Biomedical subjects

R Videbaek

Publications and source records attributed to R Videbaek.

At least 19 recordsLinked to original sources

PubMed2000

Forearm vascular and neuroendocrine responses to graded water immersion in humans.

The hypothesis that graded expansion of central blood volume by water immersion to the xiphoid process and neck would elicit a graded decrease in forearm vascular resistance was tested. Central venous pressure increased (P < 0.05) by 4.2 +/- 0.4 mmHg (mean +/- SEM) during xiphoid immersion and by 10.4 +/- 0.5 mmHg during neck immersion. Plasma noradrenaline was gradually suppressed (P < 0.05) by 62 +/- 8 and 104 +/- 11 pg mL-1 during xiphoid and neck immersion, respectively, indicating a graded suppression of sympathetic nervous activity. Plasma concentrations of arginine vasopressin were suppressed by 1.5 +/- 0.5 pg mL-1 (P < 0.05) during xiphoid immersion and by 2.0 +/- 0.5 pg mL-1 during neck immersion (P < 0.05 vs. xiphoid immersion). Forearm subcutaneous vascular resistance decreased to the same extent by 26 +/- 9 and 28 +/- 4% (P < 0.05), respectively, during both immersion procedures, whereas forearm skeletal muscle vascular resistance declined only during neck immersion by 27 +/- 6% (P < 0.05). In conclusion, graded central blood volume expansion initiated a graded decrease in sympathetic nervous activity and AVP-release. Changes in forearm subcutaneous vascular resistance, however, were not related to the gradual withdrawal of the sympathetic and neuroendocrine vasoconstrictor activity. Forearm skeletal muscle vasodilatation exhibited a more graded response with a detectable decrease only during immersion to the neck. Therefore, the forearm subcutaneous vasodilator response reaches saturation at a lower degree of central volume expansion than that of forearm skeletal muscle.

Adult↗

PubMed2000

Cardiovascular and neuroendocrine responses to water immersion in compensated heart failure.

The hypothesis was tested that cardiovascular and neuroendocrine (norepinephrine, renin, and vasopressin) responses to central blood volume expansion are blunted in compensated heart failure (HF). Nine HF patients [New York Heart Association class II-III, ejection fraction = 0.28 +/- 0.02 (SE)] and 10 age-matched controls (ejection fraction = 0.68 +/- 0.03) underwent 30 min of thermoneutral (34.7 +/- 0.02 degrees C) water immersion (WI) to the xiphoid process. WI increased (P < 0.05) central venous pressure by 3.7 +/- 0.6 and 3.2 +/- 0.4 mmHg and stroke volume index by 12.2 +/- 2.1 and 7.2 +/- 2.1 ml. beat(-1). m(-2) in controls and HF patients, respectively. During WI, systemic vascular resistance decreased (P < 0.05) similarly by 365 +/- 66 and 582 +/- 227 dyn. s. cm(-5) in controls and HF patients, respectively. Forearm subcutaneous vascular resistance decreased by 19 +/- 7% (P < 0.05) in controls but did not change in HF patients. Heart rate decreased less during WI in HF patients, whereas release of norepinephrine, renin, and vasopressin was suppressed similarly in the two groups. We suggest that reflex control of forearm vascular beds and heart rate is blunted in compensated HF but that baroreflex-mediated systemic vasodilatation and neuroendocrine responses to central blood volume expansion are preserved.

Adaptation, Physiological↗

PubMed2000

Low LBNP tolerance in men is associated with attenuated activation of the renin-angiotensin system.

Plasma vasoactive hormone concentrations [epinephrine (p(Epi)), norepinephrine (p(NE)), ANG II (p(ANG II)), vasopressin (p(VP)), endothelin-1 (p(ET-1))] and plasma renin activity (p(RA)) were measured periodically and compared during lower body negative pressure (LBNP) to test the hypothesis that responsiveness of the renin-angiotensin system, the latter being one of the most powerful vasoconstrictors in the body, is of major importance for LBNP tolerance. Healthy men on a controlled diet (2,822 cal/day, 2 mmol. kg(-1). day(-1) Na(+)) were exposed to 30 min of LBNP from -15 to -50 mmHg. LBNP was uneventful for seven men [25 +/- 2 yr, high-tolerance (HiTol) group], but eight men (26 +/- 3 yr) reached presyncope after 11 +/- 1 min [P < 0.001, low-tolerance (LoTol) group]. Mean arterial pressure (MAP) did not change measurably, but central venous pressure and left atrial diameter decreased similarly in both groups (5-6 mmHg, by approximately 30%, P < 0.05). Control (0 mmHg LBNP) hormone concentrations were similar between groups, however, p(RA) differed between them (LoTol 0.6 +/- 0.1, HiTol 1.2 +/- 0.1 ng ANG I. ml(-1). h(-1), P < 0.05). LBNP increased (P < 0. 05) p(RA) and p(ANG II), respectively, more in the HiTol group (9.9 +/- 2.2 ng ANG I. ml(-1). h(-1) and 58 +/- 12 pg/ml) than in LoTol subjects (4.3 +/- 0.9 ng ANG I. ml(-1). h(-1) and 28 +/- 6 pg/ml). In contrast, the increase in p(VP) was higher (P < 0.05) in the LoTol than in the HiTol group. The increases (P < 0.05) for p(NE) were nonsignificant between groups, and p(ET-1) remained unchanged. Thus there may be a causal relationship between attenuated activation of p(RA) and p(ANG II) and presyncope, with p(VP) being a possible cofactor. Measurement of resting p(RA) may be of predictive value for those with lower hypotensive tolerance.

Adaptation, Physiological↗

PubMed1999

Arterial pressure in humans during weightlessness induced by parabolic flights.

Results from our laboratory have indicated that, compared with those of the 1-G supine (Sup) position, left atrial diameter (LAD) and transmural central venous pressure increase in humans during weightlessness (0 G) induced by parabolic flights (R. Videbaek and P. Norsk. J. Appl. Physiol. 83: 1862-1866, 1997). Therefore, because cardiopulmonary low-pressure receptors are stimulated during 0 G, the hypothesis was tested that mean arterial pressure (MAP) in humans decreases during 0 G to values below those of the 1-G Sup condition. When the subjects were Sup, 0 G induced a decrease in MAP from 93 +/- 4 to 88 +/- 4 mmHg (P < 0.001), and LAD increased from 30 +/- 1 to 33 +/- 1 mm (P < 0.001). In the seated position, MAP also decreased from 93 +/- 6 to 87 +/- 5 mmHg (P < 0.01) and LAD increased from 28 +/- 1 to 32 +/- 1 mm (P < 0.001). During 1-G conditions with subjects in the horizontal left lateral position, LAD increased compared with that of Sup (P < 0.001) with no further effects of 0 G. In conclusion, MAP decreases during short-term weightlessness to below that of 1-G Sup simultaneously with an increase in LAD. Therefore, distension of the heart and associated central vessels during 0 G might induce the hypotensive effects through peripheral vasodilatation. Furthermore, the left lateral position in humans could constitute a simulation model of weightlessness.

Adult↗

PubMed1998

Underestimation of plasma volume changes in humans by hematocrit/hemoglobin method.

During water immersion in humans, the use of changes in hematocrit (Hct) and hemoglobin concentration (Hb) underestimates the relative changes in plasma volume (PV) as measured directly with Evans blue (EB). It is not known whether the same is the case during posture changes. Therefore, changes in PV were determined with an EB dilution technique in 10 males before, during, and after an acute posture change from seated to 6 degrees head-down tilt (HDT). The EB method was improved to take into account changes in transcapillary escape rate of albumin-bound EB. Furthermore, blood was sampled from a central venous catheter. Hct and Hb were simultaneously measured. During HDT, PV determined with EB increased by 9.3 +/- 2.0% but increased only 4.5 +/- 0.9% when calculated with the Hct/Hb method (P < 0.05 vs. EB measurements). Thus use of the Hct/Hb method in humans leads to underestimation of the change in PV by as much as 50% during an acute change in posture. Therefore, a direct tracer-dilution method must be used for accurate estimations of changes in PV during changes in posture or other antiorthostatic maneuvers.

Adult↗

PubMed1997

Left atrial distension and antiorthostatic decrease in arterial pressure and heart rate in humans.

It was investigated to what degree left atrial distension augments the hypotensive effects of a 15-min moderate antiorthostatic maneuver in humans. Ten healthy males underwent a posture change from upright seated (Seat, legs horizontal) to supine (Sup) or to supine with simultaneous lower body negative pressure (Sup + LBNP) to keep left atrial diameter (LAD) unchanged. After 2.5 min of Sup, mean arterial pressure (MAP) decreased from 94 +/- 3 to 86 +/- 3 mmHg (P < 0.05), whereas a similar decrease was delayed 7.5 min into Sup + LBNP. Heart rate (HR) decreased within 2.5 min of Sup from 68 +/- 2 to 60 +/- 3 beats/min (P < 0.05) and remained significantly decreased for at least 2.5 min longer than during Sup + LBNP. Aortic systolic distension (ASD) increased by 59 +/- 17% during Sup (P < 0.05) but was unchanged during Sup + LBNP. The 29 +/- 4% decrease in plasma norepinephrine (NE) during Sup (P < 0.05) was abolished during Sup + LBNP. In conclusion, the increases in LAD and ASD seem important stimuli for the prompt decrease in MAP, the 2.5-min longer-lasting decrease in HR, and the sustained decrease in NE during a 15-min moderate antiorthostatic posture change in humans.

Adult↗

PubMed1997

Hemodilution, central blood volume, and renal responses after an isotonic saline infusion in humans.

To test the hypothesis that hemodilution is a mediator of the renal responses to an isotonic saline infusion in the supine position, eight males underwent 1) intravenous infusion of 1.5 liter of saline over 21 min (Saline), 2) infusion of 1.5 liter of saline in combination with lower body negative pressure for 3 h (LBNP+Saline) to maintain central blood volume unchanged, and 3) a control study without infusion or LBNP. During the Saline series, central venous pressure (CVP) and left atrial diameter (LAD) increased by 4.4 +/- 0.6 mmHg and 2.6 +/- 0.4 mm (P < 0.05), respectively, whereafter they declined toward preinfusion levels. During LBNP+Saline, CVP and LAD were unchanged. Plasma colloid osmotic pressure remained unchanged during control and showed identical decreases by 5 mmHg (P < 0.05) in the Saline and LBNP+Saline series. During the 3rd h of LBNP, renal sodium excretion (U(Na)V) peaked at 296 +/- 55 micromol/min vs. a higher value of 383 +/- 54 micromol/min (P < 0.05) during Saline. The increase in U(Na)V above that of control during the 3rd h of LBNP+Saline constituted 48% of that during Saline. Plasma renin activity and plasma aldosterone concentration showed similar patterns of decrease after saline infusion irrespective of LBNP, whereas plasma norepinephrine was elevated late in the LBNP period compared with during Saline and control (P < 0.05). It is concluded that the maintenance of a constant CVP and LAD reduces the natriuresis of acute saline loading by about one-half. Thus hemodilution in conjunction with suppression of renin and aldosterone release (independent of change in CVP and LAD) might account for the remaining natriuresis of infusion.

Adult↗

PubMed1997

Atrial distension in humans during microgravity induced by parabolic flights.

The hypothesis was tested that human cardiac filling pressures increase and the left atrium is distended during 20-s periods of microgravity (microG) created by parabolic flights, compared with values of the 1-G supine position. Left atrial diameter (n = 8, echocardiography) increased significantly during microG from 26.8 +/- 1.2 to 30.4 +/- 0.7 mm (P < 0.05). Simultaneously, central venous pressure (CVP; n = 6, transducer-tipped catheter) decreased from 5.8 +/- 1.5 to 4.5 +/- 1.1 mmHg (P < 0.05), and esophageal pressure (EP; n = 6) decreased from 1.5 +/- 1.6 to -4.1 +/- 1.7 mmHg (P < 0.05). Thus transmural CVP (TCVP = CVP - EP; n = 4) increased during microG from 6.1 +/- 3. 2 to 10.4 +/- 2.7 mmHg (P < 0.05). It is concluded that short periods of microG during parabolic flights induce an increase in TCVP and left atrial diameter in humans, compared with the results obtained in the 1-G horizontal supine position, despite a decrease in CVP.

Adult↗

PubMed1997

Case report: obstructive sleep apnea--an air safety risk.

Aviation safety reports indicate that many incidents are related to fatigue. Obstructive sleep apnea (OSA) is characterized by irregular snoring with repeated apnea episodes during sleep and excessive daytime sleepiness. Deprived of sleep, patients suffer from daytime sleepiness and involuntary sleep attacks. The prevalence of OSA among adult men is more than one percent, 0.5% in women. Predisposed are men aged 40-65 yr. Many patients, including pilots, are unaware of their sleeping disturbance and the symptoms are not easily recognized. Therefore, this condition may not be discovered during a regular health examination. However, this condition can be effectively treated. In our opinion, pilots suffering from OSA do not necessarily have to lose their certificate. Diagnosis and treatment can be conducted, followed by regular check-ups. We suggest that questions about sleep be included in pilots' health examinations.

Adult↗

PubMed1996

[Prognostic values of echocardiography compared with clinical variables in suspected heart disease. Multivariate analysis of long-term prognosprognosis in 456 patients].

The aim of the study was to evaluate the prognostic significance of clinical and echocardiographic data in patients referred for echocardiography in a retrospective analysis. Four hundred and fifty-six patients from a district hospital were studied. Survival after three years was 64%. Multivariate analysis identified five factors with independent prognostic information (relative risks of death are shown in brackets): left ventricular wall motion index (WMI) < or = 1.2 by echocardiography (2.5), status as in-patient (2.1), age > 65 years (1.7), clinical heart failure (1.9) and atrial fibrillation (1.5). When information on age, hospitalisation status, heart failure and heart rhythm had already been entered in the Cox model, echocardiographic results such as decreased WMI and dilated right ventricle still gave further prognostic information. We conclude that among conventional clinical and echocardiographic data WMI was the strongest predictor of long-term survival, and, despite prior knowledge of major clinical features, echocardiography provided further prognostic information.

Adult↗

PubMed1996

Central venous pressure in humans during microgravity.

Based on the results of head-down simulation studies and the results of parabolic flights, the hypothesis was tested that central venous pressure (CVP) in humans increases during microgravity (weightlessness) compared with during the ground-based supine position. CVP was recorded with an intravascular pressure transducer in seven healthy humans during short (20-s) periods of microgravity created by parabolic-flight maneuvers and in one astronaut before, during, and up to 3 h after launch of the Spacelab D-2 mission (Space Transport System-55). When the subjects were supine during the parabolic maneuver, CVP decreased during microgravity from 6.5 +/- 1.3 to 5.0 +/- 1.4 mmHg (P < 0.05). during the Spacelab D-2 mission, CVP was 6.2 mmHg during the initial minutes of microgravity, which was very similar to the value of 6.5 mmHg in the supine position 3.5 h before launch of the space shuttle. During the subsequent 3 h of weightlessness, CVP during rest varied between 2.0 and 6.2 mmHg. We conclude that CVP during short (20-s) and longer (3-h) periods of microgravity is close to or below that of the supine position on the ground.

Adult↗

PubMed1995

Effect of microgravity on forearm subcutaneous vascular resistance in humans.

To test the hypothesis that the subcutaneous vascular constrictor response to an orthostatic stress in humans is augmented after exposure to microgravity, the following experiment was performed. Four male astronauts underwent a standardized stepwise lower body negative pressure (LBNP) profile 5 mo before and between 24 and 40 h after completion of the 10-day Spacelab D2 mission (STS-55). Forearm subcutaneous blood flow was continuously measured during LBNP by the 133Xe washout technique, and forearm subcutaneous vascular resistance (FSVR) was estimated by dividing mean arterial pressure by forearm subcutaneous blood flow. Relative to the pre-LBNP level, FSVR increased to 169 +/- 42 (P < 0.05), 176 +/- 12 (P < 0.05) and 158 +/- 27% during postflight LBNP of -11 (20 min), -23 (5 min), and -30 (7.5 min) mmHg, respectively. During the same LBNP levels of the same durations preflight, FSVR increased to 121 +/- 11 (not significant), 139 +/- 12 (P < 0.05), and 135 +/- 13% (P < 0.05), respectively. Thus, FSVR increased more promptly and, in three of the four subjects, was more pronounced during postflight than during preflight LBNP. In conclusion, the FSVR response was more prompt and tended to be accentuated after 1-2 days after exposure to 10 days of microgravity and could act as a defense mechanism to alleviate decreased orthostatic tolerance.

Adult↗

PubMed1995

Prognostic value of echocardiography compared to other clinical findings. Multivariate analysis based on long-term survival in 456 patients.

The prognostic significance of conventional clinical and echocardiographic data in patients referred to echocardiography was retrospectively analyzed. 456 patients (206 females and 250 males) were studied in the department of cardiology in a district hospital. Survival after 3 years was 64%. By multivariate analysis five factors contained independent, significant, prognostic information (hazard ratios for death are given in parentheses): left ventricular wall motion score index (WMI) < or = 1.2 by echocardiography (2.5), status as inpatient (2.1), age > 65 years (1.7), clinical heart failure (1.9) and atrial fibrillation (1.5). A stepwise multivariate analysis was performed by entering variables into a model initially forced to contain information on age, hospitalization status, treatment of heart failure and heart rhythm. In this analysis, a poor WMI (< or = 1.2) and a dilated right ventricle contained further independent prognostic information. In conclusion, among conventional clinical and echocardiographic data, WMI was the most powerful predictor of long-term survival, and despite knowledge of major clinical features echocardiography provided further prognostic information.

Aged↗

PubMed1994

An echocardiographic method for selecting high risk patients shortly after acute myocardial infarction, for inclusion in multi-centre studies (as used in the TRACE study). TRAndolapril Cardiac Evaluation.

The aim of our study was to examine if echocardiography can reproducibly be used in a multicentre study to select high risk patients with reduced left ventricular function early after an acute myocardial infarction (MI). In the TRAndolapril Cardiac Evaluation Study (TRACE) patients with reduced left ventricular systolic function were randomized 3-7 days post MI to receive either the ACE inhibitor trandolapril, or placebo. Twenty-seven Danish centres participated and 7001 consecutive MI patients were screened for entry. Local doctors and technicians who had received a brief but thorough training course recorded a two-dimensional echocardiographic examination on videotape 2-6 days after MI. Within 24 h, wall motion index (WMI) was visually assessed by one of two cardiologists (examiners) with considerable experience in echocardiography. A WMI of < or = 1.2 (corresponding to a left ventricular ejection fraction (LVEF) < or = 0.35) meant that the patient was eligible for randomization in the TRACE study. Two other experienced cardiologists with substantial experience in echocardiography (controllers) performed blind reassessment of 155 randomly chosen videotapes. We showed that 93% of the 7001 screened MIs had an assessable echocardiogram. WMI was < or = 1.2 in 37% of patients. The one-year mortality was inversely related to WMI, being 60%, 30%, 14% and 11% in patients with a WMI < 0.8, 0.8-1.2, 1.3-1.6 and > 1.6, respectively. In the random sample of 155 videorecordings that were reevaluated, 97% were found to be technically adequate for analysis both by the examiners and the controllers.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1993

Arterial pulse pressure and vasopressin release in humans during lower body negative pressure.

The hypothesis was tested that narrowing of arterial pulse pressure (PP) is a determinant of arginine vasopressin (AVP) release in humans. Six normal males completed a two-step lower body negative pressure (LBNP) protocol of -20 and -50 mmHg, respectively, for 10 min each. None of these subjects experienced presyncopal symptoms. Arterial plasma AVP and plasma renin activity (PRA) (at 2-min intervals) only increased subsequent to a decrease in PP (invasive brachial arterial measurements) and stroke volume (ultrasound Doppler technique, n = 4). Simultaneously, mean arterial pressure did not change. A selective decrease in central venous pressure and left atrial diameter (echocardiography, n = 4) at LBNP of -20 mmHg did not affect AVP or PRA, whereas arterial plasma norepinephrine increased (n = 4). During LBNP, significant (P < 0.05) intraindividual linear correlations were observed between log(AVP) and PP in four of the subjects with r values from -0.75 to -0.99 and between log(PRA) and PP in all six subjects with r values from -0.89 to -0.98. In conclusion, these results are in compliance with the hypothesis that narrowing of PP in humans during central hypovolemia is a determinant of AVP and renin release.

Adult↗

PubMed1993

Plasma immunoreactive neuropeptide Y in congestive heart failure at rest and during exercise.

The purpose of the study described here was to study plasma immunoreactive Neuropeptide Y (NPY) at rest and during exercise in patients with congestive heart failure (CHF) and in healthy subjects. Thirty-five patients, mean age 64 years, with CHF in optimal treatment and with a mean ejection fraction of 32%, were studied at rest and during exercise. Twelve age and sex matched healthy subjects were compared for resting values. Another nine healthy subjects were studied at rest and during exercise at a constant low load of 75W and at a high load defined as 80% of their individual maximal capacity. In patients with congestive heart failure mean plasma immunoreactive NPY at rest was 10.3 pmol l-1 and was not significantly different from the control group. No differences between patients with slight and severe CHF were found and there was no correlation between plasma immunoreactive NPY and left ventricular ejection fraction. Mean maximal exercise time was on average 6.3 min. Only three patients exercised more than 10 min. At maximal exercise mean plasma immunoreactive NPY was 10.6 pmol l-1 the same as at rest. Plasma noradrenaline was increased in CHF patients compared to healthy subjects, and rose further during exercise. In healthy subjects plasma immunoreactive NPY rose significantly on both workloads, but more on the high load (p < 0.05), when the rise was first significant after 10 min. Plasma immunoreactive NPY at rest and during exercise was not increased in CHF patients in optimal medical treatment. Consequently plasma immunoreactive NPY is not a useful marker of the severity of CHF in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Cerebral blood flow before and after cardioversion of atrial fibrillation.

In nine patients with atrial fibrillation (AF) of less than 3 months' duration, CBF was measured the day before and after and again 30 days after electrical cardioversion therapy to sinus rhythm. The day before cardioversion therapy, median CBF (expressed as initial slope index 1, ml/100 g.min-1) was 35.8 and the day after it was 37.1. After 30 days in sinus rhythm, CBF was 39.4 (NS), although the end-tidal PCO2 values were lower than the pretreatment values. After correction for changes in end-tidal PCO2, the median CBF had increased significantly from 35.8 to 40.3 on day 1 and to 46.7 on day 30. The reduced CBF during AF could be a contributing factor in the development of cerebrovascular complications in patients with AF.

Adult↗

PubMed1988

Myocardial contractility and performance capacity after magnesium infusions in young healthy persons: a double-blind, placebo-controlled, cross-over study.

To evaluate the effect of intravenous magnesium (Mg) treatment on the inotropic state of the heart and maximal work capacity, 9 healthy volunteers were entered in a double-blind, placebo-controlled, cross-over study. Separated by an interval of three weeks, the volunteers were tested twice, each time randomly allocated to receive either an intravenous injection of 10 mmol magnesium chloride dissolved in 100 ml isotonic sodium chloride or placebo of isotonic sodium chloride only. Before and after each infusion myocardial inotropism was evaluated by echocardiography. Mitral-septal distance (MSA) was used as a measure for ejection fraction. On each test day an ergometer bicycle exercise test was performed, and maximal work capacity was calculated. Magnesium treatment reduced the MSA (from 4.2 to 2.9 mm, p = 0.07), while no difference was found after placebo treatment. Likewise, a tendency toward increasing fractional shortening after magnesium treatment was detected, although this difference was not statistically significant (p = 0.1). No difference in maximal work capacity between the magnesium and placebo periods was found. Serum magnesium concentrations and placebo periods was found. Serum magnesium concentrations rose significantly after the infusions (from 0.82 to 1.38 mmol/l, p less than 0.001). It is concluded that intravenous magnesium does not exert a negative inotropic effect on the myocardium as previously stated. On the contrary, we found a tendency toward a positive inotropic effect. However, the observed differences are of borderline statistical significance and a more extended study, employing invasive measurements of cardiac inotropism appears to be necessary.

Adult↗