Infection after total joint replacement of the hip and knee: research programme including the INFORM RCT

Background

People with severe osteoarthritis, other joint conditions or injury may have joint replacement to reduce pain and disability. In the UK in 2019, over 200,000 hip and knee replacements were performed. About 1 in 100 replacements becomes infected, and most people with infected replacements require further surgery.

Objectives

To investigate why some patients are predisposed to joint infections and how this affects patients and the NHS, and to evaluate treatments.

Design

Systematic reviews, joint registry analyses, qualitative interviews, a randomised controlled trial, health economic analyses and a discrete choice questionnaire.

Setting

Our studies are relevant to the NHS, to the Swedish health system and internationally.

Participants

People with prosthetic joint infection after hip or knee replacement and surgeons.

Interventions

Revision of hip prosthetic joint infection with a single- or two-stage procedure.

Main outcome measures

Long-term patient-reported outcomes and reinfection. Cost-effectiveness of revision strategies over 18 months from two perspectives: health-care provider and Personal Social Services, and societal.

Data sources

National Joint Registry; literature databases; published cohort studies; interviews with 67 patients and 35 surgeons; a patient discrete choice questionnaire; and the INFORM (INFection ORthopaedic Management) randomised trial.

Review methods

Systematic reviews of studies reporting risk factors, diagnosis, treatment outcomes and cost comparisons. Individual patient data meta-analysis.

Results

In registry analyses, about 0.62% and 0.75% of patients with hip and knee replacement, respectively, had joint infection requiring surgery. Rates were four times greater after aseptic revision. The costs of inpatient and day-case admissions in people with hip prosthetic joint infection were about five times higher than those in people with no infection, an additional cost of > £30,000. People described devastating effects of hip and knee prosthetic joint infection and treatment. In the treatment of hip prosthetic joint infection, a two-stage procedure with or without a cement spacer had a greater negative impact on patient well-being than a single- or two-stage procedure with a custom-made articulating spacer. Surgeons described the significant emotional impact of hip and knee prosthetic joint infection and the importance of a supportive multidisciplinary team. In systematic reviews and registry analyses, the risk factors for hip and knee prosthetic joint infection included male sex, diagnoses other than osteoarthritis, high body mass index, poor physical status, diabetes, dementia and liver disease. Evidence linking health-care setting and surgeon experience with prosthetic joint infection was inconsistent. Uncemented fixation, posterior approach and ceramic bearings were associated with lower infection risk after hip replacement. In our systematic review, synovial fluid alpha-defensin and leucocyte esterase showed high diagnostic accuracy for prosthetic joint infection. Systematic reviews and individual patient data meta-analysis showed similar reinfection outcomes in patients with hip or knee prosthetic joint infection treated with single- and two-stage revision. In registry analysis, there was a higher rate of early rerevision after single-stage revision for hip prosthetic joint infection, but, overall, 40% fewer operations are required as part of a single-stage procedure than as part of a two-stage procedure. The treatment of hip or knee prosthetic joint infection with early debridement and implant retention may be effective in > 60% of cases. In the INFORM randomised controlled trial, 140 patients with hip prosthetic joint infection were randomised to single- or two-stage revision. Eighteen months after randomisation, pain, function and stiffness were similar between the randomised groups (p = 0.98), and there were no differences in reinfection rates. Patient outcomes improved earlier in the single-stage than in the two-stage group. Participants randomised to a single-stage procedure had lower costs (mean difference –£10,055, 95% confidence interval –£19,568 to –£542) and higher quality-adjusted life-years (mean difference 0.06, 95% confidence interval –0.07 to 0.18) than those randomised to a two-stage procedure. Single-stage was the more cost-effective option, with an incremental net monetary benefit at a threshold of £20,000 per quality-adjusted life-year of £11,167 (95% confidence interval £638 to £21,696). In a discrete choice questionnaire completed by 57 patients 18 months after surgery to treat hip prosthetic joint infection, the most valued characteristics in decisions about revision were the ability to engage in valued activities and a quick return to normal activity.

Limitations

Some research was specific to people with hip prosthetic joint infection. Study populations in meta-analyses and registry analyses may have been selected for joint replacement and specific treatments. The INFORM trial was not powered to study reinfection and was limited to 18 months’ follow-up. The qualitative study subgroups were small.

Conclusions

We identified risk factors, diagnostic biomarkers, effective treatments and patient preferences for the treatment of hip and knee prosthetic joint infection. The risk factors include male sex, diagnoses other than osteoarthritis, specific comorbidities and surgical factors. Synovial fluid alpha-defensin and leucocyte esterase showed high diagnostic accuracy. Infection is devastating for patients and surgeons, both of whom describe the need for support during treatment. Debridement and implant retention is effective, particularly if performed early. For infected hip replacements, single- and two-stage revision appear equally efficacious, but single-stage has better early results, is cost-effective at 18-month follow-up and is increasingly used. Patients prefer treatments that allow full functional return within 3–9 months.

Future work

For people with infection, develop information, counselling, peer support and care pathways. Develop supportive care and information for patients and health-care professionals to enable the early recognition of infections. Compare alternative and new treatment strategies in hip and knee prosthetic joint infection. Assess diagnostic methods and establish NHS diagnostic criteria.

Study registration

The INFORM randomised controlled trial is registered as ISRCTN10956306. All systematic reviews were registered in PROSPERO (as CRD42017069526, CRD42015023485, CRD42018106503, CRD42018114592, CRD42015023704, CRD42017057513, CRD42015016559, CRD42015017327 and CRD42015016664).

Funding

This project was funded by the National Institute for Health and Care Research (NIHR) Programme Grants for Applied Research programme and will be published in full in Programme Grants for Applied Research; Vol. 10, No. 10. See the NIHR Journals Library website for further project information.

Clinical and cost effectiveness of single stage compared with two stage revision for hip prosthetic joint infection (INFORM): pragmatic, parallel group, open label, randomised controlled trial

OBJECTIVES

To determine whether patient reported outcomes improve after single stage versus two stage revision surgery for prosthetic joint infection of the hip, and to determine the cost effectiveness of these procedures.

DESIGN

Pragmatic, parallel group, open label, randomised controlled trial.

SETTING

High volume tertiary referral centres or orthopaedic units in the UK (n=12) and in Sweden (n=3), recruiting from 1 March 2015 to 19 December 2018.

PARTICIPANTS

140 adults (aged ≥18 years) with a prosthetic joint infection of the hip who required revision (65 randomly assigned to single stage and 75 to two stage revision).

INTERVENTIONS

A computer generated 1:1 randomisation list stratified by hospital was used to allocate participants with prosthetic joint infection of the hip to a single stage or a two stage revision procedure.

MAIN OUTCOME MEASURES

The primary intention-to-treat outcome was pain, stiffness, and functional limitations 18 months after randomisation, measured by the Western Ontario and McMasters Universities Osteoarthritis Index (WOMAC) score. Secondary outcomes included surgical complications and joint infection. The economic evaluation (only assessed in UK participants) compared quality adjusted life years and costs between the randomised groups.

RESULTS

The mean age of participants was 71 years (standard deviation 9) and 51 (36%) were women. WOMAC scores did not differ between groups at 18 months (mean difference 0.13 (95% confidence interval -8.20 to 8.46), P=0.98); however, the single stage procedure was better at three months (11.53 (3.89 to 19.17), P=0.003), but not from six months onwards. Intraoperative events occurred in five (8%) participants in the single stage group and 20 (27%) in the two stage group (P=0.01). At 18 months, nine (14%) participants in the single stage group and eight (11%) in the two stage group had at least one marker of possible ongoing infection (P=0.62). From the perspective of healthcare providers and personal social services, single stage revision was cost effective with an incremental net monetary benefit of £11 167 (95% confidence interval £638 to £21 696) at a £20 000 per quality adjusted life years threshold (£1.0; $1.1; €1.4).

CONCLUSIONS

At 18 months, single stage revision compared with two stage revision for prosthetic joint infection of the hip showed no superiority by patient reported outcome. Single stage revision had a better outcome at three months, fewer intraoperative complications, and was cost effective. Patients prefer early restoration of function, therefore, when deciding treatment, surgeons should consider patient preferences and the cost effectiveness of single stage surgery.

TRIAL REGISTRATION

ISRCTN registry ISRCTN10956306.

Cost-effectiveness of adding a non-invasive acoustic rule-out test in the evaluation of patients with suspected stable angina pectoris. Design of the randomized multicenter FILTER-SCAD trial

Background

Patients with suspected stable coronary artery disease (CAD) are selected for further non-invasive or invasive diagnostic tests depending on their pre-test probability (PTP) of obstructive CAD. However, the PTP, based on age, sex, and type of angina, has shown to grossly overestimate the likelihood of obstructive CAD. Consequently, the use of diagnostic tests has increased over the last decades despite a low diagnostic yield (6–7%). The CAD-score is a risk stratification score for obstructive CAD measured using a novel non-invasive acoustic device, and when added to PTP has shown excellent rule-out capabilities.

Purpose

To investigate if the addition of the CAD-score to a standard diagnostic examination is superior in terms of reducing overall number of diagnostic procedures and non-inferior in terms of safety as compared to a standard PTP-guided strategy when evaluating patients with suspected stable CAD.

Methods

The FILTER-SCAD trial is a randomized, controlled, multicenter trial expected to include 2000 subjects ≥30 years of age without known CAD referred for outpatient assessment for suspected CAD at 5 hospitals in Denmark and Sweden. First subject was randomized on October 22, 2019.

Subjects will be randomized 1:1 to either 1) a control group undergoing standard diagnostic examination (SDE) according to current guidelines, or 2) an intervention group undergoing SDE plus a CAD-score measurement, using permuted block randomization stratified by study site and PTP (very low vs. low-intermediate). Follow-up will be 12 months for a primary endpoint of cumulative number of diagnostic tests and a combined secondary safety endpoint of all-cause death, non-fatal myocardial infarction, unstable angina pectoris, heart failure, and ischemic stroke. Questionnaires assessing symptom severity, quality of life, life style measures, and medical treatment will be collected at baseline, 3 months, and 12 months after randomization.

The study is powered to detect superiority in terms of cumulative number of diagnostic tests with a power of 80% and a significance level of 0.05, and non-inferiority on the safety endpoint with a power of 90% and a significance level of 0.05. The study is conducted in compliance to the principles of the Declaration of Helsinki of the World Medical Association. ClinicalTrials.gov ID: NCT04121949.

Results

One study site is currently enrolling. Preliminary baseline data is available on the first 77 (44% males) enrolled patients (median age 61 years IQR (51–72) and PTP 22% IQR (13–38)) showing successful randomization with even distribution of baseline characteristic between the two groups including sex, age, and PTP.

Perspectives

The FILTER-SCAD trial will investigate whether it is feasible to reduce resource consumption without compromising safety in the outpatient assessment of patients with suspected CAD using a simple, non-invasive acoustic device. Enrollment and follow-up are expected to be completed spring 2022.

Funding Acknowledgement

Type of funding source: Other. Main funding source(s): The company Acarix A/S har provided an unrestricted grant for the study. The Foundation “Fonden for Faglig Udvikling i Speciallægepraksis” has provided a grant for the study.

What are patients' preferences for revision surgery after periprosthetic joint infection? A discrete choice experiment

OBJECTIVES

Understanding patients' preferences for treatment is crucial to provision of good care and shared decisions, especially when more than one treatment option exists for a given condition. One such condition is infection of the area around the prosthesis after hip replacement, which affects between 0.4% and 3% of patients. There is more than one treatment option for this major complication, and our study aimed to assess the value that patients place on aspects of revision surgery for periprosthetic hip infection.

DESIGN

We identified four attributes of revision surgery for periprosthetic hip infection. Using a discrete choice experiment (DCE), we measured the value placed on each attribute by 57 people who had undergone either one-stage or two-stage revision surgery for infection.

SETTING

The DCE was conducted with participants from nine National Health Service hospitals in the UK.

PARTICIPANTS

Adults who had undergone revision surgery for periprosthetic hip infection (N=57).

RESULTS

Overall, the strongest preference was for a surgical option that resulted in no restrictions on engaging in valued activities after a new hip is fitted (β=0.7). Less valued but still important attributes included a shorter time taken from the start of treatment to return to normal activities (6 months; β=0.3), few or no side effects from antibiotics (β=0.2), and having only one operation (β=0.2).

CONCLUSIONS

The results highlight that people who have had revision surgery for periprosthetic hip infection most value aspects of care that affect their ability to engage in normal everyday activities. These were the most important characteristics in decisions about revision surgery.

One- and two-stage surgical revision of peri-prosthetic joint infection of the hip: a pooled individual participant data analysis of 44 cohort studies

One-stage and two-stage revision strategies are the two main options for treating established chronic peri-prosthetic joint infection (PJI) of the hip; however, there is uncertainty regarding which is the best treatment option. We aimed to compare the risk of re-infection between the two revision strategies using pooled individual participant data (IPD). Observational cohort studies with PJI of the hip treated exclusively by one- or two-stage revision and reporting re-infection outcomes were retrieved by searching MEDLINE, EMBASE, Web of Science, The Cochrane Library, and the WHO International Clinical Trials Registry Platform; as well as email contact with investigators. We analysed IPD of 1856 participants with PJI of the hip from 44 cohorts across four continents. The primary outcome was re-infection (recurrence of infection by the same organism(s) and/or re-infection with a new organism(s)). Hazard ratios (HRs) for re-infection were calculated using Cox proportional frailty hazards models. After a median follow-up of 3.7 years, 222 re-infections were recorded. Re-infection rates per 1000 person-years of follow-up were 16.8 (95% CI 13.6-20.7) and 32.3 (95% CI 27.3-38.3) for one-stage and two-stage strategies respectively. The age- and sex-adjusted HR of re-infection for two-stage revision was 1.70 (0.58-5.00) when compared with one-stage revision. The association remained consistently absent after further adjustment for potential confounders. The HRs did not vary importantly in clinically relevant subgroups. Analysis of pooled individual patient data suggest that a one-stage revision strategy may be as effective as a two-stage revision strategy in treating PJI of the hip.

One-stage or two-stage revision surgery for prosthetic hip joint infection--the INFORM trial: a study protocol for a randomised controlled trial

BACKGROUND

Periprosthetic joint infection (PJI) affects approximately 1% of patients following total hip replacement (THR) and often results in severe physical and emotional suffering. Current surgical treatment options are debridement, antibiotics and implant retention; revision THR; excision of the joint and amputation. Revision surgery can be done as either a one-stage or two-stage operation. Both types of surgery are well-established practice in the NHS and result in similar rates of re-infection, but little is known about the impact of these treatments from the patient's perspective. The main aim of this randomised controlled trial is to determine whether there is a difference in patient-reported outcome measures 18 months after randomisation for one-stage or two-stage revision surgery.

METHODS/DESIGN

INFORM (INFection ORthopaedic Management) is an open, two-arm, multi-centre, randomised, superiority trial. We aim to randomise 148 patients with eligible PJI of the hip from approximately seven secondary care NHS orthopaedic units from across England and Wales. Patients will be randomised via a web-based system to receive either a one-stage revision or a two-stage revision THR. Blinding is not possible due to the nature of the intervention. All patients will be followed up for 18 months. The primary outcome is the WOMAC Index, which assesses hip pain, function and stiffness, collected by questionnaire at 18 months. Secondary outcomes include the following: cost-effectiveness, complications, re-infection rates, objective hip function assessment and quality of life. A nested qualitative study will explore patients' and surgeons' experiences, including their views about trial participation and randomisation.

DISCUSSION

INFORM is the first ever randomised trial to compare two widely accepted surgical interventions for the treatment of PJI: one-stage and two-stage revision THR. The results of the trial will benefit patients in the future as the main focus is on patient-reported outcomes: pain, function and wellbeing in the long term. Patients state that these outcomes are more important than those that are clinically derived (such as re-infection) and have been commonly used in previous non-randomised studies. Results from the INFORM trial will also benefit clinicians and NHS managers by enabling the comparison of these key interventions in terms of patients' complication rates, health and social resource use and their overall cost-effectiveness.

TRIAL REGISTRATION

Current controlled trials ISRCTN10956306 (registered on 29 January 2015); UKCRN ID 18159.

Resetting of the carotid arterial baroreflex during dynamic exercise in humans

Recent investigations have demonstrated that at the onset of low-to-moderate-intensity leg cycling exercise (L) the carotid baroreflex (CBR) was classically reset in direct relation to the intensity of exercise. On the basis of these data, we proposed that the CBR would also be classically reset at the onset of moderate- to maximal-intensity L exercise. Therefore, CBR stimulus-response relationships were compared in seven male volunteers by using the neck pressure-neck suction technique during dynamic exercise that ranged in intensity from 50 to 100% of maximal oxygen uptake (VO(2 max)). L exercise alone was performed at 50 and 75% VO(2 max), and L exercise combined with arm (A) exercise (L + A) was performed at 75 and 100% VO(2 max). O(2) consumption and heart rate (HR) increased in direct relation with the increases in exercise intensity. The threshold and saturation pressures of the carotid-cardiac reflex at 100% VO(2 max) were >75% VO(2 max), which were in turn >50% VO(2 max) (P < 0.05), without a change in the maximal reflex gain (G(max)). In addition, the HR response value at threshold and saturation at 75% VO(2 max) was >50% VO(2 max) (P < 0.05) and 100% VO(2 max) was >75% VO(2 max) (P < 0.07). Similar changes were observed for the carotid-vasomotor reflex. In addition, as exercise intensity increased, the operating point (the prestimulus blood pressure) of the CBR was significantly relocated further from the centering point (G(max)) of the stimulus-response curve and was at threshold during 100% VO(2 max). These findings identify the continuous classic rightward and upward resetting of the CBR, without a change in G(max), during increases in dynamic exercise intensity to maximal effort.

Cardiovascular control during concomitant dynamic leg exercise and static arm exercise in humans

1. Skeletal muscle blood flow is thought to be determined by a balance between sympathetic vasoconstriction and metabolic vasodilatation. The purpose of this study was to assess the importance of high levels of sympathetic vasoconstrictor activity in control of blood flow to human skeletal muscle during dynamic exercise. 2. Muscle sympathetic nerve activity to the exercising leg was increased by static or static ischaemic arm exercise added to on-going dynamic leg exercise. Ten subjects performed light (20 W) or moderate (40 W) dynamic knee extension for 6 min with one leg alone or concomitant with bilateral static handgrip at 20% of maximal voluntary contraction force with or without forearm muscle ischaemia or post-exercise forearm muscle ischaemia. 3. Muscle sympathetic nerve activity was measured by microneurography (peroneal nerve) and leg muscle blood flow by a constant infusion thermodilution technique (femoral vein). 4. Activation of an exercise pressor reflex from the arms, causing a 2- to 4-fold increase in muscle sympathetic nerve activity and a 15-32% increase in mean arterial blood pressure, did not affect blood flow to the dynamically exercising leg muscles at any level of leg exercise. Leg vascular conductance was reduced in line with the higher perfusion pressure. 5. The results demonstrate that the vasoconstrictor effects of high levels of muscle sympathetic nerve activity does not affect blood flow to human skeletal muscle exercising at moderate intensities. One question remaining is whether the observed decrease in muscle vascular conductance is the result of sympathetic vasoconstriction or metabolic autoregulation of muscle blood flow.

Acute and adaptive responses in humans to exercise in a warm, humid environment

Acute and repeated exposure for 8-13 consecutive days to exercise in humid heat was studied. Twelve fit subjects exercised at 150 W [45% of maximum O2 uptake (V.O2,max)] in ambient conditions of 35 degrees C and 87% relative humidity which resulted in exhaustion after 45 min. Average core temperature reached 39.9 +/- 0.1 degrees C, mean skin temperature (T-sk) was 37.9 +/- 0.1 degrees C and heart rate (HR) 152 +/- 6 beats min-1 at this stage. No effect of the increasing core temperature was seen on cardiac output and leg blood flow (LBF) during acute heat stress. LBF was 5.2 +/- 0.3 l min-1 at 10 min and 5.3 +/- 0.4 l min-1 at exhaustion (n = 6). After acclimation the subjects reached exhaustion after 52 min with a core temperature of 39.9 +/- 0.1 degrees C, T-sk 37.7 +/- 0.2 degrees C, HR 146 +/- 4 beats min-1. Acclimation induced physiological adaptations, as shown by an increased resting plasma volume (3918 +/- 168 to 4256 +/- 270 ml), the lower exercise heart rate at exhaustion, a 26% increase in sweating rate, lower sweat sodium concentration and a 6% reduction in exercise V.O2. Neither in acute exposure nor after acclimation did the rise of core temperature to near 40 degrees C affect metabolism and substrate utilization. The physiological adaptations were similar to those induced by dry heat acclimation. However, in humid heat the effect of acclimation on performance was small due to physical limitations for evaporative heat loss.

Metabolic response and muscle glycogen depletion pattern during prolonged electrically induced dynamic exercise in man

Muscle glycogen depletion pattern and metabolic responses during voluntary (VOL) and functional electrical stimulated (FES) dynamic knee-extensor exercise with one leg were evaluated. Seven healthy men exercised for 60 minutes at 30 W with an pulmonary oxygen uptake of 0.8 and 1.01 min-1, and respiratory exchange ratios of 0.90 and 0.95 in VOL and FES, respectively. Heart rate reached a level around 90 beats min-1 (VOL) and up to 110 beats min-1 (FES). Muscle glycogen decreased in FES with 260 and 290 mmol kg-1 d.w. in vastus lateralis and m. rectus femoris, respectively, compared with 45 and 160 mmol kg-1 d.w. in VOL (p < 0.05). In FES the percentage of empty and almost empty fibres determined by periodic acid-Schiff staining in vastus lateralis and rectus femoris was 50 and 77% of type I, 63 and 90% of type IIa, and 59 and 84% of type IIb fibres, respectively, whereas in VOL it was 24 and 26% of type I, 7 and 19% of type IIa, and 2 and 3% of type IIb fibres. Muscle lactate reached 30 mmol kg-1 d.w. in FES and was 9 mmol kg-1 d.w. lower in VOL. The changes in blood lactate and NH3 during the exercise were slightly higher in FES than in VOL, whereas the alterations in glucose, FFA, and K+ were small in both exercise modes. The pressure in the two muscle portions at different locations (proximal-distal) and depths was always higher (approximately 50%) in FES than in VOL, reaching levels around 55 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Skeletal muscle perfusion in electrically induced dynamic exercise in humans

Leg blood flow, blood pressure and metabolic responses were evaluated in six men during incremental one-legged dynamic knee extension exercise tests (no load exercise-40 W); one performed with voluntary contractions (VOL) and one with electrically induced contractions (EMS). Pulmonary oxygen uptake was the same in both exercise modes, but the ventilatory coefficient was 2-5 L per L O2 higher in EMS than VOL (P < 0.05). Heart rate and mean arterial pressure were slightly higher with EMS than VOL at all exercise intensities reaching 138 (EMS) and 126 bpm (VOL), as well as 148 (EMS) and 137 mmHg (VOL) at 40 W, respectively (P < 0.05). Leg blood flow, oxygen uptake and conductance were similar in the two exercise modes. At 40 W, mean muscle blood flow was close to 200 (range: 165-220) mL 100 g-1 min-1, mean peak muscle oxygen uptake reached 230 mL kg-1 min-1, and mean conductance became as high as around 45 mL min-1 mmHg-1, and normalized for muscle size and arterial pressure it approached 100 mL min-1 100 g-1 100 mmHg-1. Lactate and ammonia efflux from the leg were higher with EMS than with VOL and the difference became larger with increasing exercise intensity (P < 0.05). Muscle glucose uptake was the same in each exercise mode. Femoral venous K+ concentration increased with exercise intensity and was higher with EMS than with VOL, reaching 5.1 (EMS) and 4.7 mmol L-1 (VOL) at 40 W (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin release and enhanced regional myocardial ischemia induced by cold-air inhalation in patients with stable angina

This study was designed to determine the influence of cold-air inhalation on regional myocardial perfusion in patients with ischemic heart disease. A selected group of vasoactive hormones was measured to investigate their possible roles as ischemic agents. Ten men who had recently had a myocardial infarction and anginal symptoms and with verified pathologic ST deviations during a preceding exercise test volunteered to participate in this randomized cross-over study. Two identical exercise tests were performed on different days; one with inhalation of cold (-22 degrees C) air and the other one with inhalation of thermoneutral air (22 degrees C). Scintigraphic imaging (single-photon emission computed tomography) of regional myocardial blood flow was performed with technetium 99m isonitrile flowtracer and a Bull's eye visual display with calculation of the scintigraphic ischemic severity score. The score was significantly higher during exercise with inhalation of cold air as compared to exercise with inhalation of thermoneutral air. Furthermore, only with cold-air inhalation did arterial plasma endothelin concentration increase significantly from rest to exercise and correlate with the change of ischemic severity score. In contrast, no change was observed under thermoneutral conditions. There was no significant difference between peak values of heart rate, systolic blood pressure, adrenaline, and noradrenaline concentrations in the two situations. We conclude that inhalation of cold air during exercise increases the degree of regional myocardial ischemia and that this is not caused by an increased myocardial oxygen demand. We suggest that cold air directly influences the vasomotor tone of the myocardial resistance vessels and that endothelin may be involved in the ischemic response.

Neural control of cardiovascular responses and of ventilation during dynamic exercise in man

1. Nine subjects performed dynamic knee extension by voluntary muscle contractions and by evoked contractions with and without epidural anaesthesia. Four exercise bouts of 10 min each were performed: three of one-legged knee extension (10, 20 and 30 W) and one of two-legged knee extension at 2 x 20 W. Epidural anaesthesia was induced with 0.5% bupivacaine or 2% lidocaine. Presence of neural blockade was verified by cutaneous sensory anaesthesia below T8-T10 and complete paralysis of both legs. 2. Compared to voluntary exercise, control electrically induced exercise resulted in normal or enhanced cardiovascular, metabolic and ventilatory responses. However, during epidural anaesthesia the increase in blood pressure with exercise was abolished. Furthermore, the increases in heart rate, cardiac output and leg blood flow were reduced. In contrast, plasma catecholamines, leg glucose uptake and leg lactate release, arterial carbon dioxide tension and pulmonary ventilation were not affected. Arterial and venous plasma potassium concentrations became elevated but leg potassium release was not increased. 3. The results conform to the idea that a reflex originating in contracting muscle is essential for the normal blood pressure response to dynamic exercise, and that other neural, humoral and haemodynamic mechanisms cannot govern this response. However, control mechanisms other than central command and the exercise pressor reflex can influence heart rate, cardiac output, muscle blood flow and ventilation during dynamic exercise in man.

Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment

1. Heat acclimation was induced in eight subjects by asking them to exercise until exhaustion at 60% of maximum oxygen consumption rate (VO2) for 9-12 consecutive days at an ambient temperature of 40 degrees C, with 10% relative humidity (RH). Five control subjects exercised similarly in a cool environment, 20 degrees C, for 90 min for 9-12 days; of these, three were exposed to exercise at 40 degrees C on the first and last day. 2. Acclimation had occurred as seen by the increased average endurance from 48 min to 80 min, the lower rate of rise in the heart rate (HR) and core temperature and the increased sweating. 3. Cardiac output increased significantly from the first to the final heat exposure from 19.6 to 21.4 l min-1; this was possibly due to an increased plasma volume and stroke volume. 4. The mechanism for the increased plasma volume may be an isosmotic volume expansion caused by influx of protein to the vascular compartment, and a sodium retention induced by a significant increase in aldosterone. 5. The exhaustion coincided with, or was elicited when, core temperature reached 39.7 +/- 0.15 degrees C; with progressing acclimation processes it took progressively longer to reach this level. However, at this point we found no reduction in cardiac output, muscle (leg) blood flow, no changes in substrate utilization or availability, and no recognized accumulated 'fatigue' substances. 6. It is concluded that the high core temperature per se, and not circulatory failure, is the critical factor for the exhaustion during exercise in heat stress.

Elevated muscle acidity and energy production during exhaustive exercise in humans

This study examined the effect of previous intense exercise on energy production during exhaustive exercise. Subjects (n = 6) performed dynamic knee extensor exercise to exhaustion twice (Ex1 and Ex2) separated by 16 min of recovery consisting of 10 min of rest, 3.5 min of very high-intensity intermittent exercise, and a further 2.5 min of rest. This resulted in an elevated muscle lactate concentration of 13.1 mmol/kg wet wt before Ex2. Muscle lactate concentration was the same at end of Ex1 and Ex2, but the accumulation of lactate and net lactate release during Ex2 was reduced (P < 0.05) by 67 and 38%, respectively. The time to exhaustion was 3.73 and 2.98 min, respectively, and the mean rate of net lactate production for Ex2 was lower (P < 0.05) than for Ex1 (4.6 +/- 1.2 and 9.6 +/- 1.7 mmol.min-1.kg wet wt-1, respectively). Leg O2 uptake was the same for Ex1 and Ex2. Muscle pH (6.85) was lowered (P < 0.05) before Ex2, but at the end of Ex2 (6.77) it tended (P < 0.1) to be higher compared with that at the end of Ex1 (6.73). In summary, the net lactate production rate is reduced but the aerobic energy production is not significantly altered when intense exercise is repeated. Fatigue and the lowered glycolysis do not appear to be caused by the elevated acidity per se before exercise.

Maximal oxygen uptake: "old" and "new" arguments for a cardiovascular limitation

The research performed over the last 100 yr in regard to oxygen transport during exercise is reviewed. Special focus is on major shifts in views held on which link may limit maximal oxygen uptake of an individual exercising with a large fraction of the muscle mass. Initially the pump capacity of the heart was proposed as the critical factor, a view basically unchallenged until results on the plasticity of muscle came about in the 1960-70s. The capillary bed of the muscle and its mitochondrial volumes can be enhanced with training. These adaptations were then suggested to be prerequisites for maximal oxygen uptake to become elevated. The pendulum is slowly swinging back again toward heart and lungs setting the upper limit for the oxygen transport. It appears to be in the range of 80-90 ml.kg-1.min-1 or 150-200 ml.kg-1 muscle.min-1, which can easily be consumed by a fraction of the muscle mass intensely contracting.

Beta 2-adrenergic stimulation does not prevent potassium loss from exercising quadriceps muscle

During exercise K+ is released from contracting muscle and plasma K+ concentration rises. Because beta 2-adrenergic agonists stimulate K+ uptake by skeletal muscle in vitro, we tested whether terbutaline, a selective beta 2-agonist, would reduce the loss of K+ from working muscle. Dynamic quadriceps muscle exercise was performed by 12 healthy male volunteers for 50 or 80 min at an average workload of 38 W. A steady K+ loss estimated at 0.16 +/- 0.02 mmol.min-1.kg working muscle-1 and a 0.30 +/- 0.05 mM elevation of arterial plasma K+ concentration were observed. The addition of terbutaline during exercise caused leg blood flow to increase 13% from 5.10 +/- 0.16 to 5.75 +/- 0.13 l/min and arterial K+ concentration to fall monoexponentially by 0.90 +/- 0.05 mM with a rate constant of 0.26 min-1. Terbutaline increased, rather than decreased, the washout of K+ from working quadriceps by 40% to an average value of 0.23 +/- 0.02 mmol.min-1.kg muscle-1. In an additional subject who exercised to exhaustion, terbutaline failed to diminish muscle K+ loss. We conclude that terbutaline does not augment Na(+)-K+ pump activity to a degree sufficient to prevent K+ loss from exercising muscle in humans. On the other hand, the rapid reduction in plasma K+ concentration observed with beta 2-adrenergic stimulation is compatible with an uptake of K+ by nonexercising tissue at an estimated maximal rate of 0.5 micromol.g-1.min-1.

Cardiovascular responses to carotid sinus baroreceptor stimulation during moderate to severe exercise in man

Our objective was to assess the importance of arterial baroreflexes in maintaining vasoconstriction in active muscle during moderate to severe exercise. Eight subjects exercised for 8-15 min on a cycle ergometer at three levels (averages 94, 194, 261 W) requiring 40-88% of VO2 max. Four times during each exercise level pulsatile negative pressure (-50 mmHg) was applied over the carotid sinuses for 30 s; suction was applied at each ECG R-wave for 250-400 ms. Before and during each neck suction, femoral venous blood flow (FVBF) was measured by constant infusion thermal dilution. At 94 W neck suction significantly reduced blood pressure (BP) (15 mmHg) and heart rate (HR) (7 beats min-1), and raised leg vascular conductance (LVC) (11.4%) without changing FVBF. At 194 W, neck suction reduced BP (9 mmHg), HR (4 beats min-1) and FVBF (5.1%, 240 ml min-1), and raised LVC (5.2%). At 261 W, LVC was unchanged by neck suction, but BP and FVBF both fell (9 mmHg and 650 ml min-1 or 7.4%). We conclude that competing local vasodilation and sympathetic vasoconstriction control muscle blood flow during moderate exercise, and vasoconstrictor tone can be withdrawn by baroreceptor stimulation. High levels of vasoconstrictor outflow to muscle in severe exercise may not originate from baroreflexes.

Norepinephrine spillover from skeletal muscle during exercise in humans: role of muscle mass

The purpose of this study was to determine the effect of increasing muscle mass involvement in dynamic exercise on both sympathetic nervous activation and local hemodynamic variables of individual active and inactive skeletal muscle groups. Six male subjects performed 15-min bouts of one-legged knee extension either alone or in combination with the knee extensors of the other leg and/or with the arms. The range of work intensities varied between 24 and 71% (mean) of subjects' maximal aerobic capacity (% VO2max). Leg blood flow, measured in the femoral vein by thermodilution, was determined in both legs. Arterial and venous plasma concentrations of norepinephrine (NE) and epinephrine were analyzed, and the calculated NE spillover was used as an index of sympathetic nervous activity to the limb. NE spillover increased gradually both in the resting, and to a larger extent in the exercising legs, with a steeper rise occurring approximately 70% VO2max. These increases were not associated with any significant changes in leg blood flow or leg vascular conductance at the exercise intensities examined. These results suggest that, as the total active muscle mass increases, the rise in sympathetic nervous activity to skeletal muscle, either resting or working at a constant load, is not associated with any significant neurogenic vasoconstriction and reduction in flow or conductance through the muscle vascular bed, during whole body exercise demanding up to 71% VO2max.

Insulin action in human thighs after one-legged immobilization

Insulin action was assessed in thighs of five healthy young males who had one knee immobilized for 7 days by a splint. The splint was not worn in bed. Subjects also used crutches to prevent weight bearing of the immobilized leg. Immobilization decreased the activity of citrate synthase and 3-OH-acyl-CoA-dehydrogenase in the vastus lateralis muscle by 9 and 14%, respectively, and thigh volume by 5%. After 7 days of immobilization, a two-step euglycemic hyperinsulinemic clamp procedure combined with arterial and bilateral femoral venous catheterization was performed. Insulin action on glucose uptake and tyrosine release of the thighs at mean plasma insulin concentrations of 67 (clamp step I) and 447 microU/ml (clamp step II) was decreased by immobilization, whereas immobilization did not affect insulin action on thigh exchange of free fatty acids, glycerol, O2, or potassium. Before and during the clamp step I, lactate release was significantly higher in the immobilized than in the control thigh. Seven days of one-legged immobilization causes local decreased insulin action on thigh glucose uptake and net protein degradation.

Noradrenaline spillover during exercise in active versus resting skeletal muscle in man

Increases in plasma noradrenaline (NA) concentration occur during moderate to heavy exercise in man. This study was undertaken to examine the spillover of NA from both resting and contracting skeletal muscle during exercise. Six male subjects performed one-legged knee-extension so that all measurements could be made both in the exercising and in the resting leg. Subjects exercised for 10 min at each of 50% and 100% of the peak performance capacity of the leg. Leg blood flow was measured by thermodilution and blood samples were drawn for the determination of plasma NA and adrenaline, first in the resting leg and then in the exercising leg. To calculate NA spillover, the extraction of NA (NAe) or of adrenalin (Ae) is required: NAe was measured by repeating the experiment under constant [3H]NA infusion following a 40-min rest period. During exercise, NA spillover was significantly larger in the exercising leg than in the resting leg both during 50% and 100% leg exercise. These results suggest that contracting skeletal muscle may contribute to a larger extent than resting skeletal muscle to increasing the level of plasma NA during exercise. Contractile activity may influence the NA spillover from skeletal muscle by a presynaptic and/or postsynaptic influence on the sympathetic nervous activity to this tissue.

A quantitative analysis of plasma osmotic pressure during metamorphosis of the bullfrog, Rana catesbeiana

The plasma constituents contributing to osmotic pressure are, in decreasing order: Na+, Cl-, HCO3-, K+, glucose, amino acids, urea and protein. Plasma osmotic pressure increases from 180 mmoles/1 to 200 mmoles/1 throughout development.