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Biomedical subjects

M T Hopman

Publications and source records attributed to M T Hopman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Effect of electrical stimulation of leg muscles on physiological responses during arm-cranking exercise in healthy men.

The purpose of this study was to investigate the hypothesis that changes in physiological responses during arm-cranking exercise using electrical stimulation of the leg muscles (ACE-ES) compared to arm-cranking exercise alone (ACE) in able-bodied subjects (ABS) are based on an increase in active muscle mass rather than the enhancing effect of the leg muscle pump. In ABS the sympathetic nervous system induced vasoconstriction and activity of the leg muscle pump are intact, therefore, a normal redistribution of blood takes place during exercise. Consequently, ES should have no additional effect on the redistribution of blood in these ABS during exercise and, thus, changes in physiological responses will be based on an increase in active muscle mass. A group of 11 ABS performed three maximal arm-cranking tests. In the first test peak power output (POpeak) was determined. The other tests were both submaximal and maximal ACE, once with ACE-ES and once with ACE. The POpeak was not significantly different between ACE-ES and ACE. Oxygen uptake (VO2) increased significantly during ACE-ES compared to ACE. Cardiac output (Qc), stroke volume (SV), heart rate and ventilation were not significantly different during ACE-ES compared to ACE. Respiratory exchange ratios were significantly lower during ACE-ES compared to ACE at 60% POpeak and at maximal exercise. In conclusion, ACE-ES caused significant increases in VO2 with a lack of elevation in Qc and SV during submaximal and maximal exercise in ABS. The results of this study suggest that changes in physiological responses during ACE-ES are based on an increase in the active muscle mass rather than stimulation of the leg muscle pump.

Adult↗
PubMed1997

Lipid, lipoprotein, and apolipoprotein profiles in active and sedentary men with tetraplegia.

OBJECTIVE: To investigate whether the risk profile of coronary heart disease (CHD) is more favorable in physically active men with tetraplegia compared with sedentary men with tetraplegia. DESIGN: Using a cross-sectional design, the lipid and (apo)lipoprotein concentrations of 11 active and 13 sedentary men with tetraplegia were compared. Regression analysis was applied to investigate the influence of subject characteristics and behavioral factors on the risk profile of CHD. MAIN OUTCOME MEASURES: Total plasma cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglycerides, apolipoprotein-A1 (ApoA1), and apolipoprotein-B (ApoB) concentrations were determined. Low-density lipoprotein cholesterol (LDL-C) and the ratios TC/HDL-C, LDL-C/HDL-C, ApoA1/ApoB, and HDL-C/ApoA1 were calculated. RESULTS: A significantly higher HDL-C and ApoA1/ApoB and lower TC/HDL-C were found in the active group. Age and body mass index were important determinants of the lipids and (apo)lipoproteins. Sport activity was the only significant determinant of HDL-C. CONCLUSIONS: Results suggest a positive influence of sport activity on HDL-C in men with tetraplegia, which may reduce the risk of CHD.

Activities of Daily Living↗
PubMed1997

Respiratory muscle strength and endurance in individuals with tetraplegia.

The purpose of this study was to assess the strength and endurance capacity of the respiratory muscles in individuals with tetraplegia and to compare these properties to those in able-bodied subjects. In addition, the relationship between respiratory muscle properties and respiratory function, ie, ventilation and gas exchange, was examined. Fifteen individuals with tetraplegia (TP) and 15 able-bodied controls (AB) participated in this study. Respiratory muscle strength was assessed by measuring static inspiratory (Pi-max) and expiratory (Pe-max) mouth pressure, whereas inspiratory endurance capacity (Pendu) was determined using an incremental ventilatory threshold loading test. Results were significantly lower in TP compared to AB: Pi-max (5.9 vs 8.4 kPa), Pre-max (5.6 vs 12.3 kPa), Pendu (2.7 vs 6.9 kPa), vital capacity (3.1 vs 5.5 l) and rest oxygen uptake (0.21 vs 0.29 ml/min) and significant correlations were found between the respiratory muscle properties and the respiratory function. Of note is the fact that the ratio Pendu/Pi-max was significantly lower in TP (0.49) compared to AB (0.82). This implies that the capacity to generate pressure during the endurance test was not fully used in TP, probably due to an early onset of muscle fatigue and an altered force-length relationship of the diaphragm muscle. Results of this study demonstrate a limited ability in individuals with tetraplegia to ventilate.

Adult↗
PubMed1997

Cerebral and circulatory haemodynamics before vasovagal syncope induced by orthostatic stress.

Vasovagal syncope is usually described as a sudden and transient loss of consciousness that resolves spontaneously. Cardiocirculatory changes are well described during and before syncope. However, changes in the cerebral oxygenation are not well defined. In this study, near-infrared spectroscopy (NIRS) was used to assess the cerebral oxygenation directly during 80 degree head-up (HU) tilt. To simulate central hypovolaemia, 500 ml of blood was drawn from each of 10 healthy subjects. Oxygenation index (OI) was defined as the difference between oxy- and deoxyhaemoglobin concentration. Blood pressure, heart rate and cardiac output were monitored using a finger plethysmographic device. The protocol was divided into two stages, each consisting of a 15-min stabilization period in the supine (SUP) position, 15 min in HU position and another 10 min in SUP position. Between both stages, blood was drawn from the subject. Haemoglobin concentration and haematocrit were measured before and 30 min after withdrawal of blood. No compensatory haemodilution was observed. During HU position in the second stage, six subjects showed signs of presyncope (F) and four did not (NF). A significant difference between F and NF was found in the observation that, before fainting, the OI of F showed a steady and significant (P = 0.02) decrease (-1.4 +/- 0.5 microM min-1) compared with NF (-0.18 +/- 0.16 microM min-1). This indicates that the onset of (pre)syncope is preceded by a mismatch between oxygen demand and oxygen supply in the cerebrum. Using NIRS enabled us to monitor this mismatch and to predict the onset of a syncope before clear signs in cardiocirculatory variables were visible.

Adult↗
PubMed1997

Effect of training on physical capacity and physical strain in persons with tetraplegia.

The effects of quad rugby training on physical capacity and physical strain during standardized activities of daily living were investigated in 9 trained (A) and 5 untrained quad rugby players (B), and 7 inactive persons with tetraplegia (C) at 0, 3 and 6 months after the start of a quad rugby training program (1.5h.wk[-1]). Physical capacity was measured as maximal isometric strength, peak power output (POpeak) and peak oxygen uptake (VO2peak) on a stationary wheelchair ergometer. Physical strain was expressed as a percentage of heart-rate reserve. No measurable training effects could be observed for POpeak, VO2peak and physical strain. A significant rise in maximal isometric strength was found in group B after 3 and 6 months of training, whereas no significant changes were found in groups A and C. The results suggest that a higher training frequency and/or intensity may be needed to gain significant training effects for POpeak and VO2peak.

Activities of Daily Living↗
PubMed1996

The effect of training on cardiovascular responses to arm exercise in individuals with tetraplegia.

The aim of this study was to investigate the physiological responses to maximal and submaximal arm-cranking exercise in 21 individuals with tetraplegia (TP) and to evaluate the effect of a 3 and 6-month training period (mean frequency of 1.5 h.week-1, mean intensity at 35% of the training time above 60% of the heart rate reserve) on these physiological responses. The TP were divided into 8 trained subjects (T), 7 untrained subjects (U) who started their training at the beginning of the study, and 6 sedentary subjects (S). All the subjects were tested at the beginning of training and after 6 months, whereas T and U were also tested in between, at 3 months. During maximal exercise, peak power output and peak oxygen uptake per kilogram bodymass were significantly higher in T (49.9 W and 14.2 ml.min-1.kg-1 respectively) compared to U (20.7 W and 8.8 ml.min-1.kg-1 respectively) and S (15.9 W and 7.4 ml.min-1.kg-1 respectively), whereas all other peak responses showed tendencies to be higher in T. This is most likely to have been the result of participation in sport and the effect of it on performance capacity in T, although differences in completeness of the lesion may have influenced the results. No significant differences were found for submaximal and maximal responses after 3 or 6 months of training in either T and U or in S. This may have been due on the one hand to the vulnerability of the subjects to diseases and injuries and on the other hand to the low frequency of training. On an individual basis, however, remarkable improvement was observed during the training period, especially for individuals in the U group. These results would suggest that a 3 or 6-month training period has no measurable positive effect on the fitness level of TP.

Adult↗
PubMed1996

Physical capacity and physical strain in persons with tetraplegia; the role of sport activity.

To determine the relationship between sport activity and physical capacity (PC) and physical strain (PS) during standardized activities of daily living (ADL), 25 subjects with tetraplegia were studied. To quantify PC, maximal power output, peak oxygen uptake and maximal isometric force were determined on a stationary wheelchair ergometer. PS was described as the highest heart rate (expressed as a percentage of the heart rate reserve), observed during standardized ADL tasks. Multiple regression analyses showed that sport activity, lesion level and completeness of the lesion were the most important determinants of PC. An inverse relationship was found between PS during the ADL tasks and parameters of PC. Parameters of PC and sport activity were significant determinants of PS. It is concluded that a higher PC is associated with a lower PS in daily life, and that sport activity is an important determinant of PC. Although no causal relationships could be established, due to the cross-sectional character of this study, the results support the assumption that being physically active is highly important for individuals with tetraplegia.

Activities of Daily Living↗
PubMed1996

Muscle glycogen recovery after exercise during glucose and fructose intake monitored by 13C-NMR.

The purpose of this study was to examine muscle glycogen recovery with glucose feeding (GF) compared with fructose feeding (FF) during the first 8 h after partial glycogen depletion using 13C-nuclear magnetic resonance (NMR) on a clinical 1.5-TNMR system. After measurement of the glycogen concentration of the vastus lateralis (VL) muscle in seven male subjects, glycogen stores of the VL were depleted by bicycle exercise. During 8 h after completion of exercise, subjects were orally given either GF or FF while the glycogen content of the VL was monitored by 13C-NMR spectroscopy every second hour. The muscular glycogen concentration was expressed as percentage of the glycogen concentration measured before exercise. The glycogen recovery rate during GF (4.2 +/- 0.2%/h) was significantly higher (P < 0.05) compared with values during FF (2.2 +/- 0.3%/h). This study shows that 1) muscle glycogen levels are perceptible by 13 C-NMR spectroscopy at 1.5 T and 2) the glycogen restoration rate is higher after GF compared with after FF.

Adult↗
PubMed1995

Physiological responses to asynchronous and synchronous arm-cranking exercise.

The purpose of this study was to examine mechanical efficiency (ME) and physiological responses during asynchronous (the pedal arms oriented in opposing directions) arm-cranking exercise (AACE) and compare these responses to those obtained during synchronous (the pedal arms oriented in the same direction) arm-cranking exercise (SACE). Ten male subjects participated in the study and performed two exercise tests, one AACE and the other SACE in counter-balanced order. Each test consisted of submaximal (30, 60 and 90 W) and maximal exercise. At 30 W, gross ME was significantly lower during SACE compared to AACE, whereas at 60 W and 90 W no differences between the two types of exercise could be observed. We found that at lower power output levels the flywheel mass and its moment of inertia may have induced more body movements for compensation, which may have been more pronounced during SACE than during AACE. At higher levels of power output this flywheel masseffect was less, which explained the lack of differences in ME at these levels. Physiological responses to maximal AACE or SACE exercise were not significantly different. The results indicated that there were no differences in physiological responses to AACE and SACE exercise at higher exercise intensities. However, at lower levels of power output ME seemed to decrease, most likely as a result of the flywheel-mass effect, which was more pronounced during SACE.

Adult↗
PubMed1994

Properties of the venous vascular system in the lower extremities of individuals with paraplegia.

The purpose of this study was to examine the properties of the venous vascular system in the lower extremities of individuals with long-standing paraplegia (PP). The venous volume variations (VVV), the venous capacity (VC), the venous emptying rate (VER) and the venous flow resistance (VFR) were measured in the left calf of 14 male PP and 12 male able-bodied subjects (ABS) by means of strain-gauge occlusion plethysmography. VVV and VC were significantly lower in PP compared to ABS, -45% and -50% respectively. Both groups showed a similar resting venous pressure in the calf (PP = 24.4 mmHg; ABS = 19.6 mmHg). VER was significantly lower (-60%) and hence VFR was significantly higher (+75%) in PP compared to ABS. This study demonstrates that the venous vascular properties in the legs of individuals with paraplegia have changed, i.e. a decrease in venous distensibility and capacity and an increase in venous flow resistance. This is most probably the result of vascular adaptations to inactivity and muscle atrophy rather than the effect of a non-working leg-muscle pump and sympathetic denervation.

Adult↗
PubMed1994

Circulatory responses during arm exercise in individuals with paraplegia.

Since there is an increasing demand for sport and exercise in daily life activities and rehabilitation of persons with a spinal cord injury, it is important to gain insight into the circulatory responses during exercise in these individuals. Recently, some studies have addressed this issue. The purpose of this paper, therefore, is to review briefly the current knowledge on circulatory responses during submaximal and maximal arm exercise in individuals with paraplegia and the differences in these responses compared to able-bodied persons. Emphasis is placed on the redistribution of blood during arm exercise in persons with paraplegia. Special attention is focused on the so-called "venous blood pooling" below the spinal cord lesion and the available techniques to support the redistribution. In addition, the effect of heat stress on the circulatory adjustment during exercise and the influence the level of the lesion has on the circulatory responses are outlined. Topics for future research are suggested throughout the paper.

Arm↗
PubMed1994

Cardiac output determined by the CO2 rebreathing method during arm exercise.

Since arm exercise affects the respiratory muscles the CO2 rebreathing method for determining cardiac output (Q) has to be evaluated during arm exercise. The purpose of this study was (1) to compare three different methods of determining arterial CO2 tension (PaCO2) during arm exercise, (2) to verify the linearity of the relationship between Q and oxygen uptake (VO2) during arm exercise, and (3) to investigate whether the CO2 rebreathing method according to Collier can determine accurately Q during arm exercise. Sixty male subjects performed arm-cranking exercise at 20%, 40% and 60% of their individual maximal load. Carbon dioxide output (VCO2) was measured by gas exchange measurement, and mixed venous CO2 tension (PvCO2) was determined from the CO2 rebreathing plateau at each exercise level. PaCO2 was estimated in three different ways: (A) by the modified Bohr formula for dead space, (B) by an arterialized blood sample from the hyperaemic ear-lobe, and (C) by the end-expiratory CO2 tension. A, B, and C were used to calculate Qa, Qb and Qc, respectively. The Pearson's correlation coefficient was high (P < 0.01) among the three different ways of estimating PaCO2. The Q-VO2 relationship proved to be linear (P < 0.01). The Q-values showed a good agreement with the direct Fick measurements, and were in the same range compared to other results obtained by dye dilution, electrical impedance cardiography and the exponential CO2 rebreathing method during arm exercise. In conclusion, the CO2 rebreathing method appeared to be accurate to determine Q during submaximal arm exercise.

Adult↗
PubMed1993

Cardiac output in paraplegic subjects at high exercise intensities.

The purpose of this investigation was to compare cardiac output (Qc) in paraplegic subjects (P) with wheelchair-confined control subjects (C) at high intensities of arm exercise. At low and moderate exercise intensity Qc was the same at a given oxygen uptake (VO2) in P and C. A group of 11 athletic male P with complete spinal-cord lesions between T6 and T12 and a group of 5 well-matched athletic male C performed maximal arm-cranking exercise and submaximal exercise at 50%, 70% and 80% of each individual's maximal power output (Wmax). Maximal VO2 (VO2max) was significantly lower, VO2max per kilogram body mass was equal and maximal heart rate (fc) was significantly higher in P compared to C. At VO2 of 1.3, 1.5 and 1.7 l.min-1, and for P 65%-90% of the VO2max, Qc was not significantly different between the groups, although, Qc in P was achieved with a significantly lower stroke volume (SV) and a significantly higher fc. Although the SV was lower in P, it followed the same pattern as SV in C during incremental exercise, i.e. an increase in SV until about 45% Wmax and thereafter a stable SV. The similar Qc at a given VO2 in both groups indicated that, even at high exercise intensities, circulation in P can be considered isokinetic with a complete compensation by fc for a lower SV.

Adult↗
PubMed1993

The effect of an anti-G suit on the maximal performance of individuals with paraplegia.

The purpose of this study was to examine whether lower body positive pressure (LBPP) could improve maximal performance in paraplegic subjects (P). LBPP may diminish venous blood pooling (VBP) below the lesion and, therefore, support the redistribution of blood during exercise. Twelve male P subjects with complete spinal cord-lesions between T6 and T12, and 13 male able-bodied control subjects (C), performed maximal arm-cranking exercise with and without LBPP (52 mmHg) by means of an anti-gravity suit. P and C subjects had a significantly lower maximal heart rate (HRmax) with LBPP than without (P: 176 +/- 10 vs 184 +/- 7 b.min-1; C: 174 +/- 8 vs 177 +/- 8 b.min-1), whereas maximal power output (Wmax) and oxygen uptake (VO2max) remained unchanged. This suggests that LBPP provides P and C with central hemodynamic benefits. These benefits, however, did not result in improvements in Wmax or VO2max, probably due to other limitations in the complex and closely linked oxygen uptake process. During submaximal exercise the circulatory benefits were more pronounced in P than in C, probably due to the decrease of the VBP by LBPP. The results of this study suggest that LBPP appears to offer both P and C groups a central hemodynamic benefit without improving maximal performance.

Adult↗
PubMed1993

Volume changes in the legs of paraplegic subjects during arm exercise.

The purpose of this study was to examine the inability of paraplegic (P) subjects to redistribute fluid below the spinal cord lesion during arm exercise, with emphasis on the role of the sympathetic system in this redistribution failure. Fifteen male P and 15 male able-bodied [control (C)] subjects performed arm cranking exercise, and volume changes in the calf were measured by strain gauge plethysmography before, during, and after exercise. Muscle pump activity in the legs of C subjects was eliminated. The rate of calf volume decrease at the beginning and halfway points of the exercise period, the total volume decrease during exercise, and the volume increase during recovery were significantly lower in P than in C subjects. Whereas completeness of the lesion had no influence on leg volume changes, the rate of calf volume decrease at the beginning of exercise and the total volume decrease during exercise were significantly correlated with the level of the spinal cord lesion. This study confirms that P subjects are unable to redistribute fluid effectively below the spinal cord injury during arm exercise, which is partly caused by a loss of sympathetically induced vasoconstriction and which appears to be independent of the completeness of the lesion but dependent on its level.

Adult↗
PubMed1993

Cardiovascular responses in persons with paraplegia to prolonged arm exercise and thermal stress.

The purpose of this study was to investigate cardiovascular responses in subjects with paraplegia (P) during prolonged upper body exercise in a hot environment. In addition, the effect of the level of the lesion on cardiovascular regulation of persons with paraplegia was studied. Four P with lesions between T2-T6 (P1), five P with T7-T8 lesions (P2), four P with lesions between T9-T12 (P3), and 10 control subjects (C) performed 45-min arm-cranking exercise at 40% of the individual peak power output, in a climatic room at 35 degrees C with a 70% relative humidity. From the 15th to the 45th min, cardiac output (Q) and oxygen uptake (VO2) remained unaltered in all subjects, except a significant decrease of Q in P1. Stroke volume (SV) decreased significantly in both P (-20%) and C (-18%) during the test. Heart rate (HR) increased in compensation for P2 (56%), P3 (65%), and C (55%), whereas HR in P1 did not increase significantly. Hemoglobin concentration changes, representing total plasma volume changes, increased significantly in P2, P3, and C but not in P1. Weight loss and sweat rate increased relative to the sensate skin area and, thus, to the level of the spinal cord lesion (P < 0.01). In conclusion, P with lesions below T6 are able to maintain a stable Q by increasing HR to compensate for the declining SV during exercise in a hot environment. P with lesions above T6 cannot fully compensate for the reduction in SV by an increase in HR, therefore, Q declines.

Adult↗
PubMed1992

Cardiovascular responses in paraplegic subjects during arm exercise.

The purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20%, 40% and 60% of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (fc) was significantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed in Qc between P and C; however, stroke volume (SV) was significantly lower and fc significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher fc,max. During submaximal exercise, however, this lower SV was compensated for by a higher fc and, thus at the same submaximal oxygen uptake, Qc was similar to that in the control group.

Adult↗