829
Thorax 1991;46:829-834
Changes in atrial natriuretic peptide concentrations during intravenous saline infusion in hypoxic cor pulmonale A G Stewart, P A Bardsley, S V Baudouin, J C Waterhouse, J S Thompson, A H Morice, P Howard
University Department of Medicine and Pharmacology, Royal Hallamshire Hospital, Sheffield S10 2JF A G Stewart P A Bardsley S V Baudouin J C Waterhouse J S Thompson A H Morice P Howard
Reprint requests to: Dr Stewart
Accepted 22 August 1991
Abstract of pathogenesis Background The oedema in hypoxic cor pulmonale is poorly understood. One possibility is a failure of atrial natriuretic peptide release, leading to salt and water retention. This hypothesis was tested by observing the response to an intravenous saline challenge in patients with and without cor pulmonale. Methods Plasma atrial natriuretic peptide concentrations were measured before and for three hours after an intravenous saline load (0-1 ml 2-7% saline/kg/min for 60 minutes) in 20 patients with chronic obstructive airways disease. Ten patients with cor pulmonale, as judged clinically by the presence of peripheral oedema with a previously documented increase in the jugular venous pressure or pleural effusions during an acute exacerbation of airway obstruction (mean (SE) age 67 (3) years, FEV, 0 73 (0-08) 1, arterial oxygen tension (Pao2) 6-4 (0-4) kPa, and arterial carbon dioxide tension (Paco2) 6-7 (0 3) kPa), were compared with 10 patients with hypoxic chronic obstructive airways disease who had never had oedema (mean age 63 (1) years, FEV, 1-07 (0-09) 1, Pao2 8-6 (0-4) kPa, and PacO2 53 (0-2) kPa). All patients were studied fasting and after diuretics had been stopped for three days. No supplemental oxygen was given. Results The mean four hourly urine sodium excretion was less in the patients who had oedema (27 (4-6) mmol, 13% of the intravenous load) than in those without oedema (82 (15 5) mmol, 43% of the load). Initial mean plasma atrial natriuretic peptide values were significantly higher in the patients with cor pulmonale (19 1 (1-6) compared with 10-2 (0-7) pmolIl) and the mean peak rise in atrial natriuretic peptide after the intravenous saline load had been given was 13 (8-0) pmol/l in the patients with cor pulmonale and 5 5 (2 3) pmol/l in the controls. There were no significant differences in plasma and urinary osmolality, blood pressure, or creatinine clearance between the groups. chronic with Conclusion Patients obstructive airways disease and cor pulmonale have an impaired ability to excrete a hypertonic intravenous saline load despite a normal physiological
release of plasma atrial natriuretic peptide. Atrial natriuretic peptide, a 28 amino acid hormone, is formed and stored in atrial myocytes and secreted predominantly into the right atrium in response to atrial stretch, as may occur with volume overload' or tricuspid regurgitation.2 Although plasma atrial natriuretic peptide concentrations are raised in chronic obstructive airways disease, the concentrations correlate poorly with pulmonary artery pressure.3 Atrial natriuretic peptide has potent natriuretic and diuretic actions and helps to regulate fluid balance.4 Patients with hypoxic chronic obstructive airways disease who develop oedema have a poor prognosis, 70% dying within five years.5 Cardiac output is usually normal or increased,6 renal blood flow is reduced,7 and excretion of water and salt loads is impaired.8 This defect in salt and water handling correlates strongly with the degree of hypercapnia; patients who are hypoxaemic but normocapnic are able to handle a salt and water load
fairly normally.8
Abnormalities in antidiuretic hormone secretion and activation of the renin-aldosterone system have been found in patients with chronic obstructive airways disease and hypercapnia. Investigations by Farber et al8 sugggest that the ability to handle a salt load diminishes with the development of hypercapnia as a result of a reduction in renal blood flow. The onset of oedema is associated with stimulation of the renin-angiotensin-aldosterone axis and the antidiuretic hormone system. A raised aldosterone concentration may contribute to sodium retention and the increase in antidiuretic hormone to hyponatraemia. These changes could be due to a further reduction in renal blood flow in cor pulmonale rather than being a cause of the oedema. Atrial natriuretic peptide has been reported to lower antidiuretic hormone levels9 and to antagonise the renin-angiotensinaldosterone system,'0 reducing renin and aldosterone secretion and acting as a functional antagonist to aldosterone and angiotensin II. Although these actions do not play a part in acute natriuresis they may be important in the long term control of sodium balance. In normal individuals acute volume expansion increases plasma atrial natriuretic peptide
Stewart, Bardsley, Baudouin, Waterhouse, Thompson, Morice, Howard
830
concentrations and causes natriuresis.'" To investigate whether a failure of atrial natriuretic peptide secretion or a lack of response to circulating atrial natriuretic peptide could underlie the fluid and sodium retention in patients with cor pulmonale, we compared basal concentrations of atrial natriuretic peptide and its response to an infusion of 2-7% saline in patients with cor pulmonale and in patients with hypoxaemic chronic obstructive airways disease but no current or previous evidence of fluid retention or right heart failure. Methods
4-5 hours of the test and used as a measure of the glomerular filtration rate. Filtered sodium (mmol/min) was calculated by multiplying the glomerular filtration rate by the plasma sodium concentration. Fractional sodium reabsorption was calculated by dividing excreted sodium (mmol/min) by the filtered sodium and subtracting from 1, the fraction being expressed as a percentage. Free water clearance was calculated from the average of the plasma osmolalities during the test (Posm) and the end urine osmolality (Uosm) and the minute urine volume (Uv) by means of the formula
Free water clearance = Uv - (Uosm x Uv/Posm).
PATIENTS
Ten patients with stable cor pulmonale (as judged clinically by the presence of peripheral oedema and a previously documented rise in the jugular venous pressure or pleural effusions or both) and 10 patients with hypoxaemic chronic obstructive airways disease with no previous or current history of oedema were chosen from patients attending the chest clinic. Patients with known heart disease, liver disease, renal disease, hormone disorder, or diabetes mellitus were excluded. Subjects ate a conventional diet and fasted overnight. Diuretics were stopped for three days before the study. The study was approved by the Ethical Committee of the Sheffield Health Authority. All patients gave consent freely after the aims and requirements of the study had been explained.
The negative value is the renal reabsorption of water in ml/minute. ATRIAL NATRIURETIC PEPTIDE ASSAY
Initial extraction of plasma atrial natriuretic peptide was carried out with Sep-Pak C18 cartridges (Waters Associates). One millilitre of plasma acidified with trifluoroacetic acid (0-1%) was applied to a primed cartridge, washed with 5 ml 0 15 trifluoroacetic acid, and eluted with 2-5 ml of 60% acetonitrile. Samples were vacuum dried and then reconstituted with 1 ml of assay buffer (consisting of 40 mM disodium hydrogen o-phosphate, 70 mM sodium dihydrogen o-phosphate, 7 mM sodium azide, 5 mM ethylenediaminetetra-acetate, and 0 5% bovine serum albumin with the pH adjusted to 7 4). Aliquots of 100 ml were assayed in duplicate. Assay incubations consisted of 100 jMl atrial MEASUREMENTS AND SAMPLES The patients were brought by taxi to the natriuretic peptide labelled with iodine-125 laboratory at 09 00 hours and weighed. Spiro- (4000-6000 cpm/100 pi), 100 pl sheep polymetry (Vitalograph Compact) was performed clonal anti-atrial natriuretic peptide antibody, and the patients then emptied their bladders, 200 Ml assay buffer, and 100 pl buffer containing the urine being collected for measurement of atrial natriuretic peptide standards or plasma osmolality and electrolytes. Blood pressure extracts. Samples were incubated for four to (sphygmomanometer), pulse rate, and arterial five days at 4°C. Separation of the bound and oxygen saturation (pulse oximeter, Ohmeda free fractions was achieved by adding 100 p1 Biox 3700) were recorded. Patients remained 2% IgG in assay buffer and 1 ml polyethylene seated throughout the salt load test. glycol (MW 6000) to each tube followed by Blood for determining urea and electrolyte centrifugation at 3500 rev/min for 45 minutes. About 60% of the label was bound in the concentrations (Technicon SMAC analyser) and osmolality (Advance osmometer 2WII) absence of the unlabelled peptide and 5-10% in were collected into serum tubes and plasma the absence of antibody. The intra-assay cofor assay of atrial natriuretic peptide into efficient of variation was 8-5% and the 95% tubes containing ethylenediaminetetra-acetate confidence detection limit was 2-5 pmol/l of (EDTA). The EDTA tubes were centrifuged plasma. immnediately and the plasma was removed and frozen at - 20'C until it was assayed. Samples ANALYSIS were taken 30 minutes before and at the time of Means and standard errors of the mean (SE) are the saline infusion (time zero) and 60, 120, 180, given for group data. Groups are compared by and 240 minutes afterwards. At time zero the a two sample (unpaired) t test. Values of p subjects received 6 ml/kg intravenous 2-7% below 0-05 are considered significant. (3N) saline (450 mmol/l) over 60 minutes (that is 0-1 ml/kg/min). Blood pressure and arterial oxygen saturation were recorded at each time Results point. After four hours arterial blood gases Details of the patients are shown in table 1. All were measured. The patients emptied their the patients with cor pulmonale were receiving bladders, urine volume was noted, and the long term oxygen therapy. None of the control urinary excretion of sodium and creatinine and group was having long term oxygen therapy, though two patients had intermittent oxygen. osmolality were measured. With the exception of prior diuretics, the CALCULATION OF CREATININE CLEARANCE pharmacological treatment was similar in the Creatinine clearance was calculated over the two groups. Two of the "non-oedematous"
Changes in atrial natruiretic peptide concentrations during intravenous saline infusion in hypoxic cor pulmonale
patients were taking diuretics; one had a diagnosis of hypertension and the other had had them prescribed by his general practitioner for breathlessness (without evidence of fluid retention). The 10 patients (two female) with cor pulmonale had a similar mean (SE) age (67 (3) years) and weight (81-7 (6-2 kg) as the 10 patients (three female) without cor pulmonale
831
(age 63 (1) years and weight 66-7 4-4 kg); but the patients with cor pulmonale had a lower FEV1 (0-73 (0-08) v 1-07 (0-09) 1; p < 0-05) and arterial oxygen tension (6-4 (0-4) v 8-6 (0-4) kPa; p < 0-01), and a higher arterial carbon dioxide tension (6-7 (0-3) v 5-3 (0-2) kPa; p
Thorax 1991;46:829-834
Changes in atrial natriuretic peptide concentrations during intravenous saline infusion in hypoxic cor pulmonale A G Stewart, P A Bardsley, S V Baudouin, J C Waterhouse, J S Thompson, A H Morice, P Howard
University Department of Medicine and Pharmacology, Royal Hallamshire Hospital, Sheffield S10 2JF A G Stewart P A Bardsley S V Baudouin J C Waterhouse J S Thompson A H Morice P Howard
Reprint requests to: Dr Stewart
Accepted 22 August 1991
Abstract of pathogenesis Background The oedema in hypoxic cor pulmonale is poorly understood. One possibility is a failure of atrial natriuretic peptide release, leading to salt and water retention. This hypothesis was tested by observing the response to an intravenous saline challenge in patients with and without cor pulmonale. Methods Plasma atrial natriuretic peptide concentrations were measured before and for three hours after an intravenous saline load (0-1 ml 2-7% saline/kg/min for 60 minutes) in 20 patients with chronic obstructive airways disease. Ten patients with cor pulmonale, as judged clinically by the presence of peripheral oedema with a previously documented increase in the jugular venous pressure or pleural effusions during an acute exacerbation of airway obstruction (mean (SE) age 67 (3) years, FEV, 0 73 (0-08) 1, arterial oxygen tension (Pao2) 6-4 (0-4) kPa, and arterial carbon dioxide tension (Paco2) 6-7 (0 3) kPa), were compared with 10 patients with hypoxic chronic obstructive airways disease who had never had oedema (mean age 63 (1) years, FEV, 1-07 (0-09) 1, Pao2 8-6 (0-4) kPa, and PacO2 53 (0-2) kPa). All patients were studied fasting and after diuretics had been stopped for three days. No supplemental oxygen was given. Results The mean four hourly urine sodium excretion was less in the patients who had oedema (27 (4-6) mmol, 13% of the intravenous load) than in those without oedema (82 (15 5) mmol, 43% of the load). Initial mean plasma atrial natriuretic peptide values were significantly higher in the patients with cor pulmonale (19 1 (1-6) compared with 10-2 (0-7) pmolIl) and the mean peak rise in atrial natriuretic peptide after the intravenous saline load had been given was 13 (8-0) pmol/l in the patients with cor pulmonale and 5 5 (2 3) pmol/l in the controls. There were no significant differences in plasma and urinary osmolality, blood pressure, or creatinine clearance between the groups. chronic with Conclusion Patients obstructive airways disease and cor pulmonale have an impaired ability to excrete a hypertonic intravenous saline load despite a normal physiological
release of plasma atrial natriuretic peptide. Atrial natriuretic peptide, a 28 amino acid hormone, is formed and stored in atrial myocytes and secreted predominantly into the right atrium in response to atrial stretch, as may occur with volume overload' or tricuspid regurgitation.2 Although plasma atrial natriuretic peptide concentrations are raised in chronic obstructive airways disease, the concentrations correlate poorly with pulmonary artery pressure.3 Atrial natriuretic peptide has potent natriuretic and diuretic actions and helps to regulate fluid balance.4 Patients with hypoxic chronic obstructive airways disease who develop oedema have a poor prognosis, 70% dying within five years.5 Cardiac output is usually normal or increased,6 renal blood flow is reduced,7 and excretion of water and salt loads is impaired.8 This defect in salt and water handling correlates strongly with the degree of hypercapnia; patients who are hypoxaemic but normocapnic are able to handle a salt and water load
fairly normally.8
Abnormalities in antidiuretic hormone secretion and activation of the renin-aldosterone system have been found in patients with chronic obstructive airways disease and hypercapnia. Investigations by Farber et al8 sugggest that the ability to handle a salt load diminishes with the development of hypercapnia as a result of a reduction in renal blood flow. The onset of oedema is associated with stimulation of the renin-angiotensin-aldosterone axis and the antidiuretic hormone system. A raised aldosterone concentration may contribute to sodium retention and the increase in antidiuretic hormone to hyponatraemia. These changes could be due to a further reduction in renal blood flow in cor pulmonale rather than being a cause of the oedema. Atrial natriuretic peptide has been reported to lower antidiuretic hormone levels9 and to antagonise the renin-angiotensinaldosterone system,'0 reducing renin and aldosterone secretion and acting as a functional antagonist to aldosterone and angiotensin II. Although these actions do not play a part in acute natriuresis they may be important in the long term control of sodium balance. In normal individuals acute volume expansion increases plasma atrial natriuretic peptide
Stewart, Bardsley, Baudouin, Waterhouse, Thompson, Morice, Howard
830
concentrations and causes natriuresis.'" To investigate whether a failure of atrial natriuretic peptide secretion or a lack of response to circulating atrial natriuretic peptide could underlie the fluid and sodium retention in patients with cor pulmonale, we compared basal concentrations of atrial natriuretic peptide and its response to an infusion of 2-7% saline in patients with cor pulmonale and in patients with hypoxaemic chronic obstructive airways disease but no current or previous evidence of fluid retention or right heart failure. Methods
4-5 hours of the test and used as a measure of the glomerular filtration rate. Filtered sodium (mmol/min) was calculated by multiplying the glomerular filtration rate by the plasma sodium concentration. Fractional sodium reabsorption was calculated by dividing excreted sodium (mmol/min) by the filtered sodium and subtracting from 1, the fraction being expressed as a percentage. Free water clearance was calculated from the average of the plasma osmolalities during the test (Posm) and the end urine osmolality (Uosm) and the minute urine volume (Uv) by means of the formula
Free water clearance = Uv - (Uosm x Uv/Posm).
PATIENTS
Ten patients with stable cor pulmonale (as judged clinically by the presence of peripheral oedema and a previously documented rise in the jugular venous pressure or pleural effusions or both) and 10 patients with hypoxaemic chronic obstructive airways disease with no previous or current history of oedema were chosen from patients attending the chest clinic. Patients with known heart disease, liver disease, renal disease, hormone disorder, or diabetes mellitus were excluded. Subjects ate a conventional diet and fasted overnight. Diuretics were stopped for three days before the study. The study was approved by the Ethical Committee of the Sheffield Health Authority. All patients gave consent freely after the aims and requirements of the study had been explained.
The negative value is the renal reabsorption of water in ml/minute. ATRIAL NATRIURETIC PEPTIDE ASSAY
Initial extraction of plasma atrial natriuretic peptide was carried out with Sep-Pak C18 cartridges (Waters Associates). One millilitre of plasma acidified with trifluoroacetic acid (0-1%) was applied to a primed cartridge, washed with 5 ml 0 15 trifluoroacetic acid, and eluted with 2-5 ml of 60% acetonitrile. Samples were vacuum dried and then reconstituted with 1 ml of assay buffer (consisting of 40 mM disodium hydrogen o-phosphate, 70 mM sodium dihydrogen o-phosphate, 7 mM sodium azide, 5 mM ethylenediaminetetra-acetate, and 0 5% bovine serum albumin with the pH adjusted to 7 4). Aliquots of 100 ml were assayed in duplicate. Assay incubations consisted of 100 jMl atrial MEASUREMENTS AND SAMPLES The patients were brought by taxi to the natriuretic peptide labelled with iodine-125 laboratory at 09 00 hours and weighed. Spiro- (4000-6000 cpm/100 pi), 100 pl sheep polymetry (Vitalograph Compact) was performed clonal anti-atrial natriuretic peptide antibody, and the patients then emptied their bladders, 200 Ml assay buffer, and 100 pl buffer containing the urine being collected for measurement of atrial natriuretic peptide standards or plasma osmolality and electrolytes. Blood pressure extracts. Samples were incubated for four to (sphygmomanometer), pulse rate, and arterial five days at 4°C. Separation of the bound and oxygen saturation (pulse oximeter, Ohmeda free fractions was achieved by adding 100 p1 Biox 3700) were recorded. Patients remained 2% IgG in assay buffer and 1 ml polyethylene seated throughout the salt load test. glycol (MW 6000) to each tube followed by Blood for determining urea and electrolyte centrifugation at 3500 rev/min for 45 minutes. About 60% of the label was bound in the concentrations (Technicon SMAC analyser) and osmolality (Advance osmometer 2WII) absence of the unlabelled peptide and 5-10% in were collected into serum tubes and plasma the absence of antibody. The intra-assay cofor assay of atrial natriuretic peptide into efficient of variation was 8-5% and the 95% tubes containing ethylenediaminetetra-acetate confidence detection limit was 2-5 pmol/l of (EDTA). The EDTA tubes were centrifuged plasma. immnediately and the plasma was removed and frozen at - 20'C until it was assayed. Samples ANALYSIS were taken 30 minutes before and at the time of Means and standard errors of the mean (SE) are the saline infusion (time zero) and 60, 120, 180, given for group data. Groups are compared by and 240 minutes afterwards. At time zero the a two sample (unpaired) t test. Values of p subjects received 6 ml/kg intravenous 2-7% below 0-05 are considered significant. (3N) saline (450 mmol/l) over 60 minutes (that is 0-1 ml/kg/min). Blood pressure and arterial oxygen saturation were recorded at each time Results point. After four hours arterial blood gases Details of the patients are shown in table 1. All were measured. The patients emptied their the patients with cor pulmonale were receiving bladders, urine volume was noted, and the long term oxygen therapy. None of the control urinary excretion of sodium and creatinine and group was having long term oxygen therapy, though two patients had intermittent oxygen. osmolality were measured. With the exception of prior diuretics, the CALCULATION OF CREATININE CLEARANCE pharmacological treatment was similar in the Creatinine clearance was calculated over the two groups. Two of the "non-oedematous"
Changes in atrial natruiretic peptide concentrations during intravenous saline infusion in hypoxic cor pulmonale
patients were taking diuretics; one had a diagnosis of hypertension and the other had had them prescribed by his general practitioner for breathlessness (without evidence of fluid retention). The 10 patients (two female) with cor pulmonale had a similar mean (SE) age (67 (3) years) and weight (81-7 (6-2 kg) as the 10 patients (three female) without cor pulmonale
831
(age 63 (1) years and weight 66-7 4-4 kg); but the patients with cor pulmonale had a lower FEV1 (0-73 (0-08) v 1-07 (0-09) 1; p < 0-05) and arterial oxygen tension (6-4 (0-4) v 8-6 (0-4) kPa; p < 0-01), and a higher arterial carbon dioxide tension (6-7 (0-3) v 5-3 (0-2) kPa; p
