Postural tachycardia syndrome in a 28-year-old Japanese woman.
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Postural tachycardia syndrome is defined as the development of orthostatic symptoms without orthostatic hypotension. We report a 28-year-old female patient with postural tachycardia syndrome who exhibited palpitation, low-grade fever and weight loss. Evaluation of autonomic nervous system functions showed that cardiovagal function was normal. Sweat response to acetylcholine was decreased. Excessive blood pressure elevation was seen in phase IV of the Valsalva maneuver. Pathophysiologic factors in this case were considered to be alpha adrenergic denervation and beta adrenergic hyperresponsiveness. It is important that this syndrome be widely recognized and properly diagnosed. (+info)
A human cardiopulmonary system model applied to the analysis of the Valsalva maneuver.
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Previous models combining the human cardiovascular and pulmonary systems have not addressed their strong dynamic interaction. They are primarily cardiovascular or pulmonary in their orientation and do not permit a full exploration of how the combined cardiopulmonary system responds to large amplitude forcing (e.g., by the Valsalva maneuver). To address this issue, we developed a new model that represents the important components of the cardiopulmonary system and their coupled interaction. Included in the model are descriptions of atrial and ventricular mechanics, hemodynamics of the systemic and pulmonic circulations, baroreflex control of arterial pressure, airway and lung mechanics, and gas transport at the alveolar-capillary membrane. Parameters of this combined model were adjusted to fit nominal data, yielding accurate and realistic pressure, volume, and flow waveforms. With the same set of parameters, the nominal model predicted the hemodynamic responses to the markedly increased intrathoracic (pleural) pressures during the Valsalva maneuver. In summary, this model accurately represents the cardiopulmonary system and can explain how the heart, lung, and autonomic tone interact during the Valsalva maneuver. It is likely that with further refinement it could describe various physiological states and help investigators to better understand the biophysics of cardiopulmonary disease. (+info)
The exercise metaboreflex is maintained in the absence of muscle acidosis: insights from muscle microdialysis in humans with McArdle's disease.
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1. In McArdle's disease, muscle glycogenolysis is blocked, which results in absent lactate and enhanced ammonia production in working muscle. Using McArdle patients as an experimental model, we studied whether lactate and ammonia could be mediators of the exercise pressor reflex. 2. Changes in muscle interstitial ammonia and lactate were compared with changes in blood pressure and muscle sympathetic nerve activity (MSNA) during static arm flexor exercise at 30% of maximal contraction force. Muscle interstitial changes in lactate and ammonia were assessed by microdialysis of the biceps muscle, and MSNA by peroneal nerve microneurography, in six McArdle patients and 11 healthy, matched controls. One McArdle patient also had myoadenylate deaminase deficiency, a condition associated with abolished ammonia production in exercise. 3. Exercise-induced increases were higher in McArdle patients vs. controls for MSNA (change of 164 +/- 71 vs. 59 +/- 19%) and blood pressure (change of 47 +/- 7 vs. 38 +/- 4 mmHg). Interstitial lactate increased in controls (peak change 1.3 +/- 0.2 mmol x l(-1)) and decreased in McArdle patients (peak change -0.5 +/- 0.1 mmol x l(-1)) during and after exercise. Interstitial ammonia did not change during exercise in either group, but was higher post-exercise in McArdle patients, except in the patient with myoadenylate deaminase deficiency who had a flat ammonia response. This patient had an increase in MSNA and blood pressure comparable to other patients. MSNA and blood pressure responses were maintained during post-exercise ischaemia in both groups, indicating that sympathetic activation was caused, at least partly, by a metaboreflex. 4. In conclusion, changes in muscle interstitial lactate and ammonia concentrations during and after exercise are temporally dissociated from changes in MSNA and blood pressure in both patients with McArdle's disease and healthy control subjects. This suggests that muscle acidification and changes in interstitial ammonia concentration are not mediators of sympathetic activation during exercise. (+info)
Influence of microgravity on astronauts' sympathetic and vagal responses to Valsalva's manoeuvre.
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When astronauts return to Earth and stand, their heart rates may speed inordinately, their blood pressures may fall, and some may experience frank syncope. We studied brief autonomic and haemodynamic transients provoked by graded Valsalva manoeuvres in astronauts on Earth and in space, and tested the hypothesis that exposure to microgravity impairs sympathetic as well as vagal baroreflex responses. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, respiration and peroneal nerve muscle sympathetic activity in four healthy male astronauts (aged 38-44 years) before, during and after the 16 day Neurolab space shuttle mission. Astronauts performed two 15 s Valsalva manoeuvres at each pressure, 15 and 30 mmHg, in random order. Although no astronaut experienced presyncope after the mission, microgravity provoked major changes. For example, the average systolic pressure reduction during 30 mmHg straining was 27 mmHg pre-flight and 49 mmHg in flight. Increases in muscle sympathetic nerve activity during straining were also much greater in space than on Earth. For example, mean normalized sympathetic activity increased 445% during 30 mmHg straining on earth and 792% in space. However, sympathetic baroreflex gain, taken as the integrated sympathetic response divided by the maximum diastolic pressure reduction during straining, was the same in space and on Earth. In contrast, vagal baroreflex gain, particularly during arterial pressure reductions, was diminished in space. This and earlier research suggest that exposure of healthy humans to microgravity augments arterial pressure and sympathetic responses to Valsalva straining and differentially reduces vagal, but not sympathetic baroreflex gain. (+info)
Small group teaching: clinical correlation with a human patient simulator.
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The popularity of the problem-based learning paradigm has stimulated new interest in small group, interactive teaching techniques. Medical educators of physiology have long recognized the value of such methods, using animal-based laboratories to demonstrate difficult physiological principles. Due to ethical and other concerns, a replacement of this teaching tool has been sought. Here, the author describes the use of a full-scale human patient simulator for such a workshop. The simulator is a life-size mannequin with physical findings (palpable pulses, breath/heart sounds, blinking eyes, etc.) and sophisticated mechanical and software models of the cardiovascular and pulmonary systems. It can be connected to standard physiological monitors to reproduce a realistic clinical environment. In groups of 10, first-year medical students explore Starling's law of the heart, the physiology of the Valsalva maneuver, and the function of the baroreceptor in a clinically realistic context using the simulator. With the use of a novel pre-/postworkshop assessment instrument that included student confidence in their answers, student confidence improved for all questions and survey items following the simulator session (P < 0.0001). The students give these laboratory exercises uniformly superior evaluations with > 85% of the students rating the workshop "very good" or "excellent". (+info)
Pulmonary mechanics by spectral analysis of forced random noise.
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The magnitude (Zrs) and phase angle (thetars) of the total respiratory impedance (Zrs), from 3 to 45 Hz, were rapidly obtained by a modification of the forced oscillation method, in which a random noise pressure wave is imposed on the respiratory system at the mouth and compared to the induced random flow using Fourier and spectral analysis. No significant amplitude or phase errors were introduced by the instrumentation. 10 normals, 5 smokers, and 5 patients with chronic obstructive lung disease (COPD) were studied. Measurements of Zrs were corrected for the parallel shunt impedance of the mouth, which was independently measured during a Valsalva maneuver, and from which the mechanical properties of the mouth were derived. There were small differences in Zrs between normals and smokers but both behaved approximately like a second-order system with thetars = 0 degree in the range of 5--9 Hz, and thetars in the range of +40 degrees at 20 Hz and +60 degrees at 40 Hz. In COPD, thetars remained more negative (compared to normals and smokers) at all frequencies and crossed 0 between 15 and 29 Hz. Changes in Zrs, similar in those in COPD, were also observed at low lung volumes in normals. These changes, the effects of a bronchodilator in COPD, and deviations of Zrs from second-order behavior in normals, can best be explained by a two-compartment parallel model, in which time-constant discrepancies between the lung parenchyma and compliant airway keep compliant greater than inertial reactance, resulting in a more negative phase angle as frequency is increased. (+info)
Changes in venous lumen size and shape do not affect the accuracy of volume flow measurements in healthy volunteers and patients with primary chronic venous insufficiency.
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PURPOSE: The purpose of this study was the analysis of the rapid changes in the size and shape of the peripheral vein and the associated changes in blood flow velocities and the estimation of their effect on the reliability of the ultrasound scan volume flow (VF) measurements. METHODS: Ten patients with primary chronic venous insufficiency and 10 healthy volunteers were studied. Two duplex scanners were used simultaneously: one for the velocity measurements in longitudinal plane and another for the cross-sectional area (CSA) measurements in transverse plane during quiet respiration, Valsalva's maneuver (VM), pneumatic cuff compression-decompression, and active dorsiflexion. The patients underwent examination in standing and 15-degrees reverse Trendelenburg's (RT) positions. VF was calculated on the basis of real-time CSA and velocity values. RESULTS: Rapid changes in the CSA as much as 130% for 0.2 seconds were observed. In most cases, the changes in CSA and the flow velocity were inversely related, which resulted in near constant VF. With the exception of VM in the RT position, the difference between real-time VF and mean VF was not significant (P >.05). In the RT position, significant changes in CSA were observed during and immediately after VM. These changes resulted in 23% +/- 15% changes in outflow (both groups) and in 24% +/- 13% changes in reflux (chronic venous insufficiency group). CONCLUSION: The CSA of the peripheral vein and the flow velocities undergo rapid changes during time intervals of a fraction of a second. The vein can have a noncircular cross-section. To minimize the potential error, VF measurements should be performed during quiet respiration or with cuff compression-decompression. With these conditions, the rapid changes in velocities and CSA do not significantly affect the accuracy of VF measurements because of their inverse relation. CSA should be measured planimetrically, or the site of the measurements should be where the vein is close to a circular shape. (+info)
Haemodynamic quantification of different provocation manoeuvres by simultaneous measurement of right and left atrial pressure: implications for the echocardiographic detection of persistent foramen ovale.
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AIMS: Persistent foramen ovale (PFO) is found in 9.2--32% of echocardiographic examinations. The gold standard for the detection of a PFO is transoesophageal echocardiography (TEE) and the mostly used provocation test is the Valsalva manoeuvre. The aim of our study was to evaluate the effectiveness of the Valsalva manoeuvre compared to other provocation tests by simultaneous haemodynamic measurements of the right and left atrial pressure. METHODS: Fifty patients underwent Swan-Ganz catheterization. Right atrial pressure and pulmonary capillary wedge pressure, which corresponds to the left atrial pressure, were measured simultaneously. The following manoeuvres were compared: the Valsalva manoeuvre, coughing, deep inspiration and expiration pressures of 20 mmHg, 40 mmHg and 60 mmHg. The main objective of our study was to compare the occurrence of pressure gradients (right atrial pressure> left atrial pressure). For further quantification mean gradients, time duration of pressure overlap, as well as products of mean gradients and overlap time were analysed. RESULTS: During the Valsalva manoeuvre a significant pressure gradient could be observed in 84% of the patients, followed by an expiration pressure of 60 mmHg (82%), inspiration (78%), expiration pressure of 40 mmHg (76%), coughing (75%) and an expiration pressure of 20 mmHg (62%). Comparing the mean gradients and the products of mean gradients and overlap time duration during the different manoeuvres, we could detect the significantly best results with the Valsalva manoeuvre. CONCLUSIONS: The Valsalva manoeuvre might be the most effective test to provoke a right-to-left atrial shunt for the detection of a PFO during echocardiographic examinations. (+info)