Endonasal CO2-Nd:YAG laser dacryocystorhinostomy

A preliminary series of endonasal dacryocystorhinostomy was carried out on 12 patients with nasolacrimal obstruction using a recently developed combined CO2-Nd:YAG laser that was guided by a fiberoptic light pipe inserted into the lacrimal sac through lacrimal canaliculi. The lacrimal passages were stented using silicone tubing that was kept in place for 6 months postoperatively. At an average follow-up time of 14.3 months the success rate was 83%. The advantages of the operation include a relatively short operation time, quick rehabilitation, absence of a skin wound, good hemostasis, and preservation of canthal anatomy.

Baroreflex sensitivity in men with recent myocardial infarction; impact of age

We investigated the effect of age on baroreflex sensitivity (BRS) in 39 male patients, who had survived their first myocardial infarction (MI) and in 15 age-matched controls. BRS was inversely related to age in both MI patients (r = -0.632, P < 0.0001) and controls (r = -0.706, P < 0.0001). The relationship between BRS and age, however, was significantly different in MI patients as compared with healthy controls: BRS was markedly higher and the BRS-age regression slope was significantly steeper in controls than in MI patients. As a consequence, the decrease in BRS caused by MI (delta BRS = age-specific expected BRS--measured BRS) was related inversely to age (r = -0.66, P < 0.05) i.e. delta BRS was greatest among young MI patients. However, the relative BRS (BRS% = measured BRS divided by the age-specific expected BRS) did not correlate with age. The average BRS% of MI patients was 37% lower than that of controls. MI size and left ventricular (LV) systolic function did not correlate with BRS. BRS correlated with variables related to cardiac diastolic function (peak late LV filling rate r = -0.43, P < 0.05), exercise capacity (r = 0.31, P < 0.05) and the extent of ST-depression during exercise (r = -0.40, P < 0.05), but all these correlations lost their significance after the adjustment for age. In conclusion, age is a factor that should be taken into consideration when evaluating the mechanisms of BRS impairment associated with different diseases.(ABSTRACT TRUNCATED AT 250 WORDS)

Extent of cardiac autonomic denervation in relation to angina on exercise test in patients with recent acute myocardial infarction

According to the current concept, anginal pain results from stimulation of sympathetic nerves within the heart. In this study, we evaluated the role of cardiac adrenergic denervation in exercise-induced angina pectoris in 15 men with recent acute myocardial infarction. Before discharge from the hospital, the patients were subjected to a symptom-limited exercise test. Three months after the infarction, cardiac scintigraphic studies using I-123 metaiodobenzylguanidine (MIBG), I-123 paraphenylpentadecanoic acid (pPPA), and Tc-99m sestamibi (MIBI) were performed in order to determine the extent of denervated myocardium, the size of infarction, and myocardium with reduced perfusion, respectively. MIBG defect (17.2 +/- 7.6% of left ventricular mass) (defect defined as an activity distribution < or = 30% of the maximal myocardial activity) was larger than pPPA defect (8.3 +/- 8.8%, p < 0.001) in all patients, which indicates that the area of myocardial necrosis was surrounded by viable myocardium with sympathetic denervation. The extent of viable but denervated myocardium was significantly greater in patients who developed angina pectoris than in patients without angina pectoris during the early exercise test (13.3 +/- 4.4% vs 5.0 +/- 2.4%, p < 0.001). In addition, patients with silent ischemia tended to have smaller areas of viable but denervated myocardium than patients with painful ischemia (5.7 +/- 3.8% vs 13.8 +/- 5.1%, p = 0.07). Thus, contrary to expectations, the extent of viable but denervated myocardium seems to be associated with increased pain sensitivity in patients with recent myocardial infarction.

Circadian variation of cardiac autonomic regulation during 24-h bed rest

We examined the effect of circadian variation on cardiac autonomic regulation in 11 young and middle-aged, healthy men during 24-h bed rest. Cardiac parasympathetic regulation expressed significant circadian variation: sensitivity of baroreceptor reflex, standard deviation of R-R intervals and the power of high frequency component of R-R interval variability (HFP) increased during the evening (2000-2100 h), were highest during the night (0200-0300 h), and gradually decreased again towards afternoon (1400-1500 h). Cardiac sympathetic regulation, the power of medium frequency component of R-R interval variability (MFP), did not show any significant circadian variation. The autonomic response to orthostatic stress changed after the 24-h bed rest; the sympathetic dominance in response to assuming upright position was before bed rest principally attributable to increased sympathetic activity (MFP increase), whereas after bed rest this was due to withdrawal of parasympathetic activity (HFP decrease). We conclude that the effect of circadian variation must be taken into account, while assessing cardiac autonomic regulation in patients with acute cardiovascular disorders.

Microcomputer-based monitoring of cardiovascular functions in simulated microgravity

A microcomputer-based system for non-invasive monitoring of cardiovascular system in simulated microgravity is described. The system evaluates automatically, accurately and interactively heart beat intervals, beat-to-beat non-invasive finger arterial blood pressure (systolic, diastolic, mean and pulse pressure) using a Finapres device and beat-to-beat changes of thoracic blood volume using impedance changes. In addition, beat-to-beat evaluation of cardiac mechanical function including left ventricular ejection time, diastolic time, systolic time intervals, left ventricular ejection fraction estimate and several other contractility parameters, left ventricular volume, stroke volume and cardiac output estimates are performed with high degree of automaticity.

Haemodynamic information encoded in the aortic baroreceptor discharge during haemorrhage

This study concerns the function of aortic baroreceptors during slow haemorrhage, in particular the mechanisms by which baroreceptors respond to hypovolaemia in the absence of hypotension and the manner in which haemodynamic information is encoded in the aortic nerve discharge. Beagle dogs, anaesthetized with morphine and chloralose, were instrumented for the recording of aortic pressure, aortic diameter, aortic flow and aortic nerve activity. The animals were subjected to slow haemorrhage (0.4 ml kg-1 min-1) of 20% of the estimated blood volume. Mean aortic pressure remained unchanged, whereas mean aortic diameter, mean aortic tension and aortic baroreceptor activity decreased during the haemorrhage. Baroreceptor sensitivity to mean aortic pressure, mean aortic diameter and mean aortic tension decreased as the haemorrhage proceeded. Also, the sensitivity of baroreceptors to mean aortic pressure and mean aortic diameter during acute pressure stimulation was attenuated. The results indicate that during non-hypotensive haemorrhage aortic baroreceptor discharge is reduced by two mechanisms: firstly, via constriction and stiffening of aortic smooth muscle and, secondly, via direct effects of the compensatory mechanisms on the baroreceptors. The reduced sensitivity renders the baroreceptors capable of responding to hypovolaemia prior to the onset of hypotension. In the regression analysis, systolic aortic diameter proved to be the best determinant of baroreceptor activity (r = 0.877). Of the neural variables, impulses per cardiac cycle and average discharge rate were the most reliable, but no difference in the relative importance of these two parameters could be observed.

Effect of acute intravenous volume loading on haemodynamics and aortic baroreceptor activity in dogs

This study evaluates the effect of acute intravenous volume loading on haemodynamics and aortic baroreceptor activity in order to determine the mechanistic factors responsible for divergent heart rate responses to volume loading. Eleven beagles were anaesthetized and instrumented for the recording of aortic pressure, diameter, flow and aortic baroreceptor activity. Isotonic saline, equal to 20% of the estimated blood volume, was infused intravenously within 60-90 s. The animals were divided into tachycardiac and bradycardic groups according to their heart rate response to volume loading. In the group developing the tachycardic response, aortic baroreceptor activity increased. Total peripheral resistance was reduced by 31% and variables representing aortic stretch, mean aortic pressure, diameter and tension remained unchanged. In contrast, in the group developing the bradycardiac response, aortic baroreceptor activity increased markedly. Also in this group peripheral resistance decreased, but only by 15%, which was significantly less than in the tachycardiac group. Factors determining aortic stretch, mean aortic pressure, diameter and tension also increased significantly. Earlier studies show that regardless of the resulting heart rate response, atrial receptor activity increases during volume loading. Thus, we conclude that during cardiac acceleration, marked peripheral vasodilation eliminates the stimulation of baroreceptors and therefore the tachycardic response caused by atrial receptors develops. In the case of cardiac slowing, vasodilation also takes place, but is not sufficient to prevent activation of baroreceptors. In consequence, increased baroreceptor activity overrides the tachycardic drive coming from the atrial receptors and a typical baroreceptor reflex becomes manifested.

Combined effect of low doses of propranolol and ethanol on cardiac function: a comparative study by radionuclide ventriculography in conscious dogs

Trained, chronically instrumented, conscious dogs were used to evaluate the effect of propranolol (PRO), ethanol (ETH) or their combination (P + E) on the left ventricular (LV) function by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m diethylenetriamine pentaacetic acid via the catheter to the left atrium. The data was collected for 12 sec. to a computer by frame rate of 20 frames/sec. from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60-degree head-up tilted positions. After control measurements the data were obtained with 0.5 mg/kg of PRO, 0.45 g/kg of ETH and their combination. The P + E combination increased significantly LV end-diastolic and end-systolic volumes, whereas LV peak ejection rate and ejection fraction were decreased. Upright position diminished the LV volume and increased heart rate, while ejection fraction and cardiac output remained unchanged. The first-pass RNV method proved to be promising for measuring the cardiac pharmacological effects in conscious dogs. The combination of propranolol and ethanol in low doses induced an unexpectedly strong depression of LV function, which is supposed to be followed of latent cardiac depressing effect of ETH revealed by blockade of compensatory adrenergic mechanisms with PRO.

First-pass radionuclide ventriculography in conscious dogs

Trained, chronically instrumented, conscious dogs were used to study the function of the left ventricle by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m-DTPA via the catheter to the left atrium. The data was collected for 12 s to a computer by frame rate of 20 frames/s from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60 degrees head-up tilted positions. The measurements were done with two injection volumes (0.25 and 1.0 ml/kg) to study the effect of volume on the results. The body position had effect on left ventricular end-diastolic and stroke volumes, whereas ejection fraction remained unchanged. In comparison of the two injection volumes a minor difference was found in left atrial emptying, while the differences in left ventricular function were non-significant. In spite of training and careful standardization of experimental procedures, relatively high individual variation between animals was found in most parameters studied. The first-pass RNV method proved to be promising for measuring the left ventricular function in conscious dogs. Although the left atrium has reflectory tachycardic potential to distension, the volumes used for RNV did not affect the results. The left ventricular adaptation to head-up tilting in conscious dogs seems to consist mainly of decrease in left ventricular volume without significant effect on ejection fraction.