Acetylene Rebreathing Method Research Articles

Progressive, High Intensity Endurance Exercise Training Significantly Increases Submaximal and Maximal Stroke Volume In Middle Aged, Previously Sedentary Adults

High intensity, endurance exercise increases maximal stroke volume (SV) in young, healthy adults. It is less clear whether such gains are realized among sedentary adults who begin such a program during middle-age. PURPOSE: To determine whether a progressive, high-intensity endurance exercise program will increase SV in healthy, middle-aged adults. METHODS: We studied 42 middle-aged adults (18 males; 52.1 ± 5.0yrs). 21 were randomized to a non-aerobic exercise group (Control). The remaining 21 (10 males) were assigned to an endurance training group (Exercise), all whom completed the 9-month progression phase of a 24 month exercise prescription. This progressive regimen was gradually expanded from 3*30min moderate intensity sess./wk to 1-2*30 min and 1*60 min moderate intensity (55-70% of VO2max) sess./wk + 2 high intensity interval (≥95%peakHR) sess./wk; and 1 low intensity recovery sess./wk. Endurance training sessions were recorded by each participant via both Polar heart rate monitoring and manual data logs. VO2max was measured using the Douglas Bag method via an incremental treadmill protocol. Cardiac output (Qc) was measured by a non-invasive acetylene rebreathing method. VO2 and Qc were measured at rest, two submaximal (SS1 and SS2, 30 and 60% of peak VO2, respectively) and maximal workloads. SV was calculated from the Qc and HR measured via ECG. RESULTS: Exercise participants increased their SV at the submaximal (10.2 and 11.6%, respectively; both p<0.01) and maximal (9.7%, p=0.02) workloads (reference Table 1). SV of the Control group decreased slightly at all workloads. CONCLUSION: Healthy, previously sedentary middle-aged adults who completed a progressive endurance exercise program realized a significant increase in SV during both submaximal and maximal exercise.Table 1: Stroke Volume Increases with Progressive Endurance Training

The effect of exercise training on left ventricular relaxation and diastolic suction at rest and during orthostatic stress after bed rest

A marked reduction in upright stroke volume (SV) contributes substantially to orthostatic intolerance after exposure to spaceflight or bed rest. It is unclear whether slowed left ventricular (LV) relaxation and diastolic suction contribute to the reduction in SV or whether these changes are influenced by exercise training while in bed. Twenty-seven healthy adults completed 5 weeks of -6 deg head-down bed rest (HDBR). During HDBR, nine subjects were sedentary (NOEX), while 18 performed near-daily rowing ergometry (EX). Left ventricular mass, SV, LV end-diastolic volume (LVEDV), pulmonary capillary wedge pressure and Doppler ultrasound indices of LV function were collected pre- and post-HDBR during supine rest (twice) and during reduced LV loading (lower body negative pressure; LBNP) and increased LV loading (saline infusion). Post-HDBR, LV mass increased in the EX group, but decreased in the NOEX group. The reduction in SV and LVEDV during supine rest and LBNP were greater with NOEX in comparison to EX after HDBR. Peak early mitral annular velocity, isovolumic relaxation time, early propagation velocity, a non-invasive index of early diastolic filling and ventricular diastolic suction, and peak global longitudinal early strain rate were slowed during supine rest after HDBR with NOEX; however, these variables were either unaltered or the reduction was less prominent with EX. Doppler ultrasound measures of early diastolic filling, ventricular relaxation and diastolic suction were not significantly affected during LV unloading by LBNP after HDBR in either group. All Doppler indices were restored to pre-HDBR levels in both groups during saline infusion to normalize LV filling pressure after HDBR. It is concluded that Doppler indices of dynamic LV filling were reduced in both groups after HDBR; however, these effects were more pronounced in the NOEX group. Irrespective of group, post-HDBR Doppler parameters were restored when LV filling pressure was increased to pre-HDBR levels during saline infusion. Therefore, the reduction in upright SV after HDBR is more influenced by changes in LV loading conditions, namely left atrial pressure in the setting of LV remodelling, rather than ventricular relaxation and diastolic suction.

Pulmonary blood flow measurement by acetylene rebreathing method in subjects without respiratory function disturbance

Simultaneous measurement of pulmonary blood flow by the acetylene rebreathing method and cardiac output by the thermodilution method was performed in subjects without respiratory function disturbance during right heart catheterization. After the measurement of cardiac output, the subjects rebreathing a gas mixture containing acetylene and argon from the end tidal level. The inspiratory and expiratory gases were measured by a mass-spectrometer. Results were analyzed by a lung model consisting of two compartments (rebreathing bag compartment and lung compartment), while taking into account the volume reduction due to O2 and CO2 exchange and the fluctuation of end tidal gas concentration until equilibrium between the bag and the lung. The correlation coefficient between these two methods was 0.944, which was statistically significant. The regression line was near the line of identity. The measurement of pulmonary blood flow by the acetylene rebreathing method was applicable in cases without lung function disturbance.

Pulmonary tissue volume measured by acetylene rebreathing under artificial ventilation.

In order to evaluate the pulmonary congestive state of patients being mechanically ventilated, an acetylene rebreathing method was employed. Measurement of pulmonary tissue volume by the acetylene (C2H2) rebreathing method was performed in 15 patients under artificial ventilation including four congestive heart failure cases, one renal failure case, and 12 healthy controls. The subjects rebreathed mixed gas containing 0.65% C2H2, 10% argon (Ar), and 60% oxygen (O2) from end-tidal level, and inspiratory and expiratory gas concentrations were measured by a mass spectrometer. Correction for system volume reduction during rebreathing due to gas exchange and C2H2 concentration fluctuation was performed, pulmonary tissue volume was calculated from the C2H2 and Ar concentration difference at the time zero intercept. Time zero was assumed to be the time at which C2H2 and Ar concentration started to differ. Pulmonary tissue volume per functional residual capacity and pulmonary tissue volume per pulmonary capillary blood flow for cases with congestive heart failure and renal failure cases were significantly higher than those for non-pulmonary congestion cases and normal controls. The measurement of pulmonary tissue volume by C2H2 rebreathing can be applied to the patients under artificial ventilation in order to quantitatively evaluate pulmonary congestion or edema.

CARDIAC OUTPUT IN HYPEROXIA, NORMOXIA AND HYPOXIA

816 We examined the hypothesis that maximal cardiac output (COmax) does not differ between acute hyperoxia, normoxia and hypoxia. Six male endurance athletes were measured at rest and during progressive cycling in hyperoxia (Fraction of oxygen in inspired air, F1O2, 0.30), normoxia (F1O2 0.21) and hypoxia (F1O2 0.15). The subjects started cycling at 0 W and the power was increased by 100 W in 5-minute intervals until exhaustion. CO was measured with an acetylene rebreathing method at the end of each workload. V̇O2 was measured breath-by-breath. Maximal power, V̇O2max, COmax, maximal stroke volume (SVmax) and heart rate (HRmax) as well as COmax/V̇O2max-ratio were affected by F1O2(table).TableOur results indicate that maximal cardiac output is significantly diminished along with V̇O2max and maximal exercise performance in acute hypoxia. The diminished COmax in hypoxia is affected both by decreased maximal stroke volume and heart rate. In hyperoxia, COmax increased only slightly despite a greater increase in V̇O2max.

In vivo assessment of changes in air and tissue volumes after pneumonectomy.

We examined the progression and topographical distribution of postpneumonectomy volume changes in immature foxhounds undergoing right pneumonectomy (R-Pnx, n = 5) or sham pneumonectomy (Sham, n = 6) at 2 mo of age and subsequently raised to maturity. Volumes of lung air (Vair) and tissue (Vti) were estimated by computerized tomography (CT) scan at 7, 22, and 52 wk after surgery at a transpulmonary pressure of 20 cmH2O. Estimates of Vti by CT scan included both septal tissue as well as nonseptal tissue (small- and medium-sized airways and blood vessels); these were compared with estimates of septal Vti by an acetylene rebreathing (Rb) method. We found significant correlations between these techniques (Vair(CT) = 0.83 Vair(Rb) + 275, R = 0.97; Vti(CT) = 1.62 Vti(Rb) - 30, R = 0.81). Extravascular septal Vti returned to normal 7 wk after R-Pnx and remained normal up to maturity. Nonseptal Vti remained significantly below normal. The greatest increase in Vti occurred in the midlung region just cephalad and caudal to the heart. After an early period of accelerated tissue growth after R-Pnx, the rate of septal tissue growth matched that of somatic growth, whereas nonseptal tissue growth lagged behind. Compensatory growth of the remaining left lung was not associated with selective alterations in thoracic development.

Validation of the acetylene rebreathing method for measurement of cardiac output at rest and during high-intensity exercise.

The use of the acetylene rebreathing method to estimate cardiac output (CO) during high-intensity exercise, which may be influenced by recirculation of acetylene, has not been validated. This study was designed to validate the acetylene rebreathing method to measure CO during high-intensity exercise using the direct Fick method. CO was measured at rest and during exercise at 25%, 50%, 75% and 90% of the nine subjects' maximum oxygen uptake (VO2max) by the direct Fick and acetylene rebreathing method. CO measured by the acetylene rebreathing method correlated with work rate (r = 0.90, P < 0.01) and with oxygen uptake (r = 0.94, P < 0.01). The correlation coefficient of CO between both methods was r = 0.91 (P < 0.01). There was no significant difference in CO measured by each method at rest as well as at each work rate. The difference in CO between each method was greater at lower CO than at higher CO. At 90% of VO2max, the CO measured by acetylene rebreathing was nearly identical to that measured by the Fick method. It can be concluded that acetylene rebreathing for measurement of CO is valid not only at rest but also during exercise, especially during high-intensity exercise.

The non-invasive acetylene rebreathing method for estimation of cardiac output: influence of breath-by-breath variation.

The inert gas rebreathing method enables non-invasive estimation of pulmonary capillary blood flow, lung tissue volume, transfer factor and functional residual capacity. In the present study, we have examined the influence of breathing pattern during the rebreathing manoeuvre on the precision of the rebreathing method, both theoretically and experimentally. We examined whether the precision of the method could be improved by the guidance and training of the subjects doing the rebreathing manoeuvre. The results of the theoretical study showed that the precision and accuracy of the rebreathing method are practically insensitive to random variation in the breathing pattern. Simulated breath-by-breath variations up to +/-50% of the average 3.01 VT resulted in coefficients of variation of about 3% for QC and about 5% for VTC. Simulated breath-by-breath variations indicate that with mean tidal volume or rebreathing bag volume lower than 1.01 the precision will worsen, and with tidal volume lower than 1.5 1 the accuracy will worsen. The experimental results showed no significant improvement in the precision of the rebreathing method by visual guiding and training of the subjects to optimize the breathing pattern during the rebreathing manoeuvre.

Positional effects on maternal cardiac output during labor with epidural analgesia

OBJECTIVE: Our purpose was to test the hypothesis that the supine versus the lateral position is associated with a greater decrement in cardiac output after epidural analgesia in labor. STUDY DESIGN: Twenty-one normal term subjects were randomized to the left lateral or supine position in early labor. Cardiac output measured by the acetylene rebreathing method, stroke volume, heart rate, mean arterial pressure, and systemic vascular resistance were obtained at 5-minute intervals, beginning before a 500 ml intravenous fluid bolus (baseline) and ending 45 minutes after epidural injection. RESULTS: Mean baseline supine versus lateral group differences were significant for 21% lower cardiac output, 21% lower stroke volume, 19% higher mean arterial pressure, 50% higher systemic vascular resistance, and equivalent heart rate. In the supine group fluid bolus resulted in significantly increased cardiac output and stroke volume, decreased mean arterial pressure and systemic vascular resistance, and unchanged heart rate. In the supine group cardiac output and stroke volume decreased significantly after epidural injection. The lateral position group exhibited no hemodynamic alterations after fluid bolus or epidural. CONCLUSIONS: In contrast to the lateral position, the supine position is associated with a significant postepidural decrement in cardiac output, not identified by a change in heart rate. This likely reflects an inability to maintain stable preload volume in the supine position. (Am J Obstet Gynecol 1996;175:867-72.)

Cardiac output during exercise measured by acetylene rebreathing, thermodilution, and Fick techniques

In dogs during exercise, respiratory rate can reach 200 breaths/min, blood temperature can exceed 42 degrees C, and hematocrit can approach 60%. To determine whether these changes significantly affect the measurement of cardiac output by the acetylene rebreathing method (QcRB), we compared estimates of QcRB with those measured by thermodilution and Fick (QcFI) techniques in nine dogs at rest and during steady-state exercise on a treadmill up to near-maximal workloads. Solubility of acetylene in blood was corrected to the simultaneously measured blood temperature and hematocrit. Results were also adjusted for mixing efficiency. Up to a QcFI of 20 l/min, QcRB was not significantly different from QcFI (P > 0.05). However, cardiac output measured by thermodilution was consistently higher than those measured by the other techniques (P < 0.0001). We conclude that the overall agreement between QcRB and QcFI estimates supports the validity of the rebreathing technique under exercise conditions where body temperature and hematocrit are changing rapidly and the breathing pattern is unrestrained. Systematic error by the thermodilution technique may be related to a variety of methodological issues as well as possible dissipation of cooling into the myocardial tissue and subsequent incomplete washout.

Effect of extracorporeal membrane oxygenation flow on pulmonary capillary blood flow.

To validate a new application of the modified acetylene rebreathing method for pulmonary capillary blood flow in a swine extracorporeal membrane oxygenation (ECMO) model. Prospective, sequential measurements of pulmonary capillary blood flow, using a rebreathing technique, as affected by different flows through the ECMO circuit. A cardiovascular hemodynamic research laboratory at a university medical center. Fifteen young mature farm swine (48 to 52 kg). Pulmonary capillary blood flow was measured using a modified rebreathing technique, and this measurement repeated at different flow rates through the extracorporeal membrane oxygenation circuit. Pulmonary artery flow rates were measured using both thermodilution and echo-Doppler techniques for comparison purposes. Pulmonary capillary blood flow measurements, as assessed by modified acetylene rebreathing, compared well with both the thermodilution cardiac output measurement during normal circulation and the pulmonary artery flow probe measurement while the subjects received ECMO. Mean pulmonary capillary blood flow measured by acetylene rebreathing decreased from 89.72 +/- 6.97 (baseline) to 43.59 +/- 5.66 mL/kg/min as ECMO flow was maximized to 56.22 +/- 3.62 mL/kg/min. Decreasing the ECMO flow rate by half (to 28.23 +/- 3.45 mL/kg/min) caused an increase in mean pulmonary capillary blood flow to 53.79 +/- 6.16 mL/kg/min. When ECMO flow was discontinued, pulmonary capillary blood flow returned to a near baseline value of 71.68 +/- 7.05 mL/kg/min (mean values of pooled data for both closed- and open-chest animals [n = 15]). These measurements correlated well with both thermodilution cardiac output and pulmonary artery ultrasonic flow probe measurements. The modified acetylene rebreathing method is a valid and accurate method for the measurement of pulmonary capillary blood flow in the presence of ECMO flows. Pulmonary blood flow decreases as ECMO flow is increased, and the extent of decrease is directly proportional to the amount of flow through the extracorporeal circulation.

Comparison of Acetylene Rebreathing and Thermodilution Methods for Determining Cardiac Output

The usefulness of the acetylene rebreathing method in the noninvasive determination of cardiac output was compared with that of the thermodilution method. Simultaneous measurements of cardiac output by the acetylene rebreathing method and the thermodilution method were performed at rest in 20 patients with cardiac disease or hypertension and additionally during ergometer exercise in the supine position in 9 of 20 cases. Although the acetylene rebreathing method underestimated cardiac output as compared to the thermodilution method, the values for the cardiac output obtained with the acetylene rebreathing method had a good, positive correlation with those obtained with the thermodilution method (r = 0.94; SEE = 0.67; p < 0.001). Inhalation of acetylene did not affect the pulmonary arterial pressure or femoral arterial pressure. These results indicate that the acetylene rebreathing method is a safe and useful means for the noninvasive determination of cardiac output and can be used during exercise.

Repeatability of the acetylene rebreathing method in measuring cardiac output: influence of acetylene concentration

The acetylene rebreathing method is a reliable noninvasive method for estimation of cardiac output. However, the method is not commonly used for clinical purposes. This is due mainly to the fact that acetylene is explosive at concentrations above 2% and that acetylene at concentrations above 0.5% has an unpleasant taste. In the present study we have investigated whether it is possible to reduce the concentration of acetylene to 0.3% in the rebreathing bag without degrading the repeatability of the estimated cardiac output. The problem was elucidated theoretically and experimentally. A theoretical investigation was carried out by producing an acetylene rebreathing curve from a single alveolus lung model. The theoretical study showed that the random noise arising from the gas analyzer gives rise to less than 10% of the total variation of the estimated cardiac output. The results of the experimental study showed that it is possible to reduce the acetylene concentration to 0.3% without decreasing the reproducibility of the acetylene rebreathing method.

Effect of exercise training on exercise tolerance and cardiac output in children after repair of congenital heart disease

Exercise tolerance time and cardiac output (Q) measures during peak exercise were examined in 8 children with repaired congenital heart defects to determine the effects of physical training. Children ranged in age from 4.5 to 15 years (mean age 8.5). The children had undergone the following surgical repairs: Mustard operation for d‐trans‐position of the great arteries (n = 3); mitral valve replacement (n = 1); tetralogy of Fallot (n = 2); and Fontan operation (n = 2). Subjects participated in a 24‐session, 12‐week, one‐hour session hospital‐based aerobic exercise program of graduated intensity and duration. Work loads of 60, 70 and 80% of maximal heart rate were utilized. Graded exercise testing on a treadmill was performed prior to and following the training program. Pre and post values of Q were obtained via the acetylene rebreathing method. Exercise tolerance time increased significantly from 9.4 to 10.9 minutes (p < .01). Following training, peak exercise values of Q significantly increased from 4.91 ...

Comparison of the cardiac output and stroke volume response to upright exercise in children with valvular and subvalvular aortic stenosis

Cardiac output and stroke volume were evaluated in 17 children (mean age 11.5 ± 3 years) with discrete, membranous subvalvular (Group I, n = 7) and valvular (Group II, n = 10) aortic stenosis during submaximal and maximal (>75% predicted maximal oxygen consumption) upright cycle ergometry. Patients with valvular aortic stenosis were further subdivided on the basis of their aortic valve gradient at rest determined by cardiac catheterization (Group IIA, gradient <40 mm Hg; Group IIB, gradient ≥ 40 mm Hg). These patients were matched with 17 control subjects on the basis of age, sex, height and intensity of exercise during maximal exertion. Cardiac and stroke indexes were determined by the acetylene rebreathing method at each exercise level.Stroke volume index in Group I was significantly greater at rest when compared with that in control subjects (69 ± 13 versus 53 ± 11 ml/m2, α = 0.01, p < 0.05) and that in patients in Group II (69 ± 13 versus 47 ± 12 ml/m2, α = 0.01, p < 0.05). Patients with subvalvular aortic stenosis were unable to increase their stroke volume index from rest to submaximal exercise and also decreased their stroke volume index at maximal exercise levels. In contrast, patients with mild valvular aortic stenosis (Group IIA) displayed a normal exercise response. Patients with severe valvular aortic stenosis (Group IIB) had a blunted stroke volume response at rest and at each level of exercise, as well as signs of myocardial ischemia (ST segment depression) during maximal exercise.Cardiac output measurements during exercise testing permitted analysis of stroke volume patterns that differ by anatomic type and severity of left ventricular outflow tract obstruction. These findings have implications regarding the timing of treatment and exercise prescription for children with aortic stenosis.

Cardiac output determination by simple one-step rebreathing technique

We have developed a rebreathing technique for measuring cardiac output in resting or exercising subjects. The data needed are the subject's CO 2 dissociation curve, the initial volume and CO 2 fraction of the rebreathing bag, and a record of CO 2 at the mouth during the maneuver. From these one can obtain all the values required to solve the Fick equation. The combined error due to inaccuracy in reading the tracings and to the simplifying assumptions was found to be small (mean = 0.5%, SD = 2.5%). Cardiac output values determined with this technique in normal subjects were on the average 2% higher than those obtained simultaneously with an acetylene rebreathing method (n = 49, SD = 11%). Among the advantages of the technique are that it requires analysis of a single gas, takes less than thirty seconds per determination, allows one to obtain repeated measurements at rapid intervals, is not affected by the ability of lung tissue to store CO 2, and eliminates many of the assumptions usually made in non-invasive measurements of cardiac output.

Measurements of cardiac output in maximum exercise. Application of an acetylene rebreathing method to arm and leg exercise.

An acetylene rebreathing technique suitable for the measurement of cardiac output in maximum exercise is described; results have a coefficient of variation of 2.9–3.6%, and show good agreement with observations made by other methods during arm and leg work. Gas samples are analysed by gas chromatograph, using silica gel and molecular sieve/glass columns. Recirculation of the foreign gas is avoided by collection of the final gas sample after 7 sec of rebreathing. Allowance is also made for other systematic errors, including the dead space of the sampling needles and solution of gas in the lung parenchyma.

Solubility of Acetylene in Lung Tissue as an Error in Cardiac Output Determination with the Acetylene Method

AbstractThe solubility of acetylene in lung tissue is measured by a rebreathing technique. Enough acetylene is dissolved in the lung tissue to simulate an extra gaseous lung volume between 0.274–0.48 liters. This should give an error of 7–12 % in cardiac output determination with the acetylene rebreathing method.

Quantitative Measurement of Valvular Efficiency of the Human Heart

In the preceding paper it was shown that the stroke output of the heart may be measured accurately by calculation from the diastolic and systolic areas traced on a roentgenkymogram. Actually, this is a measure of the amount of blood expelled from the heart; in the subject with normal valves it equals the net amount of blood circulated by the stroke. In the patient with aortic or mitral regurgitation, however, we should expect that such equality would not hold and the amount of blood circulated would be less than the amount expelled from the heart by the amount of regurgitation. The net amount of blood circulated may be measured by the acetylene-rebreathing method. We have found it possible to make what are essentially simultaneous roentgenkymograms and acetylene cardiac output determinations. Comparison of the two results with this procedure should give an absolute quantitative measure of the extent of the back leakage (or the efficiency) of the mitral and aortic valves. The equation we have developed for the calculation of stroke volume gives, by definition, an average efficiency of the valves of 100% when subjects with normal valves are studied in this way with the two procedures used simultaneously. We have applied this procedure to a series of cases of aortic, mitral, and double aortic and mitral regurgitation and invariably have obtained results which differ from the normal subjects in the expected way. The subjects were selected on the basis of a clearly defined clinical condition and ability to cooperate in the acetylene rebreathing. None of the subjects was decompensated, though several were on the verge of decompensation or had been decompensated at some time. The clinical evaluation of the lesions in the various patients differentiated 3 groups: (1) minimal leaks, (2) moderate leaks, (3) severe leaks.