Göran Rådegran

Maximum rate of oxygen uptake by human skeletal muscle in relation to maximal activities of enzymes in the Krebs cycle

1 Ten subjects performed incremental exercise up to their maximum work rate with the knee extensors of one leg. Measurements of leg blood flow and femoral arteriovenous differences of oxygen were made in order to be able to calculate oxygen uptake of the leg. 2 The volume of the quadriceps muscle was determined from twenty‐one to twenty‐five computer tomography section images taken from the patella to the anterior inferior iliac spine of each subject. 3 The maximal activities of three enzymes in the Krebs cycle, citrate synthase, oxoglutarate dehydrogenase and succinate dehydrogenase, were measured in biopsy samples taken from the vastus lateralis muscle. 4 The average rate of oxygen uptake over the quadriceps muscle at maximal work, 353 ml min−1kg−1, corresponded to a Krebs cycle rate of 4.6 μmol min−1 g−1. This was similar to the maximal activity of oxoglutarate dehydrogenase (5.1 μmol min−1 g−1), whereas the activities of succinate dehydrogenase and citrate synthase averaged 7.2 and 48.0 μmol min−1 g−1, respectively. 5 It is suggested that of these enzymes, only the maximum activity of oxoglutarate dehydrogenase can provide a quantitative measure of the capacity of oxidative metabolism, and it appears that the enzyme is fully activated during one‐legged knee extension exercise at the maximal work rate.

Cardiovascular responses to dynamic exercise with acute anemia in humans

We hypothesized that reducing arterial O2 content ([Formula: see text]) by lowering the hemoglobin concentration ([Hb]) would result in a higher blood flow, as observed with a low [Formula: see text], and maintenance of O2 delivery. Seven young healthy men were studied twice, at rest and during two-legged submaximal and peak dynamic knee extensor exercise in a control condition (mean control [Hb] 144 g/l) and after 1-1.5 liters of whole blood had been withdrawn and replaced with albumin {mean drop in [Hb] 29 g/l (range 19-38 g/l); low [Hb]}. Limb blood flow (LBF) was higher ( P < 0.01) with low [Hb] during submaximal exercise (i.e., at 30 W, LBF was 2.5 ± 0.1 and 3.0 ± 0.1 l/min for control [Hb] and low [Hb], respectively; P < 0.01), resulting in a maintained O2 delivery and O2 uptake for a given workload. However, at peak exercise, LBF was unaltered (6.5 ± 0.4 and 6.6 ± 0.6 l/min for control [Hb] and low [Hb], respectively), which resulted in an 18% reduction in O2 delivery ( P < 0.01). This occurred despite peak cardiac output in neither condition reaching >75% of maximal cardiac output (∼26 l/min). It is concluded that a low CaO2 induces an elevation in submaximal muscle blood flow and that O2 delivery to contracting muscles is tightly regulated.

On the mechanisms that limit oxygen uptake during exercise in acute and chronic hypoxia: role of muscle mass

Peak aerobic power in humans () is markedly affected by inspired O2 tension (). The question to be answered in this study is what factor plays a major role in the limitation of muscle peak in hypoxia: arterial O2 partial pressure () or O2 content ()? Thus, cardiac output (dye dilution with Cardio‐green), leg blood flow (thermodilution), intra‐arterial blood pressure and femoral arterial‐to‐venous differences in blood gases were determined in nine lowlanders studied during incremental exercise using a large (two‐legged cycle ergometer exercise: Bike) and a small (one‐legged knee extension exercise: Knee) muscle mass in normoxia, acute hypoxia (AH) () and after 9 weeks of residence at 5260 m (CH). Reducing the size of the active muscle mass blunted by 62% the effect of hypoxia on in AH and abolished completely the effect of hypoxia on after altitude acclimatization. Acclimatization improved Bike peak exercise from 34 ± 1 in AH to 45 ± 1 mmHg in CH (P < 0.05) and Knee from 38 ± 1 to 55 ± 2 mmHg (P < 0.05). Peak cardiac output and leg blood flow were reduced in hypoxia only during Bike. Acute hypoxia resulted in reduction of systemic O2 delivery (46 and 21%) and leg O2 delivery (47 and 26%) during Bike and Knee, respectively, almost matching the corresponding reduction in . Altitude acclimatization restored fully peak systemic and leg O2 delivery in CH (2.69 ± 0.27 and 1.28 ± 0.11 l min−1, respectively) to sea level values (2.65 ± 0.15 and 1.16 ± 0.11 l min−1, respectively) during Knee, but not during Bike. During Knee in CH, leg oxygen delivery was similar to normoxia and, therefore, also in spite of a of 55 mmHg. Reducing the size of the active muscle mass improves pulmonary gas exchange during hypoxic exercise, attenuates the Bohr effect on oxygen uploading at the lungs and preserves sea level convective O2 transport to the active muscles. Thus, the altitude‐acclimatized human has potentially a similar exercising capacity as at sea level when the exercise model allows for an adequate oxygen delivery (blood flow ×), with only a minor role of per se, when is more than 55 mmHg.

Everolimus initiation and early calcineurin inhibitor withdrawal in heart transplant recipients: a randomized trial.

In a randomized, open‐label trial, everolimus was compared to cyclosporine in 115 de novo heart transplant recipients. Patients were assigned within 5 days posttransplant to low‐exposure everolimus (3–6 ng/mL) with reduced‐exposure cyclosporine (n = 56), or standard‐exposure cyclosporine (n = 59), with both mycophenolate mofetil and corticosteroids. In the everolimus group, cyclosporine was withdrawn after 7–11 weeks and everolimus exposure increased (6–10 ng/mL). The primary efficacy end point, measured GFR at 12 months posttransplant, was significantly higher with everolimus versus cyclosporine (mean ± SD: 79.8 ± 17.7 mL/min/1.73 m2 vs. 61.5 ± 19.6 mL/min/1.73 m2; p < 0.001). Coronary intravascular ultrasound showed that the mean increase in maximal intimal thickness was smaller (0.03 mm [95% CI 0.01, 0.05 mm] vs. 0.08 mm [95% CI 0.05, 0.12 mm], p = 0.03), and the incidence of cardiac allograft vasculopathy (CAV) was lower (50.0% vs. 64.6%, p = 0.003), with everolimus versus cyclosporine at month 12. Biopsy‐proven acute rejection after weeks 7–11 was more frequent with everolimus (p = 0.03). Left ventricular function was not inferior with everolimus versus cyclosporine. Cytomegalovirus infection was less common with everolimus (5.4% vs. 30.5%, p < 0.001); the incidence of bacterial infection was similar. In conclusion, everolimus‐based immunosuppression with early elimination of cyclosporine markedly improved renal function after heart transplantation. Since postoperative safety was not jeopardized and development of CAV was attenuated, this strategy may benefit long‐term outcome.

Everolimus Initiation With Early Calcineurin Inhibitor Withdrawal in De Novo Heart Transplant Recipients: Three-Year Results From the Randomized SCHEDULE Study.

In a randomized, open‐label trial, de novo heart transplant recipients were randomized to everolimus (3–6 ng/mL) with reduced‐exposure calcineurin inhibitor (CNI; cyclosporine) to weeks 7–11 after transplant, followed by increased everolimus exposure (target 6–10 ng/mL) with cyclosporine withdrawal or standard‐exposure cyclosporine. All patients received mycophenolate mofetil and corticosteroids. A total of 110 of 115 patients completed the 12‐month study, and 102 attended a follow‐up visit at month 36. Mean measured GFR (mGFR) at month 36 was 77.4 mL/min (standard deviation [SD] 20.2 mL/min) versus 59.2 mL/min (SD 17.4 mL/min) in the everolimus and CNI groups, respectively, a difference of 18.3 mL/min (95% CI 11.1–25.6 mL/min; p < 0.001) in the intention to treat population. Multivariate analysis showed treatment to be an independent determinant of mGFR at month 36. Coronary intravascular ultrasound at 36 months revealed significantly reduced progression of allograft vasculopathy in the everolimus group compared with the CNI group. Biopsy‐proven acute rejection grade ≥2R occurred in 10.2% and 5.9% of everolimus‐ and CNI‐treated patients, respectively, during months 12–36. Serious adverse events occurred in 37.3% and 19.6% of everolimus‐ and CNI‐treated patients, respectively (p = 0.078). These results suggest that early CNI withdrawal after heart transplantation supported by everolimus, mycophenolic acid and steroids with lymphocyte‐depleting induction is safe at intermediate follow‐up. This regimen, used selectively, may offer adequate immunosuppressive potency with a sustained renal advantage.

The Effect of Everolimus Initiation and Calcineurin Inhibitor Elimination on Cardiac Allograft Vasculopathy in De Novo Recipients: One-Year Results of a Scandinavian Randomized Trial.

Early initiation of everolimus with calcineurin inhibitor therapy has been shown to reduce the progression of cardiac allograft vasculopathy (CAV) in de novo heart transplant recipients. The effect of de novo everolimus therapy and early total elimination of calcineurin inhibitor therapy has, however, not been investigated and is relevant given the morbidity and lack of efficacy of current protocols in preventing CAV. This 12‐month multicenter Scandinavian trial randomized 115 de novo heart transplant recipients to everolimus with complete calcineurin inhibitor elimination 7–11 weeks after HTx or standard cyclosporine immunosuppression. Ninety‐five (83%) patients had matched intravascular ultrasound examinations at baseline and 12 months. Mean (± SD) recipient age was 49.9 ± 13.1 years. The everolimus group (n = 47) demonstrated significantly reduced CAV progression as compared to the calcineurin inhibitor group (n = 48) (ΔMaximal Intimal Thickness 0.03 ± 0.06 and 0.08 ± 0.12 mm, ΔPercent Atheroma Volume 1.3 ± 2.3 and 4.2 ± 5.0%, ΔTotal Atheroma Volume 1.1 ± 19.2 mm3 and 13.8 ± 28.0 mm3 [all p‐values ≤ 0.01]). Everolimus patients also had a significantly greater decline in levels of soluble tumor necrosis factor receptor‐1 as compared to the calcineurin inhibitor group (p = 0.02). These preliminary results suggest that an everolimus‐based CNI‐free can potentially be considered in suitable de novo HTx recipients.

Immunosuppressive therapies after heart transplantation — The balance between under- and over-immunosuppression

Since the first heart transplantation (HT) in 1967, survival has steadily improved. Issues related to over- and under-immunosuppression are, however, still common following HT. Whereas under-immunosuppression may result in rejection, over-immunosuppression may render other medical problems, including infections, malignancies and chronic kidney disease (CKD). As such complications constitute major limiting factors for long-term survival following HT, identifying improved diagnostic and preventive methods has been the focus of many studies. Notably, research on antibody-mediated rejection (AMR) and cardiac allograft vasculopathy (CAV) has recently led to the development of nomenclatures that may aid in their diagnosis and treatment. Moreover, novel immunosuppressants (such as mammalian target of rapamycin [m-TOR] inhibitors) and strategies aimed at minimizing the use of calcineurin inhibitors (CNIs) and corticosteroids (CSs), have provided alternatives to the traditional combination maintenance immunosuppressive therapy of CSs, cyclosporine (CSA) or tacrolimus (TAC), and azathioprine (AZA) or mycophenolate mofetil (MMF). Research within this field of medicine is not only extensive, but also in constant progress. The purpose of the present review was therefore to summarize some major points regarding immunosuppressive therapies after HT and the balance between under- and over-immunosuppression. Transplant immunology, rejection, common medical problems related to over-immunosuppression, as well as induction and maintenance immunosuppressive drugs and therapies, are addressed.

Acute cellular rejection the first year after heart transplantation and its impact on survival: a single‐centre retrospective study at Skåne University Hospital in Lund 1988–2010

Acute cellular rejection (ACR) the first year after heart transplantation (HT) and its impact on survival was investigated. All 215 HT patients at our centre 1988–2010, including 219 HTs and 2990 first‐year endomyocardial biopsies (EMBs), were studied. ‘Routine’ EMBs obtained 1, 2, 3, 4, 6, 8, 10, 12, 16, 20, 24, 32, 40 and 52 weeks after HT, and ‘additional clinically indicated’ (ACI) EMBs, were graded according to the 1990‐ISHLT‐WF. The frequency and severity of first‐year ACRs was low, with 6.5% of routine EMBs and 14.1% of ACI EMBs showing ACR ≥ grade 2. Proportionally more (P < 0.05) first‐year ACRs ≥ grade 2 were found among EMBs in HTs performed during 1988–1999 (9.6%) than 2000–2010 (5.5%), EMBs performed during 16–52 weeks (8.8%) than 1–12 weeks (6.3%) after HT, EMBs in HTs with paediatric (11.3%) than adult (7.1%) donors, and EMBs in sex‐mismatched (10.4%) than sex‐matched (6.3%) HTs. Five‐ and ten‐year survival was furthermore lower (P < 0.05) among HTs with ≥1 compared with 0 first‐year ACRs ≥ grade 3A/3B (82% vs. 92% and 69% vs. 82%, respectively). Ten‐year survival was 74% compared with 53% in the ISHLT registry. In conclusion, our results indicate that first‐year ACRs ≥ grade 3A/3B affect long‐term survival. We believe frequent first‐year EMBs may allow early ACR detection and continuous immunosuppressive adjustments, preventing low‐grade ACRs from progressing to ACRs ≥ grade 3A/3B, thereby improving survival.

Prognosis and response to first-line single and combination therapy in pulmonary arterial hypertension.

Abstract Objectives. To investigate survival, treatment escalation, effects of first-line single- and first-line combination therapy and prognostic markers in idiopathic- (IPAH), hereditary- (HPAH) and connective tissue disease-associated (CTD-PAH) pulmonary arterial hypertension (PAH). Design. Retrospective analysis of medical journals from PAH patients at Skåne University Hospital 2000–2011. Results. 1-, 2- and 3-year survival was 87%, 67%, and 54%, respectively, for the entire population, but worse (p = 0.003) in CTD-PAH than IPAH/HPAH. After 1, 2 and 3 years, 58%, 41% and 24% of patients starting on single therapy were alive on single therapy. 37.5% of patients on first-line single therapy received escalated treatment at first follow-up. First-line combination therapy more greatly decreased pulmonary vascular resistance index (PVRI, p = 0.017) than first-line single therapy. Only first-line combination therapy improved (p = 0.042) cardiac index (CI). Higher mean right atrial pressure (MRAP, p = 0.018), MRAP/CI (p = 0.021) and WHO functional class (p < 0.001) and lower 6-min walking distance (6MWD, p = 0.001) at baseline, and higher PVRI (p = 0.008) and lower 6MWD (p = 0.004) at follow-up were associated with worse outcome. Conclusions. We confirm improved survival with PAH-targeted therapies. Survival is still poor and early treatment escalation frequently needed. First-line combination therapy may more potently improve haemodynamics. MRAP/CI may represent a new prognostic marker in PAH.

The principal pathways involved in the in vivo modulation of hypoxic pulmonary vasoconstriction, pulmonary arterial remodelling and pulmonary hypertension.

Hypoxic pulmonary vasoconstriction (HPV) serves to optimize ventilation–perfusion matching in focal hypoxia and thereby enhances pulmonary gas exchange. During global hypoxia, however, HPV induces general pulmonary vasoconstriction, which may lead to pulmonary hypertension (PH), impaired exercise capacity, right‐heart failure and pulmonary oedema at high altitude. In chronic hypoxia, generalized HPV together with hypoxic pulmonary arterial remodelling, contribute to the development of PH. The present article reviews the principal pathways in the in vivo modulation of HPV, hypoxic pulmonary arterial remodelling and PH with primary focus on the endothelin‐1, nitric oxide, cyclooxygenase and adenine nucleotide pathways. In summary, endothelin‐1 and thromboxane A2 may enhance, whereas nitric oxide and prostacyclin may moderate, HPV as well as hypoxic pulmonary arterial remodelling and PH. The production of prostacyclin seems to be coupled primarily to cyclooxygenase‐1 in acute hypoxia, but to cyclooxygenase‐2 in chronic hypoxia. The potential role of adenine nucleotides in modulating HPV is unclear, but warrants further study. Additional modulators of the pulmonary vascular responses to hypoxia may include angiotensin II, histamine, serotonin/5‐hydroxytryptamine, leukotrienes and epoxyeicosatrienoic acids. Drugs targeting these pathways may reduce acute and/or chronic hypoxic PH. Endothelin receptor antagonists and phosphodiesterase‐5 inhibitors may additionally improve exercise capacity in hypoxia. Importantly, the modulation of the pulmonary vascular responses to hypoxia varies between species and individuals, with hypoxic duration and age. The review also define how drugs targeting the endothelin‐1, nitric oxide, cyclooxygenase and adenine nucleotide pathways may improve pulmonary haemodynamics, but also impair pulmonary gas exchange by interference with HPV in chronic lung diseases.