THE EFFECT OF EXERCISE ON RENAL PLASMA FLOW IN NORMAL MALE SUBJECTS

Physiological confounders of renal blood flow measurement

OBJECTIVES

Renal blood flow (RBF) is controlled by a number of physiological factors that can contribute to the variability of its measurement. The purpose of this review is to assess the changes in RBF in response to a wide range of physiological confounders and derive practical recommendations on patient preparation and interpretation of RBF measurements with MRI.

METHODS

A comprehensive search was conducted to include articles reporting on physiological variations of renal perfusion, blood and/or plasma flow in healthy humans.

RESULTS

A total of 24 potential confounders were identified from the literature search and categorized into non-modifiable and modifiable factors. The non-modifiable factors include variables related to the demographics of a population (e.g. age, sex, and race) which cannot be manipulated but should be considered when interpreting RBF values between subjects. The modifiable factors include different activities (e.g. food/fluid intake, exercise training and medication use) that can be standardized in the study design. For each of the modifiable factors, evidence-based recommendations are provided to control for them in an RBF-measurement.

CONCLUSION

Future studies aiming to measure RBF are encouraged to follow a rigorous study design, that takes into account these recommendations for controlling the factors that can influence RBF results.

Food-Dependent Exercise-Induced Wheals/Angioedema, Anaphylaxis, or Both: A Systematic Review of Phenotypes

BACKGROUND

Food-dependent exercise-induced allergic reactions can manifest with wheals, angioedema, and anaphylaxis, alone or in combination.

OBJECTIVE

To systematically review the clinical manifestation, culprit foods and exercise, augmenting factors, comorbidities, and treatment options of each phenotype.

METHODS

Using predefined search terms, we assessed and analyzed the relevant literature until June 2021. Preferred Reporting Items for Systematic Reviews and Meta-Analysis recommendations were applied to this systematic review.

RESULTS

A total of 231 studies with 722 patients were included. The most common phenotype was anaphylaxis with wheals, angioedema, or both, reported in 80% of patients. This was associated with a higher number of anaphylactic episodes, augmenting factors, and use of on-demand antihistamine compared with the least common phenotype, anaphylaxis without wheals or angioedema, reported in 4% of patients. Anaphylaxis with wheals/angioedema was also associated with distinct characteristics compared with stand-alone wheals, angioedema, or both, in 17% of patients. Patients with anaphylaxis were older at the time of disease onset, less often had a history of atopy, showed more positive results in response to food and exercise provocation tests, had a more restricted spectrum of culprit foods, and more often used on-demand epinephrine.

CONCLUSIONS

The three phenotypes of allergic reactions to food and exercise differ in clinical characteristics, triggers, and response to treatment. Knowledge of these differences may help with patient education and counseling as well as disease management.

Renal and Endocrine Responses to Arm Exercise in Persons with Cervical Spinal Cord Injury

The aim of this study was to assess renal functions and endocrine responses to arm exercise in persons with cervical spinal cord injury (CSCI) under euhydrated conditions (free drinking of water), and to determine the physiological effects of exercise on renal function in these subjects. Eleven CSCI individuals (spinal lesions between C6 and C8, American Spinal Injury Association impairment scale A) and nine able-bodied (AB) persons rested for 30 min before performing 30 min arm-crank ergometer exercises at 50% of their maximum oxygen consumption, followed by 60-min of rest/recovery. Urine and blood samples were collected before and immediately after the exercise and recovery period. The CSCI patients showed no increase in plasma adrenaline and plasma renin activity compared with the AB controls, but showed similar changes in plasma aldosterone and the plasma antidiuretic hormone in response to the exercise. Creatinine clearance, osmolal clearance, free water clearance, and the fractional excretion of Na⁺ did not change during exercise in both groups of subjects, however free water clearance in the CSCI group was higher than in the AB group throughout the study. These findings suggested that activated plasma aldosterone without an increase in adrenaline or renin activity during exercise in CSCI individuals may reflect an adaptation to the disturbance of the sympathetic nervous system to compensate for renal function. As a result, no adverse effects of exercise on renal function in CSCI patients were observed.

Food-Dependent Exercise-Induced Wheals, Angioedema, and Anaphylaxis: A Systematic Review

BACKGROUND

Food-dependent exercise-induced wheals, angioedema, and anaphylaxis remain insufficiently characterized.

OBJECTIVE

We systematically reviewed the literature on clinical manifestations, laboratory investigations, culprit foods, triggering exercise, comorbidities, and treatment outcomes.

METHODS

Using predefined search terms and Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) recommendations, we searched 3 electronic databases to identify relevant literature published before July 2021.

RESULTS

Of 722 patients (median age 25 years; 55.4% male) from 231 studies (43 cohort studies, 15 cases series, and 173 case reports), 79.6% and 3.7% had anaphylaxis with and without wheals and/or angioedema, respectively. The remaining 16.6% had wheals and/or angioedema without anaphylaxis. The duration from eating to exercising and from exercising to symptom onset ranged from 5 minutes to 6 hours (median 1 hour) and from 5 minutes to 5 hours (median 30 minutes), respectively, and virtually all patients exercised within 4 hours after eating and developed symptoms within 1 hour after exercising. Wheat was the most common culprit food. Running was the most common trigger exercise. Most patients were atopic, and 1 in 3 had a history of urticaria. Aspirin and wheat-based products were the most frequent augmenting factors. On-demand antihistamines, corticosteroids, and epinephrine were commonly used and reported to be effective. Patients who stopped eating culprit foods before exercise no longer developed food-dependent exercise-induced allergic reactions.

CONCLUSIONS

Food-dependent exercise-induced allergic reactions are heterogeneous in their clinical manifestations, triggers, and response to treatment. Patients benefit from avoidance of culprit foods before exercise, which highlights the need for allergological diagnostic workup and guidance.

Physiological Function during Exercise and Environmental Stress in Humans-An Integrative View of Body Systems and Homeostasis

Claude Bernard's milieu intérieur (internal environment) and the associated concept of homeostasis are fundamental to the understanding of the physiological responses to exercise and environmental stress. Maintenance of cellular homeostasis is thought to happen during exercise through the precise matching of cellular energetic demand and supply, and the production and clearance of metabolic by-products. The mind-boggling number of molecular and cellular pathways and the host of tissues and organ systems involved in the processes sustaining locomotion, however, necessitate an integrative examination of the body's physiological systems. This integrative approach can be used to identify whether function and cellular homeostasis are maintained or compromised during exercise. In this review, we discuss the responses of the human brain, the lungs, the heart, and the skeletal muscles to the varying physiological demands of exercise and environmental stress. Multiple alterations in physiological function and differential homeostatic adjustments occur when people undertake strenuous exercise with and without thermal stress. These adjustments can include: hyperthermia; hyperventilation; cardiovascular strain with restrictions in brain, muscle, skin and visceral organs blood flow; greater reliance on muscle glycogen and cellular metabolism; alterations in neural activity; and, in some conditions, compromised muscle metabolism and aerobic capacity. Oxygen supply to the human brain is also blunted during intense exercise, but global cerebral metabolism and central neural drive are preserved or enhanced. In contrast to the strain seen during severe exercise and environmental stress, a steady state is maintained when humans exercise at intensities and in environmental conditions that require a small fraction of the functional capacity. The impact of exercise and environmental stress upon whole-body functions and homeostasis therefore depends on the functional needs and differs across organ systems.

Exhaustive Exercise Increases Spontaneous but Not fMLP-Induced Production of Reactive Oxygen Species by Circulating Phagocytes in Amateur Sportsmen

Strenuous exercise alters the oxidative response of blood phagocytes to various agonists. However, little is known about spontaneous post exercise oxidant production by these cells. In this cross-over trial, we tested whether an exhaustive treadmill run at a speed corresponding to 70% of VO2max affects spontaneous and fMLP-provoked oxidant production by phagocytes in 18 amateur sportsmen. Blood was collected before, just after, and 1, 3, 5 and 24 h post exercise for determination of absolute and normalized per phagocyte count spontaneous (a-rLBCL, rLBCL) and fMLP-induced luminol-enhanced whole blood chemiluminescence (a-fMLP-LBCL, fMLP-LBCL). a-rLBCL and rLBCL increased by 2.5- and 1.5-times just after exercise (p < 0.05) and then returned to baseline or decreased by about 2-times at the remaining time-points, respectively. a-fMLP-LBCL increased 1.7- and 1.6-times just after and at 3 h post-exercise (p < 0.05), respectively, while fMLP-LBCL was suppressed by 1.5- to 2.3-times at 1, 3, 5 and 24 h post-exercise. No correlations were found between elevated post-exercise a-rLBCL, a-fMLP-LBCL and run distance to exhaustion. No changes of oxidants production were observed in the control arm (1 h resting instead of exercise). Exhaustive exercise decreased the blood phagocyte-specific oxidative response to fMLP while increasing transiently spontaneous oxidant generation, which could be a factor inducing secondary rise in antioxidant enzymes activity.

Futility of current urine salbutamol doping control

Aims

Salbutamol is used in the management of obstructive bronchospasm, including that of some elite athletes. It is claimed that high salbutamol (oral) doses may also have an anabolic effect. Therefore, inhalation of salbutamol is restricted by the World Anti‐Doping Agency (WADA) to a maximal daily dose. Urine is tested for violations, but recent cases have resulted in a debate regarding the validity of this approach. It was our aim to determine whether current approaches are sufficiently able to differentiate approved usage from violations.

Methods

We extracted pharmacokinetic parameters from literature for salbutamol and its sulphated metabolite. From these parameters, a semi‐physiological pharmacokinetic model of inhaled and orally administered salbutamol was synthesized, validated against literature data, and used to perform clinical trial simulations (n = 1000) of possible urine concentrations over time resulting from WADA‐allowed and oral unacceptable dosages.

Results

The synthesized model was able to predict the literature data well. Simulations showed a very large range of salbutamol concentrations, with a significant portion of virtual subjects (15.4%) exceeding the WADA threshold limit of 1000 ng ml⁻¹ at 1 h post‐dose.

Conclusions

The observed large variability in urine concentrations indicates that determining the administered dose from a single untimed urine sample is not feasible. The current threshold inadvertently leads to incorrect assumptions of violation, whereas many violations will go unnoticed, especially when samples are taken long after drug administration. These issues, combined with the dubious assertion of its anabolic effect, leads us to conclude that the large effort involved in testing should be reconsidered.

Association between exercise intensity and renal blood flow evaluated using ultrasound echo

BACKGROUND

High-intensity exercise reduces renal blood flow (RBF) and may transiently exacerbate renal dysfunction. RBF has previously been measured invasively by administration of an indicator material; however, non-invasive measurement is now possible with technological innovations. This study examined variations in RBF at different exercise intensities using ultrasound echo.

METHODS

Eight healthy men with normal renal function (eGFR_cys 114 ± 19 mL/min/1.73 m²) participated in this study. Using a bicycle ergometer, participants underwent an incremental exercise test using a ramp protocol (20 W/min) until exhaustion in Study 1 and the lactate acid breaking point (LaBP) was calculated. Participants underwent a multi-stage test at exercise intensities of 60, 80, 100, 120, and 140% LaBP in Study 2. RBF was measured by ultrasound echo at rest and 5 min after exercise in Study 1 and at rest and immediately after each exercise in Study 2. To determine the mechanisms behind RBF decline, a catheter was placed into the antecubital vein to study vasoconstriction dynamics.

RESULTS

RBF after maximum exercise decreased by 51% in Study 1. In Study 2, RBF showed no significant decrease until 80% LaBP, and showed a significant decrease (31%) at 100% LaBP compared with at rest (p < 0.01). The sympathetic nervous system may be involved in this reduction in RBF.

CONCLUSIONS

RBF showed no significant decrease until 80% LaBP, and decreased with an increase in blood lactate. Reduction in RBF with exercise above the intensity at LaBP was due to decreased cross-sectional area rather than time-averaged flow velocity.

Repeated bouts of exhaustive exercise increase circulating cell free nuclear and mitochondrial DNA without development of tolerance in healthy men

Objective

Acute single strenuous exercise increases circulating cell free DNA (cf DNA). We tested whether three repeated bouts of exhaustive exercise induced the cf DNA response without development of tolerance in healthy men.

Methods

Eleven average-trained men (age 34.0±5.2 years, body mass index 26.2±3.1 kg/m2, maximal oxygen consumption—VO₂max 49.6±4.5 ml/kg*min) performed three treadmill exercise tests to exhaustion at speed corresponding to 70% VO₂max separated by 72 hours of resting. Blood was collected before and after each bout of exercise for determination of cell free nuclear and mitochondrial DNA (cf n-DNA, cf mt-DNA) by real-time PCR, selected markers of muscle damage, and blood cell count.

Results

Each bout induced the increase (p<0.05) in plasma cf n-DNA: from 3.4±1.4 to 38.5±27.5, from 4.1±3.3 to 48.5±26.2, and 3.1±1.6 to 53.8±39.9 ng/mL after the first, second, and third exercise, respectively. In a congruent way, cf mt-DNA rose significantly after the second (from 229±216 to 450±228*103 GE/mL) and third bout of exercise (from 173±120 to 462±314*103 GE/mL).

Pre-exercise cf mt-DNA decreased (p<0.05) by 2-times (from 355±219 before the first bout to 173±120*103 GE/mL before the third bout) over the study period and were accompanied by significant increase in white blood cells, platelets, creatine kinase, creatinine and lactate after each bout. However, the exercise induced percentage increment of cf n-DNA was always many times higher than corresponding increments of the afore-mentioned markers at any occasion.

Conclusions

Repeated bouts of exhaustive exercise induced remarkable increase in circulating cf n-DNA without signs of tolerance development. Baseline cf mt-DNA decreased in response to series of strenuous exercise. Since percentage increments of cf n-DNA in response to exercise were many times higher than those observed for other markers, measurement of circulating cf n-DNA could be a sensitive tool for monitoring acute exercise effects in human body.

Pathophysiological mechanisms of exercise-induced anaphylaxis: an EAACI position statement

This document is the result of a consensus on the mechanisms of exercise-induced anaphylaxis (EIAn), an unpredictable and potentially fatal syndrome. A multidisciplinary panel of experts including exercise physiologists, allergists, lung physicians, paediatricians and a biostatistician reached the given consensus. Exercise-induced anaphylaxis (EIAn) describes a rare and potentially fatal syndrome in which anaphylaxis occurs in conjunction with exercise. The pathophysiological mechanisms underlying EIAn have not yet been elucidated although a number of hypotheses have been proposed. This review evaluates the validity of each of the popular theories in relation to exercise physiology and immunology. On the basis of this evidence, it is concluded that proposed mechanisms lack validity, and it is recommended that a global research network is developed with a common approach to the diagnosis and treatment of EIAn in order to gain sufficient power for scientific evaluation.

Exercise augments weight loss induced improvement in renal function in obese metabolic syndrome individuals

OBJECTIVE

Metabolic syndrome (MetS) obesity is an independent risk factor for chronic kidney disease. This study was conducted to examine the effects of lifestyle interventions on renal parameters and putative metabolic, neuroadrenergic and hemodynamic mediators of renal injury.

METHODS

Untreated men and women (mean age 55 ± 1 years; BMI 32.7 ± 0.6 kg/m) without pre-existing renal dysfunction, who fulfilled MetS criteria were randomized to dietary weight loss (WL, n = 13), weight loss combined with aerobic exercise (WL + EX, n = 13), or no treatment (control, n = 12). Estimated glomerular filtration rate (eGFR), 24 h urinary albumin excretion, plasma renin activity (PRA), muscle sympathetic nerve activity (MSNA), baroreflex sensitivity (BRS), anthropometric, metabolic and fitness variables were measured at baseline and week 12.

RESULTS

Body weight decreased by -8.2 ± 0.8% in the WL and -10.7 ± 0.9% in the WL + EX groups (both P < 0.001). Fitness (maximal oxygen consumption) increased by 15 ± 5% and BRS by 5.5 ± 2.4 ms/mmHg in the WL + EX group only (P < 0.05). Serum creatinine decreased by -8.1 ± 4.8%, (WL, P = 0.016) and -14.9 ± 3.0% (WL + EX, P < 0.001). Estimated GFR increased commensurately but the increment was greater in the WL + EX group (P = 0.04). Albuminuria (P < 0.05) and MSNA (P < 0.001) decreased similarly in both groups, whereas PRA, high sensitivity C-reactive protein, uric acid and DBP decreased only in the WL + EX group (all P < 0.05).

CONCLUSION

Moderate weight loss in obese MetS patients is associated with a reduction in albuminuria and an improvement in eGFR which is augmented by exercise co-intervention.

Pathophysiology, diagnosis and management of exercise-induced anaphylaxis

PURPOSE OF REVIEW

The aim of this review is to challenge the current opinions of the pathophysiological mechanisms that give rise to food dependent exercise-induced anaphylaxis (FDEIA) and to consider these mechanisms within the wider context of exercise physiology to further inform our understanding and treatment of this condition.

RECENT FINDINGS

Exercise-induced anaphylaxis (food dependent and nonfood dependent) is a clinical syndrome in which anaphylaxis occurs in conjunction with exercise. Given the rarity of the condition, our current understanding relies on the many case studies and reviews of the topic. The pathophysiology of FDEIA remains to be fully elucidated with well constructed trials but current working hypotheses to date involve alterations in plasma osmolaltiy and pH, tissue enzyme activity, blood flow redistribution, altered gastrointestinal permeability and facilitated epitope recognition/allergen binding.

SUMMARY

Implications for future research are the physiological changes that occur during exercise need deeper consideration to ensure that proposed mechanisms are realistic and actually occur within the time frame and exercise-intensity domain during which the reported FDEIA occurred. These theories must be tested rigorously with sufficiently powered studies if progress is to be made in determining the perplexing pathophysiology of FDEIA.

Magnetic resonance nephrourographic techniques and applications: how we do it

Chronic kidney disease is a significant public health problem, and a comprehensive evaluation of renal disease often requires accurate evaluation of both kidney structure and function. Magnetic resonance (MR) nephrourography refers to newly developed imaging techniques that have the ability to provide a quantitative assessment of renal function, especially glomerular filtration rate and renal blood flow. Our review outlines several different methodologies that are present in the literature and also details the specifics of our own methods for renal imaging. Though varied, all MR imaging methods use the common steps of image acquisition, image postprocessing, and tracer kinetics modeling of the processed image data. The optimal methodology should be practical and based primarily on simplicity, speed, and reproducibility. The combination of anatomic and quantitative functional information of the kidneys provided by MR imaging allows for a safe, comprehensive evaluation of renal disease, with particular utility in the settings of urinary tract obstruction and renal transplantation.

Effect of exercise on fluid balance and renal function in horses

Exercise places large demands on the equine cardiovascular system which are further complicated by environmental factors. In many respects, performance is limited by fluid and electrolyte stores and the ability to maintain cardiovascular and thermoregulatory stability in the face of severe sweat losses. Studies in the exercising horse have been primarily descriptive or associative, with only a limited number seeking to identify physiologic mechanisms associated with the control of fluid and electrolyte balance. More mechanistic studies are needed to fully understand the integration of the cardiovascular, endocrine, and renal systems in the defense of plasma osmolality, blood volume, and blood pressure.

Effect of age on renal blood flow during exercise

The present study examined the effect of age on the control of renal blood flow (RBF; PAH clearance) and renal vascular conductance (RVC = RBF/mean arterial pressure) during and after a bout of dynamic exercise in a warm environment. Six healthy fit older men (O; 67 +/- 1 years) and 6 young men (Y; 24 +/- 2 years) were matched for body size, adiposity, and maximal oxygen uptake (VO2max). Subjects exercised at approximately 50% of VO2max for 90 minutes in an environment of 30 degrees C, 60% humidity on each of 4 consecutive days, with data collected on days 1 and 4. There was no effect of repeated days of exercise on RBF or RVC, despite a 4% expansion of blood volume in Y (< 1% in O). On each day, resting RBF was significantly lower in O (e.g., Y = 1127 +/- 67, O = 852 +/- 114 mL/min on day 1; p < 0.05). During exercise, Y decreased RBF to a significantly (p < 0.05) greater extent [-508 (-45%) and -365 (-36%) mL/min on days 1 and 4, respectively] than the O [-98 (-12%) and -83 (-12%) mL/min]. RVC followed a similar pattern, decreasing by 52% and 37% during exercise for Y vs only 15% and 13% for O. The relationships between delta RBF and HR and delta RBF and plasma norepinephrine concentration were independent of age, implying similar sympathetic control during exercise. During recovery, RBF and RVC increased as expected in Y, but continued to decrease in O, falling significantly below exercise values (p < 0.05). Compared to young men, fit healthy older men redistribute less blood flow away from the kidneys during dynamic exercise in the heat, an effect which appears to result from the existence of a smaller resting RBF rather than differential sympathetic control. On the other hand, chronological age seems to be associated with altered control of RBF and RVC during recovery from exercise.

Renal hemodynamics and cardiovascular reactivity in the prehypertensive stage

To examine whether sympathetic nervous activation has an impact on renal circulation in subjects at risk for high blood pressure, we assessed renal hemodynamics and cardiovascular response to mental stress in 40 healthy young white males, 12 normotensive subjects without and 14 with familial hypertension, and 14 with borderline hypertension. The response of systolic and diastolic blood pressure to mental stress was assessed while each patient performed a mental arithmetic task; this was taken as the parameter for the activation of the sympathetic nervous system. Renal plasma flow was measured by para-aminohippuric acid clearance under steady-state conditions. In parallel, glomerular filtration rate as a parameter for functional impairment of the kidneys was determined by creatinine clearance, and filtration fraction was also calculated. Patients with borderline hypertension were characterized by a reduced renal blood flow and increased filtration fraction in comparison with both normotensive groups. The increase in systolic blood pressure during mental stress was more pronounced in borderline hypertensives. We observed no significant difference in renal hemodynamics and cardiovascular response to mental stress between normotensives with and without a family history of hypertension. In the total population, cardiovascular response to mental stress was correlated with renal hemodynamics: The greater the increase in systolic blood pressure during mental stress, the lower was the renal plasma flow and the greater the filtration fraction. Thus, renal plasma flow was found to be already reduced and filtration fraction increased before sustained hypertension developed. Because this pattern in renal hemodynamics was related to cardiovascular response to mental stress, our data suggest that sympathetic activation already appeared to affect renal hemodynamics at the onset of essential hypertension.

Reference values for resting blood flow to organs of man

The lack of a reliable quantitative description of blood flow in man has hampered the development of accurate biokinetic models of essential elements, drugs, imaging agents, and carcinogens. In this paper we review and analyse data on blood flow and identify representative percentages of cardiac output and absolute blood flow rates to organs and tissues of man for use as reference values for biokinetic models. To keep the review and analysis to a manageable size we have limited attention to the resting state and have suggested reference values for absolute and relative flow rates only for adult males and females.

Renal protein excretion after exercise in man

Thirteen men were submitted to graded exhaustive cycle exercise to determine the kinetics of proteinuria in the recovery period. Venous blood samples were analysed for haematocrit, lactate, creatinine, total protein and albumin for 1 h following exercise. Urine samples were collected during a 3-h recovery period. Total protein, albumin, and creatinine levels were determined for these samples. Total protein and albumin urinary excretion increased to 581 and 315 micrograms min-1, respectively, at the end of the 1st h of recovery as compared to 42 and 15 micrograms.min-1 for resting values. Plasma volume returned to pre-exercise levels between 30 and 60 min after cessation of exercise, while urinary total protein and albumin content still remained above the resting values for the following 2 h. Both post-exercise urinary total protein and albumin excretion followed a logarithmic decline with the same half-life of 54 min, thus requiring about 4 h to regain resting values. The reduction of plasma volume and the degree of dehydration do not seem to be involved in the process. The present study indicates the delayed recovery of protein handling by the kidney, as compared with other biochemical parameters, and provides accurate information on the kinetics of post-exercise proteinuria.

Norepinephrine spillover to plasma during steady-state supine bicycle exercise. Comparison of patients with congestive heart failure and normal subjects

This study was performed to determine the relative contributions of plasma norepinephrine clearance and norepinephrine release to the increase in plasma norepinephrine concentration that occurs during exercise and to determine whether the high rates of cardiac norepinephrine release from the heart and kidney in patients with heart failure are associated with diminished reserve for regional sympathetic nervous stimulation. During supine steady-state bicycle exercise at 50% of maximum voluntary exercise capacity, the plasma norepinephrine concentration of six patients with congestive heart failure rose from 385 +/- 88 to 2,200 +/- 497 pg/ml, whereas that of nine normal subjects rose from 208 +/- 21 to 882 +/- 257 pg/ml. The change in plasma concentration in both groups was due to an increase in norepinephrine spillover to plasma without a change in plasma norepinephrine clearance. In patients with heart failure, cardiac spillover increased from 80 +/- 26 to 528 +/- 265 ng/min during exercise, and renal spillover rose from 146 +/- 71 to 418 +/- 69 ng/min. In the normal subjects, cardiac spillover rose from 5 +/- 2 to 73 +/- 23 ng/min, and renal spillover increased from 76 +/- 27 to 275 +/- 106 ng/min. There is no evidence of a reduced reserve for overall or regional sympathetic stimulation in patients with heart failure. Reduced reflex responses in these patients are more likely due to end-organ refractoriness than to inadequate stimulation.

The effects of posture on the pharmacokinetics of intramuscular benzylpenicillin

Previous reports have produced conflicting results as to whether changes in posture affected the pharmacokinetics of the penicillins. We have studied the pharmacokinetics of intramuscularly administered benzylpenicillin in normal subjects during bedrest and ambulation and compared it with data obtained following intravenous administration of the same dose to the same subjects under the same conditions. The values of area under the curve, total clearance, mean residence time and renal clearance found during ambulation were 1175 (min.min.l-1), 488 (ml.min-1), 101 (min), and 264 (ml.min-1) (means). The corresponding values for bedrest were 1032 (min.mg.l-1), 544 (ml.min-1), 96.7 (min), and 315 (ml.min-1). There was a significant difference between the areas under the curve with change of posture but not between any of the other pharmacokinetic variables. The differences observed in this study are unlikely to be of clinical relevance. We suggest that the differences between the results of this study and those of previous studies may be related to the level of exercise undertaken by the subjects in the various studies.

Myocardial uptake and clearance of thallium-201 in normal subjects: comparison of dipyridamole-induced hyperemia with exercise stress

Thallium-201 uptake and clearance after dipyridamole infusion may differ from that after exercise stress because the hemodynamic effects of these two interventions are different. In this study of normal volunteers, thallium kinetics after dipyridamole (n = 13) were determined from three serial image sets (early, intermediate and delayed) and from serial blood samples and compared with thallium kinetics after exercise (n = 15). Absolute myocardial thallium uptake was greater after dipyridamole compared with exercise (p less than 0.0001), although the relative myocardial distribution was similar. The myocardial clearance (%/h) of thallium was slower after dipyridamole than it was after exercise. Comparing dipyridamole and exercise, the differences in clearance were large from the early to the intermediate image (anterior, -11 +/- 17 versus 24 +/- 5, p = 0.0005; 50 degrees left anterior oblique, -7 +/- 11 versus 15 +/- 8, p = 0.004; 70 degrees left anterior oblique, 3 +/- 9 versus 21 +/- 6, p = 0.001). In contrast, the differences in clearance were small from the intermediate to the delayed image (anterior, 15 +/- 4 versus 20 +/- 2, p = 0.025; 50 degrees left anterior oblique, 15 +/- 4 versus 19 +/- 3, p = 0.13; 70 degrees left anterior oblique, 15 +/- 3 versus 18 +/- 2, p = 0.047). Thallium uptake and clearance in the liver, splanchnic region and spleen were greater after dipyridamole (p less than 0.001). Blood thallium levels were greater after dipyridamole (p less than 0.05) and cleared more slowly (p = 0.07). Thus, myocardial thallium-201 uptake and clearance after dipyridamole infusion differ from thallium kinetics after exercise. This difference is, in part, related to associated differences in extracardiac and blood kinetics. Diagnostic criteria for the detection of abnormal thallium-201 clearance must be specific for the type of intervention.

The effect of posture on the pharmacokinetics of intravenous benzylpenicillin

We have studied the pharmacokinetics of intravenously administered benzylpenicillin in normal subjects during bedrest and during ambulation. The values of total body clearance, mean residence time, and renal clearance found during ambulation were 487.4 +/- 100.5 ml/min, 36.23 +/- 13.45 min, and 309.4 +/- 93.4 ml/min (means +/- SD). The corresponding values for bedrest were 543.6 +/- 122.6 ml/min, 35.27 +/- 10.21 min, and 324.1 +/- 145.3 ml/min. There were no significant differences between any of these pharmacokinetic variables with the change in posture. These results differ from previously reported results for the effects of posture on the pharmacokinetics of penicillins administered by extravascular routes, and suggest that the absorption of benzylpenicillin may be dependent on posture.

On the mechanism of renin release during experimental myocardial ischaemia

An increase in plasma renin activity (PRA) following experimental coronary occlusion has previously been demonstrated in anaesthetized and conscious dogs. The purpose of the present study was to analyse the mechanism of this renin release. In two distinct models of myocardial ischaemia in anaesthetized dogs--i.e. occlusion of the left-anterior descending coronary artery (model A, n = 21) and atrial pacing in the presence of stenosis of the left-anterior descending coronary artery (model B, n = 23), an increase in arterial PRA was found from 1.68 +/- 0.43 to 3.06 +/- 0.63 ng ml-1 h-1 (model A, mean +/- SEM, P less than 0.025) and from 9.87 +/- 3.59 to 14.96 +/- 4.06 ng ml-1 h-1 (model B, P less than 0.05), respectively. The increase in PRA following coronary occlusion was not blunted by adrenergic beta-receptor blockade with propranolol (3 mg kg-1 i.v.; n = 4). Coronary sinus PRA was lower than arterial PRA and the increase in PRA did not occur in nephrectomized dogs (n = 5). The data suggest that myocardial ischaemia induces a release of renin from the kidney which is not mediated by adrenergic beta receptors.

Effect of posture on ampicillin pharmacokinetics, glomerular filtration rate and renal plasma flow in resting subjects

Differences in drug kinetics between supine rest and ambulation have been reported, but the relative contribution of postural changes and changes in the level of physical activity has not been evaluated. Ampicillin pharmacokinetics, glomerular filtration rate (GFR) and renal plasma flow (RPF) were studied in six male volunteers at rest in the sitting and lying position with an interval of 1 week. After intravenous administration ampicillin kinetics, analyzed according to a two-compartment open model, demonstrated significant changes in drug distribution when the position was changed from lying to sitting: alpha-increased by 50%, V1 and V beta increased by 19% and 22% respectively. Ampicillin clearance, the fraction of dose recovered from urine, GFR and RPF were, however, not influenced by the change in posture. Our data on effects of posture in resting subjects suggest that previously reported differences in drug elimination and RPF between lying and ambulatory subjects are largely due to differences in the level of physical activity.

Exercise-induced proteinuria in children and adolescents

Urinary albumin and beta 2-microglobulin excretion rates were measured by radioimmunological methods in 60 children and adolescents at rest and during physical exercise. The geometric mean of the albumin excretion rate was 4.4 (microgram/min)/m2 at rest and rose to 7.9 (micrograms/min)/m2 during exercise (P less than 0.001), while the geometric mean of beta 2-microglobulin was 31.9 (ng/min)/m2 at rest and 26.2 (ng/min)/m2 during exercise. These results indicate that exercise-induced proteinuria is of a glomerular leaking type. The albumin excretion rate was not dependent on the age or sex of the subjects. The exercise-induced albuminuria correlated weakly but significantly with the maximal blood pressure (r = 0.27; P less than 0.05) and with the physical fitness of the subjects (r = 0.28; P less than 0.05).

Effects of exercise on plasma viscosity in athletes and sedentary normal subjects

To assess the immediate and long-term effects of exercise on factors regulating blood flow, we measured plasma viscosity (eta p) and plasma renin activity (PRA) in 17 trained runners and 16 sedentary healthy subjects before and 10 min after graded treadmill exercise. Resting eta p was lower in runners primarily because of significantly lower fibrinogen concentration. Compared to nonrunners with similar 24-h urine electrolyte excretion rates, runners were characterized by lower PRA at rest. In view of the overall correlation between heart rate and PRA before exercise, reduced adrenergic tone was probably a major factor contributing to the lower PRA in runners. After exercise, plasma viscosity and PRA exceeded control levels, and were similar in magnitude in runners and sedentary subjects. Changes in plasma viscosity were less than expected from the degree of hemoconcentration, primarily because enhanced fibrinolysis maintained fibrinogen level constant. To the extent that plasma viscosity affects viscous flow resistance, the results suggest that tissue perfusion and oxygen delivery rate at rest are greater in trained runners than in sedentary subjects, but these variables become similar after maximum exertion.

Effect of exercise on renal clearance of atenolol

The effect of exercise on plasma atenolol was evaluated using a two-phase complete crossover study in 12 healthy volunteers. In one phase, the volunteers were subjected to physical exertion on a treadmill; in the other phase, they remained in a sitting or standing position. Following a single 100-mg atenolol dose, frequent blood samples and a complete urine collection were obtained over 24 hr. Plasma and urine atenolol levels were assayed by high-pressure liquid chromatography. Plasma atenolol was significantly (p less than 0.05) higher during the exercise phase of the study, and this result was associated with approximately an 8% decrease in the renal clearance of the drug, probably due to decreased renal blood flow during exercise.

Increased glomerular permeability to albumin induced by exercise in diabetic subjects

The urinary excretion of albumin was measured in insulin-dependent diabetics under ordinary conditions of life and in response to exercise. Possible mechanisms of exercise induced albuminuria in diabetics were also investigated. Under ordinary conditions of life the insulin-treated diabetics, as a group, had a higher mean urinary albumin excretion than normal controls; however, half of the diabetics had albumin excretion rates within the control range. A given exercise load (600 kpm/min for 20 min) produced an exaggerated albumin excretion in diabetics, particularly evident in the post-exercise period. The elevated urinary albumin excretion was due to an increased transglomerular passage of albumin, not to reduced tubular reabsorption. The increase was not associated with differences in blood pressure or urine flow between controls and diabetics. This exercise test has proved to be a suitable provocation test to unmask abnormalities in the glomerular handling of albumin that might not be recognisable at rest.

Cardiovascular adjustments to exercise: hemodynamics and mechanisms

The integrated response to severe exercise involves fourfold to fivefold increases in cardiac output, which are due primarily to increases in cardiac rate and to a lesser extent to augmentation of stroke volume. The increase in stroke volume is partly due to an increase in end-diastolic cardiac size (Frank-Starling mechanism) and secondarily due to a reduction in end-systolic cardiac size. The full role of the Frank-Starling mechanism is masked by the concomitant tachycardia. The reduction in end-systolic dimensions can be related to increased contractility, mediated by beta adrenergic stimulation. Beta adrenergic blockade prevents the inotropic response, the decrease in end-systolic dimensions, and approximately 50% of the tachycardia of exercise. The enhanced cardiac output is distributed preferentially to the exercising muscles including the heart. Blood flow to the heart increases fourfold to fivefold as well, mainly reflecting the augmented metabolic requirements of the myocardium due to near maximal increases in cardiac rate and contractility. Blood flow to the inactive viscera (e.g., kidney and gastrointestinal tract) is maintained during severe exercise in the normal dog. It is suggested that local autoregulatory mechanisms are responsible for maintained visceral flow in the face of neural and hormonal autonomic drive, which acts to constrict renal and mesenteric vessels and to reduce blood flow. However, in the presence of circulatory impairment, where oxygen delivery to the exercising muscles is impaired as occurs to complete heart block where normal heart rate increases during exercise are prevented, or in congestive right heart failure, where normal stroke volume increases during exercise are impaired, or in the presence of severe anemia, where oxygen-carrying capacity of the blood is limited, visceral blood flows are reduced drastically and blood is diverted to the exercising musculature. Thus,, visceral flow is normally maintained during severe exercise as long as all other compensatory mechanisms remain intact. However, when any other compensatory mechanism is disrupted (even the elimination of splenic reserve in the dog), reduction and diversion of visceral flow occur.

Elevation in set point for body temperature regulation after prolonged exercise

1. In nine healthy men, after prolonged exercise (approximately 37 km walk and 2.5 km ascent and descent in 9 hr) deep body temperature at rest stabilized at a higher level than in the absence of previous exercise.2. The increase, approximately 0.36 degrees C, was recorded at both oral and rectal sites. It persisted while the subjects rested in warm and in cool surroundings, and disappeared about 11 hr after the end of exercise.3. The increase in body temperature after exercise was accompanied by a similar increase in the body temperature at which sweating started during body heating.4. After exercise the subjects' metabolic response to cold air (13.6 degrees C) was normal or increased in spite of the elevation in body temperature.5. Blood glucose concentration was never lower than 3.1 mM during these experiments.6. The temperature changes are most easily explained by mild pyrexia due to the release of endogenous pyrogen associated with minor tissue damage.

Regulation of the renal circulation during severe exercise in normal dogs and dogs with experimental heart failure

The role of sympathetic nerves and circulating catecholamines in mediating the renal vascular response to severe exercise was examined in normal dogs and dogs with experimental heart failure, using paired normal and denervated kidneys. In normal dogs, mean arterial blood pressure increased gradually from 97 ± 4 to 137 ± 6 mm Hg, renal blood flow remained at control levels, and renal vascular resistance rose from 0.57 ± 0.04 to 0.84 ± 0.15 mm Hg/ml min -1 during peak steady-state exercise. The increase in resistance was similar in the denervated renal bed and persisted after alpha-receptor blockade. Exercise in dogs with heart failure increased mean arterial blood pressure slightly from 103 ± 4 to 111 ± 5 mm Hg. In the innervated kidney, blood flow dropped precipitously from 148 ± 6 to 46 ± 9 ml/min, and renal resistance increased from 0.73 ± 0.08 to 3.35 ± 0.53 mm Hg/ml min -1 . In the denervated kidney, renal blood flow decreased from 174 ± 12 to 120 ± 1 ml/min, and resistance increased from 0.59 ± 0.07 to 0.94 ± 0.09 mm Hg/ml min -1 . After alpha-receptor blockade, the decrease in flow and the increase in resistance to the denervated kidney were further attenuated. Thus, in normal, healthy dogs, the contribution of adrenergic mechanisms to renal vascular regulation appears to be minimal; blood flow remains constant in the presence of elevated pressure, suggesting that autoregulation is responsible for the elevated renal resistance during exercise. In dogs with experimental heart failure, intense renal sympathetic vasoconstriction prevails throughout exercise; the major portion of this response is neurally mediated, with an additional contribution by circulating catecholamines.

Effects of experimentally produced heart failure on the peripheral vascular response to severe exercise in conscious dogs

The peripheral vascular response to severe exercise in eight dogs with heart failure produced by tricuspid avulsion and progressive pulmonary stenosis was compared to the response determined in eight control dogs. After full recovery from implantation of Doppler flow probes and miniature pressure gauges, measurements of arterial blood pressure and blood flow were telemetered from untethered dogs running behind a mobile recording vehicle at speeds of 10-25 mph over distances averaging 1 mile. Severe exercise in control dogs increased heart rate from 78 to 281 beats/min and mean arterial blood pressure from 93 to 134 mm Hg. Iliac blood flow rose from 151 to 897 ml/min, but mesenteric and renal blood flows did not change significantly. Iliac vascular resistance decreased from 0.64 to 0.15 mm Hg/ml min -1 , but mesenteric vascular resistance increased from 0.31 to 0.47 mm Hg/ml min -1 and renal vascular resistance increased from 0.49 to 0.75 mm Hg/ml min -1 . Severe exercise in dogs with heart failure increased heart rate from 102 to 274 beats/min, but mean arterial blood pressure only increased from 100 to 107 mm Hg. Iliac blood flow rose from 96 to 360 ml/min, whereas mesenteric blood flow decreased from 237 to 89 ml/min and renal blood flow decreased from 226 to 79 ml/min. Iliac vascular resistance decreased from 1.09 to 0.34 mm Hg/ml min -1 , but mesenteric vascular resistance increased from 0.49 to 1.31 mm Hg/ml min -1 and renal vascular resistance increased from 0.47 to 1.81 mm Hg/ml min -1 . Thus, in heart failure a distinctly abnormal peripheral vascular response to severe exercise occurs, characterized by a very small elevation in mean arterial blood pressure and intense visceral vasoconstriction resulting in diversion of visceral blood flows.

The peripheral vascular response to severe exercise in untethered dogs before and after complete heart block

The peripheral vascular response to severe exercise was studied in 11 healthy conscious dogs instrumented with Doppler ultrasonic flow probes on the mesenteric, renal, and iliac arteries, and miniature pressure gauges in the aorta. The response to severe exercise was restudied in six of these dogs after recovery from a second operation producing complete heart block by the injection of formalin into the atrioventricular (AV) node. Three of these dogs also exercised while their ventricles were paced at rates of 100/min and 200/min. The untethered normal dogs ran at speeds of 15-25 miles/hr behind a mobile recording unit for a distance averaging 1.5 miles, while continuous measurements of arterial blood pressure and blood flow were telemetered and recorded on magnetic tape. Severe exercise in normal dogs increased heart rate from 84 to 259/min, arterial pressure from 89 to 140 mm Hg, flow resistance in the mesenteric and renal beds by 59 and 52% respectively, and iliac blood flow 479% above control, while mesenteric and renal blood flows remained constant and iliac resistance decreased by 73%. In dogs with complete AV block, severe exercise at speeds of 10-18 miles/hr increased heart rate from 47 to 78/min, mean arterial pressure from 81 to 89 mm Hg, iliac flow 224%, resistance in the renal bed by 273%, and mesenteric bed by 222% while it decreased blood flow in mesenteric and renal beds by 61 and 65% respectively, and iliac resistance by 62%. A similar response occurred during exercise with pacing at 100/min, but when paced at 200/min a more normal exercise response reappeared. Thus, in normal dogs the peripheral vascular response to severe exercise involved increases in heart rate, arterial pressure and visceral resistance but visceral blood flow did not decrease. In dogs with heart block, where the ability to increase heart rate is severely compromised, compensatory reduction of mesenteric and renal blood flows occurred.

Effects of carotid sinus nerve stimulation on blood-flow distribution in conscious dogs at rest and during exercise

The effects of stimulating the carotid sinus nerves on the distribution of cardiac output and peripheral vasoactivity was studied in intact, unanesthetized dogs instrumented with ultrasonic or electromagnetic flow probes on the ascending aorta, mesenteric, renal, and iliac arteries, and miniature pressure gauges in the aorta. A radiofrequency pacemaker was used to stimulate the nerves in dogs at rest, during treadmill exercise, and after autonomic blockade. Thirty-second periods of stimulation in the resting dog resulted in an average decrease in aortic pressure of 28%, cardiac output remained unchanged, total peripheral resistance fell 29%, mesenteric flow 12%, mesenteric vascular resistance 18%, renal flow 8%, and renal vascular resistance 22%. In the iliac bed flow increased by 90% while resistance declined by 62%. Heart rate decreased initially by 13%, and returned to control during stimulation. The bradycardia was determined to be predominantly due to vagal stimulation. During treadmill exercise carotid sinus nerve stimulation resulted in similar decreases in arterial pressure, mesenteric and renal resistance, and a further decrease in iliac resistance from exercise control values. Thus, electrical stimulation of the carotid sinus nerves in the conscious dog produced a differential pattern of peripheral vasodilatation, the most profound dilatation being observed in the hind-limb circulation. This release of sympathetic tone also occurred during stimulation in exercising animals when the muscular bed was already dilated on a metabolic basis.

Similarity of blood flow in the normal and the sympathectomized dog hind limb during graded exercise

The possibility of sympathetic vasoconstrictor control of blood flow to active muscles was studied in dogs during graded exercise by comparing the blood flow in the normal with that in the Sympathectomized hind limb. Blood flow was measured by electromagnetic flow transducers around each external iliac artery, or inferred from the oxygen saturation of blood samples from the common iliac veins. The dogs either ran for successive periods of 3 minutes at 5.5 km/hr and grades of 0, 7, 14, 21, and 28% or ran each level of exercise separately. Unilateral lumbar sympathectomy (L-2 through L-7) was performed when the flow transducers were implanted or later by a snare technique. The latter allowed observations during exercise as early as 4 hours after sympathectomy. The magnitude of limb blood flow during exercise and the decline of exercise hyperemia were similar in the normal and the sympathectomized limb, as were the changes in the oxygen saturation of limb venous blood. However, electric stimulation of the lumbar sympathetic chain at the L-5 level in the conscious dog by a chronically implanted electrode reduced limb blood flow at all levels of exercise, the maximal flow of 1,000 ml/min was almost halved.

Physical training in the management of coronary artery disease

The effects of 4 to 6 weeks' physical conditioning on the cardiovascular and respiratory response to exercise were studied in nine patients with coronary artery disease. Clinical improvement and increased physical working capacity were observed in all patients. The average cardiac output during exercise was unchanged. The stroke volume increased and the myocardial work, assessed by the tension-time index, decreased during exercise at a given work load. It is suggested that at submaximal work loads a reduction of the blood flow to the working muscles occurs after training. Such change might be fundamental for the altered circulatory regulation by allowing a reduced general sympathetic vasoconstriction during exercise. It is concluded that the hemodynamic changes form a rational physiologic basis for the use of physical training in the management of patients with coronary artery disease.