Multiparameter correlative study of respiratory gas exchange during exercise

Patients with chronic heart failure were evaluated simultaneously by conventional methods and by heart-lung exploration during exercise with the purpose of validating the latter method. Only 50 patients were evaluated on two occasions and therefore included in the correlative statistical study. In this study such data as NYHA classification, cardiothoracic ratio, ejection fraction, echocardiographic fibre shortening fraction and biochemical values (venous lactate, plasma noradrenaline levels) were compared with data obtained from evaluation during exercise, i.e. VO2 max, VO2 peak, anaerobic threshold, oxygen pulse, VCO2, O2 equivalent and respiratory quotient, alveolar ventilation per minute, duration and load of exercise. Very good correlation was found with the indices obtained from VO2 and in particular with the O2 pulse and the VO2 max percentage. Good correlation was also found with VCO2 and the O2 equivalent as well as with alveolar ventilation per minute. In contrast, the anaerobic threshold and respiratory quotient correlated poorly with the first set of data and therefore were disappointing. It appears from this study that the indices obtained from VO2 are highly representative of the heart-lung unit in patients with heart failure. It seems, however, that the muscular status of the patients plays a considerable role in their exercise capacity. We suggest that these indices should be used in clinical pharmacology studies.     

Mild-to-moderate obesity: implications for respiratory mechanics at rest and during exercise in young men

OBJECTIVE: To investigate the effect of mild-to-moderate obesity on respiratory mechanics at rest and during exercise in obese men. We hypothesized that the simple mass loading of obesity would alter both end-expiratory lung volume (EELV) and respiratory pressures (gastric, P(ga) and transpulmonary, P(TP)) in resting body positions and during graded cycle ergometry to exhaustion. SUBJECTS: A total of 10 obese (38+/-5% body fat; mean+/-s.d.) and nine lean (18+/-4%) men were studied. METHODS: Body composition (by body circumferences and hydrostatic weighing) and pulmonary function were measured at rest. Breathing mechanics were measured at rest in the upright-seated position, supine, and during cycling exercise. Data were analyzed by independent t-test. RESULTS: EELV was significantly lower in the obese men in the supine (30+/-4 vs 37+/-6% total lung capacity (TLC)) and seated (39+/-6 vs 47+/-5%TLC) positions and at ventilatory threshold (35+/-5 vs 45+/-7%TLC) (P<0.01). In contrast, at peak exercise, EELV was not different between groups. Respiratory pressures (P(ga) and P(TP)) were elevated (P<0.05) during one or more phases of the breathing cycle at rest and during exercise in obese men. CONCLUSION: These data demonstrate that mild-to-moderate obesity in young men results in reduced lung volumes and alterations in respiratory mechanics when supine, seated at rest, and during exercise. During moderate exercise, obesity does not appear to limit changes in EELV; however, the regulation of EELV during heavy exercise appears to be affected.     

Effect of breathing dry warm air on respiratory water loss at rest and during exercise

The changes in respiratory water loss with time, expressed as the mass of water vapour lost per liter BTPS of ventilation (MH2O), and expired temperature (TE), used to calculate the relative humidity (ERH), were investigated in ten normal subjects while breathing warm dry air by mouth (PIH2O = 0 kPa; TI = 30 degrees C): at rest for a period of 35 min; during 15 min light muscular exercise (50 W); at increasing work load from 50 to 100 W between the 5th and 10th min of the exercise. The data collected were compared to those obtained in room air conditions (PIH2O = 0.68-1.3 kPa) and under conditions with slightly heated inspired air (TI = 28-30 degrees C). At rest, when breathing dry warm air MH2O and ERH fell during the first 15 min, while they recovered their initial values during the last 20 min. In contrast no differences in MH2O or ERH were observed when breathing ambient warm air. At constant and moderate work load for 15 min, the respiratory water loss fell significantly (compared to the 5th min) at the 10th and the 15th min when breathing warm dry air. The added hyperpnea which was obtained by increasing work load from 50 to 100 W between the 5th and 10th min of exercise did not further reduce MH2O and ERH. The transient fall in MH2O and ERH, which lasted at least 15 min either at rest or during muscular exercise, suggested that the mechanism underlying humidification of expired gas is overwhelmed by thermal stress. Since the upper airways mucosa is unable to saturate expired gas, this also suggested that the mucosa is dehydrated and probably hyperosmotic. The progressive recovery in MH2O and ERH after 15 min of warm dry air breathing at rest, suggest operation of a slow adaptive mechanism.     

Effects of imposed pursed-lips breathing on respiratory mechanics and dyspnea at rest and during exercise in COPD

STUDY OBJECTIVES: To investigate the effect of volitional pursed-lips breathing (PLB) on breathing pattern, respiratory mechanics, operational lung volumes, and dyspnea in patients with COPD. SUBJECTS: Eight COPD patients (6 male and 2 female) with a mean (+/-SD) age of 58 +/- 11 years and a mean FEV1 of 1.34 +/- 0.44 L (50 +/- 21% predicted). METHODS: Wearing a tight-fitting transparent facemask, patients breathed for 8 min each, with and without PLB at rest and during constant-work-rate bicycle exercise (60% of maximum). RESULTS: PLB promoted a slower and deeper breathing pattern both at rest and during exercise. Whereas patients had no dyspnea with or without PLB at rest, during exercise dyspnea was variably affected by PLB across patients. Changes in the individual dyspnea scores with PLB during exercise were significantly correlated with changes in the end-expiratory lung volume (EELV) values estimated from inspiratory capacity maneuvers (as a percentage of total lung capacity; r2 = 0.82, p = 0.002) and with changes in the mean inspiratory ratio of pleural pressure to the maximal static inspiratory pressure-generating capacity (PcapI) [r2 = 0.84; p = 0.001], measured using an esophageal balloon, where PcapI was determined over the range of inspiratory lung volumes and adjusted for flow. CONCLUSION: PLB can have a variable effect on dyspnea when performed volitionally during exercise by patients with COPD. The effect of PLB on dyspnea is related to the combined change that it promotes in the tidal volume and EELV and their impact on the available capacity of the respiratory muscles to meet the demands placed on them in terms of pressure generation.     

Pulmonary gas exchange and central hemodynamics at rest and during exercise in patients with chronic obstructive pulmonary disease

Right-heart catheterization and ergometry with arterial and mixed venous blood gas analysis were performed in 27 patients with a wide range of chronic obstructive pulmonary diseases. The purpose of the examination was to evaluate the risk in patients for lung surgery or to detect additional heart diseases. Patients who developed exertional hypoxia (group 1) were compared with others who did not (group 2). In all patients the steady-state maximal workload was determined by ventilatory dysfunction. Both groups had normal values for mixed venous pO2 and normal increase of the circulatory parameters during exercise. The patients with exertional hypoxia differed from the others in that they showed no decrease of venous admixture and alveolar-arterial oxygen gradient. In addition, these patients had increasing pCO2 values at rest compared with exercise, indicating alveolar hypoventilation and ventilation-perfusion mismatching. Because of the good correlation of the absolute values of FEV1 (forced expiratory volume in 1 s) with pulmonary artery pressures, parameters of gas exchange and working capacity, this lung function parameter seems to have a central role in predicting the functional state of patients with chronic obstructive disease. Ergometry and blood gas analysis should be performed in addition because these values cannot be predicted with the calculated postoperative FEV1.     

Hemodynamically important right ventricular infarction: follow-up evaluation of right ventricular systolic function at rest and during exercise with radionuclide ventriculography and respiratory gas exchange

The prognosis and recovery of right ventricular systolic function in patients with hemodynamically documented right ventricular myocardial infarction (RVMI) is unclear. Therefore 27 patients who met hemodynamic criteria for RVMI were followed for at least 1 year. Four patients died within 1 year and 23 survived. Postmortem examination performed in three of the four patients showed extensive infarction of the right and left ventricles. Survivors underwent early and late follow-up resting radionuclide ventriculograms and late exercise studies. During long-term follow-up (1 to 4 years) resting radionuclide ventriculography demonstrated a significant improvement in right ventricular ejection fraction (30 +/- 7% to 43 +/- 8%; p less than .001) and right ventricular wall motion index (2.2 +/- 0.4 to 1.5 +/- 0.5; p less than .001) in 18 patients who survived longer than 1 year. Fourteen of these patients underwent upright bicycle exercise while off beta-blocking drugs and peak radionuclide ejection fraction was acquired after anaerobic threshold was achieved. Right ventricular ejection fraction increased significantly from 41 +/- 10% to 47 +/- 12% (p less than .001), as did the left ventricular ejection fraction (55 +/- 15% to 60 +/- 12%; p less than .05). The direction and magnitude of change of the right ventricular ejection fraction correlated significantly with the left ventricular ejection fraction (r = .82, p less than .02). Deviations from this correlation occurred in patients who had a decreased forced expiratory volume in 1 sec and an abnormal ventilatory reserve during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiration in heat stressed camels

Respiration and heat exchange in relation to brain temperature (Th) and body temperature (Tb) were investigated in four heat stressed camels subjected daily to high temperature (47 degrees C) in a climate chamber while resting when hydrated and dehydrated by approximately 10%, 15% and 20% of initial weight. Diurnally Tb followed patterns described previously. Th was usually 0.2-0.5 degrees C greater than Tb: occasional reversals with brain cooling were observed. Minute ventilation increased with Tb: above 37.5 degrees C it was approximately half as much in dehydrated as in hydrated animals. Respiratory frequency increased with Tb up to 60/min. Tidal volume fell with increasing frequency; above 25 breaths/min, tidal volume approximated dead space volume. Exhaled air was almost always unsaturated with no systematic effect of dehydration. Metabolic rate fell on dehydration reducing ventilatory demand. Th and Tb were measured in two of the animals walking outdoors: then Th fell below Tb if exercise exceeded 30 min. The data indicate that heat stressed camels pant, but turbinate vasoconstriction in a hot environment prevents cooling of the brain by carotid rete heat exchange.     

Ventilation during rest and exercise in pregnancy and postpartum.

The expiratory minute volume (Ve), respiratory frequency (f), tidal volume (VT), carbon dioxide production (Vco2), and end-tidal carbon dioxide concentration (FETCO2) and pressure (PETCO2) were measured at monthly intervals in 12 normal women during pregnancy and two, six and 12 weeks, and six months postpartum. At eacy study, measurements were made sitting at rest and during steady-state exercise at 306 kpm/min on a bicycle ergometer. During pregnancy, a significant increase in VE occurred, both at rest and during exercise, due to a significantly greater VT. Although VCO2 was significantly increased at rest throughout pregnancy and with exercise in late pregnancy, the respiratory exchange ratio (R) was not significantly altered during pregnancy. The FETCO2 was lower during pregnancy than postpartum, both at rest and during exercise. The ventilatory equivalent for oxygen (VE/VO2) was greater at rest near term and during exercise throughout pregnancy. However, resting physiologic dead space increased during pregnancy. Alveolar ventilation (VA) was calculated on the basis of three alternative assumptions: (1) that PETCO2 during exercise accurately reflects mean alveolar PCO2; (2) that the physiological dead space does not change during exercise; and (3) that mean alveolar PCO2 does not change from rest to exercise. Exercise VA, calculated on the basis of any of these three assumptions, is greater during pregnancy than postpartum.     

Respiration in conscious dogs at rest and during exercise.

25 mongrel dogs (average b.w. 24.6 kg) were studied on several occasions at rest and during treadmill exercise of up to 10 mph (15% incline). Minute ventilation (VE), oxygen consumption (VO2), carbon dioxide production (VCO2), tidal volume (VT) and respiratory frequency (f) were determined at rest and at each level of exercise. Individual variability in resting VO2 was considerable (71--695 ml/min). Most often the dogs panted, with VE's above 25 liters/min and f's above 100 min-1. The averate VE/VO2 was 109 at rest. VO2 was linearly related to VE (VO2 = 9.17 VE + 66.9; r = 0.80). Differences in resting VE were largely due to differences in f (f = 3.57 VE + 21.2; r = 0.82). Considerable individual variability in VO2 for a given work load was also observed during exercise. Some dogs showed significant differences in VO2 from experiment to experiment while running at a given treadmill speed. These differences were largely related to the levels of VE. VE/VO2 decreased to 50. We found a leveling off of VO2 (at about 60 ml/min/kg) at treadmill speeds of 5 mph, suggesting that the maximal VO2 in dogs is less than previously reported.     

Oxygen consumption at rest and during exercise in pregnancy.

The oxygen consumption (Vo2) of 12 normal women was measured at monthly intervals during pregnancy and 2, 6 and 12 weeks and 6 months postpartum. At each study session measurements were made sitting at rest, during standard steady-state exercise on a bicycle ergometer, and for 10 minutes of recovery. A significant increase in exercise Vo2 was observed in late pregnancy when compared to paired postpartum values. The oxygen debt incurred by standard exercise was also greater in late pregnancy than 12-14 weeks postpartum.     

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.