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Biomedical subjects

M A Frey

Publications and source records attributed to M A Frey.

At least 37 records · Page 2Linked to original sources
PubMed1989

Health and illness self-care in adolescents with IDDM: a test of Orem's theory.

Orem's theory suggests that different self-care actions are necessary to meet requisites related to health (universal self-care) and illness (health-deviation self-care). The authors differentiate these types of self-care, propose hypotheses relating these concepts to other concepts in Orem's theory, and test them in a sample of adolescents with diabetes mellitus. As predicted, universal self-care is significantly related to a measure of the global health state, and health-deviation self-care is related to control of pathology. The findings provide direction for additional research and theory development.

Adolescent↗
PubMed1989

Social support and health: a theoretical formulation derived from King's conceptual framework.

This article describes the development and initial empirical testing of a theoretical formulation of social support, family, health, and child health derived from Imogene King's conceptual framework for nursing. A correlational design was used to test the formulation with 103 families who have children with diabetes mellitus. Three hypotheses were supported: parents' social support had a direct and positive effect on family health, parents' social support and child's social support were positively related, and illness factors had a direct and negative effect on child health. Both the supported and unsupported hypotheses are discussed in terms of the present substantive knowledge base and evidence of validity for King's framework. Direction for further theory development and research are identified.

Adolescent↗
PubMed1988

Association of sex and age with responses to lower-body negative pressure.

Responses of 21 women and 29 men (29-56 yr of age) to -50 Torr lower body negative pressure (LBNP) were examined for differences due to sex or age. Responses to LBNP were normal, including fluid shift from thorax to lower body, increased heart rate and peripheral resistance, and decreased stroke volume, cardiac output, and Heather index of ventricular function. Mean arterial blood pressure did not change. Comparison of responses of the women to responses of an age-matched subset of the men (n = 26) indicated the men had larger relative increases in calf circumference and greater increases in peripheral resistance during LBNP than the women, whereas the women experienced greater increases in thoracic impedance and heart rate. Analyses of responses of the 29 men for age-related differences indicated older subjects had greater increases in peripheral resistance and less heart rate elevation in response to LBNP (P less than 0.05 for all differences, except sex-related heart rate difference, where P less than 0.10). Based on these data and the data of other investigators, we hypothesize the age-related circulatory differences in response to LBNP are due to a reduction in vagal response and a switch to predominant sympathetic nervous system influence in older men. We cannot exclude the possibility that diminished responsiveness in the afferent arm of the baroreceptor reflex also plays a role in the attenuated heart rate response of older men to LBNP.

Adult↗
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

Considerations in prescribing preflight aerobic exercise for astronauts.

Many human responses to the weightless environment have been documented from actual spaceflights. These include physiological effects on the nervous system, cardiovascular system and fluid balance, and the musculoskeletal system, as well as psychological effects. Simulations on Earth have added to our knowledge about the physiology of weightlessness. Early data on orthostatic intolerance after real and simulated spaceflight led some scientists to discourage a high level of aerobic fitness for astronauts. They believed it was detrimental to orthostatic tolerance on return to Earth. However, most of the data available today do not support this contention. Furthermore, aerobic fitness is beneficial to cardiovascular function and mental performance. Therefore, it may be important in performing extra-vehicular activities during flight. Some astronauts claim exercise enhances their feeling of well-being and self image. And, although the cardiovascular system and exercise performance may recover more slowly after flight to preflight levels when fitness level prior to flight is high, the musculoskeletal system may recover more rapidly. Research is needed to determine optimal levels of aerobic training for performing tasks in flight, maintaining health and well-being during flight, and assuring satisfactory recovery on return to Earth.

Cardiovascular Physiological Phenomena↗
PubMed1987

Aerobic fitness in women and responses to lower body negative pressure.

High aerobic fitness may be associated with impaired responsiveness to orthostatic challenge. This could be detrimental to astronauts returning from spaceflight. Thus, we examined the cardiovascular responses of a group of 45 healthy women to graded lower body negative pressure (LBNP) through 5 min at -50 mm Hg or until they become presyncopal. The ages (range = 23-43 years, mean = 30.4) and peak aerobic capacities (range = 23.0-55.3 ml.kg-1.min-1, mean = 37.8) of these subjects paralleled those of the women astronauts. We monitored heart rate, stroke volume, cardiac output, Heather index of contractility, arterial pressure, peripheral resistance, change in calf circumference, and thoracic impedance (ZO)--a measure of fluid in the chest. The women in this study exhibited the same response pattern to LBNP as previously reported for male subjects. VO2peak of the six subjects who became presyncopal was not different from VO2peak of the tolerant subjects. At rest, only systolic and mean arterial pressures were significantly correlated with VO2peak. Percent changes in calf circumference (i.e. fluid accumulation in the legs) at -30 and -40 mm Hg were the only responses to LBNP significantly related to VO2peak. The greater pooling of blood in the legs during LBNP by women with higher aerobic fitness, and lower percent body fat may be related to more muscle tissue and vasculature in the legs of the more fit subjects. These data indicated that orthostatic tolerance is not related to aerobic capacity in women, and orthostatic tolerance need not be a concern to aerobically fit women astronauts.

Adaptation, Physiological↗
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

Cardiovascular responses of women to lower body negative pressure.

Lower body negative pressure (LBNP) has provided a method for studying cardiovascular responses in men while simulating a return to the stresses of 1-G following space flight. In this study, we have monitored responses of women to the stresses provided by LBNP. There were 20 women, 23-43 years, each tested in the follicular and luteal phases of the menstrual cycle. Variables were recorded during supine control; at -30, -40, -50 mm Hg LBNP; immediately after pressure release; and after 5 min recovery. There were no significant differences in response to LBNP between the two menstrual phases. During LBNP calf circumference was enlarged; transthoracic impedance was increased; stroke volume, left ventricular ejection time, the Heather Index of contractility and systolic pressure were reduced; total peripheral resistance was elevated; and cardiac output fell despite a rise in heart rate. Differences in cardiovascular variables between 0 mm Hg LBNP and -50 mm Hg LBNP were generally similar to reported differences between supine and standing. The responses of these women to LBNP were qualitatively similar to those reported for the Apollo astronauts and other male subjects. These women appeared to compensate with a greater heart rate response; however, the net cardiovascular compensation as determined from arterial pressure appears to be similar in men and women.

Adult↗
PubMed1984

Central hemodynamics during progressive upper- and lower-body exercise and recovery.

The purpose of this study was to compare stroke volume (SV) and myocardial contractility responses during and immediately after upper- and lower-body exercise. Nine men (mean 28 yr, 78 kg) completed progressive intensity discontinuous tests on both an arm crank and cycle ergometer. Exercise for each power output (PO) was 7 min with 20-min rest periods interspersed. Impedance cardiography was used to measure cardiac output (Q), SV, and contractility on a beat-by-beat basis during exercise and a 15-s recovery period. Q increased linearly, and total peripheral resistance decreased exponentially with increasing PO levels. During recovery from exercise, the Q and heart rate (HR) values decreased immediately at all PO levels. When the exercise VO2 exceeded 1.0 1 X min-1, SV fell significantly during recovery for both exercise modes. In general, the recovery myocardial contractility indices remained similar to exercise values. It was concluded that immediately after low intensities of exercise, Q decreases because of a fall in HR. After moderate- and high-intensity exercise, Q decreases because of a fall in both HR and SV.

Adult↗
PubMed1984

Metabolic, hemodynamic, and respiratory responses to performing cardiopulmonary resuscitation.

The purpose of this study was to evaluate the cardiorespiratory demands inherent to the maintenance of continuous one- and two-man cardiopulmonary resuscitation (CPR) for 10 min. Ten male paramedics (X age = 26 yrs) certified to perform CPR participated. Each subject assumed the three possible roles for administering CPR: ventilator, compressor, and one-man technique. Cardiorespiratory responses were determined by impedance cardiography and open-circuit spirometry at 2 min intervals while performing CPR with a resuscitation manikin. Left ventricular performance was evaluated by impedance ventricular function indices (VFI) and systolic time intervals (STI). All three roles elicited an increase in oxygen uptake compared to kneeling rest, with the roles of one-man and compressor being the most demanding. There were moderate increases in cardiac output and heart rate during the exercise roles, but stroke volume remained similar to resting values. Pulmonary ventilation increased during exercise, with the greatest increase occurring for the one-man role. STI and impedance VFI reflected an enhanced ventricular performance while performing the roles of one-man and compressor. These findings suggest that the energetic demands placed on the rescuer depend upon the specific role assumed. Properly trained and experienced individuals can perform CPR efficiently for at least 10 min while eliciting only moderate physiological stress.

Adult↗
PubMed1983

Cardiovascular response to a mentally stressful stimulus.

The purpose of this study was to investigate multivariable cardiovascular responses to a non-mathematical mental task. Fifty-two subjects, 8 to 69 years of age, were monitored at rest and while attempting to solve a Raven's matrix test without prodding or pressure from the experimentors. Adults (greater than or equal to 18 years) had higher blood pressures (BP) and longer pre-ejection periods (PEP) at rest than did the children. Women had higher resting heart rates (HR) than men. The task induced significant increases in systolic and diastolic BP and HR in adults and children, with the adults exhibiting larger BP responses. During the stressful stimulus significant decreases in left ventricular ejection time occurred in men and women, and significant increases in forearm blood flow occurred in men. The stability in PEP during the stressful period when both BP and HR were increased is evidence of enhanced contractility brought on by the stress. In general, men and women responded similarly. Thus, even a mild, non-mathematical stress of short duration elicits the multiple cardiovascular responses, including increases in BP, HR, muscle blood flow, and contractility, which are observed with more threatening tasks.

Adolescent↗
PubMed1983

Correlations between ejection times measured from the carotid pulse contour and the impedance cardiogram.

Systolic time interval (STI) analysis is a commonly employed noninvasive technique for evaluating myocardial function. It requires simultaneous recording of an electrocardiogram, phonocardiogram, and the carotid pulse contour, from which left ventricular ejection time is measured. The carotid pulse contour may be difficult to record when there is subject movement, such as with exercise or other stresses utilized in aerospace medical research. Impedance cardiography is a relatively new noninvasive technique for measuring stroke volume. It also provides a measure of systolic ejection time without the necessity of recording a carotid pulse contour. The purpose of this study was to determine the correlation between left ventricular ejection time (LVET) determined from conventional STI analysis and systolic ejection time (T) obtained with impedance cardiography. The electrocardiogram, phonocardiogram, carotid pulse contour, and impedance cardiogram were monitored simultaneously in 17 male subjects 39-63 years of age (6 normotensive, 7 with established hypertension, and 4 with labile hypertension). Subjects were monitored at seated rest and during submaximal and maximal cycle ergometer exercise. Beat-by-beat analysis revealed high intrasubject correlations between LVET and T for each subject during all three activity levels. Correlations between LVET and T for the combined group of 17 subjects were: rest r = 0.990, submaximal exercise r = 0.976, maximal exercise r = 0.986; p less than 0.01. These results indicate impedance cardiography can be used in the determination of STIs for the evaluation of ventricular function, as well as for the noninvasive determination of stroke volume and cardiac output.

Adult↗
PubMed1983

Cardiac function monitored by impedance cardiography during changing seatback angles and anti-G suit inflation.

Impedance cardiography (IC) appears to be a promising noninvasive technique for monitoring small changes in pilot cardiovascular status during conditions simulating flight. Heart rate (HR), stroke volume (SV), cardiac output (CO), ventricular ejection time (VET), and thoracic impedance (Zo) were monitored in ten volunteers for 5 min at each of four seatback angles from vertical: 12 degrees, 30 degrees, 45 degrees, and 60 degrees. Data were also obtained at three seatback angles (12 degrees, 30 degrees, 60 degrees) for 6 min each before, during, and after inflation of the standard USAF anti-G suit to 1.5 psi. Significant differences (p less than 0.05) in HR, SV, CO, VET and Zo were observed among the four positions. Inflation of the standard anti-G suit to 1.5 psi at 1.0 +Gz did not significantly alter HR, SV, or CO; whereas, 1 min of deflation of the anti-G suit significantly altered HR, SV, CO compared to inflation values. The results suggest IC can detect small differences in HR, SV, CO, VET, and Zo within subjects as a function of minor changes in body position.

Cardiac Output↗
PubMed1982

Exercise does not change high-density lipoprotein cholesterol in women after ten weeks of training.

Effects of a 10 wk, three times per wk individualized bicycle ergometer training program were investigated in 16 healthy sedentary women 19-29 yr-old who were not taking oral contraceptives or other medications. Twelve women were in an interval type program, 6 in a continuous program, all performing 30 min exercise per session at 70% maximum heart rate reserve. Conditioning responses did not differ between the training regimens. Training produced increases in maximum oxygen uptake and physical work capacity. Percent body fat determined by underwater weighing was significantly reduced as was resting heart rate, after the training program. Maximum heart rate was unchanged. Despite changes in "fitness" variables, post-training values of high density lipoprotein cholesterol and triglycerides did not differ from pretraining. High-density lipoprotein cholesterol was significantly reduced at 2 and 5 wk of training and returned to control levels at 10 wk. Exercise conditioning leading to improved physical fitness in healthy women may not be associated with increments in high density lipoprotein cholesterol levels.

Adult↗
PubMed1982

Computer-assisted method for performing impedance cardiography calculations.

Impedance cardiography provides a noninvasive technique to monitor stroke volume on a beat-by-beat basis. It correlates well with other techniques at rest, with both cycle and arm-ergometer exercise, and during head-up tilt. It has the advantage that it does not require active subject participation, as does the CO2-rebreathing technique; yet it is still noninvasive. The method described herein facilitates the measurement and calculation of stroke volume, cardiac output, and indices of ventricular function when this technique is used - whether a few or many beats are recorded. This method utilizes a recording of the impedance cardiogram, which may include a simultaneously recorded electrocardiogram and phonocardiogram; a digitizer for reading the coordinates from the recording; a CRT terminal with keyboard for additional data input and for monitoring output; a printer; and a minicomputer for calculation of variables and data analysis. Data related to approximately 100 cardiac beats can be read, calculated, printed, and statistically analyzed in about an hour.

Cardiography, Impedance↗
PubMed1982

Transthoracic impedance: differences between men and women with implications for impedance cardiography.

Impedance cardiography (IC) is a reliable noninvasive technique for monitoring stroke volume (SV) and cardiac output. Transthoracic impedance (Zo) is one variable in the equation used for the calculation of SV. Thoracic impedance reflects the resistivity offered by tissues and air and the length and cross-sectional area of the thoracic volume. The purpose of this study was to evaluate possible differences in Zo between men and women. Measurements (Mean +/- S.D.) of Zo in 29 men (age 25.6 +/- 4.6 yr) and 35 women (24.2 +/- 6.0 yr) in the seated posture revealed Zo values were significantly (p less than 0.05) greater for the women (31.5 +/- 3.3 ohm) than the men (23.5 +/- 1.84 ohm). The observed differences in Zo cannot be attributed to thoracic length; distances between the monitoring electrodes were similar for the men (25.1 cm) and the women (25.7 cm). We hypothesize that the greater Zo observed for women is due to a smaller thoracic cross-sectional area and greater resistivity resulting primarily from relatively more fat tissue, smaller heart size, and lesser central blood volume as compared with men.

Adolescent↗