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Biomedical subjects

R J Barnard

Publications and source records attributed to R J Barnard.

At least 145 records · Page 8Linked to original sources
PubMed1977

Effect on training on myocardial oxygen supply/demand balance.

In five well-trained and five sedentary control subjects potential subendocardial blood supply was estimated from the diastolic pressure time index (DPTI) and myocardial oxygen demands from the tension time index (TII) during a progressive near-maximal treadmill test. DPTI/TTi was used to assess the effects of training on myocardial oxygen supply/demand balance. DPTI/TTI was significantly higher in trained subjects at rest and comparable workloads. At 6.4 km/hr, 18% grade (maximum for the controls), TTI was significantly lower (4300 +/- 76 vs 4495 +/- 99 mm Hg-sec/min) and DPTI significantly higher (2534 +/- 86 vs 2295 +/- 91 mm Hg-sec/min) in the trained subjects; DPTI/TTI was significantly higher (0.59 +/- .02 vs 0.50 vs .03). At near-maximal heart rates both groups achieved the same supply/demand balance (0.50); however, the trained subjects were working at higher workloads. We conclude that endurance conditioning increases work capacity, reduces myocardial O2 demands, increases potential O2 supply and improves the supply/demand balance at any given submaximal workload which reduces the risk of ischemia.

Adult↗
PubMed1976

Effect of training on the resting heart rate of rats.

Adult male rats were progressively trained 5 days/weeks on a motor-driven treadmill. The training period lasted 12 weeks and consisted of 60 min/day of wind-sprints and endurance work. No significant difference in resting heart rates was observed between the control and exercise groups during week 1 (394 +/- 7 vs. 388 +/- 5). However, at week 12 the exercise group had a lower resting heart rate (359 +/- 6 vs. 331 +/- 4). Heart rates observed following saline, propranolol, atropine, and propranolol plus atropine injections were lower in the exercise group in all cases. The difference in heart rates between the control and exercise groups was 19 beats/min following propranolol plus atropine which was less than the 28 beats/min difference observed under control conditions. With atropine and then with propranolol the differences were 33 and 27 beats/min. These heart rate differences were observed without the presence of cardiac hypertrophy as assesssed from ventricle weights. Our data indicate that the bradycardia resulting from exercise training is due primarily to changes other than neural influences on the heart.

Animals↗
PubMed1976

"Ischemic" heart disease in fire fighters with normal coronary arteries.

Near maximal stress testing conducted on a group (N = 90) of randomly selected Los Angeles City fire fighters (age 40-59 yrs.) revealed that 10% had ischemic ECG changes. These ischemic ECG responses were confirmed during a second test conducted two to four weeks after the initial test. Coronary heart disease (CHD) risk factor analysis revealed that in general the men were not at high risk for CHD. Six of the nine men elected to undergo cardiac catheterization and angiography. One patient had severe triple vessel disease and subsequently underwent aorto-coronary bypass surgery. Another had 50% obstruction in the circumflex branch of the left coronary while the other four men had no visable signs of coronary obstruction. The men with "normal" coronaries, however, did show signs of abnormal cardiac function during atrial pacing. One man had cardiac enlargement, hypokinesis, ischemic ECG and abnormal lactate metabolism. Another had abnormal lactate metabolism and ischemic ECG. A third man had moderate cardiac enlargement with anterior wall hypokinesis. The fourth had ischemic ECG changes with angina but otherwise normal cardiac function. All four of these men had pressures which were within normal limits. These data show that some fire fighters have "ischemic" heart disease with patent coronary arteries. This disease may be due to job related factors (i.e. carbon monoxide and other noxious fumes, catecholamines, etc.) which reduce myocardial oxygen supply or greatly increase myocardial oxygen demands.

California↗
PubMed1976

Maximum exercise heart rate reduction with maturation in the rat.

Maximum exercise heart rate decreases with maturation in the rat as well as in man. The present study was undertaken to investigate the mechanism(s) which might be responsible for this reduction in max exercise heart rate in the rat. Maximum exercise heart rates were 618 +/- 7 vs. 580 +/- 9 beats/min for the young (5 wk) and mature (19 wk) rats, respectively. Atropine had no effect on max exercise heart rate. Propranolol reduced max heart rate in both groups with the older rats having the lowest value. Resting heart rates were recorded following injections of atropine propranolol, and propranolol plus atropine. Under all conditions, including control, heart rates were lower in the mature rats. Electrical stimulation in situ showed a significant difference in the threshold voltage for stimulation at 600 beats/min: 1.1 +/- 0.2 vs. 1.6 +/- 0.1 V for the young and mature rats, respectively. These data suggest that intrinsic changes occur in the myocardium with maturation and the reduction in max exercise heart rate is due to these intrinsic changes as opposed to changes in neural influences.

Aging↗
PubMed1975

Cardiorespiratory, hematological and physical performance responses of anemic subjects to iron treatment.

Twenty-nine adult iron-deficient anemis subjects (13 men and 16 women) with hemoglobin levels of 4.0 to 12.0 g/100 ml blood were divided into either an iron treatment or placebo group. Hematological, cardiorespiratory and performance data were collected before, during, and after treatment and compared with data from a control group of subjects (4 men and 6 women) from the same socioeconomic population. Hemoglobin levels for the iron treatment group improved from 7.7 to 12.4 g for the women and from 7.1 to 14.0 g for the men. Values for the control group were 13.9 g and 14.3 g for the women and men, respectively. The placebo group showed virtually no change over the 80-day period (8.1-8.4 g for women and 7.7-7.4 g for men). Peak exercise heart rates (5 min, 40-cm step test) were significantly reduced after treatment from 155 to 113 for the iron treatment men and 152 to 123 for the women compared with the placebo group which showed no changes. Values for the control group were 119 and 142 for the men and women, respectively. In response to the exercise test, no difference in oxygen consumption was found between the iron treatment and placebo group although 15% more O2 was delivered per pulse in the iron treatment group. Blood lactates were significantly highein the placebo than iron treatment group both at rest, 1.18 versus 0.64 mmole/liter, and 1 min after exercise, 5.30 versus 2.68 mmoles/liter. No changes in handgrip or shoulder adductor strength were observed following treatment. These results clearly support the concept that performance requiring high oxygen delivery is significantly affected by hemoglobin levels.

Adolescent↗
PubMed1975

Heart rate and ECG responses of fire fighters.

Data were obtained from 35 fire fighters responding to 189 alarms. Fifteen to 30 sec after an alarm heart rate showed a mean increase of 47 beats/min (range 12-117 beats/min). Approximately one minute after the alarm, while on the truck, heart rate still showed a mean increase of 30 beats/min (range 1 to 80 beats/min) above that recorded before alarm. S-T segment changes were observed in the ECG shortly after the alarm sounded. Upon approaching a fire, heart rates as high as 150 beats/min were observed before the men got off the fire truck. During actual fire fighting extremely high heart rates were observed for prolonged periods of time. One fire fighter had a mean heart rate of 188 beats/min for 15 minutes during the initial stages of a structure fire. The heart rate responses observed immediately after the alarm as well as on the truck approaching a fire indicate that the men experience a state of high anxiety. The extremely high heart rates observed for prolonged periods during fire fighting may also indicate a state of high anxiety coupled with the heavy work performed in a hot environment. Repeated exposure to states of high anxiety as well as inhaling pollutants related to the high incidence of ischemic-stress tests previously observed in fire fighters.

Adult↗
PubMed1975

Near-maximal ECG stress testing and coronary artery disease risk factor analysis in Los Angeles City fire fighters.

Near-maximal ECG stress testing and coronary artery disease risk factor analysis including blood pressure, serum cholesterol and smoking habits were conducted on a randomly selected group (N=90) of Los Angeles City Fire Fighters ranging in age from 40 to 59 yrs. The data obtained from the fire fighters were compared to data previously reported for a group of Los Angeles insurance underwriters of the same age range. Only 12% of the fire fighters had cholesterol values greater than 260 mg% while 18% of the insurance executives fell into this category. Only 2% of the fire fighters had blood pressure values greater than 160/90 mm Hg while 25% of the insurance executives were hypertensive. Thirty-two percent of the fire fighters were smokers at the time of testing as compared to 26% for the insurance executives. Only one fire fighter had all three risk factors elevated and only five had two risk factors elevated. Forty-seven of the fire fighters had no risk factors elevated. Ten percent of the fire fighters had ischemic stress tests as compared to 8% for the insurance executives. Of the nine fire fighters with ischemic stress tests one was hypertensive, one had elevated serum triglycerides, and three were smokers at the time of testing. Since the fire fighters are a medically-selected population with low risk factors for CHD, the observed incidence of ischemic stress tests is surprising and suggests that ischemic heart disease may be job associated.

Adult↗