PubMed Health⌕ Search

Biomedical subjects

P B Raven

Publications and source records attributed to P B Raven.

At least 19 recordsLinked to original sources
PubMed1992

Aerobic fitness: I. Response of volume regulating hormones to head-down tilt.

We investigated the relationship of aerobic fitness to the response of volume-regulating hormones to acute simulated microgravity. Six untrained (UT) and six endurance-trained (ET) healthy young males were studied in the head-down tilt (HDT) position of -6 degrees for 4 h. Peak oxygen uptake (VO2peak) and plasma volume (PV) were significantly greater in the ET (VO2peak = 61.7 +/- 1.6 ml.min-1.kg-1 and PV = 53.1 +/- 2.8 ml.kg-1) than in the UT (VO2peak = 38.4 +/- 1.7 ml.min-1.kg-1 and PV = 38.8 +/- 1.0 ml.kg-1). Plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), norepinephrine (NE), renin activity (PRA), and aldosterone (PA) were measured prior to HDT and at minutes 2, 5, 15, 30, 60, 120, 180, and 240 during HDT. PRA and PA significantly decreased during the time of HDT in both groups. The changes in ANP and NE concentrations were not significantly different between the groups nor across time. However, in the ET subjects, the changes in PRA and NE were significantly correlated with the changes in ANP (r = 0.49, P less than 0.01; and r = 0.86, P less than 0.001, respectively); in the UT subjects, the changes in AVP, PRA, and PA were significantly associated with changes in NE (r = 0.34, P less than 0.03; and r = 0.59; and r = 0.53, P less than 0.01, respectively). PV significantly decreased during HDT, and was primarily related to the decrease in PA in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Aerobic fitness: II. Orthostasis and VO2peak following head-down tilt.

To determine whether endurance exercise trained (ET) subjects would experience greater reductions in peak oxygen delivery and orthostatic tolerance (OT) than untrained (UT) subjects, both peak oxygen uptake (VO2peak) during upright bicycle ergometry and tolerance time during 70 degrees head-up tilt (HUT) were compared within and between groups before and after 4 h of -6 degrees head-down tilt (HDT). Eight ET subjects with a mean VO2peak of 61.7 +/- 1.6 ml.kg-1.min-1 were matched for age, height, and weight with eight UT subjects (VO2peak = 38.4 +/- 1.7 ml.kg-1.min-1). Following HDT, decreases in plasma volume (PV) were larger for ET subjects (-3.7 +/- 0.5 ml.kg-1) than for UT subjects (-2.3 +/- 0.3 ml.kg-1), P less than 0.03. Reductions in VO2peak for ET subjects (-5.4 +/- 1.1 ml.kg-1.min-1) were also greater than for UT subjects (-2.4 +/- 0.8 ml.kg-1.min-1), P less than 0.05. The ET (N = 6) subjects also had a significant decrease in OT time (-13.0 +/- 4.2 min) during post-HDT HUT, which was not observed for the UT group (N = 6). A significant inverse correlation was found pre-HDT VO2peak and the change in OT time, r = -0.74, P less than 0.01. The decrease in OT was also significantly correlated to the PV decrease, r = 0.59, P less than 0.04. The UT subjects had significantly augmented pressor responses to HUT manifested by the increases in both HR and MAP following HDT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Effect of pedal rate on cardiorespiratory responses during continuous exercise.

The role of cycle ergometer pedal rate on the gradual increase in ventilation (VE), heart rate (HR), and oxygen uptake (VO2) accompanying continuous submaximal exercise is unknown. To examine this problem, five trained males (VO2peak = 4.00 +/- 0.27 l.min-1) performed 45 min of moderate intensity (MI, 127 W) and high-moderate intensity (HMI, 166 W) cycle ergometry both at pedal rates of 60 rpm and 90 rpm. Power output and pedal rate had an additive effect on the overall mean responses for VE, HR, and VO2, producing significantly higher values as power output and pedal rate increased. During continuous exercise, VE, HR, and VO2 increased progressively from the 10th to the 45th minute for all tests. However, the rates of increase and factors modifying the VE, HR, and VO2 responses were different. HR increased during all exercise tests an average of 10.8% independent of power output and pedal rate. VE increased 7.4% during MI exercise and 10% during HMI exercise independent of pedal rate. Similar power output dependent responses were observed for rectal temperature (Tr) and blood lactate. VO2 increased 4.4% for MI and HMI exercise at 60 rpm, and 8.2% for the same power outputs at 90 rpm, respectively. Increases in Tr, the oxygen cost of pulmonary ventilation and fat oxidation, and lactate removal were estimated to account for only 31-36% of the slow rise in VO2 for any single test. This suggests that 64-69% of the rise in VO2 was due to factors related to muscle use.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Reduction in LBNP tolerance following prolonged endurance exercise training.

Eight young men underwent an 8-month endurance exercise training program. Prior to and following the training program, the subjects' maximal oxygen uptake (VO2max), total blood volume (TBV) and plasma volume (PV), tolerance to lower body negative pressure (LBNP) assessed by the cumulative stress index (CSI) to presyncope, and their hemodynamic responses to 0 to -45 torr LBNP was determined. Hemodynamic measures included rebreathe carbon dioxide cardiac output (Qc), heart rate (HR), directly measured arterial blood pressures (ABP), and strain gauge determination of forearm blood flow (FBF) and leg volume changes (delta LgV). Calculated values of stroke volume (SV), forearm, vascular resistance (FVR), and peripheral vascular resistance (PVR) were made. Following training, each subject had an increased VO2max (mean = +27.4%, P < 0.001), TBV (mean = +15.8%, P < 0.02), and PV (mean = +16.5%, P < 0.02) and each subject had a decreased tolerance to LBNP (mean CSI = -24%, P < 0.001). Stepwise linear regression identified that the major factors to significantly predict the decreased CSI pre- to post-training were a reduced response of PVR to LBNP from -15 to -45 torr (Model R2 = 0.853), the delta TBV (model R2 = 0.981), and the greater post-training reduction in SBP to LBNP of 0 to -45 torr (model R2 = 1.0). These data suggest that physiologic adaptations associated with the increased VO2max and TBV resulting from a prolonged endurance exercise training program can alter the reflex control of vasomotion and cardiac output during LBNP and reduce the LBNP tolerance.

Adult↗
PubMed1992

Effects of exercise training on men seropositive for the human immunodeficiency virus-1.

We examined the effects of chronic exercise on fitness and immune status in Caucasian males (34.9 +/- 5.6 yr) diagnosed by Western blot as seropositive for the HIV-1 virus. The exercise regimen involved 12 wk of 1 h sessions 3 d.wk: 20 min of cycle exercise at 60-80% HRreserve was followed by 35 min of strength and flexibility training. After matching subjects on health status (modified Walter Reed criteria), subjects (N = 37) were randomly assigned to exercise or a counseling control condition. Changes in strength, responses to the YMCA cycle test, and serum lymphocytes were tested by MANOVA in a condition (exercise or counseling)-by-time (pretest, posttest) design with repeated measures on time. Results indicated significant (P less than 0.001) group-by-time interactions for strength (N.m) (chest press and leg extension) and for HR (beats.min-1) and total time (TT) on the cycle test at 150 W. Strength and TT increased and HR decreased in the exercise condition, while control subjects did not change. Total leukocyte, lymphocyte, CD4+, and CD8+ cell counts, and the CD4+/CD8+ ratio were statistically unchanged for each condition. We conclude that HIV-1+ men, including those symptomatic for AIDS-related complex, can experience significant increases in neuromuscular strength and cardiorespiratory fitness without changes in lymphocyte phenotypes or clinical diagnosis when the exercise regimen is prescribed and monitored in accordance with ACSM guidelines for healthy adults.

Adult↗
PubMed1992

The effects of oral smokeless tobacco on the cardiorespiratory response to exercise.

The purpose of this investigation was to determine the effects of oral smokeless tobacco (OST) usage on oxygen uptake (VO2), cardiac output (Qc), stroke volume (SV), heart rate (HR), and plasma lactate concentration (Lc) during rest and exercise. Fifteen asymptomatic subjects were recruited from 18 to 33-yr-old male users of OST. Comparisons of the responses of VO2, Qc, SV, HR, and Lc were made between 2.5-g OST and placebo experimental conditions during rest and at 60% and 85% maximal VO2 treadmill exercise. Plasma nicotine concentrations (Nc) were determined by radioimmunoassay. There were significant increases in HR and Lc and a decrease in SV during rest and at 60% and 85% maximal exercise (P less than 0.05). Furthermore, there were no significant differences in maximal HR, Lc, and VO2 (P greater than 0.05). In conclusion, these data indicate that the increased Nc incurred by OST usage increases anaerobic energy production and produces an increased tachycardiac response to a given relative submaximal workload.

Adolescent↗
PubMed1991

Hemodynamic responses to 6 degree head-down rest in dogs: effect of aerobic conditioning.

The -6 degree head-down position is used in humans to produce fluid shifts that resemble those occurring in microgravity. Alternative animal models of microgravity may be helpful for extensive exploration of this unique condition. The dog may be a viable candidate. Sixteen dogs were assigned to one of three conditions: anesthetized open chest, anesthetized closed chest, and awake. Dogs in groups 1 (N = 6) and 2 (N = 6) were divided into an exercise or a sedentary treatment, and dogs in group 3 (N = 4) served as their own controls. Following instrumentation the dogs were put in the head-down position for 1 h. Measurements included right atrial pressure, heart rate, and mean arterial pressure for all groups, left ventricular pressure and LV dp/dt for group 1, and cardiac output and iliac flow for group 2. Right atrial pressure increased for all groups. Heart rate demonstrated non-significant changes over time or group. Significant differences were noted for mean arterial pressure, left ventricular pressure and LV dp/dt for exercise condition in response to HDR. It appears that -6 degrees of head-down rest produces similar cardiovascular responses in dogs as those observed in humans and that exercise has a minor effect on those responses.

Animals↗
PubMed1979

The physiological consequences of wearing industrial respirators: a review.

The American Industrial Hygiene Association (AIHA) and American Conference of Govermental Industrial Hygienists (ACGIH) Respiratory Protective Devices Manual, published in 1963, has as its primary source of physiological background the work of Silverman and co-workers performed during World War II. The adoption of permanent OSHA standards governing work tasks requiring workers to use respirators has created a need for further evaluation of the physiological effects of wearing a respirator. This review was undertaken to meet the need of an in-depth evaluation of the currently available psychophysiological data. It was concluded that it was of the utmost importance to develop a physiological and psychological medical screening examination to determine the capability of the worker to use a respirator.

Body Temperature Regulation↗
PubMed1979

Stresses involved in wearing PVC supplied-air suits: a review.

A side effect of the growth and development of industrial technology is the ever increasing number of hostile environments encountered by man. This situation has resulted in the development of impermeable clothing as a barrier protection against the external environment. Unfortunately, although specific government standards concerning the design and engineering requirements of the impermeable suit have been stated, little or no standardized evaluation of the majority of available suits has been attempted. This review was undertaken to provide an in-depth summary of the physiological effects of a PVC protective suit while working. It was concluded that it was necessary to develop a standardized performance test to determine the protective and stressful characteristics of the individual manufacturer's designed suit. Recommendations of specific criteria for the test were obtained.

Body Water↗
PubMed1977

Maximal stress test performance while wearing a self-contained breathing apparatus.

Fifteen adult male volunteers (mean age = 31.0 years; eight non-smokers and seven smokers) carried out a Bruce protocol maximal treadmill stress test under four separate conditions. These four conditions were (1) without Scott Air Pak (SAP) respirator; (2) with SAP respirator apparatus but not wearing face mask; (3) with SAP apparatus, wearing face mask in "demand" breathing mode; and (4) with SAP respirator apparatus, wearing face mask in "pressure-demand" breathing mode. The data indicate that the overriding factor in the approximately 20% decrement in work performance during conditions 2, 3, and 4 was related to the weight of the SAP respirator (15.8 kg), P less than 0.05. Only during condition 3 did eight of 15 subjects report lack of air as one reason for termination. Conditions 3 and 4 resulted in a significant decrease in TFore (2.5 degrees C) and was primarily related to the decreased Tinsp which reached a maximum decrement of 9.7 degrees C. Under all conditions the smokers' work time was significantly less than nonsmokers, P less than 0.05.

Adult↗
PubMed1977

Influence of exercise and heat stress on pulmonary function during ozone exposure.

We studied the effects of a 2-h exposure to ozone (0.5 ppm) in 14 nonsmoking males under four environmental conditions (WBGT (wet bulb-globe temperature index) = 64.4, 80.0, 85.2, and 92.0 degrees F). The subjects were divided into two groups, A (n = 8) and B (n = 6). Thirty minutes of exercise at 40% Vo2 max was performed from 60 to 90 min for group A and 30 to 60 min for group B. Pulmonary function changes, determined throughout exposure, were greatest immediately after exercise in both groups. Few changes occurred before the exercise period. However, the decrease in FVC (826 ml) and FEV1.0 (937 ml) following exercise was more than twice as large as the decrement seen at end exosure (388 and 423 ml, respectively). Measures of maximum expiratory flow (FEF 25-75%, FEF 50% FEF 75%) showed similar reductions. In many cases, reversal of these changes occurred during the remainder of the exposure period. The greatest decrease in FVC occurred when heat and ozone exposures were combined (WBGT = 92.0 degrees F). We conclude that the effects of ozone are most severe immediately after exercise and that heat stress may modify the overall effect of ozone on pulmonary function.

Adult↗
PubMed1976

A physiological evaluation of professional soccer players.

The purpose of this study was to evaluate the physiological functions of a professional soccer team in the North American Soccer League (NASL). Eighteen players were evaluated on cardiorespiratory function, endurance performance, body composition, blood chemistry, and motor fitness measures near the end of their competitive season. The following means were observed: age, 26 yrs; height, 176 cm; weight 75.5 kg; resting heart rate, 50 beats/min; maximum heart rate (MHR), 188 beats/min; maximum oxygen intake (VO2 max), 58.4 ml/kg-min-1; maximum ventilation (VEmax BTPS), 154 L/min; body fat, 9.59%; 12-min run, 1.86 miles; and Illinois agility run, 15.6 secs. Results on resting blood pressure, serum lipids, vital capacity, flexibility, upper body strength, and vertical jump tests were comparable to values found for the sedentary population. Comparing the results with previously collected data on professional American Football backs indicated that the soccer players were shorter; lighter in body weight; higher in VO2 max (4 ml/kg-min-1) and body fat (1.8%); and similar in MHR, VE max, and VC. The 12-min run scores were similar to the initial values observed for the 1970 Brazilian World Cup Team. The agility run results were superior to data collected from other groups. Their endurance capabilities, agility, and low percent of body fat clearly differentiate them from the sedentary population and show them to be similar to that of professional American football backs.

Body Composition↗
PubMed1976

Thermoregulatory response of women to intermittent work in the heat.

Seven women worked intermittently in three randomly ordered sessions at 75% Vo2max at three temperatures, 28 degrees C (45% rh) 35 degrees C (65% rh), and 48 degrees C (10% rh) and recovered in a cool environment (22 degrees C) after each 6-min work period. Although Tre was higher in each successive work period, the ambient temperature had no effect on the cardiovascular or respiratory responses or on deltaTre. In all conditions SV decreased with time with a concomitant increase in HR to maintain Q. A fall in mean blood pressure from the initial to final measurement was due entirely to a decrease in diastolic pressure. The final Tre for these women was approximately equal to that previously reported for men working continuously for 1 h under conditions equivalent to time-weighted average of the thermal and metabolic loads during work and recovery in this study.

Adult↗
PubMed1975

Thermal, metabolic, and cardiovascular responses to various degrees of cold stress.

The metabolic, thermal, and cardiovascular responses of two male Caucasians to 1 2 h exposure to ambient temperature ranging between 28 degrees C and 5 degrees C were studied and related to the respective ambient temperatures. The metabolic heat production increased linearly with decreasing ambient temperature, where heat production (kcal times m- minus 2 times h- minus 1) = minus 2.79 Ta degrees C + 103.4, r = -0.97, P smaller than 0.001. During all exposures below 28 degrees C, the rate of decrease in mean skin temperature (Tsk) was found to be an exponential function dependent upon the ambient temperature (Ta) and the time of exposure. Reestablishment of Tsk steady state occurred at 90-120 min of exposure, and the time needed to attain steady state was linearly related to decreasing Ta. The net result was that a constant ratio of 1.5 of the external thermal gradient to the internal thermal gradient was obtained, and at all experimental temperatures, the whole body heat transfer coefficient remained constant. Cardiac output was inversely related to decreasing Ta, where cardiac output (Q) = minus 0.25 Ta degrees C + 14.0, r = minus 0.92, P smaller than 0.01. However, the primary reason for the increased Q, the stroke output, was also described as a third-order polynomial, although the increasing stroke volume throughout the Ta range (28-5 degrees C) was linearly related to decreasing ambients. The non-linear response of this parameter which occurred at 20 degrees C larger than or equal to Ta larger than or equal to 10 degrees C suggested that the organism's cardiac output response was an integration of the depressed heart rate response and the increasing stroke output at these temperatures.

Adult↗
PubMed1975

Maximal aerobic capacity at different levels of carboxyhemoglobin.

Previous studies had indicated that maximum aerobic power (VO2 max) would be seriously impaired when HbCO levels were above 7% but was not altered if HbCO was around 2.7%. The present studies indicated that the critical level at which HbCO influenced VO2 max was approximately 4.3%. This was accompanied as in the above-noted studied with a reduction in total work time to the attainment of VO2 max. Two procedures to raise HbCO to appropriate levels were employed, i.e., a buildup wherin HbCO was incrementally increased by breathing ambient air containing 75 or 100 ppm CO and a bolus plus maintenance procedure. In the latter, HbCO was raised to the level attained in the buildup test by giving a "bolus" of CO followed by the continued inhalation of CO at a level to just maintain this level of HbCO regardless of the magnitude of the ventilation. Regardless of the mode of presentation, the decrement in VO2 max occurred at the same level of HbCO. These observations are of considerable significance, since it indicated that even low ambient levels of CO (23.7 ppm) would result in lowering maximum aerobic power if the individual had been previously exposed to CO such that the level was raised to this critical point.

Adult↗