas exchange in the clinical exercise laboratory. Despite the growing use of these techniques to assess the severity and progression of disease or therapeutic response in patients with heart failure, the long-term reproducibility of oxygen uptake (VO2), carbon dioxide production, minute ventilation, heart rate (HR), and blood pressure at rest and during incremental exercise in such patients, to our knowledge, has not been evaluated. Therefore, the purpose of this study was to quantify the reproducibility of these variables along with exercise duration, maximum VO2 (VO2max) and anaerobic threshold in a group of 16 patients (61 +/- 7 years, 14 male) with chronic, stable cardiac failure of varying severity and etiology who had five or more incremental treadmill exercise tests over a period of time that ranged from 3 to 22 months. For each variable, reproducibility was represented by the coefficient of variation (CVAR). Except for exercise duration, CVAR was not a function of the severity of heart failure and, for all variables, patient-to-patient variation in CVAR was approximately 9 percent. The maximum CVAR for HR, systolic blood pressure, VO2, and VO2max was generally below 10.5 percent and for exercise duration and anaerobic threshold it was less than 12.5 percent. Based on this retrospective analysis, it is concluded that reproducible respiratory gas exchange and HR exercise responses are obtainable over extended periods of time in patients with stable, chronic cardiac failure. Exercise duration, however, is less reproducible in patients with moderate to severe failure.

Detecting abnormalities in left ventricular function during exercise by respiratory measurement.

The degree of exercise-induced cardiac dysfunction and its relation to the anaerobic threshold were evaluated in 23 patients with chronic heart disease. A symptom-limited exercise test was performed with a cycle ergometer with work rate increased by 1 W every 6 seconds. Left ventricular function, as reflected by ejection fraction, was continuously monitored with a computerized cadmium telluride detector after the intravenous injection of technetium-labeled red blood cells. The anaerobic threshold (mean, 727 +/- 166 ml/min) was determined by the noninvasive measurement of respiratory gas exchange. As work rate rose, the left ventricular ejection fraction increased but reached a peak value at the anaerobic threshold and then fell below resting levels. Ejection fraction at rest, anaerobic threshold, and peak exercise were 41.4 +/- 11.3%, 46.5 +/- 12.0%, and 37.2 +/- 11.0%, respectively. Stroke volume also increased from rest (54.6 +/- 17.0 ml/beat) to the point of the anaerobic threshold (65.0 +/- 21.2 ml/beat) and then decreased at peak exercise (52.4 +/- 18.7 ml/beat). The slope of the plot of cardiac output versus work rate decreased above the anaerobic threshold. The anaerobic threshold occurred at the work rate above which left ventricular function decreased during exercise. Accurate determination of the anaerobic threshold provides an objective, noninvasive measure of the oxygen uptake above which exercise-induced deterioration in left ventricular function occurs in patients with chronic heart disease.

A wind tunnel metabolism chamber with small volume and good air flow characteristics

A wind tunnel metabolism chamber is described which has a low (4.2 to 1) ratio of total to working volume to facilitate respiratory gas exchange measurements on unrestrained animals. Fine mesh screens smooth air flow to obtain 2% RMS turbulence and +or-5% uniformity. Simultaneous combinations of air temperature from -10 to 50 degrees C and wind from 0 to 3.6 m s-1can be maintained indefinitely. A window admits simulated solar radiation to the working section.