Reflex control of splanchnic blood volume in anaesthetized dogs.

1. In chloralose-anaesthetized, artificially ventilated dogs, the splenic pedicle was tied and the carotid sinuses were vascularly isolated and perfused at controlled pressures. In Series 1 experiments, the hepatosplanchnic circulation was perfused through the abdominal aorta with a tie on the aorta separating it from the caudal circulation, which was perfused through the femoral arteries. The two circulations were drained from cannulae in the inferior vena cava and the femoral veins, with a tie on the inferior vena cava separating the two. In Series 2, the splanchnic circulation drained from the portal vein. In both series, inflows and outflows were measured and integrated to derive volume changes. Capacitance responses were assessed during constant flow, and capacitance plus passive responses were obtained during constant pressure perfusion. 2. In Series 1, an increase in carotid sinus pressure (from 8 to 26 kPa) during constant flow and constant pressure perfusion increased hepatosplanchnic volume by 2.5 and 5.7 ml (kg body weight)-1, respectively. The volume of the subdiaphragmatic circulation did not increase during constant flow, but during constant pressure it increased by 2.0 ml (kg body weight)-1. 3. In Series 2, increasing carotid pressure during constant flow and constant pressure increased the volume of the splanchnic circulation by 0.5 and 4.2 ml (kg body weight)-1, respectively. 4. These results confirm that carotid baroreceptor stimulation causes larger volume changes during constant pressure perfusion than during constant flow perfusion. Also, the active capacitance change in the splanchnic circulation is small in relation to the passive response. We propose that in dogs (following splenic ligation), the major active capacitance control is from the liver. However, large passive changes in splanchnic volume occur due to changes in flow.

Blood mobilization from the liver of the anaesthetized dog.

The abdominal circulation contains a high proportion of the total blood volume and this can change either passively in response to changes in vascular distending pressure or actively (termed a capacitance response) to changes in sympathetic nervous activity. The liver is the largest abdominal organ and this study was designed to evaluate its potential contribution to overall vascular capacitance and compliance. In chloralose anaesthetized dogs, the liver was vascularly isolated, perfused through the portal vein and hepatic artery at either constant pressures or constant flows and drained from the hepatic veins at constant pressure. Changes in vascular resistance were assessed from changes in inflow pressures or flows and hepatic blood volume was determined by differences between net inflow and outflow. During constant flow perfusion the change in hepatic volume (capacitance change) in response to supramaximal stimulation of sympathetic nerves at 16 Hz was (mean +/- S.E.M.) -2.40 +/- 0.61 ml (kg body weight)-1. This response was not significantly different during constant pressure perfusion. The changes in portal venous and hepatic arterial pressures during stimulation at constant flow perfusion were +0.67 +/- 0.13 and +4.92 +/- 0.67 kPa, respectively. The compliance of the liver, assessed as the change in volume to a change in hepatic venous pressure, was +5.44 +/- 0.18 ml kg-1 kPa-1. These results indicate that the liver has a major capacitance role, comparable to that of the canine spleen and, in addition, is highly compliant. No evidence was found to suggest that a sphincter on the hepatic outflow exists. Assuming similar responses occur in humans, who do not possess a large contractile spleen, the liver would be the most important controllable blood reservoir in the body.

Mechanisms responsible for changes in abdominal vascular volume during sympathetic nerve stimulation in anaesthetized dogs.

This study was designed to determine the extent to which the decrease in volume of blood in the abdominal circulation in response to sympathetic stimulation was due to a passive effect of decreasing flow rather than active constriction of the capacitance vessels. In dogs anaesthetized with alpha-chloralose (100 mg kg-1 i.v.) the abdominal circulation was vascularly isolated and perfused either at constant flow or at constant pressure, and drained at constant pressure from the inferior vena cava. Changes in volume were determined by integration of the differences between inflow and outflow. Supramaximal stimulation of both splanchnic (sympathetic) nerves at 1 Hz decreased abdominal volume during constant pressure perfusion (active and passive components) by 3.04 +/- 0.58 ml kg-1 and at constant flow (active responses only) by 2.30 +/- 0.49 ml kg-1 (means +/- S.E.M.). The responses at 8 Hz were respectively 9.52 +/- 0.91 and 5.09 +/- 0.49 ml kg-1. The proportion of the responses calculated to be passive at 1 and 8 Hz was 23 +/- 6.3 and 45 +/- 5.1%, respectively. These responses were almost identical to those induced by changing inflow by increasing the pump speed. Following ligation of the splenic pedicle, the responses during both constant pressure and constant flow were reduced by similar amounts, indicating that only the active response was affected. After ligation of the splenic pedicle, the proportion of the response calculated to be passive at 1 and 8 Hz increased to 44 +/- 8.0 and 62 +/- 3.7% respectively. These results indicate the importance of passive volume change in affecting abdominal volume, particularly following ligation of the splenic circulation.

Perceived exertion during hypobaric hypoxia in low- and moderate-altitude natives.

Ratings of perceived exertion (RPE) were examined in six low- (LAN) and eight moderate- (MAN) altitude natives during exercise at their residence (home) altitude (366 m and 2,200 m, respectively) and 1-4 wk later following 2-d decompression to 4,270 m (447 mm Hg). Cardiorespiratory, plasma lactate, and differentiated RPE measures were obtained at exercise intensities representing 35, 55, 75, 85, and 100% VO2peak. In general, cardiorespiratory and plasma lactate values were similar in LAN and MAN at their residence altitudes and during hypobaric hypoxia. However, the decrease in VCO2 was greater (P < 0.05) in LAN than MAN. At their residence altitudes, both LAN and MAN reported local RPE values that were greater (P < 0.05) than central ratings at the moderate to high exercise intensities. At 447 mm Hg, central and local RPE were similar in LAN. However, there was a significant correlation between acute mountain sickness (AMS) symptoms and central RPE (r = 0.875) across the five exercise intensities in LAN. The differences between the central and local RPE noted in MAN during their residence testing also persisted at 447 mm Hg. Thus, differentiated ratings of perceived exertion were similar in MAN at their residence altitude and at 4,270 m, but not in LAN subjects. Several factors, including AMS, may have contributed to this group difference in the RPE response.

Effects of hypnosis on plasma proenkephalin peptide F and perceptual and cardiovascular responses during submaximal exercise.

Little information is available concerning the influence of subconscious mechanisms on neuroendocrine function, more specifically, proenkephalin peptide F release. Ten men [5 middle distance runners (21.6 (SD 0.54 years) and 5 untrained men (24.0 (SD 4.3 years)] consented to be volunteers in this investigation. Submaximal exercise intensities of 25% and 50% of peak oxygen consumption (VO2) (8 min stages) were used for both the control and hypnosis treatments. A traditional hypnotic induction was used, with the suggestion of two higher intensities of exercise stress (50% and 75% peak VO2) previously experienced in familiarization and testing by each subject. Each minute oxygen consumption was measured using open circuit spirometry, heart rate via an ECG, and ratings of perceived exertion (RPE) using the Borg scale. Plasma peptide F immunoreactivity (ir) [preproenkephalin-(107-140)] in blood sampled from an indwelling cannula was measured by radioimmunoassay at 7-8 min of each stage of the exercise test. Expected significant increases were observed for all cardiorespiratory and perceptual variables over the increasing exercise intensities and there were no significant differences between trained and untrained groups for peptide F if response patterns. Hypnosis did not significantly affect peptide F ir concentrations (P > 0.05) and did not significantly alter exercise heart rate, RPE or minute ventilation (P > 0.05). However, hypnosis did significantly increase oxygen consumption during exercise (P = 0.0095) but not of the magnitude needed for the metabolic demands of the higher exercise intensities. Thus, traditional hypnosis was unable to make functionally significant changes in the cardiorespiratory variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Substrate and hormone responses to exercise following a marathon run.

The aim of this study was to examine selected substrate and hormone responses to 30-min treadmill runs performed several days before and after a competitive marathon (42.2 km) to determine the time course for return of altered responses to pre-race levels. Six experienced male runners (30.8 +/- 9.1 years) ran at their predicted race pace (77.1% +/- 4.1% of VO2max) 8-7 days prior (S-1) to the Boston Marathon and 2-3 (S-2), 6-7 (S-3), and 13-14 days (S-4) post-marathon. All 30-min runs were performed in the morning at a constant time for each subject following a 12-h fast. Blood samples were drawn immediately before and immediately after (within 1 min) the 30-min runs. Post-exercise glucose responses were higher (P less than 0.05) during S-2 and S-3 compared with S-1 values. S-2 post-exercise lactate concentrations were also higher than the corresponding S-1 value. Pre-exercise free fatty acid (FFA) levels during S-4, and the post-exercise FFA values during S-2, S-3, and S-4, were lower (P less than 0.05) than the corresponding S-1 concentrations. Pre- and post-exercise alanine levels during S-2 were higher (P less than 0.05) than the S-1 values. Both pre- and post-exercise insulin levels during S-2, S-3, and S-4 were greater (P less than 0.05) than corresponding S-1 concentrations. Glucagon concentrations were unchanged across all sessions.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise responses after short- and long-term residence at 2,200 meters.

Submaximal and maximal exercise responses were examined in persons (age, 19-30 years) residing at a moderate altitude for different periods of time. Long-term residents (LTR; 44 males, 11 females) had lived continuously between 1,830 and 2,200 m for 2 years or longer before testing. Short-term residents (STR; 22 males, 30 females), previously lowlanders, arrived at 2,200 m within 10 to 21 days before testing. Incremented tests on a motor-driven treadmill were performed until voluntary exhaustion. Cardiorespiratory measures and ratings of perceived exertion (RPE) were examined at 60% and 100% of maximal oxygen uptake (VO2max). With the exception of minute ventilation (VE), which was higher (p less than 0.05) in STR females, maximal responses were comparable in STR and LTR females. All maximal responses were similar in STR and LTR males. Both VE and RPE at 60% VO2max were significantly higher in STR males and females than in their LTR counterparts. Plasma lipid responses to the maximal exercise may indicate a greater contribution of the triglyceride pool of adipose tissue to fatty acid mobilization during exercise in the LTR compared to STR male subjects.

Physiologic responses to heavy-resistance exercise with very short rest periods.

Heavy-resistance exercise utilizing very short rest periods is commonly used by body builders to prepare for competition. The purpose of this study was to compare the acute responses of this type of heavy-resistance exercise protocol in competitive body builders (BB) and power lifters (PL). Nine male BB and eight PL were matched for age, size and experience. A ten-station heavy-resistance exercise protocol was used. Each subject performed three sets of 10 repetition maximum (RM) with 10-s rest between sets and alternated 30-s and 60-s rest periods between exercises. No differences were observed in total work between the groups, but BB used a significantly (P less than 0.05) higher percentage of their 1 RM in the bench press and leg press exercises. Heart rate, ratings of perceived exertion (RPE), and lactate levels were obtained during the exercise protocol; significant (P less than 0.05) increases were observed above rest for these variables. RPE was significantly correlated with lactate levels (r = 0.84). Plasma epinephrine, norepinephrine, dopamine, cortisol, and lactate levels significantly increased from pre- to 5 min post-exercise. Mean plasma volumes were reduced -16.6 (+/- 3.64)% and -20.6 (+/- 8.32)% following the exercise protocol for BB and PL, respectively. Significant (P less than 0.05) decreases in eosinophil counts were observed following exercise. No significant differences were observed between BB and PL for any of the physiologic responses measured. PL exhibited a higher incidence (100%) of clinical symptoms of dizziness and nausea compared to BB (11.1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone, cortisol, and electrolyte responses to hypobaric hypoxia in moderate-altitude natives.

Serum aldosterone, cortisol, and electrolyte concentration, and urinary aldosterone and electrolyte excretion responses were examined in seven low-altitude natives (LAN) (373 m or less, aged 19-25 yr) and nine moderate-altitude natives (MAN) (1,830-2,200 m, aged 19-23 yr) for 2 d at their own residence (home) altitude (PB 740 or 585 mm Hg, respectively) and later for 2 d during decompression at a simulated altitude of 4,270 m (PB 447 mm Hg). The LAN group demonstrated higher (p less than 0.05) serum cortisol concentrations and respiration rates, and lower (p less than 0.05) serum aldosterone and potassium, and urinary aldosterone, sodium, and potassium concentrations at certain times during decompression compared to their home responses. Moderate-altitude native responses, on the other hand, were generally unchanged. Manifestations of acute mountain sickness at PB 447 mm Hg were also significantly greater in the LAN group. Thus, it appears that the MAN subjects were influenced less by the drop in ambient oxygen tension associated with PB 447 mm Hg.

Adrenocortical responses to maximal exercise in moderate-altitude natives at 447 Torr.

Serum hydrocortisone and aldosterone (Aldo) responses to maximal exercise were examined in six low-altitude natives (LAN) (373 m or less, aged 19-25 yr) and eight moderate-altitude natives (MAN) (1,830-2,200 m, aged 19-23 yr) at their residence (home) altitudes (740 and 587 Torr, respectively) and later in a hypobaric chamber at a simulated altitude of 4,270 m (447 Torr). After 2 days at their respective residence altitude and in the chamber, each subject exercised to voluntary exhaustion on the bicycle ergometer. Fluid intake was similar in both groups at all testing locations. Preexercise 24-h urinary Aldo was lower in both groups at 447 Torr but only significantly reduced in the LAN group. In general, the changes in maximum exercise cardiorespiratory variables were twice as large in LAN as in MAN subjects going from residence altitude to 447 Torr. Both serum hydrocortisone and Aldo concentrations were increased (P less than 0.01) after exercise in both groups at residence altitude and 447 Torr. Aldo was lower (P less than 0.05) postexercise at 447 Torr than at residence altitude in both groups, but this decrease was more pronounced (P less than 0.01) in the LAN group. Thus it appears that high-altitude Aldo concentrations are more like resident altitude values in MAN than in LAN subjects.

A category-ratio perceived exertion scale: relationship to blood and muscle lactates and heart rate.

The purpose of this investigation was to study the relationship between perceptual ratings from Borg's new category-ratio scale and some physiological variables during exercise. To accomplish this, scale ratings were related to blood and muscle lactate accumulation and heart rates during a progressive, maximal exercise test on the cycle ergometer. Ten physically active males were utilized as subjects; lactate data were recorded on only 7 of the 10 subjects. Three ratings of perceived exertion were made at each stage of the exercise test: leg effort (LE), cardiorespiratory effort (CE), and leg pain (LP). All ratings showed a positively accelerating increase with exercise intensity as did both blood and muscle lactate, while heart rate increased linearly. The exponents of the power functions describing the perceptual variation ranged from 1.63-1.67 compared to 2.2 for blood lactate and 2.7 for muscle lactate. Polynomial analysis revealed a similar quadratic trend for both perceptual and blood lactate data; however, muscle lactate demonstrated a cubic trend. No significant differences were found between CE and LE at 100, 200, and 300 W (P greater than 0.05). Subjects with the highest percentage of slow-twitch muscle fibers (mean ST%=51.14) rated LE and CE significantly lower ( mean of all power outputs, 0-300 W) than those with the lowest ST% (mean=34.52). It is concluded that the ratings from the category-ratio scale correspond very well with glycogenolytic metabolism leading to lactate accumulation during exercise.

Maximal exercise during hypobaric hypoxia (447 Torr) in moderate-altitude natives.

Six low-altitude natives (LAN) (373 m or less, aged 19-25 yr) and eight moderate-altitude natives (MAN) (1830-2200 m, aged 19-23 yr) were studied at both their residence (home) altitude (740 Torr and 587 Torr, respectively) and in a hypobaric chamber at a simulated altitude of 4270 m (447 Torr). Following a 2-d adaptation period, subjects performed an incremented test on the cycle ergometer until voluntary exhaustion. Significantly (P less than 0.05) greater differences in percent change of maximum exercise variables (total exercise time, exercise intensity, VO2, VCO2, VE/VO2 and HR) were noted in the LAN group than in the MAN group, going from their residence altitude to 447 Torr. The decrement in VO2max was 15% in the MAN group compared to 34% in the LAN group. The anaerobic threshold (% VO2max), estimated from VE BTPS measurements, was similar in both groups at residence altitude and at 447 Torr. In the morning prior to exercise testing at 447 Torr, LAN subjects reported greater (P less than 0.001) symptoms of acute mountain sickness (AMS) than MAN subjects. Our results indicate that, with respect to maximum exercise performance, moderate-altitude natives are at an advantage during early adaptation to hypobaric hypoxia.

Clinical applications of perceived exertion.

The purpose of this paper is to review those studies related to the clinical applications of perceived exertion. The Borg Scale has been used most widely to evaluate the subjective response of patients during graded exercise tests. More recently, ratings of perceived exertion (RPE) have been shown to be an accurate predictor of aerobic capacity. Appraisal of angina pectoris during exercise is discussed relative to its interaction with effort perceptions. Two groups of investigators have recently studied the validity of using stress-test perceptions to control exercise intensity during training. Caution is suggested when perceptual prescriptions are based upon estimation techniques in exercise tests but require production techniques by patients in exercise programs. One investigation was reviewed to illustrate the use of perceptual information in solving occupational problems: three lifting techniques were compared relative to perceptual acceptability, the recommended squat technique being the least acceptable. A variety of sport applications were discussed: perception of pace, sex differences in perception of effort, perceptual recovery from exercise, and the new Borg Category-Ratio Scale in the measurement of anaerobic stress and several recommendations were made for future study of clinical applications of perceived exertion.

Validity of perceptions during recovery from maximal exercise in men and women.

The Borg Scale, widely used to measure perceptions of exercise, has not been validated for use during recovery. Heart rate was used as the validity criterion. 11 untrained men and 10 untrained women were run to exhaustion on a treadmill. Heart rate and recovery ratings were obtained at :15, :45, 1:15, 1:45, 2:30, 3:30 and 4:30 min. following exercise. No significant differences were observed between sexes for both heart rate and recovery ratings. Trend analysis showed recovery ratings to be linear between :45 and at 4:30 while heart rate is best described by two linear trends with a break point at 2:30. Percent recovery was significantly faster for recovery ratings at :45, 1:15, 1:45 and 4:30. Heart rate and recovery ratings were not significantly correlated at any time point. A perceptual scale should be designed which more closely approximates metabolic response during recovery.

Cardio-respiratory and perceptual recovery from a marathon run.

Seven male runners (21--42 years) were examined before and after the 1976 Boston Marathon to provide data concerning the cardio-respiratory and perceptual recovery from the performance. Treadmill runs, 30 min in duration, were administered 1 week prior to the marathon and 2--3, 6--7 and 13--15 days following. Treadmill speed was held constant and based on each runner's planned race pace. Maximal performance data were collected 1 week before and 2 weeks after the race. Data were analyzed using a 2-way ANOVA (4 thirty min run data collection periods and 3 exercise time points--5, 15 and 30 min) and "t" tests. Treatment effects were not observed for either HR or VE, however, perceived exertion (RPE) was significantly elevated 2--3 and 6--7 days post-marathon and VO2 was significantly lower at 13--15 days. HR and RPE showed significant time effects indicating a non-steady state response. None of the maximal test variables were significantly displaced. All variables were returned to pre-marathon levels by 13--15 days except VO2 which was lower. Aerobic capacity was not a limiting factor in the recovery from a marathon run. Muscle soreness and stiffness seem to be related to the increased perceptual ratings following a marathon run.

Hyperthermia: effect on exercise prescription.

Ten healthy male university students pedaled a bicycle ergometer (Monark) for three sessions each lasting 30 minutes. Each subject worked at an individually predicted work load corresponding to approximately 40% of maximal aerobic capacity. The same predicted work load was conducted at 24 degrees C, 44 degrees C and 54 degrees C for each subject. For practical purposes, the results reveal approximately a one beat per minute increase in exercise heart rate for each 1 degree C increase in ambient temperature above neutral (24 degrees C). The practice of exercising cardiac patients in hot ambient temperatures which produce potentially hazardous heart rate levels was challenged. Seasonal reevaluation of exercise heart rate prescriptions is of importance. Hopefully, these findings will also be of some importance to various community gymnasiums and to self-motivated joggers.