Eur J Appl Physiol (2014) 114:2321–2329 DOI 10.1007/s00421-014-2946-2
ORIGINAL ARTICLE
Circulatory responses to lower body negative pressure in young Afghans and Danes: implications for understanding ethnic effects on blood pressure regulation Ali Asmar · Jens Bülow · Lene Simonsen · Jonas G. Rasmussen · Niels J. Christensen · Erik Frandsen · Peter Norsk
Received: 1 April 2014 / Accepted: 25 June 2014 / Published online: 25 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose We have previously shown that Afghans residing in Denmark for at least 12 years exhibit a lower 24-h ambulatory blood pressure compared to Danes. The purpose of this study was to test the hypothesis that the lower blood pressure reflects attenuated compensatory baroreflex responses in the Afghans. Methods On a controlled diet (2,822 cal/day, 55–75 mmol + 2 mmol Na+/kg/day), 12 young males of Afghan (Afghans) and 12 young males of Danish (Danes) origin were exposed to a two-step lower body negative pressure
Communicated by Michael Lindinger. A. Asmar · J. Bülow · J. G. Rasmussen · P. Norsk Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, 2200 Copenhagen, Denmark A. Asmar (*) · J. Bülow · L. Simonsen Department of Clinical Physiology and Nuclear Medicine, Bispebjerg University Hospital, 2400 Copenhagen, Denmark e-mail: [email protected] N. J. Christensen Department of Internal Medicine and Endocrinology, Herlev University Hospital, 2730 Herlev, Denmark E. Frandsen Department of Diagnostics, Clinical Physiology and Nuclear Medicine, Glostrup University Hospital, 2600 Glostrup, Denmark P. Norsk Division of Space Life Sciences, Universities Space Research Association (USRA), Houston, TX 77058, USA P. Norsk Biomedical Research and Environmental Sciences Division, NASA Johnson Space Center, Houston, TX 77058, USA
(LBNP) protocol of −20 and −50 mmHg, respectively, each of 10-min duration. Results Afghans had lower 24-h systolic blood pressure compared to Danes (115 ± 2 vs. 123 ± 1 mmHg, p 5 mmHg. The measurements were initiated 0800 h in the morning. Between 0800 and 2200 h (day time), systolic blood pressure, diastolic blood pressure, and heart rate were measured automatically each 30 min and between 2200 and 0800 h (night time) every 90 min. Arterial pulse pressure was calculated as the difference between the systolic and diastolic blood pressure. Values were averaged over the whole 24-h recording. LBNP LBNP was carried out in an airtight plexi-glass box that encased the subject in the supine position from the iliac crest and down. The pressures in the box were induced by a connection to a variable transformer, and the box pressure was continuously measured by a water manometer. Each step of LBNP was adjusted to the desired level within 5 s.
2323
Cardiac output Cardiac output was measured by noninvasive re-breathing equipment (Innocor; Innovision A/S, Odense, Denmark) developed for spaceflight by European Space Agency, and described in detail previously (Damgaard and Norsk 2005). The subjects were re-breathing through a mouthpiece back and forth into a bag with 1.4–1.8 L (30 % of vital capacity) of a gas mixture consisting of 0.5 % N2O (blood-soluble tracer gas), 0.1–1 % SF6 (non-blood-soluble tracer gas), and 25–28 % O2 in N2. The disappearance rate of N2O into blood was calculated from end-expiratory concentrations measured by photoacoustic spectroscopy connected through a tube to the mouthpiece. Based on the Bunsen blood solubility coefficients of N2O, the disappearance rate was used for calculation of pulmonary capillary blood flow, which is equal to cardiac output. End-expiratory concentrations of SF6 were used to correct for inadequate mixing of air in lungs with gas mixture from the air bag and for changes in re-breathing volume. Re-breathing lasted 30 s with a breathing frequency of 15–20 per min. Blood and urine analyses Blood samples were immediately transferred to chilled tubes and centrifuged at 1,500 g for 10 min. Thereafter, plasma samples were stored in a −80 °C freezer for later determination of plasma noradrenaline concentration analyzed by an enzyme immunoassay (LDN, Germany: Noradrenaline Research Elisa BA E-5200) and PRA measured by an immunoassay previously described by Frandsen et al. (Persson et al. 2009). The amount of collected blood was substituted with a similar amount of isotonic saline during the experiment. Urine osmolality was measured by freezing point depression (Advanced Instruments, Microosmometer 3MO, Norwood, MA, USA). Urine electrolyte concentrations (UNa and UK) were measured by an ion-selective electrode system (EML 100, Radiometer, Copenhagen, Denmark). Calculations Stroke volume was calculated from cardiac output and heart rate. Systemic vascular resistance was calculated from mean arterial pressure (1/3 × arterial pulse pressure + diastolic blood pressure) and cardiac output. Statistical analysis Data were analyzed using SigmaPlot 12 (Systat Software, Inc., Chicago, IL, USA) and are presented as mean ± SE. To detect significant changes within each group of Afghan and Danish origin, a one-way ANOVA for repeated
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Eur J Appl Physiol (2014) 114:2321–2329
Table 1 Baseline demographics and screening blood parameters in subjects of Afghan (Afghans) and Danish (Danes) origin
Table 2 24-h ambulatory blood pressure in subjects of Afghan (Afghans) and Danish (Danes) origin
Variable
Variable
N Age (years) Height (m) Weight (kg) BSA (m2) Waist (cm) Hip (cm) Waist hip ratio Daily sodium intake (g) UNa (mmol/24 h) Hemoglobin (mmol/L) Triglycerides (mmol/L) Total cholesterol (mmol/L) HDL cholesterol (mmol/L) LDL cholesterol (mmol/L) Glucose (mmol/L)
Danes 12
Afghans 12
24 ± 1 1.83 ± 0.01 78.2 ± 1.38 1.98 ± 0.04 78 ± 3 97 ± 1 0.81 ± 0.03 4.88 ± 0.17 167 ± 11
23 ± 1 1.79 ± 0.01 78.3 ± 2.7 1.97 ± 0.04 82 ± 2 94 ± 1 0.87 ± 0.01 4.89 ± 0.20 145 ± 17
9.45 ± 0.37 1.22 ± 0.11 4.20 ± 0.25 1.09 ± 0.10 2.56 ± 0.22 5.95 ± 0.16
9.77 ± 0.19 1.45 ± 0.40 3.84 ± 0.21 1.08 ± 0.08 2.27 ± 0.19 5.64 ± 0.13
83 ± 5
68 ± 4†
Creatinine (mmol/L)
Danes
N 24-h SBP (mmHg) Mean Day Night 24-h DBP (mmHg) Mean Day Night 24-h APP (mmHg) Mean Day Night 24-h HR (bpm) Mean Day Night
Afghans
12
12
123 ± 2 127 ± 2 112 ± 2
115 ± 2† 118 ± 2† 106 ± 2†
69 ± 2 72 ± 2 61 ± 2
68 ± 2 71 ± 2 61 ± 2
54 ± 2 55 ± 2 51 ± 2
46 ± 1† 47 ± 1† 45 ± 1†
60 ± 1 64 ± 2
66 ± 1† 70 ± 3†
51 ± 1
57 ± 1†
Data are mean ± SE
Data are mean ± SE
N number of subjects, BSA body surface area, UNa 24-h renal sodium excretion
N number of subjects, 24-h SBP 24-h systolic blood pressure, 24-h DBP 24-h diastolic blood pressure, 24-h APP 24-h arterial pulse pressure, 24-h HR 24-h heart rate
†
Statistically significant difference between Afghans and Danes
measurements with subsequent Students Newman–Keul’s test was applied. A Student’s unpaired t test was used to evaluate significant differences between the groups of Afghan and Danish origin. Values of p
ORIGINAL ARTICLE
Circulatory responses to lower body negative pressure in young Afghans and Danes: implications for understanding ethnic effects on blood pressure regulation Ali Asmar · Jens Bülow · Lene Simonsen · Jonas G. Rasmussen · Niels J. Christensen · Erik Frandsen · Peter Norsk
Received: 1 April 2014 / Accepted: 25 June 2014 / Published online: 25 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose We have previously shown that Afghans residing in Denmark for at least 12 years exhibit a lower 24-h ambulatory blood pressure compared to Danes. The purpose of this study was to test the hypothesis that the lower blood pressure reflects attenuated compensatory baroreflex responses in the Afghans. Methods On a controlled diet (2,822 cal/day, 55–75 mmol + 2 mmol Na+/kg/day), 12 young males of Afghan (Afghans) and 12 young males of Danish (Danes) origin were exposed to a two-step lower body negative pressure
Communicated by Michael Lindinger. A. Asmar · J. Bülow · J. G. Rasmussen · P. Norsk Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, 2200 Copenhagen, Denmark A. Asmar (*) · J. Bülow · L. Simonsen Department of Clinical Physiology and Nuclear Medicine, Bispebjerg University Hospital, 2400 Copenhagen, Denmark e-mail: [email protected] N. J. Christensen Department of Internal Medicine and Endocrinology, Herlev University Hospital, 2730 Herlev, Denmark E. Frandsen Department of Diagnostics, Clinical Physiology and Nuclear Medicine, Glostrup University Hospital, 2600 Glostrup, Denmark P. Norsk Division of Space Life Sciences, Universities Space Research Association (USRA), Houston, TX 77058, USA P. Norsk Biomedical Research and Environmental Sciences Division, NASA Johnson Space Center, Houston, TX 77058, USA
(LBNP) protocol of −20 and −50 mmHg, respectively, each of 10-min duration. Results Afghans had lower 24-h systolic blood pressure compared to Danes (115 ± 2 vs. 123 ± 1 mmHg, p 5 mmHg. The measurements were initiated 0800 h in the morning. Between 0800 and 2200 h (day time), systolic blood pressure, diastolic blood pressure, and heart rate were measured automatically each 30 min and between 2200 and 0800 h (night time) every 90 min. Arterial pulse pressure was calculated as the difference between the systolic and diastolic blood pressure. Values were averaged over the whole 24-h recording. LBNP LBNP was carried out in an airtight plexi-glass box that encased the subject in the supine position from the iliac crest and down. The pressures in the box were induced by a connection to a variable transformer, and the box pressure was continuously measured by a water manometer. Each step of LBNP was adjusted to the desired level within 5 s.
2323
Cardiac output Cardiac output was measured by noninvasive re-breathing equipment (Innocor; Innovision A/S, Odense, Denmark) developed for spaceflight by European Space Agency, and described in detail previously (Damgaard and Norsk 2005). The subjects were re-breathing through a mouthpiece back and forth into a bag with 1.4–1.8 L (30 % of vital capacity) of a gas mixture consisting of 0.5 % N2O (blood-soluble tracer gas), 0.1–1 % SF6 (non-blood-soluble tracer gas), and 25–28 % O2 in N2. The disappearance rate of N2O into blood was calculated from end-expiratory concentrations measured by photoacoustic spectroscopy connected through a tube to the mouthpiece. Based on the Bunsen blood solubility coefficients of N2O, the disappearance rate was used for calculation of pulmonary capillary blood flow, which is equal to cardiac output. End-expiratory concentrations of SF6 were used to correct for inadequate mixing of air in lungs with gas mixture from the air bag and for changes in re-breathing volume. Re-breathing lasted 30 s with a breathing frequency of 15–20 per min. Blood and urine analyses Blood samples were immediately transferred to chilled tubes and centrifuged at 1,500 g for 10 min. Thereafter, plasma samples were stored in a −80 °C freezer for later determination of plasma noradrenaline concentration analyzed by an enzyme immunoassay (LDN, Germany: Noradrenaline Research Elisa BA E-5200) and PRA measured by an immunoassay previously described by Frandsen et al. (Persson et al. 2009). The amount of collected blood was substituted with a similar amount of isotonic saline during the experiment. Urine osmolality was measured by freezing point depression (Advanced Instruments, Microosmometer 3MO, Norwood, MA, USA). Urine electrolyte concentrations (UNa and UK) were measured by an ion-selective electrode system (EML 100, Radiometer, Copenhagen, Denmark). Calculations Stroke volume was calculated from cardiac output and heart rate. Systemic vascular resistance was calculated from mean arterial pressure (1/3 × arterial pulse pressure + diastolic blood pressure) and cardiac output. Statistical analysis Data were analyzed using SigmaPlot 12 (Systat Software, Inc., Chicago, IL, USA) and are presented as mean ± SE. To detect significant changes within each group of Afghan and Danish origin, a one-way ANOVA for repeated
13
2324
Eur J Appl Physiol (2014) 114:2321–2329
Table 1 Baseline demographics and screening blood parameters in subjects of Afghan (Afghans) and Danish (Danes) origin
Table 2 24-h ambulatory blood pressure in subjects of Afghan (Afghans) and Danish (Danes) origin
Variable
Variable
N Age (years) Height (m) Weight (kg) BSA (m2) Waist (cm) Hip (cm) Waist hip ratio Daily sodium intake (g) UNa (mmol/24 h) Hemoglobin (mmol/L) Triglycerides (mmol/L) Total cholesterol (mmol/L) HDL cholesterol (mmol/L) LDL cholesterol (mmol/L) Glucose (mmol/L)
Danes 12
Afghans 12
24 ± 1 1.83 ± 0.01 78.2 ± 1.38 1.98 ± 0.04 78 ± 3 97 ± 1 0.81 ± 0.03 4.88 ± 0.17 167 ± 11
23 ± 1 1.79 ± 0.01 78.3 ± 2.7 1.97 ± 0.04 82 ± 2 94 ± 1 0.87 ± 0.01 4.89 ± 0.20 145 ± 17
9.45 ± 0.37 1.22 ± 0.11 4.20 ± 0.25 1.09 ± 0.10 2.56 ± 0.22 5.95 ± 0.16
9.77 ± 0.19 1.45 ± 0.40 3.84 ± 0.21 1.08 ± 0.08 2.27 ± 0.19 5.64 ± 0.13
83 ± 5
68 ± 4†
Creatinine (mmol/L)
Danes
N 24-h SBP (mmHg) Mean Day Night 24-h DBP (mmHg) Mean Day Night 24-h APP (mmHg) Mean Day Night 24-h HR (bpm) Mean Day Night
Afghans
12
12
123 ± 2 127 ± 2 112 ± 2
115 ± 2† 118 ± 2† 106 ± 2†
69 ± 2 72 ± 2 61 ± 2
68 ± 2 71 ± 2 61 ± 2
54 ± 2 55 ± 2 51 ± 2
46 ± 1† 47 ± 1† 45 ± 1†
60 ± 1 64 ± 2
66 ± 1† 70 ± 3†
51 ± 1
57 ± 1†
Data are mean ± SE
Data are mean ± SE
N number of subjects, BSA body surface area, UNa 24-h renal sodium excretion
N number of subjects, 24-h SBP 24-h systolic blood pressure, 24-h DBP 24-h diastolic blood pressure, 24-h APP 24-h arterial pulse pressure, 24-h HR 24-h heart rate
†
Statistically significant difference between Afghans and Danes
measurements with subsequent Students Newman–Keul’s test was applied. A Student’s unpaired t test was used to evaluate significant differences between the groups of Afghan and Danish origin. Values of p
