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Biomedical subjects

R A Kenney

Publications and source records attributed to R A Kenney.

16 recordsLinked to original sources
PubMed1990

Effect of a central redistribution of fluid volume on response to lower-body negative pressure.

We studied cardiovascular responses to lower-body negative pressure (LBNP) following 1 hour (h) of 6 degrees head-down tilt to determine whether a redistribution of blood volume toward the central circulation modifies the subsequent response to orthostatic stress. Responses of 12 men, ages 30-39 years, were evaluated by electrocardiography, impedance cardiography, sphygmomanometry, and measurement of calf circumference. During the LBNP that followed head-down tilt--as compared with control LBNP (no preceding head-down tilt)--subjects had smaller stroke volume and cardiac output, greater total peripheral resistance, and less calf enlargement. These differences reflect differences in the variables immediately preceding LBNP. Magnitudes of the responses from pre-LBNP to each pressure stage of the LBNP procedure did not differ between protocols. Mean and diastolic arterial pressures were slightly elevated after LBNP-control, but they fell slightly during LBNP post-tilt. These cardiovascular responses to simulated gravitational stress following head-down tilt may reflect the manner in which adaptation to microgravity affects subsequent responses to orthostatic stress on return to Earth.

Adult↗
PubMed1989

Adenosine nucleotide utilization in subtotally nephrectomized rabbits.

Two- to three-kilogram albino rabbits were subtotally nephrectomized and compared with sham-operated normal rabbits for the muscle content of adenosine mono (AMP)-, di (ADP)- and triphosphate (ATP) and inosine monophosphate (IMP) before and after exercise. Analysis of snap-frozen, lyophilized soleus muscle showed lower levels of AMP, ATP and total adenosine nucleotide (TAN) (p less than 0.01) and ATP/ADP (p less than 0.02) in the subtotally nephrectomized animals. IMP levels following exercise were higher in the experimental animals. Muscle adenosine nucleotide concentrations in the experimental animals were significantly different for normals, thus suggesting that minimal azotemia could adversely affect muscle function in these animals.

Adenine Nucleotides↗
PubMed1987

Hysteresis in response to descending and ascending lower-body negative pressure.

We have investigated the pattern of fluid redistribution and cardiovascular responses during graduated orthostatic stress. Twelve men, age 30-39 yr, underwent a 25-min lower-body negative pressure (LBNP) test protocol that involved sequential stages of LBNP at -8 mmHg (1 min), -16 mmHg (1 min), -30 mmHg (3 min), -40 mmHg (5 min), -50 mmHg (5 min), -40 mmHg (5 min), -30 mmHg (3 min), -16 mmHg (1 min), and -8 mmHg (1 min). Data were recorded at the end of each stage. For many measured variables values during the descending phase of LBNP (-8 to -40 mmHg) were significantly different from values during the ascending phase of (-40 to -8 mmHg). These differences appear to be due to a component of fluid translocation that occurs during LBNP and cannot be reversed within the duration of the procedure. We hypothesize that this slowly reversed component is sequestration of fluid in the interstitial and lymphatic compartments. In contrast, venous pooling is a rapidly reversible component of fluid movement during LBNP. A scheme describing fluid and cardiovascular responses to LBNP based on these data and the data of other investigators is presented.

Adult↗
PubMed1987

Cardiovascular dynamics during the initial period of head-down tilt.

The cardiovascular response to 1 h of 6 degrees head-down tilt was studied in 12 male subjects, ages 30-39 years, to simulate the early effects of weightlessness. Fluid shifts, hemodynamic variables, and indices of myocardial contractility were evaluated by utilizing electrocardiography, systolic time intervals, impedance cardiography, sphygmomanometry, and measurement of calf circumference. Most cardiovascular variables remained stable throughout the initial 30 min of the protocol, even though translocation of fluid from the legs to the thorax commenced immediately with the onset of head-down tilt. In contrast, minutes 30-60 were characterized by reduced stroke volume, cardiac output, mean stroke ejection rate, and Heather Index concomitant with an elevation in mean arterial pressure. Intrathoracic fluid volume continued to increase while leg volume continued to decrease. This latter physiological response suggests intrathoracic sequestration of fluid volume; blood was apparently redistributed to the pulmonary circulation rather than being retained in the great veins.

Adult↗
PubMed1986

The Chinese restaurant syndrome: an anecdote revisited.

The Chinese Restaurant Syndrome arose from an anecdote of discomfort experienced after eating Chinese cuisine. Monosodium glutamate has been implicated as the causative agent. Work over the past 17 years has consistently failed to reveal any objective sign accompanying the transient sensations that some individuals experience after the experimental ingestion of monosodium glutamate and it is questionable whether the term 'Chinese Restaurant Syndrome' has any validity. When some common food materials are used in the same experimental setting, similar symptoms can be produced in a limited number of people. Double-blind testing of individuals who identify themselves as suffering the 'syndrome' has failed to confirm the role of monosodium glutamate as the provocative agent.

Adult↗
PubMed1985

Oxygen uptake in exercising subjects with minimal renal disease.

Patients with varying degrees of renal failure were studied for their blood lactate response to exercise on either a treadmill or a bicycle ergometer. In the group exercised on a treadmill, blood lactate and alanine levels were measured, and in the group exercised on the bicycle ergometer blood lactate levels and oxygen uptake were measured. In both groups regardless of the method of exercise or the degree of azotemia, a rapid rise in blood lactate similar to that previously reported with exercise was observed. Blood alanine levels, which were low in subjects with renal disease, did not change with exercise even with a rise in blood lactate levels. There was no difference in the oxygen uptake between normal controls and subjects with renal disease. We conclude that blood alanine levels are low in renal disease, and that with the degree of exercise studied the rise in blood lactate in patients with renal disease is not accompanied by a change in oxygen uptake and does not evoke a rise in blood alanine levels. The mechanisms for the abnormal rise in blood lactate in these patients does not appear to be due to anoxia.

Adult↗
PubMed1985

Physiology of aging.

Physiologic aging involves changes that tend to be linear with time and are characteristically decremental in nature. A number of the functional changes can be delayed in onset or slowed in their progress by lifestyle. Aging challenges the reserves of function that allow for activity above the resting level and for regulation of the internal environment.

Acid-Base Equilibrium↗
PubMed1979

Systolic time intervals during combined hand cooling and head-up tilt.

Cardiac effects initiated by hand cooling and head-up tilt, separately and in combination, were studied in human subjects. Systolic and diastolic arterial pressures, heart rate, pre-ejection period (PEP), and left ventricular ejection time (LVET) were measured while subjects were resting supine, supine with hand immersed in 10 degrees C water, tilted 70 degrees head up, and hand immersed during head-up tilt. Hand immersion and head-up tilt individually increased diastolic blood pressure and concomitantly increased the duration of PEP. During the combined maneuver, the increase in diastolic pressure was greater than observed during either separate maneuver; however, the combined maneuver had no comparable summative effect on PEP prolongation. An interaction appears to occur during the combined maneuver which counteracts the Frank/Starling effect on PEP due to decreased venous return during head-up tilt.

Adult↗
PubMed1979

Cardiac response to whole-body heating.

Changes in ventricular function, as described by systolic time interval analysis, have been studied during heat stress and the time course of these changes, as well as changes in heart rate, have been investigated. Seven male and female subjects, 22-35 years of age, immersed their lower legs in water 42-44 degrees C for 30 min; their trunks and upper legs were enclosed in nonpermeable plastic to prevent evaporative heat loss. Total beat interval (R-R), left ventricular ejection time (LVET), pre-ejection period (PEP), arterial blood pressure, and oral temperature were monitored periodically during heating and recovery (post-hearing) periods. The stress induced significant (p less than 0.05) decreases in R-R and LVET by 5 min of heating which continued decreasing throughout the 30-min heating period. Heart rate accelerated from 72 up to 97 beats/min. LVET's during heat stress were shorter than those at similar resting heart rates. R-R and LVET were increased significantly by 1-min recovery but had not returned to preheating levels at 15 min. PEP, on the other hand, was not reduced until 15 min of heating, and did not start to recover until 3 min post-heating, after which it reached values exceeding control. A small increase in systolic blood pressure was maintained throughout heating and remained at 15 min recovery. Oral temperature increased approximately 1 degree C during the heating procedure; 50% of this was dissipated by 15 min recovery. Results are consistent with a two-stage cardiac response to heat-vagal withdrawal followed by a strong sympathetic outflow to the heart affecting both inotropic and chronotropic characteristics.

Adult↗
PubMed1977

Changes in left ventricular activity during apnea and face immersion.

Apneic face immersion in water has been analyzed with respect to its effects upon heart rate and ventricular function in a group of highly trained teenaged swimmers of both sexes. Both parameters have been studied on a beat-by-beat basis throughout the maneuvers and analysis of the systolic time intervals has provided a noninvasive tool for studying changes in ventricular function. It was observed that the pre-ejection period of systole is lengthened, while left ventricular ejection time shows little change with apnea, face wetting (27 degrees C), or a combination of these. This decrease in ventricular function, however, lags behind the previously well-recognized decrease in heart rate, a difference which is particularly obvious when face immersion is performed in the postexercise state. This suggests ventricular function changes are regulated separately from heart rate changes and thus may be a secondary effect. Analysis of the face immersion reflex on a beat-by-beat basis has also revealed a more rapid development of bradycardia with colder (15 degrees C) water. A model has been developed to describe the face immersion reflex in the light of these findings and previous information.

Adolescent↗
PubMed1976

Renal function.

Explore the source record for details and available documents.

Absorption↗
PubMed1976

Semiautomated processing of systolic time intervals.

Systolic time intervals are commonly used to identify changes in ventricular function. The method described facilitates measurement and calculation of many such intervals. This method utilizes a printed polygraph recording of electrocardiogram, phonocardiogram, and carotid pulse contour; a digitizing device for reading the necessary coordinates from the record; and a minicomputer for calculation of the intervals and for data analysis. Intervals related to approximately 100 pulse beats can be read, calculated, printed in chart and graph form, and subjected to some analyses in about an hour.

Automation↗