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Biomedical subjects

N Maassen

Publications and source records attributed to N Maassen.

At least 19 recordsLinked to original sources
PubMed2006

Local and systemic effects on blood lactate concentration during exercise with small and large muscle groups.

To evaluate the relationship between lactate release and [lac](art) and to investigate the influence of the catecholamines on the lactate release, 14 healthy men [age 25+/-3 (SE) year] were studied by superimposing cycle on forearm exercise, both at 65% of their maximal power reached in respective incremental tests. Handgrip exercise was performed for 30 min at 65% of peak power. In addition, between the tenth and the 22nd minute, cycling with the same intensity was superimposed. The increase in venous lactate concentration ([lac](ven)) (rest: 1.3+/-0.4 mmol.l(-1); 3rd min: 3.9+/-0.8 mmol.l(-1)) begins with the forearm exercise, whereas arterial lactate concentration ([lac](art)) remains almost unchanged. Once cycling has been added to forearm exercise (COMB), [lac](art) increases with a concomitant increase in [lac](ven) (12th min: [lac](art), 3.2+/-1.3 mmol.l(-1); [lac](ven), 5.7+/-2.2 mmol.l(-1)). A correlation between oxygen tension (P(v)O(2)) and [lac](ven) cannot be detected. There is a significant correlation between [lac](art) and norepinephrine ([NE]) (y=0.25x+1.2; r=0.815; p<0.01) but no correlation between lactate release and epinephrine ([EPI]) at moderate intensity. Our main conclusion is that lactate release from exercising muscles at moderate intensities is neither dependent on P(v)O(2) nor on [EPI] in the blood.

Adult↗
PubMed2000

Evaluation of noninvasive determinants for capillary leakage syndrome in septic shock patients.

OBJECTIVE: Capillary leakage syndrome (CLS) is a frequent complication in sepsis, characterized by loss of intravasal fluids leading to generalized edema and hemodynamic instability despite massive fluid therapy. In spite of its importance no standardized diagnostic criteria are available for CLS. DESIGN: Prospective clinical study. SETTING: 1,800-bed university hospital PATIENTS: Six septic shock patients with CLS were compared to six control patients. MEASUREMENTS AND RESULTS: CLS was clinically determined by generalized edema, positive fluid balance, and weight gain. Plasma volume was measured by indocyanine green, red blood cell volume by chromium-51 labeled erythrocytes, and colloid osmotic pressure before and 90 min after the administration of 300 ml 20% albumin. Extracellular water (ECW) was measured using the inulin distribution volume and bioelectrical impedance analysis. Red blood cells averaged 20.2 +/- 1.0 ml/ kg body weight in CLS patients and 23.3 +/- 4.1 in controls. ECW was higher in CLS patients than in controls (40.0 +/- 6.9 vs. 21.7 +/- 3.71; p< 0.05). ECW of inulin was correlated with that measured by bioelectrical impedance analysis (r = 0.74, p< 0.01). The increase in colloid osmotic pressure over the 90 min was less in CLS patients than in controls (1.1 +/- 0.3 vs. 2.8 +/- 1.3 mmHg;p< 0.05). CONCLUSION: These results suggest that measurements of an increased ECW using bioelectrical impedance analysis combined with a different response of colloid osmotic pressure to administration of albumin can discriminate noninvasively between patients with and those without CLS.

Adult↗
PubMed1999

Carbon dioxide storage and nonbicarbonate buffering in the human body before and after an Himalayan expedition.

Before and 7-12 days after an Himalayan expedition CO2 equilibration curves were determined in the blood plasma of 12 mountaineers by in vitro and in vivo CO2 titration; in vivo osmolality changes (delta Osm x deltaPCO2(-1), deltaOsm x delta pH(-1), where PCO2 is the partial pressure of CO2) during the latter experiments yielded estimates of whole body CO2 storage. In vitro -delta[HCO3-] x delta pH(-1) [nonbicarbonate buffer capacity (beta) of blood] was increased 7 days after descent [before 31.3 (SEM 0.4) mmol x kgH2O(-1), after 38.3 (SEM 3.9) mmol x kgH2O(-1); P<0.05] resulting from an increased proportion of young erythrocytes; in additional experiments an augmented beta was found in young (low density cells) compared to old cells [<1.097 g x ml(-1): 0.216 (SEM 0.028) mmol x gHb(-1), >1.100 g x ml(-1): 0.145 (SEM 0.013) mmol x gHb(-1), where Hb is haemoglobin; P < 0.02]. In spite of increased Hb mass in vivo delta[CO2total] x deltaPCO2(-1) [0.192 (SEM 0.010) mmol x kgH2O(-1) x mmHg(-1)] and -delta[HCO3-] x delta pH(-1) [17.9 (SEM 1.0) mmol x kgH2O(-1)] as indicators of extracellular beta rose only slightly after altitude (7 days +16%, P<0.02; +7%, NS) because of haemodilution. The deltaOsm x deltaPCO2(-1) [0.230 (SEM 0.015) mosmol x kgH2O(-1) x mmHg(-1)] remained unchanged. Prealtitude differences in deltaOsm x delta pH(-1) between hypercapnia [-41 (SEM 5) mosmol x kgH2O(-1)] and hypocapnia [-20 (SEM 3) mosmol x kgH2O(-1); P<0.01] disappeared temporarily after return since the former slope was reduced. The high value during hypercapnia before ascent probably resulted from mechanisms stabilizing intracellular pH during moderate hypercapnia which were attenuated after descent.

Acclimatization↗
PubMed1999

High-energy-phosphates measured by 31P-MRS during LBNP in exercising human leg muscle.

Subatmospheric pressure applied to the human body from the iliac crest caudally (Lower Body Negative Pressure, LBNP) has been known to cause various central and peripheral cardiovascular reactions. We investigated the effects of such a LBNP maneuver on energy metabolism of human skeletal leg muscle. We tested the hypothesis whether an altered fluid distribution induced by LBNP may cause any effect on aerobic and/or anaerobic energy metabolism and cellular pH-regulation during isometric contraction monitored by 31P-MRS.

Energy Metabolism↗
PubMed1998

Is urodilatin the missing link in exercise-dependent renal sodium retention?

The purpose of the present study was to investigate the behavior of plasma atrial natriuretic peptide [ANP-(99-126)] concentration ([ANP]) and renal urodilatin [Uro; ANP-(95-126)] excretion during and after exercise and their possible effects on renal Na+ retention. Ten male subjects performed a cycle ergometer test for 60 min at 60% of maximum workload. Blood and urine samples were collected before, during, and up to 24 h after exercise. During exercise, plasma [ANP] and renal Uro excretion were oppositely affected: whereas [ANP] increased from 46.5 +/- 5.1 to 124.1 +/- 10.6 pg/ml, urinary Uro excretion decreased from 120.8 +/- 16.0 to 49.5 +/- 9.8 fmol/min and remained at a lower level until 1 h after exercise. Glomerular filtration rate showed lowest values during exercise (from 164.9 +/- 15.3 to 75.8 +/- 10.1 ml/min), and urine flow and the fractional excretion rate of Na+ (FENa+) and Cl- (FECl-) had their nadir during the first hour after exercise. Positive relationships were observed between Uro excretion and FENa+ (P < 0.05) and FECl-, whereas a tendency toward a negative correlation was obtained between [ANP] and FENa+. It seems possible that Uro may be, among other factors, involved in the exercise-related regulation of renal Na+ retention. The specific roles Uro and ANP play during exercise, however, remain to be investigated.

Adult↗
PubMed1998

Red blood cells do not contribute to removal of K+ released from exhaustively working forearm muscle.

K+ released from exercising muscle via K+ channels needs to be removed from the interstitium into the blood to maintain high muscle cell membrane potential and allow normal muscle contractility. Uptake by red blood cells has been discussed as one mechanism that would also serve to regulate red blood cell volume, which was found to be constant despite increased plasma osmolality and K+ concentration ([K+pl]). We evaluated exercise-related changes in [K+pl], pH, osmolality, mean cellular Hb concentration, cell water, and red blood cell K+ concentration during exhaustive handgrip exercise. Unidirectional 86Rb+ (K+) uptake by red blood cells was measured in media with elevated extracellular K+, osmolarity, and catecholamines to simulate particularly those exercise-related changes in plasma composition that are known to stimulate K+ uptake. During exercise [K+pl] increased from 4.4 +/- 0.7 to 7.1 +/- 0.5 mmol/l plasma water and red blood cell K+ concentration increased from 137.2 +/- 6.0 to 144.6 +/- 4.6 mmol/l cell water (P </= 0.05), but the intracellular K+-to-mean cellular Hb concentration ratio did not change. 86Rb+ uptake by red blood cells was increased by approximately 20% on stimulation, caused by activation of the Na+-K+ pump and Na+-K+-2Cl- cotransport. Results indicate the K+ content of red blood cells did not change as cells passed the exhaustively exercising forearm muscle despite the elevated [K+pl]. The tendency for an increase in intracellular K+ concentration was due to a slight, although statistically not significant, decrease in red blood cell volume. K+ uptake, although elevated, was too small to move significant amounts of K+ into red blood cells. Our results suggest that red blood cells do not contribute to the removal of K+ released from muscle and do not regulate their volume by K+ uptake during exhaustive forearm exercise.

Adult↗
PubMed1998

[Effect of high performance sports on energy metabolism].

The knowledge about metabolism and muscular fatigue has been considerably improved during the recent years. Intramuscular pH should not generally be discussed as a factor of cellular fatigue as it has been shown to increase transiently at the beginning and to be very differently affected in ST-(6,9) and FT-fibers (6,2) at the end of exercise. During maximum exercise, we assume changes of muscle membrane potential due to increasing interstitial potassium concentrations as an important performance-limiting factor. The role, lactate is playing during exercise, has to be thought over. Its production by the binding of two protons to the pyruvate molecule is necessary for an intensive anaerobic and aerobic metabolism. The lactate molecules itself represent a source of energy, which is preferentially used by the heart muscle and by ST-fibers working at lower intensity. During long term endurance events, the glycogen stores are assumed to be a limiting factor. However, no direct casual relationship between glycogen and fatigue mechanisms has been found hithertoo. The anaerobic glycolytic metabolism decreases during long lasting exercise as a result of lowered glycogen stores. Therefore, metabolic acidosis cannot be observed after ultra-long endurance events. In contrast, a respiratory alcalosis is the common finding.

Adolescent↗
PubMed1997

After-effects of a high altitude expedition on blood.

The aim of the study was to investigate blood alterations caused by altitude acclimatization which last more than few days after return and might play a role for exercise performance at sea level. Measurements were performed in 12 mountaineers before, during and either 7/8 or 11/12 days after a Himalaya expedition (26-29 days at 4900 to 7600 m altitude). [Erythropoietin] rose only temporarily at altitude (max. +11 +/- 1 [SE] mu/ml serum). After return hemoglobin mass (initially 881 +/- 44 g, CO-Hb method) was increased by 14% (p < 0.01); aspartate aminotransferase activity in erythrocytes (initially 682 +/- 25 U/l) was augmented (day 7: +964 +/- 152 U/l, day 11: +533 +/- 107 U/l) indicating reduced mean cell age. Calculated blood volume (+14%) was influenced by red cell formation at altitude but also by plasma expansion at sea level. The half saturation pressure for Hb-O2 (pH 7.4, 37 degrees C) as well as the 2.3-diphosphoglycerate concentration were already initially high (32.1 +/- 0.5 mmHg, 20.5 +/- 0.7 mumol/g Hb) and showed only a nonsignificant tendency to increase after return. Also Hill's n was consistently high in the mountaineers, whereas the Bohr coefficients were slightly increased only after descent. Probably the preparatory physical training, partly in the Alps, and the stay in the Himalaya influenced O2-affinity for a prolonged time. The adaptations might reduce the loss of physical performance capacity at altitude and be part of altitude training effects.

Acid-Base Equilibrium↗
PubMed1996

Lung diffusion capacity, oxygen uptake, cardiac output and oxygen transport during exercise before and after an himalayan expedition.

Studies were made of pulmonary diffusion capacity and oxygen transport before and after an expedition to altitudes at and above 4900 m. Maximum power (Pmax) and maximal oxygen uptake (VO2max) were measured in 11 mountaineers in an incremental cycle ergometer test (25W.min-1) before and after return from basecamp (30 days at 4900 m or higher). In a second test, cardiac output (Qc) and lung diffusion capacity of carbon monoxide (DL,cg) were measured by acetylene and CO rebreathing at rest and during exercise at low, medium and submaximal intensities. After acclimatization, VO2max and Pmax decreased by 5.1% [from 61.0 (SD 6.2) to 57.9 (SD 10.2) ml.kg-1, n.s.] and 9.9% [from 5.13 (SD 0.66) to 4.62 (SD 0.42) W.kg-1, n.s.], respectively. The maximal cardiac index and DL,cg decreased significantly by 15.6% [14.1 (SD 1.41) 1.min-1.m-2 to 11.9 (SD 1.44)1.min-1.m-2, P < 0.05] and 14.3% [85.9 (SD 4.36) ml.mmHg-1. min-1 to 73.6 (SD 15.2) ml.mmHg-1.min-1, P < 0.05], respectively. The expedition to high altitude led to a decrease in maximal Qc, oxygen uptake and DL,cg. A decrease in muscle mass and capillarity may have been responsible for the decrease in maximal Qc which may have resulted in a decrease of DL,cg and an increase in alveolar-arterial oxygen difference. The decrease in DL,cg especially at lower exercise intensities after the expedition may have been due to a ventilation-perfusion mismatch and changes in blood capacitance. At higher exercise intensities diffusion limitation due to reduced pulmonary capillary contact time may also have occurred.

Acclimatization↗
PubMed1993

Reduction of oxylabile CO2 in human blood by lactate.

The influence of lactic acid, hydrochloric acid, and sodium lactate addition (10 mmol/l each) on oxylabile CO2 was investigated in blood of male subjects after equilibration at 37 degrees C with 3, 6, and 10% CO2 in N2 and O2, respectively. The total CO2, pH in whole blood and erythrocytes, oxygen saturation, hemoglobin concentration, and hematocrit value were measured. With these data we calculated bicarbonate and carbamate concentrations and the corresponding differences between oxygenated and deoxygenated blood. The amount of oxylabile bicarbonate was not systematically influenced by the various experimental conditions. The carbamate content, however, was larger in deoxygenated than in oxygenated blood (up to 0.08 mol/mol hemoglobin) only in the absence of lactate. In the presence of lactic acid as well as sodium lactate, the carbamate content in oxygenated blood was higher by 0.06-0.13 mol/mol hemoglobin than in deoxygenated blood. The lactate effect even increased after 2,3-diphosphoglycerate depletion. We suggest, therefore, a competition between CO2 and the lactate ion at the NH2-terminal valine of the beta-globin chain in deoxygenated hemoglobin.

2,3-Diphosphoglycerate↗
PubMed1992

Relationship between plasma potassium and ventilation during successive periods of exercise in men.

During and after two successive incremental cycle ergometer tests (tests A and B), plasma potassium concentration ([K+]p), plasma pH (pHp), plasma partial pressure of carbon dioxide, blood lactate concentration ([Lac-]b) and ventilation (VE) were measured. While there was a good correlation between the increase in [K+]p and VE or pHp, respectively, in test A, in test B a close correlation was found only between the increase in VE and [K+]p (r greater than 0.9 for nearly all single cases; r was 0.84 and 0.89 for all (pooled) cases in tests A and B, respectively; the correlation coefficients between changes in pHp and VE in tests A and B were r = 0.74 and r = 0.28, respectively, and r = 0.89 and r = 0.10 between the changes in [Lac-]b and VE in tests A and B). The close relationship for individuals between VE and [K+]p in tests A and B supported the hypothesis that the extracellular increase in [K+] may contribute to the ventilatory drive during exercise. The comparison of the results of tests A and B further indicated that the relationship between pHp and VE was dependent on the experimental design, and that pHp and VE changes are unlikely to be cause and effect.

Adult↗
PubMed1992

Plasma potassium and ventilation during incremental exercise in humans: modulation by sodium bicarbonate and substrate availability.

It has recently been demonstrated that, compared to normal conditions, ventilation (VE) was increased during exercise after glycogen depletion, in spite of a marked increase in plasma pH (pHP). It was further demonstrated that VE in patients with McArdle's syndrome was reduced when substrate availability was improved. In the present experiments, six endurance trained men performed two successive cyclo-ergometric incremental exercise tests (tests A, B) after normal nutrition (N) and after a fatty meal in conjunction with a sodium bicarbonate (NaHCO3) solution (FSB) or without NaHCO3 (F), and the relationship between VE, plasma potassium concentration ([K+]P), and pHP was checked. Plasma free fatty acid concentration ([FFA]P) was markedly increased in the F and FSB trials (P < 0.001). In FSB pHP was significantly increased, compared to N and F (P < 0.001). In all the B tests, pHP increased during moderate and intense exercise and in FSB, remained alkalotic even during maximal exercise intensity. In contrast, VE and [K+]P changes were almost equal in all the trials and in tests A and B. It was found that exercise-induced changes of VE and [K+]P in the present experiments were not markedly affected by [FFA]P or pHP values and that these changes also occurred independently of changes in pHP or plasma bicarbonate concentration. The often used glycogen depletion strategy may have slightly increased VE but apparently did not overcompensate for a possible decrease in VE due to increased pHP.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1991

Relation between plasma K+ and ventilation during incremental exercise after glycogen depletion and repletion in man.

1. We have examined the relationship between expiratory ventilation (VE), plasma potassium concentration ([K+]P), blood lactate concentration ([Lac-]B), and plasma pH (pHP) in five trained men before and after glycogen depletion and repletion in two successive incremental bicycle ergometer tests (tests A and B). 2. Though pHP was significantly higher after glycogen depletion (in relation to normal or repleted conditions) VE and [K+]P also tended to be higher. 3. There was no constant relation between the magnitude or the direction of change in lactic acidosis, or VE and [K+]P, respectively. Instead, a close temporal relationship between changes in VE and [K+]P was found. 4. A non-linear increase in VE occurred independently of changes in pHP or [Lac-]B, but could be well predicted from a non-linear increase in [K+]P. 5. These findings indicate that lactic acidosis had no deciding effect on exercise ventilation in these experiments. They are consistent with the idea that the potassium increase may contribute to the ventilatory drive during exercise.

Adult↗
PubMed1989

The relationship between lactic acid and work load: a measure for endurance capacity or an indicator of carbohydrate deficiency?

The influence of low and high carbohydrate diets on the relationship between blood lactate concentration ([Lac]) and work load (WL) in incremental exercise tests (cycle ergometer) and endurance tests was evaluated in trained subjects. The relationship between relative work load (WLrel) and [Lac] in arterialized blood was compared in untrained subjects (UT) and trained male athletes (TR) after 2 days without training while consuming a high carbohydrate diet (HCD). In both groups [Lac] of 2 mmol.l-1 was reached at about 60% [(mean +/- SD) UT 57.7% +/- 6%, TR 62.7% +/- 3.8%] and 4 mmol.l-1 at about 75% (UT 75.2% +/- 3.6%, TR 77.8 +/- 2.2) of the maximal work load (WLmax). In eight cyclists the relationship between [Lac] and WL was not influenced by a 13-day training camp; however, heart rate was lower after the training camp. During their normal training programme, trained subjects had high relative work loads at their [Lac] thresholds, but after an HCD combined with an interruption of the training of 3 days, the relationship between [Lac] and WLrel was the same as in UT. In six TR a low carbohydrate diet (LCD) combined with training led to high absolute (WLabs) and WLrel at [Lac] at 2 and 4 mmol.l-1; an HCD combined with 3 days without training led to low WLabs and WLrel at the same [Lac] and to higher WLmax. In spite of the apparently lower endurance capacities TR were able to work significantly longer after HCD than after LCD (23 +/- 10.5 min and 49 +/- 16.2 min, respectively) at 65% of their WLmax. The variability of the relationship between [Lac] and WL following the dietary regimes leads to the conclusion that the "typical" [Lac] versus WL curve of endurance TR may result from a permanent glycogen deficiency.

Adult↗
PubMed1989

Changes in plasma volume and red cell formation after a marathon competition.

The purpose of this study was to investigate middle-term influences of a marathon race on plasma volume (PV) and red cell production. We performed the following measurements in the blood of 15 male athletes: haemoglobin ([Hb]), haematocrit (Hct), plasma protein concentration ([Prot]), plasma osmolality, sodium concentration ([Na+]), potassium concentration ([K+]), aldosterone concentration ([Aldo]), haptoglobin concentration ([Hpto]), and the reticulocyte count, as well as the calculation of relative changes in PV, 3 days before and on 3-consecutive days after a marathon race. By the 2nd day of recovery PV had increased by 16%. Plasma osmolality and [K+] remained constant, whereas [Na+] had decreased slightly 2 days after the competition and [Aldo] tended to be elevated 1 day after the competition. [Hpto] was low before and 1 day after the competition and increased on the following days. Reticulocyte count was unaffected 1 day after the race, but increased by 106% on the 2nd day and was still elevated after 3 days. The causes for higher post-marathon plasma volumes and reticulocyte counts could be in the complex variations in hormonal regulation, which have not yet been sufficiently investigated.

Adult↗
PubMed1989

Interrelationship between pH, plasma potassium concentration and ventilation during intense continuous exercise in man.

During resting conditions plasma hydrogen ion concentration ([H+]P) is known to influence ventilation (VE), whereas the control of plasma potassium concentration ([K+]P) at rest and of both [K+]P and VE during exercise are controversial issues. To obtain more information about these variables during muscular work, eight trained men performed two successive intense continuous cycle-ergometer tests, the first (test I) during metabolic acidosis, the second (test II) with an alkalotic pH. No correlation was found between [H+]P and [K+]P or VE in the direction of change of these variables in test I. Furthermore, no correlation between [H+]P and [K+]P in test I and II was seen. Instead [K+]P and VE changed in relation to the exercise intensity. We suggest that the results confirm [K+]P as an indicator of muscular stress. In addition, the similar behaviour of relative values of [K+]P and VE changes in test I (r = 0.9, m = 1.0, where m is the slope of the regression curve) supports the hypothesis that extracellular potassium controls VE and thereby [H+]P also.

Adult↗
PubMed1989

The calculation of the osmotic volumes of distribution of hypertonic sodium bicarbonate and other hypertonic solutions: a theoretical approach.

Correction of a base deficit with hypertonic sodium bicarbonate (NaHCO3) according to the formula 0.3 x body weight (kg) x BE may overestimate the real demands, especially during shock and cardiopulmonary resuscitation (CPR). Life threatening alkalosis and osmolal poisoning may be the consequence. As an explanation, the possibly impaired functional distribution space related to low cardiac output and volume centralization during CPR is proposed. By application of our own and outside literature, data equations are specified for an approximate precalculation of osmolality and pH changes due to infusion of hypertonic NaHCO3. Calculation of the osmotic volumes of distribution of NaHCO3 during cardiopulmonary resuscitation (CPR) from emergency literature data demonstrates a possible reduction of the functional distribution spaces of about 70 to 80% compared with normal values. This is in good agreement with the reported reduction of cardiac output to about 25% of normal during CPR. The calculated amount of sodium bicarbonate to be recommended during CPR, thus, should not exceed 50 mmol given in time intervals of at least 10 min, severe acidosis and sufficient ventilation presumed.

Acid-Base Imbalance↗