850
CLINICAL PRACTICE
Effects of increased inspired oxygen concentrations on exercise performance in chronic heart failure
Exercise capacity in patients with stable heart failure may be influenced by prolonged drug treatment or exercise training, but acute interventions are generally thought to have little effect. Cardiorespiratory responses to exercise were studied in 12 consecutive patients with chronic congestive heart failure who underwent serial submaximal and maximal exercise tests at inspired oxygen concentrations of 21% (room air), 30%, and 50%. Mean (SD) exercise duration during progressive testing to maximum exercise capacity was prolonged from 548 (276) s on room air to 632 (285) s on 50% oxygen (p=0·012). During steady-state exercise at 45 W, oxygen enrichment to 50% was associated with significantly increased arterial oxygen saturation (94·6 [1·9] % to 97·5 [1·3] %), and significantly reduced minute ventilation (36·1 [8·6] l/min to 28·1 [5·9] l/min), cardiac output (7·5 [2·3] l/min to 6·5 [1 &mid ot;9] l/min), and subjective scores for fatigue and breathlessness (13·9 [3·1] to 11·5 [3·5]) compared with room air; intermediate changes were observed with 30% inspired oxygen. Increased inspired oxygen concentrations can
improve
exercise
ventilatory responses to steady-state and progressive exercise, and subjective perceptions of exertion and dyspnoea, in patients with stable left ventricular failure who breathed room and oxygen-enriched air. Patients and methods 12 patients with stable congestive cardiac failure, mean age 55 years (range 31-66), were studied. 11had dilated cardiomyopathy and 1 had a history of ischaemic heart disease and coronary artery
bypass surgery but had no inducible ischaemia during exercise testing (table i). Pulmonary function tests at outset showed none to have obstructive airways disease (defmed as forced expiratory volume in 1 s [FEVI]/vital capacity [VC] below 70%) and none were current smokers. 7 patients had New York Heart Association (NYHA) class II cardiac failure, and 5 were in class IIL6 Patients assessed in our exercise laboratory before enrohnent to exclude chronic airways obstruction and to assess suitability for exercise testing. The study protocol was approved by local research ethics committees and informed consent was obtained from each patient. were
TABLE I-PATIENT CHARACTERISTICS
performance acutely and modify
the ventilatory response to exercise in patients with heart failure. Hyperoxia reduces ventilatory response and circulatory demand while maintaining oxygen delivery at a given workload. The potential benefits of increased inspired oxygen concentrations in the treatment of chronic heart failure merit further assessment.
CCF=congest!ve cardiac failure, DCM =dilated cardiomyopathy, !HD=)Schaem!C heart disease, ’V02 oxygen consumption dunng exercise test
Introduction Breathlessness is a principal feature of congestive cardiac failure, but the pathophysiology that underlies this symptom is unclear. Ventilation at rest is usually normal in patients with controlled heart failure, but on exercise they show a greater increase in respiratory rate and minute ventilation than do normal controls.13Supplementary oxygen was shown to reduce the ventilatory response to strenuous exercise over 30 years ago,4 and the benefits of higher inspired oxygen concentrations on exercise in chronic respiratory failure have been known for nearly 20 years. But although oxygen is routinely used for the relief of dyspnoea in patients with acute left ventricular failure, there had been no study of its effects on exercise performance in chronic heart failure. We investigated haemodynamic and
Subjects underwent an identical series of bicycle ergometer exercise tests (Siemens ’EM 840’, Erlangen, Germany) on 3 different days, during which inspired air was either room air or oxygen-enriched to an inspired oxygen concentration (FiOz) of 30% or 50%. Three steady-state exercise bouts of3 min duration at 15,30, and 45 W, with rest periods of 10 min between bouts, were followed after a further rest period of 15 min by a final exercise test to maximum capacity in which workload was increased by 15 W at 2-min intervals. Exercise tests at the different inspired oxygen concentrations were done on three separate days, at approximately the same time; the order in which different oxygen concentrations ADDRESSES: Divisions of Clinical Cardiology (D. P. Moore, MRCPI, A. R Weston, BPhEd, C. M. Oakley, FRCP, J. G. F. Cleland, FRCP), and Respiratory Medicine (J. M. B. Hughes, FRCP), Royal Postgraduate Medical School, Du Cane Road, London W12 ONN, UK. Correspondence to Dr John Cleland.
851
TABLE II-RESTING PULMONARY FUNCTION
FEVforced expiratory volume in 1 s (lis), vevital capacity (I), DLCO = diffusing capacity for carbon monoxide (ml/mm per kPa)
administered was determined by a randomised block design, patients were blind to the oxygen concentration in the inspired reservoir, and subjective tests were administered by a non-medical assistant who was unaware of the results of gas analysis. For steady-state exercise, patients were connected via a nonrebreathe valve to a 500 1 capacity Douglas bag (inspiratory reservoir) and inspired volume (VI) was determined from a Parkinson-Cowan gas meter. Ventilation and electrocardiograph trace were monitored continuously. Cardiac output was measured during exercise at the end of each submaximal exercise period by an inert-gas rebreathing technique with modifications to correct for abnormalities in gas mixing.’ Arterial oxygen saturation (Sa02) was estimated with a Hewlett-Packard 47201A oximeter (Cambridge, UK) and a heated ear probe. Blood was taken for haemoglobin to estimation calculate oxygen delivery (oxygen delivery 1-34 x Hb [g/1] x Sa02 x cardiac output). Patients were asked to score their effort on a standard Borg scale on completion of each exercise period.8 During the progressive test to maximum exercise capacity, workload increased by 15 W every 2 min; similar measurements, with the exception of cardiac output, were made during the last 15s of each minute although visual analogue scales were used to assess dyspnoea at each workload during the continuous test. Patients were encouraged to exercise to exhaustion. Measurements of CO2 production cVC02) or O2 consumption were not repeated during exercise with oxygen-enriched air; oxygen delivery was calculated from cardiac output, haemoglobin, and oxygen saturation during exercise. VC02 was also measured with an analyser that provided averaged data every 15 s (’Horizon II’, Sensor Medics, Anaheim, Calif, USA) in 8 subjects during a separate series of exercise tests with the same protocol at identical concentrations of inspired oxygen. Paired Student’s t tests were used for within-patient analyses of the data; results are expressed as mean (SD). were
=
Fig 1-Effects of progressive exercise at various inspired oxygen concentrations.
Above, arterial oxygen saturation, middle, CO2 production; below,
analogue scores for dyspnoea Mean values shown; 0———0=air; W————W=30% inspired oxygen, A————A =50% inspired oxygen. When not shown values for 30% oxygen were intermediate between air and 50% oxygen.
visual
significant) and 75 (25) s on 50% oxygen (p = 0-0125). Expired CO, was measured in a further series of progressive exercise tests on room air and on 50% oxygen in 8 patients who had achieved more than 6 min progressive exercise in room air: the area under the curve (AUC) for CO2 production was calculated for the first 6 min of exercise. Expired CO2 was consistently lower on 50% inspired 30% oxygen (not
Results
Preliminary maximal exercise testing on a standard protocol showed a mean maximum oxygen consumption of 13-2 ml/min per kg (SD 4-5, range 7 ’0-21,1), indicative of severe limitation of aerobic capacity. Resting pulmonary function tests showed reduced lung volumes in all patients, but not airflow obstruction; carbon monoxide diffusing capacity was less than 75% of the predicted value in 4 patients (table 11). During progressive exercise, arterial oxygen saturation on room air fell by more than 1 % in 4 patients but mean arterial oxygen saturation was unchanged from resting values. A significant increase in arterial oxygen saturation was seen with oxygen-enriched air (fig 1): after 5 min exercise on room air arterial oxygen saturation was 94-1 (2-2)% compared with 96-7 (L8)% on 30% inspired oxygen and 98-4 (1’0)% on 50% inspired oxygen. Total exercise duration was prolonged from 548 (275) s on room air to 578 (275) s on 30% inspired oxygen and 632 (288) s on 50% oxygen (p < 0-05). Mean within-patient increases in exercise duration from values for room air exercise were 23 (14) s on incremental
oxygen than air and the area under the curve fell from 1 -86 to 1-36 1/W.min (p
CLINICAL PRACTICE
Effects of increased inspired oxygen concentrations on exercise performance in chronic heart failure
Exercise capacity in patients with stable heart failure may be influenced by prolonged drug treatment or exercise training, but acute interventions are generally thought to have little effect. Cardiorespiratory responses to exercise were studied in 12 consecutive patients with chronic congestive heart failure who underwent serial submaximal and maximal exercise tests at inspired oxygen concentrations of 21% (room air), 30%, and 50%. Mean (SD) exercise duration during progressive testing to maximum exercise capacity was prolonged from 548 (276) s on room air to 632 (285) s on 50% oxygen (p=0·012). During steady-state exercise at 45 W, oxygen enrichment to 50% was associated with significantly increased arterial oxygen saturation (94·6 [1·9] % to 97·5 [1·3] %), and significantly reduced minute ventilation (36·1 [8·6] l/min to 28·1 [5·9] l/min), cardiac output (7·5 [2·3] l/min to 6·5 [1 &mid ot;9] l/min), and subjective scores for fatigue and breathlessness (13·9 [3·1] to 11·5 [3·5]) compared with room air; intermediate changes were observed with 30% inspired oxygen. Increased inspired oxygen concentrations can
improve
exercise
ventilatory responses to steady-state and progressive exercise, and subjective perceptions of exertion and dyspnoea, in patients with stable left ventricular failure who breathed room and oxygen-enriched air. Patients and methods 12 patients with stable congestive cardiac failure, mean age 55 years (range 31-66), were studied. 11had dilated cardiomyopathy and 1 had a history of ischaemic heart disease and coronary artery
bypass surgery but had no inducible ischaemia during exercise testing (table i). Pulmonary function tests at outset showed none to have obstructive airways disease (defmed as forced expiratory volume in 1 s [FEVI]/vital capacity [VC] below 70%) and none were current smokers. 7 patients had New York Heart Association (NYHA) class II cardiac failure, and 5 were in class IIL6 Patients assessed in our exercise laboratory before enrohnent to exclude chronic airways obstruction and to assess suitability for exercise testing. The study protocol was approved by local research ethics committees and informed consent was obtained from each patient. were
TABLE I-PATIENT CHARACTERISTICS
performance acutely and modify
the ventilatory response to exercise in patients with heart failure. Hyperoxia reduces ventilatory response and circulatory demand while maintaining oxygen delivery at a given workload. The potential benefits of increased inspired oxygen concentrations in the treatment of chronic heart failure merit further assessment.
CCF=congest!ve cardiac failure, DCM =dilated cardiomyopathy, !HD=)Schaem!C heart disease, ’V02 oxygen consumption dunng exercise test
Introduction Breathlessness is a principal feature of congestive cardiac failure, but the pathophysiology that underlies this symptom is unclear. Ventilation at rest is usually normal in patients with controlled heart failure, but on exercise they show a greater increase in respiratory rate and minute ventilation than do normal controls.13Supplementary oxygen was shown to reduce the ventilatory response to strenuous exercise over 30 years ago,4 and the benefits of higher inspired oxygen concentrations on exercise in chronic respiratory failure have been known for nearly 20 years. But although oxygen is routinely used for the relief of dyspnoea in patients with acute left ventricular failure, there had been no study of its effects on exercise performance in chronic heart failure. We investigated haemodynamic and
Subjects underwent an identical series of bicycle ergometer exercise tests (Siemens ’EM 840’, Erlangen, Germany) on 3 different days, during which inspired air was either room air or oxygen-enriched to an inspired oxygen concentration (FiOz) of 30% or 50%. Three steady-state exercise bouts of3 min duration at 15,30, and 45 W, with rest periods of 10 min between bouts, were followed after a further rest period of 15 min by a final exercise test to maximum capacity in which workload was increased by 15 W at 2-min intervals. Exercise tests at the different inspired oxygen concentrations were done on three separate days, at approximately the same time; the order in which different oxygen concentrations ADDRESSES: Divisions of Clinical Cardiology (D. P. Moore, MRCPI, A. R Weston, BPhEd, C. M. Oakley, FRCP, J. G. F. Cleland, FRCP), and Respiratory Medicine (J. M. B. Hughes, FRCP), Royal Postgraduate Medical School, Du Cane Road, London W12 ONN, UK. Correspondence to Dr John Cleland.
851
TABLE II-RESTING PULMONARY FUNCTION
FEVforced expiratory volume in 1 s (lis), vevital capacity (I), DLCO = diffusing capacity for carbon monoxide (ml/mm per kPa)
administered was determined by a randomised block design, patients were blind to the oxygen concentration in the inspired reservoir, and subjective tests were administered by a non-medical assistant who was unaware of the results of gas analysis. For steady-state exercise, patients were connected via a nonrebreathe valve to a 500 1 capacity Douglas bag (inspiratory reservoir) and inspired volume (VI) was determined from a Parkinson-Cowan gas meter. Ventilation and electrocardiograph trace were monitored continuously. Cardiac output was measured during exercise at the end of each submaximal exercise period by an inert-gas rebreathing technique with modifications to correct for abnormalities in gas mixing.’ Arterial oxygen saturation (Sa02) was estimated with a Hewlett-Packard 47201A oximeter (Cambridge, UK) and a heated ear probe. Blood was taken for haemoglobin to estimation calculate oxygen delivery (oxygen delivery 1-34 x Hb [g/1] x Sa02 x cardiac output). Patients were asked to score their effort on a standard Borg scale on completion of each exercise period.8 During the progressive test to maximum exercise capacity, workload increased by 15 W every 2 min; similar measurements, with the exception of cardiac output, were made during the last 15s of each minute although visual analogue scales were used to assess dyspnoea at each workload during the continuous test. Patients were encouraged to exercise to exhaustion. Measurements of CO2 production cVC02) or O2 consumption were not repeated during exercise with oxygen-enriched air; oxygen delivery was calculated from cardiac output, haemoglobin, and oxygen saturation during exercise. VC02 was also measured with an analyser that provided averaged data every 15 s (’Horizon II’, Sensor Medics, Anaheim, Calif, USA) in 8 subjects during a separate series of exercise tests with the same protocol at identical concentrations of inspired oxygen. Paired Student’s t tests were used for within-patient analyses of the data; results are expressed as mean (SD). were
=
Fig 1-Effects of progressive exercise at various inspired oxygen concentrations.
Above, arterial oxygen saturation, middle, CO2 production; below,
analogue scores for dyspnoea Mean values shown; 0———0=air; W————W=30% inspired oxygen, A————A =50% inspired oxygen. When not shown values for 30% oxygen were intermediate between air and 50% oxygen.
visual
significant) and 75 (25) s on 50% oxygen (p = 0-0125). Expired CO, was measured in a further series of progressive exercise tests on room air and on 50% oxygen in 8 patients who had achieved more than 6 min progressive exercise in room air: the area under the curve (AUC) for CO2 production was calculated for the first 6 min of exercise. Expired CO2 was consistently lower on 50% inspired 30% oxygen (not
Results
Preliminary maximal exercise testing on a standard protocol showed a mean maximum oxygen consumption of 13-2 ml/min per kg (SD 4-5, range 7 ’0-21,1), indicative of severe limitation of aerobic capacity. Resting pulmonary function tests showed reduced lung volumes in all patients, but not airflow obstruction; carbon monoxide diffusing capacity was less than 75% of the predicted value in 4 patients (table 11). During progressive exercise, arterial oxygen saturation on room air fell by more than 1 % in 4 patients but mean arterial oxygen saturation was unchanged from resting values. A significant increase in arterial oxygen saturation was seen with oxygen-enriched air (fig 1): after 5 min exercise on room air arterial oxygen saturation was 94-1 (2-2)% compared with 96-7 (L8)% on 30% inspired oxygen and 98-4 (1’0)% on 50% inspired oxygen. Total exercise duration was prolonged from 548 (275) s on room air to 578 (275) s on 30% inspired oxygen and 632 (288) s on 50% oxygen (p < 0-05). Mean within-patient increases in exercise duration from values for room air exercise were 23 (14) s on incremental
oxygen than air and the area under the curve fell from 1 -86 to 1-36 1/W.min (p
