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Biomedical subjects

N H Secher

Publications and source records attributed to N H Secher.

At least 145 records · Page 8Linked to original sources
PubMed1994

Modulation of sympathetic nerve activity during posthandgrip muscle ischemia in humans.

To evaluate modulation of muscle sympathetic nerve activity (MSNA) during posthandgrip muscle ischemia (PHGMI), subjects performed 2 min of isometric handgrip at 33% of maximal voluntary contraction (MVC) followed by 2 min of PHGMI produced by forearm vascular occlusion. The response to PHGMI was studied in the absence and again during the addition of contralateral rhythmic handgrip (RHG; 40 times/min) at 15% (n = 6) and 30% (n = 10) MVC during the second minute of the PHGMI. Additionally, to isolate the effect of central command, response to PHGMI was studied during attempted RHG after sensory nerve blockade (n = 5). RHG for 2 min at 15 and 30% MVC and attempted RHG for 2 min did not increase MSNA. Isometric handgrip elicited an 130 +/- 48% increase in MSNA (P < 0.05), which was maintained during PHGMI. RHG at 15 and 30% MVC elicited an attenuation of MSNA (-10 +/- 7% and -14 +/- 6%, respectively) when performed during the second minute of PHGMI (P < 0.05). In contrast, attempted RHG did not significantly affect MSNA during PHGMI. The findings demonstrate modulation of MSNA during activation of the muscle metaboreflex. The attenuation of metaboreceptor-mediated increases in MSNA appear to be the result of mechanosensitive muscle afferents and not central command.

Adult↗
PubMed1994

Exercise-induced 31P-NMR metabolic response of human wrist flexor muscles during partial neuromuscular blockade.

The effects of a depolarizing (decamethonium, DECA) and a nondepolarizing neuromuscular blocking agent (vecuronium, VECU) on the phosphorus-31 nuclear magnetic resonance (31P-NMR)-detected metabolic response to muscle contractions were studied separately in six healthy untrained males. Subjects who showed splitting of the P(i) peak during graded rhythmic forearm exercise without the drugs were selected. It was found that both drugs abolished the P(i) peak splitting during exercise. Despite a similar reduction in phosphocreatine (PCr) during exercise with each drug, a smaller increase in P(i) was observed with DECA than with VECU (P < 0.05). End-exercise muscle pH was higher with DECA (6.93 +/- 0.07) than with VECU (6.79 +/- 0.11) (P < 0.05). The PCr and P(i) recovery was two- and threefold faster with DECA than with VECU, respectively (P < 0.05). On the basis of the concept that depolarizing and nondepolarizing agents have a preferential effect on fast- and slow-twitch muscle fibers, respectively, the present results support the hypothesis that the NMR-observed splitting of the P(i) peak reflects the metabolic differences between the two major fiber types of human skeletal muscle.

Adenosine Triphosphate↗
PubMed1994

31P-NMR spectroscopy, rsEMG, and histochemical fiber types of human wrist flexor muscles.

The metabolic response to graded rhythmic forearm exercise determined by phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy was evaluated with respect to recruitment pattern of muscles and to fiber type composition of the nondominant arm in 14 untrained subjects. Rectified smoothed surface electromyography (rsEMG) over finger and wrist flexor muscles increased similarly and progressively at 30, 45, and 60% of maximal exercise intensity. On the basis of the 31P-NMR response pattern during exercise, subjects were separated into three groups: H group (n = 4), with a single high-pH P(i) peak; M group (n = 7), with two P(i) peaks reflecting two pH components; and L group (n = 3), with a single low-pH P(i) peak. The H group demonstrated a faster recovery of P(i) and phosphocreatine than the L group (P < 0.05). The M group displayed both types of P(i) recovery and an intermediate resynthesis rate of phosphocreatine. The M group had an even distribution of slow- and fast-twitch fibers in the flexor carpi radialis muscle, whereas subjects in the H and L groups possessed a predominance of slow- and fast-twitch fibers, respectively. The results suggest that during rhythmic forearm exercise the interindividual NMR variation in energy metabolism is related closely to fiber type composition of the muscle.

Adult↗
PubMed1994

Restricted postexercise pulmonary diffusion capacity does not impair maximal transport for O2.

We evaluated whether the postexercise reduction of pulmonary diffusion capacity for carbon monoxide (DLco) is influenced by a second bout of rowing and whether it affects arterial O2 tension during maximal exercise. After exercise, DLco was reduced [from a median of 37 (range of 30-44) to 34 (27-40) ml.min-1.mmHg-1; n = 21; P < 0.001], and both the membrane diffusion capacity [from 80 (58-139) to 68 (54-104) ml.min-1.mmHg-1] and the pulmonary capillary blood volume [from 88 (74-119) to 79 (61-121) ml; P < 0.01] were affected. A second bout of exercise did not influence DLco or membrane diffusion capacity (n = 7), but during both bouts arterial O2 tension was reduced [from 105 (91-110) to 91 (77-102) Torr; P < 0.001] and arterial O2 saturation decreased [from 0.98 (0.97-0.99) to 0.95 (0.86-0.96); P < 0.001]. Furosemide (iv) did not affect DLco (n = 7), suggesting that it was influenced by the central blood volume rather than by pulmonary edema.

Adult↗
PubMed1994

Arterial blood pressure response to rowing.

Ten male oarsmen performed a 6-min bout of "all-out" exercise on a rowing ergometer in the laboratory. Intraarterial blood pressure was recorded from a catheter inserted percutaneously into the radial artery. Mean arterial pressure increased only modestly from 110 +/- 13 to 122 +/- 24 mm Hg (P < 0.05). Large fluctuations in pressure were superimposed on the normal blood pressure waveform during rowing. These rhythmic pressure fluctuations exhibited a one-to-one coupling with stroke rate and were 2-3 times the magnitude of the normal pulse pressure. Thus, the effective pulse pressure during the 1st minute of rowing (112 +/- 11 mm Hg) was markedly higher (P < 0.01) than the pulse pressure at rest (45 +/- 5 mm Hg) and remained so throughout the exercise bout. In five additional subjects in which central venous pressure (CVP) was measured, large stroke-related fluctuations in pressure were also seen in the CVP waveform. Similar fluctuations in blood pressure were observed during repetitive Valsalva maneuvers. These results suggest that the blood pressure response to rowing is principally influenced by a Valsalva-like maneuver performed at the catch of each stroke. The observed arterial pressure fluctuations may explain the degree of myocardial hypertrophy that occurs in the hearts of rowers.

Adult↗
PubMed1994

Cerebral blood flow velocity during high volume plasmapheresis in fulminant hepatic failure.

High volume plasmapheresis has previously been found to improve neurological statuses in patients with fulminant hepatic failure. We investigated the relationship between the neurological status and cerebral blood flow velocity (Vmean) during high volume plasmapheresis in 18 consecutive patients (ten females and eight males) with fulminant hepatic failure, with a mean age of 43 (range 9 to 57) years. The mean arterial pressure (MAP) and intracranial pressure (ICP) were also recorded. A total of 16% of body weight was exchanged with fresh frozen plasma per day. Thirty-six plasma exchanges wer performed with a median of 2 (range 1 to 8) per patient. Eleven of the patients survived (61%), nine after liver transplantation. Following the first high volume plasmapheresis, the coma score improved from 6 (1-8) to 2 (0-8) (p < 0.05), Vmean increased from 40 (14-152) to 62 (16-186) cm s-1 (p < 0.05), and MAP from 72 (35-118) to 94 (47-138) mmHg (p < 0.05). The intracranial pressure (ICP) was monitored and remained unchanged in nine patients whereas the cerebral perfusion pressure (MAP minus ICP) increased in the surviving group from 55 (40-74) to 80 (50-91) mmHg (p = 0.07) in contrast to no changes in the non survival group. In conclusion this study suggests that the neurological status, may improve during high volume plasmapheresis as MAP and Vmean increase the cerebral oxygen delivery.

Adolescent↗
PubMed1993

[Liver transplantation in Denmark. First-year experiences].

During the first 12 months of the Danish Liver Transplantation program, which began in October 1990, 21 transplantations were performed in 11 women, six men and three children. One patient required a retransplant. Fourteen operations were performed electively and six patients were transplanted for acute and subacute fulminant liver failure and coma, two patients had reduced size livers because of large donor liver. There were no peroperative deaths. One of the elective patients died after three weeks from multiorgan failure and sepsis. Two of the emergency patients died after 20 and 22 days. One from graft dysfunction due to stenosis of the celiac trunk and the other of exudative pericarditis. One patient died from chronic rejection and CMV-infection after seven months. Complications were relatively few and acute rejection occurred in 40% of the patients. Fifteen patients are discharged with normal liver function and 11 of these were back at work, school or previous functions in the home. It is concluded that these results are comparable to the best results from other centres but that 21 transplants in 12 months must be a minimum activity.

Adolescent↗
PubMed1993

Influence of exercise intensity and duration on post-exercise pulmonary diffusion capacity.

Pulmonary diffusion capacity has been observed to be reduced by approximately 14% 2h after 4-6 min of maximal exercise. The purpose of this study was to determine if the decrease in pulmonary diffusion capacity also occurs when the duration of exercise intensity is shorter or when the exercise intensity is lower. We measured pulmonary diffusion capacity using the single breath method in 12 competitive rowers 22 (16-31) years old, 70 (56-100) kg body weight, and 180 (171-193) cm body height under two conditions: (1) 2h after 6 min of rowing at both 61% (58%-68%) and 76% (73%-78%) of maximal oxygen uptake; (2) 2h after 1, 2, or 3 min of all-out rowing. Values are presented as medians with ranges. Pulmonary diffusion capacity was reduced by 6% (2%-17%) after 6 min of rowing at 61% and by 10% (-7%-21%) after 6 min of rowing at 76% of maximal oxygen uptake (p < 0.03). Pulmonary diffusion capacity was reduced by 7% (3%-19%), 8% (2%-17%) and 7% (1%-16%) after 1, 2, and 3 min of all-out rowing (p < 0.01). We conclude that submaximal exercise at 61% of maximal oxygen uptake will affect pulmonary diffusion capacity following exercise as will shorter duration of maximal exercise. Although the mechanism for this fall in pulmonary diffusion capacity is unclear, the fact that it occurs after even mild exercise makes a significant change in pulmonary capillary membrane integrity or subclinical pulmonary edema unlikely.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Central venous oxygen saturation during hypovolaemic shock in humans.

We compared central venous oxygen saturation and central venous pressure (CVP) as indices of the effective blood volume during 50 degrees head-up tilt (anti-Trendelenburg's position) induced hypovolaemic shock in eight healthy subjects. Head-up tilt increased thoracic electrical impedance from 31 (28-36) (median and range) to 34 (30-40) Ohm, mean arterial pressure (MAP) from 79 (70-88) to 86 (80-99) mmHg, heart rate (HR) from 67 (56-71) to 99 (78-119) beats min-1 (p < 0.01) and total peripheral resistance (TPR) from 20 (16-32) to 36 (15-52) mmHg min l-1 (p < 0.03). Cardiac output decreased from 4.3 (3.0-4.8) to 2.7 (1.8-4.8) l min-1 (p < 0.03). After 29 (9-56) min presyncopal symptoms appeared, together with a decrease in MAP to 63 (43-79) mmHg, HR to 68 (30-112) beats min-1 and TPR to 22 (13-33) mmHg min l-1 (p < 0.02). During tilting CVP decreased from 3 (1-6) to 1 (-3-5) mmHg (p < 0.05) but thereafter remained stable. In contrast, central venous oxygen saturation showed a linear decrease with time from 0.75 (0.69-0.78) at rest to 0.60 (0.49-0.67) (p < 0.01) when presyncopal symptoms appeared. Central venous catheterization is a tool for measurement of central venous oxygen saturation in addition to recording of CVP. The results suggest that a reduced central blood volume is reflected more clearly in central venous oxygen saturation than in CVP.

Adult↗
PubMed1993

Intra-arterial papaverine and leg vascular resistance during in situ bypass surgery with high or low epidural anaesthesia.

In situ saphenous vein arterial bypass flow was studied in 16 patients with respect to level of epidural anaesthesia. Arterial pressure and electromagnetic flow were used to evaluate arterial tone by intra-arterial (i.a.) papaverine. Eight patients had a low epidural block (< or = Th. 10) and eight patients were operated during high epidural anaesthesia (> Th. 10). Flow increased and arterial pressure decreased after i.a. papaverine in all patients. When compared with patients operated during high epidural anaesthesia, flow increase and decrease in vascular resistance took place in patients operated during low epidural anaesthesia (P < 0.02). Increase in arterial flow after i.a. papaverine was not significantly different in patients operated in low epidural and general anaesthesia (n = 8). In eight patients with insulin-dependent diabetes mellitus who had low epidural anaesthesia, the increase in flow after i.a. papaverine was not significantly different to that noted during high epidural anaesthesia. The results indicate that the level of analgesia influences graft flow after i.a. papaverine, probably reflecting differences in the effect of epidural anaesthesia on sympathetic tone to the leg.

Adult↗
PubMed1993

Cardioinhibitory-vasodepressor response to head-up tilt without hypoxaemia or myocardial ischaemia.

We evaluated whether hypoxaemia and/or myocardial ischaemia are of importance for development of the bradycardic hypotensive phase (cardioinhibitory-vasodepressor syncope) of central hypovolaemia. Arterial blood gas variables and a twelve-lead electrocardiogram (ECG) were followed during head-up tilt in seven men. During tilt, before presyncopal symptoms appeared, mean arterial pressure (MAP) increased (from 67 +/- 7 to 78 +/- 6 mmHg) (mean +/- SE) as did heart rate (HR) (61 +/- 4 to 99 +/- 8 beats min-1) and total peripheral resistance (TPR) (11 +/- 1 to 17 +/- 1 mmHg min l-1) (P < 0.01), while cardiac output (5.9 +/- 0.5 to 4.6 +/- 0.6 l min-1) and central venous pressure (CVP) (4.2 +/- 0.4 to 1.3 +/- 0.7 mmHg) decreased (P < 0.01). After 40 +/- 7 min of head-up tilt presyncopal symptoms appeared together with a decrease in MAP to 48 +/- 7 mmHg, HR to 71 +/- 11 beats min-1 and TPR to 9 +/- 2 mmHg min l-1 (P < 0.01). Arterial oxygen tension was not changed and there was no ST-segment depression of the ECG. The results indicate that during central hypovolaemia decreases in HR and TPR are elicited during normoxaemia and without electrocardiographic signs of myocardial ischaemia.

Adult↗
PubMed1993

Middle cerebral artery velocity during head-up tilt induced hypovolaemic shock in humans.

Middle cerebral artery mean velocity (Vmean) and pulsatility index (PI) were followed during head-up tilt induced hypovolaemic shock in nine subjects. Mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP) and thoracic (TI) electrical impedance were also recorded. Vmean, PI, and CVP did not change during head-up tilt to 50 degrees, while MAP increased from 92 (81-106) (median and range) to 100 (97-112) mmHg, HR from 63 (53-74) to 84 (68-89) beats min-1 and TI100kHz from 30 (27-36) to 32 (30-39) Ohm (P < 0.01) (n = 8). During maintained tilt, Vmean decreased from 52 (32-72) to 34 (16-59) cm s-1, whereas HR increased to 87 (52-108) beats min-1 and TI100 kHz to 33 (31-39) Ohm (P < 0.01). Presyncopal symptoms appeared after 33 (3-46) min and were associated with a MAP of 65 (32-84) mmHg (P < 0.01) and a HR of 58 (52-71) beats min-1 (P < 0.05). Vmean decreased to 25 (16-36) cm s-1, and cerebral conductance index (Vmean/MAPbrain) and PI increased (P < 0.01). Arterial collapse was observed (diastolic velocity of zero) in one subject at a brain (diastolic) blood pressure of 21 mmHg and he developed tachycardia (131 beats min-1) during presyncope. PaCO2 did not change. Maintained tilt resulted in central volume depletion reflected by changes in MAP, HR, and thoracic electrical impedance but not in CVP. Transcranial Doppler derived indices of cerebral perfusion demonstrated critically low values despite marked increase in conductance index.

Adult↗
PubMed1993

An indifference point for electrical impedance in humans.

Regional electrical impedance was used over eight sections of the human body (two thoracic; one abdominal; two thigh; two around the knee; and one lower leg) to determine the volume indifference point during passive head-up tilt in eight subjects. Head-up tilt was performed in 10 degrees increments from 0 degree to 60 degrees over 6 min. Electrical impedance increased over the thorax in proportion to the head-up tilt angle, while abdominal impedance did not change significantly, and over the thigh and the lower leg it decreased with increasing head-up tilt angle. No change in electrical impedance was noted just above the knee, and electrical impedance just below the knee decreased only marginally. Results demonstrate minimal fluid accumulation around the knee during head-up tilt. Furthermore, in humans the electrical impedance and therefore probably the volume indifference point is positioned between the umbilicus and crista iliaca.

Adult↗