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Biomedical subjects

K K Teo

Publications and source records attributed to K K Teo.

At least 91 records · Page 5Linked to original sources
PubMed1990

Effects of tissue-type plasminogen activator and anisoylated plasminogen streptokinase activator complex on mortality in acute myocardial infarction.

An overview of eight randomized controlled trials of tissue-type plasminogen activator (Alteplase or Duteplase) and 10 of anisoylated plasminogen streptokinase activator complex (Anistreplase) showed that the odds of early death were reduced by 29% by tissue-type plasminogen activator and 46% by anisoylated plasminogen streptokinase activator complex, with overlapping 95% confidence intervals. Although the beneficial effects of both agents are consistent and are strengthened when all the trials are considered together, the available data do not permit comparisons of the relative efficacy of these two agents with each other or with streptokinase.

Anistreplase↗
PubMed1989

Influence of beta blockade on exercise capacity and heart rate response after human orthotopic and heterotopic cardiac transplantation.

It has been reported that use of beta blockers may not be safe after cardiac transplantation because the denervated hearts may be largely dependent on circulating catecholamines to increase cardiac output. Therefore, the effects of intravenous propranolol were studied during maximal treadmill exercise in 7 patients with heterotopic and 6 with orthotopic cardiac transplantations. An average decrease of about 15% in exercise duration (p less than 0.001), a 34% reduction in systolic blood pressure increase (p less than 0.05) and a 40% attenuation in heart rate increase (p less than 0.001) were observed after beta blockade. In patients with heterotopic transplantation, beta blockade produced similar effects on heart rate in the denervated donor hearts and the innervated recipient hearts during and after mild exercise. During peak exercise, beta blockade attenuated the rate to a greater extent in the donor hearts. Although the denervated donor heart is more sensitive to beta blockade than the innervated recipient heart during exercise, no adverse effects were observed. Beta-blocker therapy should be considered for cardiac transplant patients if longer-term studies confirm their safe use in these patients.

Adrenergic beta-Antagonists↗
PubMed1989

Effect of pulmonary venous congestion on respiratory rate in dogs.

1. The effect of pulmonary venous congestion on the respiratory rate was examined in dogs anaesthetized with alpha-chloralose. The study was done on both spontaneously breathing and artificially ventilated animals. Pulmonary venous congestion was produced by partial obstruction of the mitral valve sufficient to raise the left atrial pressure by 5 mmHg. 2. In artificially ventilated dogs, pulmonary venous congestion increased significantly the activity in phrenic nerves. Both the number of bursts/min and the total number of impulses/min increased. However, there was no significant change in the number of impulses/burst. 3. In spontaneously breathing dogs, pulmonary venous congestion produced a significant increase in the frequency of breathing with a significant shortening of the inspiratory and expiratory durations. 4. Cooling of the cervical vagi to 8-9 degrees C abolished both the above responses. 5. Pulmonary venous congestion (left atrial pressure +5 mmHg) stimulated the rapidly adapting receptors of the airways. This effect was abolished by cooling the ipsilateral vagus proximally to 8-9 degrees C. 6. It is concluded that pulmonary venous congestion increases the respiratory rate reflexly in dogs. The afferent pathway for this reflex response resides in the vagus and the rapidly adapting receptors are likely to be the receptors involved in this response.

Action Potentials↗
PubMed1989

Action of histamine on the rapidly adapting airway receptors in the dog.

The effects of histamine on the activity of rapidly adapting receptors (RAR) of the airways were investigated in anesthetized dogs. With bolus injections given into the right atrium, the threshold dose of histamine required for the excitation of RAR (n = 7) was 0.82 microgram/kg (+1.33/-0.51, geometric mean). With increasing doses of histamine, a dose-response relationship was seen in the activity of RAR. Obstruction of the lymphatic drainage from the lungs reduced the threshold dose to histamine (i.e., shifted the dose-response curve to the left significantly). This change in the dose-response relationship was not accompanied by a corresponding change in the relationship of histamine dose to airway pressures recorded before and after lymphatic obstruction. Against a background of pulmonary venous congestion produced by partial obstruction of the mitral valve, subthreshold doses of histamine stimulated the RAR (n = 4). The excitatory effect of histamine on RAR was found to be abolished by the administration of the H1 receptor antagonist diphenhydramine but not by the H2 receptor antagonist cimetidine. Intravenous infusion of histamine (0.4 microgram.kg-1.min-1) for a period of 10 min increased the RAR activity (n = 6) significantly without producing detectable changes in airway mechanics. The results indicate that contraction of the smooth muscle of the airways may not be a prerequisite for the excitation of RAR, especially at low doses. It is suggested that some of the effects of histamine on RAR are mediated by a local expansion of the extravascular fluid caused by an increase in the permeability of the bronchial vasculature.

Action Potentials↗
PubMed1989

Effects of hydraulic circuit training on cardiovascular function.

The effect of hydraulic circuit training (HCT) on cardiovascular (CV) function was assessed in 32 healthy middle-aged males (X age = 42.2 +/- 2.1 yr). Maximal aerobic power (VO2max), with simultaneous measurement of stroke volume (SV) and cardiac output (CO), by impedance cardiography, was assessed pre- and post-training. Subjects were randomly assigned to a nonexercising control group, a cycle training group (cycle), or one of the two HCT groups. Training groups participated in a 9 wk program, 3 d.wk-1. Subjects assigned to HCT exercised on a 9 station circuit, completing 3 circuits.d-1. Each circuit consisted of three 20 s work intervals at each station with a 1:1 work:rest ratio. One HCT group (HCTmax) completed the maximal repetitions possible (RM) during each work interval. The other HCT group (HCTsub) exercised at 70-85% of RM. Following training VO2max (ml.kg-1 min-1) was significantly increased in all training groups (18.0, 12.5, and 11.3% for cycle, HCTsub, and HCTmax groups, respectively; P less than 0.05). The increase in VO2max observed in the cycle group was significantly greater than that recorded by the two HCT groups (P less than 0.05). For all three training groups, the increase in VO2max was associated with increases in SVmax and COmax (P less than 0.05 for both). These findings suggest that both maximal and submaximal HCT programs can elicit improvements in cardiovascular fitness.

Adult↗
PubMed1988

Evolution of the responses to exercise in left ventricular aneurysms after anterior wall acute myocardial infarction.

The evolution of the heart rate, blood pressure and electrocardiographic responses to exercise in 20 patients (group A) who exhibited echocardiographic evidence of left ventricular (LV) aneurysms after acute myocardial infarction (AMI) were examined. The responses were compared with those seen in 19 patients without LV aneurysms who were matched for age, gender and location of infarct (group B). Patients taking beta blockers were excluded from the study. It was found that the heart rate response to exercise was accentuated in group A at the time of discharge from hospital and that it became attenuated over 9 to 12 months. The blood pressure response was significantly increased over 9 to 12 months in group B. Persistence of ST elevation during exercise, 10 to 12 weeks after AMI, was diagnostic of an LV aneurysm. One year after AMI the sensitivity of ST elevation was 90%, specificity was 95% and the negative predictive value 90%.

Blood Pressure↗
PubMed1988

Reflex tracheal contraction during pulmonary venous congestion in the dog.

1. The effect of pulmonary venous congestion on tracheal tone was studied in dogs anaesthetized with alpha-chloralose. Pulmonary venous congestion was produced by partial obstruction of the mitral valve to increase left atrial pressure by 10 mmHg. Tracheal tone was measured in vivo by an isometric force displacement method. 2. Tracheal tone increased by 6.3 +/- 0.3 g from a control level of 91.6 +/- 2.8 g when left atrial pressure was increased by 10.5 +/- 0.3 mmHg. This response was abolished by cooling the cervical vagi to 8 degrees C at a point caudal to the origin of the superior laryngeal nerves. Also, sectioning the superior laryngeal nerves abolished this increase in tracheal tone. 3. Afferent activity recorded from rapidly adapting receptors of the airways increased significantly during pulmonary venous congestion. This increase in activity was abolished by cooling the vagi caudal to the recording site to 8-9 degrees C. 4. Administration of propranolol (0.5 mg/kg) failed to abolish this increase in tracheal tone while atropine (3 mg/kg) did so. 5. Stimulation of left atrial receptors without an increase in left atrial pressure and stimulation of right atrial receptors with and without increases in right atrial pressure did not cause any change in tracheal tone. 6. It is suggested that pulmonary venous congestion is associated with a reflex increase in tracheal tone, the afferent limb of which is formed by pulmonary receptors discharging into myelinated fibres in the cervical vagi and the efferent limb by parasympathetic cholinergic fibres in the superior laryngeal nerves. The afferent receptors are likely to be the rapidly adapting receptors. This reflex may be of importance in the development of the respiratory symptoms associated with left ventricular failure.

Animals↗
PubMed1988

Stimulation of rapidly adapting pulmonary stretch receptors by pulmonary lymphatic obstruction in dogs.

The effects of pulmonary lymphatic obstruction and pulmonary venous congestion on the activities of slowly adapting receptors (SAR) and rapidly adapting receptors (RAR) of the airways were examined in anaesthetized, artificially ventilated dogs. In 11 out of 12 RAR (12 dogs) examined, pulmonary lymphatic obstruction for a period of 20 min produced a sustained significant increase in activity without a significant change in peak airway pressure and dynamic compliance. The activity remained significantly elevated even after the pulmonary lymphatic obstruction was released. This stimulus was without effect on the SAR (n = 5 dogs). Pulmonary venous congestion alone increased the RAR activity (n = 7 dogs) significantly without producing significant changes in airway mechanics. Lymphatic obstruction, when superimposed upon congestion, did not produce a further significant increase in activity. In four dogs the effect of pulmonary venous congestion (left atrial pressure increased from 7.6 +/- 1.7 to 16.3 +/- 2.7 mmHg) (1 mmHg = 133.3 Pa) on pulmonary lymphatic flow was examined. The procedure caused a significant increase in lymph flow. These results suggest that in the dog, the RAR activity is influenced by changes in the pulmonary extravascular space.

Adaptation, Physiological↗
PubMed1988

The diagnosis and management of supraventricular tachycardia by transesophageal cardiac stimulation and recording.

Twenty-two consecutive patients underwent esophageal stimulation and recording for the diagnosis and management of supraventricular tachycardia. In 13 of these patients, the resting electrocardiogram was normal and in nine it showed pre-excitation. Of the 13 patients with a normal resting electrocardiogram, supraventricular tachycardia was initiated in all. Seven patients had a ventricular-to-atrial interval greater than 70 ms during supraventricular tachycardia suggesting the presence of a concealed accessory pathway, and six patients had a ventricular-to-atrial interval less than 70 ms during supraventricular tachycardia suggesting reentry within the atrioventricular node. Supraventricular tachycardia was initiated in four of nine patients with pre-excitation on the resting electrocardiogram and the accessory pathway was confirmed by a ventricular-to-atrial interval of greater than 70 ms during supraventricular tachycardia in these four patients. Atrial fibrillation was initiated in eight of the nine patients with pre-excitation on the resting electrocardiogram and the shortest R-R interval during atrial fibrillation was measured. The response to therapy was assessed in seven of these nine patients by further measurement of the shortest R-R interval during atrial fibrillation following treatment. Esophageal stimulation and recording provides a simple noninvasive procedure which can be utilized as a screening technique to identify patients with intranodal reentry and those with reentry utilizing an accessory pathway. Sequential assessment of the response to therapy, especially in those patients with pre-excitation, is of considerable value in treatment.

Adolescent↗
PubMed1988

Short-term cardiovascular adaptations to vertical head-down suspension.

Inversion devices have been advocated as means of therapy for patients with low back pain. The present investigation was undertaken to determine the cardiovascular responses to vertical head-down suspension with such a device. Eight men were monitored for three minutes in the upright and supine position, and for ten minutes in the vertical head-down position. Stroke volume (SV), heart rate (HR), cardiac output (QT), segmental arm blood flow (ABF), and segmental leg blood flow (LBF) were measured by impedance plethysmography. Moving from the upright to the supine positions resulted in an SV increase from 93.1 +/- 18.8 to 138.2 +/- 28.2 ml.beat-1 (p less than 0.01). During the first minute of suspension a further increase in SV to a maximum of 178.6 +/- 45.0 ml.beat-1 was noted. By the end of the suspension period, SV had declined to 159.6 +/- 34.2 ml.beat-1. Resumption of the upright position was associated with a reduction in SV to 94.3 +/- 15.8 ml.beat-1. Changes in QT across the supine and vertical head-down positions reflected the changes in SV. The vertical head-down position was also associated with a gradual reduction in both ABF and LBF. These data suggest that the primary effect of inverted suspension was a transient increase in venous return, which requires an effective ventricular response. An element of caution should be exercised in using these devices to avoid aggravating concurrent pathologic conditions.

Adaptation, Physiological↗
PubMed1987

Comparison of hemodialysis and hypertonic hemodiafiltration on cardiac function [corrected].

This study compared the acute and chronic effects on cardiac function of treatment with hypertonic hemodiafiltration (H HDF) and hemodialysis (HD). Cardiac function was assessed before, during and after a run of H HDF and HD using echocardiography and impedance cardiography in 10 patients in a randomized cross-over sequence, two months after stabilization on each treatment. Blood biochemistry was performed before and after each run. Ejection fraction and fractional shortening were significantly higher before the H HDF run, compared to the HD run, and this difference persisted during and after the treatment runs (both P less than 0.05). There was a corresponding significant difference in the increase of the velocity of circumferential fiber shortening and in the reduction of end systolic diameter during and after H HDF (P less than 0.05). Heart rate, stroke volume, cardiac output, systemic vascular resistance and mean arterial pressure did not differ significantly between the two treatments. Plasma calcium and bicarbonate were significantly higher (P less than 0.03) at the start of H HDF and this difference was enhanced at the end of the run. In conclusion, H HDF compared with HD, is associated with a better myocardial function in both the short and long term treatments. The evidence suggests that this may be due to improved levels of plasma calcium, bicarbonate, and/or the removal of an as yet unidentified myocardial toxin.

Adult↗
PubMed1987

Response to upright exercise after myocardial infarction.

The left ventricular response to upright bicycle exercise was studied in 39 unselected, non-beta blocked patients (mean(SEM) age 54.2(1.7)yr) (mean(SEM) resting ejection fraction 41.9(2.3)%) 8-10 weeks after myocardial infarction. Nine healthy, age matched, sedentary adult men were studied for comparison (mean(SEM) age 49.8(0.9)yr). The stroke volume and cardiac output were measured by impedance cardiography at rest and after each 3 min workload until symptom limited maximum. The patients were separated into three groups based on stroke volume response to graded exercise. Group 1 (n = 14) had a normal stroke volume response to increasing heart rate. In group 2 (n = 13) stroke volume increased initially then decreased by greater than 15% at a heart rate greater than 100-105 beats.min-1. In group 3 (n = 12) stroke volume failed to increase during exercise. In group 1 cardiac output and mean arterial pressure increased whereas vascular resistance decreased during exercise in a normal fashion. Group 2 had an increased mean arterial pressure and systemic vascular resistance throughout exercise while heart rate increased in a similar fashion to group 1 until work of greater than 70 W was undertaken, at which time heart rate increased in a curvilinear fashion and cardiac output was attenuated. Group 3 had an attenuated cardiac output and a higher heart rate during exercise. In this group of patients systemic vascular resistance failed to decrease normally during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise Test↗
PubMed1987

Behaviour of canine pulmonary vagal afferent receptors during sustained acute pulmonary venous pressure elevation.

1. The effects of an acute sustained increase in pulmonary venous pressure induced by partial obstruction of the mitral valve on the activity of the four types of pulmonary receptors, namely, slowly adapting, rapidly adapting, pulmonary C-fibre and bronchial C-fibre receptors, were studied in the dog. 2. Fifteen slowly adapting receptors, eleven rapidly adapting receptors and nine bronchial C-fibre receptors showed significant sustained increases in activity when stimulated by the elevated left atrial pressure by 9.4 +/- 0.2 mmHg for 15 min. Nine pulmonary C-fibre receptors did not show a significant increase (six of these nine receptors increased their activity in response to the stimulus). 3. When the left atrial pressure was increased in graded steps of 5 mmHg for 5 min each up to 15 mmHg, a significant graded response was found in all of seven slowly adapting receptors, five rapidly adapting receptors and five bronchial C-fibre receptors. The five pulmonary C-fibre receptors examined also showed increases, but the changes were not statistically significant. 4. In response to stimulation by the elevated left atrial pressure, increases in activity occurred within 1 min of application of the stimulus in all the receptors and returned to control levels within 1 min of removal of this stimulus. 5. It is concluded that in the dog, pulmonary vagal receptors are influenced by small increases in pulmonary venous pressure induced by partial obstruction of the mitral valve. The changes appeared to be greatest in the case of rapidly adapting receptors. The physiological significance of these responses remains to be investigated.

Action Potentials↗
PubMed1986

Importance of considering ventricular function when prescribing exercise after acute myocardial infarction.

This investigation was undertaken in patients who had an acute myocardial infarction 12.6 +/- 0.4 months earlier to determine, using conventional methods, the nature of stroke volume changes during training regimens. Twenty-seven patients (mean age 52 +/- 2 years; rest ejection fraction 49 +/- 2%; New York Heart Association functional class I or II) and 9 normal, age-matched sedentary control subjects (mean age 50 +/- 1 years) exercised in the upright position on a bicycle ergometer. Stroke volume was measured by impedance cardiography at rest and after each workload. Ten patients (group A) had a stroke volume response similar to that of the normal sedentary subjects. In 8 patients (group B) the stroke volume increased initially, then decreased (more than 15%) at heart rates (HRs) greater than 100 to 105 beats/min. Nine patients (group C) had a flattened stroke volume response throughout exercise. Training HR determined by conventional methods corresponded to a maximal stroke volume in the normal subjects. Training HR in group A corresponded to a stroke volume that was maximal or near-maximal. Training HR in group B corresponded to a maximal or diminishing stroke volume. In group C, the training HR corresponded to a stroke volume no different from that at rest. Thus, training HR determined by conventional methods based solely on the chronotropic responses to exercise may place patients who have abnormal stroke volume responses to upright exercise in a situation during training sessions in which an inappropriately high HR, excessive fatigue or silent ischemia may develop.

Cardiography, Impedance↗
PubMed1986

Myocardial infarction size; effect on the training response.

The influence of myocardial infarction size, as indicated by the maximum elevation of creatine kinase (CK) and its iso-enzyme CK-MB, on the exercise training response and resting left ventricular function was studied in 15 male patients who underwent exercise training for 8 weeks. Patients were found to divide themselves into two subgroups; those with maximum CK less than or equal to 200 IU/l (n = 7) and greater than or equal to 400 IU/l (n = 8). All were evaluated by treadmill exercise testing (Bruce Protocol), M-mode echocardiography and radionuclide ventriculography before training, immediately after, 3 and 6 months after training. Both of the subgroups showed statistically significant improvements in exercise duration, heart rates for doing equal workloads, energy expenditure and functional aerobic impairment immediately after training which were maintained 3 and 6 months later, with no inter-group differences. Resting left ventricular function, both by radionuclide and echocardiography, did not demonstrate significant changes throughout the study period, again with no inter-group differences. It is suggested that myocardial infarction size in the absence of heart failure does not appear to have a significant influence on the exercise training response and resting left ventricular function in those patients who recovered sufficiently to participate in exercise training.

Echocardiography↗
PubMed1985

Cardiovascular responses to early exercise in inferior wall ST acute myocardial infarction.

The heart rate and blood pressure responses to standardized exercise tests were studied in a group of patients with electrocardiographic evidence of inferior wall acute myocardial infarction (AMI). The tests were done on a bicycle ergometer at 8 to 10 days and 10 to 12 weeks after AMI. At 8 to 10 days after AMI, those with ST AMI (n = 12) had a significantly reduced heart rate response to exercise compared with patients with Q-wave AMI (n = 25). This difference was not evident at 10 to 12 weeks. The systolic blood pressure response in patients with ST AMI was lower than that of Q-wave AMI patients during the first exercise test, although the difference did not attain statistical significance but was significantly lower than the responses of both groups at the second test. The patients with ST AMI had smaller amounts of myocardial damage than those with Q-wave AMI as indicated by plasma creatine kinase values (p less than 0.01). These differences in the heart rate responses appeared to result from the preferential activation of nonmyelinated afferent fibers in the subepicardial region of the inferior wall of the myocardium.

Blood Pressure↗
PubMed1985

Cardiac output measured by impedance cardiography during maximal exercise tests.

The overall accuracy of cardiac output measurements made by impedance cardiography during maximum exercise was studied in man. Initially, the systematic error of the technique was assessed over the range 3.5 to 18 litre . min-1 by comparing with simultaneous measurements of cardiac output made using the direct Fick method. No systemic error was demonstrated in 40 estimations made in 20 subjects. The random error was assessed in 4 subjects in a steady state at rest and during exercise at 80 and 130 W and found to be less than 5% in each subject. The reproducibility of maximum exercise response was assessed in six healthy male subjects (age 26.2 +/- 4.4 years, +/- SEM) who underwent maximum exercise tests twice, 1 week apart, on a bicycle ergometer. Simultaneous recordings of cardiac output and oxygen uptake (VO2) at rest and during each 3 min stage of exercise were made. Highly significant correlations were obtained in the stroke volume (r = 0.84, p less than 0.001), cardiac output (r = 0.98, p less than 0.001) and VO2 (r = 0.98, p less than 0.001) between the two tests. Average maximum cardiac output was 27.0 +/- 1.2 litre . min-1 (+/- SEM) and maximum VO2 was 4.4 +/- 0.2 litre . min-1 (+/- SEM). These results show that measurements of cardiac output were reproducible over one week. Impedance cardiography is non-invasive technique which is as accurate as invasive methods and can be used for maximal exercise testing.

Adult↗