Biomedical subjects

K F Hossack

Publications and source records attributed to K F Hossack.

At least 37 records · Page 2Linked to original sources

PubMed1988

Hypertension in autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) has been shown to be associated with a greater than 50 percent incidence of hypertension prior to deterioration in renal function as assessed by glomerular filtration rate. The present study provides evidence for increased cardiac pre-load, as assessed by plasma atrial natriuretic factor (ANF) and cardiac index, in hypertensive as compared to normotensive ADPKD. The hypertensive ADPKD patients exhibited an increased renal vascular resistance as compared to the normotensive patients in spite of comparable glomerular filtration rates. It is hypothesized that the renal involvement of hypertensive ADPKD patients causes an impaired renal response to the observed increase in cardiac index, and also may release a venoconstrictor (such as angiotensin) which contributes to the enhanced cardiac pre-load and thus the hypertension.

Adult↗

PubMed1988

Computer analysis of oxygen consumption and minute ventilation for the detection of the lactate threshold.

A group of 15 normal subjects performed a maximal-exercise test on a treadmill. Arterial lactate measurements were related to oxygen consumption (VO2) in an exponential fashion (individual correlation coefficients ranged from 0.9 to 0.99). In the same subjects, minute ventilation (VE) was related to VO2 in an exponential fashion (individual correlation coefficients ranged from 0.98 to 1). There was a close correlation (r = 0.97, p less than 0.001) between the slope of the log of lactate versus VO2 and the slope of the log of VE versus VO2. A computer program for predicting the VO2 corresponding to the accumulation of arterial lactate above the resting normal value (1.3 mM), defined as the lactate threshold, is described. The program is based on the slopes of the exponential relationship between lactate and VO2 and between VE and VO2 derived in the normal subjects. The program analyses 30-second values of VO2 and VE. In 28 subjects, the reproducibility of the lactate threshold prediction was evaluated during two exercise tests 1-7 days apart. The mean predicted VO2 at the lactate threshold was 18.6 +/- 7 ml/(kg.min) during test 1 and during test 2 it was 17.9 +/- 7.3 ml/(kg.min); r = 0.91, p less than 0.001. The corresponding values for maximal VO2 were 30.4 +/- 13 ml/(kg.min) and 31 +/- 13 ml/(kg.min); r = 0.99, p less than 0.001. It is concluded that this program offers a reproducible method of determining the lactate threshold during exercise testing employing a frequently used clinical protocol.

Adult↗

PubMed1988

Amlodipine in angina pectoris: effect on maximal and submaximal exercise performance.

Amlodipine, a dihydropyridine calcium antagonist, was compared with placebo in a double-blind cross-over study in 16 patients with angina. After a 2-week single-blind placebo period, patients entered a double-blind crossover phase alternating between 4 weeks of placebo and 4 weeks of amlodipine, 10 mg once daily. The two 4-week periods were separated by a 1-week single-blind placebo washout period. The efficacy of drug therapy was measured using frequency of angina, nitroglycerin consumption, peak oxygen consumption during a maximal treadmill exercise test, and endurance time during a separate submaximal exercise test performed at 70% of the peak work capacity that had been determined before randomization. Compared with single-blind placebo there was a reduction in angina frequency during double-blind placebo and amlodipine, whereas nitroglycerin consumption was significantly reduced only by amlodipine. Amlodipine produced a significant increase in peak oxygen consumption and endurance time during the submaximal exercise test when compared with single-blind and double-blind placebo periods. Patients tolerated both placebo and amlodipine without clinically significant side effects.

Aged↗

PubMed1987

Comparison of nitroglycerin patches and nifedipine.

Fifteen patients with stable angina participated in a 12-week crossover study to evaluate the efficacy of nifedipine and nitroglycerin patches. There was an initial 2-week drug washout period followed by a 2-week control period when patients received no other antianginal treatment other than sublingual nitroglycerin for relief of angina episodes. At the end of the 2-week control period, exercise performance was assessed with treadmill exercise testing and measurement of oxygen consumption during the final third of the dosing interval. Myocardial perfusion was assessed using thallium scintigraphy with the injection of thallium at 85% of the maximum oxygen consumption. Patients were then randomized to nifedipine or nitroglycerin patches, and the dosage was titrated at weekly intervals according to symptomatic response. The final dose was received for at least 2 weeks. After 4 weeks, patients received the alternate medication. Maximal exercise testing and thallium scintigraphy were repeated after each drug period. Both nifedipine (mean dose, 70 mg/day) and nitroglycerin patches (mean dose, 16 cm/day) significantly reduced the frequency of angina and the consumption of sublingual nitroglycerin. Nifedipine decreased the reversible thallium defect score (49 +/- 29 vs. 28 +/- 26 U, p less than 0.01). Both drugs reduced electrocardiographic evidence of myocardial ischemia at submaximal exercise. Maximal oxygen consumption was not significantly increased by either drug when the test was done during the latter part of the dosing interval. The clinical implications of this study are that the dosage of nifedipine and nitrate patches, based on symptomatic criteria of angina frequency reduction, may not result in objective improvement in exercise performance.

Administration, Cutaneous↗

PubMed1987

Patterns of oxygen consumption during exercise testing in peripheral vascular disease.

Exercise testing on a treadmill was performed in 15 patients with peripheral vascular disease to determine the pattern of oxygen consumption during exercise. A plateau in the oxygen consumption over the final 90 s of exercise was used as a criterion for maximal effort and only 4 out of 15 (27%) obtained a plateau of oxygen consumption compared to 20 out of 26 (77%) normal subjects (chi 2 7.9, p less than 0.005). These findings may account for the limited value of exercise testing in detecting coronary artery disease in patients with peripheral vascular disease.

Adult↗

PubMed1987

Long-term follow-up of a patient with quadruple valve replacement.

A 60-year-old woman who had suffered from rheumatic fever as a child required replacement of the aortic, mitral, and pulmonary valves. Subsequently, because of severe regurgitation, the tricuspid valve was also replaced. This case proves that, with satisfactory intraoperative cardiac protection, quadruple valve replacement can produce a good long-term functional result.

Journal Article↗

PubMed1987

Cardiovascular responses to dynamic exercise.

Dynamic exercise results in a marked increase in oxygen consumption. This increase is accomplished by a significant increase in heart rate and peripheral oxygen extraction and, to a lesser extent, by an increase in stroke volume. There is a small increase in mean systemic and pulmonary artery pressures and marked decrease in systemic and pulmonary resistances with exercise. The result of changes in focal vasomotor tone is that a greater percentage of the cardiac output is directed to the working muscles.

Cardiovascular Physiological Phenomena↗

PubMed1986

Comparison of acute hemodynamic effects of nitroglycerin versus diltiazem and combined acute effects of both drugs in angina pectoris.

Fifteen patients with exertional angina underwent hemodynamic monitoring and measurement of cardiac output during a control treadmill exercise test. They were then randomized to receive sustained-release nitroglycerin, 13 mg (group I) or placebo (group II). Repeat exercise testing revealed that in group I, both maximal oxygen consumption and cardiac output increased significantly. In group II neither maximal oxygen consumption nor cardiac output increased significantly. All patients then received diltiazem, 60 mg, and repeat testing was carried out 1 hour later. In group I maximal oxygen consumption and cardiac output were higher than control, but were no higher than after nitroglycerin. In group II, maximal oxygen consumption increased significantly, but the increase in cardiac output was not significant. Thus, sustained-release nitroglycerin, 13 mg, or diltiazem, 60 mg, both improve exercise performance, but the combination does not improve exercise performance to an extent greater than either drug alone.

Aged↗

PubMed1986

Computerized detection of the lactate threshold in coronary artery disease.

A computer program for identifying oxygen consumption at the lactate threshold was evaluated by expired gas analysis during treadmill exercise testing in 15 patients with prior myocardial infarction. There was a strong correlation (r = 0.85, p less than 0.001) between computer-identified oxygen consumption (14.1 +/- 4.6 ml/kg/min) and the oxygen consumption (14.6 +/- 4.8 ml/kg/min) corresponding to an increase of arterial lactate level to above the normal value at rest (1.3 mM). The computer program was superior to previously described visual methods for identifying the ventilatory threshold.

Adult↗

PubMed1986

Effects of the limiting symptom on the achievement of maximal oxygen consumption in patients with coronary artery disease.

This study was conducted to determine if the limiting symptom in patients with coronary artery disease (CAD) influenced the pattern of oxygen consumption (VO2) over the final 90 seconds of a maximal exercise test. The pattern was classified according to the presence or absence of a plateau. Twenty-six normal persons and 55 patients with CAD were studied. They rated the severity of fatigue, dyspnea and angina at end exercise using the Borg scale and designated which symptom was the limiting factor. A plateau of VO2 over the final 90 seconds of exercise was observed in 77% of normal subjects and patients with CAD. Eighty percent of patients limited by angina achieved a plateau. In normal subjects and patients with CAD, peak VO2 was more reproducible than the pattern of VO2 over the final 90 seconds of exercise. There were no differences in the cardiac responses to exercise at maximal effort between patients who achieved a plateau of VO2 and those who did not. These results indicate that the limiting symptom of exercise, even angina pectoris, does not influence the ability to exercise maximally. Therefore, the peak value of VO2 during symptom-limited treadmill exercise is a valid measure of maximal cardiovascular capacity irrespective of the limiting symptom or the pattern of VO2 in the final 90 seconds of exercise.

Adult↗

PubMed1985

Excessive reduction in peripheral resistance during exercise and risk of orthostatic symptoms with sustained-release nitroglycerin and diltiazem treatment of angina.

Acute effects of placebo, sustained-release nitroglycerin, diltiazem capsules, and the combination of both drugs were monitored in nine stable angina patients. They were randomized to receive either placebo or 13 mg of slow-release nitroglycerin orally (double-blind). This was followed in 1 hour by 120 mg of diltiazem orally, given to all patients (unblinded). Invasive hemodynamic measurements were made before and after each treatment at supine and sitting rest, two levels of submaximal, and at maximal exercise and twice in recovery. Compared to the control test at maximal exercise, sustained-release nitroglycerin increased aerobic capacity 24%, lowered peripheral resistance -32%, and lowered systemic pressure -23%, while the respective changes with placebo were -3%, 5%, and 2%. When diltiazem was added to placebo compared to the control test, there was a 4% increase in oxygen consumption and -9% and -4% reduction in systemic resistance and systemic pressure, respectively. The addition of diltiazem to nitroglycerin was associated with a 20% increase in oxygen consumption a -42% reduction in systemic resistance and a -32% reduction in systemic pressure. Two patients who received nitroglycerin plus diltiazem experienced symptomatic hypotension, while one patient who received placebo plus diltiazem experienced hypotension. These side effects caused the study to be terminated prematurely. Thus, although the combination of nitroglycerin and diltiazem had a greater effect on afterload than either drug alone, the combination did not provide greater improvement in cardiac performance.

Aged↗

PubMed1985

Relationships of working status and cardiac capacity to functional age before and after coronary bypass surgery.

In 77 patients having coronary bypass surgery, we evaluated the interaction between chronological age, functional age, and working status pre- and postoperatively. Preoperatively the chronological age of those not working compared to those working was 60.7 +/- 8.4 years versus 53.0 +/- 8.3 years (P less than 0.001). The preoperative functional ages were 93.5 +/- 11.5 versus 87.6 +/- 10.9 years (P less than 0.05). Postoperatively no patient who was not working preoperatively started work, although functional age improved from 93.5 +/- 11.5 to 83.2 +/- 12.8 years (P less than 0.001). Postoperatively subjects who stopped working showed similar improvement in maximal cardiac output, and maximal oxygen consumption compared to those who continued working; however, the functional age after surgery was 80.6 +/- 9.4 versus 69.6 +/- 11.6 years (P less than 0.01). This study showed a poor relationship between degree of improvement in cardiac function after bypass surgery and change in working status. However, functional age and chronological age contribute to the poor results with regard to return to work.

Age Factors↗

PubMed1985

Validation of exercise-enhanced risk assessment of coronary heart disease events: longitudinal changes in incidence in Seattle community practice.

Noninvasive criteria developed in a learning series for exercise-enhanced risk assessment for events due to coronary heart disease have been applied to a test series in a later population sample. Men in the same age and risk groups for each pretest clinical classification show similar gradients of risk. Thus, exercise-enhanced criteria for risk assessment are validated. Age-standardized event rates show a reduction longitudinally in healthy men and patients who have had coronary bypass surgery.

Adult↗

PubMed1985

Long-term monotherapy of angina pectoris with diltiazem.

Eighteen patients with exertional angina were treated with diltiazem (360 mg/day). Serial exercise testing was performed and the results were compared to evaluations when patients were receiving placebo at the initiation and termination of the study. Serial exercise tests indicated significant improvement in duration of exercise (+18%, p less than 0.001), time to 1 mm ST depression (+32%, p less than 0.005), and time to angina (+46%, p less than 0.001) when patients were receiving diltiazem. During diltiazem treatment, there was a significant reduction in myocardial oxygen demand as indicated by the change in submaximal pressure rate product. This may contribute to the beneficial effect of diltiazem in patients with exertional angina. The reduction in pressure rate product was due primarily to a change in heart rate. This study provides evidence that diltiazem is an effective long-term monotherapy for angina; no evidence of drug tachyphylaxis was apparent after a total of 16 months treatment with diltiazem.

Aged↗

PubMed1984

Long-term study of high-dose diltiazem in chronic stable exertional angina.

The efficacy of a calcium slow channel-blocking drug, diltiazem (360 mg/day), was compared to placebo in 15 men with exertional angina during a 21-week study. Symptom-limited exercise testing was used to evaluate the effects of the drug. Analysis of variance indicated the increase in the values of three time-related variables, time to onset of angina, time to onset of 1 mm ST depression, and total duration of exercise, were highly significant (all p less than 0.001). The increase from the second week of placebo to the last week of diltiazem was 4 X 1 minutes for time to angina, 2 X 4 minutes for time to 1 mm ST depression, and 2 X 3 minutes for total duration. In addition, the differences between mean values of these variables for placebo and corresponding diltiazem period at weeks 3 and 4 were significant (p less than 0.01, p less than 0.01, p less than 0.05) and for diltiazem week 20 and placebo week 21 were significant (p less than 0.005, p less than 0.01, p less than 0.005). Weekly angina frequency was reduced from a mean of 17 episodes/week during placebo to one episode/week during diltiazem (p less than 0.001). Submaximal pressure-rate product was reduced significantly during diltiazem (p less than 0.001), and the ECG evidence of myocardial ischemia was reduced by diltiazem at submaximal (p less than 0.02) and maximal exercise (p less than 0.001). The drug was well tolerated and appears to be effective monotherapy for exertional angina.

Aged↗

PubMed1984

Mean systolic ejection rate after aortocoronary bypass graft surgery.

In 62 patients with coronary artery disease who underwent aortocoronary bypass graft surgery, we measured the mean systolic ejection rate invasively at rest and during upright exercise before and several months after operation. After bypass surgery, mean systolic ejection rate did not show any change at either supine or sitting rest and at submaximal exercise levels of walking on a treadmill. At maximal exercise, only patients with complete revascularization showed a significant increase in heart rate from 105 to 147 (+40%) and mean systolic ejection rate from 339 ml/sec to 404 ml/sec (+19%, P less than 0.001). Patients with incomplete revascularization did not show a substantial change in these variables. Beta-blocker withdrawal did not affect the result significantly.

Adrenergic beta-Antagonists↗

PubMed1984

Changes in cardiac functional capacity after coronary bypass surgery in relation to adequacy of revascularization.

Seventy patients having aortocoronary vein bypass grafting surgery for angina pectoris underwent preoperative invasive exercise testing to symptom limits and again 6 to 14 months postoperatively. Cardiac output was measured using the direct Fick principle. Postoperatively at maximal exercise, there was a 3.11 liters/min (p less than 0.0001) increase in cardiac output in men (n = 61) and a 2.04 liters/min (p less than 0.01) increase in women (n = 9). Patients with complete revascularization showed a significantly greater improvement in cardiac output postoperatively than did those with incomplete revascularization (26 versus 6%, p less than 0.0001). The major reason for the increased maximal cardiac output was a marked increase in heart rate while stroke volume was maintained at the same preoperative level. These findings were true irrespective of preoperative use of beta-adrenergic blocking drugs.

Adrenergic beta-Antagonists↗

PubMed1984

Diltiazem-induced blockade of sympathetically mediated constriction of normal and diseased coronary arteries: lack of epicardial coronary dilatory effect in humans.

To determine mechanisms of benefit from diltiazem, 13 patients with coronary disease performed sustained isometric handgrip exercise and repeated the procedure during intravenous infusion of diltiazem (0.25 mg/kg bolus followed by 0.003 mg/kg/min). Cardiovascular responses to handgrip, diltiazem, their combination, and nitroglycerin were assessed by hemodynamic and electrocardiographic measurements and by computer-assisted measurements of normal and diseased segments of epicardial coronary arteries. Handgrip produced increases in heart rate (12%; p less than .001), pulmonary arterial pressure (19%; p less than .005), and pulmonary wedge pressure (33%; p less than .005). Diltiazem produced significant reductions in heart rate (7%; p less than .05) and aortic pressure (14%; p less than .001). Pulmonary arterial pressure and pulmonary wedge pressure were unchanged by diltiazem. Diltiazem did not prevent the increase in heart rate or in aortic or wedge pressure associated with handgrip. Diltiazem prolonged atrioventricular conduction from 0.18 +/- 0.03 to 0.20 +/- 0.03 sec (p less than .001). Compared with control values, nitroglycerin reduced aortic pressure (14%; p less than .005), pulmonary arterial pressure (38%; p less than .001), and pulmonary wedge pressure (42%; p less than .005). Heart rate was unchanged. The constriction (20%) in lumen area of normal coronary arterial segments during handgrip was effectively prevented by infusion of diltiazem (1%; p less than .001). Nitroglycerin produced a significantly greater increase (20%) in diameter of normal coronary arterial segments than diltiazem (3%; p less than .001) and tended to have a more favorable effect than diltiazem on stenosis minimum area and flow resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzazepines↗