Biomedical subjects

D H Schmidt

Publications and source records attributed to D H Schmidt.

At least 55 records · Page 3Linked to original sources

PubMed1984

Work capacity and left ventricular function during rehabilitation after myocardial revascularization surgery.

A prospective randomized trial was conducted to evaluate the effects of exercise-based cardiac rehabilitation after myocardial revascularization surgery (MRS) on work capacity (measured in mets) and left ventricular function as determined from ejection fraction (LVEF). Twenty-eight patients undergoing MRS were randomly assigned to experimental (aerobic exercise, n = 19) or control (muscle relaxation and low-level exercise, n = 9) groups. Patients were studied before surgery (T1) and 2 (T2), 8 (T3), and 24 (T4) weeks after surgery with first-pass radionuclide angiography both while they were at rest and during maximal upright cycle ergometric exercise. Subsets of patients were also studied at T2, T3, and T4 at a standard workload of 75 W, and during maximal exercise 1 year after surgery (T5). Work capacity improved in both groups although significantly more so in the experimental group (3.9, 3.8, 6.0, and 7.3 mets and 3.7, 3.7, 4.9, and 5.7 mets at T1, T2, T3, and T4 in the experimental and control groups, respectively). The differences between groups were significant by T3. Peak exercise LVEF increased significantly in both groups from T1 to T2 then decreased at T3 and remained unchanged through T5. Peak exercise LVEF at T3 to T5 remained significantly above that observed at T1. LVEF responses were not related to the exercise program. During a standard workload, heart rate decreased, blood pressure increased, and LVEF did not change in either group. After conclusion of the formal protocol (T4), work capacity and LVEF did not change for either group throughout an additional 6 months (T5).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Trials as Topic↗

PubMed1983

Cardiovascular pharmacology of ASL-8052, an ultra-short acting beta blocker.

ASL-8052, a novel ultra-short acting beta receptor blocking agent, was infused i.v. and its cardiovascular effects were investigated in conscious, as well as anesthetized rabbits. On i.v. infusion, its effects reached a steady state within 6 min and on termination of infusion, complete recovery occurred within 20 min. In conscious rabbits it inhibited isoproterenol-induced tachycardia and hypotension. There was more pronounced inhibition of the cardioaccelerator effects of isoproterenol than its hypotensive effects. ASL-8052 produced dose dependent bradycardia in conscious rabbits which was more marked in rabbits pretreated with atropine methyl nitrate. When infused in larger doses, a significant decrease in mean arterial pressure was seen in conscious as well as anesthetized rabbits. This hypotensive effect was not blocked by prior beta receptor blockade with propranolol. ASL-8052-induced hypotension was found to be due to a significant decrease in total peripheral resistance. It also produced vasodilation in the mesenteric vascular bed. The role of the liver in the clearance of ASL-8052 was investigated. When infused into the portal vein, the response to ASL-8052 was markedly attenuated, while an equivalent dose infused into the femoral vein produced a significant level of beta receptor blockade. These results suggest that ASL-8052 is an ultra-short acting beta receptor blocking agent with vasodilator effects in rabbits. While the liver may play a significant role in the clearance of ASL-8052 from circulation, the role of extra-hepatic mechanisms in the rapid decay of its pharmacological effects remains to be investigated.

Adrenergic beta-Antagonists↗

PubMed1983

Effect of exercise protocol on the left ventricular response to exercise.

The purpose of this study was to determine whether the left ventricular response during exercise radionuclide angiography would be influenced by exercise protocol. One hundred twenty healthy volunteers (aged 18 to 40 years) performed upright bicycle exercise using 1 of 5 protocols. Ejection fraction was measured using first-pass radionuclide angiography. Exercise protocols were as follows: (1) graded exercise (25 W increase every 2 minutes) to fatigue, heart rate greater than 85% of age-predicted maximum, n = 53; (2) graded exercise to 85% of age-predicted maximal heart rate or to fatigue with heart rate less than 85% of age-predicted maximum, n = 26; (3) graded exercise to fatigue, with "exercise" imaging performed immediately after exercise, n = 15; (4) abrupt presentation of a supermaximal work load (400 W), n = 10; (5) graded exercise to a work load of 75 W preceding the abrupt presentation of a supermaximal work load (300 to 400 W), n = 16. Protocols 2 and 3, representing less than maximal stress, yield higher ejection fractions than Protocol 1 and may reduce the sensitivity of exercise radionuclide angiography. Protocols 4 and 5, representing supermaximal stress, yield lower ejection fractions than Protocol 1 and may reduce the specificity of exercise radionuclide angiography. Thus, exercise protocol has a significant influence on the left ventricular response during exercise radionuclide angiography.

Adolescent↗

PubMed1983

Severe left ventricular dysfunction in critical aortic stenosis--reversal following aortic valve replacement.

A case of aortic valve stenosis is reported with progressive left ventricular dysfunction demonstrated by radionuclide angiography. A gradient of 120 mmHg was present across the aortic valve. At the time of surgery, the patient was in severe cardiac failure with a left ventricular ejection fraction of 22%. Two months postoperatively, the patient was asymptomatic, and repeat radionuclide angiography demonstrated an ejection fraction of 93%. The reversible nature of this patient's ventricular dysfunction suggests that the cardiac failure was related to 'afterload mismatch' caused by the stenotic valve, rather than due to depressed contractility. The encouraging result in this patient reinforces the view that surgical intervention is warranted in some patients with critical aortic stenosis and extreme impairment of left ventricular function, and that the close relation between ejection fraction and operative survival may not hold true in aortic stenosis.

Aged↗

PubMed1983

Evaluation of functional capacity during exercise radionuclide angiography.

This study compared functional capacity during treadmill exercise testing and during bicycle exercise radionuclide angiography. 262 patients performed maximal upright bicycle exercise and also performed maximal graded exercise testing using either the Bruce (n = 158) or Naughton (n = 104) treadmill protocols. The functional capacity was well correlated between bicycle and treadmill for Bruce (r = 0.89), Naughton (r = 0.93), or combined treadmill (r = 0.90) protocols. However, the functional capacity was significantly lower during bicycle than during treadmill testing for Bruce (8.3 vs. 10.5 METs), Naughton (7.8 vs. 8.7 METs), or combined treadmill (8.1 vs. 9.8 METs) protocols. Treadmill functional capacity could be predicted from bicycle functional capacity using the following equations: Bruce METs = 1.00 X (bike METs) + 2.23, Naughton METs = 0.94 X (bike METs) + 1.40, and combined treadmill METs = 0.98 X (bike METs) + 1.85.

Adult↗

PubMed1983

Dysrhythmia detection in myocardial revascularization surgery patients.

Dysrhythmia detection in myocardial revascularization surgery patients. Med. Sci. Sports Exerc., Vol. 15, No. 4, pp. 281-286, 1983. In order to document the type and prevalence of significant dysrhythmias in myocardial revascularization surgery patients, cardiac electrical activity was recorded during graded exercise testing, 24-h ambulatory electrocardiography, and electrocardiographic-monitored exercise training. Patients participated in a cardiac rehabilitation program that began approximately 2 wk post-surgery, and attended three monitored exercise sessions per week for 12 consecutive weeks. Graded exercise testing and 24-h ambulatory electrocardiography were administered in the second and eighth weeks of the study (weeks 1 and 6 of the exercise program) post-surgery. Eighty-eight percent of the patients exhibited significant dysrhythmias. A greater number of significant dysrhythmias were found during the second 6 wk of the study in comparison with the first 6 wk. Graded exercise testing was not as effective as ambulatory electrocardiography and monitored exercise training in dysrhythmia detection. Not all dysrhythmias were detected by any one technique, thus a combination of methods may be best for optimal surveillance and detection.

Anti-Arrhythmia Agents↗

PubMed1982

Pentobarbital-induced changes in vagal tone and reflex vagal activity in rabbits.

The effects of pentobarbital on heart rate, reflexly mediated vagal activity and the automaticity (intrinsic rate) of the sinoatrial (SA) node were investigated in rabbits. When administered in three cumulative doses (10 mg/kg i.v. each) at 15 min intervals, each dose produced transient hypotension which was not modified by prior muscarinic receptor blockade (MRB), beta-receptor blockade (BRB), or combined MRB and BRB. Subanesthetic doses (10 mg/kg) of pentobarbital produced tachycardia in normal rabbits, as well as in rabbits with prior BRB. After pentobarbital, MRB failed to increase the heart rate, indicating total loss of resting vagal tone. Failure to induce tachycardia in rabbits with prior MRB indicated the absence of sympathetic stimulation in pentobarbital-induced tachycardia. In rabbits with prior BRB, pentobarbital enhanced the hypotensive effects of acetylcholine and nitroglycerin and abolished nitroglycerin-induced tachycardia without significant effects on the magnitude of reflex bradycardia produced by norepinephrine. Pentobarbital had minimal, transient depressant effects on the intrinsic rate of the SA node. These results indicate that pentobarbital produces total loss of resting vagal tone without major impairment of reflex vagal activation.

Animals↗

PubMed1982

Effect of habitual exercise on left ventricular response to exercise.

To evaluate the effects of chronic physical exercise on left ventricular ejection fraction (LVEF) and ejection rate (LVER), radionuclide angiography was performed at rest and during upright-bicycle exercise in 45 healthy men. The subjects varied widely in exercise habits and working capacity. They were divided into three subgroups on the basis of habitual physical activity. Aerobic training was done more than 7, 2-4, and less than 1 h/wk by subgroups of athletes, trained, and untrained men, respectively. The results indicate marked differences in work capacity (298, 233, and 181 W in the athletes, trained, and untrained groups, respectively). Resting LVEF (72, 69, and 68%) and LVER (4.1, 3.4, and 3.6 s-1) were not significantly different among the groups. With maximal exercise, however, small but statistically significant differences in LVEF (75, 69, and 68%; P less than 0.05 athletes vs. trained and athletes vs. untrained) and in LVER (7.5, 6.3, and 5.2 s-1; P less than 0.05 among all groups) were observed. Work capacity was, however, poorly correlated with exercise LVEF (r = 0.18) and LVER (r = 0.47). The results of this study indicate that the enhanced working capacity observed secondary to increases in habitual physical activity can be attributed to differences in LVEF and LVER only in the most general terms. Accordingly the results agree with previous suggestions based primarily on echocardiographic data that the primary cardiac adaptation to exercise is dimensional rather than functional in character.

Adult↗

PubMed1982

Effect of warm-up on left ventricular response to sudden strenuous exercise.

Sudden strenuous exercise (SSE) has been shown to produce ischemic electrocardiographic (ECG) responses, abnormalities of myocardial blood flow, and decreases in left ventricular ejection fraction. Prior exercise taken as warm-up has been shown to ameliorate the ECG and myocardial blood flow abnormalities induced by SSE. The purpose of this study was to determine whether warm-up would normalize the responses of the left ventricular ejection fraction to SSE. Twenty healthy male volunteers performed SSE (400-W bicycle exercise) either with (group A, n = 10) or without (group B, n = 10) warm-up. Ejection fraction was measured using first-pass radionuclide angiography under control conditions and during SSE. During SSE ejection fraction decreased from control values in both group A (70.5 +/- 6.3 to 64.8 +/- 8.2%) and group B (70.3 +/- 10.1 to 57.7 +/- 7.7%), although ejection fraction was significantly higher during SSE in group A. The results are consistent with the hypothesis that the abnormal responses to SSE are attributable to subendocardial ischemia secondary to a delay in autoregulation of myocardial blood flow. However, the decrease in ejection fraction during SSE even following warm-up suggests that the mechanism for the abnormal response to SSE is more complicated than previously hypothesized.

Cardiac Output↗

PubMed1982

Left ventricular function at rest, peak exercise and postexercise.

To determine whether the temporal sequence of imaging could influence the results of exercise radionuclide angiography, 15 healthy volunteers were studied at rest, during peak bicycle exercise and immediately postexercise using first pass radionuclide angiography. Responses at rest, peak and postexercise included: heart rate (67 to 174 to 170 bpm), double product (7.4 to 31.5 to 27.5 mm Hg X bpm X 10(3)), left ventricular ejection fraction (68 to 69 to 80%) and mean normalized left ventricular ejection rate (3.63 to 6.56 to 8.56 s-1). The results indicate that left ventricular ejection fraction and mean normalized ejection rate were different during exercise and immediately postexercise although heart rate and double product were not. The results indicate that the temporal sequence of imaging is a significant procedural variable in the conduct of exercise radionuclide angiography.

Adult↗

PubMed1982

Diagnostic capabilities of exercise testing soon after myocardial revascularization surgery.

The purpose of this investigation was to compare data on early exercise testing for variables known to be of diagnostic/prognostic value following myocardial infarction in post-myocardial revascularization surgery patients. 70 patients were evaluated soon after surgery, by cardiac catheterization, moderate-intensity treadmill exercise testing, and rest and exercise radionuclide angiography. The results indicated no significant differences among groups with satisfactory and unsatisfactory results by catheterization compared for METs, peak heart rate, double product, ST-segment change, angina pectoris, and dysrhythmias. Significant differences were found among groups when rest and exercise ejection fraction and exercise-induced regional wall motion abnormality were taken into account. It was concluded that the moderate-intensity treadmill exercise test was ineffective in differentiating current cardiac function and arterial/graft status among postmyocardial revascularization surgery patients. Exercise radionuclide angiographic studies were able to identify groups of patients with adequate or inadequate postoperative cardiac catheterization results.

Cardiac Catheterization↗

PubMed1982

Procainamide and retrograde atrioventricular nodal conduction in man.

Recent studies that show a depressant effect of procainamide (PA) on retrograde conduction in patients with atrioventricular (AV) nodal reentrant tachycardia (RT) have suggested possible incorporation of AV nodal bypass tracts. Electrophysiologic effects of i.v. PA, 10 mg/kg, on retrograde AV nodal conduction were examined in 13 patients without RT, demonstrable AV nodal refractory period curves, or accessory pathways. Ventriculoatrial (VA) conduction was recorded before and after PA using intracardiac electrograms, incremental ventricular pacing and extrastimulation. With incremental pacing during the control, VA block occurred at a mean cycle length (CL) of 364.6 +/- 87.9 msec. After PA, VA conduction was abolished in five of 13 patients due to onset of retrograde block in the AV node; in seven of 13, VA block occurred at a longer paced CL after PA (344.2 +/- 51.2 msec vs 477.1 +/- 93.2 msec). In one patient, PA did not affect VA conduction. PA invariably produced prolongation in the VA interval at comparable CL of pacing. With ventricular premature stimulation, the retrograde H2A2 intervals during the control period were short (less than 50 msec) in seven of 13, intermediate (60-100 msec) in three of 13 and long (greater than 100 msec) in three of 13 cases. PA either abolished H2A2 conduction (H2 but no A2) or prolonged the H2A2 intervals by 5-20 msec in most cases in this series. The data suggest that i.v. PA almost uniformly depresses retrograde AV nodal conduction in the intact human heart. This depressant response to PA is not indicative of presence of partial or complete AV nodal bypass tracts.

Aged↗

PubMed1982

Coronary artery bypass patients and work status.

Retrospective surgery data were obtained from 358 coronary artery bypass surgery patients 4-22 months (mean 12.5 months) after surgery. Before surgery, 69% of the subjects were working, 10% were unemployed, and 21% were retired. At follow-up, only 58% were working and 29% were retired. Employment before surgery was the most significant predictor of work status after surgery. Other factors that were positively related to returning to work include higher presurgery income and job classification, higher pre- and postoperative ejection fraction, and subjective improvement in tolerance for physical activity. Factors that were negatively related to returning to work were age, number of chronic medical problems, presence of cardiac symptoms, and receipt of disability compensation. Reported improvement in symptoms was not related to postoperative work status. Job classification, physical demands of the job, and time out of work before surgery were also related to how soon patients returned to work. Participation in an outpatient rehabilitation program was significantly related to postoperative work status for men employed before surgery. Questions were raised regarding the role of outpatient cardiac rehabilitation in altering patient perceptions and maintaining "work habits" that might facilitate work resumption after coronary artery bypass surgery. The results suggest that multiple physical, social and psychological factors interact to influence postoperative work status.

Adult↗

PubMed1982

Right anterior oblique first-pass radionuclide ejection fractions: effects of temporal smoothing and various background corrections.

Thirty-seven patients undergoing contrast left ventriculography were studied by first-pass radionuclide angiography (FPRA) in the right anterior oblique view. Ejection fraction (LVEF) was calculated from FPRA using (a) a spatially and temporally varying background correction (BGC) based on a matrix of activity in lung and left atrium and (b) BGC with temporal fluctuation but with no allowance for spatial variations. The two methods were performed on both raw and temporally smoothed data. All four LVEFs correlated well with contrast LVEF (r = 0.90 - 0.94). Absolute values differed significantly from contrast values except for the method using the spatially and temporally varying BGC on smoothed data, which provided the closest overall agreement at all levels of LVEFs, despite occasional large individual variations. The same method on raw data overestimated low LVEFs and the method applying only temporal fluctuation in background underestimated high LVWFs. Allowance for spatial and temporal variations in background is therefore important when first-pass radionuclide angiography is performed in the RAO view.

Adult↗

PubMed1981

Fifty years of training and competition in the marathon: Wally Hayward, age 70--a physiological profile.

A 70-year-old South African long-distance runner, holder of his age group's marathon record and former Olympic marathon runner, was studied to determine the effects of 52 years of regular training on functional capacity and health. Maximal treadmill exercise testing revealed no ischaemic ECG abnormalities and an excellent functional capacity (58,6 ml/kg/min). Submaximal testing showed that the subject ran at approximately 86% of maximum aerobic capacity when completing the marathon in his record time. The subject was very lean (13,6% fat) for his age. Muscles contained 82% slow-twitch fibres. Pulmonary function and blood chemical values were within normal limits. Although total cholesterol was somewhat high (247 mg/dl), high-density lipoprotein cholesterol was elevated (53 mg/dl). Twenty-four-hour Holter monitoring revealed no significant ventricular ectopic activity although frequent premature atrial contractions were noted. M-mode echocardiography revealed a normal heart with moderately hypertrophied left ventricular wall thickness. Radionuclide cine angiography showed a normal ejection fraction at rest (69%), followed by a slight drop at maximal exercise (62%). Left ventricular regional wall motion was considered normal at both rest and exercise. He had no significant orthopaedic abnormalities but showed normal flexibility and well-balanced muscular strength. Thickened heel pads were also noted. These results appear to indicate a beneficial effect of habitual physical activity upon the retention of functional capacity with ageing.

Aged↗

PubMed1981

Patency and flow response in endarterectomized coronary arteries.

Ninety patients, operated on from May, 1978, through June, 1979, underwent coronary endarterectomy and early recatheterization. Patency of grafts to endarterectomized arteries was 103 of 118 (87.3%) and patency of conventional vein grafts in the same patients was 217 of 233 (93.1%). Myocardial blood flow using xenon 133 washout, at rest and with isoproterenol-induced stress, was measured in 7 normal coronary arteries, 28 conventional saphenous vein grafts, and 33 saphenous vein grafts to endarterectomized coronary arteries. The increase in myocardial blood flow, from rest to isoproterenol-induced stress, was comparable for the three groups. The endarterectomized group was divided further by separating out the 10 patients with heavy scarring or residual disease. The remaining patients had a flow response identical to those with conventional saphenous vein grafts. The rate of perioperative infarction in patients receiving endarterectomy was 3 of 113 (2.6%), as measured by appearance of new persistent Q waves on the serial postoperative electrocardiogram. Positive pyrophosphate scans were noted in 12 of 105 (12.4%) patients. It is concluded that, in the early stages at least, grafts to endarterectomized coronary arteries stay open and perfuse the myocardium as well as conventional saphenous vein grafts unless the myocardium is heavily scarred or unless residual disease remains.

Arteriosclerosis↗

PubMed1981

Left ventricular function during sudden strenuous exercise.

Strenuous exercise without warm-up has been shown to produce ischemia-like electrocardiographic (ECG) abnormalities in 60-70% of healthy subjects. These abnormalities appeared to be related to the development of an unfavorable myocardial supply/demand balance and, in chronically instrumented dogs, to transient decreases in coronary blood flow. A mechanism involving subendocardial ischemia has been proposed to explain the response to sudden strenuous exercise (SSE). To determine whether the response to SSE included the development of changes in myocardial pump performance typical of ischemia, left ventricular (LV) function at rest, during graded exercise and during SSE was evaluated in nine young (26.6 +/- 3.4 years), well-trained male volunteers using first-pass radionuclide angiography. During graded exercise, the LV ejection fraction increased from 66.9 +/- 9.4% at rest to 73.0 +/- 7.1% during peak exercise, and the LV ejection rate increased from 3.36 +/- 0.67 sec-1 at rest to 6.58 +/- 1.10 sec-1 during peak exercise. Segmental wall motion was normal in all studies. During SSE, the LV ejection fraction decreased in very subject, from an average 72.2 +/- 8.6% at rst to 57.3 +/- 8.1% during exercise. The LV ejection rate remained relatively constant (3.98 +/- 0.92 sec-1 at rest vs 4.33 +/- 0.74 sec-1 during SSE). No segmental wall motion abnormalities were observed during SSE; however, LV wall motion appeared to be diffusely hypokinetic during SSE. In contrast to previous reports, few ECG abnormalities were observed during SSE. These results support the hypothesis that subendocardial ischemia is an important mechanism in the response to SSE. However, the lack of ECG changes and segmental wall motion abnormalities and the relatively high absolute value of the LV ejection fraction suggest that if subendocardial ischemia occurs during SSE, it is attributable to physiologic rather than pathologic mechanisms.

Adult↗

PubMed1981

Role of retrograde His Purkinje block in the initiation of supraventricular tachycardia by ventricular premature stimulation in the Wolff-Parkinson-White syndrome.

The precise mechanisms for paroxysmal reentrant supraventricular tachycardia (PSVT) initiation during right ventricular premature stimulation (V(2) method) were analyzed in 14 consecutive patients with Wolff-Parkinson-White Syndrome in whom the PSVT was inducible during retrograde refractory period studies. 9 patients had left-sided and the remaining 5 of 14 had right-sided ventriculo-atrial (VA) accessory pathway (AP). At the basic cycle lengths (V(1)V(1)) ranging from 550 to 900 ms (mean, 657.1+/-139.5), closely coupled V(2) (mean V(1)V(2), 357.3+/-59.2 ms, range 320-500) produced retrograde His bundle (H(2)) activation via the bundle branches and retrograde atrial (A(2)) activation via the AP. As the V(1)V(2) were further shortened, the V(2) showed a retrograde block in the His Purkinje system (HPS) and conducted to the atria via AP in 9 of 14 cases. Subsequently, the A(2) impulse conducted anterograde over the atrioventricular node-HPS to initiate a PSVT or an atrial echo response in all nine cases. In none of the patients was a PSVT induced by V(2) when the latter produced retrograde H(2) activation via the bundle branches. In 10 of 14 cases, however, the retrograde H(2) was followed by a V(3), due to macroreentry in the HPS. The V(3) in turn blocked retrogradely in the HPS while producing A(3) via the AP to initiate a PSVT or an atrial echo response in 9 of 10 cases. Retrograde block of V(2) and/or V(3) in the HPS resulted in PSVT initiation in 13 of 14 cases, whereas in the remaining 1 case the exact mechanism was not clear. In none of the patients in this series was the PSVT initiated with a retrograde block of V(2) in the atrioventricular node with or without concomitant retrograde A(2) activation via the AP. We conclude that within the ranges of cycle lengths tested, a retrograde block of V(2) and/or V(3) in the HPS is the most common mechanism for initiation of PSVT during ventricular premature stimulation in patients with the Wolff-Parkinson-White Syndrome.

Bundle of His↗